Ferromagnetic Nanowire Metamaterials: Theory and Applications
ABSTRACT An overview of ferromagnetic nanowire (FMNW) metamaterials is presented. First, FMNW metamaterials are placed in the historical context of antique composites and 20th Century artificial dielectrics, and presented as an example of second-generation metamaterials following the microstructured metamaterials developed in the first part of the decade. Next, the fabrication processes of FMNW metamaterials and subsequent planar devices are detailed. It is then shown how the geometrical properties of the FMNW structure, such as the wire diameter and the wire nanodisk thicknesses, determine the dc and RF responses of the material. Upon this basis, the modeling of the metamaterial is presented, using a two-level approach where the microscopic (with respect to the wires) susceptibility is derived by solving the Landau-Lifshitz equation and the macroscopic (metamaterial) permittivity and permeability tensors are obtained by effective medium theory. Next, a review of FMNW microwave devices, such as circulators, isolators, and phase shifters, is provided, and the example of an FMNW dual-band edge-mode isolator is studied. Finally, spintronic effects and applications of FMNW metamaterials, such as dc to RF generators and detectors based on the spin-torque transfer phenomenon, are reviewed.
- SourceAvailable from: Tarun Kumar[Show abstract] [Hide abstract]
ABSTRACT: This paper investigates the generalized case of scattering from a planar grid, containing infinite numbers of axially magnetized ferromagnetic microwires placed parallel to each other in free space. A semi-analytical solution is obtained by calculating the local field at the surface of the reference microwire which is the sum of the scattered field from the other microwires as well as the incident field. Graf's theorem is used to transform the scattered field from one coordinate system to the other. Scattering field coefficients for the reference microwire are obtained by matching the tangential field components at the surface of the reference microwire. Simulated results are expressed in terms of the Reflection, Transmission and Absorption Coefficients for the T M z and T E z polarizations. For validation, results of the proposed analysis specialized to the case of normal incidence with T M z polarization are compared with the results available in the literature.Progress In Electromagnetics Research M 03/2014; 35(2014):1-10.
Article: Analog Signal Processing[Show abstract] [Hide abstract]
ABSTRACT: Analog signal processing (ASP) is presented as a systematic approach to address future challenges in high speed and high frequency microwave applications. The general concept of ASP is explained with the help of examples emphasizing basic ASP effects, such as time spreading and compression, chirping and frequency discrimination. Phasers, which represent the core of ASP systems, are explained to be elements exhibiting a frequency-dependent group delay response, and hence a nonlinear phase response versus frequency, and various phaser technologies are discussed and compared. Real-time Fourier transformation (RTFT) is derived as one of the most fundamental ASP operations. Upon this basis, the specifications of a phaser resolution, absolute bandwidth and magnitude balance are established, and techniques are proposed to enhance phasers for higher ASP performance. Novel closed-form synthesis techniques, applicable to all-pass transmission-type cascaded Csection phasers, all-pass reflection-type coupled resonator phasers and band-pass cross-coupled resonator phasers are described. Several applications using these phasers are presented, including a tunable pulse delay system, a spectrum sniffer and a realtime spectrum analyzer (RTSA). Finally, future challenges and opportunities are discussed.07/2013;
- [Show abstract] [Hide abstract]
ABSTRACT: Creation and control of spatial gradients in electromagnetic properties is a central theme underlying optical device design. In this work, we demonstrate that through modification of the spatial and temporal distribution of current, we can obtain increased control over the shape of these gradients. We are able to write spatially sharp gradients with ∼50% change in the index of refraction over length scales of only a few wavelengths as observed through diffraction limited terahertz spectroscopy. Furthermore, we assess the potentials for such gradients for beam-steering applications.Applied Physics Letters 06/2013; 102(22). · 3.79 Impact Factor