The use of magnetic fields as a means to control the flow of an electrical current was spurred by the introduction of the Audion by Lee de Forest in 1906. Albert Hull of General Electric Research Laboratory began development of magnetrons as a way to avoid de Forest's patents, but these were never completely successful. Other experimenters picked up on Hull's work and a key advance, the use of two cathodes, was introduced by Habann in Germany in 1924. Further research was limited until Okabe's 1929 Japanese paper noting the production of centimeter-wavelength signals, which led to worldwide interest. The development of magnetrons with multiple cathodes was proposed by A. L. Samuel of Bell Telephone Laboratories in 1934, leading to well-known designs by Postumus in 1934 and Hans Hollmann in 1935. Production was taken up by Philips, General Electric Company (GEC), Telefunken and others, limited to perhaps 10 W output. By this time the klystron was producing more power and the magnetron was not widely used, although a 300W device was built by Aleksereff and Malearoff in USSR in 1936 (published 1940).