What is a Metamaterial?

Metamaterial (English: Metamaterial), Latin root "meta-" means "exceeding, alternative" and other meanings. Refers to a class of artificial materials with special properties that are not found in nature. They have some special properties, such as allowing light and electromagnetic waves to change their usual properties, and such effects cannot be achieved by traditional materials. There is nothing special about the composition of metamaterials. Their peculiar properties come from their precise geometry and size. The microstructure is smaller and smaller than the wavelength it acts on, so it can influence the wave. The preliminary research on metamaterials is negative refractive index metamaterials. ^[1-2]

"Metamaterial" refers to some composite materials with artificially designed structures and exhibiting extraordinary physical properties not found in natural materials. "Metamaterial" (Metamaterial) is a new type of material that has appeared since the 21st century. It has special properties that natural materials do not have, and these properties mainly come from artificial special structures.

The design idea of metamaterials is novel. The basis of this idea is to break through the limits of certain apparent natural laws through the design on a variety of physical structures, so as to obtain extraordinary material functions. The design ideas of metamaterials show that people can artificially obtain "new substances" with extraordinary physical properties that are quite different from those in nature without violating the basic laws of physics, bringing the design and development of functional materials Brand new world.

Typical "metamaterials" are: "left-handed materials", photonic crystals, "supermagnetic materials", "metal water".

1.Self-healing materials-bionic plastic

Scott White at the University of Illinois has developed a biomimetic plastic with self-healing capabilities. This polymer has a "vascular system" built into it, which can leak out and clot like blood when broken. Compared to other materials that can only repair tiny cracks, this bionic plastic can repair cracks up to 4 mm wide.

2. Thermoelectric materials

A company called Alphabet Energy has developed a thermoelectric generator that can be inserted directly into the exhaust pipe of a normal generator to convert waste heat into usable electricity. This generator uses a relatively cheap and natural thermoelectric material called copper ore, which is said to achieve energy efficiency of 5-10%. Scientists are already working on more efficient thermoelectric materials called skutterite, a cobalt-containing mineral.

Thermoelectric materials have begun small-scale applications-such as on spacecraft-but scobaltite is cheap and energy-efficient and can be used to wrap exhaust pipes for cars, refrigerators, or any machine.

3.Perovskite

In addition to crystalline silicon, perovskite can also be used as an alternative material for solar cells. In 2009, solar cells made from perovskite had a solar conversion rate of 3.8%. By 2014, that number had risen to 19.3%. More than 20% energy efficiency compared to traditional crystalline silicon batteries. Scientists believe that the performance of this material may still be improved.

Perovskites are a class of materials defined by a specific crystal structure. They can contain any number of elements. Lead and tin are commonly used in solar cells. These materials are much cheaper than crystalline silicon and can be spray-coated on glass without the need for careful assembly in a clean room.

4.Aerogel

Aerogels can be made from any number of substances, including silicon dioxide, metal oxides and graphene. Because air accounts for most of the proportion, aerogel is also an excellent insulator. Its structure also gives it super high toughness.

NASA scientists have been experimenting with a flexible aerogel made of polymers as an insulation material for spacecraft as they pass through the atmosphere.

5.Stanene-100% conductive material

Like graphene, Stanene is a material made from a single atomic layer. But because of the use of tin atoms instead of carbon atoms, it has characteristics that graphene cannot achieve: 100% conductivity.

Stanene was first theoreticalized in 2013 by Professor Zhang Shousheng of Stanford University. Predicting the electronic properties of materials such as Stanene is one of the areas that Professor Zhang's lab specializes in. According to their model, Stanene is a topological insulator, that is, its edges are conductors and its interior is an insulator. In this way, Stanene can conduct electricity with zero resistance at room temperature.

6.Light manipulation materials

The nanostructures of light-manipulated metamaterials can scatter light in specific ways, and it may really make objects invisible. Depending on the manufacturing method and materials, metamaterials can also scatter microwaves, radio waves, and lesser-known T-rays. In fact, any kind of electromagnetic spectrum can be controlled by metamaterials.

Veselago, a theoretical physicist of the former Soviet Union, raised this question in 1968 and theoretically predicted the above-mentioned "abnormal" phenomenon. It was just because there was no experimental verification, and at the time that functional materials were in the early stages of development, people did not pay enough attention to Fislag's discovery.

The US "Science" magazine listed it as one of the 10 important scientific advances in the first 10 years of this century, which has triggered major changes in areas such as new-generation information technology, defense industry, new energy technology, and micro-processing technology.

Governments, academia, and industry in developed countries attach great importance to the research and development of metamaterial technology, formulate related plans, and invest a lot of manpower and material resources.

The United States Department of Defense has launched a research program on metamaterials. Intel, AMD, and IBM, the six largest semiconductor companies in the United States, have also established joint funds to fund research in this area. The US Department of Defense has listed it as one of the "Six Major Disruptive Basic Research Fields".

The European Union has organized more than 50 top scientists in related fields to focus on research in this field and provide high funding support.

Japan has launched a research plan during the economic downturn, supporting at least two research projects on metamaterial technology, each of which is about 3 billion yen.

Some research companies predict that the global market size of metamaterials will grow at a compound annual growth rate of 41% between 2010 and 2020. It can be predicted that as the global "Industry 4.0" process continues to deepen and the "intelligent +" application field continues to expand, a scale that can drive hundreds of billions of fields such as high-speed trains, new ground travel equipment, aerospace, defense technology, and ground intelligent robots The metamaterial industry cluster is on the rise.

Using the metamaterial technology that controls electromagnetic waves to build the future world is becoming another focus of global scientific and technological innovation.

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Three important characteristics of metamaterial:

(1) metamaterial is usually a composite material with novel artificial structure;

(2) metamaterial has extraordinary physical properties (often not available in natural materials);

(3) The properties of metamaterials are often not determined mainly by the intrinsic properties of the constituent materials, but by the artificial structure therein.

At present, the pace of product transformation based on these experimental results is also accelerating. R & D and utilization of products such as metamaterial smart skins, metamaterial radar antennas, absorbing materials, electronic countermeasure radars, metamaterial communication antennas, drone radars, and acoustic stealth technologies have become the focus of competition in various countries.

The concept of "metamaterials" has slowly penetrated into many areas. This technology initially caused a sensation in the field of electromagnetics, then drove straight into many fields, including thermodynamics, and recently began to set off a stir in the field of mechanics. (Prof. Martin Wegener, Karlsruhe Institute of Technology, Germany)

The promotion of metamaterials to aerospace, defense, and civil science and technology shows that new materials will become a very important entry point and direction in scientific research, will have impacts and impacts on many fields, and generate new industries. The significance is profound. (Duan Baoyan, Academician of the Chinese Academy of Engineering)

The design ideas and methods of metamaterials are likely to become a powerful means to discover new functions of materials, lead new directions in the industry, improve the comprehensive performance of materials, and break through the bottleneck of scarce resources. It is necessary to further clarify the necessity of vigorously developing metamaterial technology at the national level, condense the development focus, choose a reasonable technical route, and formulate a metamaterial technology development strategy that is in line with the development trend of metamaterial technology and is compatible with China's national conditions. (Zhou Shaoxiong, Deputy Chief Engineer, China Iron & Steel Research Corporation)