• Journal of the Korean Mathematical Society
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• v.46 no.4
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• pp.691-699
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• 2009

In this paper, we establish a multiple existence result of T-periodic solutions for the semilinear parabolic boundary value problem with sublinear growth nonlinearities. We adapt sub-supersolution scheme and topological argument based on variational structure of functionals.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.543-548
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• 2000

Vibration localization of a periodic structure with mistuning is presented in this paper. Mistuning in periodic structures can lead to an increase of the forced response which is much larger than those of perfectly tuned assembly. Thus, mistuning has a critical impact on high cycle fatigue in structures, and it is of great importance to predict the mistuned forced response in efficient manner. In this paper, forced response of a coupled pendulum is investigated to identify localization effects of periodic structures. The effects of mistuning and damping on the maximum forced response are examined. It is seen that in certain condition of mistuning and coupling, strong localization occurs and this can be significant under weak damping.

• Journal of electromagnetic engineering and science
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• v.1 no.2
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• pp.161-165
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• 2001

The radiation characteristics of leaky wave emanated from finite strip-grating loaded dielectric coated coaxial waveguide with finite periodic thick slots are investigated theoretically. The rigorous integral equations are derived for the proposed structure using the courier transform, mode expansion, and sine series expansion of the electric current on metallic strips, and the simultaneous linear equations are obtained. The effects of finite strip-grating loading on a dielectric-coated coaxial waveguide with finite periodic thick slots are examined in terms of radiation characteristics.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.24-26
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• 1994

This paper deals with the 3 dimensional finite element analysis using the periodic boundary condition in case analyzing model has a periodic structure. Using the periodic boundary condition we can reduce computer's memories and computation tine. because only the one period of the model is analyzed. To verify the usefulness of the proposed algorithm, can stack type PM step motor which used in FDD head driver is choosen and analyzed.

• ETRI Journal
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• v.33 no.1
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• pp.13-17
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• 2011

A highly miniaturized on-chip $180^{\circ}$ hybrid employing periodic ground strip structure (PGSS) was realized on a silicon radio frequency integrated circuit. The PGSS was placed at the interface between $SiO_2$ film and silicon substrate, and it was electrically connected to top-side ground planes through the contacts. Owing to the short wavelength characteristic of the transmission line employing the PGSS, the on-chip $180^{\circ}$ hybrid was highly miniaturized. Concretely, the on-chip $180^{\circ}$ hybrid exhibited good radio frequency performances from 37 GHz to 55 GHz, and it was 0.325 $mm^2$, which is 19.3% of a conventional $180^{\circ}$ hybrid. The miniaturization technique proposed in this work can be also used in other fields including compound semiconducting devices, such as high electron mobility transistors, diamond field effect transistors, and light emitting diodes.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.4
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• pp.483-490
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• 2011

Using a coplanar waveguide employing periodic ground structure (PGS) on silicon substrate, a highly miniaturized and broadband impedance transformer was developed for application to low impedance matching in broadband. Concretely, the multi-section transformer was designed using Chebyshev polynomials design technique for ultra broadband operation. Its size was 0.026 $m^2$ on silicon substrate, which was 8.7 % of the one fabricated by conventional coplanar waveguide on silicon substrate. The transformer showed a good RF performance over a ultra broadband from 8 - 49.5 GHz.

• ETRI Journal
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• v.17 no.1
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• pp.1-10
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• 1995

We have achieved very low threshold current densities with high light output powers for InGaAs/ GaAs surface-emitting lasers using a periodic gain active structure in which three quantum wells are inserted in two-wavelength-thick (2${\lambda}$ ) cavity. Air-post type devices with a diameter of 20~40${\mu}m$ exhibit a threshold current density of 380~410$A/cm^2$. Output power for a 40${\mu}m$ diameter device reaches over 11 mW. A simple theoretical calculation of the threshold and power performances indicates that the periodic gain structure has an advantage in achieving low threshold current density mainly due to the high coupling efficiency between gain medium and optical field. The deterioration of power, expected from the long cavity length of $2{\lambda}$, is negligible.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.4
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• pp.562-568
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• 2009

In this paper, using the periodic ground structure (PGS), highly miniaturized branch-line coupler and impedance transformer were realized on Si radio frequency integrated circuit (RFIC). The branch-line couple exhibited good RF performance from 41.75 to 50 GHz, and its size was $0.46{\times}0.55mm^2$, which is 37 % of conventional one. The impedance transformer exhibited good RF performance from 1 to 40GHz, and its size was $0.01mm^2$, which is 6.99 % of conventional one.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.11
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• pp.1-7
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• 2000

Surface wave scattering by periodic grooves of arbitrary profile in a grounded dielectric slab is investigated for the TE surface wave incidence. Both the finite and infinite periodic geometries are considered. The former case is analyzed by using of hybrid FEM/MOM and the latter by using of full MOM procedure. Some numerical results for the reflected and transmitted powers in a grounded dielectric slab, radiation power into the free space, and radiation patterns in case of finite structure and for the dispersion diagram in case of infinite structure are presented. And some descriptions on the relationship between the finite and infinite structure such as the maximum beam angle are given.

• KIEE International Transactions on Electrophysics and Applications
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• v.4C no.6
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• pp.263-267
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• 2004

A new type of interaction circuitry for a broadband gyro-TWT is presented in this paper. A method for the analysis of dispersion characteristics of a periodic structure, which is composed of conducting posts in a rectangular waveguide, is presented. This method utilizes a mode matching technique and equivalent circuit model. The calculated and measured results demonstrate that this periodic structure could be utilized for the interaction circuit of a wide band Gyro-TWT.