Challenges in Printing and Shaping Soft Magnetic Flux Guides

Coupling to sufficient magnetic flux is challenging for sensing, actuating and energy microsystems, due to scaling limitations. Soft magnetic materials can provide flux density concentration by their magnetization as well as by their geometry. High relative permeability ($\mu_{r}$) ferrites can be challenging to integrate into microsystems and microfabrication processes, but materials of moderate $\mu_{\mathrm{r}}$ may have similar performance in geometrical flux concentrators. In this paper, the flux concentration performance of commercial ferrite, custom moulded and 3D printing soft magnetic materials is characterized. Magnetization loop measurements at 300 Hz to 1 kHz demonstrate $\mu_{\mathrm{r}}$ of 2.2, 36 and 520 for the printed, moulded and commercial materials respectively. In closed-loop inductive power line energy harvesting they demonstrate impedance matched average output power of 0.25 mW, 15 mW and 1.4 W respectively, at 24 A RMS, 1 kHz power line current. In open magnetic loop harvesting using H shaped flux guiding cores, an average harvesting power of $6 \mu \mathrm{~W}, 0.12 \mathrm{~mW}$ and 0.16 mW was demonstrated respectively from a 10 A RMS, 800 Hz power line current. The results indicate that moderate $\mu_{\mathrm{r}}$ materials can provide effective geometrical flux concentration for miniature magnetic sensors, actuators and energy harvesters.