Measurements of ultra-high coupling in magnetoelastic transduction materials

Abstract

Extremely high magnetomechanical coupling factors (k > 0.92) are exhibited by a new class of rapidly solidified amorphous magnetic alloys. These very high couplings produce an enormous increase in sensitivity over conventional sensor materials and make possible a wide variety of new applications. New techniques have been developed to determine coupling factors close to unity with a great deal of precision. Measurements were performed using standard resonance techniques for bar shaped samples, but with two significant improvements in data analysis: (1) Multiple resonances are readily observed in these materials. Inclusion of a mechanical loss Q factor in the basic resonance function for the bar allows a good fit to the data over the entire multiresonance spectrum. Such a fit yields significantly more accurate coupling factors than can be obtained by the standard methods. (2) The problem of appropriate assumptions of magnetic boundary conditions, which is unique to metallic magnetoelastic materials and is due to the presence of eddy currents, is satisfactorily resolved by making use of the higher resonance data.