• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.102-105
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• 2000

A simple digital control system has been developed for the frequency stabilization of an internal mirror He-Ne laser. The system is based on one chip microprocessor with embedded Basic interpreter. To stabilize the laser output frequency, the signal such as power difference or beat frequency between two modes is supplied and processed by a microprocessor, and control signal is fed to the heating coil would round the laser tube for adjusting the spacing of the laser cavity mirror. Newly developed frequency stabilization system is totally digitized. The system and the frequency stability performance are briefly described.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.6
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• pp.671-678
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• 2014

This paper presents a Ka-band FMCW sensor that has high linearity by improving a nonlinear behavior of the voltage controlled oscillator. Due to the nonlinear characteristics of the voltage controlled oscillator for the conventional method, the drift of beat frequency can cause inaccuracy and errors to the extracted results. A Ka-band FMCW signal with fast transition time could be generated by using both direct digital synthesizer and phase locked loop in this research. The implemented FMCW sensor showed very high accuracy in beat frequency through the test.

• Journal of Biomedical Engineering Research
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• v.21 no.4
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• pp.339-344
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• 2000

The mucociliary system is one of the most important airway defense mechanisms in human body and impairment of ciliary movement results in various diseases in respiratory tract. In this study, we have developed a system that can measure ciliary movement in vivo and quantified ciliary beat frequency (CBF) through autoregressive (AR) power spectrum. To measure the frequency in vivo, we applied a photoelectric method that was composed of a laser light and a fiber optic probe. Scattered signals are transferred to a PC in which they are displayed on the monitor and its CBF is determined by the AR method in were acquired. For 8 normal subjects, the analyzed CBFs ranged from 5 to 10Hz and its mean was 7.3${\pm}$1.1Hz. This result showed similar aspects to the reported results of CBFs to data. We expect that this result will be applied in various clinical studies such as analysis of CBF changes by drugs or by diseaes.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.9
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• pp.172-178
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• 2002

One of the ever-increasing demands on the performances of heterodyne interferometers is to improve the measurement resolution, of which current state -of-the-art reaches the region of sub-nanometers. So far, the demand has been met by increasing the clock speed that drives the electronics involved fur the phase measurement of the Doppler shift, but its further advance is being hampered by the technological limit of modem electronics. To cope with the problem, in this investigation, we propose a new scheme of phase -measuring electronics that reduces the measurement resolution without further increase in clock speed. Our scheme adopts a super-heterodyne technique that lowers the original beat frequency to a level of 1 MHz by mixing it with a stable reference signal generated from a special phase- locked-loop. The technique enables us to measure the phase of Doppler shift with a resolution of 1.58 nanometer at a sampling rate of 1 MHz. To avoid the undesirable decrease in the maximum measurable speed caused by the lowered beat frequency, a special form of frequency up-down counting technique is combined with the super-heterodyning. This allows performing required phase unwrapping simply by using programmable digital gates without 2n ambiguities up to the maximum velocity guaranteed by the original beat frequency.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.5
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• pp.799-804
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• 2015

This study aims at the new analysis of heart beat fluctuations by applying physiological Heart Rate Variability Model with representing the cardiac control system in sympathetic and parasympathetic-coupling oscillator constants, C_s and C_p. To find the effects of coupling constants on the beat-to-beat fluctuations, Integral Pulse Frequency Modulation (IPFM) model is adopted to generate the time series data of ECG R-peaks and represent them by poincaré scattergram plot in the time domain and HRV in the frequency domain, respectively. The actual poincaré plots and HRV spectrum are also analyzed by acquiring the experimental data from the subjects exposed to the emotional-stress invoking environment and the function of the coupling constants are verified in terms of antagonism in sympathetic and parasympathetic activity.

• International Journal of Naval Architecture and Ocean Engineering
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• v.2 no.1
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• pp.34-38
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• 2010

Field investigations have been carried out in two 60-day stages on the surf beat low frequency waves in Anzali port, one of the main commercial ports in Iran, located in southwest coast of the Caspian Sea. The characteristics of significant water waves were measured at three metering stations in the sea, one at the entrance of the port and three in the basin. The measured data were inspected to investigate the surf beat negative effects on the tranquility of the port. Using field measurements and complementary numerical modeling, the response of the basin to the infra-gravity long waves was inspected for a range of wave frequencies. It was concluded that the water surface fluctuations in the port is strongly related to the incident wave period. The long waves with periods of about 45s were recognized as the worst cases for water surfaceperturbation in the port. For wave periods higher than the mentioned range, the order of fluctuation was generally low.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.776-779
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• 2005

Liquefied Natural Gas takes up six hundredths of the volume of natural gas, which makes storage and transportation much easier. To send out natural gas via a pipeline network across the nation, high pressure LNG pumps supply highly compressed LNG to high-pressure vaporization facilities. The Number of high Pressure LNG pumps determined the send out amount in LNG receiving terminal. So it is main equipment at LNG production process and should be maintained on best conditions. In this paper, to find out the cause of high beat vibration at cryogenic pumps, vibration and motor current analysis have been performed. And high beat vibration of cryogenic pumps could be reduced due to the modification of motor rotor.

• Journal of Industrial Technology
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• v.26 no.A
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• pp.81-88
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• 2006

The Chun-cheon Citizen's Bell was cast in memory of hosting the 2010 world leasure conference and a striking ceremony was held at the city hall on December 31, 2005. In this study, vibration and sound of the bell are measured and the property of the magnificent sound of the bell is scientifically investigated. Frequency components making the sound are identified and how the frequency components decrease with time is observed using waterfall plot(3-dimensional frequency spectrum). Beat characteristics of the hum(1st frequency) and the fundamental(2nd frequency)are examined by experiment. Directivity of the sound radiation of the bell is examined by measuring the vibration and sound in several directions. Duration of the vibration and the sound is estimated using damping ratio.

• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.493-495
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• 1993

The frequency of the 633 nm internal mirror He-Ne laser has been stabilized by using the beat frequency and the intensity difference between two Zeeman split components in a transverse magnetic field. The frequency stability and the frequency temperature coefficient for the beat frequency method was $7.0{\times}10^{-11}$ and $170 kHz/^{\circ}C$, respectively, and those for the intensity difference was $1.1{\times}10^{-9}$ and $1.8 MHz/^{\circ}C$, respectively.

• Journal of Biomedical Engineering Research
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• v.31 no.1
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• pp.14-19
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• 2010

Baroreflex sensitivity (BRS) is a parameter of the cardiovascular system that is reflected in changes in pulse interval (PD and systolic blood pressure (SBP). BRS contains information about how the autonomic nervous system regulates hemodynamic homeostasis. Normally the beat-to-beat SBP measurement and the pulse interval measured from the electrocardiogram (ECG) are required to estimate the BRS. We investigated the possibility of measuring BRS in the absence of a beat-to-beat SBP measurement device. Pulse arrival time (PAT), defined as the time between the R-peak of the ECG and a single characteristic point on the pulse wave recorded from any arterial location was measured by photoplethysmography. By comparing the BRS obtained from conventional measurements with our method during controlled breathing, we confirmed again that PAT and SBP are closely correlated, with a correlation coefficient of -0.82 to -0.95. The coherence between SBP and PI at a respiration frequency of 0.07-0.12 Hz was similar to the coherence between PAT and PI. Although the ranges and units of measurement are different (ms/mmHg vs. ms/ms) for BRS measured conventionally and by our method, the correlation is very strong. Following further investigation under various conditions, BRS can be reliably estimated without the inconvenient and expensive beat-to-beat SBP measurement.