Real-time capacitance imaging: a revolutionary NDT technique

Abstract

Real Time, High-Resolution NDT Imaging Via Capacitance. A Revolutionary NDT technique We report on recent developments and field trials of a completely novel method of NDT: Capacitive Imaging. This novel method is entirely non-ionising and is capable of detection and imaging of internal features, objects and defects which are extremely difficult ‐ if not impossible ‐ to detect with existing NDT technologies such as x-rays, ultrasound, and millimetre waves (MMW). One of the first applications of thistechnology was its use by the Royal Canadian Navy to detect corrosion under paint and other coatings.However, this technology is also highly suited for a broad range of other NDT detection and imaging applications across many industrial sectors. We also report on further usage developments in other commercial environments: ‐ <ul> <li>Corrosion under paint and other coatings such as thermal insulation.</li> <li>Imaging of voids in walls and under floor tiles as an inexpensive alternative to ground penetrating radar (GPR).</li> <li>Security screening of mail for contraband such as drugs, biohazard powders, explosives, and non-metallic weapons.</li> <li>Inline inspection of glass-fibre composites for delamination, cracks and water ingress.</li> <li>Inline food and pharmaceutical quality inspection. </li> </ul> One major advantage of the CI system over widely used existing technologies such as thermography, ultrasound, back-scattered-x-ray etc. is that it is relatively inexpensive to manufacture and therefore avoids the large capex barrier to deployment that most of the commercially available state of the art suffers from. It requires no heavy power source or shielding and is completely non-radiological/ non-ionising, presenting no hazard to human health. This last, is an important factor when considering the public location of some deployments and cumulative effects on the user. It also offers great comparative advantages in speed of scanning and enhanced ability to discriminate between differing types of materials as compared to techniques such as x-rays.Some examples of the other advantages of this technology over commercially available state of the art are : ‐ <ul> <li>It can readily image items which would either be very difficult or completely impossible to detect with x-rays/radiography.</li> <li>Articles such as powders and plastics etc. are just as easily imaged as those made of metal and no pre-sorting of light and dense objects is necessary.</li> <li>Contraband Items such as ceramic knives which would not trigger a metal detection, are very easily imaged with the Capacitance Imager.</li> <li>Unlike ultrasound, the Capacitance Imager technology does not require intimate contact and/or couplant with the scanned object.</li> <li>Much higher scanning/imaging speeds than most other continuous inline industrial techniques: typically, 300 lines per second on a 45 cm wide belt moving at 30 metres per minute can be scanned, which is equivalent to an area of 800m2 per hour to a spatial resolution of 2 mm.</li> </ul>