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The material world you can't imagine: How do metamaterials affect electromagnetic waves and sound?
In our daily lives, the behavior of matter seems to be constant, but scientists have used engineering technology to create a completely new kind of matter called metamaterials. The magic of this substance, which has properties not typically found in nature, is that they are not determined by the properties of the underlying material, but rather by the newly designed structure. Such materials can not only control electromagnetic waves, but also adjust sounds and even seismic waves. This allows us to finally get a glimpse of the new situation of future technology.
These new metamaterials are made from a variety of materials, such as metals and plastics, arranged at scales smaller than the wavelengths they affect. Through precise shapes, geometries and arrangements, metamaterials can block, absorb, enhance or bend waves.
The possible applications of these metamaterials are quite wide, ranging from sports equipment to medical equipment and even related long-range aviation applications. Metamaterials have shown great potential. For example, metamaterials can be used to design metalens, whose imaging capabilities exceed the diffraction limit of traditional lenses, thereby increasing the density of optical data.
By designing appropriate structures, these metamaterials can even exhibit "invisibility" effects at different wavelengths. The demonstration of graded exponential materials is an example that gives mankind a more significant potential to realize the science fiction fantasy of "invisibility cloaks". In addition to electromagnetic waves, metamaterials have also become a popular research field in the study of acoustics and seismic waves.
Historical exploration of metamaterials
The concept of metamaterials does not appear in recent times. It can be traced back to the end of the 19th century. At that time, Jagadish Chandra Bose had already begun to explore substances with chiral properties. In the early 20th century, Karl Ferdinand Lindman also studied the effect of metal spirals on waves. Later, in the 1940s, Winston E. Kock of AT&T Bell Laboratories developed materials with similar metamaterial properties.
In 1967, Victor Veselago first theoretically described negative refractive materials and demonstrated that such materials can transmit light. Until 1995, John M. Guerra successfully fabricated a 50-nanometer-wide subwavelength transparent grating, which paved the way for the realization of metalens.
Application scope of metamaterials
With the deepening of research on metamaterials, the possibilities for scientific and technological applications of these materials have become unlimited. From improved ultrasonic sensors in medical testing devices to high-frequency battlefield communications, metamaterials continue to change our lives. Likewise, these materials have promising applications in solar energy management, laser technology and earthquake-resistant construction.
To allow readers to better understand these concepts, researchers divide metamaterials into several major branches: electromagnetic/light wave metamaterials, other wave metamaterials, and diffusion metamaterials.
Characteristics of electromagnetic metamaterials
The behavior of electromagnetic metamaterials is affected by the material's microstructure, which is smaller than the wavelength of the waves affected. The unusual properties of these metamaterials are caused by the resonant reactions of each component, rather than their spatial arrangement. Such resonance causes the effective parameters of electromagnetic waves (such as dielectric constant and magnetic permeability) to change, which is why metamaterials can show their uniqueness in many different applications.
In particular, metamaterials with negative refractive index are called negative index metamaterials (NIM), which are characterized by having both a negative dielectric constant and a negative magnetic permeability. This configuration allows these materials to demonstrate advantages in controlling the direction of electromagnetic wave propagation and enhancing imaging capabilities.
Future challenges and prospects
Although metamaterials have such a wide range of application scenarios, their manufacturing and practicalization still face many challenges. How to overcome the current technical limitations of the materials community and design metamaterials with stable performance and low manufacturing costs is still an important task for current materials scientists. However, as research progresses, metamaterials will bring more unexpected scientific and technological innovations, thereby promoting the development of society.
In the future technological blueprint, how will metamaterials change our understanding of matter?
