Valdemar Poulsen invented the telegraphone and unravelled the principle of electromagnetism. Without his discoveries, the invention of the modern day magnetic storage devices such as music cassettes, floppy discs, hard disc drives and credit cards would not have been possible. Another of his inventions, the Poulsen Arc transmitter, was the first wireless communication device ever made.

Valdemar Poulsen was born in Copenhagen in 1869. He was attracted to physics and chemistry from an early age and eventually aspired to become an engineer. Unfortunately, he lacked the necessary mathematical skills for the entrance exam to the Technical university. Instead, he became an apprentice at the machinery manufacturer Frich’s Efterfølgere in Aarhus. It was through this job his experimentation in technical engineering began. 

In 1893, Poulsen started working as an engineering assistant in the technical department of Kjøbenhavns Telefon Aktieselskab - KTAS (The Copenhagen Telephone Company). He soon became the head of the defect department because of his experimental approach. It was during this time that he discovered that magnets leave traces on steel. In 1899, this discovery led him to invent the magnetic wire recorder, patented as the telegraphone, an electromagnetic device that could record, store and replay sound.

Quitting his position at KTAS, he devoted himself to improving, promoting and patenting his invention in several other countries. His recording of the Emperor Franz Josef of Austria’s voice at the 1900 World’s Fair is regarded as the oldest surviving recording made with a magnetic audio recorder.

In 1909, together with civil engineer Poul Oluf Pedersen, Valdemar Poulsen established the first low voltage electrical engineering course in the world at Polyteknisk Læreanstalt (today’s the Technical University of Denmark, or DTU)

Valdemar Poulsen continued to develop new devices, among others the Poulsen Arc transmitter. This technology was later adopted by the US Navy as the transmitter greatly improved the range of wireless radio and telegraphy.

Poulsen was awarded several Orders of the Dannebrog (1913, 1923 and 1939) before his death in 1942. He is burried at Gentofte Cemetery.