充砂振动柱动态特性预估

本文对充砂振动柱在基础激励下的动态特性进行了理论和实验研究。把砂作为一种具有均匀密度的连续体,假设砂的弹性模量是砂柱高度的幂函数和砂柱中只存在纵向波,建立了波动方程,导出了原点导纳和传递导纳的理论公式。这个公式亦适用于非常短的砂柱。同时采用阻抗方法推导了充砂振动柱的结构损耗因子表达式。实验值和预估值基本相符。     

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.     

A magnetoresistive transducer with superconducting control lines

The design and the static and dynamic response of a thin film magnetoresistive transducer with superconducting control lines cooled at 4.2 K are described. The transducer facilitates a linear transfer of electrical signals by transformation of the impedance level and by perfect electrical insulation between the input and output circuit. In addition, voltage and power amplifications at low frequencies are achieved.The device can be used to sense supercurrents or currents generated by sources of very low impedance, such as superconducting quantum interferometers (SQUID's).     

Characterizing ultrasonic transducers using radiation efficiency and reception noise figure

Transducer performance is considered separately for transmission and reception operations. The transmission operation is traditionally characterized by its traditional transfer function. Using a Thevenin source, the transfer function may be scaled to become the absolute radiation efficiency. Transmission lines are accurately modeled, and a matched impedance design is recommended. The reception operation also is characterized by its traditional transfer function. However, reception sensitivity is defined as the signal-to-noise ratio achieved by the combined transducer, transmission line, and preamplifier. The thermal noise arises from the media and other noise sources contributed by the transducer, transmission line, and preamplifier. An absolute sensitivity measure is defined as the acoustic noise figure, which is the sum of individual transducer and preamplifier noise figures. The transducer noise figure is independent of the receiver load impedance and depends critically on dissipative loss. Preamplifier noise figure performance requires noise matching to the transducer. High performance design methods are presented that incorporate transmission lines, which include loss. Modeled examples are used to demonstrate performance.     

Off-diagonal impedance in amorphous wires and its application to linear magnetic sensors

We investigated the magnetic-field behavior of the off-diagonal impedance in Co-based amorphous wires under sinusoidal (50 MHz) and pulsed (5 ns rise time) current excitations. For comparison, we measured the field characteristics of the diagonal impedance as well. In general, when an alternating current is applied to a magnetic wire, the voltage signal is generated not only across the wire but also in a pickup coil wound on it. These voltages are related to the diagonal and off-diagonal impedances, respectively. We demonstrate that these impedances have a different behavior as functions of axial magnetic field: the diagonal impedance is symmetrical, whereas the off-diagonal one is antisymmetrical with a near-linear portion within a certain field interval. For the off-diagonal response, the dc bias current is necessary to eliminate circular domains. In the case of the sinusoidal excitation without a dc bias current, the off-diagonal response is very small and irregular. In contrast, the pulsed excitation, combining both high- and low-frequency harmonics, produces the off-diagonal voltage response without additional biasing. This behavior is ideal for a practical sensor circuit design. We discuss the principles of operation of a linear magnetic sensor based on a complementary metal-oxide-semiconductor transistor circuit.     

Pulse-echo single frequency acoustic nonlinearity parameter (B /A) measurement

A pulse-echo single-frequency method for B/A measurement is reported. The technique is based on excitation of the medium at a progressively increasing amplitude level and the computing of B/A from the deviation in linearity of the transducer input-output relationship. Starting from the nonlinear wave equation, a three-dimensional analytical formulation that predicts the approximate field distribution for finite-amplitude waves is derived. This provides the computation for the transducer output voltage for progressively increasing signal levels. It is shown that, by a suitable normalization, the effects of the diffraction can be excluded. From a nonlinear least-squares fit of the experimental data to the analytical equation, the B/A is computed. A number of simulations for the model together with preliminary experiments that were carried out at 3.5 GHz are presented     

Numerical analysis of the radiated fields of ultrasonic transducers

A finite element model is implemented for simulating the radiated fields of both planar and curved transducers in acoustic media. The approach is based on general finite element analysis developed for solving the governing equations of elastic wave propagation. The distributions of the wave fields are presented for both the nearfield and farfield regions of the transducer. Three excitation pulses with the same center frequency but different bandwidths are examined and the accuracy is indicated by a comparison of the simulation results for the axial and transverse fields with the analytical results for continuous wave excitation.     

一种超声手术刀推挽激励换能器的研究

设计了一种超声手术刀用的新型推挽激励换能器。它是在夹心式单晶堆压电超声换能器的经典构造基础上,把原先激励一组压电陶瓷晶片堆的方式,改为同时施加反相激励的前后两组晶堆。利用有限元方法,对该推挽激励换能器进行模态分析和频率响应分析。在相同大小的电压激励下,相对单晶堆换能器,推挽激励换能器可以获得更高的工作带宽和机电耦合系数,提高了换能器的电声转换效率。按照仿真结果加工推挽激励换能器,实现良好的动力学和电学特性,满足设计要求。     

Wide-band piezoelectric polymer acoustic sources

The design of a wideband acoustic source made of the piezoelectric polymer polyvinylidine fluoride (PVDF) is described. The source was developed for the characterization and absolute calibration of ultrasonic hydrophone probes. Construction details are described and performance characteristics of the wideband PVDF transmitter, including its transmitting voltage response and directivity patterns, are compared with theoretical predictions in the frequency range up to 40 MHz. The Krimholtz-Leedom-Mattaei (KLM) model was used to examine the influence of the PVDF polymer film thickness, the backing acoustic impedance, the cable length, and the electrical source resistance on overall transmit transfer characteristics. A comparison is made with traditional piezoelectric ceramic acoustic sources, and it is shown that piezopolymer transmitters exhibit some improved properties and are well suited for certain ultrasound dosimetry applications. In particular, the polymer sources have been found useful in measurements based on swept-frequency excitation. Those measurements allow characterization of transmitters and receivers to be performed as a virtually continuous function of frequency.     

Computer optimization of transducer transfer functions usingconstraints on bandwidth, ripple, and loss

Transducers, having one piezoelectric layer near its half-wave resonance and N quarter-wave layers, are designed using computer optimization to adjust the thicknesses and impedances of the various layers so as to fit the resulting transfer function to a target function. An augmented Mason model is used to evaluate the transducer. Optimization of fit is by a steepest descent algorithm. Essentially error-free fits are achieved for target functions that match the underlying dynamics. By applying classical filter theory to a lumped-element transducer model, the transducers dynamics are identified as all-pole filters, which are characterized by polynomials of order N to N+1. The design methodology is tested by designing a series of low-loss transducers that explore fractional bandwidths from 45 to 116%. From these studies there appears to be constraints on the minimum Q of the poles, and other properties. Typical power transfer efficiencies of -1 dB are achieved by impedance scale matching. Using a second-order Fano bound, it is shown that the matching layers function as an optimal compensation network for low-loss flat bandpass transducers. Finally, by the inclusion of loss, lower Q poles are demonstrated with a Bessel transducer     

纵弯复合多自由度球形超声电机的研究

摘 要：目前国内外对多自由度超声电机的研究和应用尚属探索阶段,出现了多种结构的多自由度超声电机。本文提出了一种新型单振子纵弯夹心换能器式超声电机结构,由单一驱动足产生多自由度振动轨迹,驱动球形转子作多自由度运动;对十字交叉换能器做了模态分析,对纵振和弯振做了模态简并;建立了驱动足的运动轨迹方程,并仿真分析了典型驱动方式下驱动足的振动轨迹;试验测试了样机转子绕X、Y、Z轴转动的速度与电压之间的关系和转矩与速度之间的关系,计算了相应情况下电机的最大效率;电机旋转方向与分析结果一致。
     

Development of a high voltage sensor using a piezoelectrictransducer and a strain gage

The authors describe the principle and design of an AC high-voltage sensor. When an electric stress is applied, this sensor accurately detects the mechanical strain of a piezoelectric transducer on which a foil strain gage is cemented. Two types of these sensors were designed, and a high-voltage measuring system using them was manufactured for trial. To confirm the frequency response of the trial sensors, an impedance of the trial piezoelectric transducer was performed using a YHP impedance analyzer, and the response-confirmation test of its vibration mode was carried out at the same time. Theoretical and experimental analyses are discussed in terms of the relation between the strain on the piezoelectric transducer and the applied sinusoidal AC voltage. It was ascertained that the strain was directly proportional to the voltage measured, and it was found that the measured percentage errors were less than ±2% for voltages up to 26000 V_p-p     

表面弹性波马达的工作机理和优化设计研究

探讨了表面弹性波马达的工作机理和优化设计。采用具有能量循环功能的表现弹性波换能器结构，提高了表面弹性波马达效率，将马达的驱动电压阈值从100V降到了10V以下。在频率10MHz，峰峰值为10V的正弦的电压激励下，获得振动幅度为20nm的表面性波，马达的无负载速度达到0．34m/s，最大推动力输出达到0．06N。     

An analytical model of multilayer ultrasonic transducers with an inversion layer

Inversion layer ultrasonic transducers have been investigated recently as an interesting approach in wideband transducer design. In this paper we present an analytical model of multilayer ultrasonic transducers with an inversion layer. Our analysis of the wave propagation problem of an inversion layer transducer includes a functional decomposition of the electrical input impedance. It becomes clear from this decomposition that an inversion layer transducer can be modeled as three elements in series connection, i.e., a clamped capacitance, a classical motional impedance, and a coupled motional impedance. The first two elements make up the classical model of a single element transducer. The coupled motional impedance describes the coupled interaction between the regular and the inverted piezoelectric sublayers, and thus reflects the effect of an inversion layer. We present examples which show that inversion layer transducers are advantageous in achieving such useful features as dual-frequency operation mode as used in harmonic imaging or broadband performance desired in most ultrasonic applications.     

Numerical impulse response test to identify parametric models for closed-slot deep-bar induction motors

An impulse response test for estimating the electrical parameters of a deep-bar induction motor is studied. The impulse response test is performed within the two-dimensional finite-element analysis (FEA). The impulse excitation is applied to the stator voltage. Since the test is suitable for modelling the perturbations about a certain operation point, a small-signal model for the double-cage induction machine is derived. The skin effect is taken into account by using two parallel rotor branches. In addition to the small-signal parameters, the steady-state parameters are also estimated using the time-harmonic FEA. The impulse response test is based on the assumption of linear behaviour about an operation point. Thus, the effects of nonlinearity are studied by several methods     

Protection circuits for ultrasound applications

A simple input protection circuit for ultrasound pulse-echo applications is described. Its performance is analyzed with regard to other widely used arrangements. Besides the primary function of showing high impedance during the transducer excitation time and a low impedance path to the amplifier in reception, issues of harmonic distortion, insertion losses, bandwidth, power dissipation, transient response, and noise are addressed. It is shown that the proposed circuit has many advantages, operating without any control signals or bias voltages. It is small and can be considered a good general-purpose protection circuit alternative.     

Modeling and optimization of high-frequency ultrasound transducers

Obtaining an accurate transducer model for a high-frequency transducer can be troublesome using traditional models, such as the KLM model, since it is often difficult to measure precisely the piezoelectric, dielectric, and mechanical properties of the transducer. This paper describes an alternative method of modeling transducers using network theory. The network theory model for a transducer is determined from a measurement of the transducer impedance in water and the pulse-echo response of the system for a given electrical source and load. A discussion of how this model can be used to optimize the design of an electrical matching circuit is given. This method is illustrated by designing a two-element transmission line matching circuit for a miniature 53 MHz transducer. Excellent agreement between the network model prediction and the experimental response is obtained     

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。     

一款宽带圆柱阵研究

圆柱阵换能器具有水平全向的优势,已广泛应用在水声探测领域。文章研究了一款宽带圆柱阵,利用匹配层技术拓宽圆柱阵阵元的带宽,通过有限元仿真优化单个换能器阵元带宽、发送电压响应和阻抗等参数。同时通过仿真以阵元错位密集方式形成圆柱阵,对阵元的个数及排列方式进行仿真优化,制作了一款宽带圆柱阵并进行了测量,圆柱阵直径为400 mm,高度为435 mm,圆柱阵的工作频段为20~30 kHz,频带内起伏3 dB,最大发送电压响应为160.5 dB,圆柱阵-3 dB水平波束宽度为360°。