Valdemar Poulsen

Valdemar Poulsen was a Danish engineer and inventor who developed the first device for generating continuous radio waves, thus aiding the development of radio broadcasting. He also invented the telegraphone, an electromagnetic phonograph capable of registering human speech by the alternating magnetization of a wire. He applied for a patent on this device, a forerunner of the modern magnetic sound recorder, in 1898. A working model created great interest at the Paris Exposition in 1900. He also obtained an English patent on his adaptation of a "singing arc" for radio purposes. Invented by the Englishman W. Duddell, the singing arc could generate continuous audio waves (hence its name). Poulsen transformed this device so that it could generate radio waves; the arc was formed between a copper cathode (positive terminal) and a carbon anode (negative terminal) in an atmosphere of a hydrocarbon gas and a transverse magnetic field. Subsequent efforts with this device by Poulsen and others made long-wave radio broadcasting possible by 1920. He died of cancer in 1942 and was buried in Gentofte.