Generalized Magnetic Frequency Conversion for Thin-Film Laminate Magnetoelectric Sensors

Magnetic frequency conversion is a promising technique to enhance the limit of detection of magnetoelectric sensors detecting low-frequency magnetic signals. In comparison with the direct detection in the mechanical resonance of the sensor, this method shows a limit of detection increased, i.e., worsened, by approximately 2.5 decades. For the detection of bio-magnetic signal, frequencies ranging from 0.1 Hz up to approximately 100 Hz though the method yield a better limit of detection than direct detection. Still, it is worse than theoretically expected. The cause of the deterioration of the signal-to-noise ratio during magnetic frequency conversion is investigated. Besides the conversion loss, it is due to the arising magnetic noise during excitation of a magnetostrictive material with a pumping signal, which is also in the order of approximately 2.5 decades. The noise can be reduced by applying an additional dc-bias field, which simultaneously results in less output signal. Measurements are confirmed by a numerical model. An existing equivalent noise model for magnetoelectric sensors is extended accordingly.