• Smart Structures and Systems
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• 제17권1호
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• pp.107-122
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• 2016

We propose an effective methodology using electromechanical impedance characteristics for estimating the remaining tensile force of tendons and simultaneously detecting damages of the anchorage blocks. Once one piezoelectric patch is attached on the anchor head and the other is bonded on the bearing plate, impedance responses are measured through these two patches under varying tensile force conditions. Then statistical indices are calculated from the impedances, and two types of relationship curves between the tensile force and the statistical index (TE Curve) and between statistical indices of two patches (SR Curve) are established. Those are considered as database for monitoring both the tendon and the anchorage system. If damage exists on the bearing plate, the statistical index of patch on the bearing plate would be out of bounds of the SR curve and damage can be detected. A change in the statistical index by damage is calibrated with the SR curve, and the tensile force can be estimated with the corrected index and the TE Curve. For validation of the developed methodology, experimental studies are performed on the scaled model of an anchorage system that is simplified only with 3 solid wedges, a 3-hole anchor head, and a bearing plate. Then, the methodology is applied to a real scale anchorage system that has 19 strands, wedges, an anchor head, a bearing plate, and a steel duct. It is observed that the proposed scheme gives quite accurate estimation of the remaining tensile forces. Therefore, this methodology has great potential for practical use to evaluate the remaining tensile forces and damage status in the post-tensioned structural members.

• 한국음향학회지
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• 제26권2호
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• pp.80-86
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• 2007

본 연구에서는 압전세라믹과 고분자재료를 사용하여 다이스와 필 방법으로 2-2형 압전복합재료를 제작하고 이것을 이용하며 초음파 센서를 설계하고 제작하여 전기적 및 음향 특성을 조사하였다. 제작된 시편의 공진특성은 유한요소 해석 결과와 임피던스 분석기(HP4194A)를 이용하여 실제로 측정한 결과와 유사하게 나타났다. 2-2형 압전복합재료의 고유음향 임피던스는 PZT의 부피분율이 감소함에 따라 선형적으로 감소하였다. 이것을 이용하여 제작된 초음파 센서의 공진특성 및 전기기계결합계수는 PZT의 부피분율이 0.6일 때 가장 우수하였다. 또한, 이것의 음향특성을 측정한 결과 PZT 부피분율이 0.6일때 진폭, 주파수 대역폭, 울림감쇠 특성 등이 가장 우수하게 나타났으며, 단일 압전세라믹으로 제작된 센서에 비하여 상당히 우수한 감도 특성을 나타내었다.

• Nuclear Engineering and Technology
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• 제51권4호
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• pp.1132-1141
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• 2019

Steel-concrete-steel (SCS) sandwich structures have important advantages over conventional concrete structures, however, bond-slip between the steel plate and concrete may lead to a loss of composite action, resulting in a reduction of stiffness and fatigue life of SCS sandwich structures. Due to the inaccessibility and invisibility of the interface, the interfacial performance monitoring and debonding detection using traditional measurement methods, such as relative displacement between the steel plate and core concrete, have proved challenging. In this work, two methods using piezoelectric transducers are proposed to detect the bond-slip between steel plate and core concrete during the test of the beam. The first one is acoustic emission (AE) method, which can detect the dynamic process of bond-slip. AE signals can be detected when initial micro cracks form and indicate the damage severity, types and locations. The second is electromechanical impedance (EMI) method, which can be used to evaluate the damage due to bond-slip through comparing with the reference data in static state, even if the bond-slip is invisible and suspends. In this work, the experiment is implemented to demonstrate the bond-slip monitoring using above methods. Experimental results and further analysis show the validity and unique advantage of the proposed methods.

• Smart Structures and Systems
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• 제6권5_6호
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• pp.689-709
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• 2010

In this paper, a low cost, low power but multifunctional wireless sensor node is presented for the impedance-based SHM using piezoelectric sensors. Firstly, a miniaturized impedance measuring chip device is utilized for low cost and low power structural excitation/sensing. Then, structural damage detection/sensor self-diagnosis algorithms are embedded on the on-board microcontroller. This sensor node uses the power harvested from the solar energy to measure and analyze the impedance data. Simultaneously it monitors temperature on the structure near the piezoelectric sensor and battery power consumption. The wireless sensor node is based on the TinyOS platform for operation, and users can take MATLAB$^{(R)}$ interface for the control of the sensor node through serial communication. In order to validate the performance of this multifunctional wireless impedance sensor node, a series of experimental studies have been carried out for detecting loose bolts and crack damages on lab-scale steel structural members as well as on real steel bridge and building structures. It has been found that the proposed sensor nodes can be effectively used for local wireless health monitoring of structural components and for constructing a low-cost and multifunctional SHM system as "place and forget" wireless sensors.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 하계종합학술대회 논문집(2)
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• pp.477-480
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• 2004

We studied the characteristics of impedance and electromechanical coupling coefficient in ZnO and AIN thin films by using resonance frequency spectrum method. The response peak of impedance decreased with the decrease of thickness of piezoelectrics, the number of mode of response peak increased with the increase of substrate thickness. An error of $k_{t}^{2}$ estimated from input $k_{t}^{2}$ increased as the thickness of piezoelectrics decreased and the thickness of substrate increased. Also, the error was increased in case of a large acoustic impedance of substrate. It was found that the composite resonator operating in optimized condition could be designed through the resonance frequency spectrum analysis of composited resonator consisted of piezoelectric thin film and substrate.

• Smart Structures and Systems
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• 제4권1호
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• pp.35-46
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• 2008

In this paper the authors address the problem of comparing two different smart damping techniques using the numerical modelling of the electro-mechanical impedance for plate structures partially treated with active constrained layer damping treatments. The paper summarizes the modelling procedures including a finite element formulation capable of accounting for the observed behaviour. The example used is a smart cantilever plate structure containing a viscoelastic material (VEM) layer sandwiched between a piezoelectric constrained layer and the host vibrating plate. Comparisons are made between active constrained layer and active damping only and based on the resonance frequency amplitudes of the electrical admittance numerically evaluated at the surface of the piezoelectric model of the vibrating structure.

• Smart Structures and Systems
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• 제18권3호
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• pp.501-523
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• 2016

Electromechanical impedance (EMI) based structural health monitoring is performed by measuring the variation in the impedance due to the structural local damage. The impedance signals are acquired from the piezoelectric patches that are bonded on the structural surface. The impedance variation, which is directly related to the mechanical properties of the structure, indicates the presence of local structural damage. Two traditional EMI-based damage detection methods are based on calculating the difference between the measured impedance signals in the frequency domain from the baseline and the current structures. In this paper, a new structural damage detection approach by analyzing the time domain impedance responses is proposed. The measured time domain responses from the piezoelectric transducers will be used for analysis. With the use of the Time Frequency Autoregressive Moving Average (TFARMA) model, a damage index based on Singular Value Decomposition (SVD) is defined to identify the existence of the structural local damage. Experimental studies on a space steel truss bridge model in the laboratory are conducted to verify the proposed approach. Four piezoelectric transducers are attached at different locations and excited by a sweep-frequency signal. The impedance responses at different locations are analyzed with TFARMA model to investigate the effectiveness and performance of the proposed approach. The results demonstrate that the proposed approach is very sensitive and robust in detecting the bolt damage in the gusset plates of steel truss bridges.

• Structural Monitoring and Maintenance
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• 제11권3호
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• pp.203-217
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• 2024

Electro-mechanical impedance (EMI) technique is a low-cost structural damage detection method. It reflects structural damage through the change in admittance signal which contains the structural mechanical impedance information. The ambient temperature greatly affects the admittance signal, which hides the changes caused by structural damage and reduces the accuracy of damage identification. This study introduces a convolutional neural network to compensate for the temperature effect. The proposed method uses a framework that consists of a feature extraction network and a decoding network, and the original admittance signal with temperature information is used as the input. The output admittance signal is eliminated from the temperature effect, improving damage identification robustness. The admittance data simulated by the finite element model of the spatial grid structure is used to verify the effectiveness of the proposed method. The results show that the proposed method has advantages in identification accuracy compared with the damage index minimization method and the principal component analysis method.

• Smart Structures and Systems
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• 제14권5호
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• pp.811-830
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• 2014

A numerical study has been carried out to simulate an innovative monitoring procedure to detect and localize damage in reinforced concrete beams retrofitted with carbon fiber reinforced polymer (CFRP) unidirectional laminates. The main novelty of the present simulation is its ability to conduct the electromechanical admittance monitoring technique by considerably compressing the amount of data required for damage detection and localization. A FEM simulation of electromechanical admittance-based sensing technique was employed by applying lead zirconate titanate (PZT) transducers to acquire impedance spectrum signatures. Response surface methodology (RSM) is finally adopted as a tool for solving inverse problems to estimate the location and size of damaged areas from the relationship between damage and electromechanical admittance changes computed at PZT transducer surfaces. This statistical metamodel technique allows polynomial models to be produced without requiring complicated modeling or numerous data sets after the generation of damage, leading to considerably lower cost of creating diagnostic database. Finally, a numerical example is carried out regarding a steel-reinforced concrete (RC) beam model monotonically loaded up to its failure which is also retrofitted by a CFRP laminate to verify the validity of the present metamodeling monitoring technique. The load-carrying capacity of concrete is predicted in the present paper by utilizing an Ottosen-type failure surface in order to better take into account the passive confinement behavior of retrofitted concrete material under the application of FRP laminate.

• 한국음향학회지
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• 제37권1호
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• pp.46-52
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• 2018

압전변압기에 사용되는 압전 단결정은 높은 입력 임피던스로 인하여 파워전송용량이 높지 않다는 문제점이 있다. 따라서 본 연구에서는 연산증폭기를 사용한 범용 임피던스 변환(General Impedance Convert, GIC) 회로로 구현된 정전용량 증가회로를 압전 단결정 진동자의 전기단자에 연결함으로써 입력임피던스를 저하시켜 파워전송용량을 향상시킬 수 있는 방법을 제안하였다. $128^{\circ}$회전 Y판 $LiNbO_3$ 단결정 진동자에 설계 제작된 정전용량 증가회로를 적용하여 구동 특성을 측정한 결과, 입력임피턴스는 25 % 감소, 전기-기계결합계수는 30 % 증가, 전압변환 특성에 있어서는 약 17~30배의 출력파워용량이 증가됨을 확인하였다.