Applying Spoof Surface Plasmons to Non-destructive Testing

Void defects in composite materials have negative effects on their strength and reliability. In this paper, based on spoof surface plasmons (SSPs) technology, a new microwave detector with high sensitivity is proposed for non-destructive testing of non-conductive composite materials, which are simplified as dielectrics. Firstly, spoof surface plasmon polaritons (SSPPs) are studied to detect void defects, such as blind holes in dielectrics. According to simulation, the change of defect size, such as radius of blind hole, could affect cutoff frequency of the surface wave. It is also verified that this detecting method is effective but the variation of cutoff frequency is not sensitive enough to measure and qualify. Therefore, for improvement, a new structure using SSPPs to excite spoof localized surface plasmons (spoof-LSPs) is presented to detect void defects in dielectric material. Since the coupling between SSPPs and spoof-LSPs is very strong, the resonant frequency of spoof-LSPs is shifted and the magnitude of the scattering parameter S21 is varied significantly in specific frequency when the size of defect is changed. High sensitivities are validated in both simulation and measurement.