Multilayer Transducers Research Articles

Rotary–Linear Type Piezoelectric Actuator Based on Double-Elliptical Stator

This paper introduces a novel piezoelectric actuator designed for precise linear and rotational movements of a cylindrical slider-rotor. The actuator’s design features two elliptical frames interconnected by two plates, with a cylindrical contact situated on the top of the upper plate to facilitate the motion or rotation of the slider. Two piezoelectric multilayer transducers are housed within each elliptical frame and are used to excite vibrations of the elliptical frames using two harmonic signals with a phase difference of π/2 and varying excitation schemes. This excitation pattern generates elliptical motion trajectories of the contact in two orthogonal planes, enabling both linear and rotational displacements of the slider-rotor. Numerical and experimental investigations were conducted to validate the performance and accuracy of the actuator. Additionally, harmonic response and transient analysis were performed to investigate elliptical motion trajectories of the contact in perpendicular planes under various excitation schemes and frequencies. The results confirm that the rotational and linear motions of the slider-rotor can be independently controlled. The actuator achieved a maximum rotational speed of 163.1 RPM and a maximum linear speed of 41.4 mm/s, with a corresponding peak output torque and force of 236.1 mN·mm and 368.1 mN, respectively. A resolution measurements showed that the actuator can achieve an angular resolution of 1.02 mrad and a linear resolution of 53.8 µm.

Modeling and experimental investigation of multilayer DE transducers considering the influence of the electrode layers

Modeling and experimental investigation of multilayer DE transducers considering the influence of the electrode layers

The analytical model of time-harmonic electric field and impedance spectrum in the multilayered interdigital electrode structure

Accurately determining the time-harmonic electric field and impedance spectrum in the multilayered interdigital electrode (IDE) transducers with lossy dielectrics is essential for the design of the structure, the property estimation of the dielectric, and performance optimization. This paper presents an analytical model of the electric field and impedance within a multilayered interdigitated electrode (IDE) when subjected to alternating excitation through the method of separation of variables (MSV). The equivalent circuit of IDE is established, where the impedance is the parallel of capacitive coupling and resistive coupling between electrodes. The general solutions for the electric field and impedance involving arbitrary numbers and complex permittivities of the dielectric layers are analytically derived. However, due to the approximation of boundary conditions, these physical quantities cannot be accurately obtained by the conventional analytical method using conformal mapping technique (CMT) and partial capacitance technique (PCT). The proposed model exhibits proficiency in generating precise electric field images and impedance values that closely correspond with simulated data, even when accounting for the frequency-dependent characteristics of permittivity and conductivity in lossy dielectrics. Moreover, the approaches to improve the sensitivity of a traditional three-layered IDE-based sensor are demonstrated. For a three-layered IDE-based capacitive sensor, improving the sensitivity can be accomplished through the incorporation of a ground plane at the substrate's bottom and increasing the metallization rate. Conversely, it is recommended to reduce the metallization rate, increase substrate thickness, and remove the ground plane in order to enhance the sensitivity of the IDE-based impedance sensor. The experimental results demonstrate that the proposed model generates outstanding impedance spectra (involving capacitance spectra and resistance spectra) results for various metallization ratios and top layers. This exemplifies the model's potential for predicting, designing, and enhancing a complex multilayered IDE-based transducer to achieve precise and sensitive detection.

Parallel differential evolution paradigm for multilayer electromechanical device optimization

Design optimization of multilayer piezoelectric transducers is intended for efficient and practical usage of wideband transducers for fault diagnosis, biomedical, and underwater applications through adjusting layer thicknesses and volume fraction of piezoelectric material in each layer. In this context, we propose a parallel differential evolution (PDE) algorithm to mitigate the complexities of multivariate optimization as well as the computation time to achieve an optimized wideband transducer for the particular application. For lead magnesium niobate-lead titanate (PMN PT)- and PZT5h-based piezoelectric materials, the fitness function is formulated based on uniformity of mechanical pressure at the first three harmonics to achieve wide bandwidth in the required functional frequency range. It is carried out using a one-dimensional model (ODM), while input layer thicknesses and volume fractions of active material are evaluated using PDE. The simulation is performed on a parallel computing platform utilizing three different host machines to reduce computational time. Results of the proposed methodology for PDE are statistically represented in the form of minimum, maximum, mean, and standard deviation of fitness value, while graphically represented in terms of speedup and time. It can be observed that the execution time for parallel DE decreases with the increasing number of cores.

Energy harvesting using lead-free multilayer piezo stacks based on 0.95(Bi0.5Na0.5)TiO3-0.05(BaTiO3) piezoceramics through the addition of ZrO2

This paper explores the feasibility of utilizing lead-free multilayer piezo stacks, particularly focusing on Zr-doped 0.95(Bi0.5Na0.5)TiO3-0.05(BaTiO3) piezoceramics, for energy harvesting. Various lead-free BNT-BT disk samples with different Zr concentrations undergo structural, microstructural, and electrical characterizations. The results illustrate that Zr-doping improves piezoelectric constitutive parameters, notably at a 2.0 mol% concentration. Electromechanical tests were conducted on multilayer piezo stacks, involving variations in electric load, mechanical load, frequency, and number of stacked disks. These tests demonstrate the ability of the multilayer transducer to produce up to 1.5 V (peak) under particular conditions: a 250 Hz frequency, a 10 N mechanical load, and an open circuit electric load, utilizing a stack comprising 5 disks. Employing an analytical mathematical model, an effective d33eff of the system is determined, yielding values ranging from 588 to 625 pC/N for a stack composed of 5 disks. These findings highlight the considerable potential of lead-free multilayer piezo stacks in energy harvesting applications, offering crucial insights for the development of sustainable and eco-friendly energy solutions.

Efficient multivariate optimization of an ultrasonic transducer with genetic parallel algorithms

Design optimization of a multilayer transducer is desired for flaw detection, biomedical and underwater applications by controlling layer thicknesses of active material and volume fractions of ceramic in each piezocomposite layer. To handle the computational complexity in solving such multivariate optimization and the complex nature of the problem, we propose a parallel genetic algorithm (GA)-based strategy. The complexity of the problem increases with the number of layers and layer-wise ceramic volume fraction to achieve an optimized transducer working efficiently in an operational frequency range as desired by the application specification. The fitness function is formulated based on the transducer response in terms of about the same value of pressure magnitude at the first three harmonics at functional frequencies. The fitness value is computed using a one-dimensional model (ODM) for PMNPT, PZT4d, and PZT5h-based materials initially, while input layer thicknesses and volume fractions are evaluated through GAs and passed to ODM. The overall scheme is maintained through parallel GAs. The simulation is performed by using 1, 4, 6, and 8 core machines to reduce time complexity. The results for parallel GA-ODMs are statistically represented in the minimum, maximum, mean and standard deviation of fitness, while graphically represented for speedup and time.

Neuro-Evolutionary Framework for Design Optimization of Two-Phase Transducer with Genetic Algorithms.

Multilayer piezocomposite transducers are widely used in many applications where broad bandwidth is required for tracking and detection purposes. However, it is difficult to operate these multilayer transducers efficiently under frequencies of 100 kHz. Therefore, this work presents the modeling and optimization of a five-layer piezocomposite transducer with ten variables of nonuniform layer thicknesses and different volume fractions by exploiting the strength of the genetic algorithm (GA) with a one-dimensional model (ODM). The ODM executes matrix manipulation by resolving wave equations and produces mechanical output in the form of pressure and electrical impedance. The product of gain and bandwidth is the required function to be maximized in this multi-objective and multivariate optimization problem, which is a challenging task having ten variables. Converting it into the minimization problem, the reciprocal of the gain-bandwidth product is considered. The total thickness is adjusted to keep the central frequency at approximately 50-60 kHz. Piezocomposite transducers with three active materials, PZT5h, PZT4d, PMN-PT, and CY1301 polymer, as passive materials were designed, simulated, and statistically evaluated. The results show significant improvement in gain bandwidth compared to previous existing techniques.

Development and Investigation of High-Temperature Ultrasonic Measurement Transducers Resistant to Multiple Heating-Cooling Cycles.

Usually for non-destructive testing at high temperatures, ultrasonic transducers made of PZT and silver electrodes are used, but this could lead to damage to or malfunction of the ultrasonic transducer due to poor adhesion between PZT and silver. Soldering is one of the most common types of bonding used for individual parts of ultrasonic transducers (protector, backing, matching layer, etc.), but silver should be protected using additional metal layers (copper) due to its solubility in solder. A mathematical modelling could help to predict if an ultrasonic transducer was manufactured well and if it could operate up to 225 °C. The observed von Mises stresses were very high and concentrated in metal layers (silver and copper), which could lead to disbonding under long-term cyclic temperature loads. This paper presents a multilayer ultrasonic transducer (PZT, silver electrodes, copper layers, backing), which was heated evenly from room temperature to 225 °C and then cooled down. In the B-scan, it was observed that the amplitude of the reflected signal from the bottom of the sample decreased with an increase in temperature. However, after six heating-cooling cycles, the results repeated themselves and no signs of fatigue were noticed. This ultrasonic transducer was well manufactured and could be used for non-destructive testing when the environment temperature changes in cycles up to 225 °C.

Development of Multilayer Transducer and Omnidirectional Reflection Model for Active Reflection Control.

Underwater detection is accomplished using an underwater ultrasonic sensor, sound navigation and ranging (SONAR). Stealth to avoid detection by SONAR plays a major role in modern underwater warfare. In this study, we propose a smart skin that avoids detection by SONAR via controlling the signal reflected from an unmanned underwater vehicle (UUV). The smart skin is a multilayer transducer composed of an acoustic window, a double-layer receiver, and a single-layer transmitter. It separates the incident signal from the reflected signal from outside through the time-delay separation method and cancels the reflected wave from the phase-shifted transmission sound. The characteristics of the receiving and transmitting sensors were analyzed using a finite element analysis. Three types of devices were compared in the design of the sensors. Polyvinylidene fluoride (PVDF), which had little effect on the transmitted sound, was selected as the receiving sensor. A stacked piezoelectric transducer with high sensitivity compared to a cymbal transducer was used as the transmitter. The active reflection control system was modeled and verified using 2D 360° reflection experiments. The stealth effect that could be achieved by applying a smart skin to a UUV was presented through an active reflection-control omnidirectional reflection model.

Multilayer transducer for highly efficient initiation of time-resolved Brillouin scattering

Structures made of a metallic film deposited on a substrate are conventionally used as opto-acoustic transducers for picosecond ultrasonic experiments where detection in the time domain of the Brillouin scattering in a transparent sample is sought. In this paper, we substitute the metallic film for a periodic stack of nanometric layers made of gold and lithium fluoride to increase the amplitude, at the Brillouin frequency shift, of the strain generated by the photo-thermal effect. A model is used to analyze the generated strain amplification with the volume fraction and with the total thickness of this structure and to evaluate the gain in terms of sample dynamic reflectivity changes. Amplification by a factor of 20 is measured when using the composite structure with respect to signals detected with a transducer made of a single gold layer.

Experimental validation of axially polarized multilayer piezoelectric composite cylindrical transducers with adjustable multifrequency

The axially polarized multilayer piezoelectric composite cylindrical transducers with adjustable multifrequency capability have been proposed by adjusting the external electric resistance and the ratio of piezoelectric layer numbers between the actuator part and the sensor part, which have promising potential in designing the novel cymbal transducer for underwater sound projector and ultrasonic radiator applications. In the previous studies, the multilayer models were established to guide the design of the transducers with arbitrary layer number, and analyzed the dynamic characteristics theoretically. In this work, an experimental study is performed to validate the theoretical models and predictions. Piezoelectric rings with multiple concentric annular electrodes are designed to characterize the multilayer piezoelectric composite cylindrical transducers. The top surface of the piezoelectric rings is divided into two separate parts. One part is covered by multiple concentric annular electrodes, corresponding to the piezoelectric layers, and the other part is uncovered, corresponding to the elastic layers. Four prototypes are fabricated and each consists of four concentric annular electrodes. The impedance spectra are measured by the impedance analyzer to obtain the resonance and anti-resonance frequencies. Effects of two adjusting methods on the dynamic characteristics are evaluated experimentally. The experimental results basically coincide with the theoretical ones. This comprehensive experimental work assures the feasibility of using axially polarized multilayer piezoelectric composite cylindrical transducers with adjustable multifrequencies and confirms the benefit of the developed theoretical models for guiding the fabrication and optimization of this type of transducers.

Low temperature sintering of Li2CO3 added Pb(Ni1/3Nb2/3)-Pb(Zr,Ti)O3 ceramics with high piezoelectric properties

Multilayer structure is an effective approach for reducing driving voltages or increasing output electric signal for piezoelectric devices. However, it is a challenge to achieve high piezoelectric coefficient at low sintering temperature. In this work, we fabricated Li2CO3 (LC) doped Pb(Ni1/3Nb2/3)-Pb(Zr,Ti)O3 (PNN-PZT) ceramics via solid state reaction method. Piezoelectric coefficient at low quasi-static signal d33 and effective piezoelectric coefficient under high electric field d33* are 692 pC/N, 1114 pm/V for PNN-PZT+0.2 wt% LC sintered at 950 °C, which is comparable to high temperature sintered commercial Pb(Zr,Ti)O3 (PZT) based ceramics. Detailed piezoelectric, ferroelectric, dielectric properties, temperature stability and material structure were investigated. The planar electromechanical coupling factor Kp, relative dielectric constant εr and dielectric loss tan δ at 1 kHz, Curie temperature Tc, coercive electric field Ec are measured to be 0.557, 4280, 0.025, 113 °C, 4.34 kV/cm. It shows great potential for applications in multilayer structured cofired piezoelectric actuators and transducers.

Weighted differential evolution heuristics for improved multilayer piezoelectric transducer design

Piezoelectric transducers are designed for wide applications of underwater sonar, energy harvesting, biomedical and nondestructive testing in terms of higher sensitivity and broad bandwidth. Multilayer transducers have well-known advantages of higher sensitivity and thus can be optimized by varying layer thicknesses of active material. The present study deals with mathematical optimization of multilayer transducers exploiting weighted differential evolution (WDE) based computational heuristics for optimized piezoelectric transducer design while satisfying the constraint of constant total thickness. Fitness evaluation is carried out on the basis of one dimensional model (ODM) for simple multilayer, multilayer with bondlines and transducer with bondlines and matching for piezoelectric materials including PZT5h, PMN-PT and piezocomposite with PMN-PT for different loading media. WDE exploited along with ODM for the transducer models has demonstrated the efficacy, reliability and applicability of the proposed scheme. Comparative study of the proposed WDE-ODM with its counterparts including simulated annealing, genetic algorithms, and particle swarm optimization, reveal better performance in terms of accuracy, complexity and convergence metrics for different number of layers for simple transducers. Applicability of WDE-ODM on piezoelectric structures with bondlines, and matching layers has also been accessed and validated.

Optimized Design for a Device to Measure Thermal Contact Conductance During Friction Stir Welding

Friction stir welding (FSW) is a solid-state welding process that is finding increasing use in a variety of industries, owing to its ability to create high-quality welds with less heat input than fusion welding. While the modeling of FSW has been an active effort for at least 15 years, two input parameters, namely the friction coefficient and the heat transfer coefficient, are still adjustable quantities that are difficult to measure. This lack of information compromises the predictive capability of FSW models. While the modeling of friction between the tool and workpiece remains a complex task, the measurement of heat transfer should be possible, but has not been adequately addressed because of the difficulty of accessing the relevant interface with thermocouples. This paper presents a multi-layered frequency-domain thermoreflectance (FDTR) method and transducer design to measure the heat transfer coefficient between the spinning tool and the workpiece. Due to constraints of the welding process, a multi-layered structure is needed for a useable measurement to maximize the heat flow from the modulated heating surface through the heat transfer interface into the welded workpiece. An analytical 2D thermal quadrupole model is shown to be useful in determining layer properties. A multi-layered structure for a specific tool design is validated using COMSOL and optimized. This process can be used to determine the ideal transducer structure to maximize the signal from an FDTR measurement during a friction stir welding process.

Soft Acoustic Waveguides for Strain, Deformation, Localization, and Twist Measurements

A novel type of soft tactile sensor based on polymeric acoustic waveguides is proposed. Ceramic multi-layer piezoelectric transducers generate ultrasonic acoustic wave packets (980kHz) that propagate and can be attenuated, delayed and reflected based on waveguide deformation and length. We detail the sensor design, manufacture and operation and then propose 6 experiments in which we measure the sensor performance. The sensor can detect strain (up to 80%), normal deformation (up to 1mm), simultaneous strain and deformation, compression location (0.5mm interval) and twists (up to 400 axial rotations per meter) and is insensitive to bending (up to 250m−1). This work is the first to propose using soft polymeric waveguides as a tactile element for strain, deformation, localization and twist measurement. This is also the first work to demonstrate decoupled strain and deformation sensing in a single, soft, sensing element. This research aims at introducing an innovative sensing method that can be leveraged toward the creation of simpler and denser multi-modal soft sensors.

Energy harvester for safety shoes using parallel piezoelectric links

Energy-harvesting devices in shoes have attracted much attention from the fields of elderly support, sports science, and disaster mitigation. In this study, we developed an energy harvester with a parallel link structure and six multi-layered piezoelectric transducers. By using this structure, we realized an effective energy conversion compared with conventional energy harvesters in terms of maximum power, comfort, durability, and availability of inputs with six degrees of freedom. A prototype of the parallel-link piezoelectric energy harvester generated 1.29 mW with human body weight. As a trial use, this energy harvester was installed in safety shoes for powering LEDs in the shoes. The assembly produced a brightness of 0.5 cd on average over a duration of 0.5 s, which is enough to show the wearer his or her position in a dark place.

Multilayer dielectric elastomer tubular transducers for soft robotic applications

Dielectric elastomer transducers (DET) belong to the group of electroactive polymers and consist of an elastic dielectric layer laminated between two compliant electrodes. In order to reduce the driving voltage and at the same time maintain appreciable deformation, multilayer systems are common nowadays. Due to their complex manufacturing process, available transducers typically exhibit small aspect ratios in the range of 1:10–2:1 (length/diameter or height/width). Since DET have similar properties to a human muscle, it appears logical to use them in human machine interaction. Therefore, special transducer designs and an adapted dip coating fabrication method for aspect ratios higher than 16:1, which are required for soft robotic applications, are presented within this work. The polydimethylsiloxane (PDMS) raw material Elastosil 2030 (Wacker Chemie AG) and particle-based electrode blends are used to build elongated multilayer tubular transducers with up to 10 layers and 100 mm in length. Moreover, different designs and integrated stiffening elements are simulated with Ansys multiphysics FEM tool. As shown in measurements, the absolute deformation can be increased by more than 40%.

Theory and modeling of multi-layer carbon nanotube thin film thermoacoustic transducer

A new model for a multi-layer thermoacoustic transducer that takes full advantage of the excellent the thermoacoustic characteristics of carbon nanotube (CNT) thin film is developed. Analytical exact solutions of acoustic pressure distribution for both near and far fields are presented with engineering interpretation. By assuming acoustically transparent stacking layers and a total thickness less than a tenth of the sound wavelength, the acoustic pressure field relations between parallel layers are established that subsequently yield the sound pressure for the overall stacking films. A comparison between theoretical prediction and experiment for single-layer and multi-layer CNT thin films is presented and excellent agreement is reported. Key influencing factors including the total layer number, and the spacing between separated films and gas medium on the sound pressures level (SPL) are investigated and discussed in detail. Some design criteria that increases the SPL of the multi-layer CNT thin film transducer are also established.

Development of Multi-Layer Lateral-Mode Ultrasound Needle Transducer for Brain Stimulation in Mice.

Ultrasound, a non-invasive stimulation method, has proved effective in neurostimulation. Previous studies have demonstrated that low-frequency ultrasound (less than 1 MHz) is preferable owing to better penetrability through tissue and skull. However, the large size of low-frequency transducers, which are used in ultrasound neurostimulation studies, makes it difficult to perform multiple-target neurostimulation, especially in small animals such as mice. In this paper, a proposed low-frequency ultrasound needle transducer based on the multi-layer lateral-mode coupling method with a miniature aperture of 0.6 mm × 0.6 mm and a thickness of 1.65 mm was designed and fabricated. The measured electrical impedance of the fabricated 8-layer lateral-mode PZT-5H ceramic was 50.76 Ω at a resonant frequency of 866 kHz. The -6 dB bandwidth of 8-layer lateral-mode transducer was 29% at a center frequency of 876 kHz. The maximum ultrasound peak pressure amplitude at 820 kHz reached approximately 300 kPa, 4-5 times higher than that of the single-layer thickness-mode transducer with 200 V input voltage. The ultrasound beam showed no attenuation and low shift through mouse skull. To verify the feasibility of using the needle transducer to perform multiple-target nerve stimulation in mice brains, we constructed an ultrasound stimulus system to simultaneously stimulate two areas (M2 and V1) of the mouse brain in vivo and detected the c-Fos expression by immunofluorescence to evaluate the effect of stimulation. The results showed that a high ultrasound peak pressure amplitude with this transducer configuration is useful for ultrasound neurostimulation and multiple-target stimulation in mice.

Effects of electrodes and electrical connections of piezoelectric layers on dynamic characteristics of radially polarized multilayer piezoelectric cylindrical transducers

Piezoelectric cylindrical transducer is a type of excellent smart devices that can generate radial sound radiation due to its unique structural characteristics and has been widely used for ultrasonic and underwater sound applications. In the design of a piezoelectric cylindrical transducer, especially with the multilayer structure, the electrodes and electrical connections of piezoelectric layers are two key factors affecting the device performance but have not been well evaluated, which result in the inaccurate prediction of dynamic characteristics. This work establishes the exact theoretical models for radially polarized multilayer piezoelectric cylindrical transducers by taking into account the electrodes and electrical connections of piezoelectric layers. Based on the plane stress assumption, the dynamic solutions of the models are derived. Analytical expressions of electric impedances are also derived to obtain the resonance frequencies. In addition, the analytical solutions are validated using the special example in the earlier work and comparing them with the finite element analysis results. Subsequently, the effects of the electrodes and electrical connections of piezoelectric layers on the dynamic characteristics of the transducer are analyzed and discussed. The results show that the electrode thickness, the electrode type, and the parallel and series connections significantly affect the transducer’s performance, thus providing useful guidelines in the design of piezoelectric cylindrical transducers. This work contributes to an overall analysis on the dynamic characteristics of the radially polarized multilayer piezoelectric cylindrical transducers, which is very helpful to improve the performance of two-dimensional emitter and receiver in underwater sound and ultrasonic applications.