High Frequency High Amplitude Magnetic Field Driving System For Magnetostrictive Actuators
Creators: name: Angara, Raghavendra
Publisher: name: Maryland Shared Open Access Repository
Year: 2008
Subjects: Engineering, Mechanical

description: Magnetostrictive actuators are the focus of many research and development activities,  especially for high frequency applications. A key component of these actuators is the  magnetic field driving system. In this research work, magnetic field drivers for  magnetostrictive actuators are studied and a detailed methodology to build a low cost,  power efficient, High Frequency High Amplitude ( HFHA) magnetic field driver system  is developed.  The detailed study of magnetic field drivers suitable for magnetostrictive  actuators revealed that the design of the driver must be done at a system level. Changes in  geometry of the magnetostrictive material and the mechanical structure have significant  effect on the efficiency of the driver. For the purposes of the research work, the  magnetostrictive material was limited to two forms, viz. bulk rod and thin film.  First, a suitable mechanical structure must be selected based on the amplitude and  frequency requirements. For purposes of this work, a cantilever beam was chosen so that  large amplitude can be achieved with proper sizing. Simple vibration analysis was used to  size the beam so that the designed actuator frequency is within the third bending mode.  Second, the magnetostrictive actuator was designed so that a mechanical bias and a  magnetic bias can be applied to maximize the output of the actuator. The driver design  primarily consists of a coil, a least resistant magnetic return path, a power source, and a  command signal generator. Power drawn by the magnetic field driver increases with the  frequency of operation due to increases in its inductance, skin effect losses, and eddy  current losses. The magnetostrictive material with its low resistivity, when used as a core,  therefore requires system level approach in designing the driver.  Methodology developed to drive a magnetostrictive actuator includes  determining optimal values of diameter of the magnetic wire, number of turns, length of  the coil, and overall geometry. This methodology also accounts for the skin effect losses  in the driving coil wire and the eddy current losses in magnetostrictive material. The  power consumption is further reduced by creating an electrical resonance at the desired  operating frequency by adding a capacitor in series with the driver. The least resistance  magnetic return path is ensured by using a high magnetic permeability material and  custom geometry permanent magnets.  In this research work, response of the system comprising a well known model of  cantilever beam with mirror and 1- d model of actuator with nonlinear magnetostrictive  rod is measured empirically. The developed methodology is validated experimentally  using a custom fabricated magnetostrictive mirror deflector for rapidly tunable laser  system. The fabricated mirror deflector is capable of producing a deflection of 6.1 mrad  at 5.28 kHz with a power consumption of 0.8 W and a deflection of 3.8 mrad at 10.8 kHz  with 0.65 W. The electrical resonance circuits used have further reduced the power  consumption by as much as 32%. The methodology is extended to MEMS thin film  mirror deflectors.  The work reported here is the first step towards building a comprehensive model  of High Frequency High Amplitude driver for Magnetostrictive actuators. This needs  more work to include the true nonlinear behavior of the magnetostrictive rod and the  integrated system.