What is a metamaterial? | Engineering Techniques

Metamaterials are non-natural, man-made materials that possess extraordinary physical properties. Let’s see what are the characteristics of these revolutionary materials.

Metamaterials have been appearing regularly in the science news for a long time, through research conducted in laboratories around the world.

Theorized by Russian physicist Victor Veselago in the late 1960s, metamaterials saw their properties come to light in the year 2000, thanks to experiments performed by two physicists, John Pendry and David Smithabout prototypes invisibility cloaks.

In fact, the characteristic of a metamaterial It is exhibit electromagnetic, acoustic, seismic, thermal, and mechanical properties that is not found in a natural material. These materials consist of periodic, dielectric or mechanical structures, behaving like a homogeneous material, but not existing in a natural state.

Left-handed metamaterials

The properties of metamaterials have been the subject of extensive research since the 2000s, aimed in particular at studying the different possibilities offered by metamaterials. This is the case of “left-handed” metamaterials for instance. The latter have a negative refractive index and require permeability and permittivity negative, simultaneously, for its properties to be effective. The realization, with this type of material, of a super lens in 2006, with almost infinite resolution and a cloak of invisibility, have definitively demonstrated to the scientific world that these properties can be exploited. In specific conditions that make the passage from the laboratory to the factory extremely complex, for the time being.

In addition to a negative refractive index, permittivity, and permeability, The properties of left-handed metamaterials are numerous. : amplification of evanescent waves, inversion of the Doppler effect, inversion of the Cherenkov effect, opposite phase and group velocities… all these effects observed in the laboratory could lead to specific applications in the coming years, in various fields of industry:

seismic metamaterials

the Seismic waves are the subject of much research in relation to metamaterials, in particular with the aim of developing devices to limit the propagation of seismic waves and therefore to protect populations more effectively. For this, researchers are interested in structured soils. To combat the dangers linked to the seismicity of our planet, devices have been developed that consist of structuring a terrain, with wood or cement, for example, to make the latter less sensitive to liquefaction. This involves structuring a soil to change its mechanical properties. But it is also possible, by placing materials on the ground periodically, which will have the effect of creating a metamaterial capable of limiting the propagation of waves seismic signals by modifying the path of seismic rays, or even filtering out certain frequencies.

Energy Recovery

The use of elastic materials with a strong stiffness contrast allows to obtain a metamaterial whose dynamic effective mass becomes negative at certain frequencies. Simply put, elastic waves cannot propagate in these materials at certain frequencies, they get trapped. This property can be used to concentrate energy in a predefined area of ​​a microsystem, in order toblow.

These few examples illustrate the extraordinary potential of metamaterials, whose electromagnetic, acoustic, seismic, thermal and mechanical properties make it possible to imagine revolutionary industrial applications. Meanwhile, the current technological obstacles to the industrial development of metamaterials remain numerous.

The difficulty in making these materials on large surfaces, the difficulty in designing new patterns and the many parasitic effects are among the difficulties that researchers are currently working to overcome.

By Pierre Thouverez

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