A Multiple Resonant Frequencies Sensor for Measuring Permittivity Based on Stepped Impedance Resonator

This paper presented a novel sensor based on a stepped impedance resonator, which can measure the permittivities of materials at different resonant frequencies simultaneously. The multiple resonant frequencies are generated by the fundamental frequency and harmonics. The sensitivity of designed sensor at different resonant frequencies is also analyzed in detail. For verifying the feasibility of the sensor, three different kinds of materials under test are measured. The experimental results demonstrated that the tested resonant frequencies show a multiplicative growth and are consistent with our theoretical analysis. Besides, the higher the tested resonant frequency, the greater the sensitivity. The permittivity of the material under test is derived from these measured resonant frequencies by simulation and calculation. The maximum relative error through simulation and calculation are 3.4% and 26.67%, respectively. Moreover, the proposed sensor also has the advantages of being simple to fabricate, inexpensive to manufacture, and compact in volume.