双频超声交替强化超临界流体萃取装置的设计与应用

本文针对超临界流体萃取（SFE）系统设备的特点，设计丁可用于强化SFE过程的双频超声波交替强化装置。以香椿叶中黄酮类化合物为提取对象，对超声强化USFE过程的影响因素及强化效果进行了实验研究，结果表明；低频超声利于提取，频率为20kHz的超声强化的萃取率最大，38kHz的超声最小，两者交替的居于中间。     

A novel optical subdivision method for dual-frequency interferometer

The theory of optical subdivision techniques of dual-frequency laser interferometers is stated. And a novel optical subdivision technique is proposed originally to enhance resolution of a commercial interferometer by adding some corner-cubes. Then the performance of the interferometer is tested. The interferometer resolution of 1.24 nm and the average error of below 2 nm are achieved by using the technique. The most novel of the optical subdivision technique is without λ/4 plates. It is less sensitive to environmental changes, it has prodigious potential to improve resolution farther and it can reduce polarization mixing error.     

An experimental test of the dual-frequency method for monitoring transverse currents

The dual-frequency method for monitoring the transverse component of the velocity of current is tested using the data obtained earlier in a tidally forced flow through a channel. The turbulent properties of the flow cause fluctuations in the acoustic signals propagating through it. The fluctuations of such signals emitted at two different frequencies are coherent in the low-frequency band and noncoherent in the high-frequency region of the spectrum. The frequency separating these spectral regions is determined as the cutoff frequency of the coherence function and is directly related to the component of the current in the direction perpendicular to that of signal propagation. The results of measuring this component of the current are consistent with the data obtained with other independent methods and measurements. Published in Russian in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 2, pp. 269–274. The article was translated by the authors.     

Effect of slit dual-frequency ultrasonic emulsification technology on the stability of walnut emulsions

A highly hygienic walnut emulsion beverage was prepared by using a slit dual-frequency emulsification technique. The optimal ultrasonic parameters were studied as a model system: the ultrasonic time of 50 min, the ultrasonic power density of 260 W/L, and a dual-frequency ultrasonic combination of 28/68 kHz. Walnut emulsion with an average mean volume diameter of 2.05 µm, a Zeta potential absolute value of 40 mV was obtained after ultrasonic treatment, and the emulsion stability could be maintained for more than 14 days without phase separation. At the lowest ultrasonic energy input, the vibrating emulsion could promote droplet aggregation. However, excessive energy input could result in sample overtreatment and reduced emulsion activity. The laser scanning confocal microscope (LSCM) and transmission electron microscope (TEM) confirmed that walnut emulsion processed by slit dual-frequency ultrasonic had pretty high stability. Therefore, the slit dual-frequency ultrasonic emulsification technique was found to be well suited for the preparation of complex and fine oil-in-water food emulsions.     

双频氦氖激光回馈位移测量系统的实验与应用研究

研究了一种全新的纳米尺度位移测量系统。将双折射元件插入He-Ne激光器谐振腔内产生频率分裂效应，使原本单模谐振的激光器输出变成了频差可调的2个正交偏振频率（o光和e光），而形成双频激光器。在激光谐振腔外放置沿激光轴线位移的反射表面，将输出的激光束反射回腔内，以便对激光的光强进行调制，可实现高分辨率非接触式可判向位移测量。提出了一种细分方法，该方法突破了传统干涉系统的衍射极限（1/2波长）。对于633nm波长He-Ne激光，本系统的理想分辨率为1/8波长（约为79nm）。     

Acousto-optic method for ultrasonic pulse characterization

The light distribution in a diffraction pattern produced by a sequence of ultrasonic pulses depends on a number of parameters characterizing the pulse shape, modulation and sequencing as well as changes in the spectral composition due to non-linearities in the propagation medium. Based on calculations of such light diffraction patterns it is possible to consider the inverse problem, i.e. the determination of parameters mentioned above by evaluating certain features of the diffraction pattern produced by the pulses. A number of examples are given to illustrate these possibilities.     

超声波波长数据的处理方法

对文献[1]中超声波波长的数据进行重新处理,对振幅的B类不确定进行补充,并排除了数据中的高度导常值,介绍了更合理的用逐差法处理波长数据的标准公式,使对波长的不确定度评定更合理.     

The performance and design of ultrasonic vibration system for flexural mode

The matrix method for analyzing flexural vibration system is outlined. The displacement, stress and velocity gain of ultrasonic flexural vibration systems are investigated by transfer matrix method. A design method is given for flexural transducer and vibration system.     

一种测量功率超声振动系统振速比的简单方法

本文提出了一种测量功率超声振动系统中振动速度比的简单方法。与传统的测量方法相比,本方法将力学量转变为电学量的测量,将绝对测量变成了相对测量,降低了对实验设备的要求,有利于提高测试精度。     

模式转换型超声塑焊振动系统的设计

基于弯曲振动理论和耦合振动理论,设计了一种新型大尺寸筒形超声塑焊振动系统。该振动系统由纵向振动换能器及变幅杆、弯曲振动金属圆盘和耦合振动圆筒四部分组成。换能器和变幅杆的纵向振动驱动圆盘的二次弯曲模式振动,圆盘的二次弯曲模式振动激励圆筒的纵向模式振动,实现了工具头在较高频率下谐振。实验结果表明,振动系统的测试频率与计算频率比较符合,在大信号下测试的纵-弯-纵振动模式转换效果很好。研究结果为高频大尺寸超声焊接系统的设计提供了思路。     

Air-coupled ultrasonic assessment of wood veneer

Air-coupled ultrasound (ACU) provides a tool to evaluate wood samples of small or moderate thickness (<30 mm) thereby avoiding direct contact or liquid coupling. Results of through-transmission ACU measurements on wood veneer samples and related products are reported with respect to a wide variety of quality aspects. Fluctuations in the averaged received signal levels appear to be correlated to the presence of natural or machine-induced thickness and density variations, flaws and grain damage, errors produced by the manufacturing process, insufficient bonding on a substrate, etc. In addition it is seen that the variability of the signal levels enables to distinguish between quarter and crown areas.     

Precise force measurement method by a Y-shaped cavity dual-frequency laser

A novel precise force measurement based on a Y-shaped cavity dual-frequency laser is proposed.The principle of force measurement with this method is analyzed,and the analytic relation expression between the input force and the change in the output beat frequency is derived.Experiments using a 632.8-nm Y-shaped cavity He-Ne dual-frequency laser are then performed;they demonstrate that the force measurement is proportional to a high degree over almost five decades of input signal range.The maximum scale factor is observed as 5.02×109 Hz/N,with beat frequency instability equivalent resolution of 10-5 N.By optimizing the optical and geometrical parameters of the laser sensor,a force measurement resolution of 10-6 N could be expected.     

A time-resolved method for nonlinear ultrasonic measurements

We describe a time-resolved method for measuring nonlinear ultrasonic phenomena. Current approaches rely on a narrowband measurement of harmonic generation to identify and characterize nonlinearity. Concomitant with these techniques is poor time resolution. We address this limitation with a hybrid narrowband/broadband approach that provides simultaneous time resolution and harmonic isolation for the measurement of weak nonlinearites. We discuss applications and present demonstrative results showing harmonic generation both in water and at a dry contact aluminum-aluminum interface.     

双反射膜双频He-Ne激光器双频特性及偏振特性的实验研究

本文对 5 MHz频差双反射膜双频 He- Ne激光器输出激光的双频特性及偏振特性进行了实验研究。研究结果表明 ,当磁场方向同反射膜的一个本征模方向基本重合时 ,有双频出现 ;当磁场方向同反射膜的一个本征模方向夹角在 45°左右时 ,无双频出现。输出激光的偏振方向由反射膜的本征模确定 ,其偏振非正交程度为 tgρ≤ 0 .0 0 87,椭圆化程度tgβ随激光管与磁场的相对角位置变化而发生变化。在合适的位置 ,tgβ可以小至 2 / 70 0。该种外差光源具有较好的偏振特性。     

Accuracy optimization method of ultrasonic power measurement system based on acousto-optic effect

Optical Review - Ultrasonic wave has been widely used in the medical field because of its special physical properties. However, it might cause health risk for the human body if the power is...     

固-固界面退化特性的超声反射评价方法

提出了一种基于有限宽超声束反射的固-固界面退化特性评价方法,从理论和数值仿真角度进行了分析和计算。将两固体界面间的薄层简化为界面弹簧模型,以界面法向和切向劲度系数表征界面的退化程度。通过数值计算求得有限宽超声纵波束在不同入射角和界面不同退化程度下的反射横波、反射纵波的镜面反射系数。进一步地,通过建立二维有限元模型,仿真研究了有限宽超声纵波束在给定入射角及界面不同退化程度下镜面反射系数的变化规律。结果表明,反射纵波和反射横波的镜面反射系数随有限宽超声纵波束的入射角及界面劲度系数的改变而变化,且存在镜面反射系数随界面劲度系数单调且敏感变化的入射角,据此可准确评价界面的退化程度。     

超声全聚焦成像中等声程线伪影剔除方法

针对超声全聚焦成像算法中等声程线扩散产生的原理性伪影问题,提出了一种基于超声回波声场有效等声程线和图像强度分布特征相结合的伪影剔除方法。首先分析了全聚焦成像算法中等声程线产生伪影的机理,根据数据均方根误差自适应辨识有效等声程线;通过Canny算子获取全聚焦图像待处理候选区域,再根据候选区域中有效等声程线相交次数和图像强度的分布特征辨识缺陷图像和伪影,利用图像中强度最低像素值扩展填充剔除伪影后的区域,进而达到剔除伪影的目的。通过在不同直径通孔类和槽类标准缺陷试块上声场模拟实验,结果表明伪影剔除效果显著。同时,该方法对噪声也有一定的抑制能力,在不加滤波的条件下信号信噪比高于15 dB时就可获得较好的去伪影效果。     

松质骨超声背散射信号的谱信息熵判断方法

在松质骨超声背散射评价的实际应用中,如何快速准确地判断接收到的信号中是否包含有效背散射信号是一个重要问题。提出一种基于谱信息熵的背散射信号判断方法。对在体采集的984例成人跟骨处临床数据,采用该方法判断背散射信号的有效性,将判断结果与经验判断结果进行对照分析,并分析该方法中的信号区间长度和谱信息熵分段数对判断结果的影响。结果表明,当信号区间长度为13μs,谱信息熵分段数为15~20时,该方法可以获得最佳的判断结果(准确度〉95%,灵敏度〉99%,特异度〉87%),并且计算时间极短(1.5 ms)。因此采用谱信息熵方法判断背散射信号的有效性,可以满足超声骨质评价中对准确性和实时性的要求。     

弯折波导杆的超声斜入射方法*

波导杆技术是一种有效的超声辅助检测方法,在提升高温关键承压设备安全运行方面具有重要作用。现有的波导换能器因直入式发射声波,常被用来在线监测壁厚的腐蚀进程,难以对指定方向的缺陷进行有效检测。为了解决这个难题,基于斯涅耳定理以及导波的频散特性提出了一种弯折结构的波导杆来实现超声斜入射。首先分析了弯折波导杆中水平剪切波的传播特性,探究了波导杆的厚度、弯折角度对杆中声波传播的影响规律;然后,进一步研究了弯折波导杆在半无限空间内的声束指向性;最后通过一对弯折波导杆在线检测结构内部缺陷的试验证明了波导超声斜入射的应用价值。研究结果为基于斜入射技术的波导超声在线监测提供了坚实的理论基础。     

The spectrum entropy estimation method for ultrasonic backscattering signal in cancellous bones

In the application of cancellous bone ultrasound diagnosis based on backscattering method,it is of great importance to estimate fast and accurately whether the valid backscattering signal exists in the received signal.We propose a fast estimation method based on spectrum entropy method.With 984 records of adult calcaneus clinical data,we estimate the validity of the backscatter signal using this method.The results of the proposed method and the results of experience-base judgement were compared and analyzed.And two key parameters,the signal range length and the segment number of the spectrum entropy,were analyzed.The results show when the signal range length is 13 us and the segment number is 15-20,this method can get the best result(accuracy95%,sensitivity99%,specificity87%),while taking little calculation time(1.5 ms).Therefore,this spectrum entropy method can satisfy the accuracy and real-time requirements in the ultrasonic estimation for cancellous bone.