  Major challenges of micro thermal machines are the thermal insulation and
mechanical tolerance in the case of sliding piston. Switching from piston to
membrane in microengines can alleviate the latest and lead to planar
architectures. However, the thermal isolation would call for very thick
structures which are associated to too high resonant frequencies which are
detrimental to the engine performances. A thermal and mechanical compromise is
to be made. On the contrary, based on fluid structure interaction, using an
incompressible fluid contained in a cavity sealed by deformable diaphragm it
would be possible to design a thick, low frequency insulating diaphragm. The
design involves a simple planar geometry that is easy to manufacture with
standard microelectronics methods. An analytical fluid structure model is
proposed and theoretically validated. Experimental structures are realized and
tested. The model is in agreement with the experimental results. A
dimensionless model is proposed to design hybrid fluid structures for
micromachines.
