A Wearable CMOS Impedance to Frequency Sensing System for Non-Invasive Impedance Measurements

In this paper, we demonstrate a novel non-invasive, wearable impedance sensor. The impedance sensor, using an impedance to frequency measurement, with two modes of resistance and capacitance measurement is implemented in CMOS 130 nm technology. The sensor consisting of current and voltage comparators for different mode of measurement, has a low power consumption of 30 μW per channel. The sensor is demonstrated in two applications, thoracic impedance and hand gesture recognition. Thoracic impedance is based on impedance modulation through fluid accumulation. Hand gestures are detected through tissue impedance sensing. The full thoracic impedance sensing system is smaller than a credit card, low cost, and consumes 3 mW which includes the sensor, transmitter, and power control unit. Data received by this sensor can be easily transferred for further processing and, eventually, detection of heart failure. The electrodes were implemented using conductive paint, and the system was validated using passive loads to represent human tissue models and test subjects. The hand gesture system operates on 600  μW with the maximum number of electrodes, and uses adhesive copper with electrical paint as electrodes.