Electromagnetic Compatibility Issues in 400-MHz-Band Wireless Medical Telemetry Systems and Their Management Using Simplified Methods for Safe Operation

Wireless medical telemetry systems (WMTSs) are typical radio communication–based medical devices that monitor various biological parameters, such as electrocardiograms and respiration rates. In Japan, the assigned frequency band for WMTSs is 400 MHz. However, the issues accounting for poor reception in WMTS constitute major concerns. For example, the 400 MHz frequency band is also shared by other radio communication systems. Further, the intermodulation (IM) effect significantly reduces reception in WMTS. Additionally, the electromagnetic noises generated from electrical devices, such as light-emitting diode lamps and security cameras, can exceed the 400 MHz frequency band as these devices employ the switched-mode power supply and/or central processing unit and radiate wideband emissions. In this study, we analyzed the effects of the electromagnetic interferences caused by other radio communication systems, the IM effect, and the noises generated from electrical devices on WMTS and discussed their management. Moreover, we proposed and evaluated simplified and facile methods for evaluating the electromagnetic environment.