Reflective coatings are used on building walls and roofs to reducing heating from solar radiation, and thus have a high reflectivity for the visible and near-infrared wavelengths where sunlight has most of its energy. However, the loss of solar heating during winter increases energy consumption. For temperate latitudes, the solar altitude at noon during summer approaches zenith, while at noon in winter the sun appears much lower in the sky. We propose to take advantage of this change in solar altitude from summer to winter to passively adjust the reflection properties to season. Towards this aim, we numerically calculate the diffraction efficiency of a one-dimensional periodic microstructure using rigorous coupled wave analysis (RCWA). We analyze the angular selectivity of the grating structure for its suitability to retain cooling properties in summer while allowing solar heating in winter. In order to explore angle-selective reflection properties, we explored a series of cross-sectional shapes for the grating by adjusting its geometrical parameters. We find that a rectangular cross-sectional profile produces high angular selectivity of reflection but narrow spectral bandwidth, and trapezoidal shapes produce smaller angular selectivity but broader bandwidth.
Solar heat reflective paint coated roof is known as cool roof. These cool roofs have an ability of saving energy consumption due to its high reflection against solar irradiation. However, it is suggested that these cool roofs should not be used at cold area because its reflection makes temperature of walls lower. These cool roofs should absorb a solar irradiation when cold situation to raise energy efficiency. Therefore, both reflection and absorption compatible roof is needed. This characteristic can be obtained from active or a passive characteristics-modulating technics. In this study, we focused on the geometrical relationship between the Sun and the Earth, and angular variation of reflection by microstructure. We calculated an angular solar irradiance distribution at the Earth’s arbitrary point from theoretical model and numerically analyzed an angular selective reflective microstructure at single wavelength using Rigorous coupled wave analysis (RCWA) method to verify possibility of angle-selectivity. A microstructure was optimized to its effective reflectivity and absorptivity by changing its geometrical parameters. The optimized microstructure works as the surface has 71% reflector during summer solstice while works as a 48% reflector during winter solstice, from our estimation.
In this paper, we propose an optical model of the surface color controlled by Ag nanograin structure. A forming method
of Ag nanograin structure on the surface of a silver mirror by chemical conversion treatment was discovered. The surface
has not only unique colors but also properties of bulk metal. The result of SEM observation of the Ag surface showed
nanograin structure and varying in the grain size depending on the color. The size of the grains was from 20nm to 100nm.
We focused on microscopic behavior of electrons in the Ag grain and the permittivity model was formulated based on
Drude Lorentz theory. The model was designed on the assumption that the individual grain behaved like a metallic atom
with bound electron different from the silver. The analytical values of this proposed model were compared with
measurement values in a reflectance spectrum and a chromatic variation.
The mechanical characteristics of polymer materials are of interest to the chemical industry. There are requirements for
observation of changes of internal structure to stress. A number of samples under various stress conditions have
provided interesting information upon analysis by microscopic birefringence measurement. In the present paper, we
propose a birefringence measurement method for observation of the internal structure of polymer materials and analysis
of the relationship between a given stress and the corresponding birefringence distribution. The proposed measurement
system consists of a He-Ne laser, polarizers, a half-wave plate and a quarter-wave plate. The birefringence distributions
of gelatin, such as the phase difference and azimuthal angle, are shown for the case of applied uniaxial and biaxial
The orientation control of liquid crystal (LC) molecular on the polyimide film has been necessary to fabricate LC devices. Nano-rubbing by atomic force microscope (AFM) has been proposed as the one of methods to control it precisely. In the method, a thin polyimide film was rubbed by a sharpened AFM probe-tip with relatively strong load force. However, the method has some drawbacks; the frictional wear of AFM probe-tip and the difficulty of reorientation after rubbing. In this paper, we have proposed the orientation control of LC on the polyimide film and using direct AFM nano-rubbing method with weak load forces. The change of LC alignment was quantitatively observed by a polarization microscope and birefringence-contrast scanning near-field optical microscope. The effect of scanning density was strong for azimuth angle but the effect of the scanning velocity was weak for both retardation and azimuth angle. An optical switching device was developed utilized isotropic-nematic phase change of liquid crystal which was rubbed in the grating pattern with methyl red dying, and the optical device was operated at the frequency of 0.5Hz. As a result, The proposed method had an effective method to fabricate novel liquid crystal optical devices.
A polarization measurement is proposed to detect a birefringence and an optical rotation distribution in a microscopic area. A residual stress caused by industrial processes and molecular orientation are observed by visualizing birefringence distribution. It is possible to analyze components of material with optical rotation. This measurement system consists of a He-Ne laser, polarizers, a half-wave and a quarter-wave plate. By changing combination of rotating angle of half-wave plate, quarter-wave plate and analyzer, we can obtain retardation, azimuthal angle of birefringence and optical rotation angle independently. An analytical algorithm with local-sampling phase shifting is employed for achieving a high resolution. The errors caused by the initial polarized characteristic of the optical system are corrected by subtracting the in-phase vector.
A microscopic birefringence imaging of bio-sample is proposed. This system consists of a super luminescent diode (SLD), polarizers, a quarter-wave plate and a phase retarder. The instrument is provided to map and visualize an optical anisotropy in bio-sample. A local-sampling phase shifting technique is employed for analytic algorithm with high resolution of retardance. A Bereck compensator is used a sample for checking its accuracy. Birefringence distributions of gelatin orientation such as retardance and azimuthal direction are shown in case of applied voltage and changing temperature as its demonstration. It is possible to observe molecular orientation of bio-sample.