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Unfeelability Cloak Protects the Princess from the Pea

Mechanical metamaterials open new dimensions

Author: Tiemo Bückmann - Karlsruhe Institute of Technology (KIT)

Mechanical invisibility cloak: Metamaterials protect objects on the lower side from touching.
(Photo: T. Bückmann, Karlsruhe Institute of Technology, KIT/APH)

3D galvo-scanner dip-in direct-laser-writing optical lithography using Nanoscribe´s ­Photonic Professional GT system allowed for the fabrication of mechanical metamaterial architectures with deep submicron features yet cubic millimeter overall volumes at the same time. Using these we have designed, fabricated and characterized polymeric core-shell elastostatic unfeelability cloaks composed of as many as 1024 extended face-centered cubic unit cells. The high precision of the fabrication was needed to adjust the mechanical properties of the surrounding and the cloaking shell to guide the forces around and let the solid cylinder vanish from being felt. On the other hand the millimeter scale overall volume was essential to characterize the cloak optically and get in reach of possible applications.

It is like in Hans-Christian Andersen’s fairy tale about the princess and the pea. The princess feels the pea in spite of the mattresses. When using the cloak, however, one mattress would be sufficient for the princess to sleep well. The cloak shows that mechanical metamaterials are a growing field using direct laser writing as only here the true three dimensionality and interesting size scales can be covered opening the door for interesting applications.
To date, cloaking has been demonstrated experimentally in many fields of research, including electrodynamics at microwave frequencies, optics, static electric conduction, acoustics, fluid dynamics, thermodynamics and quasi two-dimensional solid mechanics.

The results are now presented in the Nature Communications journal.
(DOI: 10.1038/ncomms5130)

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left: With the finger or a force measurement instrument, no information is obtained about the bottom side of the material. (Photo: T. Bückmann, KIT/APH)
right: Design of the mechanical core shell cloak showing the red cloaking shell and the fabricated surrounding in white. (Image: T. Bückmann, KIT/APH)