Search results

In order to investigate the vibration reduction properties of a three-dimensional elastic metastructure with spherical cavities at low frequencies.

The bandgap characteristics of a three-dimensional elastic metastructure with spherical cavities are studied based on analytical and numerical approaches.

The results of both method revealed that the vibration of the vertexes masses is important for opening bandgaps. The fact that the big sphere cavity radius or short side length of the cube unit leads to a wider bandgap, is noteworthy.

This research provides theoretical guidance for realizing the vibration attenuation application of EMs in practical engineering.

This paper aims to propose a design method for attenuating stress waves pressure using soft matrix embedded with particles.

Based on the phononic crystal theory, the particle composed of hard core and soft coating can form a spring oscillator structure. When the frequency of the wave is close to the resonance frequency of the spring oscillator, it can cause the resonance of the particle and absorb a lot of energy. In this paper, the resonant phononic crystal with three phases, namely, matrix, particle core and coating, is computationally designed to effectively mitigate the stress wave with aperiodic waveform.

The relationship between the center frequency and width of the bandgap and the geometric and physical parameters of particle core are discussed in detail, and the trend of influence is analyzed and explained by a spring oscillator model. Increasing the radius of hard core could effectively enhance the bandgap width, thus enhancing the effect of stress wave attenuation. In addition, it is found that when the wave is in the bandgap, adding viscosity into the matrix will not further enhance the stress attenuation effect, but will make the stress attenuation effect of the material worse because of the competition between viscous dissipation mechanism and resonance mechanism.

This study will provide a reference for the design of stress wave protection materials with general stress waves.

This study proposes a design method for attenuating stress waves pressure using soft matrix embedded with particles.

This paper aims to design a new bandgap reference circuit with complementary metal–oxide–semiconductor (CMOS) technology.

Different from the conventional bandgap reference circuit with operational amplifiers, this design directly connects the two bases of the transistors with both the ends of the resistor. The transistor acts as an amplifier to amplify the change of voltage, which is convenient for the feedback regulation of low dropout regulator (LDO) regulator circuit, at last to realize the temperature control. In addition, introducing the depletion-type metal–oxide–semiconductor transistor and the transistor operating in the saturation region through the connection of the novel circuit structure makes a further improvement on the performance of the whole circuit.

This design is base on the 0.18?m process of BCD, and the new bandgap reference circuit is verified. The results show that the circuit design not only is simple and novel but also can effectively improve the performance of the circuit. Bandgap voltage reference is an important module in integrated circuits and electronic systems. To improve the stability and performance of the whole circuit, simple structure of the bandgap reference voltage source is essential for a chip.

This paper adopts a new circuit structure, which directly connects the two base voltages of the transistors with the resistor. And the transistor acts as an amplifier to amplify the change of voltage, which is convenient for the feedback regulation of LDO regulator circuit, at last to realize the temperature control.

The aim of this paper is to provide an easy method of extrusion freeforming to fabricate microwave electromagnetic bandgap (EBG) crystals. EBG crystals are periodic dielectric structures that can block wave propagation and generate a bandgap. These crystals can be used in high capability antennae, electromagnetic wave semiconductors, microresonators, high‐reflectivity mirrors and polarizing beam splitters.

The effects of extrusion process parameters and paste characteristics were investigated. Finally, one‐period and two‐period woodpile EBG crystals with bandgaps in the frequency region of 90‐110 GHz were fabricated and the bandgap was measured.

The filament diameter is influenced by whether extrusion is carried out with or without a substrate and by the free fall‐distance from the nozzle. The quality of lattice structures is dependent on paste flow and properties. A ceramic paste with 60 vol. % (the fraction of ceramic powder based on solvent‐free polymer) was well suited to fabrication. The solvent content also influenced the fabrication. The experimental results show that under ∼12 per cent solvent mass fraction in the paste and relatively high extrusion ram velocity (more than 0.014 mm/s) at a pressure of 14 MPa, samples with high quality were fabricated.

This paper demonstrates that the rapid prototyping method of extrusion freeforming can be applied for the fabrication of EBG crystals from ceramic powders and the important factors which influence the product quality are identified.

Three‐dimensional photonic bandgap (PBG) structures using alumina (Al₂O₃) as the high permittivity material were modeled and then the structures were fabricated by Fused Deposition of Multi‐materials (FDMM) technology. A finite element method and a real‐time electromagnetic wave propagation software were used to simulate and design the layered PBG structures for applications in the microwave frequency range. The modeling predicted a 3‐D photonic bandgap in the 16.5–23.5 GHz range. FDMM provides a computer‐controlled process to generate 3‐D structures, allowing high fabrication flexibility and efficiency. Electromagnetic measurements displayed the presence of a bandgap between 17.1–23.3 GHz, showing a good agreement with the predicted values. These PBG structures are potential candidates for applications in advanced communication systems.

The purpose of this paper is to study the high-frequency impacts of fast switching wide-bandgap transistors on electronic and motor designs. The high-frequency power converters, dedicated to driving high-speed motors, require specific models to design predictively electronic and motors.

From magnetic and electric models, the high-frequency parasitic elements for both electronics and motor are determined. Then, high-frequency circuit models accounting for of parasitic element extractions are built to study the wide bandgap transistors commutations and their impacts on motor windings.

The results of the models, for electronics and motors, are promising. The high-frequency commutation cell study is used to optimize the layouts and to improve the commutation behaviours and performances. The impact of the switching speed is highlighted on the winding voltage susceptibility. Then, the switching frequency and commutation rapidity can be both optimized to increase the performance of motor and electronics. The electronic model is validated by experimentations.

The method can be only applied to the existing motor and electronic designs. It is not taken into account in an automized global high-frequency optimizer.

Helped by magnetic and electric FEA calculations where the parasitic element extractions are performed. The switching frequency and commutation rapidity can be both optimized to increase the performance of motor and electronics.

This work presents a topology optimization methodology for designing microarchitectures of phononic crystals. The objective is to get microstructures having, as a consequence of wave propagation phenomena in these media, bandgaps between two specified bands. An additional target is to enlarge the range of frequencies of these bandgaps.

The resulting optimization problem is solved employing an augmented Lagrangian technique based on the proximal point methods. The main primal variable of the Lagrangian function is the characteristic function determining the spatial geometrical arrangement of different phases within the unit cell of the phononic crystal. This characteristic function is defined in terms of a level-set function. Descent directions of the Lagrangian function are evaluated by using the topological derivatives of the eigenvalues obtained through the dispersion relation of the phononic crystal.

The description of the optimization algorithm is emphasized, and its intrinsic properties to attain adequate phononic crystal topologies are discussed. Particular attention is addressed to validate the analytical expressions of the topological derivative. Application examples for several cases are presented, and the numerical performance of the optimization algorithm for attaining the corresponding solutions is discussed.

The original contribution results in the description and numerical assessment of a topology optimization algorithm using the joint concepts of the level-set function and topological derivative to design phononic crystals.

The purpose of this study is to design and optimize copper indium gallium selenide (CIGS) thin film solar cells.

A novel bi-layer CIGS thin film solar cell based on SnS is designed. To improve the performance of the CIGS based thin film solar cell a tin sulfide (SnS) layer is added to the structure, as back surface field and second absorbing layer. Defect recombination centers have a significant effect on the performance of CIGS solar cells by changing recombination rate and charge density. Therefore, performance of the proposed structure is investigated in two stages successively, considering typical and maximum reported trap density for both CIGS and SnS. To achieve valid results, the authors use previously reported experimental parameters in the simulations.

First by considering the typical reported trap density for both SnS and CIGS, high efficiency of 36%, was obtained. Afterward maximum reported trap densities of 1 × 10¹⁹ and 5.6 × 10¹⁵cm⁻³ were considered for SnS and CIGS, respectively. The efficiency of the optimized cell is 27.17% which is achieved in CIGS and SnS thicknesses of cell are 0.3 and 0.1 µm, respectively. Therefore, even in this case, the obtained efficiency is well greater than previous structures while the absorbing layer thickness is low.

Having results similar to practical CIGS solar cells, the impact of the defects of SnS and CIGS layers was investigated. It was found that affixing SnS between CIGS and Mo layers causes a significant improvement in the efficiency of CIGS thin-film solar cell.

The purpose of this paper is to investigate the structural, electronic and optical properties of pure zinc oxide (ZnO) and transition metal (Tm)-doped ZnO using Tm elements from silver (Ag) and copper (Cu) by a first-principles study based on density functional theory (DFT) as implemented in the pseudo-potential plane wave in CASTEP computer code.

The calculations based on the generalized gradient approximation for Perdew-Burke-Ernzerhof for solids with Hubbard U (GGA-PBEsol+U) were performed by applying Hubbard corrections U_d = 5 eV for Zn 3d state, U_p = 9 eV for O 2p state, U_d = 6 eV for Ag 4d state and U_d = 9.5 eV for Cu 3d state. The crystal structure used in this calculation was hexagonal wurtzite ZnO with a space group of P63mc and supercell 2 × 2 × 2.

The total energy was calculated to determine the best position for Ag and Cu dopants. The band structures and density of states show that Tm-doped ZnO has a lower bandgaps value than pure ZnO because of impurity energy levels from Ag 4d and Cu 3d states. In addition, Ag-doped ZnO exhibits a remarkable enhancement in visible light absorption over pure ZnO and Cu-doped ZnO because of its lower energy region and extended wavelength spectrum.

The results of this paper are important for the basic understanding of the 3d and 4d Tm doping effect ZnO and have a wide range of applications in designing high-efficiency energy harvesting solar cells.

We present an overview of photonic textile displays woven on a Jacquard loom, using newly discovered polymer photonic bandgap (PBG) fibers that have the ability to change color and appearance when illuminated with ambient or transmitted light. The photonic fiber can be thin (smaller than 300 microns in diameter) and highly flexible, which makes it possible to weave in the weft on a computerized Jacquard loom and develop intricate double weave structures together with a secondary weft yarn. We demonstrate how PBG fibers enable a variety of color and structural patterns on the textile, and how dynamic imagery can be created by balancing the reflected ambient light and emitted light. Finally, a possible application in security wear for low visibility conditions is described as an example.