An entirely new approach to signal acquisition in nuclear magnetic resonance (NMR) systems has recently been demonstrated experimentally at Sussex. We report results which bring this method closer to realising some significant advantages over the conventional approach. The method uses a novel sensor technology, the electric potential sensor, to detect the electric field signal associated with the precessing nuclear spins. It provides an alternative non-inductive method for acquiring the signal via a weak capacitive coupling to the sample. This paper builds on previously published results and demonstrates the ability to detect spin-echo signals from liquid samples as well as free induction decays from solid samples using this technique. In addition, we demonstrate the intrinsic spatial resolution of the method by using a measurement electrodes with a range of sizes from 180 to 0.2 mm(2), corresponding to Coupling capacitance of 1 pF to 1 fF. Conclusions are drawn as to some of the likely application areas for this signal acquisition technique.

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.

A new, non-invasive, sensor technology is applied to the acquisition of surface electromyogram signals. High quality data is presented using this dry electrode technique which is suitable for long term monitoring or motor control applications. No skin or surface preparation techniques are required. Independent two degree of freedom control signals are derived from a three electrode measurement without the use of post processing. In addition, measurements are made using high resolution surface micro-electrodes.

Recent interest in the electrical activity in rock and the use of electric field transients as candidates for earthquake precursors has led to studies of pressure stimulated currents in laboratory samples. In this paper, an electric field sensor is used to measure directly the voltages associated with these currents. Stress was applied as uniaxial compression to marble and granite at an approximately constant rate. In contrast with the small pressure stimulated currents previously measured, large voltage signals are reported. Polarity reversal of the signal was observed immediately before fracture for the marble, in agreement with previous pressure stimulated current studies.

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.

In this paper we outline the application of a novel electric field sensor technology, developed and patented at the University of Sussex, to the sensing of movement and proximity, using a technique which is generally unaffected by the presence of walls and other structures. This is achieved by monitoring electric field disturbances which occur when a large dielectric object, such as a human or animal body, is moved through the ambient electric field. These sensors detect, passively, changes in spatial potential (electric field) created by a capacitively coupled electric field. To date we have already demonstrated the potential applications of these devices, in principle, across many areas of interest, including body electrophysiology, novel nuclear magnetic resonance (NMR) probes, non destructive testing of composite materials as well as the detection of a heart beat from distances of up to 40 cm. Here we show how, with multiple sensors in a variety of spatial arrangements, it is possible to use simple signal processing and analysis in Labview to detect movement, give an indication of direction and speed as well as track position within an open environment.

The application of a novel non-contact electric potential sensor technology to the location and characterisation of faults in carbon fibre reinforced composites has recently produced interesting results. The method involves inducing an a.c. current in a sample and scanning a sensor over the surface to measure the potential as a function of position. This is a non-contact version of the a.c. potential drop method. This paper describes the initial results of modelling the electric field associated with multilayer composite materials containing faults and compares them with the previously acquired data from the non-contact potential drop method.

Previous work in applying the electric potential sensor to the monitoring of body electrophysiological signals has shown that it is now possible to monitor these signals without needing to make any electrical contact with the body. Conventional electrophysiology makes use of electrodes which are placed in direct electrical contact with the skin. The electric potential sensor requires no cutaneous electrical contact, it operates by sensing the displacement current using a capacitive coupling. When high resolution body electrophysiology is required a strong (capacitive) coupling is used to maximise the collected signal. However, in remote applications where there is typically an air-gap between the body and the sensor only a weak coupling can be achieved. In this paper we demonstrate that the electric potential sensor can be successfully used for the remote sensing and monitoring of bioelectric activity. We show examples of heart-rate measurements taken from a seated subject using sensors mounted in the chair. We also show that it is possible to monitor body movements on the opposite side of a wall to the sensor. These sensing techniques have biomedical applications for non-contact monitoring of electrophysiological conditions and can be applied to passive through-the-wall surveillance systems for security applications.

We describe the biological and medical applications of a new electric field sensor technology developed at Sussex. It provides an ultra-high impedance alternative to conventional low impedance Ag/AgCl electrodes used in electrophysiology and may even be used to acquire nuclear magnetic resonance signals via the electric field component of the free induction decay. Results are reported for both of these application areas.

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.

A new generation of electric field sensors developed at the University of Sussex is enabling an alternative to contact voltage and non-contact magnetic field measurements. We have demonstrated the capability of this technology in a number of areas including ECG through clothing, remote off-body ECG, through wall movement sensing and electric field imaging. Clearly, there are many applications for a generic sensor technology with this capability, including long term vital sign monitoring. The non-invasive nature of the measurement also makes these sensors ideal for man/machine and human/robot interfacing. In addition, there are obvious security and biometric possibilities since we can obtain physiological data remotely, without the knowledge of the subject. This is a clear advantage if such systems are to be used for evaluating the psychological state of a subject. In this paper we report the results obtained with a new version of the sensor which is capable of acquiring electrophysiological signals remotely in an open unshielded laboratory. We believe that this technology opens up a new area of remote biometrics which could have considerable implications for security applications. We have also demonstrated the ability of EPS to function in closely-packed one and two dimensional arrays for real-time imaging.

Current applications of the Electric Potential Sensor operate in a strongly (capacitively) coupled limit, with the sensor physically close to or touching the source. This mode of operation screens the sensor effectively from the majority of external noise. To date however the full capability of these sensors operating in a remote mode has not been realised outside of a screened environment (Faraday cage). This paper describes the results of preliminary work in tailoring the response of the sensors to particular signals and so reject background noise, thereby enhancing both the dynamic range and signal to noise ratio significantly.

We present a design for a linear array of eight electric potential sensors arranged with 1mm spacing and configured to measure spatially varying potential at the microscopic scale. The array successfully detects a 50μm wide feature associated with one of the samples tested. In a single sensor arrangement we have demonstrated <1μm resolution, but the data acquisition times can become prohibitive. The sensors operate noninvasively by capacitively coupling to the sample. The issues associated with using an array of sensors in close proximity are addressed. Cross coupling and strategies for matching the response of the sensors are described in detail. Results are presented for a range of samples including a resistive potential divider, a ceramic microwave circuit board, and a section taken from an oil drill pipe containing a known fault. The data acquisition times are compared with those of a single sensor system, with improvements of 4.5 times in speed reported. In one case real-time simultaneous data acquisition is demonstrated using all eight sensors. Since these sensors operate via the displacement current they may also be applied to the characterization of material properties, including, for example, insulators, dielectrics, and poorly conducting composite materials. It is concluded that we see significant improvements in the data acquisition times for the linear array over a single sensor as expected and are able to overcome the difficulties associated with operating an array of sensors in close proximity.