What Is a Magnetic Head?

A magnetic head refers to a component that reads data on a magnetic medium through the principle of magnetics. Common heads include hard disk heads, tape recorder heads, and so on. The hard disk head is a key component for reading data from the hard disk. Its main function is to convert the magnetic information stored on the hard disk platter into an electrical signal for external transmission, and its working principle is that the resistance value of special materials will follow The principle of magnetic field changes is used to read and write data on the platter. The quality of the magnetic head largely determines the storage density of the hard disk platter. At present, the GMR (Giant Magneto Resistive) giant magnetoresistive head is more commonly used.

Chinese name: magnetic head

Foreign name: Head

Magnetic head

The magnetic head of a hard disk is made by winding a coil on a magnetic core. The original magnetic head was integrated with reading and writing, and the amplitude of the signal was sensed through current changes. For most computers, in the process of exchanging data with the hard disk, the read operation is much faster than the write operation, and read / write is an operation with two different characteristics. This has prompted hard disk manufacturers to develop a read / write split magnetic head. . ^[1]

Magnetic head

The internal structure of the hard disk head is the most expensive part of the hard disk, and it is also the most important and critical part of the hard disk technology. The traditional magnetic head is an electromagnetic induction magnetic head with a combination of read and write. However, the hard disk read and write are two completely different operations. For this reason, this two-in-one magnetic head must be designed.

At the same time, both read / write characteristics must be taken into consideration, which causes limitations in hard disk design. The MR head (Magnetoresistive heads), that is, the magnetoresistive head, uses a separate head structure: the write head still uses the traditional magnetic induction head (the MR head cannot perform write operations), and the read head uses the new MR head. The so-called inductive write, magnetoresistive read. In this way, the different characteristics of the two can be optimized at design time to obtain the best read / write performance. In addition, the MR head senses the signal amplitude through resistance changes rather than current changes, so it is very sensitive to signal changes, and the accuracy of reading data is correspondingly improved. And because the amplitude of the read signal has nothing to do with the track width, the track can be made very narrow, thereby increasing the disc density to 200MB / inch2, while using a conventional magnetic head can only reach 20MB / inch2, which is also an MR head The main reason for being widely used. MR magnetic heads have been widely used, and GMR magnetic heads (Giant Magnetoresistive heads) made of materials with a multilayer structure and a better magnetoresistance effect have also gradually spread. ^[1]

The magnetic head is a tool for reading and writing discs in a hard disk, and is one of the most precise parts in the hard disk. The magnetic head is made by winding a coil around a magnetic core. When the hard disk is in operation, the magnetic head reads data by sensing changes in the magnetic field on the rotating disc; it writes data by changing the magnetic field on the disc. To avoid abrasion of the magnetic head and the disk, the magnetic head is suspended above the high-speed rotating disk without direct contact with the disk during operation. Only after the power is turned off, the magnetic head will automatically return to the fixed position on the disk ( It is called the landing zone, where the disc does not store data, it is the starting position of the disc). ^[1]

Working properties of magnetic head

Due to the nature of the magnetic head's work, the requirements for its magnetic induction sensitivity and precision are very high. Earlier magnetic heads used ferromagnetic materials, which were not ideal in terms of magnetic induction sensitivity. Therefore, the capacity of single disks of early hard disks was relatively low. If the capacity of a single disk was large, the track density on the disk was large. data. This caused early hard drives to have limited capacity. With the development of technology, the magnetic head has made great progress in terms of magnetic induction sensitivity and precision. ^[1]

Initially, the magnetic head had read and write functions together, which required high manufacturing technology and technology. For personal computers, in the process of exchanging data with the hard disk, reading data is much faster than writing data. The characteristics of the read and write operations are also completely different, which results in separate read and write heads, which work separately and do not interfere. ^[1]

The magnetic head is severely magnetized, and demagnetization is sufficient.

Head head type

TFI Magnetic head thin film induction (TFI) magnetic head

Between 1990 and 1995, hard disks used TFI read / write technology. TFI heads are actually wound cores. When a disc passes under a wound core, an induced voltage is generated on the magnetic head. The reason why the TFI read head reaches its capacity limit is that while the magnetic sensitivity is improved, the write capacity is weakened. ^[1]

AMR Anisotropic magnetic resistance (AMR) head

In 1991, IBM proposed its read head technology based on magnetoresistive (MR) technology-anisotropic magnetism. The magnetic head reads data by sensing changes in the magnetic field on the disc during contact with the rotating disc . In the hard disk, the single-disk capacity of the disc and the head technology are mutually restrictive and mutually reinforcing. ^[1]

AMR (Anisotropic Magneto Resistive) In the mid-1990s, Seagate introduced hard drives using AMR heads. AMR heads use TFI heads to perform write operations, but use thin strips of magnetic material as read elements. In the presence of a magnetic field, the resistance of the thin strip changes with the magnetic field, which in turn generates a strong signal. The hard disk interprets the change in the resistance of the thin strip due to the change in the polarity of the magnetic field, which improves the read sensitivity. AMR heads further increase the areal density and reduce the number of components. Because the resistance change of the AMR film has a certain limit, the AMR technology can support a maximum recording density of 3.3 GB / square inch, so the sensitivity of the AMR head also has a limit. This led to the development of GMR heads. ^[1]

GMRGiant Magneto Resistive GMR (Giant Magneto Resistive)

GMR heads inherit the read / write technology used in TFI heads and AMR heads. But its read head shows higher sensitivity to magnetic changes on the disk. The GMR head is composed of 4 layers of conductive material and magnetic material film: a sensing layer, a non-conductive interposer, a magnetic plug layer, and an exchange layer. The sensitivity of the GMR sensor is three times greater than that of the AMR head, so it can increase the density and performance of the disc. ^[1]

The number of magnetic heads of a hard disk depends on the number of disks in the hard disk. Data is stored on both sides of the disk, so one disk corresponds to two magnetic heads to work properly. For example, a hard disk with a total capacity of 80GB uses a single disk with a capacity of 80GB. There is only one disk. The front and back of the disk have data, which corresponds to two magnetic heads. The same hard disk with a total capacity of 120GB uses two disks Disk, there are only three magnetic heads, one of which has no magnetic head on one side. ^[1]

Head of magnetic tape recorder

The recorder works on the principle of electromagnetic induction. This magnetic head is actually a hoof-type electromagnet. When the recorder is in operation, the sound of the microphone's paper disk is transformed into an induced current through vibration, which is transmitted to the magnetic head through the amplifier circuit. Magnetized, making it an electromagnet. The induced current was originally changed by sound. Under the electromagnetic action of the magnetic head, the magnetic powder on the magnetic tape was magnetized to different degrees and arranged in order. Before recording, the tape must be erased (commonly known as tape washing and degaussing) to avoid the previous sound signal during the playback of the tape, which may cause noise. The recording head and playback head on the recorder are actually the same head (the recording and playback heads are separated in high-end recorders and recording decks), but the connection positions are different. The head is connected to the microphone (or microphone) during recording, and the speaker is connected during playback. The erasing head is actually a natural magnet (also supersonic current erasing), the principle is: before the recording, the magnetic powder on the tape is arranged in the same order. In this way, the original information on the tape is washed away. ^[1]

--- Head failure-head collision

Head collision is a kind of hard disk failure, which occurs when the hard disk read-write head comes into contact with the rotating hard disk, which causes permanent and unrecoverable damage to the medium on the surface of the disk. ^[1]

The magnetic head is usually wrapped in a thin layer of air on the surface of the disc (a thin liquid layer was used in the mid-1990s). The top layer of the disc is a polytetrafluoroethylene-like substance as a lubricant. Below is a layer of sputtered carbon. These two layers protect the magnetic layer (data storage area) from accidental contact of the head.

The disk read / write head uses thin-film technology, which is hard enough to be scratched by the protective layer. The head collision is more likely due to the external force passing through the read / write head, which generates sufficient pressure on the disc, causing the magnetic storage layer to be scratched. Other dirt or debris, excessive impact or vibration, and accidental dropping can cause the read / write head to impact the disc, which usually damages the read / write head during this process. ^[1]