Stack Transducer Research Articles

Modeling and designing of a phased array comprising piezoelectric stack transducer for ultrasonic Lamb wave-based damage detection

Modeling and designing of a phased array comprising piezoelectric stack transducer for ultrasonic Lamb wave-based damage detection

High-Frequency Linear Array (20 MHz) Based on Lead-Free BCTZ Crystal.

Centimeter-sized BaTiO3-based crystals grown by top-seeded solution growth from the BaTiO3-CaTiO3-BaZrO3 system were used to process a high-frequency (HF) lead-free linear array. Piezoelectric plates with (110)pc cut within 1° accuracy were used to manufacture two 1-3 piezo-composites with thicknesses of 270 and [Formula: see text] for resonant frequencies in air of 10 and 30 MHz, respectively. The electromechanical characterization of the BCTZ crystal plates and the 10-MHz piezocomposite yielded the thickness coupling factors of 40% and 50%, respectively. We quantified the electromechanical performance of the second piezocomposite (30 MHz) according to the reduction in the pillar sizes during the fabrication process. The dimensions of the piezocomposite at 30 MHz were sufficient for a 128-element array with a 70- [Formula: see text] element pitch and a 1.5-mm elevation aperture. The transducer stack (backing, matching layers, lens, and electrical components) was tuned with the characteristics of the lead-free materials to deliver optimal bandwidth and sensitivity. The probe was connected to a real-time HF 128-channel echographic system for acoustic characterization (electroacoustic response and radiation pattern) and to acquire high-resolution in vivo images of human skin. The center frequency of the experimental probe was 20 MHz, and the fractional bandwidth at -6 dB was 41%. Skin images were compared against those obtained with a lead-based 20-MHz commercial imaging probe. Despite significant differences in sensitivity between elements, in vivo images obtained with a BCTZ-based probe convincingly demonstrated the potential of integrating this piezoelectric material in an imaging probe.

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.

A piezo stack energy harvester with frequency up-conversion for rail track vibration

To enable predictive and preventive maintenance in rail transportation systems, energy harvesting is a promising powering method. Piezoelectric energy harvesters have great powering potential, but so far the power harvested by piezoelectric railway generators is low. To explore the capability, this work presents a piezo stack energy harvester with frequency up-conversion method consisting of both the inertial mass system and the piezo stack transducer system from rail track vibration energy harvesting. The frequency up-conversion method uses the impact between the inertial mass system and the piezo stack transducer system to enable the piezoelectric transducer to operate at the transient resonant frequency response in spite that the input vibration frequency is much lower than the transducer one to achieve high-power generation. A theoretical model considering the impact between the two systems is established to describe the motion of the energy harvester. Numerical simulation and finite element analysis are conducted to model the proposed energy harvester and compared with experimental results to validate the proposed method. The time-dependent reactions, the frequency response characteristics, and the influence factors on output such as impedance, initial interval, acceleration, signal waveform are studied to evaluate the energy harvesting performance. In the experiments, the proposed energy harvester outputs a maximum power of 495.74 mW and an average power of 43.58 mW at an input rms acceleration of 0.7 g applied at 18 Hz with an optimum load impedance of 150 Ω, exhibiting good performance in comparison with the state-of-the-art piezoelectric energy harvesters applied on the rail track.

Piezoelectric energy harvesting from rail track vibration using frequency up-conversion mechanism

Piezoelectric energy harvesting has great powering potential in railway applications, but current piezoelectric literature for rail track vibration mainly focuses on a single piezoelectric element or piezoelectric cantilever, whose output power is usually at the level of µW. In this work, a piezo stack energy harvester using the frequency up-conversion method with attractive magnetic force is proposed and experimentally validated for harvesting energy from rail track vibration. It consists of two parts, an inertial mass system and a piezo stack system. The frequency up-conversion mechanism is realised by allowing the inertial mass to attach and detach the piezo stack transducer periodically with the help of the attractive magnetic force. The attractive magnetic force contributes to the collision between the two systems, especially when the excitation frequency is near the resonant frequency. A theoretical model of the proposed energy harvester considering the colliding motion and magnetic force is established. A prototype is fabricated and can generate a peak power of 96.69 mW and average power of 2.59 mW at an input acceleration of 1 g applied at 9 Hz with an optimum load impedance of 200 Ω.

A multi-pillar piezoelectric stack transducer for nanodroplet mediated intravascular sonothrombolysis

We aim to develop a nanodroplet (ND)-mediated intravascular ultrasound (US) transducer for deep vein thrombosis treatments. The US device, having an efficient forward directivity of the acoustic beam, is capable of expediting the clot dissolution rate by activating cavitation of NDs injected onto a thrombus. We designed and prototyped a multi-pillar piezoelectric stack (MPPS) transducer composed of four piezoelectric stacks. Each stack was made of five layers of PZT-4 plates, having a dimension of 0.85 × 0.85 × 0.2 mm3. The transducer was characterized by measuring the electrical impedance and acoustic pressure, compared to simulation results. Next, in-vitro tests were conducted in a blood flow mimicking system using the transducer equipped with an ND injecting tube. The miniaturized transducer, having an aperture size of 2.8 mm, provided a high mechanical index of 1.52 and a relatively wide focal zone of 3.4 mm at 80 Vpp, 0.96 MHz electric input. The mass-reduction rate of the proposed method (NDs + US) was assessed to be 4.1 and 4.6 mg/min with and without the flow model, respectively. The rate was higher than that (1.3–2.7 mg/min) of other intravascular ultrasound modalities using micron-sized bubble agents. The ND-mediated intravascular sonothrombolysis using MPPS transducers was demonstrated with an unprecedented lysis rate, which may offer a new clinical option for DVT treatments. The MPPS transducer generated a high acoustic pressure (~3.1 MPa) at a distance of approximately 2.2 wavelengths from the small aperture, providing synergistic efficacy with nanodroplets for thrombolysis without thrombolytic agents.

Modal Actuation and Sensing With an Active AFM Cantilever

Modal actuation and sensing are implemented on a microfabricated AFM cantilever with a two-layer piezoelectric stack transducer. The top transducer is shaped as the second derivative of the first mode shape. The bottom transducer is uniformly distributed along the cantilever length. The purpose of this work is to demonstrate that modal actuation and sensing can be used to eliminate other resonances from frequency response function of the active cantilever, except the first mode. First-order mathematical formulations are presented to model transverse vibrations of the cantilevers under this study. Microfabrication steps and characterization of these cantilevers are reported. Their respective actuation and sensing gains are determined for comparison with conventional active cantilevers. Electromechanical coupling coefficients are also calculated to exhibit reciprocity of modal actuation and sensing in eliminating higher modes from the frequency response. The advantages of modal actuation and sensing in avoiding instabilities in feedback controlled AFM active cantilevers are also demonstrated.

The effect of geometry on the performance of amplified flexure-guided actuators

This study presents an analytical model of a flextensional actuator comprised of a piezoceramic rod or stack transducer integrated into a flexible mechanical structure. It converts and amplifies the longitudinal in-plane strains in the transducer into the out-of-plane bending of metal beams. Two curvilinear beams mounted by means of two hinged links with an offset to a centrally located piezoceramic transducer create a monolithic hinge lever mechanism. The idea behind that solution is to reduce the bending stiffness at the hinges, while maintaining enough axial rigidity of the active beams and obtain greater magnification of the out-of-plane displacement. As the main purpose of this work is to estimate the influence of piezoelectric force on the performance of flextensional actuators of different geometric shapes and mechanical parameters, two transducers have been considered. An analytical model of the actuator has been developed on the basis of the stationary value of the total potential energy principle with the use of the von Karman non-linear strains theory. Moreover, the application of structure prestressing is considered to avoid undesired stretching of the piezoceramic transducer. A vast number of results exhibit the mechanical responses of the actuator of different geometry, initial midspan rise and beam material properties to piezoelectric stimulation. The analytical method described here may be adopted for other types of flextensional actuators. Additionally, a numerical model of flexure-guided transducer is presented to show that the analytical solution can provide a set of valuable design parameters in less time than FEM simulations.

Nonlinearity in a Medical Ultrasound Probe Under High Excitation Voltage

Tissue harmonic imaging is often the preferred ultrasound imaging modality due to its ability to suppress reverberations. The method requires good control of the transmit stage of the ultrasound scanner, as harmonics in the transmitted ultrasound pulses will interfere with the harmonics generated in the tissue during nonlinear propagation, degrading image quality. In this study, a medical ultrasound probe used in tissue harmonic imaging was experimentally characterized for transmitted second-harmonic distortion to identify and compare the sources of nonlinear distortion in the probe and transmit electronics. The system was tested up to amplitudes above what is found during conventional operation, pushing the system to the limits in order to investigate the phenomenon. Under these conditions, second-harmonic levels up to -20 dB relative to the fundamental frequency were found in the ultrasound pulses transmitted from the probe. The transmit stage consists of high-voltage transmit electronics, cable, tuning inductors, and the acoustic stack. The contribution from the different stages in the ultrasound transmit chain was quantified by separating and measuring at different positions. Nonlinearities in the acoustic transducer stack were identified as the dominating source for second harmonics in the transmitted ultrasound pulses. Contribution from other components, e.g., transmit electronics and cable and tuning circuitry, were found to be negligible compared with that from the acoustic stack. Investigation of the stack's electrical impedance at different driving voltages revealed that the impedance changes significantly as a function of excitation voltage. The second-harmonic peak in the transmitted pulses can be explained by this nonlinear electrical impedance distorting the driving voltage and current.

Acoustic Radiation Suppression of a Truss Core Sandwich Panel Using Decentralized Resonant Shunt Damping

The aim of the present work was to suppress the free space acoustic radiation of a truss-cored sandwich panel through the use of the decentralized resonant shunt method. First, the finite element model of the structure was established and its sound radiation characteristics were studied using the elemental radiators decomposition method. Then the decentralized modal piezoelectric shunt vibration control strategy of the Kagome sandwich panel was described in detail. In this approach, a small number of rods in the bottom truss of the sandwich panel were replaced by a piezoelectric stack transducer; each transducer was connected to a single resonant shunt which was tuned to suppress the vibration of a specific mode. The biggest advantage of the independent modal resonant shunt method is that the circuits of each mode are independent of each other; thus the large-scale parameter optimization can be decomposed into small-scale optimization problems. The results of the numerical simulation have shown that the approach that has been proposed in this paper is very effective in controlling the sound radiation of the examined structure at its resonant frequency. The results of this study can be useful in the study of the sound radiation suppression of a sandwich panel.

High Dynamic Range AFM Cantilever With a Collocated Piezoelectric Actuator-Sensor Pair

We present a novel approach to fundamentally eliminate electrical feedthrough (cross-talk) signal in self-sensing piezoelectric microcantilevers, used in dynamic mode atomic force microscopy (AFM). The probe is an Si microcantilever on which a two-layer piezoelectric stack transducer is microfabricated. The top transducer in the stack functions as an actuator, while the bottom transducer is used as a deflection sensor. This arrangement leads to a collocated actuator-sensor pair that co-exist on the same surface area. We report experimental results that establish the sensor’s ability to capture the full dynamic range of the cantilever with minimal feedthrough from the actuator. [2019-0143]

Modeling and electromechanical performance analysis of frequency-variable piezoelectric stack transducers

An exact analytical model of frequency-variable piezoelectric stack transducers is proposed, and their dynamic characteristics are studied in this article. Based on the linear piezoelasticity theory, the dynamic analytical solution is first derived, and then its correctness is validated by comparing it with the results of a special example in the previous literature and the ones of the experimental study. The effects of the tuning resistance and the layer number of the active element on the dynamic characteristics are discussed. Numerical results show that tuning the resistance and the layer number of the active element can enable the multi-frequency characteristics of the piezoelectric stack transducers. A proper layer number of the active element can minimize the short-circuited resonance frequency and the open-circuited anti-resonance frequency. These findings provide guidelines to design and optimize the piezoelectric stack transducers, which have promising potential in developing the multi-frequency Langevin transducers for some underwater sound and ultrasonic applications, such as ultrasonic cleaning, ultrasonic chemistry, and sonar radiators.

Improving the off-resonance energy harvesting performance using dynamic magnetic preloading

Piezoelectric stack transducers in d33 mode have a much higher mechanical-to-electric energy conversion efficiency compared with d31 mode piezoelectric harvesters. However, multilayered piezoelectric stacks usually operate in off-resonance due to the higher stiffness and thereby have a lower power output under low-frequency excitations. This paper proposes to apply the dynamic magnetic pre-loading to a piezoelectric stack transducer to significantly increase the power output. The energy harvesting system consists of a multilayered piezoelectric stack with a compliant force amplification frame, a proof mass, and two magnets configured in attraction. The static force–displacement relationship of the magnets is identified from experiments and extended to a dynamic model capable of characterizing the dynamic magnetic interaction. An electromechanical model is developed based on the theoretical derivation and the experimentally identified parameters to predict the voltage outputs under different resistive loads. Approximate analytical solutions are derived by using the harmonic balance method and show good agreements with the numerical and experimental results. The performance of the system is examined and compared with that of the harvester without magnetic pre-loading. The influences of the distance between the two magnets and the electrical resistive loads on the power output are investigated. Results indicate the energy harvesting system with magnetic pre-loading can produce over thousand times more power than the system without magnetic pre-loading at the base excitation of 3 Hz and 0.5 m/s2, far below the resonance at 243 Hz

Dry Coupling of Ultrasonic Transducer Components for High Temperature Applications.

The viability for dry coupling of piezoelectric ultrasonic transducer components was investigated, using a thin foil of annealed silver as a filler material/coupling agent at each component interface. Criteria used for room temperature evaluation were centered on signal-to-noise ratio (SNR) and echo bandwidth, for a Li-Nb based transducer operating in pulse-echo mode. A normal clamping stress of only 25 MPa, applied repeatedly over three loading cycles on a precisely-aligned transducer stack, was sufficient to yield backwall echoes with a SNR greater than 25 dB, and a 3 dB bandwidth of approximately 65%. This compares to a SNR of 32 dB and a 3 dB bandwidth of 65%, achievable when all transducer interfaces were coupled with ultrasonic gel. The respective roles of a soft filler material, alignment of transducer components, cyclic clamping, component roughness, and component flatness were evaluated in achieving this high efficiency dry coupling, with transducer clamping forces far lower than previously reported. Preliminary high temperature tests indicate that this coupling method is suitable for high temperature and achieves signal quality comparable to that at room temperature with ultrasonic gel.

Design of a Novel Two-Directional Piezoelectric Energy Harvester With Permanent Magnets and Multistage Force Amplifier.

This article presents the design and testing of a novel two-directional (2-D) piezoelectric stack-based energy harvester for capturing the mechanical energy from the human footstep. The uniqueness of the harvester lies in the fact that the energy of 2-D excitation is scavenged by a single piezoelectric stack transducer, which can reduce the loss of harvestable energy. The harvester is constructed by the integration of permanent magnets, position protection plates, and multistage force amplification frame. The input force and input displacement are restricted to guarantee the device's safety. The reported multistage force amplification frame with leverage mechanism and bridge-type amplifier enlarges the force acting on the piezoelectric stack, which further improves the power output. A linear guiding mechanism based on leaf flexure is applied to minimize the impact of input forces in other than moving directions. Through analytical modeling, the main architectural parameters of the device are determined. Simulation study with finite-element analysis is conducted to optimize the device parameters for achieving the largest force amplification ratio with a high safety factor. A prototype harvester is fabricated for experimental study. Results demonstrate the feasibility of the developed 2-D piezoelectric stack-based energy harvester.

Stiffness and damping effects of the rhombic piezoelectric stack transducer with a negative capacitance shunt

The piezoelectric shunt damping (PSD) is widely utilized to control structural vibrations based on its damping performance. Unlike previous studies, this work considers the stiffness and damping effects of a rhombic piezoelectric stack transducer with a negative capacitance shunt. The piezoelectric shunt stiffness (PSS) and the PSD concepts are proposed and theoretically modelled to investigate the stiffness and damping performance. The piezoelectric stack transducer with a negative capacitance can achieve both negative and positive stiffnesses to tune the natural frequency of the host structure. The root locus methods are utilized to judge the stability of the system. Both numerical simulation and experimental results demonstrate that the negative stiffness and the positive stiffness of the system greatly depend on the negative capacitance, while the damping depends on the resistance.

Piezoelectric Shunt Stiffness in Rhombic Piezoelectric Stack Transducer with Hybrid Negative-Impedance Shunts: Theoretical Modeling and Stability Analysis.

Negative-capacitance shunted piezoelectric polymer was investigated in depth due to its considerable damping effect. This paper discusses the novel controlled stiffness performance from a rhombic piezoelectric stack transducer with three hybrid negative-impedance shunts, namely, negative capacitance in series with resistance, negative capacitance in parallel with resistance, and negative inductance/negative capacitance (NINC) in series with resistance. An analytical framework for establishing the model of the coupled system is presented. Piezoelectric shunt stiffness (PSS) and piezoelectric shunt damping (PSD) are proposed to analyze the stiffness and damping performances of the hybrid shunts. Theoretical analysis proves that the PSS can produce both positive and negative stiffness by changing the negative capacitance and adjustable resistance. The Routh–Hurwitz criterion and the root locus method are utilized to judge the stability of the three hybrid shunts. The results point out that the negative capacitance should be selected carefully to sustain the stability and to achieve the negative stiffness effect of the transducer. Furthermore, negative capacitance in parallel with resistance has a considerably better stiffness bandwidth and damping performance than the other two shunts. This study demonstrates a novel electrically controlled stiffness method for vibration control engineering.

Piezoelectric stacked transducer evaluation and comparison for optimized energy harvesting

The primary focus of this research is on the application and optimization of direct piezoelectric effect in energy harvesting from low frequency mechanical vibrations such as from roadway traffic. The specific research aim is to evaluate the various stacked PZT transducers in their mechanisms and performance on effective electromechanical energy conversion. Piezoelectric power output has been determined based on understanding of the fundamental concepts in composites (1:3 bi-phasic) and stacked transducers. Several property structure relations are evaluated by various experimental methods including the utilization of electrodynamic test systems. Power evaluation is compared among several samples in order to understand the most efficient configuration utilizing PZT ceramics. Power density as function of applied mechanical force and pressure, are calculated and compared with the experimental results which yield good agreement. Three types of stacked PZT transducers were compared and systemically tested for their electromechanical power conversion performance. The 1:3 composite stacked PZT transducer was found to be the best performer in term of power density per unit active volume, the specially designed and fabricated stacked PZT transducers (UTSA stacked sample) were found to have the highest power density per transducer volume, 0.615 mW/mm3, measured at 965 kN/m2 (140 PSI), among the three types studied (1:3 composite stacked sample, assembled stacked sample and the commercially sourced stacked sample). The pressures and forces used were based on the traffic flow monitoring and federal and state regulations.

Optimization design and experimental investigation of piezoelectric energy harvesting devices for pavement

This study designs a compression-based pavement energy harvesting device with a group of piezoelectric transducers and investigates the selection of the component materials based on four technical device requirements for enhanced the electric energy output of power-generation pavements. The external dimensions of the proposed devices are optimized based on vehicle wheelpath distribution, tire trace patterns, and vehicle roller compaction conditions. The array pattern of the piezoelectric device is designed based on the driving characteristics. Various device material configurations are examined using different cover plates, rubber pad thicknesses, protective pads, and transducer specifications for optimal mechanic-electric response characteristics. A 150 mm × 150 mm type device is tested as an example and its electrical output performance is evaluated under typical road loading environments. Subsequently, a comparative analysis of various disclosed piezoelectric harvesting device technology were conducted and further research plan was developed. The selected modified polypropylene or aluminum plate, steel plate, modified polypropylene bar, and fiber heat insulation plate are suitable for the device which meets the application demands. The optimum device dimensions under light and heavy traffic conditions are 100 mm × 100 mm and 150 mm × 150 mm, respectively. The optimum configuration of the device includes a modified polypropylene upper cover plate, 1 mm rubber pad, ball-type protective pad, and eight laminated transducers. In addition, parallel connection of stacked transducers is more suitable for energy collection and reuse from traffic-induced pavement vibrations. Under the loading of 0.7 MPa and 15 Hz, the 150 mm × 150 mm device with nine parallel transducers achieves a maximum output power of 50.41 mW, and the corresponding optimum loading is 4 kΩ. Under the loading of 0.2 MPa and 10 Hz, the device achieves a maximum output power of 2.92 mW, and the corresponding optimum load is 10 kΩ. The performance of piezoelectric device designed in this paper excels that of many other available devices.

A distributed parameter model for the piezoelectric stack harvester subjected to general periodic and random excitations

Vibration-based energy harvesting using piezoelectric stacks has received increasing attention in recent years for its higher mechanical-to-electrical energy conversion capability in the d33 mode. However, most research on this type of harvesters is based on either the simplified one-degree-of-freedom model or transfer matrix model. This paper presents a distributed-parameter model for the multilayer piezoelectric stack transducer based on the axial vibration theory of a continuous bar. The presented analytical model is free from the assumption that the generated current is identically distributed over all the piezoelectric layers, which has been widely used by the existing models in literature. A first-order numerical model is also introduced to validate the performance of the analytical model on the prediction of voltage, current and power outputs of the harvester under different types of external excitations. Both the analytical and numerical models are firstly validated by experiments and then are used to predict the electrical responses of the stack harvester under general periodic and random excitations with different intensities. Experiment and simulation results demonstrate that the proposed distributed-parameter model has a good accuracy and reliable performance in the prediction of the electrical responses.