Hysteresis Definition Magnetic Hysteresis Electrical Hysteresis

Hysteresis phenomena occur in magnetic and ferromagnetic materials, as well as in the elastic and electromagnetic behavior of materials, in which a lag occurs between the application and the removal of a force or field and its subsequent effect. Electric hysteresis occurs when applying a varying electric field, and elastic hysteresis occurs in response to a varying force.

If the displacement of a system with hysteresis is plotted on a graph against the applied force, the resulting curve is in the form of a loop. In contrast, the curve for a system without hysteresis is a single, not necessarily straight, line. Although the hysteresis loop depends on the material's physical properties, there is no complete theoretical description that explains the phenomenon. The family of hysteresis loops, from the results of different applied varying voltages or forces, form a closed space in three dimensions, called the hysteroid .

Hysteresis was initially seen only as a problem, but is now considered to be of great importance in technology, and the property is used for example when constructing permanent memoryNon-volatile storage is a category of computer storage. Unlike volatile storage, it doesn't require power to retain stored data. Storage devices in this category include: CD, CD-ROM, CD-R, CD-RW DVD BD-ROM, BD-R, BD-RE Floppy disk Hard disk Magnetic tape for computers.

The term "hysteresis" is sometimes used in other fields, for example economicsEconomics is the social science studying how society uses its limited resources to meet desires and wants. Put otherwise, economics studies what, how and for whom society produces. This involves analyzing the production, distribution and consumption of go or biologyBiology studies the variety of life clockwise from top-left E. coli tree fern, gazelle, Goliath beetle Biology is the science of life. It is concerned with the characteristics and behaviors of organisms, how species and individuals come into existence, an. In such cases it describes a memory or lagging effect in which the order of previous events can influence the order of subsequent events.

1 Definition

The phenomenon of hysteresis can conceptually be explained as follows. A system can be divided into subsystems or domains, much larger than an atomFor alternative meanings see atom (disambiguation). An atom is a microscopic structure found in all ordinary matter around us. Atoms are composed of 3 types of subatomic particles: electrons, which have a negative charge; protons, which have a positive chic volume but still microscopic. Such domains normally occur in ferroelectric and ferromagnetic systems, since individual dipoleThis article is about the electromagnetic phenomenon. From the point of view of the mathematics of distributions, a dipole can be taken to be the directional derivative of a Dirac delta function. A dipole is also a type of radio antenna A dipole is a pairs tend to group with each other, forming a small isotropic region. Each of the system's domain s can be shown to have a metastable state. The metastable domains can in turn have two or more substates. Such a metastable state fluctates widely from domain to domain, but the average represents the configuration of lowest energy. The hysteresis is simply the sum of all domains, or the sum of all metastable states.

2 Magnetic hysteresis

Hysteresis is well known in ferromagnetic materials. When an external magnetic field is applied to a ferromagnet, the ferromagnet absorbs some of the external field. Even when the external field is removed, the magnet will retain some field: it has become magnetized.

The relationship between magnetic field strength and magnetic flux density is not linear in such materials. If the relationship between the two is plotted for increasing levels of field strength, it will follow a curve up to a point where further increases in magnetic field strength will result in no further change in flux density. This condition is called magnetic saturation .

If the magnetic field is now reversed and increased linearily, the plotted relationship will again follow a similar curve back towards and beyond zero flux density but offset from the original curve by an amount called the remanent flux density or remanence. The cause of the offset is the fact that ferromagnetic materials will tend to retain some of the magnetism induced in them and this has to be overcome each time the magnetic field across the substance reverses.

If this relationship is plotted for all strengths of applied magnetic field the result is a sort of S- shaped loop. The 'thinness' of the middle bit of the S describes the amount of hysteresis.

Its practical effects might be, for example, to cause a relay to be slow to release due to the remaining magnetic field continuing to attract the armature when the applied electric current to the operating coil is removed

This curve for a particular material influences the design of a magnetic circuit.

This is also a very important effect in magnetic tape and other magnetic storage media like hard disks. In these materials it would seem obvious to have one polarity represent a bit, say north for 1 and south for 0. However, if you want to change the storage from one to the other, the hysteresis effect requires you to know what was already there, because the needed field will be different in each case. In order to avoid this problem, recording systems first overdrive the entire system into a known state using a process known as bias. Analogue magnetic recording also uses this technique. Different materials require different biasing, which is why there is a selector for this on the front of most cassette recorders.

In order to minimize this effect and the power losses associated with it, ferromagnetic substances like Stelloy are often used. This has a low hysteresis loss.

3 Electrical hysteresis

Electrical hysteresis typically occurs in ferroelectric material, where domain s of polarisation contribute to the total polarisation. Polarisation is the electrical dipole moment (either C· m^-2 or C· m).

4 Liquid-solid phase transitions

Hysteresis is also a known phenomenon in thermodynamics. Here the molecules change properties during heat transfer (via a potential field or a higher temperature increase) and it is this change that causes hysteresis.

5 Energy

When hysteresis occurs with extensive and intensive variable s, the work done on the system is the area under the hysteresis graph.

6 Applications

Hysteresis represents states, and the characteristic curve shape is sometimes remiscent of a two-value state, also called a bistable state. The hysteresis curve really contains infinitely many states, but a simple application is to let the threshold regions (usually to the left and to the right) represent respectively the on and off states. In this way, the system can be regarded as bistable. Note that even if no external field is applied, the position of the hysteresis curve might change with time: it is not necessarily stationary, i.e. the system may not stay in the exact same state as it had previously. The system might need new energy transfer to be stationary.

The hysteresis effect can be used when connecting complex circuits with the so-called passive matrix addressing. This scheme is praised as a technique that can be used in modern nanoelectronic s, electrochrome cells , memory effect, etc. In this scheme, shortcuts are made between adjacent components (see crosstalk) and the hysteresis helps to keep the components in a particular state while the other components change states. That is, one can address all rows at the same time instead of doing each individually.

7 See also

8 External links

Systems theory Electromagnetism

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