Converse Magnetoelectric Composite Resonator for Sensing Small Magnetic Fields

Magnetoelectric (ME) thin film composites consisting of sputtered piezoelectric (PE) and magnetostrictive (MS) layers enable for measurements of magnetic fields passively, i.e. an AC magnetic field directly generates an ME voltage by mechanical coupling of the MS deformation to the PE phase. In order to achieve high field sensitivities a magnetic bias field is necessary to operate at the maximum piezomagnetic coefficient of the MS phase, harnessing mechanical resonances further enhances this direct ME effect size. Despite being able to detect very small AC field amplitudes, exploiting mechanical resonances directly, implies a limitation to available signal bandwidth along with the inherent inability to detect DC or very low frequency magnetic fields. The presented work demonstrates converse ME modulation of thin film Si cantilever composites of mesoscopic dimensions (25 mm × 2.45 mm × 0.35 mm), employing piezoelectric AlN and magnetostrictive FeCoSiB films of 2 µm thickness each. A high frequency mechanical resonance at about 515 kHz leads to strong induced voltages in a surrounding pickup coil with matched self-resonance, leading to field sensitivities up to 64 kV/T. A DC limit of detection of 210 pT/Hz1/2 as well as about 70 pT/Hz1/2 at 10 Hz, without the need for a magnetic bias field, pave the way towards biomagnetic applications.

MAGNETIC BIAS FIELD DEPENDENCE OF THE MAGNETOELECTRIC EFFECT IN A MAGNETOELECTRIC STRUCTURE: A SIMPLE MODEL

The magnetoelectric (ME) effect in a ME composite structure in which a magnetostrictive component is bonded with a piezoelectric component was studied theoretically, based on the hyperbolic nonlinear constitutive relation of magnetostriction and the piezoelectric equations. A quantitative relation was established analytically for the ME effect and the influencing factors, such as the magnetic bias field and the structure dimensions. It was verified that the theoretical model agrees qualitatively with the experimental results published in Ref. 7. It can also be predicted by the model that the ME effect can be improved by optimizing the structure dimensions.