Reflector Position Research Articles

Realistic ray-tracing model of a Scheffler reflector based on experimental data

A model of a Scheffler reflector with mirror facets is presented in the form of an open-source script for use with the free ray-tracing software Soltrace (Monte-Carlo method). It is calibrated to match the experimental results obtained with an 8 m2 (surface area) reflector of 1.43 m focal distance. It is found that the optical errors of real reflectors (slope, specularity, shape) are very large, leading to results that are far from theoretical. A sensitivity study is then carried out to assess the level of importance of reflector and receiver positioning and adjustment to obtain maximum performance. The parametric study showed that the margin of error is quite small for north–south alignment, rotation axis adjustment, horizontal receiver position, declination adjustment and tracking system, with a performance reduction of 10% for errors of 1°, 0.8°, 6 cm, 2 days and 4 min, respectively. The inclination of the receiver has lower influence on the results. The performance of Scheffler reflectors could therefore be greatly enhanced by improving the shape and characteristics of the mirrors, taking particular care with the various settings. In addition, as an application example, a secondary optical system multiplying the power density by up to 3.3 is proposed.

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.

Converted wave tomography based on inverse level set and adjoint formulation

SUMMARY Shear wave velocity (Vs) is a fundamental property of elastic media whose estimation from PS converted waves is challenging and requires modelling the boundary where P to S conversion occurs. This paper presents a PS tomography where seismic wave conversion/reflection points correspond to reflectors modelled with the level-set function set to zero [ϕ(x, z) = 0]. The proposed method aims for stable Vs inversion in a seismic acquisition setting using multicomponent receivers. Synthetic models simulating true Vs, Vp and the location of the geological reflector are used in the study. The inversion starts by locating a flat reflector, ϕ(x, z) = 0, which defines the zone Ω1 between the surface and the reflector, where the initial Vs and Vp fields are also set. To calculate the traveltimes of incident PT (P wave that propagates in Ω1 from source to the reflector), converted PS and reflected PP waves, for both observed and modelled data (forward problem), the methodology proposed by Rawlinson and Sambridge is adopted. This method uses the arrival times of the P waves, Tpt, from the seismic source at each reflector point as secondary sources generating the times Tps and Tpp. These times are calculated as a solution to the eikonal equation by using the Fast Marching method. The PS and PP residual times are minimized by updating Vs, Vp and ϕ(x, z) = 0 through adjoint variables designed from a formulation using Lagrange Multipliers in a variational context. The performance of the algorithm is evaluated for models with synclinal, sinusoidal and monoclinal reflector geometries using numerical tests considering the inversion of: (1) ϕ, given the true values of Vs and Vp; (2) ϕ and Vs, given the true value of Vp; (3) ϕ and Vp, given the true value of Vs and (4) the three parameters ϕ, Vs and Vp, simultaneously. Good results are obtained by inverting Vs and ϕ, given the true value of Vp. The simultaneous inversion of the three parameters exhibits promising results, despite the illumination problems caused by the different distribution of the PS, PP and PT time gradients due to the geometry of the reflectors and the acquisition setting (sources–receivers in the same plane). The proposed tomography estimates Vs and reflector positions which could help in statics corrections and improve the lithological characterization of near surface.

Modeling and numerical simulation of a type of pure-viscoacoustic-wave equation in attenuated transversely isotropic media

The anisotropy and attenuation features of subsurface media significantly affect seismic data processing. Ignoring anisotropy and attenuation in seismic wave propagation may result in inaccurate reflector positions, dimming amplitudes, and reduced spatial resolution in the imaging results. Therefore, accurate seismic wave modeling of anisotropy and attenuation is essential for understanding wave propagation in the earth’s interior. This paper derives three pure-viscoacoustic-wave equations from characterizing the earth’s frequency-independent Q behavior in transversely isotropic (TI) media. First, we develop three time-space domain pure-qP-wave equations in TI media based on different approximation methods, whose coefficients can be determined by different approximation methods and Thomsen’s anisotropic parameters [Formula: see text], [Formula: see text]. Subsequently, we introduce the Kelvin-Voigt attenuation model into our derived three time-space domain pure-qP-wave equations and then obtain three pure-viscoacoustic-wave equations. To further demonstrate the effectiveness and accuracy of our methods, we provide some 2D and 3D numerical tests. The numerical results indicate that the wavefield generated by pure-qP-wave equations and pure-viscoacoustic-wave equations have accurate kinematic characteristics of qP-wave in TI media and attenuated TI media and are free of S-wave artifacts while remaining stable under Thomsen’s anisotropic parameters [Formula: see text], so our methods have broader applicability compared with some existing methods. At the same time, the simulation results of pure-viscoacoustic-wave equations also reflect the absorption and attenuation characteristics of qP-waves in attenuated TI media.

Fast 3D positioning based on a simplified THz photonic stereo ISAR system.

In this work, a THz stereo inverse synthetic aperture radar scheme based on photonics is proposed, and proof-of-concept experimentally demonstrated, achieving high resolution and fast three-dimensional (3D) positioning of multiple targets. An optical frequency comb and a uni-traveling carrier photodiode are employed to photonically generate a linear frequency-modulation signal at 300-320GHz. By two incoherent measurements at different angles with one pair of antennas, 3D positioning of plane reflectors over a distance of 0.6m is successfully accomplished, achieving a resolution of 7.5mm for both range and azimuth dimensions, and a maximum experimental height error of 4mm.

Experimental determination for optimal position of reflector in solar water heater

An experimental investigation was carried out on novel solar water heater that utilizes a flat reflector positioned underneath the absorber tubes. Experiments were conducted at National Institute of Technology Patna, India, having latitude 25.61°N and longitude 85.14° E and constant insolation of 1000 The experimental data were collected for different reflector positions i.e. δ = 0 mm, 15 mm, 30 mm, 45 mm, and 60 mm and six mass flow rates of working fluid i.e. 0.0056 kg s−1, 0.0097 kg s−1, 0.0138 kg s−1, 0.0207 kg s−1, 0.0277 kg s−1, and 0.0346 kg−1s. The obtained experimental results exhibited that the location of the reflector relative to the absorber tubes significantly affects the thermal performance of the system. The effect of the mass flow rate on the outlet temperature, thermal performance, and overall performance has also been studied. For the present system under energy and exergy analysis, the optimal position of the reflector was found of δ = 30 mm. The results showed that the solar water heater with an optimally positioned reflector has a 23% increase in thermal efficiency compared to the solar water heater without a reflector. The novelty of using a flat reflector underneath absorber tube is to provide heat to rear side of the absorber tubes after reflecting the insolation falling on the reflector and hence improvement in the thermal performance of the solar water heater. The scope of present system includes providing an eco-friendly and energy-efficient solution for residential and commercial hot water needs. Limitations of the present study are requirement of sufficient roof space and direct sunlight. The use of reflectors has implications for energy savings, more efficient system designs, and enhanced thermal performance.

Optimal size and position of the planar back reflector moveable only in the direction normal to the bifacial solar collector plane

In this paper, the concept of a collector-reflector system consisting of a bifacial solar collector and a single flat-plate reflector separated and placed in parallel below the collector but moveable only in the direction normal to the collector plane is investigated. The developed mathematical model was used to optimize the size and position of the planar back reflector. The optimal hourly, daily, monthly and annual distances between the collector and reflector were determined. In addition, the daily, monthly and annual energy performance of the optimized bifacial collector-reflector system was estimated and compared with that of the corresponding monofacial solar collector. Based on the obtained results, two ways of use of the reflector are recommended, either according to the optimal hourly (moveable reflector) or optimal annual (fixed reflector) reflector positions. With optimally positioned moveable or fixed reflector the total solar radiation incident on the bifacial solar collector can be significantly higher than that for a monofacial solar collector. Its largest daily and monthly as well as average annual increase is: 74% (59%), 65.91% (46.21%) and 54% (39.4%), respectively. The proposed model can be applied to evaluate the energy performance of flat-plate bifacial thermal, photovoltaic or photovoltaic-thermal solar collector, of arbitrary size and position, which is in this arrangement with a planar reflector.

Eikonal-equation-based characteristic reflection traveltime tomography

Automatically picking reflection traveltimes from the prestack shot gathers and positioning and updating the reflector depths during inversion are challenging in conventional eikonal-equation-based adjoint-state reflection traveltime tomography methods. To solve these problems, we develop an eikonal-equation-based adjoint-state characteristic reflection traveltime tomography (ASCRT) method. This method automatically extracts the reflection traveltimes by sequentially applying characteristic reflector picking in the depth migration section, followed by eikonal-equation-based traveltime calculation and an event-tracking algorithm. We also develop an efficient eikonal-equation-based kinematic imaging method to rapidly position and update the reflector depths. With our ASCRT method, the characteristic reflector positions and the velocity above the reflector are alternately updated. Our ASCRT method is performed with a layer-stripping strategy that sequentially uses selected characteristic reflectors to update the velocity model from shallow to deep. Compared with the wave equation-based reflection traveltime inversion methods, the efficiency of the ASCRT method is improved by several orders of magnitude, and the memory consumption is remarkably reduced. Synthetic and field data examples are presented to demonstrate the effectiveness and efficiency of our method.

Frequency-dependent Q simulation and viscoacoustic reverse time migration based on the fractional Zener model

Seismic attenuation is a basic physical property of the earth, which significantly affects the characteristics of seismic wavefields. Accurately simulating wave propagation in the earth is essential to image subsurface structures. Some prevailing methods (e.g., the standard linear solid and fractional Laplacian equation) to describe seismic wave propagation in attenuating media are mainly based on the constant- Q model (CQM), which is valid at room temperature and pressure. However, laboratory measurements suggest that the quality factor Q is a function of frequencies in some regions. To simulate the frequency-dependent Q effect, we derive a viscoacoustic wave equation from the stress-strain relationship of the fractional Zener model (FZM) with variable fractional orders. During the implementation, we separate the real and imaginary parts of the modulus and introduce a low-rank decomposition method to solve the FZM equation. Because the amplitude dissipation and phase dispersion are decoupled, we establish a compensated reverse time migration ( Q-RTM) algorithm to mitigate adverse effects caused by seismic attenuation and improve the quality of seismic migration in frequency-dependent attenuating media. A two-layer model and the BP gas chimney model are used to perform Q-RTM tests. A low-pass filter with a Tukey window function is applied to suppress numerical instability during the compensation. Numerical results demonstrate that our FZM Q-RTM approach can produce high-resolution images with corrected reflector positions and amplitudes. Because the CQM equation ignores the frequency dependence of Q, it may lead to overcompensation in Q-RTM.

Identification of active faults and tectonic features through heat flow distribution in the Nankai Trough, Japan, based on high-resolution velocity-estimated bottom-simulating reflector depths

Estimates of heat flow can contribute to our understanding of geological structures in plate convergent zones that produce great earthquakes. We applied automated velocity analysis to obtain the accurate seismic profiles needed for precise heat flow estimates using six new seismic profiles acquired during R/V Kaimei KM18-10 voyage in 2018. We calculated heat flow values in the accretionary wedge of the Nankai Trough off the Kii Peninsula, Japan, from the positions of widespread bottom-simulating reflectors (BSRs) in seismic reflection profiles. Calculated conductive heat flow values from the depth of the BSR agree with previous studies where a regional trend is observed from ~ 50 mW/m2 to < 40 mW/m2 60 km landward from the deformation front. This trend is caused by thickening of accretionary sediments and the subduction of the Philippines Sea plate. Segments of profiles are marked by anomalous high heat flow values. Such anomalies represent alterations of the shallow crustal thermal structure caused either by a combination of topographic affects, surface erosion of the seafloor, or by fluid flow that transports heat by advection. We interpret heat flow anomalies (~ 100 mW/m2) as indicators of active faulting, which correspond to low seismic velocity zones along faults. Our results also showed relatively high heat flow at the landward end of several survey lines close to the Kii Peninsula, which we interpret to the possible presence of plutonic rocks that underlie the Kii Peninsula and extend offshore and may be the cause of geothermal springs, steep geothermal gradients, and high heat flow.Graphical abstract

Automatic Indoor Radio Map Construction and Localization via Multipath Fingerprint Extrapolation

For fingerprint-based localization, the time-consuming and labor-intensive construction of offline radio map is the bottleneck which hinders its large-scale implementation. In this paper, we propose a radio map extrapolation and localization algorithm by exploiting the angles and delays of specular multipath components. First, using the concept of virtual anchor nodes (VANs), we calculate the virtual transmitter (VT) of each multipath component according to angle and delay information measured at a known point. By estimating the positions of reflector with these VTs, the angles and delays of the uplink multipath components transmitted at other locations in the indoor environment are extrapolated. Then, a channel fingerprint composed of the extrapolated angles and delays is proposed to represent the channel response in the angle-delay domain, which is spatially unique and discriminative. Thus, the radio map constructed such can significantly reduce the labor and time costs. Lastly, a convolutional neural network (CNN) is applied for indoor localization. The performance of the proposed fingerprint extrapolation and localization method is validated through extensive simulations with a ray-tracing channel model, which exhibits promising localization performance for our proposed scheme with reduced construction costs.

Perbandingan Nilai Daya Luaran Panel Surya Kapasitas 50Wp Terhadap Posisi Reflektor Cermin Datar

Solar panel systems are widely used to meet energy needs at this time. Solar panels have optimal power for 4 hours, namely 10:00 to 14:00. but this is still said to be not optimal if the angle of the static solar panels does not follow the movement of the sun. This can also be caused by weather factors that are covered in clouds. Previous research conducted by Tri Wahyu Ardianto used mirror reflectors but was not equipped with sensors and data storage. Based on this, to optimize solar panel energy, a flat mirror reflector design for solar panels has been made, equipped with four flat mirror reflectors on each side to form a large square. The solar panel is placed in the middle between the four flat mirrors. In this study, the measurement of electric power was carried out by carrying 3 variable angles for reflector positions, namely 0°, 60°, and 70°. The decision of the three reflector positions is made to find out the ratio of the maximum output power values. This system is also equipped with current, voltage, and light intensity sensors. The results show that the maximum output power of solar panels is shown at the reflector position of 60° with an average power output of 19.70 Watt followed by a reflector position of 70° with an average output power of 19.18 Watt and finally the reflector position is 0° with an average output power value of 14.87 Watt.

The correct location of the optical centre of corner reflectors

I reiterate the derivation of the optical centre position of corner reflectors given by Peck (1948). However, my derivation in the paper uses the absolute optical path lengths instead of the relative optical path lengths presented by Peck. I also show that the optical centre of the corner-cube retroreflector depends on the refractive index of the surrounding medium, and thus the surrounding medium affects its position by more than 3 µm for a typical solid glass retroreflector. The effect of the surrounding medium that is acting by means of the relative index of refraction was later reinterpreted as the absolute index of refraction, and therefore lost in the calculations. The error from such a reinterpretation exceeds the optical centre adjustment error, which is typically realized to be as low as 1 µm. In the future, the correction of such an offset in the optical centre position can improve the precision of interferometric measurements, especially those of absolute gravimeters. The corresponding effect on the measurement of gravitational acceleration can be in tenths of μGal.

Photonic THz InISAR for 3D Positioning With High Resolution

Terahertz (THz) radar has been considered as a new solution to the dilemmas in performing ultra-high-resolution imaging and obtaining highly precise target information. In this work, a photonic THz interference inverse synthetic aperture radar (THz InISAR) scheme is proposed and proof-of-concept experimentally demonstrated, targeting high resolution positioning of multiple targets. We employ an optical frequency comb and a uni-traveling carrier photodiode (UTC-PD) to photonically generate a linear frequency-modulation (LFM) signal at 290-310 GHz. By using the anti-electromagnetic-interference THz photonic signal source, broadband THz transceivers and efficient InISAR algorithms, 3D positioning of corner reflectors over a distance of 2.2 m at the 300 GHz band is successfully achieved, reaching a resolution of 8 mm for both range and azimuth dimensions, and a maximum height error of 0.4 mm in a height range of 11 cm. To the best of our knowledge, our proposed system represents the ever-first accurate 3D positioning at the THz band above 300 GHz, revealing the great potential applications of THz radar systems.

A calculation method of the passive wireless surface acoustic wave sensor response phase

In this research, we propose a method to calculate the phase delay angle of the reflected wave compared to the wave emitted from the interdigital transducer (IDT) of a passive wireless surface acoustic wave (SAW) sensor by combining simulation of the finite element method (FEM) and MATLAB. Based on the result, we consider the influence of the reflector position on the phase delay of the SAW sensor consisting of an IDT and three equally spaced reflectors. The distances between the IDT and the first reflector are 870 micrometers, 939.6 micrometers, and 1009.2 micrometers, and the distances between the reflector positions are 452.4 micrometers, 522 micrometers, and 591.6 micrometers. The outputs of the FEM simulation, including delay time, amplitude loss, and the length of the reflected wave are put into the model in MATLAB to determine the phase delay of the response waves. The obtained phase delay results show that as the distance between the IDT and the reflectors increases, the phase delay angle increases to 4.49 degrees, 5.39 degrees, and 5.78 degrees, respectively.

Effect of reflector on performance of solar still

This paper goals towards fabrication and performance testing of a single slope solar still at location (13.18°N,74.93°E).The solar still performance is tested without a reflector and with a reflector. The testing has been done at four different levels of water in the basin (0.5 in., 1 in., 1.5 in. and 2 in.). The distillate output has determined at three different positions of reflector (45°, 60°and 75°). The testing has been done for the entire day for two months and the collected distillate is measured daily. From the results it is found that with the increase in water level in the basin, the distillate output reduced. The optimum performance was observed at 60°reflector tilt. It is found that with the use of reflector the performance of the still has increased by24.2% compared to a normal solar still.

The Characteristics of the Second and Third Virtual Cathodes in an Axial Vircator for the Generation of High-Power Microwaves

A virtual cathode oscillator or vircator is a vacuum tube for producing high-power microwaves (HPM). The efficiency of the vircator has been a difficult task for decades. The main reasons for low efficiency are intense relativistic electron beam (IREB) loss and few or no interactions between IREB and HPM. In this case, forming multiple virtual cathodes may be beneficial in overcoming these constraints. By reusing the axially propagating leaked electrons (LE), we could confine them and form multiple virtual cathodes (VCs). This article discussed the characteristics of newly formed VCs based on simulation results. The formation time of new VCs was discovered to be highly dependent on the reflector position and the density of LE approaching their surfaces. Furthermore, multiple VC formation in the waveguide region does not affect conventional VCs’ position or forming time. The emission mode of the generated HPM was TM01 with single and multiple VCs and remained unaffected. The formation of multiple VCs positively influenced the axial and radial electric fields. When compared to a single VC, the axial and radial electric field increased 25.5 and 18 times with multiple VCs. The findings suggested that forming multiple VCs could be a future hope for achieving high vircator efficiency.

Enhancing the thermo-economic performance of mobile solar desalination system with dual reflectors, phase change materials and insulator cover: Experimental investigations

• Insulator on top surface enhances the performance substantially. • Micro high conductivity particles are recommended for PCM. • Optimum angle for reflectors is critical. • More than double the productivity is achieved with modifications. A deficit of consumable water is the primary challenge to the people living on the seashore, tiny islands and remote regions. Although solar desalination is indeed one of the sustainable methods for producing sweet water from any form of polluted water, the low productivity of conventional systems remains a challenge. From this perspective, this research focuses on enhancing the productivity of a hemispherical solar desalination system by employing external dual reflectors, thermal conductivity enhanced latent heat storage medium and an insulator cover on the top surface during off-sun-shine hours. The experimental study is carried out in Coimbatore (India) during the March, April and May months of 2021. The experimental data are validated using uncertainty analysis, statistical analysis, and theoretical temperature data obtained from energy analysis. The novelty of the work includes the optimization of reflectors’ tilt angle, employing micro high conductivity particles embedded in energy storage medium and insulator cover on the top surface during the energy retrieval period. Because of the modifications, the proposed system can enhance productivity by 115% and energy efficiency by more than 100%. Although the system with a pure storage medium and the one with composite material exhibit more or less similar energy efficiency, the higher exergy efficiency of the latter during off-sun-shine-hours makes it superior to the former. Furthermore, the modified system is found to be economically viable as the cost of freshwater per litre and payback were reduced by 18% and 19% respectively as compared to the conventional system. Based on the analysis of the results, it can be concluded that the maximum benefit can be extracted from the hemispherical solar desalination if the reflectors’ angle is optimized and the top surface is covered with an insulator cover. The present work provides guidelines for optimizing the position of external reflectors. Further, the importance of the employment of insulation during energy retrieval is addressed.

Investigation of the planar reflector substitution method using the finite element method

The backscatter coefficient (BSC) has been shown to be an indicator of tissue state in assessing tumour response to therapy, but it is limited in its clinical applicability by the difficulty in acquiring the appropriate reference spectrum. The accuracy of a BSC estimate made by the substitution method is influenced by the quality of the reference spectrum, which normalises the measurement to the source’s diffraction field and spectral characteristics. Among the reference objects employed for normalisation, a planar reflector has been popular. With the sample region at the focus of a focused source or the last axial maximum of an unfocused source, the reflector has been placed either at this depth or half this depth by different authors. This work explores the effect of planar reflector positioning on BSC estimation. FE models were constructed to simulate BSC measurements of virtual phantoms with various sources, and the estimates compared to scattering theory. The results indicate that unfocused sources provide more accurate BSC estimates when the reflector is placed at half the distance to the last axial maximum (d), while focused sources provide better estimates with the planar reflector at the focal plane, and that focal-plane reflector positioning is preferable for source radii-of-curvature ≤ d.

Secondary Reflector and Receiver Positions for Uniform Heat Flux Distribution in Parabolic Trough Solar Thermal Collector

Abstract The distributions of heat flux over the circumference of the receiver tubes have an immense influence on the performance and reliability of the parabolic trough solar thermal collectors. The location of the receiver tube and the secondary reflector configuration may largely influence the performance of the system. Therefore, in this study, the effect of receiver tube position and parabolic secondary reflector configuration has been analyzed, and the non-uniformity of solar flux distribution, heat gradient, and power output has been compared. The results of the Monte Carlo ray-tracing analysis to homogenize the receiver tube flux distribution and maximize the output power, making the use of the cutting edge solar optical simulation tool Tonatiuh, has been presented. A parabolic trough collector with a rim angle of 80 deg and aperture area of 40 m2 have been used for the analysis. It has been confirmed that the circumferential heat flux gradient and the local hot spot could be greatly diminished, while the power output tended to reduce slightly due to the shading effect of the secondary reflector. Under the conditions investigated in this work, although the output power decreased by 4.83%, flux gradient reduced significantly, and the non-uniformity of flux distribution has reduced from 0.9757 to 0.5176. A simple design procedure for receiver tube position and secondary reflector configurations to homogenize the receiver tube temperature distribution has also been proposed.