Accurate Measurement Of Complex Permittivity Research Articles

Ac/dc conductivity and ML-based evaluation of electric characteristics of methylene blue solution

Utilizing a precision LCR meter, the complex permittivity ε*(f) of methylene blue (MB) solutions in distilled water (DW) was determined at various temperatures and concentrations in the lower frequency range from 20 Hz to 2 MHz. The complex ac conductivity σ*(f) of the liquid samples was calculated using ε*(f). DC conductivity, σdc of the samples was also calculated. The effect of changes in temperature and concentration on the σ*(f) and ε*(f) of solutions are examined. A solution of MB in DW, ranging from diluted to concentrated, greatly enhances the electrical conductivity σdc. The empirical Casteel-Amis (CA) formula was employed to fit the experimental σdc values at different concentrations. Accurate measurement of complex permittivity of liquid solutions over wide range of concentration at broad range of frequencies and temperature is laborious and uneconomical. Therefore, we performed the complex permittivity measurement of the aqueous solution of MB over a limited concentration and temperature range over 201 frequency point. Then we used this experimental data in CatBoost regression model to predict the dielectric properties at intermediate frequencies and various concentrations. This model was employed to assess the performance of material characteristics using R-squared score. The study demonstrated that the CatBoost regression model can predict material performance at intermediate frequencies and concentrations while decreasing measurement resource needs by 60 %.

Resonant cavity method based on RF measurement and simulation for measuring complex permittivity or permeability of RF absorbing materials

Accurate measurement of complex permittivity and/or permeability of radio-frequency (RF) absorbing materials is essential to predict the performances of higher-order-mode damping in damped accelerating cavities or in vacuum chambers. We propose an improved resonant cavity method that can be used as a complement to the widely used Nicolson–Ross–Weir method for measuring the RF characteristics of materials. The conventional resonant cavity method is based on the cavity perturbation theory. However, the measurements are inaccurate when losses in the materials are large. The improved method we propose determines the complex permittivity or permeability of materials from the measured resonant frequencies and Q factors based on eigenmode simulations. Because the reliability on the eigenmode calculation for RF cavities with lossy materials has become sufficiently reliable, determination of complex permittivity and permeability can be achieved using such a simulation software. We demonstrate this method using ferrite HF70 (TDK Corp.), which is useful for RF absorbers in damped accelerating cavities or in vacuum chambers.

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

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.

Modified Split Ring Resonators Sensor for Accurate Complex Permittivity Measurements of Solid Dielectrics.

In this paper, a sensor using modified Split Ring Resonators (SRRs) is designed, simulated, fabricated, and used for advanced investigation and precise measurements of the real part and imaginary part solid dielectrics’ permittivity. Adding vertical strips tightly coupled to the outer ring of the SRR leads to the appearance of two resonant frequencies at 1.24 GHz and 2.08 GHz. This modified geometry also assures an improved sensitivity. Using the full wave electromagnetic solver, both the unloaded and loaded sensors are investigated. The numerical simulations are used to develop a mathematical model based on a curve fitting tool for both resonant frequencies, allowing to obtain analytical relations for real and imaginary parts of permittivity as a function of the sample’s thickness and quality factor. The sensor is designed and fabricated on 1.6 mm thick FR-4 substrate. The measurements of different samples, such as transparent glass, acrylic glass, plexiglass, and Teflon, confirm that the modified SRR sensor is easy to implement and gives accurate results for all cases, with measurement errors smaller than 4.5%. In addition, the measurements highlight the importance of the second resonant frequency in the cases in which numerical limitations do not allow the usage of the first resonant frequency (1 mm thick sample).

Generalised probe method to measure the liquid complex permittivity

A generalised probe method is proposed for fast and accurate complex permittivity measurements. The method is based on the simulated reflection coefficients using the finite difference frequency domain method. A database is set up, which consists of the simulated complex reflection coefficients of the unknown material under test. A fast searching algorithm is performed to match the measured reflection coefficients to the reference values in the database, thus the complex permittivity of the liquid can be obtained. An in-house measurement system is developed. The unique feature of this system is that it can be applied to an arbitrarily-shaped probe. Liquid samples are measured and the results are compared with that published in the literature. Good agreements are obtained. These results could be useful for liquid microwave component designs and applications.

Full-Wave Modal Analysis of a Novel Dielectrometer for Accurate Measurement of Complex Permittivity of High-Loss Liquids at Microwave Frequencies

A novel dielectrometer to measure the complex permittivity of high-loss liquids is presented. The geometry consists of a reentrant cavity with insertion holes, where the holder filled with liquid can be introduced readily. Radii of the insertion holes are large enough for a convenient pouring of the liquid. The electromagnetic analysis has been performed by a mixed mode-matching and circuit technique with the purpose of taking the high accuracy and fast convergence of the mode-matching and the flexibility and versatility of the circuit method. The convergence of the method is studied, and a procedure to estimate the result for an infinite number of modes is proposed. A calibration procedure is presented to minimize the error introduced by the numerical method. Mode charts are shown to analyze the behavior of resonant parameters for every mode. Some reference liquids are measured at different resonant frequencies, and the results are compared with those provided by other models of the literature.

Improved reflection technique for the permittivity measurement of ferrites using slotted coaxial samples

This paper presents the effect of magnetic permeability on the permittivity measurement using coaxial line reflection technique. It discusses in detail about the design aspects, analysis and simulation of the slotted co-axial sample and fixture for dielectric characterization of the ferrites and garnets possessing both dielectric and magnetic properties. This technique makes use of improved coaxial fixture and APC 07 compatible slotted coaxial sample geometry to measure the complex permittivity of the ferrite material. Permittivity is calculated from the impedance of sample loaded fixture, which is independent of magnetic permeability, because of air slot cut in the coaxial hollow cylindrical sample along the length. Characterization data of dielectrics and ferrites is used in design of ferrite circulators, and pulse magnets for particle accelerator applications. This is also used in many other RF applications including design of dielectric resonator for spin wave line width measurement of ferrites. Design work is aimed at accurate measurement of complex permittivity; using reflection measurement in coaxial fixture over a wide frequency range of 20 kHz to 1 GHz. Reflection measurement technique is further explored for accurate measurement of complex permittivity.

Improved approach using symmetric microstrip sensor for accurate measurement of complex permittivity

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 C-band. 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%.

Whispering gallery mode resonators in microwave physics and technologies

We review the main results of the development of whispering gallery mode (WGM) resonators and their unique applications due to their quasi-optical functionality. Several types of advanced WGM resonators are proposed by the authors. The theoretical results are described for the resonators with an analytical solution of the electromagnetic problems. Special emphasis is given to the interaction of moving charged particles and waves of cylindrical resonators. Important aspects are described concerning the developed sapphire resonators, for which an exact solution can only be found by using specially designed computer program products. A separate section of the paper is devoted to application aspects of the WGM resonators. In particular, it describes advanced solutions for overcoming the problems of measuring the small microwave (MW) surface impedance of unconventional superconductors in the form of large-area thin films and small samples under study. In addition, a demonstration of accurate complex permittivity measurements of small volumes of lossy liquids is provided. Special emphasis is given to highly stable MW signal sources, namely Ka-band transistor-based feedback oscillator and solid-state maser WGM oscillators. Recently obtained results are presented of experimental studies of the auto-oscillatory system developed on the basis of the WGM resonator with relativistic electron beam.

Simple procedure for robust and accurate complex permittivity measurements of low-loss materials over a broad frequency band

In this research paper, we propose a simple procedure for accurate, stable and broadband measurements of complex permittivity of low-loss dielectric samples with considerable lengths. We identify and demonstrate by numerical and analytical analyses the main ill-behaved factor that gives rise to inaccurate peaks for measurements of electrical properties of low-loss samples in the well-known Nicolson–Ross–Weir method. Without using this factor in the expressions and combining better features of the methods available in the literature, the proposed procedure allows highly accurate permittivity measurements over a broad band. We have validated the proposed method by permittivity measurements of a low-loss sample by different methods.

Improvement of open resonator technique for dielectric measurement at millimetre wavelengths

An open resonator system is designed and constructed for the accurate measurement of complex permittivity at Ka band. It is solved successfully for the first time in how to achieve the consistency of cavity lengths corresponding to different resonant frequencies over a broad band and how to determine the proper permittivity from multiple transcendental equation roots of one sample. Many kinds of samples such as fused quartz, Teflon, quartz ceramic, MgF 2 and MgAl 2 O 4 are measured and the results are in good agreement with published data. The systematic error analysis shows that the relative standard deviation of the measurement system is less than 0.172% for permittivity and 18.35% for loss tangent. The software developed to control the system improves the measurement efficiency greatly.

Method for accurate measurement of complex permittivity of tissue equivalent liquids

A microwave method for determining the electrical properties of lossy liquids is presented. The method is optimised for measuring the complex permittivity of human tissue equivalent liquids typically used together with human head phantoms in SAR (specific absorption rate) measurements. The presented method has a considerably better performance than conventional methods.

Error Analysis for Waveguide-Bridge Dielectric-Constant Measurements at Millimeter Wavelengths

The use of the free-space waveguide-bridge dielectric-measurement technique is demonstrated for accurate complex-permittivity measurements at millimeter wavelengths. An error analysis is presented for applications of this technique with the sample rotated in the plane of incidence in order to avoid coupling between the sample and the horns, and to minimize the effects of multiple reflections from the two air/dielectric interfaces. Data are presented for slip-cast fused silica at 94 GHz to demonstrate the accuracy of the technique and to verify the error analysis.