Recently, the research team led by Jia Zhu from the College of Engineering and Applied Sciences, Nanjing University, successfully designed and fabricated a skin-like metamaterial with a highly selective spectrum based on Au nanoparticles assembled hollow pillars. This material is ideal for visible and infrared dual-band compatible camouflage at night or in outer space. They have published a research paper titled “Self-assemble skin-like metamaterials for dual-band camouflage” on Science Advances. (https://www.science.org/doi/full/10.1126/sciadv.adl1896)
The abstract of the paper is as follows:
Skin-like soft optical metamaterials with broadband modulation have been long pursued for practical applications, such as cloaking, and camouflage. Here, we propose a skin-like metamaterial for dual-band camouflage based on unique Au nanoparticles assembled hollow pillars (NPAHP), that are implemented by the bottom-up template-assisted self-assembly processes. This dual-band camouflage realizes simultaneously high visible absorptivity (~0.947), and low infrared emissivity (~0.074/0.045 for mid-/long-wavelength infrared bands), ideal for visible and infrared dual-band camouflage at night or in outer space. In addition, this self-assembled metamaterial, with a micrometer thickness and periodic through-holes, demonstrates superior skin-like attachability and permeability, allowing close attachment to a wide range of surfaces including the human body. Last but not least, benefiting from the extremely low infrared emissivity, the skin-like metamaterial exhibits excellent high-temperature camouflage performance, with radiation temperature reduction from 678 to 353 kelvin. This work provides a new paradigm for skin-like metamaterials with flexible multi-band modulation for multiple application scenarios.
Fig. 1. Schematic and mechanism of the NPAHP-based skin-like metamaterial for dual-band camouflage. (A) Schematic of the NPAHP-based skin-like metamaterial attached to the human body surface (Exposure: uncovered part; Camouflage: covered with NPAHP-based skin-like metamaterial) for the visible and infrared dual-band camouflage. (B) For the LWIR band, nanoscale structures are negligible, the optical property is mainly dependent on the filling ratio of Au (f) by effective medium theory. (C) For the MWIR band, the multiple scattering effect of Au pillars (hundreds of nanometers in scale) dominates the optical property. (D) For the visible band, the LSPR effect of Au NPs (tens of nanometers in scale) plays the dominant role.
Fig. 2. Simulated absorptivity/emissivity spectra of the NPAHP-based skin-like metamaterial with different structural designs. (A) Dependence of the absorptivity/emissivity on the Au NPs size distribution in the visible band. (B) Dependence of the absorptivity/emissivity on the D and H of Au hollow pillars in the MWIR band. (C) Dependence of the absorptivity/emissivity on the Au ratio (f) in the LWIR band. (D) Full-wave electromagnetic simulation for three representative structure models over 0.3-18 μm.
Fig. 3. Fabrication and characterization of the NPAHP-based skin-like metamaterial. (A to C) Optical photographs (left) and infrared photographs (right) for NPAHP-50 (A), NPAHP-120 (B), and NPAHP-390 (C). (D to F) Top view images of SEM for NPAHP-50 (D), NPAHP-120 (E), and NPAHP-390 (F). (G to I) Cross-section view images of SEM for NPAHP-50 (G), NPAHP-120 (H), and NPAHP-390 (I). (J) Experimental absorption spectra for NPHAP-50/120/390, show that NPAHP-120 exhibits the best dual-band camouflage performance.
Fig. 4. NPAHP-120-based skin-like metamaterial for dual-band camouflage, demonstrating good attachability and wearable potential. (A and B) Optical and infrared photographs of the NPAHP-120-based film attached to painted stainless-steel polyhedra. (C and D) Optical and infrared photographs of a spherical object uncovered (C)/covered (D) with the NPAHP-120-based film. (E) Water vapor transmission tests of the open state, the NPAHP-120-based film, MXene, and Cu foil. (F) Optical and infrared photographs of the NPAHP-120-based film attached to a finger.
Fig. 5. Demonstration of high-temperature camouflage performance of the NPAHP-120-based skin-like metamaterial. (A and B) Dependence of Pdet (A), and Tr (B) on T1 and ε1. (C) Optical photograph of the NPAHP-120-based camouflage film. (D) Infrared photographs of the hot plate covered with NPAHP-120-based camouflage film at different set temperatures (373, 473, 573, 673 K). (E) Detected radiation temperature of the hot plate (covered and uncovered with NPAHP-120-based film), and surroundings at different temperatures. (F) The unchanged experimental absorption spectra of the NPAHP-120-based camouflage film after air annealing at 673 K for 1 h, which suggests its good stability at high temperature. (G and H) Optical (G) and infrared photograph (H) of the aircraft engine models covered (①) and uncovered (②) with NPAHP-120-based camouflage film.
Source: College of Engineering and Applied Sciences
Correspondent: Xu Ning
