[5B2] Real-time capacitance imaging: a revolutionary NDT technique
G Diamond, P Kubasiak, M Metodiev and J Worskett
Inspection Tech Ltd, UK
We report here on a completely novel method of NDT: capacitive imaging. This technology was one of a small group of winners of a recent international competition organised by the Royal Canadian Navy to find new technologies to detect corrosion under paint and other coatings. However, capacitive imaging is not just limited to the detection of corrosion under paint and coatings, but can also be used for a broad range of other NDT detection/imaging applications across many industrial sectors. Some of these deployments (examples of which are presented in this paper) are either impossible to achieve with existing technologies or are in environments that are too impractical and/or costly to implement with existing state-of-the-art NDT techniques. To date, we have trialled the system in commercial environments upon: corrosion under paint and other coatings; imaging of voids in walls and under floor tiles; security screening of mail for contraband such as drugs, powders, explosives and non-metallic weapons; inline inspection of glass-fibre composites for delamination, cracks and water ingress; and inline food/pharmaceutical quality inspection.
One major advantage of the CI system over widely used existing technologies, such as metal detectors, thermography, ultrasound, back-scattered X-ray and so on, 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 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 the speed of scanning and an enhanced ability to discriminate between differing types of materials compared to techniques such as X-rays. Some examples of the other advantages of this technology over the commercially available state-of-the-art are: it can readily image items that would either be very difficult or completely impossible to detect with X-rays/radiography. Articles such as powders and plastics are just as easily imaged as those made of metal and no pre-sorting of light and dense objects is necessary; contraband items such as ceramic knives, which would not trigger a metal detection, are very susceptible to detection with the capacitance imager; unlike ultrasound, the capacitance imager technology does not require intimate contact and/or couplant with the scanned object; and it offers 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 m/min is a scanned area of 800 m² per hour to a spatial resolution of 2 mm.
One major advantage of the CI system over widely used existing technologies, such as metal detectors, thermography, ultrasound, back-scattered X-ray and so on, 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 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 the speed of scanning and an enhanced ability to discriminate between differing types of materials compared to techniques such as X-rays. Some examples of the other advantages of this technology over the commercially available state-of-the-art are: it can readily image items that would either be very difficult or completely impossible to detect with X-rays/radiography. Articles such as powders and plastics are just as easily imaged as those made of metal and no pre-sorting of light and dense objects is necessary; contraband items such as ceramic knives, which would not trigger a metal detection, are very susceptible to detection with the capacitance imager; unlike ultrasound, the capacitance imager technology does not require intimate contact and/or couplant with the scanned object; and it offers 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 m/min is a scanned area of 800 m² per hour to a spatial resolution of 2 mm.
