Magnetoelastic soliton

For the stationary solitary magnetoelastic waves (magnetoelastic solitons) propagation along the equilibrium direetions of ferro-and antiferromagnetic vectors M and L in uniaxial crystals, exact solutions of coupled magnetization motion equations (Landau-Lifshitz) and elastic equations are obtained. The types of oscillations depending on the propagating velocity are determined. It is shown that velocity spectrum in the vicinity of sound velocity has a gap of magnetoelastic origin where oscillation character changes. Changing of oscillation type can also take place near the maximum propagating velocity of the magnetoelastic soliton.     

Organic Multiferroic Magnetoelastic Complexes

The design of crystal structures aids the discovery of interesting physical phenomena in organic crystals. In this work, the optimization of the coronene–tetracyanoquinodimethane (TCNQ) structure generates non-degenerate energy levels of spin-up and spin-down electrons after charge transfer, producing spontaneous spin polarization, leading to pronounced ferromagnetism. The deformed crystal lattice can significantly affect the saturation magnetization of organic ferromagnets to present a remarkable magnetoelastic coupling. Furthermore, the magnetic-field-induced lattice shrinkage of the ferromagnetic crystals supports a spin–lattice-interaction-dependent magnetoelastic coupling. This concept of organic magnetoelastic coupling will pave the way for the rapid mechanical control of spin polarization in organic multiferroic magnetoelastic materials.     

Electromagnetic metamaterials

This paper proposes a review of electromagnetic metamaterials based on the idea that these are composite materials, their properties depending of the type and dimensions of the structural elements as well as the dimensions of unit cell. From the multitude of structural elements, only few that could present negative permittivity and negative or very high permeability in the range of radio and microwave frequency were chosen. The method of determination for the constitutive parameters (μ_eff and ?_eff) of metamaterials based on the S parameters or transmission and reflection coefficients is presented. Moreover, some applications of metamaterials are described, the attention being focused on perfect lenses and novel structures, namely conical Swiss rolls, electromagnetic cloaks and sensors for nondestructive evaluation of materials. Given that the spatial resolution of these sensors can be substantially improved in comparison to classical sensors, the metamaterial lenses are used for the manipulation of evanescent waves.     

Reconfigurable photonic metamaterials

We introduce mechanically reconfigurable photonic metamaterials (RPMs) as a flexible platform for realizing metamaterial devices with reversible and large-range tunable characteristics in the optical part of the spectrum. Here we illustrate this concept for a temperature-driven RPM exhibiting reversible relative transmission changes of up to 50%.     

Thermal camouflaging metamaterials

Thermal camouflage technologies, which aim at blending the infrared (IR) signature of targets into the background to counter the IR detection, have witnessed increasing development. To achieve thermal camouflage, the rule of thumb is to balance the thermal radiation between the target and the background, and the corresponding conductive strategy is to tune the local temperature field while the radiative strategy is to tune the local emissivity. Following these two basic strategies, the thermal metamaterials and wavelength-selective emissivity engineering to achieve thermal camouflage are first introduced. Then the more advanced dynamic strategies are reviewed that can adapt to the varying environment under the external stimuli, like electricity, light, strain, chemical, wetting, temperature, etc. Particularly the phase-changing and bioinspired materials are presented and reviewed. Finally, critical considerations on the challenges and opportunities of next-generation thermal camouflage technologies are elaborated and four future directions are cast, including temperature-responsive emissivity engineering, soft materials, multispectral camouflage, and detection-feedback system. Overall, a detailed introduction to the working principle, the state-of-the-art progress, and the critical thinking on the future development on thermal camouflage technologies are presented.     

Active nanoplasmonic metamaterials

Optical metamaterials and nanoplasmonics bridge the gap between conventional optics and the nanoworld. Exciting and technologically important capabilities range from subwavelength focusing and stopped light to invisibility cloaking, with applications across science and engineering from biophotonics to nanocircuitry. A problem that has hampered practical implementations have been dissipative metal losses, but the efficient use of optical gain has been shown to compensate these and to allow for loss-free operation, amplification and nanoscopic lasing. Here, we review recent and ongoing progress in the realm of active, gain-enhanced nanoplasmonic metamaterials. On introducing and expounding the underlying theoretical concepts of the complex interaction between plasmons and gain media, we examine the experimental efforts in areas such as nanoplasmonic and metamaterial lasers. We underscore important current trends that may lead to improved active imaging, ultrafast nonlinearities on the nanoscale or cavity-free lasing in the stopped-light regime.     

Magnetoelastic waves in yttrium orthoferrite plates

We have experimentally studied surface magnetoelastic waves in yttrium orthoferrite plates and discovered the phenomenon of energy pumping from the initial frequency (～1 kHz) to higher harmonics (～12.5 kHz).     

Magnetoelastic behavior of glass-covered amorphous ferromagneticmicrowire

Particular aspects concerning the magnetoelastic behavior of an Fe-rich glass-covered amorphous ferromagnetic microwire (diameter about 20 μm) are reported in both the as-prepared state and after various heat treatments. The main feature of such behavior is that related with the bistable behavior exhibited by the microwire. The magnetization process takes place by a single and large Barkhausen jump at a given applied field. For the as-prepared material, the value of this switching field (H*≈112 Am^-1) is about one order of magnitude larger than that reported for Fe-rich amorphous wires with a diameter of about 125 μm (H*≈8 Am^-1). The effect of the thermal treatment as well as the stress dependence of H* for as-obtained and treated microwire are also reported and discussed in terms of the stress distribution within the microwire     

Shape memory mechanical metamaterials

Shape memory materials can maintain temporary shapes without external constraints and revert to their permanent shape upon exposure to an external stimulus, such as heat, light, or moisture. This behavior, often named the shape memory effect, has led to the use of shape memory materials in a variety of applications including deployable aerospace structures, biomedical devices, flexible electronics, and untethered soft robots. Most thermally triggered reconfigurable metamaterials using shape memory polymers require a laborious process of thermomechanical programming at high temperature, above their transition value, to maintain a temporary shape. In this paper, we utilize two 3D-printable polymeric materials that do not rely upon their shape memory effect to generate robust shape memory response in a set of mechanical metamaterials. The enabling characteristic is the mismatch of the temperature-dependent moduli of the constitutive materials leveraged in rationally interconnected reconfigurable units, and their hallmark is the freedom to forego the complex programming process of typical shape memory polymers. Their shape reconfiguration and rapid recovery are solely governed by mechanical loading and temperature change, leading to sequentially programmable multistability, hyperelasticity, giant thermal deformations, and shape memory capacity. Theoretical models, numerical simulations, and thermomechanical experiments are performed to demonstrate their functionality, stability transition mechanism, and potential applications.     

负泊松比超材料和结构

负泊松比超材料和结构具有优异的抗剪切性能、抗冲击性能、抗断裂性能、吸能隔振、渗透率可变性能、曲面同向性等力学性能,在航空航天、航海、机械自动化、生物医疗、国防军事、纺织工业等领域具有广泛的应用前景.本文从负泊松比超材料和结构的变形机理出发,综述了内凹结构、旋转刚体结构、手性/反手性结构、纤维/节点结构、折纸结构、褶皱结构、弯曲-诱导结构、螺旋纱线结构等物理模型,这些模型具有广泛的适用性,可运用于轻质夹层板、流体输送、纱线等工程应用,有利于改善结构的使用性能.最后,本文对负泊松比超材料和结构未来的挑战和在航空航天、军事等领域的应用进行了展望,指出利用负泊松比逆转了正泊松比对单轴应力引起的体积和面积变化的补偿效应可有效改善发动机叶片、深空天线以及汽车吸能盒等关键构件的抗冲击性能等,以期为负泊松比超材料和结构的推广应用提供参考.     

3D optomechanical metamaterials

Ideally, many materials should have a “knob” that allows for changing its properties at will, including the possibility to flip the sign of its behavior. This “knob” could be used to continuously tune the properties or in the sense of a digital switch. Such extreme level of stimulus–responsiveness has come into reach with recently increased possibilities of manufacturing complex rationally designed artificial materials called metamaterials on the micrometer scale. Here, we present mechanical metamaterials composed of liquid–crystal elastomers, whose director field is arranged into a designed complex three-dimensional (3D) pattern during the 3D laser printing process. External light from a blue LED, with intensities in the range of 10–30 W/cm², serves as the stimulus. In the first example, we repeatedly flip the sign of the Poisson’s ratio of an achiral architecture within classical elasticity. In the second example, we flip the sign of the twist per strain in a chiral metamaterial beyond classical elasticity. The presented examples overcome major limitations in responsive mechanical metamaterials and we foresee many possible three-dimensional responsive micro-architectures manufactured along these lines.