Significant Differences In Dielectric Properties Research Articles

AY2Al4GeO12 (A = Ca, Mg) ceramics: Phase composition, microstructure, lattice vibration, bond characteristics, and microwave dielectric properties

In this work, cubic garnet-type AY2Al4GeO12 (A = Ca, Mg) ceramics were synthesized by a solid-state reaction method. XRD detected that CYAG was a single-phase, and the secondary phase existed in the MYAG. SEM, density, and dielectric properties results indicate that the optimum sintering temperature of CYAG and MYAG ceramics is 1550 °C, the CYAG and MYAG ceramics exhibited the best microwave dielectric properties of εr = 8.94, Q×f = 93805 GHz, τf = −48 ppm/°C and εr = 7.06, Q×f = 30549 GHz, τf = −26.55 ppm/°C, respectively. Rietveld refinement, Raman and XPS confirmed that the significant difference in dielectric properties is related to the secondary phase, structural disorder and oxygen vacancy. The relationship between the Q×f and lattice vibration are discussed. τf is explained by oxygen bond valence. The influence of bond characteristics on dielectric properties was analyzed. The reported microwave ceramics are expected to be used as substrate materials in the millimeter wave band.

Influence of composition, temperature, and frequency on dielectric properties of selected saltwater and freshwater fish

ABSTRACT Dielectric heating has been applied in the fishing industry for thawing and cooking. However, the difference in dielectric properties for various species of fish can greatly influence the heating rate and uniformity. In this study, the dielectric properties of saltwater fish [Pomfret (Pampus argenteus) and Hairtail (Trichiurus lepturus)] and freshwater fish [Bream (Parabramis pekinensis) and Crucian Carp (carassius auratus)] were determined within the frequency range of 1–2500 MHz at –20°C to 100°C. Results showed that the dielectric constant () and dielectric loss factor () of the four different species decrease with increasing frequency. The dielectric constants at 27.12 and 40.68 MHz increase with increasing temperature, and those at 915 and 2450 MHz increase rapidly and then decrease. The of Hairtail showed the highest increase, followed by Bream, Crucian Carp, and Pomfret; and the of Hairtail showed the highest increase, followed by Pomfret, Bream, and Crucian Carp due to the composition difference between the species. Thus, the dielectric heating process for various species of fish can be considerably different at different frequencies. Furthermore, the most significant difference in dielectric properties among all species of fish was observed at 27.12 MHz, which indicated that this frequency could be the most suitable frequency for the detection of fish species based on their dielectric properties.

Utilization of eggshell as a low-cost precursor for synthesizing calcium niobate ceramic

This study investigated the possibility of using calcium carbonate (CaCO3) from chicken eggshell biowaste as a starting material for synthesizing calcium niobate (CaNb2O6) powder through the conventional solid-state reaction. Phase formation of calcium niobate was studied as a function of calcination conditions by X-ray diffraction (XRD), Fourier transform infrared spectroscopy and Raman spectroscopy. The X-ray fluorescence results showed that the chicken eggshell contained more than 96·0% of calcium carbonate by weight. The structural characteristics of the calcium carbonate and calcium niobate powder were quantitatively evaluated by Rietveld refinement method from the XRD data. Rietveld refinement results verified that the eggshell powder exhibited a rhombohedral calcite (calcium carbonate) structure with lattice parameters a = b = 4·9812 ± 0·00059 Å (1Å = 0·1 nm) and c = 17·0342 ± 0·00292 Å with α = γ = 90° and β = 120°. Furthermore, the single phase of calcium niobate corresponded to the orthorhombic structure for space group Pbcn(60) obtained after the calcination process. The non-isothermal kinetic of calcium niobate was investigated by the Ozawa methods. Activated energy calculated using Ozawa methods was 1168 ± 29 kJ mol−1. Also, there was no significant difference in dielectric properties between calcium niobate ceramic using chicken eggshell waste as a starting material and calcium niobate ceramic using analytical-reagent-grade calcium carbonate. This study showed that calcium carbonate from chicken eggshell biowaste is an alternative starting material for synthesizing microwave dielectric calcium niobate ceramic.

Dielectric properties of glycosuria at 0.2-50 GHz using microwave spectroscopy

In this study, we analyzed the dielectric behavior of urine among subjects with diabetes mellitus. The measurements were conducted using an open-ended coaxial probe at microwave frequencies between 0.2 and 50 GHz at room temperature (25 °C), 30 °C and human body temperature (37 °C), respectively. The strongest statistically significant difference in dielectric properties across different glycosuria groups (F (2, 41) = 8.681; p < 0.01) was reported at room temperature (25 °C). Dielectric constant increased with glycosuria level more than 500 mg/dl (>0.5%) at low frequencies. Dielectric constant correlated positively with glycosuria level at frequency above 40 GHz while loss factor correlated negatively with glycosuria level at frequency above 15 GHz. The experimental data closely matched the Debye model.

A Study of Dielectric Properties of Proteinuria between 0.2 GHz and 50 GHz.

This paper investigates the dielectric properties of urine in normal subjects and subjects with chronic kidney disease (CKD) at microwave frequency of between 0.2 GHz and 50 GHz. The measurements were conducted using an open-ended coaxial probe at room temperature (25°C), at 30°C and at human body temperature (37°C). There were statistically significant differences in the dielectric properties of the CKD subjects compared to those of the normal subjects. Statistically significant differences in dielectric properties were observed across the temperatures for normal subjects and CKD subjects. Pearson correlation test showed the significant correlation between proteinuria and dielectric properties. The experimental data closely matched the single-pole Debye model. The relaxation dispersion and relaxation time increased with the proteinuria level, while decreasing with the temperature. As for static conductivity, it increased with proteinuria level and temperature.

Experimental Investigation on Flanged Parallel-Plate Dielectric Waveguide Probe for Detection of Conductive Inclusions in Lossy Dielectric Medium

A flanged parallel-plate dielectric waveguide probe (PPDW) for microwave detection and localization of small inclusions in a lossy dielectric medium, based on detecting the contrast in dielectric properties between the inclusion and embedding medium has been proposed. In this paper, experimental evaluation of this probe for the detection and localization of small conductive inclusion is presented. Investigations were performed on solid lossy dielectric phantoms with conductive spherical inclusions representing tumors embedded. Preliminary experimental results demonstrate the potential of the PPDW to detect and locate a small inclusion exhibiting significant difference in dielectric properties from the host medium, embedded at reasonable depth.

Solutions to the inverse problem in a two-dimensional model for microwave breast tumour detection

This paper presents an in vivo detection method to estimate the size and the position of a breast tumour using microwave frequencies. At these frequencies there is a significant difference in dielectric properties between a malignant tumour and healthy breast tissue. By considering these properties we solve the forward problem of the signal's scattering effect for a two-dimensional breast model. We use Newton's multidimensional iterative method to solve the inverse problem and compute the unknown location and size of the tumour. Our analytical study suggests that the approach will be capable of detecting a millimetre size tumour inside the breast. Due to the complex scattering from the non-homogeneous internal structure and other complications the microwave measurements can have errors. However, in tests, our algorithm can calculate tumour distance with 0.54% error when there is a 10% error in the value of the microwave field measurements.

Hepatic radiofrequency ablation at low frequencies preferentially heats tumour tissue

Purpose: Radiofrequency ablation is a clinically accepted treatment modality for liver cancer. There are significant differences in dielectric properties between normal and cancer tissue in the liver, which are particularly pronounced at frequencies below 100 kHz. This study performed computer simulations to determine whether radiofrequency (RF) ablation at lower frequencies than currently employed (450–500 kHz) can take advantage of this difference to preferentially deposit energy within the tumour.Materials and methods: Finite Element Method computer models were created for a cooled needle electrode and a multi-tine RF electrode inserted into a 2 cm diameter tumour. RF ablation was simulated and current density as well as tissue temperature distribution determined. In vivo data were used on electrical conductivity of normal and cancer tissue in the models to simulate RF ablation in liver at the currently used frequency of 500 kHz and at 10 kHz.Results: At 500 kHz there was little difference in RF current density and final tissue temperature between normal and cancer tissue. Due to the more pronounced differences in electrical conductivity at 10 kHz, cancer tissue was heated preferentially at this frequency. Depending on power control algorithm, this resulted in either higher intra-tumour temperatures or lower temperatures outside the tumour at 10 kHz compared to 500 kHz.Conclusion: Radiofrequency ablation at lower frequencies than currently used may preferentially heat the tumour and preserve normal tissue. A targeted device for selective tumour destruction may be designed to make use of this principle.

Dielectric properties of six different species of starch at 2450 MHz

Dielectric properties at 2450 MHz were determined for tapioca, corn, wheat, rice, waxymaize and amylomaize starches in granular (moisture content 1 and 13%) and in solution forms [starch–water ratio:1:1, 1:1.5, 1:2 (w/w)] at temperatures from 30 to 95°C. Dielectric properties were shown to be dependent on temperature, moisture content and starch type. The increase in moisture content increased dielectric constant and loss factor of all types of starches. Increasing temperatures decreased the dielectric values for starch solutions (high moisture content) but increased the dielectric values for granular starches (low moisture content). Quadratic equations were developed to show the relationship between the changes in dielectric properties with temperature for starch species. There were significant differences in dielectric properties of different types of starches.

Brine infiltration in the McMurdo Ice Shelf, McMurdo Sound, Antarctica

In recent trials near Hut Point Peninsula an impulse radar profiler was used successfully to monitor the depth characteristics and lateral extent of brine soaking in the McMurdo Ice Shelf. The success of the profiler can be attributed in large part to the significant difference in dielectric properties of dry firn and firn that has become brine soaked by infiltrating seawater. In addition to furnishing a continuous trace of the top of the brine layer, the impulse radar profiler has also revealed the existence of cracks, relict brine horizons, and deformational features within the ice shelf. Data tend to favor lateral infiltration of seawater, either through the seaward edge of the ice shelf or via tensile cracks at the bottom of the ice shelf.