Noncontact human electrophysiological measurements using a new displacement current sensor

In this paper we describe a newly developed displacement current sensor for non-contact, non-invasive human electrophysiological measurements, well suited for applications requiring remote detection of human presence. The sensor is built around an improvised transimpedance amplifier circuit, which employs a resistive feedback T-network to eliminate the need for ultra high values resistors normally needed for this type of measurements. It provides an operational bandwidth of 0.5-250 Hz and a remarkable noise floor of 7.8 μV/√Hz at 1Hz down to 30 nV/√Hz at 1 kHz. The sensor is particularly suitable for non-contact measurement of human electrophysiological signals, such as the ECG. Reported results, all obtained in normal unshielded environment, demonstrate the sensor´s capability in measuring human heart related electrophysiological signals at off-body distance up to 50 cm. Two different sensor configurations are presented; a single-ended signal measurement using one sensor, and a differential signal measurement using two sensors.