共查询到20条相似文献,搜索用时 15 毫秒
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声发射传感器的校准是声发射定量检测技术的前提,互易法和表面脉冲法是目前通常采用的两种校准方法,为探讨其一致性,从互易常数入手,比较表面波互易常数和表面脉冲法中的等效互易常数。通过加载力的等效处理、利用激光测振仪测量质点振速,获得法向速度和所加力脉冲的时域和频域分量,计算得到等效互易常数。同时,建立互易法和表面脉冲法校准系统,对实验结果进行对比分析。互易常数与等效互易常数的计算结果和基于校准系统的实验结果表明,互易法和表面脉冲法之间具有较好的一致性,电信号激励声发射换能器所引起的径向谐振产生的影响,对于互易校准而言可以忽略。 相似文献
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Kanji Ono 《Research in Nondestructive Evaluation》2019,30(1):19-64
This study systematically determined the transmission and receiving sensitivities of over twenty transducers. Four types of sensitivities were evaluated for both transmission and receiving sensitivities. These are found to be different from each other and the reversibility or reciprocity conditions exist only in exceptional cases. Using their observed behavior as the basis, we critically examined the calibration methods developed to characterize them, including those based on laser interferometry and the acoustic reciprocity principle. Serious flaws in some of the reciprocity methods are uncovered, which can be rectified by using the Hill--Adams method. Four procedures emerged as workable calibration methods for contact ultrasonic and acoustic emission transducers. However, current experimental uncertainties limit the upper frequency to 2 MHz. 相似文献
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Shou W Duan S He P Xia R Qian D 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2006,53(3):564-570
The free-field transmitting voltage response at the pressure focus of a spherically focusing transducer was defined and calibrated based on the reciprocity theorem of a free-field spherically focused acoustic wave. The acoustic power, the radiation conductance, and the pressure at the pressure focus were derived and measured accordingly from the transmitting current response on the imaginary mirror symmetric spherical surface of the radiating surface. A miniature hydrophone was calibrated by the self-reciprocity of the spherically focusing source. Comparison results show that the measured acoustic power deviation between the reciprocity method and the radiation force balance method are within +/- 5% for two air-backed focusing transducers at 1.53 MHz and 5.27 MHz, respectively, and the maximum deviation of a hydrophone calibration between the new method and the free-field plane wave reciprocity method is within 1.4 dB in the frequency range from 1 MHz to 2 MHz in experiments. 相似文献
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摘 要:针对移动滚动轴承非接触声发射检测中,一个故障源信号可能被多个传感器采集,致使这些声信号包含故障信息不完整且存在重叠的问题,综合考虑声波传播理论、多传感器声信号时差关系、滚动轴承典型故障撞击频率等,建立滚动轴承故障非接触多传感器声信号融合方法。建立滚动轴承故障非接触多传感器声发射检测试验台,分别采集移动滚动轴承滚动体、外圈和内圈故障声信号。采用融合方法对同声源信号进行处理,利用信号相似理论证明了融合信号与故障源信号的相似程度高于各传感器声信号。采用声发射累计撞击计数法对融合处理后的滚动轴承不同故障声信号进行分析。结果表明,该融合算法能有效地处理多传感器接收的同声源信号,可利用融合后信号进行准确的故障识别。 相似文献
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The study presented in this paper is placed in the context of the frequency analysis of acoustic emission in concrete. The purpose is to study the ability to identify an acoustic emission event by deducing its spectrum from a detected signal. The identification is carried out progressively so as to separate the various functions involved in the acoustic emission process, and to approach the usual conditions of acoustic emission processing during fracture tests of concrete specimens. Impulses of different forms are generated on the surface of concrete test specimens, and the signals detected are analyzed. The identification of signals takes into account the frequency response of the transducers and the wave attenuation as function of the frequency. 相似文献
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Although ultrasonic attenuation monitoring has been demonstrated to be capable of providing a quantitative assessment of integrity during fatigue, much less success has been achieved in developing the corresponding capability using acoustic emission monitoring. A thorough review of the previous work employing either technique for the examination of aluminium during fatigue is presented. In addition, results from simultaneous monitoring of ultrasonic attenuation and acoustic emission during the fatigue of 7075 aluminium demonstrate the feasibility for utilizing acoustic emission as a means of continually surveying the structural integrity of a piece. It is evident from the results that, due to the passive nature of the acoustic emission monitoring, sensor location relative to failure location is not critical, thus allowing surveillance of structures with irregular geometries. However, the utilization of high frequency sound in ultrasonic attenuation monitoring makes this technique for inspecting known problem areas extremely useful in the presence of intense environmental noise. The overall findings indicate the capability of both techniques for assessing structural integrity during fatigue while providing complementary practical advantages. 相似文献
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Zhiwang Zhang Ye Tian Yihe Wang Shuxiang Gao Ying Cheng Xiaojun Liu Johan Christensen 《Advanced materials (Deerfield Beach, Fla.)》2018,30(36)
Realizing directional acoustic signal transmittance and reception robust against surrounding noise and competing signals is crucial in many areas such as communication, navigation, and detection for medical and industrial purposes. The fundamentally wide‐angled radiation pattern of most current acoustic sensors and transducers displays a major limitation of the performance when it comes to precise targeting and probing of sound particular of interest in human speaking and hearing. Here, it is shown how topological acoustic valley transport can be designed to enable a unique beamforming mechanism that renders a superdirective needle‐like sound radiation and reception pattern. The strategy rests on out‐coupling valley‐polarized edge states, whose beam is experimentally detected in the far‐field with 10° width and a sound‐intensity enhancement factor ≈10. Furthermore, anti‐interference communication is proposed where sound is received from desired directions, but background noise from other directions is successfully suppressed. This type of topological acoustic antenna offers new ways to control sound with improved performance and functionalities that are highly desirable for versatile applications. 相似文献
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声发射检测过程中,对缺陷的定位是重要的一个步骤,传统的声发射检测利用时差定位方法,而时差定位里重要的参数是声速。通过推导,得到一种利用声衰减特性和能量参数对声发射源进行定位的新方法,并用声发射仪对普通钢件以铅笔芯折断作为模拟源进行测试,证明这种无需声速测量的新方法可行,且准确性可以得到保证。该方法的提出为声发射定位技术拓展了新方向,对提高声发射检测质量有一定的帮助。 相似文献
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植物在受到病害胁迫时会发出声发射信号。通过声发射信号的采集,以统计最优柱面近场声全息技术为理论依据,进行植物的声源信号识别和声场分析。对单声源和多声源分别进行了仿真分析,通过不断修改全息柱面半径、重建柱面半径和测量点间距等参数,探索获得最佳重建效果的参数范围,同时探讨了窗函数对重建效果的影响。将基于统计最优算法的柱面近场声全息与基于空间傅里叶变换算法的柱面近场声全息进行了比较,仿真结果表明,单声源时基于空间傅里叶变换技术计算的重建面声压幅值相对误差均在10dB以下,而统计最优柱面声全息技术计算的重建面声压幅值相对误差均在15dB以下,多声源时基于空间傅里叶变换技术计算的重建面声压幅值相对误差基本在2dB左右,而统计最优柱面声全息技术计算的重建面声压幅值相对误差在26dB以下,充分表明了统计最优柱面声全息技术的优越性。 相似文献
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Corrosion of steel reinforcement in concrete is a common type of damage. The cracks propagate from the steel bar to the surface without giving any visual sign prior to surface crack formation. As long as the surface material is intact, the sensitivity of the longitudinal wave velocity to the subsurface cracks is doubtful. In this paper, cracks were created in steel fiber reinforced concrete specimens by four point bending. Wave measurements took place on the intact surfaces (compression side) using common acoustic emission transducers. Although there was no visual sign of the crack, Rayleigh as well as longitudinal wave velocities clearly decreased relative to those of the sound material. Other parameters like the amplitude and the experimental scatter of the waves were much more sensitive to damage. Numerical simulations were conducted in order to make a parametric study concerning the depth of the sound layer, the propagating wavelength and the measured wave parameters and propose a firm methodology. It is concluded that by scanning a surface with simple acoustic one-sided measurements, the identification of the location of the subsurface damage is possible, while the propagating wave gives information about the depth of the crack. 相似文献
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Brown L.F. Mason J.L. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(4):560-568
Disposable ultrasonic contact transducers have been constructed with inexpensive PVDF films for nondestructive testing (NDT) applications. This paper reports the temperature-dependent ultrasonic performance of commercial polyvinylidene fluoride (PVDF) films and PVDF sensors. PVDF film was evaluated for its material properties of interest for ultrasonic transducer performance including the relative dielectric constant εr, dielectric loss tangent tan δe , electromechanical coupling constant kt, mechanical quality factor Qm, and acoustic impedance Z. Disposable PVDF transducers were then coupled to both low and high acoustic impedance test panels and their ultrasonic insertion loss/sensitivity and frequency bandwidth measured as a function of temperature in both the pulse-echo and pitch-catch modes. The results yielded center frequencies in the 3.5-16 MHz range, with -6-dB fractional bandwidths for some of the transducers exceeding 100%. The temperature dependence of the transducers' performance is reported for the -40 to 80°C range and shows an approximate linear decrease in center frequency and increase in fractional bandwidth with increasing temperature. These measured results are compared with predictions from computer simulations based on Mason's model. These tests showed that the same disposable transducers can be used for both ultrasonic and acoustic emission sensing NDT applications. This paper summarizes the quantitative ultrasonic and vibration sensing performance for all of the disposable PVDF film transducers which were tested 相似文献
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Holmgren O Makkonen T Knuuttila JV Kalo M Plessky VP Steichen W 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(4):861-869
Surface acoustic wave (SAW) resonators on lithium tantalate (LiTaO3) and lithium niobate (LiNbO3) are investigated. The amplitude of the acoustic fields in the resonators are measured using a scanning laser interferometer. The amplitude profiles of the surface vibrations reveal the presence of distinct acoustic beams radiated from the transducer region of the SAW resonators and propagating with low attenuation. We suggest that this radiation is generated by the charges accumulating at the tips of the finger electrodes. The periodic system of sources, namely oscillating charges at the fingertips, generates Rayleigh-wave beams in the perpendicular and oblique directions. Green's function theory is used to calculate the coupling strength and slowness of the Rayleigh waves on 42 degrees Y-cut LiTaO3 and Y-cut LiNbO3 substrates as a function of the propagation direction. Furthermore, the propagation angles of the Rayleigh-wave beams as a function of frequency are calculated. The computed angles are compared with the measured ones for both the LiTaO3 and LiNbO3 substrates. 相似文献