Enhanced Field Sensitivity by Strong Mutual Coupling and Magnetoinduction in Amorphous Film/Planar Coil Multilayers

In this paper, we propose a magnetic film/planar coil multilayer structure for the magnetic field detection, which utilizes the strong mutual coupling between the planar coils to enhance the sensitivity. In the proposed structure, the two/multiple coils are stacked together and sandwiched by magnetic films. According to the principle of the electromagnetic coupling, when one of the coils is excited by an ac signal, the inductive-voltage can be detected from another coil, the pickup coil. The analysis shows that compared with the conventional multilayer giant magnetoimpedance structure, the proposed structure can operate at the lower frequency and make full use of the inductance variation ratio in sensor output. In this structure, the sensitivity can be magnified by increasing the inductance of the pickup coil. The prototype of the proposed structure has a noise level as low as less than $1.8~\mu \text{V}$ at 1 Hz. The sensing performances of prototypes show that the proposed structure can achieve a magnetic field detection resolution of 52.17 nT (0.52 mOe) in the range of 5–10 Oe at an operating frequency of 500 kHz even when the gap between the magnetic film is in several hundred micrometer levels.