Metamaterial

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This page is about metamaterials in general.
For more specific information about the metamaterials of focus in the target technology of atomically precise manufacturing visit the
main page about: gemstone based metamaterials

Definition

A metamaterial is a material whose large scale properties are not determined by the properties of the base material it is made of, but instead by the way the base material is structured on a scale that's small enough. How small structures must be to be small enough depends on the application in question.

  • In some cases the structures are allowed to be so big that they are easily perceivable by human senses.
  • In other cases its necessary for the structures to be not perceivable by human senses.

The smaller the structures the wider the range of properties that can be emulated. On the smallest scales in particular one can decouple the material properties from the chemical elements that make up the materials.


Space of possible materials.svg

Future atomically precise metamaterials have control over the structure at the lowest physically possible level. They open up a new world of materials far beyond what we have today.

Some proposals for new materials can be found on the diamondoid metamaterial page. Those are the basis for the prospective products of advanced advanced atomically precise manufacturing (APM) systems.

Examples for (mechanical) metamaterials: past, present, future

Metamaterial
out of the past: chain maille
Base-material: metals
Structure-size: clearly visible
Metamaterial
of today: textiles
Base-material: plastics
Structure-size: microscopic
Metamaterial
of the future: "gem-gum"
Base-material: gemstones
Structure-size: a few atoms

Towards advanced AP metamaterials

A possible classification hierarchy for metamaterials in the context of APM. (AP...atomically precise; GEM...gemstone based)

This wiki will (for now) organizes advanced AP metamaterials in a hierarchy.

  • With advance in the hierarchy expanding the range of emulateable capabilities becomes easier (design).
  • The other way around currently (2017) at the beginning of the hierarchy metamaterials are limited and hard to scale. (See related page: Ban to incrementality of non-AP nanotechnology).

(TODO: add graphic of metamaterials past (chainmaille) present (textiles) and future (crystal-drawing) all held in hands)

Non-AP metamaterials of today

Today (2016..2017) the term metamaterial mostly refers to the subclass of electromagnetic metamaterials. This is likely because with current technology advanced mechanical metamaterials are not yet producible fine enough and cheap enough to be of mainstream use.

There are some examples for primitive (non AP) mechanical metamaterials though.

  • Medieval ages: chainmaille (base material metal alloy)
  • Today: synthetic textiles (and the inner structure of some sport shoe soles) (base materials various kinds of plastics)

Naturally grown materials like wood can be considered mechanical metamaterials from the perspective of nature but since we can barely influence their properties and use them as as-is given base-materials, from human/technological perspective they may not really be considered (mechanical) metamaterials.

With increasing capabilities of atomically precise manufacturing it seems likely that mechanical metamaterials will become more present than the currently dominant non mechanical metamaterials.

(Semi) atomically precise "metamaterials"

In natural systems

In natural systems (molecular biology) a prime example of a metamaterial is nacre in sea shells. Aside from that, large homogeneous chunks of base material actually rarely do occur in biology, so most biological tissues could be considered metamaterials. There is much more to it though (interesting research but not main focus of this wiki).

Nacre has only a limited amount of atomic precision and is very far from maximally easy to recycle since it's rather monolithic. (Monolithicness is somewhat tied to lack of atomic precision - more on that later).

So while nacre is one prime target direction for conventional biomineralisation research, nacre is not of interest for "unconventional biomineralisation research". Research for attainment of technology level II (where there is a focus on the synthesis of monolithic biominerals in a maximally AP way as base materials that will only later be shaped into metamaterials that do fully emulate elasticity instead of relying on the inherent elasticity of proteins when viewed as base material). (Related: "Acellerating and sidetracking attractors")

In artificial systems (far term)

One aspect in the artificial synthesis of food is (not too complicated) microscale paste extrusion 3D printing. arranging pastes in voxels (3D pixels) makes it a non-AP metamaterial. (Baking may make some pars crisp others not pattering allows for a wide range of food textures).

What is and absolutely needs to be atomically precise in the synthesis of food is a very wide range of base material molecules. Due to the advanced mechanosynthesis capabilities that are necessary for the synthesis of all these different molecules food synthesis is actually lying beyond the primary target of APM. (Synthesis of food is not part of the naked core functionality of the targeted gem-gum factories). In food synthesis there are many different base materials but not too much of higher structure is necessary.

Side-note: Putting some gel like diffusing blobs (voxels) next to each other they irreversibly blend into one another (by diffusion).

In artificial systems (near term)

Examples for metamaterials in early productive nanosystems include diffraction gratings (for light, electrons or maybe even helium matter waves) out of foldamers where even small product masses can give useful products.

We want to pass through this early stage of APM as narrow and fast as possible though, because with more advanced stages (incremental path) solving the same problems becomes many times easier.

In general

In soft nano"machinery" systems (both natural and artificial) the base material is often not too well separable from the higher metamaterial-specific structures. Going up from the very lowest size-scales with AP base structure, quickly a lot of thermodynamic randomness is becoming superimposed.

Monolithic AP metamaterials (gemstone based)

  • As mentioned above a lack of atomic precision (and stiffness) makes modularity more difficult (at the nanoscale).
  • The other way around: Once one has advanced AP manufacturing one potentially can make highly modular systems.

There are several reasons why one does not want to refrain from making modular systems despite having the opportunity.

  • Monolithic systems cannot be recycled without total thermal or chemical destruction (and may not erode when left alone in nature).
  • Gemstone based monolithic systems tend to be brittle.

Especially in combination these two points are bad for the environment. (wear, erosion, degradability)
Furthermore (and perhaps luckily):

  • Monolithic systems may actually be more difficult to make than modular ones.

To make macroscopic monolithic gemstone based products with reasonable speeds covalent welding needs to be performed (instead of direct-to-product atom-by-atom assembly – molecular assembler pitfall). Covalent welding needs to be done under practically perfect vacuum. Since the product is one giant monolithic block there needs to be one giant vacuum chamber (much more difficult to get clean and keep clean).

With the capability of making large monolithic gemstone systems (not a goal!) one could make big homogeneous chunks of base material (e.g. thumb sized flawless synthetic diamonds). This is the exact opposite of the (much more useful) metamaterials.
Note that monolithic AP products could still form non-mechanical metamaterials.

Non-monolitic AP metamaterials (gemstone based)

Nanocell crystal 1.jpg

See main article: "gemstone based metamaterials"

Once technology arrives at advanced levels of APM the easiest way to make things is by organizing often reappearing functionality into microcomponents just like in software. (Side-note: In software more advanced solutions are possible and desirable).

Productive nanosystems for non-monolithic products are easier than productive nanosystems for monolithic products since (as already mentioned) there is no need for doing covalent welding out in the wide open. instead one can do early passivation, early Vacuum lockout and many small mutually separated PPV vacuum chambers (much more likely to work).

Microcomponent based metamaterials shine at Recycling.

There are several ways to put microcomponents together (details on the page about "microcomponents"). Bottom line is that naive (low design effort) ways to put microcomponents together leads to brittle properties. So microcomponent based metamaterials with simple designs are still restricted mostly to non-mechanical properties.

In contrast to the case of monolithic products (above) though fractures are not necessarily irreversible. And with a bit more of design effort the fracturing behavior can be controlled. This can alleviating the environmental problem of spill of splinters a bit.

Elasticity emulating gemstone based metamaterials

When one connects microcomponents in advanced nontrivial ways to create a metamaterial that is capable of emulation of elasticity, then one has reached the point where mechanical metamaterials really begin.

Note: This must not be confused with utility fog (which targets ultra general purpose capabilities at the expense of performance).

With elasticity emulation the nanoscale unbreakability properties of crystolecules (and microcomponents) are to a degree lifted up all the way to the macroscale.

This gives cheap materials with ...

  • enormous toughness lying way beyond all metallic alloys in existence and ...
  • unlike most metals corrosion resistance is at the level of the base material: the chosen gemstone.

Getting well designed gem-gum materials to chip of small splinters (e.g. attack by hardened saw-blade) will probably be almost impossible.

Note that this combination of material properties has not only positive sides though. Two obvious concerns are:

  • Degradability is often a desired property. There are lots of gemstones that do degrade though (e.g. periclase MgO is slightly water soluble) so it's a matter of choosing the right material for the right application.
  • Military misuse.

From pixel to meta-voxel

Just like metamaterials pixels on computer screens or printed colored dots on paper are used to fool human senses. Luckily it is not necessary to make a perfect copy of the real thing to give a perfect experience.

A side-note to current screen technology (2016): Note that while resolution by now often far exceeds human senses dynamic range (brightness) and color gamut (saturated color) are still heavily lacking. E.g. the bright and deeply orange rising sun can't yet be authentically captured and reproduced.

Obviously metamaterials can't be shrunk down arbitrarily (e.g. to atom size). There's a minimum size (volume) which is necessary to emulate a property. Metamaterial voxels must be bigger than that. Making meta voxels bigger then the absolute minimum size may sometimes help to improve the emulation quality (statistical average). Meta voxels of various compatible types can be mixed and meshed but if the material properties are supposed to vary with location the meta-voxels must be small enough such that they won't be experienced as graininess by human senses. So in summary there's a usable size range for meta-voxels.

In advanced atomically precise products depending on their internal complexity meta voxels could be realized:

  • by a crystal of crystolecules that are a bit on the bigger side
  • by microcomponents (ideal size?)
  • or even product fragments just below the visibility limit of the human eye.

A good example for the possible usage of meta voxels fooling human senses can be found in prospective advanced food synthesis. Wile with inside knowledge it seems pretty impossible to create a perfect 1:1 copy of a natural apple. (That is every atom and molecule is present and at the identical place - when deep frozen). With sufficient effort it may be possible to create something that humans can't distinguish from a natural apple. Something that is actually completely different at the nanoscale - a meta apple. More practically, easy and maybe less morally questionable though will be to make some dough with more or less structure. Super advanced meta cake designer food so to say.

Meta - Why the word meta is used

A metamaterial does not have its properties inherently but rather describes them ("meta.." ... describing)

Examples

  • (Passive) auxetic metamaterials: Metamaterials which use their non actuated internal structure to create a negative Poisson ratio. That is they expand transversally (sidewards) when stretched longitudinally (lengthwise) and they contract transversally when compressed longitudinally.
  • Metamaterials with (clearly independent) internal degrees of freedom deliberately left under-constrained. If the structural pieces are sheet shaped and the hinges allow compression to complete collapse without destruction one ends up with origami structures. Note that metamaterials are by far not limited to origami structures. Such structures can sbe made active just by adding actuators independently cation on the seperate degrees of freedom.
  • Metamaterials using internal flexing or hinging to act as complex mechanisms / machines. Giving up on long range periodicity (translation symmetry) symmetry blurs the line to (nano)machinery and (nano)mechanical computation. What makes a metamaterial is the presence of at least a little bit of repetition.

Related

External links