• Smart Structures and Systems
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• v.19 no.6
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• pp.625-631
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• 2017

In the fields of civil engineering and seismology, it is essential to detect and tracking the vibrations, and the fiber Bragg gratings (FBGs) are typically used as sensors to measure vibrations. Where, one of the most popular and detailed approaches to use FBGs as vibration sensors involves the use of cantilever beam designs, which adds a mass to measure low and moderate frequencies (from 20 Hz up to 1 kHz) with high sensitivities (greater than 10 pm/g). The design consists of a bending strain in the cantilever that is simultaneously transferred to the FBG, resulting in a shift in the wavelength that is proportional to the strain experienced by the cantilever. In this work, we present the experimental results of a vibration sensor design using a cantilever beam to generate an axial uniform strain in the FBG in-line with the vertical axis, which modifies the cantilever's natural frequency that allows the sensor to have a wide frequency broadband without losing sensitivity. This sensor achieved a sensitivity of about 339 pm/g and a natural frequency of 227.3 Hz. The presented design compared with the traditional cantilever beam-based FBG vibration sensors, has the advantages of a simple design for detection on vibration-sensitive structures and its physical parameters can be easily modified in order to satisfy the requirements of the desired vibration measurements.

• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.4
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• pp.492-498
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• 2017

In this paper, we integrate a divide-by-3 injection-locked frequency divider (ILFD) in CMOS technology with a $0.18-{\mu}m$ BiCMOS process. We propose a self-injection technique that utilizes harmonic conversion to improve the locking range, phase-noise, and input sensitivity simultaneously. The proposed self-injection technique consists of an odd-to-even harmonic converter and a feedback amplifier. This technique offers the advantage of increasing the injection efficiency at even harmonics and thus realizes the low-power implementation of an odd-order division ILFD. The measurement results using the proposed self-injection technique show that the locking range is increased by 47.8% and the phase noise is reduced by 14.7 dBc/Hz at 1-MHz offset frequency with the injection power of -12 dBm. The designed divide-by-3 ILFD occupies $0.048mm^2$ with a power consumption of 18.2-mW from a 1.8-V power supply.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.52.2-52.2
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• 2017

Recent success of gravitational wave (GW) detection by LIGO opened a new window to expand our understanding of the Universe. In addition to LIGO, several other developments are going on or under planning. However, each of these detectors has a specific sensitive frequency range. There is a missing frequency band, 0.1-10 Hz, where detectors loose sensitivity significantly due to Newtonian noise on the Earth. We introduce a plan to develop a Superconducting Low-frequency Gravitational- wave Telescope (SLGT), which can observe massive black holes in 0.1-10 Hz. The SLGT system consists of magnetically levitated six test masses, superconducting quantum interference devices (SQUIDs), rigid support frame, cooling system, vibration isolation, and signal acquisition. By taking the advantage of nearly quantum-limited low-noise SQUIDs and capacitor bridge transducers, SLGT's detection sensitivity can be improved to allow astrophysical observation of black holes in cosmological distances. We present preliminary design study and expected sensitivity, and its technical feasibility.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.520-528
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• 2001

This paper investigates a resonant microaccelerometer that measures acceleration using a built-in micromechanical resonator, whose resonant frequency is changed by the acceleration-induced axial force. A set of design equations for the resonant microaccelerometer has been developed, including analytic formulae for resonant frequency, sensitivity, nonlinearity and maximum stress. On this basis, the sizes of the accelerometer are designed for the sensitivity of 10$^3$Hz/g in the detection range of 5g, while satisfying the conditions for the maximum nonlinearity of 5%, the minimum shock endurance of 100g and the size constraints placed by microfabrication process. A set of the resonant accelerometers has been fabricated by the combined use of bulk-micromachining and surface-micromachining techniques. From a static test of the cantilever beam resonant accelerometer, a frequency shift of 860Hz has been measured for the proof-mass deflection of 4.3${\pm}$0.5$\mu\textrm{m}$; thereby resulting in the detection sensitivity of 1.10${\times}$10$^3$Hz/g. Uncertainty analysis of the resonant frequency output has been performed to identify important issues involved in the design, fabrication and testing of the resonant accelerometer.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.1
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• pp.48-58
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• 2002

There is a purpose of this study for the proposal of the optimum technique utilized for the vibration design initial step. The stiffened plate structure for the ship hull is made for analysis model. To begin with, dynamic characteristics of stiffened plate structure is analysed using FEM. Main vibrational mode of the structure is decided in the analytical result of FEM. The simplified equation on the natural frequency of the main vibrational mode is induced. Next, sensitivity analysis is carried out using the simplified equation, and rate of change of dynamic characteristics is calculated. Then, amount of design variable is calculated using this sensitivity value and optimum structural modification method. The change of natural frequency is made to be an objective function. Thickness of panel, cross section moment of stiffener and girder become a design variable. The validity of the optimization method using simplified equation is examined. It is shown that the result effective in the optimum modification for natural frequency of the stiffened plate structure.

• Journal of Magnetics
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• v.18 no.2
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• pp.159-162
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• 2013

We present how to optimize the operation condition including frequency of the orthogonal fluxgate sensor in this paper. The orthogonal fluxgate sensor was fabricated with a Co-based amorphous wire with 10 mm long and 100 ${\mu}m$ in the diameter and a 270-turn pickup coil wound on the amorphous wire. In order to investigate the frequency dependence of the sensitivity, output spectra of the sensor which was connected by using a coaxial cable with various lengths of 0.5-5 m were measured with a RF lock-in amplifier. The maximum sensitivities were obtained at different frequencies according to coaxial cable lengths. It was found that the optimal operation frequencies, at which maximum sensitivities were appeared, were almost identical to the frequencies of impedance resonance. The maximum sensitivity and optimal operation frequency were 1.1 V/Oe (${\approx}$ 11000 V/T) and 1.25 MHz respectively.

• Journal of the Korean Magnetics Society
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• v.22 no.6
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• pp.200-203
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• 2012

In this study, we have investigated that the operation frequency dependences of the output properties of the orthogonal fluxgate sensor which was fabricated with a ferrite core. An orthogonal fluxgate sensor should be operated in as high as possible frequency to enhance its sensitivity in the case of small sized sensor, because sensitivity of the sensor is proportional to cross section area, winding number and operation frequency. In this study, we investigated the correspondence of the frequency dependence of output and the reactance (inductance and capacitance) of pickup coil and cable. Experimental results represented that we could obtain maximum output (= sensitivity) at optimal frequency which is near LC resonance frequency of the pickup coil and cable.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.705-707
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• 2004

In this paper, we propose a robust control technique against parameter uncertainties as well as external disturbances. It is robust control scheme using discrete-time state space disturbance observer. It does not require disturbance modeling, plant inverse modeling and/or Q filter. In frequency domain, its performance is evaluated in terms of sensitivity and complementary sensitivity as well as gain and phase margin. Finally we discuss design criterion of state space disturbance observer considering its performance in frequency domain.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.6
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• pp.480-488
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• 2003

The purpose of this research Is to derive the principal design parameters governing the dynamic characteristics of the high response flow control servo valve. For this purpose, a numerical modeling of the servo valve system and a parameter sensitivity analysis to a frequency response characteristics was peformed. As a result of these analysis, a basis for improvement of a dynamic characteristics of servo valve was arranged.

• Journal of KSNVE
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• v.5 no.3
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• pp.395-402
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• 1995

In general low frequency vibration characteristics like an idleshake is mainly influeced by pillar section properties and joints. So the design technique development of vehicle pillar structures is required to initial design and vehicle development stage. In this paper to develop pillar structure design technique considering low frequency vibration characteristics, strain energy method, design sensitivity analysis method, and design optimization method using commercial finite element analysis program and optimization program are presented.