Non-contact heartbeat and respiration detector using capacitive sensor with Colpitts oscillator

A capacitive sensor for detecting the heartbeat rate of a human without direct contact with the skin is investigated. Precordial movement changes the capacitance between patch electrodes and modulates the frequency of a Colpitts oscillator. Heartbeat and respiration information can be obtained by demodulating the oscillating signal. Heartbeat signal obtained by bandpass filtering the harmonics of heartbeat frequency is separated from the demodulated signal.