was a Japanese electrical engineering researcher and professor who made major contributions to
magnetron
The cavity magnetron is a high-power vacuum tube used in early radar systems and currently in microwave ovens and linear particle accelerators. It generates microwaves using the interaction of a stream of electrons with a magnetic field while ...
and
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
development. He did work after the Second World War on medical instruments using ultrasounds.
Career
Split-anode magnetron
One of Japan's best-known radio researchers in the 1920s-1930s era was Professor
Hidetsugu Yagi, who was initially at
Tohoku University
, or is a Japanese national university located in Sendai, Miyagi in the Tōhoku Region, Japan. It is informally referred to as . Established in 1907, it was the third Imperial University in Japan and among the first three Designated Natio ...
. He had become very interested in the magnetron, built and named by
Albert W. Hull at
General Electric
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable ene ...
in 1921. While Hull's magnetron was a
HF device, Yagi was convinced that it could also be a generator of
VHF
Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter.
Frequencies immediately below VHF ...
or even
UHF
Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter (on ...
signals. Kinjiro Okabe was one of Yagi's first doctoral students and was encouraged by his mentor in this pursuit.
In 1926, Okabe developed a magnetron device that significantly decreased the operating wavelength of oscillations. He filed for a U.S. patent in 1926, which was granted in 1929 (No. 1,735,294). His work continued, and based on developing the split-anode device, he was awarded the Doctor of Engineering degree in 1928.
Okabe first published his findings in a Japanese journal, and followed with a foundational paper in the prestigious ''Proceedings of the IRE''. While Hull had published on the HF magnetron years earlier, it was only after Okabe's detailed paper on generation at 17 cm that this device gained world interest. Although this was the first microwave magnetron, it was not immediately applied in communications because it was not frequency stable.
Telecommunication
Another of Yagi's early doctoral students,
Shintaro Uda
was a Japanese inventor, and assistant to Professor Hidetsugu Yagi at Tohoku Imperial University, where together they invented the Yagi–Uda antenna in 1926.
In February 1926, Yagi and Uda published their first report on the wave projector an ...
, had worked with Yagi in developing an antenna using a radically new configuration that they called a wave projector. Commonly called the
Yagi–Uda antenna
A Yagi–Uda antenna or simply Yagi antenna, is a directional antenna consisting of two or more parallel resonant antenna elements in an end-fire array; these elements are most often metal rods acting as half-wave dipoles. Yagi–Ud ...
, this was soon used by Yagi, Okabe, and Uda in demonstrating a 40-cm microwave system with a magnetron and wave projector that achieved a transmission distance of about 1 km. This and other activities at the Tohoku Radio Laboratory was described in a 1928 seminal paper by Yagi.
In the early 1930s, Yagi moved to the
Osaka Imperial University, where he was appointed Director of the Radio Research Laboratory. Okabe accompanied Yagi to Osaka and continued his research on magnetrons, ultimately making a split-anode device that generated oscillations at wavelengths down to about 12 cm (2.5 GHz). He also developed a hot-cathode discharge device (called the Osaka tube) that had characteristics similar to the
Barkhausen–Kurz tube
The Barkhausen–Kurz tube, also called the retarding-field tube, reflex triode, B–K oscillator, and Barkhausen oscillator was a high frequency vacuum tube electronic oscillator invented in 1920 by German physicists Heinrich Georg Barkhau ...
.
Research on radar
Technical specialists in the Imperial Navy became interested in the possibility of using radio to detect aircraft. For consultation, they turned to Professor Yagi who suggested that this might be done by examining the Doppler frequency-shift in a reflected signal. Funding was provided to the Osaka Laboratory for experimental investigation of this technique; Kinjiro Okabe was assigned to lead the effort. His theoretical analysis indicated that the reflections would be greater if the wavelength was approximately the same as the size of aircraft structures.
Okabe developed an experimental apparatus using a VHF transmitter and receiver with Yagi-Uda antennas separated some distance. In 1936, he successfully detected a passing aircraft by the Doppler-interference method; this was the first recorded demonstration in Japan of aircraft detection by radio. With this success, Okabe's research interest switched from magnetrons to VHF equipment for target detection.
The funding for Okabe's target detection project was not continued; the top levels of the Imperial Navy believed that any advantage of using radio for this purpose were greatly outweighed by enemy intercept and disclosure of the sender's presence. Okabe continued to devote much of his research to improving magnetrons. Although this technology was picked up by other organizations, including the Naval Technology Research Institute where
Yoji Ito
was an engineer and scientist who had a major role in the Japanese development of magnetrons and the Radio Range Finder (RRF – the code name for a radar).
Early years
Yoji Ito was born and raised in Onjuku, then a fishing village in the Chib ...
led in further improvements and the eventual incorporation in detection system for the Japanese military, Okabe continued to publish in the open literature.
During and following the war years, Okabe remained very active at the Osaka Laboratory. While Okabe's initial proposal for radio detection was not accepted by the military, time would see this position greatly change. The 1944
Order of Culture
The is a Japanese order, established on February 11, 1937. The order has one class only, and may be awarded to men and women for contributions to Japan's art, literature, science, technology, or anything related to culture in general; recipient ...
award for significant advancements in science and technology was presented to Okabe by the Emperor of Japan in recognition of his early efforts.
Medical applications
In 1955, his interest turned to medical applications of ultrasound, and he suggested to
Shigeo Satomura, one of his graduate students, that he apply
Doppler ultrasound
Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies ...
techniques to medical diagnosis. This research was very productive, and led to new applications of this technology providing non-invasive localised imaging.
[Satomura, Shigeo; “Ultrasound Doppler Method for the Inspection of Cardiac Function,” ''J. Acoustic Soc. of America'', vol. 29, no. 11 (Nov.), 1957, pp. 1181-1185]
References
{{DEFAULTSORT:Okabe, Kinjiro
1896 births
1984 deaths
Japanese electrical engineers
Japanese scientists
Tohoku University alumni
Laureates of the Imperial Prize