Abstract-A fully printable and conformal antenna array on a flexible substrate with a new LeftHanded Transmission Line (LHTL) phase shifter based on a tunable Barium Strontium Titanate (BST)/polymer composite is proposed and computationally studied for radiation pattern correction and beam steering applications. First, the subject 1 × 4 rectangular patch antenna array is configured as a curved conformal antenna, with both convex and concave bending profiles, and the effects of bending on the performance are analyzed. The maximum gain of the simulated array is reduced from the flat case level by 34.4% and 34.5% for convex and concave bending, respectively. A phase compensation technique utilizing the LHTL phase shifters with a coplanar design is used to improve the degraded radiation patterns of the conformal antennas. Simulations indicate that the gain of the bent antenna array can be improved by 63.8% and 68% for convex and concave bending, respectively. For the beam steering application, the proposed phase shifters with a microstrip design are used to steer the radiation beam of the antenna array, in planar configuration, to both negative and positive scan angles, thus realizing a phased array antenna.

Plasmonic devices, consisting of nanoparticle monolayers, are conveniently fabricated by deposition techniques, wherein thermodynamics often favor the particle shape to be close to hemispherical. The present work investigates plasmon modes in Ag nanohemispheres (NHSs) using s-and p-polarized incident radiation at varying angles. The Ag NHSs, immobilized on nanoposts, resembling mushroom structures, allow for reduced substrate coupling and convenient resolution of the modes. Additionally, the modes are studied by in situ extinction acquisitions during nanoparticle synthesis and elucidated by numerical simulations. It is revealed that the broken symmetry by asymmetric particle shape leads to dipolar modes parallel and normal to the base, which are significantly different in terms of energy, excitation dependence on polarization, and particle−particle as well as particle−substrate couplings. In particular, the major parallel mode offers distinct advantages in plasmonics applications over nanospheres. For example, its strong substrate coupling may benefit thin film photovoltaics by efficient light coupling. Higher field concentrations are induced at the sharp edges of a NHS that may enhance hot electron injection in a photocatalyst. Unlike in a spherical dimer, where the field intensity peaks in the middle of the gap, the maximum field in a NHS dimer gap occurs on the metal surface (i.e., at the edges), overlaying with the chemical enhancement. Hence, a higher surface enhancement factor can be achieved in Raman scattering.

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In many non-destructive testing and medical diagnostic applications, photoacoustic generation by optical fiber is an effective approach to meet the requirements of broad bandwidth and compact size. The energy absorption layer coated onto the fiber endface plays an important role in the conversion of laser energy into heat used to excite acoustic waves. Gold nanostructures are promising solutions to be utilized as energy absorption layers due to their capability of absorbing maximum optical energy at plasmon resonant frequencies.The appropriate selection of the organization and dimensions of the gold nanostructures is the key to achieving high absorption efficiency. Numerical modeling is an efficient way to predict the behavior of the system as a variation of select parameters. A 3D finite integral technique model was established to simulate the dependency of absorption efficiency on the organization and dimensions of the gold nanospheres and nanorods. The simulation results provided practical clues to the design and fabrication of fiber-optic photoacoustic generators.

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An ultra-thin single band metamaterial (MTM) based perfect absorber with suppressed higher order absorption modes is presented in this paper. The unit cell structure is comprised of square shaped resonant patch whose sides are attached to interdigitally coupled fingers providing strong cell to cell electromagnetic coupling, which is found to have a significant impact in reducing the effect of higher order absorption modes. The structure is designed to operate in terahertz (THz) regime with a perfect absorption band centered at 1.61 THz. The absorption behavior is computationally studied and thoroughly analyzed using full wave simulations as well as circuit model approximation. The proposed structure exhibited remarkable characteristics such as polarization insensitivity, high absorption level over wide range of incident angles for both TE and TM polarizations and very weak excited higher order bands for TM polarized wave. In addition to that, it is capable to detect thin layers analyte overlays with sensitivity of 550 GHz/RIU. The absorber is very compact, where the overall thickness is about 1.67% of the wavelength at resonance. Furthermore, it could be viewed as continuous medium since the achieved cell size is around 0.1 times the operating wavelength. The absorber has the potential to be utilized in removing the unwanted peaks in thermal emission and detection as well as in rejecting unwanted modes in resonant structures such as accelerating cavities. It also might be applied to other classes of resonant structures.

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