• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.599-600
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• 2009

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.261-262
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• 2007

• Proceedings of the Optical Society of Korea Conference
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• 2008.02a
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• pp.183-184
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• 2008

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.1
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• pp.164-170
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• 2006

Millimeter waves can be used for high resolution ranging and imaging. As the necessity of high-speed multimedia communication increases, millimeter wave systems are being developed since they are useful for wide band communication considering the shortage of available spectrum bands. However, it is necessary to analyze the characteristics of millimeter propagation in the atmosphere to assess the performance of millimeter wave systems. MCF and intensity fluctuations describe atmospheric effects on millimeter wave propagation. Using the quasi-optical method, a method is investigated to obtain MCF from the intensity distribution of focal plane. Also, a practical method is proposed to compute MCF from the flux measurement in the antenna focal plane.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.66.2-66.2
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• 2016

KASI and NAOJ are making collaborating efforts to implement faster mapping capability into the new 275-500 GHz Atacama Submillimeter Telescope Experiment focal plane array (FPA). Feed horn antenna is one of critical parts of the FPA. Required fractional bandwidth is almost 60 % while that of traditional conical horn is less than 50 %. Therefore, to achieve this wideband performance, we adopted a horn of which the corrugation depths have a longitudinal profile. A profiled horn has features not only of wide bandwidth but also of shorter length compared to a linear-tapered corrugated horn, and lower cost fabrication with less error can be feasible. In our design process the flare region is represented by a cubic splined curve with several parameters. Parameters of the flare region and each dimension of the throat region are optimized by a differential evolution algorithm to keep >20 dB return loss and >30 dB maximum cross-polarization level over the operation bandwidth. To evaluate RF performance of the horn generated by the optimizer, we used a commercial mode matching software, WASP-NET. Also, Gaussian beam (GB) masks to far fields were applied to give better GB behavior over frequencies. The optimized design shows >23 dB return loss and >33 dB maximum cross-polarization level over the whole band. Gaussicity of the horn is over 96.6 %. The length of the horn is 12.5 mm which is just 57 % of the ALMA band 8 feed horn (21.96 mm).

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.57.1-57.1
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• 2010

The SPICA (SPace Infrared Telescope for Cosmology & Astrophysics) is a next generation infrared space telescope being prepared by JAXA, ESA and other international collaborators. We propose to develop FPC (Focal Plane Camera) consisting of two near-infrared cameras: FPC-G (I band) for focal plane guidance and FPC-S (0.7 - 5 um) for a back-up of FPC-G and a NIR instrument for scientific observations. In this talk, we introduce the requirement and the design concept of the FPC as well as the development strategy of the project.

• Journal of Sensor Science and Technology
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• v.18 no.4
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• pp.301-306
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• 2009

This paper describes the design and fabrication of 16$\times$16 microbolometer infrared focal plane arrays based on iMEMS technology. Amorphous silicon was used for infrared-sensitive material, and it showed the resistance of 18 Mohm and the temperature coefficient of resistivity of -2.4 %. The fabricated sensors exhibited responsivity of 78 kV/W and thermal time constant of 8.0 msec at a bias voltage of 0.5 V. The array performances had satisfactory uniformity less than 5 % within one-sigma. Also, 1/f noise of pixel was measured and the noise factor of $6\times10^{-11}$ was extracted. Finally, we obtained detectivity of $1.27\times10^9cmHz^{0.5}/W$ and noise equivalent temperature difference of 200 mK at a frame rate of 30 Hz.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.76.2-76.2
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• 2013

SPICA(SPace Infrared Telescope for Cosmology and Astrophysics) is an infrared space observatory with cooled telescope of 3 m aperture. Because of its large aperture, near- and mid-infrared instruments onboard SPICA require fine guidance with attitude accuracy less than 0.1 arcsecond. The FPC-G is a focal plane camera to achieve this high attitude accuracy and KASI is leading its development. The SPICA project is now under the Risk Mitigation Phase 2 (RMP2) and one of major risks is to satisfy the requirement of pointing and attitude control. To assess the impacts of disturbance sources on the attitude control and devise methods to mitigate possible risks, a software simulator of the FPC-G is under the development. In this presentation, we report the status of development of the simulator and the development plan during the RMP2.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.12
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• pp.1886-1891
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• 2012

In this paper, the analytical models for the electrothermal feedback of a ${\mu}$-bolometer focal plane array(FPA) are proposed and applied to the conceptually designed FPA to investigate the electrothermal feedback effect on bolometer FPA signal. The temperature and resistance change of the ${\mu}$-bolometer by the electrothermal feedback(ETF) model are increased upto 20 and 35.7 % of those of no feedback case, respectively, while those by the effective thermal conductance(ETC) model increased 8.5 and 15.1 %. The integration current and output voltage of a CTIA used as an column amplifier of FPA are also increased upto 41.6 and 32.4 % by the ETF model, while increased upto 17.2 and 13.5 % by the ETC model. The proposed models give more accurate temperature change, accordingly larger signal than no feedback considering case. Electrothermal feedback effect should be considered to design a high performance and high density ${\mu}$-bolometer FPA. The proposed models are very useful to investigate the transient thermal analysis, also considered to be useful to predict the responsivity and dynamic range of ${\mu}$-bolometer FPAs.

• Current Optics and Photonics
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• v.3 no.1
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• pp.27-32
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• 2019

We present an autofocus tracking system implemented by the digital refocusing of digital holographic microscopy (DHM) and the tunability of an electrically tunable lens (ETL). Once the defocusing distance of an image is calculated with the DHM, then the focal plane of the imaging system is optically tuned so that it always gives a well-focused image regardless of the object location. The accuracy of the focus is evaluated by calculating the contrast of refocused images. The DHM is performed in an off-axis holographic configuration, and the ETL performs the focal plane tuning. With this proposed system, we can easily track down the object drifting along the depth direction without using any physical scanning. In addition, the proposed system can simultaneously obtain the digital hologram and the optical image by using the RGB channels of a color camera. In our experiment, the digital hologram is obtained by using the red channel and the optical image is obtained by the blue channel of the same camera at the same time. This technique is expected to find a good application in the long-term imaging of various floating cells.