Measurements on magnetostriction vibrators

The study of electromechanical vibrating systems through the measurement of motional impedance was first undertaken by Kennelly and Pierce in 1912, in their work on telephone receivers. The method was applied by K.C. Black in 1928 to the study of ferromagnetic rods centrally clamped and lying along the axis of a coil carrying alternating current superposed upon direct current. The work of Mr Black was done on rods of nickel, stainless steel, and stoic metal (invar steel), and also on nickel tubes. The natural frequencies of the rods he studied lay between 2300 and 3000 cycles per second. The present paper describes similar measurements carried out on rods with natural frequencies near 30,000 cycles per second. The study was made on rods of nichrome, monel metal, stainless steel, stoic metal, and nickel. The dependence of the vibratory characteristics on rod diameter was determined by making measurements on a nickel rod, as its diameter was reduced in successive steps. The rod was annealed before each set of measurements, by heating to redness and cooling in air. Another nickel rod cut from the same bar was bored axially with concentric holes of successively larger diameter, and measurements made at each step. This was done in an endeavor to determine something about the flux distribution across the section of the vibrating rod. The effects of annealing, and of changing the number of turns on the alternating-current coil (in which the rod was supported), were investigated. The effect on the vibratory characteristics of varying the alternating magnetic field on the rod was also measured.