PZT Array Research Articles

Design of a bulk-lead zirconate titanate ultrasonic transducer array addressing specific excitation modes

Conventional ultrasonic transducer arrays generally use simultaneous or delayed excitation methods to generate various types of wave fronts in ultrasonic testing. Such array excitation modes are relatively simple and unable to maximize the functions of the array elements or element apertures. Accordingly, this study developed a novel excitation ultrasonic transducer array with flexible excitation aperture. A minimum row-column-addressing planar array structure for ultrasonic transducers based on bulk lead zirconate titanate (PZT) was designed for industrial ultrasonic testing. In addition, a transducer structure design scheme and truth table for array addressing with excitation logic were provided. By performing an acoustic field simulation, this study analyzed the relationship between the longitudinal amplitude and resonant frequency of the array elements and the impedance distribution. The transducer was fabricated and packaged using a circuit board and bulk PZT array elements. Testing revealed that the resonant frequency of the array was 1.07 MHz, the effective electromechanical coupling coefficient was 0.40, and the fractional bandwidth of the pulse echo response and spectrum was 38.46%. Using an aluminum block, performance in single-element, row-, column-, and full-array excitation was tested, and echo curves were obtained for multiple apertures. Using a single-circuit module, the transducer realized flexible gating and excitation of the array elements. The research provided a new method for industrial ultrasonic transducer array design.

Impedance-based Identification of Strand Looseness in Multi-strand Anchorage under Temperature Effects

In this study, strand looseness in a multi-strand anchorage is identified using measured impedance features of the PZT (Lead zirconate titanate) interface array under temperature effects. Firstly, a PZT-interface method for impedance monitoring in prestressed structures is briefly described. Secondly, a finite element model of multi-strand anchorage equipped with a PZT array is established to analyze the effects of prestress loss and temperature changes in impedance features. Thirdly, variations in simulated impedance signals are quantified using statistical damage metrics for damage detection in the analyzed structure. Last, a test on real-scale multi-strand anchorage is conducted to measure impedance signatures of the PZT interface under temperature fluctuation and prestress loss. The measured signals are then quantified using damage metrics for prestress looseness monitoring. The result reveals that environmental changes cause significant changes in PZT interfaces’ impedance features and affect strand looseness monitoring results.

Contrast-enhanced ultrasound imaging using capacitive micromachined ultrasonic transducers

Capacitive micromachined ultrasonic transducers (CMUTs) have a nonlinear relationship between the applied voltage and the emitted signal, which is detrimental to conventional contrast enhanced ultrasound (CEUS) techniques. Instead, a three-pulse amplitude modulation (AM) sequence has been proposed, which is not adversely affected by the nonlinearly emitted harmonics. In this paper, this is shown theoretically, and the performance of the sequence is verified using a 4.8 MHz linear capacitive micromachined ultrasonic transducer (CMUT) array, and a comparable lead zirconate titanate (PZT) array, across 6-60 V applied alternating current (AC) voltage. CEUS images of the contrast agent SonoVue flowing through a 3D printed hydrogel phantom showed an average enhancement in contrast-to-tissue ratio (CTR) between B-mode and CEUS images of 49.9 and 37.4 dB for the PZT array and CMUT, respectively. Furthermore, hydrophone recordings of the emitted signals showed that the nonlinear emissions from the CMUT did not significantly degrade the cancellation in the compounded AM signal, leaving an average of 2% of the emitted power between 26 and 60 V of AC. Thus, it is demonstrated that CMUTs are capable of CEUS imaging independent of the applied excitation voltage when using a three-pulse AM sequence.

Surface Crack Monitoring by Rayleigh Waves with a Piezoelectric-Polymer-Film Ultrasonic Transducer Array.

This paper presents a method for measuring surface cracks based on the analysis of Rayleigh waves in the frequency domain. The Rayleigh waves were detected by a Rayleigh wave receiver array made of a piezoelectric polyvinylidene fluoride (PVDF) film and enhanced by a delay-and-sum algorithm. This method employs the determined reflection factors of Rayleigh waves scattered at a surface fatigue crack to calculate the crack depth. In the frequency domain, the inverse scattering problem is solved by comparing the reflection factor of the Rayleigh waves between the measured and the theoretical curves. The experimental measurement results quantitatively matched the simulated surface crack depths. The advantages of using the low-profile Rayleigh wave receiver array made of a PVDF film for detecting the incident and reflected Rayleigh waves were analyzed in contrast with those of a Rayleigh wave receiver using a laser vibrometer and a conventional lead zirconate titanate (PZT) array. It was found that the Rayleigh waves propagating across the Rayleigh wave receiver array made of the PVDF film had a lower attenuation rate of 0.15 dB/mm compared to that of 0.30 dB/mm of the PZT array. Multiple Rayleigh wave receiver arrays made of the PVDF film were applied for monitoring surface fatigue crack initiation and propagation at welded joints under cyclic mechanical loading. Cracks with a depth range of 0.36-0.94 mm were successfully monitored.

A Methodology for Reconstructing Source Properties of a Conical Piezoelectric Actuator Using Array-Based Methods

We investigated the force produced by a conical piezoelectric (PZT, lead zirconate titanate) transducer actuated by high voltage pulses (HVP) in contact with a steel transfer plate. Using elastic wave propagation theory in a semi-infinite plate, we aimed to quantify the magnitude and estimate the shape of the force–time function via the body waves produced in the transfer plate using the displacement field recorded on an array of 20 absolutely calibrated PZT receivers. We first calibrated the receiver array using glass capillary fracture. We proceeded to use a conical PZT transducer to actively produce a source at the origin, allowing us to study the displacement field produced on the now calibrated PZT receiver array. We studied two types of HVP: An impulsive and step source. The calibrated receiver array was used to estimate the general shape of the force–time functions for each type of HVP. From our hypothesized force–time functions we were able to estimate the peak force produced by the PZT actuator: The impulsive source generated a force of f_{peak} = 2.90 pm 0.42 N and the step source generated f_{peak} = 1.79 pm 0.30 N, respectively, for a peak applied voltage of 273 V. This translates to an applied force of sim 0.011 N/V and 0.007 N/V for the impulse and step force–time functions, respectively, which is similar to estimates found in the literature for other conical transducers in contact with metallic transfer media. This measurement was verified directly by independent measurements of the peak force f_{peak} using a dynamic force transducer. We found that our methodology correctly estimated the magnitude of the force but is limited to transducers with incident angles theta< 53^{circ }. Beyond this angle, overestimates of the force were observed due to the lack of body wave energy produced by the source. These results allow us to quantitatively determine the forces produced by active PZT techniques using only the measurement of the displacement field captured on a calibrated conical PZT array. Quantitative understanding of active PZT sources additionally constrains the transfer functions approach, which is commonly used in the non-destructive testing of materials and in other fields, such as rock physics and laboratory seismology.

Dispersive MUSIC algorithm for Lamb wave phased array

By controlling the excitation time delay on each element, the conventional phased array can physically focus signals transmitted by different elements on a desired point in turn. An alternative and time-saving strategy is that every element takes turns to transmit the excitation and the remaining elements receive the corresponding response signals, which is known as the full matrix capture (FMC) method for data acquisition, and then let the signals virtually focus on every desired point by post-processing technique. In this study, based on the FMC, a dispersive multiple signal classification (MUSIC) algorithm for Lamb wave phased array is developed to locate defects. The virtual time reversal is implemented to back propagate the wave packets corresponding to the desired focusing point and a window function is adopted to adaptively isolate the desired packets from the other components. Then those wave packets are forward propagated to the original focusing point at a constant velocity. For every potential focusing point and all receivers, the virtual array focuses the signals from all transmitters so as to obtain the focusing signals. The MUSIC algorithm with the obtained focusing signals is adopted to achieve Lamb wave imaging. Benefiting from the post-processing operations, the baseline subtraction as well as the estimation for the number of the scattering sources is no longer required in the proposed algorithm. Experiments on an aluminum plate with three artificial defects and a compact circular PZT array are implemented and the results demonstrate the efficacy of the proposed algorithm.

A focusing MUSIC algorithm for baseline-free Lamb wave damage localization

The dispersion effect of Lamb waves can cause different degree of phase distortion of array signals, which will make the classical multiple signal classification (MUSIC) algorithm no longer valid in Lamb wave based damage localization. At the same time, baseline subtraction and estimation of the number of scattering sources are required in the classical MUSIC algorithm, which limits its application. A focusing MUSIC algorithm is proposed for baseline-free Lamb wave damage localization on isotropic materials. Based on the virtual time reversal technique, the dispersive wave packets adaptively back propagate according to their respective propagation distances so that the dispersion can be completely compensated and focusing signals are obtained. Wave packet truncation is implemented on the focusing signals and then let the truncated signals forward propagate with the group velocity at center frequency. The two operations, back propagation and forward propagation, can compensate the dispersion effect and avoid estimating of the number of scattering sources as well as baseline subtraction. Experiments are conducted on an aluminum plate to investigate the performance of the proposed algorithm. A uniform linear PZT array is glued on the aluminum plate to transmit and receive Lamb waves. Experimental results of the proposed algorithm as well as the classical MUSIC algorithm are given and compared. The comparison verifies the effectiveness of the proposed focusing MUSIC algorithm.

Experimental Validation of the Piezoelectric Energy Harvester for Wearable Devices

This paper presents the experimental validation of the piezoelectric array in harvesting the vibration energy from human activity. This experiment is aimed to choose the best array topology of piezoelectric energy harvesting (PEH) for replacing the battery on our wearable devices. Based on our experiments, the no-load characteristic of PZT array shows the big hope for future implementation on wearable devices.

Impact Localization of Thin Plate Structures Using Pzt-Array Based Passive Wave Method

Impact of foreign objects is one of the main reasons for the damage of thin plate structures, resulting in property losses or unexpected accidents. Therefore, a rapid and effective impact localization of thin plate structures is of great value. In this paper, a localization method is proposed based on the passive wave method, aiming at locating the impact quickly and accurately. First, a square PZT array composed of 4 PZT sensors was designed, and a hyperbolic localization algorithm was derived according to time-different of arrival (TDoA) for different sensors in the array. Then, Matlab calculation software was used to perform DB wavelet decomposition on impact signals, the time delay was calculated by Lamb wave of A0 mode in D5 detail signals, and the velocity of A0 mode wave was determined by the dispersion curve for 1 mm thick aluminum plate. Finally, the impact point was located to experimentally verify the effectiveness of the proposed localization method. Experimental results show that the hyperbolic positioning algorithm based on TDoA can accurately identify impact locations, and wavelet decomposition can effectively identify single mode Lamb waves. The proposed method has the characteristics of fastness and accuracy, which is suitable for single object impact localization on thin plate structures.

Design and comparison of PMN-PT single crystals and PZT ceramics based medical phased array ultrasonic transducer

The design, fabrication and comparison of PMN-PT single crystals and PZT ceramics based 3 MHz phased array ultrasonic transducers were investigated. The resonance mode and electromechanical properties for PMN-PT single crystal were simulated by using the COMSOL Multiphysics software. Simulation results indicate that the electromechanical coupling coefficient k33' keeps at 0.86–0.87 when the aspect ratio G < 0.7, as well as a pure height-extensional mode was obtained. Two types of ultrasonic phased arrays using PMN-PT single crystal and PZT ceramic were fabricated and compared. The experimental results revealed that more than 27.7% broader -6 dB bandwidth, 5.2 dB higher relative sensitivity, and shorter pulse length can be obtained by using PMN-PT single crystal compared to the PZT array. The experimental results agreed well with the predictions of simulation by using the PiezoCAD software. Furthermore, PMN-PT array has the same good consistency of the performance as the PZT array, while the better acoustic performance and higher electromechanical properties compared to PZT array as a whole. In the end, the ultrasonic imaging which uses the PMN-PT based array transducer has the better definition, the higher axial resolution and lateral resolution compared to those of PZT based array transducer.

Powder injection molding process for fabrication of piezoelectric 2D array ultrasound transducer

Powder injection molding process has been developed for a cost-effective fabrication of micro PZT array in diagnostic 2D array ultrasound transducer. The developed process consists six main steps; mold insert fabrication, mixing of powder and binder, injection molding, demolding of sacrificial mold insert, solvent and thermal debinding, densification of PZT ceramics. 1–3 type PZT/polymer composite fabricated by developed process shows 0.67 of electromechanical coupling property in plain mode and 0.56 in rod array mode which are 99% and 96% of reference property. Based on high productivity and shape complexity of ceramic injection molding, micro-manufacturing process for micro-scale PZT transducer has been demonstrated with according piezoelectric performance characterization.

A scanning spatial-wavenumber filter and PZT 2-D cruciform array based on-line damage imaging method of composite structure

The spatial-wavenumber filtering technique of Lamb wave is gradually applied for damage inspection of composite structure in recent years because it is an effective approach to distinguish the wave propagating direction and mode. But for on-line damage monitoring of composite structure by using spatial-wavenumber filter, the problem is how to realize the spatial-wavenumber filtering of Lamb wave when the wavenumber response cannot be measured or modeled. This paper proposes a scanning spatial-wavenumber filter and piezoelectric sensor (referred to as PZT) 2-D cruciform array based on-line damage imaging method of composite structure. In this method, a 2-D cruciform array constructed by two linear PZT arrays is placed on composite structure permanently to acquire Lamb wave damage scattering signal on-line. For one linear PZT array, a scanning spatial-wavenumber filter which does not rely on any modeled or measured wavenumber response is designed to filter the damage scattering signal at a designed wavenumber bandwidth to give out a wavenumber-time image. Based on the image, the wavenumber of the damage scattering signal projecting at the array can be obtained. The same process can be also applied to the other linear PZT array to get the wavenumber projecting at that array direction. By combining with the two projection wavenumbers, the damage can be localized without blind angle. The method is validated on an aircraft composite oil tank of variable thickness. The validation results show that the damage direction estimation error is less than 2° and the damage distance estimation error is around 20mm in the monitoring area of nearly 600mm×300mm. It indicates an acceptable performance of the damage imaging method for complex composite structure.

Visualization and simulation of a linear explosive-induced pyroshock wave using Q-switched laser and phased array transducers in a space launcher composite structure

During space flights, pyrotechnic devices are used for various purposes such as separation of boosters, satellites, fairings, and stages. In particular, the prediction of high shock structural response induced by linear explosives is important for safe operation of pyrotechnic devices. In general, repetitive explosive testing using distributed accelerometers is widely used, but multiple test structures are usually necessary because they are easily damaged and not reusable. This paper pertains to a nondestructive technology to replace the damage-causing, time-consuming, expensive, dangerous, and low-repeatability explosive test with a laser-induced shock test. The method proposed in this paper predicts nondestructively the linear explosive-induced pyroshock wave, visualizes its propagation, and allows the simulation of some detonation conditions. A ballistic test based on a linear explosive and noncontact laser Doppler vibrometer (LDV) as well as a nondestructive pyroshock test using laser-induced shock and PZT array sensors is performed in a 12.68-mm thick composite sandwich panel. The optimal laser-induced shock experimental conditions to predict real pyroshock response spectra (SRSs) are investigated by controlling the optical characteristics of the laser beam and adjusting the frequency bands in signal acquisition. The similarity of the SRS of the conditioned laser-induced shock to that of the real explosive pyroshock is evaluated with the mean acceleration difference. Next, the experimentally-determined optimal conditions are applied to arbitrary points in the laser-induced shock scanning area. Finally, it is shown that the proposed method will allow nondestructive and quantitative pyroshock testing, pyroshock wave propagation visualization showing the direction and magnitude of principal wave propagation, and detonation speed simulation depending on explosive type and detonation initiation point and direction.

Segmented bimorph mirrors for adaptive optics: segment design and experiment.

We discuss the concept of lightweight segmented bimorph mirrors for adaptive optics. The segment consists of a monocrystal silicon substrate actuated by an array of in-plane piezoceramic (PZT) actuators with honeycomb electrodes. We focus on technological aspects of the segment design that are critical for space applications and describe a single segment demonstrator. The morphing capability of the segment is evaluated experimentally. We also discuss the local deformations (dimples) associated with the shape of the electrodes acting on the PZT array.

Quantitative damage image construction in plate structures using a circular PZT array and lamb waves

A circular PZT ceramic wafer array based on a process of receiver beamforming is developed for damage identification in plate structures, and a method of quantitative damage image construction is presented using Lamb wave signals received from the array. Design parameters of the circular PZT array, including diameter of the PZT array, number of PZT wafers and steering angle, are investigated. Characteristics related to magnitude of the array response, viz. the reflection coefficient and distance between the damage and the array, are also analyzed. It is demonstrated that, because of the unique configuration of the PZT array, the magnitude of the array response is independent of the direction of the damage location relevant to the array. Exact propagation path of wave propagation is adopted, and therefore the damage can be reconstructed even in the near field surrounding the PZT array. To validate the proposed method, a circular PZT array consisting of one PZT actuator and several PZT sensors is used in experiments to identify damage in an aluminum plate. By considering the attenuation of Lamb wave propagation in plate structures, quantitative image construction is implemented for damage of different severities and distances from the array.

Research on Parallel PZT Phased Array Based Structural Health Monitoring in CFPR

Phased array theroy can controll the Lamb wave beem steering in certain range by adding the time delay to the signals. Phased array theory is used to identify the damge in the structure. One dimensional PZT array is restricted in monitoring distance. Two parellel PZT sensors arrays are utilized to monitor the CFPR structure to extend the monitoring distance and to improve the precision of the damage locatilization. The experiment is done on the CFPR structure by using two parellel PZT arrays to detect the damage in the structure. The results of the experiment is shown on the mapped image. Gray-scale in the mapped image from dark to light corresponds to the signal amplitude from low to high. The highlight of the mapped image is the damage location in the structure. The monitoring results in the CFPR structure by two parellel PZT arrays is accurate and identical.

Lamb wave damage detection using time reversal DORT method

Among structural health monitoring methods, Lamb waves are frequently used as a diagnostic tool to detect damage in plate-like structures. The decomposition of the time reversal operator (DORT) method is a selective detection and focusing technique using an array of transmit–receive transducers. Unlike body waves, the propagation of Lamb waves is complicated due to their dispersive and multimode characteristics. So it is hard to locate different scatterers on the plate directly using the DORT method because of the asymmetry of the time reversal transfer matrix. In the present paper a damage detection technique to make the transfer matrix symmetric for the Lamb wave DORT method is proposed. It is found that the number of significant eigenvalues is not exactly equal to the number of damage targets and two significant eigenvalues are associated with one damage target. An experiment is carried out to distinguish and locate two simulated points of damage on an aluminum plate. The behavior of reflected multimode waves is analyzed by studying the eigenvalues and eigenvectors of the time reversal operator matrix. This method, which uses a PZT array and operates under multimode pulse-echo mode, can estimate the position of the damage zone in the 2D image by numerically backpropagating a selective eigenvector using the A0 and/or S0 Lamb wave propagation analytical solution. The experimental results illustrate the proposed method.

Damage Detection of Closed Crack in a Metallic Plate Using Nonlinear Ultrasonic Time Reversal Method

Initial cracks in metallic structures incline to be closed at rest. Such incipient damage generally fails to be detected and located with traditional linear ultrasonic techniques because ultrasonic waves penetrate the contact area of the closed crack. In this paper, an imaging algorithm based on nonlinear ultrasonic time reversal method is proposed to detect closed cracks in aluminum plates. Two surface-bonded piezoelectric transducer arrays are used to generate, receive, and reemit ultrasonic wave signals. The closed crack is simulated by tightening a bolt on the aluminum plate. By applying large amplitude excitation voltage on the PZT transducers, the closed crack could be opened and closed. The transmitted waves recorded by PZT array contain nonlinear components, the signals are time reversed and emitted back, and the tone burst reconstructions are achieved. The linear reciprocity and the time reversibility break down due to the presence of the nonlinear components. The correlation coefficient between the original excitation signal and the reconstructed signal is calculated to define the damage index for individual sensing path and is used to develop an imaging algorithm to locate the closed crack on the plate. The experimental results demonstrate that incident wave signals and their reconstructed signals can be used to accurately detect and locate closed cracks.

Broadband ultrasonic linear array using ternary PIN-PMN-PT single crystal

Ternary Pb(In(1/2)Nb(1/2))O(3)-Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PIN-PMN-PT) single crystal was investigated for potential application in ultrasonic linear array. Orientation and temperature dependences of height extensional electromechanical coupling coefficient k'(33) for PIN-PMN-PT single crystal were studied. It was found that the [001] poled PIN-PMN-PT diced along the [100] direction would achieve a maximum k'(33) (~87%) and the service temperature was up to 110 °C. Ultrasonic linear arrays using PIN-PMN-PT single crystal and PZT ceramic were fabricated and compared. The bandwidth at -6 dB, two-way insertion loss and pulse length of the PIN-PMN-PT array were 98.6%, -45.1 dB, and 0.28 μs, respectively, which were about 25% broader, 3.7dB higher, and 0.08 μs shorter than those of the PZT array. The experimental results agreed well with the theoretical simulation. These superior performances were attributable to the excellent piezoelectric properties of PIN-PMN-PT single crystal.

Design of Active Structural Acoustic Control System Using Volume Displacement Sensors and Uniform Force Actuators

With an example of simply supported beam, it is presented a new volume displacement sensor and uniform force actuator design method to active control of structure-borne sound. An array of rectangular segments of PVDF film and PZT attached on the front and back surface of the beam are taken as sensor and actuator respectively. The output signals of the PVDF films are multiplied by appropriate weights so that the weighted combinations of the outputs directly lead to the volume displacement of the beam. The input control of each PZT actuator is driven by the same control input voltage but with different appropriate weights so that PZT array generates a uniform force over the beam. Finally, optimal control simulations are performed to validate this sensor/actuator strategy