• Journal of the Korean Society for Precision Engineering
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• v.12 no.5
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• pp.126-135
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• 1995

An exhaust muffler is one of the simple and effective means to meet the demand for a quiet vehicle, and it deserves a close attention to effectively reduce the engine noise. The transfer function technique is one of the tools that have been used to analyze the noise characteristics of the exhaust muffler. In this paper we obtained a transfer function using the forward-going and backward-going components of sound pressure in the exhaust muffler, which is compatible wiht lattice filter algorithm. This form of transfer function is obtained for the basic elements of a muffler, such as uniform tube, open termin- ation, closed termination, anechoic termination, expansion, contraction, extended-tube resonator, hole, Helmholtz resonator, and concentric hole-cavity resonator. The results are combined to produce the transfer function of various types of mufflers. With this transfer function we calculate the transmission and insertion losses of mufflers, and examined the effects of various design parameters. Comparisons were made between the calculation and experimental results, which showed a good agreement, and we conclude that the transfer function of lattice form can be used to analyze the noise characteristics of the exhaust mufflers.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.29B no.1
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• pp.26-33
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• 1992

This paper presents lattice structure of bilinear filter and the conversion equations from lattice parameters to direct-form parameters. Billnear models are attractive for adaptive filtering applications because they can approximate a large class of nonlinear systems adequately, and usually with considerable parsimony in the number of coefficients required. The lattice filter formulation transforms the nonlinear filtering problem into an equivalent multichannel linear filtering problem and then uses multichannel lattice filtering algorithms to solve the nonlinear filtering problem. The lattice filters perform a Gram-Schmidt orthogonalization of the input data and have very good easily extended to more general nonlinear output feedback structures.

• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.99-103
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• 2006

A tunable wavelength filter was proposed and demonstrated by using the UV nanoimprint technique. It consists of a Bragg grating in polymer waveguides and a heating electrode. The manufacturing of the grating was substantially simplified with the introduction of a smart imprint stamp containing a waveguide pattern integrated with the grating pattern. The center wavelength of the filter was successfully tuned by taking advantage of the thermooptic effect in polymers, which was induced by supplying electrical power to the electrode. For the fabricated device, a transmission dip of ${\~}$15 dB and a 3-dB bandwidth of 0.8 nm were obtained at the Bragg wavelength of ${\~}$l560 nm. The achieved thermooptic tuning efficiency was ${\~}$0.28 nm/mW, while the center wavelength was shifted from 1560 nm to 1558 nm with the electrical power consumption of 7 mW.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1996.10a
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• pp.725-727
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• 1996

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1996.10a
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• pp.728-731
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• 1996

• Proceedings of the Optical Society of Korea Conference
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• 1998.08a
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• pp.172-173
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• 1998

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1220-1225
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• 2009

In this paper, a tunable fiber feedback laser based on the use of Sagnac loop filter and fiber Bragg grating (FBG) is proposed. The Sagnac loop filter using a high birefringence fiber provides precise 0.33-nm channel spacing as a multi-wavelength grid filter. Ni-Cr wire wound on the FBG is useful to induce the thermo-optic effect of the fiber. Two types of FBG structures, which have a different length of wire, are demonstrated to show the wavelength shift and separation. To tune FBG by resistant heat, some current is supplied into the wire. When the wavelength matched with one of the cavity modes of Sagnac loop filter, the mode-locked lasing is occurred. The electrical power sensitivity of the resonant wavelength is measured to 1.75pm/mW. This laser configuration can be applied the electrical power system for monitoring the power fluctuation.

• Korean Journal of Optics and Photonics
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• v.8 no.2
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• pp.149-153
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• 1997

We demonstrate the operating characteristics(center wavelength, bandwidth, TE/TM polarization, tuning range) of grating-assisted co-directional coupler(GACC) filter fabricated with InGaAsP compound semiconductor. A design of waveguide structure has been focused on the narrow bandwidth characteristics of the filter. Reactive ion etching technique was employed for the uniform waveguide formation. The bandwidths(FWHM) and center wavelengths of the fabricated GACC filter were measured by 1.5 nm and 1530.6 nm for TE polarization and 1.3 nm and 1494.0 nm for TM polarization. This is the one of the narrowest bandwidth at 1530 nm region ever reported. The center wavelength shifted form 1530 nm to 1538 nm when the current of 100 mA was injected at 4.5 mm-long device. Good agreement between the designed and measured operating characteristics for some waveguide structures is demonstrated.

• Korean Journal of Optics and Photonics
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• v.3 no.4
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• pp.244-251
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• 1992

Buried Bragg filters of single mode $Si_{3}N_{4}$ rib waveguide with a cover layer of $SiO_{2}$ and grating at the interface of $Si_{3}N_{4}$ and $SiO_{2}$ are designed and fabricated. Etching of the grating on $Si_{3}N_{4}$ waveguide core by buffered HF showed uniform etching with good control up to 1 nm. This buried type of Bragg filters are immune to contamination of the surface of device. The mode index and bandwidth of filters are determined by measurements of the transmission spectrum of Bragg filters and compared with that of calculation. Waveguide Bragg filters loaded with the micro-heater of Cr film and the cladding of silicone rubber are made to control the Brag wavelength of the filter. As a result the filter wavelength of the device moved by 0.41 nm for 10 mA current to the shorter side of wavelength proportional to the square of the current.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.7
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• pp.723-733
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• 2011

A numerical method of the CSF(Continuum Surface Force) model is presented for the calculation of the surface tension force and implemented in an in-house solution code(PowerCFD). The present method(code) employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with volume capturing method(CICSAM) in a volume of fluid(VOF) scheme for phase interface capturing. The application of the present method to a 2-D liquid drop problem is illustrated by an equilibrium and nonequilibrium oscillating drop calculation. It is found that the present method simulates efficiently and accurately surface tension-dominant multiphase flows.