•Colloidal self-assembly enables self-cleaning broadband anti-reflection (AR) coatings.•Bioinspired moth-eye AR coatings show much better AR performance than quarter-wavelength AR coatings.•AR ...gratings with high aspect ratios can be superhydrophobic.•Langmuir–Blodgett and spin-coating based colloidal self-assemblies are inexpensive and scalable.
Anti-reflection (AR) coatings are widely used in a spectrum of optical and optoelectronic devices, such as monitors, car dashboards, optical lenses, photodiodes, and solar cells. Narrowband quarter-wavelength single-layer and broadband multilayer dielectric AR coatings are typically fabricated by expensive and low-throughput vapor deposition processes (e.g., sputtering). Inspired by the subwavelength-structured cornea of some nocturnal moths, nanostructured broadband moth-eye AR coatings that can significantly suppress optical reflection over a wide range of wavelengths and light incident angles have been extensively exploited by both top-down and bottom-up approaches. Among many available bottom-up technologies, colloidal self-assembly is a promising approach as it is simple, fast, and inexpensive. In this review article, we will discuss two scalable colloidal self-assembly technologies based on Langmuir–Blodgett assembly and spin-coating for fabricating quarter-wavelength and moth-eye AR coatings with unique self-cleaning functionalities on transparent substrates (e.g., glass) and semiconductor wafers (such as crystalline silicon and GaAs).
A common approach in the literature when obtaining surrogate models of reflectarray unit cells is to include, among other variables, the angles of incidence as input variables to the model. In this ...work, we use support vector regression (SVR) to compare this approach with a new strategy which consists in grouping the refletarray elements under a small set of angles of incidence and train surrogate models per angle of incidence pair. In this case, the dimensionality of the SVR decreases in two with regard to the former approach. In both cases, two geometrical variables are considered for reflectarray design, obtaining 4-D and 2-D SVRs, respectively. In contrast to the common approach in the literature, the comparison between the 4-D and 2-D SVRs shows that a proper discretization of the angles of incidence is more competitive than introducing the angles as input variables in the SVR. The 2-D SVR offers a shorter training time, faster reflectarray analysis, and a similar accuracy than the 4-D SVR, making it more suitable for design and optimization procedures.
Photovoltaic systems have gained a great deal of interest in the world and these studies performed on this subject have been gaining more and more importance. In order to design new PV systems that ...will be installed to operate in more efficient and more feasible way, it is necessary to analyze parameters like solar radiation values, the angle of incidence of the genus, temperature etc. Therefore, in this study, theoretical works have been performed for solar radiation and angle of incidence values of any location, plus an experimental study was carried out on a system tracking the sun in two axes and in a fixed system. The performed prototype is also adapted into a PV system with 4.6kW power. Theoretical data are consistent with the data obtained from the PV system with 4.6kW power. This study will be an important guide for the future PV power stations.
Conventional target localization algorithms for the multiple-input multiple-output (MIMO) radar with widely separated antennas are mainly based on the centralized localization framework, which suffer ...from huge burdens of computation and communication as well as robustness defect in complex environments. To overcome these issues, this article first considers the MIMO radar with widely separated directional transmitters and omnidirectional receivers generating the bistatic range (BR) and angle of incidence (AOI) measurements for target localization, which is proven that the position of the target can be uniquely determined with one transmitter and one receiver. Then, the distributed localization framework using the hybrid BR and AOI measurements is developed, where each receiver acts as a fusion center extracting the BR and AOI measurements to perform the localization process, and the localization problem is formulated as solving a linear matrix equation. The distributed constrained total least squares (DCTLS) algorithm considering errors in both data matrix and observation vector is proposed for each receiver for target localization. The localization performance regarding the Cramér–Rao lower bound is derived for theoretical analysis. Numerical simulations are performed to validate the efficacy and superiority of the proposed DCTLS algorithm over other typical localization algorithms.
In this study, a new method for designing low profile frequency selective surfaces (FSS) with second-order bandpass responses is presented. The FSSs designed using this technique utilize non-resonant ...subwavelength constituting unit cells with unit cell dimensions and periodicities in the order of 0.15lambda 0 . It is demonstrated that using the proposed technique, second-order FSSs with an overall thickness of lambda 0 /30 can be designed. This is considerably smaller than the thickness of second-order FSSs designed using traditional techniques and could be particularly useful at lower frequencies with long wavelengths. To facilitate the design of this structure, an equivalent circuit based synthesis method is also presented in this paper. Two bandpass FSS prototypes operating at X-band are designed, fabricated, and tested. A free space measurement setup is used to thoroughly characterize the frequency responses of these prototypes for both the TE and TM polarizations and various angles of incidence. The frequency responses of these structures are shown to have a relatively low sensitivity to the angle of incidence. Principles of operation, detailed design and synthesis procedure, and measurement results of two fabricated prototypes are presented and discussed in this paper.
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•Class AAA solar simulator based on high power LED.•The collimating beam is uniform in volume space.•Adjustable output spectrum and irradiance.•Complex terrestrial solar spectra and ...orientations are simulated simultaneously.
Light-emitting diodes (LEDs) have shown advantages in simulating complex terrestrial solar spectrum. However, it has difficulty to simulate the geometric characteristics of direct sunlight with one solar constant (100 mW/cm2). In this paper, A method to collect full aperture light with hyper-hemispherical aplanatic lens has been proposed, and a multi-source integrated collimating system was built. The terrestrial solar spectra and orientations under various conditions have been simulated simultaneously. Also, we conducted a control experiment with polycrystalline silicon solar cells under outdoor sunlight conditions. It has good spectral accuracy and orientational consistency. The system meets the Class AAA specifications and achieves one solar constant irradiance of AM1.5G spectrum. The divergence angle of the collimating beam is around ±3°, and the temporal instability of irradiance is less than 0.3%. Within the range of volume space, the simulator achieves uniform illumination and the output beam follows the cosine law. The simulator has widely application in the photovoltaic industry, photochemistry, photobiology and many other fields.
A new method is introduced to ensure accurate reconstruction of two-dimensional thin film thickness in a spectroscopic imaging reflectometer. Its simple configuration is an advantage of a system that ...employs color camera as a detector, however, it has the problem of ambiguity in determination of the thin film thickness. To secure reliable measurement performance, multi-reflectance method is applied. The angle of incidence can be changed by adjusting the diameter of the tunable aperture. After integrating multiple reflectance signals acquired at different angles of incidence, one combined signal enables exact determination of thin film thickness.
A terrestrial laser scanner measures the distance to an object surface with a precision in the order of millimeters. The quality of the individual points in a point cloud, although directly affecting ...standard processing steps like point cloud registration and segmentation, is still not well understood. The quality of a scan point is influenced by four major factors: instrument mechanism, atmospheric conditions, object surface properties and scan geometry. In this paper, the influence of the scan geometry on the individual point precision or local measurement noise is considered. The local scan geometry depends on the distance and the orientation of the scanned surface, relative to the position of the scanner. The local scan geometry is parameterized by two main parameters, the range, i.e. the distance from the object to the scanner and the incidence angle, i.e. the angle between incoming laser beam and the local surface normal. In this paper, it is shown that by studying the influence of the local scan geometry on the signal to noise ratio, the dependence of the measurement noise on range and incidence angle can be successfully modeled if planar surfaces are observed. The implications of this model is demonstrated further by comparing two point clouds of a small room, obtained from two different scanner positions: a center position and a corner position. The influence of incidence angle on the noise level is quantified on scans of this room, and by moving the scanner by 2 m, it is reduced by 20%. The improvement of the standard deviation is significant, going from 3.23 to 2.55 mm. It is possible to optimize measurement setups in such a way that the measurement noise due to bad scanning geometry is minimized and therefore contribute to a more efficient acquisition of point clouds of better quality.
A zero-order (tau-omega) microwave radiative transfer model (RTM) is coupled to the Goddard Earth Observing System, version 5 (GEOS-5) catchment land surface model in preparation for the future ...assimilation of global brightness temperatures (Tb) from the L-band (1.4 GHz) Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) missions. Simulations using literature values for the RTM parameters result in Tb biases of 10–50 K against SMOS observations. Multiangular SMOS observations during nonfrozen conditions from 1 July 2011 to 1 July 2012 are used to calibrate parameters related to the microwave roughnessh, vegetation opacityτand/or scattering albedoωseparately for each observed 36-km land grid cell. A particle swarm optimization is used to minimize differences in the long-term (climatological) mean values and standard deviations between SMOS observations and simulations, without attempting to reduce the shorter-term (seasonal to daily) errors. After calibration, global Tb simulations for the validation year (1 July 2010 to 1 July 2011) are largely unbiased for multiple incidence angles and both H and V polarization e.g., the global average absolute difference is 2.7 K for TbH(42.5°), i.e., at 42.5° incidence angle. The calibrated parameter values depend to some extent on the specific land surface conditions simulated by the GEOS-5 system and on the scale of the SMOS observations, but they also show realistic spatial distributions. Aggregating the calibrated parameter values by vegetation class prior to using them in the RTM maintains low global biases but increases local biases e.g., the global average absolute difference is 7.1 K for TbH(42.5°).
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