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Camras

Magnetic Recording Tape

Marvin Marvin Camras (1916-1995) invented the magnetic tape recording method that underlies most electronic and digital media, including audio and video cassettes, floppy disks and credit card magnetic strips.

Born in Chicago in 1916, Camras was known to his family as an "inventor" by the age of five. As he got older, he began to focus his talents on electronics: he even built a telephone, so that he could talk with his cousin, William. In the late 1930s, Camras was studying electrical engineering at the Armour Institute of Technology (now the Illinois Institute of Technology), where he later earned a BS (1940) and MS (1942). At the same time, his cousin was aspiring to become an opera singer.

In order to make temporary recordings of his cousin's voice, Camras resurrected an idea of Valdemar Poulsen (1869-1942), whose telegraphphone had proved that sounds could be recorded magnetically. Camras first used magnetized piano wire to record his cousin singing, but the wire twisted as it was wound through the machine, distorting the playback.

Camras had an ingenious solution: he created a magnetic recording head that would surround but not touch the wire, so that the actual recording would be impressed symmetrically on the wire by the gap of air between the head and it. Eventually, Camras made this idea work. Based on the results, cousin William gave up his singing career; but Camras himself won his first patents and a position at the Armour Research Foundation.

There, he adapted his device for use by the Navy, who simulated depth charge attacks in order to train submarine pilots, and the Army, who used Camras' "Model 50" machines in World War II to terrorize the enemy with high-volume, "decoy" attacks. After the war, Camras switched his medium from wires to tapes. After thousands of experiments, he developed a ferric oxide "paint" for the tape, whose particles would align uniformly when magnetized, forming the perfect surface on which to record.

Soon thereafter, Camras invented high-frequency bias recording, a method of using high frequency sounds to sensitize magnetic tapes to lower-frequency sounds, resulting in greater clarity across the spectrum. Camras also invented stereo sound recording and reproduction by tape, long before standard phonograph records were recorded that way. His other inventions include multi-track recording, magnetic soundtracks for motion pictures, and a prototype video tape recorder (1950).

Marvin Camras' magnetic tapes and their coatings were, and remain, the basis of most of the media, entertainment and computer recording and storage being done today---in total, perhaps $40 billion worth of devices and supplies per year.

Camras spent a fifty-year career at the Armour Research Foundation and the Illinois Institute of Technology, where he taught until 1994. By the time of his death in 1995, he had earned over 500 US and international patents for his work. He was inducted into the National Inventors Hall of Fame in 1985, and in 1990 he won the National Medal of Technology.

 

[June 1999]

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