A Novel Acoustic Emission Fiber Optic Sensor Based on a Single Mode Optical Fiber Coupler

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基于光纤耦合器的声发射传感器

为检测变压器内局部放电产生的声发射信号,介绍了一种基于特殊光纤熔融拉锥耦合器型声发射传感器。它是利用声波引起的扰动改变耦合器两臂光功率输出的特点来检测声发射信号。实验结果表明：此种传感器在10kHz～250kHz范围内对声发射信号有良好响应,在155kHz灵敏度为5.6×10^-6V/Pa,噪声为1.8Pa声压,有望在复合材料与结构、电力无损检测方面得到应用。     

Fiber optic acoustic emission sensor and its applications in the structural health monitoring of CFRP materials

A fiber optic acoustic emission sensor based on fused-tapered coupler and its applications in structural health monitoring are proposed in this paper. The fiber optic acoustic emission sensor (FOAES) was tested using pencil lead break tests compared with the commercial acoustic emission sensor (R15 PZT). Besides, the sensor was embedded into the carbon fiber reinforced plastics (CFRP) materials and tested in the same way. It successfully detected the AE signals. FOAES was applied in the structural health monitoring (SHM) of CFRP materials. Damages of carbon fiber/epoxy composite laminates during three-point-bending test were monitored by surface-mounted and embedded FOAES, respectively. Results identified that the sensor embedded into composite structures could monitor damage of composite laminates on-line as the surface-mounted sensor did.     

All-fiber optic acoustic sensor based on multimode-single mode-multimode structure

A simple and low cost optical fiber acoustic sensor based on multimode-single mode-multimode (MSM) fiber structure is presented. The optical coupling efficiency between hetero-core fibers spliced structure is modulated by acoustic pressure through a thin metal foil. Acoustic wave is detected by measuring the intensity change of transmission light. Experiments are carried on to testify the performance of MSM fiber acoustic sensor and the experimental results show that the acoustic wave can be sensitively detected within 11 kHz frequency range.     

光纤Fizeau干涉仪的声发射检测研究

验证了一种基于光纤Fizeau干涉仪的声发射传感器,可用于固体表面传播的超声波的检测.这种传感器的特点是能够精确地检测由固体表面传播的超声波产生的微弱振动.当超声波信号通过光纤传感器到达探测器时,干涉仪的输出光强度受到了超声信号的调制.通过检测干涉仪的输出光强度并利用Fourier变换,测得了超声信号的振幅和频率.对传感系统的相位调制特性进行了仿真,并对实验结果进行了分析.     

光纤熔锥耦合器的声光调制特性

对光纤熔锥方向耦合器的声光强度调特性进行了实验研究,得到了工作波长为1310nm、声波频率为20.19kHz,电驱动功率为2.6mW,插入损耗为0.5dB,调制深度为64％的声光强度调制特性。     

304不锈钢点蚀声发射监测研究

为研究304不锈钢在高于常温条件下的点蚀声发射特性,对70℃下6%氯化铁溶液中304不锈钢点蚀过程进行了声发射监测。采用参数和波形分析相结合的方法处理信号,并通过点蚀形貌观察进行验证。结果表明声发射撞击和能量随时间逐渐增加,在某一时段达到峰值,随后下降并维持平稳状态。信号波形主要由幅度、能量较大的低频段(<100kHz)弯曲波和幅度、能量较小的高频段(>100 kHz)扩展波构成。研究结果对304不锈钢高于常温条件下声发射点蚀监测具有一定意义。      

共光声池腔芯轴型空气衬底光纤麦克风

声传感器和光声池是激光光声光谱技术的核心组件.结合光纤迈克耳孙干涉仪、相位载波解调技术和纵向共振光声池,提出一种共光声池腔的芯轴型空气衬底光纤麦克风.光纤麦克风中的铜毛细管被用作光声池的共振腔,传感臂由10 m长的超细光纤缠绕在铜毛细管上构成,参考臂为5 cm长的短臂且已进行隔声隔振处理.基于结构共振频率稳定的特点,优...     

Theoretical analysis of a quartz-enhanced photoacoustic spectroscopy sensor

Quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors are based on a recent approach to photoacoustic detection which employs a quartz tuning fork as an acoustic transducer. These sensors enable detection of trace gases for air quality monitoring, industrial process control, and medical diagnostics. To detect a trace gas, modulated laser radiation is directed between the tines of a tuning fork. The optical energy absorbed by the gas results in a periodic thermal expansion which gives rise to a weak acoustic pressure wave. This pressure wave excites a resonant vibration of the tuning fork thereby generating an electrical signal via the piezoelectric effect. This paper describes a theoretical model of a QEPAS sensor. By deriving analytical solutions for the partial differential equations in the model, we obtain a formula for the piezoelectric current in terms of the optical, mechanical, and electrical parameters of the system. We use the model to calculate the optimal position of the laser beam with respect to the tuning fork and the phase of the piezoelectric current. We also show that a QEPAS transducer with a particular 32.8 kHz tuning fork is 2–3 times as sensitive as one with a 4.25 kHz tuning fork. These simulation results closely match experimental data.     

光纤熔锥耦合器的声光强度调制特性

对光纤熔锥方向耦合器的声光强度调制特性进行了实验研究。得到了工作波长为1310nm,声波频率为20.19kHz,电驱动功率为2.6mW,插入损耗为0.5dB,调制深度为64％的声光强度调制特性。     

A conical piezoelectric transducer with integral sensor as a self-calibrating acoustic emission energy source

The experimental results of a conical piezoelectric transducer with integral backing sensor as a self-calibrating simulated acoustic emission (SAE) energy source are presented. It has been shown that there is a negative linear relationship between the energy of SAE signal detected by the backing sensor and the relative strength (signal energy) of SAE source in the structure detected by a reference sensor under different transducer-to-structure coupling efficiencies, with AC drives of the same wave packet, frequency and peak amplitude to excite the conical transducer as a SAE source at all the investigated frequencies over the frequency range of interest in AE measurements (nominally from 50 kHz to around 1 MHz). This should enable the relative strength of the SAE source in a structure to be determined using the SAE measurement from the backing sensor for the selected electrical inputs to the conical transducer, and hence to remove the concerns about inconsistent transducer-to-structure coupling affecting the relative strength of the SAE source for calibration.     

Fiber Sensing of Micro -Crack

Optical fiber sensors are used for sensing micro -cracking in composite and metal materials in aerospace applications.The sensing mechanism is based on the detection of acoustic emission signals, which are known to emanate from micro-cracks when they grow under further loading. The sensor head consists of a fiber Bragg grating that is capable of detecting acoustic emission signals generated by pencil lead breaking, of frequencies up to 200 kHz.     

一种确定光纤传感器中3×3耦合器输出信号相位差的新算法

本文提出了一种基于Bessel函数展开,在频域内精确确定光纤传感器3×3耦合器输出信号相位差的算法。在Mach-Zehnder干涉仪原理的基础上,通过建立3~3耦合器输出信号的数学模型和利用耦合器输出光功率的Bessel展开,完成了算法的理论推导,并且在实验室中进行了声学实验。数据处理结果表明,该算法能够较精确地确定3×3耦合器输出信号的相位差,且相位差与调制频率无关,与理论相符。     

光纤Sagnac传感器对材料频率特性的实验研究

不同的材料由于物理性质不同,在断裂时会产生不尽相同的声发射信号。光纤声发射传感器以其频带宽,抗电磁干扰,灵敏度高,体积小等优点在声发射（AE）信号探测方面有着广泛的应用前景。本文采用光纤Sangac传感器,对不同材料断裂过程的声发射信号进行检测,通过快速傅立叶变换分析其频谱。实验得知同一种材料断裂的声发射信号具有相同的...     

Beamforming array techniques for acoustic emission monitoring of large concrete structures

This paper introduces a novel method of acoustic emission (AE) analysis which is particularly suited for field applications on large plate-like reinforced concrete structures, such as walls and bridge decks. Similar to phased-array signal processing techniques developed for other non-destructive evaluation methods, this technique adapts beamforming tools developed for passive sonar and seismological applications for use in AE source localization and signal discrimination analyses. Instead of relying on the relatively weak P-wave, this method uses the energy-rich Rayleigh wave and requires only a small array of 4–8 sensors. Tests on an in-service reinforced concrete structure demonstrate that the azimuth of an artificial AE source can be determined via this method for sources located up to 3.8 m from the sensor array, even when the P-wave is undetectable. The beamforming array geometry also allows additional signal processing tools to be implemented, such as the VESPA process (VElocity SPectral Analysis), whereby the arrivals of different wave phases are identified by their apparent velocity of propagation. Beamforming AE can reduce sampling rate and time synchronization requirements between spatially distant sensors which in turn facilitates the use of wireless sensor networks for this application.     

干涉型长距离分布式光纤传感系统

提出了并验证了一种新型的以迈克耳辽干涉为基础的调频连续波干涉型长距离分布式光纤伟系统，系统在干涉仪的参考回路巧妙地引入了一个带有移频器的光学回路，使系统连续测量范围增加到４倍，达４８ｍ。     

新型光纤光栅水声传感器的研究

提出了一种新型的光纤布拉格光栅(FBG)水声传感探头结构以及光纤光栅传感信号的自解调方法。利用一对匹配光栅构成推挽结构,实现了传感-解调的合二为一,大大地减小了系统的复杂度;并通过筒状弹性体结构,解决了裸光纤光栅测量水声信号的灵敏度过小的问题,并具有温度补偿作用。仿真与初步实验结果表明,该水听器探头的测量动态范围超过100 dB,在100~200 dB re 1μPa的水声压范围内,测量灵敏度为0.36 nm/Mpa。     

Modern acoustic emission technique and its application in aviation industry

This paper proposes the concept of modern acoustic emission (MAE) technique and describes its application in aviation industry. Modern AE is characterized by the combination of AE parameter and waveform analysis based on the understanding of AE source mechanism, the property of sound wave propagation and the interaction between sound wave and the medium in which the sound wave is propagating. Another feature of MAE is characterized by the application of so-called fully digital AE apparatus with low noise, high speed of data transmission and accurate AE source locating capability. MAE is merely an imagination without the realization of the advanced fully digital AE instrument. The application of MAE in monitoring the conditions of aircraft structures during a fatigue test was taken as an example for showing the important role played by AE. Roles of AE in the evaluation of (environment-related) corrosion damage of aircraft were also presented.     

Coherent Beam Combination of Three Fiber Amplifiers with Multi-dithering Technique

Coherent beam combination of three W-level fiber amplifiers with multi-dithering technique is demonstrated. The multi-dithering technique is used for phase control in two channels. In the experiment, two channels are modulated by sine wave with 70 kHz and 100 kHz respectively, and two regular commercial DSP lock-in amplifiers and an industrial computer are used for electric signal processing in the feedback loop. The fringe contrast is advanced from 12% to 81%, and 78% coherent combination efficiency is obtained when the feedback loop is closed.