• Smart Structures and Systems
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• 제15권4호
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• pp.1159-1175
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• 2015

In this study, the effect of temperature variation on the wireless impedance monitoring is analyzed for the tendon-anchorage connection of the prestressed concrete girder. Firstly, three impedance features, which are peak frequency, root mean square deviation (RMSD) index, and correlation coefficient (CC) index, are selected to estimate the effects of temperature variation and prestress-loss on impedance signatures. Secondly, wireless impedance tests are performed on the tendon-anchorage connection for which a series of temperature variation and prestress-loss events are simulated. Thirdly, the effect of temperature variation on impedance signatures measured from the tendon-anchorage connection is estimated by the three impedance features. Finally, the effect of prestress-loss on impedance signatures is also estimated by the three impedance features. The relative effects of temperature variation and prestress-loss are comparatively examined.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2010년도 정기 학술대회
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• pp.347-351
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• 2010

판과 같은 구조물의 손상 감지를 위해, 손상 전 구조물의 임피던스 신호를 기저신호(Baseline impedance signal)로 이용하여 직접적으로 비교하지 않는 새로운 개념의 무기저 손상진단 기법(Reference-free impedance method)을 제시한다. 박막 압전소자(이하 PZT)를 판의 상하 표면에 부착시킨 한 쌍의 병치 PZT를 이용하여 손상으로 인해 모드변환을 일으키는 전기역학적 신호(Electro Mechanical Signatures ; 이하 EMS)를 추출한다. 이 연구에서는 스펙트럼 요소법(Spectral Element Method ; 이하 SEM)을 이용하여 주파수 영역에서 병치된 PZT의 EMS를 파악하기 위한 수치해석을 수행한다. 특히, 손상에 의해 발생된 모드변환 EMSMC를 병치된 PZT의 극성에 기인한 신호분해 기법을 적용하여 추출하고, 분해된 모드변환 EMSMC가 손상의 위치와 크기에 따라 받는 영향을 추가로 분석한다.

• International Journal of Precision Engineering and Manufacturing
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• 제5권2호
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• pp.46-52
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• 2004

Numerous connectors are used in automobiles for transmission of electrical signals across various electro-mechanical components. The connectors must operate with high reliability in order to minimize failures due to signal degradation. In this work, the effects of contamination at the contact interface of connectors used fur automobile crankshaft position sensor on the impedance change were investigated. An experimental set-up was built to simulate the electrical signal transmitted from the sensor to the engine control unit through a connector. Output from the connector was investigated using connectors contaminated with engine block residues and water droplets. It was found that slight contamination of the connectors could lead to significant signal degradation which can lead to engine failure. Also, the effect of water in the connector altered the signal severely. However, the signal gradually regained the original state as the water evaporated from the interface.

• 한국음향학회지
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• 제21권7호
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• pp.600-605
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• 2002

본 연구에서는 두께 모드 압전 진동자의 특성제어 부임피던스 변환 (NIC) 회로를 적용하였다. 두 개의 두께 모드 압전 진동자를 적층한 후, NIC 회로를 적용하여 입력 어드미턴스와 전기기계 변환효율을 측정한 결과를 시뮬레이션 결과와 비교하였다. 그 결과 NIC 회로에서 구현되는 부저항의 값에 따라 압전 진동자의 품질계수 및 전기음향 변환효율이 제어되었으며 NIC 회로를 적용한 경우에 품질계수는 약 20배, 전기음향 변환효율은 약 2.5배 정도 향상됨을 확인하였다.

• Smart Structures and Systems
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• 제6권7호
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• pp.851-866
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• 2010

This paper presents a new concept of using PZT (lead zircornate titanate) transducers as a non-destructive testing (NDT) tool for evaluating quality of concrete. Detection of defects in concrete is very important in order to check the integrity of concrete structures. The electro-mechanical impedance (EMI) response of PZT transducers bonded onto a concrete specimen can be used for evaluating local condition of the specimen. Measurements are carried out by electrically exciting the bonded PZT transducers at high frequency range and taking response measurements of the transducers. In this study, the compression test results showed that concrete specimens without sufficient compaction are likely to fall below the desired strength. In addition, the strength of concrete was greatly reduced as the voids in concrete were increased. It was found that the root mean square deviation (RMSD) values yielded between the EMI signatures for concrete specimens in dry and saturated states showed good agreement with the specimens' compressive strength and permeable voids. A quality metric was introduced for predicting the quality of concrete based on the dry-saturated state of concrete specimens. The simplicity of the method and the current development towards low cost and portable impedance measuring system, offer an advantage over other NDE methods for evaluating concrete quality.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2010년도 정기 학술대회
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• pp.783-786
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• 2010

This paper presents a finite element analysis on impedance parameters of anchor plates of structural cables under the change in cable forces. To achieve the objective, four approaches are implemented as follows: Firstly, theoretical background of electro-mechanical impedance is described. Secondly, anchor plates of structural cables are selected to experimentally examine the relationship between impedance parameters and cable force changes. Thirdly, finite element analysis is performed to verify the experimental results. Fourthly, a comparison between the experimental and numerical analysis on impedance parameters of anchor plate of structural cables under cable force changes is carried out.

• Smart Structures and Systems
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• 제2권2호
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• pp.101-113
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• 2006

Structural health monitoring results obtained with the electro-mechanical (E/M) impedance techniqueand Lamb wave transmission methods during fatigue crack propagation of an Arcan specimen instrumented with piezoelectric wafer active sensors (PWAS) are presented. The specimen was subjected in mixed-mode fatigue loading and a crack was propagated in stages. At each stage, an image of the crack and the location of the crack tip were recorded and the PWAS readings were taken. Hence, the crack-growth in the specimen could be correlated with the PWAS readings. The E/M impedance signature was recorded in the 100 - 500 kHz frequency range. The Lamb-wave transmission method used the pitch-catch approach with a 3-count sine tone burst of 474 kHz transmitted and received between various PWAS pairs. Fatigue loading was applied to initiate and propagate the crack damage of controlled magnitude. As damage progressed, the E/M impedance signatures and the waveforms received by receivers were recorded at predetermined intervals and compared. Data analysis indicated that both the E/M impedance signatures and the Lamb-wave transmission signatures are modified by the crack progression. Damage index values were observed to increase as the crack damage increases. These experiments demonstrated that the use of PWAS in conjunction with the E/M impedance and the Lamb-wave transmission is a potentially powerful tool for crack damage detection and monitoring in structural elements.

• 센서학회지
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• 제26권2호
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• pp.73-78
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• 2017

A tetrode is one of the neural electrodes, and it is widely used to record neural signals in the brain of a freely moving animal. The impedance of a neural electrode is an important parameter because it determines the signal-to-noise ratio of the recorded neural signals. Here, we developed a modification technique using carbon nanotube-polypyrrole composite nanostructures to decrease the impedances of tetrodes. The synthesis of the carbon nanotube and polypyrrole nanostructures was performed in two steps. In the first step, randomly dispersed carbon nanotubes and pyrrole monomers were gathered and aligned on the tetrode electrode. Next, they were electro-polymerized on the electrode surface. As the applied time (step-1 and step-2) and the offset voltage increased, the impedances of the tetrodes decreased. The modification technique is, therefore, an important and useful of lowering the impedances of tetrodes.

• Smart Structures and Systems
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• 제11권2호
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• pp.217-240
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• 2013

In this paper, practical methods to utilize PZT's dual piezoelectric effects (i.e., dynamic strain and electro-mechanical (E/M) impedance responses) for damage detection in beam-type structures are presented. In order to achieve the objective, the following approaches are implemented. Firstly, PZT material's dual piezoelectric characteristics on dynamic strain and E/M impedance are investigated. Secondly, global vibration-based and local impedance-based methods to detect the occurrence and the location of damage are presented. Finally, the vibration-based and impedance-based damage detection methods using the dual piezoelectric responses are evaluated from experiments on a lab-scaled beam for several damage scenarios. Damage detection results from using PZT sensor are compared with those obtained from using accelerometer and electric strain gauge.

• 한국지반공학회논문집
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• 제34권2호
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• pp.33-42
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• 2018

본 연구에서는 소형 압전소자의 전기-역학적 임피던스를 이용하여 모래의 단위중량이나 강도를 평가하였다. 다짐 몰드 내 크기가 다른 세 종류의 미고결 낙동강모래를 느슨하거나 조밀하게 성형한 다음 내부에 직경 20mm 원형모양의 납작한 압전소자를 설치하고 임피던스를 측정하였다. 또한, 가는 낙동강모래에 시멘트비 4, 8, 12, 16%로 직경 50mm, 높이 100mm의 고결 공시체를 6층으로 다져서 제작하였다. 고결 공시체의 3층 내부에 압전소자를 수평방향으로 설치한 다음 3일 동안 임피던스 신호를 측정하였으며, 측정 후 일축압축시험을 실시하였다. 미고결 모래의 단위중량이 증가함에 따라 공진주파수는 102kHz에서 105kHz까지 약간 증가하였으며, 공진주파수 발생 시 컨덕턴스는 감소하였다. 고결 모래의 양생시간과 시멘트비가 증가함에 따라 공진주파수는 129kHz에서 266kHz까지 크게 증가하였으며, 공진주파수 발생 시 컨덕턴스는 반대로 감소하는 경향을 보였다. 고결 모래의 일축압축강도는 시멘트비에 따라 289-1,390kPa 정도이며, 공진주파수와는 뚜렷한 정비례 관계를 보이지만 공진주파수 발생 시 컨덕턴스와는 반비례 관계를 보였다.