Signal-to-Noise Ratio in Cantilever Magnetoelectric Sensors

Abstract

The signal-to-noise ratio (SNR) is investigated for compound magnetoelectric (ME) sensors on cantilever substrates (SUBs) for the detection of low-level magnetic fields. Operated at the mechanical resonance, the magnetic field deforming the magnetostrictive (MS) layer causes a resonant bending-mode response in the ME cantilever. The deformation of the piezoelectric (PE) layer allows for the extraction of a voltage or charge signal. Here, the influence of the PE layer thickness and electrode length on the SNR is evaluated in a theoretical study. The signal levels are calculated using the finite-element method. Noise voltages are calculated including the intrinsic electric noise of the ME sensor and amplifier noise for the case of a voltage amplifier and a charge amplifier. AlN and PZT are considered as PE materials. For a cantilever geometry with 10 mm-length, 10 mm-width, and 300 μm-thick silicon SUB and a Metglas MS layer of 2 μm thickness, a limit of detection (LOD) in the pT-range is predicted for 2 μm-thick AlN layers, while the LOD of PZT ME sensors is approximately one order of magnitude worse. A doubling of the SNR is obtained for choosing an upper electrode covering only the fixed side of the cantilever. Operation with a charge amplifier shows at least ~50% better SNR values compared with PE voltage amplification.