Electromechanical Impedance Research Articles

A Deep Learning Approach for Autonomous Compression Damage Identification in Fiber-Reinforced Concrete Using Piezoelectric Lead Zirconate Titanate Transducers.

Effective damage identification is paramount to evaluating safety conditions and preventing catastrophic failures of concrete structures. Although various methods have been introduced in the literature, developing robust and reliable structural health monitoring (SHM) procedures remains an open research challenge. This study proposes a new approach utilizing a 1-D convolution neural network to identify the formation of cracks from the raw electromechanical impedance (EMI) signature of externally bonded piezoelectric lead zirconate titanate (PZT) transducers. Externally bonded PZT transducers were used to determine the EMI signature of fiber-reinforced concrete specimens subjected to monotonous and repeatable compression loading. A leave-one-specimen-out cross-validation scenario was adopted for the proposed SHM approach for a stricter and more realistic validation procedure. The experimental study and the obtained results clearly demonstrate the capacity of the introduced approach to provide autonomous and reliable damage identification in a PZT-enabled SHM system, with a mean accuracy of 95.24% and a standard deviation of 5.64%.

A proof of concept study on reliability assessment of different metal foil length based piezoelectric sensor for electromechanical impedance techniques

Lead zirconate titanate (PZT) patches gained popularity in structural health monitoring (SHM) for its sensing and cost effective. However, a robust installation of PZT patches is challenging due to the often-complex geometry and non-accessibility of structural parts. For tubular structures, the curved surface can compromise the perfect bonding of PZT patches. To alleviate the above-mentioned challenges, the non-bonded and reusable configuration of sensor received considerable interest in the field of SHM. However, ensuring the repeatability and reproducibility of Electro-Mechanical Impedance (EMI) measurements is crucial to establish the reliability of these techniques. This work investigated the repeatability and reproducibility measures for one of non-bonded configuration of PZT patch i.e., Metal Foil Based Piezo Sensor (MFBPS). In addition, the concept, application, and suitability of MFBPS for impedance-based monitoring technique of Civil infrastructure are critically discussed. This study evaluates the effect of length of MFBPS on piezo coupled admittance signature. Also, this study evaluates repeatability and reproducibility of EMI measurements via statistical tools such as ANOVA and Gage R&R analysis. The statistical index CCDM was used to quantify the deviations of impedance signals. The overall result shows that the repeatability of the EMI measurements improves with a metal foil length of 500 mm. Overall, this investigation offers a useful point of reference for professionals and scholars to ensure the reliability of MFBPS for EMI techniques, a variant of piezoelectric sensor for SHM applications.

A Baseline‐Free Electromechanical Impedance Resonance Method for Measuring the Modulus of Elasticity of Concrete Cubes Using Surface‐Bonded PZT Patches

The modulus of elasticity of concrete (Ec) is an essential parameter commonly used in concrete design, concrete curing monitoring, and deterioration evaluation and damage detection of concrete structures. A quick and reliable in situ determination of Ec helps in accurate decision‐making for construction and maintenance. The electromechanical impedance (EMI) technique using surface‐bonded lead zirconate titanate (PZT) patches (referred to as SBP) has become a popular nondestructive method for monitoring concrete structures due to ease of operations. The existing research mainly utilized baseline‐dependent approaches to monitor the changes (e.g., hardening or damage evolution) of concrete structures. However, relevant baselines are greatly influenced by the status of PZT sensors and bonding layers, limiting the practical applications of this technique. This paper presents a baseline‐free EMI resonance method for measuring Ec of concrete without using prior baseline data for the first time. Numerical and experimental studies on standard concrete cubes (100 mm in width) with SBP were conducted to examine the proposed method. A dimensionless physical quantity was first proposed to view the EMI signals. Then, resonance peaks highly related to concrete properties but insensitive to the status of the sensor system were selected, physically described, and correlated to the concrete parameters through numerical analyses. Finally, experimental validations, covering the measurement of Ec, repeatability of the chosen resonance peaks, and temperature effects, were conducted to illustrate the proposed method’s stability, accuracy, and sensitivity.

Application of EMI technique in crack propagation under the block loading conditions for AA6061 alloy

The behaviour of a component under real/random loading conditions can be studied by converting the random load into block load. Therefore, knowledge of the initiation and propagation of a crack under block loading conditions is very important for the safety and reliability of machine components / structures. Electromechanical impedance (EMI) is a real-time damage evaluation technique in which simultaneous use of the high-frequency mechanical excitations and responses of the structure are made by employing a piezoelectric transducer. In the present study, an experimental methodology to monitor fatigue crack initiation and propagation under block loading conditions for AA6061 aluminium alloy has been studied with the help of the EMI technique. The piezoelectric sensor bonded on the Compact Tension (CT) specimen acts as an actuator and sensor both. The conductance signature provided a sufficient information about the damage and crack growth under high low and low high block loading conditions. The conventional crack growth rate versus range of stress intensity factor plot matches well with the crack growth rate versus shift in resonant frequency.

Real-Time Structural Damage Detection Using EMI under Varying Load a and Temperature Conditions

Structural Health Monitoring (SHM) is a critical aspect of maintaining the safety and integrity of infrastructure. In recent years, there has been a significant shift towards adopting innovative techniques, and one of the most promising methods is Electromechanical Impedance (EMI). EMI involves the utilization of piezoelectric transducers to assess the health of structures in real-time by examining changes in their electrical characteristics. The presence of load causes a change in structural stiffness, which alters the resonant characteristics of the structure. Understanding how external factors like load and temperature influence the electrical impedance of these sensors is essential for its reliable application in damage detection. This article presents an experimental and numerical study to investigate the effects of load and temperature on the electrical impedance of a piezoelectric sensor used in the electromechanical impedance (EMI) technique. The experimental setup uses an impedance analyzer (Agilent 4294A model) to measure the in-situ EMI of piezoelectric wafer active sensors (PWAS) attached to the monitored structure. The numerical model uses ANSYS software to simulate an aluminum beam at varying temperatures. The results show that the load and temperature have a significant effect on the impedance of the transducer. However, it is shown that it is still possible to detect damage using EMI even under varying load and temperature conditions. The results also show that the accuracy of EMI-based damage detection can be improved by using temperature and load compensation techniques.

Numerical and Statistical Analysis of the Influence of Damage and Temperature on EMI for Structural Health Monitoring

Structural health monitoring (SHM) is a process of implementing a system to monitor the structural condition of a structure and assess the structural health. SHM is used to detect damage, predict future performance, and monitor the overall structural health of a structure. Electromechanical impedance (EMI)-based SHM is a non-destructive evaluation (NDE) technique that can be used to detect damage in structures by measuring the changes in the electrical impedance of a piezoelectric transducer that is bonded to the structure. EMI has several advantages over other NDE techniques, including being a passive, local, and relatively inexpensive technique. However, one of the challenges of using EMI for structural health monitoring (SHM) is the effect of damage and temperature on the impedance of the piezoelectric transducer. As the damage and temperature changes, the impedance of the transducer will also change. This can make it difficult to detect small damage if the damage and temperature co-exist on the same structure (aluminum plate). This research presents a numerical and statistical study to investigate the effects of damage and temperature on EMI-based SHM. The numerical model uses ANSYS software to simulate an aluminum plate at different temperatures. The findings have shown that both damage and temperature have a significant effect on the impedance of the transducer. However, the study has also demonstrated that it is still possible to detect structural damage using EMI even under varying damage and temperature conditions. This underscores the robustness of EMI-based damage detection methodologies in practical applications.

Application of wavelet transform techniques for corrosion assessment of embedded rebars in RC elements using electromechanical impedance

Corrosion of steel reinforcement embedded in concrete significantly influences the integrity and durability attributes of reinforced concrete structures. Monitoring of the early age corrosion of the reinforcements can contribute to an effective planning of structural maintenance and restoration. This paper demonstrates an innovative approach of monitoring the rate of corrosion (mass loss due to corrosion) of steel bars embedded in concrete by capturing conductance signature using Piezoelectric sensors (PZT) by Electromechanical Impedance Technique. In the recent times Wavelet Transform (WT) based different techniques have been proved to be promising techniques for different structural health monitoring assessment. This study aims to comprehensively use the WT techniques based on EMI signals to assess the corrosion levels in the reinforcement embedded in RC members. Specifically, the study focuses on capturing the progression of corrosion levels using the RMSD index derived from the DWT, CWT and WPT analysis of conductance signatures. WT techniques provides energy values of conductance signatures. Energy level of the signatures decreases with the increase of corrosion levels and deviation of energy level between current and pristine stage is measured using statistical index Root Mean Square Deviation (RMSD). Robust relationship between the RMSD index and the corrosion mass loss ratio through nonlinear curve fitting have been derived and presented using data captured from the 48 specimens of concrete cylinders with embedded reinforcement. At last, the comparison between the actual mass loss ratio and the predicted mass loss ratio derived from these techniques have been made for the validation of the proposed relation of predicted mass loss due to corrosion.

Evaluation of ground conductor corrosion based on EMI technique with asymmetric sensor layout

ABSTRACT The ground conductor is prone to corrosion, which affects its ability to diverge current and the normal operation of the power system. The traditional detection method can’t detect its corrosion degree intuitively. This paper proposes a novel method based on Electromechanical impedance (EMI) technique to evaluate the corrosion degree of the grounding conductor. Firstly, based on the analysis of corrosion of metals. The change of ground conductor radius Δr is used as the corrosion parameter. A linear model of peak frequency Δf m and corrosion parameter Δr in asymmetric layout is established by analysing EMI and conductor mechanical admittance. Secondly, the EMI coupling models with different sensor layouts were built on the finite element software. It is verified that the asymmetric sensor layout effectively improves the sensitivity to corrosion. The linear model greatly improves the assessment accuracy compared with the Mean Absolute Percentage Deviation (MAPD) and Root Mean Square Deviation (RMSD) damage index. Thirdly, the proposed method is verified in a real grounding conductor corrosion experiment. The method based on the EMI technique with asymmetric sensor layout can evaluate the corrosion of the grounding conductor well.

Health monitoring of steel structures using surface mountable and detachable PZT sensor

A lot of collapse in the infrastructure were reported in the last decades, hence the need for monitoring the health of the structures also arises. There are various techniques available to monitor the health of the structure, in which Electromechanical impedance (EMI) technique is one of them. In EMI technique, the PZT sensor is bonded to/embedded in the structure using epoxy. The thickness of epoxy layer used as an adhesive should be maintained as thin as possible, which cannot be achieved ideally, which introduces shear lag effect such that is, complete strain transfer cannot take place between PZT and host structure. The shear lag effect caused is one of the major drawbacks in the EMI technique and due to this effect, the damage detection sensitivity decreases. To overcome this drawback, in this study a new sensor named Surface Mounted PZT Sensor (SMPS) is proposed for the steel structure. Along with this, the performance of other sensor configurations such as conventionally bonded PZT with epoxy that is Surface Bonded PZT Sensor (SBPS) and Adhesive Covered Surface Bonded PZT Sensor (ACSBPS) are also been compared. The results show that, SMPS was working effectively and was more sensitive compared to SBPS and ACSBPS.

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Study on Monitoring of Vacuum Preloading Process of Soft Soil Based on Electromechanical Impedance Technique

Study on Monitoring of Vacuum Preloading Process of Soft Soil Based on Electromechanical Impedance Technique

Research on the monitoring friction hysteresis for the bolted interface by electromechanical impedance

Friction hysteresis manifests at the bolted interface when subjected to external excitation, leading to nonlinear structural responses. But the interface evolution is rarely considered in the health monitoring. In this paper, we introduce the pioneering concept of effective mechanical impedance of the contact interface (EMICI) and formulate a coupled structural impedance model that comprehensively incorporates both tangential loading and contact impedance considerations. EMICI was deemed to encapsulate intricate information pertaining to contact nonlinearity, and the theoretical equation was derived using principles of contact mechanics. Tangential loading experiments, time domain impedance analysis and impact hammer tests were conducted to confirm the close relationship between EMICI and the structural properties. The coupled structural impedance model is proved to be effective, in which EMICI can be identified by changing the tangential force and torque. Subsequent analysis revealed that the proposed model could additionally serve in the identification of system-related parameters. The loading coefficient in the model is linearly related to the tangential force, and the calculated EMICI corresponds to the slip characteristics of the bolted interface. The introduced concept of EMICI could be considered as a metric for assessing interface properties, offering dependable insights into contact evolution, and facilitating a deeper understanding of interface dynamics.

Pavement damage monitoring using electromechanical impedance of embedded piezoelectric plate

Piezoelectric transducers have seen widespread usage in the monitoring of structural health. It has tremendous potential for monitoring the health of infrastructure, especially pavement monitoring. In the present study, the impedance characteristics of a piezoelectric plate embedded in the pavement is utilized to monitor the health status of the pavement. Based on the piezoelectricity principle, a model of an electromechanical piezoelectric plate embedded in pavement is established. The damage of the pavement is considered as the thickness decreasing of the pavement layer. The present proposed model is verified by comparing its degeneration with the exact solution of a single layer model. Numerical results demonstrated that with the deceasing of the thickness of the pavement, which is considered as the deterioration of the pavement, the achievable maximum electromechanical impedance characterization including impedance, admittance and conductance decreased. This demonstrated that the achievable maximum impedance, admittance and conductance of an embedded piezoelectric plate could be used as the indicator of pavement health monitoring. This study primarily presents theoretical underpinnings for pavement monitoring using electromechanical impedance of piezoelectric plates.

Analysis of FRP-Strengthened Reinforced Concrete Beams Using Electromechanical Impedance Technique and Digital Image Correlation System.

Fiber-reinforced polymer (FRP) strengthening systems have been considered an effective technique to retrofit concrete structures, and their use nowadays is more and more extensive. Externally bonded reinforcement (EBR) and near-surface mounted (NSM) technologies are the two most widely recognized and applied FRP strengthening methods for enhancing structural performance worldwide. However, one of the main disadvantages of both approaches is a possible brittle failure mode provided by a sudden debonding of the FRP. Therefore, methodologies able to monitor the long-term efficiency of this kind of strengthening constitute a challenge to be overcome. In this work, two reinforced concrete (RC) specimens strengthened with FRP and subjected to increasing load tests were monitored. One specimen was strengthened using the EBR method, while for the other, the NSM technique was used. The multiple cracks emanating in both specimens in the static tests, as possible origins of a future debonding failure, were monitored using a piezoelectric (PZT)-transducer-based electromechanical impedance (EMI) technique and a digital image correlation (DIC) system. Clustering approaches based on impedance measurements of the healthy and damaged states of the specimens allowed us to suspect the occurrence of cracks and their growth. The strain profiles captured in the images of the DIC system allowed us to depict surface hair-line cracks and their propagation. The combined implementation of the two techniques to look for correlations during incremental bending tests was addressed in this study as a means of improving the prediction of early cracks and potentially anticipating the complete failure of the strengthened specimens.

Elastic, piezoelectric coefficients, and internal frictions of a single alpha-quartz crystal determined by partial-electrode electromechanical impedance spectroscopy.

In this work, all independent elastic coefficients, piezoelectric coefficients, and internal frictions of a single alpha-quartz crystal are determined at room temperature using our recently proposed partial-electrode electromechanical impedance spectroscopy (PE-EMIS). In PE-EMIS, the rectangular parallelepiped quartz sample with two small partial electrodes fabricated on a corner is self-excited/sensed. The conductance spectrum (equivalent to the acoustic resonance spectrum) measured by an impedance analyzer under a free boundary condition is noiseless, allowing the first 100 eigenmodes ranging from 50 to 310kHz to be accurately fitted. To avoid mode misidentification, the off-plane displacement distributions of the quartz sample under different eigenmodes are determined using a scanned-laser vibrometer. The resonance spectrum measured by a traditional sandwich-like RUS apparatus is also presented for comparison, and the results show that the clamping force in sandwich-like RUS shifts the sample's resonance frequencies, causing 13% and 75% overestimations for the piezoelectric coefficients e11 and e14, respectively. In comparison with the RUS, our proposed PE-EMIS is more effective and convenient, and will be widely used for characterization of piezoelectric crystals.

The Efficacy of Electromechanical Impedance Monitoring of Embedded Piezoelectric Ceramic Lead Zirconium Titanate Sensors in Different Orientations for Hybrid Fiber-Reinforced Concrete Structures Hydration

Abstract In this study, the influence of the orientation of embedded piezoelectric ceramic lead zirconium titanate (PZT) on the mechanical performance of hybrid fiber-reinforced (polypropylene and glass fiber) concrete beams was evaluated. The performance of concrete was evaluated under self-weight, followed by assessing the mechanical property using the electromechanical impedance (EMI) technique after optimization of M30 grade concrete with polypropylene fiber and glass fiber. PZT patches are embedded at different orientations, i.e., 0 deg, 45 deg, and 90 deg, with the axis of the structure for monitoring the hydration of the RC beam. The change in stiffness due to heat hydration in the concrete structure after 5, 7, 14, 21, and 28 days was observed by curing hybrid concrete beams and examining them after 5, 7, 14, 21, and 28 days. On the fifth day, beams were simply supported and allowed to deflect under their weight, and measurements of heat hydration in terms of conductance at frequencies ranging between 1 and 1000 kHz were done. Similarly, days 7, 14, 21, and 28 were done. Day 5 was considered the baseline. It is noted that the PZT sensor placed at an angle of 45 deg is the least effective in recording the incremental changes in hydration that occurred in the concrete beam. The highest quality results were obtained at 90 deg, which is further demonstrated by statistically quantifying the changes using the root-mean-square deviation (RMSD) percentage method and proves to be the most optimized orientation to obtain the stiffness of the hybrid reinforced beam in terms of conductance.

Solar cell micro crack detection technique using electromechanical impedance and finite element analysis

Electromechanical impedance (EMI) is one of the modern techniques employed in the field of structural health monitoring (SHM) and has witnessed a great expansion in many domains due to its ability to ensure continuous monitoring and high reliability with a lower cost. Hence, the purpose of this study is to investigate the effectiveness of EMI in monitoring and detecting pre-existing cracks in the silicon layer of the photovoltaic (PV) solar cells. Indeed, a detailed finite element analysis (FEA) on the effect of piezoelectric lead zirconate titanate (PZT) patch shape on the EMI of crystalline-silicon (c-Si) layer of the PV solar cells were performed. The typical structure (c-Si + PZT) of different scenarios were stimulated by giving a lower voltage and high frequency as input data to extract the EMI signature as an explainable output result. Different models were investigated based on PZT patch types and crack position in the silicon layer. The results indicate that the EMI technique is effective in detecting crack, even in its incipient stage. The analysis suggests using a higher frequency range (350–650 kHz) for characterizing damage with an invisible depth due to the higher sensitivity of the EMI technique in this specific frequency.

Structural Condition Monitoring Using Deep Learning on a Metallic Part Fabricated by Additive Manufacturing

Additive manufacturing (AM) was originally developed to manufacture polymer prototypes. Today, it has been used for the manufacturing of many critical machine components. Most of the structural health monitoring (SHM) methods were developed for monitoring the condition of large and thin plates on airplane fuselages. Additively manufactured parts are generally small, thick, and have complex geometries. SHM methods have been improved to sense load, detect defects, and identify loose bolts with the help of a permanently installed sensor. In this study, the adaptability of SHM methods was researched with additively manufactured metal parts with complex geometry. Magnets were used to apply pressure to 9 different locations on the surface of a stainless steel additively manufactured thick plate with deep groves. SHM was used to estimate the magnets’ location. Many SHM (Lamb wave) methods cannot work on smaller parts since their dimensions are shorter or very close to the wavelength of the created oscillations. Surface response to excitation (SuRE) method which has similar characteristics to electromechanical impedance methods was used for data collection. To obtain descriptive features of the time domain data, fast Fourier transformation (FFT), short-time Fourier transformation (STFT), continuous wavelet transformation (CWT), and synchrosqueezing transform (SST) were applied to CWT. 1D and 2D convolutional neural networks (CNN) were used to classify the cases. When CNN was optimized for the analysis of our data, 100% location estimation accuracy was obtained by using 50% of 320 scalograms for training. The scalograms were obtained by enhancing the CWT results with SST. STFT-CNN combination was the second best. It obtained 95% accuracy with the same number of spectrograms and training allocation.

Early detection of thermal instability in railway tracks using piezo-coupled structural signatures

Rail accidents caused by rail track derailments have been a growing concern due to repetitive thermal changes resulting from high temperature stresses in rails due to rail traction and environmental thermal variation. This leads to thermal buckling, which can result in catastrophic failure. Structural health monitoring (SHM) using the electromechanical impedance (EMI) technique has emerged as a promising technology to detect structural deterioration and its severity before it leads to failure. This study used piezoelectric sensors to collect piezo-coupled structural signatures of different rail-joint bars for high-temperature repetitive thermal cycles, which were then analyzed using an impedance analyzer. The results show that the piezo-coupled signatures could identify structural changes, and the damage metric, could be employed for continuous monitoring of structural rail defects due to excessive thermal stress and residual strain. The method also derived piezo-equivalent structural parameters, such as mass, stiffness, and damping, which were very satisfactory in detecting significant changes and consequent damage. Overall, this study presents a pre-emptive experimental method that can see thermal deterioration and instability in rails and rail joints, thereby reducing the risk of rail accidents caused by derailments.

Cloud-based pipe corrosion monitoring using electromechanical impedance instrumented piezoelectric ring sensor

The corrosion of small-diameter pipes has resulted in numerous significant accidents and substantial economic losses in both industrial and civil sectors. This paper presents a wireless smart corrosion monitoring system based on electromechanical impedance (EMI) technology. This system comprises a smart corrosion sensing node (SCSN) designed using EMI principles and a wireless impedance monitoring system (WIMS) for remote impedance measurement. A finite element simulation was conducted to assess the performance of the SCSN under uniform corrosion conditions. Additionally, a comparative test, with and without fluid inside the pipe, was performed to determine the impact of the fluid on test results. To validate the effectiveness of the proposed wireless smart corrosion monitoring node, corrosion monitoring experiments were conducted on pipe specimens equipped with the sensing node. These findings were complemented by separate corrosion experiments, and it was revealed that as corrosion increased, the peak frequency decreased, indicating a strong linear relationship. The study demonstrates that the wireless smart corrosion monitoring node is highly capable of monitoring pipe corrosion in an experimental setting.