Defect depth effect on the reflection coefficient of an open-ended coaxial sensor

In this paper we present a realization of an open-ended coaxial sensor of internal diameter (2a) and the outer diameter (2b) for the detection of defects in a plate of aluminum, those defects are with deferent depth and created by using electro-erosion technique. Wire with a pressure of the order of µm, the measurements of the reflection coefficients (S11) are carried out using a VNP vector network analyzer. The network analyzer has been calibrated in a frequency band from 200MHz to 20GHz. The AC voltage created between the two conductors generates an electromagnetic field across the internal dielectric. This field extends outside the cylinder to a distance comparable to its diameter 2b, which represents the thickness of the sensor-sensing material in contact with the plate. The waves are subsequently reflected to the inside of a sensor carrying information on the electromagnetic properties of the medium in contact with the sensor opening. Therefore, the sensor provides measurements in reflection mode only, giving the reflection coefficient as a function of the frequency of the waves guided and reflected at the sensor opening. The experimental results were valid in comparison comparing with the found in the literature. (paper)