Vincenzo Fiumara

AN EXACT SYNTHESIS METHOD FOR DUAL-BAND CHEBYSHEV IMPEDANCE TRANSFORMERS

We propose an exact synthesis method which allows the design of dual-band transformers with an arbitrary even number of uniform sections giving equi-ripple impedance matching in two separate bands centered at two arbitrary frequencies. This method is a generalization of the exact Collin-Riblet synthesis of Chebyshev single-band transformers. As compared to a single-band Collin-Riblet transformer encompassing both required passbands, the proposed design yields significantly better performance in terms of passband tolerance and width.

Simulation and analysis of prismatic bioinspired compound lenses for solar cells

Inspired by the apposition compound eyes of many dipterans, we formulated a fractal scheme to design prismatic lenses to improve the performance of silicon solar cells. We simulated the absorption of light, both directly illuminating and diffuse, using the geometrical-optics approximation. We found that properly designed bioinspired compound lenses (BCLs) can significantly improve the light-harvesting capabilities of silicon solar cells. The degree of improvement will depend on the material chosen to make the BCLs as well as the operating conditions.

Simulation and analysis of prismatic bioinspired compound lenses for solar cells: II. Multifrequency analysis

Multifrequency numerical simulations of the light-coupling efficiency of a prismatic bioinspired compound lens (BCL) of silicon atop a thick silicon substrate were carried out within the framework of geometrical optics. Comparison was made with untextured and groove-textured silicon substrates as well as with untextured silicon substrates with a double-layer anti-reflection (DLAR) coating. Taking into account the broadband nature and the sea-level spectral irradiance of the insolation flux, and averaging over all admissible directions and both linear polarization states of the incident light, we found that the light-coupling efficiency can be almost doubled with respect to the untextured silicon substrate and enhanced by about a third with respect to a DLAR-coated untextured silicon substrate, by adopting a DLAR-coated silicon BCL.

Free-space antenna field/pattern retrieval in reverberation environments

Simple algorithms for retrieving free-space antenna field or directivity patterns from complex (field) or real (intensity) measurements taken in ideal reverberation environments are introduced and discussed.

Composite surface-plasmon-polariton waves guided by a thin metal layer sandwiched between a homogeneous isotropic dielectric material and a periodically multilayered isotropic dielectric material

Abstract. Multiple p- and s-polarized compound surface-plasmon-polariton (SPP) waves at a fixed frequency can be guided by a structure consisting of a metal layer sandwiched between a homogeneous isotropic dielectric (HID) material and a periodic multilayered isotropic dielectric (PMLID) material. For any thickness of the metal layer, at least one compound SPP wave must exist. It possesses the p-polarization state, and is strongly bound to the metal/HID interface when the metal thickness is large but to both metal/dielectric interfaces when the metal thickness is small. When the metal layer vanishes, this compound SPP wave transmutes into a Tamm wave. Additional compound SPP waves exist, depending on the thickness of the metal layer, the relative permittivity of the HID material, and the period and composition of the PMLID material. Some of these are p-polarized, the others are s-polarized. All of them differ in phase speed, attenuation rate, and field profile, even though all are excitable at the same frequency. The multiplicity and dependence of the number of compound SPP waves on the relative permittivity of the HID material when the metal layer is thin could be useful for optical sensing applications and intrachip plasmonic optical communication.

Field localization inside a lossy dielectric slab by means of cantor dielectric multilayers

A Cantor multilayer is an electromagnetic band-gap structure consisting of a stack of alternating high-/low-permittivity dielectric layers whose optical lengths follow the fractal Cantor construction. The deepest stop band is bounded by two narrow transmission peaks centered at frequencies where a strong field localization occurs inside the structure. This phenomenon also occurs if a lossy dielectric slab is inserted at the midpoint of the multilayer as a defect layer and can be conveniently used to make the field intensity inside the slab significantly stronger than the intensity of the field incident on the Cantor structure.

Cantor Dielectric Filters in Rectangular Waveguides

Abstract A triadic Cantor fractal multi-layer is a stack of two different dielectric materials whose thicknesses are determined according to the triadic Cantor fractal scheme. When inserted in a rectangular waveguide, the spectral response of a triadic Cantor multi-layer can be tailored to feature a narrow single transmission peak in the waveguide single-mode frequency range, with a low insertion loss and a high rejection level of forbidden frequencies. The experimental characterization of alumina-polystyrene and plexiglass-polystyrene Cantor multi-layers inserted in a WR90 waveguide (Hewlett-Packard, USA) matches thoroughly with the results of the theoretical modeling and demonstrates that triadic Cantor multi-layers can be used to realize feasible narrow-band microwave filters.

Compound guided waves that mix characteristics of surface-plasmon-polariton, Tamm, Dyakonov–Tamm, and Uller–Zenneck waves

Solutions of the boundary-value problem for electromagnetic waves guided by a layer of a homogeneous and isotropic (metal or dielectric) material sandwiched between a structurally chiral material (SCM) and a periodically multilayered isotropic dielectric (PMLID) material were numerically obtained and analyzed. If the sandwiched layer is sufficiently thick, the two bimaterial interfaces decouple from each other, and each interface may guide one or more electromagnetic surface waves (ESWs) by itself. Depending on the constitution of the two materials that partner to form an interface, the ESWs can be classified as surface-plasmon-polariton waves, Tamm waves, Dyakonov–Tamm waves, or Uller–Zenneck waves. When the sandwiched layer is sufficiently thin, the ESWs for single bimaterial interfaces coalesce to form compound guided waves (CGWs). The phase speeds, propagation distances, and spatial profiles of the electromagnetic fields of CGWs are different from those of the ESWs. The energy of a CGW is distributed in both the SCM and the PMLID material, if the sandwiched layer is sufficiently thin. Some CGWs require the sandwiched layer to have a minimum thickness. Indeed, the coupling between the two faces of the sandwiched layer is affected by the ratio of the thickness of the sandwiched layer to the skin depth in that material and the rates at which the fields of the ESWs guided individually by the two interfaces decay away from their respective guiding interfaces.

Analysis of prismatic bioinspired texturing of the surface of a silicon solar cell for enhanced light-coupling efficiency

Abstract. Investigating the use of prismatic lenses with cross-sectional shapes inspired by the apposition compound eyes of some dipterans, we found through numerical simulations that the exposed surfaces of silicon solar cells should be textured as arrays of bioinspired compound lenses in order to improve performance. We +used a ray-tracing algorithm to evaluate the light-coupling efficiency over a large and relevant portion of the solar spectrum and determined the array configuration that maximizes the coupling of light. Our simulation results show that the light-coupling efficiency can be significantly enhanced with respect to that of a silicon cell with a flat surface.

Insect Eyes Inspire Improved Solar Cells

Taking a cue from nature, these researchers looked to the compound eyes of insects as a model for developing their unique approach to harvesting sunlight.