This paper deals with development of an extremely high frequency ultrasonic transducer of magneto-striction type with vibration frequency of up to 400kHz and its application to ultrasonic grinding. The developed transducer provides longitudinal, torsional and complex vibration modes. When the transducer is applied to boring for ferrite and alumina ceramic workpieces, grinding force becomes stable and chipping is reduced, especially in the complex mode vibration.
