Magnetic Pendulum Arrays for Efficient ULF Transmission.

The frequencies lying between 300 Hz to 3 kHz have been designated as Ultra Low Frequency (ULF) with corresponding wavelengths from 1000 Km to 100 Km. Although ULF has very low bandwidth it is very reliable, penetrating and difficult to jam which makes it a great choice for communication in underwater and underground environments. Small and portable ULF antennas within a diameter of 1 meter would operate under an electrical length on the order of 10-4 to 10-6 wavelengths in free space, making them very inefficient because of fundamental limits on radiation from electrically small antennas. To overcome this problem, Mechanical Antennas or 'Mechtennas' for Ultra Low Frequency Communications have been proposed recently. For efficient generation of ULF radiation, we propose a portable electromechanical system called a Magnetic Pendulum Array (MPA). A proof of concept demonstration of the system at 1.03 kHz is presented. The theory and experimental results demonstrate that such a system can achieve a significantly higher quality factor than conventional coils and thus order of magnitude higher transmission efficiency. The concept can be easily scaled to the ULF range of frequencies.

Plasmonic spiderweb nanoantenna surface for broadband hotspot generation.

In this study, we demonstrate a general framework for obtaining a plasmonic nanoantenna surface with a broadband polarization-independent response. The plasmonic spiderweb nanoantenna surface is composed of unit cells, which form multiple resonance paths due to patterning of the metallic conductor such that electrons can find multiple ways to oscillate between the poles of the conductor. The tailoring of the conductor paths and shapes of the unit cells' patterns results in a broadband spectral response. At various resonance frequencies, the electrons oscillate along different paths between the poles of the antenna, generating broadband hot spots around those poles.

Absorption efficiency enhancement in inorganic and organic thin film solar cells via plasmonic honeycomb nanoantenna arrays.

We demonstrate theoretically that by embedding plasmonic honeycomb nanoantenna arrays into the active layers of inorganic (c-Si) and organic (P3HT:PCBM/PEDOT:PSS) thin film solar cells, absorption efficiency can be improved. To obtain the solar cell absorption spectrum that conforms to the solar radiation, spectral broadening is achieved by breaking the symmetry within the Wigner-Seitz unit cell on a uniform hexagonal grid. For optimized honeycomb designs, absorption efficiency enhancements of 106.2% and 20.8% are achieved for c-Si and P3HT:PCBM/PEDOT:PSS thin film solar cells, respectively. We have demonstrated that the transverse modes are responsible for the enhancement in c-Si solar cells, whereas both the longitudinal and transverse modes, albeit weaker, are the main enhancement mechanisms for P3HT:PCBM/PEDOT:PSS solar cells. For both inorganic and organic solar cells, the absorption enhancement is independent of polarization.

Unidirectional broadband radiation of honeycomb plasmonic antenna array with broken symmetry.

Emerging plasmonic and photovoltaic applications benefit from effective interaction between optical antennas and unidirectional incident light over a wide spectrum. Here, we propose a honeycomb array of plasmonic nanoantennas with broken symmetry to obtain a unidirectional radiation pattern over a wide spectrum. The honeycomb nanoantenna array is based on a hexagonal grid with periodically arranged nanostructure building blocks. To analyze the far-field optical distribution and spectral behavior of the plasmonic antenna honeycomb, a two-dimensional Wigner-Seitz unit cell is used together with periodic boundary conditions. As a result of the vectoral superposition of the fields produced by the Wigner-Seitz unit cells, far-zone optical fields interfere constructively or destructively in different directions. The constructive interference along the array's normal direction engenders unidirectional radiation. Due to the broken symmetry of the Wigner-Seitz cell, multiple resonances are supported by the plasmonic antenna honeycomb array over a broad spectrum.

Broadband plasmonic nanoantenna with an adjustable spectral response.

Six-particle and eight-particle common-gap plasmonic nanoantennas are utilized to obtain a broadband spectral response when illuminated with circular and elliptical polarization. Due to the insensitivity of dipole antennas to circular polarization, the resonant structures are brought together around the common-gap to expand the spectrum of the whole system. Their ability to focus light at different frequencies is demonstrated. The spectral response is manipulated by geometrical parameters and the strength of the spectral peaks is tailored through the ellipticity of the elliptically polarized light.