[2C1] Real-time capacitance imaging: a revolutionary NDT technique
G Diamond, P Kubasiak and M Metodiev
Inspection Tech Ltd, UK
This paper reports on recent developments and field trials of a completely novel method of non-destructive testing (NDT): capacitive imaging (CI). This novel method is completely non-ionising and is capable of the detection and imaging of internal features, objects and defects that are extremely difficult, if not impossible, to detect with existing NDT technologies such as X-rays, ultrasound and millimetre waves (MMWs).
One of the first applications of this technology 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.
The authors also report on further usage developments in other commercial environments:
One major advantage of the CI system over widely used existing technologies, such as thermography, ultrasound, backscattered 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 last consideration 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 material when compared to techniques such as X-rays. Some examples of the other advantages of this technology over commercially available state-of-the-art alternatives are:
It can readily image items that would either be very difficult or completely impossible to detect with X-rays/radiography;
One of the first applications of this technology 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.
The authors also report on further usage developments in other commercial environments:
- Corrosion under paint and other coatings such as thermal insulation;
- Imaging of voids in walls and underfloor tiles as an inexpensive alternative to ground-penetrating radar (GPR);
- Security screening of mail for contraband such as drugs, biohazard powders, explosives and non-metallic weapons;
- In-line inspection of glass-fibre composites for delamination, cracks and water ingress; and
- In-line food and pharmaceutical quality inspection.
One major advantage of the CI system over widely used existing technologies, such as thermography, ultrasound, backscattered 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 last consideration 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 material when compared to techniques such as X-rays. Some examples of the other advantages of this technology over commercially available state-of-the-art alternatives 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, etc, 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 detector, are very easily imaged with the capacitance imager;
- Unlike ultrasound, the capacitance imager technology does not require intimate contact and/or couplant with the scanned object; and
- Much higher scanning/imaging speeds than most other continuous in-line 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 800 m2 per hour to a spatial resolution of 2 mm.
