A New Electromagnetic Nondestructive Testing Method for Non-metallic

The electromagnetic nondestructive testing techniques are usually considered only suitable for NDT of conductive materials such as the metals and nonmetallic composites like graphite, carbon fiber etc. In view that the electric permittivity may also affect the impedance of the testing coil, a new NDT method for non-metallic materials is proposed, which detects defects in the non-metallic materials based on the change of the electric permittivity. In practice, as the impedance change due to the electric permittivity is very weak, bridge, amplifier, phase sensitive detection are used to pick up signals and to enhance the signal to noise ratio. Through theoretical analysis, the proposed method is proved efficient to detect defects in non-metallic materials.