Detection of magnetic force fields at macroscopic distances with a micromechanical cantilever oscillator

Abstract

We report a procedure for measuring variations of the magnetic field gradients generated by a macroscopic coil. A micromechanical cantilever oscillator covered with a magnetic material is used to detect variations of the magnetic force field at distances exceeding several times the coil diameter (4 mm). The detection is based on the phase of the first eigenmode of the cantilever while modulating the magnetic field at low frequencies. The nanoscale oscillation of the cantilever along with the high-quality resonance factor are responsible for a coherent oscillation allowing high sensitivity. A detection sensitivity, under ambient conditions, of the order of 10−13 T/nm2 is estimated with the help of numerical calculations. The approach is useful for evaluating the spatial variation of the magnetic field gradients generated by any source of magnetic field when the magnetic field can be modified at rates below the resonant frequency of the cantilever. These results can be useful for gradient fields monitoring in macro- and micro-scale magnetic resonance imaging, non-contact electric currents identification from stray magnetic fields, electrical power monitoring, 3D-magnetic fields mapping, or miniature orientation devices.