Flat Reflector Research Articles

Micro-Cap on 2-Core-Fiber Facet Hybrid Interferometer for Dual-Parameter Sensing

In this article, we demonstrate a “Fabry-Perot + Michelson” hybrid interferometer based on a polymer micro-cap located on asymmetric 2-core fiber (2CF) facet. Because the polymer micro-cap comprises a flat reflector and a concave reflector, the light propagating in the centric core will be reflected twice forming Fabry-Perot interference. Due to the bias angle between the eccentric core and the concave reflector, the light in the eccentric core reflects only once on the flat reflector and would interfere with the other reflected light in the 2CF. The experimental results show that Fabry-Perot and Michelson interference occur and are superimposed on the directly detected spectrum. Independent interferometric spectrums can be separated by Discrete Fourier Transform to achieve humidity-temperature simultaneous measurement based on coefficient matrix demodulation. Moreover, this new optical fiber sensing platform is all-solid, high-integration, and flexible, so it has potential in lab-on-fiber applications.

Reflective optics for redirecting convergent radiative beams in concentrating solar applications

We investigate optical characteristics of flat, ellipsoidal, hyperboloidal, and paraboloidal reflectors for redirecting convergent radiative beams common in concentrating solar applications. Optical simulations are performed with selected types of radiative sources including a generic uniformly-emitting spherical cap and a specific realization of a multi-source high-flux solar simulator. Two-dimensional ray-tracing simulations are conducted for an ideal optical system without optical imperfections consisting of a spherical cap source, a beam-redirecting reflector, and a target tailored to capture all radiation. System optical performance is evaluated in terms of output beam optical characteristics of rim angle, ray distribution and relative position to the input beam. Three-dimensional Monte-Carlo ray-tracing simulations are performed for a practical optical system with a realistic solar simulator as radiation source and the four beam-redirecting reflectors. We predict optical characteristics of resulting radiative power, spatial and directional flux distribution, optical efficiencies on specified flat and hemispherical targets, and clearance between simulator, reflector and target. From the model system with a solar simulator and exemplary parameters, it is concluded that the investigated four types of reflectors enable redirection of the horizontal-axis beam from the solar simulator to non-horizontal axis targets. The flat reflector enables the highest system optical efficiency of 97% at the expense of the smallest clearance between the source, the reflector and the reflected image. Curved reflectors render a larger degree of freedom to design the characteristics of the output beam. Thus, curved reflectors are suitable for applications that require large clearance between system components and/or high radiative flux output on cavity surface, but at the expense of lower system optical efficiency.

The shining world of beetles

Twisted liquid-crystalline organizations are ubiquitous in living matter [1] , [2] . Many insects own a tessellated carapace with bumps, pits, indentations, stripes or spots ( Fig. 1 ). These geometric variation often exhibit iridescent colors, which are the consequence of a complex twist of chitin macromolecules. Such optical information with vivid structural colors might be of paramount importance in the life and the evolution of most day-living insects. Many biological functions are yet debated. They are related to conspecific or intra-species communication, thermoregulation, camouflage, survival or navigation [1] , [3] . For example, the cuticle of the scarab beetle Chrysina gloriosa exhibits two bands ( Fig. 2 ). The green band serves as a wavelength-selective (green) diffuser due to the set of polygons arranged on a curved surface and, at the mesoscopic scale, it behaves as an array of wavelength-selective micromirrors [4] . The silver stripe plays the role of a flat metallic reflector operating over the visible spectrum and into the infrared spectrum [4] . The orientation of the helicoidal structure varies in green stripes ( Fig. 3 ), whereas it is fixed in silver stripes. The outermost part of insect cuticles is very often covered with wax, which restricts water loss, prevents desiccation, may lend superhydrophobic and self-cleaning properties to the cuticle, and serves for chemical communication in many species. While cuticular waxes are considered isotropic, the wax layer of the cuticle of C. gloriosa exhibits an intriguing nanoscale laminate texture, as revealed by electron microscopy of the transverse sections [5] . Micro-textured cuticles of scarabs may inspire researchers and engineers to make their replicas as optical materials. Potential applications are in the field of wavelength-specific light modulators in routing technologies, broadband reflectors for energy savings, coatings for cryptography purposes (wavelength-dependent and polarization-dependent micro- and nanoscale patterns), camouflage (suits with a broad reflection in the IR spectrum identical to the one of the background) or thermoregulation for buildings.

A comparison of planar convex dielectric lens loaded flat reflector with parabolic reflector and reflectarray

AbstractIn this article, experimental demonstration in the X‐band of a flat reflector backed dielectric lens is reported. Equivalence between the reflector‐lens and parabolic reflector of equivalent cross‐section is shown by comparing their radiation characteristics. The reflector‐lens is also compared with a reflectarray resonating at 10 GHz, and their radiation patterns show good match at this frequency.

High Enhancement of Unidirectional UWB Array Antenna’s Gain Using Flat Reflector Structure for Microwave Applications

UWB array antenna with the high enhancement of gain is proposed. New additional flat reflector with a distance of 20 mm enhances the proposed antenna gain. UWB antenna performance with reflector is better than UWB antenna without reflector structure. Antenna with reflector recorded wider operating bandwidth; 1.9GHz-10.6GHz with higher gain ranged from 3.5dB until 14.2dB compared with without reflector antenna operated from 2.2GHz to 10.6GHz with lower gain ranges of 1.9dB to 9.8dB. The reflector structure enhanced the antenna gain by 50% where the average gain throughout operating frequency for an antenna with reflector and antenna without a reflector is 10.2dB and 6.8dB respectively.

A Novel Coplanar-Strip-Based Excitation Technique for Design of Broadband Circularly Polarization Antennas With Wide 3 dB Axial Ratio Beamwidth

In this communication, a novel excitation technique for the design of a single-point-fed compact low-profile wide-slot antennas with broadband circular polarization (CP) and wide 3 dB axial ratio (AR) beamwidth is presented. Two inverted L-shaped parasitic strips placed coplanar to the microstrip line of an asymmetric coplanar waveguide (CPW) and a horizontal strip that protrudes from the vertical edge of the backside ground plane of the substrate are used for CP excitation. The overall footprint of the structure is only $L_{s} \times W_{s} = 0.3\lambda _{0} \times 0.28\lambda _{0}$ when measured at the lowest operating frequency. The antenna prototype has been experimentally validated. The measured results indicate that a wide impedance bandwidth of 72% (2.26–4.85 GHz) and a CP bandwidth of 66% (2.44–4.87 GHz) can be achieved. In addition to the wideband characteristics in terms of the impedance bandwidth and CP, a stable bidirectional radiation pattern with a wide 3 dB beamwidth of 85° ± 5° is obtained for 58% of the total CP bandwidth without involving any complex circuitry. Furthermore, by placing a flat metallic reflector behind the antenna, a unidirectional radiation pattern is produced without changing the geometrical dimensions of the proposed antenna. The average realized gain of the antenna without a reflector is 3.3 dBi, whereas it increases up to 6.3 dBi with the substrate-size reflector.

An Automatic Method for Subglacial Lake Detection in Ice Sheet Radar Sounder Data

During the past decades, radar sounder (RS) instruments have been effectively used to detect subglacial lakes (SLs). SLs appear as flat, smooth, and bright reflectors in RS radargrams. The visual interpretation has been the main approach to SL detection in radargrams. However, this approach is subjective and inappropriate for processing large amounts of radargrams. While the analysis of RS data for understanding the subglacial hydrology has recently received increased attention, the literature on the development of automatic methods specifically designed for SL detection is still limited. In order to fill this gap, in this paper, we propose a novel automatic technique for SL detection. The technique is made up of two steps: 1) feature extraction and 2) automatic detection. In the first step, we define and extract three families of features for discriminating between the lake and nonlake radar reflections. The features model locally the basal topography, the shape of the basal reflected waveforms, and the statistical properties of the basal signal. In the second step, we provide the features as input to a support vector machine classifier to perform the automatic SL detection. The proposed technique has been applied to radargrams acquired over two large regions in East Antarctica and Siple Coast. The obtained results, which are validated both quantitatively and qualitatively, confirm the robustness of the features and their capabilities to effectively characterize SLs. Moreover, they prove the potentiality of the method to process large amounts of radargrams and update the current SL inventory.

High Gain of Directional Ultra-Wideband Array Antenna Using Flat Reflector Structure for Microwave Imaging

UWB array antenna with high gain is proposed. The 4 × 1 array antenna consists of four identical copper circular patches are appropriately connected using quarter-wavelength transformer transmission line. The array elements and its feed network are properly optimized to have a high gain performance over wide range bandwidth frequencies. New additional flat reflector with distance of 20 mm enhances the proposed antenna gain. UWB antenna performance with reflector is better than UWB antenna without reflector structure. Antenna with reflector recorded wider operated bandwidth; 1.9GHz-10.6GHz with higher gain ranged from 3.5dB until 14.2dB compared with without reflector antenna operated from 2.2GHz to 10.6GHz with lower gain ranges of 1.9dB to 9.8dB. The reflector structure enhanced the antenna gain by 50% where the average gain throughout operated frequency for antenna with reflector and antenna without reflector is 10.2dB and 6.8dB respectively. Dimensions of 80 mm × 45 mm is considered as small UWB array antenna. The high gain and wide operator bandwidth of proposed antenna finds it very suitable to be integrated in human brain microwave imaging system due to ability of the wide signal with high energy penetrating human head structure.

Numerical modeling and parametric study of an innovative solar oven

A unique design of a double glazed box-type solar oven with flat foldable external reflectors at the top and front and an internal reflector beneath the L-shaped absorber plate is numerically and parametrically studied. The maximum temperatures attained in the absorber cavity of the oven are observed to be in the range of 100–135 °C. A numerical model is formulated to solve the overall energy balance on the absorber plate of the proposed solar oven by incorporating the effects of the top, front, and bottom reflectors for a given set of input parameters. CFD simulations are utilized to predict the unknown buoyancy driven convective heat transfer coefficient from the L-shaped absorber plate to the surrounding glass cover forming an enclosure. Modeling results are found to be in good agreement with the experimental results which leads to the parametric study of the solar oven. The effects of various design parameters on the oven‘s performance such as spacing between glazings, influence of the vertical component of the absorber plate and internal reflector, glazing thickness number of glazings and the effect of absorber plate coatings are also discussed.

Eksperimental Study the Effect of Additional Flat Plate Reflector to Performance the Sinusoidal Solar Water Heater

New Renewable Energy is currently not fully utilized. Energy sourced from the sun is one of the most exploited energy sources today in several countries in the world, which in large scale has been used as a power plant. The solar collector is a heat exchange device that serves to convert solar radiation energy into a form of heat energy to heat a working fluid, such as water and air. Various methods have been undertaken to improve the performance of solar collectors, including using flat plate reflectors. Reflectors are used to reflect the diffused sunlight to focus on solar cells and ultimately increase the value of solar cell output power. Experimental studies in this study were conducted to see the performance of a solar collector sinusoidal with and without the addition of reflectors under varying discharge conditions. Variations of mass flow rate in this study were 18 and 20 liters/hour. The reflector angle on the solar collector is set at 40° on both sides of the reflector. From this study, the results for the efficiency of a solar collector with the addition of a reflector are the highest at 43,91% at a mass flow rate of 20 liters / hour.

Two-Dimensional Manipulation in Mid-Air Using a Single Transducer Acoustic Levitator.

We report a single transducer acoustic levitator capable of manipulating objects in two-dimensions. The levitator consists of a centrally actuated vibrating plate and a flat reflector. We show that the levitation position of the object depends not only on the vibration frequency, but also on the tilting angle between the plate and the reflector. Additionally, new levitation positions can be created by actuating the plate with a composite signal of two frequencies using frequency switching. Based on recorded levitation positions, such single transducer acoustic levitator can manipulate a cluster of levitated microspheres in predefined trajectories, with mean position error of 155 ± 84 µm.

Influence of Corrugated Booster Reflectors in a Centrally Finned Twist Inserted Solar Thermal Collector on Heat Transfer and Thermal Performance Characteristics

In this present work, the influence of corrugated booster reflectors (CBR) in a centrally finned twist (CFT) inserted solar thermal collector (SC) on heat transfer and thermal performance characteristics has been approached experimentally. The experimental trials have been made with two different twist ratios (Y = 3 and 6) for typical twist (TT) and CFT under same working conditions. The results were compared with the plain tube SC with CBR plain and also with the plain tube SC with flat booster reflectors (FBR plain). The experimental result of the CBR plain has been verified with the standard equations and found the deviations within ±10.05% for Nusselt number and ±9.42% for friction factor. The CBR has 1.6% higher effective reflection area than the FBR. Hence, the CBR augmented the Nusselt number around 8.25% over the FBR. When compared to the CBR plain, the CFT of minimum twist ratio (Y = 3) offered 10.09% higher thermal efficiency. In addition, empirical correlations have been derived for predicting the Nusselt number and friction factor. The deviations of the predicted value from the experiment value fall within ±10.62% for Nusselt number and ±11.28% for friction factor.

Performance of Solar Module with Presence of Two Types of Reflectors in Concentrator System

Any work to improve the performance of the solar modules could add to their economic competitiveness against fossil fuels. In the present work the performance of PV solar module was improved by using V-Trough concentrator system (CPV) which moved by two axis tracking system. The concentrator consists of two flat reflectors of area 2 m2 for each one with geometric concentration ratio of 2X. To optimize the performance of the V-Trough CPV systems, two types of reflector material, Aluminum and mirror (glass coated by silver nitrate) were used. The results indicated that the temperature of PV reference module was higher than the ambient temperature by 27oC but there is too small difference in temperature between the tracking PV module with the reference which ranged to 2oC, while the temperature of the CPV system was higher than reference by 37oC. The temperature of the PV module under mirror reflectors was lower than module combined with Aluminum reflectors by 3oC. As a result of arising of the temperature of CPV system in compare with PV reference module, the open circuit voltage was droop by 0.7 V, 0.5 V for PV module under mirror and Aluminum reflectors respectively. The reflectors increased the short circuit current values by 2.1 A, 2.6 A for PV module combined with mirror and Aluminum reflectors respectively. Accordingly the performance (as an average daily gain of output power) of the PV solar module was improved by using V-Trough CPV system, 44%, 34% by using Aluminum and mirror reflectors respectively.

Terahertz multichannel metasurfaces with sparse unit cells.

Reflective multichannel metasurfaces are flat reflectors that can control incident and reflected waves in a number of propagating directions simultaneously. However, they are always densely discretized with a high spatial resolution, which increases the manufacturing complexity. In this Letter, to the best of our knowledge, a new method that combines the array antenna theory with the metagratings theory is proposed. We demonstrate that the unit cells with a linear gradient phase in each period of the metasurfaces can eliminate specific space harmonics. With this method, multichannel metasurfaces can be designed with sparse unit cells, and high efficiency is maintained simultaneously. As proofs of the method, we design three different terahertz multichannel metasurfaces with no more than three unit cells per period. The simplification of structures can efficiently reduce the manufacturing complexity. This work may open up new routes in designing multichannel metasurfaces.

Graphene transistor based on tunable Dirac fermion optics

We present a quantum switch based on analogous Dirac fermion optics (DFO), in which the angle dependence of Klein tunneling is explicitly utilized to build tunable collimators and reflectors for the quantum wave function of Dirac fermions. We employ a dual-source design with a single flat reflector, which minimizes diffusive edge scattering and suppresses the background incoherent transmission. Our gate-tunable collimator-reflector device design enables the quantitative measurement of the net DFO contribution in the switching device operation. We obtain a full set of transmission coefficients between multiple leads of the device, separating the classical contribution from the coherent transport contribution. The DFO behavior demonstrated in this work requires no explicit energy gap. We demonstrate its robustness against thermal fluctuations up to 230 K and large bias current density up to 102 A/m, over a wide range of carrier densities. The characterizable and tunable optical components (collimator-reflector) coupled with the conjugated source electrodes developed in this work provide essential building blocks toward more advanced DFO circuits such as quantum interferometers. The capability of building optical circuit analogies at a microscopic scale with highly tunable electron wavelength paves a path toward highly integrated and electrically tunable electron-optical components and circuits.

Experimental study on a new solar refrigerator with intermittent adsorption cycle

This paper presents experimental results for a prototype intermittent solar adsorption ice-maker using water as the refrigerant and silica gel as the adsorbent. Four external flat reflectors made of polished stainless steel were used to enhance the performance. On a cloudy day, without reflectors, a minimum temperature of 7 °C was reached, so no ice was made. With reflectors 0.5 kg of ice was made from a 9 kg load. Increasing the load of water tended to increase the solar COP. The effect of the initial mass of refrigerant was also investigated.

Achieving Directive Radiation and Broadband Microwave Absorption by an Anisotropic Metasurface

Simultaneously integrating electromagnetic absorption and wavefront-shaping into a single metasurface with flat and low profile is crucial for many practical applications both in science and engineering community. Here, by introducing lossy components to properly design the impedance of metasurface, we propose an anisotropic metasurface capable of broadband absorption and high-efficient wavefront manipulation, which is sensitive to the excitation of different polarizations. As a practical example, we present a flat metasurface reflector to achieve high-directional radiation with reduced backward scatterings. When a standard waveguide antenna is used to illuminate the metasurface, the reflected wavefront is shaped to directive beam across X-band in microwave regime, with the gain reaches about 25 dBi around 10 GHz. Under the illumination of an orthogonally polarized wave, the incident power is dissipated by the chip resistors to achieve broadband and high-efficient microwave absorption. Experiments are carried out to validate the design principle, and good agreements are observed between the measured and simulated results.

Optimisation of planer's tilts angles reflectors for solar hybrid photovoltaic thermal air collector

Using concentrators to the output of hybrid photovoltaic thermal (PV/T) solar collectors has been proven cost effective. Flat reflectors offer a simpler, reliable and cheap solution to increase the amount of solar radiations that fall on the solar collector. They provide a uniform concentration of solar radiation over the PV/T collector and prevent a hot-spot phenomenon. In this study, an optimisation of planer's tilts angles reflectors for solar hybrid photovoltaic thermal (PV/T) air collector by implementing the particle swarm optimisation (PSO) method is done. The PV/T air solar collector is south oriented with tilted at site latitude angle. Then the total incident solar radiation on the PV/T air collector surface is estimated. An experimental test was conducted in the southern region of Algeria on a prototype of the hybrid PV/T air collector, with two reflectors mounted on the lower and upper parts of the PV/T air collector. A 9%-19% increase in quantity of solar radiation incidents on the PV/T air collector was observed with the addition of planer reflectors. The adding reflectors and cooling system causes a 7%-30% increase in the current and voltage of the PV module.

Optimisation of planer's tilts angles reflectors for solar hybrid photovoltaic thermal air collector

Using concentrators to the output of hybrid photovoltaic thermal (PV/T) solar collectors has been proven cost effective. Flat reflectors offer a simpler, reliable and cheap solution to increase the amount of solar radiations that fall on the solar collector. They provide a uniform concentration of solar radiation over the PV/T collector and prevent a hot-spot phenomenon. In this study, an optimisation of planer's tilts angles reflectors for solar hybrid photovoltaic thermal (PV/T) air collector by implementing the particle swarm optimisation (PSO) method is done. The PV/T air solar collector is south oriented with tilted at site latitude angle. Then the total incident solar radiation on the PV/T air collector surface is estimated. An experimental test was conducted in the southern region of Algeria on a prototype of the hybrid PV/T air collector, with two reflectors mounted on the lower and upper parts of the PV/T air collector. A 9%-19% increase in quantity of solar radiation incidents on the PV/T air collector was observed with the addition of planer reflectors. The adding reflectors and cooling system causes a 7%-30% increase in the current and voltage of the PV module.

ВИЗУАЛИЗАЦИЯ И ХАРАКТЕРИЗАЦИЯ МАЛЫХ ОБЪЕКТОВ В ЛИНЗОВОМ АКУСТИЧЕСКОМ МИКРОСКОПЕ С ДВУМЕРНОЙ РЕШЕТКОЙ

Application of a lens multi-element acoustic microscope for the visualization and quantitative characterization of small discontinuities with dimensions of the spatial resolution level is considered. On the basis of the paraxial approximation it was found that the recorded spatio-temporal signal of the microscope ultrasonic array can be treated as an estimation of the scattering function of visualized objects. It was theoretically established that the scattering functions of the observed inhomogeneities can be used for the interpretation of the generated acoustic images. It is shown that the finite size of the array elements constrains the angular resolution of the method due to smoothing of the measured scattering function. Experimental testing of the proposed method was carried out using the developed prototype microscope with a two-dimensional array of square elements and a polystyrene spherical acoustic lens. It was experimentally confirmed that the spatial resolution of the device corresponds to a theoretical estimate obtained by a classical criterion. The generated images of small flat reflectors with different angles of inclination obtained by means of electronic scanning are presented. It is shown that the output array data set is more informative for the quantitative characterization of the discontinuities than their acoustical images. In particular, on the basis of the obtained estimation of the scattering function it was possible to estimate the angle of inclination of the reflectors.