Piezoelectric Wafer Active Sensors Research Articles

Exact analytical modeling of power and energy for multimode lamb waves excited by piezoelectric wafer active sensors

This article presents an analytical model for power and energy transfer between excited piezoelectric wafer active sensors and host structure. This model is based on exact multimodal Lamb waves, normal mode expansion technique, and orthogonality of Lamb waves. Modal participation factors are presented to show the contribution of every mode to the total energy transfer. The model assumptions include the following: (1) straight-crested multimodal ultrasonic guided wave propagation, (2) propagating waves only, (3) ideal bonding (pin-force) connection between piezoelectric wafer active sensors and structure, and (4) ideal excitation source at the transmitter piezoelectric wafer active sensors. Constrained piezoelectric wafer active sensor admittance is reviewed. Electrical active power, mechanical converted power, and Lamb wave kinetic and potential energies are derived in closed-form formulae. Numerical simulations are performed for the case of symmetric and antisymmetric excitation of thin aluminum structure. The simulation results are compared with axial and flexural approximation for the case of low-frequency Lamb waves. In addition, a thick steel structure example is considered to illustrate the case of multimodal guided waves. A parametric study for different excitation frequencies and different transducer sizes is performed to show the best match of frequency and piezoelectric wafer active sensor size to achieve maximum energy transfer into the excited structure.

Sensor Performance Assessment Based on a Physical Model and Impedance Measurements

The employment of a large number of embedded sensors in advanced monitoring systems becomes more common, enabling in-service detection, localization and assessment of defects in mechanical, civil and aerospace structures. These sensors could be optical fibre sensors, accelerometers, strain gauges or piezoelectric wafer active sensors (PWAS). As the latter are quite popular, due to its multipurpose application as actuators and sensors and its low cost, this type will be investigated. Within this paper a possible approach of sensor performance is presented. The method uses the coupled electro-mechanical admittance to detect damage of the PWAS and its bonding layer. The help of a temperature dependent theoretical model provides for influences of changing environmental and operational conditions. The model will be compared with FEM-results, before showing the successful application on experimental results.

Time-domain hybrid global–local concept for guided-wave propagation with piezoelectric wafer active sensor

This article presents a combined finite element method and analytical process to predict the one-dimensional guided-wave propagation for nondestructive evaluation and structural health monitoring application. Analytical methods can perform efficient modeling of wave propagation but are limited to simple geometries. In response to today’s most complex cases not covered by the simulation tools available, we aim to develop an efficient and accessible tool for structural health monitoring application. This tool will be based on a hybrid coupling between analytical solution and time-domain numerical codes. Using the principle of reciprocity, global analytical calculation is coupled with local finite element method analysis to utilize the advantages of both methods and obtain a rapid and accurate simulation method. The phenomenon of interaction between the ultrasonic wave, the defect, and the structure, leading to a complex signature, is efficiently simulated by this hybrid global–local approach and is able to predict the specific response signal actually received by sensor. The finite element mesh is used to describe the region around the defects/flaws. In contrast to other hybrid models already developed, the interaction between Lamb waves and defects is computed in the time domain using the explicit solver of the commercial finite element method software ABAQUS.

Towards spacecraft applications of structural health monitoring

The first part of the paper presents recent developments in the field of structural health monitoring (SHM) with special attention on the piezoelectric wafer active sensors (PWAS) technologies utilizing guided waves (GW) as propagating waves (pitch-catch, pulse-echo), standing wave (electromechanical impedance), and phased arrays. The second part of the paper describes the challenges of extending the PWAS GW SHM approach to in-space applications. Three major issues are identified, (a) cryogenic temperatures; (b) high temperatures; and (c) space radiation exposure. Preliminary results in which these three issues were address in a series of carefully conducted experiments are presented and discussed. The third part of the paper discusses a new project that is about to start in collaboration between three Romanian institutes to address the issues and challenging of developing space SHM technologies based on PWAS concepts. The paper finishes with conclusions and suggestions for further work.

Exact Shear-Lag Solution for Guided Waves Tuning with Piezoelectric-Wafer Active Sensors

This paper addresses some unresolved predictive modeling issues related to the use of piezoelectric-wafer active sensors for ultrasonic structural health monitoring. An exact model for the shear-lag transfer between the piezoelectric-wafer active sensor transducer and the structure in the presence of N generic guided wave modes is derived from first principles using the normal-mode expansion formulation. The resulting integral–differential equation is solved using the variational iteration approach. The resulting solution is used to derive an improved modelforthetuningbetweenpiezoelectric-waferactivesensortransducersandthemultimodalguidedwavesusedin ultrasonic structural-health-monitoring applications. The numerical predictions generated by the improved tuning model are compared with experimental results obtained through pitch–catch experiments between two 7 mm piezoelectric-waferactivesensortransducersplacedona1-mm2024-T3aluminumplate.The10–700kHzfrequency range was explored. It was concluded that the improved model using the exact shear-lag solution matches much better the experimental results than previous models. Further theoretical and experimental work is warranted as a follow-up on the work reported in this paper to study the accuracy and convergence properties of the solution, to explore experimental comparison beyond the A1-mode cutoff frequency, and to extend the approach to layered structures and composite materials.

STRUCTURAL HEALTH MONITORING WITH PIEZOELECTRIC WAFER ACTIVE SENSORS by VICTOR GIURGIUTIU - University of South Carolina © ELSEVIER - Academic Press, 2008, pp. 747, Book review

STRUCTURAL HEALTH MONITORING WITH PIEZOELECTRIC WAFER ACTIVE SENSORS by VICTOR GIURGIUTIU - University of South Carolina © ELSEVIER - Academic Press, 2008, pp. 747, Book review

Active structural health monitoring during sub-orbital space flight

Increasing involvement of commercial enterprises in space activities is among leading forces behind a renewed interest in structural diagnostic methodologies promising potential for improving safety, operability and cost effectiveness of launch vehicles and spaceships. It is envisioned that unobtrusive, real time structural health monitoring (SHM) systems may assist in space vehicle’s prelaunch qualification, orbital operation, safe disintegration during reentry or recertification for a next flight. SHM experiment utilizing piezoelectric wafer active sensors in conjunction with electro-mechanical impedance measurements has been develop to explore feasibility of active structural health monitoring during suborbital space flight. Details of experiment are discussed and some results obtained in real time for all segments of vehicle’s trajectory are presented. Experimental data collected during suborbital space flight has shown feasibility of SHM in the challenging environment, utility of thin wafer piezoelectric sensors as active elements of spacecraft SHM system, and potential of the electro-mechanical impedance method for real time structural integrity assessment of the payload.

Damage detection on hollow cylinders by Electro-Mechanical Impedance method: Experiments and Finite Element Modeling

Damage detection using the Electro-Mechanical Impedance method (EMI) is based on measuring the electrical impedance spectrum of piezoelectric wafer active sensors (PWAS) attached to the structure. Any changes in the structure, such as a crack, lead to changes in the mechanical impedance of the structure, which affect the PWAS electrical impedance by the electromechanical coupling effect of PWAS. The motivation here is to examine the performance of the EMI technique for damage detection on hollow cylinders. For this purpose, the EMI technique on hollow cylinders was implemented experimentally. Damage detection was realized by comparison of damage metrics extracted from measured PWAS electrical impedance for undamaged and damaged cylinders. A Finite Element Model (FEM) of a hollow cylinder considering the EMI technique has been developed. FEM results are in accordance with experimental data and similar trends are also observed for damage metrics. The influence of different damage types and damage location on damage metrics has been explored both by experiments and FEM. Moreover, the effects of accumulated damage on damage metrics are explored both by FEM and experiments. To examine the influence of host material stiffness on damage metrics, the EMI technique was performed on aluminum and steel hollow cylinders with different thicknesses.

Predictive modeling of electromechanical impedance spectroscopy for composite materials

The advancement of composite materials in aircraft structures has led to an increased need for effective structural health monitoring technologies that are able to detect and assess damage present in composite structures. The study presented in this article is interested in understanding self-sensing piezoelectric wafer sensors to conduct electromechanical impedance spectroscopy in glass fiber reinforced polymer composite to perform structural health monitoring. For this objective, multi-physics-based finite element method is used to model the electromechanical behavior of a free piezoelectric wafer active sensor and its interaction with the host structure on which it is bonded. The multi-physics-based modeling permits the input and output variables to be expressed directly in electric terms, while the two-way electromechanical conversion is done internally in the multi-physics-based finite element method formulation. The impedance responses are also studied in conditions when the sensor bonding layer is subject to degradation and when the sensor itself is subjected to breakage, respectively. To reach the goal of using the electromechanical impedance spectroscopy approach to detect damage, several damage models are generated on simplified orthotropic structure and laminated glass fiber reinforced polymer structures. The effects of the modeling are carefully studied through experimental validation. A good match has been observed for low and high frequencies.

Piezoelectric Wafer Active Sensors in Lamb Wave-Based Structural Health Monitoring

Recent advancements in sensors and information technologies have resulted in new methods for structural health monitoring (SHM) of the performance and deterioration of structures. The enabling element is the piezoelectric wafer active sensor (PWAS). This paper presents an introduction to PWAS transducers and their applications in Lamb wave-based SHM. We begin by reviewing the fundamentals of piezoelectric intelligent materials. Then, the mechanism of using PWAS transducers as Lamb wave transmitters and receivers is presented. PWAS interact with the host structure through the shear-lag model. Lamb wave mode tuning can be achieved by judicious combination of PWAS dimensions, frequency value, and Lamb mode characteristics. Finally, use of PWAS Lamb wave SHM for damage detection on plate-like aluminum structures is addressed. Examples of using PWAS phased array scanning, quantitative crack detection with array imaging, and quantitative corrosion detection are given.

Damage detection at cryogenic temperatures in composites using piezoelectric wafer active sensors

An experimental evaluation of the structural health monitoring capability of piezoelectric wafer active sensors on composite structures at cryogenic temperatures is presented. The piezoelectric wafer active sensor–based electromechanical impedance and the pitch–catch methods were first qualified for cryogenic temperatures using piezoelectric wafer active sensor–instrumented composite specimens dipped in liquid N2. Subsequently, damage detection experiments were performed on laboratory-scale composite specimens with (a) impact damage and (b) built-in Teflon patches simulating in service delaminations. Finally, a comprehensive damage detection test was performed on a full-scale specimen subjected to pressure and cryogenic temperature cycles. Based on these tests, we conclude that piezoelectric wafer active sensor–based structural health monitoring methods show promise for damage detection in composite materials even in extreme cryogenic conditions. Recommendations for further work are also included.

Predictive modeling of piezoelectric wafer active sensors interaction with high-frequency structural waves and vibration

The modeling of the interaction between piezoelectric wafer active sensors (PWAS) and structural waves and vibration is addressed. Three main issues are discussed: (a) modeling of pitch-catch ultrasonic waves between a PWAS transmitter and a PWAS receiver by comparison between exact Lamb wave solutions and various finite element method (FEM) results; (b) analytical modeling of the power and energy transduction between PWAS and ultrasonic guided waves highlighting the tuning opportunities between PWAS and the waves; (c) the use of the transfer matrix method to model the electromechanical (E/M) impedance method for direct reading of high-frequency local structural vibration and comparison with FEM results. The paper ends with a summary and conclusions followed by recommendations for further work.

Enhanced Composites Integrity Through Structural Health Monitoring

This paper discusses the topic of how the integrity of safety-critical structural composites can be enhanced by the use of structural health monitoring (SHM) techniques. The paper starts with a presentation of how the certification of flight-critical composite structures can be achieved within the framework of civil aviation safety authority requirements. Typical composites damage mechanisms, which make this process substantially different from that for metallic materials are discussed. The opportunities presented by the use of SHM techniques in future civil aircraft developments are explained. The paper then focuses on active SHM with piezoelectric wafer active sensors (PWAS). After reviewing the PWAS-based SHM options, the paper follows with a discussion of the specifics of guided wave propagation in composites and PWAS-tuning effects. The paper presents a number of experimental results for damage detection in simple flat unidirectional and quasi-isotropic composite specimens. Calibrated through holes of increasing diameter and impact damage of various energies and velocities are considered. The paper ends with conclusions and suggestions for further work.

The Finite Element Simulation of Lamb Wave Propagation in a Cracked Structure with Coupled Filed Elements

Crack detection by Piezoelectric Wafer Active Sensors (PWAS) is one of the emerging methods of Non-destructive Evaluation (NDE). These sensors can assess the health state of the structure in far filed through the analyzing the high frequency Lamb wave propagation. As PWAS is the essential part of this method, simulation and modeling of these sensors and their interaction with the host structure, strongly affect the accuracy of results. In this study, unlike the previous works, in which some certain areas of the host structure were considered as a sensor and actuator, the direct simulation of electro-mechanical interaction of the PWAS and the host structure is modeled among modeling the PWAS with a FEM coupled-field element. After verification of the FEM analysis with theoretical group velocity of S0 mode, capability of the S0 mode in crack detection was examined. Different length and angles of the crack in an aluminum plate modeled. The crack growth effect was defined among a damage index by using the strain energy magnitude that received by sensor localized behind the crack. The result showed that transmitted energy from the cracks decreases as the crack length increases. In addition, as the angle crack to the sensor increases, the ability of sensor to crack detection will increase.

Dual Mode Sensing with Low-Profile Piezoelectric Thin Wafer Sensors for Steel Bridge Crack Detection and Diagnosis

Monitoring of fatigue cracking in steel bridges is of high interest to many bridge owners and agencies. Due to the variety of deterioration sources and locations of bridge defects, there is currently no single method that can detect and address the potential sources globally. In this paper, we presented a dual mode sensing methodology integrating acoustic emission and ultrasonic wave inspection based on the use of low-profile piezoelectric wafer active sensors (PWAS). After introducing the research background and piezoelectric sensing principles, PWAS crack detection in passive acoustic emission mode is first presented. Their acoustic emission detection capability has been validated through both static and compact tension fatigue tests. With the use of coaxial cable wiring, PWAS AE signal quality has been improved. The active ultrasonic inspection is conducted by the damage index and wave imaging approach. The results in the paper show that such an integration of passive acoustic emission detection with active ultrasonic sensing is a technological leap forward from the current practice of periodic and subjective visual inspection and bridge management based primarily on history of past performance.

Non-axisymmetric Lamb wave excitation by piezoelectric wafer active sensors

A Lamb wave-based structural health monitoring system requires the exact knowledge of the dynamical behavior of piezoelectric actuators. Since piezoelectric wafer active sensors (PWASs) with a disk-wrapped electrode are used in many practical applications, a detailed description of the radiation field is essential to enhance the damage detection sensitivity. It has been shown in the literature that the radiation pattern is often directional and frequency-dependent. While a uniform radiation occurs at low excitation frequencies of several tens of kilohertz, the radiation pattern becomes strongly non-axisymmetric when the excitation frequency increases. The theoretical considerations and experimental studies in this paper show that this effect can be attributed to the influence of the complex actuator shape with disk-wrapped electrode. Therefore, simulation procedures based on an integral approach and a pin-force model are compared with experimental measurements with a laser-Doppler vibrometer (LDV).

Piezoelectric Wafer Active Sensors for Structural Health Monitoring of Composite Structures Using Tuned Guided Waves

Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive transducers that enable a large class of structural health monitoring (SHM) applications such as: (a) embedded guided wave ultrasonics, i.e., pitch-catch, pulse-echo, phased arrays; (b) high-frequency modal sensing, i.e., the electro-mechanical (E/M) impedance method; and (c) passive detection (acoustic emission and impact detection). The focus of this paper is on the challenges posed by using PWAS transducers in the composite structures as different from the metallic structures on which this methodology was initially developed. After a brief introduction, the paper reviews the PWAS-based SHM principles. It follows with a discussion of guided wave propagation in composites and PWAS tuning effects. Then, it discusses damage modes in composites. Finally, the paper presents some experimental results with damage detection in composite specimens. Hole damage and impact damage were detected using pitch-catch method with tuned guided waves being sent between a transmitter PWAS and a received PWAS. Root mean square deviation (RMSD) damage index (DI) were shown to correlate well with hole size and impact intensity. The paper ends with summary and conclusion; suggestions for further work are also presented.

Temperature variation effect compensation in impedance-based structural health monitoring using neural networks

In this article, a new method for temperature compensation on the basis of artificial neural networks (ANNs) in impedance-based structural health monitoring (ISHM) has been introduced. ISHM using piezoelectric wafer active sensors (PWAS) has been extensively developed to provide detection of fault in structure. The principle of this method is based on the electromechanical coupling effect of PWAS materials. Any change in structure leads to changes in mechanical impedance of structure. The electrical impedance of PWAS can sense this change by the electromechanical coupling effect of PWAS. Therefore, the difference in this electrical impedance for undamaged and damaged structures can be considered as a damage index to detect the damage in structure. Since physical and mechanical properties of structure also PWAS materials are temperature dependent, so this electrical impedance of PWAS will be affected by temperature changes. Consequently, the variation in environmental or service temperatures can be detected erroneously as damage in ISHM method. In this article, a new method using ANN based on radial basis function (RBF) has been proposed and developed to compensate the temperature effect on the damage index. A steel plate and gas pipe with bolted joints are considered as two case studies for the performance evaluation of the proposed fault detection methodology. Results confirm that the proposed method using the ANN can be effectively utilized to compensate temperature variation for damage detection in different structures.

Time Reversal Health Monitoring of Composite Plates using Lamb waves

In this work, the use of time reversal technique along with Lamb wave active sensing is investigated for health monitoring of composite plate structures. Piezoelectric wafer active sensors (PWAS) were used for the actuation and reception of the Lamb wave modes in the composite plates. Experiments were conducted on glass-epoxy composite plates with different lay-up sequences to study the time reversal behavior of A0 and S0 Lamb wave modes. Damage in the form of delamination was simulated by inserting a Teflon release film between the sixth and seventh layer of the glass-epoxy composite plate. The change in the shape of the broad band Gaussian pulse under time reversal in the presence of delamination was studied experimentally. Time reversal experiments were further carried out on carbon-epoxy composite t-pull specimen and the specimenwas subjected to a tensile loading in a universal testing machine. PWAS measurements were carried out for healthy and also during different stages of delamination due to tensi...

Space Application of Piezoelectric Wafer Active Sensors for Structural Health Monitoring

Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive enablers for a large class of structural health monitoring (SHM) applications. This paper presents and discusses the challenges and opportunities related to the use of PWAS in the structures specific to space applications. The challenges posed by space structures are often different from those encountered in conventional structures. After a review of PWAS principles, the paper discusses the multi-physics power and energy transduction between structurally guided waves and PWAS; predictive modeling results using a simplified analytical approach are presented. Experimental results on space-like specimen structures are presented. Survivability of PWAS transducers under cryogenic space-like conditions is experimentally verified. The paper ends with conclusions and suggestions for further work.