Abstract
A new method for magnetic field mapping based on the optical response of organized dense arrays of flexible magnetic cantilevers is explored. When subjected to the stray field of a magnetized material, the mobile parts of the cantilevers deviate from their initial positions, which locally changes the light reflectivity on the magneto-optical surface, thus allowing to visualize the field lines. While the final goal is to be able to map and quantify non-uniform fields, calibrating and testing the device can be done with uniform fields. Under a uniform field, the device can be assimilated to a magnetic-field-sensitive diffraction grating, and therefore, can be analyzed by coherent light diffraction. A theoretical model for the diffraction patterns, which accounts for both magnetic and mechanical interactions within each cantilever, is proposed and confronted to the experimental data.
Highlights
The remaining photoresist is lifted-off and the Si substrate is isotropically etched by reactive ion etching using a sulfur hexafluoride (SF6) plasma, which liberates the beams
The magnetic microelements are free to be actuated by an external magnetic field
Optical microscopy coupled with a high-speed camera system allows to observe the real-time spontaneous motion of the beams when they are exposed to a magnetic field (Fig. 1d,e)
Summary
Considering the arrays of microcantilevers as an actuable diffraction grating, we establish a theoretical model that relates the diffraction pattern to the deflection caused by a magnetic field with a certain magnitude and direction. The total energy per unit length of the beam, expressed as a function of the curvilinear coordinate s, includes the bending energy Ec(s), and the magnetic energy Em(s), which contains the Zeeman term due to the external field and the shape anisotropy term.
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