In order to improve the efficiency and capability of ultrasonic machining system, the design method of Giant magnetostrictive ultrasonic machining systems(GMUMS) is presented and the influence of magnetic material for the closed magnetic circuit on the vibration performance is studied. Three kinds of magnetic materials, including silicon steel, ferrite and magnetic powder core, are applied and the equivalent circuit is proposed. Based on impedance analysis method, the impedance circle is plotted to determin...