What is Metamaterials

What is a metamaterial? Before defining what a metamaterial is, let us first introduce one example. The metamaterial in this video is a simple geometric structure of holes in a common flexible material such as rubber or elastomer, but it produces an unusual deformation.
On the other hand, the metamaterial in the video shrinks perpendicular to the direction of compression without expanding, creating an unusual deformation in which the overall volume expands and contracts. Such structures are called metamaterials with negative Poisson's ratios (auxetic).

There are many definitions of the term metamaterial, but we employ the broadest definition. Metamaterials are objects whose desired "macroscopic properties" are controlled by appropriately designing their geometric structure and material arrangement, such as by designing artificial geometries into specific materials or by compositing different materials in appropriate spatial arrangements, etc. As a result, they can surpass the functions of conventional materials. In other words, very broadly speaking, objects whose new functions are created by designing their shapes can be considered metamaterials. The Auxetic structure in the video is said to be one of the Mechanical Metamaterials.

Auxetic structures not only have interesting deformations, but also have the potential for industrial applications. For example, when an object touches the Auxetic structure, the Auxetic structure has an extremely large contact area compared to flexible materials such as rubber or elastomer with a positive Poisson's ratio, and the Auxetic structure has a high tracking/pressure dispersion that enables "deformation as if it were adsorbing the object.

Furthermore, this structure has a simple geometry with only holes, so it can be mass-produced. Therefore, if this structure is incorporated into bedding, office chairs, etc., it is (probably) possible to create highly functional products that significantly disperse body pressure.

Auxetic structures are said to have the potential to produce properties that exceed those of conventional materials in terms of shock absorption, vibration absorption, and acoustic insulation, in addition to high tracking/pressure dispersion.

Auxetic structures with negative Poisson's ratios were first discovered in 19871, and a simple structure with holes in the video clip above was first reported in 2007, less than 20 years after its discovery2. The study of metamaterials, in general, is still a new field of research, and there are still many new functions that have never been experienced by humans.

Although we are not often aware of it in our daily lives, if we look back in history, the discovery/development/dissemination of new materials has greatly changed the activities of humankind. For example, without the discovery of glass, microscopes and glasses would not have existed, and science and culture would not have developed to this extent. Also, without optical fiber (a type of glass), we might not have had access to high-speed Internet. Glass is too great an example, but honeycomb structures, which is a type of metamaterial, are also widely used in the mobility and aerospace industries as lightweight, highly rigid in-wall components that support our lives behind the scenes.
I believe that Nature Architects has the ability to realize and spread new functions through metamaterials design, and to update human activities. We would like to make a big impact with concrete design examples that I can show you in the next 2~5 years.

Reference

*1Lakes, R.S. (1987) Foam Structures with a Negative Poisson’s Ratio. Science, 235, 1038-1040.

*2 "Pattern Transformation Triggered by Deformation" September 2007Physical Review Letters 99(8):084301