Optical MEMS-based micromirror arrays for active light steering in smart windows

Hillmer, Hartmut; Al-Qargholi, Basim; Khan, Muhammad Ahsan; Worapattrakul, Natalie; Wilke, Hans; Woidt, Carsten; Tatzel, Andreas

doi:10.7567/jjap.57.08pa07

Cited by 40 publications

(41 citation statements)

References 39 publications

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“…Recently, there has been a strong interest in passive and active smart windows that could operate yearlong, while providing heating in the cold and cooling in the hot weathers [24,29]. Much research is focusing on developing materials that can simultaneously, while independently manage radiation across several widely spaced spectral ranges covering, for example, visible / near-IR light [12,30,31], or solar / mid-IR light [20].…”

Section: Introductionmentioning

confidence: 99%

“…In any case, to switch between the heating and cooling states the intelligent windows should allow large difference in its transmittance/reflectance properties between the two states, while always featuring low absorption of solar radiation [32]. Therefore, much attention was payed to improving the performances of the smart windows through materials research and structural optimization [29,[34][35][36][37][38][39].…”

Section: Introductionmentioning

confidence: 99%

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Improving thermo-optic properties of smart windows via coupling to radiative coolers

et al. 2020

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In this work we first solve the radiative heat transfer problem in one dimension to perform a comparative analysis of the time averaged performance of the partially transparent radiative windows and radiative coolers. In doing so we clearly distinguish the design goals for the partially transparent windows and radiative coolers and provide optimal choice for the material parameters to realize these goals. Thus, radiative coolers are normally non-transparent in the visible, and the main goal is to design a cooler with the temperature of its dark side as low as possible relative to that of the atmosphere. For the radiative windows, however, their surfaces are necessarily partially transparent in the visible. In the cooling mode the main question is rather about the maximal visible light transmission through the window at which the temperature on the window somber side does not exceed that of the atmosphere. We then demonstrate that transmission of the visible light through smart windows can be significantly increased (by as much as a factor of 2) without additional heating of the windows via coupling of the windows to the radiative coolers using transparent cooling liquid that flows inside of the window and radiative cooler structures. We demonstrate that efficient heat exchange between radiative coolers and smart windows can be realized using small coolant velocities (sub 1mm/s for ~1m-large windows) or even using a purely passive gravitationally driven coolant flows between a hot smart window and a cold radiative cooler mounted on top of the window with only a minimal temperature differential (sub-1K) between the two. We believe that our simple models complimented with an in-depth comparative analysis of the standalone and coupled smart windows and radiative coolers can be of interest to a broad scientific community pursuing research in these disciplines.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Improving thermo-optic properties of smart windows via coupling to radiative coolers

et al. 2020

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“…Other groups 22,27,32 have taken advantages of the different coefficients of thermal expansion (CTEs) of bilayers. Universities of Kassel 24 and Stuttgart 35 have used plasmaenhanced vapor deposition (PECVD) layers with stress gradient. Controlling and characterizing the stress are the keys to reproducible and reliable devices.…”

Section: Fabrication Stepsmentioning

confidence: 99%

“…Microblinds were also compared with other switchable glass technologies in review papers 14,15 and market reports. [19][20][21] Several groups have worked on various versions of microshutters, namely NRC, 17 New Visual Media Group (NVMG), 22,23 University of Kassel, 24,25 Institut National d'Optique (INO), 26 University of Tokyo, 27 Samsung, 28 U.S. Air Force (USAF), 29 Korea Advanced Institute of Science and Technology (KAIST), 30,31 Microelectronic Center of North Carolina (MCNC), 32 Fiat, 33,34 and University of Stuttgart. 35 These groups used various versions of curling electrodes actuated by electrostatic forces for switchable glass applications (window, display, imaging, eyewear, etc.).…”

Section: Introductionmentioning

confidence: 99%

Review of microshutters for switchable glass

Lamontagne

Fong

Song

et al. 2019

J. Micro/Nanolith. MEMS MOEMS

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Background: Switchable glasses allow the control of light transmission-an attractive property for applications such as car sunroofs, aircraft windows, building windows, augmented reality, imaging, and displays. Commercialized switchable glasses have severe limitations, such as speed, cost, and operating conditions, among others. Microshutters, a type of switchable glass with very distinctive properties, are reviewed, as they are a technology that could significantly improve some or all of the shortcomings mentioned above. Aim: We will summarize the various types of microshutters and tentatively identify various critical designs, fabrication schemes, and performance criteria by the many research groups implementing them and investigating their properties. Approach: We will describe the various approaches used to control light transmission through microelectromechanical systems. It will compare their performances and comment on fabrication and implementation challenges. Conclusions: Microshutters have performance levels that could make them good candidates for switchable glasses. Many research groups have investigated various approaches to fabricate microshutters and have shown that they can be implemented reliably on a small scale, with fast actuation, low power, and high contrast and are relatively easy to manufacture. Work is needed to demonstrate that they can be scaled-up and still be economical to produce.

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“…In any case, to switch between the heating and cooling states the intelligent windows should allow large difference in its transmittance/reflectance properties between the two states, while always featuring low absorption of solar radiation [38]. Therefore, much attention was payed to improving the performances of the smart windows through materials research and structural optimization [35,[40][41][42][43][44][45].…”

Section: Introductionmentioning

confidence: 99%

Simple models for the operation of partially transparent radiative windows and their comparison to the radiative coolers

Skorobogatiy¹,

Caloz²,

Zhung³

2019

Preprint

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In this work we solve approximately the radiative heat transfer problem in one dimension to perform a comparative analysis of the time averaged performance of the partially transparent radiative windows and radiative coolers. Our physical model includes the atmosphere, the window, and the backwall that are all in the thermal equilibrium with each other, and that can exchange energy via radiative heat transfer or convection. Moreover, we use a simplified two-state model for the optical properties of an atmosphere and a window material which assumes two distinct sets of the optical reflection/absorption/transmission parameters in the visible/near-IR versus mid-IR spectral ranges. Furthermore, we have distinguished the design goals for the partially transparent windows and radiative coolers and provided optimal choice for the material parameters to realize these goals. Thus, radiative coolers are normally non-transparent in the visible, and the main goal is to design a cooler with the temperature of its dark side as low as possible compared to that of the atmosphere. For the radiative windows, however, their surfaces are necessarily partially transparent in the visible. In the cooling mode, therefore, the main question is about the maximal visible light transmission through the window at which the temperature on the window somber side does not exceed that of the atmosphere. We believe that our simple physical models complimented with an in-depth comparative analysis of the radiative windows and coolers can be of interest to a number of scientists and engineers pursuing research in these disciplines.

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Optical MEMS-based micromirror arrays for active light steering in smart windows

Cited by 40 publications

References 39 publications

Improving thermo-optic properties of smart windows via coupling to radiative coolers

Improving thermo-optic properties of smart windows via coupling to radiative coolers

Review of microshutters for switchable glass

Simple models for the operation of partially transparent radiative windows and their comparison to the radiative coolers

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