| Abstract Scope |
Magnetoelectric (ME) effect is the appearance of an electrical signal upon applying a magnetic field H and/or the appearance of a magnetic signal upon applying an electric field E. This has attracted a lot of interest because the materials featuring the ME effect have potential to be used as high sensitivity magnetic sensors, electrical current sensors, and other devices. Although the ME effect was first observed in single phase materials (e.g. Cr2O3), the composite laminates of the magnetostrictive layer (e.g. Terfenol-D and Metglas) and the piezoelectric layer (e.g. Pb(ZrTi)O3 (PZT), Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), and Polyvinylidene fluoride (PVDF)) have attracted much attention due to the strong coupling effect between the magnetostrictive and piezoelectric layers, which derive large ME response at room temperature. The principle of composite laminates is that a magnetic field induces a strain in the magnetostrictive layer by magnetostriction, and the strain is coupled to the piezoelectric layer, resulting in an electric polarization. Strain coupling requires suitable combination of magnetostrictive and piezoelectric layers for efficient displacement transfer. Among the ME composite laminates which exhibit large ME coupling coefficients, the ones with Metglas are particularly attractive due to their low saturation magnetization field and consequently a relatively low dc bias magnetic field (<20 Oe), which is highly desirable for high sensitivity magnetic sensors. In this paper, Metglas and PVDF are used as the magnetostrictive and piezoelectric layers respectively. To realize the applications for medical and life science research, it is desirable for ultra sensitive magnetic sensors to be highly sensitive, miniaturized, low-cost, and easy to operate. Successful exploitation of magnetic sensors is often inhibited by the presence of large volume of sensors and parasitic effects such as environmental noise and parasitic capacitances. In order to mitigate these problems, it is important to integrate the magnetic sensor with the signal conditioning circuitry as directly as possible. To obtain the electric signal from the piezoelectric layer, a custom-made charge mode read-out circuit is used to maximize the signal-to-noise ratio (SNR) and avoid the effect of stray capacitances. For charge mode read-out circuit, the noise analysis shows that the SNR is proportional to the square root of capacitance of the piezoelectric layer, which is confirmed by the experimental results in this paper. A multilayer structure for the piezoelectric layer is employed to increase the sensitivity without increasing the size of the sensor. Since the elastic modulus of Metglas (100-110 GPa) is much higher than that of PVDF (1-3 GPa), it’s possible for one Metglas layer to drive multiple PVDF layers. Also the SNR for the custom-made charge mode read-out circuit is compared with that of a commercial charge amplifier. |