At present, functional fabrics are very popular among consumers. When people mention this kind of fabric, the first thing that people think of is moisture absorption and quick drying. Maybe in the near future, functional fabrics will add a new feature: invisibility.
Sudden appearance and sudden disappearance may not be difficult to achieve in a movie with the help of special effects, but in reality, this kind of thing is unbelievable. Not long ago, the research results completed by Professor Chen’s team from the Department of Information and Telecommunications of Zhejiang University on “Invisibility of large objects in the visible light band – the mechanism of electromagnetic wave ‘invisibility cloak'” were published in the authoritative scientific journal “Nature Communications”.
Control the light path to achieve invisibility
The “invisibility cloak” developed by the team is currently a hexagonal column with each side about 5 centimeters, surrounded by ordinary organic glass, and the core “invisibility channel” is composed of special optical glass.
This “invisibility cloak” is different from the invisibility principle of the stealth aircraft we are familiar with in reality. Dr. Zheng told reporters that it can “control” the path of light – once it encounters a cloaking device, the light will naturally detour, and people will not be able to see objects in the device area.
Traditional stealth aircraft use special coatings and fuselage structures to prevent the reflection of radar waves to achieve the purpose of invisibility. The results of Professor Chen’s team have greatly reduced the design and implementation difficulty of the invisibility cloak. This invisibility cloak can not only avoid being Detected by radar, it can also escape the search of the naked eye.
Dr. Zheng explained: “To be invisible, the light entering the invisibility cloak must travel faster than the external light.”
In the experiment of this research group, a kitten squats in a hexagonal cloaking device. At a certain angle, the light can directly bypass the kitten and return to the original path, resulting in the kitten’s “invisibility”. “The effect. In order to explore the adaptability of the invisibility cloak to different life environments, the research team also developed a set of devices suitable for invisibility in water: when a goldfish swims into this “invisibility cloak”, the objects behind it can still be seen clearly.
“This means that the stealth device can not only hide large objects and creatures like cats and fish, but can also move with the stealth device, and the stealth effect will not be affected.” Professor Chen said.
Professor Chen said that in order to study “invisibility”, we must first understand why objects become “visible”: when electromagnetic waves are irradiated onto an object, they will be scattered on the object. The scattered electromagnetic waves are received by “sensors” such as the human eye, and the presence of objects there can be identified.
The new development this time is how to make objects disappear before the naked eye. The research team proposed a design method for polygonal invisibility cloaks in the visible light band. Through the method of uniform linear optical transformation, the parameters of each part of the invisibility cloak were designed and simplified, which played a role in promoting the invisibility cloak from theory to practicality.
“The human eye is not sensitive to the phase and slight delay of light.” Professor Chen said that by further simplifying the theoretical system, “stealth devices can use more readily available materials and do not require nanoscale craftsmanship, which reduces the cost of invisibility cloaks.” Difficulty in design and implementation ”
The reporter learned that as early as 2012, Professor Chen’s research group developed a set of cylindrical cloaking devices using a naturally occurring birefringent crystal to make objects as thick as a chopstick invisible. In 2013, the research team conducted a comprehensive evaluation and design of the implementation plan of the invisibility device, and finally selected a glass that can be produced on a large scale in industry as the material of the invisibility cloak, expanding the “size” of the invisibility cloak to a diameter of It is larger than a meter and can be invisible under any polarized natural light.
At present, this subject has achieved the stealth effect at a specific angle. Professor Chen said that the next step of research and development will focus on improving the stealth performance, such as increasing the stealth angle and reducing the weight of the device. After improving to a certain extent, this product is expected to play a role in the fields of security, entertainment and surveillance.
Foreign countries: Has quantum invisibility been successful?
In fact, “invisibility cloaks” have endless charm all over the world, attracting scientists to continue to explore. As early as 2012, according to the British “Daily Mail” report, the head of a Canadian biotechnology company admitted to the media for the first time They have long developed invisible fabrics. The surface of the fabric can form a refraction projection, and people hiding behind it can completely integrate with the surrounding scenery without being discovered. This research was supported by the U.S. Department of Defense. At present, invisible fabrics have been used in the Canadian and American armies to make invisible camouflage clothing.
People generally understand that invisibility cloaks require light to bypass the central invisibility area, and the parameters will be more stringent than “carpet-type invisibility devices.” If visible light invisibility is to have good applications, it must be capable of wide-band, omni-directional, and omni-directional capabilities. Polarizing work makes it very difficult to achieve this ultimate goal.
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