Frequency Of Dielectric Resonator Research Articles

Impedance characterization of wheat starch at various water contents

Wheat starch is used extensively in the food, entertainment, and papermaking industries. It is classified as a non-hazard material and an electrical insulator, but recent events manipulating dispersed grains found that electrical properties can vary in different environmental conditions. In order to make advancements in the safety of processes involving these materials, it is necessary to understand their electrical properties. Here, we study wheat starch grains in terms of the aggregation, dielectric resonant frequency, and moisture level. Samples are characterized by Scanning Electron Microscopy (SEM) and Impedance Spectroscopy (IS) using an interdigital planar electrode array. Results showed that the capacitance measurements increase with an increase in the water content (>27.4 Wt%) and therefore it enhances the ability to store an electric field in the polarization of the starch sample. Nyquist plots showed that the internal resistance of the medium decreases for larger grains at low and intermediate stimulus frequencies and at high moisture contents (21–27 Wt%). At high frequencies, the materials behave indistinguishably. We were also able to demonstrate the predictability of water content based on one samples IS measurements. We propose that by extracting the resonant frequencies from the measurements and identifying the resistance of the sample at those frequencies, we can use a regression to predict the water content of the mixture within 1.5 Wt%. Our results show that in the case of 15 − 50μm starch grains, there is a sharp increase in capacitance resulting from the addition of water (10–30 Wt%) which may increase risks of auto-ignition by approaching the Minimum Ignition Energy (MIE). This research offers useful information on how to use IS techniques for understanding both the starch properties and their moisture condition at the same time. This information will allow the industry to asses not only the quality but also the storage safety and handling conditions.

Structure and microwave dielectric properties of ZnTa2O6 ceramics with TiO2 and ZrO2 additions

Ceramic samples based on ZnTa2O6 and ZnTa2O6–MO2 (M = Ti, Zr) systems have been obtained by the solid state ceramic route. The phase composition and microstructure of samples were investigated. The effect of the aliovalent substitution of ions Zn2+ and Ta5+ by M4+ (M = Ti, Zr) in the structure of ZnTa2O6 on microwave dielectric properties of ceramics was studied. The way of the compensation of the positive temperature coefficient of resonant frequency of dielectric resonators based on ZnTa2O6 ceramics with using the aliovalent substitution of cations was proposed. Dielectric resonators with the high temperature stability of the resonant frequency and high dielectric properties in the microwave range based on the ZnTa2O6–ZrO2 system were obtained for application in electronics.

FDTD analysis of dielectric resonators with curved surfaces

In this paper, the finite-difference time-domain (FDTD) method is applied to calculate the resonant frequency of dielectric resonators (DRs) with curved surface. The contour-path integral FDTD (CFDTD) is modified to deal with the curved surface of the dielectric body while the traditional rectangular cells are maintained. Results are compared with theoretical values and staircase approximation, and show that the present method is more accurate than the staircase approximation.

Calculation of dielectric resonators with complicated constitutive parameters

A novel approach for calculation of resonant frequencies of dielectric resonators in waveguides or cavities is presented. The resonant sample may be made from different materials: high-permittivity dielectrics, magnetic materials, chirals or general bi-anisotropic materials. The resonant frequencies of high-permittivity dielectric resonators in a cylindrical cavity are calculated and compared with the literature to validate the proposed method. Numerical results of chiral and Faraday chiral resonators are also given.

Frequency-dependent FDTD modeling of optically controlled dielectric resonators

A theoretical analysis is carried out to describe the performance of optically controlled dielectric resonators. A previously developed frequency-dependent finite-difference-time domain (FDTD) formulation has been used to estimate the effect that solid state plasmas have on the resonant frequency on dielectric resonators. Optical generation of plasmas in contact with dielectric resonators is being considered here as a possible means of controlling the resonator's frequency. The effect that carrier diffusion and recombination-generation have on plasma permittivity and penetration depth are taken into account in this analysis. The results are compared with measurement and are shown to yield a quantitative estimate of the optically induced dielectric resonator frequency shift as a function of the illumination, properties of the plasma host semiconductor, and the properties of the dielectric resonator. >

Solution of the resonant frequencies of a microwave dielectric resonator using boundary element method

The methods currently used for computation of resonant frequencies of a microwave dielectric resonator all require knowledge of the field structures, both inside and outside the resonator, and therefore are strictly limited. The paper discusses the general principle of solution of resonant frequencies of the dielectric resonator by the boundary element method (BEM). Through discretisation, the boundary integral equations are reduced to a generalised eigenvalue equation, with the eigenvalues as the resonant frequencies. The method presented is, in principle, applicable to an arbitrarily shaped dielectric resonator. Some results are given and compared with previous data published as a demonstration of the validity of the method.

Resonant frequencies of dielectric resonators containing guided complex modes

It is shown that unless complex modes are included in the mode-matching analysis to determine the resonant frequencies of dielectric-loaded resonators, some resonant frequencies could be missed. Field distributions, mode charts, and mode coefficients of dielectric-loaded resonators in which complex modes exist are presented. Experimental measurements for the verification of the computed results are presented and show good agreement with theory. >

Mode matching method for determination of the resonant frequency of a dielectric resonator placed in a metallic box

A method for the determination of the resonant frequency of a cylindrical dielectric resonator inserted into a cylindrical metallic box is presented. The method can be applied to asymmetrical structures.

Design Consideration for Frequency-Stabilized MIC IMPATT Oscillators in the 26-GHz Band

A 26-GHz frequency-stalbilized MIC IMPATT oscillator using a dielectric resonator has been developed. In designing such an oscillator in the high-frequency range, many parameters affecting frequency stability should be considered. This paper discusses oscillation frequency variations caused by deviations in the resonant frequency of dielectric resonators, in diode reactance, and in the electrical length between the diode and resonator, all of which are due to temperature variation. Design criteria for a highly frequency-stabilized oscillator are also presented. With these techniques, we have obtained an MIC IMPATT oscillator with frequency stability of less than +-5.0x10/sup -5/, output power deviation of less thau +-2.0 dB, and output power of more than 23 dBm over the temperature range of 0°C to 50°C.

Correction to "Accurate Resonant Frequencies of Dielectric Resonators" (Letters)

After a study (ATP 2365 of the French CNRS) we have detected an error in Fig. 11 of the above paper. In fact, it is necessary to replace the curves of this figure by those presented here.

Accurate Resonant Frequencies of Dielectric Resonators

The applications of dielectric resonators are currently of considerable interest in microwave integrated circuits. The design of a dielectric resonator depends on its natural resonant frequencies. Since exact solutions of dielectric rectangular and cylindrical resonators cannot be rigorously computed a new and more accurate method has been developed to solve this problem. In this method all the surfaces are simultaneously considered as imperfect magnetic walls. Theoretical values agree very well with experimental results. The difference being less than 1 percent.

New Method for Computing the Resonant Frequencies of Dielectric Resonators (Short Papers)

A new method is develop for accurately predicting resonant frequencies of dielectric resonators used in microwave circuits. By introducing an appropriate approximation in the field distribution outside the resonator an analytical formulation becomes possible. Two coupled eigenvalue equations thus derived are subsequently solved by a numerical method. The accuracy of the results computed by the present method is demonstrated by comparison with previously published data.

Higher accuracy for the resonance frequencies of dielectric resonators

An improved new method is developed which allows the determination, with great accuracy of the resonance frequencies of dielectric resonators. By introducing appropriate approximation for field distribution, two coupled eigenvalue equations are derived, which have been solved by a numerical method. Theoretical and experimental results agree very well (to a few parts in 103)

The Influence of Conducting Walls on Resonant Frequencies of the Dielectric Microwave Resonator (Correspondence)

Equations are given from which the resonant frequencies of dielectric resonators can be calculated taking into account the influence of the conducting walls of the microwave structures in which these resonators are inserted. The comparison between theoretical and experimental results shows the validity of the theoretical model.