PZT Wafer Research Articles

Rapid guided wave delamination detection and quantification in composites using global-local sensing

This paper presents a rapid guided ultrasonic wave inspection approach through global inspection by phased array beamforming and local damage evaluation via wavenumber analysis. The global-local approach uses a hybrid system consisting of a PZT wafer and a non-contact laser vibrometer. The overall inspection is performed in two steps. First, a phased array configured by a small number of measurements performs beamforming and beamsteering over the entire plate in order to detect and locate the presence of the damage. A local area is identified as target damage area for the second step. Then a high density wavefield measurement is taken over the target damage area and a spatial wavenumber imaging is performed to quantitatively evaluate the damage. The two-step inspection has been applied to locate and quantify impact-induced delamination damage in a carbon fiber reinforced polymer composite plate. The detected delamination location, size and shape agree well with those of an ultrasonic C-scan. For the test case studied in this work the global-local approach reduced the total composite inspection (damage detection and characterization) time by ∼97% compared to using a full scan approach.

Temperature dependent ferroelectric and ferroelastic behaviour of PZT wafers

A study is carried out to understand the temperature dependent non-linear behaviour of PZT wafers under electrical and mechanical loading. Experiments are conducted on PZT wafers at room and elevated temperatures under a high cyclic electric field to examine their behaviour. Experimental characterization is also extended to pure mechanical loading (uni-axial compressive stress) condition at room and elevated temperatures. A temperature dependent micro-mechanical model is proposed based on internal energy to evaluate the ferrolectric and ferroelastic behaviour of PZT wafer. The developed model is incorporated into a 3D finite element framework and numerical simulations are performed. The simulated results for electrical loading are compared with experimental observations which show a significant decrease in dielectric response at elevated temperature and it is also observed that the operating temperature influences the electrical displacement and strain along poling direction (thickness direction) under mechanical loading. A parametric study has also been conducted to understand the performance of PZT wafer in which macro-state variables such as remnant polarization, remnant strain, maximum polarization, and maximum strain are extracted and discussed as a function of temperature.

Severity evaluation of the transverse crack in a cylindrical part using a PZT wafer based on an interval energy approach

Transverse cracks in cylindrical parts can be detected by using the ultrasound based pulse–echo method, which has been widely used in industrial applications. However, it is still a challenge to identify the echoes reflected by a crack and bottom surfaces of a cylindrical part due to the multi-path propagation and wave mode conversion. In this paper, an interval energy approach is proposed to evaluate the severity of the transverse crack in a cylindrical part. Lead zirconate titanate patch transducers are used to generate the ultrasound pulse and to detect the echoes. The echo signals are preprocessed and divided into two zones, the normal reflection zone and the crack reflection zone. Two energy factors evaluating the severity of the crack are computed based on the interval energy. When using this proposed method, it is not necessary to identify the echo sources since all the crack and boundary echoes are automatically taken into consideration by using the proposed method. The experimental results indicate that proposed approach is more suitable and sensitive to evaluate the transverse crack severity of cylindrical part than the traditional method.

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.

Design and Fabrication of a Novel Biaxial Piezoelectric Micro-Gyroscope

Despite the popularity of piezoelectric vibratory micro-gyroscope in the past decades for their small size, low cost, batch fabrication and energy efficient, most of them can only detect single axis angular rate. In this paper, a novel biaxial piezoelectric micro-gyroscope fabricated with PZT wafer is proposed. To acquire two-axial angular rate sensing, a bouncing mode of the vibrator is utilized as the drive mode and two rocking modes are used as the sense modes. PZT is used as the vibration body instead of transducer, which enhances the drive and sense efficiency of the sensor. In this paper, the structure and working principle of the novel biaxial piezoelectric micro-gyroscope are introduced firstly. In addition, modal analysis has been made to research the voltage distribution of the piezoelectric vibrator and the drive and sense electrodes of the gyroscope are designed. By the optimization design of the proof mass, the frequency split between the drive mode (bouncing mode) and sense modes (rocking modes) is reduced and the sensitivity of the gyroscope is improved. Harmonic analysis has been made to research the Coriolis Effect of the gyroscope. The data get from the harmonic analysis is demodulated by Matlab and the sensitivity is given. The simulation results verify the principle of the novel biaxial piezoelectric micro-gyroscope. With the optimized design, the sensor is fabricated with MEMS technology at last.

Experimental and Theoretical Investigations of the Impact Localization of a Passive Smart Composite Plate Fabricated Using Piezoelectric Materials

Two passive smart composite plates are fabricated using one and two PZT patches that are cheaper than the PZT wafer. The composite plate is fabricated in low temperature through the hand lay-up method to avoid PZT patch decoupling and wire spoiling. The locus of the impact point is identified using the output voltage to identify the impact location using one sensor. The output voltages of the sensors are analyzed to identify the impact location using two sensors. The locations of the impacts are determined based on the crossing points of two circles and the origin of an intended Cartesian coordinate system that is concentric with one of the sensors. This study proposes the impact location identification of the passive smart composite using the low-cost PZT patch PIC155 instead of common embedded materials (wafer and element piezoelectric).

Displacement and resonance behaviors of a piezoelectric diaphragm driven by a double-sided spiral electrode

This paper presents the design of a lead zirconate titanate (PZT) diaphragm actuated by double-sided patterned electrodes. Au/Cr electrodes were deposited on bulk PZT wafers by sputtering while patterned by a lift-off process. SU-8 thick film was used to form the structural layer. Double-spiral electrode induced in-plane poling and piezoelectric elongation are converted to an out-of-plane displacement due to the confined boundary condition. The influence of different drive configurations and electrode parameters on deflection has been calculated by finite element methods (FEM) using a uniform field model. Impedance and quasi-static displacement spectra of the diaphragm were measured after poling. A double-sided patterned electrode diaphragm can be actuated by more drive configurations than a single-sided one. Compared with a single-sided electrode drive, a double-sided out-of-phase drive configuration increases the coupling coefficient of the fundamental resonance from 7.6% to 11.8%. The displacement response of the diaphragm increases from 2.6 to 8.6 nm V−1. Configurations including the electric field component perpendicular to the poling direction can stimulate shear modes of the diaphragm.

Damage localization in plate-like structure using built-in PZT sensor network

In this study, a Lamb-wave based damage detection approach is proposed for damage localization in plate. A sensor network consisting of three PZT wafer type actuators/sensors is used to generate and detect Lamb waves. To minimize the complication resulted from the multimode and dispersive characteristics of Lamb waves, the fundamental symmetric Lamb mode, S0 is selectively generated through designing the excitation frequency of the narrowband input signal. A damage localization algorithm based upon the configuration of the PZT sensor network is developed. Time-frequency analysis method is applied to purify the raw signal and extract damage features. Experimental result obtained from aluminum plate verified the proposed damage localization approach.

Effects of loading rate and temperature on domain switching and evolutions of reference remnant state variables during polarization reversal in a PZT wafer

A PZT wafer poled in thickness direction is subject to through-thickness electric field cyclic loads at four different loading rates and four different temperatures. Electric displacement in thickness direction and in-plane extensional strain are measured and plotted during a complete cycle of polarization reversal. Reference remnant polarization and reference remnant in-plane extensional strain are calculated from the measured data. Effects of electric field loading rate and temperature on domain switching process and evolutions of reference remnant state variables are discussed and explained using consecutive two step slow 90° domain switching processes and reduced coercive field at high temperatures.

Direct Writing Micro/Nano Structures on PZT Wafer by Laser Micromaching

The PZT is used for piezoelectric actuators that have high area efficiency but no good machinability. A direct writing micro structures on PZT wafer by excimer laser micromaching method has been proposed and confirmed. PZT nano-needle structures have also been fabricated by the direct writing method only by changing the laser micromachiong process parameters. The fabricated nano-needle structures can be very useful because of the need for studies on ferroelectric size effects as well as for potential applications such as ultra-high density memory devices.The relationship of process depth with the excimer laser parameters has been tested.

A Quantitative Damage Identification Method for CF/EP Composite Laminates Based on Lamb Waves

This paper describes a quantitative damage identification method for CF/EP composite laminates based on Lamb waves excited by distributed PZT wafers. The fundamental symmetric mode S0 is considered to detect defects (hole) in the plate. The Morlet wavelet and the cross-correlation analysis are introduced as signal processing tools for determining the time-of-flight (ToF) of Lamb wave. Considering the difference of Lamb wave velocities in different directions in a composite plate, the relationship of Lamb wave velocity in a unidirectional fibre reinforced laminate is studied and validated experimentally and numerically. In addition, a defect identification approach is revealed based on a regular arrangement of PZT wafers. Then, on the basis of the relationship of the wave velocity and the ToF, the location of a hole is identified by proposed method. Results demonstrate that the method is feasible in quantitative diagnosis of composite structures.

Effect of PbO content, loading rate and poling on mechanical properties of tape-cast and sintered PZT wafers

Abstract The effect of PbO content on the elastic modulus, hardness and fracture toughness of tape-cast and sintered PZT wafers was investigated using instrumented indentation based techniques. It was found that hardness and elastic modulus remained more or less unchanged whereas the fracture toughness increased with increasing PbO content. The effect of loading rate of indentation on the hardness and elastic modulus of the PZT wafer having near-morphotropic composition was also studied. It was found that the hardness increased initially with increasing loading rate up to a loading rate of 50 mN/min and subsequently decreased with further increase in loading rate. On the other hand, elastic modulus remained more or less unaffected. The effect of poling on the mechanical properties of the near-morphotropic PZT wafer was also investigated. Poling was found to result in a decrease in fracture toughness, although it did not have a significant effect on the hardness and elastic modulus.

Multi-scale modeling of time-dependent response of smart sandwich constructions

Polymer and polymer based composite structures exhibit time-dependent response, leading to their being described as viscoelastic bodies. The rate of creep (or stress relaxation) in viscoelastic bodies increases with increasing the temperature of the bodies. In this study, we are interested in analyzing the time-dependent response of smart sandwich composites comprising of glass fiber reinforced polymer (GFRP) skins, polyurethane foam core, and lead zirconate titanate (PZT) wafers embedded in the GFRP skins. The PZT is used to monitor lifetime performance of sandwich composites. A multi-scale model is developed to integrate different constitutive models of the constituents in the sandwich structures. Quasi-static and creep tests are conducted for bulk epoxy, GFRP, polyurethane foam, and sandwich specimens under uniaxial tension and bending. The tests were done at room temperature and at 80 °C. The experimental data are used for material characterization and model verification. The multi-scale model that is developed can be used to understand the effect of different responses of the constituents on the overall time-dependent behavior of sandwich structures and examine the feasibility of using PZT wafers for monitoring lifetime performance of sandwich structures.

Macroscopic comparison of ferroelectric domain switching processes in a PZT wafer at high temperatures

The so-called reference remanent polarization and reference remanent in-plane strain are calculated from a set of creep data of a PZT wafer subjected to constant through-thickness electric fields at high temperatures. Using the calculated reference remanent quantities, domain switching processes at different temperatures are compared with each other. From the macroscopic comparison, it is found that the fraction of the variants aligned parallel to the plane of the wafer decreases with increase in temperature during an electric field-induced polarization reversal. Other interesting phenomena were also observed and all of them were discussed from the view point of 90° domain switching.

An electro-mechanical impedance model of a cracked composite beam with adhesively bonded piezoelectric patches

A model of a laminated composite beam including multiple non-propagating part-through surface cracks as well as installed PZT transducers is presented based on the method of reverberation-ray matrix (MRRM) in this paper. Toward determining the local flexibility characteristics induced by the individual cracks, the concept of the massless rotational spring is applied. A Timoshenko beam theory is then used to simulate the behavior of the composite beam with open cracks. As a result, transverse shear and rotatory inertia effects are included in the model. Only one-dimensional axial vibration of the PZT wafer is considered and the imperfect interfacial bonding between PZT patches and the host beam is further investigated based on a Kelvin-type viscoelastic model. Then, an accurate electro-mechanical impedance (EMI) model can be established for crack detection in laminated beams. In this model, the effects of various parameters such as the ply-angle, fibre volume fraction, crack depth and position on the EMI signatures are highlighted. Furthermore, comparison with existent numerical results is presented to validate the present analysis.

Characterization of a large-area PVDF thin film for electro-mechanical and ultrasonic sensing applications

Large-area PVDF thin films have been prepared and characterized for quasi-static and high frequency dynamic strain sensing applications. These films are prepared using hot press method and the piezoelectric phase (β-phase) has been achieved by thermo-mechanical treatment and poling under DC field. The fabricated films have been characterized for quasi-static strain sensing and the linear strain–voltage relationship obtained is promising. In order to evaluate the ultrasonic sensing properties, a PZT wafer has been used to launch Lamb waves in a metal beam on which the PVDF film sensor is bonded at a distance. The voltage signals obtained from the PVDF films have been compared with another PZT wafer sensor placed on the opposite surface of the beam as a reference signal. Due to higher stiffness and higher thickness of the PZT wafer sensors, certain resonance patterns significantly degrade the sensor sensitivity curves. Whereas, the present results show that the large-area PVDF sensors can be superior with the signal amplitude comparable to that of PZT sensors and with no resonance-induced effect, which is due to low mechanical impedance, smaller thickness and larger area of the PVDF film. Moreover, the developed PVDF sensors are able to capture both A 0 and S 0 modes of Lamb wave, whereas the PZT sensors captures only A 0 mode in the same scale of voltage output. This shows promises in using large-area PVDF films with various surface patterns on structures for distributed sensing and structural health monitoring under quasi-static, vibration and ultrasonic situations.

State dependent pyroelectric and thermal expansion coefficients in a PZT wafer

A PZT wafer is subjected to a temperature increase from the reference temperature 20–111 °C under no electric field. During the temperature increase, the variations of remanent polarization in thickness direction and remanent in-plane strain are measured. From the measurements, the values of pyroelectric coefficient in thickness direction and in-plane thermal expansion coefficient are estimated. The temperature experiment is repeated starting at various different values of initial remanent polarization, and the dependency of pyroelectric and thermal expansion coefficients on initial remanent polarization is obtained. In the tested range of temperature, it is found that the pyroelectric coefficient can be given as a linear function of remanent polarization and that the in-plane thermal expansion coefficient is given as a linear function of remanent in-plane strain or as a quadratic function of remanent polarization.

Domain switching and creep behavior of a poled PZT wafer under through-thickness electric fields at high temperatures

Various constant magnitudes of through-thickness electric field are applied to a poled PZT wafer for about 1800 s at four different high temperatures. The wafer is then removed swiftly from the field and kept at zero electric field for about 1000 s. During the whole period of nonzero and zero electric field loading time, the electric displacement in thickness direction and the in-plane strain of the wafer are measured over time. The measured responses at different electric fields and temperatures are discussed and compared with one another. The dependence of various linear moduli on remanent quantities and temperature is obtained; the creep responses of the wafer at high temperatures are compared and discussed; and finally the domain-switching processes at different electric fields and temperatures are discussed in terms of reference remanent quantities.

인장하중을 받을 때 PZT 웨이퍼의 크립 거동: 실험과 모델링

두께방향으로 분극처리되어 있는 상업용 PZT 웨이퍼가 폐쇄회로와 개방회로의 두 가지 전기적 경계조건에서 길이 방향으로 일정한 크기의 인장하중을 받는다. 하중과정 동안 두께 방향으로의 전기밀도와 평면내 변형률의 시간에 따른 변화를 측정한다. 두 가지 전기적 경계조건에서의 서로 다른 거동 특성을 시편 내부에서 발생하는 전기장과 분극역전 현상으로 설명한다. 마지막으로 관측된 크립 거동을 예측하기 위한 정규분포 형식을 가지는 자유에너지 함수를 도입하고 모델의 예측과 실험결과를 비교한다.

Integrity of piezoceramic patch transducers under cyclic loading at different temperatures

In this study the loading limits, damage behavior and long-term integrity of piezoceramicpatch transducers, based on monolithic PZT (lead zirconium titanate) wafers (PIC 255),were investigated. The study involved quasi-static and long-term cyclic testing undertensile and compressive mechanical loading of the patches, at different temperatures. Astrain-cycle lifetime diagram was established for tensile loading at room temperature, and+60,+100 and−40 °C. In all cases of tensile loading, cracking in the PZT ceramic was found to bethe relevant failure mechanism which was shown to be correlated with theobserved degradation of sensor performance of the patches. No mechanicaldamage was found under compressive loading at strain levels of up to−0.6%. Finite element (FE) analyses were performed using 3D material modeling withelectromechanical coupling, achieving very good predictability of the sensor and actuatorperformance. Analytical calculations and numerical simulation were used to interpretexperimental findings and to allow the transfer of results to various applications. Based onmicro-structural investigations of the cracked PZT wafers and FE simulation, fracturemechanics analyses of the local stress situation in the PZT ceramic were carried out.