Silicon Micromachined Sensors and Actuators for Fluid Mechanics Applications

Citation

Liu, Chang (1996) Silicon Micromachined Sensors and Actuators for Fluid Mechanics Applications. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/k8pm-8g13. https://resolver.caltech.edu/CaltechETD:etd-01072008-151023

Abstract

The major contributions of this thesis are the developments of silicon micromachined flow shear-stress sensors and magnetic actuators, together with original studies on two fundamental issues of micro fabrication. Sensors and actuators applications in two fluid-mechanics projects have been successfully demonstrated.

Micro shear-stress sensors utilize boundary-layer thermal transfer principles. For the proposed fluid-mechanics applications these sensors must have higher sensitive compared with conventional sensors, among other requirements. This has been realized by implementing a unique vacuum-sealed cavity which greatly reduces heat loss to the substrate silicon.

Fluid applications present unique challenges to micromachined actuators: they must achieve large out-of-plane motion and withstand large forces. We have developed two types of magnetic actuators that fit these requirements. The first type is based on interaction between the magnetic dipole moment of a current-carrying coil and an external magnetic field. A second-type uses the torque generated by an electroplated Permalloy (Ni[subscript 80]Fe[subscript 20] plate inside an external magnetic field.

The two fundamental micro-fabrication issues are the reactive sealing of cavities and the magnetic-levitation assisted release of surface structures. We have conducted systematic experiments to determine the dependance of sealing performance on the test- structure geometric parameters, sealing materials and other factors. Release/drying of micro actuators, with their large surface areas, is especially challenging. The idea for magnetic-levitation assisted release is obtained while we were developing the Permalloy magnetic actuator. Magnetic forces counteract the surface tension forces during the drying to avoid structure stiction to the substrate. Original results from these fundamental studies add to the general micromachining knowledge base.

The applications of developed sensors and actuators are demonstrated in two fluid- mechanics projects. In the first, we explore a unique scheme for active drag reduction, which is possible only by using a Micro Electro Mechanical System (MEMS). The MEMS consists of an array of shear-stress sensors, actuators and embedded neural-network (NN) circuitry. The goal of the second project is to achieve enhanced maneuverability of delta-wings using MEMS devices. Shear-stress sensors are successfully applied to identify the flow separation lines along the delta-wing's leading edges. Permalloy magnetic actuators interact with the leading-edge flow for controlling the wing motion.

Thesis Files