Magnetoelastic Parametric Interaction due to the ΔE Effect

摘要

A calculation is presented for the instability of elastic waves parametrically pumped by a time‐varying elastic modulus in long, thin nickel rods or tubes at kilocycle frequencies. The modulus is varied by varying the biasing magnetic field according to the ΔE effect. The instability has been observed in nickel tubes (but not in rods) by driving the parametric magnetic pump at twice the fundamental mechanical resonant frequency of the tube, and observing that the vibrations corresponding to fundamental resonance of the tube set in at a very definite value of the pump amplitude, i.e., the threshold value. The form of the curves of threshold amplitude vs dc bias field in annealed tubes is in agreement with theory, using the previously measured modulus vs field curves. The observed threshold amplitudes are in satisfactory agreement with the theoretical estimate. The form of the above curves and threshold amplitudes are quite different in tubes which presumably still retain some of the effects of cold work experienced in fabrication.