Sub-μW signal power doppler radar heart rate detection

Periodic motion, such as that resulting from cardiopulmonary activity, can be measured by direct-conversion microwave Doppler radar. In such systems, motion is measured as phase modulation and measurement sensitivity is significantly affected by phase noise and amplitude modulation sidebands in the local oscillator. Presented here are experimental results of heart rate measurements under various signal output power conditions, with consideration for the impact of respiration. Measurements were made using a custom compact quadrature direct conversion Doppler radar circuit, and results indicate that heart rate can be accurately assessed with transmit power for levels as low as 20nW for a subject distance of one meter. This is the lowest power ever reported for ISM band CW doppler radar heart beat detection.