Milestones:Development of Ferrite Materials and Their Applications, 1930-1945

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In 1930, at Tokyo Institute of Technology, Drs. Yogoro Kato and Takeshi Takei invented ferrite, a magnetic ceramic compound containing oxides of iron and of other metals with properties useful in electronics. TDK Corporation began mass production of ferrite cores in 1937 for use in radio equipment. The electric and electronics industries use ferrites in numerous applications today. 

Dr. Takeshi Takei, the professor at the Tokyo Institute of Technology, discovered that composite oxides containing zinc and iron have distinguished magnetic properties. In 1930, Prof. Takei submitted a paper on his work to Japanese Electro-chemical Society and also presented a paper at 57th General Meeting of American Electrochemical Society in St. Louis. That same year, Prof. Takei applied a patent for his discovery, which was granted in 1932(Japan PAT-98844).
Tokyo Denki Kagaku Kogyo (now TDK Corporation) was founded in 1935 to commercialize this newly invented ferrite cores. The collaborative work of Tokyo Institute of Technology and TDK led to the development of Cu-Zn ferrite well suited to practical applications in high-frequency ranges up to 1.2MHz. 

TDK started mass production of ferrite cores in 1937 under the product name of “Oxide Core”. 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 compared with air coil. Until the end of the World War II, TDK was the only company who can supply ferrite cores, and shipped a cumulative total of nearly 5 million pieces of ferrite cores.
Today, around 400 thousand tons of ferrite cores are still produced per year, reflecting the critical role that this material continues to play in the electrical and electronics fields. The achievements highlighted in this proposal were critical to the commercialization of ferrite, and contributed heavily to the rapid expansion in the ferrite industry that was to come later.

In 1990, being recognized his earlier achievements on ferrite, Prof. Takei was honored by the American Ceramic Society at its annual meeting in Dallas, Texas, where he was praised as “The father of ferrite.”

In 1909, S. Hilpert announced in Germany that relative resistance would be large in magnetic materials created mainly from iron oxide, and that such materials would be suitable for high-frequency applications. However, he never succeeded in developing practical materials at the level necessary for high-frequency applications.

In contrast, Prof. Takei and engineers at TDK successfully developed a material with the sufficiently large magnetic permeability and small loss properties suited to high-frequency range applications by controlling chemical composition, impurities and process conditions.
TDK and active collaborators expanded the usage of ferrite to military radios as well as radio receivers, television receivers and direction-finding antennas for aircraft around 1940.

The work that the Tokyo Institute of Technology and TDK accomplished in the 1930s with respect to ferrite core commercialization was never made public in worldwide for long time because of the complete disruption of information during the World War II, and the patent dispute between TDK and Philips after the war. Under these circumstances, many people believe that Philips was the first to develop practical ferrite materials and first to use ferrite in wireless device applications. However, Philips restarted full-scale ferrite research after 1940, when they received ferrite cores from TDK with related technical data on the material.

Philips researcher J.L. Snoek is duly recognized for his outstanding contributions to the later growth in ferrite applications, thanks to his work on the feasible frequency range for the use of ferrite (the so-called “Snoek Limit”), the development of Ni-Zn ferrite and Mn-Zn ferrite, and related discoveries.

Establishing the collaborative work between university and industry was strongly needed. TDK was a small venture company just originated from the university patent on ferrite, and at the early stage of development, very few people knew the ferrite and noticed its usefulness. Tokyo Institute of Technology sent a graduate student to radio manufacturing company to verify that the coil with ferrite core is suitable and effective for high frequency radio applications. To make the usefulness of ferrite public, engineers from TDK and radio companies submitted papers on the usage of ferrite at high frequency around 1939.

The milestone plaque may be seen at the Ferrite Hall in the centennial memorial building of Tokyo Institute of Technology. The building was constructed adjacent to the non-extant building where the original research was done and the idea was invented. The site is located very close to the main gate of Tokyo Institute of Technology, and the ferrite exhibition in this building is open to the public