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This article explores the potential of epoxy resin/silicon carbide whisker (EP/SiCw) composites (1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%) as the field-dependent conductivity (FDC) packaging materials for the high-voltage power modules by investigating their thermal and electrical properties at different temperatures. The cross-sectional morphology of the prepared materials is characterized by field emission-scanning electron microscopy (FE-SEM). The thermal analysis consists of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The electrical properties, such as dc conductivity, dielectric spectroscopy, thermally stimulated discharge current (TSDC), space charge distribution, and dc breakdown strength, are measured. The molecular orbital energy levels of the EP and SiCw monomers are calculated by quantum chemical calculation (QCC) to analyze the effect of EP interfacial trap sites on the electrical properties. The effect of the EP/SiCw interfacial charges and electrical field distortion on the electrical properties of the EP/SiCw composites with different filler content is investigated by the finite-element method (FEM) simulation. It is found that the 2 wt% EP/SiCw composite has a better thermal performance. The 1 wt% has lower real permittivity, lower trap density, lower space charge accumulation, and higher breakdown strength. The EP/SiCw composites have a higher trap level than the pure EP. The nonlinearity percolation threshold of the EP/SiCw composites is 3 wt%. As the filler content increases, the nonlinear conductivity coefficient of the EP/SiCw composites becomes higher, whereas the breakdown strength decreases due to the electric field distortion near the electrodes caused by the apparent hetero charge accumulation at high filler content. [ABSTRACT FROM AUTHOR]

This work reports on the significant enhancement of the thermal properties of the FR3 natural ester dielectric oil after the addition of pentyl-graphene nanosheets, as confirmed by thermal diffusivity and specific heat studies at different concentrations and temperatures (30 °C–90 °C). Experimental results of the dielectric constant demonstrated a constant value in the kHz region while increased in the low-frequency region, decreased with increased temperature, and saturated at 0.008% w/w concentration. In addition, light absorption is used for a better understanding of the properties variation upon changing graphene’s concentration as a method to estimate the agglomeration level. The optimum concentration for its best performance in terms of thermal and dielectric properties is 0.008% w/w, whereby the thermal diffusivity and the dielectric constant increased by 43.04% and 6.18%, respectively. [ABSTRACT FROM AUTHOR]

An accurate and efficient algorithm is presented, which allows deriving the structure function of a discretized 3-D heat conduction problem. In this approach, the partial thermal conductances and capacitances in the structure function are computed in terms of weighted spatial averages of thermal resistivity and volumetric heat capacity. As a result, the exact influence of all materials and geometric details on each part of the structure function is determined. The approach is validated on a state-of-the-art SiGe heterojunction bipolar transistor (HBT) for high-frequency applications. [ABSTRACT FROM AUTHOR]

Epoxy resin (EP) insulations are widely considered as potential candidates for various applications. However, it is not suitable for high frequency (HF) and high temperature (HT) applications due to its low thermal conductivity. This research presents the tuning of thermal and electrical properties of EP via resin stoichiometry and incorporation of surface-modified hexagonal boron nitride (h-BN) nanofillers. In this research, the curing agent concentration for pure EP is optimized first based on high thermal stability and sufficiently reliable electrical properties. Second, the optimized pure EP is used as a base material to prepare epoxy/h-BN nanocomposites. Various physicochemical, thermal, and electrical characterizations are performed to analyze the properties of prepared materials. Results show that the higher curing agent concentrations offer a good balance between the thermal and electrical performance of the EP. However, the HF and HT stress exhibits detrimental effects on the breakdown strength and dielectric properties of the materials. Also, the addition of nanofillers further enhances the thermal properties while exhibiting sufficient electrical properties. By the control of resin stoichiometry and nanofiller addition, suitable composites for the HF and HT environment can be realized. [ABSTRACT FROM AUTHOR]

The traditional cup-shaped LED packaged with epoxy molding compound materials (EMC-LED) and chip-scale packaged LED (CSP-LED) were prepared and analyzed in this article. It is found that high temperature can result in the spectrum red shift and the photoelectric performance degradation for these LEDs due to the degradation of chip and packaging materials. Compared with EMC-LED, the CSP-LED device has a lower thermal resistance of 3.31 °C/W due to the shorter thermal dissipation path and has better stability under the different temperature and drive current conditions. All the simulation results agree well with experimental and theoretical results, indicating that the photoelectric and thermal properties of the CSP-LED can be improved by introducing ceramic substrate and optimizing the material of the interconnected surface and the size of the conduction area. These results have guiding significance for the future CSP-LED design and application. [ABSTRACT FROM AUTHOR]

Objective: Tissue electroporation is achieved by applying a series of electric pulses to destabilize cell membranes within the target tissue. The treatment volume is dictated by the electric field distribution, which depends on the pulse parameters and tissue type and can be readily predicted using numerical methods. These models require the relevant tissue properties to be known beforehand. This study aims to quantify electrical and thermal properties for three different tissue types relevant to current clinical electroporation. Methods: Pancreatic, brain, and liver tissue were harvested from pigs, then treated with IRE pulses in a parallel-plate configuration. Resulting current and temperature readings were used to calculate the conductivity and its temperature dependence for each tissue type. Finally, a computational model was constructed to examine the impact of differences between tissue types. Results: Baseline conductivity values (mean 0.11, 0.14, and 0.12 S/m) and temperature coefficients of conductivity (mean 2.0, 2.3, and 1.2 % per degree Celsius) were calculated for pancreas, brain, and liver, respectively. The accompanying computational models suggest field distribution and thermal damage volumes are dependent on tissue type. Conclusion: The three tissue types show similar electrical and thermal responses to IRE, though brain tissue exhibits the greatest differences. The results also show that tissue type plays a role in the expected ablation and thermal damage volumes. Significance: The conductivity and its changes due to heating are expected to have a marked impact on the ablation volume. Incorporating these tissue properties aids in the prediction and optimization of electroporation-based therapies. [ABSTRACT FROM AUTHOR]

To reduce the electric field distortion and increase the thermal conductivity of the dielectric materials in cable accessories, this paper proposes a method to prepare composites with good nonlinear electrical conductivity and high thermal conductivity. Silver nanoparticles grown on hexagonal boron nitride (AgNPs/BN) were prepared as a powder and introduced into ethylene propylene diene monomer (EPDM) to obtain AgNPs/BN/EPDM composites. The nonlinear electrical conductivity, thermal conductivity and breakdown field strength of the composites were investigated at different temperatures. The nonlinear electrical conductivity and thermal conductivity of the composites increased with increasing AgNPs content grown on BN. Moreover, the breakdown field strength decreased with increasing AgNPs, and exhibited a weaker temperature dependence than neat EPDM. Simulations showed that the composites could improve the electric field distribution in a cable accessory. [ABSTRACT FROM AUTHOR]

The thermal response test (TRT) is the standard method for characterizing the thermal properties of the ground and those of a borehole heat exchanger (BHE). During the TRT, the inlet and outlet temperatures of the BHE are monitored. However, this test typically considers the ground as a homogeneous, isotropic, and infinite media, and therefore, it only determines the bulk and effective parameters, such as effective thermal conductivity and thermal borehole resistance. Hence, the enhanced TRT protocols are necessary where the depth-dependent temperatures are measured to estimate depth-specific thermal properties. Thus, a novel instrument with a data logger to automatically obtain the temperature measurements along the BHE is introduced. This device is based on a Zynq-7000 all programmable system on a chip. It has a dual-core central processing unit and a field-programmable gate array on one chip, thus providing a versatile architecture that reduces cost and improves efficiency in comparison with other systems of similar characteristics. This paper describes the implemented hardware and software developments that range from user interface application to a free-distribution operating system based on an embedded Linux. The proposed instrument can be easily incorporated throughout a TRT, and the nonspecialized staff can remotely manage or visualize the results through a menu-driven interface. The device is tested in a specific BHE installation and validated with standard Pt100-temperature-sensors. The results are comparable and, therefore, demonstrate the applicability of this novel instrument called Geowire. [ABSTRACT FROM AUTHOR]

Thermal interface materials (TIMs) play a major role in the performance of semiconductor devices by optimizing the thermal contact between device and heatsink. Their influence is further increasing with the usage of novel chip materials such as SiC and GaN. In this methodology study, we compared five of the most established evaluation methods for solid TIMs with each other: transient plane source, LaserFlash, DynTIM, TIMA, and an application-oriented $R_{\mathrm{ th}}$ measurement system. We investigated a wide range of typical TIMs in order to explore the limits of the different measurement systems. The results show that, despite existing norms, the used characterization method has a significant influence on the measured thermal conductivity. We also show that the temperature and pressure dependence has a significant influence on the thermal performance of TIMs and that these data need to be included in device specifications. Additionally, detailed error analysis and discussion about sample selection, error influence, and measurement effort for the presented methods are given. [ABSTRACT FROM AUTHOR]

Flow channel inserts (FCIs) are the key elements in the high-temperature dual-coolant lead-lithium blanket, since in this concept the flowing PbLi reaches temperatures near 700 °C and FCIs should provide the necessary thermal and electrical insulations to assure a safe blanket performance. In this paper, the use of a SiC-sandwich material for FCIs consisting of a porous SiC core covered by a dense chemical vapor deposition-SiC layer is studied. A fabrication procedure for porous SiC is proposed and the resulting materials are characterized in terms of thermal and electrical conductivities (the latter before and after being subjected to ionizing radiation) and flexural strength. SiC materials with a wide range of porosities are produced; in addition, preliminary results using an alternative route based on the gel-casting technique are also presented, including the fabrication of hollow samples to be part of future lab-scale FCI prototypes. Finally, to study the corrosion resistance of the material in hot PbLi, corrosion tests under static PbLi at 700 °C and under flowing PbLi at ~10 cm/s and 550 °C, with and without a 1.8–2T magnetic field, were performed to materials coated with a 200–400- $\mu \text{m}$ -thick dense SiC layer, obtaining promising results. [ABSTRACT FROM AUTHOR]

Electrosurgical vessel joining is commonly performed in surgical procedures to maintain hemostasis. This process requires elevated temperature to denature the tissue and while compression is applied, the tissue can be joined together. The elevated temperature can cause thermal damages to the surrounding tissues. In order to minimize these damages, it is critical to understand how the tissue properties change and how that affects the thermal spread. The purpose of this study is to investigate the changes of tissue thermal conductivity and how the changes correlate to thermal dose during the joining process. We propose a hybrid method combining experimental measurement with inverse heat transfer analysis to determine thermal conductivity of thin tissue sample. Porcine aorta arterial tissues were used to investigate tissue thermal conductivity with variable thermal dose. Different joining times were used to create different amounts of thermal dose. A 36% decrease in tissue thermal conductivity was found when the thermal dose reaches the threshold for second-degree burn. When thermal dose is beyond the threshold of third-degree burn, the tissue thermal conductivity does not decrease significantly. A regression model was also developed and can be used to predict tissue thermal conductivity based on the thermal dose. [ABSTRACT FROM AUTHOR]

The thermal conductivity between winding and lamination is one of the most critical parameters in electrical machine thermal analysis. Its value depends on the insulation material and on the manufacturing process of the winding system, and for this reason cannot be computed using analytical equations. In this paper, a practical investigation of equivalent thermal conductivity of electrical machines stator winding is presented and discussed. The fully experimental approach is based on a fast transient thermal test to evaluate the winding equivalent thermal conductivity. The test campaign is carried out on two sets of Total Enclosed Fan Cooled (TEFC) industrial induction motors produced by two different manufacturers; the rated power of the devices under test ranges from 1.5 to 55 kW. [ABSTRACT FROM PUBLISHER]

Liquid helium is used as the coolant for high field superconducting magnets or samples tested in the high magnetic field at the National High Magnetic Field Laboratory. When the magnetic field is ramping up, the boil-off helium gas generated by heat losses in the coil and from external environment of the cryostat can be trapped in the liquid helium bath in a region where \Bz\cdot\dBz/dz is less than $-$2100 \T^2/\m due to the weakly diamagnetic property of helium. It results to the surfaces of the magnet or samples being covered partially or even fully with the accumulated helium gas instead of liquid helium. The very low thermal conductivity of helium gas may cause an inefficient cooling for the magnets or samples. In the beginning stage of YBCO coils development, the trapped gas bubble caused a temperature increase in the region of trapped gas bubble and prevented the test coils ramped up to a higher current. This raised an issue for the cooling of the 32-T magnet, which is to be cooled in a liquid helium bath, because the trapped gas bubble may cause inefficient cooling of the magnet in this gas bubble region. Relevant tests were performed, and the trapped gas bubble was observed in recent tests of the 32-T magnet prototype coils. The impact of the gas bubble on the cooling of the 32-T YBCO prototype coils was tested, and the test results are presented. [ABSTRACT FROM PUBLISHER]

We present a novel transient measurement method to characterize effective values of the thermal conductivity, thermal diffusivity, and emissivity of a thin-film membrane implemented in a micromachined multiparameter wind sensor. Accurate values for these parameters are mandatory as they considerably influence the thermal heat shunt induced by the membrane, which is the main limiting factor for reliable sensor operation in gases with low thermal admittance and thus determines the ultimate device sensitivity. Compared with commonly used measurement techniques for these thermal thin-film parameters, our method does not require custom-built specimens, i.e., the results can directly be obtained from transient excess temperature measurements on the wind sensor device utilizing the embedded thin-film heater and thermistors. The presented method as such is universal and can easily be applied to other configurations of heating and temperature sensing elements placed on a circular thin-film membrane. In this contribution, we describe the theoretical background of this method, provide an efficient semianalytical model for the data evaluation including its validation by computer numerical simulations, and showcase sample measurements on multilayer SixNy–SiO2 thin films. [ABSTRACT FROM PUBLISHER]

Transformer oil is widely used in electric transformers serving the dual functions as insulating medium and cooling material. However, safety and stability of power system is interrupted due to the operation failure of electric transformers in certain case. Therefore efforts should be focused on improving the property of transformer oil for the stable operation of insulating system. The purpose of this paper is to obtain a new type of nanomodified transformer oil with improved dielectric and thermal properties. Boron nitride (BN) nanoparticles with high thermal conductivity were dispersed into transformer oil to form the nanooil. Dielectric and thermal properties of the samples before and after modification were measured. Dielectric property experiments were performed in accordance with IEC standard. Discharge phenomenon in breakdown process was captured by a high speed CCD camera. In order to investigate the effect of BN nanoparticles on thermal property, temperature change and heat distribution of the samples in heat transfer process were measured by an infrared thermal imager and a temperature sensor. It is found that the nanooil has higher dielectric breakdown strength and lower dissipation factor which indicate better dielectric property compared with nonmodified oil. Obtained results show significant improvement in heat transfer process with increasing the concentration of BN nanoparticles. It is proposed that the nanoparticles create an interfacial region which contributes to the enhancement of dielectric strength. For thermal property the ballistic phonon transport of the nanoparticles acts as the key factor in the remarkable improvement. Furthermore, the improved thermal property of the nanooil has an inhibitory effect on the breakdown process according to the bubble theory. [ABSTRACT FROM AUTHOR]

Electrical power switching devices based on widebandgap (WBG) semiconductors have the potential for transformative impact on a wide range of energy conversion applications. Significantly improved electrical and thermal conductivities of WBG semiconductors compared with the semiconductor silicon have the potential for more efficient, compact, and robust power conversion systems. However, to offset inherently higher manufacturing cost of WBG power devices and obtain system-level benefits, power converters need to be operated at higher semiconductor chip junction temperatures and/or at higher switching frequencies. This paper discusses the future prospects of WBG-based power electronics by considering the current state of the art of WBG chip manufacturing, packaging, and thermal management technologies. [ABSTRACT FROM AUTHOR]

A key limitation, especially for the continuous-wave operation of terahertz quantum cascade lasers, is the large amount of heat dissipated in the active region. We demonstrate an all-electrical technique for monitoring the lattice temperature and characterizing the thermal properties of the active region, using the waveguide of the device as a temperature sensor. We report a measured temperature difference between the heat sink and top waveguide layer of up to 27 K during the continuous-wave operation of GaAs/Al0.15Ga0.85As-based devices, lasing at 2.4 THz. A thermal model of the devices is used to determine the thermal conductivity of the active region perpendicular to the semiconductor interfaces to be 7.3 W/(m·K). [ABSTRACT FROM PUBLISHER]