Piezo-impedance Transducers Research Articles

Development and evaluation of an external reusable piezo-based concrete hydration-monitoring sensor

Hydration of concrete is a very complicated and multiphase process, where the cement gel transforms into a hardened state from plastic/semiplastic phase. Proper progression of the hydration process ensures the development of targeted mechanical properties such as the elastic modulus, the coefficient of thermal expansion, the Poisson’s ratio, and finally, the characteristic strength of concrete. Concrete experiences large thermal variations during the early phase of hydration due to the heat generated during the formation of cement hydration compounds, which contributes to shrinkage and cracking, somewhat making ground for the ultimate failure in the long run. Therefore, it is utmost important to monitor the progression of hydration for enhancing performance during the curing and the early service life. This article presents a new reusable external configuration of piezo-impedance transducers to monitor the hydration process in concrete structures using the electro-mechanical impedance technique. The proposed configuration consists of a thin metal foil instrumented with piezoelectric ceramic patch at the free end with the other end of the foil embedded inside the concrete. This configuration is compared against a piezoelectric ceramic patch directly bonded on the rebar used for reinforcement and another one embedded in the concrete surrounding the rebar. The sensing capability of the proposed metal foil configuration is clearly evident from the coupled admittance signature quantitatively vis-à-vis the other configurations. As a preliminary analysis, root mean square deviation values are employed to monitor the hydration process quantitatively. A piezo-equivalent mechanical model is also developed wherein the piezo-identified mass, stiffness and damping parameters are investigated for the cement hydration process so as to chalk out rigorous quantifiers of hydration progression. The employability of the proposed configuration is further proven by explanation of the physio-chemical products developed during various stage of hydration with step-by-step explanation along with corelation of the piezo-identified mass, stiffness and damping parameters. Overall, the proposed reusable configuration carries a high potential for field deployment in concrete industry for early detection of physio-chemical changes.

Characterization of the Electromechanical Admittance Signatures of Piezo-Impedance Transducers based on its Location

Abstract The Electromechanical Impedance method (EMI), using piezoelectric ceramics transducers such as Lead-Zirconate-Titanate (PZT), has applications in the fields of non-destructive evaluation (NDE) and structural health monitoring (SHM). The piezo-ceramic transducer chip (PZT) serves as an actuator supplying vibrational energy when it is bonded to the structure and subjected to harmonic voltage at ultrasonic frequency ranges. The electrical admittance of the PZT is known to be dependent on the dynamic coupling of the mechanical impedances of the PZT and the host structure. The admittance signature obtained over a frequency range serves as a diagnostic signal to monitor structural health. Any defect or damage changes the structure’s mechanical impedance which gets reflected in the admittance signature. This paper examines the changes in the admittance signatures of the same PZT transducer when it is bonded at different locations of a thin plate with cantilever type end conditions. The study is purely numerical using the coupled-field FE simulations in ANSYSTM, yet it gives better insight into admittance signature analysis, which is essential to assessing the structural health.

Monitoring early hydration of reinforced concrete structures using structural parameters identified by piezo sensors via electromechanical impedance technique

Abstract Concrete is the most widely used material in civil engineering construction. Its life begins when the hydration process is activated after mixing the cement granulates with water. In this paper, a non-dimensional hydration parameter, obtained from piezoelectric ceramic (PZT) patches bonded to rebars embedded inside concrete, is employed to monitor the early age hydration of concrete. The non-dimensional hydration parameter is derived from the equivalent stiffness determined from the piezo-impedance transducers using the electro-mechanical impedance (EMI) technique. The focus of the study is to monitor the hydration process of cementitious materials commencing from the early hours and continue till 28 days using single non-dimensional parameter. The experimental results show that the proposed piezo-based non-dimensional hydration parameter is very effective in monitoring the early age hydration, as it has been derived from the refined structural impedance parameters, obtained by eliminating the PZT contribution, and using both the real and imaginary components of the admittance signature.

Comparison of PZT and FBG sensing technologies for debonding detection on reinforced concrete beams strengthened with external CFRP strips subjected to bending loads

The development of monitoring technologies particularly suitable to be used with novel CFRP strengthening techniques has gained great attention in recent years. However, in spite of the high performance of these advanced composite materials in the strengthening and repairing of structures in service, they are usually associated with brittle and sudden failure mainly caused by debonding phenomena, originated either at the CFRP-plate end or at the intermediate areas in the vicinity of flexural cracks in the RC beam. Thus, it is highly recommended for these structures to be monitored in order to ensure their integrity while in service. Specifically, the feasibility of smart sensing technologies such as Fiber Bragg Grating (FBG) sensors and piezo-impedance transducers (PZT) has been studied. To the knowledge of the authors, none serious study has been carried out until now concerned to the topic of damage detection due to debonding in rehabilitated structures with CFRP composites.

Diagnosis of carbonation induced corrosion initiation and progression in reinforced concrete structures using piezo-impedance transducers

In addition to chloride induced corrosion, the other commonly occurring type of rebar corrosion in reinforced concrete structures is that induced by the ingress of atmospheric carbon dioxide into concrete, commonly referred to as ‘carbonation induced corrosion’. This paper presents a new approach for detecting the onset and quantifying the level of carbonation induced rebar corrosion. The approach is based on the changes in the mechanical impedance parameters acquired using the electro-mechanical coupling of a piezoelectric lead zirconate titanate (PZT) ceramic patch bonded to the surface of the rebar. The approach is non-destructive and is demonstrated though accelerated tests on reinforced concrete specimens subjected to controlled carbon dioxide exposure for a period spanning over 230days. The equivalent stiffness parameter, extracted from the frequency response of the admittance signatures of the PZT patch, is found to increase with penetration of carbon dioxide inside the surface and the consequent carbonation, an observation that is correlated with phenolphthalein staining. After the onset of rebar corrosion, the equivalent stiffness parameter exhibited a reduction in magnitude over time, providing a clear indication of the occurrence of corrosion and the results are correlated with scanning electron microscope images and Raman spectroscopy measurements. The average rate of corrosion is determined using the equivalent mass parameter. The use of PZT ceramic transducers, therefore, provides an alternate and effective technique for diagnosis of carbonation induced rebar corrosion initiation and progression in reinforced concrete structures non-destructively.

Damage Detection for Curved Surfaces Using Advanced Piezo Impedance Transducers

In recent years, it is necessary to monitor every civil and mechanical structure for the safety of human life and property. By using PZT, monitoring of structures is possible with some limitations such as direct attachment to the host structure, structure subjected to impact from external forces, inaccessible structure, high temperature locations, and structures with complex geometry and curved surfaces. To overcome these limitations, a new technique is employed for structural health monitoring. Using the advanced technique, transducer is prepared by attaching PZT with metal connectors which is in turn attached to the monitored structure. This paper demonstrates experimental study on mild steel pipes. Different aspects of SHM are studied. The proposed technique effectively detects locations of damages and severity of damages of pipe specimen. The technique is also employed to study effect of temperature variation along with detecting progressive damage of pipe specimen when it is subjected to steady constant high temperature. This technique is applicable to high temperature locations as the temperature of PZT maintained below its Curie temperature by introducing metal connector between structure and PZT patch. For the quantification of damages, the RMSD index formula is used.

Fatigue Damage Detection Using Smart Senor

In civil engineering field, huge amount of structural health monitoring work is required throughout the service life of the structures. In pursuing an autonomous, real-time and online non-destructive evaluation (NDE) method, piezo-impedance transducer (PZT) has attracted more and more attention from researchers in recent years. Although up to now, the real application of Electro-Mechanical Impedance (EMI) method with PZT on structure health monitoring is not utilized, experiments results shows its impressive potential.

Influence of adhesive bond layer on power and energy transduction efficiency of piezo-impedance transducer

This article deals with the analysis of the power consumption in the piezoelectric ceramic patch of lead zirconate titanate and the losses arising from the adhesive bonding with the host structure. When a lead zirconate titanate patch is utilized as an impedance transducer in the electromechanical impedance technique, it acts both as a sensor and as an actuator (dual effect) for the range of frequency. Power consumption occurs in two forms. First part of the energy is used to actuate the lead zirconate titanate patch and produce deformations. The other part of the energy is dissipated within the piezo-mechanical system due to the internal mechanical loss and the associated heat generation. The determination of the power consumption characteristics for an active piezo-system is very important for designing an efficient intelligent structure with optimized mass and energy combination. Adhesive bond itself acts as an added stiffness, mass and damper and plays an important role in mechanical and electrical energy conversion. Hence, a detailed investigation is needed to characterize the power consumption and energy issues associated with bond layer driven by lead zirconate titanate patch, which is the main aim of this article.

Damage detction and characterization using EMI technique under varying axial load

Recently, researchers in the field of structural health monitoring (SHM) have been rigorously striving to replace the conventional NDE techniques with the smart material based SHM techniques, employing smart materials such as piezoelectric materials. For instance, the electromechanical impedance (EMI) technique employing piezo-impedance (lead zirconate titanate, PZT) transducer is known for its sensitivity in detecting local damage. For practical applications, various external factors such as fluctuations of temperature and loading, affecting the effectiveness of the EMI technique ought to be understood and compensated. This paper aims at investigating the damage monitoring capability of EMI technique in the presence of axial stress with fixed boundary condition. A compensation technique using effective frequency shift (EFS) by cross-correlation analysis was incorporated to compensate the effect of loading and boundary stiffening. Experimental tests were conducted by inducing damages on lab-sized aluminium beams in the presence of tensile and compressive forces. Two types of damages, crack propagation and bolts loosening were simulated. With EFS for compensation, both cross-correlation coefficient (CC) index and reduction in peak frequency were found to be efficient in characterizing damages in the presence of varying axial loading.

Piezo-impedance transducers for residual fatigue life assessment of bolted steel joints

This article presents a new approach for fatigue life assessment of bolted steel joints using the equivalent stiffness determined by surface-bonded piezo-impedance transducers. The piezo transducers acquire electromechanical admittance signatures comprising the conductance (real part) and the susceptance (imaginary part), from which the equivalent system parameters of the joint are identified. The equivalent stiffness, one of the identified parameters, is experimentally found to be related to the residual stiffness of the joint and is correlated with the remaining life of the component in terms of the cycles of loading that can be further sustained by the joint. Through tests on three prototype steel joints, empirical equations are derived to relate the residual fatigue life to the loss of equivalent identified stiffness. The most promising feature of the proposed approach is that it employs the admittance signature of the surface-bonded piezo transducers directly, thereby circumventing the determination of the in situ stiffness of the joint.

A refined shear lag model for adhesively bonded piezo-impedance transducers

The performance (sensing/actuating) of a piezotransducer highly depends upon the ability of the bond layer to transfer the stress and strain (through shear lag mechanism) between the transducer and the structure. Therefore, the coupled electromechanical response of the piezotransducer should consider the effect of dynamic behaviour, geometry and composition of the adhesive layer used to bond the transducer patch on the structure. This article presents a new refined analytical model for inclusion of the shear lag effect in modelling of adhesively bonded piezoelectric ceramic (lead zirconate titanate) patches for consideration in the electromechanical impedance technique. The previous models neglected the inertial term in shear lag formulations for simplicity. The present refined model, on the other hand, considers the inertial and the shear lag effects simultaneously, and is therefore more rigorous and complete. In this article, the formulations are first derived for one-dimensional case, and then extended to two-dimensional lead zirconate titanate–structure interaction. The overall results are found to be in better proximity to experimental observations. The refined formulations are employed for a detailed stress analysis of the bond layer. The article concludes with a parametric study on the influence of various sensor parameters on the electromechanical impedance signatures.

Fatigue Life Assessment of Structures Using Electro-Mechanical Impedance Technique

This paper describes a new experimental approach for fatigue life assessment of structures based on the equivalent stiffness determined by surface bonded piezo-impedance transducers through the electro-mechanical impedance (EMI) technique. The remaining life of the component (in terms of the cycles of loading that can be sustained) is non-dimensionally correlated with the equivalent identified stiffness. The proposed approach circumvents the determination of the absolute stiffness of the joint and employs the admittance signature of the surface-bonded piezo-transducers directly. The second part of the paper briefly describes the recent advances made in the field of impedance based structural health monitoring (SHM) in terms of low-cost hardware system and improved damage diagnosis through the integration of global dynamic and EMI techniques using the same set of piezo-sensors. Other recent applications such as bio-sensors and traffic sensors pioneered at the Smart Structures and Dynamics Laboratory (SSDL) are also briefly covered.

Effect of varying axial load under fixed boundary condition on admittance signatures of electromechanical impedance technique

In recent years, researchers in the field of structural health monitoring have been rigorously striving to replace the conventional nondestructive evaluation techniques with the smart material–based structural health monitoring techniques. These techniques possess distinct advantages over the conventional techniques, such as capable of providing autonomous, real-time, reliable, and cost-efficient monitoring. For instance, the electromechanical impedance technique employing smart piezo-impedance transducer (lead zirconate titanate) is known for its sensitivity in detecting damage. The admittance signatures of the electromechanical impedance technique for structural health monitoring are susceptible to variation in the static load applied on the host structure, which should not be ignored. This article presents a series of experimental, analytical, and numerical studies conducted to investigate the effect of varying axial load in the presence of fixed boundary condition on the admittance signatures. Theoretically, the extensional vibration is not affected by any static axial load acting in the same direction. However, it is useful in identifying the effect of stiffening caused by the boundary condition upon increase in the axial force, which contributes to the discrepancy between the experiments and the analytical models. This study suggests that the effect of boundary condition is substantial, which should be carefully considered in real-life application of the electromechanical impedance technique for structural health monitoring.

Fatigue life estimation of a 1D aluminum beam under mode-I loading using theelectromechanical impedance technique

Structures in service are often subjected to fatigue loads. Cracks would develop and lead tofailure if left unnoticed after a large number of cyclic loadings. Monitoring the process offatigue crack propagation as well as estimating the remaining useful life of a structure isthus essential to prevent catastrophe while minimizing earlier-than-required replacement.The advent of smart materials such as piezo-impedance transducers (lead zirconatetitanate, PZT) has ushered in a new era of structural health monitoring (SHM) based onnon-destructive evaluation (NDE).This paper presents a series of investigative studies to evaluate the feasibility of fatiguecrack monitoring and estimation of remaining useful life using the electromechanicalimpedance (EMI) technique employing a PZT transducer. Experimental tests wereconducted to study the ability of the EMI technique in monitoring fatigue crack in 1Dlab-sized aluminum beams. The experimental results prove that the EMI technique is verysensitive to fatigue crack propagation. A proof-of-concept semi-analytical damage model forfatigue life estimation has been developed by incorporating the linear elastic fracturemechanics (LEFM) theory into the finite element (FE) model. The prediction of the modelmatches closely with the experiment, suggesting the possibility of replacing costlyexperiments in future.

Parallel and Individual Interrogations of Piezo-Impedance Transducers for Damage Detection

Lead zirconate titanate (PZT)-based piezo-impedance transducers have been successfully used in structural health monitoring (SHM) of various engineering structures in the recent years. To effectively monitor structural health, identification of damage location is of great importance. Although a single PZT is sensitive enough to detect damage, it is insufficient to indicate the location of damage. Therefore, in this study, nine PZT transducers are surface bonded on an aluminum plate to investigate the feasibility of locating the damages induced in the plate. At each damage state, electromechanical admittance signatures of all PZT sensors are recorded and analyzed using the root mean square deviation (RMSD) index. Results show that the damage location can be estimated by the RMSD patterns obtained from both parallel and individual interrogations of PZTs.

Simplified Impedance Model for Adhesively Bonded Piezo-Impedance Transducers

The electromechanical impedance technique employs surface-bonded lead zirconate titanate piezoelectric ceramic patches as impedance transducers for structural health monitoring and nondestructive evaluation. The patches are bonded to the monitored structures using finitely thick adhesive bond layer, which introduces shear lag effect, thus invariably influencing the electromechanical admittance signatures. This paper presents a new simplified impedance model to incorporate shear lag effect into electromechanical admittance formulations, both one-dimensional and two-dimensional. This provides a closed-form analytical solution of the inverse problem, i.e. to derive the true structural impedance from the measured conductance and susceptance signatures, thus an improvement over the existing models. The influence of various parameters (associated with the bond layer) on admittance signatures is investigated using the proposed model and the results compared with existing models. The results show that the new mod...

Detection and Characterization of Fatigue Induced Damage Using Electromechanical Impedance Technique

In this paper, the feasibility of damage detection and characterization using the EMI technique on high cycles fatigue induced damage is investigated. Cyclic tensile load is applied on a lab sized aluminium beam up to failure. Piezo-impedance transducer in the form of PZT patch (lead zirconate titanate) is surface bonded on the specimen for crack detection. Progressive shift in admittance signatures measured by the PZT patch corresponding to increase of loading cycles reflects effectiveness of the EMI technique in tracing the process of fatigue damage progression.

Practical issues related to the application of the electromechanical impedancetechnique in the structural health monitoring of civil structures: II. Numericalverification

This paper, the second in a two-part series, presents various finite element simulations onthe interaction between a piezo-impedance transducer (lead zirconate titanate, PZT) and astructure, inclusive of the bonding layer, in the application of the electromechanicalimpedance (EMI) technique with varying temperature. Simulation of the PZT–structureinteraction at the high frequency range (up to 1000 kHz) using the commercially availablefinite element method (FEM) software, ANSYS version 8.1, was successfully performed.Promising results were found when compared to the experimental results. Advantages overthe conventional finite element analysis (FEA) based impedance model and the impedancebased analytical models include higher accuracy, direct acquisition of electricaladmittance/impedance, and the ability to model the PZT and the bonding layer as well asthe ambient temperature. This finite element model also successfully verified some vitalexperimental observations in part I. This study proves that the FEM could emerge asan excellent alternative to experimentation in the study of the EMI technique.

Practical issues related to the application of the electromechanical impedance technique inthe structural health monitoring of civil structures: I. Experiment

The advent of smart materials such as the piezo-impedance transducer (lead zirconatetitanate, PZT) and optical fiber (FBG) has ushered in a new era in the field ofstructural health monitoring (SHM) based on non-destructive evaluation (NDE). Sofar, successful research and investigations conducted on the electromechanicalimpedance (EMI) technique employing a piezo-impedance transducer are oftenlaboratory based and mainly theoretical. Real-life application of the technique,especially under harsh environments, has frequently been questioned. In this researchproject, investigative studies were conducted to evaluate the problems involved inreal-life applications of the EMI technique, attempting to reduce the gap betweentheory and application. This two-part paper presents a series of experimentation(part I) and numerical verification (part II) on various issues related to real-lifeapplication, including the durability of PZT transducers, and the effects of bonding andtemperature under conceivable nominal construction site conditions. The repeatability ofelectrical admittance signatures acquired from the PZT patches surface bonded onaluminum structures was found to be excellent up to a period of one and a half years.Experimental investigations revealed that the bonding thickness should preferably bethinner than one-third of the patch to avoid any adverse effect caused by the PZTpatch’s resonance on the admittance signatures which reflect the host structuralbehavior. On the other hand, the effect of temperature on the admittance signatureswas found to be closely related to the thickness of bonding, as an increase intemperature would reduce the stiffness of the bonding layer, thus affecting straintransfer. It was concluded that PZT patches with thick bonding thickness andhigh frequency of excitation are undesirable, especially at elevated temperatures.

Monitoring of rocks using smart sensors

This paper examines the feasibility of employing the new generation fibre optic and piezoelectric sensor systems for comprehensive monitoring of rocks, covering load history monitoring/retrieval as well as damage assessment. A detailed experimental study was conducted on the Bukit Timah granite rock samples obtained from a cavern site in Singapore. The rock specimens were subjected to cyclic loading and their conditions were continuously monitored using such smart sensors. Optical fibres with multiplexed fibre Bragg gratings (FBGs), surface bonded on the rock specimens, were used as strain and temperature sensors. Their performance was compared with the conventional electric strain gauges (ESGs). Piezo-electric ceramic patches made up of lead zirconate titanate (PZT) were employed as piezo-impedance transducers for detecting the onset of damages. These typically employed high frequencies of the order of kHz to extract impedance information of the specimens. Typically, the piezo-impedance transducers detected cracks even before they reached macroscopic dimensions. The results of this experimental study demonstrate the superior performance and cost-effectiveness of the new generation smart technologies as compared to the conventional sensor systems for monitoring rock-structures such as caverns and tunnels.