Differential Permittivity Sensor Using Microstrip Terminated Cross-Shaped Resonator Structure for Material Characterization

Chi-Hou Chio,Cheng Teng,Sut-Kam Ho,Pedro Cheong,Kam-Weng Tam,Wai-Wa Choi

doi:10.1109/access.2019.2930747

Chi-Hou Chio, Cheng Teng + Show 4 more

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Journal: IEEE Access	Publication Date: Jan 1, 2019
Citations: 14	License type: CC BY 4.0

Affiliation: University of Macau

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A differential planar microwave resonator permittivity sensor for material characterization is proposed in this paper. The sensor is based on asymmetric terminated cross-shaped resonator (TCSR) to provide multi-band notch frequency characteristics, allowing permittivity measurement of a small dielectric material under test (MUT) with a single resonator. Differential sensing is robust against varying ambient factors that cause frequency variations in the measurements. The dielectric properties of the MUT can be measured from the difference in notch frequencies with the reference material. To illustrate the technique, a tri-band sensor is prototyped using the proposed resonator configuration to measure the permittivity of both solid and liquid samples. The empirical equations for the determination of the MUT permittivity in relation to the notch frequencies have been derived. The sensor operates at 0.97, 1.69, and 2.91 GHz with an average sensitivity of 1.18, 4.45, and 1.22 MHz, respectively. The measured results are in a good agreement with the theoretical analysis.

Highlights

Microwave sensors come in many forms and have numerous applications in the industry [1]
Differential sensing with microwave resonators has been gaining attention lately for their ability to reduce the effects of environmental factors such as temperature and humidity to the measurement
The capacitor loaded terminated cross-shaped resonator (TCSR), for instance, allows the generation of multiple in-band transmission zeros with notch frequencies fz controllable by changing the capacitance, and this property can be used for material sensing

Summary

INTRODUCTION

Microwave sensors come in many forms and have numerous applications in the industry [1]. Differential sensing with microwave resonators has been gaining attention lately for their ability to reduce the effects of environmental factors such as temperature and humidity to the measurement This type of sensor determines the permittivity of the MUT by using the difference in resonant frequencies between the MUT and a reference material, where the reference can be a material similar to the MUT or being left vacant. The capacitor loaded TCSR, for instance, allows the generation of multiple in-band transmission zeros with notch frequencies fz controllable by changing the capacitance, and this property can be used for material sensing. A tri-band differential microwave sensor based on TCSR technique, useful for characterization of small liquid and solid sample, is proposed This design uses a single resonator to achieve multi-band differential sensing, which has the advantage of compact size and only requires a single small sample to operate. The frequencies of transmissions zero fz and fz can be expressed as fz

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