Microwave Sensor Based on Complementary Spiral Resonator with Fitting Equation to Evaluate Dielectric Substrates

In this paper; a microwave sensor is presented based on complementary spiral resonator (CSR) to evaluate dielectric substrates. CSR is excited by an electric field produced by the microstrip transmission line. At resonance frequency of CSR, electromagnetic energy is stored inside the CSR which can be employed to detect various electromagnetic properties of materials under test (MUT). By changing the dielectric constant of MUT the resonance frequency of sensor changes which can be approximated by a parabolic equation. The transmission coefficient and electric field concentration of the proposed sensor is obtained using high frequency structure simulator (HFSS). Ten dielectric materials with relative permittivity range from 2.2 to 10.2 are simulated as MUTs. A fitting equation is derived from simulated results to calculate the dielectric constant of unknown MUTs. The change in resonance frequency of known MUTs can also be predicted using the fitting equation.