Birds-of-paradise are nature's prime examples of the evolution of color by sexual selection. Their brilliant, structurally colored feathers play a principal role in mating displays. The structural ...coloration of both the occipital and breast feathers of the bird-of-paradise Lawes' parotia is produced by melanin rodlets arranged in layers, together acting as interference reflectors. Light reflection by the silvery colored occipital feathers is unidirectional as in a classical multilayer, but the reflection by the richly colored breast feathers is three-directional and extraordinarily complex. Here we show that the reflection properties of both feather types can be quantitatively explained by finite-difference time-domain modeling using realistic feather anatomies and experimentally determined refractive index dispersion values of keratin and melanin. The results elucidate the interplay between avian coloration and vision and indicate tuning of the mating displays to the spectral properties of the avian visual system.
We demonstrate a new class of bandpass frequency selective surface (FSS), the building block of which, unlike the traditional FSSs, makes use of resonant dipole and slot structures that have ...dimensions much smaller than the operating wavelength. This design allows localization of bandpass characteristics to within a small area on the surface which in turn facilitates flexible spatial filtering for an arbitrary wave phasefront. The proposed FSS is made up of periodic array of metallic patches separated by thin air-gaps backed by a wire mesh having the same periodicity (Ltlambda). The array of metallic patches constitute a capacitive surface and the wire mesh a coupled inductive surface, which together act as a resonant structure in the path of an incident plane wave. Like traditional FSSs, the capacitive and inductive surfaces of the proposed FSS can easily be fabricated using printed circuit technology on both sides of microwave substrates. It is shown that by cascading such bandpass surfaces in a proper fashion, any arbitrary multipole filter or non-commensurate multiband response can be obtained. The frequency response of the proposed miniaturized-element frequency selective surface (MEFSS) is demonstrated for various incident angles and it is shown that one-pole designs are less sensitive than two-pole designs to the angle of incidence. Dual band designs are also possible based on two-pole designs, but are more sensitive to incident angle than single band designs because of their larger (in terms of wavelengths) spacing. Prototypes of single-pole and dual-pole MEFSSs are fabricated and tested in a waveguide environment at X-band frequencies and excellent agreements between the measured and simulated results are demonstrated
Modification of nanoscale surface topography is inherent to low-energy ion beam erosion processes and is one of the most important fields of nanotechnology. In this report a comprehensive study of ...surface smoothing and self-organized pattern formation on Ge(100) by using different noble gases ion beam erosion is presented. The investigations focus on low ion energies ( 2000 eV) and include the entire range of ion incidence angles. It is found that for ions (Ne, Ar) with masses lower than the mass of the Ge target atoms, no pattern formation occurs and surface smoothing is observed for all angles of ion incidence. In contrast, for erosion with higher mass ions (Kr, Xe), ripple formation starts at incidence angles of about 65° depending on ion energy. At smaller incident angles surface smoothing occurs again. Investigations of the surface dynamics for specific ion incidence angles by changing the ion fluence over two orders of magnitude gives a clear evidence for coarsening and faceting of the surface pattern. Both observations indicate that gradient-dependent sputtering and reflection of primary ions play crucial role in the pattern evolution, just at the lowest accessible fluences. The results are discussed in relation to recently proposed redistributive or stress-induced models for pattern formation. In addition, it is argued that a large angular variation of the sputter yield and reflected primary ions can significantly contribute to pattern formation and evolution as nonlinear and non-local processes as supported by simulation of sputtering and ion reflection.
This paper presents the latest characterization results of a novel Low Cross-Talk (LCT) large-area (6×6-mm2) Multi-Pixel Photon Counter (MPPC) detector manufactured by Hamamatsu, belonging to the ...recent LCT5 family and achieving a fill-factor enhancement and cross-talk reduction. In addition, the newly adopted resin coating is demonstrated to yield improved photon detection capabilities in the 290–350nm spectral range, making the new LCT MPPC particularly suitable for emerging applications like Cherenkov Telescopes. For a 3×3-mm2 version of the new MPPC under test, a comparative analysis of the large pixel pitch (75-µm) detector versus the smaller pixel pitch (50-µm) detector is also undertaken. Furthermore, measurements of the 6×6-mm2 MPPC response versus the angle of incidence are provided for the characterized device.
A broadband polarisation-independent circuit analogue absorber comprising multi-layer resistive frequency selective surfaces (FSS) has been presented in this study. The proposed structure consists of ...a periodic arrangement of square loops loaded with lumped resistors and these square loops are printed on dielectric substrates separated by an air spacer. The simulated result shows the reflectivity below −10 dB in the frequency range from 4.96 to 18.22 GHz (fractional bandwidth of 114.40%) under normal incidence, covering C, X, and Ku bands. An equivalent circuit analysis has been introduced to characterise the proposed absorber, which shows good matching with the full-wave analysis. The effects of the individual FSS layers and the air spacer have been studied and several parametric variations have been carried out to examine the sensitivity of the design parameters on the absorption bandwidth. Finally, the designed absorber has been fabricated and measured in anechoic chamber, which shows good agreement between the experimental results and the simulated responses, under different angles of incidence as well as for various polarisation angles.
A reconfigurable reflectarray which exploits the dielectric anisotropy of liquid crystals (LC) has been designed to operate in the frequency range from 96 to 104 GHz. The unit cells are composed of ...three unequal length parallel dipoles placed above an LC substrate. The reflectarray has been designed using an accurate model which includes the effects of anisotropy and inhomogeneity. An effective permittivity that accounts for the `real effects' of the LC has also been used to simplify the analysis and design of the unit cells. The geometrical parameters of the cells have been adjusted to simultaneously improve the bandwidth, maximize the tunable phase-range and reduce the sensitivity to the angle of incidence. The performance of the LC based unit cells has been experimentally evaluated by measuring the reflection amplitude and phase of a reflectarray consisting of 52 × 54 identical cells. The good agreement between measurements and simulations validates the analysis and design techniques and demonstrates the capabilities of the proposed reflectarray to provide beam scanning in F band.
•Effects of incident radiation, spectrum, angle included using concept of wavelength.•PV module temperature in window remains more in winter than summer season.•Difference in simulated and measured ...room temperature found negligible (0.67 °C).•Incident spectrum shows positive impact in conversion efficiency in some season.•For same incident radiation actual output is lower than at STC due to efficiency.
Standard test condition (STC) is widely used to measure the efficiency of solar photovoltaic modules. But, the specified values of different factors of this standard are rarely found in the actual field. Some of the crucial factors of the said standard are module temperature, angle of incidence (AOI), amount of incident solar radiation, and type of spectrum. This research paper presents the energy generation of a photovoltaic module integrated double pane window system under the effect of the above factors. The type of the considered photovoltaic module is thin-film semi-transparent made of Cadmium Telluride (CdTe). For the calculation, the material characteristics were initially processed using different software. The validity of the simulated values was checked with experimental findings. In the study, except the incident spectrum, all other factors found to affect the output negatively. For example, because of higher operating cell temperature, the decreases in energy generation ranges between 2.9% and 6.3% among the months in the year. Further, with the influence of the investigated factors, the considered STPV system is found to generate maximum energy of 95.3 kWh/m2 per annum. This energy generation is 10.5% less than the energy calculated using the conversion efficiency found at STC. One of the outcomes of this analysis is the incorporation of the combined effects of four critical factors in the energy generation of photovoltaic systems. The results and the method of this work provide a useful reference to the scientific community for the development of an improved testing procedure of solar photovoltaic modules.
Velocity distribution in the stern region over a generic submarine hull form (SUBOFF) at high angles of incidence was investigated through steady velocity measurements in the Wind Tunnel Facility at ...Naval Science & Technological Laboratory, India. Velocity measurements were performed for a range of angles of incidence in angle of attack (+8° to - 40°) and drift (0°–28°) on 1.372 m model at Reynolds number 1.7 × 106. The present study for high angles of incidence is to depict a submarine motion during extreme manoeuvers in case of emergency situations. The particulars of the SUBOFF model, experimental facility and measurement technique, test results for axial, tangential and radial velocity measurements, non-uniformity and circumferential mean velocity, derived quantities for vorticity and circulation are highlighted in the paper. The velocity measurements data generated from the above studies will greatly complement the current research on turbulent flows over submerged bodies both computationally and experimentally.
•Steady velocity measurements in the stern region over a generic submarine hull form at high angles of incidence for a range of angle of attack (+8° to - 40°) and drift (0 to 28°).•Experimental test results for axial, tangential and radial velocity measurements, non-uniformity and circumferential mean velocity, derived quantities for vorticity and circulation.•Validation of experimental test data and derived parameters with published information and theoretical formulations respectively.•Evaluation of typical range of values for velocity components, circumferential mean velocity, vorticity and circulation with respect to angle of incidence.•Flow physics observations with respect to complex vortical structures during high angles of incidence.
Preliminary lens-walled CPC (compound parabolic concentrator) was proposed owing to its larger half acceptance angle, but in fact, it has another advantage of more uniform flux distribution than ...mirror CPC with the same geometrical concentration ratio. In this paper, in order to firstly evaluate the flux distribution of lens-walled CPC comprehensively, a lens-walled CPC PV (compound parabolic concentrator photovoltaic) was fabricated and tested at the different incidence angles comparison with mirror CPC PV. The experimental results showed that the FF (fill-factor) of the mirror CPC PV dropped more sharply than that of the lens-walled CPC PV, which indicated that the lens-walled CPC has a more uniform flux distribution on PV (photovoltaic). In addition, a software simulation of the flux distribution between mirror CPC and lens-walled CPC was carried out. The simulation illustrated clearly this advantage of the lens-walled CPC, which directly demonstrated the experimental inference and would be significant for lens-walled CPC application.
•Lens-walled CPC PV module was fabricated and tested compared with the mirror CPC PV.•The flux distribution of the lens-walled CPC was analyzed through the experiment results.•Software simulation was carried out to verify the flux distribution.•Formulation of the structure of the lens-walled CPC was described.
Tunable metasurfaces provide enormous degrees-of-freedom for dynamic control of light-matter interactions at sub-wavelength scales. However, the realization of polarization- and angle-insensitive ...active nanophotonic devices with low energy-consumption and high modulation depth remains a challenge. This letter reports gap plasmon resonance based electro-tunable metasurface for optical intensity modulation. The proposed metasurface features a 2D array of Au-nanograting on top of indium-tin-oxide (ITO)-Al 2 O 3 -Au stack. The external electrical biasing accumulates the free-carriers of ITO at ITO-Al 2 O 3 interface, which results in an electro-tunable resonance response in the reflectance spectrum. With a 2V electrical biasing, we observe the resonance dip shifts to the vicinity of 1.55 μm wavelength. Thus, a modulation depth of ~25 dB at 1.55 μm can be achieved for random polarization-angle of incident light. For the first time, the proposed modulator can operate over a wide range of incidence angle (up to 50 degrees) for both x- and y-polarized light. With ~303 fJ/bit energy-consumption and ~900 Mbps modulation speed, the proposed electro-tunable metasurface could help to realize polarization- and angle-independent active flat optics for nanophotonic systems.
PDF
