Study of Electromagnetic Interference Caused by Passive Intermodulation of Wireless Medical Telemetry Services

Abstract

Passive intermodulation may generate when two signals are input in the receiver and is an issue that threatens wireless communications. It has been recommended that medical facilities operating wireless medical telemetry services should be conduct zone management for avoiding the effect of passive intermodulation. In this study, the occurrence frequency of passive intermodulation in a wireless medical telemetry service was investigated using simulated environment. Passive intermodulation occurred when two input signal levels were high and frequency deviation of two signals were narrow. The amplitude of passive intermodulation depends on the input signal level in which near its frequency. Passive intermodulation effected the reception of wireless medical telemetry services and degraded carrier to noise ratio as 2 to 4 dB worse rather than Gaussian noise. The signal level of wireless medical telemetry service coming from another floor has no potential to cause passive intermodulation by conducting zone management as properly. However, the output power of wireless communication devices that using same frequency of wireless medical telemetry services such as telecontrol devices is generally greater (10 mW). When the introduction of these devices, it would be desirable for clinical settings to conduct prepare zone management to avoiding passive intermodulation.