Review of Recent Microwave Planar Resonator-Based Sensors: Techniques of Complex Permittivity Extraction, Applications, Open Challenges and Future Research Directions.

Rammah Ali Alahnomi,Ayman Abdulhadi Althuwayb,Hussein Alsariera,Zahriladha Zakaria,Ammar Alhegazi,Zulkalnain Mohd Yussof,Norhanani Abd Rahman

doi:10.3390/s21072267

Rammah Ali Alahnomi, Ayman Abdulhadi Althuwayb + Show 5 more

Open Access

https://doi.org/10.3390/s21072267

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Abstract

Recent developments in the field of microwave planar sensors have led to a renewed interest in industrial, chemical, biological and medical applications that are capable of performing real-time and non-invasive measurement of material properties. Among the plausible advantages of microwave planar sensors is that they have a compact size, a low cost and the ease of fabrication and integration compared to prevailing sensors. However, some of their main drawbacks can be considered that restrict their usage and limit the range of applications such as their sensitivity and selectivity. The development of high-sensitivity microwave planar sensors is required for highly accurate complex permittivity measurements to monitor the small variations among different material samples. Therefore, the purpose of this paper is to review recent research on the development of microwave planar sensors and further challenges of their sensitivity and selectivity. Furthermore, the techniques of the complex permittivity extraction (real and imaginary parts) are discussed based on the different approaches of mathematical models. The outcomes of this review may facilitate improvements of and an alternative solution for the enhancement of microwave planar sensors’ normalized sensitivity for material characterization, especially in biochemical and beverage industry applications.

Highlights

By definition, microwave sensors utilize electromagnetic fields and are devices internally operating at frequencies starting from 300 MHz up to the terahertz range
The aim of this paper is to review recent research into Radio frequency (RF) planar resonator sensors, mainly focused on passive resonators
The study critically addresses the low normalized sensitivity as the main challenge related to planar resonator sensors for material characterization and identifies research directions to motivate and facilitate researchers to contribute to this topic

Summary

Introduction

Microwave sensors utilize electromagnetic fields and are devices internally operating at frequencies starting from 300 MHz up to the terahertz range. Various types of microwave planar sensors have been developed over the past decade. Resonator sensors are some of these types, which are configured to have a resonance frequency or relative oscillation phase dependent on the measured parameters [2]. Resonant techniques are normally given very much attention due to the high accuracy and sensitivity compared to prevailing techniques. Several techniques are new concepts, whereas others have been developed from previous research works in the literature. This compilation of research studies can lead to a change in developing and enhancing planar sensors for material properties’ characterization. Researchers have competed with each other to design techniques that have a high accuracy, sensitivity and compact size.

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