Study on multi-frequency characteristics of a longitudinal ultrasonic transducer with stepped horn

Multi-mode coupled vibration analysis and radiation sound field investigation of a novel multidirectional piezoelectric ultrasonic transducer

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.

Effect of electric impedance on the electromechanical characteristics of tunable spherical piezoelectric transducer

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.

A critical review of piezoelectric ultrasonic transducers for ultrasonic-assisted precision machining

Piezoelectric ultrasonic-assisted precision machining (PUAPM) technology is considered to be an efficient and environmentally friendly machining strategy by virtue of cutting force reduction, ductile cutting promotion, tool wear and machining noise reduction. Piezoelectric ultrasonic transducer (PUT) provides ultrasonic energy for PUAPM system, which is the core component to ensure the normal operation of the system. PUTs for PUAPM devices have emerged endlessly in recent decades and have been successfully applied in many fields, such as MEMS, biomedicine, optoelectronics, aerospace, etc. However, there is no comprehensive classification and analysis of the basic configurations, excitation principles, typical structures, performance analyses and control strategies for PUT. This work gives a critical review of research on PUT in recent years, especially the structural optimization, application expansion and ultrasonic energy stabilization in PUAPM. The influence mechanism of excitation mode, modal type, modal combination, horn structure and ceramic arrangement on the optimization of PUT structure is summarized. The improvement effect and mechanism of PUT vibration dimension, amplitude, frequency and structural characteristics on surface roughness, surface texture and cutting force are discussed. In addition, the causes of PUT amplitude fluctuation, and the influence of sensing and control methods on PUT amplitude regulation and system integration are analyzed. This review will help in understanding the current development and diversified applications of PUT and will promote the application of ultrasonic technology in more fields.

Systematic design and experimental realization of a radially cascaded spherical piezoelectric transducer

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.

Analysis on electric impedance-controlled active ultrasonic horn in radial vibration

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.

Feasibility study on multifrequency excitation of the melt pool during ultrasonic-assisted laser beam welding

The constantly increasing demands on components and their resource-efficient production require new strategies in modern process chains. The Collaborative Research Centre (CRC) 1153 "Tailored Forming" is working on the production of hybrid solid components made from joined semi-finished products with subsequent forming. Laser beam welding with ultrasonic assistance has proven to be advantageous in the production of semi-finished products due to the active influence on the microstructure as a result of the excitation. In this work, the feasibility of extending the monofrequency excitation of the melt pool used so far during welding to a multifrequency excitation is investigated. Results from simulations and experiments show that a multi-frequency excitation of the weld pool can be effectively realised. Furthermore, it is shown that a combination of previously separately used excitation methods (positioning of the melt pool in the vibration node and in the vibration antinode, respectively) with two different frequencies is successful and leads to a combination of effects as desired, what can be seen from micrographs.

An improved analytic model for designing the polymer-composite stepped-plate transducer using the modified Mindlin plate theory

A stepped-plate transducer (SPT) uses an extensive radiating plate to produce highly-directional ultrasound beams. In this paper, we present an improved analytical model for designing the polymer-composite stepped-plate transducer (PCSPT). The polymer-composite features the lightweight and flexible properties, and there can be little change in the resonant frequency and mode shape when the steps are attached. With the outstanding merit, it is feasible to construct SPTs with polymer-composite steps without taking the steps into consideration. The modified Mindlin plate theory (MMPT) is applied to improve the accuracy in the equivalent circuit model (ECM) that is used to predict the high-frequency vibratory responses. Our analytical model can be used to design well-tuned SPTs to achieve the desired dynamic responses such as resonant frequencies, mode shape and bandwidth for various high-power ultrasonic applications. We use several numerical design examples to illustrate that the design of the transducer can be accomplished without analyzing the sophisticated stepped-plate's behavior. We also perform a series of experiments to verify that the PCSPT is capable of functioning as a high-power ultrasonic transducer.

AZ31B magnesium alloy matching layer for Lens-focused piezoelectric transducer application

Compared with planar transducers, focused transducers have higher ultrasound intensity and better lateral resolution in the focal zone. At present, the matching layer materials for focused transducers are mainly 0-3 composite materials, which have problems such as non-uniformity, difficulty to fabricate at high frequencies, and large sound attenuation. In this paper, finite element analysis is carried out to simulate lens-focused transducers with different matching layer structures and materials. It is found that the focused transducer with magnesium alloy matching layer has the best comprehensive performance. A lens-focused PZT-5H ultrasonic transducer was then fabricated with AZ31B magnesium alloy as the first matching layer. The measured results show that the center frequency of the transducer is 4.38 MHz, the -6-dB bandwidth is 68.35 % and the insertion loss is -13.88 dB. Benefiting from the high uniformity, high acoustic impedance and extremely low acoustic attenuation of magnesium alloy, the transducers in this research exhibit superior performances than other reported transducers with conventional matching layer. The current work suggests that AZ31B magnesium alloy is a promising matching layer material for ultrasonic transducers.