Analytical Solution of Heat Exchange in Typical Electrocaloric Devices

Most of electrocaloric devices reported so far can be simplified as a multilayer structure in which thermal source and sink are different materials at two ends. The thermal conduction in the multilayer structure is the key for the performance of the devices. In this paper, the analytical solutions for the thermal conduction in a multilayer structure with four layers are introduced. The middle two layers are electrocaloric materials. The analytical solutions are also simplified for a hot/cold plate with two sides being different media - a typical case for thermal treatment of materials. The analytical solutions include series with infinite terms. It is proved that these series are convergent so the sum of a series can be calculated using the first N terms. The equation for calculating the N is introduced. Based on the case study, it is found that the N is usually a small number, mostly less than 40 and rarely more than 100. The issues related to the application of the analytical solutions for the simulation of real electrocaloric devices are discussed, which includes the usage of multilayer ceramic capacitor, influence of electrodes, and characterization of thin film.

Microstructure and phonon behavior in W/Si periodic multilayer structures

The crystallinity of the tungsten (W) phase was improved with an increase in the thickness of this layer in the periodic W/Si multilayer structure. Both the α- and β- W phases were grown simultaneously and the contribution of these phases has modified upon a change in the thickness of the W layers. For thinner W layers, the thermodynamically metastable β- W phase was dominated, and with an increase in thickness, this phase has suppressed, and the stable α- W phase became prominent. The crystallite size of these phases was almost linearly proportional to the thickness of the W layers in the multilayers. With the increase in thickness of Si layers in multilayers, Raman scattering showed a decrease in bond-angle deviation of Si-Si bonding in the amorphous Si phase. The study revealed, ordering of Si-Si bonding in the amorphous phase of Si with an increase in thickness of these layers in periodic W/Si multilayers.

Multi-layer structure formation of relativistic electron beams in plasmas

A two-dimensional(2D) electromagnetic particle-in-cell(PIC) simulation model is proposed to study the density evolution and collective stopping of electron beams in background plasmas. We show here the formation of the multi-layer structure of the relativistic electron beam in the plasma due to the different betatron frequency from the beam front to the beam tail. Meanwhile, the nonuniformity of the longitudinal wakefield is the essential reason for the multilayer structure formation in beam phase space. The influences of beam parameters (beam radius and transverse density profile) on the formation of the multi-layer structure and collective stopping in background plasmas are also considered.

Shielding Analysis of Metal Hydride-based Materials for Both Neutron and Gamma Rays Using Monte Carlo Simulation

Radiation causes damage to the human body, the environment, and electronic equipment. Shielding against neutron and gamma rays is particularly difficult because of their strong ability to penetrate materials. Conventional gamma ray shields are typically made of materials containing Pb. However, they pose problems in that Pb is a heavy metal, and human poisoning and/or pollution can result from the manufacturing, use, and disposal of these materials. In addition, neutron rays are shielded by materials rich in H2 or concrete. In the case of the latter, the manufacturing cost is high. Thus, it is necessary to develop a new multilayer structure that can shield against both neutron and gamma rays. We set up a simulation model of a multilayered structure consisting of metal hydrides and heavy metals, and then evaluated the simulations using Monte Carlo N-Particle Transport Code. Monte Carlo simulation is an accurate method for simulating the interaction between radiation and materials, and can be applied to the transport of radiation particles to predict values such as flux, energy spectrum, and energy deposition. The results of the study indicated the multilayer structure of ZrH2, U, and W could shield both neutron and gamma rays, thus showing potential as a new shielding material to replace Pb and concrete.

Simulating the spectral characteristics of reflection in planar porous structures with antireflection coatings ZnS/DyF3

This paper presents the results of modeling a planar multilayer structure with layers of porous silicon, ZnS and DyF3 coatings by the optical matrix method. It was shown that the optical matrix method, taking into account the model of porous silicon with a variable band gap, which takes into account the porosity gradient, allows us to approximate the course of the curve of the real experiment