Soft Magnetic Materials for Audio Transformers: History, Production, and Applications
The history of soft magnetic materials is traced from 1000 B.C. to the present time. This includes a description of the work of Oersted and Faraday who invented the first transformer, and the gradual improvements in core material over the last 150 years. These cover soft iron, silicon iron, grain orientation, Hi-B steels, domain control by lasers, and spark ablation. Amorphous metallic glasses are also detailed. Finally the design and characteristics of a wide range of audio transformers and magnetic shields are discussed, in particular with regard to Mumetal, which with other nickel-iron alloys as been the author's lifetime occupation.
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