高频超声激励源

对于频率高于50MHz的超声换能器,如何得到有较高幅度、近似于理想δ脉冲的激励信号是比较重要的。在高频换能器允许的条件下,适当提高激励信号的幅度和采用较陡的脉冲前沿,对于提高换能器的灵敏度及分辨率大有益处。一般驱动换能器多使用高频脉冲信号发生器,存在幅度低(<100V)、带容性负     

四激励二维正交复合夹心式压电超声换能器的设计

提出了一种四激励二维正交复合夹心式压电超声换能器,换能器由四组纵向极化压电陶瓷晶堆、一个中心耦合金属块和四个外部金属圆锥组成。基于二维耦合振动机理和机电类比原理,建立了换能器的等效电路模型并推导了其谐振频率方程。利用有限元软件仿真分析了四激励正交复合换能器的频响特性和振动特性,并与其单独一个方向振子的振动特性进行了对比。加工了反相和同相模态的换能器,利用阻抗分析仪和激光测振仪测试了其频率响应和二维四向纵振动输出特性,并进行了大功率二维四向超声乳化实验测试。理论、仿真和实验结果表明:换能器具有反相和同相两个纵向正交共振模态,在这两种共振模态下均可实现二维四向纵振动输出,且换能器两个正交方向振子的纵向振动具有相互耦合加强的作用;等效电路法和有限元法所得换能器的共振频率和有效机电耦合系数与实验测试结果吻合,通过与单激励正交复合夹心式压电超声换能器的有效机电耦合系数对比,发现该换能器具有更高的有效机电耦合系数。     

超声换能器辐射场应力定量测量方法研究

提出了一种基于动态光弹观测系统的超声换能器在透明固体中辐射场应力定量测量新方法。该方法关注到激光束穿过非均匀应力区时的双折射累积效应和Senarmont补偿法均匀应力假设与真实应力非均匀分布之间的差异,利用滤波反投影算法重建出应力场;根据应力与换能器激励电压的线性关系,用4种激励电压动态校准重建后的应力数据。实验定量测量了圆形晶片超声换能器在固体内部辐射的瞬态纵波场的应力分布,结果表明应力幅值与激励电压成正比,符合线性规律。     

衰减匹配的超声Barker码激励方法

为增加超声穿透高声衰减介质的能力,提出了一种衰减匹配的超声Barker码激励方法。基于换能器高斯响应与材料非频散线性衰减的假设,得到了Barker码激励的信号模型,求解旁瓣抑制滤波后脉冲压缩的信噪比表达式可知,该方法仅需要根据材料衰减特性与轴向分辨率的要求,分别调整Barker码的中心频率与时长,便可以获得更高的信噪比。取衰减系数为1.4 Np/(MHz·cm)、厚度为5 cm的橡胶为试样进行验证。当与方波激励方法的轴向分辨率相近时,衰减匹配的Barker码激励方法比传统Barker码激励方法的信噪比增益提高接近5 dB;当牺牲一定轴向分辨率时,信噪比增益提高接近11 dB。结果表明,衰减匹配的Barker码激励方法可以降低依频率衰减对脉冲压缩的影响,有效提高衰减回波的信噪比。      

双激励全波长压电陶瓷超声换能器工作特性分析

对由两个半波长夹心式压电陶瓷换能器级联而成的双激励全波长压电陶瓷超声换能器进行了研究,给出了这种换能器优值的相关参量表达式,通过数值计算分析了该换能器的结构和材料参数对其特性的影响。研究结果表明,当两组压电陶瓷堆分别位于各自所在半波长换能器的位移节点,或者在压电陶瓷片数量确定情况下两组压电陶瓷堆的片数相同时,换能器均能得到最大的优值;在相当大的范围内增加压电陶瓷片的数量,换能器的优值稍有降低,但力因子迅速增大;金属块材料对换能器的优值影响甚微。可见双激励全波长换能器能在不明显降低换能器综合性能的情况下有效增加压电陶瓷的体积,因而可大幅提高换能器的功率容量和负载能力,更适用于大功率重负载的场合。      

磁致伸缩超声换能器阻抗匹配网络的设计*

根据磁致伸缩超声换能器的等效电路模型和阻抗匹配理论,该文设计了一种优化的型匹配网络。该网络具有调谐、变阻和滤波的功能,适用于工作在中低频超声频率范围内的磁致伸缩超声换能器系统的阻抗匹配。仿真和实验结果表明:接入该型阻抗匹配网络后,驱动电源与换能器之间实现了最大功率传输,换能器两端电信号的波形质量得到优化,换能器激励电流提升了40%。该研究可为大功率磁致伸缩超声换能器的应用提供技术支持。     

混合激励纵振换能器的研究

纵振式换能器是水声领域中不可或缺的一类中频段换能器,本文以超磁致伸缩材料Terfenol-D和压电陶瓷材料PZT作为驱动元件设计混合激励纵振式换能器。利用ANSYS有限元软件建立了有限元模型,对换能器的电声参数进行了优化,并制作一宽带混合激励纵振式换能器,实验测得的换能器与仿真的结果较为吻合,实测换能器的最大发送电压响应为145dB,其工作频带为4kHz-16kHz,频带内发送电压响应起伏为±4.5dB。     

磁致伸缩-压电联合激励凹筒型发射换能器

设计制作了一种新型磁致伸缩-压电联合激励凹筒型发射换能器,采用稀土超磁致伸缩材料Terfenol-D与PZT压电陶瓷作为联合激励元件,模拟计算与实测结果均表明,与采用单一振子激励的凹筒型发射换能器相比,此种新型换能器在保持尺寸小、频率低等优点的同时,显著拓宽了工作频带并提高了辐射声功率.换能器外型尺寸为φ88 mm×316 mm,水中谐振频率1.30 kHz,-3 dB带通Q值1.43,谐振频率下发射电压响应级135.1 dB.     

磁致伸缩-压电联合激励凹简型发射换能器

设计制作了一种新型磁致伸缩-压电联合激励凹简型发射换能器,采用稀土超磁致伸缩材料Terfenol-D与PZT压电陶瓷作为联合激励元件,模拟计算与实测结果均表明,与采用单一振子激励的凹筒型发射换能器相比,此种新型换能器在保持尺寸小、频率低等优点的同时,显著拓宽了工作频带并提高了辐射声功率。换能器外型尺寸为φ88 mm×316 mm,水中谐振频率1．30 kHz,-3 dB带通Q值1．43,谐振频率下发射电压响应级135．1 dB。     

双激励纵弯耦合宽带复合棒水声换能器

为研究进一步拓宽双激励复合棒水声换能器的工作带宽方法。利用等效电路法和有限元方法研究了双激励换能器的振动模态,分析了中间质量块的材料、长度对换能器发射电压响应的影响,提出结合较低工作频段的纵向振动和较高工作频段的纵向振动与径向振动耦合引起的弯曲振动进一步展宽带工作频带的方法。根据优化参数后的仿真模型制作的样品工作频带为14 kHz～47 kHz。采用这种纵弯振动模态耦合的方法可以有效拓宽双激励宽复合棒换能器的工作带宽。     

Gamma-ray tuning by stimulated emission of recoilphonons

Tuning of gamma radiation by exciting the ultrasonic vibrations of different coherency degree in crystals is discussed. The quantum approach based on the formalism of coherent quantum states is used to take into account statistical properties of the stimulating ultrasonic wave. Multi-quantum transitions with emission of gamma quanta and simultaneous stimulated emission of recoil phonons or absorption of one or several phonons from an external ultrasonic wave are considered as an example of multi-quantum transitions with quanta coupled to different degrees of freedom of the radiating nuclei. The spectrum of gamma radiation is determined for a partially coherent stimulating ultrasonic wave with fixed amplitude and uncertain phase, and completely incoherent casual acoustic oscillations. A comparison is made with some known results obtained by both classical and quantum methods. This revised version was published online in August 2006 with corrections to the Cover Date.     

高频调制电弧的声学特性及其细化焊缝组织的应用

以等离子体电弧作为声源,利用高频电流进行调制,激发电弧可以产生超声波。研究了高频调制电弧的激发特性和声场特征,发现调制电弧所发射超声波在激励频段内呈现平坦的幅频特性,激励电流是影响电弧超声强度的主要因素,声压幅值与电弧等离子体流力的变化量成正比,声场呈现轴向强两侧弱的特征。同时介绍了利用电弧激发超声波在改善焊缝组织性能方面的应用。     

Effect of secondary radiation force on aggregation between encapsulated microbubbles

Secondary radiation force can be an attractive force causing aggregates of encapsulated microbubbles in ultrasonic molecular imaging. The influence of the secondary radiation force on aggregation between two coated bubbles is investigated in this study. Numerical calculations are performed based on four simultaneous differential equations of radial and translational motions. Results show that the secondary force can change from attraction to repulsion during approach, and stable microbubble pairs can be formed in the vicinity of resonant regions; the possibility of microbubble aggregations can be reduced by using low exciting amplitude, ultrasonic frequencies deviating from the resonant frequencies or microbubbles with small compressibility.     

超声波声孔效应中气泡动力学的研究

在超声快速制取组织细胞病理切片的过程中，发现激励信号对切片制取效果有明显的影响.为了掌握超声激励信号对组织细胞的影响规律，达到快速制取病理切片的最佳状态，从气泡空化模型入手，通过改变激励信号频率、声压、气泡初始半径和液体黏滞系数等参量，研究了声孔效应中气泡动力学激励机制.数值计算表明：空化泡振动随激励声压增强而升高，随液体黏滞系数增强而减弱；一定频率范围内空化泡振动能保持在膨胀、收缩和振荡的稳定空化状态，存在空化泡稳态振动的最佳激励频率；一定初始半径能保证空化泡产生稳定的振动，存在空化泡稳态振动幅度最大的初始半径.实际操作中，在频率、声压、初始半径和黏滞系数综合作用的若干空化阈内，声孔效应使超声快速法制取细胞组织切片获得最佳效果. 关键词： 声孔效应 超声空化 气泡振动 稳态空化域     

An electric contact method to measure contact state between stator and rotor in a traveling wave ultrasonic motor

Performances of ultrasonic motor (USM) depend considerably on contact state between stator and rotor. To measure the contact state in a traveling wave ultrasonic motor (TWUSM), a special test method is necessary. This paper develops a new method named electric contact method to measure contact state of stator and rotor in traveling wave type USM. The effects of pre-load and exciting voltage (amplitude) of stator on contact state between stator and rotor are studied with this method. By a simulating tester of friction properties of TWUSM, the variations of stalling torque and no-load speed against the pre-load and the exciting voltage have been measured. The relative contact length that describes the contact characteristic of stator and rotor is proposed. The relation between the properties of TWUSM and the contact state of stator and rotor are presented. Additionally, according to a theoretical contact model of stator and rotor in TWUSM, the contact lengths at given conditions are calculated and compared with the experimental results.     

Continuous contact- and contamination-free ultrasonic emulsification-a useful tool for pharmaceutical development and production

A novel concept was developed here for the continuous, contact- and contamination-free treatment of fluid mixtures with ultrasound. It is based on exciting a steel jacket with an ultrasonic transducer, which transmitted the sound waves via pressurised water to a glass tube installed inside the jacket. Thus, no metallic particles can be emitted into the sonicated fluid, which is a common problem when a sonotrode and a fluid are in direct contact. Moreover, contamination of the fluid from the environment can be avoided, making the novel ultrasonic flow-through cell highly suitable for aseptic production of pharmaceutical preparations. As a model system, vegetable oil-in-water emulsions, fed into the cell as coarse pre-emulsions, were studied. The mean droplet diameter was decreased by two orders of magnitude yielding Sauter diameters of 0.5 microm and below with good repeatability. Increasing the residence time in the ultrasonic field and the sonication power both decreased the emulsion mean diameter. Furthermore, the ultrasonic flow-through cell was found to be well suited for the production of nanoparticles of biodegradable polymers by the emulsion-solvent extraction/ evaporation method. Here, perfectly spherical particles of a volume mean diameter of less than 0.5 microm could be prepared. In conclusion, this novel technology offers a pharmaceutically interesting platform for nanodroplet and nanoparticle production and is well suited for aseptic continuous processing.     

近场超声悬浮启浮瞬态行为的理论分析及实验测试

超声悬浮气膜瞬态行为的认识对悬浮体运动规律及悬浮精度控制等都有着重要作用。运用气体动力学理论研究超声挤压问题,建立了自由悬浮体瞬态气膜压力及其非线性动力学模型.应用数值方法对模型进行求解,获得超声激励下气体挤压膜在启浮过程中的瞬态压力分布、承载能力以及悬浮盘位移的变化规律。分析发现激励盘振幅、频率等参数对启浮过程的瞬态行为有着显著的影响,激励盘振幅越小、激励频率越高,启浮过渡过程达到稳态所需时间越长。在理论分析的基础上还对瞬态启浮过程进行实验研究,应用激光位移传感器对瞬态悬浮位移进行测试,发现理论分析和实验测试结果一致性较好。      

Ultrasonic characterization of liquids using resonance antireflection

This paper presents an ultrasonic method for measuring the density of liquids with a solid layer separating a reference fluid and a test fluid. By adjusting the frequency of the exciting signal according to the thickness of the layer, it is possible to generate destructive interference of the waves reflected at the first and at the second boundary of the layer. Thus, the layer appears to vanish for the incident waves. The resulting echo signal depends only on the acoustic impedances of the reference fluid and the test fluid and the density which is of interest can be extracted. Short and long-term drifts of the electronics and the ultrasonic transducer implied are eliminated by using the well-known pulse-echo technique with additional frontwave detection.     

Amplitude modulation excitation for cancellous bone evaluation using a portable ultrasonic backscatter instrumentation

The ultrasonic backscatter (UB) has the advantage of non-invasively obtaining bone density and structure, expected to be an assessment tool for early diagnosis osteoporosis. All former UB measurements were based on exciting a short single-pulse and analyzing the ultrasonic signals backscattered in bone. This study aims to examine amplitude modulation (AM) ultrasonic excitation with UB measurements for predicting bone characteristics. The AM multiple lengths excitation and backscatter measurement (AM-UB) functions were integrated into a portable ultrasonic instrument for bone characterization. The apparent integrated backscatter coefficient in the AM excitation (AIB_AM) was evaluated on the AM-UB instrumentation. The correlation coefficients of the AIB_AM estimating volume fraction (BV/TV), structure model index (SMI), and bone mineral density (BMD) were then analyzed. Significant correlations (|R| = 0.82-0.93, p < 0.05) were observed between the AIB_AM, BV/TV, SMI, and BMD. By growing the AM excitation length, the AIB_AM values exhibit more stability both in 1.0-MHz and 3.5-MHz measurements. The recommendations in AM-UB measurement were that the avoided length (T1) should be lower than AM excitation length, and the analysis length (T2) should be enough long but not more than AM excitation length. The authors conducted an AM-UB measurement for cancellous bone characterization. Increasing the AM excitation length could substantially enhance AIB_AM values stability with varying analyzed signals. The study suggests the portable AM-UB instrument with the integration of real-time analytics software that might provide a potential tool for osteoporosis early screening.     

Pulsed Sounding of Cracks with the Use of the Modulation of Ultrasound by Vibrations

The possibility of using the effect of the modulation of ultrasound by vibrations due to the presence of cracks for the nonlinear acoustic detection of cracks is demonstrated. The method is based on a pulsed ultrasonic sounding with gating the received signal and simultaneously exciting low-frequency vibrations in the sample. The presence of a crack is characterized by the modulation of the ultrasonic wave reflected from the crack. The visualization of the crack position in a model object (a metal rod) is performed. The possibility of selecting a crack on the background of an intense signal reflected from a cavity is experimentally demonstrated. The manifestation of the nonlinear properties of a crack is studied as a function of the polarization of the flexural vibrations of the rod.