Effect of Hydrostatic Pressures on Magnetostrictive Vibrators

Abstract

The investigation detailed here was carried out on a ring magnetostrictor vibrating in radial mode and exposed to hydrostatic pressures ranging from ambient to 5000 psi. The hydrostatic environment was produced in an oil-filled annular pressure cavity dimensioned so that the radiating surfaces of the ring were separated by less than 110 of a sound wavelength from the cavity walls. Pressure-induced changes in the oil radiation impedance were thereby minimized and amounted to less than 5%. Analysis of electrical-impedance diagrams obtained at polarization levels up to 25.2 Oe showed that the magnetic permeability μr, changed by less than 1% between ambient pressure and 5000 psi while the magnetostriction constant λr changed by 4% over the same pressure range. The transducer mechanical “Q” was constant to within 5% over the 5000 psi pressure range even though the laminations were “soit” bonded. Quasistatic measurements of λr, and μr confirmed the previous findings to within the experimental-error limits (5%). These results are compared with measurements previously reported for axial, compressive, bonding of a bar magnetostrictor. [Work was supported by the U. S. Office of Naval Research.]