Cymbal压电发电换能器有限元分析

通过建立Cymbal压电发电换能器的机电耦合有限元分析模型,计算分析了换能器结构参数对输出电压和谐振频率的影响以及外接负载对Cymbal换能器输出电压和输出功率的影响。研究表明,为了降低换能器的工作频率和提高换能器的输出电压,应增大换能器的空腔底部直径和减小换能器的空腔高度;在选择金属端冒和压电陶瓷厚度等参数时,应综合考虑换能器系统的刚度和外界振动源的频率特性和加速度特性;在任意一个频率点上,Cymbal换能器均存在一个最佳的外接负载,使得换能器的输出功率最大,而这个最佳的负载阻抗就等于Cymbal换能器在这个工作频率点上的输出阻抗。文中还提出并分析了基于外加预应力的多振子级联方式Cymbal压电发电换能器系统的结构。     

面向电磁水声换能器的高静低动型悬架动力学研究

针对目前线性悬架无法兼顾电磁水声换能器降低谐振频率与承载较大静水压力的难题,设计引入了高静低动型悬架装置,并分析其对换能器声辐射性能的影响。建立了系统动力学模型和动态特性微分方程组,仿真分析了引入非线性刚度前后换能器系统声源级及谐振频率的变化。研究了输入电压对不同系统谐振频率的影响,探究了不同高静低动系统之间的差异。通过锤击试验测得引入高静低动刚度前后悬架的固有频率和加速度导纳。研究结果表明：相较于原线性悬架,高静低动型悬架在承受相同负载时具备更低的固有频率,低频段内具有更高的加速度。在电磁换能器中引入具有高静低动刚度特性的悬架装置可以获得比原系统更低的谐振频率,使低频区域内的声源级得到提升。     

超声换能器的“电感-变压器”阻抗匹配模型研究

在分析超声换能器阻抗特性和电路匹配的基础上,对传统纯电感电容匹配电路模型进行电路仿真和阻抗分析,证明该模型在谐振频率附近有大范围的电抗变化,存在电路不稳定和电阻调节精度低的问题;提出"电感-变压器"阻抗匹配模型,通过电感和变压器分别调节换能器电阻和电抗,实现电路的精确匹配,以提高超声换能器阻抗匹配的精度和稳定性,并给出了理想的匹配条件和匹配参数。利用匝数可调的变压器和电感制作了超声换能器的匹配电路,对20.8 k Hz的变幅杆换能器进行了阻抗匹配的实验测量,结果证明这种"电感-变压器"阻抗匹配模型在谐振频率附近具有较小的电抗变化范围、较低的电阻变化率和较高的电抗调节精度,在超声换能器的自动阻抗匹配中具有良好的应用前景。     

超声波电源频率跟踪系统的研究

当超声波换能器在长时间工作时,受发热的影响,谐振频率会发生漂移。为了保证超声波换能器一直工作在最佳谐振状态,本文提出了一种自动频率跟踪系统。该系统通过鉴相电路检测超声波换能器电压与电流的相位和方向,将PI调节频率变化大小与相位关系调节频率方向相结合来实现精确的频率跟踪。经过试验验证,该方法能够精确锁定最佳谐振频率并跟踪上超声波换能器的动态变化。     

欧米伽换能器振动辐射特性计算分析

对一种新型的弯张换能器即欧米伽换能器的辐射特性进行了有限元分析,并与钹式换能器进行对比。通过有限元计算,对相同体积的欧米伽换能器与钹式换能器的电导纳、发射电压响应级以及接收灵敏度级进行了对比,结果表明:欧米伽换能器的低频性能和第一谐振频率处的接收灵敏度要好于钹式换能器,而发射电压响应要低于钹式换能器,比钹式换能器更好地解决了小体积与低工作频率之间的矛盾,更宜实现基阵的小型化。舰船的机械噪声主要集中在500Hz以下,体积较小的欧米伽换能器非常适合作为侦察舰船活动的被动声纳基元。     

声波测井压电换能器多频点阻抗匹配技术研究

针对声波测井压电换能器的多频点阻抗匹配技术展开研究,首先采用多模态等效电路精确描述了换能器的导纳特性;然后通过分析多模态阻抗匹配理论,设计电感-电容复合阻抗匹配网络,并结合换能器等效电路进行参数优化和电路仿真。实验表明,相比于换能器没有阻抗匹配的测试结果,该阻抗匹配技术可大幅提高换能器在谐振频率附近多个频率处的有功功率,频带内的有功功率平均提高了30倍,从而改善换能器的激励带宽和激励效率,提高测井仪器的适应性、探测深度和分辨率。     

气体超声流量计换能器温度特性研究

温度会影响气体超声流量计换能器的性能,进而影响换能器的一致性,因此研究换能器在变温条件下性能变化有重大意义。通过测量换能器的阻抗特性,计算换能器的电声参数,研究了温度对换能器谐振频率、静态电容及动态参数的关系以及不同激励信号频率下换能器收发波形的变化。结果显示,谐振频率与温度成反比关系,变化率为-0.11 kHz/℃;静态电容与温度成正比关系,变化率为0.015 nF/℃;越远离谐振频率,换能器的输出幅值越小,暂态过程振荡现象越剧烈。研究结果表明,温度变化会引起气体超声换能器的性能发生变化,激励信号变化会引起换能器收发波形变化,进而影响超声流量计换能器的配对特性。     

一种确定换能器参数的方法

一、前言 大家知道,换能器工作在谐振频率时,可以用集总参数来表示换能器等效线路中的各元件。这对于分析换能器在谐振点的性能是有用的。但仅仅知道谐振点的等效线路是不够的。如果能够在谐振频率以外的其他频率也用等效线路的方法来描述换能器,这对于分析换能器和换能器阵的性能是很有用的。这样做的前提是承认等效线路的各参数是频率的函数,并且能够确定在各个频率下的等效线路的参数。知道了不同频率下各参数的值,就可分析和计算换能器的带宽,不同频率工作时的效率,换能器的相位变化、互辐射阻抗的大小和随频率的变化、互辐射对换能器和…     

高静水压下换能器阻抗特性的测量方法研究

针对在小腔体中阻抗分析仪发射连续波无法准确测得换能器阻抗的问题,提出一种在高静水压下使用脉冲正弦信号激励换能器测量阻抗的方法。以采样电阻法为基础,根据腔体尺寸确定发射脉冲个数以及可测频率范围来有效避免腔体边界反射对测量造成的影响。通过设置不同的发射频率,分别采集换能器两端及采样电阻两端的电压波形信号,利用已知频率的三参数正弦曲线拟合法分别得到波形信号的幅值和初始相位角,计算得到换能器的导纳值。改变静水压力,利用脉冲法测得0~10 MPa静水压下换能器导纳特性。实验结果表明,采用脉冲正弦信号激励的方法可在有限空间内准确测量换能器的阻抗特性;且随着静水压力的升高换能器的谐振频率发生偏移,导纳圆直径减小。     

三叠片压电复合换能器弯曲振动的比较研究

用瑞利法对三叠片弯振圆盘换能器在三种不同边界条件下的振动特性进行理论研究,推导了谐振频率及有效机电耦合系数的表达式,通过数值计算分析了复合换能器的谐振频率及有效机电耦合系数随换能器各结构参数的变化规律并进行比较研究,同时将计算结果与有限元模拟结果比较,结果表明不同边界条件下换能器的结构参数对谐振频率和有效机电耦合系数影响不同:在换能器结构参数一定时,自由边界条件下谐振频率最大,简支边界条件下最小,固定边界条件下次之;有效机电耦合系数随着金属片厚度、陶瓷片厚度和陶瓷片半径变化时,分别有一个最大值;其他参数一定时,有效机电耦合系数在简支边界条件下最大,自由边界条件下的值稍大于固定边界条件下的值。上述研究结果可为三叠片弯曲振动换能器的设计和实际应用提供一定的理论支持。     

Sandwiched piezoelectric ultrasonic transducers oflongitudinal-torsional compound vibrational modes

Sandwiched piezoelectric ultrasonic transducers of longitudinal-torsional compound vibrational modes were studied. The transducers consist of coaxially segmented, longitudinally and tangentially polarized piezoelectric ceramic rings, a back metal cylinder, and a front exponential solid metal horn. Based on the plane-wave approximation, the equivalent circuits of the longitudinal and torsional vibrations in the sandwiched transducer were obtained and the resonance frequency equations of the transducer in longitudinal and torsional vibrations were derived. By means of choosing the radius decay coefficient of the front exponential horn, the longitudinal and torsional vibrations are made to resonate at the same frequency in the transducer. Sandwiched piezoelectric ultrasonic transducers of longitudinal-torsional compound modes were designed and fabricated according to the frequency equations. It is demonstrated that the measured resonance frequencies of the transducers are in good agreement with the theoretical results, and the measured resonance frequencies of the transducers in longitudinal and torsional vibration modes are also in good agreement with each other. Theoretical and experimental results show that this kind of transducer can be used in ultrasonic welding, ultrasonic machining, ultrasonic motors, and other ultrasonic applications which need large displacement amplitudes     

Magnetoacoustic resonance in tangentially magnetized ferrite-piezoelectric bilayers

The magnetoelectric (ME) effect in ferrite-piezoelectric bilayers has been theoretically studied at coinciding frequencies of the electromechanical resonance in the electric subsystem and ferromagnetic resonance in tangentially magnetized ferrite. Giant values of the ME voltage coefficient (50–70 V/A at 5 GHz) are predicted for the YIG-PZT system. In contrast to the case of a normally magnetized plate, the magnetoacoustic resonance in a tangentially magnetized sample takes place at a lower value of the magnetic bias field and a smaller ferrite layer thickness. This effect can be used for the development of multifunctional ME nanosensors and transducers operating in the microwave range.     

A U-shaped linear ultrasonic motor using longitudinal vibration transducers with double feet

A U-shaped linear ultrasonic motor using longitudinal vibration transducers with double feet was proposed in this paper. The proposed motor contains a horizontal transducer and two vertical transducers. The horizontal transducer includes two exponential shape horns located at the leading ends, and each vertical transducer contains one exponential shape horn. The horns of the horizontal transducer and the vertical transducer intersect at the tip ends where the driving feet are located. Longitudinal vibrations are superimposed in the motor and generate elliptical motions at the driving feet. The two vibration modes of the motor are discussed, and the motion trajectories of driving feet are deduced. By adjusting the structural parameters, the resonance frequencies of two vibration modes were degenerated. A prototype motor was fabricated and measured. Typical output of the prototype is no-load speed of 854 mm/s and maximum thrust force of 40 N at a voltage of 200 V(rms).     

In-air and underwater performance and finite element analysis of a flextensional device having electrostrictive poly(vinylidene fluoride-trifluoroethylene) polymers as the active driving element

A flextensional transducer, in which the electrostrictive poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer was used as the active driving element, was fabricated and characterized. The results show that transducers of several millimeters thick can produce an axial displacement of more than 1 mm in air along the thickness direction, and a transmitting voltage response of 123 dB re 1 /spl mu/Pa/V at 1 m in water at frequencies of several kilohertz. A finite element code (ANSYS, Inc., Canonsburg, PA) was used to model the in-air and underwater responses of the flextensional transducer over a broad frequency range. The calculated resonance frequencies and transmitting voltage response spectra show good agreement with the experimental data. In addition, the performance of both the in-air actuator and underwater transducer was analyzed for different design parameters of the flextensional structure. These results show that the performance of the flextensional transducer could be tailored readily by adjusting the parameters of the flextensional metal shell.     

超声波流量计换能器系统理论分析及应用

为了使超声波流量计能够获得最佳的超声波信号,从理论上分析了超声波流量计的换能器系统,在此基础上提出了用收发电压灵敏度参数来表征换能器系统的综合发射和接收性能。采用等效网络理论,计算了超声波压电换能器的发射特性和接收特性,同时给出了收发电压灵敏度的表达式以及在流量计工作频率下换能器的最优设计准则。应用该准则设计并制作了适用于热量表的超声波换能器。实验结果表明:采用该设计理论研制的换能器系统可以使热量表在工作频率上获得最优的超声波信号,同时也证明了采用该理论设计的超声波流量计换能器系统的有效性。     

Piezoceramics for high-frequency (20 to 100 MHz) single-elementimaging transducers

The performance of transducers operating at high frequencies is greatly influenced by the properties of the piezoelectric materials used in their fabrication. Selection of an appropriate material for a transducer is based on many factors, including material properties, transducer area, and operating frequency. The properties of a number of piezoceramic materials have been experimentally determined by measuring the electrical impedance of air-loaded resonators whose thickness corresponds to resonance frequencies from 10 to 100 MHz. Materials measured include commercially available compositions of lead zirconate titanate (PZT) with relatively high dielectric constants and a modified lead titanate (PT) composition with a much lower dielectric constant. In addition, materials which have been designed or modified to result in improved properties at high frequencies are studied. Conclusions concerning the influence of the microstructure and composition on the frequency dependence of the material properties are made from the calculated properties and microstructural analysis of each material. Issues which affect transducer performance are discussed in relation to the properties. For transducers larger than about 1 mm in diameter, the use of a lower dielectric constant material is shown to result in a better electrical match between the transducer and a standard 50 Ω termination. For transducers whose impedance is close to that of the connecting cables and electrical termination, equivalent circuit model simulations show improved performance without the need for electrical matching networks. Measurements of fabricated transducers show close agreement with the simulations, validating the measurements and showing the performance benefits of electrically matched transducers     

On the performance characterization of ultrasonic air transducerswith radiating membranes

An ultrasonic air transducer used for sensing essentially requires an efficient transduction into the surrounding medium. A transducer consisting of a metal membrane coupled with a resonating piezoelectric disk, the latter being driven in its radial mode of vibrations, has been found to be significantly applicable in this aspect. The present study reports the performance characterization at resonance and at higher frequencies of two such transducers with different dimensions of the housings. Vibrational amplitude characteristics are studied employing phase-locked laser interferometry technique that presents sufficiently high displacement amplitude of the membrane at resonance. A consequent high-acoustic pressure field is also obtained. The design aspects for such ultrasonic air transducers with efficient transduction capability and adjustable bandwidth are discussed     

Characterization of Piezoelectric Ceramic Transducer for Accurate Speed-of-Sound Measurement

Piezoelectric ceramics mounted on the endplates of a cylindrical resonator were used as the source and detector for speed-of-sound measurements. The perturbations of the longitudinal gas modes of the cavity due to the compliance of the diaphragms (10 mm diameter, 0.3 mm thick) and the attached transducers were estimated from first-order perturbation theory. The fractional shift of the resonance frequencies in argon caused by the source and detector was 0.03 × 10⁻⁶ at 0.1 MPa and 273.16 K. The high signal-to-noise ratio (up to 1 × 10⁴ with a 6 s integration time) that was obtained with these transducers makes them suitable for acoustic thermometry. The heat dissipation in the source transducer was measured to be only 0.7 μW at the working voltage (7 V) and frequency (1 kHz).     

Miniature multimode monolithic flextensional transducers

Traditional flextensional transducers classified in seven groups based on their designs have been used extensively in 1-100 kHz range for mine hunting, fish finding, oil explorations, and biomedical applications. In this study, a new family of small, low cost underwater, and biomedical transducers has been developed. After the fabrication of transducers, finite-elements analysis (FEA) was used extensively in order to optimize these miniature versions of high-power, low-frequency flextensional transducer designs to achieve broad bandwidth for both transmitting and receiving, engineered vibration modes, and optimized acoustic directivity patterns. Transducer topologies with various shapes, cross sections, and symmetries can be fabricated through high-volume, low-cost ceramic and metal extrusion processes. Miniaturized transducers posses resonance frequencies in the range of above 1 MHz to below 10 kHz. Symmetry and design of the transducer, polling patterns, driving and receiving electrode geometries, and driving conditions have a strong effect on the vibration modes, resonance frequencies, and radiation patterns. This paper is devoted to small, multimode flextensional transducers with active shells, which combine the advantages of small size and low-cost manufacturing with control of the shape of the acoustic radiation/receive pattern. The performance of the transducers is emphasized.     

Lead zirconate titanate/poly(vinylidene fluoride-trifluoroethylene) 1-3 composites for ultrasonic transducer applications

A new procedure for preparing lead zirconate titanate (PZT)/poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) 1-3 composites with both phases piezoelectrically active is described. Sintered PZT rods are inserted into a prepoled copolymer matrix, and the composite is repoled under a lower electric field. Using this new procedure, the dipoles in the two phases are aligned in either the same or opposite directions. Composite disks, of 12.7-cm diameter and 0.33- to 0.60-mm thicknesses, have been fabricated with PZT rods of 0.8 or 1 mm diameter distributed in a square pattern with 3 mm center-to-center separation. The ceramic volume contents of the composite disks are 3.6 and 5.6%, respectively. The resonance characteristics of the composite disks consist of the resonance modes of the two constituent phases, but they are dominated by the coupled longitudinal thickness mode (H-mode) of the PZT rods. The coupled radial mode (L-mode) resonance of the PZT rods is significant only for thin disks. The observed resonance frequencies of the H- and L-modes agree well with the values calculated from the coupling theory. The thickness mode resonance of the copolymer matrix (T-mode) is present but hardly observable in thick disks. The composite disks have been fabricated into transducers with air-backing and with no front face matching layer, and their performance characteristics have been evaluated in water. The transmitting and receiving voltage responses of a PZT/P(VDF-TrFE) composite transducer are better than those of a PZT/epoxy composite transducer. The transmitting and receiving voltage responses are improved when the PZT rods and copolymer matrix are poled in opposite directions, especially when the resonance frequencies of the H- and T-modes are approximately equal. When the phases are poled in the same direction and the resonance peaks associated with the Hand T-modes just overlap, the bandwidth is improved. Using 0.33-mm thick composite disks, a transducer can be produced with three operating frequencies by poling the constituent phases in the same direction, or with two operating frequencies at equal efficiency by poling the constituent phases in opposite directions. The PZT/P(VDF-TrFE) 1-3 composite transducer, especially the one with multiple operating frequencies, should be very promising in the applications of medical ultrasonic imaging.