Magnetoelectric sensors: Sensitive and potentially low-cost magnetic sensors

Abstract

The sensor element of magnetoelectric (ME) sensors generate an output with requiring an input energy. In addition they are relatively sensitive, but in common with most other magnetic sensors, their performance deteriorates at low frequency. We have found that, by applying an additional higher frequency, magnetic modulation field to ME sensors, we can increase the sensitivity by a factor of 10 at l Hz. When a modulation field is applied, the signal appears as sidebands around the modulation frequency. A further improvement can be achieved if one adjusts the modulation frequency so that the sideband occurs at the mechanical resonant frequency of the sensor. Using this modulation, ME sensors can detect 4 pT/√Hz at 1 Hz in an unshielded room. We have found that we can increase the resonant frequency of asymmetric ME sensors by using a weight to apply a restoring torque. These sensors can also detect acoustic disturbances. By sweeping a magnetic field at the same time one is applying either a magnetic or acoustic field, one can distinguish between acoustic and magnetic sources.