Vocal Fold Impact Stress Analysis

Vocal fold impact stress (force/area) has been implicated as a factor possibly contributing to the formation of nodules and polyps. The force of impact of a moving body is related to its acceleration. Since the mass of the folds is relatively constant, one expects impact force to be directly proportional to acceleration. A measure that reflects the relative displacement of the vocal folds is photoglottography (PGG). The velocity and acceleration of the folds are easily obtained by calculating the first and second derivatives of the PGG displacement waveform. This study, therefore, compared the second derivative of the PGG signal with simultaneously measured impact stress in an excised canine larynx model. Glottal transillumination (PGG) was measured with a subglottic transducer. A miniature force transducer placed in the midline between the vocal folds measured impact stress at the midglottal position. For nine different larynges, there was a positive and linear relationship between the second derivative of PGG and impact stress. The statistically significant results support the hypothesis that the second derivative of PGG m ay provide a use fulnoninvasive way to estimate relative vocal fold impact stress.     

基于小波神经网络的振动速度传感器幅频特性补偿研究

为了实现超低频振动速度测量, 提出补偿其幅频特性的小波神经网络方法.该方法以振动速度传感器动态实验数据为基础, 通过小波神经网络训练来确定传感器幅频特性补偿网络.介绍振动速度传感器幅频特性补偿原理, 分析网络的拓扑结构, 给出网络参数训练和初始化方法.采用引入动量项的最速下降法训练网络权值、尺度因子和平移因子, 将小波网络参数的初始化与小波类型、小波时频参数和学习样本等联系起来.结果表明, 采用小波神经网络进行振动速度传感器幅频特性补偿具有良好的鲁棒性,并能实现在线补偿,网络训练的速度和精度优于同等规模的BP网络,在测试领域有重要的实用价值. 关键词： 振动速度传感器 小波神经网络 幅频特性 补偿     

On the effect of conductivity of a shock-compressed gas on interferometric recording of parameters of motion of a liner

We report on the results of a study of the acceleration dynamics of an aluminum liner to a velocity of 5.5 km/s using continuous recording of velocity (velocity interferometer system for any reflector (VISAR) and Fabry-Perot interferometer) and motion trajectory (radiointerferometer and resistive transducer) in air and in a helium atmosphere. It is found that for liner velocities exceeding 4.0 and 5.0 km/s, the displacement of the shock wave front is recorded by the radiointerferometer in air and helium, respectively. At these velocities, the conductivities of air and helium behind the shock wave front are estimated.     

基于飞秒光频梳的压电陶瓷闭环位移控制系统

利用飞秒光频梳、外腔可调谐半导体激光器和法布里-珀罗干涉仪建立了一套压电陶瓷亚纳米级闭环位移控制系统. 将可调谐半导体激光器锁定至光频梳, 通过精确调谐光频梳的重复频率, 实现了半导体激光器在其工作频率范围内的精密调谐. 利用Pound-Drever-Hall锁定技术将带有压电陶瓷的法布里-珀罗腔锁定至半导体激光器, 进而通过频率发生系统控制压电陶瓷产生亚纳米级分辨率的位移. 实验研究发现锁定至光频梳后可调谐半导体激光器1 s的Allan标准偏差为1.68×10^-12, 将其在30.9496 GHz范围内进行连续闭环调谐, 可获得压电陶瓷的位移行程约为4.8 μm; 以3.75 Hz的步长扫描光频梳的重复频率, 实现了压电陶瓷的450 pm闭环位移分辨率并测定了压电陶瓷的磁滞特性曲线. 该系统不存在非线性测量误差, 且激光频率及压电陶瓷位移均溯源至铷钟频率源. 关键词： 光频梳 压电陶瓷 法布里-珀罗腔 可调谐半导体激光器     

一种弯张换能器及其共振频率计算方法

提出一种弯张换能器即欧米伽换能器,推导出其共振频率和位移振形函数。把欧米伽换能器分成四个构成部分,利用旋转薄壳理论和压电理论分别求出各部分的能量并进行相加,得到整个欧米伽换能器能量的泛函表达式;把几何边界连续条件和包含待定系数的位移振形函数代入到欧米伽换能器能量泛函中,运用Rayleigh-Ritz法求出欧米伽换能器的共振频率,再把共振频率代入Rayleigh-Ritz偏微分方程和边界方程中求出位移振形函数的待定系数以获得确定的位移振形函数。该方法也被推广到对钹式换能器共振频率和位移振形函数的求解上。上述求解结果与实验结果和数值软件相结合论证了该方法的有效性。可获得以下结论:(1)欧米伽换能器陶瓷片的径向振动与金属端帽顶部的纵向振动同相,减少了声场中的反相分量,易作为低频换能器使用;(2)为解决欧米伽换能器和钹式换能器的优化设计提供了理论支持;(3)文中求解共振频率和位移振形函数的方法,即可以应用在由旋转薄壳组成的弯张换能器上也可以应用在由旋转薄壳组成的其它结构上,具有普遍性。      

Optimum vibration absorber (tuned mass damper) design for linear damped systems subjected to random loads

Optimum design of dynamic vibration absorbers (DVAs) installed on linear damped systems that are subjected to random loads is studied and closed-form design formulas are provided. Three cases are considered in the optimization process: Minimizing the variance of the displacement, velocity and acceleration of the main mass. Exact optimum design parameters for the velocity case, which to the best knowledge of the author do not exist in the literature, are derived for the first time. Exact solutions are found to be directly applicable for practical use with no simplification needed. For displacement and acceleration cases, a solution for the optimum absorber frequency ratio is obtained as a function of optimum absorber damping ratio. Numerical simulations indicate that optimum absorber damping ratio is not significantly related to the structural damping, especially when the displacement variance is minimized. Therefore, optimum damping ratio derived for undamped systems is proposed for damped systems for the displacement case. When acceleration variance is minimized, however, the optimum damping ratio derived for undamped systems is found not as accurate for damped systems. Therefore, a more accurate approximate expression is derived. Numerical comparisons with published approximate expressions at the same level of complexity indicated that proposed design formula yield more accurate estimates. Another important finding of the paper is that for specific applications where all of the response parameters are desired to be minimized simultaneously, DVAs designed per velocity criteria provide the best overall performance with the least complexity in the design equations.     

Analysis of the sandwich piezoelectric ultrasonic transducer in coupled vibration

The coupled vibration of the sandwich piezoelectric transducer with a large cross-section is analyzed using an approximate analytic method. The resonance frequency equations of the transducer are derived and the effect of the geometrical dimensions on the resonance frequency is studied. It is illustrated that when the radial vibration in the transducer is considered, the vibration of the sandwich transducer becomes more complex. Apart from the longitudinal resonance frequency, the radial resonance frequency can also be obtained. For comparison, numerical methods are also used to simulate the coupled vibration; the resonance frequency and the vibrational displacement distribution are computed. Compared with one-dimensional longitudinal theory, the radial dimensions of the transducer are no longer limited because the coupled vibration is considered. Compared with numerical methods, the physical meaning of the analytic method is concise. It is illustrated that the resonance frequencies obtained from the coupled resonance frequency equations are in good agreement with those from numerical methods, and they are in better agreement with the measured results than those from one-dimensional theory. Since the radial and the coupled vibration are considered in the analysis, more resonance frequencies can be obtained. Therefore, using the coupled resonance frequency equations, the sandwich transducer with multifrequency or wide frequency bandwidth can be designed and used in ultrasonic cleaning, ultrasonic sonochemistry and other applications.     

Investigations of the barbell ultrasonic transducer operated in the full-wave vibrational mode

In this paper, the resonance frequency equation and expression of displacement amplitude magnifications of a full-wave barber ultrasonic horn are obtained. By discussing the relationships between the displacement amplitude magnifications and the geometrical dimensions, the optimized design of the horn for the largest magnification is proposed, which is helpful to improve the radiation power and the transfer efficiency of the acoustic energy of the ultrasonic oscillatory system. Based on the optimized design of the horn, we introduced a barbell ultrasonic transducer operated in the longitudinal full-wave vibrational model and obtained the resonance frequency equations. For comparison, the resonance frequencies of the full-wave barbell horn and the full-wave barbell transducer are also analyzed by finite element method (FEM). It is shown that the values obtained by theoretical analysis and FEM are in good agreement with experimental observations. We hope that the research of this paper is helpful for the use of the barbell horn and transducer in the applications such as ultrasonic liquid processing.     

Load characteristics of high power sandwich piezoelectric ultrasonic transducers

Based on the equivalent circuit theory, the load characteristics of high power piezoelectric ultrasonic sandwich transducers are studied. Two types of loads are studied. One is liquid load as in ultrasonic cleaning, and the other is solid load as in ultrasonic drilling and machining. The effect of load and structure of the transducer on the resonance frequency of the transducer is analyzed. It is shown that the effect of load on the resonance frequency of sandwich transducers with different structures is different. For liquid load as in ultrasonic cleaning, the effect of the load on the resonance frequency of the sandwich transducer with symmetrical structure is the largest. It is the smallest for the transducer with its displacement node in the back metal cylinder. For solid load as in ultrasonic drilling and machining, the effect of the load on the resonance frequency of the sandwich transducer with its displacement node in the front metal cylinder is the largest. It is also the smallest for the transducer with its displacement node in the back metal cylinder. On the other hand, for some applications, such as ultrasonic drilling, when the lateral dimension of the tool is much less than that of the transducer, its effect on the resonance frequency of the transducer is small. The conclusions are useful in designing vibrating systems for different ultrasonic applications.     

叠合结构超低频弯张换能器

研究了一种将多个椭圆弯张壳体在短轴方向进行机械叠合的超低频弯张换能器,每个弯张壳体采用超磁致伸缩材料进行驱动。推导了多个叠合壳体的等效电路,利用支路阻抗方法得到了换能器频率和阻抗的方程表达式。针对多个壳体叠合的结构复杂性,采用有限元方法计算并分析了叠合壳体换能器的多个结构点的振动位移分布,通过平动位移分布设计了活塞辐射面的结构参数。将有限元方法计算的换能器在空气中和水中的谐振频率与等效电路法计算的结果进行了对比,符合较好。研制了6个壳体叠合的超低频弯张换能器样机,换能器外形尺寸为Φ230×630 mm,重量为39 kg。换能器经湖上试验,水中谐振频率130 Hz,最大发送电流响应161.1 dB,最大发射声源级为180.4 dB,实现了超低频、小尺寸的发射能力。      

标准圆筒试验技术与数据处理方法研究

 对标准圆筒试验技术与数据处理方法进行了深入研究,在狭缝扫描实验中建立了新型、高效的照明技术、底片判读方法以及数据处理方法,得到了精度高、信息丰富的圆筒壁质点上的位移、速度、加速度和比动能结果。同时,通过VISAR技术直接测量了圆筒外表面径向膨胀速度-时间曲线,进而积分得到位移-时间曲线,与狭缝扫描结果相互印证和补充,进一步提高了测试可靠性。     

径向复合圆柱压电超声换能器

提出一种三元径向复合圆柱压电超声换能器,并对其径向振动特性进行了研究。基于弹性力学理论及机电类比原理,导出了柱坐标系中分割处理径向极化压电陶瓷管准厚度模振动及薄壁短圆管径向振动的机电等效电路;利用径向力和振速连续的边界条件,得出了径向复合圆柱压电换能器系统的径向振动机电等效电路及其共振频率方程。探讨了换能器径向共振频率及有效机电耦合系数随其几何尺寸的变化关系。研究表明,换能器的径向共振频率及有效机电耦合系数随其内芯半径和预应力管壁厚度增大而降低。研制了一些径向复合圆柱压电换能器,并对其径向共振频率进行了测试。结果表明,理论与实验结果基本一致。      

Generating “idealised” impulse response functions to improve or repair single degree of freedom system measurements

A single degree of freedom (SDOF) system can be characterised using transient or continuous time signals and both should lead to the same frequency response function. As commonly defined, the equation of the displacement response of a SDOF system to impulse excitation alone is ambiguous leading to two possible interpretations: the impulse response (IR) and one corresponding to solely the free oscillation of the system (FR). These are analysed in detail for idealised and practical cases and it is found that the IR and FR yield two distinct acceleration spectra, and that only the phase distinguishes the normalised FR between displacement, velocity and acceleration alleviating the need to perform differentiation and integration to generate the response in other parameters. An unambiguous mathematical definition of the IR is suggested for the velocity response. Finally, it is shown that an idealised version of the IR can be artificially generated from the FR. This can be used to repair acceleration signals that have a truncated or distorted impulsive part, alleviate spectral windowing effects and generally allow cleaner response spectra. This is demonstrated experimentally.     

Design of new seismometer based on laser Doppler effect

In order to improve the resolution of seismic acquisition, a new seismic acquisition system based on tangential laser Doppler effect with an optimized differential optical configuration is proposed. The relative movement of the inertia object and the immobile frame is measured by laser Doppler effect, which can avoid the electromagnetic and thermometric interference, and the adoption of frequency-modulated (FM)transmission can improve the ability of anti-jamming. The frequency bandwidth is properly determined by analyzing the frequency of the Doppler signal. The velocity, displacement, acceleration, and frequency to be measured can be real-time acquired by frequency/velocity (F/V) converting the FM Doppler signal.A 100-dB dynamic range and the linear frequency range of 1.0 to 1000 Hz are realized.     

Measurements of the longitudinal wave speed in thin materials using a wideband PVDF transducer

A flat transducer was constructed, using a 9-microm-thick PVDF (polyvinylidene fluoride) film for generation and detection of high-frequency ultrasonic waves, and used for measurements of the phase velocity of longitudinal waves traveling along the thickness direction in a very thin material. The transducer has a useful wideband frequency characteristic extending from 10 MHz to over 150 MHz. Measurements of the phase velocity of the longitudinal waves are carried out using a 0.212-mm-thick glass slide and a 0.102-mm-thick stainless-steel shim, using water as a coupling medium. The thickness limit for this measurement appears to be approximately 20 microm. The phase velocity of the longitudinal mode is obtained as a function of frequency in the frequency domain by using a modified sampled continuous wave (cw) technique. It can also be measured in the time domain by using a broadband pulse of short duration.     

压电陶瓷非线性对大功率换能器结构参数匹配影响的计算分析

在Guyomar非线性模型基础上,通过机电等效法将晶堆前向负载作为等效质量和阻尼加入振动方程的质量项和阻尼项,推导了换能器振速、辐射声压级和谐振频率偏移率等表达式,计算分析了压电陶瓷非线性参数和结构参数对换能器声辐射性能的影响,研究了压电陶瓷的非线性对换能器结构参数匹配的影响。结果表明,换能器节面靠前,前盖板厚度越小,前盖板大径越小,都可以减少压电陶瓷非线性引起的换能器频率偏移。当设计频率确定时,压电陶瓷处于非线性工作域的换能器的结构参数有所减小。换能器加入辐射端匹配后,可以改善压电晶堆前向负载匹配,降低换能器的谐振频率偏移率。换能器激励电流也会出现频率偏移现象。在提高换能器激励电压时,换能器的结构参数应适当减小。得到的结论可为换能器设计提供理论依据和帮助。     

Characterization of a fiber-optic displacement sensor for measurements in high-intensity focused ultrasound fields

A fiber-optic sensor is presented that is capable of measuring the particle displacement in high-intensity focused ultrasound (HIFU) fields. For this probe, a secondary calibration was performed, and the resulting complex frequency response is discussed. As a first practical application, the setup was used to measure the pressure in the field of a weakly focusing ultrasound transducer. The result is compared with that of a membrane hydrophone measurement. The feasibility of measurements in HIFU fields is demonstrated by means of measurements of the spatial distribution of the peak particle velocity within the focus of a HIFU transducer and of the dependence of the peak values on the acoustical power level.     

基于二维声子晶体的大尺寸夹心式换能器的优化设计

夹心式换能器应用极为广泛,但当其横向尺寸过大时,存在耦合振动,影响其辐射面的位移分布.本文通过在大尺寸夹心式换能器的前盖板中加工周期排列的槽,来形成一种二维声子晶体结构.随后,采用有限元法对基于二维声子晶体的大尺寸夹心式换能器的振动传输特性、共振频率以及发射电压响应进行仿真模拟,讨论了开槽高度和开槽宽度对其带隙、共振与反共振频率、带宽以及辐射面位移分布的影响.研究结果表明,通过在大尺寸夹心式换能器中应用声子晶体结构可对其进行优化设计.当大尺寸夹心式换能器的工作频率位于其带隙范围内时,二维声子晶体结构能有效地抑制其横向振动,从而改善换能器辐射面位移分布的均匀程度.此外,在大尺寸夹心式换能器的前盖板中加工二维声子晶体结构,能有效提升换能器的带宽,进而拓宽大尺寸夹心式换能器的工作频带.     

Collisions with relative acceleration and cross sections in velocity space

The kinetic formula for collisional frequency as a product of particle concentration, cross section and relative velocity is based on the assumption that the latter is constant before and after the collision. This result is here generalized to include the case of collisions with relative acceleration and this is found to involve a cross section in velocity space and the number of particles per unit volume of velocity space. The argument proceeds from the relaxational Boltzmann equation satisfied by the probability density of localization in phase space. The Gauss divergence theorem is applied in the positional and velocity subspaces to convert a space integration and a velocity space integration into the corresponding surface integrations and under the assumptions of unidirectional relative velocity and relative acceleration the two kinds of cross section are obtained naturally.     

A new type of high power composite ultrasonic transducer

A new type of high power composite ultrasonic transducer was proposed and studied. The composite transducer consists of a sandwich longitudinal piezoelectric transducer, an isotropic metal hollow cylinder with large radial dimension, and the front and back metal radiation mass. By means of its special structure and Poisson’s effect, the composite transducer can produce vibrations both in its longitudinal and radial directions, and therefore, it can radiate sound waves in three-dimensional space. The electro-mechanical equivalent circuit of the composite transducer was derived and the resonance frequency equation was obtained analytically. Numerical methods were used to simulate the vibration of the composite transducer, and the vibrational displacement distribution, the resonance frequency and the radiation sound field are given. Some composite transducers are designed and manufactured; their resonance frequencies and the radiation acoustic field are measured and compared with the analytical and numerical results. It can be seen that the measured frequencies and acoustic field contour are in good agreement with the analytical and numerical results. It is expected that this kind of composite ultrasonic transducer can be used in more and more power ultrasonic applications, such as ultrasonic cleaning, ultrasonic extraction, ultrasonic sonochemistry and other ultrasonic liquid processing, where high ultrasonic power and large ultrasonic processing space are needed increasingly.