Nonreciprocal Metamaterial Research Articles

A Nonreciprocal CRLH Full-Duplex Metamaterial Leaky Wave Antenna Based on Distributed Mixing Principle

A Nonreciprocal CRLH Full-Duplex Metamaterial Leaky Wave Antenna Based on Distributed Mixing Principle

Design and Analysis of an Electronically Tunable Magnet-Free Non-Reciprocal Metamaterial

In this communication, we develop and experimentally test a fully tunable magnet-free, non-reciprocal, split-ring resonator-based metamaterial. Non-reciprocity in the material response is introduced by bridging the split-ring gap with a biased field-effect transistor (FET) transistor, which allows the non-reciprocity to be tuned with respect to gate–source and drain–source bias conditions. As a measure of non-reciprocity, we consider the Faraday rotation of a normally incident linearly polarized planewave, which is a function of the co-polarized and cross-polarized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters associated with two horn antennas that transmit and receive the wave. Faraday rotation is calculated with respect to the operating frequency of the horn antennas and manually measured with respect to drain–source current at the resonant frequency. Interestingly, we find a linear relationship between Faraday rotation and drain–source current at the resonance.

Experimental realization of an active non-reciprocal metamaterial using an eigen-structure assignment control strategy.

This paper presents a class of active non-reciprocal metamaterials (ANMMs) in an attempt to control the flow of acoustic waves along a one-dimensional acoustic duct. The proposed method distinguishes itself from the available approaches where the non-reciprocities are generated either actively or passively by various sources of nonlinearities, circulators and gyroscopic/gyrator components, and/or spatiotemporal modulation. The proposed method relies in its operation on a controller that is designed by simultaneous allocation of both the eigenvalues and eigenvectors. In other words, the entire eigen-structure of the closed-loop system is assigned as deemed necessary. Conventionally, the placement of the eigenvalues has been employed to enhance both the damping and response of the system. However, in this study, the focus is placed on adjusting the eigenvectors in a way that enables the spatial control and redistribution of the wave propagation along the acoustic duct in order to produce any desirable non-reciprocal behavior. During this entire process, the system continues to behave in a linear fashion. The theory governing the operation of this proposed approach is introduced, and a comprehensive experimental validation effort is presented to demonstrate the basic features, non-reciprocal behavior, and control characteristics. Generalization of the presented strategies to two-dimensional acoustic systems is a natural extension of the present work.

Active nonreciprocal metamaterial using an eigen-structure assignment control strategy.

A class of active nonreciprocal metamaterials (ANMMs) is developed to control the flow and distribution of energy along periodic dynamical systems. Such a development constitutes a radical departure from the currently available approaches where the non-reciprocities are generated either by utilizing various sources of passive nonlinearities, gyroscopic circulators, spatiotemporal modulation, or active control of nonlinear systems. The proposed ANMM cell consists of a one-dimensional acoustic duct provided with linear active control capabilities. The controller is designed by simultaneous assignment of both the eigenvalues and eigenvectors, i.e., the entire eigen-structure, of the closed-loop system. Conventionally, the placement of the eigenvalues has been considered to improve the damping and system's response. However, in this study, the emphasis is placed also on tailoring the eigenvectors in order to enable the spatial control and redistribution of the wave propagation energy flow along the acoustic duct in such a manner that it can introduce non-reciprocity as well as control its direction and reversal. During this entire process, the system remains behaving in a linear fashion. Numerical examples are presented to demonstrate the basic features and non-reciprocal behavior, as well as the energy flow characteristics.

Active Control of the Spoof Plasmon Propagation in Time Varying and Non-reciprocal Metamaterial

We present an efficient concept based on time varying and non reciprocal metamaterials to achieve an active control of the spoof plasmon (SP) propagation at sub-wavelength scale. An experimental demonstration of non-reciprocal guiding device based on split ring resonator is proposed as an application of this concept in the microwave regime. We show that this device is able to blue-shift the propagated SP waves and to achieve an active steering of these SPs at sub-wavelength scale by controlling the modulation frequency of the time varying metamaterial. This approach could be extended plainly to infrared and optical regimes by considering suitable technologies.

Metal-coated magnetic nanoparticles in an optically active medium: A nonreciprocal metamaterial

We report on the optical response of a nonreciprocal bianisotropic metamaterial, consisting of spherical, metal-coated magnetic nanoparticles embedded in an optically active medium, thus combining gyrotropy, plasmonic resonances, and chirality in a versatile design. The corresponding effective medium is deduced by an appropriate two-step generalized Maxwell-Garnett homogenization scheme. The associated photonic band structure and transmission spectra are obtained through a six-vector formulation of Maxwell equations, which provides an efficient framework for general bianisotropic structures going beyond existing approaches that involve cumbersome nonlinear eigenvalue problems. Our results, analyzed and discussed in the light of group theory, provide evidence that the proposed metamaterial exhibits some remarkable frequency-tunable properties, such as strong, plasmon-enhanced nonreciprocal polarization azimuth rotation and magnetochiral dichroism.

Voltage controlled duplexer-integrated leaky-wave antenna using Magnet-less Non-reciprocal Metamaterial (MNM)

A novel voltage controlled duplexer-integrated leaky-wave antenna, consisting of an array of traveling-wave resonant particle by metal ring resonator with variable capacitance and uni-lateral component is proposed, analysed, and measured. In contrast to ferrite-based leaky-wave antenna, this antenna does not require a biasing magnet but only an bias voltage for the FETs, and beam steering voltage for varactor diodes. Bias voltage beam steering in addition to unique duplexer operation is confirmed numerically and experimentally. As a result, beam scanning property from −30° to 45° is realized for 7GHz operation. One non-conventional property of this antenna is non-reciprocity, and duplexer integrated operation is also confirmed just in one antenna element by utilizing non-reciprocity.

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.

Switchable Magnetless Nonreciprocal Metamaterial (MNM) and its Application to a Switchable Faraday Rotation Metasurface

Recently introduced magnetless nonreciprocal metamaterials (MNMs) may represent a flexible, low-cost and integrated alternative to ferrites for nonreciprocal electromagnetic structures and microwave components. In those MNMs, the direction of gyrotropy is fixed by the fixed unilaterality of the FETs used as loads of the MNM ring particles. This letter makes the MNM's gyrotropy direction switchable, using switchable anti-parallel FET circuit loads. This switchability property is demonstrated experimentally via reversal of the direction of the Faraday angle induced by a switchable MNM metasurface.