Sensing Depth Analysis of Open-Ended Coaxial Probes at Different Input Powers and Frequencies

Abstract

The open-ended coaxial probe has been widely used to measure the permittivity of different materials. Input power and frequency are two important factors that affect the sensing depth of an open-ended coaxial probe. Existing studies in the literature on the effect of input power and frequency on the sensing depth of probes are mainly qualitative studies of the effect of frequency variation on the sensing depth of open-ended coaxial probes at a particular input power. However，the central prerequisite for accurate sample preparation is precise knowledge of the magnitude of the sensing depth of an open-ended coaxial probe at any input power and at any frequency. In this paper, the effect of frequency (0.5 GHz to 20 GHz) and input power (-20 dBm to 20 dBm) variations on the sensing depth of an open-ended coaxial probe is investigated for the first time from an experimental point of view using methanol as an example. Then, the theoretical formula for the sensing depth size of the open-ended coaxial probe is given by fitting to the experimental data, and its validity is proved by experimental verification. The experimental results show that the sensing depth of the open-ended coaxial probe for methanol does not exceed 2 mm in the frequency range of 0.5 GHz to 20 GHz and the input power range of -20 dBm to 20 dBm