A Non-Invasive Phase Sensor for Permittivity and Moisture Estimation Based on Anomalous Dispersion.

Omar Siddiqui,Omar M Ramahi,Muhammad Amin,Rashad Ramzan

doi:10.1038/srep28626

Omar Siddiqui, Omar M Ramahi + Show 2 more

Open Access

https://doi.org/10.1038/srep28626

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Abstract

The traditional microwave resonance sensors are based on the measurement of the frequency shift and bandwidth of a resonator’s amplitude spectrum. Here we propose a novel sensing scheme in which the material properties are estimated by determining the changes in the phase spectrum of an anomalous-phase resonator. In the proposed phase sensing, we exploit the unique double phase reversal which takes place on the edges of the anomalous dispersion region as a signature to detect the resonance. We show that with the phase sensing, a significant reduction in detection errors compared to the traditional sensing can be obtained because of the noise immunity offered by the phase detection and also due to the strong dispersive phase response that reduces the sensor’s dependence on the external environment. We also show that the bandwidth determination procedure of the resonance which is needed to characterize the sample losses is significantly simplified. The concept of phase sensing is shown by devising an experimental microstrip open stub resonator whose frequency response lies in the anomalous dispersion region. The dielectric characteristics of the samples placed on the stub are extracted from the resonant frequency and the slope of the phase response. We also demonstrate that the changes in moisture levels can also be detected by utilizing the phase sensing method.

Highlights

The microwave sensors can be grouped into two broad categories i.e., the resonant and non-resonant methods[1]
We presented a non-invasive and non-destructive microwave resonance sensor based on the principle of phase sensing in the anomalous dispersion frequency region
We have shown experimentally for the first time that by only measuring the phase response of the sensor, the complex permittivity or the moisture content of material samples can be estimated

Summary

Introduction

The microwave sensors can be grouped into two broad categories i.e., the resonant and non-resonant methods[1]. Resonance based microwave sensing methods have been traditionally applied in situations where dielectric properties are required in a narrow range of frequencies[2,3,4,5,6,7]. The non-resonant measurement techniques are employed where a generalized view of material properties is required over a broad range of frequencies[10,11,12] They require accurate calibration of the measurement setup over a wide spectrum, and involve considerably more computational resources with mathematical rigour. We exploit the anaomolous dispersion phenomenton for non-invasive and non-destructive sensing by introducing the dielectric sample in an anomalously dispersive microstrip cavity and determining the spectral location and slope of the shifted phase spectrum. We first present the details of the phase sensing microstrip structure followed by a comparison between the amplitude and phase sensing, and experimental results of dielectric and moisture sensing

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Results

Conclusion