A Novel Strategy in Electromagnetic Wave Absorbing and Shielding Materials Design: Multi-Responsive Field Effect

Metamaterials are composed of periodic subwavelength metal/dielectric structures that resonantly couple to the electric and magnetic fields of the incident electromagnetic waves, exhibiting unprecedented properties which are most typical within the context of the electromagnetic domain. However, the practical application of metamaterials was found critical due to the high losses, strong dispersion associated with the resonant responses, and the difficulty in the fabrication of nanoscale 3D structures. The optical metasurface is termed as 2D metamaterials that inherent all of the properties of metamaterials and also provide a solution to the limitation of the conventional metamaterials. Over the past few years, metasurfaces have been employed for the design and fabrication of optical elements and systems with abilities that surpass the performance of conventional diffractive optical elements. Metasurfaces can be fabricated using standard lithography and nanoimprinting methods which is easier in terms of fabrication of its counterpart 3d metamaterials. In this review article, the progress of the research on metasurfaces is illustrated. Concepts of anomalous reflection and refraction, applications of metasurfaces with the Pancharatanm-Berry Phase, and Huygens metasurface are discussed. The development of soft metasurface opens up a new dimension of application zone in conformal or wearable photonics, the progress of soft metasurface also been discussed in this review. Meta-devices that are being developed with the principle of the shaping of wavefronts are elucidated in this review. Furthermore, it was established that properties of novel optical metasurface can be modulated by the change in mechanical, electrical, or optical stimuli which leads to the development of dynamic metasurface. Research thrust over the area of tunable metasurface has been reviewed in this article. Over the recent year, it has been found that optical fibers and metasurface are coagulated for the development of optical devices with the advantage of both domains. The metasurface with lab-on fiber-based devices is being discussed in this review paper. Finally, research trends, challenges, and future scope of the work are summarized in the conclusion part of the article.

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A Review on Metasurface: From Principle to Smart Metadevices

By introducing vanadium dioxide film into a multilayer structure, the dual functionalities of perfect absorption and high transmission are presented using the insulator-to-metal phase transition of vanadium dioxide. When vanadium dioxide is in the conducting state, the designed system acts as a narrowband absorber. The proposed absorber is composed of the top metallic ring, silica spacer, and the vanadium dioxide film. The absorption peak is originated from localized magnetic resonance between metallic ring and vanadium dioxide film. When vanadium dioxide is in the insulating state, the designed system acts as a transparent conducting metal. The top metallic ring, the middle dielectric spacer, and the subwavelength metallic mesh are combined together to form an antireflection coating. The influences of incident angle and structure parameter on absorption and transmission are also discussed. This work has demonstrated a new route for developing vanadium dioxide-based switchable photonic devices in the fields of filter and modulator at terahertz frequencies.

Simultaneous realizations of absorber and transparent conducting metal in a single metamaterial.

Sensors are core elements to directly obtain information from surrounding objects for further detecting, judging and controlling purposes. With the rapid development of soft electronics, flexible sensors have made considerable progress, and can better fit the objects to detect and, thus respond to changes more sensitively. Recently, as a newly emerging electronic ink, liquid metal is being increasingly investigated to realize various electronic elements, especially soft ones. Compared to conventional soft sensors, the introduction of liquid metal shows rather unique advantages. Due to excellent flexibility and conductivity, liquid-metal soft sensors present high enhancement in sensitivity and precision, thus producing many profound applications. So far, a series of flexible and wearable sensors based on liquid metal have been designed and tested. Their applications have also witnessed a growing exploration in biomedical areas, including health-monitoring, electronic skin, wearable devices and intelligent robots etc. This article presents a systematic review of the typical progress of liquid metal-enabled soft sensors, including material innovations, fabrication strategies, fundamental principles, representative application examples, and so on. The perspectives of liquid-metal soft sensors is finally interpreted to conclude the future challenges and opportunities.

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Advances in Liquid Metal-Enabled Flexible and Wearable Sensors.

Terahertz toroidal metasurface biosensor for sensitive distinction of lung cancer cells

Novel manipulation techniques for the propagation of electromagnetic waves based on metamaterials can only be performed in narrow operating bands, and this drawback is a major challenge for developing metamaterial-based practical applications. We demonstrate that the scattering of metamaterials can be switched and that their operating band can be tuned by introducing liquid metal in the design of functional metamaterials. The proposed liquid metal-based metamaterial is composed of a copper wire pair and a tiny pipe filled with a liquid metal, namely eutectic gallium-indium. The interference of the sharp magnetic resonance of the copper wire pair and the broad dipolar mode of the liquid metal rod lead to an electromagnetically induced transparency (EIT)-like spectrum. We experimentally demonstrate that this EIT-like behavior can be switched on or off by exploiting the fluidity of the liquid metal, which is useful for multi-frequency modulators. These findings will hopefully promote the development of fluid matter-based metamaterials for extending the operating band of novel electromagnetic functions.

Realization of switchable EIT metamaterial by exploiting fluidity of liquid metal

https://onlinelibrary.wiley.com/doi/pdf/10.1002/inf2.12174

Subwavelength optical localization with toroidal excitations in plasmonic and Mie metamaterials

Broadband and wide angle microwave absorption with optically transparent metamaterial

Coherent perfect absorber (CPA) is a novel strategy proposed and demonstrated for solving the challenge to attain efficient control of absorption by exploiting the inverse process of lasing. The operation condition of CPA results in narrow-band, which is the main limitation obstruct it from practical applications. Here, we demonstrate a CPA with tunable operation frequency employing the liquid metal made reconfigurable metasurface. The flow of liquid metal is restricted with a plastic pipe for realizing a controllable liquid metal cut-wire. The adjustable electric dipolar mode of the reconfigurable cur-wire metasurface ensures that the quasi-CPA point can be dynamically controlled; the measured CPA under proper phase modulation is in good agreement with the simulation results. The proposed CPA system involving liquid metal for dynamic control of operation frequency will have potential applications and may stimulate the exploitation of liquid based smart absorption control of optical waves.

Controllable coherent perfect absorber made of liquid metal-based metasurface

The performance of metamaterial is limited in designed narrow band due to its resonant nature, it is highly desirable to incorporate active inclusions in metamaterials to extend the operation bandwidth. This review summarizes the development in realizing tunability of electromagnetic response in metamaterials incorporated with nematic liquid crystal (LC). From rigorous comparison, it is found that the anisotropic property of nematic LC is essential to predict the influence of LC molecular director orientation on the resonant frequency of metamaterials. By carefully designing the metamaterials and properly infiltrating LC, the operation frequency of single/double negative parameters of metamaterials can be dynamically modulated with remarkable red/blue-shift, depending on the LC molecular orientation angle. Moreover, the recent liquid-crystal-based developments and novel applications are investigated and highlighted.

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Jing Xu

Papers

Realization of switchable EIT metamaterial by exploiting fluidity of liquid metal

Subwavelength optical localization with toroidal excitations in plasmonic and Mie metamaterials

Broadband and wide angle microwave absorption with optically transparent metamaterial

Controllable coherent perfect absorber made of liquid metal-based metasurface

A Review of Tunable Electromagnetic Metamaterials With Anisotropic Liquid Crystals