Reflector Dimensions Research Articles

Artificial ground reflector size and position effects on energy yield and economics of single‐axis‐tracked bifacial photovoltaics

AbstractArtificial ground reflectors improve bifacial energy yield by increasing both front and rear‐incident irradiance. Studies have demonstrated an increase in energy yield due to the addition of artificial reflectors; however, they have not addressed the effect of varying reflector dimensions and placement on system performance and the impact of these parameters on the reflectors' financial viability. We studied the effect of high albedo (70% reflective) artificial reflectors on single‐axis‐tracked bifacial photovoltaic systems through ray‐trace modeling and field measurements. In the field, we tested a range of reflector configurations by varying reflector size and placement and demonstrated that reflectors increased daily energy yield up to 6.2% relative to natural albedo for PERC modules. To confirm the accuracy of our model, we compared modeled and measured power and found a root mean square error (RMSE) of 5.4% on an hourly basis. We modeled a typical meteorological year in Golden, Colorado, to demonstrate the effects of artificial reflectors under a wide range of operating conditions. Seventy percent reflective material can increase total incident irradiance by 1.9%–8.6% and total energy yield by 0.9%–4.5% annually after clipping is considered with a DC–AC ratio of 1.2. Clipping has a significant effect on reflector impact and must be included when assessing reflector viability because it reduces reflector energy gain. We calculated a maximum viable cost for these improvements of up to $2.50–4.60/m2, including both material and installation, in Golden. We expanded our analysis to cover a latitude range of 32–48°N and demonstrated that higher‐latitude installations with lower energy yield and higher diffuse irradiance content can support higher reflector costs. In both modeling and field tests, and for all locations, the ideal placement of the reflectors was found to be directly underneath the module due to the optimized rear irradiance increase.

Wide-field endoscope accessory for multiplexed fluorescence imaging

A wide-field endoscope that is sensitive to fluorescence can be used as an adjunct to conventional white light endoscopy by detecting multiple molecular targets concurrently. We aim to demonstrate a flexible fiber-coupled accessory that can pass forward through the instrument channel of standard medical endoscopes for clinical use to collect fluorescence images. A miniature scan mirror with reflector dimensions of 1.30 × 0.45 mm2 was designed, fabricated, and placed distal to collimated excitation beams at λex = 488, 660, and 785 nm. The mirror was driven at resonance for wide angular deflections in the X and Y-axes. A large image field-of-view (FOV) was generated in real time. The optomechanical components were packaged in a rigid distal tip with dimensions of 2.6 mm diameter and 12 mm length. The scan mirror was driven at 27.6 and 9.04 kHz in the fast (X) and slow (Y) axes, respectively, using a square wave with 50% duty cycle at 60 Vpp to collect fluorescence images at 10 frames per sec. Maximum total divergence angles of ± 27.4° and ± 22.8° were generated to achieve a FOV of 10.4 and 8.4 mm, respectively, at a working distance of 10 mm. Multiplexed fluorescence images were collected in vivo from the rectum of live mice using 3 fluorescently-labeled peptides that bind to unique cell surface targets. The fluorescence images collected were separated into 3 channels. Target-to-background ratios of 2.6, 3.1, and 3.9 were measured. This instrument demonstrates potential for broad clinical use to detect heterogeneous diseases in hollow organs.

Improved design of LBE cooled solid reactor using 3D neutronics thermal-hydraulics coupling method

The goal of this study is to improve a micro reactor core into uniform power distribution, a smaller and safer core. Neutronic thermal-hydraulics coupling is an effective means to study the characteristics of microreactors. This paper performs an improvement work of lead–bismuth eutectic alloy (LBE) cooled solid core using the three-dimensional neutronics/thermal-hydraulics coupling method. Based on the Monte Carlo code RMC and the three-dimensional thermal-hydraulics code STAR-CCM+, the coupling code processes the power distribution, fuel temperature, coolant temperature, and coolant density. The improvement of the solid core is carried out in these aspects: reflector material, reflector dimensions, fuel materials, coolant channel dimensions, the volume fraction of fuel phase in dispersion fuel, and critical enrichment. This paper studies the effect of reflector material and dimensions on the solid core and its mechanism. After improvement, the power peaking factor is effectively reduced, while the size and weight of the solid core are also reduced than before due to the excellent ability of beryllium oxide (BeO), making it compact and lightweight. In addition, the core eigenvalues keff and thermal characteristics of different ceramic fuels, uranium dioxide (UO2), uranium nitride (UN), and uranium carbide (UC), are compared. UO2 was replaced by UN, which improves the thermal conductivity and reduces the maximum temperature of the solid core. At the same pressure difference, the mass flow rate of the coolant and temperature distribution of the fuel and the variation trend of neutron characteristics are studied when the coolant channel diameter changes. The results indicate that the coolant channel diameter of 1.775 cm has the best safety effect on the core. The variation of critical enrichment and thermal conductivity of the fuel at different volume fractions is compared, and 60 % is chosen as the volume fraction of the fuel phase. The final design of the shutdown rod and control drums is performed to ensure that the core is subcritical under all conditions. The improved core can operate at full power for five years and is characterized by miniaturization, high thermal conductivity, low volumetric swelling rate, flattened power distribution, and abundant reactivity control measures.

Model construction and performance investigation of multi-section compound parabolic concentrator with solar vacuum tube

Multi-section Compound Parabolic Concentrator (M-CPC) has advantages of non-tracking device, adjustable operation time, concentrating diffuse radiation, convenient system integration, etc. In this study, the structure optimization, experimental verification and optical performance analysis of M-CPC with solar vacuum tube absorber are investigated. Combined with Monte Carlo Ray Tracing (MCRT) method and Particle Swarm Optimization (PSO) intelligent algorithm, based on Novel Compound Parabolic Concentrator (N-CPC), five M-CPCs of different reflector dimensions, namely, M-CPC2, M-CPC3, M-CPC4, M-CPC5 and M-CPC6, are constructed, and experimental results show that the concentrating performance of M-CPC is consistent with the numerical results of self-designed VC++ program. It is also found that the uniformity index of energy flux distribution for M-CPC is improved, and the effective operation time of concentrating solar beam radiation for M-CPC3 to M-CPC6 is increased by 1.82%, which indicates that M-CPC has better adaptability to weather changes. The average optical efficiency of M-CPC4 and M-CPC5 come up to 60.01% and 61.68%, respectively, and it has excellent performance of collecting solar radiation. In consequence, under the condition of the design method and N-CPC model, M-CPC4 and M-CPC5 are suitable choices in application, moreover, the cost of M-CPC reflector decreased significantly.

Visible Light Communications via Intelligent Reflecting Surfaces: Metasurfaces vs Mirror Arrays

We propose two types of intelligent reflecting systems based on programmable metasurfaces and mirrors to focus the incident optical power towards a visible light communication receiver. We derive the required phase gradients for the metasurface array reflector and the required orientations of each mirror in the mirrors array reflector to achieve power focusing. Based on which, we derive the irradiance expressions for the two systems in the detector plane to characterize their performance in terms of aiming and focusing capabilities. We show analytically that the number of reflecting elements along with the relative source - reflector dimensions determine the system power focusing capability. Moreover, we quantify analytically the received power gain compared with reflector-free systems. In addition, we introduce a new simple metric to assess the relative reflectors’ performance for a given source, detector, reflector layout. Finally, we verify the analytical findings regarding absolute and relative reflectors’ performance via numerical simulations.

Slab geometry type cold neutron moderator development based on neutronic study for Riken Accelerator-driven compact Neutron Source (RANS)

Cold neutrons with energy less than several meV are good probes for material research, and they have been available on large neutron facilities, whereas it is not commonly available on compact accelerator-driven neutron source. RIKEN Accelerator-driven Neutron Source (RANS) is a pulsed neutron facility which provides thermal neutrons and high energy neutrons at several MeV. We started a project to implement a cold neutron moderator for RANS to broaden cold neutrons applications. A cold neutron moderator system with a mesitylene moderator at 20K and a polyethylene pre-moderator at room temperature in the slab geometry was designed for RANS. So far, the thickness of the pre-moderator and mesitylene have been optimized to get the highest cold neutron flux by using a Monte Carlo simulation code, PHITS. Graphite reflector dimensions were also proven to have significant effect to increase the cold neutron intensity.

Eliminating saturation-type distortions in ultrasonic signals by the least-squares and Papoulis–Gerchberg algorithms

Situations may occur in ultrasonic testing in which the values of recorded echo-signals exceed the dynamic range of the receiving amplifier and defectoscope’s analog-to-digital converter. As a result, high-amplitude signals are subjected to a cutoff (clipping) operation and drop in amplitude, thus introducing error in the estimation of reflector dimensions. A declipping method that is based on the Papoulis–Gerchberg algorithm has been suggested and compared against a declipping technique that uses least squares. In numerical and model experiments, the Papoulis–Gerchberg algorithm has demonstrated more stable operation than the least squares for noisy signals and in the case of coarse signal sampling interval.

Diffraction-resistant scalar beams generated by a parabolic reflector and a source of spherical waves.

In this work, we propose the generation of diffraction-resistant beams by using a parabolic reflector and a source of spherical waves positioned at a point slightly displaced from its focus (away from the reflector). In our analysis, considering the reflector dimensions much greater than the wavelength, we describe the main characteristics of the resulting beams, showing their properties of resistance to the diffraction effects. Due to its simplicity, this method may be an interesting alternative for the generation of long-range diffraction-resistant waves.

Numerical analysis of small parabolic antennas using the method of current and change integral equations

The method of current and charge integral equations [1] is applied to numerical electrodynamic analysis of radiation and impedance matching characteristics of parabolic antennas with reflector diameter from 0.5 to 10λ. As a result as opposed to the current method relying on physical optics approximation the influence of feed on reflector’s radiation pattern, the influence of reflector on feed’s impedance matching and the contribution of feed’s rear radiation into reflector’s radiation pattern are all accounted for. A new model of representing a parabolic surface in the form of its square approximation is suggested, which provides almost uniform partitioning grid and has at least 2.5 times less boundary elements that the common revolution surface representation while having the same sampling coefficient. Dependences of antenna’s directivity on reflector dimensions (0.5–10λ) are calculated for six different focus distance to reflector’s diameter ratios using the developed by the authors crystal_U software package. The calculated results are confirmed by good matching with well-known experimental results.

Beam shaping assembly of a D–T neutron source for BNCT and its dosimetry simulation in deeply-seated tumor

This article involves two aims for BNCT. First case includes a beam shaping assembly estimation for a D–T neutron source to find epi-thermal neutrons which are the goal in the BNCT. Second issue is the percent depth dose calculation in the adult Snyder head phantom. Monte-Carlo simulations and verification of a suggested beam shaping assembly (including internal neutron multiplier, moderator, filter, external neutron multiplier, collimator, and reflector dimensions) for thermalizing a D–T neutron source as well as increasing neutron flux are carried out and our results are given herein. Finally, we have simulated its corresponding doses for treatment planning of a deeply-seated tumor.

A mathematical model for determining the optimal reflector position of a double exposure flat-plate solar collector

A double exposure, flat-plate solar collector (DEFPC) can absorb solar irradiation from both its upper and lower absorber surfaces (LAS). Absorption from the LAS is accomplished using a flat-plate reflector placed below and parallel to the collector. This paper presents a mathematical model for determining the optimum reflector position of the DEFPC in the condition where the LAS is fully irradiated. Compared to other models, this model enables the calculation of the instantaneously irradiated area of the LAS for arbitrary finite dimensions of the reflector and the collector, their arbitrary mutual positions and at any position of the sun in the sky. The optimum reflector positions were obtained by simulating the model in FORTRAN for the spring (autumn) equinox and the winter and summer solstices. The simulations were performed for the optimal yearly position of the collector at 44° N Latitude (Kragujevac, Serbia) and for equal dimensions of the collector and the reflector whose minimum dimensions allow the full irradiation of the LAS. The model was experimentally verified, and the range of the reflector movement during a single year, as well as the optimal reflector dimensions for minimum movement, was determined.

Effect of Boundary Support and Reflector Dimensions on Inflatable Parabolic Antenna Performance

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Effect of Boundary Support and Reflector Dimensions on Inflatable Parabolic Antenna Performance

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Thermal effects in semiconductor saturable-absorber mirrors

A semianalytical evaluation of laser-beam-induced thermal deformation of III–V semiconductor-based saturable Bragg reflectors is presented. The thermally induced bowing and resulting optical aberrations for different incident laser spot sizes and saturable Bragg reflector dimensions are calculated. Also discussed are the effects of the major physical and optical SESAM and laser parameters.

Differences between learning Styles in Professional Courses at University Level

Problem statement: As shown by research studies, knowledge of learning styles of students on the part of teachers is helpful in enhancing effectiveness of teaching-learning process. The present study was conducted to study and compare learning styles of students pursuing different professional courses at the university stage. The ultimate purpose was to facilitate learning in professional education in Indian conditions by way of improving learning styles of learners. Approach: The sample consisted of 200 students studying in B. Tech., MBBS, LLB and MBA courses selected from Aligarh Muslim University Aligarh, India, by using cluster sampling method. For measuring learning styles, Honey and Mumford’s Learning Style Questionnaire (LSQ) was used which was considered appropriate in terms of its validity and reliability. For analyzing data Student’s t-statistic was applied which is useful for comparing mean scores based on two groups at a time. Results: The students pursuing various professional courses were compared on four dimensions of learning styles, namely, activist, reflector, theorist and pragmatist. The study led to some useful conclusions. It was found that B. Tech. and MBBS students differed significantly on reflector and theorist dimensions and those of M.B.A. and B. Tech. also differed on the same dimensions. The students of LLB and MBA differed on activist and theorist dimensions while students of MBBS proved better than those of MBA on activist reflector and theorist dimensions. The students of LLB and B. Tech. and those of LLB and MBBS, also differed significantly on the same dimensions. The students of LLB and MBA did not show significant differences on any aspect of learning style. Conclusion: The findings of the study provided, useful guidelines to teachers of all professional courses to improve their teaching styles. They should devise their teaching strategies in such a way that students of varying learning styles may take their full advantage.

An omnidirectional ADE reflector antenna

AbstractIn this work, an axially‐displaced‐ellipse (ADE) dual‐reflector antenna for the achievement of an omnidirectional coverage is proposed. Its geometry is briefly presented and some relevant features are compared against previously suggested reflector antennas, designed for the same purpose. The present ADE configuration is capable of yielding the desired aperture illumination with relatively smaller reflector dimensions, thus providing a compact arrangement suited for use at base stations of point‐to‐multi‐point radio links. Numerical simulations are presented to illustrate the usefulness and advantages of the proposed reflector antenna. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 250–254, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11344

Angular errors in trihedrals used for radar calibrations

The effects of non-orthogonality of trihedral corner reflectors are significant when the reflector dimensions are large compared to the wavelength. Therefore, a high frequency approach is adopted combining geometrical and physical optics. A simple frequency dependent relationship is proposed for the maximum cross-section loss due to a given angular uncertainty. Polarization purity and phase stability are also addressed.

Characteristics of Millimeter-Wave Imaging Optics Using a Single Offset Paraboloidal Reflector

ABSTRACT All-reflective systems with focal–plane arrays of monolithic elements promise major improvements in millimeter wave imaging applications. In this work high resolution, diffraction limited, wide–field imaging performance is investigated for a single offset paraboloidal reflector. Using accurate electromagnetic vector diffraction analysis, off-axis image degradation is computed for progressively larger field-of-view. Comparisons validate the estimates obtained from the closed-form expressions used to initiate the design process. As a practical example of the design process, a system with an unobstructed 500 wavelengths entrance aperture diameter is designed and its imaging performance, at various locations within a 6048 elements image plane, is computed. The offset reflector dimensions result in a less than 0.2 degree half-power beamwidth and about 50 percent directivity loss at the edges of a rectangular 13 × 6.5 degrees image field of view. Review of these results demonstrate the high–performance...

Application of spherical wave expansions to direct GO far field synthesis

Diffraction effects which arise in the direct far field geometrical optics synthesis of shaped beam reflector antennas are examined. A spherical wave expansion technique is introduced which allows the optical coverage area and reflector dimensions to be specified in Westcott's complex co-ordinate synthesis technique. Examples are given of the method when applied to the synthesis of typical beam shapes encountered in satellite communications.

Twist reflector design using E-type and H-type modes

A complete solution of plane wave scattering from a twist reflector of infinite extent for arbitrary incidence is presented. The solution is accomplished through the use of an E -and H -type modal representation of the fields in the twister and free space regions. The equivalent circuits for strip and parallel plate twister gratings are derived by transforming E and H mode results [5] to appropriate type mode parameters. The modal reflection coefficients \Gamma' and \Gamma'' are determined from these equivalent circuit parameters and together with the use of a type mode description of the incident and reflected fields lead to two simple conditions for an optimum design; one geometric, namely \tan \phi = \sec \theta and one electrical, \Gamma/\Gamma' = - 1 . The computed performance of this optimum twist reflector in terms of a cross-polarized suppression ratio versus incidence angle for various planes of incidence represents the best that can be done with any physical structure. A design procedure including design formulas and curves is given from which twist reflector dimensions can be determined. Experimental verification for two specific implementations, parallel plates and parallel strips twist reflectors, is described.