High aspect ratio galfenol flakes for high strain efficiency and sensing performance of magnetostrictive polymer composites

Abstract

The production of piezoelectric–magnetostrictive composites consisting of a magnetostrictive phase in a piezoelectric polymer matrix requires the application of high electrical fields to pole the piezoelectric matrix. This requires the magnetostrictive phase be present in volume fractions below the electrical percolation threshold to prevent leakage currents which hinder field generation. In order to maximise the performance of this low volume fraction magnetostrictive phase, herein we investigate the use of magnetic field alignment of high aspect ratio magnetostrictive flakes fabricated by a high energy ball milling method. The resultant composites demonstrate an increase of two orders of magnitude in the strain efficiency at low field strengths compared to their low-aspect ratio counterpart. The effects of particle aspect ratio, alignment, and volume fraction on the magnetostriction of the composites have been systematically investigated through experimental measurements and crystallographic examinations. Complex aspect ratio, particle size and alignment distributions generated from experimental observations are, for the first time, used in a fully-coupled multi-physics model of these low volume composites, providing new insights into the contributions these variables have on magnetostrictive composites for sensing, actuation and transducer applications.