Dielectric Properties Of Powders Research Articles

Microwave Resonant Sensor Based on MCSRR Research

This paper presents a low-cost and easy-to-fabricate microwave resonant sensor for characterising the dielectric properties of solids and powders. The designed sensor is based on a FR-4 dielectric substrate with a Multiple Complementary Split-Ring Resonator (MCSRR) etched on its bottom, and this resonant unit is used to place the sample to be tested (Material Under Test, MUT). The sensor was operated at a resonant frequency of 4.9GHz and used the offset resonance to detect the dielectric properties of different solids and powders. The relationships established by the simulation were experimentally verified by the fabricated sensor. The percentage error between the calculated dielectric constant and the reference dielectric constant is less than 8.7% for a certain thickness of the sample to be tested, which verifies the feasibility of the proposed loaded MCSRR sensor. Therefore, this sensor is expected to be a cost-effective and convenient solution for accurate characterisation of solid, powder dielectric properties.

Measurement and Analysis of Dielectric Properties of Agricultural By-product Powders in Microwave Frequency Range

Dielectric properties play an important role in the microwave-assisted application of nonmagnetic agriculture-related media. In this paper, the practical requirements for the lack of quantitative data on the dielectric properties of agricultural media in microwave-assisted applications are obtained. The dielectric properties data of four kinds of agricultural by-products powder (Potato powder, Pseudo -ginseng Powder, Gastrodia elata powder, Dendrobium chrysotoxum Lindl powder) under microwave frequency were measured, and related factors were analyzed. The results show that the uncalibrated coaxial transmission reflection method can be used to measure and analyse the dielectric properties of high frequency bands of powder materials. Dielectric constant (ε ′) and Dielectric loss factor (ε '') of agricultural by-products at room temperature have a relationship between microwave frequency and moisture content. It is a dependent and the mathematical relation is satisfied. The influence of microwave frequency and moisture content on the dielectric properties is as follows: lows: ε′>ε′′>tanδ. Under the conditions of civil microwave frequency (2.45GHz) and moisture content (2% ~ 25%), the dielectric constant and the dielectric loss factor of different kinds of agricultural by-products powder are in the range of 3.5 ~ 9 and 0.1 ~ 3.2 respectively. The results provide data basis for microwave processing and quality monitoring of agricultural by-products powder. The technical method is suitable for the measurement and analysis of the dielectric properties of powder materials.

Determination of complex permittivity of surfactant treated powders using an open-ended coaxial cavity resonator

An indirectly coupled open-ended coaxial cavity resonator was used to detect the effect of stearic acid surface treatments on the dielectric properties of powders in the frequency range 2.17–3.79GHz. The Bruggeman symmetric and Looyenga classical mixing rules and a general mixing model were used to determine changes in permittivity and loss tangent of the inclusions. Surfactant processed powders with stearic acid 0.05–1.36vol.% induced only a small change in inclusion permittivity but caused a notable change in dielectric losses. The dielectric loss tangents of SiO2 and Al2O3 increased from 2×10−4 to 4×10−4 and 5×10−3 to 6.1×10−3, respectively. However, a significant decrease in dielectric loss tangent, from 6.2×10−3 to 3.8×10−3, was noted with surfactant treated ZrO2. The investigated novel characterization method proved to be able to detect even very slight changes in dielectric properties to be utilized in various types of powdery material characterization, e.g., in composite applications and material quality monitoring.

Method to characterize dielectric properties of powdery substances

An open ended coaxial cavity method for dielectric characterization of powdery substance operating at 4.5 GHz in TEM mode is presented. Classical mixing rules and electromagnetic modeling were utilized with measured effective permittivities and Q factors to determine the relative permittivity and dielectric loss tangent of different powders with εr up to 30. The modeling enabled determination of the correction factor for the simplified equation for the relative permittivity of an open ended coaxial resonator and mixing rules having the best correlation with experiments. SiO2, Al2O3, LTCC CT 2000, ZrO2, and La2O3 powders were used in the experiments. Based on the measured properties and Bruggeman symmetric and Looyenga mixing rules, the determined dielectric characteristics of the powders exhibited good correlation with values in the literature. The presented characterization method enabled the determination of dielectric properties of powdery substances within the presented range, and therefore could be applied to various research fields and applications where dielectric properties of powders need to be known and controlled.

Microwave dielectric properties of Al-doped ZnO powders synthesized by coprecipitation method

Al-doped ZnO (AZO) powders with different Al concentrations were synthesized by coprecipitation method. Crystal structural and dielectric properties of the powders as a function of aluminum doping concentration as well as annealing temperature were investigated. The XRD results reveal that Al atoms are doped into ZnO lattice successfully and all the samples are polycrystalline with a hexagonal wurtzite structure. The real part (ε′) and imaginary part (ε″) of the complex permittivity of the powders were carried out by a vector network analyzer in the microwave frequency range of 8.2–12.4 GHz. The results show that the ε′ and ε″ of the doped ZnO powders increase with the doping content and both of them are higher than that of the pure one. For the AZO powder with 7 mol% Al, both ε′ and ε″ increase firstly and then decrease with increasing annealing temperature.

Microstructural evolution and dielectric properties of 1D AlN powders synthesized by microwave technique

Low temperature synthesis of Aluminum nitride (AlN) powders through NH4Cl assisted nitridation have been studied by microwave technique. The effect of processing time on the synthesis of AlN powders has been investigated. The optimum processing time was determined to be 120min at 630W, 200°C. The powders were characterized by X-ray diffraction method (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray analyzer (EDS), Fourier transform infrared spectrometer (FTIR) and Impedance analyzer. XRD results revealed that the product has wurtzite phase of AlN. SEM micrographs show a 1D nanorod of AlN with a granular morphology. FTIR spectra exhibit A1 (TO) and E1 (LO) modes of wurtzite AlN. Dielectric properties of the powders were investigated by means of C–V and C–f and ε′–f characteristics. The reported results indicate a reasonable quality of the obtained AlN powders with high dielectric constant, suitable for application in the fabrication of specific electronic devices.

Millimeter- and Submillimeter-Wave Dielectric Measurements of Household Powders Using Fourier Transform Spectroscopy

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents the first step in characterizing and detecting common household powders as hoax materials by investigating their broadband dielectric characteristics. Pesticide is also studied due to its similarities to anthrax. A modified two-beam polarizing interferometer and custom-made sample holders were utilized to obtain the refractive index (RFI), absorption coefficient, complex real and imaginary permittivity, and loss tangent of flour, dry milk, cornstarch, pesticide, baking soda, and talc as a continuous function of frequency in the range of 400–1200 GHz. Dispersive Fourier transform spectroscopy was employed to provide phase and amplitude information, leading to the accurate and direct acquisition of the complex RFI and complex dielectric permittivity spectra. It is the first time that such measurements were carried out over such an extended frequency range for common powders to reveal marked variation in absorption and RFI values for different powders. The powders exhibit high-absorption characteristics, and the RFI values lie between 2.4 and 3.4 in this spectral range. A unique resonance signature for talc was detected at 1135 GHz with an associated anomalous dispersion. Parameters such as grain size and orientation were analyzed for their effect on the dielectric properties of powders. Relationships between density, permittivity, and RFI are explored to provide the ability to extrapolate results for other densities. The RFI and the real part of the dielectric permittivity were found to be the most reliable for identification and detection purposes. </para>

Preparation of nm-Sized Barium Titanate Fine Particles and Their Powder Dielectric Properties

Barium titanate (BaTiO3) crystallites with various particle sizes from 17 to 100 nm were prepared by the 2-step thermal decomposition method of barium titanyl oxalate (BaTiO(C2O4)2·4H2O). The crystal structure of these BaTiO3 particles was assigned to cubic m-3m by a X-ray diffraction (XRD) measurement while it was assigned to tetragonal 4mm by a Raman scattering measurement. Investigation of impurity in these particles using both TG-DTA and FT-IR measurements revealed that no impurity was detected in the BaTiO3 lattice while hydroxyl and carbonate groups were detected only on the surface. The dielectric constants of these powders were measured using suspensions by a modified powder dielectric measurement method. As a result, the dielectric constant of BaTiO3 particles with a size of around 70 nm exhibited a maximum of over 15,000. This study revealed that BaTiO3 particles with a size around 70 nm were the most desirable for capacitor application.