Eddy Current Testing of the Lightning Strike Protection Layer in Aerospace Composite Structures

The lightning strike protection layer, which is a mesh of metal stripes, is adhered to composite materials to dissipate the huge current induced during lightning strike. This paper presents an eddy current imaging method to inspect defects in the lightning strike protection layer. A tuning method was applied to tune the resonant frequency of excitation and sensing coils and enhance the testing results. Two parameters, namely the amplitude of induced voltage in the sensing coil and the amplitude of the voltage across a sampling resistor in the excitation circuit, were used to image the defects. The results show that the image formed by sensing coil voltage is less noisy and more accurate.