(A) Long-stroke thermopneumatic microactuator

Abstract

The thesis presents the analysis, design, fabrication, and testing of a thermopneumatic microactuator that utilizes the slope-deflection of a pressurized diaphragm to obtain a long-stroke actuation in millimeter range. In a theoretical study, large deflections of flat and corrugated diaphragms are analyzed and their deflection-stress relationships are compared. A thermopneumatic actuation mechanism is analyzed using an equivalent circuit model to predict the temperature and pressure of an expansion fluid contained in a heated cavity. On this basis, the sizes and materials of the microactuator have been selected for a minimum stroke of 1 mm; thereby designing a microactuator where a 150㎛-thick beryllium-copper diaphragm of 1cm-radius seals the cavity volume of $94.2mm^3$, containing a $45Ω$ tantalum resistor and an expansion fluid of the perfluoro normal hexane (FC-72). In the fabrication process, heater and electrical interconnection pads are fabricated on a glass plate by surface-micromachining technique and the other components are manufactured by conventional mechanical machining techniques, including milling, sand blustering, and electrical discharge machining. In the experimental test of the fabricated microactuator, a DC power of 12 V is supplied to the tantalum heater for 2 minutes. The microactuator generates a 400 ㎛ deflection of diaphragm and 2˚ slope-deflection of the drive-plate, which in turn produces a 1.2 mm stroke at the end of the drive-plate. A set of design variants having four different cavity volumes with three different resistive heaters, has been also fabricated and tested for the power supply of voltage levels. The experimental results are compared with the theoretical values, and guidelines for the design of long-stroke thermopneumatic actuators have been presented. Theoretical and experimental performance characteristics of the thermopneumatic microactuator are also discussed.