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子带自适应滤波在层状介质脱粘超声检测中的应用 总被引:3,自引:1,他引:2
高声阻抗下低声阻抗的脱粘检测一直是超声检测领域中的难题。文章针对钢层下橡胶层分层信号,互相关最大为准则,采用小波包子带分解自适应滤波方法提取橡胶层脱粘的二界面信号,给出了仿真信号和实验信号的处理结果,显示了该方法的有效性和可行性。 相似文献
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固体火箭发动机多层装药结构中的脱粘类型、位置和尺寸决定了其对整体安全性能构成的威胁程度。该文研究了多层结构中脱粘缺陷的超声检测方法,通过对不同脱粘缺陷超声脉冲回波的特征分析与统计,实现缺陷的定性、定位和定量。首先,采集含有多类脱粘缺陷的粘接结构的超声脉冲回波信号,分析信号中主能量波包所代表的声程,提取五种声程的波峰时刻和幅值作为特征值,组建已知脱粘类型训练样本并输入至BP神经网络,实现特征值域到类别域的非线性映射,即脱粘类型分类;其次,采用阈值法确定缺陷的界面位置;最后,提出分段线性插值-相关性定量法将待检测缺陷的定量结果缩小到±2 mm以内。该文利用COMSOL有限元仿真和实验操作验证了多层粘接结构中脱粘缺陷的定性、定位和定量方法的可行性和可靠性。 相似文献
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多层粘接结构中脱粘界面的人工神经网络余弦变换谱特征识别 总被引:5,自引:1,他引:4
针对钢-橡胶多层粘接结构中界面脱粘的超声检测难题,利用余弦变换(DCT)提取的表征检测信号的模式特征矢量,通过人工神经网络模式识别方法对不同界面脱粘时实验检测信号的正确识别,实现了脱粘一、二、三和四界面的检测。本文脱粘界面信号模式的人工神经网络识别系统对现代工业中NDT&NDE的自动化有着积极的意义。 相似文献
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提出一种基于互逆光纤色散的微波光子雷达系统设计方案,既可以产生宽带线性调频信号,又可以实现线性调频信号的光域脉冲压缩.在发射端利用互逆色散光纤产生线性调频信号.在接收端,雷达回波信号通过马赫-曾德调制器调制到预啁啾的光信号上,然后经过色散光纤的进一步色散.最终在探测器端可以得到目标回波信号脉冲压缩后的结果.该方案无需脉冲压缩过程中数字化和离线处理,且具有脉冲压缩比的调谐作用.理论、数值仿真和实验证明了该设计方案能有效进行线性调频信号的光域脉冲压缩.实验产生了C波段下时宽1.2ns,带宽3.2GHz的线性调频信号,并通过互逆色散光纤将该信号压缩到了0.09ns,脉冲压缩比达13.3. 相似文献
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本文从声信号检测的观点出发分析了时间压缩相关器的有关理论问题。结合处理常用的线性调频脉冲信号及拟随机信号的情况,在相关器的输出信号及其频谱结构、多普勒滤波器组的设置、噪声背景及信噪比增益、信号包络的平滑化等方面得到了一些有用的结论和基本计算公式。改进和部分修正了已有的设计理论,为合理地设计近代声信号脉冲压缩接收机提供了依据。 相似文献
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Fan Y Mandelis A Spirou G Vitkin IA 《The Journal of the Acoustical Society of America》2004,116(6):3523-3533
In conventional biomedical photoacoustic imaging systems, a pulsed laser is used to generate time-of-flight acoustic information of the subsurface features. This paper reports the theoretical and experimental development of a new frequency-domain (FD) photo-thermo-acoustic (PTA) principle featuring frequency sweep (chirp) and heterodyne modulation and lock-in detection of a continuous-wave laser source at 1064 nm wavelength. PTA imaging is a promising new technique which is being developed to detect tumor masses in turbid biological tissue. Owing to the linear relationship between the depth of acoustic signal generation and the delay time of signal arrival to the transducer, information specific to a particular depth can be associated with a particular frequency in the chirp signal. Scanning laser modulation with a linear frequency sweep method preserves the depth-to-delay time linearity and recovers FD-PTA signals from a range of depths. Preliminary results performed on rubber samples and solid tissue phantoms indicate that the FD-PTA technique has the potential to be a reliable tool for biomedical depth-profilometric imaging. 相似文献
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Backing effects on the underwater acoustic absorption of a viscoelastic polymer slab embedded with locally resonant scatterers are reported. The polymer slab is embedded with two layers of locally resonant scatterers, i.e. Al spheres coated by soft silicon rubber. Theoretical absorption coefficients of the polymer slab under different backings using a layer multiple scattering method show good agreement with the experimental results, which supports unambiguously the experimental observation. Then relations between the resonance modes and the low-frequency absorption peaks of the composite slab are clarified to address the absorption mechanisms. It shows that the mass of the steel backing affects evidently the low-frequency absorption, the absorption peak shifts to lower frequency range while increasing the backing mass. 相似文献
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Rubber layers with air-filled cavities or local resonance scatters can be used as anechoic coatings. A lot of researches have focused on the absorption mechanism of the anechoic coatings. As the anechoic coatings are bonded to the hull of submarine, the vibration of the hull should not be neglected when the analysis of the absorption characters is carried out. Therefore, it is more reasonable to treat the anechoic coating and the backing as a whole when the acoustic performance is analyzed. Considering the effects of the steel plate backing, the sound absorption performances on different models of anechoic coatings are investigated in this paper. The Finite Element Method is used to illustrate the vibrational behaviors of the anechoic coatings under the steel backings by which the displacement contours is obtained for analysis. The theoretical results show that an absorption peak is induced by the resonance of the steel slab and rubber layer. At the frequency of this absorption peak, the steel plate and the coating vibrates longitudinally like a mass-spring system in which the steel slab serves for mass and the coating layer is the spring. To illuminate the effects of the steel slab backing on the acoustic absorption, the thicknesses of the steel slab and the anechoic layer are discussed. Finally, an experiment is performed and the results show a good agreement with the theoretical analysis. 相似文献
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An air-coupled NDE-system has been used for the inspection and imaging of discontinuities and inhomogenities in different kinds of materials, such as coating variations on tissue, spot welds on steel, and air inclusions in metal plates and welds. The measurement system operates in either continuous or pulse mode at sound frequencies between 0.65 and 1.2 MHz. Air-coupled piezo-based transducers with matching layers are used to overcome the acoustic impedance gap with air. 相似文献
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A method of the experimental study of the diffraction of acoustic waves with the use of the maximum length sequences is described.
This method allows one to measure the pulse response of a system, which makes it a suitable instrument for a diffraction experiment.
As an example, the results of an observation of the edge waves appearing at the base of a cylinder at the normal incidence
of the acoustic waves were presented. The results of the measurements are compared with the results of the numerical simulation. 相似文献
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The chirped optical pulses undergoing self-focusing and splitting into multiple filamentation passing through a Kerr medium—carbon
disulfide (CS2) are studied experimentally and numerically. At the particular spatial position, modulation growth takes place from the experimental
result. The process of modulation growth with different pulsed chirp is analyzed. It is found that with the pulsed chirp increasing
(equal to the pulse width increasing), modulation growth of chirped optical pulses is delayed and the average input power
also increases. The simulation results are in agreement with the experimental results. 相似文献
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Enhanced pulse compression induced by the interaction between the third—order dispersion and the cross—phase modulation in birefringent fibres 总被引:1,自引:0,他引:1 下载免费PDF全文
In this paper,we report on the enhanced pulse compression due to the interaction between the positive third-order dispersion (TOD) and the nonlinear effect (cross-phase modulation effect) in birefringent fibres.Polarization soliton compression along the slow axis can be enhanced in a birefringent fibre with positive third-order dispersion,while the polarization soliton compression along the fast axis can be enhanced in the fibre with negative third-order dispersion.Moreover,there is an optimal third-order dispersion parameter for obtaining the optimal pulse compression.Redshifted initial chirp is helpful to the pulse compression,while blueshifted chirp is detrimental to the pulse compression.There is also an optimal chirp parameter to reach maximum pulse compression.The optimal pulse compression for TOD parameters under different N-order solitons is also found. 相似文献
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采用两段级联单模光纤对高阶孤子脉冲进行压缩。两段光纤具有不同的反常色散值,当高阶孤子脉冲在第一段光纤中获得最大程度压缩时,通过转换色散值不同的光纤,使压缩脉冲继续以高阶孤子的形式在第二段光纤中再次被压缩。每段光纤的长度都进行了优化,使得脉冲在每段光纤中都获得最大程度的压缩。基于非线性薛定谔方程,数值研究了初始啁啾对高阶孤子脉冲压缩的影响。研究结果表明,初始啁啾对高阶孤子脉冲的压缩有重要影响。与无初始啁啾时的情形相比,正的初始啁啾能增强每段光纤中脉冲的压缩效果,降低压缩脉冲的基座能量,而负初始啁啾的影响则相反。随着初始啁啾参量Cp的增大,脉冲在每段光纤中的压缩因子均增加,而基座能量、最优光纤长度均减小。 相似文献
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整形激光直接驱动准等熵压缩实验技术对新材料科学、冲击波物理、地球物理学研究等领域有重要意义. 设计特定的实验条件, 可以将材料压缩到冲击压缩和等熵压缩都无法达到的状态, 从而为材料研究提供新的技术途径. 介绍了在神光III原型装置上开展的直接驱动准等熵压缩实验, 对理论基础、实验靶型、实验结果、关键技术、实验特点和数据都进行了较详细的分析. 通过实验和相应的数据处理程序, 获得了加载面上压力超过400 GPa的数据, 这是目前国际上用激光直接驱动的方式获得的Al材料中最高的压力. 同时, 对经过LiF窗口获得的表观粒子速度与真实粒子速度的关系进行了分析, 获得了一条对表观粒子速度进行动态修正的曲线, 从而使粒子速度的计算更加准确. 对实验的改进方向进行了比较明确的分析. 所提供的数据和分析过程对该领域的研究人员有一定的参考价值. 相似文献
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设计一种电磁加载系统应用于分离式霍普金森杆实验装置,能够克服传统气压驱动的缺点,达到精确控制入射应力波的目的。通过对电磁加载技术的调研,了解不同加载方式的电压等级,确定低压加载方式;构建系统等效RLC回路,推导回路参数与入射应力波的函数关系。结合理论计算,利用有限元软件进行耦合场仿真,仿真发现放电线圈匝数对入射应力波的幅频特性影响较大,同时为了保证电磁能量的利用效率,需要保证感应线圈的厚度大于磁渗透深度,最后根据实验要求确定电磁加载系统各参数。按照加载系统参数搭建实验平台,进行霍普金森杆冲击实验,通过对入射应力波的测量,验证了理论计算及软件仿真的正确性。 相似文献