A Method for Detecting Metal Surface Cracks Based on Coaxial Resonator

A method based on the resonance frequency shift of coaxial resonator is presented to detect metal surface cracks. Theoretical analysis prove that the resonance frequency shift is always greater than a threshold instead of decreasing as the crack size decreases. Therefore, it can avoid the problem of missing inspection in crack detection. The experiment detects that the threshold of the designed sensor is 2.12 GHz, which is only 3.6% error from the theoretical result. And the designed sensor will produce a frequency shift of 2.16GHz when detecting a 0.2 mm wide crack. Further analysis shows that the sensor can be used to detect tiny cracks on the metal surface with micro-roughness. The width information of the crack can be obtained by scanning, which proves that this method has good potential in the imaging of metal surface cracks. In addition to detecting surface cracks on metal plates, the sensor can also be used to detect the crack on the surface of metal balls.