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1.
Song SP  Que PW 《Ultrasonics》2006,44(2):188-193
The noise suppression techniques with wavelet transform (WT) are widely used in non-destructive testing and evaluation (NDT&E), especially in ultrasonics. Complete reconstruction theory with hard or soft thresholds, reconstruction technique based on the singularities of noise and signal, matched filter with an impulse response, and optimal frequency-to-bandwidth ratio of wavelet technique have all been used to analyze ultrasonic signals for noise suppression. But a more simple and effective technique has been pursued for decades. This paper develops a new technique using WT for the right purpose. In this work, WT is treated as a band-pass filter whose central frequency and frequency bandwidth (CF&FB) are determined by the spectra distribution of an ultrasonic signal captured from real testing situation. For the purpose of matching their CF&FB well, a technique for evaluating the optimal scale of a daughter wavelet is carried out too. By acting this daughter wavelet as a band-pass filter, we can obtain excellent de-noising results, even when the signal to noise ratio (SNR) is below -18 dB. The performance of the technique has been done by ultrasonic signals with computer generated white noises. Finally, the experimental verification is performed on a pipeline specimen with man-made small flaws with good results obtained. The results show that the technique is more suitable for processing heavy noised ultrasonic signals, and it can also be used in automatic flaw detection.  相似文献   

2.
Vicen R  Gil R  Jarabo P  Rosa M  López F  Martínez D 《Ultrasonics》2004,42(1-9):355-360
Structure noise from inhomogeneous micro-structures makes the detection of flaws present in highly scattering materials difficult. Several techniques have been applied to improve the signal-to-noise ratio (SNR) in order to make flaw detection easier. Linear filtering does not provide good results because both structure noise and flaw signal concentrate energy in the same frequency band. Non-linear filtering can be used to reduce the structure noise of ultrasonic signals. Therefore, neural networks are applied in this work for this purpose. In order to use neural networks for non-linear filtering, dynamic structures must be applied. The easiest way to implement a neural network with the capability of processing temporal patterns is to consider them spatial ones, applying the signal into a tapped delay line of finite extension, that is the input of a static neural network (for example, a multi-layer perceptron). In this work, a dynamic neural network has been built to filter ultrasonic signals with structure noise, and has been trained with the real-time back-propagation algorithm, using as inputs 3000 synthetic ultrasonic signals of 896 samples each. Target signals for training are the same as the ones used as inputs but without noise. The neural network is trained in order to generate as output the target signal when the noisy input one is applied. For testing the performance of the non-linear filter, a new set of 500 noisy signals has been used. The SNR improvement is about 6 dB average. The results show that this non-linear filtering method is quite useful as pre-processing stage in flaw detection systems.  相似文献   

3.
We have developed a fetal movement monitoring system based on small displacement measurement of internal tissues. When ultrasonic pulses are transmitted to the fetus, the reflected ultrasonic waves which have a Doppler frequency shift due to the fetal movements are detected by using an ultrasonic pulsed Doppler technique. In this paper, we propose a displacement measurement method for internal tissues which is based on the Doppler signal digital detection technique. In the method, the received ultrasonic RF signals are sampled with a sampling frequency of four times higher than the centre frequency of the ultrasonic waves; the Doppler frequency shift signals are derived using digital signal processing. From the detected signals, the internal displacements are estimated using the arc-tangent method. The basic algorithm of the detection method has already been used in the area of blood flow sensing, however, we apply the algorithm to the displacement measurement of internal tissues. The comparison between the proposed method and the conventional method is presented. The fetal movement quantitative monitoring system based on the method which has been constructed is shown.  相似文献   

4.
一种强噪声背景下微弱超声信号提取方法研究   总被引:1,自引:0,他引:1       下载免费PDF全文
王大为  王召巴 《物理学报》2018,67(21):210501-210501
为解决在强噪声背景下获取超声信号的难题,基于粒子群优化算法和稀疏分解理论提出一种强噪声背景下微弱超声信号提取方法.该方法将降噪问题转换为在无穷大参数集上对函数进行优化的问题,首先以稀疏分解理论和超声信号的结构特点为依据构建了粒子群优化算法运行所需要的目标函数及去噪后信号的重构函数,从而将粒子群优化算法和超声信号降噪联系在一起;然后根据粒子群优化算法可以在连续参数空间寻优的特点建立了用于匹配超声信号的连续超完备字典,并采用改进的自适应粒子群优化算法在该字典中对目标函数进行优化;最后根据对目标函数在字典上的优化结果确定最优原子,并利用最优原子按照重构函数重构出降噪后的超声信号.通过对仿真超声信号和实测超声信号的处理,结果表明本文提出的方法可以有效提取信噪比低至-4 dB的强噪声背景下的微弱超声信号,且和基于自适应阈值的小波方法相比本文方法表现出更好的降噪性能.  相似文献   

5.
长骨中振动声激发超声导波的方法   总被引:1,自引:0,他引:1       下载免费PDF全文
刘珍黎  宋亮华  白亮  许凯亮  他得安 《物理学报》2017,66(15):154303-154303
为了实现一定频段内任意低频下在长骨中激励导波信号,本文提出一种采用聚焦高频(5 MHz)超声换能器在长骨皮质骨中激发低频(150 kHz)超声导波的振动声方法.首先介绍了板状超声导波理论和双声束共聚焦法与单声束调幅法激发振动声的基本原理;进而采用三维有限元仿真方法分析振动声激发低频超声导波的基本现象,然后结合牛胫骨板离体实验,验证振动声激发低频超声导波的可行性.结果均表明,双声束共焦与单声束振动超声均可在骨板中激发低频超声导波.相关研究方法有助于提高空间域长骨中超声导波测量精度,以及在一定频段内实现任意频率激励等,对发展低频超声导波在体测量长骨皮质骨的新技术具有一定的指导意义.  相似文献   

6.
多通道超声兰姆波检测板状结构中的裂纹   总被引:1,自引:1,他引:0       下载免费PDF全文
张正罡  刘丹  他得安 《应用声学》2015,34(3):189-194
超声兰姆(Lamb)波在结构缺陷检测方面愈来愈受到重视,但目前Lamb波的应用局限于单信号源激励,单通道接收的方法,容易受到噪声干扰,其后续的信号分析处理也比较复杂。本文旨在采用多通道Lamb波对板状结构中的裂纹进行定量分析与诊断。在铝板的表面凿刻出不同深度的凹槽作为裂纹,通过线阵换能器采集在一定传播距离内的多通道Lamb波信号,并采用二维傅里叶变换分析在不同深度的裂纹下,Lamb波模式能量的变化规律。结果表明,相对于完好铝板中的Lamb波信号,裂纹的存在会使Lamb波发生模式转换现象,并且转换模式能量百分比随裂纹深度的增加而线性增加。其结果为Lamb波评价板状结构中的裂纹状况提供了一种可能的方法。  相似文献   

7.
Buffer rods (BR) as waveguides in ultrasonic time domain reflectometry (TDR) can somewhat extend the range of industrial applications of ultrasonics. Level, temperature and flow measurements involving elevated temperatures, corrosive fluids and generally harsh environments are some of the applications in which conventional ultrasonic transducers cannot be used directly in contact with the media. In such cases, BRs with some design modifications can make ultrasonic TDR measurements possible with limited success. This paper deals with TDR in conjunction with distance measurements in extremely hot fluids, using conventional ultrasonic transducers in combination with BRs. When using BRs in the ultrasonic measurement systems in extreme temperatures, problems associated with size and the material of the buffer, have to be addressed. The resonant frequency of the transducer and the relative size of the transducer with respect to the diameter of BR are also important parameters influencing the signal to noise ratio (SNR) of the signal processing system used in the ultrasonic TDR. This paper gives an overview of design aspects related to the BRs with special emphasis on tapers and cladding used on BRs. As protective cladding, zirconium oxide–yttrium oxide composite was used, with its proven thermal stability in withstanding temperatures in rocket and jet engines up to 1650 °C. In general a BR should guide the signals through to the medium and from and back to the transducer without excessive attenuation and at the same time not exacerbate the noise in the measurement system. The SNR is the decisive performance indicator to consider in the design of BR based ultrasonic TDR, along with appropriate transducer, with suitable size and operating frequency. This work presents and analyses results from extensive experiments related to fine-tuning both geometry of and signals in cladded/uncladded BRs used in high temperature ultrasonic TDR with focus on overall performance based on measured values of SNR.  相似文献   

8.
陈晓  汪陈龙 《物理学报》2014,63(18):184301-184301
为降低噪声对超声兰姆波检测信号的影响,提高信噪比和增加特征提取的精度,提出了一种赛利斯模型下分数阶微分方法用于超声兰姆波信号去噪.该方法对含噪声的兰姆波信号幅值谱进行各阶分数微分,用赛利斯分布作为待处幅值谱的模型,提出了幅值谱分数阶微分最大值和过零点与微分阶数的拟合三次关系式,建立了幅值谱特征参数的计算式来提取特征参数和重建原始信号的幅值谱,并结合相位谱重构去噪后的兰姆波信号.仿真结果表明,该方法可以有效地提高兰姆波信号甚至微弱兰姆波信号的信噪比,同时降低均方误差和平滑度.实验结果显示,与小波去噪和集合经验模态去噪方法相比,该方法在没有信号先验知识的情况下,可以更有效地去除兰姆波信号的噪声,同时更好地保留主信号的细节特征.因此,本文提出的方法可以有效地去除兰姆波检测信号中混入的噪声.  相似文献   

9.
The ultrasonic signals in long bones contain multiple guided modes which are mutual superposed.The velocities of guided waves in long bones are very sensitive to cortical thickness (CTh).In this paper,Hilbert-Huang transform(HHT) was proposed to analyze multi-mode guided waves,which can decompose superposed waves into many independent modes.Then the group velocity of each mode was obtained at corresponding frequency,which was compared with the results of short time Fourier transform(STFT).The CTh was also obtained by comparing with the theoretical calculation.The results showed that the experimental determined thickness was in agreement with the actual CTh,indicating that measuring the velocity of the guided mode can be used to estimate the CTh.The HHT is an effective method to identify multimode guided waves.  相似文献   

10.
王大为  王召巴  陈友兴  李海洋  王浩坤 《物理学报》2019,68(8):84303-084303
信号降噪与特征提取是超声检测数据处理的关键技术.基于超声信号有特定结构而噪声和超声信号的结构无关,本文提出一种旨在解决强噪声背景下超声回波的参数估计和降噪问题的方法.该方法将超声回波的参数估计和降噪问题转换为函数优化问题,首先根据工程经验建立超声信号的双高斯衰减数学模型,然后根据观测回波和建立的超声信号模型确定目标函数,接着选择人工蜂群算法对目标函数进行优化从而得到参数的最优估计值,最后由估计出的参数根据建立的超声信号数学模型重构出无噪的超声估计信号.通过仿真和实验表明本文方法可以准确估计出信噪比大于-10 dB的含噪超声回波中的无噪信号,且效果优于基于自适应阈值的小波降噪方法和经验模态分解方法;此外相比常用的指数模型和高斯模型,本文提出的双高斯衰减超声信号模型与实测超声信号更接近,其均方误差为9.4×10~(-5),波形相似系数为0.98.  相似文献   

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