Auxetic Metamaterials for Pressure to Strain Conversion

The purpose of this study is to investigate how metamaterials with a negative Poisson ratio, so-called auxetic metamaterials, can be used for conversion of pressure from a fluid to strain in a solid for application in a medical pressure sensor. As a first step, a literature review was carried out to identify the potential of auxetic metamaterials as a solution direction for pressure to strain conversion. From considering three optimal case scenarios for solution directions to create strain in a fiber, the approach of auxetic metamaterials stood out. High axial strains and a linear straining behavior, which is important for the read-out of the sensor, were expected. Auxetic Chiral structures were designed and fabricated and their effective Poisson ratios were experimentally evaluated. It was found that the boundary effects that are introduced during experiments influence the behavior of the auxetic structure, especially on the unit cells close to the boundaries. A region was found where the unit-cells behave as theory describes and the boundary effects are dissipated. Additionally, it was found that for the an-isotropic Meta Tetra Chiral structure the Poisson ratio is influenced by applied strain. The isotropic Anti Tetra Chiral structure did not show strain dependent behavior. The relation between pressure to strain conversion and the effective properties of auxetic structures indicated that an-isotropic effective properties are preferred. Using this finding Re-entrant Honeycomb structures were designed for high pressure to strain conversion. From measuring the force input and output while deforming the structure, the expectations were verified. In this research it was found that auxetic metamaterials with an-isotropic effective properties, such as Re-entrant Honeycomb structures, are an effective intermediate for converting pressure from the fluid domain to strain in a fiber