November 07, 2022
Minneapolis, United States
Development of a compact magnet for applying a highly uniform magnetic field to a diamond magnetic sensor by inverse problem analysis
Magnetometer with diamond nitrogen-vacancy (NV) centers 1 is a highly-sensitive magnetic sensor under the application of a highly uniform (99.9%) bias magnetic field
2. The integration of magnetometer with diamond NV magnetic sensors is required for various applications. However, there is a problem about the design of small magnet generating
uniform magnetic field in the conventional methods. Therefore, in the study, we propose innovative method based on inverse problem approach for optimizing the shape of magnet.
To optimize the shape of magnet, we estimate the shape of the magnet from the perfectly uniform magnetic field we set up. The magnet is groups of magnetic moment m as shown in Fig.
1(a). Figure 1(b) shows the optimized shape of magnet from the model of vertical rectangle. In Figure 1(c), we depicted cross-section of each z-stage of optimized the magnet vertical
rectangle. Figure 1(d) shows the magnetic field Bz on the diamond surface. The uniformity was 98.5% before optimization and improved to 99.9% after optimization on the diamond
surface. However, the uniformity on the entire diamond was low at 89.0%. To achieve the target magnetic field uniformity, we changed the thickness of the diamond NV center from 2mm
to 0.1 mm and model from vertical rectangle to horizontal rectangle. Figure 2(a)(b) show the model of horizontal rectangle and the optimized shape of magnet. In Fig. 2(c), we depicted
cross-section of each z-stage of optimized the magnet of horizontal rectangle. The magnetic field on the diamond surface was 99.6% and the uniformity of the entire diamond improved to
97.5%. We developed a method to determine the shape of a magnet from a highly uniform magnetic field. As the next step, we fabricate the optimized small magnet for diamond NV center
and evaluate the improvement in magnetic sensitivity.
This work was supported by the Uehara Memorial Foundation and Hitachi Global Foundation.