Effect of dc bias field on resonance frequency and vibration amplitude in a magnetomechanical bimorph resonator

Abstract

In previous works, we have developed silicon-based, bimorph resonators, using a uniaxial giant magnetostrictive thin film. Such material has the unique feature to produce both bending and torsional vibration with a single magnetic field excitation. We have used these resonators to build a 2D-Micro-Optical scanner, which has shown actuation capabilities high enough for most applications. Even with non-optimized magnetostrictive material and mechanical design, it has shown comparable performances with those of its piezoelectric or electrostatic counterparts. In this paper, we present new characterizations, which have been made when applying a magnetic DC bias field in addition for the AC field needed for the excitation. Though this DC field is not essential for the operation of the device, it can be used for instance to tune the ratio of bending/torsional vibration amplitudes. In addition to this behavior, it was found that the bias field has also a strong effect on the resonance frequencies of the mechanical structure. This dependence was also found to be dependent on the AC excitation field amplitude. These experimental results are discussed and analyzed in both a qualitative and a quantitative way using a theoretical model. On one hand, the dependence on the AC field amplitude is ascribed to the so-called Hard- spring effect, due to the nonlinear term of the elastic restoring force in large deflection amplitude regime. On the other hand, the dependence on DC field is ascribed to the so-called Delta-E effect, which is a variation of the effective Young's modulus due to the magneto-mechanical coupling.