Magnetic Recording Essay

Magnetic Recording Theory
Until recently, there was one dominant way of recording signals so that they could be reproduced at a later time or in a different location: analog magnetic recording (of course, there were mechanical methods like phonograph records, but they could not be easily recorded). In fact, magnetic recording techniques are still the most common way of recording signals. The system relies on the imposition of a magnetic field, derived from an electrical signal, on a magnetically susceptible medium, which becomes magnetized. The magnetic medium employed is magnetic tape: a thin plastic ribbon with randomly oriented microscopic magnetic particles glued to the surface. The record head magnetic field alters the polarization (not the physical orientation) of the tiny particles so that they align their magnetic domains with the imposed field: the stronger the imposed field, the more particles align their orientations with the field, until all of the particles are magnetized. The retained pattern of magnetization stores the representation of the signal. When the magnetized medium is moved past a read head, an electrical signal is produced. Unfortunately, the process is very non-linear, so the resulting playback signal is different from the original signal. Much of the circuitry employed in an analog tape recorder is necessary to undo the non-linear distortion introduced by the physics of the system. Recording The record head converts an electrical signal into a magnetic field which can be used to create a pattern of magnetization in the tiny magnetic particles of the tape. The head consists of a torroidal core with a small air gap. A coil of wire is wound around the core, which is made of a magnetically permeable metal. Much like a transformer, the record head converts an electrical signal into a changing magnetic field. Since the gap in the head exhibits