Coaxial aperture electrical sensor and its application-a tutorial overview

Many scientific and industrial applications require nondestructive techniques for the characterization of associated materials. An open-ended coaxial probe has been studied extensively in order to use it as an electromagnetic sensor for such applications. These sensors are broadband and have been used in the frequency range of 1-MHz to over 40-GHz. Further, the coaxial probes have been found useful from the cryogenic temperatures to over 1000 C. Studies conducted on the coaxial sensors include static as well as quasi-static formulations of the aperture admittance under various simplifying assumptions. A stationary expression has also been reported in the literature that is based on the variational principle with principal mode fields of the signal excitation. A full-wave analysis of the signal distribution requires numerical solution to an integral equation. This analysis is then used to determine the characteristics of the material. This paper presents a tutorial overview of these techniques. Selected results are included to illustrate the procedure and application of the sensor