Optimum Incidence Research Articles

The impact of the V-corrugation on the thermal efficiency of a solar collector

Solar energy plays an essential role in the process of the energy transition to renewable sources, and so too do technological innovations for exploring these energy sources, and for improving the thermal efficiency of conventional flat solar collectors. This study set out to model, simulate, and investigate the effect of modifying the geometry of the absorber plate of standard solar collectors for heating liquids, by inserting V corrugations. This leads to making consequent modifications to geometrical and optical parameters that improve the efficiency of the equipment. This paper presents the application of a mathematical-graphical model that seeks an optimum incidence angle to corrugate an absorber plate. This model, based on available optical experimental data, was built to improve the efficiency of solar collectors. During its application, an investigation could be made of the effect of the corrugation on the radiation and on the convection coefficients, the correlations of which were introduced into the mathematical model, and some of them were neither mentioned nor used in previous publications. A case study was carried out to investigate the behavior of three different collectors and the improvement in the efficiency of these collectors. It was shown that by using V grooves the efficiency was improved for all three flat solar collectors studied. As seen, the geometric modification contributes to improving efficiency when associated with selective absorption layers of solar collectors. The combination of both strategies can enhance the thermal efficiency of solar collectors and this can be further explored by researchers and manufacturers.

Evaluating the effect of the incidence angle of ALOS-2 PALSAR-2 on detecting aquaculture facilities for sustainable use of coastal space and resources.

Driven by the growing world population, aquaculture plays a key role in meeting the increasing demand for food. However, aquaculture facilities in Japan are widely installed in coastal waters where natural disasters, such as typhoons and tsunamis, might wash these facilities away, thereby interfering with maritime navigation safety. Therefore, it is imperative to efficiently monitor the state of aquaculture facilities daily, particularly after a disaster in real time. To this end, several new space-borne L-band synthetic aperture radars (SARs) continue to be launched now and in the future, whose utilizations are expected to increase nationally and internationally. An example is the Japan Aerospace Exploration Agency, currently operating a SAR that can be operated day and night, and even under cloudy conditions, called ALOS-2 PALSAR-2. Based on the above facts, this study evaluated the effect of the incidence angle of ALOS-2 PALSAR-2 HH single-polarization data, using 3 m spatial resolution, on aquaculture raft detection. As the study site, we selected Ago Bay, located on the Pacific coast of Mie Prefecture in central Japan since the Nankai Trough Megathrust Earthquake and tsunamis have been predicted to occur in the future around this area. Then, we analyzed the sigma zero (backscattering coefficient) of aquaculture rafts and their surrounding sea surfaces, including the relationships between satellite orbits and aquaculture raft directions. Investigations revealed that the optimum incidence angle for detecting aquaculture rafts in this study was 33.8°-45.1°. Differences in the sigma zero values existed between the ascending and descending orbits. However, the incidence angles differed on the orbits. Then, differences in the median sigma zero values across a range of incidence angles were evaluated under the descending orbit. In addition, when the directions of the aquaculture rafts were closely perpendicular to the satellite orbit, aquaculture rafts tended to show the highest values of sigma zero due to Bragg resonance scattering. Hence, this knowledge may allow for the rapid detection of aquaculture rafts during an emergency without going on-site.

Time-series polarimetric bistatic scattering decomposition using comprehensive modified first-order radiative transfer model at C-band for vegetative terrain and validation

ABSTRACT The sensitivity of the bistatic scattered signal to both the soil and vegetation physical properties in microwave sensing of vegetation is subject to uncertainties. A multi-angular and fully polarimetric data acquisition from a bistatic system increases the number of observations. Thus, optimum bistatic system parameters for vegetation monitoring are necessary to develop an understating of microwave interactions with the surface and vegetation properties. In this study, C-band fully polarimetric bistatic scatterometer (BiSCAT) system was designed to measure the scattering response of vegetated terrain in the forward specular plane. The correlation analysis between the measured bistatic scattering coefficient () and in-situ soil/vegetation properties, such as plant water content (PWC) and soil moisture (), was used to find the optimum specular incidence angle of the BiSCAT system. The optimum parameters of the BiSCAT system were used as input to the modified first-order radiative transfer model (MRTM) for the simulation for vegetation. Kirchhoff’s approximate (KA) model for soil surface in forward specular plane was simplified for soil contribution within MRTM. Additionally, the temporal patterns of are modelled by employing the empirical formulation between the vegetation optical depth and PWC. The MRTM offers an understanding of co-polarized electromagnetic signal interaction with the temporal change in vegetation constituents and soil surface parameters. The model is limited to providing insights into co-polarized radar return from the target due to the incapability of yielding the cross-polarization factor from the KA model in the forward specular direction. The contributions of surface, vegetation, surface-vegetation, vegetation-surface and surface-vegetation-surface were quantified to better understand microwave’s interaction with the vegetation. The model is calibrated using a constrained non-linear least-square optimization algorithm. The performance indices of simulating yields good agreement with the BiSCAT measurements.

Investigation on the Flow Angle of a Mixed Flow Turbocharger Turbine Under Steady State Operating Conditions Authors

Turbocharger is widely used in automotive field for the capability to extract or boost the downsizing internal combustion (IC) engine as it has been considered as a way to provide highly efficient of small engine. Turbocharger also reduces the fuel consumption as well as the carbon dioxide (CO2) emission. Turbine is one of the main components of a turbocharger. Generally, this study is mainly focusing on a mixed flow turbine that work under steady flow operation. Numerical work using Computational Fluid Dynamics (CFD) is presented in this report. This report aims to compare the flow angle analysis of three selected cases under steady state flow operating conditions. A 3D modelling on a mixed flow turbine is generated accordingly to ‘Rotor A’ design by using a commercial software of Ansys CFX. Three selected cases were selected in order to compare the flow angle at the mid span circumference location at vane and rotor inlet. The simulation results show the capabilities of the 3D model developed in capturing the trend of available experiment data at turbine speed of 48kRPM. The mixed flow turbine achieves optimum total-to-static efficiency of 74.16 % at velocity ratio of 0.65 with mass flow rate of 0.5kg/s. Besides that, the results shown that the flow angle distribution at the rotor inlet is varied throughout the rotor circumference location between the three cases. Case 2 achieved the optimum incidence angle compared to the other cases thus showing the impact of incidence angle in determining the turbine performance.

A Convenient Way to Determine the Optimum Angle of Incidence of Fizeau Interferometer

In a Fizeau interferometer, off-axis illumination will lead to fringe optimization. Primarily due to the unique structure of our interferometer, we first analyze the influence of the optical properties of the parallel plate as a part of the interferometer on the optimal incident angle. Generally, the incident angle determination is mainly based on the graphing method proposed by Langenbeck and the estimation formula proposed by Kajava. However, Langenbeck’s method is cumbersome, and the error of Kajava’s estimation formula is large. Based on the predecessors, this paper proposes a modified method of determining the optimal angle of incidence and further derives more accurate optimal angle expressions than Kajava’s. By simply substituting the wedge angle of the wedge cavity and the reflectivity of the cavity, the optimum incidence angle can be obtained immediately. Thus, it eliminates the tedious and complex process of finding the optimum incident angle by graphing method and makes the formula method the simplest method to find the optimum incident angle. Finally, the comparison of the interference intensity at the optimum incidence angle calculated by the improved method and normal incidence is given. It is found that the beam has a good suppression effect on the sub-peak when it is incident at the optimum incident angle calculated by the method in this paper.

Delta-Winglet-Pair for Enhancing Cooling Performance of a Single Dimple Imprinted Internal Channel

Improving the cooling performance of internal channels is important to extend the lifespan of hot components exposed to heat in many types of machinery. This study was performed to examine the effects of placing a delta-winglet-pair (DWP) upstream of a single dimple in an internal cooling channel. The local heat/mass transfer coefficients (H/MTCs) were measured in the vicinity of the dimple by the naphthalene sublimation method (NSM). The cooling performances under laminar, transitional, and turbulent flow conditions were compared at different values of the DWP incidence angle (β). The DWP enhanced local H/MTCs within the dimple cavity due to intensified secondary vortices. With increasing the DWP incidence angle, the distance between the symmetrical vortices increased resulting in a different level of H/MTC enhancement. The optimum DWP incidence angle ranged between 30∘<β<45∘ depending on the flow condition. The resulting area-averaged H/MTCs clearly indicated enhancement from the DWP. Under the laminar flow conditions, the H/MTCs were enhanced by 87%–125% from installing the DWP. The absolute H/MTCs were highest under the transitional flow conditions. Based on the present investigation, the installation of the DWP in the dimpled channel is highly recommended for both laminar and transitional flow conditions.

Generalised bisection method for optimum ultrasonic ray tracing and focusing in multi-layered structures

Ultrasonic testing has been used for many decades, proving itself very efficient for detecting defects in many industrial sectors. The desire to apply ultrasonic testing to geometrically complex structures, and to anisotropic, inhomogeneous materials, together with the advent of more powerful electronics and software, is constantly pushing the applicability of ultrasonic waves to their limits. General ray tracing models, suitable for calculating the proper incident angle of single element probes and the proper time delay of phased array, are currently required. They can support the development of new imaging techniques, as Full Matrix Capture and Total Focusing Method, and the execution of very challenging ultrasonic inspections. This paper introduces a generalized iterative method for the computation of ultrasonic ray paths, when ultrasonic source and target are separated by multiple complex material interfaces in the two dimensional and three dimensional domains. The manuscript starts with a review of the well-known bisection method, and extends the applicability of the method to cases with increasing complexity. An application example, in the field of in-process weld inspection, shows that the introduced generalised bisection method can enable the computation of optimum incidence angles and focal delays for accurate ultrasonic focusing. There is no restriction on the analytical interfaces to be surjective. Interface folding is permitted. It is not necessary to know, a priori, with what sequence the interfaces are crossed by the rays. The presented implementation of the method completes each iteration of the bisection method in 4 ms, for a case with a single interface, and in 960 ms for the case with 52 interfaces.

Robust machine learning techniques for rice crop variables estimation using multiangular bistatic scattering coefficients

The present study is designed to explore the potential of bistatic scattering coefficients (σ ° ) and machine learning algorithms for the estimation of rice crop variables using ground-based multiangular, multitemporal, and dual-polarized bistatic scatterometer data. The bistatic scatterometer measurements are carried out at eight different growth stages of the rice crop in the angular range of incidence angle 20 deg to 70 deg for HH- and VV-polarization at 10-GHz frequency in the specular direction with an azimuthal angle (φ = 0). Several field measurements are taken for the measurement of rice crop variables, such as vegetation water content, leaf area index, and plant height at its various growth stages. Machine learning algorithms—such as fuzzy inference system (FIS), support vector machine for regression (SVR), and generalized linear model (GLM)—are used to estimate the rice crop variables using bistatic scatterometer data. The linear regression analysis is carried out for the evaluation of the multiangular, multitemporal, and dual-polarized datasets for the selection of optimum incidence angle and polarization for accurate estimation of rice crop variables. The highest value of the coefficient of determination (R2) is found at 30-deg incidence angle for VV-polarization. The sensitivity of copolarized ratio of σ ° with the rice crop variable is also evaluated using linear regression analysis for the estimation of rice crop variables. The highest value of R2 is found to be at 35-deg incidence angle between the copolarized ratio of σ ° and rice crop variables. The performance of SVR model is found superior in comparison to the FIS and GLM at VV-polarization and the copolarized ratio of σ ° for the estimation of rice crop variables. However, the copolarized ratio of σ ° is found superior to VV-polarized bistatic scatterometer data for the estimation of rice crop variables.

Strong Solar Radiation Forces from Anomalously Reflecting Metasurfaces for Solar Sail Attitude Control

We examine the theoretical implications of incorporating metasurfaces on solar sails, and the effect they can have on the forces applied to the sail. This would enable a significant enhancement over state-of-the- art attitude control by demonstrating a novel, propellant-free and low-mass approach to induce a roll torque on the sail, which is a current limitation in present state-of-the-art technology. We do so by utilizing anomalous optical reflections from the metasurfaces to generate a net in-plane lateral force, which can lead to a net torque along the roll axis of the sail, in addition to the other spatial movements exhibited by the sail from solar radiation pressure. We characterize this net lateral force as a function of incidence angle. In addition, the influence of the phase gradients and anomalous conversion efficiencies characteristics of the metasurfaces are independently considered. The optimum incidence angle that corresponded with the maximum net lateral-to-normal force ratio was found to be −30° for a metasurface exhibiting 75% anomalous conversion efficiency with a phase gradient of 0:71k0.

Compact gain-saturated x-ray lasers down to 685 nm and amplification down to 585 nm

Plasma-based x-ray lasers allow single-shot nano-scale imaging and other experiments requiring a large number of photons per pulse to be conducted in compact facilities. However, compact repetitively fired gain-saturated x-ray lasers have been limited to wavelengths above λ=8.85 nm. Here we extend their range to λ=6.85 nm by transient traveling wave excitation of Ni-like Gd ions in a plasma created with an optimized pre-pulse followed by rapid heating with an intense sub-picosecond pump pulse. Isoelectronic scaling also produced strong lasing at 6.67 nm and 6.11 nm in Ni-like Tb and amplification at 6.41 nm and 5.85 nm in Ni-like Dy. This scaling to shorter wavelengths was obtained by progressively increasing the pump pulse grazing incidence angle to access increased plasma densities. We experimentally demonstrate that the optimum grazing incidence angle increases linearly with atomic number from 17 deg for Z=42 (Mo) to 43 deg for Z=66 (Dy). The results will enable applications of sub-7 nm lasers at compact facilities.

A Detailed Comparison on the Influence of Flow Unsteadiness Between the Vaned and Vaneless Mixed-Flow Turbocharger Turbine

A turbocharger is a key enabler for lowering CO2 emission of an internal combustion engine (ICE) through the reutilization of the exhaust gas energy that would otherwise have been released to the ambient. In its actual operating conditions, a turbocharger turbine operates under highly pulsating flow due to the reciprocating nature of the ICE. Despite this, the turbocharger turbines are still designed using the standard steady-state approach due to the lack of understanding of the complex unsteady pressure and mass propagation within the stage. The application of guide vanes in a turbocharger turbine stage has increased the complexity of flow interactions regardless of whether the vanes are fixed or variable. Although it is enticing to assume that the performance of the vaned turbine is better than the one without (vaneless), there are currently no tangible evidences to support this claim, particularly during the actual pulsating flow operations. Therefore, this research looks into comparing the differences between the two turbine arrangements in terms of their performance at flow field level. For this purpose, a three-dimensional (3D) “full-stage” unsteady turbine computational fluid dynamics (CFD) models for both volutes are constructed and validated against the experimental data. These models are subject to identical instantaneous inlet pressure profile of 60 Hz, which is equivalent to an actual three-cylinder four-stroke engine rotating at 2400 rpm. A similar 95.14 mm diameter mixed-flow turbine rotor rotating at 48,000 rpm is used for both models to enable direct comparison. The complete validation exercises for both steady and unsteady flow conditions are also presented. Results have indicated that neither vaned nor vaneless turbine is capable of maintaining constant efficiency throughout the pulse cycle. Despite that, the vaneless turbine indicated better performance during peak power instances. This work also showed that the pulsating pressure at the turbine inlet affected the vaned and vaneless turbines differently at the flow field level. Furthermore, results also indicated that both the turbines matched its optimum incidence angle for only a fraction of pulse cycle, which is unfavorable.

Downforce variation dependence of angle of incidence modification for the rear wing of high speed vehicles

The conventional downforce devices (with fixed geometry) of high speed vehicles have parameters such as area, angle of incidence and head resistance coefficients, all with constant values. The downforce is proportional with the square of movement speed and the power consumed for the neutralization of aerodynamic road resistance is proportional with the cube of speed. The authors carried out an analytical study of downforce, adjustable/monitored by optimum incidence (modification of incidence angle of rear wing for performance improvement).

Effects of Cone Angle and Inlet Blade Angle on Mixed Inflow Turbine Performances

The development of the aerofoil-shaped turbomachine blades is of prime importance for achieving the appropriate deflection of a three dimensional flow through desired angles, to work at the same degree of incidence and thereby providing the required performances for the specific machine. The sensitivity of the rotor to incidence effects and tendency of the flow to separate from one or the other blade surface have given rise to considerations of the optimum incidence angle and cone angle for a mixed inflow turbine by a numerical investigation using the ANSYS-CFX code. In order to keep the rotor in the same casing some geometrical parameters have been hold constant and the Bezier polynomial is used to generate the new shape of the rotor blade when changing the cone angle magnitude.

Optimum pelvic incidence minus lumbar lordosis value after operation for patients with adult degenerative scoliosis

Background ContextSchwab classification for adult degenerative scoliosis (ADS) concluded that health-related quality of life was closely related to curve type and three sagittal modifiers. It was suggested that pelvic incidence minus lumbar lordosis value (PI-LL) should be corrected within −10°~+10°. However, recent studies also indicated that ideal clinical outcomes could also be achieved in patients without the ideal PI-LL mentioned above. PurposeThis study evaluated the relation between the clinical outcomes and the PI-LL of Chinese patients with ADS who received long posterior internal fixation and fusion. Study DesignThis was a single-center retrospective comparative study of patients treated by long posterior internal fixation and fusion in our hospital between 2010 and 2014. Patient SampleInclusion criteria were age >45 years at the time of surgery, Cobb angle of lumbar curves ≥10°, long posterior internal fixation and fusion ≥least 3 motion segments, follow-up ≥2 years, complete preoperative and postoperative radiographic data, and functional evaluation results. Exclusion criteria were history of previous lumbar spine surgery, other kinds of scoliosis, history of severe spinal trauma, spinal tumor, ankylosing spondylitis, and spinal tuberculosis. Seventy-four patients were enrolled in this study. Outcome MeasuresOperative parameters included intraoperative blood loss, duration of surgery, length of hospital stay, number of fusion levels, and decompression. The radiological measurements included Cobb angle of the curves and PI-LL. Clinical outcomes were evaluated by the Japanese Orthopaedic Association score, Oswestry Disability Index (ODI), visual analog scale, and Lumbar Stiffness Disability Index (LSDI). In addition, the complications of surgery were also collected. One-way analysis of variance, Student t test, Kruskal-Wallis test, Pearson chi-square test, and curve estimation were calculated for variables. MethodsAll the patients were divided into Group 1 (long instrumentation and fusion to L5) and Group 2 (long instrumentation and fusion to S1). Operative parameters, radiological measurements, clinical outcomes, and complications of surgery were compared between two groups to confirm whether distal fusion level could influence therapeutic effect. Then patients were divided into PI-LL<10° (Group A), 10°≤PI-LL≤20° (Group B), PI-LL>20° (Group C). Operative parameters, radiological measurements, clinical outcomes, and complications of surgery were compared between each of the two groups. Curve estimation was performed to evaluate the relationship between postoperative PI-LL and clinical outcomes. ResultsNo difference was found between Group 1 and Group 2 in all postoperative parameters (p>.05). There were significant differences in final ODI (p<.001) and final LSDI (p<.001) among Group A, Group B, and Group C. Cubic curve model fitted the relationship between PI-LL and final ODI better than other models (R2=0.379, p<.001). Cubic curve model fitted the relationship between PI-LL and final LSDI better than other models (R2=0.691, p<.001). There was a significant difference in proximal junctional kyphosis (PJK) among groups (p=.038). No significant difference was found in other parameters. ConclusionsOptimal PI-LL value may be achieved between 10° and 20° in Chinese patients with ADS after long posterior instrumentation and fusion surgery with excellent clinical outcomes and a lower PJK occurrence.

Optimum pelvic incidence minus lumbar lordosis value can be determined by individual pelvic incidence.

Adult spinal deformity (ASD) classification showing that ideal pelvic incidence minus lumbar lordosis (PI-LL) value is within 10° has been received widely. But no study has focused on the optimum level of PI-LL value that reflects wide variety in PI among patients. This study was conducted to determine the optimum PI-LL value specific to an individual's PI in postoperative ASD patients. 48 postoperative ASD patients were recruited. Spino-pelvic parameters and Oswestry Disability Index (ODI) were measured at the final follow-up. Factors associated with good clinical results were determined by stepwise multiple regression model using the ODI. The patients with ODI under the 75th percentile cutoff were designated into the "good" health related quality of life (HRQOL) group. In this group, the relationship between the PI-LL and PI was assessed by regression analysis. Multiple regression analysis revealed PI-LL as significant parameters associated with ODI. Thirty-six patients with an ODI<22 points (75th percentile cutoff) were categorized into a good HRQOL group, and linear regression models demonstrated the following equation: PI-LL=0.41PI-11.12 (r=0.45, P=0.0059). On the basis of this equation, in the patients with a PI=50°, the PI-LL is 9°. Whereas in those with a PI=30°, the optimum PI-LL is calculated to be as low as 1°. In those with a PI=80°, PI-LL is estimated at 22°. Consequently, an optimum PI-LL is inconsistent in that it depends on the individual PI.

Enhanced microwave-to-terahertz absorption in graphene

Fresnel equations predict that an ultrathin free standing conductive film, thousands times thinner than skin depth, is capable to absorb up to 50% of incident electromagnetic radiations. In the microwave range, the same holds true for a free standing graphene sheet. We demonstrate theoretically and prove experimentally that microwave absorptance of graphene can be enhanced considerably by depositing graphene on a dielectric substrate. On the experimental side, we obtain 80% and 65% absorptance at 30 GHz and 1 THz, respectively. Theory predicts that higher absorptance can be achieved with a suitable choice of the dielectric permittivity and the thickness of the substrate. Absorption can also be maximized by choosing the optimum incidence angle for s-polarized waves in free space or by working in the vicinity of the cut-off frequency of the transverse electric mode in waveguide configuration. The polarization sensitivity of the transmittance and reflectance of graphene layers can be used to tune the polarization state of the transmitted and reflected radiations.

EXPERIMENTAL AND NUMERICAL INVESTIGATION ON FLOW ANGLE CHARACTERISTICS OF AN AUTOMOTIVE MIXED FLOW TURBOCHARGER TURBINE

To date, turbocharger remains as a key enabler towards highly efficient Internal Combustion Engine. Although the first turbocharger was patented more than 30 years ago, the design is still being improved, thus signifying its importance in modern vehicles. One of the key features that contribute to the challenges in designing highly efficient turbine is the complex nature of the flow field within the turbine stage itself. Experimental method could be used to extract parameters such as pressure and temperature traces but still unable to provide a full description of the flow field. Therefore, the use of Computational Fluid Dynamics (CFD) in resolving this issue is necessary. Out of many feature of fluid flow in turbomachinery, the flow angle at rotor inlet plays significant role in determining turbine efficiency. However, due to geometrical complexity, even at optimum averaged incidence flow angle, there still exist variations that could impair the turbine ability to produce work. This research attempts to provide insight on the complexity of flow angle distribution within the turbocharger turbine stage. To achieve this aim, a numerical model of a full stage turbocharger turbine operating at 30000rpm under its optimum condition was developed. Results indicated that even though use of guide vanes has reduced flow angle fluctuations at mid-span of the rotor inlet from ±10° to only ±1°, significant variations still exist for velocity components in spanwise direction. This in turns effected the distribution of incidence flow angle at the rotor leading edge. In the current research, variation of incidence flow angle in spanwise direction is recorded to be as high as 60°.

Framework for Fusion of Ascending and Descending Pass TanDEM-X Raw DEMs

A novel method for calculating optimum incidence angle for the TanDEM-X system using any available digital elevation model (DEM) for the given area is proposed in this study. This method includes the plotting of slopes and aspect of the test area in a statistical way and applying mathematical approach using acquisition geometry in ascending and descending pass TanDEM-X data to optimize the incidence angle for obtaining precise DEM. Furthermore, the TanDEM-X raw DEMs in ascending and descending pass over Mumbai, India are combined using a simple weighted fusion algorithm and the quality of fused DEM thus generated is enhanced. The method adopted for fusion is just an experimental study. The problem of optimum weight selection for fusion has been addressed using height error map and a robust layover shadow mask calculated in “Integrated TanDEM-X Processor” (ITP) during TanDEM-X DEM generation. The height error map is calculated from the interferometric coherence with geometrical considerations and the robust layover and shadow map is calculated using TanDEM-X DEM and the corresponding slant range. Results show a significant reduction in the number of invalid pixels after fusion. In the fused DEM, invalids are only 2.14%, while ascending and descending pass DEMs have 5.02% and 6.34%, respectively. Statistical analysis shows a slight improvement in standard deviation of the error in fused DEM by 8% in urban area and about 5% for the whole scene. Only slight improvement in accuracy of fused DEM can be attributed to the coarse resolution of the SRTM-X DEM used as reference.

Polarisation independent resistively loaded frequency selective surface absorber with optimum oblique incidence performance

This study presents the design of a thin electromagnetic absorber which exhibits radar backscatter suppression that is independent of the wave polarisation at large incidence angles. The structure consists of a metal backed printed frequency selective surface (FSS), with resistors placed across narrow gaps inserted in the middle of each of the four sides of the conductor loops. The geometry of the periodic array and the value of the vertical and horizontal resistor pairs are carefully chosen to present a real impedance of 377 Ω at the centre operating frequency for both TE and TM polarised waves. Angular sensitivity and reflectivity bandwidth have been investigated for FSS absorber designs with thicknesses of 1, 2 and 3 mm. Each of the three structures was optimised to work at a centre frequency of 10 GHz and an incident angle of 45°. The design methodology is verified by measuring the radar backscatter suppression from a 3 mm (λ / 10) thick screen in the frequency range 8–12 GHz. The absorber construction was simplified by filling the four metal gaps in each unit cell with shielding paint, and selecting the ink thickness to give the two required surface resistance values.

Comparative Research on Different Solutions of a High-Performance Thin-Film Polarizing Beam Splitter

In the process of fabricating an ultra-high precision thin-film polarizing beam splitter (PBS), which is the key element in a new kind of Y-shaped cavity dual-frequency laser, low production yield is a serious problem. Based on the robust design method by controlling sensitivity of optical films to production errors, response characteristics to production errors of different kinds of PBSs are comparatively studied. By experimental study of robust design, essential determinant of sensitivity of PBSs to production errors is found to be the physical requirement that the propagation angle should be larger than the critical angle of total reflection of the interface between the substrate and outer space. By fulfilling the physical requirement, optimum incidence angle has been found by repeated robust design on different incidence angles, and a high-performance thin-film PBS with low sensitivity to production errors has been designed. The coating structure of the obtained PBS is simple and it is easy to be batch manufactured, which will make a positive impact on fabrication, engineering and application of the new Y-shaped cavity dual-frequency laser.