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VALIDATION OF A CONVOLUTION INTEGRAL FOR CONDUCTIVITY IMAGING
摘要： Magnetic induction tomography has been under consideration for imaging electrical conductivity distributions within the human body. Multi-coil systems are most commonly employed for this task, requiring a numerical solution of Maxwell’s equations at each position of the coil array. An alternative uses a single coil placed near the conductive target while measuring coil self-impedance changes at a number of unique locations. Recently, a closed-form solution of Maxwell’s equations, in the form of a 3D convolution integral, was found for a single coil consisting of concentric circular loops that relates impedance change (loss) to an arbitrary conductivity. Its development required spatially uniform permittivity and permeability, yet showed quantitative agreement with experiment. Here, we provide a much more rigorous test of the convolution integral in experiments that allow large permittivity changes across coil dimensions. Loss is measured while the coil is placed at known positions relative to plastic columns of variable diameter which are ?lled with salt solutions of varying conductivity. In all cases, coil loss varies linearly with conductivity and with zero intercept. Quantitative agreement is observed only when column diameter is greater than or equal to coil diameter. Because of linearity, the convolution integral is useful for image reconstruction, though contrast could be either reduced or enhanced in those circumstances when relative permittivity change exceeds ～ 70.
关键词： single-coil system,conductivity imaging,convolution integral,Maxwell’s equations,Magnetic induction tomography
更新于2025-09-04 15:30:14
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The impact of Eu3+ ion substitution on dielectric properties of Y3?xEuxAl5O12 (0.00?≤?x?≤?0.10) ceramics
摘要： This study reported the effect of Eu substitutions on the conductivity and dielectric properties of Y3?xEuxAl5O12 (0.0 ≤ x ≤ 0.1), YAG:xEu3+. All products were fabricated by solid state route. The formation of YAG was approved through X-ray diffraction powder diffraction and high-resolution transmission electron microscope. It was found that the lattice parameters are increasing with increase the substitution content due to the difference in ionic radii between Y3+ and Eu3+. Electrical and dielectric properties of YAG (Y3Al5O12) and YAG:xEu3+ ceramics were investigated extensively for a variety of concentrations (0.00 ≤ x ≤ 0.1) of the substitutional Eu3+ ion from the 4f lanthanide group. The temperature dependence of dielectric loss, dielectric constant, loss tangent and ac/dc conductivity were examined up to 5.0 MHz to understand the electrical and dielectric properties for both doped and undoped YAG ceramics. The experimental results revealed that Eu3+ ion substitutions (especially x = 0.05) in YAG ceramics meaningfully influence the lossy mechanisms, conductivity and dielectric constant which is probably due to the contribution to the conduction mechanism of the 4f–Eu and 3d–Al ions. So, this can be incorporated at the exceptional sites of both Oh (octahedral) and Td (tetrahedral) symmetries in YAG: xEu3+ ceramics.
关键词： conductivity,solid state route,YAG,dielectric properties,Eu3+ ion substitution
更新于2025-09-04 15:30:14
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The study on negative dielectric properties of Al/PVA (Zn-doped)/p-Si (MPS) capacitors
摘要： In this research, PVA (doped with 7% Zn) was sandwiched between Al and p-Si as a polymer interfacial layer. Voltage and frequency effect on the real and imaginary components of complex dielectric constant (e0 and e00), electric modulus (M0 and M00), loss tangent (tan d) and electrical conductivity (r) of the MPS-type capacitor has been studied. Impedance spectroscopy method was used between 5 and 5000 kHz at room temperature. Almost all frequency-related parameters were found as quite susceptible, especially in the accumulation and depletion regions. These changes in real and imaginary components of dielectric properties in depletion region were attributed to the interface layer and dipole polarization, the existence of surface states (Nss) and their relaxation time (s), especially at low frequencies. But these changes in the accumulation region were attributed to the existence of interfacial layer and series resistance (Rs) of the capacitor owing to the voltage divided between them and capacitor. As a result, frequency, applied biases, interfacial polymer layer, polarization processes, Nss and Rs of the capacitor are more effective on the values of e0, e00, tan d, M0, M00 and r. Therefore, the effects of them must be considered in determining the dielectric parameters, electric modulus, conductivity and conduction mechanisms in the capacitors with and without an interfacial layer such as insulator/oxide, polymer, ferroelectric materials.
关键词： Electric modulus,Impedance spectroscopy method,Electrical conductivity,Negative dielectric properties
更新于2025-09-04 15:30:14
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Improve spectroscopic structural and AC electrical conductivity of PC/PEO blend using graphene
摘要： Nanocomposites of polycarbonate (PC) and polyethylene oxide (PEO) embedded with graphene oxide (GO) nanopowder have been prepared using casting method. Prepared nanocomposites are studied and investigated using di?erent characterization techniques. The X-ray di?raction (XRD) pattern reveals the semi-crystalline nature of PC/PEO blend. There are no signi?cant peaks characterizing pure graphene. The intensity of the main X-ray peak characterizing the blend is decreased with the increase of graphene content con?rming a mod- i?cation in the blend due to an addition of graphene oxide. The FT-IR spectra display the main characteristic IR bands due to vibrational function groups for the components. The Optical absorption spectra are measured as a function of wavelength in the range of 190–1100 nm. The UV/V spectra show two absorption bands at 290 and 620 nm due to electronic transitions. The value of Eg is obtained using indirect transition and its decrease with increasing the amount of graphene. The behavior of ε′ and ε″ decreased with the increase of frequencies is observed. After adding graphene, the frequency is increased due to the dipole moment. The decrease of ε″ with increases of both the frequency and the temperature attributed to the origin of ε″ is the conduction losses. The decrease of dissipation factor (tan δ) is ascribed to the internal polarization mechanism related to applied fre- quencies. The maximum value of the peak at M″ relation explained as being the result of the distribution of relaxation time.
关键词： Graphene nanopowder,AC conductivity,FT-IR,XRD,PC/PEO blend
更新于2025-09-04 15:30:14
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[IEEE 48th European Solid-State Device Research Conference (ESSDERC 2018) - Dresden (2018.9.3-2018.9.6)] 2018 48th European Solid-State Device Research Conference (ESSDERC) - Experimental extraction of BEOL composite equivalent thermal conductivities for application in self-heating simulations
摘要： Self-heating effects can seriously accelerate FEOL and BEOL degradation mechanisms. Moreover, as FET dimensions are continiously decreasing, the thermal resistance towards the Si bulk is increasing. As a result, the thermal properties of the BEOL become increasingly important. We develop dedicated test-structures and assess the equivalent thermal properties of the BEOL composite, which consists of Cu metallization and low-k interlayer dielectric (ILD). We study the impact of via density and configurations typical for those used in VLSI circuit designs. We can find through 3DFEM simulations, that equivalent anisotropic thermal properties can be provided for this composite, which can serve as calibrated parameters for FET thermal simulations.
关键词： BEOL,self-heating,thermal conductivity,FET,3DFEM simulations
更新于2025-09-04 15:30:14
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[IEEE 48th European Solid-State Device Research Conference (ESSDERC 2018) - Dresden (2018.9.3-2018.9.6)] 2018 48th European Solid-State Device Research Conference (ESSDERC) - Effect of Electron-phonon Scattering on the Thermal Conductivity of Si Nanowires
摘要： Even the effect of electron-phonon scattering on the electronic properties of Si nanowires has been widely studied, its impact on phonon transport has received much less attention. Recent experiments gave the first evidence of a doping-induced reduction of the thermal conductivity in highly B-doped (~5?×?1019?cm-3) Si nanowires with a diameter of 31?nm. Here, we present a model that can fully explain these data. We also simulated the thermal conductivity of P-doped Si nanowires and found a smaller reduction compared to the B-doped samples. Our model includes the effect of incomplete ionization due to interface states, trapped charges, and the dielectric mismatch between nanowire and its surrounding. This effect is most pronounced close to a doping level of 1018?cm-3 for B- and P-doped Si nanowires with an electronic diameter of 31?nm at room temperature. In mitigating the dielectric mismatch, both an increasing diameter and coating the nanowire by an oxide reduce the effect of incomplete ionization. At high doping concentration (~5?×?1019?cm-3) it can be neglected.
关键词： electron-phonon scattering,incomplete ionization,Si nanowires,thermal conductivity,doping
更新于2025-09-04 15:30:14
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[IEEE 2018 Global Smart Industry Conference (GloSIC) - Chelyabinsk, Russia (2018.11.13-2018.11.15)] 2018 Global Smart Industry Conference (GloSIC) - Mesophase Materials as Smart Media for Emerging Pressure Sensors: Capacitive Method of Measurement of DC Conductivity
摘要： Liquid crystals are a perspective type of materials for application in the field of tactile pressure sensors owning to their unique physical properties. One of such properties is the anisotropic electric conductivity, the value of which can be controlled by the external electric field. In this report we will consider a capacitive method of the measurement of the direct current conductivity in the liquid crystal layer, confined in the cell with blocking electrodes. It will be demonstrated that this technique allows estimating the direct current conductivity of a liquid crystal in a broad temperature range. The retrieved results can be used
关键词： blocking electrodes,impedance spectroscopy,liquid crystals,electric conductivity
更新于2025-09-04 15:30:14
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Photocontrol of magnetic structure in an itinerant magnet
摘要： We study the photoinduced magnetic transition in an itinerant magnet described by the double-exchange model, in which conduction electrons couple with localized spins through the ferromagnetic (FM) Hund coupling. It is shown that intense light applied to the FM ground state induces an antiferromagnetic (AFM) order, in contrast to the AFM-to-FM transition due to the photocarrier injection. In particular, we focus on the mechanism for instability of the FM structure by the light irradiation. The magnon spectrum in the Floquet state is formulated on the basis of the perturbative expansion of the Floquet Green’s function. The magnon dispersion shows softening at momentum (π, π ) in the square lattice with increasing the light amplitude, implying photoinduced AFM instability. This result is mainly attributed to a nonequilibrium electron distribution, which promotes low-energy Stoner excitations. The transient optical conductivity spectra characterized by interband excitations and Floquet sidepeaks are available to identify the photoinduced AFM state.
关键词： photoinduced magnetic transition,magnon spectrum,double-exchange model,itinerant magnet,optical conductivity,Floquet state
更新于2025-09-04 15:30:14
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Light Emitting Diodes Based on Inorganic Composite Halide Perovskites
摘要： CsPbBr3 is a promising type of light-emitting halide perovskite with inorganic composition and desirable thermal stability. The luminescence efficiency of pristine CsPbBr3 thin films, however, appears to be limited. In this work, light emitting diodes based on CsPbBr3|Cs4PbBr6 composites are demonstrated. Both quantum efficiency and emission brightness are improved significantly compared with similar devices constructed using pure CsPbBr3. The high brightness can be attributed to the enhanced radiative recombination from CsPbBr3 crystallites confined in the Cs4PbBr6 host matrix. The unfavorable charge transport property of Cs4PbBr6 can be circumvented by optimizing the ratio between the host and the guest components and the total thickness of the composite thin films. The inorganic composition of the emitting layer also leads to improved device stability under the condition of continuous operation.
关键词： stability,conductivity,composite perovskite,light emitting diode,Cs4PbBr6
更新于2025-09-04 15:30:14
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Pressure tuning of the thermal conductivity of gallium arsenide from first-principles calculations
摘要： In this paper, the variation of the lattice thermal conductivity of GaAs under pressure within the range of 0–20 GPa at room temperature is investigated by combining first-principles calculations with an iterative solution of the phonon Boltzmann transport equation. Firstly, we calculated the lattice thermal conductivity of GaAs at 12 GPa, which increases by more than 37% in comparison with that under atmospheric pressure. The detailed analysis of phonon heat transport properties shows that the pressure contributes to increased phonon group velocity coupled with decreased phonon relaxation time, resulting in the pressure-induced nonlinear increase of the thermal conductivity of zinc blende GaAs. Besides, not only the structure but also the phonon heat transport properties of GaAs transform from isotropic to anisotropic beyond the phase transition pressure. This study provides a quantitative understanding of the thermal conductivity of GaAs considering pressure-induced phase transitions and highlights the importance of pressure in tuning lattice thermal conductivity, especially in pressure-induced phase change materials.
关键词： first-principles calculations,gallium arsenide,pressure,thermal conductivity,phonon Boltzmann transport equation
更新于2025-09-04 15:30:14