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13/10/2011
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An electric potential sensor originally designed for the world of quantum physics is finding increasing use in industry. Justin Cunningham reports.
 A non-contact sensor developed for use in fundamental physics is finding increasing application in industry. The sensor was spun out of the University of Sussex last year and has since been licensed to Plessey Semiconductors, which have found a diverse range of applications in numerous industries.
The non-contact sensor, known broadly as the electric potential sensor (EPS), is a wideband (quasi-DC to 200MHz) ultra high impedance sensor capable of detecting spatial potential, electric fields and charge. Essentially, the EPS is able to make use of disruptions in the Earth's electric field, caused by human movement, enabling it to track position and motion.
The EPS technology works at normal room temperatures and functions as an ultra high, input impedence sensor that acts as a highly stable, extremely sensitive, contactless digital voltmeter to measure tiny changes in an electric field down to mV.
Most places on Earth have a vertical electric field of about 100V/m and as the human body is mostly made up of water it interacts and disrupts it. The EPS technology is able to then detect these changes, and transpose position, movement and other information, even at a distance or through a solid wall. One of the biggest areas of development is in medical monitoring, where it can be used to detect the electrical activity of the heart.
This makes it ideal for use within an Electrocardiography (ECG) or Electroencephalography (EEG) monitoring device as they do away with contact pads. Current monitoring equipment uses sticky electrode pads that are taped to the surface of the body. EPS offer a non-invasive sensing alternative, which also opens up the potential for continual monitoring in home health sectors.
The technology was developed and patented by Professor Robert Prance and his team at the Centre for Physical Electronics and Quantum Technology at the University of Sussex. He says: "We created this technology initially as a non-invasive, non-contact sensor for measurements in fundamental physics research. However, we quickly realised the many important applications for which this technology could be used.
"Our Research Council's UK Basic Technology programme has allowed us to develop a generic Electric Potential Sensor and we have been able to demonstrate its application in a number of areas where the non-contact detection of electric fields can be used to deliver new innovative solutions and products. For example, these include medical diagnosis and imaging, security, and the human-machine interface."
The technology has also shown potential for more obscure applications such as detecting movements, and even the heartbeat of players in computer games. Motion based interfaces such as the Xbox Kinect are gaining massive popularity, and already use a suite of sensors and proprietary software to interpret the movements of gamers. The ability of the EPS to detect movement and acquire biophysiological signals without contact offers numerous exciting possibilities.
But, for the time being Plessey Semiconductors and Prance are eyeing more industrial uses. As well as roles in the medical industry, they are also being developed for non-destructive testing of composites. The sensors have the particularly useful ability to detect the location of faults and voids, inclusions, disbanding and delamination on poor conductive materials such as carbon reinforced plastics.
As composites become more widely used in all manner of industries, so does the need to non-destructively test the internal structure. Composites can have impurities form during curing or have damage to their internal structure that significantly weakens their properties. However, they often have no visible cracks, marks or damage on the structure's surface, making it difficult to assess properly. This is an issue particularly for safety critical industries such as aerospace.
EPS-based technology allows the detection and location of such damage or faults by using a non-contact version of the AC potential drop method (the product of the current and impedance of the circuit) giving it the ability to sense variations in local properties over a range of length scales from 5µm upwards.
A similar technique enables the sensors to measure the local dielectric properties of insulating materials. The sensor electrode size may be designed to suit the application and spatial resolution required. This flexibility allows variations in local material properties, including the electrical conductivity of metals and carbon composites and the dielectric properties of insulators to be sensed. As with conventional techniques, the sensors will operate through insulating surface coatings including epoxy resin or paint.
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Author
Justin Cunningham
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