Heartbeat Measurement Results by a VHF-Band Antenna with an Adaptive Matching Control Algorithm

Non-contact detection using a Doppler sensor has been studied for heartbeat measurement. However, Doppler sensors are affected by reflected waves from surrounding objects, making accurate acquisition of heartbeats difficult. To solve this problem, we have proposed the heartbeat sensor using of the small loop antenna with low radiation efficiency. When it is placed near subject's heart, the antenna input impedance change according to surroundings. In this paper, we show an adaptive control algorithm of a variable matching circuit according to changes in the surroundings of the antenna. The effectiveness of the proposed method is verified by measurements for multiple persons.