Electric potential probes - new directions in the remote sensing of the human body

Abstract

In this paper we describe a new approach to the detection of human body electrical activity which has been made possible by recent advances in ultra-low-noise, ultra-high-input-impedance probes. As we demonstrate, these probes, which do not require a real current conducting path in order to operate, can be used non-invasively both on and off body. We present remarkable new data showing the application of these probes to the remote, off-body, sensing of the electrical activity of the heart at distances of up to 1 m from the body and to high-resolution electrocardiograms. We suggest that in the future such probes may form the basis of a radically new technology for measuring the dynamics of the human body as well as in non-contact, imaging systems for pre-emptive and diagnostic medicine.

A comparative study of electrical potential sensors and Ag/AgCl electrodes for characterising spontaneous and event related electroencephalagram signals

“…The input capacitance is ~8 pF with an associated voltage noise between 0.1-10 Hz of 0.5 µVp-p. After consideration of the expected signal amplitudes and frequencies the sensor was configured to have an operational bandwidth of 0.1 Hz to 78 Hz and a voltage gain of x50. The voltage gain was distributed between two stages with x5 and x10 respectively for the first and second stages (for details of the operation of EPS devices see (Harland et al, 2002), for block diagram see Figure 1). Potential Sensor used in this study (12 mm and 18 mm), the microchip version of the Electrical Potential Sensor for ECG purposes (not used in this study) and a 5 pence coin, shown for scale.…”

“…Volume conductance is a general property of electrical currents to follow the path of least resistance, which causes activity from a cortical dipole to spread out further from the source and also to be smeared or diverted as it tries to pass through the highly resistant skull (Harland et al, 2002). These limitations have been addressed in other imaging techniques by using SQUID (super conducting quantum interference device) magnetometer systems in magnetoencephalography (MEG), which are less susceptible to volume conductance compared to Ag/AgCl electrodes and which do not require direct contact with the scalp (Ahonen et al, 1991).…”

“…Finally, it has been shown that it is possible to remotely record ECG from up to 1m away from a subject using the EPS (Harland et al, 2002). Future studies investigating the EPS will focus on the possibility for remote detection of EEG, in a similar (more cost effective) manner to the SQUID magnetometers, to assess if a similar increase in the spatial resolution is gained with the EPS.…”

“…Electric Potential Sensor technology has already demonstrated its efficacy for research and clinical applications in electrocardiographic (ECG) data acquisition, where the inherent DC stability and short settling time of the EPS is advantageous compared to other insulated electrode implementations (Harland, Clark, & Prance, 2002;H. Prance, 2011).…”

“…Previously it has been demonstrated that the EPS are sensitive to fluctuations in free running brain activity, such as alpha (8-14 Hz) and beta oscillations (14-30 Hz), as well as alpha blocking , an increase in the prominence of the alpha rhythm when the eyes are closed that is replaced by a beta rhythm when the eyes are open (Harland et al, 2002). We sought to expand upon these findings by characterising alpha activity recorded simultaneously from EPS and a standard EEG system using Ag/AgCl electrodes, in terms of the raw signal, frequency spectrum and similarities between the two signals measured by cross correlation.…”