Piezoelectric Disk Research Articles

3D-Printable Piezoelectric Composite Sensors for Acoustically Adapted Guided Ultrasonic Wave Detection.

Commercially available photopolymer resins can be combined with lead zirconate titanate (PZT) micrometer size piezoelectric particles to form 3D-printable suspensions that solidify under UV light. This in turn makes it possible to realize various non-standard sensor geometries which might bring benefits, such as increased piezoelectric output in specific conditions and less interference with incoming waves due to better acoustical adaptation compared to solid PZT ceramics. However, it is unclear whether piezoelectric composite materials are suitable for guided ultrasonic wave (GUW) detection, which is crucial for structural health monitoring (SHM) in different applications. In this study, thin piezoelectric composite sensors are tape casted, solidified under UV light, covered with electrodes, polarized in a high electric field and adhesively bonded onto an isotropic aluminum waveguide. This approach helps to demonstrate the capabilities of tape casting’s freedom to manufacture geometrically differently shaped, thin piezoelectric composite sensors for GUW detection. In an experimental study, thin two-dimensional piezoelectric composite sensors demonstrate successful detection of GUW for frequency-thickness products of up to 0.5 MHz mm. An analytical calculation of the maximum and minimum amplitudes for the ratio of the wavelength and the sensor length in wave propagation direction shows good agreement with the sensor-recorded signals. The output of the piezoelectric composite sensors and occurring reflections as measure for wave interactions are compared to commercial piezoelectric discs to evaluate their performance.

Surface crack detection by using vibrothermography technique

ABSTRACT This paper aims to optimise the vibration frequency that produces the highest temperature difference between crack location and non-defect location. The optimisation was based on thermoelastic damping analysis, and the analytical frequencies were varied between 10 Hz and 100 kHz. The result of optimisation was frequency 20 kHz for this study. In experiments, the effects of vibration frequency and vibration amplitude were studied. The experimental frequencies were 4.7, 20, 24 and 28 kHz. The piezoelectric disc was used as a sensor to measure the vibration amplitude on crack location. Then, the measured amplitudes were read in terms of the output voltage from the piezoelectric disc as 2, 4, 6 and 10 Vrms. The maximum difference in temperature between crack and non-defect locations was 0.33°C, which was obtained from vibration frequency of 20 kHz. Using high vibration amplitude did not significantly increase the temperature difference between crack and non-defect locations.

Analysis of Force Sensing Accuracy by Using SHM Methods on Conventionally Manufactured and Additively Manufactured Small Polymer Parts.

Fabricating complex parts using additive manufacturing is becoming more popular in diverse engineering sectors. Structural Health Monitoring (SHM) methods can be implemented to reduce inspection costs and ensure structural integrity and safety in these parts. In this study, the Surface Response to Excitation (SuRE) method was used to investigate the wave propagation characteristics and load sensing capability in conventionally and additively manufactured ABS parts. For the first set of the test specimens, one conventionally manufactured and three additively manufactured rectangular bar-shaped specimens were prepared. Moreover, four additional parts were also additively manufactured with 30% and 60% infill ratios and 1 mm and 2 mm top surface thicknesses. The external geometry of all parts was the same. Ultrasonic surface waves were generated using three different signals via a piezoelectric actuator bonded to one end of the part. At the other end of each part, a piezoelectric disk was bonded to monitor the response to excitation. It was found that hollow sections inside the 3D printed part slowed down the wave travel. The Continuous Wavelet Transform (CWT) and Short-Time Fourier Transform (STFT) were implemented for converting the recorded sensory data into time–frequency images. These image datasets were fed into a convolutional neural network for the estimation of the compressive loading when the load was applied at the center of specimens at five different levels (0 N, 50 N, 100 N, 150 N, and 200 N). The results showed that the classification accuracy was improved when the CWT scalograms were used.

Design of RF MEMS Piezoelectric Disk Resonator for 5G Communication

With the growing impact of 5G communication system, Radio-Frequency Micro-Electro-Mechanical-Systems (RF MEMS) technologies are becoming increasingly important in our daily lives. Resonators have wide applications in filters for generation or selection of specific frequency signals. Bulk mode resonators have a larger rigidity than flexural mode resonators of the same size, resulting in higher frequencies that are ideal for 5G communication. Owing to this reason, bulk mode resonators are utilized for generation of frequency ranges greater than 2 GHz. As compared to electrostatic actuation, piezoelectric actuation techniques have a substantially lower motional resistance, lower operating voltages, and greater power handling capabilities. Thus, in this work, a 5 GHz piezoelectric micro-disk resonator has been designed and simulated using MEMS CAD tool. The quality factor, admittance, and scattering parameters of a radial-contour mode disk resonator are designed and tested. Along with this study, a comparative evaluation of three different piezoelectric materials based on the quality factor of the dominant resonant mode has been carried out. All three resonators are simulated for resonant frequency f0 = 5 GHz, and various analysis have been carried out. It was proposed that Lithium Niobate is preferred amongst the three piezoelectric materials for higher selectivity applications. The quality factors reported for the materials ZnO, AlN, and LiNbO3 are 1720, 1740 and 1850, respectively. Thus, this study indicates that RF piezoelectric disk resonators can achieve higher frequencies, at the cost of complicated fabrication process.

Piezoelectric shear rheometry: Further developments in experimental implementation and data extraction

The piezoelectric shear gauge (PSG) [Christensen and Olsen, Rev. Sci. Instrum. 66, 5019 (1995)] is a rheometric technique developed to measure the complex shear modulus of viscous liquids near their glass transition temperature. We report recent advances to the PSG technique: (1) The data extraction procedure is optimized, which extends the upper limit of the frequency range of the method to between 50 and 70 kHz. (2) The measuring cell is simplified to use only one piezoelectric ceramic disk instead of three. We present an implementation of this design intended for liquid samples. Data obtained with this design revealed that a soft extra spacer is necessary to allow for thermal contraction of the sample in the axial direction. Model calculations show that flow in the radial direction is hindered by the confined geometry of the cell when the liquid becomes viscous upon cooling. The method is especially well-suited for—but not limited to—glassy materials.

Remote wireless monitoring of localized corrosion using compact solitary waves

This article presents a method to monitor corrosion remotely, based on highly nonlinear solitary waves, which are compact and nondispersive. In the study presented in this article, two types of solitary wave transducers were used to monitor accelerated localized corrosion on a steel plate. The first type consists of a chain of spherical particles surmounted by a commercial solenoid wired to, and controlled by, a data acquisition system used to lift and release the first particle of the chain and induce the mechanical impacts and stress waves in the chain. The chain included a piezoelectric wafer disk, also wired to the same data acquisition system, to sense, digitize, and store the propagating waves for post-processing. The second type of transducer was identical to the first one but the data acquisition system was replaced by a wireless node that communicated with a mobile device using a Bluetooth connection. Eight transducers were used to monitor the plate for over a week to detect the onset and progression of localized corrosion. Corrosion detection was performed by extracting a few features from the time waveforms and feeding these features to an outlier analysis algorithm based on the Mahalanobis distance. The results of the experiment showed the effectiveness of the proposed monitoring approach at detecting defects close to the transducers and confirm previous numerical predictions by the authors. The experiments also provided evidence that the performance of the wireless transducers is nearly identical to the performance of their wired counterparts, paving the way to a new paradigm for the structural health monitoring of remote structural components in harsh environments.

An Investigation on Energy Harvesting Behavior of an Array Piezoelectric Coupled Disc Damper.

In order to make full use of the vibration energy in the process of attenuating vibration, an array piezoelectric coupled disc damper is developed, which works by converting part vibration energy into electrical energy. The piezoelectric damper is made of a pair of piezoelectric coupled discs built in a case cylinder. Its energy harvesting behavior is studied by a series of forced-vibration experiments and simulations. The influences of some factors, such as the excitation frequency, substrate thickness, the size of the piezoelectric patch, the paste form of the piezoelectric patch and the load resistance, on the energy harvesting behavior of the damper are analyzed and concluded. The experimental results show that the maximum peak-to-peak voltage and average power from one piezoelectric patch with an inner diameter of 35 mm, an outer diameter of 80 mm, and a thickness of 1 mm can reach up to 163 V and 161 mW, respectively. This research provides a practical piezoelectric damper attenuating harmful vibration by converting them into useful electric power, and the corresponding theoretical models are derived to predict its electrical output.

Design and Dynamics of Oil Filled Flexural Ultrasonic Transducers for Elevated Pressures

The flexural ultrasonic transducer has traditionally been limited to proximity measurement applications, such as car-parking systems and industrial metrology. Principally, their classical form is unsuitable for environments above atmospheric 1 bar pressure, due to an internal air cavity which creates a pressure imbalance across the transducer’s vibrating membrane. This imbalance leads to physical deformation and degradation of the transducer’s structure, restricting the membrane’s capacity to vibrate at resonance to transmit and receive ultrasound. There is a requirement for ultrasonic sensors which can withstand environments of elevated pressure, for example in ultrasonic gas metering. Recent research demonstrated the dynamic performance of flexural ultrasonic transducers with vented structures, allowing the pressure to balance across the transducer membrane. However, a hermetically sealed transducer is a more practical and robust solution, where the internal components of the transducer, such as the piezoelectric ceramic disc, will be protected from harmful environmental fluids. In this research, the design and fabrication of a new form of flexural ultrasonic transducer for environments of elevated pressure is demonstrated, where the internal air cavity is filled with an incompressible fluid in the form of a non-volatile oil. Dynamic performance is measured through acoustic microphone measurements, electrical impedance analysis, and pulse-echo ultrasound measurement. Together with finite element analysis, stable ultrasound measurement is achieved above 200 bar in air, opening the possibility for reliable ultrasound measurement in hostile environments of elevated pressure.

Finite Element Modeling and Test of Piezo Disk with Local Ring Electrodes for Micro Displacement.

A new piezoelectric actuator combining interdigitated ring electrodes and a PZT-52(Lead Zirconate Titanate) disk was investigated for the large displacement requirements of piezoelectric actuators. Finite element models were established according to the structural characteristics of the actuator and static analysis was carried out based on ANSYS software. Then Ø25 mm × 2 mm samples were prepared. The displacement detection system was established, and the influence of electrode structure on radial displacement was studied experimentally. A comparison between the experimental results and the finite element analysis confirmed that the finite element model was correct. The results showed that the effect of electrode width on displacement was small. With decrease in electrode center distance and increase in the number of electrodes pairs, the radial displacement increased correspondingly. The peak of radial displacement was 1.63 μm under a 200 V voltage excitation voltage of 0.2 Hz. This was 2.5 times that for a conventional electrode piezo disk with the same structure. The actuator demonstrated better displacement properties. The piezoelectric disk could be valuable in applications involving micro-nano devices.

Energy harvesting of Rayleigh surface waves by a phononic crystal Luneburg lens

In this paper, a phononic crystal (PnC) Luneburg lens is designed for harvesting the mechanical energy of Rayleigh surface waves. The square-latticed PnC is formed by drilling holes periodically in an aluminum matrix. The PnC Luneburg lens for Rayleigh surface waves is constructed by spatially modulating the hole radius of each PnC unit-cell according to the refractive index profile of a conventional Luneburg lens. To convert mechanical energy into electricity, a piezoelectric disk is attached at the focal point of the PnC Luneburg lens, where the Rayleigh surface waves are focused. Compared with the reference harvester on a homogeneous aluminum matrix, the electric power outputs are significantly enhanced by the PnC Luneburg lens harvester for two typical directions, namely the ΓX and ΓM directions. For either the ΓX or ΓM direction, the amplification ratio of the PnC Luneburg lens harvester is over 14.

Non-Hermitian planar elastic metasurface for unidirectional focusing of flexural waves

Metasurfaces exhibiting spatially asymmetric inner structures have been shown to host unidirectional scattering effects, benefiting areas where directional control of waves is desired. In this work, we propose a non-Hermitian planar elastic metasurface to achieve unidirectional focusing of flexural waves. The unit cells are constructed by piezoelectric disks and metallic blocks that are asymmetrically loaded. A tunable material loss is then introduced by negative capacitance shunting. By suitably engineering the induced loss profile, a series of unit cells are designed, which can individually access the exceptional points manifested by unidirectional zero reflection. We then construct a planar metasurface by tuning the reflected phase to ensure constructive interference at one side of the metasurface. Unidirectional focusing of the incident waves is demonstrated, where the reflected wave energy is focused from one direction, and zero reflection is observed in the other direction. The proposed metasurface enriches the flexibility in asymmetric elastic wave manipulation as the loss and the reflected phase can be tailored independently in each unit cell.

Topological imbalanced phononic crystal with semi-enclosed defect for high-performance acoustic energy confinement and harvesting

Phononic crystals (PnCs) attract attentions in acoustic energy conversion and harvesting due to their excellent properties in regulating elastic and acoustic waves. Topological imbalance and semi-enclosed defect has been proposed in this work to systematically broaden the band gap of PnCs and improve the localization of elastic wave in defect. Parametric equations are introduced to generate nine square lattice unit cells with four-fold rotationally symmetric shapes. The imbalance between the long and short branches is utilized to describe the topological evolution of the perfect PnCs. With the increase of topological imbalance, the jump of the Bloch mode appears and thus leads to the band gap opening and expansion. The defect supercell with the highest topological imbalance has the best energy confinement effect. The 2D and 3D transient numerical simulations for the PnC of the highest topological imbalance indicate that the energy confinement effect of the semi-enclosed line defect is more intensive than the semi-enclosed arrow or bottle defect, which is confirmed by piezoelectric energy harvesting experiments. Under the excitation of 50 kHz, the period-2 nonlinear phenomena of the output voltage by piezoelectric disk are experimentally noticed in the PnC with the semi-enclosed line defect. The peak-to-peak power is 3.08 mW at the optimal resistance. Compared with the traditional point defect case, the voltage of the semi-enclosed line defect case is increased by 12.0 times and its power is increased by 75.1 times due to combination of perfect mirror effect and nonlinear defect state mechanism. This study provides a new avenue in design of high-frequency nonlinear acoustic devices and self-powered acoustic sensors.

Multi-method modeling to predict the onset conditions and resonance of the piezo coupled thermoacoustic engine.

This article seeks to perform a combination of methodologies to fully model and evaluate the rudimentary performance of a thermoacoustic engine integrated with a piezoelectric energy harvester (TAP). First, the root locus method was employed to determine the critical design operating values of the thermoacoustic engine. Later, a lumped parameter model was developed as a matlab Simulink program to calculate the transient temperature and pressure responses of the thermoacoustic engine. In addition, a two-element reduced model (executed on matlab) and finite element analysis tools were used to simulate and assess the performance of aluminum-piezo (lead zirconate titanate (PZT-5H) and lead manganese niobate-lead titanate (PMN-PT)) disks that are to be integrated with the thermoacoustic engine. Last but most importantly, the piezo-diaphragm and thermoacoustic engine were coupled using the electrical analogy technique through which the onset conditions and resonance frequency of the integrated TAP system were determined. We take a traveling wave thermoacoustic engine and a commercially available piezoelectric disk as a test case for the analysis. It is concluded that the outcomes from the multiple methods are in good agreement with the experimental results.

Fabrication and flow rate characterization of a DRIE process based valveless piezoelectric micropump

Micropumps have become one of the major research topics in the field of microfluidics. Different actuators have been used in active micropumps including piezoelectric ones, which convert electrical energy to mechanical energy. In this study, a piezoelectric disc was designed as an actuator and was integrated into a fabricated piezoelectric micropump. Unlike wet etching methods, which is generally used to etch layers of relatively high thickness in the silicon wafer, dry etching was used in this study. Aluminum was used as a mask material during the fabrications-steps, and the fabrication process was shortened with the use of the masking steps. The etching process of the slot, in which the piezoelectric disc was placed, and etching of the inlet/outlet channels were performed simultaneously. Thus, the processing time was significantly shortened. The fabrication of this silicon-based valveless micropump was accomplished by using the DRIE (deep reaction-ion etching) technique, which provided controlled etching. Experiments were conducted on the fabricated micropump with the use of the bulk micromachining technology to deliver the desired pumping action. The leakage and the air entrapment between the consecutive micropump structural layers were satisfactorily eliminated. This micropump is capable of delivering a promising flow rate of 52 (µl min−1) for deionized water, which corresponds to a 150 [Hz] square wave type and a peak-to-peak voltage of 60 (V) Vp -p . No moving mechanical valves were included so that the risks of clogging, reduced performance, and reduced reliability due to wear and fatigue were minimized. Not only gases and liquids but also fluids containing particles could be used as the working fluid for this micropump. The piezoelectric micropump design was optimized to achieve a high time-averaged flow rate (>50 (µl min−1)) with a relatively low excitation voltage (<100 (V) Vp -p ) as opposed to the use of a high excitation voltage.

Noncontact measurement of sub-micrometer ultrasonic vibration by near-field microwave

In this article, we proposed a noncontact testing scheme for micrometer to sub-micrometer level ultrasonic vibration mainly generated by laser ultrasound upon the novel utilization of near-field microwaves. The measurement was performed based on a Ku-band near-field resonator-probe, which was optimized to perceive the low amplitude out-of-plane vibration in the ultrasonic range. A near-field electromagnetic measurement theory was established to help analyze the sensitivity and responsivity of the resonator-probe outfit. The electric field parameters were extracted with respect to the port based on a lumped-circuit model, which was further validated using a finite-element model. Experiments were carried out with respect to a piezoelectric ceramic disk designed to generate vibrations of desired amplitude, which is compatible to that in laser ultrasonic testing. The accuracy of the technique was assessed by comparing with the laser vibrometer measurement results. It was verified that the proposed near-field microwave probe can achieve considerable accuracy in perceiving sub-micrometer ultrasonic vibration up to 180 kHz.

Modeling, Simulation and Analysis of Intermediate Fixed Piezoelectric Energy Harvester

To address the problem that piezoelectric energy harvesters are difficult to apply in certain environments, this paper establishes the theoretical study of the intermediate fixed disc piezoelectric energy harvester (IFDPEH) based on the unimorph under concentrated force. The reliability of the model was indirectly verified by numerical simulation and Computer-Aided Engineering (CAE) simulation. The effects of load, radius ratio (piezoelectric layer/intermediate support), thickness ratio (piezoelectric layer/total thickness), and elastic modulus ratio (substrate/piezoelectric layer) on electrical energy were studied. The results indicate that the radius/thickness ratios of the IFDPEH based on aluminum and beryllium bronze are 0.05/0.31 and 0.05/0.48, respectively. In addition, through parameter comparison, it is found that the most important parameters affecting IFDPEH power are radius ratio and large load. The results are demonstrated to be meaningful for broadening the application of piezoelectric energy harvesters by the derived closed-form equations for the electrical energy along the diameters of the piezoelectric discs in the z-direction.

Design and experimental study of a piezoelectric energy harvester embedded in a rotating spindle excited by magnetic force

A piezoelectric energy harvester based on rotational motion is a promising technique to generate unlimited electrical energy. However, the necessity for an effective harvester that can be mounted on a rotating system has become an important issue as a support for self-powered wireless sensor systems. The purpose of this study is to develop a novel magnetically impelled piezoelectric rotating energy harvester integrated into a rotating spindle, which is excited by multiple magnetic pairs between symmetrically opposed stationary and spinning magnets on the surface of piezoelectric discs. The theoretical examination of the magnetic excitation on a harvester system is provided to determine magnetic the force and torque, while the voltage and power generation capability of a magnetically impelled piezoelectric rotational energy harvester under various series and parallel configurations, and spindle speed excitations were examined experimentally. The experimental results are in line with the analytical model of magnetic force, which showed that the resistance torque can be decreased significantly. A maximum instantaneous output voltage of -15–19 V and 7.5–8 V was achieved at series and parallel connection respectively. The maximum power can be obtained at parallel connection and the RMS and peak power are 870 µW and 3500 µW, respectively and a high power density of 9.67 µW/mm3. The harvester can also charge the capacitors with voltage and power saturation of 6 V and 327 µW respectively. These results showed that the suggested harvester has high durability and the potential to power wireless sensors that are integrated into spindle machines.

Detection and Classification of Corrosion-related Damage Using Solitary Waves

ABSTRACT This paper presents an inspection technique based on highly nonlinear solitary waves, wireless transducers, and machine learning. The technique was demonstrated on a plate subjected to accelerated corrosion while monitored with wired and wireless transducers, designed and assembled in laboratory. The tethered device consisted of a chain of spheres surmounted by a solenoid wired to and driven by a data acquisition system to control the first particle of the chain in order to induce the impact between the particle and the chain needed to generate the stress wave. The chain contained a piezoelectric wafer disk, also wired to the same data acquisition system, to sense the waves. The wireless transducers were identical to their wired counterparts, but the data acquisition system was replaced by a wireless node that communicated with a tablet via Bluetooth. Four wired and four wireless transducers were used to monitor the plate for nearly a week to detect the onset and progression of electrochemical corrosion. A few features were extracted from the time waveforms and then fed to a machine learning algorithm to classify damage. The results showed the effectiveness of the proposed approach at labeling defects close to the transducers.

Sparse binary metasurfaces for steering the flexural waves

As an analogue of the binary acoustic metasurfaces (BAMs), the sparse binary elastic metasurfaces (SBEMs) which consist of two different coding units with sparse arrangement is designed. A systematic design method based on topology optimization (TO) is developed to search the coding units. With the remarkable ability in regulating flexural waves, splitting and focusing of the flexural waves are achieved by using SBEMs. Furthermore, a piezoelectric disc is attached to the focus spot as a simple energy harvester. The output voltages are measured and the performance of the SBEM energy harvester is evaluated. Compared to a bare plate, the average power output on the SBEM is amplified significantly. The numerical simulation and experimental measurement are in good agreements. The good results prove the effectiveness of the SBEMs, and the design strategy provides a new routine for tailoring flexural waves.

Dependence of Piezoelectric Discs Electrical Impedance on Mechanical Loading Condition

The piezoelectric effect, along with its associated materials, fascinated researchers in all areas of basic sciences and engineering due to its interesting properties and promising potentials. Sensing, actuation, and energy harvesting are major implementations of piezoelectric structures in structural health monitoring, wearable devices, and self-powered systems, to name only a few. The electrical or mechanical impedance of its structure plays an important role in deriving its equivalent model, which in turn helps to predict its behavior for any system-level application, such as with respect to the rectifiers containing diodes and switches, which represent a nonlinear electrical load. In this paper, we study the electrical impedance response of different sizes of commercial piezoelectric discs for a wide range of frequencies (without and with mechanical load for 0.1–1000 with resolution 20 ). It shows significant changes in the position of resonant frequency and amplitude of resonant peaks for different diameters of discs and under varying mechanical load conditions, implying variations in the mechanical boundary conditions on the structure. The highlight of our work is the proposed electrical equivalent circuit model for varying mechanically loaded conditions with the help of impedance technique. Our approach is simple and reliable, such that it is suitable for any structure whose accurate material properties and dimensions are unknown.