• Smart Structures and Systems
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• 제18권3호
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• pp.471-484
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• 2016

Optical fiber sensors have been proven that they have the potential to detect high-frequency ultrasonic signals, in structural health monitoring field which generally refers to acoustic emission signals from active structural damages and guided waves excited by ultrasonic actuators and propagating in waveguide. In this work, the sensing properties of optical fiber sensors based on Mach-Zehnder interferometer were investigated in the metal plate. Analytical formulas were conducted first to explore the parameters affecting its sensing performances. Due to the simple and definable frequency component, the Lamb wave excited by the piezoelectric wafer was employed to study the sensitivity of the proposed optical fiber sensors with respect to the frequency, rather than the acoustic emission signals. In the experiments, according to above investigations, spiral shape optical fiber sensors with different size were selected to increase their sensitivity. Lamb waves were excited by a circular piezoelectric wafer, while another piezoelectric wafer was used to compare their voltage responses. Furthermore, by changing the excitation frequency, the tuning frequency characteristic of the proposed optical fiber sensor was also investigated experimentally.

• 센서학회지
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• 제14권4호
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• pp.225-230
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• 2005

This paper describes a novel tip position sensor made of a triangularly shaped piezoelectric PVDF (polyvinylidene fluoride) film for a cantilever beam. Due to the boundary condition of the cantilever beam and the spatial sensitivity function of the sensor, the charge output of the sensor is proportional to the tip position of the beam. Experimental results with the PVDF sensor were compared with those using two commercially available position sensors: an inductive sensor and an accelerometer. The resonance frequencies of the test beam, measured using the PVDF sensor, matched well with those measured with the two commercial sensors and the PVDF sensor also showed good coherence over wide frequency range, whereas the inductive sensor became poor above a certain frequency.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.625-629
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• 1999

In this study, in order to develop high sensitivity and low noise acoustic emission sensor, we manufactured the Pb(Zr, Ti)O$_3$ ceramics with the addition of WO$_3$ wt% to search for its required characteristics. Dielectric constant was increased as a function of the increase of WO$_3$ wt%. The Pb(Zr, Ti)O$_3$ (EC-65) ceramics added with 0.1lwt% WO$_3$ showed excellent dielectric constant and piezoelectric constants of 1931 and 199.55$\times$10$^{-12}$ (C/N), respectively. Accordingly It was shown as the composition ceramics suitable for AE sensor.

• 대한전기학회논문지
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• 제41권2호
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• pp.192-198
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• 1992

The electrical properties of the ultrasonic probes and the piezoelectric composite materials with 1-3 connectivity by the extrusion method have been studied. The relative permittivity and piezoelectric coefficient increase linearly as PZT volume% increases and resonance frequency moves to low frequency as the sample thickness increases. The acoustic impedance matching with body and water is better than PZT ceramics' and the reception sensitivity is fine as the thickness thins down.

• Smart Structures and Systems
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• 제8권3호
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• pp.321-341
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• 2011

Acoustic emission (AE) monitoring was conducted for mortar specimens under three types of static loading patterns (cubic-splitting, direct-shear and pull-out). Each of the applied loading patterns was expected to produce a particular fracture process. Subsequently, the AEs generated by various fracture or damage processes carried specific information on temporal micro-crack behaviors of concrete for post analysis, which was represented in the form of detected AE signal characteristics. Among various available characteristics of acquired AE signals, frequency content was of great interest. In this study, cement-based piezoelectric sensor (as AE transducer) and home-programmed DEcLIN monitoring system were utilized for AE monitoring on mortar. The cement-based piezoelectric sensor demonstrated enhanced sensitivity and broad frequency domain response range after being embedded into mortar specimens. This broad band characteristic of cement-based piezoelectric sensor in frequency domain response benefited the analysis of frequency content of AE. Various evaluation methods were introduced and employed to clarify the variation characteristics of AE frequency content in each test. It was found that the variation behaviors of AE frequency content exhibited a close relationship with the applied loading processes during the tests.

• 정보저장시스템학회논문집
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• 제3권1호
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• pp.47-53
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• 2007

In this paper, a thermo-piezoelectric mechanism with integrated heaters and piezoelectric sensors has been studied for low power probe-based data storage. Silicon nitride cantilever integrated with silicon heater and piezoelectric sensor has been developed to improve the uniformity of cantilevers. Data bits of 40 nm in diameter were recorded on PMMA film. The sensitivity of the piezoelectric sensor was 0.615 fC/nm after poling the PZT layer. And, the $34\times34$ probe array integrated with CMOS circuits has been successfully developed by simple one-step bonding process. The process can simplify the process step and reduce tip wear using silicon nitride tip.

• Smart Structures and Systems
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• 제15권4호
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• pp.997-1018
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• 2015

Structural health monitoring along with damage detection and assessment of its severity level in non-accessible reinforced concrete members using piezoelectric materials becomes essential since engineers often face the problem of detecting hidden damage. In this study, the potential of the detection of flexural damage state in the lower part of the mid-span area of a simply supported reinforced concrete beam using piezoelectric sensors is analytically investigated. Two common severity levels of flexural damage are examined: (i) cracking of concrete that extends from the external lower fiber of concrete up to the steel reinforcement and (ii) yielding of reinforcing bars that occurs for higher levels of bending moment and after the flexural cracking. The purpose of this investigation is to apply finite element modeling using admittance based signature data to analyze its accuracy and to check the potential use of this technique to monitor structural damage in real-time. It has been indicated that damage detection capability greatly depends on the frequency selection rather than on the level of the harmonic excitation loading. This way, the excitation loading sequence can have a level low enough that the technique may be considered as applicable and effective for real structures. Further, it is concluded that the closest applied piezoelectric sensor to the flexural damage demonstrates higher overall sensitivity to structural damage in the entire frequency band for both damage states with respect to the other used sensors. However, the observed sensitivity of the other sensors becomes comparatively high in the peak values of the root mean square deviation index.

• 센서학회지
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• 제32권2호
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• pp.88-94
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• 2023

Recently, piezoelectric tactile sensors have garnered considerable attention in the field of texture recognition owing to their high sensitivity and high-frequency detection capability. Despite their remarkable potential, improving their mechanical flexibility to attach to complex surfaces remains challenging. In this study, we present a flexible piezoelectric sensor that can be bent to an extremely small radius of up to 2.5 mm and still maintain good electrical performance. The proposed sensor was fabricated by controlling the thickness that induces internal stress under external deformation. The fabricated piezoelectric sensor exhibited a high sensitivity of 9.3 nA/kPa ranging from 0 to 10 kPa and a wide frequency range of up to 1 kHz. To demonstrate real-time texture recognition by rubbing the surface of an object with our sensor, nine sets of fabric plates were prepared to reflect their material properties and surface roughness. To extract features of the objects from the detected sensing data, we converted the analog dataset to short-term Fourier transform images. Subsequently, texture recognition was performed using a convolutional neural network with a classification accuracy of 97%.

• Composites Research
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• 제17권4호
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• pp.61-67
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• 2004

Micromechanical 시험법과 음향방출을 이용하여 단일 basalt 섬유 강화 에폭시 복합재료의 비파괴 손상감지능을 평가하였다. 음향방출 센서로는 PZT 및 고분자 PVDF와 P(VDF-TrFE)를 사용하였고 단섬유 강화 시험법에서 각 센서 종류에 따른 손상감지능을 상호 비교하였다. 고분자 센서는 시편 표면에 부착시키거나 내부에 함침시켜 사용하였지만 PZT 센서는 표면에 부착하여 사용하였다. 고분자 센서를 시편 표면에 부착시킨 경우와 함침시킨 경우 감지능은 비슷하였지만 부착의 경우 debonding 신호가 많아 함침 시키는 방법이 손상감지에 더 효과적이었다. 손상 감지능은 PZT센서가 가장 높았고, 함침 및 부착 모두에서 PVDF와 P(VDF-TrFE) 센서의 손상감지능은 거의 비슷하였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권5호
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• pp.289-293
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• 2000

This paper presents a study on the linear compensation of nonlinear hysteric actuators using the highly magnetostrictive film pattern as a strain sensor. Elements had a hybrid structure, in which thin soft glass substrate with the highly magnetostrictive amorphous FeCoSiB film was bonded on the PZT piezoelectric substrate. The magnetostrictive film as a strain sensor detects the deflection of an actuator, and a voltage signal from the strain sensor related to the deflection of an actuator is used for the linear control of an actuator.