How to obtain materials with unusual properties

Yulia Yu. Ershova, senior lecturer at the Department of Mathematics, SPbGASU, became one of the authors of the article on “The property of time dispersion as a feature of media with critical contrast”, published in SIAM Journal on Applied Mathematics. The article describes a mathematical model of mesh metamaterials that can be obtained by means of geometric critical contrast from thin periodic structures. We asked the teacher to tell us more.

Yulia Yershova speaks:

– Metamaterials, as well as materials with memory and composites, are the subject of close study of modern scientists. The fact is that metamaterials have temporary dispersion and unusual acoustic and electromagnetic properties. Materials with such properties cannot be found in nature, but they can be obtained technologically.

– How one can do that??

– At present, metamaterials are created mainly as composites. These are periodic media that consist of two or more kinds of materials. To achieve unusual electromagnetic and acoustic properties, a “hard” and a “soft” components should be combined. The resulting properties of the composite depend on the properties of the initial elements. If the contrast between the properties of the components is selected correctly, it is called critical, and the composite will have the properties of a metamaterial.

Let me give an example: if the rubber matrix is periodically filled with ebonite balls, the resulting material does not allow sound waves to pass in some ranges.

– Is it really as simple?

– No, in practice, is not always easy to obtain a composite with strictly desired properties. But not only composites possess the properties of metamaterials. 

There is an alternative way to create metamaterials: those are materials structured as a periodic grid of thin tubes and nodes of their connections. The tubes are made of homogeneous ordinary material; however, the correct selection of this material, as well as the geometric structure of the network, gives a mesh medium that behaves like a metamaterial. This is called geometric critical contrast.

With the development of 3D printing, the creation of such metamaterials has become technically feasible and in some cases easier than selecting a composite.

– Have studies of the kind been conducted before?

– The appearance of metamaterials was predicted in the 1960s by Soviet physicist Victor Veselago. He proved that a negative refractive index of light is possible only with negative dielectric and magnetic permeability, and a plane-parallel plate of such material should transmit images without distortion..

Thanks to these studies, the “negative materials” and super lenses appeared in the 2000s; they create much sharper images with elements shorter than half the wavelength. Conventional lenses have a diffraction limit, so this degree of clarity is not obtainable to them.

– Where else can metamaterials be used?

– In optics, when creating improved lenses and “invisibility” at certain frequencies; in radio engineering for noise isolation at certain frequencies, to create batteries. The practical application of mesh media is the field of modern research by physicists, engineers, and mathematicians.

Text: Tatyana Petrova

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