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13 May 2019 Visual appearance of microcontacts for solar windows
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Fig. 1
Schematic of an ETC window: triangular cross-section microsilver grids are integrated with a glass window.

Fig. 2
Schematic of the ray optical model.

Fig. 3
Schematic of the experimental setup.

Fig. 4
Series of images seen through ETC windows measured (a–d) and computationally simulated with (e–h) high resolution ray tracing, (i–l) resolution correction, and (m–p) depth of field correction. The images were captured under (a, e, i, m) normal incidence, (b, f, j, n) 20 deg, (c, g, k, o) 40 deg, and (d, h, l, p) 60 deg angle of incidence with rotation axis along the ETC lines.

Fig. 5
Quantitative comparison between experimental results and computational simulation. The (a) luminance, (b) contrast, (c) structure, and (d) SSIM values are plotted as a function of the angle of incidence.

Fig. 6
Picture taken through an ETC window (with ND filters).

Fig. 7
Visualization of the optical model for scenes observed through an ETC window under an angle.

Fig. 8
The same scene observed in four different ways: (a) through an ETC window under normal incidence; (c) through a window with flat contacts under 50 deg viewing angle with a height of 10 and 80  μm periodicity; (b) and (d) through ETC windows under 50 deg viewing angle with ETCs, with (b) 10  μm height and 80  μm periodicity and (d) 15  μm height and 40  μm periodicity.

Fig. 9
(a) Percentage of ETC redirected rays as a function of the viewing angle α for different ETC periodicities and different aspect ratios. 1:2, 80 means: aspect ratio 1:2, periodicity 80  μm. (b) β-angle of the redirected rays as a function of the viewing angle α for different aspect ratios.



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