基于GPU的超声弹性成像并行实现研究

为了提高超声弹性成像计算速度,提出使用GPU硬件加速基于互相关技术和相位零估计的弹性成像技术。先描述这两种弹性成像技术的实现细节及特点,然后分析这两种技术的计算密集操作部分的并行化计算可能性,最后通过GPU程序开发工具ArrayFire实现了基于GPU的互相关和相位零估计的超声弹性成像技术。通过模拟和扫描仿真人体组织的弹性成像体模获得的压缩前后数据帧对基于GPU的超声弹性成像方法进行测试与验证。实验结果表明,基于GPU的方法可以大幅提高弹性图计算速度,在处理单帧弹性图条件下,与基于互相关方法比较,加速比达到42,而基于相位零估计的方法在提高数据吞吐量的情况下加速比可达到65。     

相位噪声标准的研制

为解决相位噪声测量系统校准无法溯源的问题,设计一套相位噪声标准系统,把相位噪声溯源到可调高斯白噪声源上。该系统可用来测试相位噪声测量系统的准确度及其本底噪声,解决传统比对方法各相位噪声测量系统之间精度较低的问题。利用不同频点的带通滤波器对相位噪声测试系统PN9000在5,10,100 MHz频点下的相位噪声测量结果进行校准,验证方案和整套系统的准确性。     

相位噪声标准的研制

为解决相位噪声测量系统校准无法溯源的问题,设计一套相位噪声标准系统,把相位噪声溯源到可调高斯白噪声源上.该系统可用来测试相位噪声测量系统的准确度及其本底噪声,解决传统比对方法各相位噪声测量系统之间精度较低的问题.利用不同频点的带通滤波器对相位噪声测试系统PN9000在5,10,100 MHz频点下的相位噪声测量结果进行校准,验证方案和整套系统的准确性.     

微波、毫米波相位噪声测试系统的研制

提出了首先对微波、毫米波信号进行下变频,再利用锁相环提取被测试信号相位噪声的相位噪声提取方法,采用现代谱分析技术对提取出的相位噪声信号在频率中进行分析,并利用"反卷积"技术实现测试系统的误差校正,研制实现了微波、毫米波相位噪声测试系统.实验测试结果表明该系统具有测试灵敏度高和被测信号频率范围广的优点,证明了它具有较大的应用价值.     

一种原子钟频率稳定度的估计方法

为了更合理地评估处于相同实验条件下原子钟的绝对频率稳定度,以理论视角分析了算法模型及求解过程,研究了噪声相关条件下绝对频率稳定度的估计方法。用3台原子钟仿真数据对该方法进行了评定,假设噪声独立条件下随着噪声相关性的增强测试结果不断偏离频率稳定度真值;考虑噪声相关条件下测试结果与频率稳定度真值相对误差不超过1.7%。该方法被进一步应用到中国计量科学研究院实验室4台铯原子钟,360天实际测量数据验证了其有效性。     

高速扫频OCT消伪影算法

扫频光学相干层析成像(swept source optical coherence tomography,SSOCT)是一种新型的基于傅里叶变换的医学成像技术.为了抑制SSOCT图像中的直流噪声、寄生项以及由傅里叶变换产生的伪影项,提出单次相位变化方法,设计并搭建了SSOCT成像系统,轴向扫描速度可以达到50 k Hz.利用该系统对3层玻璃片进行成像,干涉信号经过该方法消伪影处理后,玻璃片成像的信噪比提高了18.22 d B,同时成像深度增加为原来的2倍,证明该方法可以提高低浑浊介质的成像质量.     

振动条件下的晶振稳健性机理研究

晶振在振动环境下产生严重的相位噪声恶化,由于其多学科交融的物理性质和在电子系统参考源中的应用价值而受到广泛关注。随着机电一体化设计理念的发展,研究振动环境下的信号调谐模式和探索它们独特的物理性质已经成为可能。该文从晶振的工作原理出发,分析了振动条件下相位噪声恶化的调谐原理,首次提出了一种新的晶振相位噪声振动恶化特征的物理表征方法。此外,搭建了晶振相位噪声测试系统,利用实验数据定量研究了各种输入条件对晶振电气性能的影响,并编制了相应的算法来进行求解,得出了非线性数学关系。最后,结合实验数据验证了机电一体化分析思路及物理表征方法的合理性,得到了晶振模块的振动稳健性矢量。     

相位噪声测试结果的分析与应用

本文简单介绍了相位噪声测量的各种方法,主要对相位噪声测试结果的正确分析与应用方法进行了介绍,并就工程技术人员关心的相位噪声与阿伦方差和时域抖动的换算方法进行了描述。     

基于相位翻转的超声波风速风向测量EI北大核心CSCD

针对超声波测风中由于噪声影响收发时刻点不易确定导致测量精度不高的问题,提出了一种基于超声波相位翻转的风速风向测量方法。所提方法采用依据相对时差法的对射式阵列测风结构,通过改变超声波发射信号的相位,即在某一时刻使得超声波信号发生相位翻转标记为超声波发射信号时刻点,随后采用锁定放大器对接收的超声波信号进行处理,利用相敏检波器对相位的敏感特性以及对噪声较强的抑制能力,可准确地获得超声波接收信号相位翻转之处,并将其标记为接收信号时刻点。最后通过测量两个时刻点之间的超声波传播时间计算得到风速分量,进而可得实际的风速风向值。通过模拟仿真试验和实测数据验证了所提方法的可行性和有效性,试验结果表明所提方法在高斯噪声或与非高斯冲击噪声混合背景下均具有良好的测量性能,与阵列式测风法及相关法相比具有更高的测量精度。     

某型吸油烟机的振动和噪声源辨识

对某型吸油烟机进行振动和噪声测试与分析,目的是找出该机型的主要振动和噪声源。根据国家标准,在半消声室条件下,采用传声器和振动加速度计等精密仪器对其振动和噪声进行测量,并采用频谱分析等手段分析了测量数据,找出了主要的噪声源,并对产品设计提出了改进意见。     

对道路声屏障声学设计公式的讨论

一些行业标准推荐的声屏障绕射声衰减量计算公式含有严格的适用条件,从而限定公式的使用范围,可能不宜直接应用于道路声屏障的工程设计。为此,提出几点改进建议：（1）对存在反射地面的情况,建议采用虚声源和虚受声点的普适计算方法;（2）对声源和受声点都接近刚性地面的情况,介绍相应的绕射声衰减计算公式;并在点声源公式中对大菲涅尔数区段另行表述,以明确反映实际屏障存在的绕射声衰减限值;（3）应用虚声源概念计算双屏障的反射声修正量。计算实例不仅佐证这些建议的合理性,同时得到一些规律性的结果：（1）地面反射将增加受声点的声压级,减小屏障的绕射声衰减量;当声源和受声点都接近刚性地面时,受声点的声压级在无屏障时增加3 dB,有屏障时增加6 dB,屏障的绕射声衰减量减小3 dB。（2）对于点声源和线声源,不论是否存在地面反射,双屏障的反射声修正量基本相同,且随着屏障内壁吸声系数的增加而同步减小。     

基于图像处理的声相云图评价方法研究

基于图像处理,提出了声相云图评价方法,用于评价声相仪的声源定位误差。分析了声相仪的成像原理,提出将方位角误差和俯仰角误差作为声相云图声源定位误差的评价指标。利用差影法提取声相云图的声源定位成像区域,并经过灰度二值化、腐蚀膨胀和加权平均之后,计算出成像区域中心的像素坐标。在声相仪不同抓拍距离平面内,通过图像标定得到成像区域中心在实际物理空间上的位置坐标,将其与所定位的声源实际位置坐标相比较,计算得到方位角误差和俯仰角误差。实验结果表明,该方法所得方位角和俯仰角与声源实际位置坐标计算所得到的真实值相比,两者差异较小,能够客观地对声相仪的声源定位误差进行评价,且操作简单。     

Using the synthetic aperture focusing technique with velocity responses to detect the defects inside reinforced concrete structures

In civil engineering, imaging can be a useful non-destructive testing (NDT) tool for revealing defects in a concrete structure. To date, there is no effective method for imaging the defects inside in situ concrete structures. In this study, a new elastic wave-based NDT method has been developed and then applied to reveal the defects inside concrete specimens using an imaging method. This method integrates the point-source/point-receiver method with the synthetic aperture focusing technique (SAFT) to achieve a scanning effect when using a phase array system. This method operates with a large functioning depth because the transient elastic wave method possesses a high-energy feature, whereas the traditional ultrasonic method does not. As an alternative to using displacement responses, this method uses velocity responses to construct the SAFT image. Based on the numerical simulation and the experimental results, using the proposed method allowed a high image quality to be produced and successfully revealed defects underneath a layer of rebars. The results of this study indicate the great potential for using the elastic wave-based imaging method to inspect defects in situ concrete structures.     

Quantitative metallography of sigma phase precipitates in AISI 347 stainless steel – a comparison between different methods

Abstract

A reliable method to perform volume fraction measurements of sigma (σ) phase in a niobium stabilised steel (AISI 347) has been developed. The most accurate results of the tested methods were obtained using backscattered electrons in a scanning electron microscope (SEM) and samples etched with oxalic acid. Both optical microscopy (OM) and SEM either on polished samples or on etched samples have been evaluated to come to this conclusion. Several etchants were also tested and careful etching with oxalic acid gave a well defined rim. The measurement of σ-phase fraction has been performed using manual point counting and digital image analysis using manual threshold. It was concluded that image analysis is usually to be preferred since it is faster and also results in higher precision The phase boundary caused by etching was evaluated, and it was found that the boundary area should be included in the measurement when using the recommended SEM method.     

Optical detection of evanescent ultrasound waves in water

Acoustical perturbation by targets smaller than the wavelength can generate evanescent waves, which decay with the distance of propagation. By putting such targets immediately under the free surface of water, the diffracted acoustical field can excite the surface membrane before evanescence, and it produces a static ripple because of the radiation pressure. A collimated beam of light reflects at the perturbed surface, and it becomes modulated in phase. In this work we show experimental results where we achieve an optical image of the acoustical evanescent waves produced by an array-like target. Arising from the theory, we present a numerical calculus of the optical image produced by the ultrasonic field diffracted from the target in order to verify the experimental results. With this method, we look for a spatial resolution smaller than acoustical wavelength, for normal incidence and plane waves. In our experimental device, we use a sound wavelength in water greater than 1.5 mm, generated by a PZT transducer. We can resolve an array of 1.0 mm of periodicity.     

调频信号发射超声成像的参数优化与成像实验

研究调频信号发射超声成像中影响成像质量的各种参数,提高现有超声图像的信号噪声比.用仿真计算和声学实验来研究不同调频超声信号发射参数下的成像质量.增加超声发射能量,提高图像的信号噪声比;同时,采用相关算法对接收的超声信号解码,保证图像的轴向精度不会下降.优化了调频信号发射超声成像的发射参数,并得到了仿体的B型超声图像,此图像的质量优于传统成像方法的图像质量.该成像方法能够提高超声图像的信号噪声比,尤其是提高超声衰减严重的深部组织图像的信号噪声比.     

X-ray phase-contrast imaging: transmission functions separable in Cartesian coordinates

In-line, x-ray phase-contrast imaging is responsive to both phase changes and absorption as the x radiation traverses a body. Expressions are derived for phase-contrast imaging of objects having transmission functions separable in Cartesian coordinates. Starting from the Fresnel-Kirchhoff integral formula for image formation, an expression is found for the phase-contrast image produced by an x-ray source with nonvanishing dimensions. This expression is evaluated in limiting cases where the source-to-object distance is large, where the source acts as a point source, and where the weak phase approximation is valid. The integral expression for the image is evaluated for objects with simple geometrical shapes, showing the influence of the source dimensions on the visibility of phase-contrast features. The expressions derived here are evaluated for cases where the magnification is substantially greater than one as would be employed in biological imaging. Experiments are reported using the in-line phase-contrast imaging method with a microfocus x-ray source and a CCD camera.     

Improved emission uniformity from a liquid-jet laser-plasma extreme-ultraviolet source

Many modern compact soft-x-ray and extreme-ultraviolet (EUV) imaging systems operate with small fields of view and therefore benefit from the use of small high-brightness sources. Such systems include water-window microscopes and EUV lithography tools. We show that the photon losses in such systems can be minimized while uniformity of object-plane illumination is maintained by controlled scanning of the source. The improved collection efficiency is demonstrated both theoretically and experimentally for a scanned laser-plasma source compared with static sources. A prospective aerial image microscope and a liquid-xenon-jet laser-plasma source are offered as examples of modern imaging tools that may benefit from such scanning of the source.     

Real-time heterodyne imaging interferometry: focal-plane amplitude and phase demodulation using a three-phase correlation image sensor

A method of real-time heterodyne imaging interferometry using a three-phase correlation image sensor (3PCIS) is proposed. It simultaneously demodulates the amplitude and phase images of an incident interference pattern at an ordinary frame rate with good accuracy, thus overcoming the trade-off among measurement time, spatial resolution, and demodulation accuracy suffered in conventional interferometry. An experimental system is constructed with a 64x64 3PCIS camera operated at 30 frames/s and a two-frequency He-Ne laser with a beat frequency of 25 kHz. The results obtained for a scanning mirror and heated silicone oil confirm the proposed method.     

Warped basis pursuit for damage detection using lamb waves

This paper presents a novel time-frequency procedure based on the warped frequency transform (WFT) to process multi-mode and dispersive Lamb waves for structural health monitoring (SHM) applications. The proposed signal processing technique is applied to time waveforms recorded at an array of scan points after waveguide excitation. The WFT is combined with a basis pursuit algorithm to extract the distance traveled by the ultrasonic waves even in the case of multi-modal dispersive propagation associated with broadband excitation of the waveguide. This is obtained through a decomposition of the acquired signals using dictionaries composed by optimized atomic functions which are designed to match the spectro-temporal structure of the various propagating modes. The warped basis pursuit (W-BP) analysis of several acquired waveforms results in distance signals that can be combined through classical beamforming techniques for acoustical source imaging purposes. A masking procedure is also proposed to suppress imaging noise. This approach is tested on experimental data obtained by broadband guided wave excitation in a 1-mm-thick aluminum plate with an artificially introduced through crack and tiny holes, followed by multiple waveguide displacement recording through a scanning laser Doppler vibrometer. Dispersion compensation, high-resolution source, and defect imaging are demonstrated even in domain regions that are not directly accessible for measurement.