High-loss Materials Research Articles

Field Representation Microwave Thermography Utilizing Lossy Microwave Design Materials.

In this contribution, we are investigating a technique for the representation of electromagnetic fields by recording their thermal footprints on an indicator material using a thermal camera. Fundamentals regarding the interaction of electromagnetic heating, thermodynamics, and fluid dynamics are derived which allow for a precise design of the field illustration method. The synthesis and description of high-loss dielectric materials is discussed and a technique for a simple estimation of the broadband material’s imaginary permittivity part is introduced. Finally, exemplifying investigations, comparing simulations and measurements on the fundamental TE10-mode in an X-band waveguide are presented, which prove the above introduced sensing theory.

Synthesizing CNx heterostructures on ferromagnetic nanoparticles for improving microwave absorption property

To solve high-frequency electromagnetic interference and pollution issues, microwave absorption materials composited with dielectric and magnetic loss capacities have been employed for optimizing such problems. In this work, we demonstrate an effective approach for synthesizing graphite shells and CNx heterostructures outside the ferromagnetic nanoparticles (FMNPs) via an in-situ microwave-assisted heating approach. Ascribing to the high conductivity and eddy loss property, FMNPs act as the “heating points” during treatment, realizing the electromagnetic energy into thermal energy for in-situ decomposing the urea precursor. Microstructure characterizations coupled with microwave absorption performance reveal that the loss capacity for FMNP@CNx is correlated with particle sizes, substituted heteroatom contents, and impendence matching. In particular, the Fe@CNx nanoparticles treated in 1 min obtain a minimized RL of −26.8 dB at 5.0 GHz and an effective absorption bandwidth (<-10 dB) of 5.4 GHz with the thickness in a range of 3.8 ~ 5.0 mm. The present study exhibits a novel approach for in-situ synthesizing graphite shells and substitutional heterostructures of ferromagnetic materials and has promising potentials to extend to other high magnetic loss materials.

Hybrid Thermal Treatment Based on Microwaves and Heating Resistance for Composite Materials

Nowadays, it is well known that volumetric heating through microwaves inhibits certain surface properties from being achieved. Similarly, exclusively heating via thermal radiation is neither deep nor homogeneous enough for short periods of time. But combining both approaches can alleviate such issues. In fact, this kind of hybrid heating has been used for many years in real processes for thermal treatment of composite materials. Nonetheless, many questions remain unsettled. In this manuscript, we discuss the modeling and simulation of such a hybrid system, when heating a heterogeneous load composed of a solid core with three concentric spherical shells. The heating sources are given by electromagnetic waves in the microwave range, and by constant thermal radiation over one of the outer hemispheres. Only the core is considered to absorb the energy transported by the electromagnetic waves (high dielectric loss material). Hence, shells are transparent to microwaves (low dielectric loss materials). The thermophysical properties were considered constant with position. For all cases, peak temperature was observed in the geometrical center of the system, as has been shown by experimentation. Furthermore, simulation results revealed that this hybrid heating strategy has a drastic effect on the temperature profiles generated with only microwave, although the surface temperature homogeneity can be improved using an external electrical resistance.

Complex Permittivity Measurement of High-Loss Biological Material with Improved Cavity Perturbation Method in the Range of 26.5–40 GHz

In this paper, we performed and designed a new rectangular cavity to identify and analyze the complex permittivity of two cancer cells (Breast-MDA231, Uveal melanoma) that have a high dielectric constant and dielectric loss. The rectangular cavity device is based on the improved cavity perturbation technology. The sample of the improved cavity perturbation device is placed at the position of a/n close to the wall of the cavity, where a is the wide side of the cavity and n is the positive even number. For high-loss biological materials, the improved cavity perturbation method has higher accuracy than the traditional cavity perturbation method. The results present that the relative dielectric constants of a single cell at Ka-band (26.5–40 GHz) are in the range 8–15, and the relative dielectric loss is 24–31. The information of the cancer cells at Ka-band waves can be helpful for further cancer detection and clinical treatment.

Broadband Quasi-Optical Dielectric Spectroscopy for Solid and Liquid Samples

Dielectric materials play a supporting role for electronic circuits. With the development of 5G millimeter wave communication, precision measurement of dielectric property becomes increasingly important. This paper introduces a free-space quasi-optical spectroscopy for complex dielectric property measurement. This spectroscopy can work in both transmission and reflection modes to accommodate both low-loss and high-loss materials. By applying the transfer matrix theory, both solid and liquid samples can be characterized using this system. In addition, the system employs a Gaussian telescope design, giving a possibility of broadband operation. Furthermore, this system is much simpler in calibration compared to other systems. A detailed description of the quasi-optical system is presented. Four materials are measured in the E-band (60–90 GHz). De-ionized water is also measured to represent liquid substrates in electronic circuits. The measurement is in good agreement with published data within a discrepancy of 5%.

Double-layer packed bed used for heating non-polar liquid under microwave irradiation

There are some reports showing that microwave heating has a positive effect on the non-polar reaction liquid with polar solute. For the continuous-flow microwave heating of non-polar reaction liquid, the methods such as the addition of a high-loss dielectric material are generally used, but there is a problem that the temperature of the fluid will continue to rise, which cannot be maintained within a stable range. In this paper, a novel double-layer packed bed is designed in order to solve the above problem. The double-layer packed bed is divided into a heating layer and a thermostatic layer: the packing of heating layer is composed of the high-loss dielectric material; the packing of thermostatic layer is composed of a mixture of the high-loss and low-loss dielectric material in a certain proportion. Both the experimental and simulation results verified that the non-polar liquid temperature can rapidly rise to the preheating temperature in the heating layer and remain stable in the thermostatic layer while passing through the double-layer packed bed under microwave irradiation. The practicality of the double-layer packed bed was exemplified in the continuous synthesis of geranyl butyrate that proceeded more rapidly under microwave irradiation than conventional heating.

A New Stand-Alone Microwave Instrument for Measuring the Complex Permittivity of Materials at Microwave Frequencies

This article reports the development of a stand-alone and portable instrument designed to measure the complex permittivity of dielectric materials at microwave frequencies. The equipment consists of an in-house single-port vectorial reflectometer and a resonant coaxial bireentrant microwave cavity where the material under test (MUT) is placed inside a Pyrex vial, making the device appropriate for measuring liquids, semisolids, powders, and granular materials. The relationship between the dielectric properties of involved materials and the cavity resonance has been determined by numerical methods based on mode-matching and circuit analyses. In order to increase the measurement range, so that low to high loss materials can be characterized in the same cavity, the effect of the coupling network is deembedded from the resonance measurements. The performance of the newly devised instrument is evaluated by error/uncertainty analysis and comparative studies with other well-established instruments and methods. Errors lower than 2% in the dielectric constant and 5% in the loss factor are found. This simple, portable, affordable, and robust device could help nonspecialized personnel to accurately measure the dielectric properties of materials used in a wide range of microwave applications.

A K-Band Complex Permittivity Sensor for Biomedical Applications in 130-nm SiGe BiCMOS

In this brief, an integrated K-band complex permittivity sensor for characterization of biomaterials is presented. The circuit enables determining both real and imaginary part of the permittivity of a material under test exposed to the sensor. We propose several enhancements of the classical capacitive sensing concept, which is based on an oscillator with a resonant tank and a capacitor realized as an integrated stub. To resolve the inherent trade-off of this method between sensitivity to variation of ${\varepsilon }$ ’ and frequency tuning range of the oscillator, we propose using magnetic tuning of the resonant tank inductor. Additionally, the amplitude of oscillation gives an indication about the quality factor of the resonant tank, which can be translated into material losses, quantified by ${\varepsilon }$ ” or loss tangent. To guarantee the oscillator startup even for high loss materials, we propose using a feedback loop sensing the amplitude of the oscillation and controlling the bias current. Finally, we integrate a digitally tunable reflection type phase shifter to enhance the sensitivity. The chip is fabricated in a 130-nm SiGe BiCMOS technology. It consumes only 24 mA from a single 1.5-V supply and occupies a chip area of 1.8 mm2. The sensor has been calibrated using ethanol–water solutions in steps of 5% of concentration change.

Broadband terahertz metamaterial absorber enabled by using high-loss dielectric materials

Metamaterial absorbers consisted of two metallic layers separated by low-loss dielectric materials have been extensively presented and studied. However, these absorbers using low-loss dielectric materials usually exhibit narrow bandwidth, which are not conductive to the practical applications. Here, we demonstrate a novel terahertz meta-device that can obviously widen the absorption bandwidth of metamaterial absorber. This meta-device is composed of a high-loss dielectric material sandwiched by a metallic strip and an opaque metallic mirror. Absorption of greater than 80% of the meta-device can cover a continuous frequency range of 2.43 THz, and its relative absorption bandwidth can reach 89.17%. These two indexes are both much larger than those of previous absorption devices using low-loss dielectric materials. Physical mechanism of the meta-device originates from the superposition of two different resonant modes. More importantly, the variation of meta-device parameters can provide considerable degree of freedom to regulate the absorption bandwidth and relative absorption bandwidth of the device

高損失材料(グラファイト混合物)の誘電率と導電率の関係

高損失材料(グラファイト混合物)の誘電率と導電率の関係

Characterization of Electromagnetic Properties of In Situ Soils for the Design of Landmine Detection Sensors: Application in Donbass, Ukraine

To design holographic and impulse ground penetrating radar (GPR) sensors suitable for humanitarian de-mining in the Donbass (Ukraine) conflict zone, we measured critical electromagnetic parameters of typical local soils using simple methods that could be adapted to any geologic setting. Measurements were recorded along six profiles, each crossing at least two mapped soil types. The parameters selected to evaluate GPR and metal detector sensor performance were magnetic permeability, electrical conductivity, and dielectric permittivity. Magnetic permeability measurements indicated that local soils would be conducive to metal detector performance. Electrical conductivity measurements indicated that local soils would be medium to high loss materials for GPR. Calculation of the expected attenuation as a function of signal frequency suggested that 1 GHz may have optimized the trade-off between resolution and penetration and matched the impulse GPR system power budget. Dielectric permittivity was measured using both time domain reflectometry and impulse GPR. For the latter, a calibration procedure based on an in-situ measurement of reflection coefficient was proposed and the data were analyzed to show that soil conditions were suitable for the reliable use of impulse GPR. A distinct difference between the results of these two suggested a dry (low dielectric) soil surface, grading downward into more moist (higher dielectric) soils. This gradation may provide a matching layer to reduce ground surface reflections that often obscure shallow subsurface targets. In addition, the relatively high dielectric deeper (10 cm–20 cm) subsurface soils should provide a strong contrast with plastic-cased mines.

Microwave strengthens decomposition of mixed rare earth concentrate: Microwave absorption characteristics

The potential application of microwave heating technology for processing the mixed rare earth concentrate was systematically investigated by analyzing the microwave absorption characteristics in this study. The complex permittivity was measured through resonant cavity perturbation method. The variations of permittivity, the loss factor, loss tangent and the penetration depth with the increasing temperature were investigated numerically. The results indicate that the permittivity increases as the temperature increases, and temperature has a pivotal effect on it. The mixed concentrate is high loss material at the temperature range from 600 to 800 °C according to theoretical analyses of loss tangent and penetration depth. The results of phase transition analysis prove that the variation of microwave absorption characteristics of mixed concentrate is caused by the changes of crystal and lattice structures. The reflectivity, loss factor and penetration depth of the mixed concentrate were also calculated, and the results indicate that processing the mixed concentrate by microwave heating is of high feasibility and industrial potential.

A novel characterization method of piezoelectric composite material based on particle swarm optimization algorithm

This paper presents a novel characterization method for high-loss piezoelectric composite material based on particle swarm optimization algorithm. This proposed method was applied to determine the properties parameters of 1–3 PZT5A/epoxy composite piezoelectric material with the thickness vibration mode. The analysis results show that this method has more accurate reconstructed values, faster convergence speed compared to the method using simulated annealing algorithm published in the literature under the same condition. Good agreement between the measured electrical impedance curve and the fitting one also verifies that this method can determine precise materials parameters. This is very useful for the accurate characterization of piezoelectric materials with the unknown parameters.

Simulation and Analysis of Oleic Acid Pretreatment for Microwave-Assisted Biodiesel Production

Oleic acid needs to be heated when it is utilized for biodiesel production, but, as a low-loss solution, oleic acid is difficult to heat by microwave. An efficient heating method for oleic acid is designed. A high loss material porous media is placed in a quartz tube, and a microwave directly heats the porous medium of the high loss material. The oleic acid flows through the pores of porous media so that the oleic acid exchanges heat during this process and rapid heating of oleic acid is achieved. A coupling model, based on the finite element method, is used to analyze the microwave heating process. The multiphysics model is based on a single mode cavity operating at 2450 MHz. An elaborate experimental system is developed to validate the multiphysics model through temperature measurements carried out for different flow velocities of oleic acid and different microwave power levels. The computational results are in good agreement with the experimental data. Based on the validated model, the effects of different sizes, porosities, and materials on microwave heating efficiency are analyzed.

Microwave absorbing and shielding properties of inhomogeneous conductors and high-loss dielectrics

Microwave dielectric spectra of the relaxor ferroelectric PbMg1/3Nb2/3O3 single crystals, (Nb + In) co-doped rutile ceramics, inhomogeneous conducting polyaniline pellets, composites of poly(ethylene terephthalate) and multi-walled carbon nanotubes were used for calculation of transmission and reflection spectra of the material slabs in the free space and estimation of absorbing and shielding properties of the materials. Studied high-permittivity high-loss materials with a strong and broad dielectric dispersion in the microwave range were shown to have a high potential for microwave shielding and absorbing applications. Broadband (two decades of frequency) 40 dB shielding and high attenuation constant were demonstrated in the microwave range.

Switching microwave dielectric resonators from a high-Q on state to an off state using low-field electron paramagnetic resonance transitions

We show that the application of a small (&amp;lt;75 G) magnetic field can be used to switch a low-loss microwave dielectric to a high-loss material. This enables high performing microwave dielectric resonators and filters to be switched between a high-Q on state and a low-Q off state electronically. In this study, the absorption mechanism inducing the low Q state is from electron paramagnetic resonant transitions of an Fe3+ state in a host Al2O3 dielectric. Our modeling efforts show that it is possible to further optimize the performance of these switchable devices through a material selection process, which will entail the choice of host lattice and the J &amp;gt; ½ impurity and its concentration.

Effect of structural damping on the tuning between piezoelectric wafer active sensors and Lamb waves

Piezoelectric wafer active sensors have been widely used for Lamb-wave generation and acquisition. For selective preferential excitation of a certain Lamb-wave mode and rejection of other modes, the piezoelectric wafer active sensor size and the excitation frequency should be tuned. However, structural damping depends on the structure material and the excitation frequency and it will affect the amplitude response of piezoelectric wafer active sensor–excited Lamb waves in the structure, that is, tuning curves. Its influence on the piezoelectric wafer active sensor tuning reflects the effect of structural health monitoring configuration considered in the excitation. Therefore, it is important to have knowledge about the effect of structural damping on the tuning between piezoelectric wafer active sensor and Lamb waves. In this article, the analytical tuning solution of undamped media is extended to damped materials using the Kelvin–Voigt damping model, in which a complex Young’s modulus is utilized to include the effect of structural damping as an improvement over existing models. This extension is particularly relevant for the structural health monitoring applications on high-loss materials, such as metallic materials with viscoelastic coatings and fiber-reinforced polymer composites. The effects of structural damping on the piezoelectric wafer active sensor tuning are successfully captured by the improved model, with experimental validations on an aluminum plate with adhesive films on both sides and a quasi-isotropic woven composite plate using circular piezoelectric wafer active sensor transducers.

Reliability of Strip Line Method for Determination of Conductivity for Lossy Conductive Materials

Designing electro-textile antenna requires complex analysis as the material cannot be simply modeled as a conventional antenna with perfect metallic surface. Electro-textile has relatively lower conductivity compared with an ideal conductor. Due to its inhomogeneous and unique thread structure, exact conductivity, $\sigma _{c}$ , is difficult to be determined, which will result in inaccurate modeling during antenna designing. Significant deterioration in antenna efficiency can be observed when low conductivity element is used, and thus, accurate determination of bulk conductivity for customized electro-textile shall be performed. Previously, a strip-line method was proposed, and however, the reliability of the technique in correlation with material’s loss characteristics was not clarified. Furthermore, the practicality of the technique for higher frequency, such as ISM band, was not demonstrated. In this paper, the validity of the technique for lossless, low-loss, and high-loss materials for 2.45-GHz wearable application is clarified. A more practical and straightforward equation to calculate electro-textile’s bulk conductivity is derived, and the accuracy and reliability range of the equation is demonstrated through comprehensive electromagnetic simulation. Through analysis, the correlation between $\sigma _{c}$ , dielectric loss and attenuation loss is shown. For validation, two samples that consist of two conductors, namely copper and SHIELDIT, are fabricated on a low-loss RO5880 substrate. The $\sigma _{c}$ values of the conductors are calculated from transmission loss (S21) measurement. Good agreement of $\sigma _{c}$ is obtained for both cases, particularly when the actual $\sigma _{c}$ is within the threshold range of around 107 S/m.

Improvement of Transmission/Reflection Method for Permittivity Measurement Using Long Fixtures With Time-Domain Analysis Approach

A transmission/reflection (T/R) method using a coaxial fixture is conventionally employed for permittivity measurements of high-loss materials. However, in this method, ripples often appear in the frequency characteristics of the measured permittivities owing to the reflections at the fixture ends. Although gating analysis for the time-domain signals have been employed to reduce these ripples, it cannot be applied to conventional T/R methods at microwave frequencies because of the short distance of the time interval between the required signal and unwanted signals to be eliminated in the gating process. To deal with the problem of eliminating the reflection effects at fixture interfaces, we used a long air line as a fixture, and analyzed the measured S-parameters by using the improved gating analysis in the time domain, where unwanted reflection signals in S-parameters in the time domain were eliminated while maintaining the continuity of the waveforms. We demonstrated its efficacy by performing numerical calculations, as well as using actual measurement data for polytetrafluoroethylene obtained with a PC-7 air line with the length of 30 cm. Furthermore, we developed a new algorithm for a rigorous uncertainty analysis of the time-domain analysis of S-parameters that considers the correlations between the measured S-parameters at different frequencies. By applying this algorithm, we evaluated the uncertainty of the proposed method for permittivity measurements.

Dielectric Properties of Zinc Sulfide Concentrate during the Roasting at Microwave Frequencies

Microwave technology has a potential application in the extraction of zinc from sulphide ores, knowledge of the dielectric properties of these ores plays a major role in the microwave design and simulation for any process. The dielectric properties of zinc sulfide concentrate for two different apparent densities-1.54 and 1.63 g/cm3-have been measured by using the resonance cavity perturbation technique at 915 and 2450 MHz during the roasting process for the temperature ranging from room temperature to 850 °C. The variations of dielectric constant, the dielectric loss factor, the dielectric loss tangent and the penetration depth with the temperature, frequency and apparent density have been investigated numerically. The results indicate that the dielectric constant increases as the temperature increases and temperature has a pivotal effect on the dielectric constant, while the dielectric loss factor has a complicated change and all of the temperature, frequency and apparent density have a significant impact to dielectric loss factor. Zinc sulfide concentrate is high loss material from 450 to 800 °C on the basis of theoretical analyses of dielectric loss tangent and penetration depth, its ability of absorbing microwave energy would be enhanced by increasing the apparent density as well. The experimental results also have proved that zinc sulfide concentrate is easy to be heated by microwave energy from 450 to 800 °C. In addition, the experimental date of dielectric constant and loss factor can be fitted perfectly by Boltzmann model and Gauss model, respectively