Interest in underwater transducers has persisted since the mid-1900s. Underwater transducers are designed in various shapes using various materials depending on the purpose of use, such as to achieve high power, improve broadband, and enhance beam steering. Therefore, in this study, an analysis is conducted according to the structural shape of the transducer, exterior material, and active material. By classifying transducers by structure, the transducer design trends and possible design issues can be identified. Researchers have constantly attempted new methods to improve the performance of transducers. In addition, a methodology to overcome this problem is presented. Finally, this review covers old and new research, and will serve as a reference for designers of underwater transducer.

https://www.mdpi.com/1424-8220/23/4/1821/pdf?version=1675680238

Design of Piezoelectric Acoustic Transducers for Underwater Applications

To reduce the heating of the Terfenol-D rod and evaluate its working efficiency, six kinds of Terfenol-D rods were designed, and the temperature field of the rods was simulated and calculated using the finite element method to obtain the temperature distribution. The results showed that the untreated rod had the highest temperature; the temperature was higher in the middle and lower at both ends; higher on the outer diameter surface; and lower on the inside. When compared to the untreated rod, the temperatures of sliced rods and slit rods decreased, and the temperature of sliced rods was lower than that of slit rods; the temperature of slit rods was higher in the middle and lower at both ends; the temperature distribution of sliced rods was more uniform relatively; the slice treatment rod had the lowest temperature and the best heat suppression effect. Three structural rods were chosen and manufactured from a total of six that were tested. It shows that the temperature of all rods was higher in the middle and lower at both ends after 30 min of operation. The actual temperature of untreated rod was 34 °C, the actual temperature of radially slit rod was 32 °C, and the actual temperature of sliced rod at both ends was 28 °C. The tested temperature distributions of three rods agreed with the calculated ones.

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Thermal Analysis of Terfenol-D Rods with Different Structures

High-power giant magnetostrictive transducers are widely used in underwater acoustics. Because of the low magnetic permeability of giant magnetostrictive materials (GMMs) and permanent magnets (PMs), there must exist significant magnetic flux leakage. For establishing the equivalent model of high-power giant magnetostrictive transducers, it is of great necessity to accurately obtain an accurate magnetic spatial distribution and couple it to the mechanical domain. In this way, it can reflect the difference in the magnetic field of each giant magnetostrictive rod (GMR). However, most existing models for giant magnetostrictive transducers rarely consider the spatial distribution of the magnetic field and its coupling effect on the mechanical domain. The multi-degree-of-freedom (multi-DOF) lumped-parameter model (LPM) has been widely used due to its ability to reflect the motion of each degree of freedom in a vibration system and flexibility for multifield simulation. This study proposes a multi-DOF LPM of the high-power giant magnetostrictive transducer, which considers the magnetic flux leakage on both GMRs and PMs. To verify the effectiveness of the proposed technique, the variations of the magnetic flux on GMR before and after considering the flux leakage were compared. Moreover, a comparative analysis with the magnetomechanical coupling in the state-of- the-art plane wave model (PWM) is carried out, which verifies the superiority of our proposed model. Finally, the proposed model is used to simulate the impedance of the transducer, as well as the maximum transmitting current response (TCR), showing excellent agreement with the experimental results.

Multi-DOF Lumped-Parameter Modeling of High-Power Giant Magnetostrictive Transducer Coupled With Spatial Distribution of Magnetic Field

A magnetic field induced by an electromagnetic coil is the key variable that determines the performance of a magnetically driven actuator. The applicability of the empirical models of the coil turns, static resistance, and inductance were discussed. Then, the model of the mean magnetic field induced by the coil was established analytically. Based on the proposed model, the sinusoidal response and square-wave response were calculated with the wire diameter as the decision variable. The amplitude and phase lag of the sinusoidal response, the time-domain response, steady-state value, and the response time of the square-wave response were discussed under different wire diameters. From the experimental and computational results, the model was verified as the relative errors were acceptably low in computing various responses and characteristic variables. Additionally, the optimization on the wire diameter was carried out for the optimal amplitude and response time. The proposed model will be helpful for the analytical analysis of the mean magnetic field, and the optimization result of the wire diameter under limited space can be employed to improve the performance of a magnetically driven actuator.

https://www.mdpi.com/2226-4310/10/3/270/pdf?version=1678448284

Optimization of the Wire Diameter Based on the Analytical Model of the Mean Magnetic Field for a Magnetically Driven Actuator

High-power giant magnetostrictive transducers are widely used in underwater acoustics. Because of the low magnetic permeability of giant magnetostrictive materials (GMMs) and permanent magnets (PMs), there must exist significant magnetic flux leakage. For establishing the equivalent model of high-power giant magnetostrictive transducers, it is of great necessity to accurately obtain an accurate magnetic spatial distribution and couple it to the mechanical domain. In this way, it can reflect the difference in the magnetic field of each giant magnetostrictive rod (GMR). However, most existing models for giant magnetostrictive transducers rarely consider the spatial distribution of the magnetic field and its coupling effect on the mechanical domain. The multi-degree-of-freedom (multi-DOF) lumped-parameter model (LPM) has been widely used due to its ability to reflect the motion of each degree of freedom in a vibration system and flexibility for multifield simulation. This study proposes a multi-DOF LPM of the high-power giant magnetostrictive transducer, which considers the magnetic flux leakage on both GMRs and PMs. To verify the effectiveness of the proposed technique, the variations of the magnetic flux on GMR before and after considering the flux leakage were compared. Moreover, a comparative analysis with the magnetomechanical coupling in the state-of- the-art plane wave model (PWM) is carried out, which verifies the superiority of our proposed model. Finally, the proposed model is used to simulate the impedance of the transducer, as well as the maximum transmitting current response (TCR), showing excellent agreement with the experimental results. 

The loss effect in smart materials, the active part of a transducer, is of significant importance to acoustic transducer designers, as it directly affects the important characteristics of the transducer, such as the impedance spectra, frequency response, and the amount of heat generated. It is therefore beneficial to be able to incorporate energy losses in the design phase. For high-power low-frequency transducers requiring more smart materials, losses become even more appreciable. In this paper, similar to piezoelectric materials, three losses in Terfenol-D are considered by introducing complex quantities, representing the elastic loss, piezomagnetic loss, and magnetic loss. The frequency-dependent eddy current loss is also considered and incorporated into the complex permeability of giant magnetostrictive materials. These complex material parameters are then successfully applied to improve the popular plane-wave method (PWM) circuit model and finite element method (FEM) model. To verify the accuracy and effectiveness of the proposed methods, a high-power Tonpilz Terfenol-D transducer with a resonance frequency of around 1 kHz and a maximum transmitting current response (TCR) of 187 dB/1A/μPa is manufactured and tested. The good agreement between the simulation and experimental results validates the improved PWM circuit model and FEA model, which may shed light on the more predictable design of high-power giant magnetostrictive transducers in the future.

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Modeling of High-Power Tonpilz Terfenol-D Transducer Using Complex Material Parameters

The properties of giant magnetostrictive material (GMM) are very sensitive to external compressive stress. Knowledge of these key properties is of essential importance in practical applications such as high-power underwater transducers. Although the parameters of GMM have been extensively studied, characterization and analysis of magnetic, elastic, and piezoelectric losses under different compressive stresses are rarely reported due to the difficulty in experimentally realizing the ideal mechanical free or clamped boundary conditions. In this study, we designed a longitudinal transducer for complex parameters characterization of GMM. We successfully characterize the key three losses in GMM using a multi-degree-of-freedom (MDOF) lumped parameter equivalent circuit model (LECM), meticulously incorporating the surface contact damping, stiffness, and structural losses. MDOF LECM provides a novel idea for loss characterization of GMM under compressive stress. In contrast to prior-art parameters characterization based on the distributed parameter equivalent circuit model (DECM), the proposed characterization based on MDOF LECM shows apparent superiority in terms of global sensitivity. The intensive losses of GMM for ten-time characterizations show high stability and are all positive. Statistical analysis of intensive losses’ dependency on the compressive stress is performed. A longitudinal transducer is designed for experimental verification. Finally, 95% prediction and confidence intervals for the variation trend of the intensive losses in relationship with compressive stress are obtained.

/pdf/loss-characterization-of-giant-magnetostrictive-material-3n6hcnvd.pdf

Loss Characterization of Giant Magnetostrictive Material Under Compressive Stress

Abstract Of crucial importance for giant magnetostrictive transducers (GMTs) design is to quickly and accurately analysis the temperature distribution. With the advantages of low calculation cost and high accuracy, thermal network modelling has been developed for thermal analysis of GMT. However, the existing thermal models have their limits to describe these complicated thermal behaviors in the GMTs: most of researches focused on steady-state which is incapable of capturing temperature variances; the temperature distribution of giant magnetostrictive (GMM) rods is generally assumed to be uniform whereas the temperature gradient on the GMM rod is remarkable due to its poor thermal conductivity; the non-uniform distribution of GMM’s losses is seldom introduced into thermal model. Therefore, a transient equivalent thermal network (TETN) model of GMT is established in this paper, considering the aforementioned three aspects. Firstly, based on the structure and working principle of a longitudinal vibration GMT, thermal analysis was carried out. Following this, according to the heat transfer process of GMT, the TETN model was established and the corresponding model parameters were calculated. Finally, the accuracy of the TETN model for the temporal and spatial analysis of the transducer temperature are verified by simulation and experiment. 

https://www.nature.com/articles/s41598-022-22959-7.pdf

Research on equivalent thermal network modeling for rare-earth giant magnetostrictive transducer

Stack giant magnetostrictive actuators (SGMAs) are widely used in various fields for its merits such as saving the space and improving the evenness of the bias magnetic field provided for the giant magnetostrictive material (GMM). In this paper, based on the flow path of the magnetic flux in SGMA, a magnetic equivalent network corresponding to quasistatic conditions is proposed taking flux leakage and fringing effect into account. Meanwhile, complex reluctances of the GMM rods are introduced to describe the decrease and phase shift of magnetic field intensities caused by eddy current under high-frequency excitation signals. Furthermore, the magnetic equivalent network, determining the relationship between excitation signals and magnetic field intensities, is combined with the Jiles–Atherton model, nonlinear constitutive theory of GMM concerning multi-field coupling, and structural dynamics of SGMA so as to derive a multi-field coupling model predicting the tracking behaviors of SGMA to the excitation signals. Moreover, a finite element method is conducted, an SGMA prototype is fabricated, and an experimental platform is set up to verify the proposed model. Comparison between results derived from the magnetic equivalent network and those calculated by the finite element method indicates that the proposed network is able to predict the magnetic field distribution inside the SGMA prototype in quasistatic conditions; further comparison between results obtained from the proposed multi-field coupling model and those from experiments indicates that the model can accurately predict tracking behaviors of the SGMA prototype to the excitation signals.

Yukai Chen

Papers

Modeling of High-Power Tonpilz Terfenol-D Transducer Using Complex Material Parameters

Loss Characterization of Giant Magnetostrictive Material Under Compressive Stress

Research on equivalent thermal network modeling for rare-earth giant magnetostrictive transducer

Dynamic modeling of stack giant magnetostrictive actuator with magnetic equivalent network considering eddy current effect

Multi-DOF Lumped-Parameter Modeling of High-Power Giant Magnetostrictive Transducer Coupled With Spatial Distribution of Magnetic Field