Analysis of Light Load Efficiency Characteristics of a Dual Active Bridge Converter Using Wide Band-Gap Devices

In this paper, the zero voltage switching (ZVS) region of a dual active bridge (DAB) converter with wide band-gap (WBG) power semiconductor device is analyzed. The ZVS region of a DAB converter varies depending on output power and voltage ratio. The DAB converters operate with hard switching at light loads, it is difficult to achieve high efficiency. Fortunately, WBG power semiconductor devices have excellent hard switching characteristics and can increase efficiency compared to silicon (Si) devices. In particular, WBG devices can achieve ZVS at low load currents due to their low parasitic output capacitance (Co,tr) characteristics. Therefore, in this paper, the ZVS operating resion is analyzed based on the characteristics of Si, silicon carbide (SiC) and gallium nitride (GaN). Power semiconductor devices. WBG devices with low Co,tr operate at ZVS at lower load currents compared to Si devices. To verify this, experiments are conducted and the results are analyzed using a 3 kW DAB converter. For Si devices, ZVS is achieved above 1.4 kW. For WBG devices, ZVS is achieved at 700 W. Due to the ZVS conditions depending on the switching device, the DAB converter using Si devices achieves a power conversion efficiency of 91% at 1.1 kW output. On the other hand, in the case of WBG devices, power conversion efficiency of more than 98% is achieved under 11 kW conditions. In conclusion, it is confirmed that the WBG device operates in ZVS at a lower load compared to the Si device, which is advantageous in increasing light load efficiency.

Flexural wave band-gaps in phononic metamaterial beam with hybrid shunting circuits

Periodic arrays of hybrid-shunted piezoelectric patches are used to control the band-gaps of phononic metamaterial beams. Passive resistive-inductive （RL） shunting circuits can produce a narrow resonant band-gap （RG）, and active negative capacitive （NC） shunting circuits can broaden the Bragg band-gaps （BGs）. In this article, active NC shunting circuits and passive resonant RL shunting circuits are connected to the same piezoelectric patches in parallel, which are usually called hybrid shunting circuits, to control the location and the extent of the band-gaps. A super-wide coupled band-gap is generated when the coupling between RG and the BG occurs. The attenuation constant of the infinite periodic structure is predicted by the transfer matrix method, which is compared with the vibration transmittance of a finite periodic structure calculated by the finite element method. Numerical results show that the hybrid-shunting circuits can make the band-gaps wider by appropriately selecting the inductances, negative capacitances, and resistances.

Doping Induced Tailoring in the Morphology,Band-Gap and Ferromagnetic Properties of Biocompatible ZnO Nanowires, Nanorods and Nanoparticles

The modification of nanostructured materials is of great interest due to controllable and unusual inherent properties in such materials. Single phase Fe doped Zn O nanostructures have been fabricated through simple, versatile and quick low temperature solution route with reproducible results. The amount of Fe dopant is found to play a significant role for the growth of crystal dimension. The effect of changes in the morphology can be obviously observed in the structural and micro-structural investigations, which may be due to a driving force induced by dipole-dipole interaction. The band gap of Zn O nanostructures is highly shifted towards the visible range with increase of Fe contents, while ferromagnetic properties have been significantly improved.The prepared nanostructures have been found to be nontoxic to SH-SY5 Y Cells. The present study clearly indicates that the Fe doping provides an effective way of tailoring the crystal dimension, optical band-gap and ferromagnetic properties of Zn O nanostructure-materials with nontoxic nature, which make them potential for visible light activated photocatalyst to overcome environmental pollution, fabricate spintronics devices and biosafe drug delivery agent.

Tuning of band-gap of phononic crystals with initial confining pressure

The mechanism of the shift of the band-gap in phononic crystal （PC） with different initial confining pressures is studied experimentally and numerically. The experimental results and numerical analysis simultaneously indicate that the confining pressure can efficiently tune the location in and the width of the band-gap. The present work provides a basis for tuning the band-gap of phononic crystal in engineering applications.

Excitation of defect modes from the extended photonic band-gap structures of 1D photonic lattices

This paper stuides numerically the model equation in a one dimensional defective photonic lattice by modifying the potential function to a periodic function. It is found that defect modes （DMs） can be regarded as Bloch modes which are excited from the extended photonie band-gap structure at Bloch wave-numbers with kx = 0. The DMs for both positive and negative defects are considered in this method.

Theoretical investigation of band-gap and mode characteristics of anti-resonance guiding photonic crystal fibres

With the full-vector plane-wave method （FVPWM） and the full-vector beam propagation method （FVBPM）, the dependences of the band-gap and mode characteristics on material index and cladding structure parameter in anti- resonance guiding photonic crystal fibres （ARGPCFs） are sufficiently analysed. An ARGPCF operating in the near- infrared wavelength is shown. The influences of the high index cylinders, glass interstitial apexes and silica structure on the characteristics of band-gaps and modes are deeply investigated. The equivalent planar waveguide theory is used for analysing such an ARGPCF filled by the isotropic materials, and the resonance and the anti-resonance characteristics r：~n h~ w~｜] r^r~dlrtpd

Energy Band-gap Calculation of d-Ta_2O_5 Using sX-LDA and B3LYP Methods

The energy band-gap and related factors of tantalum pentoxide with hexagonal phase were investigated using hybrid functional B3LYP and sX-LDA methods. The results showed that both sX-LDA and B3LYP techniques reveal the indirect semiconductor nature of δ-Ta2O5, whereas the obtained value of energy band-gap is much higher than previous theoretical reports but closer to the experimental data. The optical band- gap of δ-Ta2O5 is expected to originate from the O 2p→Ta 5d transition which may benefit from the d-s-p hybridization.

Modification of Optical Band-Gap of Si Films After Ion Irradiation

Amorphous silicon （a-Si）, nanocrystalline silicon （nc-Si） and hydrogenated nanocrys- talline silicon （nc-Si：H） films were fabricated by using chemical vapor deposition （CVD） system. The a-Si and nc-Si thin films were irradiated with 94 MeV Xe-ions at fluences of 1.0 × 10^11 ions/cm2, 1.0 × 10^12 ions/cm^2 and 1.0 × 10^13 ions/era2 at room temperature （RT）. The nc-Si：H films were irradiated with 9 MeV Xe-ions at 1.0 ×10^12 Xe/cm^2, 1.0 × 10^13 Xe/cm2 and 1.0×10^14 Xe/cm2 at RT. For comparison, mono-crystalline silicon （c-Si） samples were also irradiated at RT with 94 MeV Xe-ions. All samples were analyzed by using an UV/VIS/NIR spectrometer and an X-ray powder diffractometer. Variations of the optical band-gap （Eg） and grain size （D） versus the irradiation fluence were investigated systematically. The obtained results showed that the optical band-gaps and grain size of the thin films changed dramatically whereas no observable change was found in c-Si samples after Xe-ion irradiation. Possible mechanism underlying the modification of silicon thin films was briefly discussed.

Investigation of the guided-mode characteristics of hollow-core photonic band-gap fibre with interstitial holes

This paper investigates the guided-mode characteristics of hollow-core photonic band-gap fibre （HC-PBGF） with interstitial holes fabricated by an improved twice stack-and-draw technique at visible wavelengths. Based on the simulation model with interstitial holes, the influence of glass interstitial apexes on photonic band-gaps is discussed. The existing forms of guided-mode in part band gaps are shown by using the full-vector plane-wave method. In the experiment, the observed transmission spectrum corresponds to the part band gaps obtained by simulation. The fundamental and second-order guided-modes with mixture of yellow and green light are observed through choosing appropriate fibre length and adjusting coupling device. The loss mechanism of guided-modes in HC-PBGF is also discussed.

Synthesis and Characterization of Small Band-gap Conjugated Polymers - Poly(pyrrolyl methines)

A kind of small band-gap conjugated polymers-poly (pyrrolyl methines) and their precursors-(poly pyrrolyl methanes) have been synthesized by a simple method and characterized by 1HNMR, FT-IR, TGA and UV-Vis. These polymers can be dissolved in high polar solvents such as DMSO, DMF or NMP. The results reveals that the band-gap of the synthesized conjugated polymers are in the range of 0.96~1.14 eV and they all belong to the small band-gap polymers. The conductivity of doped products with iodine is in the range of semiconductor.

A band-gap voltage reference for interface circuit of microsensor

A high performance CMOS band-gap voltage reference circuit that can be used in interface integrated circuit of microsensor and compatible with 0. 6 μm ( double poly) mix process is proposed in this paper. The circuit can be employed in the range of 1. 8 - 8 V and carry out the first-order PTAT ( proportional to absolute temperature) temperature compensation. Through using a two-stage op-amp with a NMOS input pair as a negative feedback op-amp,the PSRR ( power supply rejection ratio) of the entire circuit is increased,and the temperature coefficient of reference voltage is decreased. Results from HSPICE simulation show that the PSRR is - 72. 76 dB in the condition of low-frequency,the temperature coefficient is 2. 4 × 10 -6 in the temperature range from - 10 ℃ to 90 ℃ and the power dissipation is only 14 μW when the supply voltage is 1. 8 V.

The Propagation, Excitation and Coupling of Acoustic Waves in Phonon Band-gap Materials

Acoustic wave exhibits inherently different characters of propagation, excitation and coupling in phonon band-gap materials in which its elastic, piezoelectric constants are modulated in order of acoustic wavelength. These kinds of novel materials were exampled by phononic crystals with elastic constants modulation, acoustic superlattice and ionic-type phononic crystals with piezoelectric constants modulation. In this talk, phonic crystals were constructed with steel rods embedded in air. Negative refraction of acoustic wave was both experimentally and theoretically established in the phononic crystals. The propagation of acoustic wave in the crystals show acoustic band structures because the waves are strong scattered at the Brillouin Zone Boundaries, analogy to electron band structure in real crystals and photonic band structure in photonic crystals. In the acoustic superlattice, ultrasonic waves could be excited by applied alternative electric fields by piezoelectric effect. The frequency, mode and amplitude of the excited wave are determined by the microstructured parameters of the acoustic superlattice at the condition of phase matching. Ionic-type phononic crystals describe the coupling between superlattice phonon and electromagnetic wave. The coupling process resulted in the polariton with a dispersion relation totally different from that of both superlattice phonon and E-M waves, analogy to the polariton of the ionic crystals but in microwave instead of infrared light. These microstructural dielectric materials show artificial abnormal properties and will find novel application in ultrasonic devices and microwave devices.

Three-dimensional simulation of a Ka-band relativistic Cherenkov source with metal photonic-band-gap structures

This paper presents a three-dimensional particle-in-cell （PIC） simulation of a Ka-band relativistic Cherenkov source with a slow wave structure （SWS） consisting of metal photonic band gap （PBG） structures. In the simulation, a perfect match layer boundary is employed to absorb passing band modes supported by the PBG lattice with an artificial metal boundary. The simulated axial field distributions in the cross section and surface of the SWS demonstrate that the device operates in the vicinity of the π point of a TM01-1ike mode. The Fourier transformation spectra of the axial fields as functions of time and space show that only a single frequency appears at 36.27 GHz, which is in good agreement with that of the intersection of the dispersion curve with the slow space charge wave generated on the beam. The simulation results demonstrate that the SWS has good mode selectivity.

NONDESTRUCTIVE BAND-GAP PROFILE DETERMINATION OF HgCdTe LPE GROWN LAYERS

Infrared transmission and photoconductivity spectra of mercury cadmium telluride (MCT) epitaxial layers, grown by liquid phase epitaxy (LPE) on CdTe and CdZnTe wide band gap substrates, were investigated both theoretically and experimentally at temperatures T =82 K and T =300 K in the infrared (IR) wavelength region 3 15 μm. The photoresponse position of the diodes was determined at cryogenic temperatures from the transmission spectra of room temperature. Theoretical calculations of optical density D(h-ω), needed for analysis of experimental optical transmission data, were performed in the framework of WKB approximation.

Synthesis and properties of novel low band-gap polymers bearing squaraine units

Novel main-chain-conjugated poly(carbazol-alt-squaraine) and poly(dipyridyl-alt-squaraine) were successfully synthesized through direct polycondensation of 9-(2-ethylhexyl)carbazole-bridged or dipyridyl-bridged bispyrrole and squaric acid.The structures and properties of the polymers were characterized using ~1H NMR,FT-IR,UV-vis and cyclic voltammetry.Both polymers exhibit excellent solubility in common organic solvents and good thermal stability.Their UV-vis absorption spectra indicated the polymers have b...

Controllable Absorption and Dispersion Properties of an RF-driven Five-Level Atom in a Double-Band Photonic-Band-Gap Material

驾驶五水平的原子在 photonic 晶体嵌入的无线电频率(RF ) 的探查吸收分散系列被考虑各向同性的双乐队 photonic-band-gap (PBG ) 水库调查。在使用的模型，分别地，二转变被上面、更低的乐队在如此的 PBG 材料联合，因此导致一些好奇的现象。数字模拟为光系列被执行。当一转变频率在乐队差距内，其它在差距外面时，它被发现那，在那里出现在吸收系列的三座山峰。然而，为案例，二转变频率躺着在内或在乐队差距外面，系列显示四吸收侧面。特别，在那里出现在系列的二座锋利的山峰当两转变频率在乐队内存在时，豁开。吸收性、散的反应上的驾驶 RF 的地的紧张和频率的影响在不同乐队边位置下面被分析。一个透明性窗口出现在吸收系列，这被发现并且被调整系统参数被分散侧面的一个很陡峭的变化伴随。这些结果证明系统的吸收分散性质强烈取决于导致 RF 的量干扰和 PBG 水库的状态(DOS ) 的密度。

Design and Synthesis of N-Alkylaniline-Substituted Low Band-Gap Electron Acceptors for Photovoltaic Application

A novel electron donating unit,namely N-octyl-N-phenyl-thiophene(OPT),was designed in preparing electron acceptors with non-fused ring chemical structures.By introducing different functional atoms/groups into the para-position of phenyl in the OPT units,three non-fused ring acceptors(NFREAs),C8-2F,FC8-2F and MeC8-2F,were synthesized.The absorption spectrum of the three acceptors can be extended to about 950 nm with band-gaps of 1.28—1.32 eV due to the strong electron donating ability of OPT.The frontier molecular orbital distribution of OPT based molecules obtained by quantum chemistry calculation results reveals that their energy alignment can be finely tuned to meet different requirements.Moreover,by changing the substituents on the OPT units,their Flory-Huggins interaction parameter(χ)with the donor will be greatly influenced and different phase separation behavior can be accomplished.After blended with PBDB-TF,the FC8-2F-based cell yields short circuit current density(J_(sc))of 23.21 mA·cm^(-2),fill factor(FF)of 72.11%and the highest power conversion efficiency(PCE)of 12.42%.This work provides a new pathway for molecular design of new NFREAs,and demonstrates the application potential of OPT unit in realizing low band-gap photovoltaic materials.

基于局域共振型声子晶体塔筒结构海上风机减振特性研究

针对海上风机的振动控制问题,提出一种局域共振型声子晶体塔筒结构,基于周期结构的Bloch定理,采用有限元法计算该结构的能带结构、特征模态所对应的位移场以及相应有限周期声子晶体塔筒结构的振动传输曲线,对其展现出的带隙特性进行分析。基于局域共振带隙的形成,研究声子晶体塔筒结构的振动控制问题,可将其应用于不同海洋环境中海上风机特定频率的减振。得出声子晶体塔筒结构在xy平面内与z方向上受激励时的振动传输曲线,选取两者在特定频率下的结构位移图分别进行分析,计算出非理想化声子晶体塔筒结构在xy平面内与z方向上受激励时的振动传输曲线并加以对比。研究各参数对声子晶体塔筒结构带隙衰减频段的影响规律,通过合理调整设计参数,可以实现结构特定范围内的低频隔振,证明其在复杂海洋环境中海上风机减振方面具有很好的应用前景。

基于振幅放大机制的无砟轨道周期结构弯曲波调控研究

【目的】轨道结构的振动一直是相关领域亟待研究和解决的问题。传统减隔振装置受到自身重量与列车行车安全性的限制,难以实现对轨道结构弯曲波的宽频调控。【方法】通过引入振幅放大机制,设计了一种杠杆式轨道综合减隔振装置。以CRTSⅢ型板式无砟轨道结构为研究对象,采用能量泛函变分法和人工弹簧技术建立了配置有轨道综合减隔振装置的周期性轨道结构波动分析模型和振动响应分析模型,研究了轨道综合减隔振装置对弯曲波的调控能力,并分析了轨道综合减隔振装置工作能力与振幅放大系数的关系。【结果】结果表明:采用振幅放大机制,能够有效增大减隔振装置的惯性质量,增强减隔振装置的阻尼特性和刚度特性,进而显著提升其工作能力。【结论】实现了轨道综合减隔振装置“低频隔振高频吸振”的超宽频弯曲波调控设计目标。