  We introduce a class of ultra-light and ultra-stiff sandwich panels designed
for use in photophoretic levitation applications and investigate their
mechanical behavior using both computational analyses and micro-mechanical
testing. The sandwich panels consist of two face sheets connected with a core
that consists of hollow cylindrical ligaments arranged in a honeycomb-based
hexagonal pattern. Computational modeling shows that the panels have superior
bending stiffness and buckling resistance compared to similar panels with a
basketweave core, and that their behavior is well described by Uflyand-Mindlin
plate theory. By optimizing the ratio of the face sheet thickness to the
ligament wall thickness, panels maybe obtained that have a bending stiffness
that is more than five orders of magnitude larger than that of a solid plate
with the same area density. Using a scalable microfabrication process, we
demonstrate that panels as large as 3x3 cm^2 with a density of 20 kg/m^3 can be
made in a few hours. Micro-mechanical testing of the panels is performed by
deflecting microfabricated cantilevered panels using a nanoindenter. The
experimentally measured bending stiffness of the cantilevered panels is in very
good agreement with the computational results, demonstrating exquisite control
over the dimensions, form, and properties of the microfabricated panels.
