Toshiro Kodera

Artificial Faraday rotation using a ring metamaterial structure without static magnetic field

A metamaterial structure composed of a periodic array of conductive rings including each a semiconductor-based isolator is experimentally shown to produce Faraday rotation. Due to the presence of the isolators, a unidirectional traveling-wave regime is established along the rings, generating rotating magnetic moments and hence emulating the phenomenon of electron spin precession. The metamaterial exhibits the same response as a magnetically biased ferrite or plasma, but without the need of any static magnetic field bias, and therefore, it is easily integrated in printed circuit technology.

Uniform Ferrite-Loaded Open Waveguide Structure With CRLH Response and Its Application to a Novel Backfire-to-Endfire Leaky-Wave Antenna

A uniform ferrite-loaded open waveguide structure with composite right/left-handed (CRLH) response and its application to a novel backfire-to-endfire leaky-wave antenna are presented. The structure consists of a ferrite-filled rectangular waveguide open to free space at one of its small sides and biased perpendicularly to its large sides. Based on the fact that the leakage from the open side represents only a small perturbation in terms of guidance, an analytical dispersion relation for the approximately equivalent perfect magnetic conductor closed waveguide structure is derived. The unique dispersive properties of this structure, including its inherent CRLH balanced response (gapless nonzero group velocity transition between the left- and right-handed bands) and low-loss characteristics due to off-resonance operation, are extensively described, parametrically studied, and concretized by design guidelines. This theory is validated by both finite-element method and finite integration technique full-wave results and demonstrated experimentally. The leakage of the structure is exploited to build a full-space backfire-to-endfire scanning leaky-wave antenna, which is capable of both fixed-bias frequency scanning and fixed-frequency bias scanning, while being a perfectly uniform structure not requiring any chip tuning components. This feature, and its subsequent design simplicity, represents a fundamental advantage over previous CRLH metmaterial implementations. To the best of our knowledge, the proposed ferrite waveguide is the first and unique uniform structure exhibiting a CRLH response.

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

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.

Double ferromagnetic resonance in nanowire arrays

Microstrip line measurements are used to determine the frequency dependent microwave response of 40 nm diameter CoFeB ferromagnetic nanowire arrays, with external static applied field parallel to the nanowire axis. The ferromagnetic resonance (FMR) response of the wires is obtained for applied fields below and above magnetization saturation. For applied magnetic fields above saturation, a single FMR peak is observed, while below saturation, two sets of peaks are obtained. The two FMR peaks below saturation are associated with two magnetization populations, one for nanowires with upward magnetization and one with downward magnetization. A model based on a Maxwell–Garnett homogenization procedure has been established and used to predict the frequency response of the FMR peaks. There is good agreement between the model and experimental results.

Electromagnetic Modeling of a Magnetless Nonreciprocal Gyrotropic Metasurface

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.

Integrated Leaky-Wave Antenna–Duplexer/Diplexer Using CRLH Uniform Ferrite-Loaded Open Waveguide

A novel integrated leaky-wave antenna-duplexer/diplexer, based on the CRLH uniform ferrite-loaded open radiating waveguide is introduced, demonstrated and characterized both numerically and experimentally. The duplexing operation, characterized by equal Tx and Rx frequencies, is performed directly within the antenna thanks to the non-reciprocity of the ferrite, thereby suppressing the need for a circulator external to the antenna. The diplexing function, where the Tx and Rx frequencies are different, is achieved by inclining the plane of the antenna structure with respect to the normal of the radiation direction. The duplexer may be seen as the particular case of the diplexer with an inclination angle of zero. Virtually unlimited Tx → Rx isolation is provided by the leaky-wave nature of the device, which avoids typical problems of demodulation and detection/ranging errors and possible destruction of the receiver. Another advantage of this duplexer/diplexer is the possibility to tune the operation frequency by the applied magnetic bias field, whereas such tuning is prevented both by the antenna and by the circulator in conventional designs. The fabricated prototype exhibits a gain of 2.3 dBi with isolation of more than 15 dB at all ports. The diplexing frequency range reaches 400 MHz.

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

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.

Ferrite Based Non-Reciprocal Radome, Generalized Scattering Matrix Analysis and Experimental Demonstration

A non-reciprocal antenna radome based on the Faraday rotation effect in a ferrite slab is proposed and analyzed. This radome allows transmission in one direction and attenuates the signal in the opposite direction. It includes two layers of strip gratings on each side of the ferrite slab, consisting of highly conductive strips for proper reflection, and thin highly lossy strips for reflection/dissipation, and three dielectric layers for matching. The radome is analyzed rigorously by the generalized scattering matrix (GSM) method and its performance experimentally demonstrated between two broadband antennas. The measured results show 21 dB and 0.85 dB loss in the isolation and transmission directions, respectively.

Low-Profile Leaky Wave Electric Monopole Loop Antenna Using the

A novel low-profile leaky-wave electric monopole loop antenna in the regime of a composite right/left-handed (CRLH) ferrite-loaded open waveguide is presented. Despite its closed configuration, this structure supports a traveling-wave mode due to its non-reciprocity. Moreover, this mode exhibits an infinite wavelength in the regime, achieved at the transition frequency between the backward and forward CRLH bands, which leads to an electric monopole antenna field distribution when the loop is electrically small. The structure is analyzed theoretically and shown to admit, for a given loop width, different groups of discrete modes. The modes within each group converge to the unique mode of the straight waveguide when the radius of the loop becomes very large, as a consequence of the decreased curvature of the structure. A complete antenna, with a wire feed and a stub matching section, is demonstrated by both full-wave and experimental results. The omnidirectional azimuthal gain of the antenna is of -5 dBi with a co-to-cross polarization discrimination in excess of 20 dB. Removal of the ground plane would lead to a unique electric dipole loop antenna.

\beta=0

Four types of ferrite-loaded CRLH waveguide with different characteristics and merits have been investigated and compared.