Electromagnetic Disturbance Issues in 400 MHz Wireless Medical Telemetry Systems and Its Countermeasures for Safety Operation

A wireless medical telemetry system (WMTS) is typical medical device that use radio communications and monitor various biological parameters. In Japan, the frequency band of 400 MHz is allocated for WMTS. However, the issues that cause poor reception of WMTS are considerable concern. For example, 400 MHz frequency band is also shared for other radio communication systems. It has been reported that passive intermodulation effect is fatal poor reception effects on WMTS. Additionally, the electromagnetic noises generated from switched-mode power supply, especially installed in light-emitting diode (LED) lamp and can reach over 400 MHz frequency band. In this study, we observed the potential of electromagnetic disturbance in communication+ in WMTS caused by other radio communication systems, an effect of passive intermodulation and noises generated from LED lamp and discussed countermeasures for this serious issue.