Partially Loaded Magnetoelastic Sensors With Customizable Sensitivities for Large Force Measurements

Magnetoelastic sensors are typically made of strips of magnetostrictive materials that efficiently convert magnetic energy into mechanical energy, and vice versa. When exposed to an ac magnetic field, the sensor vibrates, producing a secondary magnetic flux that can be remotely detected. If the frequency of the ac magnetic field matches the sensor´s resonant frequency, the magnetic-mechanical energy conversion is optimal, resulting in a large secondary magnetic flux. The magnetoelastic sensor has been used to monitor physical parameters relevant to force, such as mass or stress, since its resonant frequency, indirectly through the $Delta E$ effect, is dependent on the magnitude of an applied force. Typically, the applied force must be significantly less than the weight of the sensor or it completely dampens the sensor´s resonance. Presented here is the design and operation of a magnetoelastic sensor capable of monitoring large forces by applying partial loading to strategic points on a sensor. The characterization and analysis of this new magnetoelastic sensor is presented along with numerical modeling to illustrate the proposed sensing mechanism. Additionally, an array of magnetoelastic sensors were deployed to demonstrate monitoring of force loading on the lock-in portion of a lock-in style lower limb prosthetic sleeve.