The Simons Observatory: Metamaterial Microwave Absorber (MMA) and its Cryogenic Applications. (arXiv:2010.02233v3 [astro-ph.IM] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Xu_Z/0/1/0/all/0/1">Zhilei Xu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chesmore_G/0/1/0/all/0/1">Grace E. Chesmore</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Adachi_S/0/1/0/all/0/1">Shunsuke Adachi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ali_A/0/1/0/all/0/1">Aamir M. Ali</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bazarko_A/0/1/0/all/0/1">Andrew Bazarko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Coppi_G/0/1/0/all/0/1">Gabriele Coppi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Devlin_M/0/1/0/all/0/1">Mark Devlin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Devlin_T/0/1/0/all/0/1">Tom Devlin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dicker_S/0/1/0/all/0/1">Simon R. Dicker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gallardo_P/0/1/0/all/0/1">Patricio A. Gallardo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Golec_J/0/1/0/all/0/1">Joseph E. Golec</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gudmundsson_J/0/1/0/all/0/1">Jon E. Gudmundsson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Harrington_K/0/1/0/all/0/1">Kathleen Harrington</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hattori_M/0/1/0/all/0/1">Makoto Hattori</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kofman_A/0/1/0/all/0/1">Anna Kofman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kiuchi_K/0/1/0/all/0/1">Kenji Kiuchi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kusaka_A/0/1/0/all/0/1">Akito Kusaka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Limon_M/0/1/0/all/0/1">Michele Limon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matsuda_F/0/1/0/all/0/1">Frederick Matsuda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McMahon_J/0/1/0/all/0/1">Jeff McMahon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nati_F/0/1/0/all/0/1">Federico Nati</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Niemack_M/0/1/0/all/0/1">Michael D. Niemack</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sutariya_S/0/1/0/all/0/1">Shreya Sutariya</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Suzuki_A/0/1/0/all/0/1">Aritoki Suzuki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Teply_G/0/1/0/all/0/1">Grant P. Teply</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Thornton_R/0/1/0/all/0/1">Robert J. Thornton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wollack_E/0/1/0/all/0/1">Edward J. Wollack</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zannoni_M/0/1/0/all/0/1">Mario Zannoni</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhu_N/0/1/0/all/0/1">Ningfeng Zhu</a>

Controlling stray light at millimeter wavelengths requires special optical
design and selection of absorptive materials that should be compatible with
cryogenic operating environments. While a wide selection of absorptive
materials exists, these typically exhibit high indices of refraction and
reflect/scatter a significant fraction of light before absorption. For many
lower index materials such as commercial microwave absorbers, their
applications in cryogenic environments are challenging. In this paper, we
present a new tool to control stray light: metamaterial microwave absorber
tiles. These tiles comprise an outer metamaterial layer that approximates a
lossy gradient index anti-reflection coating. They are fabricated via injection
molding commercially available carbon-loaded polyurethane (25% by mass). The
injection molding technology enables mass production at low cost. The design of
these tiles is presented, along with thermal tests to 1 K. Room temperature
optical measurements verify their control of reflectance to less than 1% up to
65$circ$ angles of incidence, and control of wide angle scattering below
0.01%. The dielectric properties of the bulk carbon-loaded material used in
the tiles is also measured at different temperatures, confirming that the
material maintains similar dielectric properties down to 3 K.

Controlling stray light at millimeter wavelengths requires special optical
design and selection of absorptive materials that should be compatible with
cryogenic operating environments. While a wide selection of absorptive
materials exists, these typically exhibit high indices of refraction and
reflect/scatter a significant fraction of light before absorption. For many
lower index materials such as commercial microwave absorbers, their
applications in cryogenic environments are challenging. In this paper, we
present a new tool to control stray light: metamaterial microwave absorber
tiles. These tiles comprise an outer metamaterial layer that approximates a
lossy gradient index anti-reflection coating. They are fabricated via injection
molding commercially available carbon-loaded polyurethane (25% by mass). The
injection molding technology enables mass production at low cost. The design of
these tiles is presented, along with thermal tests to 1 K. Room temperature
optical measurements verify their control of reflectance to less than 1% up to
65$circ$ angles of incidence, and control of wide angle scattering below
0.01%. The dielectric properties of the bulk carbon-loaded material used in
the tiles is also measured at different temperatures, confirming that the
material maintains similar dielectric properties down to 3 K.

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