Lead Zirconate Titanate Patches Research Articles

Corrosion monitoring for transmission line based on electromechanical impedance instrumented circular piezoelectric corrosion sensor

Corrosion-induced thickness loss is a common form structural damage in transmission lines. In our previous work, a novel circular piezoelectric-metal transducer for corrosion sensing using the electromechanical impedance (EMI) technique was proposed. This transducer was fabricated by attaching a lead zirconate titanate (PZT) patch to a metal plate. In the present study, the piezoelectric-metal transducer was encapsulated and enhanced, and two types of corrosion sensors were developed: piezoelectric-steel and piezoelectric-zinc sensors. To assess the practical performance of the corrosion sensors, the piezoelectric-steel and piezoelectric-zinc sensors were connected to the angle steels and the steel strands, which are highly prone to corrosion in transmission lines. Corrosion monitoring experiments were conducted in the laboratory. The results demonstrate that the peak frequencies in the conductance signatures decrease linearly with increasing corrosion-induced thickness loss. Furthermore, it was found that piezoelectric-steel sensors are effective for quantitative monitoring of metallic corrosion, whereas piezoelectric-zinc sensors are better suited for early-stage corrosion monitoring and warning.

Experimental Study on the Detection of the Existence and Location of Mimicked and Unexpected Interface Debonding Defects in an Existing Rectangular CFST Column with PZT Materials.

Interface bonding conditions between concrete and steel materials play key roles in ensuring the composite effect and load-carrying capacity of concrete-steel composite structures such as concrete-filled steel tube (CFST) members in practice. A method using both surface wave and electromechanical impedance (EMI) measurement for detecting the existence and the location of inaccessible interface debonding defects between the concrete core and steel tube in CFST members using piezoelectric lead zirconate titanate (PZT) patches as actuators and sensors is proposed. A rectangular CFST specimen with two artificially mimicked interface debonding defects was experimentally verified using PZT patches as the actuator and sensor. By comparing the surface wave measurement of PZT sensors at different surface wave travelling paths under both a continuous sinusoidal signal and a 10-period sinusoidal windowed signal, three potential interface debonding defects are quickly identified. Furthermore, the accurate locations of the three detected potential interface debonding defects are determined with the help of EMI measurements from a number of additional PZT sensors around the three potential interface debonding defects. Finally, the accuracy of the proposed interface debonding detection method is verified with a destructive observation by removing the local steel tube at the three detected interface debonding locations. The observation results show that the three detected interface debonding defects are two mimicked interface debonding defects, and an unexpected debonding defect occurred spontaneously due to concrete shrinkage in the past one and a half years before conducting the test. Results in this study indicate that the proposed method can be an efficient and accurate approach for the detection of unknown interface debonding defects in existing CFST members.

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 Flexible Surgical Robot with Hemispherical Magnet Array Steering and Embedded Piezoelectric Beacon for Ultrasonic Position Sensing

This article proposes a flexible surgical robot featuring strong magnetic steering achieved by a hemispherical magnet array actuation, and high‐accuracy ultrasonic position sensing achieved by a beacon total focusing method (b‐TFM). The hemispherical magnet array with magnetic focusing is described and its array parameters are optimized through finite element analysis to increase the magnetic field for actuation. The magnetic field strength at 100 mm for the array with the same mass as the cylindrical magnet is about 1.8 times higher than that of the cylindrical magnet. Using the magnet array actuation, the flexible robot exhibits the capability of agile steering to navigate along a predefined trajectory. In addition, a 1 mm × 1 mm lead zirconate titanate (PZT) patch is embedded into the tip of the flexible robot as a beacon for b‐TFM ultrasonic imaging to detect the position of the robot. Therefore, the entire navigation process can be executed under the supervision of the ultrasonic position sensing system, and the maximum error is 0.8 mm when the steering radius is 100 mm.

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.

Deep learning of electromechanical admittance data augmented by generative adversarial networks for flexural performance evaluation of RC beam structure

Deep learning networks facilitate automated damage identification and performance evaluation for concrete structures using electromechanical impedance/admittance (EMI/EMA) technique, while data quantity and quality limit the performance of such a data-driven network. For the first time, this paper proposed a data-augmentation approach using deep-convolutional admittance generative adversarial networks (AdmiGAN) to solve data deficiency and measurement inefficiency for deep learning-based flexural performance evaluation of reinforced concrete (RC) structures. In the approach, a new data normalization procedure was developed to collaboratively foster AdmiGAN-based EMA data synthesis, and synthetic datasets were fed into an adaptive convolutional neural network (CNN) for deep learning. Proof-of-concept experiment was conducted on a four-point bending RC beam structure, which was continuously monitored from initial loading to final failure by three surface-bonded piezoelectric ceramic lead zirconate titanate (PZT) patches. Qualitative detection of stress and damage was performed by traditional feature analysis of EMA signatures, automated performance evaluation was attempted by using CNN approach. Results demonstrated that the AdmiGAN required merely 5 groups of EMA signatures to generate high-accuracy dataset with 174 times of speed faster than conventional measurement method, and the AdmiGAN cooperated with CNN provided a new paradigm of data-driven structural performance evaluation with high accuracy, efficiency, and intelligence.

Experimental investigation on interfacial defect detection for SCCS with conventional and novel contact NDT techniques

In order to ensure the mechanical performance and structural safety of steel–concrete composite structures (SCCS), advanced nondestructive testing (NDT) technique for bonding status at steel–concrete interfaces needs to be developed. In this study, the feasibility of multichannel analysis of surface waves (MASW)-based interfacial debonding detection is validated using the contact sensors array. Herein, the multichannel sensor arrays are composed of piezoceramic lead zirconate titanate patches and high-frequency acceleration meters, respectively. For comparison, the impact-response (IR) method and impact-transmission (IT) method are performed utilizing a force hammer and high-frequency acceleration meters, and corresponding damage imaging algorithms are developed. The applicability of ultrasonic computed tomography (CT) scanning test, scanning impact echo (IE) method, ultrasonic tomography (UT) technique on interfacial debonding detection is further discussed in depth. Research findings indicate that the developed contact MASW measurement can fully capture the variation of dispersion characteristics of surface waves induced by debonding defects in SCCS. The developed IR and IT methods are suitable for detecting interfacial debondings in different dimensions. Besides, the damage nephogram resolution of IR is higher than that of the IT method. In addition, the practicability of traditional ultrasonic CT scanning tests, scanning IE method, and UT techniques using commercial equipment is investigated. Experimental observations show that classical NDT testing techniques are incapable of effectively identifying the existence of interfacial damage and are unsuitable for NDT tests on SCCS. The research findings in this study clearly exhibit the precision and limitation of various contact NDT techniques and lay a solid foundation for interfacial debonding detection in practical SCCS.

HPSA: a high-performance smart aggregate for concrete structural health monitoring based on acoustic impedance matching method

Piezoceramic-based ultrasonic transducers have demonstrated the feasibility and effectiveness of functioning as smart aggregates (SAs) to detect damages for concrete structures in laboratory-sized structural members. The restriction of its further engineering application is the limited propagation distance due to the large energy loss during wave transmission. Aiming to reduce the energy loss of piezoceramic-based sensors, the authors proposed a high-performance piezoceramic-enabled SA based on acoustic impedance matching principle. The main contribution to the performance enhancement comes from the proposed surface treatment of the lead zirconate titanate patch and acoustic impedance matching layer. Comparative experiments with commercial SAs validate the improved performance. Besides, a field test with different wave propagation distances fully illustrates the perspective of the proposed superior transducer in large infrastructure engineering applications.

Vibration acoustic modulation for bolt looseness monitoring based on frequency-swept excitation and bispectrum

The monitoring of bolt looseness is crucial to ensure the safety and reliability of structures. Prior studies have demonstrated that the vibro-acoustic modulation (VAM) method based on the nonlinear ultrasonic theory is sensitive to the early looseness of bolted connections. However, one limitation of the traditional VAM method is that the low frequency (LF) and high frequency (HF) for excitation should be specified in advance. The resonant frequency of the bolted structures changes after loosening, leading to inaccuracies in monitoring results if pre-specified excitation frequencies are used and not adapted to the new situation. To address this limitation, this paper improves the VAM method by using swept sine signals for both LF and HF excitations and relying on the bispectrum energy of the measured response to indicate the bolt pre-load. A steel bolted connection was fabricated and loaded on a universal testing machine to simulate different bolt pre-loads. Three low-cost lead zirconate titanate patches served as the LF actuator, HF actuator and sensor in the experiment. The experimental results demonstrate that the improved VAM method can evaluate the bolt looseness with better efficiency and robustness than the traditional VAM methods which use fixed frequencies as excitations. Therefore, the proposed method in this paper can potentially monitor the damages in complex structures based on nonlinear ultrasound theory.

Cracking and Fiber Debonding Identification of Concrete Deep Beams Reinforced with C-FRP Ropes against Shear Using a Real-Time Monitoring System.

Traditional methods for estimating structural deterioration are generally costly and inefficient. Recent studies have demonstrated that implementing a network of piezoelectric transducers mounted to critical regions of concrete structural members substantially increases the efficacy of the structural health monitoring (SHM) method. This study uses a recently developed electro-mechanical-admittance (EMA)-based SHM system for real-time damage diagnosis of carbon FRP (C-FRP) ropes installed as shear composite reinforcement in RC deep beams. The applied SHM technique uses the frequency response measurements of a network of piezoelectric lead zirconate titanate (PZT) patches. The proposed strengthening methods using C-FRP ropes as ETS and NSM shear reinforcement and the applied anchorage techniques significantly enhanced the strength and the overall performance of the examined beams. The retrofitted beams exhibited increased shear capacity and improved post-peak response with substantial ductility compared with the brittle failure of the non-strengthened specimens. The health condition and the potential debonding failure of the applied composite fiber material were also examined and quantified using the proposed SHM technique. Damage quantification of C-FRP ropes is achieved by comparing and assessing the values of several statistical damage indices. The experimental results demonstrated that the proposed monitoring system successfully diagnosed the region where the damage occurred by providing early warning of the forthcoming critical shear cracking of concrete and C-FRP rope debonding failures. Furthermore, the internal PZT transducers showed sound indications of the C-FRP rope's health condition, demonstrating a direct correlation with the mechanical performance of the fibers.

Non-Destructive Evaluation of Preload Loss of Bolted Spherical Joints Based on Time Reversal Acoustics: A Numerical Simulation

Bolted spherical joints are widely used in space grid structures. However, the preload loss, which may arise from fabrication error, insufficient twist of the screw and some other unknown reasons can undermine the structural integrity and even lead to the collapse of the whole structure. Therefore, a method for evaluating the preload status of bolted spherical joints is vital to the structural health monitoring of the space grid structures. To this end, a non-destructive evaluation of the preload loss of bolted spherical joints based on time reversal acoustics (TRA) is presented. In this method, an excited signal generated by a lead zirconate titanate (PZT) patch at the bolted sphere is reconstructed after the signal recorded by another PZT patch at the bar is time-reversed and re-emitted. The deviation of the reconstructed signal from the initial signal allows identification of preload loss of the bolted spherical joint. This method is demonstrated to be effective by a finite element simulation. Furthermore, the effect of preload loss of the bolted spherical joint on its ultimate flexural capacity is studied, which highlights the necessity for the non-destructive evaluation.

Modeling and electromechanical performance of improved smart aggregates using piezoelectric stacks

Smart aggregates (SAs) are often formed by embedding lead zirconate titanate (PZT) patches into concrete or marble blocks. They not only have the advantages of low cost, quick response, high reliability, and long service life, but also possess comprehensive actuating and sensing abilities, and have been widely used in structural health monitoring in the field of civil engineering. However, due to the plate-like geometry of the PZT patch and the limited number of layers, SAs have a relatively short sensing range. To solve this issue, a new type of SA using piezoelectric stacks was developed. Theoretical modeling of this new transducer was established, and prototypes were fabricated. Comparisons between the theoretical predictions and the experimental results are presented, and good agreement can be found. The effects of the key parameters, including the total height of the specimen, the elastic modulus of the cement, the radius of the piezoelectric stack, the thickness of the piezoelectric layer, and the number of piezoelectric layers in the piezoelectric stack, on the electromechanical properties were analyzed, and the guidelines for optimal design were presented. In addition, the improved and the traditional SAs were used to monitor the water content in soil specimens based on the electromechanical impedance technique. The results showed that the improved SAs using piezoelectric stacks are more sensitive than the traditional ones, and have good potential in structural health monitoring in the field of civil engineering.

Feasibility of Application for the SHG Technology of Longitudinal Wave in Quantitatively Evaluating Carbonated Concrete

The ultrasonic transmission detection method is used to investigate the applicability for the second-harmonic generation (SHG) technology of longitudinal wave to quantitatively assess carbonated concrete. The principal of this method is to use the piezoelectric lead zirconate titanate (PZT) patch to detect the second-harmonic of longitudinal waves during the concrete carbonation process and extract non-linear parameters from observed signals. Non-linear parameters of concretes with two water–cement ratios (CI (w/c=0.47), CII (w/c=0.53)), two moisture contents (CI 0%, CI-W 100%), and three ultrasonic incident frequencies (50 kHz, 75 kHz, 100 kHz) were measured in this study. Results of the experiment demonstrate that non-linear ultrasonic parameters of longitudinal ultrasonic waves with high frequencies (75 kHz, 100 kHz) exhibit a better resolution regarding changes in concrete microstructure. Moisture (CI 0%, CI-W 100%) has little effect on the rate (CI: 62.73%, CI-W: 60.25, carbonation depth: 15 mm) for the change in relative non-linear parameters in the same concrete. The carbonation depth of concrete (CI (w/c=0.47), CI-W (w/c=0.47), CII (w/c=0.53)) can be well reflected by the change in relative non-linear parameters. Furthermore, there exists a good fit between the relative non-linear parameters of longitudinal waves and the concrete carbonation process. The relative non-linear parameters of longitudinal waves demonstrate feasibility in the quantitative assessment of concrete carbonation.

Potential Evaluation of Electro Mechano Gram (EMG) for Osteoporosis Detection

Good health of bones is of the utmost importance to human beings. Smart materials like lead zirconate titanate (PZT) patches are small in size and carry less weight, which makes them most apt for biomedical structural health monitoring (BSHM). In the past, focus on the development of low-cost non-invasive techniques for real-time monitoring of critical bones has been undertaken as an alternative to current diagnosis techniques such as dual x-ray absorptiometry (DEXA), which is not portable and emits radiations. This paper presents a study to evaluate a previously developed non-bonded piezo sensor (NBPS)-based diagnostic technique for non-invasive detection of osteoporosis, in the framework of the electro-mechanical impedance (EMI) technique. As part of the study, the experimental trials in the paper are performed for comparing DEXA and bone electro-mechano gram (BEMG) on healthy subjects as well as those with osteoporosis. It was found that BEMG identified structural system for healthy and osteoporotic subjects were quite different leading to a new technique to identify osteoporosis.

Smart monitoring system of composite plates for structural health monitoring using electromechanical impedance approach

<span>The damage detection in structural health monitoring was performed in glass fiber composite plates and carbon nanotude composite plates. Electromechanical Impedance technique was used for identification of damage using lead zirconate titanate patches. Impact on composite structure was created artificially by drilling a hole in composite structures. Bolt stiffnesss were detected by loosening of bolts and nuts in the composite structures. Corrosion occurs due to the aging and change of environmental conditions. The novelty in this paper is the use of corroded bolts in composite structures and identified the effects of corrosion and compared the output signatures with potentiostat. In this paper common deformation detection in composite plates, measurement of bolt stiffness and effects of corrosion has been performed. Measurement of Impedance at different frequencies were normalized with the undamaged composite structures and considered as the reference signatures. These results have been analyzed and verified with the output from potentiostat.</span>

Corrosion assessment in rebars of high-strength concrete using electromechanical impedance technique

The corrosion of steel rebar in reinforced concrete structures is one of the main reasons for early deterioration and premature failure of concrete structures, leading to enormous restoration costs worldwide infrastructure restoration. In the past, many sensors and techniques have been developed to monitor corrosion in steel rebar. However, the Electromechanical Impedance (EMI) technique using the piezoelectric Lead Zirconate Titanate (PZT) patches has been immersed as a promising technique to detect damages at an incipient level. This paper presents the corrosion assessment in embedded rebar in high-strength concrete using surface-bonded PZT patches through the EMI technique. The High Yield Strength Deformed (HYSD) rebars of Fe415 grade embedded in high-strength M60 grade concrete cylindrical specimens were used for the experimental work. The artificial corrosion in the embedded rebar was simulated through the accelerated corrosion test for 180 days. The conductance signatures were acquired through a surface-bonded PZT patch on embedded rebar. First, qualitative and quantitative corrosion assessment was carried out based on the conductance signature and the Root Mean Square Deviation (RMSD). Second, the effectiveness of extracted equivalent parameters was demonstrated for capturing the degradation of stiffness and mass due to corrosion. Finally, the corrosion rate is evaluated through equivalent parameters, and a comparison was made with the actual mass loss. The experimental study demonstrated that the EMI technique could be used very effectively through the statical index RMSD and equivalent parameters to identify corrosion phases and resulting losses in stiffness and mass of the structure.

Health monitoring of cracked concrete structure by impedance approach

Cracks/damages in concrete structures are the core concern for reduction of service life of infrastructures. Therefore, the effective technique is required for the prevention of cracks growth to improve the durability of structures. The cracks growth can be minimised by the incorporation of bacteria in the cementitious materials. The development of calcium carbonate heals the cracks automatically without any kind of human effort. The health of structures can be monitored and the presence of damages/cracks can be determined using various structural health monitoring techniques. In this paper, the research is focused on the monitoring of concrete cubes to explore the effect of bacteria. Two types of cube specimens were considered such as control concrete and bacterial concrete cubes, respectively. The six cubes of control concrete and six cubes of bacterial concrete of dimension 150 × 150 × 150 mm were cast. The compressive load of 300 kN was applied on control concrete cubes and bacterial concrete cubes to induce the incipient cracks/damages. After inducing the damages in the cubes, these cubes were tested after 7 days and 28 days curing. It was observed that the compressive strength of bacterial concrete was increased with respect to the control concrete by 19 % and 23 % at 7 and 28 days, respectively. The Electro-Mechanical Impedance (EMI) technique was used for monitoring the development of strength in both the cubes continuously. Piezo-ceramic lead Zirconate Titanate (PZT) patches were used to extract the signature. Admittance signatures were determined to access the health of cube specimens. Any deviation in signature from the healthy state that is baseline signature designates the change in compressive strength of concrete cubes. The increased strength was quantified in terms of signature change. The proposed investigation is applicable for monitoring of bacterial concrete structures. The research paper will be resulted new research directions and develop sustainable advancements in concrete technology.

Piezo-impedance based fatigue damage monitoring of restrengthened concrete frames

The present study proposes a novel application of wavelet transform energy of piezo-impedance signatures in monitoring the premature fatigue damage of restrengthened reinforced concrete (RC) frames. The steel plates on one column of the damaged RC frame and carbon fibre reinforced polymer (CFRP) wrap on the other are utilized as the local strengthening elements. The lead zirconate titanate (PZT) patches bonded externally to the retrofitted elements were used to acquire the global and local vibration response of the test frame under high-cycle and low-strain fatigue loading environment. The electro-mechanical impedance (EMI) technique combined with discrete wavelet transform (DWT) is employed on frequency domain PZT-admittance signatures to identify, localize, and quantify the severity of premature fatigue damages. The EMI-identified structural damping and DWT energy based damage dependent models shows extraordinary ability in estimating residual fatigue life of the structure. The results of combined local and global dynamics technique indicate the higher performance of the PZT-identified equivalent stiffness parameters (ESP) in detecting and quantifying plate debonding failures. Further, for the first time, the miniature AD5933 chipset displays a higher correlation of ESP in estimating premature fatigue damages, ultimately proving its efficacy for using it as a low-cost impedance-based health monitoring solution for retrofitted RC structures.

Experimental analysis of the feasibility of deep slide monitoring with low-cost piezoelectric diaphragms-based EMI technique

Slope instability, especially the soil slope instability, is a common occurrence in mountainous areas. It poses a huge threat to people’s lives and properties under the slope body. Effective slope monitoring techniques can provide detailed information and precursor about the real-time deformation, which is of great importance to provide early warning to the public. In this paper, a novel electromechanical impedance (EMI)-based slope deep slide monitoring bar (DSMB) was proposed. The main purpose was to investigate the application of the EMI technique for deep slide detection. In this study, a small soil slope specimen with a DSMB embedded inside it was fabricated in laboratory. To verify the practicality of the low-cost piezoelectric diaphragms (commonly known as buzzers), four conventional lead zirconate titanate (PZT) patches and four buzzers were bonded onto the front surface and back surface of the bar at specific positions, respectively. The slope specimen was then subjected to a horizontal thrust to initiate an interlayer slide along the slip surface. The whole process was monitored with a precision impedance analyzer by measuring the admittance of these transducers at specific sliding displacement. In order to reduce the error and increase the reliability, the experiment was repeated three times under the same conditions. It was concluded that the conventional PZT patches and buzzers have similar sensitivities to interlayer slide damage. The results indicate that both the severity and sliding location could be identified via the two metrics including root mean square deviation (RMSD) and correlation coefficient deviation (CCD). The experimental results verify the feasibility and practicality of using novel and low-cost piezoelectric diaphragm-based EMI technique to detect the deep slide in soil slope.

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.