A Novel Genetic Algorithm Based Method for Measuring Complex Permittivity of Dielectric, Lossy and Multilayered Materials with Thin Features Using Open-Ended Coaxial Probe

Abstract

The growing demands for novel smart and enabling metamaterial designs and semiconductor devices in health, energy, communication, and automatic industries have attracted researchers to develop designs of materials with “thin” features. For broadband complex permittivity measurements using open-ended coaxial probe (OECP), thin sample measurements present sig- nificant challenges since a large amount of power may go through the sample making the measured complex permittivity values unreliable. We developed a new approach for accurate measurement of thin material properties by back- ing the thin sample with a thick material of known complex permittivity. The process involves measuring the reflection coefficient of the layered unknown and known materials and using genetic algorithm (GA) to determine the complex permittivity in a broadband frequency range (can be from 200MHz to 20GHz) by comparing measurements with the simulated reflection coef- ficient of the same experimental arrangement using HFSS simulation. We have obtained complex permittivity results of multiple thin, dielectric, lossy, and multilayered materials in 1 to 10 GHz. Air gap between the OECP and thin material under test (MUT) can dominate the error terms in obtaining accurate measurement results, particularly for high permittivity and lossy materials. Some possible solutions to overcome the air gap problem, limi- tations of measuring high complex permittivity of materials, and minimum sample thickness are discussed.