• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.476-481
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• 2004

This paper proposes the modeling scheme of the Miniature Universal Testing Machine (MUTM) composed of 36 thin-beam-type bimorph PZTs and the control algorithm to minimize the residual vibration of the MUTM in the dynamic testing of specimens. In the operation of the MUTM, hysteresis, residual displacement and vibration of it are major issues. From the analysis of the MUTM behaviors, the hysteresis is described by the curving fitting scheme with the function of an input voltage. The dynamic characteristics of the MUTM are identified by the frequency domain modeling technique base on the experimental data. The interest bandwidth is focused on 125-315HZ for effective modeling and control. For the robust vibration control of the MUTM, the sliding mode control and the Kalman filter as observer are proposed. The paper also proposes the best input signal type to operate the MUTM effectively. The feasibility of the proposed modeling scheme and control algorithm are tested and verified experimentally.

• 센서학회지
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• 제31권5호
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• pp.301-306
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• 2022

With the recent widespread implementation of Internet of Things (IoT) technology driven by Industry 4.0, self-powered sensors for wearable and implantable systems are increasingly gaining attention. Piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs), which convert biomechanical energy into electrical energy, can be considered as efficient self-powered sensor platforms. These are energy harvesters that are used as low-power energy sources. However, they can also be used as sensors when an output signal is used to sense any mechanical stimuli. For sensors, collecting high-quality data is important. However, the accuracy of sensing for practical applications is equally important. This paper provides a brief review of the performance advanced by the materials and structures of the latest PENG/TENG-based wearable sensors and intelligent applications applied using artificial intelligence (AI)

• Smart Structures and Systems
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• 제32권6호
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• pp.393-402
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• 2023

Recently, hybrid and electric vehicles have been actively developed to replace internal combustion engine (ICE) vehicles. However, their vibrations and noise with complex spectra cause discomfort to drivers. To reduce the vibrations transmitted through primary excitation sources such as powertrains, structural changes have been introduced. However, the interference among different parts is a limitation. Thus, active mounting systems based on smart materials have been actively investigated to overcome these limitations. This study focuses on diminishing the source movement when a structure with two active mounting systems is excited to a single sinusoidal and a multi-frequency signal, which were investigated for source movement reduction. The overall structure was modeled based on the lumped parameter method. Active vibration control was implemented based on the modeled structure, and a multi-normalization least mean square (NLMS) algorithm was used to obtain the control input for the active mounting system. Furthermore, the performance of the NLMS algorithm was compared with that of the quantification method to demonstrate the performance of active vibration control. The results demonstrate that the vibration attenuation performance of the source component was improved.

• 비파괴검사학회지
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• 제29권2호
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• pp.93-97
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• 2009

자기변형 탐촉자는 유도초음파를 적용한 장거리 배관 검사 시에 유용하게 사용되는데 특히 그 신호패턴이 배열형 압전탐촉자를 사용한 유도초음파 신호보다 깨끗하고 단순하기 때문에 단일 결함에 의한 신호패턴을 해석할 수 있을 뿐만 아니라 결함 신호의 진행 상황을 분석함으로써 배관의 구조 건전성 감시(structural health monitoring)에도 사용되고 있다. 그러나 실제 현장 검사에서는 유도초음파의 방향성신호, 잔향효과, 모드변환, 구조물 등에 의한 의사 신호 또는 거짓 신호가 나타나기 때문에 결함 평가 시에 주의를 요한다. 본 연구에서는 실제 상황을 모의한 장거리배관 mock-up에서 발생하는 모드변환 신호를 실험적으로 검증하고 해석하였다. 자기변형 스트립 탐촉자에서 발생한 비틀림진동 T(0,1) 모드와 휨진동 F(1,3) 모드 또는 종진동 L(0,2) 모드 간에 모드변환이 발생함을 확인하였고 이러한 모드변환이 발생하는 원인을 스트립 탐촉자 및 검사대상체의 전자기적 재료 특성 및 구조 측면에서 해석하였다.

• Smart Structures and Systems
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• 제15권4호
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• pp.1121-1137
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• 2015

This study presents probabilistic-based damage identification technique for highlighting damage in metallic structures. This technique utilizes distributed piezoelectric transducers to generate and monitor the ultrasonic Lamb wave with narrowband frequency. Diagnostic signals were used to define the scatter signals of different paths. The energy of scatter signals till different times were calculated by taking root mean square of the scatter signals. For each pair of parallel paths an error function based on the energy of scatter signals is introduced. The resultant error function then is used to estimate the probability of the presence of damage in the monitoring area. The presented method with an autofocusing feature is applied to aluminum plates for method verification. The results identified using both simulation and experimental Lamb wave signals at different central frequencies agreed well with the actual situations, demonstrating the potential of the presented algorithm for identification of damage in metallic structures. An obvious merit of the presented technique is that in addition to damages located inside the region between transducers; those who are outside this region can also be monitored without any interpretation of signals. This novelty qualifies this method for online structural health monitoring.

• 센서학회지
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• 제27권4호
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• pp.254-258
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• 2018

A Wi-Fi signal network (WSN) system is introduced in this paper. This system consists of several data-transmitting sensor modules and a data-receiving server. Each sensor module and the server contain a unique intranet IP address. A piezoelectric accelerometer with a bandwidth of 12 kHz, a 24-bit analog-digital converter with a sampling rate of 15.625 kS/s, a 32-bit microprocessor unit, and a 1-Mbps Wi-Fi module are used in the data-transmitting sensor module. A 300-Mbps router and a PC are used in the server. The system is verified using an accelerometer calibrator. The voltage output from the sensor is converted into 24-bit digital data and transmitted via the Wi-Fi module. These data are received by a Wi-Fi router connected to a PC. The input frequencies of the accelerometer calibrator (320 Hz, 640 Hz, and 1280 Hz) are used in the data transfer verification. The received data are compared to the data retrieved directly from the analog-to-digital converter used in the sensor module. The comparison shows that the developed system represents the original data considerably well. Theoretically, the system can acquire vibration signals from 600 sensor modules at an accelerometer bandwidth of 15.625 kHz. However, delay exists owing to software processes, multiplexing between sensor modules, and the use of non-real time operating system. Hence, it is recommended that this system may be used to acquire vibration signals with up to 10 kHz, which is approximately 70% of the theoretical maximum speed of the system. The system can be upgraded using parts with higher performance

• 대한기계학회논문집A
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• 제25권10호
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• pp.1551-1558
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• 2001

Recently, a number of underground pipelines have been drastically increased. The integrity of these buried pipelines, especially gas transmitting pipelines, is of importance due to an explosive characteristic of natural gas. The third party damage is known as one of the most critical factor which causes fatal accidents. For this reason, a number of systems detecting third party damage are under development. The major concern in the development of third party damage detection system is to transmit vibration signals out of accelerometer to signal conditioner and data acquisition system without any interference caused by noise. The objective of this paper is to develope a fiber optic accelerometer applicable to third party damage detection system. A fiber optic accelerometer was developed by use of combining principles of one degree of freedom vibration model and an extrinsic Fabry-Perot interferometer. The developed fiber optic accelerometer was designed to perform with a sensitivity of 0.06mVg, a frequency range of less than 6kHz and an amplitude range of -200g to 200g. The developed, accelerometer was compared with a piezoelectric accelerometer and calibrated. In order to verify the developed accelerometer, the field experiment was performed. From the field experiment, vibration signals and the location of impact were successfully detected. The developed accelerometer is expected to be used for the third party damage detection system which requires long distance transmission of signals.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권3호
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• pp.149-155
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• 2006

This paper presents a torsional micromirror detached from PZT actuators (TMD), whose rotational motion is achieved by push bars in the PZT actuators detached from the micromirror. The push bar mechanism is intended to reduce the bending, tensile and torsional constraints generated by the conventional bending bar mechanism, where the torsional micromirror is attached to the PZT actuators (TMA). We have designed, fabricated and tested prototypes of TMDs for single-axis and dual-axis rotation, respectively. The single-axis TMD generates the static rotational angle of $6.1^{\circ}$ at 16 VDC, which is 6 times larger than that of single-axis TMA, $0.9^{\circ}$. However, the rotational response curve of TMD shows hysteresis due to the static friction between the cover and the push bar in the PZT actuator. We have shown that 63.2% of the hysteresis is due to the static friction caused by the initial contact force of the PZT actuaor. Without the initial contact force, the rotational response curve of TMD shows linear voltage-angle characteristics. The dual-axis TMD generates the static rotational angles of $5.5^{\circ}$ and $4.7^{\circ}$ in x-axis and y-axis, respectively at 16 VDC. The measured resonant frequencies of dual-axis TMD are $2.1\pm0.1$ kHz in x-axis and $1.7\pm0.1$ kHz in y-axis. The dual-axis TMD shows stable operation without severe wear for 21.6 million cycles driven by 16 Vp-p sinusoidal wave signal at room temperature.

• 한국항공우주학회지
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• 제32권7호
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• pp.51-59
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• 2004

저속충격에 의한 복합재의 파손 모드를 규명하기 위하여 PVDF 센서를 이용한 신호취득 방법과 측정된 PVDF 센서 신호를 시간-주파수 분석법 (time-frequency analysis)인 국소 퓨 리에 변환 및 웨이블렛 변환을 적용하여 분석할 수 있는 실험적 전차에 대하여 고찰하였다. 고분자 암전센서를 이용하여 저속충격시 발생할 수 있는 여러 충격손상 형태 모재균열, 층간분리, 섬유파단에 의한 응력파 측정 가능성을 고찰하기 위하여 일련의 저속충격 시험을 수행하였다. 충격 시험 후, 저속 충격을 받은 적층판에 대하여 C-scan 과 단면 검사를 통하여 센서 신호, 손상 모드 및 크기에 대한 상관관계를 고찰하였다. 센서신호의 취득과 신호분석을 통하여 저속충격의 발생/진행과정을 알 수 있는 많은 중요한 정보가 PVDF 센서신호에도 내재되어 있음을 알 수 있으며 PVDF 센서 신호를 주의 깊게 분석함으로써 저속 충격에 의한 복합재료의 손상 모드 규명이 가능하며 저속충격 위협에 대한 복합재 구조물의 건전성 모니터링에 활용할 수 있는 가능성을 제시하였다.

• 센서학회지
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• 제23권2호
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• pp.94-98
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• 2014

Aluminum nitride (AlN) thin films with a TiN buffer layer have been fabricated on SUS430 substrate by RF reactive magnetron sputtering at room temperature under 25~75% $N_2$ /Ar. The characterization of film properties were performed using surface profiler, X-ray diffraction, X-ray photoelectron spectroscopy(XPS), and pressure-voltage measurement system. The deposition rates of AlN films were decreased with increasing the $N_2$ concentration owing to lower mass of nitrogen ions than Ar. The as-deposited AlN films showed crystalline phase, and with increasing the $N_2$ concentration, the peak of AlN(100) plane and the crystallinity became weak. Any change in the preferential orientation of the as-deposited AlN films was not observed within our $N_2$ concentration range. But in the case of 50% $N_2$ /Ar condition, the peak of (002) plane, which is determinant in pressure sensing properties, appeared. XPS depth profiling of AlN/TiN/SUS430 revealed Al/N ratio was close to stoichiometric value (45:47) when deposited under 50% $N_2/Ar$ atmosphere at room temperature. The output signal voltage of AlN sensor showed a linear behavior between 26~85 mV, and the pressure-sensing sensitivity was calculated as 7 mV/MPa.