Non - Destructive Method for Thickness Measurement of Dielectric Films using Metamaterial Resonator

This paper describes an efficient method for the precise measurement of thickness of dielectric films using metamaterial Broadside Coupled Split Ring Resonator (BCSRR). The experimental arrangement is based on the frequency shift occurring in the metamaterial resonating structure due to the changes in effective capacitance between the rings of BCSRR due to the field perturbation effect occurring in its neighborhood. The measurement setup includes a BCSRR structure fabricated using two separate dielectric substrates, kept in between the transmitting and receiving probes of a Vector Network Analyzer (VNA). Dielectric samples of different thicknesses are introduced between the BCSRR rings, which in turn produces a shift in the resonant frequency of the sensing probe. Thin samples made of FR4 epoxy board, polyamide and polyethylene sheets are used for the study. The resonant frequency shifts are noted for sheets of known thicknesses and a calibration graph between the frequency shift and thickness is plotted. This graph is used for obtaining the unknown thickness of any sample of the same material by observing its corresponding resonant frequency. This method may be extended to the thickness measurement of thin films of low loss dielectric materials.