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

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.

A High-Resolution Reflective Microwave Planar Sensor for Sensing of Vanadium Electrolyte

“…Split ring resonators (SRR), along with their complementary version (CSRR), are the main building blocks of these sensors [ 11 ]. They provide regions that are highly sensitive to capacitive and resistive variations in the surrounding environment [ 12 ]. These metamaterial-inspired particles are used in liquid characterization [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ], gas sensing [ 24 ], mechanical deformation sensing [ 25 ], temperature sensing [ 26 , 27 ], etc.…”

Efficient approach for dielectric permittivity measurements of liquids adopting a 3D‐printed cavity resonator

“…A thorough review of microwave planar resonator-based sensors was recently presented in. 6 For applications requiring a good compromise between compact size, easy manufacturing, and good electrical performance, an interesting example of a 3D-printed cavity resonator with embedded fluidic channel was proposed in 7 : This structure is based on a planar resonant cavity filled with a 3D-printed dielectric material, implemented in substrate integrated waveguide (SIW) technology, 8 with a channel for the liquid realized inside the cavity during the printing process. This solution is particularly interesting, as it leads to a compact and planar structure, compatible with integration of other PBC structures, and fabricated by simple printing and metallization processes.…”

The Automatic Design of Multimode Resonator Topology with Evolutionary Algorithms

“…Microwave sensors based on microstrip resonators [23] are used for measuring complex permittivity of materials, dielectric measurements of solids and liquids [24][25][26], gas sensing [15], non-invasive medical measurements [26][27][28][29] and other applications [30][31][32]. Permittivirt measurement methods of dielectric materials available in sheet, liquid, paste, powder, etc., forms by microwave resonators used as sensors were summarized in [33,34].…”