High-temperature invariant and Deformation-durable h-BN/PVA Nanocomposite for Highly-reliable Humidity Sensor enabling Morse Code Communication and Real-Time Wireless Respiratory Monitoring

High-temperature invariant and Deformation-durable h-BN/PVA Nanocomposite for Highly-reliable Humidity Sensor enabling Morse Code Communication and Real-Time Wireless Respiratory Monitoring | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article High-temperature invariant and Deformation-durable h-BN/PVA Nanocomposite for Highly-reliable Humidity Sensor enabling Morse Code Communication and Real-Time Wireless Respiratory Monitoring shahzad iqbal, Shenawar Ali Khan, Bibi Ruqia, Syed Adil Sardar, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4565983/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Nowadays, two-dimensional (2D) materials with layered structures and high surface area are highly appealing in humidity sensing applications. Boron nitride emerges as a promising material owing to its exceptional mechanical strength, chemical resistance, and thermal stability. Herein, flexible humidity sensors based on 2D hexagonal boron nitride (h-BN) were synthesized by sonication-assisted exfoliation to introduce oxygen-rich groups to its surface. This process resulted in h-BN nanoflakes with 50–180 nm sizes. Polyvinyl alcohol (PVA), a well-known hydrophilic polymer, was used as the polymer matrix to disperse the h-BN nanoflakes, and the resulting nanocomposite was coated on a flexible interdigitated electrode as a sensing layer. The sensor's response was measured between 10 to 90%RH of humidity levels, and the maximum change in capacitance from 2.2 nF to 79.3 nF, at 1 kHz was recorded with fast response and recovery times of 3.5 s and 4 s, respectively. Moreover, the h-BN/PVA nanocomposite shows remarkable stability under various conditions, such as bending, high temperature, and longer periods, highlighting its durability. The developed sensor was successfully tested in practical applications such as respiratory and proximity-sensing, real-time wireless monitoring for Internet of Things (IoT) applications, and Morse code communication. Boron Nitride nano flakes nanocomposite Humidity Sensor IOT wireless senor Morse code Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Sensors play a vital role in our modern lives by transforming physical and environmental changes into electrical signals. These signals are then analyzed for various applications such as lifestyle, healthcare, fitness, manufacturing, and daily life [ 1 , 2 ]. Humidity sensors detect the amount of water vapor present in the air, and they can be classified into two distinct categories: relative humidity (RH) and absolute humidity[ 3 ], [ 4 ]. The most commonly used sensors for humidity measurement are RH sensors, which have been widely employed in weather monitoring, respiratory monitoring, wearable electronics, agriculture, and building comfort control [ 5 – 7 ]. Moreover, RH sensors exhibit lower sensitivity to temperature fluctuations than absolute humidity sensors, enhancing their versatility across diverse environments [ 8 ]. Various types have been developed for humidity sensing based on sensing mechanisms, including capacitive, resistive, Impedance type, surface acoustic wave (SAW), and colorimetry-based [ 8 – 10 ]. Among these, the capacitive type has several advantages over other sensor types because it exhibits a linear response to humidity and can be operated over a wide range of relative humidity and temperature; it requires less complex electronics that can fully recover from condensation and are resistant to chemical vapor [ 11 , 12 , 13 ]. Several materials have been used as active humidity sensing layers, such as organic, inorganic, polymers, ceramic, 2D materials, Mxenes, and their nanocomposites [ 14 – 17 ]. Among these, the polymer-based materials that possess a high affinity for water resulting from the inherent hydrophilic functional groups are considered a feasible option for humidity sensor applications, and their low‐cost process, high mechanical stability and flexibility are vital for future applications in wearable devices. [ 18 ]. However, polymeric materials for humidity sensors have the drawback of poor sensitivity and long response/recovery time over the wide humidity range, which is not desired for daily life applications[ 19 ]. Numerous methods have been reported to enhance the performance of polymer-based materials in humidity sensors to achieve rapid transient response, higher sensitivity, and wide range detection. Several polymer nanocomposites based sensing materials aim to improve the effectiveness of humidity sensors for various applications, such as PEG/Gold nanoparticles[ 10 ], BATiO 3 /PVDF[ 20 ], In 2 Se 3 /PEDOT: PSS[ 21 ], cellulose/graphene oxide/polydimethylsiloxane[ 22 ], and graphene oxide (GO)/PVA[ 23 ]. Few challenges that these reported studies faced, is the electrical performance of these sensors, which deteriorates when devices are posed to deformation by bending, stretching, or twisting[ 19 , 24 ]. In addition, device functionality is compromised when subjected to adverse environmental conditions. This indicates that the applications requiring constant mechanical movement, such as in wearable electronics, or utilization in harsh environments such as industries with high temperatures or freezing cold areas, these sensing devices require high deformability to maintain conformal skin contact and high thermal and mechanical stability for long-term usage. In order to address these issues, many studies focused on developing flexible humidity sensors with high chemical and thermal stability, inherent flexibility, and ease of chemical functionalization. Hexagonal boron nitride (h-BN), an atomically thin hexagonal structured two-dimensional (2D) material similar to graphene, with many distinguished properties, also often known as white graphene[ 25 ] offers many interesting properties, such as wide band gap, and large surface area[ 26 , 27 ]. The h-BN monolayer is stable up to 800°C in air, compared to graphene, which oxidizes at 300°C. h-BN monolayer possesses Young’s modulus of 0.865 ± 0.073 TPa and fracture strength of 70.5 ± 5.5 GPa due to its perfect atomic arrangement[ 28 ]. he strong interlayer interaction in h-BN nanoflakes shows an enormous potential for use in sustainable electronics [ 29 ]. The h-BN nanoflakes offering a unique surface adsorption capability and high surface-to-volume ratio can provide greater sensitivity and fast responsiveness in sensing applications [ 28 , 30 , 31 ]. [ 32 ]. In addition, h-BN shows van der Waals (vdW) force and π–π interactions with polymers; the partial ionic electronic structure of B-N bonding can be advantageous for molecular interactions with polymer materials [ 33 ]. Molecular dynamics (MD) simulation predicted that the molecular interaction between polymers and BN materials could be more efficient because of the polarized nature of B-N bonding, the high bonding potentials of B and N atoms, along with vdW force and Coulomb interactions between BN and polymer matrix [ 29 ]. Tutgun et al. studied the paramount effect of h-BN on the polymer composite in terms of thermal and mechanical stability, showing thermal stability up to 190°C [ 34 ]. In another study Zhi et al. synthesized a self-organized composite membrane based on polyaniline and boron nitride nanotubes (BNNTs). The composite exhibits excellent mechanical stability and strong BNNT interactions with the polymer and their uniform distribution make the BNNT polymer composite an interesting material for various applications [ 35 ]. Wang et al. synthesized highly water dispersed functional boron nitride, and its composite with polyvinyl alcohol (PVA), the nanocomposite films showed high flexibility and retained their properties with improving mechanical performance [ 36 ]. Owing to these excellent properties, h-BN/polymer films show enormous potential for their use in flexible devices. For wearable electronics, flexibility is certainly essential, yet additional key features including great thermal stability, fast response times, a broad detection range, and high sensitivity are also essential. Thus, introducing h-BN into the polymer is a practical approach to improving humidity sensors' flexibility and thermal stability. Amongst these polymer materials, polyvinyl alcohol (PVA) stands out as a excellent humidity-sensing material due to its hydrophilicity, mechanical strength, flexible nature, thermostability, biocompatibility, transparency, and cost-effectiveness[ 32 ]. From a chemical perspective, PVA offers a large number of hydroxyl (OH) groups. The dielectric properties of PVA vary as hydrogen bonds are created in the presence of water molecules [ 10 ]. PVA has suitable film-forming properties when composited with other 2D materials. Despite the remarkable properties of h-BN/polymer composites, research has predominantly focused on enhancing their mechanical properties [ 37 ]. This work aims to synthesize the h-BN/PVA nanocomposite with easy processing, improved conductivity, thermal stability, flexibility, and transparency of h-BN polymer composites, and good mechanical properties for humidity-sensing applications. We have developed a cost-effective, flexible humidity sensor with an Au electrode deposited on a PET substrate in a capacitive design. This sensor utilizing h-BN/PVA nanocomposite detects humidity levels with changing capacitance under varied conditions such as bending, high temperature, and longer periods. h-BN nanoflakes synthesized via an ultrasonic method introduce oxygen-rich groups to its surface, enhancing the adsorption of the water molecule [ 37 ]. Incorporation of h-BN into PVA increases its water absorption capacity due to a larger surface area, thus boosting moisture sensitivity [ 38 ]. Different proportions of h-BN/PVA to develop an ideal humidity-sensitive layer. The sensor's performance was thoroughly examined across a 10–90 %RH rane, assessing its bendability, thermal stability, and response times. The humidity sensing device shows promise for diverse applications, including noncontact control, successful demonstration of Morse code communication and voice recognition. An IoT-based wireless sensing system for real-time breath and proximity detection is also presented. 2. Experimental 2.1 Materials and methods Polyvinyl alcohol (PVA) was procured from Sigma-Aldrich, Seoul, Korea, while Boron nitride was obtained from Graphene Supermarket. Ethanol (CH 3 CH 2 OH) and deionized water were purchased from Sigma Aldrich, Seoul, Korea. Firstly, the PVA solution was prepared by blending PVA powder with DI water at a 1:10 mass ratio and left at room temperature for 24 hours to facilitate swelling. Subsequently, the solution was subjected to magnetic stirring on a hot plate at 70°C for 12 hours to ensure complete dissolution of the PVA. Secondly, 5.4 mg BN powder was added to 1 liter of ethanol/water as a dispersion solvent. The sealed flask was sonicated for 8 hours, and then the dispersion was centrifuged at 3000 rpm for 20 mins to remove aggregates; detailed process can be found in [ 39 ]. As a result, 2D flakes consisting of 50–200 nm lateral size were obtained. The preparation process of the h-BN and PVA is shown in Fig. 1 b. In order to evaluate the effect of the concentration of h-BN on the moisture sensitivity. The PVA solution was divided into two parts, and h-BN with concentrations of (2:1) and (1:1) were added. Finally, the solution was placed on a magnetic stirrer for 1 hour at 1000 rpm at room temperature to ensure a homogenous dispersion of the h-BN in the PVA solution 2.2 Sensor Fabrication The process of fabricating humidity sensors based on Flexible PET involved meticulous steps. The first comprehensive cleaning procedure for PET substrate uses an ultrasonic bath with ethanol, isopropanol, and de-ionized water, respectively. This treatment extended over a 20-minute duration to remove any dust particles and contaminants adhering to the substrate's surface. Following this, the substrate was left to air dry at room temperature. Then, the PET substrate with a shadow mask was put inside the chamber and underwent a 10-minute processing phase. The Gold (Au) electrode was deposited on a PET substrate using plasma sputter coating, featuring an interdigitated comb-like structure comprising seven pairs of electrode fingers. The width of each electrode finger was 0.25mm, and the spacing between electrode fingers was 0.75mm as shown in detail schematic diagram of Fig. 1 a. After electrode fabrication, the active sensing layer of h-BN/PVA was drop casted on the interdigital electrode and was placed at room temperature for 24 hours to dry to complete the preparation of the humidity-sensitive layer. 3. Characterizations We precisely examined the nanostructure and surface characteristics of our samples, and the top view of the h-BN/PVA active layer was captured using a high-resolution desktop scanning electron microscope (SEM) (phenom pharos G2) while dispersive X-ray spectroscopy (EDS) was used to understand the elemental composition of h-BN/PVA layer, as shown in Fig. 2 c,d. The composite films are further characterized through FTIR (Nicolet 6700). The crystalline structure of sensing layer was analysed by Wide-angle X-ray diffraction (WAXD), using a PAN anlytical Empyrean X-ray diffractometer. The instrument was equipped with a Co (Kα1 (λ) = 1.789 Å) source, a PIXcel 3D detector, a tube voltage of 45 kV and current of 40 amps. Thermo Scientific DXR3xi Raman Imaging Microscope was used to gain insights into the structural properties, lattice dynamics, and phonon behavior of h-BN/PVA nano composite, which are vital for understanding and optimizing its performance in sensing applications. 3.1 Sensor Evaluation We measured the electrical capacitance during our sensor assessment using a U1733C Keysight LCR meter. The measurements were conducted at frequencies of 1 kHz, 10 kHz, and 100 kHz while maintaining a constant ambient temperature of 25°C. To ensure precise control over the humidity environment, we utilized a custom-built airtight glass box equipped with a humidifier and an N 2 gas cylinder, as shown in Fig. 1 c. Adjacent to the IDE humidity sensor, we placed a reference sensor (HTU-21D) and employed an Arduino circuit to accurately measure the percentage of relative humidity (%RH). We systematically increased the humidity inside the chamber while continuously collecting data to compare our custom IDE sensor with the reference sensor. We introduced N 2 gas into the chamber through a nozzle to reset the experimental conditions, effectively reducing the humidity to 10% RH. Simultaneously, we connected the LCR meter to a laptop to capture real-time capacitance spectra, ensuring precise evaluation of our sensor’s performance. 4. Results and Discussion 4.1 Surface morphology. The surface morphology of the h-BN/PVA nanocomposite was examined in depth through SEM characterization. Before imaging, the samples were sputter coated using a Pt metal target. The SEM images can be seen in Fig. 2 a,b verified the exfoliated h-BN materials and particle size, shape, and texture distribution. The nanometer scales are arranged in a layered structure with irregular round shapes, whereas they have lateral dimensions on the nanometer scale ranging from 80 nm to 180 nm. High-resolution particles in more detail are shown in Fig. 2 c. The h-BN particles exhibited diverse morphologies, such as spherical, and ellipsoidal shapes, which increased their surface area, enhancing interaction with water molecules in the surrounding atmosphere. During the sonication procedure, the h-BN bounds interact with water molecules, which causes the hydroxyl functionalization of h-BN and penetration of water molecules between the BN layers. This led to enhanced sensing sensitivity. The elemental composition of PVA/hBN was examined by using Energy Dispersive Spectroscopy (EDS), as shown in Fig. 2 d. EDS-mapped picture with a magnification of 1 µm. The elemental mapping demonstrates a uniform distribution of C, O, B, and N atoms throughout the sample. The B K, N K, C K, and O K, series were presented with a magnification level of 1 µm in Fig. 2 e, respectively. The h-BN/PVA nano composite major peaks indicate the compositions of B, N, C, and O with 23.23%, 17.67%, 10.75%, and 48.35%, of each element in the humidity sensing layer, respectively as illustrated in Fig. 2 f. The composite films are further characterized through FTIR and presented in Fig. 2 g. The low-intensity PVA peak at 1600 cm − 1 is due to the C–H and O–H bond bending. The 900–1200 cm − 1 peak in composites indicates the co-existence of h-BN and PVA. The strong broadband at 3000–3600 cm − 1 corresponds to the O–H stretching vibration of the hydroxyl group of PVA [ 40 ]. The FT-IR spectrum shows many hydrophilic groups of PVA/hBN composite film along with the FT-IR, h-BN/PVA nanocomposite is also characterized through Raman spectroscopy, as shown in Fig. 2 h. The obtained the characteristic peaks of h-BN/PVA material at wavenumbers of 1410 cm − 1 , corresponds to the characteristic vibrational phonon mode (E2g) of h-BN. The absence of other Raman peaks confirms that the chemical structure has been preserved after exfoliation. For the PVA, the most intense band centered at 2912 cm − 1 is assigned to the stretching vibrations of –CH 2 [ 27 ]. The XRD patterns of h-BN/PVA are shown in Fig. 2 i. The XRD pattern of PVA illustrates a broad peak at 2θ ≈ 19.55, corresponding to (101) crystal reflection planes. The sharp peak at 31° confirms the presence of h-BN in the nano composite [ 26 ]. it is evident that the peaks remained unchanged in both materials in terms of diffraction angle and shape, suggesting that the high-pressure homogenisation exfoliation process did not damage the crystalline structure of the pristine material. h-BN retained the high crystalline structure of the bulk BN. 4.2 Electrical Characterization of h-BN/PVA humidity sensor The performance of a humidity sensor is determined by design factors, which are the sensing layer diameter, thickness of the layer, and electrode. The capacitance of a typical parallel plate electrode type for a capacitive humidity sensor can be expressed as Eq. ( 1 ): $$C= {\upvarepsilon }\left(\text{R}\text{H}\right)* {{\upvarepsilon }}_{0}\text{*}\left(\frac{\text{A}}{\text{d}}\right)$$ 1 where A is the area of the plate, d is the distance between the two plates, ɛ(RH) is the dielectric permittivity that is a function of the relative humidity and ɛ 0 the dielectric permittivity at 0%RH [ 40 ]. The capacitance of a material is influenced by its dielectric properties, which can be affected by the presence of moisture. This study uses a thin film of a h-BN/PVA composite as the active layer of a capacitive humidity sensor. The dielectric constant of the active layer changes as a result of water vapour adsorption or desorption, leading to a change in the sensor’s capacitance. PVA was chosen because it responds well to humidity owing to the large number of hydroxyl groups present that can interact through hydrogen bonds. By absorbing water molecules, PVA swells, indicating an altering of chain conformation and also enhancing the flexibility and response to capacitance in the humidity sensor. Boron Nitride is introduced due to its chemical stability, mechanical strength, and flexibility. To study the effect of different concentrations of h-BN nanoparticles on the output performance of the humidity sensor, we kept the concentration of PVA fixed and varied the concentration of h-BN. Therefore, the comparison analysis of two humidity sensor (1:1 and 1:2) samples reveals notable performance differences. The impact of the 1:2 of h-BN in a PVA solution the sensor displays a capacitance change ranging from 566 pF to 16.5 nF. This change is evident across a relative humidity range from 10% RH to 90% RH at 1 kHz, as illustrated in Fig. 3 a. However, the output capacitance of the sensor increased with the increase of h-BN concentration 1:1 in the range of 10–90% RH, which exhibited a certain of regularity, the capacitance response increased from around 2.27 nF to 79.3 nF, 1.47 nF to 12.7 nF, and 26 pF to 2.32 nF at a test frequency of 1, 10, and 100 kHz, respectively. It is crucial to note that this response is significantly lower compared to the performance achieved with h-BN in PVA at a 1:1. In Fig. 3 b,c. The sensor exhibits a nearly linear response of at frequencies of 1 kHz, 10 kHz, and 100 kHz across the range of 10–90%RH and also normalized capacitance demonstrates consistent performance across these frequencies, showcasing its effectiveness in humidity detection. Stability and repeatability are the fundamental characteristics of a proficient humidity sensor to be used in everyday applications [ 6 ]. To evaluate the flexibility of the sensor, we have tested the proposed humidity sensor at three different angles of deformation (30°, 60°, and 80°), as illustrated in Fig. 3 d. During the experiment, the sensor transitioned from RH 10% to RH 90% conditions. As depicted in Fig. 3 e, there was no significant difference in response across varying bending degrees, highlighting the sensor's excellent stability, durability, and flexibility performance. Furthermore, to examine the long-term consistency of the h-BN/PVA-based humidity sensor, it was opened to humidity conditions for 90 days, and the capacitive response was measured at various relative humidity conditions. The capacitance responses remained highly stable with minimal error, affirming the sensor's reliability over an extended duration. Humidity measurements at higher temperatures are substantially more challenging because at high temperatures relative humidity is generally very low and also most organic sensor materials are not stable at high temperatures. In addition, many industrial processes a high durability and resistance to harsh environments are of particular importance. For example, industrial branches with high energy saving potential, such as wood drying or textile processing, demand sensors with high tolerance to corrosive/oxidizing species or contaminants with high molecular weight at high temperatures. These requirements often exclude the utility of conventional sensor materials as they are usually unstable under these conditions[ 41 , 42 ]. Hence, for high-temperature humidity sensing extremely sensitive devices are necessary, in this respect h-BN shows superior properties due to their temperature stability and chemical stability[ 36 , 43 , 44 , 45 ]. Here we report on a h-BN/PVA nanocomposite sensor device, we show humidity-sensing data up to 80°C under constant humidity (70 %RH) in a sealed envionment. The synthesized sensor in this work showed a high thermal stability which makes it generally eligible for high-temperature applications investigations as shown in Fig. 3 e. The results indicate minimal capacitance variation at 40°C and 60°C. However, at 80°C, a decrease in capacitance is observed, which is attributed to water vapor evaporation and reduced humidity levels at higher temperatures. The sensor shows a near-linear response behavior to relative humidity with only a little influence of the temperature. The transient responses of the sensors were analyzed to assess the device response and recovery times during humidification and dehumidification. Two distinct air streams were injected for this evaluation: one stream consisted of compressed dry air, while the other conveyed extremely humid air directly from the humidifier. In this experimental setup, a humidifier was utilized to alternate between 10 and 90%RH levels. A Nitrogen gas was connected to the control chamber and gradually introduced to reduce the humidity levels from 90%RH to 10%RH, as depicted in Fig. 3 h. h-BN/PVA (1:1) shows rough surface and porous structure to facilitate adsorption/desorption and diffusion of moisture. Accordingly, it presents repeatable responses during cyclic switching between 90%RH and 10%RH, exhibiting relatively fast response time of 3.5 s and 4 s for t adsorption and t desorption , respectively as can be seen in Fig. 3 i. These results suggest that the proposed sensor is well-suited for real-time practical applications, underscoring its commendable transient response and recovery times. 5. Humidity Sensing Mechanism The humidity sensing mechanism of h-BN can be explained based on the fact that water molecules are firstly adsorbed on the surface-active sites of the h-BN through double hydrogen bonding[ 30 ]. Two sequential processes, chemisorption and physisorption, can be used in this humidity sensing process to describe the adsorption of water molecules onto the sensor surface[ 10 , 46 ] as shown in Fig. 4 . Water molecules initially come into contact with the h-BN/PVA film and are absorbed by the hydrophilic PVA matrix and BN atoms of the boron nitride nanoflakes. The protons can pass through the center pores of the hexagonal rings of h-BN. The electron negativity of N atom of h-BN is much stronger than that of B atom, so the electron clouds on N atoms are much larger than those on B atoms. Based on the different electron negativity values of B and N atoms, the pores in h-BN have triangular shapes, the pore size of h-BN (approximately 3.0 Å2)[ 47 ]. At low relative humidity (RH), water molecules physiosorb onto the sensor surface, and as RH increases, they chemisorb onto the chemisorbed layer, forming a bulk liquid-like multilayer. Both h-BN and PVA have moisture-absorbing properties, making them sensitive to humidity. When combined in a composite with proper dispersion, these materials can potentially enhance the sensor’s overall humidity sensitivity. The composite’s improved dielectric properties, resulting from combining a hydrophilic polymer like PVA with a insulating material like h-BN, increase the sensor’s permittivity. This higher permittivity amplifies the capacitance change caused by moisture absorption, leading to increased sensitivity. The active sensing film between the interdigitated electrodes, with its higher permittivity, polarizes more under the applied electric field, thus increasing the device’s capacitance. PVA can act as a physical linker in the composite, emphasizing the importance of achieving a uniform dispersion of h-BN particles within the h-BN matrix. A secondary purpose of the h-BN flakes is to increase the surface area of the thin film that is clear from the surface SEM images Fig. 2 (a,b) . This increase in surface roughness and area results in higher sensitivity and easier diffusion of water molecules into and out of the active layer. Furthermore, upon adsorption of water molecules into the thin film, the overall dielectric constant of the active region increases as compared to a dry film. This results in an increase in the capacitance of the sensing device with increasing relative humidity. Table 1 compares the performance parameters of high-end materials and the composite based humidity sensors published in literature. The study successfully achieves a desirable property: high flexibility, thermal stability, and excellent durability. These benefits translate to the proposed h-BN/PVA humidity sensor exhibiting exceptional performance. Sensing material Range (% RH) Response time (s) Recovery time (s) Sensitivity % RH Flexibility/ Temp Stability ref BaTiO 3 /PVDF 40–90 40 25 0.2416 pF X [ 20 ] In 2 Se 3 /PEDOT: PSS 5–95 0.9 2.1 0.177 µ F X [ 48 ] GO/MWCNT 43–97 5 2.5 7980 pF X [ 49 ] MCM-41/PEDOT 11–75 77 30 3x X [ 21 ] PVDF/ZnO 10–80 30 51 O/X [ 50 ] SnO2/RGO 11–97 120 7 1604.89 pF X [ 51 ] Liquid exfoliated MoS 2 nanosheets 11–96 30 40 178.38 pF X [ 52 ] MoS 2 /Go 11–97 20 12 369 pF X [ 53 ] h-BN/ PVA 10–90 3.5 4 963 pF O/O This work Table 1 : Comparison of the performance parameters of high-end materials and composite-based humidity sensors 6. Applications The humidity-detecting capability of the h-BN/PVA composite was examined for various applications to explore emerging sensor applications, including proximity, breathing test, morse code, and IOT-based Real-time. As shown in Fig. 5 a, the sensor's ability to detect breathing patterns through the mouth was evaluated. Dynamic capacitance changes were observed during inhalation and exhalation, correlating with moisture fluctuations around the mouth. In addition, in figure b , the proximity test was conducted by placing a dry finger at varying distances of 6, 9, and 12 mm from the sensor, resulting in capacitances of 35, 20, and 10 nF, respectively, at 1 kHz. Moreover, the repeatability and cyclic response tests further demonstrated the consistency and reliability of our sensor, shown in Fig. 5 c,d. The distances of 6 and 12 mm have been tested as the suitable experimental values for Morse code as a communication protocol in the message transmission process, and the corresponding capacitance values are defined as high response and low response, respectively. According to this principle, contactless message transmission can be achieved. Morse code is adopted as a communication protocol in the message transmission process. Figure 5 e exhibits the Morse code table, which consists of different letters in a combination of dashes and dots. The capacitance value in the output greater than 30 nF is recorded as a dot; otherwise, it will be noted as a dash, as shown in Fig. 5 f. Thus, letters can be coded by diverse combinations of high and low responses. To intuitively perform the excellent capability of the sensor, three words, JNU (Jeju National University), were input by using this system. The inputting accuracy of this system is impressive through a three-word demonstration, which is enough to realize the message transmission. IoT-enabled electronic systems are rapidly gaining prominence across various sectors, such as healthcare, consumer goods, security, and agriculture. The Node MCU is an open-source IoT platform featuring the ESP8266 Wi-Fi module equipped with GPIO pins for sensor and actuator connections. In this context, we leverage the Node MCU for real-time monitoring of proximity and breathing tests via IoT cloud-based platforms. The wireless system comprises a proposed flexible humidity sensor, a data processing unit, an inbuilt Wi-Fi module for data transmission, and a power supply unit. The electronic system is operated through a ∼3 V supply and a 32-bit microcontroller incorporated with an ESP-12E module (Wi-Fi SoC). The Arduino IDE platform is used to write the source code in embedded C programming language and upload it to the microcontroller to receive analog input from a flexible humidity sensor based on capacitance variations. Cloud technologies are ideal for remotely monitoring physical activity and transmitting data to a cloud computing database accessible via mobile devices. This enables real-time monitoring from any location, especially in the healthcare sector, by improving communication between patients, physicians, and healthcare professionals. Arduino Cloud is a platform provided by Arduino that enables users to monitor and control their Arduino devices remotely over the internet. We developed an IoT-based humidity sensor for real-time wireless monitoring of breathing and proximity, as illustrated in the Fig. 5 g. The detected humidity data is received and displayed in real-time on a smartphone. 7. Conclusion A Capacitive sensor design with h-BN/PVA nanocomposite as the sensing layer and gold layers as electrodes enables effective humidity measurement across diverse conditions. Boron nitride emerges as a promising material owing to its exceptional mechanical strength, chemical resistance, and thermal stability. Also, the large surface area and rich hydrophilic functional groups of h-BN nanoflakes with PVA boost sensing performance. The h-BN/PVA composite demonstrates a linear response with response and recovery times of 3.5s and 4s, respectively. Furthermore, sensor exhibit remarkable stability even under high temperatures. The stability tests conducted at various temperatures (40°C to 80°C) and bending conditions (30° to 80° angles) underscore its robustness. The humidity sensor developed underwent successful testing for practical applications, including respiratory monitoring and proximity sensing (finger test at varying distances from the sensor). Its precise humidity monitoring capability enables implementing Morse code communication and real-time wireless monitoring for Internet of Things (IoT) applications. Declarations Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding information This work was supported by "Regional Innovation Strategy (RIS)" through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE)(2023-RIS009). Author Contribution Conceptualization, Shahzad Iqbal; Methodology, Shahzad Iqbal, and Shenawar Ali Khan; Software, Shahzad Iqbal; Formal analysis, Shenawar Ali Khan and Bibi Ruqia; Investigation, Woo Young Kim and Shenawar Ali Khan; Resources, Woo Young Kim; Data curation, Shahzad Iqbal and Shenawar Ali Khan; Writing—original draft, Shahzad Iqbal; Writing—review and editing, Shenawar Ali Khan, Bibi Ruqia, and Woo Young Kim; Visualization, Shahzad Iqbal and Syed Adil Sardar; Supervision, Woo Young Kim; Project administration, Woo Young Kim; Funding acquisition, Woo Young KimAll authors have read and agreed to the published version of the manuscript. Acknowledgement This research was supported by "Regional Innovation Strategy (RIS)" through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE)(2023-RIS009). 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IOP Publishing, p 012027 Guo W-T, Tang X-G, Tang Z, Sun Q-J (2023) Polym (Basel) 15:2176 Mallick S, Ahmad Z, Qadir KW, Rehman A, Shakoor RA, Touati F, Al-Muhtaseb SA (2020) Ceram Int 46:2949 Siddiqui GU, Sajid M, Ali J, Kim SW, Doh YH, Choi KH (2018) Sens Actuators B Chem 266:354 Yang Y, Su G, Li Q, Zhu Z, Liu S, Zhuo B, Li X, Ti P, Yuan Q (2021) RSC Adv 11:1543 Rahman SA, Khan SA, Rehman MM, Kim W-Y (2022) Nanomaterials 12:1026 Romero FJ, Rivadeneyra A, Salinas-Castillo A, Ohata A, Morales DP, Becherer M, Rodriguez N (2019) Sens Actuators B Chem 287:459 Nazarov AS, Demin VN, Grayfer ED, Bulavchenko AI, Arymbaeva AT, Shin H, Choi J, Fedorov VE (2012) Chemistry–An Asian J 7:554 Guerra V, Wan C, Degirmenci V, Sloan J, Presvytis D, McNally T (2018) Nanoscale 10:19469 Shi Y, Xiong D, Li J, Wang K, Wang N (2017) RSC Adv 7:1045 Glavin NR, Muratore C, Jespersen ML, Hu J, Hagerty PT, Hilton AM, Blake AT, Grabowski CA, Durstock MF, McConney ME (2016) Adv Funct Mater 26:2640 Falin A, Cai Q, Santos EJG, Scullion D, Qian D, Zhang R, Yang Z, Huang S, Watanabe K, Taniguchi T (2017) Nat Commun 8:15815 Cai Q, Du A, Gao G, Mateti S, Cowie BCC, Qian D, Zhang S, Lu Y, Fu L, Taniguchi T (2016) Adv Funct Mater 26:8202 Ogawa S, Fukushima S, Shimatani M (2023) Materials 16:2005 Mazhar S, Qarni AA, Haq YU, ul Haq Z, Murtaza I, Ahmad N, Jabeen N, Amin S (2020) Microchem J 157:104974 Rasul MG, Kiziltas A, Arfaei B, Shahbazian-Yassar R (2021) NPJ 2D Mater Appl 5:56 Tutgun MS, Sinirlioglu D, Celik SU, Bozkurt A (2015) Ionics (Kiel) 21:2871 Zhi C, Bando Y, Tan C, Golberg D (2005) Solid State Commun 135:67 Wang J, Wu Y, Xue Y, Liu D, Wang X, Hu X, Bando Y, Lei W (2018) J Mater Chem C Mater 6:1363 Wang W, Li Z, Marsden AJ, Bissett MA, Young RJ (2022) Compos Sci Technol 218:109131 Lin Y, Williams TV, Xu T-B, Cao W, Elsayed-Ali HE, Connell JW (2011) J Phys Chem C 115:2679 Zhou K, Mao N, Wang H, Peng Y, Zhang H (2011) Angew Chem Int Ed 46:10839 Sahoo P, Chaturvedi A, Ramamurty U, Matte HSSR (2022) Nanotechnology 34:095703 Traversa E (1995) Sens Actuators B Chem 23:135 Chen N, Zhou X, Li X (2020) IEEE Trans Instrum Meas 70:1 Guerra V, Wan C, McNally T (2019) Prog Mater Sci 100:170 Zhang D-L, Zha J-W, Li W-K, Li C-Q, Wang S-J, Wen Y, Dang Z-M (2018) Compos Sci Technol 156:1 Wagner T, Krotzky S, Weiß A, Sauerwald T, Kohl C-D, Roggenbuck J, Tiemann M (2011) Sensors 11:3135 Zhang Z, Chen M, Alem S, Tao Y, Chu T-Y, Xiao G, Ramful C, Griffin R (2022) Sens Actuators B Chem 359:131620 Yoon SI, Ma KY, Kim T-Y, Shin HS (2020) J Mater Chem Mater 8:2898 Khan SA, Saqib M, Khan M, Rehman MM, Rahman SA, Kim WY (2023) ACS Appl Electron Mater 5:4473 Li X, Chen X, Chen X, Ding X, Zhao X (2018) Mater Chem Phys 207:135 Arularasu MV, Harb M, Vignesh R, Rajendran TV, Sundaram R (2020) Surf Interfaces 21:100780 Yang M-R, Chen K-S (1998) Sens Actuators B Chem 49:240 Siddiqui MS, Mandal A, Kalita H, Aslam M (2022) Sens Actuators B Chem 365:131930 Guo L, Li X, Li W, Gou C, Zheng M, Zhang Y, Chen Z, Hong Y (2022) Mater Chem Phys 287:126146 Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4565983","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":326125085,"identity":"55c8ed97-518e-41fb-b1dd-0d7820f07658","order_by":0,"name":"shahzad iqbal","email":"","orcid":"","institution":"Jeju National University","correspondingAuthor":false,"prefix":"","firstName":"shahzad","middleName":"","lastName":"iqbal","suffix":""},{"id":326125086,"identity":"f64aafba-6c13-46fc-ac28-5882d3f96550","order_by":1,"name":"Shenawar Ali Khan","email":"","orcid":"","institution":"Jeju National University","correspondingAuthor":false,"prefix":"","firstName":"Shenawar","middleName":"Ali","lastName":"Khan","suffix":""},{"id":326125087,"identity":"7ad27270-7ddb-438f-809f-c75e82e33f00","order_by":2,"name":"Bibi Ruqia","email":"","orcid":"","institution":"Kyungpook National university","correspondingAuthor":false,"prefix":"","firstName":"Bibi","middleName":"","lastName":"Ruqia","suffix":""},{"id":326125088,"identity":"81a56376-e140-4607-b7ea-400822c23a4f","order_by":3,"name":"Syed Adil Sardar","email":"","orcid":"","institution":"Jeju National University","correspondingAuthor":false,"prefix":"","firstName":"Syed","middleName":"Adil","lastName":"Sardar","suffix":""},{"id":326125089,"identity":"78ae1773-aae4-4a7b-a00c-b5ca5ff02869","order_by":4,"name":"Woo Young Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7klEQVRIie2RvwrCMBCHTwJOKV1b8M8rpARcHHwVOzk5CeJYENLBF3ARX6EgiGPKgS5RV6GLk5ugg+BoWgW3VDfBfJDLEe47fhAAi+VHkfpQV1/s9UA+U/zoG6WAyXdvVprxJExvYlnjKcqBs0JwY0n4yLRcbROsi4y25LrLHYXgqS4JlUnx+gn6haIYdwQCHICkkSnY/PxUeLS/FEqzTIGDk6RXrTBQUChMK6FJYUoHg11GPblmwUz0aKDCcWAMFm8X1/sw67hTPLGzaDcaG0TfGExDaF49Wc2/UveVMkGP3PPqRuRYOmqxWCx/yQNmx1RVjITl+wAAAABJRU5ErkJggg==","orcid":"","institution":"Jeju National University","correspondingAuthor":true,"prefix":"","firstName":"Woo","middleName":"Young","lastName":"Kim","suffix":""}],"badges":[],"createdAt":"2024-06-11 18:45:38","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4565983/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4565983/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":60607755,"identity":"73e63ef4-97b8-41fe-a405-ae914116d232","added_by":"auto","created_at":"2024-07-18 17:32:10","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2399698,"visible":true,"origin":"","legend":"\u003cp\u003e(a)Fabrication of process of patterned IDE. (b) preparation of PVA/hBN composite humidity sensor. (c) Schematic diagram of humidity measurement setup.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4565983/v1/aa08638612e251619d384dc0.png"},{"id":60607913,"identity":"19a73606-ca3f-4fea-87a9-022cc25fff4c","added_by":"auto","created_at":"2024-07-18 17:40:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":3293521,"visible":true,"origin":"","legend":"\u003cp\u003e(a) SEM image at 1um to obtain a closer view of h-BN particles. (b) h-BN particle size varies from 50 nm to 200 nm. (c) Electron image for EDS analysis (d) \u0026nbsp;EDS layered image, (e) B k series, N K series, C K series, and O K series of composite materials (e) FT-IR h-BN/PVA nanocomposites to characterize the composite layer materials (f) XRD analysis h-BN/PVA to characterize the composite sensing layer.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4565983/v1/8d5310c9e52aab1488fd64b1.png"},{"id":60607758,"identity":"e8fd58d9-d2be-45d8-8fe4-4b74b0ddc3fd","added_by":"auto","created_at":"2024-07-18 17:32:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1202660,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Capacitance response of the h-BN/PVA composite humidity sensor (1:1 and 1:2) (b) h-BN/PVA composite humidity sensor capacitance response at 1, 10, and 100 kHz, within the range of 10-90%. (c) Normalized response of h-BN/PVA show linearity at 1kHz, 10kHz and 100kHz (d) Optical images of flexible humidity sensor at various bending angles in bending machine (e) Impedance stability of flexible humidity sensor across multiple bending angles showing mechanical robustness (f) Stability of the humidity sensor at different RH levels (g) temperature stability test. (h) Repeatability test of the humidity sensor over various cycles of humidification and desiccation. (i) Response and recovery time graph.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4565983/v1/eb2de2a8891dc0f2ce17d92b.png"},{"id":60607759,"identity":"d1bd12f9-d592-40ec-bb5e-2ca384f25f5e","added_by":"auto","created_at":"2024-07-18 17:32:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2887072,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eHumidity sensing mechanism for the h-BN/PVA humidity sensor\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4565983/v1/ccec0d66361222cead2359cc.png"},{"id":60607756,"identity":"9a220052-605b-48b9-a5f9-82deb06cd86d","added_by":"auto","created_at":"2024-07-18 17:32:10","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":2126678,"visible":true,"origin":"","legend":"\u003cp\u003eCapacitance response to (a) flexible humidity sensor for monitoring health, showing its ability to distinguish between normal and rapid breathing rates.(b) Capacitance measurements of the sensor at different proximities of 6, 9, and 12 mm (c,d) Reproducibility of the humidity sensor over various cycles of humidification and desiccation at 6mm and 12mm (e) Morse code table and (f) morse code communication (g) schematic illustration of IOT based real time wireless monitoring.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4565983/v1/0559d4f604bd9c5bb1a47c2b.png"},{"id":64529304,"identity":"1040aad3-4715-43a8-82e0-d8ea47949393","added_by":"auto","created_at":"2024-09-14 15:08:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":11423082,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4565983/v1/63bd17a6-8ebe-4d39-a71a-1754744024dc.pdf"},{"id":60607761,"identity":"fb896c15-d734-4cfc-804b-c86329c0ade3","added_by":"auto","created_at":"2024-07-18 17:32:10","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":18111318,"visible":true,"origin":"","legend":"","description":"","filename":"breathingtest..mp4","url":"https://assets-eu.researchsquare.com/files/rs-4565983/v1/3a39cd1c7e8a90f90eaf91c0.mp4"},{"id":60607760,"identity":"e33d20ea-60a3-4621-8051-ede8a64e66cf","added_by":"auto","created_at":"2024-07-18 17:32:10","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":5484019,"visible":true,"origin":"","legend":"","description":"","filename":"supplmentry.docx","url":"https://assets-eu.researchsquare.com/files/rs-4565983/v1/8d6d69d8bf3b36b7279ded59.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"High-temperature invariant and Deformation-durable h-BN/PVA Nanocomposite for Highly-reliable Humidity Sensor enabling Morse Code Communication and Real-Time Wireless Respiratory Monitoring","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eSensors play a vital role in our modern lives by transforming physical and environmental changes into electrical signals. These signals are then analyzed for various applications such as lifestyle, healthcare, fitness, manufacturing, and daily life [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Humidity sensors detect the amount of water vapor present in the air, and they can be classified into two distinct categories: relative humidity (RH) and absolute humidity[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The most commonly used sensors for humidity measurement are RH sensors, which have been widely employed in weather monitoring, respiratory monitoring, wearable electronics, agriculture, and building comfort control [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Moreover, RH sensors exhibit lower sensitivity to temperature fluctuations than absolute humidity sensors, enhancing their versatility across diverse environments [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Various types have been developed for humidity sensing based on sensing mechanisms, including capacitive, resistive, Impedance type, surface acoustic wave (SAW), and colorimetry-based [\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Among these, the capacitive type has several advantages over other sensor types because it exhibits a linear response to humidity and can be operated over a wide range of relative humidity and temperature; it requires less complex electronics that can fully recover from condensation and are resistant to chemical vapor [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSeveral materials have been used as active humidity sensing layers, such as organic, inorganic, polymers, ceramic, 2D materials, Mxenes, and their nanocomposites [\u003cspan additionalcitationids=\"CR15 CR16\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Among these, the polymer-based materials that possess a high affinity for water resulting from the inherent hydrophilic functional groups are considered a feasible option for humidity sensor applications, and their low‐cost process, high mechanical stability and flexibility are vital for future applications in wearable devices. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. However, polymeric materials for humidity sensors have the drawback of poor sensitivity and long response/recovery time over the wide humidity range, which is not desired for daily life applications[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Numerous methods have been reported to enhance the performance of polymer-based materials in humidity sensors to achieve rapid transient response, higher sensitivity, and wide range detection. Several polymer nanocomposites based sensing materials aim to improve the effectiveness of humidity sensors for various applications, such as PEG/Gold nanoparticles[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], BATiO\u003csub\u003e3\u003c/sub\u003e/PVDF[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], In\u003csub\u003e2\u003c/sub\u003eSe\u003csub\u003e3\u003c/sub\u003e/PEDOT: PSS[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], cellulose/graphene oxide/polydimethylsiloxane[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], and graphene oxide (GO)/PVA[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Few challenges that these reported studies faced, is the electrical performance of these sensors, which deteriorates when devices are posed to deformation by bending, stretching, or twisting[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. In addition, device functionality is compromised when subjected to adverse environmental conditions. This indicates that the applications requiring constant mechanical movement, such as in wearable electronics, or utilization in harsh environments such as industries with high temperatures or freezing cold areas, these sensing devices require high deformability to maintain conformal skin contact and high thermal and mechanical stability for long-term usage. In order to address these issues, many studies focused on developing flexible humidity sensors with high chemical and thermal stability, inherent flexibility, and ease of chemical functionalization.\u003c/p\u003e \u003cp\u003eHexagonal boron nitride (h-BN), an atomically thin hexagonal structured two-dimensional (2D) material similar to graphene, with many distinguished properties, also often known as white graphene[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] offers many interesting properties, such as wide band gap, and large surface area[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The h-BN monolayer is stable up to 800\u0026deg;C in air, compared to graphene, which oxidizes at 300\u0026deg;C. h-BN monolayer possesses Young\u0026rsquo;s modulus of 0.865\u0026thinsp;\u0026plusmn;\u0026thinsp;0.073 TPa and fracture strength of 70.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.5 GPa due to its perfect atomic arrangement[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. he strong interlayer interaction in h-BN nanoflakes shows an enormous potential for use in sustainable electronics [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The h-BN nanoflakes offering a unique surface adsorption capability and high surface-to-volume ratio can provide greater sensitivity and fast responsiveness in sensing applications [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn addition, h-BN shows van der Waals (vdW) force and π\u0026ndash;π interactions with polymers; the partial ionic electronic structure of B-N bonding can be advantageous for molecular interactions with polymer materials [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Molecular dynamics (MD) simulation predicted that the molecular interaction between polymers and BN materials could be more efficient because of the polarized nature of B-N bonding, the high bonding potentials of B and N atoms, along with vdW force and Coulomb interactions between BN and polymer matrix [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Tutgun et al. studied the paramount effect of h-BN on the polymer composite in terms of thermal and mechanical stability, showing thermal stability up to 190\u0026deg;C [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. In another study Zhi et al. synthesized a self-organized composite membrane based on polyaniline and boron nitride nanotubes (BNNTs). The composite exhibits excellent mechanical stability and strong BNNT interactions with the polymer and their uniform distribution make the BNNT polymer composite an interesting material for various applications [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Wang et al. synthesized highly water dispersed functional boron nitride, and its composite with polyvinyl alcohol (PVA), the nanocomposite films showed high flexibility and retained their properties with improving mechanical performance [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Owing to these excellent properties, h-BN/polymer films show enormous potential for their use in flexible devices. For wearable electronics, flexibility is certainly essential, yet additional key features including great thermal stability, fast response times, a broad detection range, and high sensitivity are also essential.\u003c/p\u003e \u003cp\u003eThus, introducing h-BN into the polymer is a practical approach to improving humidity sensors' flexibility and thermal stability. Amongst these polymer materials, polyvinyl alcohol (PVA) stands out as a excellent humidity-sensing material due to its hydrophilicity, mechanical strength, flexible nature, thermostability, biocompatibility, transparency, and cost-effectiveness[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. From a chemical perspective, PVA offers a large number of hydroxyl (OH) groups. The dielectric properties of PVA vary as hydrogen bonds are created in the presence of water molecules [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. PVA has suitable film-forming properties when composited with other 2D materials. Despite the remarkable properties of h-BN/polymer composites, research has predominantly focused on enhancing their mechanical properties [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis work aims to synthesize the h-BN/PVA nanocomposite with easy processing, improved conductivity, thermal stability, flexibility, and transparency of h-BN polymer composites, and good mechanical properties for humidity-sensing applications. We have developed a cost-effective, flexible humidity sensor with an Au electrode deposited on a PET substrate in a capacitive design. This sensor utilizing h-BN/PVA nanocomposite detects humidity levels with changing capacitance under varied conditions such as bending, high temperature, and longer periods. h-BN nanoflakes synthesized via an ultrasonic method introduce oxygen-rich groups to its surface, enhancing the adsorption of the water molecule [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Incorporation of h-BN into PVA increases its water absorption capacity due to a larger surface area, thus boosting moisture sensitivity [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Different proportions of h-BN/PVA to develop an ideal humidity-sensitive layer. The sensor's performance was thoroughly examined across a 10\u0026ndash;90 %RH rane, assessing its bendability, thermal stability, and response times. The humidity sensing device shows promise for diverse applications, including noncontact control, successful demonstration of Morse code communication and voice recognition. An IoT-based wireless sensing system for real-time breath and proximity detection is also presented.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials and methods\u003c/h2\u003e \u003cp\u003ePolyvinyl alcohol (PVA) was procured from Sigma-Aldrich, Seoul, Korea, while Boron nitride was obtained from Graphene Supermarket. Ethanol (CH\u003csub\u003e3\u003c/sub\u003eCH\u003csub\u003e2\u003c/sub\u003eOH) and deionized water were purchased from Sigma Aldrich, Seoul, Korea. Firstly, the PVA solution was prepared by blending PVA powder with DI water at a 1:10 mass ratio and left at room temperature for 24 hours to facilitate swelling. Subsequently, the solution was subjected to magnetic stirring on a hot plate at 70\u0026deg;C for 12 hours to ensure complete dissolution of the PVA. Secondly, 5.4 mg BN powder was added to 1 liter of ethanol/water as a dispersion solvent. The sealed flask was sonicated for 8 hours, and then the dispersion was centrifuged at 3000 rpm for 20 mins to remove aggregates; detailed process can be found in [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. As a result, 2D flakes consisting of 50\u0026ndash;200 nm lateral size were obtained. The preparation process of the h-BN and PVA is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb. In order to evaluate the effect of the concentration of h-BN on the moisture sensitivity. The PVA solution was divided into two parts, and h-BN with concentrations of (2:1) and (1:1) were added. Finally, the solution was placed on a magnetic stirrer for 1 hour at 1000 rpm at room temperature to ensure a homogenous dispersion of the h-BN in the PVA solution\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Sensor Fabrication\u003c/h2\u003e \u003cp\u003eThe process of fabricating humidity sensors based on Flexible PET involved meticulous steps. The first comprehensive cleaning procedure for PET substrate uses an ultrasonic bath with ethanol, isopropanol, and de-ionized water, respectively. This treatment extended over a 20-minute duration to remove any dust particles and contaminants adhering to the substrate's surface. Following this, the substrate was left to air dry at room temperature. Then, the PET substrate with a shadow mask was put inside the chamber and underwent a 10-minute processing phase. The Gold (Au) electrode was deposited on a PET substrate using plasma sputter coating, featuring an interdigitated comb-like structure comprising seven pairs of electrode fingers. The width of each electrode finger was 0.25mm, and the spacing between electrode fingers was 0.75mm as shown in detail schematic diagram of Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. After electrode fabrication, the active sensing layer of h-BN/PVA was drop casted on the interdigital electrode and was placed at room temperature for 24 hours to dry to complete the preparation of the humidity-sensitive layer.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Characterizations","content":"\u003cp\u003eWe precisely examined the nanostructure and surface characteristics of our samples, and the top view of the h-BN/PVA active layer was captured using a high-resolution desktop scanning electron microscope (SEM) (phenom pharos G2) while dispersive X-ray spectroscopy (EDS) was used to understand the elemental composition of h-BN/PVA layer, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec,d. The composite films are further characterized through FTIR (Nicolet 6700). The crystalline structure of sensing layer was analysed by Wide-angle X-ray diffraction (WAXD), using a PAN anlytical Empyrean X-ray diffractometer. The instrument was equipped with a Co (Kα1 (λ)\u0026thinsp;=\u0026thinsp;1.789 \u0026Aring;) source, a PIXcel 3D detector, a tube voltage of 45 kV and current of 40 amps. Thermo Scientific DXR3xi Raman Imaging Microscope was used to gain insights into the structural properties, lattice dynamics, and phonon behavior of h-BN/PVA nano composite, which are vital for understanding and optimizing its performance in sensing applications.\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Sensor Evaluation\u003c/h2\u003e \u003cp\u003eWe measured the electrical capacitance during our sensor assessment using a U1733C Keysight LCR meter. The measurements were conducted at frequencies of 1 kHz, 10 kHz, and 100 kHz while maintaining a constant ambient temperature of 25\u0026deg;C. To ensure precise control over the humidity environment, we utilized a custom-built airtight glass box equipped with a humidifier and an N\u003csub\u003e2\u003c/sub\u003e gas cylinder, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec. Adjacent to the IDE humidity sensor, we placed a reference sensor (HTU-21D) and employed an Arduino circuit to accurately measure the percentage of relative humidity (%RH). We systematically increased the humidity inside the chamber while continuously collecting data to compare our custom IDE sensor with the reference sensor. We introduced N\u003csub\u003e2\u003c/sub\u003e gas into the chamber through a nozzle to reset the experimental conditions, effectively reducing the humidity to 10% RH. Simultaneously, we connected the LCR meter to a laptop to capture real-time capacitance spectra, ensuring precise evaluation of our sensor\u0026rsquo;s performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Surface morphology.\u003c/h2\u003e \u003cp\u003eThe surface morphology of the h-BN/PVA nanocomposite was examined in depth through SEM characterization. Before imaging, the samples were sputter coated using a Pt metal target. The SEM images can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea,b verified the exfoliated h-BN materials and particle size, shape, and texture distribution. The nanometer scales are arranged in a layered structure with irregular round shapes, whereas they have lateral dimensions on the nanometer scale ranging from 80 nm to 180 nm. High-resolution particles in more detail are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec. The h-BN particles exhibited diverse morphologies, such as spherical, and ellipsoidal shapes, which increased their surface area, enhancing interaction with water molecules in the surrounding atmosphere. During the sonication procedure, the h-BN bounds interact with water molecules, which causes the hydroxyl functionalization of h-BN and penetration of water molecules between the BN layers. This led to enhanced sensing sensitivity. The elemental composition of PVA/hBN was examined by using Energy Dispersive Spectroscopy (EDS), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed. EDS-mapped picture with a magnification of 1 \u0026micro;m. The elemental mapping demonstrates a uniform distribution of C, O, B, and N atoms throughout the sample. The B K, N K, C K, and O K, series were presented with a magnification level of 1 \u0026micro;m in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee, respectively. The h-BN/PVA nano composite major peaks indicate the compositions of B, N, C, and O with 23.23%, 17.67%, 10.75%, and 48.35%, of each element in the humidity sensing layer, respectively as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef. The composite films are further characterized through FTIR and presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg. The low-intensity PVA peak at 1600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is due to the C\u0026ndash;H and O\u0026ndash;H bond bending. The 900\u0026ndash;1200 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e peak in composites indicates the co-existence of h-BN and PVA. The strong broadband at 3000\u0026ndash;3600 cm\u0026thinsp;\u0026minus;\u0026thinsp;1 corresponds to the O\u0026ndash;H stretching vibration of the hydroxyl group of PVA [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. The FT-IR spectrum shows many hydrophilic groups of PVA/hBN composite film along with the FT-IR, h-BN/PVA nanocomposite is also characterized through Raman spectroscopy, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh. The obtained the characteristic peaks of h-BN/PVA material at wavenumbers of 1410 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponds to the characteristic vibrational phonon mode (E2g) of h-BN. The absence of other Raman peaks confirms that the chemical structure has been preserved after exfoliation. For the PVA, the most intense band centered at 2912 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is assigned to the stretching vibrations of \u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe XRD patterns of h-BN/PVA are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei. The XRD pattern of PVA illustrates a broad peak at 2θ\u0026thinsp;\u0026asymp;\u0026thinsp;19.55, corresponding to (101) crystal reflection planes. The sharp peak at 31\u0026deg; confirms the presence of h-BN in the nano composite [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. it is evident that the peaks remained unchanged in both materials in terms of diffraction angle and shape, suggesting that the high-pressure homogenisation exfoliation process did not damage the crystalline structure of the pristine material. h-BN retained the high crystalline structure of the bulk BN.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Electrical Characterization of h-BN/PVA humidity sensor\u003c/h2\u003e \u003cp\u003eThe performance of a humidity sensor is determined by design factors, which are the sensing layer diameter, thickness of the layer, and electrode. The capacitance of a typical parallel plate electrode type for a capacitive humidity sensor can be expressed as Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e):\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$C= {\\upvarepsilon }\\left(\\text{R}\\text{H}\\right)* {{\\upvarepsilon }}_{0}\\text{*}\\left(\\frac{\\text{A}}{\\text{d}}\\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere A is the area of the plate, d is the distance between the two plates, ɛ(RH) is the dielectric permittivity that is a function of the relative humidity and ɛ\u003csub\u003e0\u003c/sub\u003e the dielectric permittivity at 0%RH [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe capacitance of a material is influenced by its dielectric properties, which can be affected by the presence of moisture. This study uses a thin film of a h-BN/PVA composite as the active layer of a capacitive humidity sensor. The dielectric constant of the active layer changes as a result of water vapour adsorption or desorption, leading to a change in the sensor\u0026rsquo;s capacitance. PVA was chosen because it responds well to humidity owing to the large number of hydroxyl groups present that can interact through hydrogen bonds. By absorbing water molecules, PVA swells, indicating an altering of chain conformation and also enhancing the flexibility and response to capacitance in the humidity sensor. Boron Nitride is introduced due to its chemical stability, mechanical strength, and flexibility. To study the effect of different concentrations of h-BN nanoparticles on the output performance of the humidity sensor, we kept the concentration of PVA fixed and varied the concentration of h-BN. Therefore, the comparison analysis of two humidity sensor (1:1 and 1:2) samples reveals notable performance differences. The impact of the 1:2 of h-BN in a PVA solution the sensor displays a capacitance change ranging from 566 pF to 16.5 nF. This change is evident across a relative humidity range from 10% RH to 90% RH at 1 kHz, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. However, the output capacitance of the sensor increased with the increase of h-BN concentration 1:1 in the range of 10\u0026ndash;90% RH, which exhibited a certain of regularity, the capacitance response increased from around 2.27 nF to 79.3 nF, 1.47 nF to 12.7 nF, and 26 pF to 2.32 nF at a test frequency of 1, 10, and 100 kHz, respectively. It is crucial to note that this response is significantly lower compared to the performance achieved with h-BN in PVA at a 1:1. In Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb,c. The sensor exhibits a nearly linear response of at frequencies of 1 kHz, 10 kHz, and 100 kHz across the range of 10\u0026ndash;90%RH and also normalized capacitance demonstrates consistent performance across these frequencies, showcasing its effectiveness in humidity detection.\u003c/p\u003e \u003cp\u003eStability and repeatability are the fundamental characteristics of a proficient humidity sensor to be used in everyday applications [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. To evaluate the flexibility of the sensor, we have tested the proposed humidity sensor at three different angles of deformation (30\u0026deg;, 60\u0026deg;, and 80\u0026deg;), as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed. During the experiment, the sensor transitioned from RH 10% to RH 90% conditions. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, there was no significant difference in response across varying bending degrees, highlighting the sensor's excellent stability, durability, and flexibility performance. Furthermore, to examine the long-term consistency of the h-BN/PVA-based humidity sensor, it was opened to humidity conditions for 90 days, and the capacitive response was measured at various relative humidity conditions. The capacitance responses remained highly stable with minimal error, affirming the sensor's reliability over an extended duration. Humidity measurements at higher temperatures are substantially more challenging because at high temperatures relative humidity is generally very low and also most organic sensor materials are not stable at high temperatures. In addition, many industrial processes a high durability and resistance to harsh environments are of particular importance. For example, industrial branches with high energy saving potential, such as wood drying or textile processing, demand sensors with high tolerance to corrosive/oxidizing species or contaminants with high molecular weight at high temperatures. These requirements often exclude the utility of conventional sensor materials as they are usually unstable under these conditions[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Hence, for high-temperature humidity sensing extremely sensitive devices are necessary, in this respect h-BN shows superior properties due to their temperature stability and chemical stability[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. Here we report on a h-BN/PVA nanocomposite sensor device, we show humidity-sensing data up to 80\u0026deg;C under constant humidity (70 %RH) in a sealed envionment. The synthesized sensor in this work showed a high thermal stability which makes it generally eligible for high-temperature applications investigations as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee. The results indicate minimal capacitance variation at 40\u0026deg;C and 60\u0026deg;C. However, at 80\u0026deg;C, a decrease in capacitance is observed, which is attributed to water vapor evaporation and reduced humidity levels at higher temperatures. The sensor shows a near-linear response behavior to relative humidity with only a little influence of the temperature.\u003c/p\u003e \u003cp\u003eThe transient responses of the sensors were analyzed to assess the device response and recovery times during humidification and dehumidification. Two distinct air streams were injected for this evaluation: one stream consisted of compressed dry air, while the other conveyed extremely humid air directly from the humidifier. In this experimental setup, a humidifier was utilized to alternate between 10 and 90%RH levels. A Nitrogen gas was connected to the control chamber and gradually introduced to reduce the humidity levels from 90%RH to 10%RH, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh. h-BN/PVA (1:1) shows rough surface and porous structure to facilitate adsorption/desorption and diffusion of moisture. Accordingly, it presents repeatable responses during cyclic switching between 90%RH and 10%RH, exhibiting relatively fast response time of 3.5 s and 4 s for t\u003csub\u003eadsorption\u003c/sub\u003e and t\u003csub\u003edesorption\u003c/sub\u003e, respectively as can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei. These results suggest that the proposed sensor is well-suited for real-time practical applications, underscoring its commendable transient response and recovery times.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"5. Humidity Sensing Mechanism","content":"\u003cp\u003eThe humidity sensing mechanism of h-BN can be explained based on the fact that water molecules are firstly adsorbed on the surface-active sites of the h-BN through double hydrogen bonding[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Two sequential processes, chemisorption and physisorption, can be used in this humidity sensing process to describe the adsorption of water molecules onto the sensor surface[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Water molecules initially come into contact with the h-BN/PVA film and are absorbed by the hydrophilic PVA matrix and BN atoms of the boron nitride nanoflakes. The protons can pass through the center pores of the hexagonal rings of h-BN. The electron negativity of N atom of h-BN is much stronger than that of B atom, so the electron clouds on N atoms are much larger than those on B atoms. Based on the different electron negativity values of B and N atoms, the pores in h-BN have triangular shapes, the pore size of h-BN (approximately 3.0 \u0026Aring;2)[\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. At low relative humidity (RH), water molecules physiosorb onto the sensor surface, and as RH increases, they chemisorb onto the chemisorbed layer, forming a bulk liquid-like multilayer. Both h-BN and PVA have moisture-absorbing properties, making them sensitive to humidity. When combined in a composite with proper dispersion, these materials can potentially enhance the sensor\u0026rsquo;s overall humidity sensitivity. The composite\u0026rsquo;s improved dielectric properties, resulting from combining a hydrophilic polymer like PVA with a insulating material like h-BN, increase the sensor\u0026rsquo;s permittivity. This higher permittivity amplifies the capacitance change caused by moisture absorption, leading to increased sensitivity. The active sensing film between the interdigitated electrodes, with its higher permittivity, polarizes more under the applied electric field, thus increasing the device\u0026rsquo;s capacitance. PVA can act as a physical linker in the composite, emphasizing the importance of achieving a uniform dispersion of h-BN particles within the h-BN matrix.\u003c/p\u003e \u003cp\u003eA secondary purpose of the h-BN flakes is to increase the surface area of the thin film that is clear from the surface SEM images Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e \u003cb\u003e(a,b)\u003c/b\u003e. This increase in surface roughness and area results in higher sensitivity and easier diffusion of water molecules into and out of the active layer. Furthermore, upon adsorption of water molecules into the thin film, the overall dielectric constant of the active region increases as compared to a dry film. This results in an increase in the capacitance of the sensing device with increasing relative humidity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ecompares the performance parameters of high-end materials and the composite based humidity sensors published in literature. The study successfully achieves a desirable property: high flexibility, thermal stability, and excellent durability. These benefits translate to the proposed h-BN/PVA humidity sensor exhibiting exceptional performance.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSensing material\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRange (% RH)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eResponse time (s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRecovery time (s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSensitivity % RH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eFlexibility/ Temp Stability\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eref\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"1\" nameend=\"c9\" namest=\"c9\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBaTiO\u003csub\u003e3\u003c/sub\u003e/PVDF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40\u0026ndash;90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e0.2416 pF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIn\u003csub\u003e2\u003c/sub\u003eSe\u003csub\u003e3\u003c/sub\u003e/PEDOT: PSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u0026ndash;95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e0.177 \u003cem\u003e\u0026micro;\u003c/em\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGO/MWCNT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e43\u0026ndash;97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e7980 pF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMCM-41/PEDOT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11\u0026ndash;75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e3x\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePVDF/ZnO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u0026ndash;80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eO/X\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSnO2/RGO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11\u0026ndash;97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e1604.89 pF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLiquid exfoliated MoS\u003csub\u003e2\u003c/sub\u003e nanosheets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11\u0026ndash;96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e178.38 pF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMoS\u003csub\u003e2\u003c/sub\u003e/Go\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11\u0026ndash;97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e369 pF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eh-BN/ PVA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u0026ndash;90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e963 pF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eO/O\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003eThis work\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e: \u003cb\u003eComparison of the performance parameters of high-end materials and composite-based humidity sensors\u003c/b\u003e\u003c/p\u003e"},{"header":"6. Applications","content":"\u003cp\u003eThe humidity-detecting capability of the h-BN/PVA composite was examined for various applications to explore emerging sensor applications, including proximity, breathing test, morse code, and IOT-based Real-time. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, the sensor's ability to detect breathing patterns through the mouth was evaluated. Dynamic capacitance changes were observed during inhalation and exhalation, correlating with moisture fluctuations around the mouth. In addition, in \u003cb\u003efigure b\u003c/b\u003e, the proximity test was conducted by placing a dry finger at varying distances of 6, 9, and 12 mm from the sensor, resulting in capacitances of 35, 20, and 10 nF, respectively, at 1 kHz. Moreover, the repeatability and cyclic response tests further demonstrated the consistency and reliability of our sensor, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec,d. The distances of 6 and 12 mm have been tested as the suitable experimental values for Morse code as a communication protocol in the message transmission process, and the corresponding capacitance values are defined as high response and low response, respectively. According to this principle, contactless message transmission can be achieved. Morse code is adopted as a communication protocol in the message transmission process. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee exhibits the Morse code table, which consists of different letters in a combination of dashes and dots. The capacitance value in the output greater than 30 nF is recorded as a dot; otherwise, it will be noted as a dash, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef. Thus, letters can be coded by diverse combinations of high and low responses. To intuitively perform the excellent capability of the sensor, three words, JNU (Jeju National University), were input by using this system. The inputting accuracy of this system is impressive through a three-word demonstration, which is enough to realize the message transmission.\u003c/p\u003e \u003cp\u003eIoT-enabled electronic systems are rapidly gaining prominence across various sectors, such as healthcare, consumer goods, security, and agriculture. The Node MCU is an open-source IoT platform featuring the ESP8266 Wi-Fi module equipped with GPIO pins for sensor and actuator connections. In this context, we leverage the Node MCU for real-time monitoring of proximity and breathing tests via IoT cloud-based platforms. The wireless system comprises a proposed flexible humidity sensor, a data processing unit, an inbuilt Wi-Fi module for data transmission, and a power supply unit. The electronic system is operated through a \u0026sim;3 V supply and a 32-bit microcontroller incorporated with an ESP-12E module (Wi-Fi SoC). The Arduino IDE platform is used to write the source code in embedded C programming language and upload it to the microcontroller to receive analog input from a flexible humidity sensor based on capacitance variations. Cloud technologies are ideal for remotely monitoring physical activity and transmitting data to a cloud computing database accessible via mobile devices. This enables real-time monitoring from any location, especially in the healthcare sector, by improving communication between patients, physicians, and healthcare professionals. Arduino Cloud is a platform provided by Arduino that enables users to monitor and control their Arduino devices remotely over the internet. We developed an IoT-based humidity sensor for real-time wireless monitoring of breathing and proximity, as illustrated in the Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg. The detected humidity data is received and displayed in real-time on a smartphone.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"7. Conclusion","content":"\u003cp\u003eA Capacitive sensor design with h-BN/PVA nanocomposite as the sensing layer and gold layers as electrodes enables effective humidity measurement across diverse conditions. Boron nitride emerges as a promising material owing to its exceptional mechanical strength, chemical resistance, and thermal stability. Also, the large surface area and rich hydrophilic functional groups of h-BN nanoflakes with PVA boost sensing performance. The h-BN/PVA composite demonstrates a linear response with response and recovery times of 3.5s and 4s, respectively. Furthermore, sensor exhibit remarkable stability even under high temperatures. The stability tests conducted at various temperatures (40\u0026deg;C to 80\u0026deg;C) and bending conditions (30\u0026deg; to 80\u0026deg; angles) underscore its robustness. The humidity sensor developed underwent successful testing for practical applications, including respiratory monitoring and proximity sensing (finger test at varying distances from the sensor). Its precise humidity monitoring capability enables implementing Morse code communication and real-time wireless monitoring for Internet of Things (IoT) applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eDeclaration of Competing Interest\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding information\u003c/h2\u003e \u003cp\u003eThis work was supported by \"Regional Innovation Strategy (RIS)\" through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE)(2023-RIS009).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization, Shahzad Iqbal; Methodology, Shahzad Iqbal, and Shenawar Ali Khan; Software, Shahzad Iqbal; Formal analysis, Shenawar Ali Khan and Bibi Ruqia; Investigation, Woo Young Kim and Shenawar Ali Khan; Resources, Woo Young Kim; Data curation, Shahzad Iqbal and Shenawar Ali Khan; Writing\u0026mdash;original draft, Shahzad Iqbal; Writing\u0026mdash;review and editing, Shenawar Ali Khan, Bibi Ruqia, and Woo Young Kim; Visualization, Shahzad Iqbal and Syed Adil Sardar; Supervision, Woo Young Kim; Project administration, Woo Young Kim; Funding acquisition, Woo Young KimAll authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis research was supported by \"Regional Innovation Strategy (RIS)\" through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE)(2023-RIS009).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eJavaid M, Haleem A, Rab S, Singh RP, Suman R (2021) Sens Int 2:100121\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhan SA, Iqbal S, Rahman SA, Saqib M, Rehman MM, Kim WY (2024) J Science: Adv Mater Devices 9:100706\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHe C, Korposh S, Correia R, Liu L, Hayes-Gill BR, Morgan SP (2021) Sens Actuators B Chem 344:130154\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKimura M (1996) Sens Actuators B Chem 33:156\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou C, Zhang X, Tang N, Fang Y, Zhang H, Duan X (2020) Nanotechnology 31:125302\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrung TQ, Duy LT, Ramasundaram S, Lee N-E (2017) Nano Res 10:2021\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShinghal DK, Noor A, Srivastava N, Singh R (2011) Int J Wirel Mob Networks (IJWMN) 3:118\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu T-T, Chen Y-Y, Chou T-H (2008) J Phys D Appl Phys 41:085101\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSu P-G, Wang C-S (2007) Sens Actuators B Chem 123:1071\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYao W, Chen X, Zhang J (2010) Sens Actuators B Chem 145:327\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee C-Y, Lee G-B (2005) Sens Lett 3:1\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBlank TA, Eksperiandova LP, Belikov KN (2016) Sens Actuators B Chem 228:416\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZampetti E, Pantalei S, Pecora A, Valletta A, Maiolo L, Minotti A, Macagnano A, Fortunato G, Bearzotti A (2009) Sens Actuators B Chem 143:302\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNajeeb MA, Ahmad Z, Shakoor RA (2018) Adv Mater Interfaces 5:1800969\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee C-W, Park H-S, Kim J-G, Choi B-K, Joo S-W, Gong M-S (2005) Sens Actuators B Chem 109:315\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBlank TA, Eksperiandova LP, Belikov KN (2016) Sens Actuators B Chem 228:416\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhan K, Tareen AK, Iqbal M, Ye Z, Xie Z, Mahmood A, Mahmood N, Zhang H (2023) Small 19:2206147\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHarith Z, Zain HAA, Batumalay M, Harun SW (2019) J Phys Conf Ser. 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Boron nitride emerges as a promising material owing to its exceptional mechanical strength, chemical resistance, and thermal stability. Herein, flexible humidity sensors based on 2D hexagonal boron nitride (h-BN) were synthesized by sonication-assisted exfoliation to introduce oxygen-rich groups to its surface. This process resulted in h-BN nanoflakes with 50\u0026ndash;180 nm sizes. Polyvinyl alcohol (PVA), a well-known hydrophilic polymer, was used as the polymer matrix to disperse the h-BN nanoflakes, and the resulting nanocomposite was coated on a flexible interdigitated electrode as a sensing layer. The sensor's response was measured between 10 to 90%RH of humidity levels, and the maximum change in capacitance from 2.2 nF to 79.3 nF, at 1 kHz was recorded with fast response and recovery times of 3.5 s and 4 s, respectively. Moreover, the h-BN/PVA nanocomposite shows remarkable stability under various conditions, such as bending, high temperature, and longer periods, highlighting its durability. The developed sensor was successfully tested in practical applications such as respiratory and proximity-sensing, real-time wireless monitoring for Internet of Things (IoT) applications, and Morse code communication.\u003c/p\u003e","manuscriptTitle":"High-temperature invariant and Deformation-durable h-BN/PVA Nanocomposite for Highly-reliable Humidity Sensor enabling Morse Code Communication and Real-Time Wireless Respiratory Monitoring","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-18 17:32:05","doi":"10.21203/rs.3.rs-4565983/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"702a04ac-c55a-4bda-bba2-102e755db0ae","owner":[],"postedDate":"July 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-09-14T14:59:48+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-18 17:32:05","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4565983","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4565983","identity":"rs-4565983","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}