直流大电流比较仪谐波影响问题的研究

本提出了在谐波影响下直流大电流比较仪的等效电路模型及计算方法,通过仿真给出了该模型的频率特性,通过试验数据与仿真结果的比较证实了电路模型的可行性,对研究直流大电流比较仪和电流互感器的谐波影响具有指导意义。     

闭环光纤电流传感器高阶动态模型及仿真

为研究光纤电流传感器脉冲电流测量能力,建立了传感器离散域高阶动态模型,并基于Simulink对传感器阶跃响应及频率响应特性进行仿真分析.结果表明:增大前向增益可提高传感器的响应速度和带宽,但过大的前向增益将会使系统超调振荡;滑动平均滤波器对超调振荡有明显的抑制作用,但同时也会降低系统的响应速度和测量带宽.搭建了频率响应...     

光纤电焊电流测量技术研究

针对直流逆变电阻焊机焊接电流精确测量的需求,提出基于光纤电流传感技术的焊接电流测量方法。建立了光纤电流传感器闭环检测系统动态模型,通过优化系统的前向增益,提升了传感器响应速度和带宽。仿真和实验结果表明:传感器的上升时间约为4.1 μs,在DC~30kHz范围内幅频特性衰减小于0.3%。基于该动态模型计算传感器对焊接电流纹波分量的响应,仿真结果表明:系统的动态跟踪能力可满足对纹波电流的测量需求。利用等安匝法对光纤电流传感器进行校准,在直流5~50kA范围内,传感器的测量误差优于±0.05%。现场实验结果证明了光纤电流传感器用于直流逆变焊接电流测量及电焊电流测试仪现场校准的可行性。     

传递矩阵法的排气消声器声学性能分析

以某型号的汽车排气消声器为对象,研究其声学性能。由传递矩阵法划分消声器的基本消声单元,并分析消声单元的传递矩阵,得到消声器总的传递矩阵,从而建立该消声器的声学模型。应用Matlab软件编程计算得到消声器的传递损失频率特性。应用有限元仿真软件Fluent和Sysnoise对消声器进行仿真计算,得到准确的传递损失频率特性。通过比较两种方法得到的结果,验证基于传递矩阵法建立的声学模型的准确性,为消声器的优化和改进提供依据。     

Ka波段滤波器加载三间隙耦合腔输出回路的仿真和测试

扩展相互作用速调管由多个重入式多间隙耦合腔构成,毫米波段高功率微波源的需求推动了Ka波段扩展互作用速调管的研制.本文采用基于微波网络理论的多间隙耦合腔输出回路间隙阻抗冷测方法,对Ka波段滤波器加载三间隙耦合腔输出回路进行冷参数测试,得到该回路的间隙阻抗频率特性曲线与群时延曲线.并将冷测结果与三维电磁场软件仿真结果进行对比,分析了两者产生异同点的原因.从阻抗频率特性的测量结果可观察到该输出回路的相对“冷”带宽达到4.3％,满足设计要求.     

一种高速大功率电子开关测试系统的建模与试验研究

分析了高速大功率RSD(Reversely Switched Dynistor)电子开关开关暂态电流试验平台的构建原理、试验回路的简化模型和基于自积分式罗氏线圈检测系统的工作机理.为便于优化包括RSD开关暂态电流试验平台和罗氏线圈检测装置的整个系统的电气参数,利用MATLAB/SINMULINK仿真环境,建立整个系统的仿真模型,并利用该模型开展试验验证.研究表明,文章获得的描述基于自积分式罗氏线圈整个试验测试系统的仿真模型是可行的,它可以为开关试验状态电流测试试验提供一套合适的计算机仿真平台,有利于优化试验回路和检测系统的电气参数,确保试验成功.     

飞机点火火花电流的测试

设计了一种基于霍尔电流传感器的飞机点火火花电流测试系统.与分流器、互感器、Rogowski线圈等测试装置比较,发现基于霍尔传感器的测试系统响应时间短、频带宽、精度高、测试方便.介绍了霍尔电流传感器测试原理,搭建了实验装置,实现了瞬间大电流的非侵入式自动化测量.测试过程中特别注意到抗电磁干扰和接地问题,得到了准确的火花电流数据和波形.提出了用相关性分析方法分析测试结果的重复性.     

直线电机驱动的微小型活塞压缩机特性分析

讨论了微小型化的直线电机驱动的活塞压缩机特性.运用电磁场有限元方法对直线电动机电磁场模型进行求解,分析了电动机内部的磁场和磁力线分布情况;建立了电动机动子动力学模型和驱动电路模型,得到系统的运行方程组并对其求解,根据计算结果对压缩机的驱动力、活塞行程、绕组电流和频率特性等进行了分析,同时就余隙容积和泄漏对这种微小型活塞压缩机的影响进行了探讨.结果表明直线电机驱动的微小型活塞压缩机在理论上是可行的,有进一步研究、优化的必要.     

快速控制反射镜系统中的传递函数辨识

提出一种传递函数辨识方法。该方法使用非线性最小二乘曲线拟合法,结合控制对象的传递函数模型选取参数初始值,针对不同的频率特性分段拟合。使用该方法可以将复杂的控制系统频率特性转化为高精度的传递函数。在系统的中低频段内获得幅频±1dB和相频±1°的传递函数辨识精度。由此设计的数字补偿器有效补偿了机械谐振带来的影响,扩宽了控制系统的闭环带宽。传递函数辨识方法摆脱了数字补偿器设计依赖手工调试的状况,并可以提供复杂的数字补偿器以得到高性能的控制系统。     

医用泄漏电流测试仪频率特性的校准方法

针对采用GB 9706. 1—2007测量网络的医用泄漏电流测试仪,分析了影响测试仪频率特性的因素,研究了频率特性的校准方法。提出在DC～1MHz频率范围内,通过输入阻抗和传输电压比校准测量网络的频率特性;根据GB 9706. 1—2007对测量网络中阻容器件的容差要求,分析了输入阻抗和传输电压比的标准值及允许偏差。为了解决传输电压比校准中存在的问题,提出了根据泄漏电流示值进行整体校准的方法,从而同时实现了对测量网络的传输特性和泄漏电流示值频率特性的校准。     

High-temperature acoustic transducer based on lanthanum-gallium tantalate piezocrystals

Constructions for high-temperature acoustic transducers of submersible and clamped types, and a bench for testing them, are described. Transducer technical characteristics are provided and the fields of their potential practical application are indicated.     

A finite-element formulation for the study of ultrasonic NDT systems

The authors present a finite-element formulation for an overall ultrasonic NDT (nondestructive testing) system, including appropriate models for transmitter and receiver transducers. Transducer considerations are discussed. Results are given for two-dimensional plane-strain geometry simulations that agree qualitatively with corresponding experimental measurements and show the potential of the method.     

设计用于圆环链裂纹检测的表面波EMAT

电磁声传感器是一种非接触式的电磁能与声能的换能装置,象运动圆环链这类带有锈蚀的粗糙表面上,常规的压电晶体传感器无法使用的场合,电磁声传感器充分显示出了它的优越性。本文介绍了所设计研制的表面波电磁声传感器的结构、工作原理以及部分试验结果分析。     

基于力传感器并联方式的测力仪测量误差来源分析

介绍了基于力传感器并联方式的测力仪的工作原理和信号输出特点。以两支力传感器并联连接的测力仪为例,详细分析了力传感器灵敏度和直线度因素对并联测力仪测量误差的影响,并进行了相关试验验证,为并联测力仪的应用提供技术参考。     

Long-Term Stability of the NIST Conical Reference Transducer

The National Institute of Standards and Technology (NIST) Conical Reference Transducer (CRT) is designed for purposes requiring frequency response characteristics much more uniform than those attainable with ultrasonic transducers conventionally used for acoustic emission (AE) nondestructive testing. The high performance of the CRT results from the use of design elements radically different from those of conventional transducers.The CRT was offered for sale for 15 years (1985 to 2000). Each CRT was furnished with data which expressed, as a function of frequency, the transducer sensitivity in volts per micrometer of normal displacement on the test block. Of the 22 transducers constructed, eight were reserved for long term research and were stored undisturbed in a laboratory with well controlled temperature and humidity. In 2009, the sensitivities of these eight units were redetermined. The 2009 data have been compared with data from similar tests conducted in 1985. The results of this comparison verify the claim “Results of tests of the long term stability of CRT characteristics indicate that, if proper care is taken, tens of years of service can reasonably be expected.” made in the CRT specifications document furnished to prospective customers.     

基于QFD与FBS的可移动电力检测设备创新设计

目的为了客观准确地将目标用户认知需求转化为产品技术特性的设计要求,提升可移动电力检测设备目标用户认知需求满意度及明确产品创新方向,提出QFD和FBS集成的创新设计模式。方法首先,通过访谈和问卷调研获取用户需求,借助AHP法求解用户认知需求权重;其次,运用QFD法构建质量屋,明确可移动电力检测设备待改进的关键技术特性指标;最后,将用户旅程图引入FBS的功能—行为—结构展开模型中,以解决可移动电力检测设备的关键技术特性问题,指导产品创新设计。结论QFD与FBS理论的融合应用能够将用户认知需求精准转化为技术特性层面的设计要求,对可移动电力检测设备的人机、造型、功能、收纳等方面的不足提出了相应的解决方案,实现了用户认知需求与产品技术特性之间的映射转换,证明了该方法具有可行性。     

A multi-layer model for the early detection of COVID-19

Current COVID-19 screening efforts mainly rely on reported symptoms and the potential exposure to infected individuals. Here, we developed a machine-learning model for COVID-19 detection that uses four layers of information: (i) sociodemographic characteristics of the individual, (ii) spatio-temporal patterns of the disease, (iii) medical condition and general health consumption of the individual and (iv) information reported by the individual during the testing episode. We evaluated our model on 140 682 members of Maccabi Health Services who were tested for COVID-19 at least once between February and October 2020. These individuals underwent, in total, 264 516 COVID-19 PCR tests, out of which 16 512 were positive. Our multi-layer model obtained an area under the curve (AUC) of 81.6% when evaluated over all the individuals in the dataset, and an AUC of 72.8% when only individuals who did not report any symptom were included. Furthermore, considering only information collected before the testing episode—i.e. before the individual had the chance to report on any symptom—our model could reach a considerably high AUC of 79.5%. Our ability to predict early on the outcomes of COVID-19 tests is pivotal for breaking transmission chains, and can be used for a more efficient testing policy.     

直线交变冲击机构磁电式速度传感装置分析

针对直线交变冲击机构高频、高速、难以检测的特点,提出了基于电磁感应原理的检测方法,完成了对直线交变冲击机构的冲击特性检测。基于ANSYS Maxwell软件建立了检测系统电磁场仿真模型。通过仿真计算与试验结果的对比分析,验证了电磁感应检测方法的可行性以及电磁仿真模型的正确性。进一步,分析了气缸材料、线圈匝数、线圈柱面径向位置等不同参数对磁电式速度传感装置性能的影响。研究结论为方便、准确地测量气驱直线交变冲击机构冲击特性参数提供了有效依据。     

A parallel tracking method for acoustic radiation force impulse imaging

Radiation force-based techniques have been developed by several groups for imaging the mechanical properties of tissue. Acoustic Radiation Force Impulse (ARFI) imaging is one such method that uses commercially available scanners to generate localized radiation forces in tissue. The response of the tissue to the radiation force is determined using conventional B-mode imaging pulses to track micron-scale displacements in tissue. Current research in ARFI imaging is focused on producing real-time images of tissue displacements and related mechanical properties. Obstacles to producing a real-time ARFI imaging modality include data acquisition, processing power, data transfer rates, heating of the transducer, and patient safety concerns. We propose a parallel receive beamforming technique to reduce transducer heating and patient acoustic exposure, and to facilitate data acquisition for real-time ARFI imaging. Custom beam sequencing was used with a commercially available scanner to track tissue displacements with parallel-receive beamforming in tissue-mimicking phantoms. Using simulations, the effects of material properties on parallel tracking are observed. Transducer and tissue heating for parallel tracking are compared to standard ARFI beam sequencing. The effects of tracking beam position and size of the tracked region are also discussed in relation to the size and temporal response of the region of applied force, and the impact on ARFI image contrast and signal-to-noise ratio are quantified.     

声学风洞中的高速列车模型气动噪声试验研究

研究借助气动-声学风洞试验平台,首先针对某高速列车的1：8缩尺比例的三车编组模型建立了气动噪声试验方法和突显不同的噪声源的模型处理方法,并结合流场外自由场传声器和传声器阵列的测量结果,分析了模型上的主要噪声源特性及对整个模型的贡献量大小。研究表明：转向架和受电弓噪声是模型的最主要噪声源,其次是车连接部位间隙,再次是鼻尖和排障器,最后是尾车,同时,并给出了这些噪声源的特性,这对于认识高速列车气动噪声和改善设计有重要的参考价值。研究也说明所提出的试验研究方法是一种研究高速列车气动噪声较为有效地方法。