mathematical theories for engineers. Emergence of radio and electronics During the development of radio, many scientists and inventors contributed to radio technology and electronics. In his classic UHF experiments of 1888, Heinrich Hertz demonstrated the existence of electromagnetic waves (radio waves) leading many inventors and scientists to try to adapt them to commercial applications, such as Guglielmo Marconi (1895) and Alexander Popov (1896). Millimetre wave communication was first investigated by Jagadish Chandra Bose during 18941896, when he reached an extremely high frequency of up to 60GHz in his experiments. He also introduced the use of semiconductor junctions to detect radio waves, when he patented the radio crystal detector in 1901. 20th-century developments John Fleming invented the first radio tube, the diode, in 1904. Reginald Fessenden recognized that a continuous wave needed to be generated to make speech transmission possible, and by the end of 1906 he sent the first radio broadcast of voice. Also in 1906, Robert von Lieben and Lee De Forest independently developed the amplifier tube, called the triode. Edwin Howard Armstrong enabling technology for electronic television, in 1931. In the early 1920s, there was a growing interest in the development of domestic applications for electricity. Public interest led to exhibitions such featuring "homes of the future" and in the UK, the Electrical Association for Women was established with Caroline Haslett as its director in 1924 to encourage women to become involved in electrical engineering. World War II years The second world war saw tremendous advances in the field of electronics; especially in radar and with the invention of the magnetron by Randall and Boot at the University of Birmingham in 1940. Radio location, radio communication and radio guidance of aircraft were all developed at this time. An early electronic computing device, Colossus was built by Tommy Flowers of the GPO to decipher the coded messages of the German Lorenz cipher machine. Also developed at this time were advanced clandestine radio transmitters and receivers for use by secret agents. An American invention at the time was a device to scramble the telephone calls between Winston Churchill and Franklin D. Roosevelt. This was called the Green Hornet system and worked by inserting noise into the signal. The noise was then extracted at the receiving end. This system was never broken by the Germans. A great amount of work was undertaken in the United States as part of the War