• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.297-300
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• 2006

In this paper, the EM wave absorbers were designed and fabricated for X-band sensors using Carbon of dielectric material with CPE. The complex relative permittivity of samples is calculated by the measured S-parameter data. We simulated the double-layered type EM wave absorber with broad bandwidth using the measured complex relative permittivity by changing the thickness and layer, which was fabricated based on the simulated design. The fabricated EM wave absorber consist of 1mm first layer sheet facing metal with Carbon composition ratio 70 vol% and 1.5 mm second layer sheet with Carbon composition ratio 60 vol%. The comparisons of simulated and measured results are good agreement. As a result, the optimized absorption ability of double-layered type EM wave absorber with thickness of 2.5 mm is higher than 10 dB from 7.8 GHz to 13.3 GHz.

• 한국소음진동공학회논문집
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• 제20권10호
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• pp.983-990
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• 2010

Reduction of acoustic loads of space launch vehicles can be achieved by acoustic absorbers satisfying strict cleanness requirements. This limited the use of general porous materials and requires non-porous sound absorbers. Micro-perforated panel absorbers(MPPA) is one of promising sound absorbers satisfying the cleanness requirement for launch vehicles. However, its applicability was limited to low sound pressure levels according to the acoustic impedance model of micro-perforated panels. In this paper the applicability of micro-perforated panel absorbers at high incident sound pressure was investigated in experimental ways. The absorption characteristics of a micro-perforated panel absorber was simulated according to its design variables, e.g., minute hole diameters and aperture ratios. It was shown that optimal design can be readily done by using proposed design charts. Experiments were conducted to measure acoustic properties of the designed micro-perforated panel absorbers. The results showed that acoustic resistance increases rapidly as incident sound pressure level does but change of acoustic reactance can be neglected in a practical point of view. This caused the decrease of peak value of absorption coefficient at high incident sound pressure level, but the amount of reduction can be accepted in practice. The major advantage of the micro-perforated panel absorber(wide absorption bandwidth) was still kept at high sound pressure level.

• Journal of Photoscience
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• 제9권2호
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• pp.364-366
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• 2002

Photoadaptation of Chlorobium (Cb.) phaeobacteroides was investigated under dim and strong light intensity. Absorption spectra of these whole cellIs were different each other. The Soret band intensity and the Qy bandwidth of BChl e in c디l grown under dim light intensity were smaller and more broadened than those under strong light intensity. From HPLC analysis of the pigments, total carotenoid (Car) / bacterochorolphyll (BChl) e ratio of cell increased wi1h increase of light intensities. But camposition of BChl e hamologs almost unchanged. Cb. phaeobacteroides contains 11 kinds of Car including isorenieratene and beta-isorenieratene as major Car. The campositions of Car were different for cells grown under dim and strong light intensities. In conclusion, Cb. phaeobacteroides changes total amount and canposition of Car to adapt various light intensities, while homolog canposition of BChle unchange.

• 전자공학회논문지A
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• 제32A권11호
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• pp.29-34
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• 1995

Mirror coating is applied to laser facets to improve properties of edge emitting laser diodes. In this experiment, InGaAsP/GaAs high power laser diodes were studied with respect to different degrees of anti-reflective coating. Sputterred $Al_{2}$O$_{3}$ was used as the coating material and the HR coating was kept constant at 90%. Threshold current density, differential quantum efficiency, emission wavelength and the operating current at 500mW were measured for a range of AR coating and compared with theoretically calculated values; that showed good agreements. Precise wavelength control is important for laser diodes for solid state pumping because of small absorption bandwidth. In addition, since these lasers operate under CW condition, a lowest possible operating current for a given power is desired in order to minimize the heat produced. From the results of this experiment, we were able to obtain a optimum range of AR coatings for minimum operating current. The wavelength can be varied up to 4nm within this range.

• Journal of electromagnetic engineering and science
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• 제13권1호
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• pp.1-7
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• 2013

This paper proposes a metamaterial (MTM) absorber for 2.45 GHz band applications. The unit cell of the proposed absorber consists of an electric LC (ELC) resonator and a strip line, which are printed on opposite sides of the substrate. The ELC resonator comprises two split ring resonators (SRRs) and a connecting line with a resistor. The designed absorber exhibits an absorption of 94 % and a half-max bandwidth of 0.16 GHz at 2.45 GHz.

• 한국위성정보통신학회논문지
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• 제12권4호
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• pp.166-169
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• 2017

This paper describes atmospheric phenomena and effects for satellite-to-ground laser communication channel. Satellite laser communication has advantages such as very high bandwidth, inherent security, robustness to electromagnetic interference, unlicensed frequency band. However, satellite laser communication is affected by various factors. Transmission quality is degraded by factors as system loss, geometric loss, misalignment loss, atmospheric loss. Atmospheric loss is major factor of performance degradation. In this paper, the atmospheric phenomena such as absorption, scattering and turbulence are discussed and analyzed for developing satellite laser channel model and laser transmission scheme robust to atmospheric phenomena.

• ETRI Journal
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• 제28권4호
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• pp.533-536
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• 2006

A distributed Bragg reflector (DBR) laser and a high speed electroabsorption modulator (EAM) are integrated on the basis of the selective area growth technique. The typical threshold current is 4 to 6 mA, and the side mode suppression ratio is over 40 dB with single mode operation at 1550 nm. The DBR laser exhibits 2.5 to 3.3 mW fiber output power at a laser gain current of 100 mA, and a modulator bias voltage of 0 V. The 3 dB bandwidth is 13 GHz. A 10 Gbps non-return to zero operation with 12 dB extinction ratio is obtained. A four-channel laser array with 100 GHz wavelength spacing was fabricated and its operation at the designed wavelength was confirmed.

• Journal of the Optical Society of Korea
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• 제13권4호
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• pp.423-427
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• 2009

The results of the experimental and theoretical studies conducted on terahertz filtering using two parallel-plate waveguides (PPWGs) are presented herein. The first PPWG with 355 ${\mu}m$ plate separation generates 4 THz bandwidth TM modes ($TM_0,\;TM_2,\;and\;TM_4$), whereas the second PPWG with 100 ${\mu}m$ plate separation operated the THz filter for the generated TM modes with 1.5 THz cutoff frequency. The outgoing THz wave of the two PPWGs was truncated until 1.5 THz, and the system was operated using a high-pass THz filter. The absorption and dispersion of the combined TM and TE modes for the filtering system were calculated. The theoretical calculation and measurement results for the cutoff and oscillation frequency in the spectrum domain agreed well.

• Journal of electromagnetic engineering and science
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• 제10권4호
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• pp.206-211
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• 2010

In this paper, an implantable planar inverted-F antenna (PIFA) for an artificial cardiac pacemaker is proposed. The antenna has a simple structure with a low profile and is placed on the top side of the pacemaker. The dimensions of the pacemaker system, including the antenna element, are $42{\times}43.6{\times}11$ mm. When the antenna is embedded in pig tissue, its $S_{11}$ value is -10.94 dB at 403 MHz and the -10 dB impedance bandwidth of the antenna is 6 MHz (399~406 MHz). The proposed PIFA in tissue has a peak gain of -20.19 dBi and a radiation efficiency of 1.12 % at 403 MHz. When the proposed antenna is placed in a flat phantom, its specific absorption ratio (SAR) value is 0.038 W/kg (1 g tissue). Performances of the proposed PIFA is sufficient to operate at the MICS band (402 ~ 405 MHz).

• Journal of Electrical Engineering and Technology
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• 제8권4호
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• pp.850-855
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• 2013

This paper proposes a novel design for a compact, high-isolation WCDMA indoor repeater antenna. The proposed antenna consists of a patch antenna and metamaterial absorber. The required WCDMA bandwidth is obtained by utilizing the coupling between the main and the parasitic patches. In addition, high isolation is achieved using the metamaterial absorber, which has an absorption of about 98% at 2.1 GHz. Overall, the proposed antenna has a gain of over 7 dBi, a Voltage Standing Wave Ratio (VSWR) of less than 2, more than 85 dB of isolation between the service and donor antennas over the WCDMA band and a total volume of the proposed antenna only $70mm{\times}70mm{\times}43.8mm$.