Abstract :
The extensive results of the investigations on the ultimate mechanical output power of magnetostrictive vibrators are summarized. The description is arranged in such a way that the results can be utilized in industrial design procedures in which large amplitude use should be taken into account. The concept of a working ellipse on the stress-strain plane of the material physical state is explained. Through a suitable arrangement for the waveforms of magnetization and magnetostrictive driving force of large amplitudes, the theoretical formulas for the ultimate mechanical output power per unit area of the radiation surface are derived. The formulas are expressed in terms of the basic constants of the acoustic medium and the magnetostrictive material and a dimensionless factor, named form factor, which represents every configuration and physical dimension of the vibrators. Several useful charts of the form factors are provided for numerical design procedures. By using Ball´s formula, etc., and the results of Kikuchi et ai., obtained in their studies on magnetic hysteresis loss of magnetostrictive materials, under large mechanical stress, the electroacoustic efficiency for large amplitude use can be estimated theoretically. Some numerical examples are given of the rectangular and ring-type vibrators made of nickel sheets in the cases of biased excitation and nonbiased excitation. Some figures on ultimate output power of a ferrite vibrator are also shown. Although only the case in which vibrators work under the load condition of under-mismatching is described, the theory and provided charts themselves are applicable to any other load conditions.
