Squid are the ultimate camouflage artists, blending almost flawlessly with their backgrounds so that unsuspecting prey can't detect them. Using a protein that's key to this process, scientists have designed "invisibility stickers" that could one day help soldiers disguise themselves, even when sought by enemies with tough-to-fool infrared cameras. The researchers will present their work today at the 249th National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world's largest scientific society, is holding the meeting here through Thursday. It features nearly 11,000 presentations on a wide range of science topics. Take a look at a brand-new video on the research:
"Soldiers wear uniforms with the familiar green and brown camouflage patterns to blend into foliage during the day, but under low light and at night, they're still vulnerable to infrared detection," explains Alon Gorodetsky, Ph.D. "We've developed stickers for use as a thin, flexible layer of camo with the potential to take on a pattern that will better match the soldiers' infrared reflectance to their background and hide them from active infrared visualization." To work toward this effect, Gorodetsky of the University of California at Irvine (UCI) turned to squid skin for inspiration. Squid skin features unusual cells known as iridocytes, which contain layers or platelets composed of a protein called reflectin. The animal uses a biochemical cascade to change the thickness of the layers and their spacing. This in turn affects how the cells reflect light and thus, the skin's coloration. Gorodetsky's group coaxed bacteria to produce reflectin and then coated a hard substrate with the protein. To induce structural -- and light-reflecting -- changes just like those of iridocytes, the film needed some kind of trigger. An initial search revealed that acetic acid vapors could cause the film to swell and disappear when viewed with an infrared camera. But these conditions won't work for soldiers in the field. "What we were doing was the equivalent of bathing the film in acetic acid vapors -- essentially exposing it to concentrated vinegar," Gorodetsky says. "That is not practical for real-life use." Now Gorodetsky has fabricated reflectin films on conformable polymer substrates, effectively sticky tape one might find in any household. This tape can adhere to a range of surfaces including cloth uniforms, and its appearance under an infrared camera can be changed by stretching, a mechanical trigger that might more realistically be used in military operations. Although the technology isn't ready for field use just yet, he envisions soldiers or security personnel could one day carry in their packs a roll of invisibility stickers that they could cover their uniforms with as needed. "We're going after something that's inexpensive and completely disposable," he says. "You take out this protein-coated tape, you use it quickly to make an appropriate camouflage pattern on the fly, then you take it off and throw it away." Gorodetsky says that some major challenges remain. The team will have to figure out how to increase the brightness of the stickers and get multiple stickers to respond in the same way at the same time, as part of an adaptive camouflage system. He's also working on ways to make the stickers more versatile. The current version reflects near-infrared light. Gorodetsky's team is continuing to tweak the materials, so variants of the stickers could also work at mid- and far-infrared wavelengths. These could have applications for thwarting thermal infrared imaging. They also could have uses outside the military -- for example, in clothing that can selectively trap or release body heat to keep people comfortable in different environments. Moreover, in collaboration with Francesco Tombola, Ph.D., and Lisa Flanagan, Ph.D., from the UCI School of Medicine, Gorodetsky's lab has shown that reflectin supports cell growth. This could have implications for making new types of bioelectronic devices and even growing "living" semi-artificial squid skin. Title Infrared invisibility stickers inspired by cephalopods Abstract The skin structure of cephalopods endows them with remarkable dynamic camouflage capabilities. Consequently, much research effort has focused on understanding and emulating these animals' color changing abilities in the visible region of the electromagnetic spectrum. In contrast, despite the importance of infrared signaling and detection for many industrial and military applications, few studies have attempted to translate the principles underlying cephalopod adaptive coloration to infrared camouflage. We have drawn inspiration from nanostructures implicated in cephalopods' camouflage abilities and developed strategies for the self-assembly of unique cephalopod structural proteins into dynamically tunable biomimetic camouflage coatings on both transparent and flexible substrates. Our substrates can adhere to arbitrary surfaces, and their reflectance can be reversibly modulated from the visible to the near-infrared regions of the electromagnetic spectrum with both chemical and mechanical stimuli. Thus, we can endow common objects with any shape or form factor with tunable camouflage capabilities. Our work represents a key step toward the development of wearable biomimetic color and shapeshifting technologies for stealth applications.
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"Soldiers wear uniforms with the familiar green and brown camouflage patterns to blend into foliage during the day, but under low light and at night, they're still vulnerable to infrared detection," explains Alon Gorodetsky, Ph.D. "We've developed stickers for use as a thin, flexible layer of camo with the potential to take on a pattern that will better match the soldiers' infrared reflectance to their background and hide them from active infrared visualization." To work toward this effect, Gorodetsky of the University of California at Irvine (UCI) turned to squid skin for inspiration. Squid skin features unusual cells known as iridocytes, which contain layers or platelets composed of a protein called reflectin. The animal uses a biochemical cascade to change the thickness of the layers and their spacing. This in turn affects how the cells reflect light and thus, the skin's coloration. Gorodetsky's group coaxed bacteria to produce reflectin and then coated a hard substrate with the protein. To induce structural -- and light-reflecting -- changes just like those of iridocytes, the film needed some kind of trigger. An initial search revealed that acetic acid vapors could cause the film to swell and disappear when viewed with an infrared camera. But these conditions won't work for soldiers in the field. "What we were doing was the equivalent of bathing the film in acetic acid vapors -- essentially exposing it to concentrated vinegar," Gorodetsky says. "That is not practical for real-life use." Now Gorodetsky has fabricated reflectin films on conformable polymer substrates, effectively sticky tape one might find in any household. This tape can adhere to a range of surfaces including cloth uniforms, and its appearance under an infrared camera can be changed by stretching, a mechanical trigger that might more realistically be used in military operations. Although the technology isn't ready for field use just yet, he envisions soldiers or security personnel could one day carry in their packs a roll of invisibility stickers that they could cover their uniforms with as needed. "We're going after something that's inexpensive and completely disposable," he says. "You take out this protein-coated tape, you use it quickly to make an appropriate camouflage pattern on the fly, then you take it off and throw it away." Gorodetsky says that some major challenges remain. The team will have to figure out how to increase the brightness of the stickers and get multiple stickers to respond in the same way at the same time, as part of an adaptive camouflage system. He's also working on ways to make the stickers more versatile. The current version reflects near-infrared light. Gorodetsky's team is continuing to tweak the materials, so variants of the stickers could also work at mid- and far-infrared wavelengths. These could have applications for thwarting thermal infrared imaging. They also could have uses outside the military -- for example, in clothing that can selectively trap or release body heat to keep people comfortable in different environments. Moreover, in collaboration with Francesco Tombola, Ph.D., and Lisa Flanagan, Ph.D., from the UCI School of Medicine, Gorodetsky's lab has shown that reflectin supports cell growth. This could have implications for making new types of bioelectronic devices and even growing "living" semi-artificial squid skin. Title Infrared invisibility stickers inspired by cephalopods Abstract The skin structure of cephalopods endows them with remarkable dynamic camouflage capabilities. Consequently, much research effort has focused on understanding and emulating these animals' color changing abilities in the visible region of the electromagnetic spectrum. In contrast, despite the importance of infrared signaling and detection for many industrial and military applications, few studies have attempted to translate the principles underlying cephalopod adaptive coloration to infrared camouflage. We have drawn inspiration from nanostructures implicated in cephalopods' camouflage abilities and developed strategies for the self-assembly of unique cephalopod structural proteins into dynamically tunable biomimetic camouflage coatings on both transparent and flexible substrates. Our substrates can adhere to arbitrary surfaces, and their reflectance can be reversibly modulated from the visible to the near-infrared regions of the electromagnetic spectrum with both chemical and mechanical stimuli. Thus, we can endow common objects with any shape or form factor with tunable camouflage capabilities. Our work represents a key step toward the development of wearable biomimetic color and shapeshifting technologies for stealth applications.
Graphene-PMMA heterostructure. (click on image to enlarge) Lambin and his colleagues demonstrated that the conductivity of several graphene layers adds arithmetically when thin polymer spacers separate them. Maximum microwave absorption in the Ka communications band between 26.5 and 40 GHz is achieved with six graphene planes separated by layers of poly-methyl methacrylate (PMMA), a transparent plastic also known as acrylic glass. Multilayer microwave barriers constructed by researchers based at Joensuu University in Finland start with a first graphene layer deposited on a copper foil substrate by chemical vapour deposition. This layer is then covered with a 600-800 nanometre PMMA spacer obtained by spin coating, following which the copper is etched away with ferric chloride, and the graphene/PMMA heterostructure transferred to a quartz substrate. The procedure is repeated until the required number of graphene layers is reached. A single layer of graphene can absorb up to 25% of incident microwave radiation, which is a lot for a one atom-thick material. With a multilayer graphene/PMMA arrangement, the absorption rises to 50%. This can be understood by analysing the transmission and reflection of a plane wave at the interface between two dielectric media, when the interface contains an infinitesimally thin conducting layer. In this way, the researchers were able to optimise their graphene-PMMA structures for maximum absorption, with the results confirmed by rigorous electromagnetic testing. Moreover, notes Lambin, there is the interface between the shielding material and air to consider... “We have found that the static conductivity of graphene is close to the value which relates the magnetic and electric fields in any electromagnetic radiation propagating in air. Thanks to this happy coincidence, graphene is an ideal material for absorbing radio waves, thus protecting sensitive electronic devices.” The idea of using graphene/dielectric multilayers for electromagnetic wave absorption is not new. For example, a few years ago there was published a theoretical proposal for an ultra-broadband absorbing multilayer operating in the terahertz region, far higher than the Ka communications band discussed here. A multilayer terahertz shield would be a complex affair, with its graphene planes patterned at the micron scale in order to generate surface plasmon resonances – oscillations in the electrons which propagate along the interfaces between different material layers. The microwave barrier devised by the Graphene Flagship team is relatively simple by comparison, with advantages in terms of fabrication and scalability. In real-world applications, graphene/PMMA multilayers require protection against external chemical and mechanical agents. The quartz substrate should therefore face outwards, and be combined with a softer material. The choice and thickness of over-layer material used are additional parameters that will influence the microwave absorbance. Process scalability will increase considerably if stacks of few-layer graphene are deposited in one step, instead of piling up graphene monolayers with their PMMA shuttles. In addition, any process that raises the conductivity of graphene will reduce the number of atomic planes required to maximise the level of microwave absorption.
The new CVD-reactor for the deposition of graphene at Fraunhofer IAF. In future, a cost-efficient and simplified technology will make the deposition and the transfer of graphene onto aluminum-nitride-based bandpass filters possible. Industry compatible graphene deposition technologies As one of the partners in the "Graphene Flagship", the largest funding initiative in the history of the European Union, Fraunhofer IAF is working on the development of an efficient technology for graphene deposition and graphene transfer onto aluminum nitride. As surprising as it may be to be able to manufacture and process graphene as atomically thin material at all – it is just as difficult to do so on an industrial scale. Many of the possible applications of graphene have not yet been successful since the production of the material is still too complex. Hence, the development of economical manufacturing and processing technologies is essential for the use of the outstanding theoretical properties of graphene in practice. A promising approach for the realization of graphene deposition on substrate sizes typical for the semiconductor industry can be found in chemical vapor deposition. Here, a catalyst surface such as copper is heated to nearly 1000 °C until gas containing carbon is broken down on the hot surface and reorganized into graphene. In future, this method is supposed to be further developed into a technology compatible for industry applications, to directly integrate graphene into existing aluminum-niride-based bandpass filters.