Mechanical design of microsystems: dynamic and fatigue behavior

The most relevant issues of mechanical design of microsystems are presented. Micro electro-mechanical systems (MEMS) are characterized by high levels of miniaturization and integration; they base their functioning on many different principles such as mechanical, electrical, optical, thermal, chemical, etc. and can combine a number of functions within an extremely tiny space by providing sensing and actuating performances. The interdisciplinary nature of MEMS introduces many problems for designers because very different competences may be required to define a single device; this evidence is accentuated by the strong coupling among different physical domains (structural, electric, fluidic, magnetic, etc) characterizing microsystems. The theories elaborated in the past for traditional macro-mechanical environments are not completely suitable for microsystems, thus a scientific approach supported by dedicated models and analytic formulations for the microscale become fundamental to provide general tools for the design; then, experimental measurements should be used to validate the proposed theories. The structural-fluidic coupling was analyzed by means of compact analytic models, numerical simulations and measurements on dedicated samples; a climatic chamber was also fabricated for tests at controlled pressures and temperatures. The dynamic behavior of free vibrating and forced structures was deeply studied and modeled, with particular attention to the effects due to electro-mechanical coupling and to residual stress distribution. The reliability and lifetime of microcomponents under the effect of mechanical fatigue was studied by means of experimental validation on dedicated test structures; an original procedure is introduced for the evaluation of S-N curves at microscale. Finally, the design and fabrication of MEMS energy harvesters able to convert vibrations to electric power was presented as a case study.