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Thermal metamaterials have garnered significant attention for their potential to manipulate heat flow, leading to the development of various thermal metadevices such as thermal cloaks, concentrators, and rotators. However, the theoretical study of thermal metadevices with nonconformal geometry remains limited due to design and fabrication challenges. This letter proposes a method for designing and manufacturing nonconformal thermal metamaterials using the conformal discrete theory to simplify the anisotropic thermal conductivity tensors. The method involves 3D printing three thermal metadevices (a thermal cloak, concentrator, and rotator) with complex nonconformal geometry. Simulation and experimental results demonstrate the successful implementation of cloaking, concentrating, and rotating functionalities. Moreover, the thermal metadevices still maintained thermal functionality well under the condition of omnidirectional heat flow. This work provides guidance for the design and manufacture of nonconformal thermal metamaterials, as well as their potential applications in other fields such as electrics/magnetics, electromagnetics/optics, and acoustics. [ABSTRACT FROM AUTHOR]

The increasing needs for new types of computing lie in the requirements in harsh environments. In this study, the successful development of a non‐electrical neural network is presented that functions based on mechanical computing. By overcoming the challenges of low mechanical signal transmission efficiency and intricate layout design methodologies, a mechanical neural network based on bistable kirigami‐based mechanical metamaterials have designed. In preliminary tests, the system exhibits high reliability in recognizing handwritten digits and proves operable in low‐temperature environments. This work paves the way for a new, alternative computing system with broad applications in areas where electricity is not accessible. By integrating with the traditional electronic computers, the present system lays the foundation for a more diversified form of computing. [ABSTRACT FROM AUTHOR]

A modular design method is introduced to design an acoustic metamaterial based on nested Helmholtz resonators that target low‐frequency sound attenuation. The method combines a performance evaluation using finite element methods with structural evolution, and uses a genetic algorithm to optimize the acoustic metamaterial to attain the desired properties. Both the simulated and experimental results demonstrate the noise attenuation property of the optimized acoustic metamaterials. The modular design method proposed by this study may potentially design acoustic metamaterials for practical sound attenuation applications in industries by considering different environments and constraints. [ABSTRACT FROM AUTHOR]

Highlights • Graphene composite was used to prepared multilayer structure for microwave absorbing. • The multilayer absorber possesses a gradient index of characteristic impedance. • Characteristic impedance was tailored by graphene content and rod width of unit cell. • The seven-layer absorber achieved an absorption above 90% in 4.5–40 GHz. • 3D printing process was used to fabricate the complex structure. Abstract An ultra-broadband electromagnetic (EM) absorber composed of composite metamaterials was designed, fabricated and characterized. Polylactic-acid/reduced graphene oxide (PLA/RGO) composites with different amounts of RGO were prepared as a primary material collection. To provide good impedance matching and efficient wave attenuation, the multilayer absorbers were designed with a gradient index (GRIN) of characteristic impedance by manipulating the RGO content and the geometric parameters of the unit cell. The absorbers with different numbers of layers were fabricated by a material extrusion process, and then the reflection loss (RL) of the prepared samples was measured. Results showed that the methodology for designing a metamaterial absorber with gradient impedance and fabricating through a 3D printing process was effective in producing ultra-broadband absorbers. The seven-layer absorber achieved an absorption above 90% in a broad bandwidth of 4.5–40 GHz. This work could provide inspiration for upgrading the performance of some conventional absorbing composites through a rational design of the composite proportion and structure. [ABSTRACT FROM AUTHOR]

A gradient-refractive-index radar absorbing structure(GRINRAS) for stealth aircraft is proposed in this paper. It is a layered shell composed of a gradient-refractive-index (GRIN) refractor, an absorber and a reflector. The GRIN refractor consists of the isotropic non-resonant woodpile metamaterials, which was designed according to the permittivity distribution equation of the electromagnetic(EM) black hole to bend and match the waves from the air to the radar absorbing structure. The absorber dissipates the EM waves and transforms them into the heat energy. The reflector reflects the EM waves to the absorber and prevents them from entering the inner space of the structure. A ring and a board GRINRAS were designed, and then fabricated by the three-dimensional (3D) printing process of stereolithography (SL). Simulation and experimental results show that the GRINRASes can control the wave propagation and their absorption capacity is better than −10 dB in the broadband of 12–18 GHz. The GRIN refractor and the absorber have almost equal contributions to the absorption capability. This is the first radar absorbing composite structure composed of the gradient 3D metamaterials. It demonstrates the feasibility of using the metamaterials and 3D printing technology in the innovative radar absorbing structure (RAS) of the stealth aircraft. [ABSTRACT FROM AUTHOR]