Electromechanical Impedance Technique Research Articles

Pipeline corrosion assessment using piezo-sensors in reusable non-bonded configuration

In this paper, a piezoelectric sensor is used in its non-bonded configuration for non-destructive evaluation of a pipeline segment subjected to progressive corrosion damage. A new non-bonded sensor configuration, specially adapted for small diameter pipelines, known as modified non-bonded sensor (MNS), is proposed and evaluated. The new sensor configuration is evaluated for sensitivity in monitoring corrosion induced damage in pipeline segments in controlled laboratory setup through accelerated corrosion tests. The conventional surface-bonded piezo-sensor (SBPS) configuration is used as standard for comparison. Signature analysis using different methods is carried out in the study. Using the principles of the electro-mechanical impedance (EMI) technique, equivalent stiffness, damping and mass parameters are computed from the admittance signatures of both the configurations (MNS & SBPS) and compared. Experimental results show that piezo based a non-dimensional mass parameter from the MNS measurements are very effective in damage detection and quantification. The results are correlated with actual mass loss measurements and consequent corrosion rates are calibrated. The results clearly make case for practical usage of MNS configuration in corrosion detection and health monitoring of pipeline systems. The new MNS configuration proves to be a successful alternative to the conventional bonded piezo configuration.

Smart materials and electro-mechanical impedance technique: A review

Smart materials are catalyzed by a technological revolution that will explode several emerging technologies viz., material science, neural network, artificial intelligence, nanotechnology and biotechnology etc. These smart materials are now used in aerospace, mechanical and civil industries for the development and monitoring. The several types of smart materials are available such as PZT patches, optical fibers, piezo-polymers, shape memory alloys, magnetostrictive, shape memory polymers, bi-component fibers, self-healing materials and electro-rheological fluid, respectively. The Electro-Mechanical Impedance (EMI) technique is a local technique, which is based on smart materials. EMI technique is applied in the different fields of engineering to evaluate several parameters of the materials or structures. Moreover, this technique is used to measure cracks in steel as well as in concrete, corrosion of reinforcement, loosening of the bolt, strength gain, hydration of cement and debonding phenomenon etc. The conductance and susceptance signature is used for the determination of the presence of damage. The change in conductance signature from the baseline signature indicates the presence of damage/crack in the materials or structures. The review paper is focused on smart materials and their compatibility related to structures. The formulations concerning the EMI technique for the measure of structural impedance and electro-mechanical admittance were also considered. Furthermore, the smart materials based EMI technique and their appropriateness have been covered. Therefore, the application of smart materials in the field of engineering and industries is to provide new research directions.

Sustainable concrete construction by microorganism and monitoring using EMI technique: A review

Construction of concrete infrastructures is developing worldwide from the ancient period therefore; sustainable concrete is required for clean environment reason. The formation of cracks/fissures creates problems to the concrete which reduces durability of concrete structures. These cracks/fissures in concrete originate due to the natural forces viz., weathering and landslide, seismic, flooding and human interventions which affect the service life of structures. The application of microorganisms in concrete is the innovative technology for sustainable construction and self-healing of cracks. These microorganisms' bacterium produces calcium carbonate in presence of moisture and carbon dioxide. The use of bacteria in concrete consumes carbon dioxide available in the atmosphere and produces solid substances like calcium carbonate for self-healing of the cracks and develop sustainable infrastructure. Electro-Mechanical Impedance (EMI) technique is based on smart materials and used for monitoring of crack/fissures present in structures. The impedance and admittance signatures can be used for determination of the presence of damage. Admittance signature consists of conductance (real part) and susceptance (imaginary part) signature, respectively. The changes in the signature from the healthy state baseline signature indicate presence of damage in structures. The research review article is focused on microbial-based concrete and its importance related to the clean environment and sustainable construction development. Furthermore, the types of bacteria used in concrete and its optimal concentration have been covered. Moreover, the EMI technique and its application on concrete industry for monitoring the health of structures have been taken into consideration. The use of EMI technique to monitor the performance of bacterial concrete will be helpful for sustainable buildings. The review article will suggest new research directions in the field of sustainable construction industry.

Structural Health Monitoring of Timber Using Electromechanical Impedance (EMI) Technique

Nowadays, the electromechanical impedance method has been widely used in the field of structural healthy monitoring, especially for the concrete and steel materials. However, the electromechanical impedance studies on damage detection for timber are limited due to the anisotropic and ununiform biomaterial properties. As a low‐cost and environment‐friendly building material, timber has been widely used in the construction. Thus, it is beneficial to develop electromechanical impedance technique for structural healthy monitoring of timber so as to ensure the stability and safety of the entire timber structures. In this paper, two damage factors, i.e., the damage location factor and the damage size factor of timber specimens are investigated by using the electromechanical impedance method. The method is implemented by using a patch of Lead Zirconate Titanate transducer both as an actuator to generate stress waves and a sensor to detect stress waves after propagating across the timber specimens. Then, the damage index‐root mean square deviation is employed to evaluate the damage severity of the timber specimens. The results indicate that the damage index changes consistently with the change of damage location and size factors, and the proposed method using electromechanical impedance technique can efficiently estimate the damage and its severity.

EMI Technique for Monitoring the Damage Evolution of Initial Damaged Tunnel Invert Concrete Subjected to High Traffic Cyclic Loading

The electromechanical impedance (EMI) technique based on the PZT transducer, in the past twenty years of research progress, has demonstrated its potential for cost‐effective and high damage‐sensitive structural health monitoring. This paper presents an application of EMI technique for damage evolution investigation of initial damaged tunnel invert concrete under high traffic cyclic loading. In the tests, six different levels of initial damage inside the specimens, as the influencing factor, were firstly created by applying a certain number of impacts with a free‐falling iron ball. Then, these specimens were applied typical mechanical boundaries similar to that of tunnel invert concrete by an installation specially designed. Finally, the traffic cyclic loading carefully determined was exerted by the MTS815 hydraulic zero‐control testing system, to investigate the evolution characteristic of piezoelectric signature of the PZT sensor. The experimental result shows that the conductance signature follows a consistent rightward shifting with the number of cycles increasing, and the larger the initial damage of the specimen, the more obvious the rightward shifting. It indicates that, in general, the traffic cyclic loading is not large enough to make the microcracks propagate to fatigue failure in tunnel invert concrete even if there is a large initial damage. On the contrary, with special mechanical boundaries, the local nominal stiffness of tunnel invert concrete will gradually increase. This phenomenon may be interpreted as an effect of generalized damage recovery. A new damage index, with values between 0 and 1, was then defined to quantify the damage level for quantitative analysis. It was found that the damage recovery behaviors for different initial damaged specimens can be well and uniformly described by an empirical expression, which may be helpful for the damage assessment of tunnel invert concrete under high traffic cyclic loading in the future.

An improved impedance-based damage classification using Self-Organizing Maps

The identification and severity of structural damages, especially in the early stage, is critical in structural health monitoring (SHM) systems. Among several approaches used to accomplish this goal, the electromechanical impedance (EMI) technique has taken place within non-destructive evaluation (NDE) methods. On the other hand, neural networks (NN) based on self-organizing maps (SOM) has been a promising tool in many engineering classification problems. However, there is a gap of application regarding the combination of the EMI technique and SOM NN. To encourage this, an enhanced EMI-based damage classification method using self-organizing features is proposed in the present research paper. A SOM NN architecture was implemented whose inputs were derived from representative features of the impedance signatures. As a result, self-organizing maps can be used as an effective tool to enhance the damage classification in EMI-based SHM applications. For the present application, the results indicated a promising and useful contribution to the grinding field.

A novel method for diagnosing defective PZT-Substrate bonding in electromechanical (EM) impedance technique

Surface mounted PZT (Lead Zirconate Titanate) patches are extensively used to monitor the localized and distributed damage in concrete structures in recent times. To avoid the misinterpretation of damage in the real structures the development of reliable techniques for detection and detailing of de bonding is necessary. In this study the electro mechanical impedance method is employed to detect the partial de bonding of surface mounted PZT patch. The effect of defective bonding of PZT patch on electrical impedance (EI) response spectrum investigated by combining experimental and numerical approaches. The investigation is carried out in two steps. In the first step, the experiments are carried with surface mounted PZT patches attached to the concrete substrate in perfectly bonded condition and 10% de bonded condition and the EI response spectrum is extracted in both perfectly bonded and partially de bonded conditions. The influence of finite size of substrate is eliminated from EI response spectrum to identify the influence of de bonding alone on EI response spectrum. In the second step, a numerical model is developed for a PZT patch attached to a concrete substrate using COMSOL Multiphysics. The developed numerical model is then calibrated using experimental studies, surface mounted PZT patches with different de bonding percentages are studied and their influence on the electromechanical impedance response of the bonded PZT is explored using the calibrated numerical model. The current study proposes a new effective method for diagnosing defective PZT-substrate bonding in surface mounted PZT patches attached to concrete substrate.

Electromechanical impedance (EMI) measurements to infer features from the grinding process

This paper discusses the correlations between the electromechanical impedance (EMI) technique and grinding parameters. The EMI technique applied in grinding is novel and has the advantage of employing cheaper equipment and requiring a simpler monitoring system when compared to traditional techniques, such as acoustic emission. Experimental tests were conducted in a controlled environment to isolate the variables of interest, and real and imaginary parts of the impedance were investigated for several frequency bands. Strong correlations among EMI and equivalent chip thickness, roughness, and microhardness of the workpiece, as well as power signals, were found. The RMSD (root-mean-square deviation) index for the real part of the signature in the band 80–85 kHz showed good correlation with roughness and power, while the CCDM (correlation coefficient deviation metric) index for the imaginary part of 50–55 kHz showed good correlation with microhardness. Those correlations allow the user to infer information about the grinding process through indirect monitoring.

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.

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.

Piezoelectric Impedance-Based Non-Destructive Testing Method for Possible Identification of Composite Debonding Depth.

Detecting the depth and size of debonding in composite structures is essential for assessing structural safety as it can weaken the structure possibly leading to a failure. As composite materials are used in various fields up to date including aircrafts and bridges, inspections are carried out to maintain structural integrity. Although many inspection methods exist for detection damage of composites, most of the techniques require trained experts or a large equipment that can be time consuming. In this study, the possibility of using the piezoelectric material-based non-destructive method known as the electromechanical impedance (EMI) technique is used to identify the depth of debonding damage of glass epoxy laminates. Laminates with various thicknesses were prepared and tested to seek for the possibility of using the EMI technique for identifying the depth of debonding. Results show promising outcome for bringing the EMI technique a step closer for commercialization.

Depolarization diagnosis of PWAS used for EMI based structural health monitoring system for composite plates

Implementation of Electromechanical Impedance (EMI) as a technique to carry out Structural Health Monitoring (SHM) has been proved to be such effective tool in the last two decades, especially for structures made of composite material. EMI technique is the revolutionary evolution of the conventional Vibrational Based Damage Identification (VBDI) techniques. Unlike VBDI techniques, EMI technique has the privilege of employment tinny permanent piece of equipment which is known as Piezoelectric Wafer Active Sensor (PWAS). Although it has such advantage, it brings the necessity of continuous and robust diagnosis process of the PWAS used in the SHM system to ensure that output signals are caused by real variation of the modal parameters for the host structure rather than being occurred due to degradation and-or physical damage of the PWAS system itself. The study presented in this paper is focused on the self-diagnosis of PWAS used to carry out SHM via implementation of EMI technique. The main concern of this research is to study the ability of EMI technique to determine depolarization of PWAS and its influence on the performance of EMI based SHM system employed for structures made of composite plates. The used specimen (s) is / are underwent controlled excitation over desired frequency range, the imaginary part of admittance is plotted over desired frequency range. The whole process is then repeated for different levels of depolarization for the same specimen (s). The modeling process is carried out using a finite element commercial package, ANSYS v.15.0 in which multi-physics-based modeling can be used for such coupling field of piezoelectricity. MATLAB code is written to process the output data received from numerical simulations into counterpart spectrum and to calculate the statistical damage index Root Mean Square deviation (RMSD) that is used in damage detection. The calculated RMSD found to be non-zero values, which means false prediction. These results shows how important to have self-diagnosis for PAWS used in SHM system for further reliable measurements and data interrogation using EMI technique.

Shape memory alloy actuation of non-bonded piezo sensor configuration for bone diagnosis and impedance based analysis.

In the recent years, there has been a growing interest in research community towards the application of smart materials for bio-medical structural health monitoring. Amongst the smart materials, directly bonded piezo sensors (DBPS), based on the electro-mechanical impedance (EMI) technique, have been successfully employed for the above purpose. The principle behind the EMI technique is that high frequency excitations (typically > 30kHz) generated by a surface bonded PZT patch are used to detect changes in structural drive point impedance caused by cracks or any other type of damage. Bone healing and damage have been shown to be successfully monitored using the DBPS. However, in most of the diagnostic cases of live human and animal subjects, directly bonding a PZT patch is always an irritant or hazard for a live subject. To circumvent direct bonding, the authors have developed and experimentally demonstrated a non-bonded piezo sensor (NBPS) configuration as a good alternative to DBPS while maintaining the effectiveness of measurement well within discernible limits. This paper presents further improvement in the NBPS configuration aiming at autonomous operation of the gripping mechanism using shape memory alloy (SMA) wires. The experiments are performed on replicas of femur bone in healthy and osteoporosis state. This paper shows the effective use of SMA clamping for bone identification and its damage assessment in comparison to earlier mechanical gripping using jubilee clamps. This paper also covers impedance based identification applied to SMA and clamp based NBPS configurations. In place of raw admittance signatures, effective drive point impedance is utilized for the purpose of bone diagnostics which provides a more realistic assessment of the condition of bone.

Toward Creating a Portable Impedance-Based Nondestructive Testing Method for Debonding Damage Detection of Composite Structures

Debonding detection of composite structures is a vital task as such damage weakens the structure leading to a failure. As adhesive bonding is a more preferable choice over the conventional mechanical fastening method, detecting debonding as early as possible could minimize the overall maintenance costs. For this reason, a vast amount of research in the nondestructive testing field is being conducted as we speak. However, most of the methods may require well-trained experts or heavy equipment. In this study, the piezoelectric (PZT) material-based method known as the electromechanical impedance technique is investigated to seek the possibility of making the technique very cheap and portable by temporarily attaching the sensor. Furthermore, ANSYS simulation studies using smaller PZT patches as small as 0.1 mm × 0.1 mm are simulated to investigate the impedance signatures acquired from the simulations. The results show the possibility of using smaller PZT patches compared to the conventional PZT sizes of 10 mm × 10 mm for a successful damage identification process.

Instantaneous monitoring the early age properties of cementitious materials using PZT-based electromechanical impedance (EMI) technique

The use of piezoelectric materials based Electromechanical Impedance (EMI) technique for monitoring the hydration of cementitious materials has caught much attention recently. However, very few literatures have explored the feasibility of using this method on monitoring the stiffness development and compressive strength gain at the very early age properties (4th–8th h) of cementitious materials. This research serves as a comprehensive study to verify the reliability of using lead zirconate titanate (PZT) based EMI method in monitoring the compressive strength gain and elastic modulus of mortar at both very early age (4th–8th h) and early age (1st, 3rd, and 7th day). Extensive experiments and data analysis have been done on ten different mixes with various water-to-cement ratio and Type I & III cement. The EMI signatures are measured for each sample at the period of interest, and post-processed with three statistic model including the root mean square deviation (RMSD), correlation coefficient deviation (CCD), and mean absolute percentage deviation (MAPD) as indices. To examine the correlation and linearity between the compressive strength/elastic modulus obtained via conventional cubic testing using ASTM C109 and the EMI indices, a linear least square regression analysis is performed. As the authors postulated, all the mixes display a good linear correlation of R2. Among all three statistical indices, RMSD index is proved as the most accurate statistical index on strength gain monitoring of cementitious materials. The results indicated the feasibility of using piezoelectric-based EMI method for monitoring the cementitious material’s strength gain at very early age, regardless the concrete mix design.

History data free piezoelectric based non-destructive testing technique for debonding detection of composite structures

In this study, a possibility of detecting debonding of composite structures without an onsite reference signature is presented. The approach is based on the electromechanical impedance (EMI) technique which can be created into a compact system, light and reliable enough to be equipped even onto an unmanned aerial vehicle (UAV). To make this idea possible, the piezoelectric (PZT) materials was modified to be able to attach and re-attach temporarily onto a structure surface. Although that reattaching the PZT transducer caused the signature to changed, it was found that the peak amplitude height of the impedance signatures were similar for certain thickness composites. From this, it was possible to propose an idea of creating a process of detecting debonding of composites without the need for the onsite reference impedance signature. Both experimental and simulation results are obtained to verify the presented concept where promising outcome has been shown.

Removal of temperature effect in impedance-based damage detection using the cointegration method

Electromechanical impedance technique has been widely used in the area of structural health monitoring. However, both damage and variation in environmental temperature can cause the changes in electromechanical impedance signature, which may cause false damage diagnosis. The temperature effect on the electromechanical impedance-based method has been one of its main drawbacks in practical application. This article proposes a new approach based on cointegration to eliminate temperature interference in the electromechanical impedance technique. The augmented Dickey–Fuller test is used to analyze the stationary characteristics of the time series and determine the degree of non-stationarity. The Johansen test is used to obtain the cointegrating residuals instead of the direct electromechanical impedance responses for damage detection. The proposed method is verified on the undamaged and damaged steel plates with the consideration of environmental temperature variations. The damage detection was based on the electromechanical impedance technique in which the peak frequency is chosen as a cointegrated variable. The experimental results show that the cointegration method can remove the temperature effect on the electromechanical impedance responses, and the cointegrating residuals are effective indices to indicate the occurrence of damage.

An electromechanical impedance-instrumented corrosion-measuring probe

Corrosion of metallic structures widely existed in multiple industries, such as oil and gas, civil infrastructure, aerospace, mechanical, mining, and processing. Current available corrosion-monitoring methods are based on different sensing principles, which have their own advantages, and some drawbacks that may limit their application on some aspects. This article presents an electromechanical impedance-instrumented corrosion-measuring probe for corrosion monitoring. The proposed probe is fabricated by attaching a circular lead zirconate titanate patch onto a metal rod. Compared to other electromechanical impedance-based corrosion-monitoring methods, the probe is capable of isolating the influence of structural complexity, variations in loading and boundary conditions. Five probes were fabricated in the experimental study and three of them were subjected to accelerated corrosion tests to mimic the corrosion-induced mass loss damage. Results showed that the peak magnitude of the conductance signatures was reduced with the increase in corrosion amount. The variations in the conductance signatures were quantified by three statistical quantifying metrics, that is, root-mean-square deviation, mean absolute percentage deviation, and correlation coefficient deviation. All these metrics increase with the increase in corrosion amount, which can be used as an indicator of the corrosion process. This study proves that the proposed corrosion-measuring probe is effective in monitoring corrosion and shows promising application potential. This research also serves as a proof-of-concept study to demonstrate the capability of the electromechanical impedance technique in monitoring mass loss due to corrosion.

Health monitoring of reinforced concrete structures under impact using multiple piezo-based configurations

With new advancements in construction technologies, the researchers and engineers have started taking a greater interest in structural health monitoring (SHM). Some of these techniques involve monitoring of structures using piezo sensors, made of smart materials such as Lead Zirconate Titanate (PZT) in form of thin patches. One of such techniques which has shown promising results in detecting damage at incipient stages is the electro-mechanical impedance (EMI) technique. In this study, damages incurred due to impact loading on reinforced concrete (RC) slabs were studied using four types of piezo-based configurations, namely concrete vibration sensor (CVS) with circular PZT patch (CVS-C), CVS with square PZT patch (CVS-S), resin jacketed piezo (RJP) sensor with a single layer of epoxy (RJP-I) and RJP with double layer of epoxy (RJP-II). The tests showed a successful detection of damage due to impacts by all the four types of piezo-based configurations. The CVS-C and RJP-I proved to be more sensitive in quantifying damage via root mean square deviation (RMSD) variation, i.e. increasing RMSD values with an increase in the number of impacts. In addition, CVS-C, CVS-S, and RJP-II, specifically detected an imminent failure in one of the RC slabs. The equivalent structural parameters computed from the admittance signatures showed a reduction in the equivalent stiffness with the incremental damage. An empirical model was successfully developed for each of the sensors to determine the remaining life of the structure based on a non-dimensional stiffness loss factor. The equivalent stiffness-based model was found to be an improvement over the previous damping-based models which can be reliably used in the field.

Modeling, Simulation, Experimentation, and Compensation of Temperature Effect in Impedance-Based SHM Systems Applied to Steel Pipes.

Pipelines have been widely used for the transportation of chemical products, mainly those related to the petroleum industry. Damage in such pipelines can produce leakage with unpredictable consequences to the environment. There are different structural health monitoring (SHM) systems such as Lamb wave, comparative vacuum, acoustic emission, etc. for monitoring such structures. However, those based on piezoelectric sensors and electromechanical impedance technique (EMI) measurements are simple and efficient, and have been applied in a wide range of structures, including pipes. A disadvantage of such technique is that temperature changes can lead to false diagnoses. To overcome this disadvantage, temperature variation compensation techniques are normally incorporated. Therefore, this work has developed a complete study applied to damage detection in pipelines, including an innovative technique for compensating the temperature effect in EMI-based SHM and the modeling of piezoceramics bonded to pipeline structures using finite elements. Experimental results were used to validate the model. Moreover, the compensation method was tested in two steel pipes—healthy and damaged—compensating the temperature effect ranging from −40 °C to +80 °C, with analysis on the frequency range from 5 kHz to 120 kHz. The simulated and experimental results showed that the studies effectively contribute to the SHM area, mainly to EMI-based techniques.