Silicon Micromachined Magnetic Actuators for Interaction with Strong and Dynamic Air Flow

s It has been demonstrated that micromachined sensors and actuators offer unique capabilities for adaptively controlling fluid flow through small-scale actuation [1, 2]. Magnetic micro actuators based on Permalloy material (Ni8oFe2O) have been demonstrated. A piece of electroplated Permalloy is electroplated on top of the structural plate supported by cantilever beams made from Low Pressure Chemical Vapor Deposition (LPCVD) materials. The actuator is fabricated using surfacemicromachining techniques. These actuators provide relatively large forces. For example, deflected actuators with 2 by 2 cm area can withstand vertical loading on the order of 1 mN under an external magnetic field of 2.7 KGauss (measured in air). A large vertical (out of plane) displacement, on the order of 1-2 μm, can be achieved. Such a combination of force magnitude and displacement range can not be realized in conventional electrostatic driven micro actuators. Two types of actuators have been demonstrated that utilize two different flexural beam supports, cantilever beams (Type 1) or torsion beams (Type 2). Fluid experiments show that Type I actuators are prone to damages due to twisting motion caused by flow induced vibration in laminar or turbulent air flow (with average velocity < 40 m/s). Type-2 actuators, on the other hand, can withstand stronger, more turbulent fluid loading compared with TypeI actuators. Nonetheless, both types are not ideal as these can be damaged in harsh flow fields. In these two types of actuators, the flexural support mechanism that facilitates the bending must also withstand flow turbulence. A new type of magnetic actuators (Type 3), based on parallel assembly processes has been developed. Such actuators can remain mechanically stable within the fluid flow even after the magnetic biasing has been removed. It is supported by anchored mechanical assembly and has the potential of withstanding very strong and dynamic airflow. Mechanically-stable actuators also improve the power efficiency of the actuation system. This paper focuses on the discussion of the analysis, design, and actuation-testing results of all three types of magnetic actuators. Finite element analysis has also provided understanding of the failure mode for micro actuators. [1] Ho, C.M., and Tai, Y.C.,"Micro Electro Mechanical Systems (MEMS) and fluid flows," Ann. Rev. Fluid Mech., 30, p. 570, 1998. [2] Chang Liu, "Micromachined sensors and actuators for fluid mechanics applications," Ph.D. thesis, California Institute of Technology, 1996.