压电圆管换能器振动特性的薄壳理论分析

本文运用弹性力学中的薄壳理论，分析了径向极化压电陶瓷圆管换能器的振动特性，并在此基础上推导出换能器等效电路的特性阻抗，为换能器的设计提供了依据。分析及计算结果表明，本文的理论与以往常用的薄膜理论相比，不仅在物理模型的描述上更为完整准确，在计算精度上也更接近实际。     

Measurements of mutual radiation impedance between baffled cylindrical shell transducers

The mutual radiation impedances between two baffled cylindrical shell transducers, made of PZT-4 piezoelectric rings with one half of the cylindrical surface covered by a compliant baffle, were determined in experiments as a function of separation distance using an experimental technique recently described [B. Aronov, J. Acoust. Soc. Am. 119, 3822-3830 (2006)]. Two baffled cylindrical shell transducers were connected electrically in parallel and the input electrical admittance was measured at different separations when the two transducers were operated in phase and then 180 degrees out-of-phase in both the coaxial and horizontal (side-by-side) alignments. The mutual radiation impedances were then computed using an electrical equivalent circuit to determine the significance of interaction for cylindrical elements in these array geometries.     

Energy trapping in power transmission through a circular cylindrical elastic shell by finite piezoelectric transducers

We study the transmission of electric energy through a circular cylindrical elastic shell by acoustic wave propagation and piezoelectric transducers. Our mechanics model consists of a circular cylindrical elastic shell with finite piezoelectric patches on both sides of the shell. A theoretical analysis using the equations of elasticity and piezoelectricity is performed. A trigonometric series solution is obtained. Output voltage and transmitted power are calculated. Confinement and localization of the vibration energy (energy trapping) is studied which can only be understood from analyzing finite transducers. It is shown that when thickness-twist mode is used the structure shows energy trapping with which the vibration can be confined to the transducer region. It is also shown that energy trapping is sensitive to the geometric and physical parameters of the structure.     

Analysis of unidirectional broadband piezoelectric spherical shell transducers for underwater acoustics

This paper presents an analytical investigation and experimental verification of the properties of unidirectional broadband piezoelectric acoustic transducers utilizing axisymmetric vibrations of both complete and incomplete spherical piezoelectric shells and is a continuation of a previous paper that presented the electromechanical modal analysis part of the problem [J. Acoust. Soc. Am. 130(2), 753-763 (2011)]. The analysis covers the treatment of the acoustic radiation and reception problem by including analysis of the acoustic impedances and diffraction coefficients as a function of geometry and modal excitation as well as providing specific design examples including multimode spherical acoustic transducers with conformal baffles, and transducers made of incomplete shells (e.g., hemispheres and caps) with free circumferential boundary conditions. The energy method is used to obtain equivalent parameters for a multi-contour electromechanical circuit representation of the transducer and to calculate the transducer performance characteristic as sound projectors and as receivers. Experimental results are obtained on representative piezoceramic transducer prototypes and are in good agreement with the analytical results.     

Analysis of transient responses in a laminated piezoelectric cylindrical shell

A hybrid numerical method is proposed for analysis of transient responses in a multilayered piezoelectric cylindrical shell.In the present method,the associated equations of the displacement field and the electro-potential field are developed using an analytical-numerical method.The piezoelectric cylindrical shell is discretized into layered annular elements along the wall thickness direction.The governing equations are determined by Hamilton's Principle considering the coupling between the elastic and elec...     

Brushed-on piezoelectric transducers

Design considerations and operation of vibration-sensitive transducers that are brushed into place are described. These transducers are made of a slurry of crushed piezoelectric ceramic and a liquid binding material that becomes rigid upon exposure to the air. The resulting hard coating is electroded and polarized in place prior to its use as a vibration-detecting transducer. The parameters for optimum particle size, concentration and electrode shape are determined for transducers that are suitable for detecting vibration. Feasibility of the technique is determined by its use in detecting ultrasonic vibration of small rigid members. The technique permits deposition of coats less than 1mm thick with a particle concentration of up to 77 percent of active material. The sensitivities obtained are compared to those of solid piezoelectric materials.     

Simulation of elastic wave propagation in cylindrical structures including excitation by piezoelectric transducers

The development and optimization of non-destructive testing procedures usually needs experimental data. As experiments are time-consuming and expensive to conduct, we would like to use numerical data instead. This is admissible, if the simulation describes the physical experiments accurately. A three-dimensional displacement-stress finite-difference model is presented for a piezoelectric transducer coupled to an anisotropic tube. The allocation of the displacement and stress components on a staggered grid leads to a stable scheme. A full piezoelectric model of the transducer is used, including transverse isotropy in the elastic, dielectric, and piezoelectric constants. Similar to an experiment, elastic waves are excited in the corresponding simulation by applying a voltage signal to the electrodes of the piezoelectric transducer. Predictions of the simulation model for a piezoelectric ring transducer coupled to a carbon-fibre-reinforced shell are compared to experimental results to test the validity of the numerical data.     

Effects of coupled vibrations on the acoustical performance of underwater cylindrical shell transducers

An experimental investigation of the effects of coupled vibrations on the acoustical performance of underwater transducers made from radially polarized, thin walled, air-backed, piezoelectric cylinders as a function of their height-to-diameter aspect ratio is presented. Characteristics of the frequency response, directivity patterns, and effectiveness of the transducers are considered in comparison with analogous characteristics for the transducers comprised of mechanically separated rings, otherwise having the same geometry. Recommendations are made on the application of cylindrical piezoelectric elements with different aspect ratios for underwater transducer applications.     

Active control of low-frequency sound radiation by cylindrical shell with piezoelectric stack force actuators

A novel active control method of sound radiation from a cylindrical shell under axial excitations is proposed and theoretically analyzed. This control method is based on a pair of piezoelectric stack force actuators which are installed on the shell and parallel to the axial direction. The actuators are driven in phase and generate the same forces to control the vibration and the sound radiation of the cylindrical shell. The model considered is a fluid-loaded finite stiffened cylindrical shell with rigid end-caps and only low-frequency axial vibration modes are involved. Numerical simulations are performed to explore the required control forces and the optimal mounting positions of actuators under different cost functions. The results show that the proposed force actuators can reduce the radiated sound pressure of low-frequency axial modes in all directions.     

KLM model for lossy piezoelectric transducers

A KLM model has been developed using equivalent circuits to analyze the effects of different loss mechanisms on the transducer performance in the time and frequency domain. Transducers from two different piezoelectric materials (lead-zirconate-titanate (PZT) and polyvinylidene fluoride) were constructed to validate our model. Experimental results are in good agreement with the theoretical simulation.     

压电MEMS超声换能器研究进展

MEMS(micro-electromechanical systems)超声换能器(MEMS ultrasonic transducer,简称MUT)是采用微电子和微机械加工技术制作的新型超声换能器。与传统超声换能器相比,MUT具有体积小、重量轻、成本低、功耗低、可靠性高、频率控制灵活、频带宽、灵敏度高以及易于与电路集成和实现智能化等特点。是超声换能器的重要的研究方向之一。MUT的研究主要包括压电MUT(piezoelectric MUT,简称PMUT)和电容MUT(capacitiveMUT,简称CMUT)两个方面。本文概述了PMUT研究的发展进程和研究成果,展望了PMUT的研究和应用前景。     

Acoustic radiation from a shell-encapsulated baffled cylindrical cap

An exact study of radiation of an acoustic field due to radial/axial vibrations of a baffled cylindrical piston, eccentrically positioned within a fluid-filled thin cylindrical elastic shell, into an external fluid medium is presented. This configuration, which is a realistic idealization of a liquid-filled cylindrical acoustic lens with a focal point inside the lens when used as a sound projector, is of practical importance with a multitude of possible applications in underwater acoustics and ocean engineering. The formulation utilizes the appropriate wave field expansions along with the translational addition theorems for cylindrical wave functions to develop a closed-form solution in the form of an infinite series. Numerical results reveal the key effects of excitation frequency, cap angle, radiator position (eccentricity), dynamics of the elastic shell, and cap surface velocity distribution on sound radiation.     

Vibration characteristics of piezoelectric torsional transducers

The vibrational characteristics of Langevin-type torsional transducers, which consist of two piezoelectric torsional disks and two elastic blocks, are studied theoretically and experimentally in this paper. The differential equations of piezoelectric torsional motions are derived in terms of the circumferential displacement and the electric potential. Solutions of the boundary-value problem yield the natural frequencies and mode shapes of the transducers, and the natural frequencies are verified by comparing the numerical results with the experimental ones. The theoretical results enable one to quantitatively predict the effect of the elastic blocks on the reduction of the natural frequencies of a Langevin-type torsional transducer.     

Radial vibration characteristics of spherical piezoelectric transducers

This paper presents the vibration characteristics of the radial mode in spherical piezoelectric transducers. The differential equations of piezoelectric radial motion have been derived in terms of radial displacement and electric potential. Applying mechanical and electrical boundary conditions yielded a characteristic equation for radial vibration. Theoretical calculations of the fundamental natural frequency have been compared with numerical and experimental results for transducers of several sizes, and have shown a good agreement. This paper discusses the dependence of natural frequencies on the radius and thickness of the piezoelectric spheres and the difference between piezoelectric and elastic resonances. From the results it has been concluded that the natural frequency was not affected for the first radial mode but was reduced by the piezoelectric phenomenon. It has also been concluded that the natural frequency of the first radial mode depended mostly on the radius rather than on the thickness of the sphere whereas the natural frequency of the second radial mode depended mostly on the thickness rather than the radius.     

Modeling of functionally graded piezoelectric ultrasonic transducers

The application of functionally graded material (FGM) concept to piezoelectric transducers allows the design of composite transducers without interfaces, due to the continuous change of property values. Thus, large improvements can be achieved, as reduction of stress concentration, increasing of bonding strength, and bandwidth. This work proposes to design and to model FGM piezoelectric transducers and to compare their performance with non-FGM ones. Analytical and finite element (FE) modeling of FGM piezoelectric transducers radiating a plane pressure wave in fluid medium are developed and their results are compared. The ANSYS software is used for the FE modeling. The analytical model is based on FGM-equivalent acoustic transmission-line model, which is implemented using MATLAB software. Two cases are considered: (i) the transducer emits a pressure wave in water and it is composed of a graded piezoceramic disk, and backing and matching layers made of homogeneous materials; (ii) the transducer has no backing and matching layer; in this case, no external load is simulated. Time and frequency pressure responses are obtained through a transient analysis. The material properties are graded along thickness direction. Linear and exponential gradation functions are implemented to illustrate the influence of gradation on the transducer pressure response, electrical impedance, and resonance frequencies.     

A programmable pulse generator for piezoelectric multielement transducers

A pulse generator for multielement ultrasonic transducers has been developed with digital control of pulse timing and firing. It can optimize matching to the probe characteristics, and can consequently maximize the amplitude of the received echo.     

Characterization of cylindrical ultrasonic transducers using acoustic holography

We present the results of studying the vibrational velocity distribution over the surface of cylindrical ultrasound transducers by acoustic holography. We describe two approaches for acoustic holography: the spatial spectrum method and the Rayleigh integral method. In the case of cylindrical sources the spectral method has a specific feature in comparison to the case of quasi-plane sources: small-scale spectrum components having the form of evanescent (nonpropagating) waves near the source, turn into propagating waves at a certain distance from the source. The use of such a mixed type of waves makes it possible to increase the holographic resolution. To conduct holography of cylindrical sources by the Rayleigh integral method, a modification consisting in the superimposing of boundaries on the integration region is proposed. We present the results of numerical simulation and physical experiments on holography of small cylindrical piezoelectric transducers. We demonstrate that the proposed methods of holography make it possible to recover the vibration structure of source surfaces up to order of the wavelength scales.     

The energy method for analyzing the piezoelectric electroacoustic transducers

The energy method of calculating the properties of piezoelectric electroacoustic transducers is considered. The Lagrangian of an electroacoustic transducer as a system performing multiple energy conversions is introduced. The Euler equations describing operation of a transducer with many mechanical degrees of freedom are derived from the least action principle. The corresponding multicontour equivalent circuit of the transducer is introduced. For the particular case of a transducer having one mechanical degree of freedom the governing equations are obtained by applying the Energy Conservation Law, and equivalent circuit with one mechanical branch also introduced. Application of the energy method is illustrated with examples of the pulsating spherical transducer as the one degree of freedom system and the multimode cylindrical transducer comprised of circular rings as the system with multiple degrees of freedom. Advantages of the method for application with electroacoustic transducers are summarized.     

Time-domain analyses of acoustics-structure interactions for piezoelectric transducers.

Piezoelectric transducers coupled with a surrounding medium are analyzed in time domain using the coupled finite element and boundary element method. Three-dimensional solid elements are employed to model the piezoelectric transducer, while the surrounding medium is described by the boundary integral equation and the boundary of the medium is modeled by two-dimensional spatial elements. Verification studies were conducted to evaluate the accuracy and convergence of the present numerical algorithm and they show that the present numerical solutions agree well with the analytical ones. The influence of the surrounding medium on the acoustic field is studied. The interaction between the structure and surrounding medium affects the structure dynamic performances and acoustic pressure distributions significantly. However, in the present study we show that the radiation directivity is insignificantly influenced by the surrounding medium.