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The cylindrical piezoelectric transducer has the advantages of large radiation area, high electromechanical coupled coefficient, and omni-direction radiation along the radius. In this paper, a piezoelectric transducer consisting of a radially polarized piezoelectric cylinder and an outer metal cylinder of varying height is presented. The metal cylinder of varying height is approximated as the radial superposition of multiple uniform height metal cylinders, and the equivalent impedance of the transducer's coupled vibration is obtained by using the impedance matrix method, and then the resonance frequency, anti-resonance frequency, effective electromechanical coupled coefficient, and displacement amplification coefficient are obtained. In this paper, the relationship between the vibration characteristics of the cylindrical piezoelectric transducer and its geometric dimensions is studied. An experimental sample of the transducer is fabricated and assembled, and its electrical impedance curve is measured. The measured results are in good agreement with the simulation results and the theoretical calculation results. The displacement distribution of the radiation surface of the transducer at resonance frequency is measured, which verifies that the two coupled vibration modes of the transducer can be effectively excited. [ABSTRACT FROM AUTHOR]

As a critical component of ultrasonic vibration systems, piezoelectric transducers play an essential role in various practical application scenarios. Recent advances in spherical transducers have been widely used in underwater sound and structural health monitoring, while the cascaded spherical piezoelectric transducer with arbitrary piezoceramic shell thickness has not been investigated. Here, we propose a radially cascaded spherical piezoelectric transducer (RCSPT) and derive its electromechanical equivalent circuit with mechanical losses, dielectric losses, and load mechanical impedances. The resulting device is composed of three concentric spherical metal shells and two radially polarized spherical piezoceramic shells. The underlying physical mechanism is the inverse piezoelectric effect, which converts electrical signals into mechanical vibrations. The effects of the spherical piezoceramic shell's thickness and location on the RCSPT are studied. We also analyze the effects of mechanical losses, dielectric losses, and load mechanical impedances on the modulus of input electric impedance of the cascaded spherical transducer. The experiments are conducted to verify the electromechanical characteristics of the resulting device, which are in good agreement with the simulated results and theoretical predictions. Our methodology will offer new possibilities for designing RCSPTs and may promote applications in various fields, such as underwater acoustic detection and structural health monitoring. [ABSTRACT FROM AUTHOR]

This article develops a high-power piezoelectric transformer based on the sandwiched piezoelectric transducer with multioutput characteristics. An advanced high-power voltage transformation technology is realized via using the superior mechanical robustness of the sandwiched piezoelectric transducers. High-power sandwiched piezoelectric transformers (s-PTs) with the unique crisscrossed structure are constructed by four sandwiched piezoelectric transducers with two modes, i.e., antiphase mode and in-phase mode, due to the coupled vibration of the central metal cuboid. Moreover, the related electromechanical equivalent circuit model (EECM) of the s-PTs is established in which two loss factors are introduced into this model, and its impedance characteristics, voltage gains, and power gains are studied as well. The accuracy of EECM is verified by the finite element method and experiments. Results reveal that s-PT has three outputs, and its voltage gains and power ratios are affected by load resistance and loss. The output power of the s-PTs can reach at least 45 W, and the s-PTs can keep the efficiency of ∼35% under high-input electric power, which provides a new idea for high-power piezoelectric transformers. [ABSTRACT FROM AUTHOR]

In this work, a functionally graded spherical piezoelectric transducer (FG-sPET) is proposed and an accurate theoretical model is constructed, mainly composed of a three-port electromechanical equivalent circuit model (EECM). The EECM of FG-sPET can be connected to that of other vibration systems according to the boundary conditions (force and vibration velocity), making it easier to evaluate the whole mechanical vibration system. The validity of the EECM for FG-sPET is verified by comparison with other literature. The effects of geometric dimensions and non-uniform coefficients on the vibration characteristics (resonance/anti-resonance frequencies and effective electromechanical coupling coefficient) of FG-sPET are also studied, contributing to systematically evaluating the key factors determining the vibration characteristics of FG-sPET. The proposed analytical system is of excellent guidance for the structural optimization design of functionally graded piezoelectric devices. [ABSTRACT FROM AUTHOR]

The piezoelectric spherical transducers have attracted extensive attention in hydroacoustics and health monitoring. However, most reported piezoelectric spherical transducers are merely analyzed by the thin spherical shell theory, which is unsuitable for the gradually increased spherical shell thickness. Therefore, it is necessary to develop the radial vibration theory of the piezoelectric spherical transducer with arbitrary wall thickness. Herein, an exact analyzing model for the radial vibration of the piezoelectric spherical transducer with arbitrary wall thickness is proposed. The radial displacement and electric potential for radial vibration of the piezoelectric spherical transducer are precisely given, and then, the electromechanical equivalent circuit is obtained. Based on the electromechanical equivalent circuit, the resonance/antiresonance frequency equations of piezoelectric spherical transducers in the radial vibration are obtained. Besides, the relationship between performance parameters and wall thicknesses is discussed. The wall thickness has a significant influence on the performance parameters of the spherical transducer. The accuracy of the theory is validated by comparing the results with the experiment and finite element analysis. [ABSTRACT FROM AUTHOR]

• A tunable spherical piezoelectric transducer with adjustable resonance and antiresonance frequencies and the effective electromechanical coupling coefficient is proposed. • The electromechanical equivalent circuit model to analyze the characteristics of the tunable spherical piezoelectric transducer is established. • The variation of the resonance/antiresonance frequency and the effective electromechanical coupling coefficient with different electric impedances are performed. Spherical piezoelectric transducers are a critical component of ultrasonic vibration systems with significant applications in various practical scenarios such as underwater acoustic detection and structural health monitoring. The existing spherical piezoelectric transducers have fixed electromechanical characteristics that limit their applications in scenarios with multi-frequency or frequency variation requirements. It would therefore be intriguing, from the viewpoints of both science and technology, to break through this limit by introducing external electric load impedance. Here we propose a tunable spherical piezoelectric transducer (TSPT) capable of adjusting the electromechanical characteristics by changing the resistance, inductance, and capacitance applied to the passive piezoceramic shell. The theoretical and numerical results show that when the resistance is exerted on the inner and outer piezoceramic shells, the resonance is accompanied by large variations at low values of resistance, while it becomes almost constant at high values of resistance. When the inductance is exerted on the outer piezoceramic shell, the resonance frequency obtained by the finite element method can be changed from 72730 Hz to 42928 Hz by adjusting the inductance, indicating that the TSPT can realize a rich and selective resonance frequency region. The resonance/antiresonance frequency decreases while the effective electromechanical coupling coefficient increases, when the capacitance applied on the inner and outer piezoceramic shells increases. The experiments are conducted to verify the effectiveness of the proposed TSPT, which is in agreement with the simulated results and theoretical predictions. Our methodology will offer possibilities to extend the working frequency range of the existing piezoelectric spherical transducer for underwater acoustic detection, hydrophones, and the spherical smart aggregate for civil structural health monitoring. [ABSTRACT FROM AUTHOR]

A longitudinally polarized piezoelectric ceramic stack with two piezoelectric ceramic elements is an important part of sandwich piezoelectric transducers. The three-dimensional coupled vibration of piezoelectric ceramic stack is analyzed. Since the longitudinal and radial dimensions of particular piezoelectric ceramic stacks are approximately equal, one-dimensional theory cannot be used for analysis. The piezoelectric ceramic stack is analyzed by the equivalent elastic method, which is an approximate analytical method, and it is considered that the coupled vibration of a piezoelectric ceramic stack is composed of equivalent radial and longitudinal vibrations. These two equivalent vibrations are connected by a mechanical coupling coefficient. The radial and longitudinal electromechanical equivalent circuits are obtained, and the resonance frequency equations are derived. The dependency of the radial and longitudinal resonance frequencies on the geometrical dimensions for piezoelectric ceramic stack is analyzed. The height or radius has a large influence on the longitudinal resonance frequency or the radial resonance frequency. Two sets of piezoelectric ceramic stacks are fabricated. The experimental results, COMSOL simulated results, and theoretical results are in good agreement. [ABSTRACT FROM AUTHOR]

Electromechanical equivalent circuit of the radially polarized cylindrical piezoelectric transducer in coupled vibration is obtained. The equivalent elasticity method is used to analyze the coupled vibration. It is an approximate analytical method, ignoring the shear and torsion stresses and strains, dividing the coupled vibration into the extensional radial and longitudinal vibrations. A mechanical coupling coefficient is introduced to connect these two equivalent vibrations. According to the electromechanical equivalent circuit, the resonance frequency equations as functions of the frequency and the mechanical coupling coefficient are acquired. The sound pressure level and far field sound pressure distribution for the transducer in water are simulated. It is demonstrated that the radiation range of the cylindrical transducer is larger than that of the ring-type transducer. Several prototypes of the transducer are fabricated; the radial and longitudinal resonance frequencies are measured. The experimental resonance frequencies are in good agreement with the analytical results. The acquisition of the electromechanical equivalent circuit contributes to analyzing the electromechanical characteristics of the radial polarized cylindrical transducer. [ABSTRACT FROM AUTHOR]

Highlights • A radially composite cylindrical piezoelectric transducer consisting of a piezoelectric ceramic cylinder and the inside and outside concentric metal cylinders is analyzed. • Equivalent elasticity method is used to study the coupled vibrations of the cylinders. The electromechanical equivalent circuit is deduced, which provides a theoretical basis for the transducer in practice applications. • When the radius is comparable with the height of the transducer, the radial vibrational displacement is close to the longitudinal vibrational displacement, where the coupling between the radial vibration and the longitudinal vibration is strong. • The greater is the proportion of the piezoelectric cylinder in the transducer, the smaller are radial and longitudinal resonance frequencies, and the larger are effective electromechanical coupling coefficients. • COMSOL-Multiphysics 5.3 is employed to simulate the vibration mode and the displacement distribution of the transducer. The measured resonance frequencies of the transducer are consistent with the simulated and theoretical results. Abstract Electromechanical equivalent circuit for the radially composite cylindrical piezoelectric transducer in coupled vibration is deduced. The transducer is composed of a piezoelectric cylinder sandwiched by two concentric metal cylinders. Equivalent elasticity method is used to study the coupled vibrations of the three cylinders. A ratio named the mechanical coupling coefficient is introduced to divide the coupled vibration into the radial and longitudinal vibrations. The electromechanical equivalent circuits for the transducer and the resonance frequency equations are obtained. When the height is close to the radius of the transducer, the coupling between the radial vibration and the longitudinal vibration is strong. The thicker is the piezoelectric cylinder, the larger is the effective electromechanical coupling coefficient. Several prototypes of the transducer are fabricated. It is demonstrated that the theoretical resonance frequencies are in good agreement with the numerical and experimental results. [ABSTRACT FROM AUTHOR]

The longitudinally cascaded piezoelectric ultrasonic transducer is studied which is composed of two longitudinally sandwiched piezoelectric transducers connected together mechanically in series and electrically in parallel. When the losses and load are taken into account, the electromechanical equivalent circuit of the transducer is obtained; the input electric impedance is analyzed and the resonance/anti-resonance frequency equations are obtained assuming one dimensional longitudinal vibrational theory. The relationship among the resonance/anti-resonance frequency, the effective electromechanical coupling coefficient, the mechanical quality factor and the electro-acoustic efficiency with the geometrical dimension, the losses, and the load is analyzed. Two longitudinally composite transducers are designed, made, and measured. It is shown that the theoretical resonance/anti-resonance frequencies, the effective electromechanical coupling coefficient, and the mechanical quality factor are in good agreement with the experimental results. It is expected that this kind of composite transducer can be used in large power and high intensity ultrasonic applications, such as ultrasonic liquid processing, ultrasonic metal machining, and ultrasonic welding and soldering. [ABSTRACT FROM AUTHOR]

Three-dimensional coupled vibration of the composite cylindrical piezoelectric transducer is analyzed. The composite cylindrical piezoelectric transducer consists of an inner axially polarized piezoelectric ceramic cylinder and an outer metal cylinder with the same height. Coupled vibration of the composite cylindrical piezoelectric transducer is analyzed by equivalent elasticity method, which is an approximate analytical approach. According to this method, coupled vibration of the cylindrical transducer is regarded as an interaction between a plane radial vibration and a longitudinal vibration. The radial and longitudinal electromechanical equivalent circuits of the piezoelectric transducer are acquired. Input impedances as functions of the resonance frequency and the mechanical coupling coefficient are derived to obtain resonance frequency equations. The analytical results are supported by experimental and numerical simulated results of two prototypes of the piezoelectric transducer. The composite cylindrical piezoelectric transducer presented in this paper is superior to single cylindrical piezoelectric transducers, composite ring-type, and tube-type transducers in the field of high output power and efficiency. [ABSTRACT FROM AUTHOR]

• An active radial ultrasonic horn with adjustable performance is proposed. • The active adjustment of resonance frequency and displacement magnification is performed. • The ability of inductance to modulate the resonance frequency and displacement magnification is greater than that of resistance and capacitance. As a key component of high-powered ultrasonic vibration systems, ultrasonic horns play an important role in various practical application scenarios. Recent advances in longitudinal ultrasonic horns have enabled them to magnify the Langevin transducer's mechanical vibration and efficiently transmit the mechanical vibration to the mechanical load. However, limited research has been devoted to active radial ultrasonic horns in radial vibration. Here we propose an electric impedance-controlled active radial ultrasonic horn (ARUH) capable of tuning both resonance frequency and displacement magnification in radial vibration. The resulting device consists of a radially polarized piezoelectric ring connected with adjustable electric impedance and two metal rings with variable sections. The underlying mechanism is that the change of the converted mechanical impedance of the piezoelectric material by the external electric impedance connected to the piezoelectric material modulates the resonance frequency and displacement magnification of the ARUH. It can be found that the resonant frequency shifts to higher frequencies as the resistance increases and the resonant frequency shifts to lower frequencies as the inductance and capacitance increase, while the displacement magnification has the opposite trend to the resonance frequency. For example, the resonance frequency of the constant-section radial horn is 41130.2 Hz. When the inductance increases from −0.007 to 0.007H, the resonance frequency shifts from 41171.3 to 34606.2 Hz and the displacement magnification moves from 1.189 to 3.5. The experiments are conducted to verify the effectiveness of the resulting device, which is in good agreement with the simulated results and theoretical predictions. Our design with functionality and flexibility opens up possibilities for the design of ARUHs and may find important application prospects in diverse fields such as cold-drawn steel tubes and ultrasonic plastic welding. [ABSTRACT FROM AUTHOR]

A new type of wireless power transmission system is proposed. It is composed of two sandwiched composite piezoelectric transducers in length extensional vibration, which are connected together by an intermediate metal transmission cylinder. When the dielectric and mechanical losses are considered, the resonance/antiresonance frequency equations are obtained. The effect of the mechanical and the dielectric loss, the geometrical dimension and the load electric impedance on the effective electromechanical coupling coefficient, the voltage gain, and the power ratio is analyzed. It is shown that the mechanical and the dielectric losses almost have no effect on the resonance/antiresonance frequency. The geometrical dimension has obvious effect on the resonance/antiresonance frequency, the voltage gain, the effective electromechanical coupling coefficient and the power ratio. Corresponding to definite geometrical dimensions, the effective electromechanical coupling coefficient and the voltage gain have maximum values. There is optimum load electric impedance at which the power ratio reaches the maximum value. Two wireless power transmission systems are designed and manufactured; the resonance/antiresonance frequencies, the voltage gain, and the power ratio are measured. It is shown the measured frequencies are in good agreement with the theoretical results. [ABSTRACT FROM AUTHOR]

Abstract: The cylindrical radial composite piezoelectric ceramic transducer is presented and studied. The transducer consists of an inner radially polarized piezoelectric ceramic thin-walled circular tube and an outer metal thin-walled cylindrical shell which are composed in the radial direction. The radial vibrations of a metal thin-walled cylindrical shell and a piezoelectric ceramic thin-walled circular tube are analyzed. Their radial electro-mechanical equivalent circuits are obtained. Based on the equivalent circuits and the radial boundary conditions, the composite electro-mechanical equivalent circuit of a cylindrical radial composite piezoelectric ceramic transducer is obtained, the resonance frequency and anti-resonance frequency equations of the cylindrical radial composite piezoelectric transducer are derived. Then the relationship between the resonance frequency, the anti-resonance frequency, the effective electro-mechanical coupling coefficient and the geometrical dimensions of the cylindrical radial composite piezoelectric ceramic transducer is analyzed. It is illustrated that the resonance frequencies and the anti-resonance frequencies from the frequency equations are in a good agreement with that of the experimental results. [Copyright &y& Elsevier]

• A radially sandwiched spherical transducer is proposed for the first time. • The radially sandwiched spherical transducer can design in the second mode. • The proposed equivalent circuit model can be extended to other spherical transducer. With the development of ultrasonic technology, some ultrasonic processing technologies require a wide processing range. In this paper, a radially sandwiched spherical piezoelectric transducer is proposed and analyzed, which is composed of a spherical piezoelectric ceramic sandwiched by two concentric spherical metal shells. The electromechanical equivalent circuits of the spherically isotropic spherical shell and the spherical piezoelectric ceramic with arbitrary wall thickness are derived from their motion equations. According to the mechanical boundary conditions, the electromechanical equivalent circuits and frequency equation of various piezoelectric composite vibration systems can be obtained, including the radially sandwiched spherical piezoelectric transducer. The correctness of the proposed theory is verified via comparison with the finite element method and the previous theoretical model. In addition, the 2nd-order effective mechanical coupling coefficient for the radially sandwiched spherical piezoelectric transducer is higher than that of 1st-order within a specific range of wall thickness, which can be designed as the high-frequency transducer. The radially sandwiched spherical piezoelectric transducer is expected to be used in underwater sound, structural health monitoring, and high-frequency ultrasound. [ABSTRACT FROM AUTHOR]

The radial vibration of a radial composite tubular transducer with a large radiation range and power capacity is studied. The transducer is composed of a longitudinally polarized piezoelectric ceramic tube and a coaxial outer metal tube. Assuming that the longitudinal length is much larger than the radius, the electromechanical equivalent circuits of the radial vibration of a piezoelectric ceramic long tube and a metal long tube are derived and obtained for the first time following the plane strain theory. As per the condition of the continuous forces and displacements of two contact surfaces, the electromechanical equivalent circuit of the tubular transducer is obtained. The radial resonance/anti-resonance frequency equation and the expression of the effective electromechanical coupling coefficient are obtained. Then, the effects of the radial geometry dimension of the transducer on the vibration characteristics are analyzed. The theoretical resonance frequencies, anti-resonance frequencies, and the effective electromechanical coupling coefficients at the fundamental mode and the second mode are in good agreement with the finite element analysis (FEA) results. The study shows that when the overall size of the transducer is unchanged, as the proportion of piezoelectric ceramic increases, the radial resonance/anti-resonance frequency and the effective electromechanical coupling coefficient of the transducer at the fundamental mode and the second mode have certain characteristics. The radial composite tubular transducer is expected to be used in high-power ultrasonic wastewater treatment, ultrasonic degradation, and underwater acoustics, as well as other high-power ultrasonic fields. [ABSTRACT FROM AUTHOR]

To increase the ultrasonic intensity and power of a piezoelectric transducer, a cascaded piezoelectric ultrasonic transducer with the three sets of piezoelectric ceramic stacks is analyzed. The cascaded piezoelectric ultrasonic transducer consists of four metal cylinders and three sets of piezoelectric ceramic stacks in the longitudinal direction. In analysis, the electromechanical equivalent circuit of the cascaded piezoelectric ultrasonic transducer is obtained, as well as the resonance/anti-resonance frequencies equations. By means of an analytical method, when the position of piezoelectric ceramic stacks PZT-2/PZT-3 changes, the resonance/anti-resonance frequencies and the effective electromechanical coupling coefficient of the cascaded piezoelectric ultrasonic transducer have certain characteristics. Several prototypes of the cascaded piezoelectric ultrasonic transducer are manufactured. The experimentally measured resonance frequencies are in good agreement with the theoretical and simulated results. The cascaded piezoelectric ultrasonic transducer with three sets of piezoelectric ceramic stacks presented in this paper is expected to be used in the field of high power ultrasound. [ABSTRACT FROM AUTHOR]

• A multidirectional piezoelectric ultrasonic transducer (MPUT) in mutli-mode coupled vibration is proposed. • An accurate theoretical analysis model of the MPUT is established to estimate its mutli-frequency characteristics. • The MPUT has adjustable coupled vibration intensity and enables dual-frequency and multi-directional uniform radiation. • The MPUT's three-dimensional radiation in water is satisfactory after increasing the radial size. Nowadays, expanding the operating range and realizing multifrequency operation have emerged as focal and imperative objectives in the design of ultrasonic transducers. Due to the limitations of structure and radial sizes, conventional Langevin transducers encounter challenges in meeting the increasingly stringent requirements across diverse ultrasonic applications. Hence, this paper proposes a multidirectional piezoelectric ultrasonic transducer (MPUT) consisting of a large-dimension sandwich piezoelectric transducer (LSPT) and a metal tube in mutli-mode coupled vibration, capable of achieving wide-ranging and multifrequency acoustic radiation. Based on the analytical method, a two-dimensional electromechanical equivalent circuit model (2D-EECM) of the MPUT is established, and its frequency calculation results are validated through the finite element method (FEM) and impedance analysis experiment. The vibration testing results indicate that adjusting the radial size can control the coupled vibration intensity of the MPUT and achieve dual-frequency and multidirectional uniform radiation. The radiation sound field testing results confirm the MPUT's satisfactory three-dimensional radiation capability in water and significant improvement in acoustics operating range. [ABSTRACT FROM AUTHOR]

• An improved radial composite transducer is proposed, which consists of a metal ring and a radially polarized piezoelectric stack. This structure effectively solves the problem of difficult excitation due to large wall thickness of radially polarized piezoelectric ceramics. • A new electromechanical equivalent circuit model (EECM) and a numerical model of the nRCT in radial vibration are established, and the relationship between frequency characteristics of the nRCT and geometric size is analyzed. • Compared with the tRCT, under the same electrical excitation, the equivalent electrical impedance of the nRCT designed in this paper decreases to 26%, and the radial vibration displacement increases to 142%. • The nRCT and the tRCT are fabricated, and the experimental results have well verified the results of the theoretical modeling analysis. In the ring radial transducer, the wall thickness of the radially polarized piezoelectric ceramic is limited by the polarization technology and operating voltage, resulting in the limited power capacity and vibration ability of the transducer. Hence, an improved novel radial composite transducer (nRCT) is proposed in this paper, which consists of a radially polarized piezoelectric stack and a metal ring. Piezoelectric stack is used to enhance vibration and effectively solve the problem of difficult excitation caused by large wall thickness. A new electromechanical equivalent circuit model (EECM) of the nRCT in radial vibration is established, and the relationship between frequency characteristics of the nRCT and geometric size is analyzed. The finite element method (FEM) is used to carry out numerical modeling of the nRCT and the traditional radial composite transducer (tRCT), and preliminarily verify the calculation results of EECM. Compared with the tRCT, under the same electrical excitation, the equivalent electrical impedance of the nRCT designed in this paper decreases to 26%, and the radial vibration displacement increases to 142%. Finally, the nRCT and the tRCT are fabricated, and the experimental results have well verified the results of the theoretical analysis. The proposed radial piezoelectric stack model provides a new idea for the optimal design of radial vibration piezoelectric devices, which is expected to be further applied to the design of hydrophones, piezoelectric transformers, and medical ultrasound devices. [ABSTRACT FROM AUTHOR]

• An equivalent circuit model for functionally graded ring piezoelectric transducer is proposed. • The proposed model can degenerate to the model for traditional transducer. • The model-derived results are in good agreement with those of FEM and experiment. Ring piezoelectric transducers (rPETs) have attracted multitudinous attentions due to their widespread applications in hydro-acoustic engineering, structural health monitoring, and energy harvesting. However, cracks are inevitably occurred by the concentrated stress at the interface between metal and piezoelectric ceramics, which will seriously affect the performance and service life of the devices. Hence, a novel functionally graded ring piezoelectric transducer (FG-rPET) has been designed and an accurate analytical system is constructed mainly including a three-port electromechanical equivalent circuit model (EECM) which can acquire exact solutions in radial vibration. In addition, the proposed three-port EECM has excellent generalizability, which is also applicable to conventional rPETs. The validity of the EECM is verified by experiments and the finite element method. The vibration characteristics (resonance/anti-resonance frequencies and effective electromechanical coupling coefficient (k eff)) with fundamental and second modes for the FG-rPETs can be regulated via the inhomogeneity index and wall thickness. Markedly enhanced k eff at second modes can be obtained for the FG-rPETs with specific wall thicknesses. The proposed analytical system has important guiding significance for structure optimization design of piezoelectric devices, and the designed FG-rPET is expected to break the bottleneck of mechanical properties for the conventional rPETs. [ABSTRACT FROM AUTHOR]

In this work, we proposed an effective way to fabricate a tangentially polarized composite cylindrical transducer with high electro-mechanical coupling coefficient (EMCC) by radially connecting an inner tangential polarized piezoelectric tube with an outer metal ring. The resonance frequency and EMCC of the proposed transducer are calculated according to frequency equations, which are obtained from the equivalent circuit of the transducer, and the results indicate that EMCC of the tangentially polarized cylindrical transducer is much higher than that of the cylindrical transducer polarized in radial direction. Furthermore, the Finite Element Method (FEM) model of the transducer is established and used for numerical simulation of the vibration models and the optimum configuration parameters. On the basis of those theoretical results, serials of prototype transducers are manufactured with an inner tangential polarized piezoelectric tube connecting with different outer metal cylindrical shells. The admittance characteristics of the fabricated transducers measured by Impedance Analyzer clearly demonstrate that the resonance frequencies of the transducers are in good agreement with those of simulation results, and the effective EMCC of transducers varies with the material of metal cylindrical shell, in which aluminum metal shell possesses the highest EMCC. [ABSTRACT FROM AUTHOR]

• A bimorph rectangular transducer based on type 2-2 piezoelectric composites is proposed. • Resonance frequency equations of the thickness-polarized transducer are derived with simply supported boundary conditions by using the equivalent elastic method. • The results obtained by numerical simulation agree well with those obtained by theoretical analysis. • Compared with the PB transducer, the PCB transducer has a larger bending vibration displacement amplitude, a larger transmitting voltage response, and better acoustic matching and radiation capabilities. In order to improve the acoustic radiation capability of piezoelectric ultrasonic transducer in gas, a bimorph rectangular transducer based on type 2-2 piezoelectric composites is proposed in this paper, which is composed of two piezoelectric composite rectangular slices with thickness polarization. First, the bending vibration of the rectangular transducer is divided into two bending vibrations of the thin rods in the x and y directions using the equivalent elastic method. When the mechanical coupling coefficient is introduced and combined with the anisotropic piezoelectric equations, the resonance frequency equations of the thickness-polarized transducer are derived with simply supported boundary conditions. Then the bending vibration of the transducer is numerically simulated. The results show that the resonance frequency obtained by the analytical method is in good agreement with the numerical simulation results. Finally, the influence of geometrical size and two-phase volume ratio on the bending vibration performance of the transducer is analyzed. Compared with the piezoelectric bimorph transducer, the piezoelectric composite bimorph transducer has a larger bending vibration displacement amplitude, a larger transmitting voltage response, a lower resonant frequency and better acoustic radiation capability. [ABSTRACT FROM AUTHOR]