Piezoelectric Ceramic Transducers Research Articles

Conformable Shear Mode Transducers from Lead‐Free Piezoelectric Ceramic Coatings: An Innovative Ultrasonic Solution for Submerged Structural Health Monitoring

AbstractShear mode‐guided ultrasonic waves are highly regarded for submerged or subterranean structural health monitoring (SHM), owing to their non‐dispersive feature and minimized acoustic energy loss when in contact with liquid or solid. High‐performance shear mode ceramic ultrasonic transducers with robustness and cost‐effectiveness are highly demanded for underwater or underground SHM applications, especially in harsh environments. However, the implementation of discrete shear mode piezoelectric ceramic ultrasonic transducers is hindered by the inconsistency with manual installation, lack of conformability on curved surfaces, and unreliable acoustic coupling between the transducers and the structure. Here, direct‐write conformable shear mode ultrasonic transducers made from piezoelectric lead‐free ceramic coatings, which are in situ produced on steel structures by a scalable thermal spray process, are proposed. The obtained lead‐free lithium‐doped potassium sodium niobate (KNN‐LN) ceramic coatings exhibit a high effective shear piezoelectric strain coefficient (d24, f) above 60 pm V−1 in a broad frequency range from 100 Hz to 200 kHz. The resulting conformable shear mode KNN‐LN ceramic coating transducers successfully showcase the functions of exciting and detecting stable shear mode ultrasonic wave signals with operation temperature exceeding 200 °C and demonstrate reliable capability in defect detection in both air and liquid environments.

Empirical models for the error induced in piezoelectric ceramic transducer-based acoustic ranging instrumentation and measurement

This article presents experimental methods and analytics for developing statistical models for ultrasonic sensors to improve reliability, repeatability, and signal-to-noise ratio (SNR) in static environments. The experiments use commercial piezoelectric ceramic transducers and over 4100 calibrated readings for three specimens of different materials. Using commercial piezoelectric ceramic transducers, the spatial-temporal approach considers range, environmental factors, material characteristics, and their interactions. A true value approach is used to formulate the error as a function of the distance measured in the time-of-flight (ToF) method at zero azimuth angular directivity. The three statistical models, linear temperature, averaged linear regression, and averaged cubic regression models, are formulated and validated. The most influential parameters in the calibrating distance with an acoustic sensor are the range, coupled effect of temperature, and material characteristics, followed by temperature. The linear model increases the SNR within 0–40 cm from ±20 dB to ≈80 dB, and the cubic model increases the repeatability of the measurement by reducing the absolute error for the entire range of sensors from ±3 cm to less than −1 cm.

Response Analysis of a Piezoelectric Ceramic Transducer Pair Excited by Phase-Modulated Signals for Improved Echo Measurement

Response Analysis of a Piezoelectric Ceramic Transducer Pair Excited by Phase-Modulated Signals for Improved Echo Measurement

Designing an Automatic Frequency Stabilization System for an External Cavity Diode Laser Using a Data Acquisition Card in the LabVIEW Platform

The frequency stability of free-running lasers is susceptible to the influence of environmental factors, which cannot meet the long-term frequency stabilization requirements for atom interferometry precision measurements. To obtain a frequency-stabilized 780 nm laser beam, an automatic frequency stabilization system for an external cavity diode laser (ECDL) based on rubidium (Rb) atomic saturated absorption spectrum was designed using a commercial data acquisition (DAQ) card. The signals acquired by the A/D terminal are processed and analyzed by LabVIEW, which can automatically identify all the locking points and output the piezoelectric ceramic transducer (PZT) scan and digital feedback through the D/A terminal. The experimental results show that the system can lock to six different frequencies separately and realize automatic relocking within 3.5 s after unlocking. The system has a stability of 1.68 × 10−10@1 s and 4.77 × 10−12@1000 s, which meets the laboratory’s requirements for atomic interference experiments.

A Gas Flow Measurement System Based on Lead Zirconate Titanate Piezoelectric Micromachined Ultrasonic Transducer.

Ultrasonic flowmeter is one of the most widely used devices in flow measurement. Traditional bulk piezoelectric ceramic transducers restrict their application to small pipe diameters. In this paper, we propose an ultrasonic gas flowmeter based on a PZT piezoelectric micromachined ultrasonic transducer (PMUT) array. Two PMUT arrays with a resonant frequency of 125 kHz are used as the sensitive elements of the ultrasonic gas flowmeter to realize alternate transmission and reception of ultrasonic signals. The sensor contains 5 × 5 circular elements with a size of 3.7 × 3.7 mm2. An FPGA with a resolution of ns is used to process the received signal, and a flow system with overlapping acoustic paths and flow paths is designed. Compared with traditional measurement methods, the sensitivity is greatly improved. The flow system achieves high-precision measurement of gas flow in a 20 mm pipe diameter. The flow measurement range is 0.5-7 m/s and the relative error of correction is within 4%.

Research on low-frequency bender disk transducer driven by multiple relaxor ferroelectric single crystal disks

In this paper, we investigate the low-frequency bender disk transducer designed by the relaxor ferroelectric single crystal. First, we introduce the principle of the bender disk transducer, and use multiple single crystal disks as driving materials to excite the bending vibration mode of the metal plate, which reduces the operating frequency of the transducer. Then we establish the three-dimensional finite element model of the bender disk transducer driven by multiple single crystal disks, analyze the influence of the number and position distribution of single crystal disks on the transducer performance, and compare with that of the piezoelectric ceramic transducer with the same structure. Finally, we manufacture the proposed relaxor ferroelectric single crystal, piezoelectric ceramic transducers and the conventional piezoelectric ceramic bender disk transducer respectively, and carry out the experimental measurement in an anechoic water tank. The experimental results show that for the proposed single crystal transducer, its measured maximum transmitting voltage response (TVR) is 126.2 dB at 1.1 kHz, which is 13.4 dB higher than that of the proposed piezoelectric ceramic transducer, and its frequency corresponding to the maximum TVR is reduced by 700 Hz compared with the conventional piezoelectric ceramic bender disk transducer.

Design of a Wearable Real-Time Hand Motion Tracking System Using an Array of Soft Polymer Acoustic Waveguides.

Robust hand motion tracking holds promise for improved human-machine interaction in diverse fields, including virtual reality, and automated sign language translation. However, current wearable hand motion tracking approaches are typically limited in detection performance, wearability, and durability. This article presents a hand motion tracking system using multiple soft polymer acoustic waveguides (SPAWs). The innovative use of SPAWs as strain sensors offers several advantages that address the limitations. SPAWs are easily manufactured by casting a soft polymer shaped as a soft acoustic waveguide and containing a commercially available small ceramic piezoelectric transducer. When used as strain sensors, SPAWs demonstrate high stretchability (up to 100%), high linearity (R2 > 0.996 in all quasi-static, dynamic, and durability tensile tests), negligible hysteresis (<0.7410% under strain of up to 100%), excellent repeatability, and outstanding durability (up to 100,000 cycles). SPAWs also show high accuracy for continuous finger angle estimation (average root-mean-square errors [RMSE] <2.00°) at various flexion-extension speeds. Finally, a hand-tracking system is designed based on a SPAW array. An example application is developed to demonstrate the performance of SPAWs in real-time hand motion tracking in a three-dimensional (3D) virtual environment. To our knowledge, the system detailed in this article is the first to use soft acoustic waveguides to capture human motion. This work is part of an ongoing effort to develop soft sensors using both time and frequency domains, with the goal of extracting decoupled signals from simple sensing structures. As such, it represents a novel and promising path toward soft, simple, and wearable multimodal sensors.

Finite element-based diffraction correction for piezoelectric transducers accounting for diffraction at transmission, propagation, and reception.

Existing diffraction correction models for ultrasonic transmit-receive measurement systems rely on simplifying assumptions with respect to the boundary conditions at the transmitter or receiver. Common simplifications include approximating the sound field radiated by a piezoelectric transducer using a baffled piston model and assuming that the receiver's electrical response is proportional to the spatially averaged free-field pressure over its front surface. In many applications, such simplifications may be adequate, but their validity and accuracy need to be evaluated and quantified. Here, a diffraction correction model utilizing the full set of electrical and mechanical boundary conditions at the transmitter and receiver is presented, avoiding these simplifications. The model is based on finite element modeling of coaxially aligned piezoelectric transducers in a fluid medium. Comparison is made with existing models for an example case of cylindrical piezoelectric ceramic disk transducers operating in air at 50-300 kHz and 0.03-2 m apart, relevant for, e.g., sound velocity and absorption measurements in fluids and ultrasonic gas flow metering. In the near-field, errors introduced by the simplifications are up to 3 dB and 47° for the first radial resonance. Generally, such errors are application-specific and depend on distance, frequency, transducer construction, vibration pattern, and medium properties.

Field experiments of watt-level piezoelectric energy harvester for different embedded depths

Road piezoelectric energy-harvesting technology uses the positive piezoelectric effect to convert vibrational energy produced by vehicular load to electrical energy. Road piezoelectric energy harvesters (RPEHs) are the core elements behind this technology. A new disc-type metal–piezoelectric ceramic transducer structure was developed to promote road piezoelectric energy collection and increase power generation from RPEHs. Finite element analyses and field tests were then conducted. The experimental results show that the disc transducers have excellent road compatibility. The greater the embedded depth of the transducer, the smaller is the output power of the RPEH; hence, an embedded depth of 2 cm was selected as the optimal value for comprehensive durability and electrical performance. When a small car travelling at a speed of 60 km/h passed over the RPEH embedded at a depth of 2 cm, a maximum voltage of 62 V, maximum current of 62 mA, and maximum utput power of 3844 mW (power density: 43 W/m2) were observed. The influence of the vehicle weight on the RPEH output power decreased with increase in speed. Therefore, this study confirms that the new disc-type RPEH is less costly, has excellent power generation, and requires less piezoelectric transducer material.

Accurate damage localization and enhanced mechanical performance of self‐sensing epoxy nanocomposites using graphene platelets

AbstractRecently, there has been growing interest in the use of composites structure with self‐sensing functionalities in the aerospace, automotive, and renewable energy industries. However, the integration of sensors such as Fiber Bragg Grating or piezoelectric ceramic transducers into the composite structure can significantly reduce the structure's inherent strength. To address this issue, we present a novel approach for developing self‐sensing composites by incorporating graphene platelets (GnPs) as an electric filler into an epoxy matrix. Our method involves the uniform dispersion of GnPs in epoxy, with some GnPs connected to each other to achieve a low electrical threshold of 0.61 vol% in the resulting nanocomposites. The resulting composite film exhibits high sensitivity to tensile strains ranging from 0% to 1.8%, with gauge factors (GFs) ranging from 19 to 172. This variation in GF is due to the calibration process, which relies on the relationship between input and output data and does not require a constant factor. In addition to its high sensitivity to tensile strains, the composite film also demonstrates excellent self‐sensing performance for bending deformation. Moreover, the composite film effectively responds to impact damage evolution, making it a promising candidate for practical applications. This work represents an advancement in the development of self‐sensing nanocomposites using two‐dimensional materials, offering exceptional sensitivity and adaptability for potential future use.

Ultrasonic characterization of multi-layered porous lithium-ion battery structure for state of charge

A multi-layered porous finite element model of lithium-ion battery is proposed by using Voronoi polygons. The time domain simulation of ultrasonic transmission characteristics with different state of charge (SOC) are carried out, and the variation of acoustic parameters versus SOCs is explored. Then, in the experiment research, the ultrasonic transmission signals are obtained by employing piezoelectric ceramic transducers during the discharging step. By extracting the time domain characteristic parameters, it is discovered that the amplitude and time-of-flight (TOF) have a strong correlation with SOC, the slow pressure-wave (SPW) velocities of the experiments correspond well with the simulation results. In addition, the frequency domain analysis shows a linear link between the amplitude of the frequency spectrum and SOC. Moreover, via repeated experiments, it is found that the ultrasonic transmission method has good repeatability in probing the SOC, and the SPW velocities acquired by experiments can almost be covered by 95% confidence interval formed based on the results of the simulation. Furthermore, according to the results of the experiments, a gray model based on the particle swarm optimization-based-simulated annealing (GM-PSO-SA) is established, which realized the prediction of the SOC under the condition of small sample data. The research results can serve as a reference for creating a comprehensive finite element model of the multi-layered porous structure of lithium-ion battery. Meanwhile, it also provides a detection and evaluation tool for the monitoring of the SOC.

Performance Analysis and Prospect of Piezoelectric Ultrasonic Transducers Based on Vibration Modes

With the maturity of ultrasonic transducer technology, as a traditional ultrasonic transducer, piezoelectric ultrasonic transducer has leaped into the public view. This article briefly summarizes the development of ultrasonic transducers and the classification of piezoelectric ultrasonic transducers. In practical applications, different piezoelectric ultrasonic transducers are mostly selected based on the different sound source vibrations in the application scenarios. The principle analysis and structure introduction of longitudinal vibration type ultrasonic transducers, longitudinal bending vibration mode conversion type ultrasonic transducers, and torsional vibration piezoelectric ceramic ultrasonic transducers are conducted respectively, and the application fields are pointed out. Besides, heat dissipation is an important link that affects the energy transfer efficiency of piezoelectric ultrasonic transducers. For traditional air-cooled heat dissipation and phase change heat dissipation, the heat dissipation ability is investigated and analyzed separately, and the advantages and disadvantages of the two are compared. It is concluded that phase change heat dissipation can effectively solve the impact caused by excessive temperature difference inside the transducer, while traditional heat dissipation methods cannot solve this problem.

A floating piezoelectric electromagnetic hybrid wave vibration energy harvester actuated by a rotating wobble ball

This paper presents a floating piezoelectric electromagnetic hybrid wave vibration energy harvester actuated by a rotating wobble ball. The kinematic equation of the rotating wobble ball under the influence of the wave is established by simplifying the ocean wave model. One merit of the proposed harvester is that it can harvest wave vibration energy via a frequency up-conversion mechanism. The vibration energy of a wave is converted into electrical energy by the electromagnetic generator (EMG) and the piezoelectric ceramic transducer (PZT). Low-frequency vibration energy is converted into the high frequency vibration of the PZTs using frequency up-conversion mechanism. The results show that the maximum power generated by the proposed hybrid energy harvester is 21.95 mW when the external frequency of the wave is 1.4 Hz. Additionally, two PZTs and the EMG successfully output about 11.26 mW of power to light up LEDs throughout a test of low-power electronics. The results demonstrate that low-frequency wave vibrations can be efficiently harvested using the proposed hybrid vibration energy harvester.

Vibration monitoring of optical fiber composited in overhead transmission line using φ-OTDR

In order to evaluate the vibration state of the overhead line, the φ-OTDR (phase-sensitive optical time-domain reflectometry) is applied to the vibration monitoring for the optical fiber composited in overhead transmission line. The principle of φ-OTDR and the IQ demodulation algorithm is introduced. Common mono-mode dark optical fiber simulates the optical fiber composited in an overhead line. The sinusoidal vibration is applied to the optical fiber using an arbitrary waveform generator and piezoelectric ceramic transducer (PZT). The vibration status in the optical fiber is measured by optical fiber vibration monitoring system using φ-OTDR. The result reveals that this system can demodulate the vibration applied to the optical fiber. This paper provides a reference for vibration monitoring optical fiber composite overhead lines.

Energy harvesting and storage with ceramic piezoelectric transducers coupled with an ionic liquid-based supercapacitor

One of the main issues of wearable electronic devices regards their power supply and autonomy. The exploitation of mechanical energy from body motion and vibrations can be realized by using piezoelectric materials coupled with a proper energy storage device. To this aim, Self-Powered Supercapacitors (SPSCs) have been investigated over the last decades, either as internally integrated SPSC (iSPSC), where the piezoelectric element of the device is used as Super Capacitor (SC) separator, or via an external integration (eSPSC), where the piezoelectric unit and the SC are connected by a bridge rectifier. In this paper, an eSPSC power supply is developed by integrating a stuck of commercial ceramic piezoelectric disks and an ionic liquid-based micro-SC. In detail, a stack of 15 commercial lead zirconate titanate (PZT) disks is used as the energy harvesting unit and mechanically stressed by a compressive force of 85 N at 2 Hz. The piezoelectric output successfully charged the 22 mF supercapacitor up to 3.1 V after 2 h of test, achieving a stored energy value equal to 110 mJ. The proposed integrated system outperforms the state-of-the-art SPSC assembled with micro-SC (both iSPSC and eSPSC). The use of the two different units (piezo-energy harvesting unit and micro-SC energy storage unit) allows an independent sizing and tuning of the supercapacitor according to the output current of the piezoelectric unit.

An Impact Localization Solution Using Embedded Intelligence-Methodology and Experimental Verification via a Resource-Constrained IoT Device.

Recent advances both in hardware and software have facilitated the embedded intelligence (EI) research field, and enabled machine learning and decision-making integration in resource-scarce IoT devices and systems, realizing "conscious" and self-explanatory objects (smart objects). In the context of the broad use of WSNs in advanced IoT applications, this is the first work to provide an extreme-edge system, to address structural health monitoring (SHM) on polymethyl methacrylate (PPMA) thin-plate. To the best of our knowledge, state-of-the-art solutions primarily utilize impact positioning methods based on the time of arrival of the stress wave, while in the last decade machine learning data analysis has been performed, by more expensive and resource-abundant equipment than general/development purpose IoT devices, both for the collection and the inference stages of the monitoring system. In contrast to the existing systems, we propose a methodology and a system, implemented by a low-cost device, with the benefit of performing an online and on-device impact localization service from an agnostic perspective, regarding the material and the sensors' location (as none of those attributes are used). Thus, a design of experiments and the corresponding methodology to build an experimental time-series dataset for impact detection and localization is proposed, using ceramic piezoelectric transducers (PZTs). The system is excited with a steel ball, varying the height from which it is released. Based on TinyML technology for embedding intelligence in low-power devices, we implement and validate random forest and shallow neural network models to localize in real-time (less than 400 ms latency) any occurring impacts on the structure, achieving higher than 90% accuracy.

Large-scale piezoelectric ultrasonic transducers with tubular near-period phononic crystal point defect structure

&lt;sec&gt;The coupling vibration of large-scale piezoelectric ultrasonic transducer will make the average value of the longitudinal displacement amplitude of its radiation surface small and the amplitude distribution uneven, which seriously affects the performance and reliability of the system. In order to improve the performance of large-scale ultrasonic vibration system, a two-dimensional hole/slot near-periodic phononic crystal structure is used to suppress the transverse vibration, but the structure will in turn affect the mechanical strength of the transducer while achieving the suppression of the transverse vibration. The working bandwidth and other performance parameters have adverse effects. Based on this, a new idea of optimizing the large-scale sandwich longitudinal vibration piezoelectric ceramic transducer by using the tubular near-periodic phononic crystal point defect structure is proposed. This method can not only use the point defect mode of the constructed solid/gas two-dimensional near-periodic phononic crystal structure to obtain extremely low energy loss, but also effectively improve the longitudinal displacement amplitude and amplitude distribution uniformity of the radiation surface of the system. The double annular holes in the pipe string structure can also be used to enhance the multiple scattering of sound waves, so that the transducer can also produce a band gap under the low conditions of the pipe string, effectively suppressing the transverse vibration, at the same time, significantly broadening the working bandwidth of the transducer system, enhancing the stability and mechanical strength of the system, and reducing the processing cost. Simulation results and experimental processing test results also prove the effectiveness of the optimization.&lt;/sec&gt;&lt;sec&gt;In order to find the best parameters for the performance of the large-scale longitudinal vibration piezoelectric ultrasonic transducer, in the paper the finite element analysis software is used to study the influence of the inner radius &lt;i&gt;r&lt;/i&gt;&lt;sub&gt;1&lt;/sub&gt; of the pipe string, the width &lt;i&gt;r&lt;/i&gt; of the pipe string ring, the radius &lt;i&gt;R&lt;/i&gt; of the outermost air cylinder hole, and the height &lt;i&gt;h&lt;/i&gt;&lt;sub&gt;2&lt;/sub&gt; of the pipe string at the longitudinal resonance frequency of the transducer performance, the longitudinal displacement amplitude distribution uniformity of the radiation surface, and the average longitudinal displacement amplitude. In the research is finally found the range of parameters that can make the performance of the transducer reach a relatively ideal state. The simulation results show that the tubular near-periodic phononic crystal point defect structure can improve the performance of large-scale longitudinal vibration piezoelectric ultrasonic transducer.&lt;/sec&gt;

A self-powered wearable seizure-monitoring/brain-stimulating system for potential epilepsy treatment

A new self-powered wearable body-detecting/brain-stimulating system for monitoring and restraining epilepsy has been fabricated. The system can monitor body motion in real time and transmit the stimulus signals to brain for restraining the epileptic seizures. The system is composed of energy harvesting module, the body motion detection sensor, the data processing center, and neural stimulator. An arch-shaped device made of piezoelectric ceramic transducer (lead zirconate titanate; PZT) as energy harvesting module can convert the mechanical energy generated by body movement into electricity power. The motion detection sensor is made of polyvinylidene fluoride (PVDF) doped with zinc oxide (ZnO) nanostructures, which can detect the tiny movements of the human body and transmit sensing signals to the data processing center. The data processing center can determine the epileptic seizure and generate neural stimulating signals. By stimulating the dentate gyrus/hilus brain region of mice, the total duration of epileptic seizures in mice is significantly reduced by 40–50%. This new self-powered strategy demonstrates the potential of brain-machine-interface system for personalized treatment of brain disease.

Study of wavelength-switchable watt-level blue external cavity diode laser for NO2 S-DIAL

A 2.3 W wavelength-switchable blue external cavity diode laser (ECDL) was studied. The laser was built on Littrow configuration and a piezoelectric ceramic transducer (PZT) driver was employed to change the Littrow angle for wavelength tuning. Its emitting wavelength can be switched between 447.46 nm and 448.10 nm which are the required wavelengths for NO2 differential absorption lidar application. The measured spectral linewidth of the proposed ECDL was 0.08 nm. The main peak was at least 35 dB stronger than its adjacent freely running emission peak and background amplified spontaneous emission (ASE). The wavelength switching dynamics were inspected and shows good repeatability at frequencies of 16.7 Hz and 50 Hz.

Optimization of a sandwich longitudinal vibration transducer with a large radiation surface based on hole structure of near-periodic phononic crystal

<p indent="0mm">The existence of radial vibration in a large-dimension sandwich longitudinal vibration piezoelectric ceramic transducer will reduce the longitudinal radiated sound power and shorten the service life of the transducer, which seriously affects its performance and reliability. To reduce the strong coupling between longitudinal and radial vibration, ensure high longitudinal working efficiency and reliability, and overcome the disadvantages of narrow working bandwidth, poor uniformity of amplitude distribution, and small displacement amplitude, the large-dimension sandwich longitudinal vibration piezoelectric ceramic transducer is optimized through machining several periodic holes on the front cover plate of the transducer to form a multi-point deformation defect structure. In this study, the simulation software is used to simulate and analyze the performance index of the optimized transducer, and the optimization effect is verified through experiments. The results show that the large-dimension piezoelectric ceramic transducer based on a multi-point deformation defect near-periodic phononic crystal structure has a single longitudinal vibration mode, which can effectively improve the displacement amplitude and amplitude distribution uniformity of the radiation surface of a large-dimension transducer and broaden the transducer’s working bandwidth.