The development of magnetic storage devices is attributed to several scientific pioneers. Magnetic storage developed as a result of the discovery of electromagnetism by a Danish Physicist, Hans Christian Oersted in 1819. Hans discovered the deflection property of a compass needle away from the north when brought a wire with an electric current flowing through it. His further experiment revealed to him that when the current was removed from flowing, the compass needle aligned itself with the earth’s magnetic field pointing the north direction. From here, he concluded that there was a relationship between electric current and magnetism. However, the invention of sound magnetic storage devices would have remained at halt without a brilliant Scottish Mathematician, James Clerk Maxwell who managed to calculate the virtual inevitability of radio waves existence. Sound recording utilizes the principle of radio waves. This is the fundamental principle that has been applied by most of the scientists in the development of magnetic storage devices as illustrated below.
Magnetic storage, as a term used in engineering, refers to the storage of data on a magnetized medium. Magnetic storage uses different methods to store different amounts of data in magnetic materials. These storage materials ensure that data stored is non-volatile. The access of the information stored uses the technology of read or write heads. The following paragraphs aim to analyze and trace the discovery of this important storage device in the technological world.
One of the trusted pioneers of magnetic storage was an American engineer, Oberlin Smith. He did an experiment, which provided the foundation for the development of magnetic storage devices. In his experiment, he passed string filled with iron filings through a coil of wires. An existing telephone circuit next to the string converted the sound into modulated electrical current that had the ability to magnetize and demagnetize the iron filings as they travelled past the coil. He rewound the string and passed it through the coil again. The magnetic state of the coil re modulated the current in the coil and produced electrical signal that could reproduce the original sound.
Taking on this, iron is a ferromagnetic material and got magnetized easily to produce a strong magnet with stronger magnetic field surrounding it. The telephone converted electrical energy into sound energy. The sound energy in the sound waves was converted into electrical energy. The electrical current then magnetized the iron filings through electrical method of magnetization. Rewinding the string and passing it through the coil again ensured that no electric current was next to it any more. This is in accordance to Faraday’s law of electromagnetism, which explains that magnetic fields have the ability to produce electrical current and vice versa. The same principle is found in Andre-Marie Ampere’s discovery that wires carrying electrical current normally exert magnetic force on each other. Ferromagnetic materials have small magnetic particles known as dipoles. Exposing these particles to electrical current make them realign themselves facing one direction to make a stronger magnet. The existence of the dipoles is also attributed to Marie Ampere.
Unaware of Oberlin’s work, a Danish scientist, Valdemar Poulsen, discovered the first scientific idea behind magnetism in 1898 (Wang & Aleksand, 1999, p197). He was the first to invent the first magnetic device, that is, the first telephone answering machine.Therefore, Poulsen is considered a profound contributor in the field of electromagnetism and magnetic storage devices. He came up with a wire storage device, a fundamental basis that made other scientists improve on the storage technology. Wire storage device works amazingly utilizing only the relationship of magnetism and current, that is, electromagnetism as explained below.
Magnetic materials are clasifiedategorized as soft and hard magnetic materials. Hard magnetic materials have the ability to retain their magnetic properties even after its removal from a magnetic field. Soft magnetic materials, on the other hand, have negligible magnetic materials ones they are taken away from the magnetic field, or the field is removed by termination of magnetization process. These two types of magnetic materials had crucial roles to play in the making of the first wire recorder (Spaldin, 2010, p122). The following sentences will analyze the Poulsen’s first wire recorder and the laws and theories applied in the making of the machine. The system has a storage medium at the middle point where signal stored is easily retrieved later. This storage medium is a hard magnetic material. The choice of a magnetic material was a very crucial stage that Poulsen underwent while making the recorder. When a material of too high coercivity (Hc) was used, then he would have faced the difficulty of recording the signal. If he had obtained a small product of saturation Volume and Saturation Magnetization (Ms), then another serious problem of replay signal being small would have arisen.
Besides, he took care of the mechanical properties of the medium he had chosen to use. He took care of the surface roughness, magnetic grain size and the corrosive resistance of the magnet. Moreover, he ensured that the material he chose could store magnetism for a considerable time length over a suitable temperature range with the existence of stray magnetic fields. From the last statement, it can be seen that Poulsen was aware of the existence of stray magnetic fields caused by the earth’s natural magnetic field as discovered by David and Brunhes in 1904, in France, after an observation of a reversed lava flow in the Central Mountain. He used a single magnetic transducer (recording head) for writing to the magnetic medium (Spaldin, 2010, p89). The transducer converts electric current into a magnetic field. It is also responsible for writing on a disk drive. He used a magnetic influx coupled or fit into a soft magnetic core. The influx is responsible for inducing a voltage potential across the coil. The voltage across the coil (V) is directly proportional to the change influx change experienced by the coil (Cregan, 2009, p99). This is an application of Faraday’s law of electromagnetism that states the electromotive force (EMF) generated is proportional to the influx rate of change. The law is expressed in the equation below:
V=-N dP/dX, where V is the EMF or voltage across the coil, dp/dt is the rate of influx change and N represents the number of turns in the coil.
The negative sign implies that the voltage is opposite in polarity to the magnetic influx change. The recording medium is moved past the writing and reading head faster (with higher velocity) so as to increase the output voltage. Another convenient method of increasing the output amplitude is by increasing the number of turns on the coil. To explain the negativity of N (-N) further Lenz’s law is applicable. The law states that induced EMF always yield current whose magnetic fields oppose any change in the original magnetic influx. The law, which is an improvement of Faraday’s law of electromagnetism, was put forward by a Russian physicist, Heinrich Lenz (Cregan, 2009, p102).
As described above, a wire recorder has three basic components; a recording medium, which is the wire, the write/ read head together with required electronics and mechanical means of moving the head past the wire or the wire past the head. That was the basic scientific explanation behind the invention of the first magnetic storage device.
A German Austrian engineer, Fritz Pfleumer, was the first one to think and come out with an idea of magnetic tape for recording sound in 1927. He first developed a process of putting metal strips on cigarette papers. From there, he reasoned out that he could similarly do some coating on magnetic stripes to be used as alternative wire recordings. He used a thin paper coated with an oxide of iron by the use of lacquer as glue. Iron is a ferromagnetic material and once magnetized do not lose its magnetism easily. Moreover, the strength of the magnetic field would be higher compared to Poulsen’s one which was induced through electromagnetism (Mee & Erick, 1996, p143).
The American Telegraphone Company acquired Poulsen’s patent in 1905. Nevertheless, the telegraphone never competed well with the more reliable wax cylinder, louder and less expensive wax cylinders. This led to rekindling if practical use of magnetic recording. The first progress was electronic amplification by use of vacuum tubes. The vacuum tube technology gave the magnetic recorders the sensitivity and power for a new loudspeaker playback. Carpenter and Carlos at the US naval Research laboratory later patented an AC biasing. This yielded more permanent recordings and a lower level of noise than before using different magnetic media.
More development came about in the 1930s when a German company, AEG in Berlin began the development of a new tape based recorder. The tape was made of cellulose acetate base with an oxide of iron (iron oxide) bound to one of its sides. The use of magnetophone was demonstrated at Berlin Radio Fair in 1935. It was conducted by Thomas Beechman (Mee & Erick, 1996, p143).
Dr. Clarence Hickman demonstrated new material technology that had the ability of recording more signal on a less medium. This had a significantly important impact of reducing the speed with which the tape had to move. From here, there has been significant development of magnetic storage devices among them are the analog ones.
The current magnetic storage devices use the same principle as explained later in the paper. Hard disk, for example, utilizes the same electromagnetic principles discovered and invented by the early scientists in storing bulk of useful information. However, due to the current advancement of technology, there have been some changes on the speed, methods, and size of the storage devices. Modern magnetic storage devices utilize as well Faraday and Maxwell’s laws. A magnetic tape has three crucial parts namely, the heads and the plate. When recording information, the head changes the electrical impulses into magnetic fields. When reading back, it changes the magnetic fields into the initial electrical impulses. The read/write heads are always U-shaped (Oja & Parsons, 2010, p29). Their situation is directly above or next to the surface of the intended storage medium. These heads are wrapped with windings or coils of wire of conductive wires through which electric current can easily flow. When the drive logic passes through the coils, a magnetic field is generated in the drive head. The polarity of the generated field reverses when that of the current changes. To summarize, the heads of a magnetic tape are simply electromagnets whose voltage can be switched quickly in polarity.
The disc or tape, on the other hand, constitutes the actual storage medium. It has some form of substrate, aluminium for the case with hard disk. It is on this substrate where layer of magnetizable materials have been deposited. Each of the individual magnetic material is characterized by its own magnetic field. However, the polarities of the medium are always in a disarray when the medium is blank (Cregan, 2009, p101). Since the all the particles point in random directions, the tiny magnetic fields are cancelled out by other magnetic fields that point its opposite direction. The effect of this is a surface with no observable polarity or unified field.
When the read/write head creates a magnetic field, the field automatically jumps the gap existing between the heads of a U-shape. Since the field passes more easily through a conductor than it does through the air, it bends outwards and uses the storage medium as a part of least resistance. This is in accordance to Ohm’s law relating current and potential difference in a closed electric circuit(Hadjipanayis, 2001, p97). According to Faraday’s law, the magnetic field has an associated electric current (induced current). Existence of current definitely reveals the existence of electromotive force. To reduce energy loss, the electric field lines passes through a path of least resistance, the tape in this case. This is from the formula of Ohm’s law, which states that the potential difference across a conductor is always directly proportional to the amount of current flowing through the conductor. V=IR, where, I the current, V is the potential difference and R the resistance (Cregan, 2009, p87).
As the magnetic field passes through the medium under the gap, it polarizes most of the magnetic particles it passes through, and they become aligned with the field, that is, they face the same direction as the field as far as magnetic polarities are concerned. The direction of the field or polarity induced in the magnetic medium is always based on the direction of current flow in the coils. Any change in the direction of the flow of current always produces a change in the magnetic field direction. When making a magnetic storage, the distance between the read/write head and that of the medium is decreased. When Ohm’s idea of factors affecting the strength of the magnetic field is applied in this case, it can be seen that the distance between a conductor and the field is an important factor to consider (Cregan, 2009, p107). This makes the size of the magnetic domain recorded smaller. A smaller magnetic domain ensures a higher density of data that the drive can store.
Passing of the magnetic field through the medium ensures that the particles are in alignment, and they do not cancel one another out as before. This is in according to Oersted’ theory on magnetic dipole characteristics. Due to this, an observable magnetic field exists in such a region of the medium. As the surface of the storage moves past the drive head, the head generates a given polarity of magnetic flux over a certain region of the medium. Reversing the flow of the electric current reverses the polarities of the magnetized particles on the disk medium (flux reversal). A drive head causes or creates a reversal on the medium to record data. This leads to the formation of transition cells or bit cells (points of flux reversals on the medium). Each particular pattern used in storage the data on the medium is referred to as the encoding method (Wang & Aleksand, 1999, p54).