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Multi-Material Stereolithography 3D Printing

This research project aims at manufacturing structures with multi materials at micrometer scale. Metamaterials are engineered materials with macroscopic ‘material’ properties not seen in nature. The materials are often comprised out of multiple materials, in microscopic repetitive structures of a size smaller than the wavelength of the phenomenon affected by the material, such as the wavelength of a specific electromagnetic wave. An example of a new application using metamaterial is the possibility to produce lenses with optical properties that go beyond conventional lenses and mirrors.

Commercially available technologies are limited in their resolution (≥100 µm) and some also in their material properties.
Two important requirements exist for electromagnetic metamaterials: 1) a higher resolution is required; and 2) the use of both conductive and isolating materials is required.

Vat photopolymerisation allows for higher resolution printing than the previous mentioned technologies. However, it prints selectively by selective phase changing a resin, which leaves behind uncured resin making multi-material printing more challenging. A machine and a process need to be developed for this. Furthermore, the resins themselves are electrically isolating, therefore, as conductive material other materials should be used such as silver paste. Silver paste also needs curing,  which in general will not be under the same conditions as the resins. For selectively depositing silver paste within the Vat photopolymerisation process, a new process has to be developed.

COMPETITIVE  ADVANTAGE

Currently no 3D Printing technology exists that fulfils the requirements of both the resolution and the material parameters (conductivity). One could manufacture the metamaterial using technology from the semiconductor industry. However, these manufacturing technologies are too slow, or the required metamaterial products have a volume that is to large.

Furthermore, within TNO we already have expertise on vat photopolymerisation, on screen printing conductive pstes and on novel structures for advanced antennas.

APPLICATION  AREAS

Metamaterials in general are of great interest since it gives access to unique material properties that were previously not available, which in turn can be applied in all kinds of technologies where for example electromagnetic radiation, or vibrations play a role. An example of a new application using metamaterial is the possibility to produce lenses with optical properties that go beyond conventional lenses and mirrors. The use case targeted here is for use on radar systems to increase the viewing angle. The technology developed here can have wider applications, producing other metamaterials and embedded electronics.

PROVEN  SPECIFICATIONS

  • Two dimensional conductive tracks have been produced in laboratory setting with a conductivity equal to 10% of copper bulk conductivity (Figs 1 and 2).
  • A structure is designed and printed as a metamaterial for electromagnetic waves at a specific wavelength (Fig 3).
  • A multi-material structure was successfully made at comparable sizes (Figs 4 and 5).

TARGET  SPECIFICATIONS

Process development for multi-material additive manufacturing for embedded conductive tracks with structures of 100 µm, and a conductivity of 10% copper bulk conductivity, leading to a functioning metamaterial for radar applications.

The Lepus Next Gen machine for large area multi-material vat photopolymerisation for large area printing with a resolution of 20 micron.

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