A non-iterative partial discharge source location method for transformers employing acoustic emission techniques

Partial discharge (PD) causes premature insulation failure of transformers. It is essential to detect PD to avoid unwanted failure of transformers. Only detection of PD is not sufficient for a transformer of huge size, unless it is possible to locate. Acoustic partial discharge measurement is advantageous for PD source location. There are different algorithms for PD source location. These are iterative and require large number of acoustic emission (AE) sensors. This paper presents a non-iterative source location algorithm employing four AE sensors. This algorithm is applied to experimental data. Proposed algorithm is also applied to published data and compared with existing iterative methods. Main error for source location is due to arrival time calculation. In order to reduce the error in AE signal arrival time calculation, different arrival time calculation methods are discussed and a comprehensive method is proposed. By applying these methods, arrival time is calculated from measured signal.     

Acoustic imaging using a volumetric array

A method is described for producing images of acoustic sources using a volumetric array. Theoretical results are presented and compared to those obtained experimentally from an acoustic 64 element random spherical volumetric array. Application areas for such a system include auditorium characterisation, recording studio optimisation and covert surveillance operations.     

一种超声速运动目标的被动声定位算法

超声速运动目标在空气中飞行时产生激波，本文利用激波到达时间，提出了一种基于波前方向矢量的算法，确定目标的速率和位置。最后，通过对三站均匀圆阵的估计精度的分析计算，讨论了该算法的有效性。     

Experimental study in correlation variation of acoustic propagation channel in Philippine sea

I.IntroductionSonarsignalisoftcndistortcdbythcwcightingofthcacousticchanncl'stransfcrfunction.Inthiscase,therearetwosonarsignaIproccssingmcthodswhichcanbcuscdtodccrcascthedistortionofthcsignal.Oneisthcsclcctionofamorcto1crantsignalwithcorrcspondingsigna1proeessingmethod.Forexamp1e,astcpfrcqucncymodulatcdsignalwithpostintcgratcdpro-ccssingcanbeusedinthiscasc.Theanothcrisobtainingthcrcsponscfunctionofthcacousticchanne1andmatchingitwithamatehfiltCr.Bothofthcscmcthodsrcquirethcstudyofhme-frequen…     

Adverse Effects of Environmental Noise on Acoustic Voice Quality Measurements

An accurate analysis of voice quality is imperative when using acoustic measurements to diagnose vocal pathologies. It is known that noise has a significant effect on the reliability and validity of acoustic voice measurements, but the precise relationship has not been established. The purpose of this study was to investigate the influence of noise on the accuracy, reliability, and validity of acoustic voice quality measurements while balancing for gender, age, intersubject and intrasubject variability, microphones, computer hardware, analysis software, and type of noise. Level of noise was precisely controlled. The specific focus of interest was to determine the critical levels of noise that can invalidate voice quality measurements and to generate practical recommendations. Results suggest that the recommended, acceptable, and unacceptable levels of noise in the acoustic environment are above 42 dB, above 30 dB, and below 30 dB signal-to-noise ratio, respectively.     

Boundary regularity for a family of overdetermined problems for the Helmholtz equation

If a nonconstant solution u of the Helmholtz equation exists on a bounded domain with u satisfying overdetermined boundary conditions (u and its normal derivative both required to be constant on the boundary), then under certain assumptions the boundary of the domain is proved to be real-analytic. Under weaker assumptions, if a real-analytic portion of the boundary has a real-analytic extension, then that extension must also be part of the boundary. Also, an explicit formula for u is given and a condition (which does not involve u) is given for a bounded domain to have such a solution u defined on it. Both of these last results involve acoustic single- and double-layer potentials.     

A PSD-based electronic system for AC response studies of superionic conductors

An electronic system based on quadrature oscillator, current-to-voltage converter and phase sensitive detector (PSD) has been designed and constructed for measurement of AC electrical conductivity and complex impedance/admittance on ionic and superionic conductors at several frequencies upto 60 kHz. The design incorporates a CMOS FET switch controlled by two anti-square reference signals for rectification and a differential amplifier for summation and impedance matching. The performance of the system has been demonstrated and the measurement possibilities discussed.     

Study on the anodizing of AZ31 magnesium alloys in alkaline borate solutions

A kind of environmentally friendly anodizing route for magnesium alloys, based on a new kind of organic additive (AA) contained traditional alkaline borate solution and 50 Hz civil ac current, has been studied. It is found that the formation of the anodic films is always coupled with the additive depended sparking and oxygen evolution, and the optimized ivory-white smooth anodic film possesses high corrosion resistance and excellent binding strength to AZ31 substrate. Meanwhile, The results also show that the structure, the corrosion resistance and the morphology of the anodic films are mainly dependent on the anodizing voltage, time and additives.     

数字化声学测量技术 Ⅱ.数字式声强及声功率测量系统

本文介绍在数字声学测量分析系统中，通过双传声器信号互谱密度的计算进行声强及声功率测量的基本原理。该数学分析系统由微计算机，数字信号处理卡和Ａ／Ｄ变换卡组成。在一个数字系统中，通过快速傅里叶变换（ＦＥＴ）进行互谱计算是十分有效的。本文着重介绍了，在声强的测量分析中对声强探头两传声器的固有相位差进行补偿的重要性和补偿方法，这是声强测量的重要环节。