Hadi Razavipour

Bio: Hadi Razavipour is an academic researcher from École Polytechnique de Montréal. The author has contributed to research in topics: Isolator & Magnet. The author has an hindex of 2, co-authored 2 publications receiving 14 citations.

Field displacement in a traveling-wave ring resonator meta-structure

Abstract: Field displacement is demonstrated for the first-time in a non-molecular-scale structure, namely a meta-structure composed of rings equipped with an isolator. The structure is explained in terms of rotating magnetic dipole moments and demonstrated to produce typical gyrotropic field displacement.

Ferromagnetic nanowire (FMNW) self-biased H-plane resonance isolator

Abstract: A novel resonant type H-plane isolator based on a ferromagnetic nanowire (FMNW) slab is presented. As a result of the remanence property of FMNW materials, the device is self-biased and therefore does not require any magnet. Moreover, the structure does not suffer from the conventional H-plane isolator drawback of demagnetization, which renders this configuration, characterized by superior heat dissipation capability, a competitive alternative to the E-plane resonance isolator. The inherent remanence of the FMNW material makes the shorter double and quadruple slab configurations more practical than their conventional ferrite counterparts. The proposed device is very compact, lightweight, and low-cost. Simulations based on two different methods, the finite integration technique (FIT) and the finite element method (FEM), predict an isolation of over 20 dB and insertion loss of less than 1 dB for a relatively high band width of 6 GHz at the center frequency of 20 GHz.

Magnetless Nonreciprocal Metamaterial (MNM) Technology: Application to Microwave Components

Abstract: A magnetless nonreciprocal metamaterial (MNM), consisting of traveling-wave resonant ring particles loaded by transistor and exhibiting the gyromagnetic properties as ferrites, without their size, weight, cost, and monolithic microwave integrated circuit incompatibility drawbacks, was recently introduced in 2011 by Kodera et al. This paper presents the first extensive investigation of the applicability of MNM technology to nonreciprocal microwave components. It recalls the key principle of the MNM, provides basic MNM design guidelines, explains coupling mechanism between a microstrip line and MNM rings, and demonstrates two nonreciprocal MNM components based on a microstrip-ring configuration, an isolator, and a circulator. Although these components have not been fully optimized, they already exhibit attractive performance and provide a proof-of-concept that MNM technology has a potential for microwave nonreciprocal microwave components with substantial benefits compared to their ferrite and active-circuit counterparts.

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.

Electromagnetic Modeling of a Magnetless Nonreciprocal Gyrotropic Metasurface

Abstract: An analytical model of a recently invented magnetless nonreciprocal and gyrotropic traveling-wave ring metamaterial is developed. The metamaterial is, in fact, a metasurface, which consists of a 2D periodic array of pairs of broadside-parallel micro-rings loaded with a semiconductor-based unidirectional component. It emulates the operation of ferrites by inducing a rotating magnetic moment in the ring pairs. However, instead of requiring a magnetostatic bias, it operates with an electrostatic voltage bias, thus avoiding the classical issues related to permanent magnets in ferrites. The metamaterial has two modes of operation: a desired magnetic mode and a parasitic electric mode, which are related to the excitation of equal and opposite currents in the two rings of the pairs, respectively. The metamaterial exhibits these magnetic and electric responses when excited by a uniform magnetic and electric field, respectively. The magnetic response is analyzed through a transmission line model with a distributed voltage source that incorporates the voltage impressed in the rings by the external field. The magnetic moment and the subsequent magnetic polarizability are related to a traveling-wave resonance along the ring pair. For a perfectly matched unidirectional component, this resonance, and hence the magnetic polarizability, are lossless. However, in the presence of mismatch, the metamaterial becomes lossy, due to reflection and absorption of power at the ports of the component. Comparisons with full-wave simulations show the validity of the proposed model.

Nonreciprocal Magnetless CRLH Leaky-Wave Antenna Based on a Ring Metamaterial Structure

Abstract: A nonreciprocal ferrite-loaded open rectangular composite right/left-handed (CRLH) waveguide structure was introduced by the authors in 2009, and later shown to operate as a novel and useful antenna system. However, this structure suffers from the classical drawbacks of ferrites (bulkiness, heaviness, high cost, nonintegrability, and limitation below the X-band). In order to remedy these issues, this letter replaces the ferrite in that structure with a recently introduced magnetless nonreciprocal ring metamaterial exhibiting essentially the same properties as a ferrite and demonstrates, theoretically and experimentally, its equivalent leaky-wave antenna operation.

Unidirectional amplification and shaping of optical pulses by three-wave mixing with negative phonons

Abstract: A possibility to greatly enhance frequency-conversion efficiency of stimulated Raman scattering is shown by making use of extraordinary properties of three-wave mixing of ordinary and backward waves Such processes are commonly attributed to negative-index plasmonic metamaterials This work demonstrates the possibility to replace such metamaterials that are very challenging to engineer by readily available crystals which support elastic waves with contra-directed phase and group velocities The main goal of this work was to investigate specific properties of indicated nonlinear optical process in short-pulse regime and to show that it enables elimination of fundamental detrimental effect of fast damping of optical phonons on the process concerned Among the applications is the possibility of creation of a family of unique photonic devices such as unidirectional Raman amplifiers and femtosecond pulse shapers with greatly improved operational properties