J. Choi, H. Ishitsuka, S. Mima, S. Oguri, K. Takahashi, O. Tajima
In the field of radiowave detection, enhancement of the amount of detected light is essential for greater scientific achievements. A large aperture system is a promising way to increase the number of photons that are received at the detectors. One challenge in the application of radio transmittable apertures is keeping the detectors cool. This is because transparency to thermal radiation above the radio frequency range increases the thermal load. For shielding from thermal radiation, the general strategy involves installation of thermal filters in the light path between the aperture and the detectors. However, enlargement of the aperture gives rise to a new difficulty: warming of the filter. A thermal radiation shielding technology that does not warm the associated filter while allowing enlargement of the aperture is long-awaited. We propose radio-transparent multi-layer insulation (RT-MLI), which comprises a set of stacked insulator layers that are transparent in the radiowave frequency range. The basic idea for cooling is similar to conventional multi-layer insulation. It leads to reduction of the thermal radiation while maintaining a uniform surface temperature. We use foamed polystyrene as the insulator material, which has high radiowave transmittance, making an anti- reflection coating unnecessary. We measured the basic performance of the RT-MLI. We also demonstrated its effects with a combination of absorptive type filters with aperture diameters of 200 mm. We conclude that this technology is applicable to the cooling of radiowave receivers, and is particularly suitable for large aperture systems. This technology is expected to be applicable to various fields, including radio astronomy, geo-environmental assessment, and radar systems.
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http://arxiv.org/abs/1306.5040
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