Our RCUK Basic Technology programme is concerned with taking a new class of non-invasive (non-contact) sensor- the electric potential sensor - and turning it into the basis for a major instrumentation and imaging technology, with many important applications in industry and research. The generic electric potential sensor was created and patented by us at Sussex and, as part of the current programme, we have improved radically the overall performance of individual sensors - i.e. in terms of noise level, input impedance and bandwidth. We expect these sensors to be applied in any areas where the non-contact detection of electric fields (potentials) is required, for example, in medical diagnosis and imaging, VLSI circuit imaging, biological cell imaging, the human-machine interface and earthquake monitoring. The sensors can be used both individually and in array format for imaging applications - either at the sub-micron level or on a much larger spatial scale, typically for application to non-destructive testing of materials or geophysical surveying.
Details of the development and applications of our electric potential sensor systems may be obtained through our publications, which include references to recent and forthcoming published conference presentations.
Body electrophysiology
The electric potential sensor (ultra high impedance electric field probe) has been used to produce high quality signals from the heart (ECG) with no resistive contact to the body. Indeed, we are able to monitor the periodic heart signal at up to 1m away from the body. This contrasts with conventional ECG detectors where a highly conductive connection is required. We have implemented an ambulatory ECG system comprising wrist mounted sensors and wireless transmission of the ECG. We have also developed a 2D sensor array which is capable of mapping the electrical signal from the heart across the chest.
The sensitivity of these probes is now at a level to allow their use in the detection of brain signals (EEG), evoked responses, nerve fibre signals and muscle signals (EMG). We are able to detect alpha and beta rhythms in the brain, as well as the alpha blocking phenomenon, and also the optical muscle signal generated when the eye is moved (EOG). In all cases, we require no resistive contact with the skin, or removal of body hair.
Non-destructive testing of materials and structures
Our ultra high input impedance electric potential sensors are also suitable for characterising the structural properties of both conductors and insulators. In order to demonstrate this capability, we have constructed a 3 axis scanning instrument, which incorporates one of our sensors, to allow the non destructive evaluation of faults and defects in metal structures. We have detected strain faults in metal bars prior to failure, simulated corrosion pits in both steel and aluminium samples and faults in steel and aluminium welds.
We have shown that our technology is particularly applicable to both composite materials and ceramics, where conventional methods such as eddy current testing are less effective. In particular, we are investigating the use of these sensors to study delaminations in carbon composite materials and defects in brittle, powder based alloys, as used in the machining industry.
 |
The three axis scanning test bed |
Scanning electric potential microscope
One area of development for our electric potential sensors is a scanning microscope system. This has been used to image the electrical signals within a high speed digital circuit, the conduction paths in an integrated circuit and the dielectric properties of materials. We have also detected the time delay of a pulse propagated through saline, as a precursor to the study of conduction mechanisms in biological cells. The microscope can be set up with an 8-element linear array of sensors for faster data acquisition.
 |
 |
Setting up the scanning electric potential microscope |
A single sensor, coaxial probe for use with the microscope |
|
|||||
