GB2531815A

GB2531815A - Radiation absorbing/emitting materials

Info

Publication number: GB2531815A
Application number: GB1419585.3A
Authority: GB
Inventors: Johansson Cox Erik; G Cubbin Peter
Original assignee: INCLUSIVE DESIGNS Ltd
Current assignee: INCLUSIVE DESIGNS Ltd
Priority date: 2014-11-03
Filing date: 2014-11-03
Publication date: 2016-05-04
Anticipated expiration: 2034-11-03
Also published as: GB2531815B; GB201419585D0

Abstract

A metamaterial that is an absorber or emitter of electromagnetic radiation comprising a 3D printed sponge structure having intersecting channels leading from apertures in its surface to its interior. The structure may be fractal such as a Menger sponge or Sierpinski tetrahedron, or it may be formed from periodic, quasi-periodic, random or quasi-random patterns.

Description

Radiation Absorbing/Emitting Materials This invention relates to radiation absorbing or emitting materials.

An ideal black body absorber in thermal equilibrium, in theory, absorbs all incident electromagnetic radiation. A black body emitter in thermal equilibrium radiates electromagnetic energy isotropically and at maximum efficiency. An ideal white body reflects all incident radiation, absorbing none.

In practice, there is no such thing as an ideal black or white body.

Metamaterials -artificial materials that have properties not found in natural materials -have been devised that better approximate to ideal black or white bodies. US4598206 I 5 describes a metamaterial comprising an infrared absorber made from a stack of razor blades. Other metamaterials involve microscopic honeycomb structures and chiral media.

The present invention provides new metamaterials that are absorbers and emitters of 20 electromagnetic radiation and methods for making them.

The invention comprises a metamaterial that is an absorber or emitter of electromagnetic radiation comprising a 3D printed sponge structure having intersecting channels leading from apertures in its surface to its interior.

The sponge structure may be hyperpermeable, and may be so constructed that there is a path from any aperture to any other aperture. The structure may have straight-through channels or tortuous channels or both.

The sponge structure may involve a repeating pattern, or may be random or quasi-random, periodic or quasiperiodic.

A repeating pattern may be such as will give rise to resonance, so that the metamaterial can absorb or emit particular frequencies, while a random or quasi-random structure will in general have no resonance or a diffuse resonance rather than sharp peaks.

The sponge structure may comprise a structure with self-similar architecture, and may be a fractal structure, which may be a Menger sponge or a Sierpinski tetrahedron -a Sierpinski sieve is disclosed in W093/24897, fabricated by homothetic downscaling of a mother generator.

The invention comprises a method for making metamaterials that are absorbers or emitters of electromagnetic radiation by additive manufacturing, or 3D printing, in which perforate layers are superimposed one on another to form a 3D structure with intersecting channels leading from apertures in its surface to its interior.

The layers may be similar or identical but laterally displaced so as to give rise to tortuous channels. Layers of different perforate patterning may be alternated to produce intersecting channels.

Surface apertures and intersecting channels may have dimensions from as small as can be printed up to the order of 1cm or even larger, perhaps up to the order of 100cm. Intersecting channels may get smaller towards the interior of the sponge. The sponge, however, may contain internal structure for resonance, such as a cavity constituting a Helmholtz resonator.

3D printing may involve the deposition of successive patterned layers of a meltable or softenable material such as a plastic, or laser sintering or fused deposition, or selective curing, as by UV radiation, of liquid ink For micro and even nano aperture and channel dimensions, UV crosslinking photolitho techniques may be used such as are used to make microchips. Other technologies either existing or yet to be developed may be found suitable for particular applications.

The dimensions of apertures and channels may be selected to determine the response of the metamaterials to radiation of different frequencies.

Embodiments of metamaterials according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a repeating unit of a first embodiment; Figure 2 is a plan view of first and partial second layers of a 3D printing procedure; Figure 3 is a perspective view of an assembly of units of the first embodiment' Figure 4 is a plan view of first and second layers of a second embodiment; Figure 5 is a perspective view of a Menger sponge Figure 6 is a section through an embodiment including a Helmholtz resonator; and Figure 7 is a section through an embodiment including multiple Helmholtz resonators.

The drawings illustrate metamaterials 11 that are absorbers or emitters of electromagnetic radiation comprising a 3D printed sponge structure having intersecting channels 12 leading from apertures 13 in its surface to its interior.

The sponge structures illustrated are hyperpermeable, and are so constructed that there is a path from any aperture 13 to any other aperture 13. The structures have straight-through channels 12 (Figures 4 and 5) or only tortuous channels 12 (Figures 1, 2 and 3).

The illustrated sponge structures involve repeating patterns, which are produced by repeated layering of a single or a small number of patterns, but can be random or quasi-random, produced by successive layering of patterns generated by algorithms which, despite being random or quasi-random pattern generators, are constrained to produce continuous channels 12.

Figure 2 shows a first layer 14A of identical 'building blocks' comprising an array of eight 'pixels' 14 of print material with a central aperture. The blocks are in rows laterally displaced by one pixel. The first layer 14A is overprinted by a second layer 14B, laterally displaced from the first layer 14A by one pixel in each direction. The resulting structure is shown in Figure 3, which shows only three layers deep, two layers back. When more layers are added in each direction, there will be no line of sight though any aperture, but each aperture 13 will be connected to every other aperture through intersecting channels 12. The channels will be of corkscrew configuration.

Instead of similar, but displaced, print layers, adjacent layers can have different patterning. Repeating patterns can be such as will give rise to resonance, so that the metamaterial can absorb or emit particular frequencies. Random or quasi-random structure, will in general have no resonance and may serve as absorbers or emitters of frequencies over a wide range.

Figure 4 illustrates a different structure founded on the first layer 14A of Figure 2, but with a second layer 14C comprised simply of an array of pixels 14. Channels 13 will be straight-through.

Figure 5 illustrates a sponge structure comprising a fractal structure, which in this case is a Menger sponge, seen in its third iteration.

A fractal structure involves repeated patterning at different scales, so apertures 13 are of different sizes, as are intersecting channels 12. Channels 13 are straight-through. A print file for such a structure can be based on an algorithm that iterates at different scales between a selected maximum and minimum.

Instead of a cube-based Menger sponge, a Sierpinski tetrahedron could also be used -a Sierpinski sieve is disclosed in W093/24897, fabricated by homothetic downscaling of a mother generator, and the Sierpinski sponge is a 3D version of the sieve.

More complex structures can be created by 3D printing techniques. Figure 6 illustrates a 3D printed hollow structure 61, with a cavity 62 forming, together with the apertures 63 and passages 64, a Helmholtz resonator. Figure 7 shows a more complex metamaterial structure comprising multiple such cavities 62 situated at nodes of the intersecting channels 12.

Metamaterials according to the invention can be made of any material adapted to 3D printing or other form of additive manufacturing, including thermally and electrically conductive or resistive materials, and may be made in block or sheet form.

Claims

Claims: 1 A metamaterial that is an absorber or emitter of electromagnetic radiation comprising a 3D printed sponge structure having intersecting channels leading from apertures in its surface to its interior.
2 A metamaterial according to claim I, in which the sponge structure is hyperpermeahle.
3 A metamaterial according to claim 2, in which the sponge structure is so constructed that there is a path from any aperture to any other aperture.
4 A metamaterial according to any one of claims 1 to 3, in which the structure has straight-through channels.
A metamaterial according to any one of claims 1 to 3, in which the structure has only tortuous channels.
6 A metamaterial according to any one of claims 1 to 5, in which the sponge structure involves a repeating pattern.
7 A metamaterial according to claim 6, in which the sponge structure involves a periodic or quasiperiodic pattern.
8 A metamaterial according to any one of claims 1 to 5, in which the sponge structure is random or quasi-random.
9 A metamaterial according to any one of claims 1 to 8, in which the sponge structure comprises a fractal or fractal-like structure.
A metamaterial according to claim 9, comprising a Menger sponge.
11 A metamaterial according to claim 9, comprising a Sierpinski tetrahedron.
12 A method for making metamaterials that are absorbers or emitters of electromagnetic radiation by additive manufacturing, or 3D printing, in which perforate layers are superimposed one on another to form a 3D structure with intersecting channels leading from apertures in its surface to its interior.
13 A method according to claim 11, in which the layers are similar or identical but laterally displaced so as to give rise to tortuous channels.
14 A method according to claim 12 or claim 13, in which layers of different perforate patterning are alternated to produce intersecting channels.
A method according to any one of claims 12 to 14, in which surface apertures and intersecting channels have dimensions from as small as can be printed to the order of lcm.
16 A method according to any one of claims 12 to 14, in which surface apertures and intersecting channels have dimensions of the order of 100cms.
17 A method according to any one of claim 12 to 16, in which intersecting channels get smaller towards the interior of the sponge.
18 A method according to any one of claims 12 to 17, in which the sponge contains internal structure for resonance, such as a cavity constituting a Helmholtz resonator.