The prediction of loss tangent of sewed multilayer fabric

The thickness and dielectric properties (dielectric constant and loss tangent) of fabric substrate play a key role in the design and properties of wearable antennas. Related research shows that a thicker substrate with a low dielectric constant and high loss tangent can enhance the bandwidth of antennas. Here, sewing multiple fabrics together was a good way to increase the thickness while maintaining flexibility, but it is hard to control the dielectric properties because of the lack of the relationship between the dielectric properties and that of the components. Although previous works have established the equivalent capacitance model of sewed multilayer fabric, they cannot obtain its dielectric properties completely. In this work, based on the circuit model proposed by Chin and Lee, the equivalent capacitance and resistance models of sewed multilayer fabric were established to predict its loss tangent. The sewed multilayer fabrics were fabricated and measured by split post dielectric resonator at 1.11 GHz to validate the model. From the comparison of the predicted and measured loss tangents of sewed multilayer fabrics, it was found that the predicted loss tangents agreed well with the experimental results. It is believed that the proposed model is beneficial to the rapid and rational configuration of the components for multilayer fabric according to thickness and dielectric properties of the components, and will provide a theoretical basis for the design of multilayer flexible electronic substrate.

Comparative Study of Complex-Ratio-Measuring Circuits and Coaxial Probe in Diagnosis of Breast Tumors

A developed six-port reflectometry (SPR) system was integrated to measure the relative permittivity of tumor and normal breast tissue for medical diagnostic purpose. In order to obtain an accurate and precise measurement, the calibration process was done to the SPR using the well-known three-standard technique. Next, the studied dielectric probe was connected to the calibrated measurement-port of the SPR. The open end of the probe aperture was dibbed into the normal and tumor synthetic breast tissue samples to measure the synthetic breast tissues dielectric constant, ɛrʹ, and loss factor, ɛrʺ in the frequency range of 1.5 GHz to 3.3 GHz. Finally, the comparative studies were conducted between commercial VNA with Keysight 85070E dielectric probe and the studied SPR-probe system based on the measured magnitude of the reflection coefficient, phase shift, dielectric constant, and loss factor of the synthetic breast samples. The maximum absolute errors of the measured reflection coefficient magnitude, phase shift, dielectric constant, and loss factor were found to be 0.01, 1.07°, 1.12, and 0.75, respectively. It was ascertained that the predicted dielectric constant, ɛrʹ, is able to differentiate between normal, (ɛrʹ < 50) and tumor, (ɛrʹ > 50) breast tissues.

An Experimental Study on the Dielectric Properties of Rubber Materials

According to specific formulas, the mixing of rubber samples occurs by two methods: open mixing and internal mixing. The effects of frequency, mixing process, carbon black (CB) content, zinc oxide (ZnO) content, and stearic acid (SA) content on the dielectric properties of rubber materials were studied. The results showed that the effects of the mixing process on the dielectric properties of the rubber samples cannot be ignored, and the appropriate mixing process should be selected when preparing the required rubber materials. The dielectric constant and loss factor of the rubber samples vary depending on the frequency. The dielectric constant had a peak and valley value, while the loss factor only had a peak. The dielectric constant and loss factor of rubber samples were significantly affected by the content of CB, ZnO, and SA. The peak frequency decreased with the increase in CB content, however, the dielectric constant increased with an increase in CB content. The higher the ZnO content, the lower the peak frequency. In addition, the dielectric constant and loss factor increased with an increase in ZnO content. The higher the SA content, the greater the peak frequency. In addition, the dielectric constant and loss factor decreased with an increase in SA content. It is hoped that the experimental results obtained can provide guidance for the study of the dielectric properties, microwave absorption properties, and microwave heating characteristics of rubber polymers.

Structural and electrical properties of pure and doped lanthanum oxide

In this communication, structural and electrical properties of rare earth oxides La2O3 (LO) and LaNdO3 (LNO) have been studied. To understand the structural properties of the LO and LNO samples, X-ray diffraction (XRD) measurement was carried out at room temperature. The XRD patterns have been analyzed by Rietveld refinement to confirm the single-phase nature of both the samples. The crystal structures of studied samples were created from the derived parameters of Rietveld parameters. The crystal size and lattice strain have been estimated using Williamson–Hall (W–H) plot analysis. Frequency-dependent dielectric constant and loss tangent have been studied for a frequency range of 20 Hz to 2 MHz. To estimate the relaxation time and contribution of the charge carriers in the studied samples, relaxation mechanism and universal dielectric response (UDR) model have been employed. The ac conductivity measurements were carried out for the same frequency range (i.e., 20 Hz to 2 MHz) which has been understood on the basis of Jonscher’s power law. The barrier height has been calculated by fitting the power law. Frequency-dependent impedance behavior has been discussed in the context of grains and grain boundaries for both the samples under study.

Effects of the FR 4 Substrate Realized in a Circularly Polarized UHF-RFID Reader Antenna with Fractal Geometry for Enhancing Parameters

The proposed RFID reader antenna progressed with perfect electric conductor (PEC) as the radiating element and FR 4 as the substrate to achieve circular polarization, enhancement in bandwidth, and read range. The design presents a CPW feed RFID antenna for near-field reading applications, between the range of 903 MHz to 929 MHz. The operating frequency of the proposed design is 900 MHz, axial ratio of the model is less than 3 dB, impedance bandwidth is 256 MHz, and axial bandwidth is 36 MHz, proving to be adequate for near-field RFID reader applications such as item-level tagging and smart shelf. The proposed antenna model is realized with fractal structure to achieve miniaturization. The developed antenna is optimized using EM software for numerical analysis. The designed antenna is fabricated, and the prototype is characterized in terms of dielectric constant and loss tangent. The obtained results indicate high correlation with simulation results.

Synthesis of cross-linked polyurethane elastomers with the inclusion of polar-aromatic moieties (BA, PNBA and 3, 5-DNBA): Electrical and thermo-mechanical properties analysis

In this work, we used the design strategy “doped nonpolar polymers” and synthesized the polyurethane elastomers (PUEs) by doping with highly polar aromatic molecules such as benzoic acid (BA), 4(para)-nitro-benzoic acid (PNBA), and 3, 5-di-nitro-benzoic acid (3, 5-DNBA) by using the solution casting method. The effect of each molecule in three different weight percentages 2%, 4%, and 6% on electrical and thermo-mechanical properties of the material has studied. Experiments were carried out to determine electrical properties such as DC volume resistivity, dielectric constant, and loss factor. DMA and DSC measurements were done to assess thermo-mechanical properties. Also, thermal conductivity measurement was carried out and a strong nitro group and doping percentage dependent results have been observed. A comparative analysis of the effect on the said properties was done among the doped and undoped PUEs.

Measurement of the Dielectric Constant and Loss Tangent of Polyester / Walnut Shells by the Cavity Perturbation Method at the Microwave X-band Frequencies

In this paper, the cavity perturbation method was used to measure the dielectric properties of materials that are important for understanding the response to microwave waves, in terms of the ability of these materials to store energy and dissipate it as heat, respectively. Compounds (polyester / walnut shells) were prepared, and for different weight concentrations of walnut shells (WS) additive, the proportions ranged between (0% - 25%). The used cavity is rectangular in shape with a theoretically resonance frequency of around (9.9978 GHz) and exiting the dominant mode (TE101). The study shows the highest values of each dielectric constant with a weight concentration (25%) of the walnut shells, and the loss tangent without any material change to the sample. These compounds have been found to be useful in applications of electromagnetic materials such as microwave engineering and protection from biological influences when exposed to the field of microwaves, which is why it is very important to test their dielectric properties.

High-thermally conductive AlN-based microwave attenuating composite ceramics with spherical graphite as attenuating agent

High-thermally conductive AlN-based microwave attenuating composite ceramics with spherical graphite (SG) as the attenuating agent were fabricated through hot-pressing sintering. The SG maintains its three-dimensional (3D) morphology within the sintered bodies, which considerably impedes the sintering of the composites to some extent but slightly influences on the growth of AlN grains. The addition of SG reduces the strength of the composites, but provides a moderate toughening effect at the optimal addition amount (3.8 MPa·m1/2 at 4 wt% SG). Benefiting from the low anisotropy, high thermal conductivity, and the 3D morphology of SG, the composites exhibit a relatively higher thermal conductivity (76.82 W·m−1·K−1 at 10 wt% SG) compared with composites added with non-spherical attenuating agent. The dielectric constant and loss (8.2–12.4 GHz) increase remarkably as the amount of SG added increases up to 8 wt%, revealing that the incorporation of SG improves the dielectric property of the composite. The composite with 7 wt% SG exhibits the best absorption performance with a minimum reflection loss of −13.9 dB at 12.4 GHz and an effective absorbing bandwidth of 0.87 GHz. The excellent overall properties of the SG/AlN microwave attenuating composites render them as a promising material for various applications. Moreover, SG has a great potential as an attenuating agent for microwave attenuating composites due to its strong attenuation upon integration, high thermal conductivity, and low anisotropy.

Zinc Substituted Nickel-cobalt Nano-ferrites via Citrate-gel Auto-combustion Method for High-frequency Applications: Studies on Crystal Structure and Dielectric Properties

Ni0.8−xZnxCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) were prepared by citrate-gel auto-combustion method. The structural investigation using powder X-ray diffraction (XRD) showed the formation of single-phase cubic spinel structures with Fd-3m space group for all prepared samples. As the Zn2+ concentration is increased, the values of the lattice constant, tetrahedral and octahedral bond lengths undergo significant change. The absolute experimental lattice parameters are closely to the Vegard’ s law derived ones, suggesting that the cations concentration fairly correspond with those calculated prior chemical synthesis. Fourier transform infrared (FTIR) absorption bands at 594–400 cm− 1 confirm the formation of spinel structure. The values of dielectric constant and loss tangent were reported to decline with frequency and the Zn2+composition (x). Incorporation of Zn at nickel-cobalt resulted in decrease in ac conductivity at RT. Here, we report a low loss tangent factor of the order of 8 × 103for the sample with x = 0.20 make this composition suitable for high frequency applications. Imaginary electric modulus studies unveil the presence of non-Debye type of dielectric relaxation phenomenon. The activation energy of our samples calculated from modulus spectra is found to increase with further substitution of Zn2+ concentration.