• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.10
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• pp.160-167
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• 1996

A new pathlength deviation detection technique which is composed of michelson interferometer is described and verified experimentally. The technique uses a sub-threshold biased visible laser diode of 20$\mu$m coherence length as a low-coherent light source. And for zeroth-order fringe(which is the largest among fringes) identification we used a piezoelectric transducer with a large modulation smplitude, which enables without the need of constant velocity scanning, to distinguish reflection surfaces separated by more than 10$\mu$m with a resolution of less than half-wavelength.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.208-217
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• 1999

This paper presents spectrum analysis technique to identify abnormal noise produced in diesel railcars. Coherence and coherent power spectrum are very useful in determining source identifications. Experiments are applied to two different cars with similar phenomena about the case of stop and running condition. Metal contact in mounting bracket part which is excited by excessive transmission vibration is found to cause abnormal noise.

• Laser Solutions
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• v.18 no.3
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• pp.9-13
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• 2015

The development of a reliable, high-power source of mind-IR laser light gives process develop important tool with unique characteristics that will significantly impact a diverse range of applications.

• The Journal of the Acoustical Society of Korea
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• v.24 no.4
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• pp.230-237
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• 2005

The angle-tracking of maneuvering targets is required to the state estimation and classification of targets in underwater acoustic systems. The Problem of angle-tracking multiple closed and crossing targets has been studied by various authors. Sword et al. Proposed a multiple target an91e-tracking algorithm using angular innovations of the targets during a sampling Period are estimated in the least square sense using the most recent estimate of the sensor output covariance matrix. This algorithm has attractive features of simple structure and avoidance of data association problem. Ryu et al. recently Proposed an effective multiple target angle-tracking algorithm which can obtain the angular innovations of the targets from a signal subspace instead of the sensor output covariance matrix. Hwang et al. improved the computational performance of a multiple target angle-tracking algorithm based on the fact that the steering vector and the noise subspace are orthogonal. These algorithms. however. are ineffective when a subset of the incident sources are coherent. In this Paper, we proposed a new multiple target angle-tracking algorithm for coherent and incoherent sources. The proposed algorithm uses the relationship between source steering vectors and the signal eigenvectors which are multiplied noise covariance matrix. The computer simulation results demonstrate the improved Performance of the Proposed algorithm.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1819-1830
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• 1991

The problems associated with noise/energy source identification using multiple input/single output model in linear systems are investigated. Partial coherence function is formulated for the model introducing a virtual force and extraneous noises into the conventional two input/single output system. The analytical results show that the partial coherence function in two input/single output linear system is the function of noise/signal ratios when multiple inputs are mutually coherent and extraneous noises exist. Parametric studies for ordinary and partial coherence functions are carried out to demonstrate the effects of noise/signal ratios for these functions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.691-698
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• 1985

This paper presents a method for the identification of vibration sources in a multiple input system where the input source may be coherent with each other. Using multi-dimensional spectral analysis, it is found that one of the most significant vibration sources of a gasoline engine is the pressure variation within the cylinder. In this analysis the concepts of residual spectral analysis and the partial coherence function are applied. Finally, the overall levels of the acceleration on the cylinder block obtained by multi-dimensional spectral analysis are compared with those by the frequency response function approach. The experimental results have shown a good agreement with the results calculated by this method the input sources are coherent strongly each other.

• Journal of Sensor Science and Technology
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• v.8 no.2
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• pp.148-153
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• 1999

In this paper, we developed and implemented the geological magnetic filter for the improvements of the signal to noise ratio of the magnetic detection system. Using the geological magnetic filter, we can remove the coherent noises in the time domain and improve the signal to noise ratio of the magnetic detection system. Numerical simulation results show that geological magnetic filter can excellently remove the sensor misalignment effects and the regular short range local noise as well as it delete the coherent noises. We confirmed that the geological magnetic filter improved the signal to noise ratio about 19dB and deleted the coherent noises with restoring the source magnetic signal through experiments by implemented system.

• Current Applied Physics
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• v.18 no.11
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• pp.1182-1184
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• 2018

The combination of angular spin momentum with electronics is a promising successor to charge-based electronics. The conduction bands in GaAs may become spin-polarized via optical spin pumping, doping with magnetic ions, or induction of a moment with an external magnetic field. We investigated the spin populations in GaAs with x-ray magnetic circular dichroism for each of these three cases. We find strong anti-symmetric lineshapes at the Ga $L_3$ edge indicating conduction band spin splitting, with differences in line width and amplitude depending on the source of spin polarization.

• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.355-359
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• 2004

Differential Faraday Rotation measurements between the images of same background source, of multiply-imaged gravitational lens systems can be effectively used to provide a valuable probe to establish the existence of large-scale ordered magnetic fields in lensing galaxies as well as galaxy clusters. Estimates of the magnetic field in lens galaxies, based on the radio polarization measurements do not appear to show any clear evidence for evolution with redhsift of the coherent large scale magnetic field between redshift of 0.9 and the present epoch. However, our method clearly establishes the presence of coherent large scale magnetic field in giant ellitpical galaxies.

• Journal of Sensor Science and Technology
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• v.20 no.1
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• pp.8-13
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• 2011

We present measurements of the Brillouin frequency shift in an optical fiber using a 1550 nm distributed feedback laser diode(DFB-LD) as a light source. By modulating the probe light with an electro-optic modulator, we confirm the stimulated Brillouin gain spectrum(BGS) and spontaneous BGS using the coherent detection method. We also confirm the applicability of the technique to distributed temperature sensors that measure the change in Brillouin frequency shift due to temperature variations.