Losses In Metamaterials Research Articles

Design of Low‐Loss Electromagnetic Metamaterial with Non‐uniform Linewidth for Magnetic Field Convergence in WPT System

Electromagnetic metamaterial (EM metamaterial) with a double‐layer spiral structure is often used to enhance the transmission efficiency of wireless power transfer (WPT). When EM metamaterial is used as an array, its AC resistance and loss cannot be ignored due to the high‐frequency magnetic field of WPT. This paper decreases EM metamaterial's loss by increasing its quality factor according to the quality factor theory and proposes a novel structure. This structure adopts a non‐uniform linewidth, which can decrease the proximity effect resistance of the EM metamaterial as well as maintain its high inductance. When using the proposed EM metamaterial to form an array, to enhance its effect in modulating the magnetic field, a hybrid EM metamaterial slab (HMS) is constructed by adjusting the series resonance capacitor. The corresponding samples of EM metamaterial with the non‐uniform linewidth structure are developed. The experiment results prove that compared to the uniform linewidth structure, the equivalent resistance and loss of the non‐uniform linewidth structure respectively are decreased by about 5.48% and 19.73%, and the quality factor is enhanced to 556.874. The HMS constructed by the proposed EM metamaterial can enhance the transmission efficiency of the experimental WPT system to 59.8%, which is about 2.1% higher than the HMS constructed by the normal EM metamaterial. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Low‐Loss Epsilon‐Near‐Zero Metamaterials

AbstractDifferent from the classical periodic‐resonator‐based metamaterials, epsilon‐near‐zero (ENZ) metamaterials provide a unique paradigm to achieve equivalent electromagnetic characteristics in deep subwavelength scales, exhibiting unprecedented impacts on a broad variety of extreme‐small‐volume applications. By doping regular dielectric rods in the ENZ host, the effective permeability µeff of ENZ metamaterials is properly tuned for desired scattering properties and intrinsic impedance. However, losses in ENZ metamaterials severely limit the tuning range of the real part of µeff and result in an undesired imaginary part. Here, to mitigate the loss issue of ENZ metamaterials, a dielectric‐free approach is theoretically studied and experimentally verified by substituting dielectric dopants with metal‐layer dopants to construct a low‐loss resonant cavity. Therefore, the largest tuning range of µeff is achieved, which advances ENZ metamaterials from ideal cases to more extensive and practical applications. In addition to existing photonics and electronics applications of regular ENZ metamaterials, additional examples are studied to demonstrate the low‐loss benefits of layer‐type ENZ metamaterials, including integrated microfluidic switches and high‐sensitivity sensors with a sensitivity of 11.2% and quality factor of 2800. These examples reveal universal significance for wide‐range applications in extreme‐small‐volume devices and systems, such as integrated circuits, chips, and implanted devices.

Study of acoustic transmission losses in particle-reinforced rubber-based membrane-type acoustic metamaterials

In this work, the mechanical properties of particle reinforced ethylene propylene diene monomer (EPDM)/ethylene tetrafluoroethylene (ETFE) copolymer material were determined by molecular dynamics (MD) method, and the copolymer material was used in the structural design of acoustic metamaterials. Secondly, based on the discrete point matching method, the acoustic transmission loss characteristics of the material are predicted, and the accuracy and effectiveness of the theory are verified through the multi physical field coupling finite element model. Finally, seven key parameters that affect the material structure are studied, and their influencing rules and mechanisms are analyzed. The results show that the structure makes up for the sound insulation defect of traditional ETFE film materials at low frequencies. Through reasonable selection of key parameters, high sound insulation design can be carried out for specific frequency bands, which is of great significance to the potential application in the construction field (new building materials).

Reconfigurable enhancement of actuation forces by engineered losses in non-Hermitian metamaterials

While boosting signals with amplification mechanisms is a well-established approach, attenuation mechanisms are typically considered an anathema because they degrade the efficiency of the structures employed to perform useful operations on these signals. An emerging alternate viewpoint promotes losses as a novel design element by utilizing the notion of exceptional point degeneracies (EPDs)—points in parameter space where the eigenvalues of the underlying system and the associated eigenvectors simultaneously coalesce. Here, we demonstrate a direct consequence of such eigenbasis collapse in elastodynamics—an unusual enhancement of actuation force by a judiciously designed non-Hermitian metamaterial supporting an EPD that is coupled to an actuation source. Intriguingly, the EPD enables this enhancement while maintaining a constant signal quality. Our work constitutes a proof-of-principle design which can promote a new class of reconfigurable nano-indenters and robotic-actuators. Importantly, it reveals the ramifications of non-Hermiticity in boosting the Purcell emissivity enhancement factor beyond its expected value, which can guide the design of metamaterials with enhanced emission that does not deteriorate signal quality for mechanical, acoustic, optical, and photonic applications.

Incoherent Active Convolved Illumination Enhances the Signal-to-Noise Ratio for Shot Noise: Experimental Evidence

Imaging is indispensable for nearly every field of science, engineering, technology, and medicine. However, measurement noise and stochastic distortions pose fundamental limits to accessible spatiotemporal information despite impressive tools such as structured-illumination microscopy (SIM), stochastic optical reconstruction microscopy or photoactivated localization microscopy (STORM or PALM), and stimulated-emission-depletion (STED) microscopy. How to combat this challenge ideally has been an open question for decades. Inspired by a virtual-gain technique to compensate losses in metamaterials, active convolved illumination (ACI) has recently been proposed to significantly improve the signal-to-noise ratio and hence the data acquisition. In this technique, the light pattern of the object is superimposed with a correlated auxiliary pattern, the function of which is to reverse the adverse effects of losses, noise, and random distortion based on their spectral characteristics. Despite enormous implications in statistics, any experimental evidence verifying the theory of this novel technique has been lacking to date. We find experimentally that ACI boosts not just the resolution limit and image contrast but also the resistance to pixel saturation. The results confirm the previous theories and may open up horizons in a wide range of disciplines from atmospheric sciences, seismology, biology, statistical learning, finance, and information processing to quantum noise beyond the fundamental boundaries.

Improving sound absorption via coupling modulation of resonance energy leakage and loss in ventilated metamaterials

Achieving broadband sound absorption in two-port open ducts is of fundamental importance in the acoustics, with wide applications ranging from noise control to duct sound mitigation. Yet the existing metamaterial designs are usually based on the use of Helmholtz-type cavities, posing limitations on the resulting absorption performance. Here, we propose and experimentally demonstrate a mechanism that uses coupling modulation of the resonance energy leakage and loss in ventilated metamaterials to realize optimal sound absorption. We design a slit-type unit cell as a practical implementation of the proposed mechanism and analytically prove its potential to obtain the desired leakage and loss factors simultaneously by properly adjusting the structural parameters. We benchmark our designed metamaterial with a conventional Helmholtz resonator-based design to demonstrate its advantage of sound absorption. Good agreement is observed between the theoretical predictions and experimental measurements. Our strategy represents a paradigm extending beyond classical models and opens up possibility for the design of high-efficiency acoustic absorbing devices and their applications in diverse scenarios especially broadband duct noise muffling.

Overview of Approaches for Compensating Inherent Metamaterials Losses

Metamaterials are synthetic composite structures with extraordinary electromagnetic properties not readily accessible in ordinary materials. These media attracted massive attention due to their exotic characteristics. However, several issues have been encountered, such as the narrow bandwidth and inherent losses that restrict the spectrum and the variety of their applications. The losses have become the principal limiting factor when employing metamaterials in real-world applications. Consequently, overcoming them is crucially important and of practical necessity. This paper discusses the practical applications of metamaterials in constructing functional devices and the effects of the losses on such devices. In more depth, it reviews the available approaches for reducing the metamaterial losses developed over the last two decades in the light of available literature. These approaches include the utilization of the principles of electromagnetically induced transparency (EIT), geometric tailoring of the metamaterial structures, and embedding gain materials. Further, computational optimization techniques, such as particle swarm optimization (PSO) and genetic algorithm (GA), are also discussed to design low-loss metamaterials. The EIT-like metamaterial and the including of gain materials are systematic and universal approaches exhibiting low loss approaching zero. In contrast, the other two are not systematic and universal approaches.

Effect of loss on linear optical quantum logic gates

Linear optical quantum gates have been proposed as a possible implementation for quantum computers. Most experimental linear optical quantum gates are constructed with free-space optical components with negligible loss. In this work, we analyze symmetric and asymmetric partially polarizing lossy beam splitters. Using the generalized beam splitter equations, we study the effects of loss on two linear optical quantum gates: the first is a commonly used CNOT gate, and the second is a W state expansion gate. Envisioning inherent loss in plasmonics and metamaterials as a new degree of freedom and those materials systems as a route for miniaturization, we reconsider the requirements of the lossy CNOT gate and show it is possible to simplify the three-beam-splitter design to a single beam splitter without sacrificing success probability.

Theory of coherent active convolved illumination for superresolution enhancement

Recently an optical amplification process called the plasmon injection scheme was introduced as an effective solution to overcoming losses in metamaterials. Implementations with near-field imaging applications have indicated substantial performance enhancements even in the presence of noise. This powerful and versatile compensation technique, which has since been renamed to a more generalized active convolved illumination, offers new possibilities of improving the performance of many previously conceived metamaterial-based devices and conventional imaging systems. In this work, we present, to the best of our knowledge, the first comprehensive mathematical breakdown of active convolved illumination for coherent imaging. Our analysis highlights the distinctive features of active convolved illumination, such as selective spectral amplification and correlations, and provides a rigorous understanding of the loss compensation process. These features are achieved by an auxiliary source coherently superimposed with the object field. The auxiliary source is designed to have three important properties. First, it is correlated with the object field. Second, it is defined over a finite spectral bandwidth. Third, it is amplified over that selected bandwidth. We derive the variance for the image spectrum and show that utilizing the auxiliary source with the above properties can significantly improve the spectral signal-to-noise ratio and resolution limit. Besides enhanced superresolution imaging, the theory can be potentially generalized to the compensation of information or photon loss in a wide variety of coherent and incoherent linear systems including those, for example, in atmospheric imaging, time-domain spectroscopy, P T symmetric non-Hermitian photonics, and even quantum computing.

Loss compensation in metamaterials and plasmonics with virtual gain [Invited

Metamaterials and plasmonics potentially offer an ultimate control of light to enable a rich number of non-conventional devices and a testbed for many novel physical phenomena. However, optical loss in metamaterials and plasmonics is a fundamental challenge rendering many conceived applications not viable in practical settings. Many approaches have been proposed so far to mitigate losses, including geometric tailoring, active gain media, nonlinear effects, metasurfaces, dielectrics, and 2D materials. Here, we review recent efforts on the less explored and unique territory of “virtual gain” as an alternative approach to combat optical losses. We define the virtual gain as the result of any extrinsic amplification mechanism in a medium. Our aim is to accentuate virtual gain not only as a promising candidate to address the material challenge, but also as a design concept with broader impacts.

Analytical and Numerical Investigation of Radiation Enhancement by Anisotropic Metamaterial Shells

This paper presents analytical and numerical investigations of a 3D cylindrical metamaterial shell possessing a cylindrically anisotropic permeability that is excited by a finite-sized electric line source. A comprehensive field analysis of the system reveals that the compact metamaterial shell exhibits resonances akin to those observed in isotropic 2D cylindrical metamaterial structures, which may be used to enhance the radiated power of a nearby antenna. An analytical resonance condition that relates the dimensions of the cylindrical shell to its anisotropic effective-medium parameters is shown to be accurate in predicting the resonances of 2D and 3D metamaterial shells obtained using full-wave simulations. The effects of anisotropy and finite shell/antenna height on the system's near-fields, radiation patterns, and power-ratio enhancements are explored. It is shown through both theory and simulations that the condition for resonance is largely independent of shell/antenna height but that the quality factor reduces dramatically as these heights approach electrically small values. Also, a dispersion and loss analysis assuming Lorentz model is carried out, which indicates that practical metamaterial losses do not significantly degrade the power enhancement.

Low-loss near-zero-index metamaterial based on a single board for broadband electromagnetic-wave switches

Zero-index metamaterials have excellent potential for applications in electromagnetic devices, but severely suffering from inadequate bandwidth or high loss. Here we present an easy-fabricating zero-index metamaterial, composed of the wires on the surface and through the substrate. The near-zero-index metamaterial presents a low loss in the wide frequency range from 10.72 GHz to 11.4 GHz. A general approach of low-loss near-zero refraction is proposed based on the relationship between electric plasma frequency and magnetic plasma frequency, which provides an effective way for governing electromagnetic loss of metamaterials. The near-zero-index metamaterial can service as the broadband electromagnetic-wave switch covering the range of 10.5 GHz to 11.54 GHz, with a relative transmission ratio up to 97.8%.

Membrane- and plate-type acoustic metamaterials with elastic unit cell edges

Membrane- and plate-type acoustic metamaterials are thin membranes or plates consisting of periodic unit cells with small added masses. It has been shown in numerous studies, that these metamaterials exhibit tunable anti-resonances with transmission loss values much higher than the corresponding mass-law. However, in most studies it is assumed that the unit cell edges (or grid) of the metamaterial are fixed. This idealised boundary condition is not applicable to real world applications in noise control. Therefore, the acoustic performance of these metamaterials under more realistic circumstances, where the grid structure cannot be perfectly rigid, can be expected to be different. In this contribution, the vibro-acoustic behavior of membrane- and plate-type acoustic metamaterials with a non-rigid grid is investigated. For this purpose, an efficient analytical model is developed to predict the eigenmodes and sound transmission loss of such metamaterials. In this model, elastic unit cell edges are modelled using a grid of Euler-Bernoulli beams and the sound transmission loss can be calculated for oblique incidence. A comparison to FEM simulations shows that the proposed model yields the same results but with a considerably reduced computational effort. The analytical model is then used to discuss the vibro-acoustic properties of the metamaterial, with particular focus on the influence of the mass and stiffness of the grid beams. It is shown that even when a non-rigid grid and diffuse incident sound fields are considered, the transmission loss of the metamaterial exhibits anti-resonances with remarkably high noise reduction values. These anti-resonances can be tuned by choosing appropriate values of the grid parameters. Furthermore, the formation of band gaps in the propagation of bending waves is discussed by investigating the dispersion curves of the metamaterial. The results in this contribution show that membrane- and plate-type acoustic metamaterials can still efficiently reduce low-frequency noise, even when the unit cell edges are not assumed to be fixed. This important finding and the proposed analytical modal can support the utilization of these metamaterials in practical noise control applications.

Four wave mixing and compensating losses in metamaterials

The conditions under which losses can be compensated in the case of propagation of an backward signal wave under parametric four-wave interaction are analyzed. It is shown that, in the presence of a parametric coupling between forward and backward waves, compensation of signal wave losses by losses of direct waves will allow the parametric amplification and generation of the backward wave to be realized at the threshold pump amplitude. An analytical expression is obtained for the threshold pumping amplitude under phase-matching conditions. It is shown that the threshold pump amplitude increases with increasing losses, the input intensity of the idler wave, and with increasing nonlinear coupling coefficients for pump waves. As a consequence, it is possible to control the threshold pump intensity. and it is possible to obtain significant amplification in the metamaterial, as well as parametric generation of the backward wave.

A broadband tunable terahertz negative refractive index metamaterial

A strategy to greatly broaden negative refractive index (NRI) band, reduce loss and ease bi-anisotropy of NRI metamaterials (MMs) has been proposed at terahertz frequencies. Due to the symmetric structure of the MM, the transmission and refractive index are independent to polarizations of incident radiations, and a broadband NRI is obtainable for the range of the incident angle from 0° to 26°. In addition, THz MMs’ properties such as transmission, phase and negative refraction exhibit a real-time response by controlling the temperature. The results indicate that the maximum bands of the negative and double-negative refraction are 1.66 THz and 1.37 THz for the temperature of 40 °C and 63 °C, respectively. The figure of merit of the MMs exceeds 10 (that is, low loss) as the frequency increases from 2.44 THz to 2.56 THz in the working temperature range, and the maximum figure of merit is 83.77 at 2.01 THz where the refractive index is −2.81 for a given temperature of 40 °C. Furthermore, the negative refraction of the MMs at the low loss band is verified by the classical method of the wedge, and the symmetric slab waveguide based on the proposed MM has many unique properties.

Analytical and Experimental Investigation on Sound Transmission of Double Thin Plates with Magnetic Negative Stiffness

Transmission loss of acoustic metamaterials (AM) made of double thin plates with magnetic (negative) stiffness was analyzed using theory, finite element analysis and experimental techniques. The theoretical formulation was done using a rectangular duct below the first cut off frequency, the model is then validated against finite element method and experiment. Two cubic magnets were used, their interaction force and the resulted magnetic stiffness were calculated. The sound transmission loss (STL) of the structure is calculated for plane wave condition, the addition of magnetic mass shifts STL peaks to the lower frequency compared to a structure without mass. The slight increase in STL for small negative stiffness in experiment is not enough to cancel the effect of air compressibility. However, a significant enhancement could be expected if negative stiffness can be made large enough in the double thin plates. The developed AM can be employed as a prospective sound engineering control at low frequency.

Fine manipulation of sound via lossy metamaterials with independent and arbitrary reflection amplitude and phase

The fine manipulation of sound fields is critical in acoustics yet is restricted by the coupled amplitude and phase modulations in existing wave-steering metamaterials. Commonly, unavoidable losses make it difficult to control coupling, thereby limiting device performance. Here we show the possibility of tailoring the loss in metamaterials to realize fine control of sound in three-dimensional (3D) space. Quantitative studies on the parameter dependence of reflection amplitude and phase identify quasi-decoupled points in the structural parameter space, allowing arbitrary amplitude-phase combinations for reflected sound. We further demonstrate the significance of our approach for sound manipulation by producing self-bending beams, multifocal focusing, and a single-plane two-dimensional hologram, as well as a multi-plane 3D hologram with quality better than the previous phase-controlled approach. Our work provides a route for harnessing sound via engineering the loss, enabling promising device applications in acoustics and related fields.

Enhanced superlens imaging with loss-compensating hyperbolic near-field spatial filter.

Recently a coherent optical process called plasmon-injection (Π) scheme, which employs an auxiliary source, has been introduced as a new technique to compensate losses in metamaterials. Here, a physical implementation of the Π scheme is proposed for enhanced superlens imaging in the presence of absorption losses and noise. The auxiliary source is constructed by a high-intensity illumination (above 1 mW/μm2) of the superlens integrated with a near-field spatial filter. The integrated system enables reconstruction of an object previously unresolvable with the superlens alone. This work elevates the viability of the Π scheme as a strong candidate for loss compensation in near-field imaging systems without requiring nonlinear effects or gain media.

Metamaterial engineered transparency due to the nullifying of multipole moments.

Here we propose, to the best of our knowledge, a novel transparency effect in cylindrical all-dielectric metamaterials. We show that the cancellation of multipole moments of the same kind leads to almost zero radiation losses in all-dielectric metamaterials due to the counter-directed multipolar moments in metamolecule. The nullifying of multipoles, mainly dipoles, and suppression of higher multipoles, results in the ideal transmission of an incident wave through the designed metamaterial. The observed effect could pave the road to the new generation of light-manipulating transparent metadevices such as filters, waveguides, and cloaks.

Methods of decreasing losses in optical metamaterials

In this work we review methods to decrease the optical absorption losses in metamaterials. The practical interest for metamaterials is huge, but the possible applications are severely limited by their high inherent optical absorption in the metal parts. We consider the possibilities to fabricate metamaterial with a decreased metal volume fraction, the application of alternative lower-loss plasmonic materials instead of the customary utilized noble metals, the use of all-dielectric, high refractive index contrast subwavelength nanocomposites. Finally, we dedicate our attention to various methods to optimize the frequency dispersion in metamaterials by changing their geometry and composition in order to reach lower absorption, which includes the use of the hypercrystals. The final goal is to widen the range of different metamaterialbased devices and structures, including those belonging to transformation optics. Maybe the most important among them is the fabrication of a novel generation of alloptical or hybrid optical/electronic integrated circuits that would operate at optical frequencies and at the same time would offer a packaging density and complexity of the contemporary integrated circuits, owing to the strong localization of electromagnetic fields enabled by plasmonics.