Measurement Of Complex Permittivity Research Articles

Complex Permittivity Measurement Utilizing Multiple Modes of a Rectangular Cavity

A novel method for measuring the dielectric constant and loss tangent of dielectric substrates is presented in this article. Four resonant modes of the rectangular resonant cavity, TE101, TE105, TE109, and TE1015, are utilized to realize the multiband measurement from 0.9 to 10 GHz. The introduction of additional slots cuts down the quality factor of some miscellaneous modes, making the working modes more obvious and convenient for extraction. Based on the traditional perturbation formulas, considering the sinusoidal field distribution in the sample, modified formulas are deduced to obtain more accurate results. An experimental resonant cavity is fabricated and measured to demonstrate the effectivity of the proposed method.

A Dielectric Loaded Resonator for the Measurement of the Complex Permittivity of Dielectric Substrates

A new configuration of dielectric-loaded resonator (DR), particularly versatile for the complex permittivity measurement of substrates for microwave circuits, even in the presence of back metal plates, is shown here. To test this technique in a wide interval of the values of the complex permittivity, the versatility of 3-D printing is exploited to print samples with different densities, thus artificially changing the effective permittivity in the interval (1.7–3.1) for the real part and (0.02–0.06) for the imaginary part. The designed resonator, tuned at ~12 GHz, is experimentally validated by the comparison of measurements obtained on these samples with a split ring resonator (SRR) and standard transmission/reflection waveguide methods. Then, the versatility of the designed resonator is shown in the characterization of FR4-fiberglass and Kapton polyimide samples.

Slow water dynamics in dehydrated human Jurkat T cells evaluated by dielectric spectroscopy with the Bruggeman-Hanai equation.

The picosecond orientational dynamics of intracellular water was measured by dielectric spectroscopy, with the aim of revealing the effects of cryoprotective agents (CPAs) on biological cells. As a first step, Jurkat cells (human T lymphocyte cells) suspended in aqueous sucrose solutions of different concentrations ranging from 0.3 M (isotonic) to 0.9 M (hypertonic) were examined at 25 °C with a frequency range up to 43.5 GHz. The Bruggeman-Hanai equation was employed to obtain a cellular dielectric spectrum without extracellular contributions from the measured complex permittivity of the cell suspensions. By analyzing the γ process around 1010 Hz based on the Debye relaxation function, two types of water (bulk-like water and hydration water with slower molecular dynamics) were observed. An increase in the fraction of intracellular slower water was observed in the dehydrated cells which had a highly concentrated environment of biomolecules.

A modified AMC-based antenna sensor for contactless measurement of complex permittivity

The paper proposes a modified artificial magnetic conductor (M-AMC)-based antenna sensor for retrieving the complex permittivity of material under test (MUT). The antenna sensor measurement system is composed of a coplanar waveguide (CPW) antenna and a M-AMC structure. The M-AMC structure consists of a 3×3 array, and each unit cell is fabricated by two-layer dielectric substrates. The M-AMC unit cell is evolved from the traditional square unit one, and in each cell, four bent microstrip lines are embedded in the middle plane of M-AMC structure to connect the top square metallic patch through metallic holes. Compared with traditional AMC structure, the added bent microstrip line can increase the current path. Besides, four complementary split-ring resonators (CSRRs) are etched on the top plane of each unit to improve the density of electrical field. A large metallic patch covers the bottom plane of M-AMC. The resonant frequency of M-AMC structure is reduced a lot than the traditional one, which is beneficial to realize miniaturization. In measurement, the antenna is placed on the upper surface of M-AMC structure with an appropriate distance, and the MUT is placed on top plane of M-AMC. The MUTs with different thicknesses and complex permittivity will alter the resonant frequency and quality factor of the antenna sensor. Experiment is carried out to demonstrate the performances of proposed antenna sensor. An average sensitivity of 1.89 % is achieved and the maximum error is less than 3.516 % in extracting the real permittivity. All in all, the proposed antenna sensor has a potential superiority in the scope of material characterization.

Identification of polar liquids using support vector machine based classification model

<div align="left">The dispersive nature of polar liquids creates ambiguity in their identification process. It requires a long time and effort to compare the measured values with the available standard values to identify the unknown liquid. Nowadays machine learning techniques are being used widely to assist the measurement techniques and make predictions with great accuracy and less human effort. This paper proposes a support vector machine (SVM) based classification model for the identification of six polar liquids- butan-1-ol, dimethyl sulphoxide, ethanediol, ethanol, methanol and propan-1-ol for a temperature range of 10 °C–50 °C and frequency range of 0.1 GHz – 5 GHz. The model is constructed using the data from the National Physical Laboratory (NPL) report MAT 23. The identification of unknown liquid is based on complex permittivity measurement. If the measurement error in complex permittivity is less than ±6% of the standard value in NPL report, the proposed model identifies the liquids with 100% accuracy in the entire temperature and frequency range. The performance of the model is validated by testing the model with data external to the dataset used. The findings show that the proposed model is a useful and efficient tool for identifying unknown polar liquids.</div>

New Measurement Technique for Complex Permittivity in Millimeter-Wave Band Using Simple Rectangular Waveguide Adapters

This research presents a novel methodology for measuring the complex permittivity of a material under test (MUT) in a millimeter-wave (mmWave) band by using two rectangular waveguide adapters. Contrary to the conventional Nicolson-Ross-Weir (NRW) method, the proposed complex permittivity measurement method does not require a material fabrication process for exact MUT insertion into a waveguide. In our complex permittivity measurement, simple commercial waveguide adapters are employed instead of large flange structures. The proposed complex permittivity measurement of a non-destructive MUT is achieved by combining the NRW method, the Gaussian weighting moving average filtering technique, a full-wave electromagnetic analysis, and an optimization technique. Furthermore, the proposed methodology is validated by fabricating a Teflon-based MUT and by measuring the complex permittivity of the MUT in the Ka band (26.5–40 GHz). The results indicate that the proposed methodology exhibits good agreement with the data sheet.

Square Waveguide Cavity for Complex Permittivity and Permeability Measurement by Perturbation Method Without Repositioning

This article presents a novel configuration for the simultaneous complex permittivity and permeability determination with only a single sample placement inside the resonant cavity. The proposed structure incorporates two waveguide orthomode transducers (OMTs) and a square cavity. The square cavity is designed to overcome the limitation of permeability measurement by the rectangular cavity perturbation method. These components allow the product of two orthogonal transverse electric (TE) resonant modes (TE10L and TE01L) with the same cutoff frequencies. Based on Maxwell equations and perturbation theory, new relations are developed to characterize the complex permeability of specimens at TE01L modes. The proposed structure eliminates the main drawbacks of previous studies such as depolarization effect of partial-height samples, radiation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula> -plane sample hole, need to apply the sample holder and precision positioner, multistate positioning, iterative calculations, extra calibration process, and employing complicated mathematical equations. The proposed configuration was designed using CST Microwave Studio (MWS) and ANSYS high-frequency structural simulator (HFSS) and then manufactured and measured. The operating frequency has been selected from 7.5 to 12.5 GHz. Good agreement is achieved between measurement and simulation. The performance of the developed structure was verified by measuring the material characteristics of bar-shaped dielectric and magneto-dielectric specimens and compared with other studies.

Measurement of complex permittivity of liquids in the frequency range 100-1000MHz by using a re-entrant cavity.

For many liquid materials and biological media, their complex permittivity varies with frequency in the P-band (100-1000MHz). In this paper, a re-entrant coaxial cavity resonance test system with intensive multi-frequency points testing capability is designed for the P-band to realize the test of the complex permittivity of P-band materials. For this system, a test algorithm has been written, and on the basis of this system, a perturbation block has been designed, using stepper motors to control the up and down movement of the perturbation block to achieve frequency tunability of the cavity, enabling more P-band frequency test data to be obtained. The experimental results show that the system is suitable for testing the electrical parameters of P-band biological media and liquid materials and for testing solid materials in aerospace, electromagnetic shielding, and other fields where there is a great demand for P-band testing.

Novel Microwave Frequency-Locked-Loop-Based Sensor for Complex Permittivity Measurement of Liquid Solutions

In this article, a new microwave frequency-locked-loop (FLL)-based sensor is proposed for complex permittivity measurement of liquid solutions. An interdigitated electrode split-ring resonator (IDESRR) is embedded in the FLL and used as a sensing device to distribute electric field in the near-field region and sense the permittivities of the liquid solutions with different concentrations. When the test liquid is placed on the IDESRR, a deviation will be introduced to the resonance frequency based on the perturbation theory. This frequency deviation accompanies a corresponding phase shift in the FLL operating frequency. The phase-shifted signal then leads the FLL to output a frequency-modulated (FM) signal, whose frequency deviation depends on the concentration level of the test liquid. The quadrature frequency discriminator is used to demodulate this FM signal and transfer it into dc voltages, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{I}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{Q}$ </tex-math></inline-formula> . Reference liquids with known permittivities are used to calibrate the proposed sensor and relate the measured voltages to the dielectric constant and loss tangent. In this article, the water–ethanol mixtures and water–glucose solutions are used as the test liquids to evaluate the measurement performance of the proposed FLL-based permittivity sensor. The measured results obtained using the proposed sensor agree very well with those obtained using the commercial dielectric probe. Moreover, since the proposed permittivity sensor has the benefits of a simple system architecture, high sensitivity, and not requiring a vector network analyzer (VNA), it has great potential to be developed as a new type of biomedical sample sensor.

Lithium Orthosilicate-Linear Low-Density Polyethylene Nano-Composite as Substrate for High Frequency Devices: Dielectric Characterization

Dielectric properties of nanosized Lithium Orthosilicate (Li 4 SiO 4 ) and linear low-density polyethylene composite at X-Band frequencies are investigated, to realize its utility as a substrate for microwave devices. Solid state technique is used to synthesize nano Li 4 SiO 4 . To confirm the structural and morphological properties of the synthesized nano Li 4 SiO 4 , X-ray diffraction, Fourier transformed infrared spectroscopy and transmission electron microscopy are used. Composites of nano Li 4 SiO 4 and linear low-density polyethylene matrix are synthesized with varying weight fraction of nano Li 4 SiO 4 viz. 2%, 4% and 6%. The lateral portion of a fractured sample (composite) is examined using scanning electron microscope to confirm homogeneous dispersion of nano Li 4 SiO 4 in linear low-density polyethylene matrix. Water absorption measurement of all the composites are carried out based on ASTM D570-98 . Densities of the composites are measured via hydrostatic weighing by using Archimedes principle. Complex permittivity and permeability measurement of the composites are recorded by utilizing Nicholson-Ross approach. For all weight fraction of the nano inclusions, the real component of permittivity and dielectric loss tangent of the composites in the X-band are found to be in the range of 2.2 – 2.6 and 10 -2 –10 -4 , respectively. Return losses for the composites are calculated from complex permittivity and permeability values to validate its applicability as substrate for various high frequency applications.

Coaxial resonant cavity for measuring complex permittivity of liquids

Abstract In this letter, a new microwave sensor of the coaxial resonant cavity with a single-open-ended circuit loaded capacitor is proposed and used to detect the liquids’ complex permittivity. The improved cavity has a higher internal electric field and smaller size when compared with the cylindrical cavity, which gives the sensor a high sensitivity in measuring liquids’ complex permittivity. A coaxial resonant cavity operating in 1.9 GHz was designed in this work. The silicone hose used for the test is inserted vertically from the center of the cavity, and the liquids under test (LUTs) are guaranteed to be 2 ml each time. The dielectric properties of LUTs will cause perturbation to the internal electric field of the cavity. By analyzing the measured data, the sensitivity of the cavity is 0.12%, and the relative errors of the real part of the measured value and the reference value are 3.67%. which shows the measured value has a good agreement with the reference value.

Complex permittivity measurement technique using metamaterial broadside coupled split ring resonator

A simple and effective method for the determination of complex permittivity of dielectric materials at microwave frequencies using a Broadside Coupled Split Ring Resonator (BCSRR) metamaterial structure is presented. A single BCSRR unit cell placed between the transmitting and receiving probes of a Vector Network Analyzer (VNA) is used as the test probe. Resonance frequencies and bandwidths of transmission curves, measured with and without the sample placed over the BCSRR test probe, are used to determine the real and imaginary parts of the complex permittivity by treating the BCSRR as an LC resonant circuit. Relevant equations connecting equivalent capacitance and resonance frequencies are derived from the basic equivalent circuit parameters of the BCSRR through a quasi-static analysis by considering the fringing fields in its vicinity, especially on the top and bottom. Accuracy of the theoretical formula derived for determining the complex permittivity using the BCSRR is verified through experiments and simulations.

An active microfluidic sensor based on slow-wave substrate integrated waveguide for measuring complex permittivity of liquids

In this paper, a microfluidic sensor based on slow-wave substrate integrated waveguide (SW-SIW) is proposed to measure the complex permittivity of liquids and it achieves an ultrahigh quality factor of 51156, which is much higher than previous reported designs. The proposed sensor consists of three-layer dielectric substrates and an active circuit. The traditional SIW has the fundamental mode of TE101, whose electric field is concentrated inside the SIW structure. The SW-SIW, which is evolved from traditional SIW structure, has the characteristic of relatively small electrical size due to large equivalent capacitance and the capability to confine the electrical field density further. The internal rows of blind via holes are connecting the top layer of second substrate to the bottom layer of third substrate. In order to further reduce the electrical size, an air cavity is formed in second substrate around blind via holes as it can increase the equivalent capacitance of SW-SIW resonator. The air cavity has an important impact on the resonant frequency of the sensor, and the electrical size could be reduced by enlarging the air cavity. In this paper, an appropriate air cavity is adopted with comprehensive consideration of detection sensitivity and electrical size. The polydimethylsiloxane (PDMS) microfluidic substrate is embedded in first substrate. When the resonator is excited, the electric field is confined above the surface of blind vias. The electric field varies with the volume fraction of aqueous solution injected into the microfluidic channel, and the resonant frequency and quality factor alter correspondingly. The variations in the resonant frequency and quality factor are applied to retrieve the complex permittivity of liquid samples. The proposed sensor is fabricated and tested, it has a dimension of 0.678λ0 × 0.432λ0 (λ0 is the wavelength in free space at 3.7 GHz), and the peak sensitivity and unloaded quality factor are about 2.5 % and 51156, which are improved by 67 % and 5015 % than traditional SIW sensor, respectively. In particular, the sensitivity of measuring loss tangent of liquid sample is improved by several times to hundreds of times with the loss tangent range from 0.1 to 0.9 than other reported sensors. The measured data has a good agreement with the reference complex permittivity.

Complex Permittivity Measurement of Low-Loss Anisotropic Dielectric Materials at Hundreds of Megahertz

Resonant methods are well known for their accuracy in determining the complex permittivity of materials. However, to guarantee the accuracy, interference modes must be suppressed in the measurement band. In this paper, a multi-mode split rectangular cavity is designed and fabricated to measure low-loss anisotropic dielectric materials in the frequency range from 300 to 1000 MHz. Details of the cavity design are presented. Simulation results for a uniaxially anisotropic material validate both the setup and the processing. Moreover, validation measurements on a sheet of polytetrafluoroethylene (PTFE) are in agreement with the literature data, which indicate that the proposed method in this paper is reliable and accurate for low-loss complex permittivity characterization at hundreds of megahertz.

Frequency-Variation Sensors for Permittivity Measurements Based on Dumbbell-Shaped Defect Ground Structures (DB-DGS): Analytical Method and Sensitivity Analysis

It is shown in this paper that a microstrip line loaded with a dumbbell-shaped defect ground structure (DB-DGS) is useful for complex permittivity measurements. The working principle of the sensor is the variation in the notch (resonance) frequency and depth caused by the material under test (MUT), when it is put in contact with the sensitive region of the device, i.e., the capacitive slot. It is demonstrated that the relative sensitivity of the sensor, defined as the variation of the resonance frequency of the DB-DGS with the dielectric constant of the MUT relative to the resonance frequency of the bare structure, does not depend on the geometry of the DB-DGS, provided the substrate is thick enough. The relative sensitivity, the key figure of merit, is dictated by the equivalent dielectric constant of the substrate, and it increases as the substrate permittivity decreases. Using the circuit model of the sensing structure, simple analytical expressions providing the dielectric constant and the loss tangent of the MUT are derived. Such analytical formulas depend on the notch frequency and depth of the sensor with and without MUT in contact with it, i.e., easily measurable quantities. The analysis carried out is corroborated through full-wave electromagnetic simulation and experiments.

Measurement of the broadband complex permittivity of soils in the frequency domain with a low-cost Vector Network Analyzer and an Open-Ended coaxial probe

The performance of a handheld Vector Network Analyzer (VNA), the nanoVNA, a low-cost, open-source instrument, was evaluated. The instrument measures the complex permittivity of dielectric media from 1-port reflection parameters in the 1 – 900 MHz bandwidth. We manufactured an open-ended coaxial probe using a SMA-N coaxial adapter to perform dielectric measurements. The accuracy of the nanoVNA was comparable to that of a commercial VNA between 1 and 500 MHz according to tests in reference organic liquids, while a lack of stability was found beyond 700 MHz. The self-manufactured open-ended coaxial probe was subjected to a Finite Element Method (FEM) analysis and its electromagnetic (EM) field penetration depth was determined to be 1.5 mm at 100 MHz, being reduced to 1.3 at 900 MHz and thus demonstrating a frequency-dependent support volume. The broadband complex permittivity of three mineral soils of varied textures was obtained for a range of bulk densities and water contents from dry to water-saturated conditions. The dielectric response of the soils approximated the well-known Topp et al. (1980) equation at high frequencies. At lower frequency however, higher permittivities were exhibited due to dielectric dispersion, which emphasizes the importance of EM-based soil moisture sensor operating frequency when considering sensor calibration or comparing the response of different sensors.

Standoff High-Frequency Electromagnetic Induction Response of Unsaturated Sands: A Tank-Scale Feasibility Study

Standoff electromagnetic induction (EMI) measurements of complex conductivity and complex permittivity for engineering soil properties have the potential to revolutionize the way the US Army handles route planning and infrastructure assessment. An unmanned aerial system (UAS) based EM platform for soil interrogation would have wide reaching impact in a variety of applications including: civil infrastructure inspection, in-theater ingress and egress routing, reduction of false positives in IED detection, and permafrost mapping, among many others. Traditional frequency domain EMI instruments assess conductivity at low-frequencies, generally in the range of 1–20 kHz; however, recent advancements have resulted in instrumentation targeting a broadband range of frequencies, from 10 kHz through 20 MHz. This advancement, known as high-frequency electromagnetic induction (HFEMI) allows the potential to evaluate frequency domain relaxation effects in soils by acquiring both the in phase and quadrature response of the secondary field from the soil. Relaxation phenomena such as induced polarization and dielectric permittivity are related to important soil properties that can potentially be exploited using this HFEMI system. While conductivity measurements using the quadrature component of the EMI response are well established in EMI instrumentation, understanding of the relationship between direct electrical measurements and standoff HFEMI measurements is lacking. In an effort to illuminate this relationship between various electrical and electromagnetic methods at a scale suitable for soil property estimation, we perform side-by-side measurements using galvanic geoelectrical methods (ERT, IP), electromagnetics, time-domain reflectometry (TDR) and ground penetrating radar (GPR). We compare HFEMI obtained quadrature and in-phase responses to ERT, IP, TDR and GPR measurements. A tank-scale test cell was developed for comparison of the above methods and allowed assessment of sand at varying saturation levels. Further, the HFEMI response at varying heights above the sand surface was also assessed. Qualitative observations are reported in an initial attempt to relate the HFEMI response to important soil parameters.

Dual-band measurement of complex permittivity in a microwave waveguide with a flexible, thin and sensitive metamaterial-based sensor

A dual-band metamaterial-based sensor is proposed to determine the complex dielectric constant of ethanol-methanol mixtures. The original sensor structure incorporates one connected dual H-shaped slot resonators at the center and one H-shaped slot resonator at the left and right sides of a rectangular copper patch to provide two distinct resonance frequencies. Polycarbonate is chosen as the substrate material due to its lightness, flexibility, robustness and transparency. Full-wave simulations of electric field distributions reveal that the dual resonances at 3.7 GHz and 4.6 GHz stem from different parts of the metamaterial. Measurements are carried out with a WR-229 microwave waveguide and the electromagnetic simulation results are confirmed with good agreement. A first-order equation that relates the complex dielectric constant to the shift of resonance frequency and peak attenuation is used to determine the complex dielectric constant of ethanol-methanol mixtures in the vicinity of 3.3 GHz and 4.4 GHz frequencies. A good agreement with the literature values is obtained validating the accuracy of the used model. Experimental results revealed that the frequency detection resolution and sensitivity parameter values of the proposed sensor are 25.3 MHz and 0.73% for the lower-frequency band and 9.6 MHz and 0.22% for the higher-frequency band, respectively. In addition to being able to operate at dual frequencies, the proposed metamaterial-based sensor has high sensitivities for the two resonance frequencies. Moreover, the advantages of the proposed sensor, as being electrically-small, flexible, noncontact and reusable, provide a good option for discrimination of binary liquid mixtures at multiple frequencies.

Multifrequency Inversion of Complex Electrical Conductivity Measurements for Simultaneous Assessment of Wettability, Porosity, and Water Saturation

Summary Multifrequency complex electric measurements are influenced by the joint effects of mineralogy, spatial distribution of fluids and solids, properties of fluids and minerals, and interfacial polarization mechanisms. The interpretation of multifrequency electrical conductivity and dielectric permittivity dispersion can yield information about the dominant dielectric polarization mechanisms. The dielectric polarization mechanisms detected in sedimentary rocks are linked to grain size, shape, and orientation relative to the externally applied electric field, electrochemical adsorption/desorption complexation reactions, wettability, porosity, and fluid saturations. In this work, we introduce a new workflow for multifrequency interpretation of complex permittivity measurements. The introduced workflow enables simultaneous assessment of dominant wettability, porosity, and hydrocarbon reserves. These properties are estimated by minimizing a cost function using a combination of downhill gradient-descent and an evolutionary algorithm. The cost function quantifies the difference between measured and numerically calculated multifrequency complex dielectric permittivity through a recently introduced rock-physics model. We successfully applied the new interpretation workflow to multifrequency electrical resistivity/permittivity measurements obtained from two water-wet and two hydrocarbon-wet sandstone core samples. Simultaneous estimates of wettability, water saturation, and porosity obtained by applying the new interpretation workflow were in agreement with experimental measurements. Assessment of hydrocarbon reserves, porosity, and dominant wettability solely from the interpretation of multifrequency complex-valued electrical measurements is a unique contribution of the introduced workflow. Additionally, the new workflow honors rock fabric and, thus, it minimizes the necessity of extensive calibration efforts. All the parameters needed as inputs to the new interpretation workflow are associated with physical mechanisms at microscopic- and pore-scale domains or realistic and quantitative pore geometry features of the rock.

Study of variation of complex permittivity of tree leaves with moisture content, over microwave frequency range

The vector network analyzer (Anritsu Shockline Model-MS46322A) is used for the measurement of complex permittivity of the Banyan (Ficus benghalensis), Neem (Azadirachta indica), and Papaya (Carica papaya) tree leaves over 0.5 GHz to 15 GHz frequency range. The dielectric constant (ε’) and dielectric loss (ε”) of the leaves are found to decrease with decrease in moisture content at given frequency. Further the ε’ of leaves decreases with increase in frequency at a fixed moisture content. ε” of wet leaves increases with increase in frequency at higher moisture content towards relaxation frequency of water but at lower moisture contents in the leaves, ε” decreases with increase in frequency. The measured values of ε’ and ε” are compared with the values calculated using Debye-Cole dual-dispersion dielectric model, and results are found to match very well with the values calculated using the model.