Development of low frequency, insulating thick diaphragms for power MEMS applications

Abstract

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 fluidstructure 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. Highlights One major challenge of micro thermodynamics machines is to keep high temperature difference.  Membrane avoids leakage and mechanical friction of piston but is not insulating and lead to too high resonant frequencies.  We propose an innovative membrane architecture which allows efficient thermal isolation and low resonant frequency.  We model, design and tested the fluid-structure membranes which are validated.

Vibration energy harvesting device using P(VDF-TrFE) hybrid fluid diaphragm

“…The architecture is based on the work of Formosa et al [16] which demonstrates the possible use of fluid-membrane interaction to realize thick low resonant frequency membranes. It consists in an incompressible fluid confined between two thin membranes.…”

“…The model in [16] was based on the Ritz method to obtain approximate solutions for both the fluid motion and the diaphragms' deformation. In the present work, this mechanical model is simplified and the piezoelectric membrane behavior is added.…”

“…This work aims at demonstrating the modeling, the fabrication and testing of a new piezoelectric hybrid fluid diaphragm structure VEH. A diaphragm architecture aiming at the drastic reduction of the resonant frequency was proposed in [16]. It is based on an incompressible fluid encapsulated between two flexible membranes.…”

An experimental device designed to obtain repeatable condensation peaks in a closed system

“…Due to these drawbacks, new concepts have emerged to harvest waste heat [3][4][5][6][7][8]. Recently, many attempts for realizing MEMS comprising liquid/vapor phase change have been done.…”

“…Recently, many attempts for realizing MEMS comprising liquid/vapor phase change have been done. Most of the time the architecture remains simple and presents a planar shape with two diaphragms and a working liquid entrapped between them [3,4]. One of the first prototypes presenting this architecture seems to be the P 3 micro-engine realized by Whalen et al [4].…”