• Korean Journal of Optics and Photonics
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• v.22 no.1
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• pp.40-45
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• 2011

Design and fabrication of a TCRR (Triple-coupler Ring Resonator) filter which can provide a doubled FSR (Free Spectral Range) compared with a conventional DCRR (Double-coupler Ring Resonator) filter, are discussed. Through the use of a polymer material with a good thermo-optic property and with high contrast between core and cladding polymer, a compact TCRR filter composed of straight and curved buried waveguides of small radius is designed and fabricated. The transmission characteristics from the through and drop ports are measured using a tunable laser and a fiber array block, and the FSR is observed to be 4.4 nm, about twice that of DCRR filter, and almost the same as that obtained from the analysis using a transfer matrix method.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.337-340
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• 2001

We show that the microstrip ring with a narrow gap exhibits a photonic band gap (PBG) that is generally believed to be created by a periodic array. The discontinuity of impedance at the narrow gap induces the multiple reflections with fixed phase correlation necessary to make the PBG. We have also discussed the tuning of the PBG frequency by applying an external voltage on a varactor mounted on the gap and the applications of this PBG ring as a tunable bandstop filter and a microwave switch.

• Bulletin of the Korean Mathematical Society
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• v.58 no.6
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• pp.1387-1400
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• 2021

Suppose that $T=\(\array{A&0\\U&B}\)$ is a formal triangular matrix ring, where A and B are rings and U is a (B, A)-bimodule. Let ℭ₁ and ℭ₂ be two classes of left A-modules, 𝔇₁ and 𝔇₂ be two classes of left B-modules. We prove that (ℭ₁, ℭ₂) and (𝔇₁, 𝔇₂) are admissible balanced pairs if and only if (p(ℭ₁, 𝔇₁), h(ℭ₂, 𝔇₂) is an admissible balanced pair in T-Mod. Furthermore, we describe when ($P^{C_1}_{D_1}$, $I^{C_2}_{D_2}$) is an admissible balanced pair in T-Mod. As a consequence, we characterize when T is a left virtually Gorenstein ring.

• Bulletin of the Korean Mathematical Society
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• v.58 no.6
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• pp.1483-1494
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• 2021

Let A and B be rings and U be a (B, A)-bimodule. If _BU has finite flat dimension, U_A has finite flat dimension and U ⊗_A C is a cotorsion left B-module for any cotorsion left A-module C, then the Gorenstein flat-cotorsion modules over the formal triangular matrix ring $T=\(\array{A&0\\U&B}\)$ are explicitly described. As an application, it is proven that each Gorenstein flat-cotorsion left T-module is flat-cotorsion if and only if every Gorenstein flat-cotorsion left A-module and B-module is flat-cotorsion. In addition, Gorenstein flat-cotorsion dimensions over the formal triangular matrix ring T are studied.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.7
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• pp.840-843
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• 2012

In this paper, the authors present a new design for a dual-band metamaterial(MTM) absorber that utilizes resonant-magnetic inclusion of a split-ring resonator(SRR). The proposed MTM unit cell is constructed by two open complementary split-ring resonators(OCSRRs) and an SRR arrangement. To avoid the need for metallic back plate a planar array of SRRs for resonant-magnetic inclusion is placed facing toward the incident wave propagation direction. Each unit cell is printed on the two sides of a FR-4 substrate. A prototype absorber was fabricated with a planar array of $39{\times}39$ unit cells, and measured. The proposed backplane-less absorber can be used for microwave applications.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.3 s.118
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• pp.323-333
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• 2007

In this paper, a new MDAS-DR antenna structure designed to efficiently shape a flat-topped radiation pattern is proposed. The antenna structure is composed of a stacked micro-strip patch exciter and a multi-layered disk array structure(MDAS) surrounded by a dielectric ring. The MDAS, which was supplied by a stacked microstrip patch exciter with radiating power, can form a flat-topped radiation pattern in a far field by a mutual interaction with the surrounding dielectric ring. Therefore, the design parameters of the dielectric ring and the MDAS structure are important design parameters for shaping a flat-topped radiation pattern. The proposed antenna used twelve multi-layered disk array elements and a Teflon material with a dielectric constant of 2.05. An antenna operated at 10 GHz$(9.6\sim10.4\;GHz)$ was designed in order to verify the effectiveness of the proposed antenna structure. The commercial simulator of CST Microwave $Studio^{TM}$, which was adapted to a 3-D antenna structure analysis, was used for the simulation. The antenna breadboard was also fabricated and its electrical performance was measured in an anechoic antenna chamber. The measured results of the antenna breadboard with a flat-topped radiation pattern were found to be in good agreement with the simulated one. The MDAS-DR antenna gain measured at 10 GHz was 11.18 dBi, and the MDAS-DR antenna was capable of shaping a good flat-topped radiation pattern with a beam-width of about $40^{\circ}$, at least within a fractional bandwidth of 8.0 %.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.1
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• pp.26-36
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• 2000

A circularly polarized $12\times12$ array with application in the satellite communications is designed at 10 GHz. The radiator is an aperture-coupled ring patch, which is suitable of large arrays. The element spacing of the array is chosen to be $0.7\lambda_0$to maintain the main beam in the broadside direction. The array is a sequential array constructed on a series-parallel feed network to obtain high gain and low axial ratio. Measurement results for the array, acquired by experiments in the compact range of POSTECH, showed a directivity of 27.88 dB, a high gain of 25.55 dB, an efficiency of 60%, an axial ratio of 1.74 dB, and a side-lobe level of -13 dB. The bandwidth of the array was 43% when the VSWR was 2, and the bandwidth of the axial ratio was 16%.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.4
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• pp.357-364
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• 2011

In this study, ring-shaped acoustic resonators were proposed to be installed in a silencer to increase the acoustic performance of silencer in the low-frequency range. Evaluation of noise reduction performance of acoustic resonator arrays was carried out by measuring the random-incidence absorption coefficient. It was found that the absorption coefficient of resonator array was measured up to 1 at 125 Hz of 1/3-octave band center frequency. Insertion losses of silencers with ring-shaped acoustic resonator arrays were measured based on ISO 7235. The results were shown that the ring-shaped resonator could increase the insertion loss up to 13 dB without flow, whereas 7 dB when flow speed reached 15 m/s. As increasing the flow speed above 15 m/s, the effect of acoustic resonator decreased due to the effect of nonlinear air damping of the resonator. It was also found that the increment of pressure drop by the presence of resonator arrays was about 9 % at flow speed of 25 m/s.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.11
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• pp.960-967
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• 2013

Shape recognition of solder ball bumps in a BGA (Ball Grid Array) is an important issue in flip chip bonding technology. In particular, the semiconductor industry has required faster and more accurate inspection of micron-size solder bumps in flip chip bonding as the density of balls has increased dramatically. The difficulty of this issue comes from specular reflection on the metal ball. Shape recognition of a metal ball is a very realproblem for computer vision systems. Specular reflection of the metal ball appears, disappears, or changes its image abruptly due to tiny movementson behalf of the viewer. This paper presents a practical shape recognition method for three dimensional (3-D) inspection of a BGA using a 5-step ring illumination device. When the ring light illuminates the balls, distinctive specularity images of the balls, which are referred to as "iso-slope contours" in this paper, are shown. By using a mathematical reflectance model, we can drive the 3-D shape information of the ball in aquantitative manner. The experimental results show the usefulness of the method for industrial application in terms of time and accuracy.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12C
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• pp.240-248
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• 2001

This paper describes the design of a space-division switch which can support a self-healing operation of 2-fiber bidirectional line switched ring in 2.5Gb/s SDH-based transmission system. The switch having a 1.25Gb/s throughput has been designed and implemented with COMPASS tool and 0.87$\mu\textrm{m}$ CMOS gate-array. The proposed switch is suitable for the quickly self-healing operations when a failure occurs in a 2-fiber bidirectional switched ring composed of ADM transmission systems. The switch is composed of an add/drop control part, a cross-point switch, a frame-phase aligner, processor interface and an unequipped data framer. The test results of the switch adapted to 2.SGb/s SDH-based transmission system, show immediate restoration when a failure occurs.