Non-destructive testing of complex permittivity using a slot antenna

A planar resonant slot antenna with a ground plane aperture was developed for nondestructive testing of planar dielectric materials. Using an existing design methodology, a circuit was developed where the complex permittivity could be determined from the shift of the resonant frequency and knowledge of the thickness of the test substrate. The device was simulated using the method of moments and these simulations validated experimentally. The electric field around the aperture has also been investigated by simulation and measurement. It was found that the substrate manufacturers' values for the permittivity and tan /spl delta/ and the values as determined using this work are in agreement. In addition, the permittivity of carbon fibre composite (CFC) and nanoclay polymer substrates has also been investigated using this method.