Wideband frequency and in situ characterization of aluminum nitride (AlN) in a metal/insulator/metal (MIM) configuration

This paper deals with the electrical wideband frequency and in situ characterization of aluminum nitride (AlN) material. This material is interesting for bulk acoustic wave (BAW) or surface acoustic wave (SAW) devices. In a first step, low frequency characterizations allow to know current versus voltage characteristics, leakages and temperature dependence of the electrical properties. Then, AlN properties in an integrated “metal/insulator/metal” configuration are characterized using MIM waveguide and RLCG parameters are measured up to 20 GHz. An electrical field breakdown of 7.5 MV cm⁻¹ and a relative permittivity between 9 and 10 are extracted. Acoustic resonances, validated with Mason one-dimensional simulation, occur near 5 and 12 GHz. Finally, the MIM devices performances are determined in a wideband frequency: from 1 MHz to 10 GHz.     

压力容器声发射信号人工神经网络模式识别方法的研究

采用人工神经网络模式识别技术对现场压力容器各种声发射源信号特征参数进行了模式识别分析,提出了采用人工神经网络分类方法对压力容器声发射源信号进行定量分析的概念,从而找到了评价声发射源严重程度的方法,设计和培训的人工神经网络可以给出一个多种因素产生的复合声发射源中裂纹扩展、氧化夹渣断裂、残余应力释放和机械摩擦信号所占的百分比,这一结果使声发射技术对压力容器安全状态的无损评价成为可能。     

声无限元进展

声无限元在近几年来的发展尤为迅猛。相对于声学领域常用的边界元等其他方法,声无限元应用于声学问题的计算效率是极为优越的,因而适于求解很宽的声学频率和复杂声源形成的声场。介绍了声无限元的引出、原理和早期的声无限元,并根据提出方法的新颖性和受关注的程度,对近年来的声无限元统一归纳为五类,然后扼要介绍了各种方法的原理、所产生的问题以及参考文献中解决的办法。最后,对声无限元进行了前景展望。     

压力管道泄漏点的新型声发射定位研究

压力管道在泄漏时会产生声发射信号,根据此信号传播时声压遵从指数衰减规律,提出了一种利用声信号衰减特性和能量累计对管道泄漏点进行精确定位的新方法,并用多通道声发射仪以塑料管道和金属管道为介质、以压电换能器产生的信号为模拟泄漏信号进行了精确定位的试验验证,表明该方法可行并具有较好的定位精度。     

Damage classification in carbon fibre composites using acoustic emission: A comparison of three techniques

Classifying the type of damage occurring within a structure using a structural health monitoring system can allow the end user to assess what kind of repairs, if any, that a component requires. This paper investigates the use of acoustic emission (AE) to locate and classify the type of damage occurring in a composite, carbon fibre panel during buckling. The damage was first located using a bespoke location algorithm developed at Cardiff University, called delta-T mapping. Signals identified as coming from the regions of damage were then analysed using three AE classification techniques; Artificial Neural Network (ANN) analysis, Unsupervised Waveform Clustering (UWC) and corrected Measured Amplitude Ratio (MAR). A comparison of results yielded by these techniques shows a strong agreement regarding the nature of the damage present in the panel, with the signals assigned to two different damage mechanisms, believed to be delamination and matrix cracking. Ultrasonic C-scan images and a digital image correlation (DIC) analysis of the buckled panel were used as validation. MAR’s ability to reveal the orientation of recorded signals greatly assisted the identification of the delamination region, however, ANN and UWC have the ability to group signals into several different classes, which would prove useful in instances where several damage mechanisms were generated. Combining each technique’s individual merits in a multi-technique analysis dramatically improved the reliability of the AE investigation and it is thought that this cross-correlation between techniques will also be the key to developing a reliable SHM system.     

浅谈声波法技术在采矿中的应用

矿山开采过程中冲击矿压是严重威胁矿井安全生产的动力灾害。随着矿井开采深度的不断增加,冲击矿压的危险和危害也日趋严重。本文通过对弹性波方程的建立与解释,说明岩石的弹性特征决定着开采应力的动态变化,因而采用测定纵横波速的方法可以测定岩体的弹性常数。并且说明了采用声波法在观测记录弹性波传播规律或参数变化来反演出煤岩体的物理力学参数变化,进而进行动力灾害的预测和评价的可行性。指出在21世纪弹性波技术有着极好的应用前景。     

Gatifloxacin–Ionic Surfactant Interactions: Volumetric,Acoustic, Voltammetric,and Spectroscopic Studies

Surfactant systems have been frequently used as pseudomodels for investigating interactions of drugs with biological membranes because of their structural similarities with the latter. This helps to understand complicated yet very important biological processes like diffusion of bioactive moieties through biomembranes. The current study deals with voltammetric and spectroscopic studies to evaluate the interaction of a potential antibacterial drug, gatifloxacin (GTF), with a cationic surfactant, dodecyltrimethylammonium bromide (DTAB), and an anionic surfactant, sodium dodecyl sulfate (SDS), under physiological conditions (phosphate buffer, pH 7.4). For more detailed insight into the GTF–ionic surfactant interactions, density and acoustic data were also recorded and used to calculate several important parameters, namely, apparent molar volume (ɸ_V ), isentropic compressibility (K_s ), and apparent molar isentropic compressibility (ɸ_K ) at T = 298.15, 303.15, 308.15, and 313.15 K. Values for partial molar volume (, partial molar expansivity , specific acoustic impedance (Z), relative association (RA), intermolecular free length (L_f), and sound velocity number (U) were also obtained. The interpretation of the concentration dependence of the above-mentioned quantities using a cosphere overlap model led to a better apprehension of solute–solute and solute–solvent intermolecular interactions present in the investigated system, whereas cyclic voltammetry and ultra violet (UV)–visible spectroscopic studies assisted in predicting the location of adsorbed GTF molecules within the DTAB and SDS micelles.     

Correlations of electrochemical noise, acoustic emission and complementary monitoring techniques during intergranular stress-corrosion cracking of austenitic stainless steel

Specimens of sensitized type AISI 304 stainless steel were subjected to constant load and exposed to an aqueous sodium thiosulphate solution. Intergranular stress-corrosion cracking was monitored simultaneously for electrochemical noise, acoustic emission, and specimen elongation. A section of the gauge length was monitored optically with subsequent analysis by digital image correlation. Correlations between the results were observed and analysed. Electrochemical noise and elongation are associated with crack propagation from the early stages, whereas acoustic emission is associated with the final stages of fracture. Digital image correlation analysis is sensitive to crack development, and is used to measure crack length and crack openings.     

An Acoustically Driven Magnetized Target Fusion Reactor

We propose a new acoustic compression scheme for a MTF power plant. A strong acoustic wave is produced by piston impacts. The wave focuses in liquid PbLi to compress a pre-formed FRC plasma. Simulations indicate the possibility of building an economical 60 MWe power plant. A proof-of-principle experiment produces a small D-D fusion yield of 2000 neutrons per shot.     

Sonar detection and measurements of ice in a freezing river I: Methods and data characteristics

The basic concepts and operating principles of SWIPS (Shallow Water Ice Profiling Sonar) measurements in freezing rivers are outlined and described with reference to ongoing BC Hydro ice- and flow monitoring programs in the Peace River. Emphasis is given to identifying the nature of the measured quantities and their connections to the parameters conventionally used to describe and model rivers and their ice contents. Difficulties in deployment and data recovery, mostly associated with the growth of anchor ice, are described in terms of the evolution of successful approaches and the pitfalls encountered along the way. Distinctions are made among results obtained from targets at or inside floating surface ice and from particulate targets, suspended in the water column. Example results are presented in each case and put in the context of seasonal changes in the monitored quantities of interest. The usefulness of lower frequency measurements for ice cover studies is highlighted. Limited results from simultaneous multifrequency measurements on suspended particulate (frazil) targets are reviewed and analyzed to show the likely applicability of Rayleigh Law assumptions for observations made prior to ice cover stabilization and in, at least, the lower water column. This applicability is combined with estimates of absolute return strengths to make rough assessments of the ranges of particle sizes and concentration encountered in the Peace River studies.