Electromechanical Impedance Model Research Articles

Research on the influence of an adhesive layer on the monitoring signal of piezoelectric sensors

Electromechanical impedance (EMI) technology, as one of the important methods for analyzing and studying the interaction between sensors and structures, has the characteristics of clear physical meaning and high computational efficiency. However, for complex structures, it is difficult to quantitatively combine the measured impedance signal with the physical parameters of the tested structure. Therefore, establishing an appropriate EMI model is crucial to facilitate the quantitative analysis of structural health monitoring. The impedance models developed so far assume perfect adhesion between PZT and the structure, with displacement compatibility, and ignore the shear lag effect of the adhesive layer. Therefore, this research focuses on analyzing how surface-bonded PZT couples with the structure through the adhesives and conducting a shear layer analysis on two-dimensional (2-D) circular PZT to derive a closed-form solution for shear lag distribution. The shear lag effect is integrated into the 2D impedance formula. The influence of the adhesive layer on bolt loosening monitoring is studied, and it is proven that the modified EMI model can effectively predict the shear lag effect of the adhesive layer. The result of relative error analysis proves that conventional adhesive PZT also exhibits the shear lag phenomenon. The influence of different thicknesses of adhesive layers on sensor sensitivity is studied. The experimental results show that as the thickness of the adhesive layer decreases, the monitoring sensitivity of the sensor increases. Moreover, for slight bolt loosening, the thickness of the adhesive layer can affect the monitoring frequency.

Electro-mechanical impedance technique for concrete strength monitoring: Three-dimensional model development and experimental verification

During the application of the electro-mechanical impedance (EMI) technique for detecting the strength development of concrete, in some cases, the piezoelectric sensor is embedded in the concrete. Normally, there are two methods to embed the piezoelectric sensor: PS-EMI and CPS-EMI. For both methods, the observed resonance frequency of the piezoelectric sensor increases with the increase of the concrete strength. However, there is a contradiction in the trend of conductance amplitude at the resonance frequency, which has to an extent puzzled the researchers in this area. In this paper, we developed a three-dimensional EMI model for the embedded piezoelectric sensor. We discussed the underlying mechanism, which induces the conductance spectrum difference for the PS-EMI and CPS-EMI, and experimental verification was carried out. By plotting the evolution of the concrete strength as a function of the resonance frequency shift, it was found that both embedding methods can be used in practical applications.

Early-age concrete strength monitoring using smart aggregate based on electromechanical impedance and machine learning

It is crucial to monitor the real-time strength development of early-age concrete, which is related to the structure safety and construction efficiency of concrete. This paper proposed a new method to predict and monitor concrete strength development. The basic idea is using embedded smart aggregates (SAs), combining the electromechanical impedance (EMI) technology and machine learning to monitor the strength development of early-age concrete. An EMI model of the embedded SA was firstly established and the relationship between the conductance resonant frequency (CRF) and conductance resonant peak (CRP) of the SA and the development of concrete strength was investigated. The conductance signatures were continuously monitored and the compressive strength of the specimens at different ages was tested. Hence, the EMI model results that the CRF decreases but CRP increases as the compressive strength of concrete increases were verified by analyzing the collected data. The four different models of a linear regression model (LR), a convolutional neural network (CNN), a hybrid (LR-CNN) model, and an empirical equation were established. The conductance of SAs as the developed models inputs, the compressive strength of specimens as outputs. Finally, these four models were compared with each other. Meanwhile, the performance indicators of the LR-CNN model and other hybrid models were compared. The results show that the LR-CNN model has excellent performance and successfully achieves quantitative prediction of concrete strength development. The proposed method for evaluating and predicting the compressive strength of concrete is simple, accurate, quantitative and reliable, and has promising application.

Optimum PZT Patch Size for Corrosion Detection in Reinforced Concrete Using the Electromechanical Impedance Technique.

This paper proposes the use of a 1-dimensional (1-D) electromechanical impedance model to extract proper design guidelines when selecting patch-size and frequency range for corrosion detection in reinforced concrete structures using the electromechanical impedance (EMI) technique. The theoretical results show that the sensitivity mainly lies in the peak frequencies of the impedance spectrum, while outside resonant frequencies the sensitivity levels are low, and are prone to natural variation. If the mechanical impedance ratio between the host structure and patch is too large, the peaks and thereby the sensitivity decreases. This can be counteracted by increasing the patch thickness. Tests were carried out in reinforced concrete structures, where lead zirconate titanate (PZT) patches were attached to the rebars. Patches measuring 10 × 10 mm in length and width, with thicknesses of 0.3, 0.5 and 1.5 mm, were used. The results show that only the 10 × 10 × 1.5 mm patch, was able to generate a clear peak in the 50 kHz to 400 kHz impedance spectrum. Furthermore, a reinforced concrete structure with the 1.5 mm patch attached was induced significant corrosion damages, resulting in cracking of the structure. Due to this, a leftward shift of the main peak, and creation of new peaks in the spectrum was observed.

Aging of Solid Propellants Investigated by Electromechanical Impedance Technique

Aging induced changes in the mechanical properties of solid propellant can lead to defects, such as cracks and grain–liner separations, which limit the service lifetime of solid rocket motors. This Paper presents an active sensing in situ identification method based on the electromechanical impedance technique, which is particularly suited for monitoring aging of solid propellants. This Paper first instructs a one-dimensional viscoelastic electromechanical coupling impedance model. A relationship between the dynamic modulus of solid propellants and its mechanical impedance is established. Then numerical calculation and experimental verification of the viscoelastic impedance model are conducted. Experimental research on aging monitoring of real solid propellant rocket and thermal accelerated aging hydroxyl-terminated polybutadiene solid propellant specimens are carried out. The results show that the real part of mechanical impedance curves decreases with the increase of aging time of solid propellants, and there is an approximate exponential relationship model between the peak value of real part of mechanical impedance and thermal accelerated aging time. It can be seen that the electromechanical impedance technique is an innovative method which can effectively characterize in situ the dynamic modulus of solid propellants, monitor the aging of solid propellants, and construct the aging life prediction model.

Electromechanical Impedance Model for Free 1D Thin-Walled Piezoelectric Ceramics with a Novel Derivation.

The electromechanical impedance model of the piezoelectric ceramics in a free state can be used for screening and quality control in the structural health monitoring community, but the derivation process of the existing model is usually complicated. This paper describes a novel theoretical derivation methodology based on the assumption of zero-stress on the free boundary of the one-dimensional transducer, which can simplify the derivation of the model to a large extent. To assess the accuracy of the model, a signal processing method based on frequency shifting transformation and the Pearson correlation coefficient is also proposed to calculate the similarity between theoretically predicted and experimentally measured data. Two different piezoelectric ceramics were used in experiments to verify the effectiveness of the model. Experimental results convincingly demonstrate that the assumption proposed in this paper possesses good feasibility for one-dimensional thin-walled piezoelectric ceramics and the model has excellent precision.

Detection of post-earthquake damage inside a concrete arch dam using the electromechanical impedance method

The detection of post-earthquake damage inside concrete dams has recently attracted great interest in academia and industry. A novel electromechanical impedance (EMI) method using embedded EMI sensors (EMISs) is proposed in this paper to detect earthquake-induced damage within concrete dams. The basic concept of the proposed EMI method is to use high-frequency excitations to monitor local changes in the monitored dams caused by damage. Based on the effective impedance, a three-dimensional (3D) EMI model for embedded EMISs is proposed. Then, a new damage-sensitive feature factor is derived based on the proposed 3D EMI model. A high arch dam model with embedded EMISs is studied experimentally. Moreover, shaking table tests are conducted on the dam model. The proposed 3D EMI method is used to monitor the evolution of earthquake-induced damage inside the dam model. The experimental results demonstrate the efficiency and feasibility of the proposed EMI method for detecting earthquake-induced damage in concrete dams.

Electro-mechanical impedance model of a laminated rectangular plate with imperfect interfaces

A laminated orthotropic rectangular plate surface-bonded or embedded with a piezoelectric actuator/sensor is investigated based on the state-space approach. A linear spring-like model is utilized to simulate the interfacial imperfections. Besides, to establish the global transfer relations between the elastic variables of the elastic layers and the piezoelectric films, a matrix reduction technique is employed. Then, an analytical expression of electro-mechanical impedance, which contains the information of the interfacial bonding, is derived based on the three-dimensional theory of elasticity (or piezoelasticity). Numerical results show that the signals extracted from the present electro-mechanical impedance model can detect the interfacial conditions of laminates, and hence, the present analysis provides an efficient and convenient approach to monitor the interfacial defects in the laminated structures.

Monitoring of Fiber-Reinforced Composite Single-Lap Joint with Electromechanical Impedance of Piezoelectric Transducer.

The single-lap joint of fiber-reinforced composites is a common structure in the field of structure repair, which has excellent mechanical properties. To study and monitor its quasi-static response behavior under external load, two methodologies called effective structural mechanical impedance (ESMI) and reduced-ESMI (R-ESMI) are presented in this article. A two-dimensional electromechanical impedance (EMI) model for a surface-bonded square piezoelectric transducer (PZT) is adopted to extract more sensitive signatures from the measured raw signatures. There are two major advantages of the monitoring scheme based on ESMI and R-ESMI signatures: (1) excellent monitoring results with less signatures to process, (2) the ability to monitor the quasi-static behavior of a single-lap joint with previously ignored susceptance signatures. Combining the extracted ESMI signatures with the index of root-mean-square deviation, the quasi-static behavior of single-lap joints can be effectively quantified. To test the effectiveness of ESMI methodology, verifying experiments were conducted. The experimental results convincingly demonstrated that the presented ESMI and R-ESMI methodologies have good feasibility in monitoring the quasi-static behavior of a fiber-reinforced composite single-lap joint. The proposed method has potential application in the field of structural health monitoring (SHM).

A novel electromechanical impedance model for surface-bonded circular piezoelectric transducer

The electromechanical impedance (EMI) technique is one of common used methods for damage diagnosis. However, the mechanism of EMI-based damage diagnosing is usually complicated and difficult to be comprehensively described. To solve this problem to a certain extent, a novel EMI model for describing the interaction between piezoelectric transducer (PZT) and host structure is developed in this paper. The developed EMI model has advantages of simplicity in formula and excellent precision in signatures prediction. An efficaciously equivalent SMD (Spring-Mass-Damping) system is adopted to obtain the local structural mechanical impedance (LSMI) and to calculate the equivalent parameters ( ) in the vicinity of PZT. To verify the effectiveness of the novel model, a series of experiments are separately conducted on the specimen under healthy condition and damage condition. Through comparing the predicted curves with the experimental ones, the effectiveness of the developed model is demonstrated when used for predicting signatures, especially for resistance signatures. The developed EMI model has shown the potential application in the field of structural health monitoring and damage diagnosis.

Preload Monitoring in Bolted Connection Using Piezoelectric-Based Smart Interface.

In this study, a preload monitoring method using impedance signatures obtained from a piezoelectric-based smart interface is presented for bolted girder connections. Firstly, the background theory of the piezoelectric-based smart interface and its implementation into the health monitoring of bolted connections are outlined. A simplified electro-mechanical (EM) impedance model of a smart interface-embedded bolted connection system is formulated to interpret a mechanistic understanding of the EM impedance signatures under the effect of bolt preload. Secondly, finite element modeling of a bolted connection is carried out to show the numerical feasibility of the presented method, and to predetermine the sensitive frequency band of the impedance signatures. Finally, impedance measurements are conducted on a lab-scaled bolted girder connection, to verify the predetermined sensitive frequency range and to assess the bolt preload changes in the test structure.

A Novel Fractal Contact-Electromechanical Impedance Model for Quantitative Monitoring of Bolted Joint Looseness

Bolted joint are among the key components that enable the robust assembly of a wide variety of structures. However, due to wear and tear over time, bolted joint may loosen, and if not detected in its early stages, can lead to devastating results. A monitoring method that can detect bolted joint looseness prior to bolt failure will be essential for the continued operation of the host structure and depending on the situation, the safety of the occupants. Prior research has proven the electromechanical impedance method (EMI) to be an effective technique for detecting the loosening of bolted joints, however, EMI-based methods until now are focused on qualitative health monitoring, which can only provide limited information about the damage. Thus, this paper attempts to quantify EMI based methods through the integration of fractal contact theory, the result of which is a novel electromechanical impedance model for quantitative monitoring of bolted looseness. The method determines the effective impedance of the bolted joint and is applied to develop the relationship between the electrical impedance of a piezoceramic patch installed on the joint and the mechanical impedance of the bolted joint. The mechanical impedance of the bolted joint under various preloads is computed by using the fractal contact theory. Then, the bolted looseness can be monitored quantitatively. At last, a set of verification tests under different applied preload of bolted joint are conducted to verify the validity of the proposed model in this paper.

Crack detection in pipelines using multiple electromechanical impedance sensors

An extensive network of pipeline systems is used to transport and distribute national energy resources that heavily influence a nation’s economy. Therefore, the structural integrity of these pipeline systems must be monitored and maintained. However, structural damage detection remains a challenge in pipeline engineering. To this end, this study developed a modified electromechanical impedance (EMI) technique for crack detection that involves fusing information from multiple sensors. We derived a new damage-sensitive feature factor based on a pipeline EMI model that considers the influence of the bonding layer between the EMI sensors and pipeline. We experimentally validated the effectiveness of the proposed method. Finally, we used a damage index—root mean square deviation—to examine the degree and position of crack damage in a pipeline.

A new three-dimensional electromechanical impedance model for an embedded dual-PZT transducer

In the past twenty years, the electromechanical (EM) impedance technique has been investigated extensively in the mechanical, aviation and civil engineering fields. Many different EM impedance models have been proposed to characterize the interaction between the surface-bonded PZT transducer and the host structure. This paper formulates a new three-dimensional EM impedance model characterizing the interaction between an embedded circle dual-PZT transducer and the host structure based on the effective impedance concept. The proposed model is validated by experimental results from a group of smart cement cubes, in which three circle dual-PZT transducers are embedded respectively. In addition, a new EM impedance measuring method for the dual-PZT transducer is also introduced. In the measuring method, only a common signal generator and an oscilloscope are needed, by which the exciting and receiving voltage signals are obtained respectively. Combined with fast Fourier transform the EM impedance signatures of the dual-PZT transducers are obtained.

Sensitivity of embedded active PZT sensor for concrete structural impact damage detection

Lead zirconate titanate (PZT) actuator/sensor is generally surface-bonded to structure in the electromechanical impedance (EMI) technique for structural health monitoring. However, in consideration of fragility and fugitiveness of surface-bonded PZT patch, it may lose serviceability when external impact happens especially in real-life applications. This paper covered the sensitivity of a new kind of embedded active PZT sensor in structural impact damage detection through theoretical and experimental analysis. Firstly, a new embedded 2D electromechanical impedance model was formulated, in which the PZT patch can be protected from external impact or disturbance. The proposed model was verified by experimental result of testing a manufactured embedded PZT sensor. Then the embedded PZT sensors were qualitatively compared with surface-bonded ones in the experiment of detecting a concrete beam which was damaged by successively knocking off concrete covers. Finally, the effectiveness of embedded PZT sensor in quantification on structural damage was investigated by using slope-based root mean square deviation (RMSD) index. Moreover, a new baseline-changeable RMSD index was also proposed to evaluate the impact effect for the two types of PZT sensor. It was found that the embedded PZT sensor can effectively filter out the impact effect in structural damage indication and quantification, which benefits the accurate evaluation on structural damage.

A Parametric Study on Admittance Signatures of a PZT Transducer Under Free Vibration

Piezoelectric material is proven to be a versatile collocated sensor and actuator. Its specific application includes electromechanical impedance (EMI)-based structural health monitoring (SHM). To date, several EMI models are available in the literature but parametric studies are scarcely available. This study aims at providing a parametric study on selected models, considering a freely vibrating piezoelectric transducer. The effect of varying mechanical and electrical parameters of the transducer on the admittance signatures was investigated. The theoretical results were compared against the experiments. Accuracy of the model was successfully refined upon model updating.

Debonding detection of FRP strengthened concrete beams by using impedance measurements and an ensemble PSO adaptive spectral model

An impedance-based midspan debonding identification method for RC beams strengthened with FRP strips is presented in this paper using piezoelectric ceramic (PZT) sensor–actuators. To reach this purpose, firstly, a two-dimensional electromechanical impedance model is proposed to predict the electrical admittance of the PZT transducer bonded to the FRP strips of an RC beam. Considering the impedance is measured in high frequencies, a spectral element model of the bonded-PZT–FRP strengthened beam is developed. This model, in conjunction with experimental measurements of PZT transducers, is used to present an updating methodology to quantitatively detect interfacial debonding of these kinds of structures. To improve the performance and accuracy of the detection algorithm in a challenging problem such as ours, the structural health monitoring approach is solved with an ensemble process based on particle of swarm. An adaptive mesh scheme has also been developed to increase the reliability in locating the area in which debonding initiates. Predictions carried out with experimental results have showed the effectiveness and potential of the proposed method to detect prematurely at its earliest stages a critical failure mode such as that due to midspan debonding of the FRP strip.

Embedded 3D electromechanical impedance model for strength monitoring of concrete using a PZT transducer

The electromechanical (EM) impedance approach in which piezoelectric ceramics (PZT) simultaneously act as both a sensor and an actuator due to their direct and inverse piezoelectric effects has emerged as a powerful tool for structural health monitoring in recent years. This paper formulates a new 3D electromechanical impedance model that characterizes the interaction between an embedded square PZT transducer and the host structure based on the effective impedance. The proposed formulations can be conveniently used to extract the mechanical impedance of the host structure from the electromechanical admittance measurements of an embedded PZT patch. The proposed model is verified by experimental and numerical results from a smart concrete cube in which a square PZT transducer is embedded. Subsequently, this paper also presents a new methodology to monitor the compressive strength of concrete based on the effective mechanical impedance. By extracting the effective mechanical impedances from the electromechanical admittance signatures, measuring the compressive strength of the concrete cubes at different ages and combining these measurements with the index of the correlation coefficient (CC), a linear correlation between the concrete strength gain and the CC of the real mechanical admittances was found. The proposed approach is found to be feasible to monitor the compressive strength of concrete by age.

Damage Detection in a Cracked Rod Using High-Frequency Electro-Mechanical Impedance Signatures

Electro-mechanical impedance (EMI) analysis is conducted in the paper for a one-dimensional rod. Two identical PZT patches bonded symmetrically onto the top and bottom surfaces of the rod are activated in phase and hence a pure axial excitation is created. Based on the finite element software ANSYS, an electro-mechanical impedance (EMI) model for the coupled structural system consisting of the host rod, bonding layer and the piezoelectric patches is established for structural health monitoring. A comparison study with the mode superposition method usually employed in the conventional EMI model is implemented to validate the effectivity and accuracy of the proposed EMI model. Finally, the numerical results indicate that the cracks appearing in the structures can be detected by using the proposed analysis.

Finite Element EMI Model for Cracked Portal Frame and Parameter Study

Based on the three-dimensional finite element method (3D FEM), an electro-mechanical impedance (EMI) model is established for a cracked portal frame. In this analysis, the effect of the interfacial properties between the piezoelectric patches and the host structure on the EMI signatures is considered and thus a coupled structural system consisting of PZT patches, bonding layer and host structure is then investigated. Comparison with numerical results by other methods is made to validate the effectivity and accuracy of the proposed EMI model. The effects of various parameters including the material properties of the adhesive, the crack depth and the crack position etc. on the EMI signatures are highlighted. Numerical results indicate that the present model can be employed for structural damage detection.