High Sensitivity Differential Microwave Sensor Based on Siw Technology for Measuring the Permittivity and Thickness of the Solid Materials

Abstract

This paper introduces a high-sensitivity sensor for applying in measuring material properties like permittivity and thickness with reducing environmental surrounding effects. The sensor in question consists of a Substrate Integrated Waveguide (SIW) as a host and two Split Square Resonators (SSRs) with a via in the center as the sensing area. The SSRs are located where the density of electromagnetic fields is maximum, to achieve high sensitivity. The sensor operates based on a composition of a band pass and a band stop filter, filtering 2.95 GHz to create a Transmission Zero (TZ) and passing 1.62 GHz to create a Transmission Pole (TP). The relationship between the TZ frequency and material properties and thickness is almost linear. In the proposed sensor, the TZ resonance frequency decreases according to the change in materials under test (MUTs) and their thickness range, from 2.95 GHz to 2.1 GHz and from 2.95GHz to 2.48GHz, respectively. The TP band remains almost constant, this feature creates differential mode and increase the accuracy of sensor by minimizing ambient effects. The overall structure of the sensor is fabricated based on PCB technology on a RO4003c substrate. The fabricated sensor indicating high sensitivity (3.27%) for permittivity and (30.63%) for thickness measurement of solid materials and it has desirable sensitivity compared to similar works. The size of the designed sensor is 64(mm) ×60(mm) ×0.508(mm).

Keywords: Microwave SensorDifferential ModeSubstrate Integrated Waveguide (SIW)Permittivity CharacterizationThickness Measurement