Resonant Cavity Perturbation Method Research Articles

A modified rectangular resonant cavity utilizing frequency selective coupled end‐plate for dielectric constant measurement by perturbation technique

In this article, a modified rectangular resonant cavity consisting of a rectangular waveguide (RWG) and two frequency selective coupled (FSC) end-plates with embedded parallel metallic strips (PMS) is proposed. The proposed FSC end-plate converts the semi-constant coupling mechanism of the conventional iris-coupled end-plate to the tunable FSC characteristics. This is due to adding capacitive coupling properties to inductive coupling characteristics of the conventional iris-coupled end-plate by embedding PMS inside the iris-hole. So, the proposed FSC end-plate enhances output power of the resonant frequency of the cavity. Consequently, the proposed modified cavity can determine the permittivity properties of the high-loss specimens. Also, the parametric study of the effect of variation of the physical dimensions and position of these strips to tune and trim the performance of the proposed FSC end-plate is presented. Also, the present study proposes an approach for determining the maximum complex permittivity with the rectangular resonant cavity perturbation method. Based on WR-229 RWG specifications, conventional and investigated cavities are fabricated and measured. The evaluated results of the proposed configuration and conventional model indicate about 184% determination enhancement in the imaginary part of the dielectric constant. Also, this design is validated by distilled water specimen and TiO2 films at a various partial pressure of oxygen that are deposited by utilizing radio frequency magnetron sputtering technologies and their complex permittivity are determined by manufactured cavities.

Determination of dielectric properties of titanium carbide fabricated by microwave synthesis with Ti-bearing blast furnace slag

The preparation of functional material titanium carbide by the carbothermal reduction of Ti-bearing blast furnace slag with microwave heating is an effective method for valuable metals recovery; it can alleviate the environmental pressure caused by slag stocking. The dynamic dielectric parameters of Ti-bearing blast furnace slag/pulverized coal mixture under high-temperature heating are measured by the cylindrical resonant cavity perturbation method. Combining the transient dipole and large n bond delocalization polarization phenomena, the interaction mechanism of the microwave macroscopic non-thermal effect on the titanium carbide synthesis reaction was revealed. The material thickness range during microwave heating was optimized by the joint analysis of penetration depth and reflection loss, which is of great significance to the design of the microwave reactor for the carbothermal reduction of Ti-bearing blast furnace slag.

Microwave Dielectric Properties of the Binary System BiNbO4–FeNbO4

The microwave dielectric properties of BiNbO4–FeNbO4 ceramics prepared by the conventional solid-state reaction method, and co-fired at low temperature, had been investigated. The structure, phase composition and surface morphology were studied by X-ray diffraction and scanning electron microscopy techniques, respectively. The dielectric properties of the prepared samples were determined at ≈2.8 GHz, using the modified resonant cavity perturbation method, which accuracy was previously studied using typical cylindrical samples of polytetrafluorethylene. The experimental dielectric constant values of the samples were then fitted to the theoretical curves of different mixture laws.

Dielectric properties and microwave upgrading characteristics of Zhaotong lignite

ABSTRACT The dielectric properties of lignite were studied by using the resonant cavity perturbation method. The effect of temperature, particle size, moisture content, and microwave frequency were investigated. Results showed that the variation of dielectric parameters could be divided into four stages: Stage I (25–200°C), Stage II (200–550°C), Stage III (550–800°C), and Stage IV (800–1000°C). The dielectric properties increased with particle size due to its high void ratio. The higher moisture content leads to the higher dielectric properties. The frequency of 915 MHz was more appropriate to dispose the tonnage material in high power industrial than that of 2450 MHz. Additionally, the micro-structure of lignite was analyzed by the scanning electron microscope (SEM) and the fourier transform infrared spectroscopy (FT-IR). The characterization analyses demonstrated that a large quantity of pores and cracks were generated in lignite surface because of the microwave pumping effect. The polar substances in sample selectively absorbed and transferred microwave into heat and then evaporated water to steam, causing an instantaneous increase in internal pressure. There was a uni-directional mass and heat transfer process from the interior to the surface under the steam driving force, which caused a great number of pores and cracks emergence to substantially facilitate the removal of moisture content and accelerate heat dissipation. And the apparent aromaticity of lignite dried by microwave could be increased and the capability of potential re-absorption could be decreased. Meanwhile, the mechanisms of microwave heating and generation of cracks and pores were analyzed in detail. These results could provide a theoretical basis for microwave processing of lignite.

Microwave Dielectric Properties and Reduction Behavior of Low-Grade Pyrolusite

Manganese ore is an important mineral having a strategic role in the development of the national economy and society. In this study, the dielectric properties, heating curve, crystal structure, and reduction ratio of a low-grade pyrolusite were investigated. The dielectric constant, dielectric loss factor, and loss tangent coefficient of low-grade pyrolusite at room temperature were evaluated using the resonant cavity perturbation method, yielding values of 5.854, 0.146, and 0.0249, respectively. Owing to the excellent microwave absorption properties of low-grade pyrolusite with 10% coal (22 g), it could be heated to a temperature of 800°C within 200 s. X-ray diffraction results confirmed that MnO2 was partially transformed into MnO at 450°C, while, at 650°C, no diffraction peak of MnO2 was observed. At a reduction temperature of 550°C, a reduction ratio of MnO2 to MnO of 96.65% could be achieved within a holding time of 50 min. This study demonstrates that the microwave carbothermal reduction of a low-grade pyrolusite is efficient, and thus could promote the clean production and sustainable development of the manganese industry.

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.

Material Testing Based on Cylindrical Cavity

This design of alcohol detection system uses DSP technology, ADF4350 frequency synthesizer chip developed microwave source controlled by DSP controller, the source excites the microwave resonator cavity, the output signal of the resonator is detected by the detector, then sampled and processed by the DSP processor, and the concentration of alcohol is calculated by perturbation theory and dielectric properties of alcohol. The human-computer interaction of this system is realized by touch screen, so that the display looks easy to operate and very user-friendly. This paper analyzes the feasibility of microwave resonant cavity perturbation method in alcohol materials, and derives the relationship between the concentration of alcohol mixed solution, the dielectric constant and the output frequency of the resonant cavity, and the theoretical basis of this paper is derived. The dielectric properties of different alcohol concentration at different frequencies were studied, and the standard curves of different concentration alcohol dielectric spectra were established by the theoretical model and a large number of experimental data.

Resonant cavity perturbation: a promising new method for the assessment of total body water in children

The accurate measurement of total body water (TBW) in children has important clinical and nutritional applications. Resonant cavity perturbation (RCP) is a new method for estimating TBW. This method measures the dielectric properties of the body which are related to body water. For RCP measurements, each subject lay supine on a bed inside a screened room which acts as a resonant cavity. A network analyser measures the frequencies of two low-order cavity resonances of the room, with electric-field vectors that were respectively vertical and horizontal, the resonant frequency shifts relative to the empty room are then derived. These frequency shifts correlates with TBW. The aims of this present study were to (a) develop TBWRCP predictive equations for children using TBWdil as the criterion method, (b) cross-validate the derived equations, (c) determine precision of the TBWRCP method, and (d) compare the criterion method TBWdil with three methods of estimating TBW: RCP, MFBIS and anthropometry.Predictive equations, independent of sex, were developed with linear regression in a group of 36 children. The relationship between combined RCP frequency shifts and TBWdilution had an r2 = 0.90 and standard error of the estimate (SEE) =1.42 kg. Multiple regression analysis, that included a term for body mass index, only had a small effect on r2 = 0.93 and SEE = 1.25 kg. In vivo TBW precision for the vertical, horizontal and combined frequency modes ranged from 0.7 to 3.4%. Bland–Altman analysis indicated close agreement between the criterion method TBWdil and the three other methods of TBW estimation. Mean differences were TBWRCP(2) = 0.01 ± /− 1.34 kg, TBWMFBIS = 0.45 ± /− 1.35 kg, TBWAnthropometry = 0.29 ± /− 1.29 kg.Currently the RCP method does not significantly improve the prediction of TBW compared to MFBIS and anthropometry in this initial study. However the derived equation was independent of sex and body size had only a small effect.

Electromagnetic Characteristics of Iron-Based Microwave Absorbing Materials

Nowadays human are exposed to an environment filling with electromagnetic waves over a wide frequency range. The electromagnetic properties of microwave absorbing materials plays an important role in the performance of civilian electromagnetic interference (EMI) shielding at low frequency range and military stealth technology at high frequency one. The electromagnetic properties include complex permittivity and permeability and its combination determines the electromagnetic wave absorption ability of a material. Complex permittivity and permeability can be measured by three different methods, i.e., free-space method, coaxial/waveguide method, and resonant cavity perturbation method. The first one requires a large space, expensive equipment, and not suitable for academic usage. In the present study, using coaxial/waveguide and resonant cavity perturbation methods, electromagnetic characteristics of iron-based microwave absorbing materials will be obtained and its microwave absorption performance will be investigated. In addition, a comparison between the measurements by these two methods will be addressed.

Dielectric Properties of EVA Rubber Composites at Microwave Frequencies Theory, Instrumentation and Measurements

This work describes and evaluates a technique for determining the dielectric properties of carbon-black filled Ethylene Vinyl Acetate (EVA) rubber and presents results on the studies of the effect of frequency on the permittivity and microwave conductivity using resonant cavity perturbation method. The measurements are performed with the aid of a Network Analyzer in X-band. The simplicity of this method lies in the fact that the dielectric properties can be obtained directly from the analytical formula without taking recourse to calibration.

Experimental and the Theoretical Studies of the Dielectric Properties of DMSO–H2O Mixtures

This paper focuses on the measurement of the permittivity of dimethyl sulfoxide (DMSO)–water (H2O) mixture solutions, at 2.45 GHz by using a resonant cavity perturbation method. A specific phenomenon was found, in that the imaginary part of the permittivity for the mixture solution was larger than the imaginary part for each component. Theoretical calculation indicated that the reason for that phenomenon was that the high frequency friction of the mixture was larger than that of each component. When comparing the theoretical results with the experimental data, it was found that the classical Debye equation must be modified in order to calculate the complex permittivity.

Experimental and Theoretic Study of the Dielectric Properties of Ethanol + Methanol Mixtures

The main objective of this work is to measure the complex permittivity of ethanol + methanol liquid solutions over the full composition range at the temperatures 293, 303 and 313 K by the resonant cavity perturbation method. Dielectric parameters were derived using mixture formulae, and the values of excess permittivity and excess inverse relaxation time were determined using these parameters. By comparing the calculated results to the experiment values it was found that the classical Debye equation needs to be modified to calculate the complex permittivity.

The electromagnetic loss characteristics of SiC/C materials with a three-dimensionally connected porous structure

SiC/C foams and their monoliths of the same compositions, with various electrical Conductivities were prepared by polymer sponge replication/carbonization and hot-press solidification/carbonization respectively. Both materials have a three-dimensionally connected pore Structure with the former on a macroscopic scale and the latter a microscopic scale. The electromagnetic parameters of the SiC/C foams and the monoliths Versus their electric conductivities were measured at a frequency of 2 450 MHz by the TE(10) resonant cavity perturbation method. Results show that when the electrical conductivities of the SiC/C foams and the monoliths increase gradually, their dielectric constants epsilon(r') increase gradually and their dielectric losses tg delta(e) exhibit a maximum. The magnetic loss tg delta(m) of the SiC/C foams increases Continually while that of the monoliths first increases quickly then decreases slowly with increasing electric conductivities. When the effective electric conductivities of the SiC/C foams and the monoliths are the same, the epsilon(r') Values of the SiC/C foams are about a half and the to partial derivative(e) values are at least 2 times larger than those of the monoliths, while the tg delta(m) values of the monoliths are more than 4 times those of the SiC/C foams. The SiC/C foams and the monoliths are both non-magnetic, and their magnetic losses are found to be caused by their special structures interacting with the incident electromagnetic waves. Thus it is apparent that this kind of magnetic loss is extrinsic.

Influence of strength and asymmetry of the coupling between a cavity and a transmission line on measurement of complex permittivity

AbstractInfluence of the strength and the asymmetry of input‐output ports on the measurement of complex permittivity by the resonant cavity perturbation method was investigated experimentally.We adopted the |S21| as the criterion of the strength, and the difference between S11 and S22 as the criterion of the asymmetry. When the coupling is symmetric, the real part of permittivity can be evaluated in strong coupling state up to −3 dB of coupling. The imaginary part of permittivity can be evaluated up to −14 dB of coupling. Imaginary part of the relative permittivity ε″r was calculated using the conventional equation, which is based on the complete symmetry of the coupling of input‐output ports. For the measurement of high‐Q materials, calculated ε″r is strongly affected by the asymmetry in the strongly coupled region. For the measurement of lossy materials, the inevitable asymmetry and the strong coupling allow enough exact evaluation of ε″r. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 706–709, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24988

Reduction of microwave dielectric losses in KTa 1 − xNb xO 3 thin films by MgO-doping

KTa 1 − x Nb x O 3 (KTN) thin films were grown by pulsed laser deposition on sapphire and MgO substrates. Their structural and high frequency dielectric characteristics evidenced the strong influence of the substrate and suggested possible KTN/MgO interdiffusion that could be responsible for the lower dielectric losses obtained on this substrate. Both undoped and 6% MgO-doped KTN thin films were then grown on sapphire. Dielectric measurements performed at 12.5 GHz by a resonant cavity perturbation method evidenced reduction of losses by MgO-doping. Loss tangent (tan δ) was reduced by a factor of 3 in comparison with undoped films grown on sapphire.

Measurement of the complex permittivity of dry rocks and minerals: application of polythene dilution method and Lichtenecker's mixture formulae

The complex permittivity of dry rocks and minerals varies over a very wide range, even within a sample there are variation at different temperatures and frequencies. Most rocks and minerals are inhomogeneous materials, therefore, most of the present methods of dielectric measurement designed for artificial homogeneous materials are not suitable for rocks and minerals. The resonant cavity perturbation (RCP) method is a reliable and simple technique to determine the complex permittivity of dielectric materials in the GHz range, and this method is also used extensively. However, the traditional RCP method is sensitive to the measurement of low dielectric constant (ε΄) and low loss factor (ε˝ or tanδ materials. The complex permittivity of most dry rocks and minerals exceeds the span vibration of the RCP method, and cannot be measured by the RCP method directly. This paper proposes a new method to measure the complex permittivity of dry rocks and minerals with the RCP method incorporated in the application of polythene (PE) dilution method and Lichtenecker’s mixture formulae. Dry rocks and minerals were ground into fine powder. The powder of rocks and minerals was mixed with polythene powder in a definite volume per cent. The mixture was heated and pressed into a thin circular slice. The slice was processed into a small rectangular strip sample, the size of which was fitted to the demands of the RCP method. The complex permittivity of the strip was obtained by the RCP method. The relationship between the dielectric properties of the two-phase mixture and those of each phase in the mixture can be expressed by Lichtenecker’s mixture formula. Thus the complex permittivity of dry rocks and minerals can be calculated from the complex permittivity of the mixture in case the complex permittivity of polythene is known. The presented method was verified by measurements of reference materials of various known complex permittivity and other reliable dielectric measurement methods. The results of the experiment showed that this new method is of high accuracy, small sample requirement, and convenient application. Moreover, the complex permittivity of rocks and minerals measured by this method is more reliable than the direct dielectric measurement of rocks or minerals without application of the polythene dilution method and Lichtenecker’s mixture formulae.

Measurement of the Dielectric Properties of Volcanic Scoria and Basalt at 9370 MHz

Dielectric data for volcanic scoria and basalt on the earth at microwave frequency are extremely sparse, and also crucial for volcanic terrains imaging, and development. In consideration of their similarity to lunar regolith (soils and rocks) in chemical and mineral composition, the dielectric data is significative for passive and active microwave remote sensing on the Moon. This study provides the data about the dielectric properties of three kinds of scoria and two kinds of basalt in China. The method put forward in this paper is also applicable for measuring the dielectric properties of dry rocks and other granular ground materials with low complex dielectric constants. Firstly, the authors measured the e' and tanδ values of strip specimens prepared from the mixture of scoria or basalt powder and polythene with the resonant cavity perturbation method at 9370 MHz. Secondly, from the e' and tanδ values of the mixture, the e's and tanδs values of solid scoria and basalt were calculated using Lichtenecker's mixture formulae. Finally, the effective complex dielectric constants, e'e and tanδe, of scoria at different bulk densities were calculated. The results have shown that the e's and tanδs values of all solid basaltic materials measured (both solid basaltic scoria or basalt) are approximately 7 and 0.05, respectively. With increasing bulk density of scoria, the e'e and tanδe values of scoria increase significantly.

Dielectric measurement of ferroelectric Sr0.61Ba0.39Nb2O6 single crystal fiber using cavity perturbation method

The nonlinear dielectric property of the ferroelectric Sr0.61Ba0.39Nb2O6 (SBN) crystal is essential to device application at various frequency ranges. The dielectric constant of the SBN single crystal fiber was investigated at x band microwave frequency using the resonant cavity perturbation method. It was found that compared with large and decreasing dielectric constant of SBN at low frequency, the dielectric property of the SBN crystal at x band frequency was smaller with similar value controlled by dipole orientation or atomic vibration.

Total body water measurements using resonant cavity perturbation techniques

A recent paper proposed a novel technique for determining the total body water (TBW) of patients suffering with abnormal hydration levels, using a resonant cavity perturbation method. Current techniques to measure TBW are limited by resolution and technical constraints. However, this new method involves measuring the dielectric properties of the body, by placing a subject in a large cavity resonator and measuring the subsequent change in its resonant frequency, fres and its Q-factor. Utilizing the relationship that water content correlates to these dielectric properties, it has been shown that the measured response of these parameters enables determination of TBW. Results are presented for a preliminary study using data estimated from anthropometric measurements, where volunteers were asked to lie and stand in an electromagnetic screened room, before and after drinking between 1 and 2 l of water, and in some cases, after voiding the bladder. Notable changes in the parameters were observed; fres showed a negative shift and Q was reduced. Preliminary calibration curves using estimated values of water content have been developed from these results, showing that for each subject the measured resonant frequency is a linear function of TBW. Because the gradients of these calibration curves correlate to the mass-to-height-ratio of the volunteers, it has proved that a system in which TBW can be unequivocally obtained is possible. Measured values of TBW have been determined using this new pilot-technique, and the values obtained correlate well with theoretical values of body water (r = 0.87) and resolution is very good (750 ml). The results obtained are measurable, repeatable and statistically significant. This leads to confidence in the integrity of the proposed technique.

Microwave cavity perturbation technique: Part III: Applications

The resonant cavity perturbation method as described in the preceding two parts of this series is applied to study the electrodynamical properties of different materials in the microwave and millimeter wave spectral range. We briefly discuss the relevant uncertainties which are asociated with the different measurement techniques and we find that employing the amplitude technique it is possible to measure both the width and frequency to nearly the same precision. We then demonstrate the broad range of applicability of this technique by showing results obtained on several different materials, ranging from an insulator to a superconductor. The performance limitations of this technique are discussed in detail.