Transparent coupled membrane metamaterials with simultaneous microwave absorption and sound reduction

High temperature infrared-radar compatible stealthy metamaterial based on an ultrathin high-entropy alloy

In this work, a high temperature infrared (IR) and radar compatible stealthy metamaterial based on ultrathin high-entropy alloy are proposed. From room temperature to 600°C, the fabricated radar absorption layer (RAL) can have wideband absorption in X-band (8.2-12.4 GHz) with average absorption 78% owing to magnetic resonance and ohmic loss. The ultrathin high-entropy alloy film is further design as infrared shielding layer (ISL) due to low-emissivity property. The ISL and RAL consist of the IR-microwave compatible stealth metamaterial. It can give rise to the strong reduction of both radar wave reflection and infrared thermal emission. Its bandwidth (absorption over 90%) is 2.15 GHz. In the infrared atmosphere window, it can suppress a half of thermal radiation. This is realized by the subtle combination between the RAL and specifically designed ISL that control the infrared emission and microwave absorption. These results show that they are practically very promising for the application of a radar-infrared bi-stealth technology in high temperature environment.

Reconfigurable meta-radiator based on flexible mechanically controlled current distribution in three-dimensional space

In this paper, we provide an experimental proof-of-concept of this dynamic three-dimensional (3D) current manipulation through a 3D-printed reconfigurable meta-radiator with periodically slotted current elements. By utilizing the working frequency and the mechanical configuration comprehensively, the radiation pattern can be switched among 12 states. Inspired by maximum likelihood method in digital communications, a robustness-analysis method is proposed to evaluate the potential error ratio between ideal cases and practice. Our work provides a previously unidentified model for next-generation information distribution and terahertz-infrared wireless communications.

Ultra-wideband flexible transparent metamaterial with wide-angle microwave absorption and low infrared emissivity

Optically transparent metamaterials with the performance of infrared radar compatible stealth have been designed and manufactured on the basis of the continuous in-depth research on single-band stealth technology. In this paper, metamaterials are designed through theoretical calculations and modeling simulations. The designed structure can achieve higher than 90% broadband (8.7-32 GHz) absorption at wide-angle (45 degrees), emissivity of 0.3 in infrared atmospheric window, and optical transparency. In addition, the material can be bent, which greatly expands its application scenarios. The experimental results are consistent with the theoretical calculation and simulation results.

Thermal infrared and broadband microwave stealth glass windows based on multi-band optimization

With the rapid development of detection technologies, compatible stealth in the infrared and radar ranges has become increasingly essential not only for military application but also for personal privacy protection. In this study, we design a metamaterial window that possesses stealth ability in both the thermal infrared and broadband microwave ranges, using a particle swarm optimization algorithm to realize multi-band optimization. We experimentally verify that the proposed structure can achieve over 90% microwave absorption in the range 5.1 to 19.2 GHz (covering the X and Ku bands), with low infrared emissivity (∼0.15), and also maintain visible transmittance above 60%. Moreover, the window retains good performance up to 200 °C owing to the intrinsic properties of the material. Our multi-band optimization method enables the application of the transparent metamaterial windows in electromagnetic shielding and stealth and can potentially be applied in smart window related industries.

Cross-wavelength invisibility integrated with various invisibility tactics

As a superior self-protection strategy, invisibility has been a topic of long-standing interest in both academia and industry, because of its potential for intriguing applications that have only appeared thus far in science fiction. However, due to the strong dispersion of passive materials, achieving cross-wavelength invisibility remains an open challenge. Inspired by the natural ecological relationship between transparent midwater oceanic animals and the cross-wavelength detection strategy of their predators, we propose a cross-wavelength invisibility concept that integrates various invisibility tactics, where a Boolean metamaterial design procedure is presented to balance divergent material requirements over cross-scale wavelengths. As proof of concept, we experimentally demonstrate longwave cloaking and shortwave transparency simultaneously through a nanoimprinting technique. Our work extends the concept of stealth techniques from individual invisibility tactics targeting a single-wavelength spectrum to an integrated invisibility tactic targeting a cross-wavelength applications and may pave the way for development of cross-wavelength integrated metadevices.

A multimode, broadband and all-inkjet-printed absorber using characteristic mode analysis

In this paper, we demonstrate a multimode and broadband absorber that is fabricated directly on PET substrate using a commercial direct-to-garment (DTG) inkjet printer. A design procedure of this kind of absorber is presented. Based on the theory of characteristic mode, the underlying modal behaviors of the absorber structure are firstly analyzed to guide the design of multimode absorber. Two modes on the absorber structure are designed to resonate around 1.83 GHz and 4.28 GHz to cover the working frequency range. Simulation and measurement results show that the multimode absorber with a total thickness of 0.0883λ_L at the lowest operating frequency can achieve broadband microwave absorption with efficiency over 90% in the frequency band of 1.0 ∼ 4.5 GHz (127.3% in fractional bandwidth) through deliberate design. Both the simulated and experimental results demonstrate the validity of the proposed method and indicate that the method can be applied to other microwave and millimeter-wave regions.

Surface transformation multi-physics for controlling electromagnetic and acoustic waves simultaneously

A multi-physics null medium that performs as a perfect endoscope for both electromagnetic and acoustic waves is designed by transformation optics, which opens a new way to control electromagnetic and acoustic waves simultaneously. Surface transformation multi-physics, which is a novel graphical method to design multi-physics devices, is proposed based on the directional projecting feature of a multi-physics null medium. Many multi-physics devices, including beam shifters, scattering reduction, imaging devices and beam steering devices, for both electromagnetic and acoustic waves can be simply designed in a surface-corresponding manner. All devices designed by surface transformation multi-physics only need one homogeneous anisotropic medium (null medium) to realize, which can be approximately implemented by a brass plate array without any artificial sub-wavelength structures. Numerical simulations are given to verify the performances of the designed multi-physics devices made of brass plate array.

Multiphysical Digital Coding Metamaterials for Independent Control of Broadband Electromagnetic and Acoustic Waves with a Large Variety of Functions

Fabricating materials with customized characteristics for both electromagnetic (EM) and acoustic waves remain a significant challenge using the current technology, since the demand of multiphysical manipulation requires a variety of material parameters that are hard to satisfy in nature. However, the emergence of artificially structured materials provides a new degree of freedom to tailor the wave-matter interactions in dual physical domains at the subwavelength scale. Here, a bifunctional digital coding metamaterial (MM) is proposed to engineer the propagation behaviors of EM and acoustic waves simultaneously and independently. Four kinds of rigid pillars with various material properties are employed to serve as 1-bit reflection-type digital meta-atoms with antiphase responses in both frequency spectra, thus offering the opportunities for independent field control as desired. The MM demonstrates excellent performance of scattering manipulations from 5700 to 8000 Hz in the acoustic region and 5.80-6.15 GHz in the microwave region. The bifunctional MM is verified through full-wave simulations and experimental measurements with good agreement, which stands out as a powerful tool for related applications in the future.

Reconfigurable and optically transparent microwave absorbers based on deep eutectic solvent-gated graphene

Electrolytically tunable graphene “building blocks” for reconfigurable and optically transparent microwave surfaces and absorbers have been designed and fabricated by exploiting Deep Eutectic Solvents (DESs). DESs have been first explored as electrolytic and environmentally friendly media for tuning sheet resistance and Fermi level of graphene together with its microwave response (reflection, transmission and absorption). We consider the tunability of the reconfigurable surfaces in terms of transmittance, absorption and reflectance, respectively, over the X and Ku bands when the gate voltage is varied in the −1.4/+1.4 V range. The numerical simulations and experimental measurements also show the ability of the absorber, in the Salisbury screen configuration, to achieve near perfect absorption with a modulation of about 20%. These results could find applications in several technological fields, ranging from electromagnetic pollution to integrated multi-physical regulation systems, thereby helping the advance of the performance of microwave cloaking systems, stealth windows, frequency selective surfaces, modulators and polarizers.