Optical sensors using materials with unusual mechanical properties or photonic bandgaps

We describe here optical sensors whose performance depends on materials having quite unusual mechanical properties. These properties include negative Poisson´s ratios and negative linear compressibilities (meaning that expansion occurs in one or more directions when the material is hydrostatically compressed). Because of the symmetry of the elastic constant compliance matrix (Sij=Sji), a material that has a negative linear compressibility must also increase density when stretched in an appropriate direction. Such a material is here referred to as a stretch-densified, which is a distinctly different property than having a negative Poisson´s ratio. We will show that both the stretch-densification property (negative linear compressibility) and negative Poisson´s ratios can be used to obtain dramatic enhancements in sensitivity