  Metasurfaces advanced the field of optics by reducing the thickness of
optical components and merging multiple functionalities into a single layer
device. However, this generally comes with a reduction in performance,
especially for multifunctional and broadband applications. Three-dimensional
metastructures can provide the necessary degrees of freedom for advanced
applications, while maintaining minimal thickness. This work explores 3D
mechanically reconfigurable devices that perform focusing, spectral
demultiplexing, and polarization sorting based on mechanical configuration. As
proof of concept, a rotatable device, auxetic device, and a shearing-based
device are designed with adjoint-based topology optimization, 3D-printed, and
measured at microwave frequencies (7.6-11.6 GHz) in an anechoic chamber.
