Jyh Sheen

Comparisons of microwave dielectric property measurements by transmission/reflection techniques and resonance techniques

This review provides a general comparison of the two most commonly used techniques for measurement of complex permittivity at microwave frequencies: transmission/reflection and resonance. The transmission/reflectance techniques are analyzed using distributed and lumped impedance models. The resonance techniques are analyzed using both dielectric and cavity resonance models. The analysis, combined with experimental results, enables us to illustrate the advantages and disadvantages of the various techniques and provide guidance on which techniques to use under particular circumstances. In general, transmission/reflection techniques can be used over a broad band of frequencies, and are suitable for loss measurements on high loss materials. Resonance techniques do not have swept frequency capability, but have higher accuracy for measurement of the real part of permittivity and can measure the loss tangent of low loss materials with high resolution.

Amendment of cavity perturbation technique for loss tangent measurement at microwave frequencies

Theoretically, the quality factor of a metal resonant cavity will be increased after introducing a lossless dielectric sample. However, this increment of quality factor is not put into the consideration of the calculation of loss tangent measurement for the conventional cavity perturbation method, widely used on the measurements of microwave dielectric properties. Therefore, the conventional resonant perturbation formulas for dielectric loss measurement should be amended. This amendment is introduced in this study and the amended formulas for loss tangent measurement are given. With the amended formulas, no standard sample is required for measurement which simplifies the measuring procedure suggested by the previous publication. In addition, the measuring error on loss tangent on the conventional formula is discussed. Experiments have shown the improvement of measurement accuracy by this modification.

Microwave Measurements of Dielectric Constants by Exponential and Logarithmic Mixture Equations

This article reports on a study of the dielectric constants of ceramic dispersions in the polyethylene matrix at microwave frequency. The exponential and logarithmic mixture rules are studied in three ceramic powders of flllers with dielectric constants 10, 20, and 36, respectively. The experimental values of the dielectric constants of the mixtures are compared to those obtained by using difierent mixing laws. The mixing rules are also adopted to calculate the dielectric constants of pure ceramics from the measured dielectric constants of composites with various concentrations. The theories on errors of calculations are studied. The most adequate mixture equation for measuring the dielectric constants of pure ceramics is suggested.

An integrated portable vision assistant agency for the visual impaired people

This paper is designed to develop a portable auxiliary system for those visually impaired, such as color blindness or serious low vision, to enhance their visual sensitivity or substitute the original visual function thus improve their life quality. Individual vision model for each user can be constructed and the optimal visual compensation process is designed accordingly. For the blind user, an automatic traffic light recognition function is also integrated into the portable system to help them across the road safely. Experimental results show that the proposed vision assistance works well for the visually impaired in improving the awareness of the surroundings and enhancing the visual perception effectively.

Microwave Measurements of Dielectric Properties Using a Closed Cylindrical Cavity Dielectric Resonator

Microwave measurements of the dielectric constant and loss tangent of homogeneous isotropic samples in rod form, using a closed cylindrical cavity resonator, are described. The measurements are made at the resonant frequency of the TE01delta is mode. A new simple field model of the resonator is developed. This model provides a very simple and clear description of the field distribution within the resonator. The dielectric properties are computed from the resonant frequency, sample dimensions and unloaded quality factor of the resonator. The effect of conductivity losses within the metal cavity is examined. The measurement accuracy is assessed by comparing the results with those obtained using other well-known techniques.

A dielectric resonator method of measuring dielectric properties of low loss materials in the microwave region

A technique for the measurement of dielectric properties of low loss and homogeneously isotropic media in the microwave region is studied. The measuring structure is a resonator made up of a cylindrical dielectric rod and conducting plates. The dielectric constants and loss tangents are computed from the resonant frequencies, structure dimensions and unloaded Qs of the TE01δ mode. A simple field model is introduced to analyze this resonator structure. Unlike other simple models, this model does not have the defect of low measurement accuracy of dielectric properties. Important factors affecting the dielectric properties measurements are introduced. Error sources for measurements are also discussed. The measurement accuracy is justified by comparing the results with those of other techniques. In addition, various methods for calculating the power factor and conducting loss and for measuring the conductivity of the conducting plates are discussed. The accuracies of certain of these methods have not previously been studied, but are given in this paper. The swept frequency capability was also studied. It was found that dielectric properties in microwave frequencies could be measured within a frequency range of 3 GHz.

Microwave measurements of dielectric constants for high dielectric constant ceramic materials by mixture equations

The microwave dielectric properties of binary composites made by high dielectric constant ceramic fillers and polyethylene matrix are studied in this paper. Three ceramic powders of fillers with dielectric constants of 100 and 170, respectively, are adopted. The experimental dielectric constants of ceramic dispersions in the polyethylene matrix at microwave frequencies of 5 to 10 GHz are compared to those obtained by using different mixing laws. Six powder mixture rules derived from three basic filler particle shapes with random distributions; as well as six exponential and the logarithmic mixture laws are investigated. The mixing rules are also adopted to estimate the dielectric constants of pure ceramics from the measured dielectric constants of composites with various concentrations. The theoretical error of each law for estimation is studied. Two new exponential rules are proposed. It was found the rule derived from filler particles of prolate spheroid with low filler concentration and exponential rules with the order of 1/3 to 1/5 have better estimation accuracy.

Dielectric Dispersion at Microwave Frequencies of Some Low Loss Mixed Oxide Perovskites

This paper reports the dielectric permittivities of several low loss ceramics of A(B11/2B21/2)O3 mixed oxide perovskites, Ba(Mg1/3Ta2/3)O3 (BMT), Sr(Al1/2Nb1/2)O3 (SAN), Sr(Al1/2Ta1/2)O3 (SAT), Sr(Ga1/2Ta1/2)O3 (SGT), and their modified compositions 0.7Sr(Al1/2Nb1/2)O3-0.3NdGaO3 (SAN-NG) and 0.7Sr(Al1/2Ta1/2)O3-0.3NdGaO3 (SAT-NG), measured at microwave frequencies. Measurements of the frequency-dependent dielectric constant and loss tangent are reported. Their loss tangent values are on the order of 10− 4 to 10− 5, which can not be evaluated by the traditional reflection/transmission spectra or impedance measurement techniques. A parallel-plate dielectric resonance method was adopted for dielectric measurements for such low loss materials. The frequency spectra of dielectric constants and loss tangents of were investigated by the well known classical oscillator model.

Unambiguous BPSK-like CSC method for Galileo acquisition

Galileo will be Europes own Global Navigation Satellite System (GNSS), which is aiming to provide highly accurate and guaranteed positioning services. Galileo E1 system has a code period of 4ms which is quadruple that of GPS C/A code. In other words, due to the large number of hypotheses in code phase at acquisition stage, a longer searching time or more hardware resource is required. It is difficult to acquire Galileo signal because of longer code length and the multiple peaks of autocorrelation function of BOC modulation. In this paper, the cyclically shift-and-combine (CSC) and BPSK-like architectures are employed to resolve the unambiguous acquisition for BOC modulation and acquires these satellite signals with hardware complexity reduction. The concept of CSC code is to modify the code structure and shorten the code period such that the acquisition burden can be decreased. Simulation results show that our proposed search algorithm can provide better performances in terms of low hardware complexity for acquiring these satellite signals and detection probability at the low value of CNR.

Microwave Dielectric Properties Measurements Using the Waveguide Reflection Dielectric Resonator

Measurements of dielectric properties of the homogeneous and isotropic medium in the microwave frequencies by a waveguide reflection dielectric resonator are studied. A dielectric rod sample is put inside of a rectangular cavity made by a microwave waveguide. The samples dielectric constant and loss tangent are measured at the resonant frequency of the TE01delta mode. A simple field model of the waveguide reflection resonator is developed for the measurements of dielectric properties. This field model is developed from that of the parallel-plate dielectric resonator. Reflection signal is measured for the calculations of dielectric properties. The dielectric properties are computed from the resonant frequency, structure dimensions, and unloaded quality factor. The effect of the conductor loss of the metal cavity is studied. The measurement accuracy of dielectric properties is discussed by comparing the results with those measured by other well known techniques.