Advanced non-contact near-field proximity vital sign sensor using phase locked loop

A non-contact near-field vital sensor based on phase locked loop (PLL) circuit is proposed for vital signal detection, such as heartbeat and respiration. The main idea of the proposed vital sensor is to utilize the oscillation frequency deviation caused by the input impedance variation of the planar type circular resonator within near-field region due to respiration exercise of a human. A low loaded quality factor resonator and the small gain of the voltage controlled oscillator (VCO) allow the sensor to increase the detection range. Also, the PLL is employed as a frequency deviation detector, which converts the amount of the frequency deviation into a voltage difference in this work. Experimental results reveal that the proposed vital sensor can be used to detect the heartbeat and respiration signals within 50 mm measurement distance.