Showing papers on "Relative permittivity published in 2022"

Low permittivity cordierite-based microwave dielectric ceramics for 5G/6G telecommunications

Abstract: 5G and forthcoming 6G communication systems require dielectric ceramics with low relative permittivity (εr) and near-zero temperature coefficient of resonant frequency (τf) for the lower part of the microwave (MW) band and at sub-Terahertz. Mg2Al4Si5O18 (MAS) ceramics are promising candidates due to their low εr (~ 6) and high-quality factor (Q×f > 40,000 GHz) but have a large τf. In this study, 5.5 wt% TiO2 (MAS-T5.5) was used to adjust τf of MAS to −2.8 ppm/℃ whilst retaining low εr (5.24) and good Q×f (33,400 GHz), properties consistent with those obtained by infrared reflectance. A demonstrator microstrip patch antenna with gain 4.92 dBi and 76.3% efficiency was fabricated from MAS-T5.5.

Ultraweakly and fine-tunable negative permittivity of polyaniline/nickel metacomposites with high-frequency diamagnetic response

Abstract: Metacomposites have drawn considerable attention due to their enticing prospect in electronic and dielectric devices, which meanwhile unfortunately suffered from extremely high negative permittivity (ε' < 0). Herein, we put forward a strategy to suppress the plasma oscillation in metacomposites and thereby constrain the value of negative permittivity by introducing the semiconductive polyaniline to construct polyaniline/nickel (PANI/Ni) metacomposites. Weakly negative permittivity was obtained at a magnitude of 102 over the whole test frequency band, which is remarkably lower by at least three orders of magnitude than that of most metacomposites. The ε′-negative value was resultantly fine-tuned by about 102 with equally adjusting Ni content. Lorentz and Drude models were employed to describe ε′-negative spectra, indicating that both dielectric resonance and plasma oscillation contributed to negative permittivity. Negative susceptibility of ε′-negative materials was mainly ascribed to high-frequency diamagnetic response within Ni networks. The well-designed PANI/Ni metacomposites with weakly and fine-tuning negative permittivity can greatly benefit the practical applications on electromagnetic (EM) shielding, microwave absorption and novel EM sensors.

Broadband Complex Permittivity and Electric Modulus Spectra for Dielectric Materials Research

Abstract: Measurement of the complex permittivity of a substance in a wide frequency range, for example, from 10 mHz to 100 kHz, provides useful information on the dielectric properties of the substance. In this regard, some of such dielectric properties can be analyzed more clearly if we pay attention to the frequency spectra of electric modulus, which is a reciprocal of complex relative permittivity. Especially, the imaginary part of the electric modulus can be a powerful tool for dielectric materials research. In this paper, this fact is demonstrated clearly by showing abundant examples acquired by the author's laboratory. First, the equations of electric modulus that hold for various dielectric relaxation processes, including their derivation, are shown in an easy‐to‐understand manner. After that, for several insulating polymers, actual measurement examples of broadband complex permittivity spectra are shown, up to frequencies of about 100 kHz and a much broader range up to several THz. In the first example of showing permittivity spectra, polyamide exhibits an incredibly high relative permittivity value of 106 at high temperatures such as 200 °C at a frequency as low as 10 mHz. This is a result of the phenomenon often called electrode polarization. In other words, if electric charge carriers accumulate in an insulator facing a nearby electrode and have the polarity opposite to that of the electrode, the permittivity of the insulator goes up. In such a case, the dielectric loss factor usually shows a very high value in the low‐frequency range and decreases in inverse proportion to the frequency. This reflects the fact that the charge carriers are transported, and the conductivity can be derived from this frequency dependence much more easily with apparently higher reliability than measuring the dc leakage current. Furthermore, it is shown that the coefficient of thermal expansion can be estimated from the permittivity spectra relatively accurately for several polymers that satisfy the necessary condition. Next, taking examples in electric modulus spectra measured in important insulating polymers such as engineering ones, it is demonstrated that the processes of dielectric polarization and relaxation, which are difficult to see in permittivity spectra, can be recognized obviously. Moreover, the effects of the addition of nanosized or microsized fillers to epoxy resin on its thermal property and filler‐induced inhomogeneity are analyzed using the electric modulus spectra measured in these samples. The effects of thermal aging treatment and simultaneous aging treatment with heat and radiation on the degradation of cross‐linked polyethylene are also analyzed by paying attention to the frequency spectra of its imaginary electric modulus. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Defect-induced insulator-metal transition and negative permittivity in La1-Ba CoO3 perovskite structure

Abstract: The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity. Low electron density is beneficial to reduce plasma frequency so that negative permittivity is achieved in kHz region. Negative permittivity achieved by percolating composites is restricted in practicality due to its instability nature at high temperatures.To achieve temperature-stable negative permittivity in kHz region, mono-phase La1-xBaxCoO3 ceramics were prepared, and the transition from dielectric to metal was elaborated in the perspective of electrical conductivity and negative permittivity. The plasma-like negative permittivity is attained in kHz region, which is interpreted by the collective oscillation of low electron density. The temperature-stable negative permittivity is based on the fact that the plasmonic state will not be undermined at high temperatures. In addition, zero-crossing behavior of real permittivity is observed in La0.9Ba0.1CoO3 sample, which provides a promising alternative to designing epsilon-near-zero materials. This work makes the La1-xBaxCoO3 system a source material for achieving effective negative permittivity.

Enhanced Thermal Stability in Dielectric Properties of NaNbO3–Modified BaTiO3–BiMg1/2Ti1/2O3 Ceramics for X9R-MLCC Applications

Abstract: 0.5BaTiO3–(0.5 − x)BiMg1/2Ti1/2O3–xNaNbO3 (x = 0.10–0.30) ceramics were processed via a conventional solid state sintering route. X-ray diffraction analysis and Raman spectroscopy showed the formation of a cubic perovskite structure. Microstructural analysis of the samples revealed densely packed grains. The addition of NaNbO3 resulted in the enhancement in dielectric properties as a function of temperature. Relative permittivity decreased from 850 to 564 (at room temperature) with an increase in x; however, the stability in dielectric properties was improved with an increase in NaNbO3 concentration. At x = 0.25, relative permittivity (εr) was ~630 ± 15% in a temperature range of −70–220 °C with low dielectric loss (tan δ) < 0.025 (−57 to 350 °C) and high recoverable energy density ~0.55 J/cm3 which meet the criterion for X9R MLCC applications.

Microwave Sensor for Liquid Classification and Permittivity Estimation of Dielectric Materials

Abstract: This paper presents a material detection sensor based on SIW technique. Three electric walls of the SIW cavity resonator are made by metallic vias whereas the fourth one is made by λg4 stub. The dielectric substrate under stub is partially removed and by immersing this empty space inside the cup filled with the liquid under test or by inserting the dielectric material inside the sensor, the effective permittivity of the medium under stub will change, shifting the resonant frequency of the cavity resonator. These shifts are taken as an indicator of presence of the liquid or the dielectric material. An analytical model based on mixing rule formula is presented and the obtained result is compared with the simulated one. The comparison indicated that the analytical model is an accurate approximation method of this proposed sensor. In addition, the measurement results showed that the proposed sensor can detect a large dynamic range of permittivity ranging from 1 to 83 and has a high frequency shift (296 MHz). The unique feature of this sensor can be that by changing the volume of the MUT by changing the length of the empty space under stub, the dynamic range and the sensitivity increase greatly.

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

Abstract: 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.

Research on a high-sensitivity asymmetric metamaterial structure and its application as microwave sensor

Abstract: In this paper, an Asymmetric Electric Split-Ring Resonator (AESRR) metamaterial structure is proposed to explore the interaction between metamaterials and electromagnetic waves with the influence of Fano resonance on electromagnetic properties. With the symmetry of basic electric Split-Ring Resonator (eSRR) being broken, a new Fano resonant peak appears at around 11.575 GHz and this peak is very sensitive to the dielectric environment. Based on the proposed high sensitivity of AESRR, a microwave sensor based on a 13 × 13 arrays of AESRR was designed and verified using printed circuit board (PCB) technology. T-shape channel was integrated to the sensor by grooving in the FR-4 substrate which improved the integration and provided the feasibility of liquids detection. Seven organic liquids and four dielectric substrates are measured by this sensor. The measured results show the transmission frequency shifts from 11.575 to 11.150 GHz as the liquid samples permittivity changes from 1 to 7 and the transmission frequency shifts from 11.575 to 8.260 GHz as the solid substrates permittivity changes from 1 to 9. The results have proven the improved sensitivity and the larger frequency shift ∆f on material under test (MUTs) compared with the conventional reported sensor. The relative permittivity of liquid samples and solid samples can be obtained by establishing approximate models in CST, respectively. Two transcendental equations derived from measured results are proposed to predict the relative permittivity of liquid samples and solids samples. The accuracy and reliability of measured results and predicted results are numerically verified by comparing them with literature values. Thus, the proposed sensor has many advantages, such as low-cost, high-sensitivity, high-robustness, and extensive detecting range, which provided a great potential to be implemented in a lab-on-a-chip sensor system in the future.

Epitaxial ScxAl1−xN on GaN exhibits attractive high-K dielectric properties

Abstract: Epitaxial Sc xAl1− xN thin films of ∼100 nm thickness grown on metal polar GaN substrates are found to exhibit significantly enhanced relative dielectric permittivity (εr) values relative to AlN. εr values of ∼17–21 for Sc mole fractions of 17%–25% ( x = 0.17–0.25) measured electrically by capacitance–voltage measurements indicate that Sc xAl1− xN has the largest relative dielectric permittivity of any existing nitride material. Since epitaxial Sc xAl1− xN layers deposited on GaN also exhibit large polarization discontinuity, the heterojunction can exploit the in situ high-K dielectric property to extend transistor operation for power electronics and high-speed microwave applications.

Compact and Highly Sensitive Bended Microwave Liquid Sensor Based on a Metamaterial Complementary Split-Ring Resonator

Abstract: In this paper, we present the design of a compact and highly sensitive microwave sensor based on a metamaterial complementary split-ring resonator (CSRR), for liquid characterization at microwave frequencies. The design consists of a two-port microstrip-fed rectangular patch resonating structure printed on a 20 × 28 mm2 Roger RO3035 substrate with a thickness of 0.75 mm, a relative permittivity of 3.5, and a loss tangent of 0.0015. A CSRR is etched on the ground plane for the purpose of sensor miniaturization. The investigated liquid sample is put in a capillary glass tube lying parallel to the surface of the sensor. The parallel placement of the liquid test tube makes the design twice as efficient as a normal one in terms of sensitivity and Q factor. By bending the proposed structure, further enhancements of the sensor design can be obtained. These changes result in a shift in the resonant frequency and Q factor of the sensor. Hence, we could improve the sensitivity 10-fold compared to the flat structure. Subsequently, two configurations of sensors were designed and tested using CST simulation software, validated using HFSS simulation software, and compared to structures available in the literature, obtaining good agreement. A prototype of the flat configuration was fabricated and experimentally tested. Simulation results were found to be in good agreement with the experiments. The proposed devices exhibit the advantage of exploring multiple rapid and easy measurements using different test tubes, making the measurement faster, easier, and more cost-effective; therefore, the proposed high-sensitivity sensors are ideal candidates for various sensing applications.

Characterization of Conductor-Backed Dielectric Substrates Using a Novel Resonance-Based Method

Abstract: A novel microwave resonance-based method is presented in this paper for complex permittivity characterization of conductor-backed materials. The proposed method constructs a nondestructive technique for extracting complex permittivity proprieties of thin conductor-backed dielectric substrates. The conductor-backed sample is integrated with a planar resonator by employing the conductor backing plane as a grounding surface to the resonance structure. The planar resonator is a finite circular conductive patch hosting a complementary split ring resonator (CSRR). The proposed method exhibits high sensitivity to the conductor-backed material measurements and characterization. Experimental validation of the numerical analysis of the proposed method is provided. Commonly used conductor-backed dielectric substrates with a wide range of relative permittivity values ranging from 2.2 to 10.2 were characterized using the proposed method. Compared to the state of the art material characterization methods using planar resonators, the presented method provides a nondestructive technique for complex permittivity characterization of thin conductor-backed dielectric substrates with high sensitivity to the dielectric properties.

Influence of Nanoparticles on the Dielectric Response of a Single Component Resin Based on Polyesterimide

Abstract: The influence of various types of nanoparticle fillers with the same diameter of 20 nm were separately incorporated into a single component impregnating resin based on a polyesterimide (PEI) matrix and its subsequent changes in complex relative permittivity were studied. In this paper, nanoparticles of Al2O3 and ZnO were dispersed into PEI (with 0.5 and 1 wt.%) to prepare nanocomposite polymer. Dielectric frequency spectroscopy was used to measure the dependence of the real and imaginary parts of complex relative permittivity within the frequency range of 1 mHz to 1 MHz at a temperature range from +20 °C to +120 °C. The presence of weight concentration of nanoparticles in the PEI resin has an impact on the segmental dynamics of the polymer chain and changed the charge distribution in the given system. The changes detected in the 1H NMR spectra confirm that dispersed nanoparticles in PEI lead to the formation of loose structures, which results in higher polymer chain mobility. A shift of the local relaxation peaks, corresponding to the α-relaxation process, and higher mobility of the polymer chains in the spectra of imaginary permittivity of the investigated nanocomposites was observed.

Permittivity Measurement Method for Thin Sheets Using Split-Cylinder Resonator With Protrusions

Abstract: We propose a permittivity measurement method for a thin, low-loss sheet sample using a split-cylinder resonator (SCR) with protrusions. In the SCR, the TM111 mode is separated from the TE011 mode because the resonant frequency of the TM111 mode is shifted toward a higher frequency band because of the protrusions. If an SCR does not have protrusions (or grooves), it is impossible to measure the permittivity of thin samples, which are commonly measured samples in the marketplace. When a sample is inserted between the flanges of the SCR with protrusions, the resonance curve of the TE011 mode never overlaps with that of the TM111 mode, and the permittivity of the sample is measurable until the resonance curve of the TE011 mode overlaps with that of the TM110 mode, where the resonant frequency of the TM011 mode is much lower than that of the TE011 mode. In addition, we newly derive an inequality that expresses a range for measurable permittivity based on the thickness of a sample and show that the range is much greater than that for an SCR with grooves. Moreover, we demonstrate the estimation accuracy for permittivity using a dimension correction method in which only the TE011 mode is used, and we demonstrate that relative permittivity can be estimated within 0.3% over a permittivity range of less than 10 below 50 GHz if the real dimensions of the radius and length of an SCR have no deviation or deviate from the design dimension by the same ratio.

A Compact CSRR-Based Sensor for Characterization of the Complex Permittivity of Dielectric Materials

Abstract: A sensor is proposed to characterize the complex permittivity of dielectric materials in a non-destructive and non-invasive way. The proposed sensor is based on a rectangular patch microstrip two-port circuit with a complementary split-ring resonator (CSRR) element. The slotted CSRR element of the sensor plays a key role in determining the electrical properties of the materials under test (MUT). The sensitivity analysis is determined by varying the permittivity of the MUT. The proposed sensor is simulated and analyzed using Ansoft HFSS software. A prototype was fabricated and measurements were made on two different samples of dielectric materials with complex permittivity values available in the literature. The simulated and measured results showed good agreement.

mm-Wave Complex Permittivity Extraction of LTCC Substrate Under the Influence of Surface Roughness

Abstract: As many emerging technologies require the use of high-speed signals, the understanding of dielectric properties of materials used in manufacturing printed circuit boards (PCBs) is an essential aspect for accurate high-speed circuit designs, especially at millimeter-wave (mm-wave) frequencies. This work demonstrates a methodology for extracting complex relative permittivity of dielectric substrates covering mm-wave frequencies. For this purpose, low-temperature cofired ceramic (LTCC) substrate was measured up to 85 GHz and its complex relative permittivity was extracted. The approach used in this work is based on multiline thru–reflect–line (TRL) calibration for measuring the propagation constant and electromagnetic (EM) simulations to estimate the losses contributed by the conductor while accounting for surface roughness. An estimate of complex relative effective permittivity is obtained, from which the actual relative dielectric constant and the loss tangent of LTCC substrate are extracted. The estimated values for the relative dielectric constant and the loss tangent show an excellent agreement compared with the results obtained via split cavity resonator measurements.

Dielectric Permittivity Measurement Using Open-Ended Coaxial Probe—Modeling and Simulation Based on the Simple Capacitive-Load Model

Abstract: The study aim was to validate that dielectric permittivity measurement using the open-ended coaxial probe can be reliably modeled using electromagnetic modeling and simulations, followed by the postprocessing calculations based on the simple capacitive-load model. Saline solutions with various NaCl concentrations were used as materials under test (MUTs) to investigate how ionic conductivity affects the model validity. Two different solvers and simulation methods were used: FEKO for the frequency domain and CST for the time domain. Furthermore, we performed physical experiments with the same probe and MUTs, again implementing the capacitive-load model on the measurement data to observe the model validity. Relative error of the capacitive-load model with respect to the reference permittivity values, both in measurements and simulations, was within 10% for all cases except for the measured εr′ of 1M solution at the lowest frequencies. The model yielded average relative errors well below 1% for the physiological saline, which is relevant for biological materials. The error increased for higher concentrations and for the lowest simulated frequencies but was within the declared measurement accuracy of the probe itself. This makes the simple capacitive-load model valid for all analyzed concentrations in the microwave frequency range from 0.5 to 18 GHz.