Effect of Local Annealing on Magnetic Flux Distribution and Noise in a Micro-Generator with Amorphous Shell

Abstract

This study examined micro-alternators with two different housing structures––an uncoated shell and a shell coated with an iron-based amorphous-alloy soft magnetic material. The electromagnetic power and noise characteristics of generators with these shell structures were measured and analyzed. The material used for the shell coating was the SA1 amorphous alloy. The magnetic property of the SA1 material was evaluated, including its hysteresis expansion, hysteresis-loop parameters, α-Fe crystal formation, thermogravimetric transfer, and Curie temperature. The center point of the casing was subjected to flame local-heating annealing to attain ferromagnetism and paramagnetism material characteristics. The experimental shell was between these magnetic-phase-transition properties and was used to observe the magnetic power and noise characteristics of the microgenerator. The measured magnetic flux at the center of the amorphous shell was 1.2–2.4 mT, and the magnetic flux distributed around the shell was 0.6–1.0 mT. The generator with the amorphous-alloy shell had the lowest demagnetization rate in the permanent magnet region, which was close to the bottom of the pole piece, and the magnetic flux leakage of the pole-piece side frame changed the magnetic flux path, thus affecting the demagnetization performance. For the noise experiment, the flame-annealing temperature of the local center point of the amorphous casing reached the Curie temperature, and the noise characteristics of the casing can be reduced by 15 dB compared to those of the generator without the casing. However, the overall performance of generator harmonics and power were not fully improved.

Application of Amorphous and Nanocrystalline Soft Magnetic Materials in Balanced-Force-Type Electromagnetic Relay

“…For example, Guo, L. et al improved the resolution of a MEMS-based micro-fluxgate sensor by using a magnetic core composed of a Fe-Co-B amorphous strip composite material [ 11 ]. Hsu, C et al designed a micro-alternator using a shell coated with a ferro-based amorphous alloy soft magnetic material, reducing the noise characteristics by 15 dB compared with an uncoated shell [ 12 ]. Nanocrystalline soft magnetic materials often have a nanometer grain size, with high initial permeability and low coercivity in their spatial structure, which can be obtained by applying a certain heat treatment process to an amorphous matrix.…”