Impact of load impedance on the performance of a thermoacoustic system employing acoustic pressure amplifier

An acoustic pressure amplifier （APA） is capable of improving the match between a thermoacoustic engine and a load by elevating pressure ratio and acoustic power output. A standing-wave thermoacoustic engine driving a resistance- and-compliance （RC） load through an APA was simulated with linear thermoacoustics to study the impact of load impedance on the performance of the thermoacoustic system. Based on the simulation results, analysis focuses on the distribution of pressure amplitude and velocity amplitude in APA with an RC load of diverse acoustic resistances and compliance impedances. Variation of operating parameters, including pressure ratio, acoustic power, hot end temperature of stack, etc., versus impedance of the RC load is presented and analyzed according to the abovementioned distribution. A verifying experiment has been performed, which indicates that the simulation can roughly predict the system operation in the fundamental-frequency mode.     

Development of a linear compressor for two-stage pulse tube cryocoolers

A valveless linear compressor was built up to drive a self-made two-stage pulse tube cryocooler. With a designed maximum swept volume of 60 cm^3, the compressor can provide the cryocooler with a pressure volume （PV） power of 400 W. Preliminary measurements of the compressor indicated that both an efficiency of 35%-55% and a pressure ratio of 1.3-1.4 could be obtained. The two-stage pulse tube cryocooler driven by this compressor achieved the lowest temperature of 14.2 K.     

谈功率放大器中负载阻抗的确定

通常认为在放大器中实现阻抗匹配就可以得到最大功率输出，本拟从应用这一原理的前提条件入手分析在功率放大器中负载的确定并不能应用这一原理，并提出了如何确定功率放大器负载的方法。     

Novel Electro-Optical Modulator Utilizing GeO2-Doped Silica Waveguide

In order to achieve a modulator with broad bandwidth and perfect impedance match,a novel electro-optical modulator based on GeO2-doped silica waveguides on silicon substrate is designed.The finite element model of the whole electro-optical modulator is established by means of ANSYS.With the finite element method analysis,the performance of the novel modulator is predicted.The simulation reveals that the designed modulator operates with a product of 3 dB optical bandwidth and modulating length of 226.59 GHz-cm,and a characteristic impedance of 51.6 Ω at 1 550 nm wavelength.Moreover,the calculated electrical reflected power of coplanar waveguide electrode is below -20 dB in the frequency ranging from 45 MHz to 65 GHz.Therefore,the designed modulator has wide modulation bandwidth and perfect impedance match.     

淮矿电调系统潮流图的创建

淮南矿业集团公司电力公司电力调度系统潮流图克服了原有电力调度系统一大缺陷,利用画图软件(MG)经过自行设计,结合数据库编制而成。这其中经过界面设计、图元生成、数学模型建立(数据库中)、文件关联等诸道程序,最后调试而成。它能直观地反映电力网络上的电流、功率的流向和分布,全面、实时地反映出电力网络上主供电源端与用户端的负荷供应及负荷分配情况,及时、方便地调整峰、腰、谷负荷,有利于提高发电机组运行效率,提高电力网络系统功率因素。使原有电力调度系统的调度功能更加强大。     

Novel electro-optical modulator utilizing GeO2-doped silica waveguide

In order to achieve a modulator with broad bandwidth and perfect impedance match, a novel electro-optical modulator based on GeO₂-doped silica waveguides on silicon substrate is designed. The finite element model of the whole electro-optical modulator is established by means of ANSYS. With the finite element method analysis, the performance of the novel modulator is predicted. The simulation reveals that the designed modulator operates with a product of 3 dB optical bandwidth and modulating length of 226.59 GHz·cm, and a characteristic impedance of 51.6 Ω at 1 550 nm wavelength. Moreover, the calculated electrical reflected power of coplanar waveguide electrode is below −20 dB in the frequency ranging from 45 MHz to 65 GHz. Therefore, the designed modulator has wide modulation bandwidth and perfect impedance match. Supported by National Natural Science Foundation of China (No.60577023)and Key Laboratory of Opto-Electronics Information and Technical Science of Ministry of Education, China. LI Jiusheng, born in 1976, male, Dr.     

Doherty射频功率放大器研究与实践

在分析经典Doherty放大器工作原理基础上,对主从放大器使用不同的漏极偏置电压和电路匹配,设计出一种新型Doherty功率放大器,分析了该结构对于效率和线性化的影响.以飞思卡尔公司的MRF6S20010N功放模型,利用ADS2008对放大器进行静态工作点选取,源负载网络匹配和微带线的计算.结果表明这种功率放大器不但能够提高性能指标,还增强了放大器的稳定性.     

智能微网中平衡负载下逆变器并联控制研究

传统下垂控制没有考虑本地负荷和并联逆变器间线路阻抗等因素,无功功率不能实现准确分配,系统稳定性也会随之降低。为了实现对无功功率的合理分配,在微网系统传统下垂控制算法基础上,在电压电流双闭环控制中设计虚拟阻抗,以降低有功和无功耦合程度。然后针对低压微电网中线路阻性成分较大的问题,设计虚拟负阻抗的下垂控制算法,从而进一步降低了有功和无功耦合程度。仿真结果表明,改进下垂控制前后均可以实现对有功功率的合理分配。传统下垂控制的无功功率无法合理分配,偏差达到了 20%。加入虚拟阻抗控制算法后提高了无功功率分配精度,引入虚拟负阻抗的控制算法可使该精度进一步提高。因此,相比传统下垂控制,加入该控制算法后逆变器可以获得更好的功率分配效果。     

基于直接寻找法的电阻抗断层成像

Solution to impedance distribution in electrical impedance tomography （EIT） is an ill-posed nonlinear inverse problem. It is especially difficult to reconstruct an EIT image in the center area of a measured object. Tikhonov regularization with some prior information is a sound regnlarization method for static electrical impedance tomography under the condition that some true impedance distribution information is known a priori. This paper presents a direct search method （DSM） as pretreatment of image reconstruction through which one not only can construct a regularization matrix which may locate in areas of impedance change, but also can obtain an initial impedance distribution more similar to the true impedance distribution, as well as better current modes which can better distinguish the initial distribution and the true distribution. Simulation results indicate that, by using DSM, resolution in the center area of the measured object can be improved significantly.     

2.4GHz CMOS低噪声放大器的设计

基于0.18μm CMOS工艺,采用共源共栅源极电感负反馈结构,设计了一个针对蓝牙接收机应用的2.4GHz低噪声放大器(LNA)电路.分析了电路的主要性能,包括阻抗匹配、噪声、增益与线性度等,并提出了相应的优化设计方法.仿真结果表明,该放大器具有良好的性能指标,在5.4mW功耗下功率增益为18.4dB,噪声系数为1.935dB,1dB压缩点为-14dBm.     

Underwater Sound Scattering from a Submerged Rectangular Plate with Absorbent Coating

lintroductionStudiesofsoundscatteringfi.omobjectsarethebasisofInanyunderwaterapplicationssuchastargetstrength(TS)predictionandfree-fieldmeasurementsofacousticmaterials.Thegeometrictheoryofdiffraction(GTD)I"']issuitedfortheseproblems,asitprovidessolutionsw…     

Acoustic design sensitivity analysis of structural sound radiation

This paper presents an acoustic design sensitivity(ADS)analysis on sound radiation of structures by using the boundary element method(BEM).We calculated the velocity distribution of the thin plate by analytical method and the surface sound pressure by Rayleigh integral,and expressed the sound radiation power of the structure in a positive definite quadratic form of the Hermitian with an impedance matrix.The ADS analysis of the plate was thus translated into the analysis of structure dynamic sensitivity and ...     

Influence of input acoustic power on regenerator＇s performance

Performance of a pulse tube cooler significantly depends on the efficient operation ofits regenerator. Influence of input acoustic power on regenerator＇s performance is simulated and analyzed with simple harmonic analysis method. Given regenerator＇s dimensions and pressure ratio, there is an optimal input acoustic power for achieving a highest coefficient of performance, due to a compromise between relative time-averaged total energy flux in regenerator and relative acoustic power at regenerator＇s cold end. Additionally, optimal dimensions of regenerator are also estimated and presented for different input acoustic powers. The computed optimal diameter obviously increases with increase of input acoustic power, while the optimal length decreases slightly, and as a result, a larger input acoustic power requires a smaller aspect ratio （length over diameter）.     

计及温控负荷的小干扰稳定性分析

温控负荷是电力系统最为重要的负荷类型之一,它对电力系统的小干扰稳定具有重要的影响。针对这类以恒温控制器控制的负荷（温控负荷）展开研究,通过对恒温控制器动态加热方程的分析,建立用于小干扰稳定分析的温控负荷的数学模型。以3机9节点系统为算例在MATLAB的电力系统分析工具箱（PSAT）中对温控负荷接入电力系统后对系统小干扰稳定影响进行仿真分析。最后以简单的单机无穷大系统为例,进一步分析其负荷参数变化对系统小干扰稳定的影响。仿真分析结果表明:相对于传统的静态负荷温控负荷不利于系统小干扰电压稳定;温控负荷比例控制增益,环境温度,参考温度,对系统的小干扰稳定影响较大;积分控制器增益,积分控制器时间常数,负荷时间常数对系统小干扰稳定性影响较小。     

Analysis of Penetration Model for Geo-Material by Rigid Projectile

Based on the cylindrical cavity expansion theory, a plastic-damage-elastic model is proposed for the penetration problem of geo-material. In the model, the unified strength criterion (Yu, 1991) is adopted as the failure criterion. The distributions of the radial stress and velocity are analyzed. According to the Newton's second law, a series results of the final penetration depth and the impedance load are obtained to different parameter b, when a rigid projectile normally impacts and penetrates a semi-infinite geo-material target with an impact velocity of 300-1200 m/s. By comparing with the test data available, it appears that the method can be used in analyzing the final depth and the impedance load of a rigid projectile penetrating into a semi-infinite target with different impact velocities.     

表面声阻抗近似局域k-k关系的实验研究

利用石棉多孔材料对表面声阻抗近似局域k-k关系进行了实验研究,通过最小频率分辨率分别为0.25Hz、0.5Hz和1Hz的理论和实验值的对比研究发现理论值与实验值相互吻合,从实验上很好地验证了表面声阻抗近似局域k-k关系的正确性.     

电力负荷分析与系统调控

电力负荷源于用电设备,鉴于用电设备的容量、结构、工作方式、用电时段的不同,呈现出不同的动态参量。电力系统的中心任务就是保障电力的供应,讨论了电力负荷分析及调控。     

250Kw、1kHz可控硅中频电源的负载匹配

对250Kw、1KHz可控硅中频电源负载匹配问题，可采用电感升压法和电容升压法使炉体与电源达到良好匹配。     

DVC动态电压补偿器

电压陷落(电压骤降)是电能质量的重要问题,也是电力工程领域的一个重要研究方向。电压陷落不仅会引起电力系统的安全和电能质量问题,也会危及用电设备的可靠运行。为了解决这个问题,该文提出了一种新型动态电压补偿器的设计,它并无注入变压器,直接串联在低压线路中、保护用电设备。该设计主要解决90%以上的电压陷落,它充分利用电压陷落时电网所剩的电压,达到用最少量的直流电容量来储能的目的。     

低压电力线信道特性分析

利用低压电力线传输通信数据具有十分重要的意义,但是低压电力线路网络结构和负载特性复杂,需要对信道有深入的了解。文中分析了电力线信道的阻抗、噪声、衰减特性,有助于深入理解低压电力线通信的特点。