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Modeling and testing of PZT and PVDF piezoelectric wafer active sensors
Abstract and Figures
Piezoelectric wafer active sensors (PWAS) used in structural health monitoring (SHM) applications are able to detect structural damage using Lamb waves. PWAS are small, lightweight, unobtrusive and inexpensive. They achieve direct transduction between electric and elastic wave energies. PWAS are charge mode sensors and can be used as both transmitters and receivers. The focus of this paper is to find a suitable in situ piezoelectric active sensor for sending and receiving Lamb waves to be used in the SHM of structures with a curved surface. Current SHM technology uses brittle piezoceramic (PZT) wafer active sensors. Since piezoceramics are brittle, this approach could only be used on flat surfaces. The motivation of our research was to explore the use of flexible piezoelectric materials, e.g. piezoelastic polymers such as PVDF. However, PVDF stiffness is orders of magnitude lower than the PZT stiffness, and hence PVDF Lamb wave transmitters are much weaker than PZT transmitters. Thus, our research proceeded in two main directions: (a) to model and understand how piezoelectric material properties affect the behaviour of piezoelectric wafer active sensors; and (b) to perform experiments to test the capabilities of the flexible PVDF PWAS in comparison with those of stiffer but brittle PZT PWAS. We have shown that, with appropriate signal amplification, PVDF PWAS can perform the same Lamb wave transmission and reception functions currently performed by PZT PWAS. The experimental results of PZT-PWAS and PVDF-PWAS have been compared with a conventional strain gauge. The theoretical and experimental results in this study gave a basic demonstration of the piezoelectricity of PZT-PWAS and PVDF-PWAS.
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... Comparing to non-destructive inspection (NDI), the sensors are integrated with or mounted on structures in SHM for real time monitoring. For SHM applications related to the Lamb waves, the waves are generally generated and received by piezoelectric transducers with thin and compact sizes, which are mounted on thin plate structures [3][4][5]. For metallic structures, the cracks usually initiate at hot spots such as holes or corners. ...
... Suppose the damage location is estimated at a point . In order to determine this point, consider (3,4) the distance between and the mean angle line for path group . According to Eq. (11), ...
... The geometric meaning of is the summation for the distance square from the point to the G 2 (3,4) preserved mean angle lines. Then the solution for can be determined by solving the following (3,4) simultaneous equations: ...
In this paper, a Lamb-wave based SHM for multi-damage localizations in large composite plate is presented. The Lamb waves are generated and received by piezoelectric transducers, which are arranged in array on the composite plate. In the experiments, three composite plates with various laminate stacking sequences and taper designs were prepared. The damages were created on the specimens by impact testing. In each specimen, 24 piezoelectric transducers were utilized and mounted on the specimen surface. This study proposed an algorithm to identify the damage localizations. The transducer layout is classified by 10 subsets. In each subset, the wave propagation paths can be grouped into path groups pivoted by actuators and that by sensors. Based on the damage index, the mean angle line for each path group in a subset can be obtained. By assuming that the mean angle line pass through the actual damage, the damage localization can be achieved if there exist more than two mean angle lines in one subset. In this study, two exclusion rules are proposed to exclude a path group from the damage localization calculations. The damage localization results show that, for a composite plate with multiple damages, their locations can be identified by using multiple subsets. The damage localization results show that the damage location can be accurately predicted for the case that a damage exists in the interior of a subset. The experiment results also show that the Lamb wave characteristics and the localization results are not affected by the thickness variation of the plate, indicating that the proposed algorithm is available for tapered composite plate.
... PZT transducers are widely used in SHM applications, covering both low and high frequencies methods. PZT ceramics have many advantages over other materials, such as good electromechanical coupling, good stability, high rigidity, linear response to low-intensity electric fields, and low-cost [9]. According to [10], piezoelectric diaphragms consist of a metallic disk, that acts as a support and bottom electrode, on which is mounted a piezoelectric ceramic disk. ...
Considering the increased demand for using natural resources sustainably, water is an ultra-valuable resource to be preserved. Notwithstanding, Polyvinyl Chloride (PVC) pipes, which are mainly used in complex building water distribution systems, are still in use and present a considerable rate of water loss. Unfortunately, the recently developed Structural Health Monitoring (SHM) has not deeply covered leaks in those pipes. To fill this gap, this approach proposes an experimental study to assess the feasibility of using Lead Zirconate Titanate (PZT) diaphragms to detect water leaks in these structures. Experimental tests were conducted by attaching one PZT diaphragm to a mini-scale water distribution system, where the leakage scenarios were simulated by opening taps. To attest to the effectiveness of the methodology, it calculated statistical metrics between the baseline (without leaks) and unknown conditions. The experimental results are promising and may be extrapolated to detect water losses in a full-scale water-distributing system.
... This section explains the fundamentals of PVDF transducers and governing equations. The main feature of PVDF films is relatively high dielectric permittivity, resistance to chemical substances, high voltage constant, insulation, and waterproofing [39][40][41][42]. However, compared to PZT ceramics, they are more costly since PZT ceramics are single-phase materials and can be made easier at a lower cost [39]. ...
Monitoring the condition of bearings in rotating machinery is crucial to ensure reliability, safety, and efficiency. Recently, integrated sensors have become more popular than traditional accel-erometers in bearing condition monitoring because of their compact design, cost-effectiveness, and improved efficiency in fault detection through a short transmission path. This study presents a new approach to bearing condition monitoring by developing a bearing with an integrated Polyvinylidene Fluoride transducer. This polymer-based transducer, known as PVDF, has a piezoelectric effect which generates electric charge in response to mechanical excitation. The PVDF transducer was selected for its high sensitivity, flexibility, and thin structure. The developed bearing with the integrated PVDF transducer can detect faults under constant and variable speeds, and the damage size can be estimated with an accuracy of 10%. It outperformed a commercial accelerometer in noisy environments with artificial impacts from an air motor, making it a highly reliable option for bearing condition monitoring in noisy industrial settings. The PVDF transducer can also be used as a low-cost speed sensor with an accuracy of 5.2%, offering a versatile solution for machine monitoring. By simultaneously recording rotational speed and vibration, the developed integrated transducer provides a comprehensive view of machine health and performance as a multi-function transducer, enabling more accurate and efficient maintenance scheduling.
... Among various types of materials, the development and characterization of piezoelectric materials for harvesting ambient power sources has become a major research area due to the key role they play in terms of device efficiency. In the past decade, lead zirconated titanite (PZT) has been extensively studied, and its brittle response to externally applied mechanical strain(s) [1] was identified as a major disadvantage. An interesting way to address this challenge is by aligning and laminating PZT fibers-of various lengths ranging between 15 and 250 µm-in epoxy matrices to induce mechanical flexibility [2]. ...
This study investigates the feasibility of utilizing a flow-induced vibration actuator as a potential energy source using piezoelectric energy harvesting. The focus is on exploring the behavior of piezo films configured as cantilever beams subjected to flow-induced vibration, which can be induced with fluid or wind streams. The primary objective is to maximize the harvested energy from the vibrating structure. This paper develops theoretical models to analyze the resonant frequencies and energy-harvesting potential of the piezo films in the context of flow-induced vibration. Experimental validations are conducted to verify the theoretical predictions. The findings indicate that higher operating frequencies in the second mode offer improved energy harvesting efficiency compared with lower modes. With the strategic adjustment of resonant frequencies using attached masses on individual piezo films, the harvestable energy output of a single film can be significantly increased from less than 1 μW to approximately 18 μW. However, the phase differences among individual piezo films can impact frequency measurements, necessitating careful fine-tuning of the physical conditions of individual components. To optimize energy harvesting, this study emphasizes the importance of implementing efficient charging mechanisms. By identifying suitable environmental vibration sources, the required charging duration for a synthesized energy harvesting array can be reduced by 25% as well. Despite certain challenges, such as phase deviations and turbulence, this study demonstrates the promising potential of flow-induced vibration resonators as sustainable energy sources. This work lays the foundation for further advancements in energy harvesting technology, offering environmentally friendly and renewable energy solutions.
... Piezoelectric materials show a linear relation between electric polarization and mechanical strain. Unfortunately, this electro-mechanical coupling is restricted to a few materials and piezoelectric polymers, e.g., polyvinylidene difluoride (PVDF) [12,13,14,15]. ...
Flexoelectric sensors respond with an electric polarization when they are subjected to inhomogeneous deformation. When these are based on polymeric materials, the electro-mechanical coupling relates to the loss of microstructural symmetries of the polar polymer chains. The object of this work is to explore the mechanisms that induce flexoelectricity in soft (co)polymers via a micromechanical model that explicitly considers the spatial composition distribution of polymer chains. To this end, we analyze the deformation of the Arruda-Boyce 8-chain cell under inhomogeneous deformation and its influence on the overall polarization resulting from the polar monomers. Cells with random-walk chains and tailored degree of entanglement feed Monte Carlo simulations to inform an effective chain dipole that drives the flexoelectric polarization. Homogeneous stretch/compression of the cell accompanying bending deformation reinforce the flexoelectric response. In addition, we focus on stochastic chain-growth processes and the insertion of different types of polar monomers within a same chain. Here, we introduce a model where reactivity ratios of real copolymerization reactions control the resulting flexoelectric coupling. Since the framework allows to relate the effective flexoelectric polarization to any structure isomer distribution, it is especially convenient to model copolymers. Overall, the model is proposed as a versatile framework to explore the intricacies of flexoelectric (co)polymers and to foster the design of flexoelectric devices from real manufacturing parameters.
In this paper, the effects of rotation on a phononic crystal (PnC) operated in whispering-gallery modes (WGMs) are investigated for the first time. According to the results of a finite element method, the vibration pattern of the WGMs under the action of rotation will undergo a linear precession with the integral of rotation, which agrees with the theoretical models. In addition, the precession of WGMs will linearly induce a phase difference between the transmissive waves with a fixed phase gain. The difference displacement is utilized to characterize the effects of rotation on the transmissive wave, showing periodicity, linearity, and directionality as theoretical predictions. These findings offer a rate-integrating scheme to sense rotation and have promising applications, especially in high-performance SAW gyroscopes.
This review presents the important applications of piezoelectric materials in civil engineering in recent years. Studies on the development of smart construction structures have been carried out by using materials such as piezoelectric materials around the world. Piezoelectric materials have attracted attention in many civil engineering applications, as a result of their capability of generating electrical power when subjected to a mechanical stress, or of generating mechanical stress when subjected to an electric field. In civil engineering applications, piezoelectric materials are used in energy harvesting not only in superstructures but also in substructures, control strategies, the creation of composite materials with cement mortar, and structural health monitoring systems. With this perspective, the civil engineering applications of the piezoelectric materials were reviewed and discussed, especially for their general properties and effectiveness. At the end, suggestions were made for future studies using piezoelectric materials.
The development of structural health monitoring (SHM) techniques is of great importance to improve the structural efficiency and safety. With advantages of long propagation distances, high damage sensitivity, and economic feasibility, guided-ultrasonic-wave-based SHM is recognized as one of the most promising technologies for large-scale engineering structures. However, the propagation characteristics of guided ultrasonic waves in in-service engineering structures are highly complex, which results in difficulties in developing precise and efficient signal feature mining methods. The damage identification efficiency and reliability of existing guided ultrasonic wave methods cannot meet engineering requirements. With the development of machine learning (ML), numerous researchers have proposed improved ML methods that can be incorporated into guided ultrasonic wave diagnostic techniques for SHM of actual engineering structures. To highlight their contributions, this paper provides a state-of-the-art overview of the guided-wave-based SHM techniques enabled by ML methods. Accordingly, multiple stages required for ML-based guided ultrasonic wave techniques are discussed, including guided ultrasonic wave propagation modeling, guided ultrasonic wave data acquisition, wave signal pre-processing, guided wave data-based ML modeling, and physics-based ML modeling. By placing ML methods in the context of the guided-wave-based SHM for actual engineering structures, this paper also provides insights into future prospects and research strategies.
A built-in cost-effective diagnostic system is being developed to monitor fatigue crack growth in aircraft structures. The proposed system consists of a SMART layer with an embedded network of distributed piezoelectric sensors/actuators, a diagnostic unit, and software. The layer is surface-mounted on the critical area where crack initiation and growth are suspected. Using the software, pre-selected diagnostic signals from a designated piezoelectric actuator to its neighboring sensors are generated by the diagnostic unit. The corresponding sensor signals are recorded and compared to a baseline reference, which was previously recorded. Based on the changes in the sensor signals, the software interprets the crack growth condition at the time of measurement. The results of this technique have been verified by experiments.
The objective of this study is to model the diagnostic transient waves in an integrated piezoelectric sensor/actuator plate with a view to using it as a first step towards establishing an entire structural health monitoring system and to provide experimental verification of the proposed models. PZT ceramic disks are surface mounted on an aluminum plate acting as both actuators and sensors to generate and collect A0 mode Lamb waves. Mindlin plate theory is adopted to model the propagating waves by taking both transverse shear and rotary inertia effects into account. Actuator and sensor models are both proposed. The interaction between an actuator and the host plate is modeled based on classical lamination theory. The converse piezoelectric effect of the actuator is treated as an equivalent bending moment applied to the host plate. The sensor acts as a capacitor that converts the sensed strain change into a voltage response. An analytical expression for the sensor output voltage in terms of the given input excitation signal is derived, and then experimental work is performed to verify the accuracy of the analytical model. Experimental results show that single-mode Lamb waves in the plate can be successfully generated and collected through the integrated PZT disks. The experiment also shows that the predicted sensor output for both amplitude and phase agrees well with experimentally collected data.
This paper demonstrates a feasibility study of applying migration, which is widely used as an advanced data processing technique in geophysical exploration, to detect damage in a plate. This technique suggests a scheme that may build a real time, in situ, and quantitative health monitoring system. A linear actuator/sensor array is placed along a horizontal central axis on a square homogeneous isotropic plate. A technique is proposed to utilize piezoelectrics as both actuators and sensors to generate and collect the flexural waves in the plate. Migration technique is then adopted to interpret the recorded data and image the damage that formed in the plate. The wave field reflected from the damage is synthesized by using a two-dimensional explicit finite difference method to model the plate using Mindlin plate theory. A one-way version of flexural wave equation is derived. The one-way wave equation based poststack reverse-time migration is then used to back-propagate the synthetic wave field to their secondary sources, and the damage is imaged by applying appropriate imaging condition. The data pre-processing procedures before migration, such as muting direct arrival, deconvolution and stacking, are also discussed. The satisfactory determination of the locations and dimensions of the damages in several numerical simulation examples validates the feasibility of proposed monitoring system.
A project to develop non-intrusive active sensors that can be applied on existing aging aerospace structures for monitoring the onset and progress of structural damage (fatigue cracks and corrosion) is presented. The state of the art in active sensors structural health monitoring and damage detection is reviewed. Methods based on (a) elastic wave propagation and (b) electro-mechanical (E/M) impedance technique are cited and briefly discussed. The instrumentation of these specimens with piezoelectric active sensors is illustrated. The main detection strategies (E/M impedance for local area detection and wave propagation for wide area interrogation) are discussed. The signal processing and damage interpretation algorithms are tuned to the specific structural interrogation method used. In the high-frequency E/M impedance approach, pattern recognition methods are proposed for comparing impedance signatures taken at various time intervals and to identify damage presence and progression from the change in these signatures. In the wave propagation approach, the acousto-ultrasonic methods for identifying additional reflections generated from the damage site and changes in transmission velocity and phase are suggested. Design and fabrication of a set of structural specimens representative of aging aerospace structures (pristine, with cracks, and with corrosion damage) are presented. Their instrumentation with piezoelectric-wafer active sensors is discussed. Damage detection results obtained with the E/M impedance and wave propagation techniques on simple-geometry specimens and on the realistic aging aircraft specimens are presented.
A project to develop non-intrusive active sensors that can be applied on existing aging aerospace structures for monitoring the onset and progress of structural damage (fatigue cracks and corrosion) is presented. The state of the art in active sensors structural health monitoring and damage detection is reviewed. Methods based on (a) elastic wave propagation and (b) electro-mechanical (NM) impedance technique are sighted and briefly discussed. The instrumentation of these specimens with piezoelectric active sensors is illustrated. The main detection strategies (E/M impedance for local area detection and wave propagation for wide area interrogation) are discussed. The signal processing and damage interpretation algorithms are tuned to the specific structural interrogation method used. In the high-frequency EIM impedance approach, pattern recognition methods are used to compare impedance signatures taken at various time intervals and to identify damage presence and progression from the change in these signatures. In the wave propagation approach, the acoustic-ultrasonic methods identifying additional reflection generated from the damage site and changes in transmission velocity and phase are used. Both approaches benefit from the use of artificial intelligence neural networks algorithms that can extract damage features based on a learning process. Design and fabrication of a set of structural specimens representative of aging aerospace structures is presented. Three built-up specimens, (pristine, with cracks, and with corrosion damage) are used. The specimen instrumentation with active sensors fabricated at the University of South Carolina is illustrated. Preliminary results obtained with the E/M impedance method on pristine and cracked specimens are presented.
The focus of this paper is on the axial impact of long rods, to investigate major features of wave speed and impulse transfer, and to introduce techniques necessary to measure them experimentally. The longitudinal waves are generated by impacting the rod with a steel ball. The resulting waves are detected by using electrical-resistance strain gages and are recorded by an oscilloscope. A description of the equipment with typical data is given. Sample calculations are also included.
Among novel non-destructive evaluation techniques for structural health monitoring, the magnetostrictive (MS)-tagged fiber-reinforced composites stands out as especially suitable due to: (a) distributed sensory properties, (b) non-contact damage detection, and (c) straightforward manufacturing implementation. Experimental data and mathematical modeling of a MS-tagged fiber reinforced composite beam under bending (flexural) loading are presented. A brief review of the state of the art identifies previous work on axially loaded MS composites, but finds no previous work on bending. Description of bending beam design and fabrication is followed by theoretical analysis and by the description of the experimental set-up and equipment used. Several analysis models were used. Test data, with and without applying magnetic bias field between loading cycles, is presented and results are discussed. Numerical values for the stress and strain versus magnetic flux density coefficients are given for both annealed and non-annealed cases. Piezomagnetic coefficients for the MS composite are calculated. The correlation between the results developed in the present paper for bending and previously published results for axial loading is found to be within 10% after correction factors depending on the quantity of the MS material.
Piezoelectric paints have a potential to change a conventional structural material into an intelligent material system with health-monitoring capabilities such as vibration sensing and damage detection. Such paints were prepared using lead zirconate titanate (PZT) ceramic powder as a pigment and epoxy resin as a binder. The obtained paints were coated on aluminum test specimens, and were cured at room temperature or at 150 , thus forming the paint films having different thicknesses of 25-300 . These films were then poled at room temperature, and were evaluated with regard to the sensitivities as vibration and acoustic emission sensors in the frequency ranges of 0-250 Hz and 0-1.0 MHz, respectively. This paper mainly describes the effects of the film thickness and the cure temperature on the poling behavior of the PZT/epoxy paint film. This paper describes also the application of the paint film as a vibration modal sensor integrated into a structural material.
High-field theoretical and experimental analysis of piezoelectric and magneto-strictive actuators is presented. First, the analysis of a piezoelectric stack actuator (PiezoSystems Jena PAHL 120/20) is described. A theoretical model based on the linear theory of piezoelectricity is developed. Extensive experiments were conducted, aimed at low-frequency dynamic electro-mechanical behavior characterization. Curve fitting procedures are used to adjust the model coefficients for various load levels. Through comparison with experimental data, the model is adjusted to include nonlinear terms related to higher losses on the unloading cycle. Second, the impedance analysis of a magnetostrictive actuator (Etrema AA140J025) is described. Linear piezomagnetism is assumed, as an approximation to nonlinear magnetostrictive behavior about a bias point. Low-field and high-field impedance measurements were performed, revealing left shifting of the actuator resonance as the power is increased. Model tuning of the impedance model on the experimental data showed material parameters trends similar with those reported in the literature. Although the numerical values developed during this phenomenological study are particular for the actuators under consideration, the characterization approach can be extended to analysis of other actuators of this type.