• Transactions of the Korean Society of Mechanical Engineers A
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• 제41권5호
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• pp.401-407
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• 2017

This paper describes wavenumber filtering for damage detection using single-frequency standing wave excitation and laser scanning sensing. An embedded piezoelectric sensor generates ultrasonic standing waves, and the responses are measured using a laser Doppler vibrometer and mirror tilting device. After scanning, newly developed damage detection techniques based on wavenumber filtering are applied to the full standing wave field. To demonstrate the performance of the proposed techniques, several experiments were performed on composite plates with delamination and aluminum plates with corrosion damage. The results demonstrated that the developed techniques could be applied to various structures to localize the damage, with the potential to improve the damage detection capability at a high interrogation speed.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• 제8권4호
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• pp.79-86
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• 1999

Electronic Speckle Pattern Interferometry(ESPI) is a powerful tool to measure the vibration mode shape and resonance frequency for modal analysis. As for ESPI this method is very suited for full-field measurement of objects in industrial areas because the interferograms are recorded with a video camera and evaluated in real-time with a computer. In this study We performed experiments at the same constraint conditions as disk brake of the practical vehicle as far as possible and obtained the resonance frequencies and vibration mode shapes by using time-averaged ESPI at once. Finally to assure the expetimental results by time-averaged ESPI we also compare those with results obtained by Laser Doppler Vibrometer and obtained good agreement.

• Journal of Welding and Joining
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• 제27권5호
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• pp.68-73
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• 2009

The bar horn is designed to increase uniformity of the displacement on the output face through simulation and experiments. Three-dimensional modal analysis is conducted using the finite element method to calculate the vibration mode and displacement on the output face, and the design of experiment (DOE) technique is employed to determine the optimum dimensions of the groove and slot so that the high amplitude uniformity of the bar horn is produced. Displacement of the bar horn was measured using the Laser Doppler Vibrometer (LDV), and the experimental results show good agreements with the predicted results. High uniformity of the bar horn is achieved with the dimensions of the groove and slot determined using the design equations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.150-155
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• 2006

Speech intelligibility is investigated on a conference room-window glass coupled system. Using MLS(Maximum Length Sequency) signal as a sound source, acceleration and velocity responses of the window glass are measured by accelerometer and laser doppler vibrometer. MTF(Modulation Transfer Function) is used to identify the speech transmission characteristics of the room and window system. STI(Speech Transmission Index) is calculated by using MTF and speech intelligibility of the room and the window glass is estimated. Speech intelligibilities by the acceleration signal and the velocity signal are compared and the possibility of the wiretapping is investigated. Finally, intelligibility of the conversation sound is examined by the subjective test.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제17권4호
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• pp.363-369
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• 2007

The purpose of the study is to obtain acoustical information to prevent eavesdropping of the glass window. Speech intelligibility was investigated on the vibration sound detected from the glass window of a conference room. Objective test using speech transmission index(STI) was performed to estimate quantitatively the speech intelligibility. STI was determined based on tile modulation transfer function(MTF) of the room-glass window system. Using Maximum Length Sequency(MLS) signal as a sound source, impulse responses of the glass window and MTF were determined by signals from accelerometers and laser doppler vibrometer. Finally, speech intelligibility of the interior sound and window vibration were compared under different sound pressure levels and amplifier gains to confirm the effect of measurement condition on the speech intelligibility.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.649-654
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• 2007

Eavesdropping prevention performance is evaluated on a commercial window shaker, which is used to prevent a glass window from eavesdropping. Speech transmission index (STI) is introduced in order to estimate quantitatively the speech intelligibility of the sound detected on the glass window. Objective test by IEC standard using modulation transfer function (MTF) is performed to determine STI. Using Maximum Length Sequency (MLS) signal as a sound source, MTF is measured by accelerometers and laser doppler vibrometer. STI under different level of disturbing wave are compared to confirm the disturbing effect on the speech intelligibility.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.620-623
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• 2003

Non-linear behaviors of multilayer piezoelectric ceramic actuator (MCA) were investigated under electrical and mechanical stress. DC 100 V bias was applied to the MCA to obtain displacement. Laser vibrometer, which using Doppler effect, was employed to characterize displacement caused by $d_{33}$ mode of MCA. To understand this non-linear behavior of MCA, displacement was measured and compared under different load states. By increasing load, electric field-induced strain and piezoelectric constant($d_{33}$) of MCA was decreased. We attribute this phenomenon to the domain wall motion and depoling of MCA under heavy load.

• Proceedings of the KSME Conference
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• 대한기계학회 2003년도 추계학술대회
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• pp.670-675
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• 2003

With the increase in recording density and higher rotation speeds, the aerodynamic aspect of hard disk drives (HDDs) is now quite significant. To achieve high TPI (tracks per inch) for hard disk drives, the actuator must induce less air turbulence. Also, alternative cross sections for the actuator arms are proposed for the reduction of air turbulence. In this study, off-track vibration of actuator arms used in of 3.5" hard disk drives with different cross sections have been measured by using Laser Doppler Vibrometer (LDV). It has been found that the vibration of the actuator arms with modified cross sections is lower than the conventional one.

• The Transactions of the Korean Institute of Electrical Engineers D
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• 제50권8호
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• pp.392-399
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• 2001

This paper presents an auxiliary beam-assisted adaptive compensation technique applied to alleviate the problem of LDV's body vibration. The LMS algorithm is applied to adaptively compensate the body vibration utilizing the reference signal provided by the auxiliary beam. The usefulness of the proposed technique is verified via computer simulations performed for diverse types of target signals and body vibration.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.333-337
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• 2003

The use of reactive shearing structural intensity to place small patches of constrained layer damping material in order to achieve the largest reduction in the radiated sound power of Air-conditioner outdoor unit is described. The normal surface velocity of each panel was measured using a laser doppler vibrometer. Experimental results indicated that patches of constrained layer damping material placed over areas of high reactive structural intensity reduced the radiated sound power significantly more than patches of the same area placed over areas of low reactive structural intensity