Transducer Design Research Articles

Design of Piezopolymer Interdigital Transducers with Scaled Electrode Geometries Based on FEM Analysis

The design of interdigital transducers (IDT) for active structural health monitoring (SHM) systems often requires a tuning of their characteristics for specific applications. IDTs are generally preferred for the selectivity of Lamb’s guided modes, but the directivity of the radiation pattern is a design parameter that is often difficult to customize for complex mechanical structures. This work proposes a comprehensive experimental study of the IDT with regular geometry, highlighting the dimensional parameters that can optimize the overall performance. From this study, a scaled electrode geometry emerged as a possible solution to shape the directivity diagram while maintaining the selectivity of the guided wave modes. This study based on FEM simulators led to a more versatile design of IDTs built with piezopolymer films of polyvinylidene fluoride (PVDF). The experimental validation showed the directivity diagrams and the ultrasonic guided mode selection were in very good agreement with the simulations. Another outcome of the investigation was the off axis propagation due to the contribution of the bus bars for connecting the IDT fingers to the excitation electronic circuit.

Analysis of Ultrasonic Machining Characteristics under Dynamic Load.

This research focuses on the load characteristics of piezoelectric transducers in the process of longitudinal vibration ultrasonic welding. We are primarily interested in the impedance characteristics of the piezoelectric transducer during loading, which is studied by leveraging the equivalent circuit theory of piezoelectric transducers. Specifically, we propose a cross-value mapping method. This method can well map the load change in ultrasonic welding to the impedance change, aiming to obtain an equivalent model of impedance and load. The least-squares strategy is used for parameter identification during data fitting. Extensive simulations and physical experiments are conducted to verify the proposed model. As a result, we can empirically find that the result from our model agrees with the impedance characteristics from the real-life data measured by the impedance meter, indicating its potential for real practice in controller research and transducer design.

Nonlinear Equivalent Circuit of High-Power Sandwich Piezoelectric Ultrasonic Transducer.

In the theoretical design and analysis of the sandwich piezoelectric ultrasonic transducer, the transducer is considered to be an ideal linear system, where the dielectric, piezoelectric, and mechanical losses are neglected. However, when the transducer is driven at high power, the losses are becoming several times higher comparing them to low signal measurements, and the transducer works in a nonlinear state. In order to predict the performance of the transducer at high power, the nonlinear parameters (complex constants) of the piezoelectric materials are introduced. The corresponding nonlinear equivalent longitudinal wave sound velocity and the nonlinear equivalent longitudinal wavenumber of the piezoelectric ceramics are derived. Then, the nonlinear equivalent circuit (NEC) and the nonlinear resonance frequency equation of the high-power sandwich piezoelectric ultrasonic transducer that related with the losses are deduced. Then, the nonlinear finite element model (NFEM) of the transducer is constructed. The performance parameters of the transducer obtained by the NEC method and the finite element (FE) method are compared with each other, and consistent results have been achieved by two methods. Finally, the contribution of various losses is obtained through theoretical calculation, simulation, and experimental measurement, and the correctness of the theoretical model in this article is verified.

Design and Fabrication of 15-MHz Ultrasonic Transducers Based on a Textured Pb(Mg1/3Nb2/3)O3-Pb(Zr, Ti)O3 Ceramic.

Ultrasound medical imaging is an entrenched and powerful tool for medical diagnosis. Image quality in ultrasound is mainly dependent on performance of piezoelectric transducer elements, which is further related to the electromechanical performance of the constituent piezoelectric materials. With rising need for piezoelectric materials with better performance and low cost, a highly 〈001〉 textured piezo ceramic, Pb(Mg1/3Nb2/3)O3-Pb(Zr, Ti)O3, has been developed. Recently, textured ceramic materials can be produced at low cost and exhibit high piezoelectric strain constants and large electromechanical coupling coefficients. In this work, 15-MHz ultrasonic transducers with an effective aperture of 2.5 mm in diameter based on these highly 〈001〉 textured ceramics have been successfully fabricated. The fabricated transducers achieved a central frequency of 15 MHz, a fractional bandwidth of 67% (at -6 dB), a high effective electromechanical coupling coefficient [Formula: see text] of 0.55, and a low insertion loss (IL) of 21 dB. Ex vivo ultrasonic imaging of a porcine eyeball was used to assess the tomography quality of the transducer. The results show that utilized textured ceramic has a great potential in developing ultrasonic devices for biomedical imaging purposes.

Design, modelling and testing of a compact piezoelectric transducer for railway track vibration energy harvesting

To enable wireless sensor networks to monitor rail infrastructures in real-time, a cost-effective power source is in need. This work presents the design, modelling and testing of a piezo stack energy harvester with frequency up-conversion mechanism for scavenging energy from railway track vibration. The proposed harvester is designed to meet railway track applications’ size, frequency, and stress requirements. A compact design integrating the inertial mass and the piezo stack transducer systems is used to enable the mechanical collision for realising the frequency up-conversion mechanism and ensure the size of the energy harvester is suitable for the limited space on the railway track. The frequency bandwidth of the energy harvester is broadened by utilizing the longitudinal and torsional oscillation of the designed plate springs which enable the system to have two adjacent natural frequencies. The mechanical transformer of the piezo stack transducer system is designed to achieve the required stress level under both the impact force caused by the collision motion and the inertial force generated by the random vibration of the rails. A finite element model (FEM) analysing the free vibration of the piezo stack transducer caused by the frequency up-conversion mechanism is developed to analyse the dynamic characteristics of the coupled system. Lab tests are carried out to validate the proposed FEM and evaluate the impact of different factors such as load resistance, acceleration, initial interval, plate spring, and pulse excitation on power generation. Experimental results show that the energy harvester has two resonant frequencies of 17 Hz and 20 Hz. The frequency up-conversion mechanism can convert this low-frequency vibration into the piezo stack transducer’s high resonant frequency vibration of 94 Hz. A maximum average power of 6.72 mW with a 1-mW-bandwidth of 15 Hz is obtained when actuated at 0.7 RMS g acceleration. • A piezo stack energy harvester for railway track vibration is designed, modelled and tested. • A compact design is proposed to enable the mechanical collision for realising the frequency up-conversion mechanism. • Two adjacent natural frequencies are achieved to broaden the frequency bandwidth. • The mechanical transformer is designed to achieve the required stress level under the impact force and inertial force. • A maximum average power of 6.72 mW with a 1-mW-bandwidth of 15 Hz is obtained when actuated at 0.7 RMS g acceleration.

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

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.

Research on Broadband Matching Method for Capacitive Micromachined Ultrasonic Transducers Based on PDMS/TiO2 Particles.

The study of impedance matching between a transducer and its working medium is an important part of acoustic transducer design. The traditional quarter wavelength matching (Q-matching) scheme is not suitable for broadband capacitive micromachined ultrasonic transducers. To mitigate this issue, a 0-3 composite broadband matching layer based on polydimethylsiloxane (PDMS) substrate/TiO2 particles is designed to achieve electrical insulation and efficient acoustic energy transfer of underwater capacitive micromachined ultrasonic transducer (CMUT) devices. In this work, the coherent potential approximation model is used to analyze the properties of 0-3 composite materials. Samples are prepared for performance testing to determine the proportion of TiO2 particles that enable the 0-3 composite materials to have the same longitudinal acoustic impedance as water. The CMUT device is packaged by a spin coating and pouring process, and its performance tests are carried out. The experimental results show that the central frequency of the transducer remains at 1.74 MHz, the -6 dB fractional bandwidth increases from 97.3% to 100.3%, the 3 dB directional main beam width increases from 8.3° to 10.3°, the side lobes decrease significantly, and the device has good reception sensitivity. These values imply that the 0-3 composite material has good matching performance, and this matching scheme has the advantages of high efficiency and wide bandwidth. This broadband matching method endows CMUTs with great advantages in underwater detection systems, and it facilitates underwater ultrasonic imaging of CMUT.

Design and 3D FEM Analysis of a Flexible Piezoelectric Micromechanical Ultrasonic Transducer Based on Sc-Doped AlN Film.

In this paper, a flexible piezoelectric micromachined ultrasonic transducer (PMUT) based on Scandium (Sc)-doped Aluminum Nitride (AlN) film was designed and modeled by the three-dimensional finite element method (3D-FEM). The resonant frequency of 218.1 kHz was reported. It was noticeable that a high effective electromechanical coupling coefficient (k2eff) of 1.45% was obtained when a combination of a flexible PI and a thin Si layer was used as the PMUT supporting structure layer. Compared with a pure Si supporting layer counterpart, the coupling coefficient had been improved by 110.68%. Additionally, the increase of Sc doping concentration in AlN film further enhanced the device electromechanical coupling coefficient and resulted in an improvement for transmitting/receiving sensitivity of the proposed flexible PMUT. When the doping concentration of Sc reached 30%, the emission sensitivity was as large as 1.721 μm/V, which was 2.86 times greater than that of conventional AlN film-based PMUT. The receiving sensitivity was found to be 2.11 V/KPa, which was as high as 1.23 times the performance of an undoped device. Furthermore, the bending simulation result showed that the proposed flexible PMUT device can maintain a good mechanical stability when the bending radius is greater than 1.5 mm. The simulation of sound field characteristics demonstrated that the flexible PMUT based on AlScN could receive stable sound pressure signals under the bending radius of 1.5 cm.

Study on magnetic interference characteristics and optimization design of magneto-optic current transducer

The paper aims at the phenomenon of the magnetic field between phases of magneto-optical current transducer, studies the magnetic field interference distribution characteristics and proposes the orthogonal optical path optimization scheme to improve the ability of the magneto-optic current transducer to resist the external magnetic field interference. The mathematical model of magnetic field interference degree of magneto-optic current transducer is established, and the distribution characteristics of magnetic field interference degree of magneto-optical current transducer under the effect of interfering current are studied. The research shows that the position of interfering current has a specific law on the magnetic field interference degree of the magneto-optic current transducer, and the interfering current at a specific position has no interference effect on magneto-optic current transducer. It is pointed out that magnetic field interference degree is larger when the magneto-optic current transducer is arranged in the conventional way, and the error caused by the magnetic field interference between phases cannot be ignored. The orthogonal optical path optimization scheme of magneto-optic current transducer is put forward, which can improve the anti-interference ability from external magnetic field of magneto-optic current transducer without changing its body structure and installation condition. The experimental results show that the relative error of magneto-optic current transducer caused by the interfering current is less than 0. 1% when the orthogonal optical path optimization scheme is adopted, which proves the correctness and practicability of the orthogonal optical path optimization scheme.

Guided Ultrasound Inspection of Small Features Using a Horn-Type Transducer Design

Guided Ultrasound Inspection of Small Features Using a Horn-Type Transducer Design

Supervision, control, and data acquisition system of a heat exchanger

<span>Today, when industry 4.0 is already being talked about, and its advantages at the organizational level, there are still industrial processes that show a lack of automatic regulation mechanisms, which means that an optimal operating process is not guaranteed, nor that monitoring and supervision capacity. In this sense, the purpose of the article is to demonstrate the feasibility of the integration between the programmable logic controller and the Arduino nanocontrollers, this as an alternative to automate a concentric tube heat exchanger, for monitoring and data acquisition through a supervision, control and data acquisition system. The integration is shown through the design and implementation of a temperature transducer made up of a MAX6675 converter module and an Arduino Nano controller, which is amplified through its pulse width modulation (PWM) interface and the integrated TL081CP and coupled to the analog inputs of the automaton. As a result of the experimental tests, it was possible to determine that the flow rate of the automated system is directly proportional to the drop or difference in temperature in the hot fluid and inversely proportional to the increase in temperature in the cold fluid, verifying the effectiveness of the automated heat exchanger.</span>

Array Transducer Design: A Vibrant Research Theme in Medical Ultrasonics

Since the 1970s, when portable transducer arrays were first introduced for medical ultrasound imaging, they have undergone substantial technological developments. The development of advanced arrays is often motivated by the need to achieve high diagnostic and therapeutic efficacy and to serve new fields of application. In the past few decades, medical ultrasound array design has been an active research area with challenging technical requirements that continually seek to reduce physical size, improve sensitivity, optimize the number of array elements, realize wide bandwidth, and achieve high output power. The need to devise arrays with increased performance has concurrently stimulated advances in transducer technologies, microelectronics, and array layout design. Nowadays, representative examples can be found for both 2-D and 3-D applications such as high-intensity-focused ultrasound arrays, very-high-frequency or dual-frequency probes, kerf-less arrays, 2-D sparse arrays, and probes with embedded application-specific integrated circuits. The emergence of these advanced arrays has, in turn, stimulated the development of novel, customized transmission and reception approaches, image reconstruction algorithms, and data recovery strategies to exploit or deal with the peculiarities of a specific array.

Excitation by shot circuited coaxial transducer of magnetostatic modes in rectangular yttrium iron garnet film

The purpose of this work is the study of design of new short-circuited coaxial transducer with thin linear jumper, that circuites on both sides of the grounded coaxial cylinder, located above the rectangular iron-yttrium garnet (YIG) film, in homogeneous constant magnetic field with rectangular film along its length or width. The thin linear jumper is directed parallel to the width of the YIG film. Methods. In the CST Microwave Studio environment, an electrodynamic analysis of the model was carried out using the finite element method. To study the efficiency of modes excitation in a ferrite film at different distances between the coaxial transducer and the surface of the YIG film, the frequency dependencies of the inverse losses S11 of the model were calculated. Results. 1. The identification of modes in a homogeneous static magnetic field H, directed parallel to the plane of a rectangular YIG film along its width (y-axis) was carried out. 2. The identification of modes in a homogeneous static magnetic field H directed parallel to the plane of the rectangular YIG film along its length (z-axis) was carried out. 3. A comparison of modes spectra was made at H, directed parallel to the plane of the YIG film along its width (y axis) and length (z axis). Conclusion. In this paper short-circuited transducer with a thin linear jumper, circuited on both sides of the grounded coaxial cylinder, is investigated. By the electrodynamic method distributions of high-frequency magnetic field of the excited magnetostatic modes were calculated and their identification was carried out for two directions of homogeneous static magnetic field: along width and along length of rectangular YIG film. The dependence of number of excited modes on the distance between a short-circuited transducer and rectangular YIG was also studied. A comparison of modes spectra is carried out at H, directed parallel to the plane of the YIG film along its width and length. With this rotation of H vector, the band of effectively excitable modes shifts from 4.6...4.9 GHz to 4.5...4.75 GHz. However, the excitation of these modes in the case of the vector H, directed along the width of YIG film (z-axis), is much more effective in the band 4.65...4.9 GHz than in the case when this vector is directed along the length of YIG film (z-axis). At the same time, excitation of these modes in the case of the vector H, directed along the length of YIG film (z axis) is much more effective in the band 4.4...4.6 GHz.

Simulation and Optimization of Ultrasonic Transducer

The ultrasonic transducers have numerous applications in industries, including medical probes for performing ultrasound scans. One of the significant drawbacks of the ultrasonic transducer is the wastage of a large portion of energy, due to high acoustic impedance, while transmitting ultrasonic waves to the target object. The present study is aimed to investigate the material design of the piezo-composite transducer and improve its performance. Different piezo-composite transducers were simulated in the COMSOL environment by varying input parameters, and three key performance indicators (KPI) were calculated. Many constraint-based multivariable optimization algorithms have been used to maximize the KPIs. A set of parameters, such as Sensitivity and Fractional Bandwidth, have been found to increase the performance of piezo-composite transducer model and its overall efficiency. This study is intended to impinge unidirectional property to the transducer which is found to be beneficial in more accurate medical as well as structural reports and cost savings.

Design and Development of a Solar Electric Delivery Pod

The ultrasonic transducers have numerous applications in industries, including medical probes for performing ultrasound scans. One of the significant drawbacks of the ultrasonic transducer is the wastage of a large portion of energy, due to high acoustic impedance, while transmitting ultrasonic waves to the target object. The present study is aimed to investigate the material design of the piezo-composite transducer and improve its performance. Different piezo-composite transducers were simulated in the COMSOL environment by varying input parameters, and three key performance indicators (KPI) were calculated. Many constraint-based multivariable optimization algorithms have been used to maximize the KPIs. A set of parameters, such as Sensitivity and Fractional Bandwidth, have been found to increase the performance of piezo-composite transducer model and its overall efficiency. This study is intended to impinge unidirectional property to the transducer which is found to be beneficial in more accurate medical as well as structural reports and cost savings.

Design and Implementation of Low-Voltage Tunable Capacitive Micro-Machined Transducers (CMUT) for Portable Applications.

Capacitive micromachined ultrasonic transducers (CMUT) are MEMS-based transducers with advantages over conventional ultrasonic transducers, such as their small size, the ease of integration with semiconductor electronics, and batch fabrication. In this study, the effect of different membrane topologies on the displacement, resonant frequency, and output pressure of the CMUT membrane is investigated in the transmission mode in an air environment. A novel structural-support feature, the rocker stem, is introduced, where the membrane is weakly held to the substrate in order to minimize mechanical constraints. Four different CMUT topologies are designed and assessed to analyze the impacts of topological variations. A new CMUT array configuration is also designed to provide an approach for maximizing CMUT density. This study aims to contribute to efficient CMUT design and the determination of optimum structural parameters for portable applications in air.

Posterior photoacoustic/ultrasound imaging of the periodontal pocket with a compact intraoral transducer

Periodontitis is a public issue and imaging periodontal pocket is important to evaluate periodontitis. Regular linear transducers have limitations in imaging the posterior teeth due to their geometry restrictions. Here we characterized a transducer that can image the posterior teeth including assessment of periodontal pockets via a combination of photoacoustic and ultrasound imaging. Unlike conventional transducer design, this device has a toothbrush-shaped form factor with a side-view transducer to image molars (total size: 1 ×1.9 cm). A laser diode was integrated as the light source to reduce the cost and size and facilitates clinical transition. The in vivo imaging of a molar of a periodontal patient demonstrated that the transducer could image in the posterior area of gum in vivo; the value determined by imaging was within 7 % of the value measured clinically.

Temperature characterization of magnetic and elastic parameters of TFD giant magnetostrictive materials

The magnetic and elastic parameters of the Terbium Dysprosium Iron (abbreviated as TFD)giant magnetostrictive material are important fundamental parameters for the design of magnetostrictive transducer based on the piezomagnetic analogy method. Therefore, the study of temperature characteristics of magnetic and elastic parameters of giant magnetostrictive material can help to grasp the law of temperature influence on the working performance of the giant magnetostrictive transducer. In this paper, the variation patterns of magnetic and elastic parameters with temperature for a total of three tangential types of giant magnetostrictive material samples, including the sample along the magnetostrictive direction(TFD-1#), the sample perpendicular to the magnetostrictive direction(TFD-3#) and the sample at an angle of 45° to the magnetostrictive direction(TFD-2#), were comprehensively measured under different external magnetic field conditions. The experimental results showed that: The magnetostriction coefficient is linearly related to the external magnetic field in the range of 10 MPa pre-stress and 50∼150 kA/m external magnetic field (the same below), corresponding to the dynamic operating range of the magnetostrictive transducer. In this interval, the magnetostrictive strain constants d31 and d33 show a single-peak pattern of increasing and then decreasing with increasing external magnetic field, it changes slowly and modestly with increasingly temperature; The relative permeability of the giant magnetostrictive materials μr11 and μr33 decreases with increasing external magnetic field and temperature at an external magnetic field below 150 kA/m; The elastic constant increases with increasing external magnetic field and decreases with increasing temperature.

Design and Simulation of a Ring Transducer Array for Ultrasound Retinal Stimulation.

Argus II retinal prosthesis is the US Food and Drug Administration (FDA) approved medical device intended to restore sight to a patient’s blind secondary to retinal degeneration (i.e., retinitis pigmentosa). However, Argus II and most reported retinal prostheses require invasive surgery to implant electrodes in the eye. Recent studies have shown that focused ultrasound can be developed into a non-invasive retinal prosthesis technology. Ultrasound energy focused on retinal neurons can trigger the activities of retinal neurons with high spatial-temporal resolution. This paper introduces a novel design and simulation of a ring array transducer that could be used as non-invasive ultrasonic retinal stimulation. The array transducer is designed in the shape of a racing ring with a hemisphere surface that mimics a contact lens to acoustically couple with the eye via the tear film and directs the ultrasound to avoid the high acoustic absorption from the crystalline lens. We will describe the design methods and simulation of the two-dimensional pattern stimulation. Finally, compared with other existing retinal prostheses, we show that the ultrasound ring array is practical and safe and could be potentially used as a non-invasive retinal prosthesis.

A lumped parameter model of the longitudinal NiMnGa transducer based on piezomagnetic equations.

The NiMnGa alloy is a typical magnetic shape memory alloy with up to 6% immense strain, high energy density, and low effective elastic modulus. These comprehensive characteristics make it possible to realize a low-frequency underwater acoustic transducer. To describe the field-induced dynamic strain, an equivalent circuit model (ECM) of a longitudinal NiMnGa transducer is presented as a lumped parameter model, which couples magnetics, mechanics, and acoustics. In this paper, we focus on the piezomagnetic equations as the constitutive relationship of the NiMnGa element with a dynamic magnetic field. Furthermore, combined with the dynamic kinetic equation, the equivalent circuit is derived, and it has the advantage of containing acoustical terminals. The proposed model can predict the resonance frequency, effective stiffness, and input impedance of the NiMnGa transducer. Finally, a finite element model (FEM) is developed to verify the lumped parameter model. The results indicate that the spring's stiffness increases the resonance frequency, while the mass load is on the contrary, and they both agree well with the results of ECM. In addition, the FEM and ECM can also predict the dynamic responses, which provide a guideline for the design of longitudinal NiMnGa transducers.