Temperature Dependence Of Permittivity Research Articles

In-situ characterization of temperature-dependent domain structure and permittivity of KTN crystals with applied field

In-situ characterization of temperature-dependent domain structure and permittivity of KTN crystals with applied field

Assessment of thermochromic phantoms for characterizing microwave ablation devices.

Thermochromic gel phantoms provide a controlled medium for visual assessment of thermal ablation device performance. However, there are limited studies reporting on the comparative assessment of ablation profiles assessed in thermochromic gel phantoms against those in ex vivo tissue. The objective of this study was to compare microwave ablation zones in a thermochromic tissue-mimicking gel phantom and ex vivo bovine liver and to report on measurements of the temperature-dependent dielectric and thermal properties of the phantom. Thermochromic polyacrylamide phantoms were fabricated following a previously reported protocol. Phantom samples were heated to temperatures in the range of 20°C-90°C in a temperature-controlled water bath, and colorimetric analysis of images of the phantom taken after heating was used to develop a calibration between color changes and the temperature to which the phantom was heated. Using a custom, 2.45GHz water-cooled microwave ablation antenna, ablations were performed in fresh ex vivo liver and phantoms using 65W applied for 5min or 10min (n=3 samples in each medium for each power/time combination). Broadband (500MHz-6GHz) temperature-dependent dielectric and thermal properties of the phantom were measured over the temperature range of 22°C-100°C. Colorimetric analysis showed that the sharp change in gel phantom color commences at a temperature of 57°C. Short and long axes of the ablation zone in the phantom (as assessed by the 57°C isotherm) for 65W, 5min ablations were aligned with the extents of the ablation zone observed in ex vivo bovine liver. However, for the 65W, 10min setting, ablations in the phantom were on average 23.7% smaller in the short axis and 7.4 % smaller in the long axis than those observed in ex vivo liver. Measurements of the temperature-dependent relative permittivity, thermal conductivity, and volumetric heat capacity of the phantom largely followed similar trends to published values for ex vivo liver tissue. Thermochromic tissue-mimicking phantoms provides a controlled, and reproducible medium for comparative assessment of microwave ablation devices and energy delivery settings. However, ablation zone size and shapes in the thermochromic phantom do not accurately represent ablation sizes and shapes observed in ex vivoliver tissue for high energy delivery treatments (65W, 10min). One cause for this limitation is the difference in temperature-dependent thermal and dielectric properties of the thermochromic phantom compared to ex vivobovine liver tissue, as reported in the present study.

Investigate the effect of co-doping on the grain size and diffuse phase transition of barium titanate ceramics

An investigation examined the impact of co-doping BaTiO3 ceramics with La3+ and Nd3+ on their microstructural, dielectric, and phase transition properties. The synthesis of BaTiO3 with co-doping of La3+ and Nd3+, using the general formula Ba1-x(La1/3, Nd1/3)xTiO3 (BLNdTx) with varying concentrations of x (0%, 2%, 4%, and 8%), is achieved by the solid-state reaction technique. A temperature-dependent dielectric permittivity investigation was conducted at four distinct frequencies (1 kHz, 10 kHz, 100 kHz, 500 kHz, and 1 MHz) within the 30–200 °C temperature range. The findings indicate that the samples show a diffuse phase transition and a noticeable divergence from the typical Curie-Weiss equation. The diffuseness parameters γ for phase transition rose from 1.15 to 1.75 as x grew from 0 to 8%, respectively. The concurrent impact of surface phenomena, mechanical stress phenomena, and the external effect of grain boundaries might explain the substantial size reduction. An in-depth understanding of the grain size effect and its underlying mechanism would be advantageous for advancing and practically using BaTiO3-based ceramics and other ferroelectrics.

An investigation of the structure property relation of Na2MnWO6 for device application

An investigation of the structure property relation of Na2MnWO6 for device application

Temperature-dependent dielectric behavior of A6B2O17 (A = Zr, Hf; B = Nb, Ta) phases

We report on temperature-dependent dielectric behavior of disordered ternary A6B2O17 (A = Zr, Hf; B = Nb, Ta)-form oxides in the GHz frequency range. The microwave dielectric properties including relative permittivity, dielectric loss, and temperature-dependent relative permittivity were characterized using cylindrical dielectric resonators using a resonant post measurement technique. Dielectric measurements through the resonant post method approach generally agree with dielectric measurements of A6B2O17 bulk ceramics measured through standard resonant post techniques. Coefficients describing the temperature-dependent relative permittivity for ternary A6B2O17 phases are strongly positive, suggesting contributions to polarizability arising from long-range mechanisms potentially associated with structural disorder. These observations support the working hypothesis that material functionality can be engineered by the chemical diversity and structural disorder possible in high configurational entropy A6B2O17 phases.

Assessment of thermochromic phantoms for characterizing microwave ablation devices.

Thermochromic gel phantoms provide a controlled medium for visual assessment of thermal ablation device performance. However, there are limited studies reporting on the comparative assessment of ablation profiles assessed in thermochromic gel phantoms against those in ex vivo tissue. The objective of this study was to compare microwave ablation zones in a thermochromic tissue mimicking gel phantom and ex vivo bovine liver, and to report on measurements of the temperature dependent dielectric and thermal properties of the phantom. Thermochromic polyacrylamide phantoms were fabricated following a previously reported protocol. Phantom samples were heated to temperatures in the range of 20 - 90 °C in a temperature-controlled water bath, and colorimetric analysis of images of the phantom taken after heating were used to develop a calibration between color changes and temperature to which the phantom was heated. Using a custom, 2.45 GHz water-cooled microwave ablation antenna, ablations were performed in fresh ex vivo liver and phantoms using 65 W applied for 5 min or 10 min ( n = 3 samples in each medium for each power/time combination). Broadband (500 MHz - 6 GHz) temperature-dependent dielectric and thermal properties of the phantom were measured over the temperature range 22 - 100 °C. Colorimetric analysis showed that the sharp change in gel phantom color commences at a temperature of 57 °C. Short and long axes of the ablation zone in the phantom (as assessed by the 57 °C isotherm) for 65 W, 5 min ablations were aligned with extents of the ablation zone observed in ex vivo bovine liver. However, for the 65 W, 10 min setting, ablations in the phantom were on average 23.7% smaller in short axis and 7.4 % smaller in long axis than those observed in ex vivo liver. Measurements of the temperature dependent relative permittivity, thermal conductivity, and volumetric heat capacity of the phantom largely followed similar trends to published values for ex vivo liver tissue. Thermochromic tissue mimicking phantoms provide a controlled, and reproducible medium for comparative assessment of microwave ablation devices and energy delivery settings, though ablation zone size and shapes may not accurately represent ablation sizes and shapes observed in ex vivo liver tissue under similar conditions.

Broad temperature range with stable permittivity and low dielectric loss in (1–2x)Na0.5Bi0.5TiO3-xNaNbO3-xGdFeO3 system

Broad temperature range with stable permittivity and low dielectric loss in (1–2x)Na0.5Bi0.5TiO3-xNaNbO3-xGdFeO3 system

Crystal structure and dielectric properties of Ln2Ti2SiO9 (Ln = Pr and Nd)

Crystal structure and dielectric properties of Ln2Ti2SiO9 (Ln = Pr and Nd)

Synthesis and characterization of the electrical and energy storage properties of new Barium titanate - Europium titanate solid solution

Synthesis and characterization of the electrical and energy storage properties of new Barium titanate - Europium titanate solid solution

The role of Ca/Zr ratio on the local structure and phase transitions in lead-free (Ba,Ca)(Zr,Ti)O3

The role of Ca/Zr ratio on the local structure and phase transitions in lead-free (Ba,Ca)(Zr,Ti)O3

Phase Transitions under the Electric Field in Ternary Ferroelectric Solid Solutions of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 near the Morphotropic Phase Boundary: Electric Approach

Temperature–field phase diagrams in the [001]c and [011]c directions in the cubic coordinate in 24%Pb(In1/2Nb1/2)O3–46%Pb(Mg1/3Nb2/3)O3–30%PbTiO3 (24PIN–46PMN–30PT) and 31PIN–43PMN–26PT near the morphotropic phase boundary have been clarified by measuring the temperature dependences of permittivity under an electric field. Field-induced intermediate orthorhombic and tetragonal phases have been newly found in 24PIN–46PMN–30PT and 31PIN–43PMN–26PT, respectively. The temperature dependences of the remanent polarization have also been determined by polarization–electric field (P–E) hysteresis loop evaluation. On the basis of our experimental results, the phase transition and dielectric anisotropy in PIN–PMN–PT have been discussed.

Excellent high-temperature dielectric stability of BNT-based ceramics modified by NaNbO3

Excellent high-temperature dielectric stability of BNT-based ceramics modified by NaNbO3

Simultaneously achieving large energy storage density and high efficiency in the optimized Sr2NaNb5O15 system with excellent temperature stability at a low electric field

Simultaneously achieving large energy storage density and high efficiency in the optimized Sr2NaNb5O15 system with excellent temperature stability at a low electric field

Description of electrolytes at high temperatures within the binding mean spherical approximation (BiMSA)

In this work, the binding mean spherical approximation (BiMSA) theory is used to describe osmotic and activities coefficients for electrolytes solutions up to high temperatures. Four salts are analysed: NaCl, LiCl, MgCl2 and CaCl2, in the temperature range of 25∘C to 300∘C and molalities from 0.05 to 6 molal. A good representation of experimental data is obtained for all salts and temperatures considered by introducing temperature-dependent cation size and permittivity in a suitable way. The proportion of ion pairs (that are formed at sufficiently high temperature in these solutions) for each salt is predicted from the theory, showing a pronounced increase for temperatures above 100∘C. A good agreement is found between the values of optimised and experimental association constants given in the literature.

Temperature-dependent complex dielectric permittivity: a simple measurement strategy for liquid-phase samples

Microwaves (MWs) are an emerging technology for intensified and electrified chemical manufacturing. MW heating is intimately linked to a material’s dielectric permittivity. These properties are highly dependent on temperature and pressure, but such datasets are not readily available due to the limited accessibility of the current methodologies to process-oriented laboratories. We introduce a simple, benchtop approach for producing these datasets near the 2.45 GHz industrial, medical, and scientific (ISM) frequency for liquid samples. By building upon a previously-demonstrated bireentrant microwave measurement cavity, we introduce larger pressure- and temperature-capable vials to deduce temperature-dependent permittivity quickly and accurately for vapor pressures up to 7 bar. Our methodology is validated using literature data, demonstrating broad applicability for materials with dielectric constant ε' ranging from 1 to 100. We provide new permittivity data for water, organic solvents, and hydrochloric acid solutions. Finally, we provide simple fits to our data for easy use.

Modeling the effects of salt concentration on aqueous and organic electrolytes

Understanding the thermodynamic properties of electrolyte solutions is of vital importance for a myriad of physiological and technological applications. The mean activity coefficient γ± is associated with the deviation of an electrolyte solution from its ideal behavior and may be obtained by combining the Debye-Hückel (DH) and Born (B) equations. However, the DH and B equations depend on the concentration and temperature-dependent static permittivity of the solution εr(c, T) and the size of the solvated ions ri, whose experimental data is often not available. Here, we use a combination of molecular dynamics and density functional theory to predict εr(c, T) and ri, which enables us to apply the DH and B equations to any technologically relevant aqueous and nonaqueous electrolyte at any concentration and temperature of interest.

A New Relaxor Ferroelectrics Ba4SrBiTi3Nb7O30 with Tungsten Bronze Structure

This paper reports the synthesis, microstructure and electrical properties of a new Ba4SrBiTi3Nb7O30 ceramic. X-ray diffraction analysis shows that the sample crystallizes into tungsten bronze structure, and the space group is P4bm. The electrical measurement results show that Ba4SrBiTi3Nb7O30 exhibits good dielectric and ferroelectric properties. The temperature-dependent dielectric permittivity indicates that the transition temperature of the prepared Ba4SrBiTi3Nb7O30 sample is around Tm ≈ 250K. With increasing the frequency, the dielectric peak moves to a lower temperature. Below 250 K, obvious polarization current can be detected, corresponding to the formation of spontaneous ferroelectric polarization. These results indicate the relaxor ferroelectric behavior of Ba4SrBiTi3Nb7O30 ceramic.

Temperature dependences of permittivity and conductivity of sodium-lithium niobate ceramics

As a result of comparative studies of the electric and dielectric properties of sodium-lithium niobate ceramics with a percentage of Li equal to 10 and 40 mass %, it was found that both materials have a hopping conduction mechanism. At frequencies from 500 Hz to 100 kHz, thermal ionic polarization predominates. In the low-frequency region, migratory polarization predominates. The revealed difference in the temperature behavior of the complex conductivity of the studied samples made it possible to explain the presence of ferroelectric properties in the sample with 10% Li and their absence in the sample with 40% Li.

Temperature-Induced Contrast Enhancement for Radar-Based Breast Tumor Detection at K-Band Using Tissue Mimicking Phantoms

Conventional approaches for microwave breast tumor detection are limited by the imaging resolution due to the low operating frequency. The objective of this work is to provide a proof of concept for radar-based detection of breast tumors in K-band using the temperature-dependent permittivity of the tissue for contrast enhancement. The innovation of this work is given by i) investigating higher microwave frequencies for breast cancer diagnostics and improved resolution; ii) exploiting variations in tissue temperature as a non-invasive approach for contrast-induced radar imaging eliminating the need for contrast agents such as nanoparticles; iii) using a well-defined setup with the breast compressed similar to mammography; iv) eliminating the need for coupling liquid through the usage of ultra-wideband bow-tie antennas operating from 16.55 to 40 GHz for a reflection coefficient lower than −10 dB; v) validating the experimental findings through numerical modelling. The experimental setup in this work consists of a single-pixel transmission setup with the antennas placed in a 3D printed container. Two different tissue mimicking phantoms have been studied that both model the temperature-dependent permittivity of biological tissue. The first phantom represents homogeneous fatty tissue properties and the second phantom simulates fatty tissue with a tumor inclusion. A uniform phantom warming is realized through a water bath combined with a continuous monitoring of the phantoms temperature. We show that a homogeneous phantom without tumor can be distinguished from a heterogeneous phantom with tumor in the temperature range of 28 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> C to 38 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> C.

Temperature-dependent dielectric properties and high-temperature microwave absorption performance of Ti3SiC2/Al2O3-13%TiO2 coatings

Temperature-dependent dielectric properties and high-temperature microwave absorption performance of Ti3SiC2/Al2O3-13%TiO2 coatings