Life in American Immigration: When a pair of chopsticks is placed in a cup of water, the submerged part bends slightly, but the parts above and below the water surface remain aligned in the direction of the tilt; if a pair of chopsticks is placed in a "negative refractive index" metamaterial, you will see the chopsticks in the metamaterial appear completely "broken," meaning the angle of inclination is opposite to that of the chopsticks in the air... this is the magic of metamaterials. Yesterday, Chinese-American scientist and professor of physics at the University of Arizona, Xin Hao, visited the Science Hall and introduced his latest research achievements in the field of metamaterials at the Shanghai Association for Science and Technology Forum—successfully developing active metamaterials in the laboratory, overcoming key technical barriers to the "invisible cloak."
The so-called metamaterials are synthetic materials that possess properties not found in nature. Among them, electromagnetic metamaterials can control the propagation of light (electromagnetic waves) in unusual and effective ways, allowing for the artificial design of arbitrary refractive indices for light, including negative and zero refractive indices. Since the beginning of this century, metamaterials have become a hot topic in materials science, with many research results leading people to believe that the "invisible cloak" described in novels such as "Harry Potter" will become a reality.
Until last year, the most advanced electromagnetic metamaterials in laboratories still had three major defects: first, they were only suitable for narrow or even single frequencies; for example, under red light, the metamaterial-made "invisible cloak" could make light bypass the object it enveloped, but under another frequency of blue light, the object would reveal itself; second, the material had high losses, with most of the light incident on the metamaterial being absorbed, failing to achieve the invisibility effect; third, the metamaterials had complex three-dimensional structures, making them difficult to manufacture.
In response to the first two defects, the research team led by Xin Hao recently discovered a new method: integrating battery-powered tunnel diodes and micro-nano manufacturing technology into the design, they developed an active negative refractive index material. It possesses the ability to negatively refract light without reducing the energy of the light; instead, it enhances the energy of the light with the support of an external power source. "This is the first time in the world that a metamaterial with both negative refractive index and gain has been prepared in the laboratory; the gain can be converted into bandwidth, allowing visible light across various wavelengths to bypass the 'invisible cloak.'" Xin Hao stated.
"British media asked me: 'In your lifetime, will you see the invisible cloak from 'Harry Potter' come to fruition?' I gave a positive answer." Xin Hao told the audience that in his view, researchers in Shanghai should fully utilize 3D printing technology in the development of metamaterials to solve the third defect of current metamaterials and quickly manufacture materials with complex three-dimensional structures.
