低阶扭转模态电磁声阵列传感器研制及其在厚壁小径管中的试验研究

管道检测是发电厂热力设备安全的重要问题,由于高温以及检测区域的限制,常规无损检测方法很难满足电站管道检测要求。低阶扭转T(0,1)模态导波,由于其非频散特性,对管道缺陷大范围检测十分有效。为在管道中实现非接触激励T(0,1)模态,设计并研制了一种电磁声阵列传感器。利用所研制的电磁声阵列传感器,实现了厚壁小径管中T(0,1)模态激励和接收。通过优化电磁声阵列传感器各元件间不同连接方式可知,当各元件并联连接时,不仅提高了所激励信号的能量,还抑制了其它模态产生。同时测试了电磁声阵列传感器的频率特性,并对有周向人工缺陷的样管进行检测。试验结果表明,该电磁声阵列传感器可以实现对样管中周向缺陷的检测与准确定位,为在管道中激励接收T(0,1)模态并实现非接触检测缺陷奠定了基础。     

智能轮胎传感器的研究现状及发展趋势(一)

智能轮胎传感器是智能轮胎实现的关键。介绍了目前研究较多的集成MEMS传感器、胎面阻抗传感器、超声波传感器、电磁传感器、无源无线声表面波传感器和虚拟传感器的发展,阐述了工作原理和优缺点。其中集成MEMS传感器包括英飞凌的SP12系列、GE的NPX系列、飞思卡尔的MPXY8000系列传感器,电磁传感器包括霍尔磁场传感器和磁化轮胎传感器。最后,对智能轮胎传感器研究中存在的主要问题和智能轮胎传感器的发展趋势进行了探讨。     

新型PVDF声发射传感器的设计方法及应用

基于声发射技术研制了一种新型PVDF压电传感器。介绍了声发射传感器的结构、工作原理以及声发射传感器压电元件、背衬材料、声匹配层和前置放大器接口电路设计对传感器灵敏度、分辨率和信噪比的影响。利用美国物理声学公司声发射信号数据采集处理DiSP系统进行了断铅信号采集试验。测试结果表明：设计的新型PVDF声发射传感器对断铅信号具有宽频带响应。应用研制的新型PVDF声发射传感器、数字示波器和计算机组成的数据采集处理系统对4M20氮氢气压缩机六段排气阀进行了状态监测，结果表明新型声发射传感器能够用于设备状态监测，设计方法可行。     

LabVIEW下基于EPP模式的电磁声数据采集

为了对电磁声数据进行采集,设计了基于EPP模式的采集系统.介绍了增强型并口(EPP)工作方式的特点,并根据电磁声数据采集的需求,设计了LabVIEW环境下以EPP并口作为外设和主机接口的电磁声数据采集方案.PC通过直接端口操作产生EPP读写时序,配合外部FIFO和握手电路,完成地址的写出与数据的读入.将此方案用于电磁声数据的实时采集,通过EPP用5 MHz的采样频率成功地采集到了1 MHz的电磁声裂纹检测系统发射电路的激励脉冲串.结果表明,该方案能够对电磁声信号进行实时地波形显示和数据存储.     

用于钢管缺陷检测的电磁超声传感器优化设计研究

电磁铁是电磁超声传感器的重要组成部分，它与钢管构成的磁场是电磁超声传感器产生超声波的基础。本文建立磁感应强度与分子振动幅值的关系函数，用均匀实验设计对电磁超声传感器进行优化设计，实现了电磁超声传感器的小型化。实验研究证明，优化设计方法是正确的。     

双Fabry-Perot干涉腔型光纤声发射传感器

设计了一种新型的双Fabry-Perot腔光纤传感器用于材料损伤引起的声发射信号检测。基于低细度Fabry-Perot腔多光束干涉原理,建立了光纤Fabry-Perot传感器检测声发射信号的数学模型。分析双Fabry-Perot腔正交点稳定工作机制,设计并制作了具有双Fabry-Perot腔结构的光纤声发射传感器来保持传感器正交点的稳定性。通过模拟AE信号检测与热应力干扰实验对设计的传感器进行了实验验证。实验一通过冲击振动与折断铅笔芯产生两类模拟声发射信号,使用商用的压电传感器和光纤传感器进行对比实验,结果表明光纤传感器能够成功检测到两类模拟声发射信号,灵敏度为12.9nm,带宽达到30kHz。实验二对传感器进行工作点稳定测试,结果表明双F-P腔的控制机制能够保证传感器工作在正交点,解决了传感器输出信号衰减的问题。     

一种新型电磁耦合位移传感器

通过分析三相和两相电磁耦合传感器的信号模型和测量原理，提出和开发了一种用于角度测量的新型两相非等节距电磁耦合型传感器，在不增大加工难度的情况下，增加了传感器的极对数，从而可提高传感器的检测精度。     

非接触式超声测厚的研究与开发

本文从电磁声换能器的理论入手，说明电磁声的工作原理及其特征。对电磁声在超声无损测厚方面的应用，可行性，关键技术理论依据进行详细阐述。同时介绍我们的研究结果，讨论了今后发展的方向。     

基于相敏检波原理的电涡流传感器电路

电涡流传感器的输出特性与被测对象的电磁特性有着密切的关系,严重限制了电涡流传感器的使用范围.通过对相敏检波原理的研究,采用相敏检波技术对传感器探头线圈阻抗信号进行正交分解,结合矢量投影方法来消除被测对象的电磁特性对传感器输出的影响.实验表明:在不同被测对象、同一检测距离下测得的传感器探头线圈的电阻分量和电抗分量存在线性的关系,利用归一化阻抗能够消除被测对象的电磁特性对传感器的影响.     

电磁流量计衬里和电极对流体噪声影响及工艺处理方法

提高电磁流量计衬里和电极的加工粗糙度水平,从本质上降低流体噪声产生的几率和幅度,从而提高流量计测量的灵敏度和稳定性。本文从传感器衬里和电极粗糙度引起电磁流量计动态零点的流体噪声分类、产生,引导出能够降低流体噪声提高信噪比的重要措施,并介绍电磁流量计传感器制造中一些关键工艺措施。     

Development of EMA transducer for inspection of pipelines

Electromagnetic acoustic transducers (EMATs) have potential for In-line inspection (ILI) of pipelines compare to other Nondestructive evaluation (NDE) methods, since EMAT doesn’t need to contact and/or coupling material and can detect defects in outside of pipelines. However, improvement of transduction efficiency of EMATs is needed to secure integrity of the pipelines. To improve performance of EMAT, optimization of major parameters, such as strength of permanent magnet, shape of coil, configuration of static and dynamic magnetic fields is required. Thus, in this paper, investigation of transduction efficiency with variation of major parameters are performed by comparison of generated ultrasonic signals. Based on the investigation results, EMATs for ILI of pipelines are designed and fabricated with optimized Periodic solenoid array (PSA) types of meander-line sensor, static magnetic field, and then, performance of the developed EMATs are evaluated by detecting defects in the gas pipelines mounted in the one-bed testing system.     

Excitation and detection of shear horizontal waves with electromagnetic acoustic transducers for nondestructive testing of plates

The fundamental shear horizontal（SH0） wave has several unique features that are attractive for long-range nondestructive testing（NDT）. By a careful design of the geometric configuration, electromagnetic acoustic transducers（EMATs） have the capability to generate a wide range of guided wave modes, such as Lamb waves and shear-horizontal（SH） waves in plates. However, the performance of EMATs is influenced by their parameters. To evaluate the performance of periodic permanent magnet（PPM） EMATs, a distributed-line-source model is developed to calculate the angular acoustic field cross-section in the far-field. Numerical analysis is conducted to investigate the performance of such EMATs with different geometric parameters, such as period and number of magnet arrays, and inner and outer coil widths. Such parameters have a great influence on the directivity of the generated SH0 waves that arises mainly in the amplitude and width of both main and side lobes. According to the numerical analysis, these parameters are optimized to obtain better directivity. Optimized PPM EMATs are designed and used for NDT of strip plates. Experimental results show that the lateral boundary of the strip plate has no perceivable influence on SHO-wave propagation, thus validating their used in NDT. The proposed model predicts the radiation pattern ofPPM EMATs, and can be used for their parameter optimization.     

Applications of electromagnetic acoustic transducers in the NDE of non-conducting composite materials

An electromagnetic acoustic transducers (EMAT) can usually generate or detect an ultrasonic wave in an electrically conducting material across a small gap. The transducer is a unique ultrasonic EMAT probe that does not require a couplant or gel. Therefore it can be applied in a noncontact mode with a high degree of reproducibility. Shear waves and Lamb waves can be easily generated with EMATs in single-sided access. However, the application of EMAT has been limited to electrically conducting materials. In this work, EMAT was applied to the inspection of nonconducting composites by adhering a removable aluminum foil tape on the part surface. Ultrasonic waves generated in the aluminum layer by the EMAT readily propagated into the nonconducting composite. The reversed process was used in the reception of ultrasonic waves by EMAT. For composites that contained surface metallizations (e. g., metal foil or mesh) for lightning protection and electromagnetic interference (EMI) purposes, EMAT probes were placed directly on the composite surface. Finally, EMAT-generated, normal-incidence shear waves were used for the inspection of “green” laminates before curing to detect errors in ply orientation and layup sequence. This study was supported by the Center for Nondestructive Evaluation at Iowa State University, 1A, U. S. A. and by the Factory Automation Research Center for Parts of Vehicles (FACPOV) in Chosun University, Kwangju, Korea, designated by KOSEF     

Real sensitivity of EMA instruments

Results of experimental investigation into the detection of internal, surface, and subsurface flaws by ultrasonic vibration pulses that are excited and received via different types of EMATs are reported. The sensitivity of the EMA instruments developed is shown to be close to the sensitivity of modern contact flaw detectors. An EMAT and a flaw detector that take advantage of the EMA flaw-detection method for the inspection of surface and near-surface zones of metal products are developed.     

高精度可连续调节宽带猝发信号发生器设计

本文设计了一种使用纯硬件的设计方法，实现低失真率，频率精度高，且产生连续可调的猝发信号。使用模拟乘法器调幅和模拟开关关断实现矩形窗、汉宁窗、海明窗等不同的加窗形式。另外猝发信号发生器采用了以单片机为核心的嵌入式控制系统，方便地上位机对信号发生器控制。通过串口通信上位机（个人计算机）可以在线修改信号发生器的猝发时间间隔，猝发脉冲宽度，以及信号频率。该信号发生器最高频率达1.8MHz，可以广泛应用于超声导波，电磁超声检测，以及激光脉冲控制等。     

霍尔电流传感器在输电线路行波故障定位中的应用

电流行波的采集是输电线路行波故障定位的首要环节，由于行波频率很高，因此了解电流传感器在高频环境下的传输特性是十分必要的，结合霍尔电流传感器在输电线路行波故障定位的应用，列出了磁补偿式霍尔电流传感器的数学模型，对它的幅频、相频特性作了进一步分析，并且讨论了其对行波高频噪声的抑制作用。     

插入式超声波流量计在供水大口径管道中的应用

在供水系统计量中,工业流量测量普遍存在着大管径、大流量测量困难的问题,机械式水表使用较多,大管径流量的水表存在误差较大,计量不准,无校验手段。本文探讨在供水大口径管道中应用超声波流量计,并对该性能进行分析对比,提高供水计量的准确性。分别选用MF-G2和TDS-100型插入式超声波流量计,在现场应用,效果较好,精确度达到1%。     

一种磁致伸缩式超声波激发/接收传感器的研究

以研制磁致伸缩式超声波传感器为目标，分析了磁致伸缩式超声波传感器的工作原理——磁致伸缩效应及逆效应，重点讨论传感器结构设计及线圈参数选择计算，制作了磁致伸缩式超声波传感器。本文研制的传感器在脉冲激励电流的作用下，可在细丝中激发超声波，同时还可以接收细丝中传播的超声波；该传感器既可以激发扭转波，又可以激发纵波。可用于测量液位、温度、液体密度和材料的声速、弹性模量等物理量。     

新型油井含水率测量仪的研制

由于水、油介电特性差异较大，导致电磁波在不同含水率的油水混合介质中传播时的相位系数有很大不同。新型含水率测量仪器是利用同轴线作传感器，油水混合介质在同轴线内流过，并构成传播电磁波的载体，通过测量同轴线两端电磁波在同轴线内油水混合介质中传播的相位系数，来得到油水混合介质的含水率。该仪器能够实现油井含水率的连续测量，室内试验和初步现场试验证明该方法能够解决高含水油田油井含水率很难测准这一难题。     

Propagation characteristics of compression waves reflected from the open end of a duct

The present study addresses the distortion of the compression wave reflected from an open end of a shock tube. An experiment is carried out using the simple shock tube with an open end. Computational work is also performed to represent the experimented flows. The second-order Total Variation Diminishing scheme is employed to numerically solve the unsteady, axisy-mmetric, inviscid, compressible governing equations. Both the experimented and predicted results are in good agreement. The generation and development mechanisms of the compression wave, which is reflected from the open end of the shock tube, are obtained in detail from the present computations. The effect of size of the baffle plate at the open-end that causes the reflection of the incident expansion wave is found negligible. A good correlation is obtained for transition of the reflected compression wave to a shock wave inside the tube. The present data show that for a given wave length of the incident expansion wave the transition of the reflected compression wave to a shock wave can be predicted with good accuracy.