Evaluation of the shape and size of 3D cracks using microwaves

A method to evaluate the shape and size of a small 3D crack by microwaves was demonstrated. By considering the interference phenomenon occurring in the case of 3D cracks, a parameter reflecting microwave interference effect, which is a function of the position of the sensor in the direction of the crack length, was introduced into the usual dual frequency evaluation-equation. From the modified dual frequency equation, a new component named interference waveform, which is based on the amplitude of the reflection coefficient measured at two different frequencies, was obtained. On the other hand, based on the interference model, a corresponding interference waveform, which can be calculated from the assumed shape and size of a 3D crack, was also introduced. By comparing these two interference waveforms, the evaluation of the shape and size of the 3D crack were carried out. Four 3D fatigue cracks having different shape and size were treated. The shape and size of all the cracks were estimated well by using the proposed method.