Selective thermal emission and infrared camouflage based on layered media

Infrared camouflage based on artificial thermal metasurfaces has recently attracted significant attention.By eliminating thermal radiation differences between the object and the background,it is possible to hide a given object from infrared detection.Infrared camouflage is an important element that increases the survivability of aircraft and missiles,by reducing target susceptibility to infrared guided threats.Herein,a simple and practicable design is theoretically presented based on a multilayer film for infrared stealth,with distinctive advantages of scalability,flexible fabrication,and structural simplicity.The multilayer medium consists of silicon substrate,carbon layer and zinc sulfide film,the optical properties of which are determined by transfer matrix method.By locally changing the thickness of the coating film,the spatial tunability and continuity in thermal emission are demonstrated.A continuous change of emissive power is further obtained and consequently implemented to achieve thermal camouflage functionality.In addition,other functionalities,like thermal illusion and thermal coding,are demonstrated by thickness-engineered multilayer films.

Study on the Camouflage-Protective and Dyeing Properties of Natural Dye Indigo

There are two major camouflage protections in modern military tactics:UV-protection and near infrared camouflage.However,not all natural and composite dyestuffs provide the mentioned properties.In this study,the cotton fabric was dyed with natural indigo and the natural indigo dyeing process was optimized.Green leaves were chosen as the simulating object,and the camouflage properties of the dyed cotton fabric were evaluated.It was observed that the dyed cotton fabric had good UV-protection and near-infrared camouflage properties.The UV-protection effect was strongly dependent on the absorption characteristics of natural indigo for UV radiation.The near infrared camouflage effect was mainly dependent on the reflection spectrum characteristics of natural indigo in the near infrared waveband.

Recent Progress of Bio-inspired Camouflage Materials:From Visible to Infrared Range

The adaptability of biological organisms to the environment is reflected in many aspects,especially in their camouflage of appearance.Inspired by biological camouflage strategies,a number of adaptive camouflage materials and devices have been developed to protect soldiers,vehicles,or equipment in the military.Today,the need for adaptive camouflage extends into people’s lives,whose privacy and information security need to be protected in the era of big data.Herein,a review is provided on the recent advancements of adaptive camouflage from the perspective of biological organisms and bio-inspired materials.Firstly,according to different biological mechanisms,we review the typical organisms that use pigmentary color,structural color,and morphological variation for adaptive camouflage,as well as those combine these strategies.Then,we provide an up-to-date review on recent developments in bio-inspired adaptive camouflage materials and devices with an emphasis on visible,infrared,and multispectral camouflage.At last,this review concludes the challenges and prospects for the future development of adaptive camouflage materials.It is noteworthy that there is never the best camouflage.To counter advanced detection techniques,it is necessary to unremittingly develop new materials and technologies to meet the increasing need for adaptive camouflage.

Foam-gelcasting preparation of porous Si C ceramic for high-temperature thermal insulation and infrared stealth

Porous SiC ceramics(PSCs)are promising lightweight and efficient thermal insulators that can evade infrared detection by reducing the surface temperature of the protected object,which plays a crucial role in the development of new military equipment.However,the controllable synthesis of PSCs with both hierarchical pore structure and thermal/mechanical stability remains challenging.In this work,such PSCs were prepared by a facile foam-gelcasting/solid-state reaction method,using silicon powders and glucose-derived carbon as starting materials.The favorable dispersibility and wettability of hydrophilic carbon microspheres and the in-situ formed SiC guarantee the highly porous structure(92.8%porosity),comparable bulk density(0.20 g·cm^(-3))and reasonable mechanical property of the product.The designed PSCs performed outstanding high-temperature performance,especially thermal insulation in both oxidizing and inert atmospheres.More importantly,the composite architecture of PSCs and low emissivity layer(Al foil)exhibited desirable infrared stealth property(at a temperature up to 1100℃),significantly extending the operating temperature range of thermal camouflage material.The unique combination of excellent properties would make PSCs a potential candidate material for future thermal protection and infrared stealth applications in an extreme environment.

Functional photonic structures for external interaction with flexible/ wearable devices

In addition to vital functions,more subsidiary functions are being expected from wearable devices.The wearable technology thus far has achieved the ability to maintain homeostasis by continuously monitoring physiological signals.The quality of life improves if,through further developments of wearable devices to detect,announce,and even control unperceptive or noxious signals from the environment.Soft materials based on photonic engineering can fulfil the abovementioned functions.Due to the flexibility and zero-power operation of such materials,they can be applied to conventional wearables without affecting existing functions.The achievements to freely tailoring a broad range of electromagnetic waves have encouraged the development of wearable systems for independent recognition/manipulation of light,pollution,chemicals,viruses and heat.Herein,the role that photonic engineering on a flexible platform plays in detecting or reacting to environmental changes is reviewed in terms of material selection,structural design,and regulation mechanisms from the ultraviolet to infrared spectral regions.Moreover,issues emerging with the evolution of the wearable technology,such as Joule heating,battery durability,and user privacy,and the potential solution strategies are discussed.This article provides a systematic review of current progress in wearable devices based on photonic structures as well as an overview of possible ubiquitous advances and their applications,providing diachronic perspectives and future outlook on the rapidly growing research field of wearable technology.