Valdemar Poulsen was a Danish engineer and inventor who lived from November 23, 1869, to July 23, 1942. In 1898, he created a device called the telegraphone, which was a magnetic wire recorder used to record sound. He also played an important role in early radio technology. Poulsen developed the first continuous wave radio transmitter, known as the Poulsen arc. This invention was widely used for most early audio radio transmissions until vacuum-tube transmitters were later introduced.

Early life

Poulsen was born on November 23, 1869, in Copenhagen. His father was Jonas Nicolai Johannes Poulsen, a Supreme Court judge, and his mother was Rebekka Magdalene, who was born Brandt. Poulsen studied natural sciences at the University of Copenhagen from 1889 to 1893. He left the university before graduating and began working as an assistant engineer at the technical department of the Copenhagen Telephone Company. Later, he left this job to work as an independent inventor.

Recording innovations

Magnetic recording was first shown as a basic idea in 1898 by Poulsen, who created a device called the telegraphone (or telephonograph). Magnetic wire recording and later magnetic tape recording use a material that can be magnetized. This material moves past a recording head, which receives an electrical signal that matches the sound being recorded. The signal causes the material to develop a magnetization pattern that stores the sound. A playback head, which may be the same as the recording head, detects the changes in the magnetic field and turns them into an electrical current. This current can be played as sound through a telephone receiver.

Poulsen received a patent for the Telegraphone in 1898. With help from his assistant, Peder Oluf Pedersen, he later created other magnetic recorders that used steel wire, tape, or disks. These devices did not have electronic amplification, but the recorded sound was strong enough to be heard through a headset or sent over telephone wires.

At the 1900 Exposition Universelle in Paris, Poulsen showed the invention. He recorded the voice of Emperor Franz Josef of Austria, which is believed to be the oldest surviving magnetic audio recording.

People expected the Telegraphone to be useful for tasks like dictation and recording telephone messages. It could also be used by telephone newspapers to repeat announcements. A reviewer praised the device for its 30-minute recording time and other features, saying it could be as important to businesses and the world as the telephone itself. However, the device’s complexity and the lack of a way to amplify its recordings limited its use. The invention did not become financially successful.

Radio development

In 1903, Poulsen created a radio device called the "Poulsen Arc Transmitter." This device was used for sending audio signals over radio waves before vacuum tubes were invented. Poulsen improved upon William Duddell's "singing arc" to make it work at much higher frequencies. This change allowed the device to produce continuous radio waves, which could carry sound, unlike earlier spark-gap transmitters that could not. The most important change was adding hydrogen gas in a powerful magnetic field.

In 1907, the system sent messages between Lyngby and Newcastle using a 100-foot (30-meter) mast. In 1908, Poulsen made a phone call 145 miles (230 kilometers) from Ejerg to Lyngby in Denmark using only 3 kilowatts of power. In 1910, he made a phone call 295 miles (475 kilometers) from Los Angeles to San Francisco using 12 kilowatts. Music played in a station in Berlin was heard 215 miles (345 kilometers) away in Copenhagen.

The Federal Telegraph Company, which specialized in arc transmitters, used Poulsen's design in the United States. However, the company mainly used high-powered arc transmitters for long-distance telegraphy.

Arc transmitters were no longer used by the early 1920s. They were replaced by Alexanderson alternators for long-distance telegraphy and vacuum-tube transmitters. In 1909, Einar Dessau used a shortwave transmitter to contact Paulsen. Starting in 1907, Lee de Forest used arc transmitters for early radio experiments but later switched to vacuum-tube transmitters. In his 1950 autobiography, de Forest wrote that he did not realize the audion tube, which he used as a radio detector, could also produce radio waves. He said this discovery would have led him to abandon his arc transmitters, which happened globally a few years later.

Personal life

Poulsen married Frederikke Marie Rasmussen in 1894. Frederikke died in 1921. In 1923, Poulsen married Asta Stoltz Nielsen. From his first marriage, he had a son named Christian Henrik Otto Poulsen, who became a geologist. Poulsen passed away on August 6, 1942, in Gentofte. He is buried in the Gentofte Cemetery there.

Honors

In 1907, he received the Gold Medal from the Royal Danish Society for Science. In 1909, he was given an honorary Doctor of Philosophy degree by the University of Leipzig. He also earned the Medal of Merit from the Danish government. At the time of his death, he was a member of the Danish Academy of Sciences, the Danish Academy of Technical Science, and the Swedish Institute for Engineering Research.

Legacy

The Valdemar Poulsen Gold Medal was given each year to recognize important research in radio technology and related areas by the Danish Academy of Technical Sciences. The award was presented on November 23, the day of Poulsen's birth, and he received the first medal in 1939. The award was no longer given after 1993.

Poulsen is one of the men shown in Peder Severin Krøyer's large 1904 oil painting called Men of Industry at Frederiksborg Castle. A memorial plaque on the outside of Landemærket 3 in Copenhagen marks the place where Poulsen was born. The plaque was placed there in 1043. A Danish stamp was created in 1969 to celebrate the 100th anniversary of Poulsen's birth.

On November 23, 2018, a Google Doodle honored Poulsen on his 149th birthday.