The Invention of Ferrites and Their Contribution to the Miniaturization of Radios

Dr. Takeshi Takei, the professor at Tokyo Institute of Technology, discovered that oxides containing zinc and iron have distinguished magnetic properties. In 1930, Prof. Kato and Prof. Takei applied a patent for their discovery of oxide magnetic core materials, which was granted in 1932 in Japan. Tokyo Denki Kagaku Kogyo (now TDK Corporation) was founded in 1935 to commercialize this newly invented ferrite cores as a venture company originated from the university patent of ferrite TDK started mass production of ferrite cores in 1937. Most of the shipped products were used in the local oscillators, mixers, and intermediate frequency transformers of military radios. These are the world first usage of ferrite to radio communication equipments. Ferrite largely contributed to reduce volume and weight of radio receiver compare with air coil. Until the end of the World War II, TDK was the only company in the world who could supply ferrite cores. TDK shipped a cumulative total of nearly 5 million pieces of ferrite cores by 1945. Many people believe that Philips invented ferrites and they applied them to radio. But their first patent was applied in 1941 in Netherlands after they examined ferrite samples from TDK. This paper also explains about the patent dispute between Philips and TDK after the World War II which caused such misunderstanding.