Example

Consider the same MEMS beam similar to that discussed in the Example of Lecture 30. However, instead of piezoelectric layers on top and bottom the host beam is excited by a magnetostrictive mini-actuator of same length as that of the host beam. The MMA has a cross-sectional area of 4x10^-8m² and thickness 100 μ-m. The elastic modulus of the magnetostrictive actuator is 50 GPa, the magneto-mechanical constant is 15 nM/A and a current of 750 mA is passed through the coil. Considering the coil-constant G to be 10,000 and neglecting the thermal effect, find out the strain induced at the host beam.

Solution

Neglecting the thermal effect, the free-strain that could be developed by the MMA could be obtained using eqn. (33.2) as

Using eqn. (33.1), the strain induced on the host beam is

Magnetostrictive sensors are developed based on three phenomena:

1. The Villari effect, which refers to the changes in magnetization when a magnetostrictive material is subjected to applied uniaxial stress.
2. The Matteuci effect, referring to the changes in axial magnetization of a current carrying amorphous wire when it is twisted.
3. The change in permeability of these materials when subjected to applied stress. Magnetostrictive delay line sensors are based on this phenomenon.

Congratulations! You have finished Lecture 33.