Detection of Inhomogeneous Magnetic Fields by Magnetoelectric Composite

Magnetoelectric (ME) composites can be useful due to their wide range of possible applications, especially as sensors of weak magnetic fields at room temperature for magnetocardiography and magnetoencephalography techniques in medical diagnostic equipment. In most works on the topic of ME composites, structures are tested in uniform magnetic fields; however, for practical application, a detailed consideration of the interaction with inhomogeneous magnetic fields (IMF) is necessary. In this work we made measurements of IMF with radial symmetry of individual thin wire with AC voltage with different placements of ME sensor. A ME self-biased structure b-LN/Ni/Metglas with a sensitivity to magnetic field of 120 V/T was created for IMF detection. The necessity of external biasing magnetic field is avoided by a nickel layer and its remanent magnetization. ME composite shows a non-zero ME coefficient of 0.24 V/(cm·Oe) in absence of DC external magnetic field. It is shown that output voltage amplitude from ME composite, which is located in AC IMF, is dependent from relative position of investigated sample and magnetic field lines. Maximum ME signal is obtained when long side of ME sample is perpendicular to the wire, and symmetry plane which divides the long side in two similar pieces contains an axis of the wire. In frequency range from 400 Hz to 1000 Hz in absence of vibrational and other noises a limit of detection has value of (2 ± 0.4) nT/Hz 1/2 .