• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.1
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• pp.139-149
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• 1999

In this paper, we estimate the scale factor error and random walk characteristics of the ring laser gyro which has the body dither for Lock-in compensation. And then, we compared those results with the static test results for 28cm square ring laser gyro which has about 0.5 deg/sec static Lock-in. In the case of sinusoidal body dither, dynamic Lock-in occurs periodically at the points where the gyro output pulse becomes the integer multiples of body dither frequency. The width of dynamic Lock-in is changed by variation of dither amplitude, and, between the width of dynamic Lock-in which occurs at the even multiple points of body dither frequency and that at the odd muliple points of body dither frequency, it has 180o phase difference. Generally random body dither is adopted to compensate for dynamic Lock-in. Then if the irregularity is not large enough, the scale factor error by dynamic Lock-in is not vanished. And if the irregularity is large enough, the scale factor error decreases, but random walk becomes larger relatively. And we confirmed that the larger body dither amplitude, the smaller random walk.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.4
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• pp.515-523
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• 2002

Effects of rotary oscillation on unsteady laminar flow past a circular cylinder have been investigated in this study. Numerical simulations are performed for the flow at Re=100 in the range of 0.2<$\Omega$<2.5 and 0.02<$St_f$<0.8, where $\Omega$ and $St_f$ are, respectively, the maximum rotation velocity and rotation frequency normalized by the free-stream velocity and cylinder diameter. Results show that rotary oscillation has significant effects on the flow. When the rotation frequency is near the natural vortex-shedding frequency, lock-on occurs and the lock-on frequency range becomes wider as the rotation velocity increases. In a certain range of the rotation frequency and velocity, modulations in the velocity, lift and drag signals occur and this modulation frequency is expressed as a linear combination of the rotation frequency and vortex-shedding frequency. The mean drag and amplitude of the lift fluctuations show local minima near the boundary between the lock-on non and lock-on regions.

• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.4
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• pp.534-542
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• 2017

This paper presents a fast locking technique for a fractional-N PLL frequency synthesizer. The technique directly measures $K_{VCO}$ on a chip, computes the VCO's target tuning voltage for a given target frequency, and directly sets the loop filter voltage to the target voltage before the PLL begins the normal closed-loop locking process. The closed-loop lock time is significantly minimized because the initial frequency of the VCO are put very close to the desired final target value. The proposed technique is realized and designed for a 4.3-5.3 GHz fractional-N synthesizer in 65 nm CMOS and successfully verified through extensive simulations. The lock time is less than $12.8{\mu}s$ over the entire tuning range. Simulation verifications demonstrate that the proposed method is very effective in reducing the synthesizer lock time.

• Journal of information and communication convergence engineering
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• v.10 no.2
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• pp.187-193
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• 2012

A 1 GHz CMOS fast-lock phase-locked loop (PLL) is proposed to support the quick wake-up time of mobile consumer electronic devices. The proposed fast-lock PLL consists of a conventional charge-pump PLL, a frequency-to-digital converter (FDC) to measure the frequency of the input reference clock, and a digital-to-analog converter (DAC) to generate the initial control voltage of a voltage-controlled oscillator (VCO). The initial control voltage of the VCO is driven toward a reference voltage that is determined by the frequency of the input reference clock in the initial mode. For the speedy measurement of the frequency of the reference clock, an FDC with a parallel architecture is proposed, and its architecture is similar to that of a flash analog-to-digital converter. In addition, the frequency-to-voltage converter used in the FDC is designed simply by utilizing current integrators. The circuits for the proposed fast-lock scheme are disabled in the normal operation mode except in the initial mode to reduce the power consumption. The proposed PLL was fabricated by using a 0.18-${\mu}m$ 1-poly 6-metal complementary metal-oxide semiconductor (CMOS) process with a 1.8 V supply. This PLL multiplies the frequency of the reference clock by 10 and generates the four-phase clock. The simulation results show a reduction of up to 40% in the worstcase PLL lock time over the device operating conditions. The root-mean-square (rms) jitter of the proposed PLL was measured as 2.94 ps at 1 GHz. The area and power consumption of the implemented PLL are $400{\times}450{\mu}m^2$ and 6 mW, respectively.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.6
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• pp.1353-1361
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• 2001

Vortex lock-on or resonance behind a circular cylinder is visualized using a time-resolved PW when a single frequency oscillation is superimposed on the mean incident velocity. For vector processing, a cross-correlation algorithm in conjunction with a recursive correlation and interrogation window shifting techniques is used. Measurements are made of the Karmas and streamwise vertices in the wake-transition regime at Reynolds lumber 360. When lock-on occurs, the vortex shedding frequency is found to be half the oscillation frequency as expected from previous experiments. At the lock-on state, the Karman vortices are observed to be more disordered by the increased strength and spanwise wavelength of the streamwiee vortices, which lead? to a strong three-dimensional motion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.5
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• pp.573-583
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• 1998

Effects of the oscillating incoming flow on vortex shedding and lock-on behind a square cylinder are investigated using numerical simulations at a Reynolds number of 100. Vortex shedding occurred at low forcing frequencies of the incoming flow similar to the natural vortex shedding. As the forcing frequency further increases, the shedding frequency decreases to the half of the forcing freqnency. For a sufficiently large frequency, vortex shedding returns to the natural vortex shedding irrespective of the forcing amplitude. Also, the lock-on region becomes wider with higher forcing amplitudes. The phase diagram between the drag and lift shows a simple periodic behavior in the lock-on region, while a complicated periodic phase relation is observed when there is no lock-on.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.40-45
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• 2013

The purpose of this study was to detect the pin hole defect of dental composite restoration using lock-in thermography method. Amplitude and phase images of the composite resin specimens were analyzed according to the lock-in frequency and the diameter of defect area. Through the amplitude image analysis, at lock-in frequency of 0.05 Hz, defect diameters 2-5 mm exhibited the highest amplitude contrast value between defective area and sound area. The lock-in frequency range of 0.3-0.5 Hz provided good phase angle contrast for the defect area. At lock-in frequency range of 0.5 Hz, defect diameter of 5 mm exhibited the highest phase contrast value. It is concluded that the infrared lock-in thermography method verified the effectiveness for detecting the pin hole defect of dental composite restoration.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.9
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• pp.44-51
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• 2019

Three types of samples with defects were measured by lock-in med-IR (infrared) thermography with various lock-in frequencies for different materials. The lock-in method can be used to detect defects when an external energy source is applied to the object, the non-uniformity of the incident thermal energy distribution is eliminated, and the camera's measurement cycle is synchronized with the load cycle of the incident energy source. For inspecting samples with defects, results of thermal images are analyzed when three types of materials, i.e., SM45C, STS316L, and AL6061 are tested and three lock-in frequencies, i.e., 0.08, 0.1, and 0.12 Hz are applied. In this study, the optimal lock-in frequencies were determined by comparing the results of each material and lock-in frequency measured using the mid-IR camera.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.8 s.239
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• pp.895-902
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• 2005

Lock-on characteristics of flow around a circular cylinder oscillating rotationally with a relatively high forcing frequency have been investigated experimentally. Dominant governing parameters are Reynolds number (Re), angular amplitude of oscillation (${\theta}_A$), and frequency ratio $F_R=f_f/f_n,\;where\;f_f$ is a forcing frequency and $f_n$ is a natural frequency of vortex shedding. Experiments were carried out under the conditions of $Re=4.14{\times}10^3,\;{\pi}/90{\leq}{\theta_A}{\leq}{\pi}/3,\;and\;F_R=1.0$. The effect of this active flow control technique on the lock-on flow characteristics of the cylinder wake was evaluated with wake velocity measurements and spectral analysis of hot-wire signals. The rotational oscillation modifies the flow structure of near wake significantly. The lock-on phenomenon always occurs at $F_R=1.0$, regardless of the angular amplitude ${\theta}_A$. In addition, when the angular amplitude is less than a certain value, the lock-on characteristics appear only at $F_R=1.0$,. The range of lock-on phenomena expands and vortex formation length is decreased, as the angular amplitude increases. The rotational oscillation create a small-scale vortex structure in the region just near the cylinder surface. At ${\theta}_A=60^{\circ}$, the drag coefficient was reduced about $43.7\%$ at maximum.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.210-211
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• 2004

The effect of oscillating on the unsteady laminar flow past a circular cylinder is numerically investigated in the present study. Our study is to analyze the vortex formation behind a circular cylinder for different rotary oscillation conditions. And then we are study to portray the unsteady dynamics of wake flows. We decide lock-on region by observing the phase switching phenomena We classify the vortex formation patterns in the primary lock-on region The present study is to identify the quasi-periodic state around lock-on region. At the boundary between lock-on and non-lock-on the shedding frequency is bifurcated. After the bifurcation, one frequency follow the forcing frequency ($S_f$) and the other returns to the natural shedding frequency ($St_0$). In the quasi-periodic state, the variation of magnitudes and relevant phase changes of $C_L$ with forcing phase are examined.