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We describe the measurement of human electrophysiological and movement signals remotely from a seated subject. An ultrahigh impedance electric potential sensor, designed specifically to reject external noise, is used to measure the electric field at distances of up to 40cm from the surface of the body. The sensor is able to provide continuous data acquisition, at full sensitivity, without saturation by external noise sources. Respiration and heart signals are seen simultaneously and are separated using digital filtering techniques. All of the results reported were obtained in an open unshielded environment in close proximity to line operated computer equipment.

We describe a system for the measurement of changes in electric field which occur as a result of the movement of people, or objects, in ambient electric fields with standoff distances of several metres. A passive sensor system is used to measure the changes in electric field which are due to several different mechanisms. From this we are able to extract presence, movement and position information with a positional accuracy of ∼10 cm. Furthermore, by examining the disturbances in ambient ac fields, such as those created by domestic electricity networks, we show that it is possible to recover static field information with a sensor that lacks dc sensitivity. In this way, we demonstrate that tracking of individuals within large room-scale spaces is possible. As a simple, passive, undetectable technique, with no line of sight requirement, these measurements open up new possibilities in security, telehealth and human computer interfacing applications.

We describe the measurement of spatial charge distribution, using a new non-invasive technique. This measurement, based on a 16-element array of ultra-high impedance electric field sensors, is capable of producing both quantitative results for the total amount of surface charge present, as well as imaging the charge to produce plots representing spatial charge distribution. We calibrate the measurement against a conventional induction field meter charge measurement which discharges the sample. Further to this, we show that our technique has no discharging effect on the sample and that therefore it is possible to observe the discharging of insulating materials over periods of several days.

Limitations on the performance of electric potential sensors are due to saturation caused by environmental electromagnetic noise. The work described involves tailoring the response of the sensors to reject the main components of the noise, thereby enhancing both the effective dynamic range and signal to noise. We show that by using real-time analogue signal processing it is possible to detect a human heartbeat at a distance of 40 cm from the front of a subject in an unshielded laboratory. This result has significant implications both for security sensing and biometric measurements in addition to the more obvious safety related applications.