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Transient radar method (TRM) is introduced as a novel non-destructive testing (NDT) technique that is capable of analyzing fully blindly and simultaneously the electromagnetic (EM) properties as well as geometric parameters of deep sub-wavelength thin single layer slabs. This study focuses on the minimum detectable layer thickness by means of TRM, which mainly depends on the experimental setup configuration. In this article, the complex permittivity and thickness of three polyvinyl chloride (PVC) sheets are extracted by means of a differential TRM set-up. The thickness of these PVC sheets was 1 mm, $500 ~\mu \text{m}$ , and $300 ~\mu \text{m}$ that corresponded to $\lambda $ /30, $\lambda $ /60, and $\lambda $ /100, respectively ($\lambda $ is the wavelength in free space). The carrier frequency was 10 GHz and the experiments were done in a bistatic radar setup. A differential TRM structure was used in this experiment. Some error sources, such as switch leakage and non-perpendicular illumination as well as systematic errors are considered as well. The experimentally obtained results are as follows: the thickness of these samples were 1033 ± 12, 535 ± 11, and 302 ± $9 ~\mu \text{m}$ with 1.18%, 0.94%, and 2.89% relative error, respectively. Additionally, the complex permittivity of these samples was found as (2.73 ± 0.02)–(0.23 ± 0.01)j, (2.70 ± 0.02)–(0.20 ± 0.02)j, and (2.65 ± 0.02)–(0.37 ± 0.01)j, respectively. This novel technique has the potential for deployment in a wide range of applications ranging from the piping, wind energy industry, and automotive to biotechnology, food industry, clinical monitoring, and pharmacy. [ABSTRACT FROM AUTHOR]

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 novel symmetrical planar sensor based on splitter/combiner microstrip sections with a pair of interdigital capacitors (IDCs) and 2 complementary split ring resonators (CSRRs) structure is presented. A high sensitivity area to the dielectric property of surrounding materials has been established by locating IDC unit on the top-plane while a rectangular CSRR structure etched out on the ground plane. The symmetrical circuit makes the sensitivity further improved to the introduction of sample to be tested because of the destruction of the symmetry. The complex permittivity of the dielectric samples has been evaluated from the actual experimental scattering parameters by using back propagation neural network techniques. The proposed methodology is validated by fabricating the sensor on Rogers5880 substrate and testing various standard dielectric samples viz. PVC, Glass epoxy, FR4, and Glass in Cband. The measured complex permittivity of the test specimens is found to be in close agreement with their values available in literature with maximum error of <5%. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Microwave nonresonant methods generally require some sort of calibration before conducting the measurements. Calibration-independent nonresonant methods are very attractive since they eliminate this need. In the literature, different calibration-independent methods for complex permittivity determination of materials have been proposed. While some of them use uncalibrated S-parameter measurements of two identical samples with different lengths, the others utilize the same measurements of one sample. The advantage of the latter methods is that they eliminate any impurity and/or inhomogeneity present in the second sample and avoid any thickness uncertainty that can arise from using the second sample. In the literature, the proposed approaches in latter methods, however, require precise location of the sample inside its cell (a waveguide or coaxial-line section) or exact shifting distance of the sample inside its cell. This letter proposes a method to eliminate these requirements using uncalibrated S-parameter measurements of an extra cell (empty) and the cell, in which the sample is arbitrarily located. [ABSTRACT FROM PUBLISHER]