Perfect Wave Absorption Research Articles

A Mid-Infrared Perfect Metasurface Absorber with Tri-Band Broadband Scalability.

Metasurfaces have emerged as a unique group of two-dimensional ultra-compact subwavelength devices for perfect wave absorption due to their exceptional capabilities of light modulation. Nonetheless, achieving high absorption, particularly with multi-band broadband scalability for specialized scenarios, remains a challenge. As an example, the presence of atmospheric windows, as dictated by special gas molecules in different infrared regions, highly demands such scalable modulation abilities for multi-band absorption and filtration. Herein, by leveraging the hybrid effect of Fabry-Perot resonance, magnetic dipole resonance and electric dipole resonance, we achieved multi-broadband absorptivity in three prominent infrared atmospheric windows concurrently, with an average absorptivity of 87.6% in the short-wave infrared region (1.4-1.7 μm), 92.7% in the mid-wave infrared region (3.2-5 μm) and 92.4% in the long-wave infrared region (8-13 μm), respectively. The well-confirmed absorption spectra along with its adaptation to varied incident angles and polarization angles of radiations reveal great potential for fields like infrared imaging, photodetection and communication.

Design of Perfect Absorber Based on Metagratings: Theory and Experiment

This article proposes an analytical design methodology for different kinds of perfect absorbers (PAs) based on metagratings (MGs). In the specific analysis and design, the period of the MG is chosen to ensure that there is only the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0^{\textrm {th}}$ </tex-math></inline-formula> order diffraction mode. Using the established theory, the supercell of the MG is rigorously analyzed to derive a specific load impedance density expression that allows achieving destructive interference of specular reflection of the substrate and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0^{\textrm {th}}$ </tex-math></inline-formula> mode diffraction such that perfect wave absorption is realized. Four kinds of PAs composed of different supercells of MG with different bandwidths are systematically analyzed, designed, simulated, and experimentally verified. The simulation and measurement results are in good agreement and consistent with the theoretical analysis, showing the validity of the provided theory and technique for electromagnetic wave absorption.

Experimental study of a tunable perfect flexural wave absorber with a piezoelectric shunted resonator

Metamaterials and metasurfaces have been widely developed recently for extraordinary acoustic and elastic wave control at a deep subwavelength scale. Perfect wave absorption as an extreme case to totally absorb the impinged waves has gained great attention, whereas most existing designs based on local resonance lack tunabilities, making perfect absorption be observed at a single frequency. To overcome this drawback, in this work, we design and fabricate a tunable inductance-resistance (LR) shunted mechanical resonator via a bonded piezoelectric patch for perfect flexural wave absorption at low frequency. The LR shunted absorber could be reconfigured to a broad frequency range for perfect flexural wave absorption. The tunable perfect absorption performances are validated through experiments and unit absorption is achieved in experiments. In the end, to further highlight the advantages of shunted damping we numerically demonstrate that the absorption spectrum could be enhanced to broadband absorption with a negative capacitance and an inductance-resistance circuit (NC-LR) connected in parallel. The approach proposed provides an alternative solution to achieve perfect wave absorption in the low-frequency range and enables practical application in complex engineering structures.

A carbon nanotube coated metawall with ultra-wideband perfect wave absorption utilizing cement dielectric

Metamaterials (MMs) have attracted intense attention owing to their unprecedented control over the propagation of electromagnetic waves. Researches on MMs usually concentrate on the metallic resonators layer, while the carbon materials-based resonators and the dielectric layer of MMs are relatively overlooked. Here, a novel and simple “metawall” perfect MM absorber based on carbon nanotube (CNT) is conducted, which enables ultra-wideband perfect absorption, showing three peaks with 99% absorption and yielding over 97% absorption in 5.6–11.0 GHz. A reproducible and cost-efficient fabrication method is proposed, using CNT paste as the resonator and the combination of lossy cement board and lossless ceramic fiberboard as the dielectric. Moreover, only one kind of one-dimensional gratings CNT pattern is required to achieve multi-band perfect absorption. Through the control experiments to investigate the roles of the components of the metawall structure, it is found that the wideband perfect absorption of the metawall can be attributed to its unique structure and the absorption performance of the cement board. The proposed metawall provides a new perspective for achieving wideband perfect absorption and may serve as a promising platform to combine carbon nanomaterials with practical load-bearing engineering components.

Tuning Negative Permittivity by Anodization of A 3D Copper Network

Negative permittivity is a required physical property of metamaterials which has been widely used in some emerging and unconventional applications, such as cloaking, perfect lens and perfect wave absorption. In addition to periodic meta-structured units, a composite with conductive networks, so-called metacomposite, is equivalent to diluted metals, which also exhibits negative permittivity properties at microwave frequency. The percolative metacomposites have the advantages of isotropic property, flexible preparation methods and low cost in achieving negative permittivity. However, building a percolation network from conductive fillers in an insulating matrix is a complicated process, and the dispersion of fillers is difficult to control. In this study, the percolation network was modulated on the basis of the conductive copper foam by anodization treatment. The conductivity and negative permittivity of the foam varied with the anodization time. As the anodization time increased, the foam changed from a typical Drude metal to a less conductive 3D structure with mitigated negative permittivity. The absolute value of the negative permittivity of Cu-30V-5h sample was two orders of magnitude lower than that of the samples anodised for 30V-3h, 20V-3h and 20V-1h. Therefore, anodization is a facile and effective method to control the conductivity and negative permittivity of copper epoxy metacomposites.

Wave absorption of an orthotropic rectangular panel based on direct feedback

This paper presents a new methodology of realizing an active wave control for an orthotropic rectangular panel. In general, an ideal wave controller is expressed by non-causal function which is impossible to be realized practically. The static direct feedback is introduced to overcome this problem. Firstly, a transfer matrix method for an orthotropic rectangular panel is introduced to describe the wave dynamics of the structure. This is followed by the derivation of feedback control laws for absorbing reflected waves. Then, static direct feedback is presented to realize the perfect wave absorption at single frequency. Finally, from a viewpoint of numerical analyses, control effects of the proposed method are verified by evaluating the absolute displacement distribution. It is found that the reflected wave absorbing control enables the inactivation of all vibration modes in the controlled direction.

A novel metamaterial absorber with perfect wave absorption obtained by layout design

In this work, a novel metamaterial absorber (MMA) with perfect wave absorption is designed through the layout optimization. The rotationally symmetrical design domain is determined by considering polarization insensitivity. The symmetrical design variables are related with each other. The optimization objective is to maximize the absorption index which is described by the reflection and transmission coefficients in the frequency range of 8–12 GHz with the constraint of volume fraction. The maximum absorptivity of the optimized MMA reaches 99.89%. And it has the polarization insensitivity, the wide range of oblique incident angles and the ideal impedance matching with the free space. Furthermore, the absorption frequencies exhibit regular variations while changing the sizes of unit cell and the thickness of dielectric substrate. Inspired by these analysis results and the existing researches, the multilayer MMA is designed in order to broaden the absorption band efficiently. The absorption frequency band reaches 1.1 GHz while the absorptivity is more than 85%.

Manipulating the loss in electromagnetic cloaks for perfect wave absorption

We examine several ways to manipulate the loss in electro-magnetic cloaks, based on transformation electromagnetics. It is found that, by utilizing inherent electric and magnetic losses of metamaterials, perfect wave absorption can be achieved based on several popular designs of electromagnetic cloaks. A practical implementation of the absorber, consisting of ten discrete layers of metamaterials, is proposed. The new devices demonstrate super-absorptivity over a moderate wideband range, suitable for both microwave and optical applications. It is corroborated that the device is functional with a subwavelength thickness and, hence, advantageous compared to the conventional absorbers.

VIBRATION ATTENUATION OF AN AXIALLY MOVING STRING VIAACTIVE IN‐DOMAIN CONTROL METHODS

A study of active vibration control of axially moving string‐like system is presented in this paper. The approach is based on the concept of wave absorption or impedance matching through placement of both sensors and actuators in domain. A classical model‐matching framework for disturbance rejection is used to solve the control laws. For SISO cases, perfect wave absorption can be achieved if one of the boundary conditions is known. Further, by moving both the sensor and actuator to the boundary, the in‐domain control laws become the boundary controllers derived by previous researchers. To avoid the requirement of knowing the boundary condition precisely, a two‐sensor control law is then proposed. The resulting controller, though boundary independent, contains an infinite number of poles on the imaginary axis, and the closed‐loop system is not internally stable. A simple “notch filter” is added to the control law, and the stability of as well as deterioration in performance are analyzed. Numerical results for a moving string system under external excitation are presented to demonstrate the effectiveness of this controller.

A Fundamental Study on the Wave Absorber

It has been shown theoretically by Bessho that it is possible to absorb a train of regular waves passed a floating body if its motion is properly controlled. It has also been shown experimentally by J. H. Milgram that in a specified case, the “perfect wave absorption” could be realized.In this paper, the authors rearrange Bessho's theory and show that when an incident wave is diffracted by a fixed body, the height of symmetric wave system and asymmetric wave system which are fundamental components of the reflected and the transmitted waves is exactly one half of the height of the incident wave, and show that this relation is valid independent of the form of the body. They also show that this relation holds in the case when the body is allowed to move provided the body is of symmetric.Making use of these relation, the authors show theoretically and experimentally that it is possible to absorb completely the energy of an incident wave by actively controlling the motion of a floating body.They also show that at the “wave absorption point” at which no reflected and transmitted wave exist, the work done by the mechanism which activated the body is negative and is equal to the energy of the incident wave.