Dependency of Waveforms in Intermittent Transmission at Mobile Phone Frequencies on Electromagnetic Interference With Medical Devices

This study focuses on the effect of waveforms, i.e., signal length and period in intermittent transmission, on electromagnetic interference (EMI) with medical devices. It was already shown that intermittent transmission with the period of 1 s (500 ms: ON and 500 ms: OFF) tends to cause EMI on medical devices compared to continuous transmission. To evaluate the impact of waveforms on EMI with medical devices, we conducted an experiment at 837.5 MHz and 1950 MHz using five medical devices that yielded the following results. For EMI dissipation, the input power of an antenna simulating mobile phones increased and the separation distance between the antenna and medical device decreased as the signal length became shorter in the case of a signal length of less than 10 ms. On the other hand, the signal period exhibited no specific tendency regarding such power and distance. We confirmed that previous EMI tests, in which we used a radio signal with the length and period of 100 ms in intermittent transmission, were conservative from the viewpoint of waveforms. Results of this investigation indicate that the influence of EMI on medical devices does not depend on the average power but on the burst power. Based on this, EMI characteristics with medical devices for a certain radio system could be estimated based on previous EMI test results for other radio systems if their frequencies are close to each other and their signal specifications are clearly determined.