Simple low-power demodulator for the measurement of basal and physiological changes of electrical bioimpedance

Wearable sensors constitute a growing trend both as a research tool as well as an end-consumer products. In the physiological signal monitoring fields, the changing signals have a low bandwidth hence most sensing techniques are not power-hungry. Electrical bioimpedance is a non-obtrusive sensing technique and is an interesting choice as it can recover both breathing and pulse rate signals. However, it works at comparatively higher frequencies and usually need demodulation circuitry, meaning higher power consumption. In this work, we show an alternative technique to demodulate the impedance response that need very few components and whose power consumption can be tailored as needed. We show that, by using a 24-bit ADC, the respiration and pulse rate signals as well as the basal impedance are recovered from the demodulated signal and further digital band-pass filters that are easily implemented with currently available low-power microcontroller technology. Further, it constitutes a compact solution, as the sensor needs not to change location to measure these signals.