Applications of Electric Potential (Displacement Current) Sensors in Human Body Electrophysiology

C J Harland, T D Clark and R J Prance

Centre for Physical Electronics and Quantum Technology, School of Science and Technology, University of Sussex, Brighton, Sussex BN1 9QT, U.K, t.d.clark@sussex.ac.uk

ABSTRACT

We have been exploring the use of ultra high input impedance, very low noise floor, electric potential sensors in the detection of a variety of electrical signals generated by the human body. In this paper we review the progress we have made so far. In the design of electric potential sensors we have combined an efficient source/sensor coupling with an electrometer amplifier to which we have applied a range of feedback and stabilisation techniques. These sensors detect displacement current rather than real electric charge current with the consequence that they are very well suited to the non-contact measurement of electric potentials created by various sources. They also function at room temperature, they are cheap and they are eminently scalable in size. In this paper we discuss the detection of three characteristic human body electrical signals, namely electrocardiograms (ECGs), electroencephalograms (EEGs) and electro-oculograms (EOGs). With a base noise floor as low as 30nV/√Hz from 1Hz upwards, we have been able to record ECGs, EEGs and EOGs with remarkable fidelity, either with the sensors in mechanical (but not charge current) contact with the body or off-body without any direct mechanical or electrical contact. Given this low noise floor and the ultra high input impedance, we have recorded the electrical activity of the human heart (ECG) at a distance of 1 metre from the surface of the body. We have also recorded the electrical activity of the brain (EEG), in particular the α and β rhythms, from 3mm above the surface of the hair. The high quality of ECGs, EEGs and EOGs shown in this paper, indicate to us that a whole new direction in electrophysiological measurement is opening up. There is now the prospect of high resolution spatio-temporal array imaging of the human body (e.g. the heart and the brain) becoming a reality in the near future using this new sensor technology.

Keywords Electric potential sensor, displacement current, body electrophysiology