Hysteresis in general concept(from Greek - lagging behind) - this is a property of certain physical, biological and other systems that respond to appropriate influences, taking into account current state as well as backstory.

Hysteresis is characteristic of the so-called. "saturation", and various trajectories of the corresponding graphs that mark the state of the system at a given time. The latter, as a result, have the shape of an acute-angled loop.

If we consider specifically electrical engineering, then each electromagnetic core after the end of exposure to electric current for some time retains its own magnetic field, called residual magnetism.

Its value depends, first of all, on the properties of the material: for hardened steel, it is significantly higher than for soft iron.

But, in any case, the phenomenon of residual magnetism is always present when the core is remagnetized, when it is necessary to demagnetize it to zero, and then change the pole to the opposite one.

Any change in the direction of the current in the winding of an electromagnet provides (due to the presence of the above material properties) a preliminary demagnetization of the core. Only after that it can change its polarity - this is a well-known law of physics.

For remagnetization in the opposite direction, an appropriate magnetic flux is required.

In other words: the core change does not "keep up" with the corresponding changes. magnetic flux, which promptly creates a winding.

It is this time delay in the magnetization of the core from changes in magnetic fluxes that has received the name in electrical engineering as hysteresis.

Each remagnetization of the core provides for getting rid of residual magnetism by exposing it to an opposite magnetic flux. In practice, this leads to certain losses of electricity, which are spent on overcoming the "wrong" orientation of molecular magnets.

The latter manifest themselves in the form of heat generation, and represent the so-called hysteresis costs.

Thus, steel cores, for example, stators or armatures of electric motors or generators, as well as, should have the smallest possible correlation strength. This will reduce hysteresis losses, ultimately increasing the efficiency of the corresponding electrical unit or device.

The magnetization process itself is determined by the corresponding graph - the so-called hysteresis loop. It is a closed curve showing the dependence of the magnetization rate on changes in the dynamics of the external field strength.

A large loop area implies, respectively, and high costs for remagnetization.

Also, in almost all electronic devices, there is such a phenomenon as thermal hysteresis - non-return after warming up the equipment to its original state.

In and the phenomenon of hysteresis is used in various magnetic storage media (for example, Schmidt triggers), or in special hysteresis electric motors.

This physical effect is also widely used in various devices, designed to suppress various noises (bounce of contacts, fast oscillations, etc.) in the process of switching logic circuits.

Magnetization curve and hysteresis loop

To characterize the phenomenon of magnetization of a substance, the quantity I is introduced, called the magnetization of matter. Magnetization in SI is determined by the formula

For ferromagnetic bodies, the magnetization I is a complex non-linear function of B 0 . The dependence of I on the value Bo/µ 0 is called the magnetization curve (Fig. 2). The curve indicates the phenomenon of magnetic saturation: starting from a certain value Во/µ 0 = В 0н /µ 0 , the magnetization practically remains constant, equal to In (saturation magnetization).

Magnetic hysteresis (From the Greek "hysteresis" - the lag of the effect from its cause) a ferromagnet is called the lag of a change in the magnitude of the magnetization of a ferromagnetic substance from a change in the external magnetic field in which the substance is located. The most important reason for the magnetic hysteresis is the dependence of its magnetic characteristics (µ, I) characteristic of a ferromagnet not only on the state of the substance at a given moment, but also on the values ​​of µ and I at previous times. Thus, there is a dependence of the magnetic properties on the previous magnetization of the substance.

A hysteresis loop is a curve of dependence of the change in the magnitude of the magnetization of a ferromagnetic body placed in an external magnetic field, on a change in the induction of this field from + Bo / µ 0 to - Bo / µ 0 and vice versa. The value + In/µ 0 corresponds to the saturation magnetization I n. In order to completely demagnetize a ferromagnetic body, it is necessary to change the direction of the external field. At a certain value of the magnetic induction - B 0k, which corresponds to the value B 0k /µ 0, called the coercive (retarding) force, the magnetization I of the body will become equal to zero.

The coercive force and the shape of the hysteresis loop characterize the property of a ferromagnet to retain residual magnetization and determine the use of ferromagnets for various purposes. Ferromagnets with a wide hysteresis loop are called hard magnetic materials (carbon, tungsten, chromium, aluminum-nickel and other steels). They have a large coercive force and are used to create permanent magnets. various shapes(strip, horseshoe, magnetic arrows). Soft magnetic materials with a low coercive force and a narrow hysteresis loop include iron, iron-nickel alloys. These materials are used for the manufacture of cores of transformers, generators and other devices, under the operating conditions of which magnetization reversal occurs in variable magnetic loops. The remagnetization of a ferromagnet is associated with the rotation of the regions of spontaneous magnetization. The work required for this is done by the energy of the external magnetic field. The amount of heat released during remagnetization is proportional to the area of ​​the hysteresis loop.

At temperatures below the Curie point, any ferromagnetic body consists of domains - small areas with linear dimensions of the order of 10 -2 -10 -3 cm, within which there is the greatest value of magnetization, equal to the saturation magnetization. Domains are named differently regions of spontaneous magnetization. In the absence of an external magnetic field, the vectors of the magnetic moments of individual domains are completely randomly oriented inside the ferromagnet, so that the total magnetic moment of the entire body is zero (Fig.). Under the influence of an external magnetic field in ferromagnets, there is a rotation along the field of magnetic moments not of individual atoms or molecules, as in paramagnets, but of entire regions of spontaneous magnetization - domains. With an increase in the external field, the sizes of domains magnetized along the external field grow due to a decrease in the sizes of domains with other (not coinciding with the direction of the external field) orientations. With a sufficiently strong external magnetic field, the entire ferromagnetic body is magnetized. The magnitude of the magnetization reaches its maximum value - magnetic saturation occurs. In the absence of an external field, some of the magnetic moments of the domains remain oriented, and this explains the existence of residual magnetization and the possibility of creating permanent magnets.

Application of ferromagnets in engineering. Rotors of generators and electric motors; cores of transformers, electromagnetic relays; in electronic computers (computers), telephones, tape recorders, on magnetic tapes.

Paramagnetic substances are characterized by being magnetized in an external magnetic field; if this field is turned off, the paramagnets return to the non-magnetized state. The magnetization in ferromagnets is preserved even after the external field is turned off. On fig. 2 shows a typical hysteresis loop for a magnetically hard (high loss) ferromagnetic material. It characterizes the ambiguous dependence of the magnetization of a magnetically ordered material on the strength of the magnetizing field. With an increase in the magnetic field strength from the initial (zero) point (1), the magnetization proceeds along the dashed line 1-2, and the value of m changes significantly as the magnetization of the sample increases. At point 2, saturation is reached, i.e. with a further increase in the intensity, the magnetization no longer increases. If we now gradually reduce the value of H to zero, then the curve B(H) no longer follows the same path, but passes through point 3, revealing, as it were, the "memory" of the material about " past history", hence the name "hysteresis". Obviously, some residual magnetization is preserved (segment 1-3). After changing the direction of the magnetizing field to the opposite, curve B (H) passes point 4, and segment (1) - (4) corresponds to the coercive force that prevents demagnetization.Further increase in the values ​​of (-H) leads the hysteresis curve to the third quadrant - section 4-5.The subsequent decrease in the value of (-H) to zero and then an increase positive values H will close the hysteresis loop through points 6, 7 and 2.

Rice. 2. TYPICAL HYSTERESIS LOOP for a magnetically hard ferromagnetic material. At point 2, magnetic saturation is reached. Segment 1-3 determines the residual magnetic induction, and segment 1-4 - the coercive force, which characterizes the ability of the sample to resist demagnetization.

Magnetically hard materials are characterized by a wide hysteresis loop covering a significant area on the diagram and therefore corresponding to large values ​​of residual magnetization (magnetic induction) and coercive force. A narrow hysteresis loop (Fig. 3) is characteristic of soft magnetic materials such as mild steel and special alloys with high magnetic permeability. Such alloys were created in order to reduce energy losses due to hysteresis. Most of these special alloys, like ferrites, have a high electrical resistance, which reduces not only magnetic losses, but also electrical losses due to eddy currents.

Rice. 3. A TYPICAL HYSTERESIS LOOP for a magnetically soft material (for example, iron). Since the area of ​​the loop is proportional to the energy losses, such materials have little resistance to demagnetization and are characterized by low energy losses.

Magnetic materials with high permeability are produced by annealing, which is carried out by holding at a temperature of about 1000 ° C, followed by tempering (gradual cooling) to room temperature. At the same time, preliminary mechanical and heat treatment, as well as the absence of impurities in the sample. For transformer cores at the beginning of the 20th century. silicon steels were developed, the value of m of which increased with increasing silicon content. Between 1915 and 1920, permalloys (alloys of Ni with Fe) appeared with their characteristic narrow and almost rectangular hysteresis loop. Especially high values magnetic permeability m at low values ​​of H differ in hypernic (50% Ni, 50% Fe) and mu-metal (75% Ni, 18% Fe, 5% Cu, 2% Cr) alloys, while in perminvar (45% Ni, 30% Fe, 25% Co) the value of m is practically constant over a wide range of changes in the field strength. Among modern magnetic materials, supermalloy should be mentioned - an alloy with the highest magnetic permeability (it contains 79% Ni, 15% Fe and 5% Mo).

(taken from http://www.phyzika.ru/Magnitnoe.html)

Hysteresis

The phenomenon of magnetic hysteresis is observed not only when the field changes H in magnitude and sign, but also in its rotation (magnetic rotation hysteresis), which corresponds to a lag (delay) in changing direction M with direction change H. Magnetic rotation hysteresis also occurs when the sample rotates about a fixed direction H.

The theory of the hysteresis phenomenon takes into account the specific magnetic domain structure of the sample and its changes during magnetization and magnetization reversal. These changes are due to the displacement of domain walls and the growth of some domains at the expense of others, as well as the rotation of the magnetization vector in domains under the action of an external magnetic field. Everything that delays these processes and promotes the entry of magnets into metastable states can cause magnetic hysteresis.

In single-domain ferromagnetic particles (in particles of small sizes, in which the formation of domains is energetically unfavorable), only rotation processes can occur M. These processes are hindered by magnetic anisotropy of various origins (the anisotropy of the crystal itself, the anisotropy of the particle shape, and the anisotropy of elastic stresses). Thanks to the anisotropy, M seems to be held by some internal field (the effective field of magnetic anisotropy) along one of the easy magnetization axes corresponding to the energy minimum. Magnetic hysteresis occurs because the two directions M(along and opposite) this axis in a magnetically uniaxial sample or several equivalent (in energy) directions M in a magnetically multiaxial sample, they correspond to states separated from each other by a potential barrier (proportional to ). In the case of magnetization reversal of single-domain particles, the vector M turns in a series of successive irreversible jumps in the direction H. Such rotations can occur both homogeneously and inhomogeneously in volume. With uniform rotation M coercive force. More universal is the non-uniform rotation mechanism M. However, it has the greatest influence on the case when the anisotropy of the particle shape plays the main role. However, it may be significantly less effective field shape anisotropy.

Ferroelectric hysteresis- ambiguous loop-like dependence of polarization P ferroelectrics from an external electric field E during its cyclic change. Ferroelectric crystals have a spontaneous (spontaneous, that is, occurring in the absence of an external electric field) electric polarization in a certain temperature range P c. Polarization direction can be changed electric field. At the same time, the dependence P(E) in the polar phase is ambiguous, the value P given E depends on the background, that is, on how it was electric field at previous times. The main parameters of the ferroelectric hysteresis are:

• residual polarization of the crystal P ost, at E = 0
• field value E Kt (coercive field) at which repolarization

Elastic hysteresis

Hysteresis is used to suppress noise (rapid oscillations, contact bounce) at the moment of switching logic signals.

In electronic devices of all kinds, the phenomenon of thermal hysteresis is observed: after heating the device and its subsequent cooling to the initial temperature, its parameters do not return to the initial values. Due to the unequal thermal expansion of semiconductor crystals, crystal holders, microcircuit packages and printed circuit boards mechanical stresses arise in the crystals, which persist even after cooling. The phenomenon of thermal hysteresis is most noticeable in precision ones used in measuring analog-to-digital converters. In modern microcircuits, the relative shift of the reference voltage due to thermal hysteresis is on the order of 10-100 ppm.

In biology

Hysteresis properties are characteristic of mammalian skeletal muscles.

In soil science

One of them indicates the relationship between the efforts made by the subject of influence and the result achieved. The level of educational and propaganda work spent by the subject can be correlated with the level of "magnetization" (the degree of involvement in new idea) of the carrier object public opinion, social group, collective, social community or society as a whole; in this case, some lag of the object from the subject may be detected. Persuasion, including those with supposed destructive consequences, is not always successful. It depends on one's own moral values, customs, traditions, the nature of previous upbringing, on the ethical norms that dominate in society, etc.

The second circumstance is related to the fact that new stage the formation of public opinion can be correlated with the history of the object, its experience, its assessment by those who previously acted as the object of the formation of public opinion. At the same time, it can be found that the "starting point" of the time of formation of public opinion is shifting relative to the previous one, which is a characteristic of the system itself and its current state.

Literature on the topic

• Raddai Raikhlin Civil war, terror and banditry. Systematization of Sociology and Social Dynamics. Crowd Control Section
• Kapustin Valery Sergeevich An Introduction to the Theory of Social Self-Organization. Topic 11. The phenomenon of hysteresis in the formation national forms and ways of self-organization. Modern paradoxes and mysteries of the "beginning"

In philosophy

Mathematical models of hysteresis

Appearance mathematical models hysteresis phenomena was caused by a fairly rich set of applied problems (primarily in the theory automatic regulation), in which the hysteresis carriers cannot be considered in isolation, since they were part of some system. The creation of the mathematical theory of hysteresis dates back to the 60s of the XX century, when in Voronezh University a seminar began to work under the guidance of M. A. Krasnoselsky, "hysteresis" topics. Later, in 1983, a monograph appeared in which various hysteretic phenomena were formally described in the framework of systems theory: hysteresis converters were treated as operators depending on their initial state as a parameter, defined on a sufficiently rich functional space(for example, in the space of continuous functions) acting in some function space. A simple parametric description of various hysteresis loops can be found in the work (replacing harmonic functions in this model with rectangular, triangular or trapezoidal pulses also allows one to obtain piecewise linear hysteresis loops, which are often found in discrete automation, see an example in Fig. 2).

Literature

Notes

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Synonyms:

See what "Hysteresis" is in other dictionaries:

- (from the Greek hysteresis lagging) the delay in the change in a physical quantity characterizing the state of a substance (magnetization M of a ferromagnet, polarization P of a ferroelectric, etc.) from a change in another physical quantity that determines ... ... Big Encyclopedic Dictionary

Shift, lag Dictionary of Russian synonyms. hysteresis noun, number of synonyms: 2 lag (10) … Synonym dictionary

HYSTERESIS, a phenomenon characteristic of elastic bodies; lies in the fact that the DEFORMATION of the body with an increase in STRESS is less than with its decrease due to the delay in the effect of deformation. When mechanical stress is completely removed, it remains ... ... Scientific and technical encyclopedic dictionary

- (from the Greek hysteresis lagging, delay) 1) G. in aerodynamics, the ambiguity of the structure of the flow field and, consequently, the aerodynamic characteristics of a streamlined body for the same values ​​of kinematic parameters, but with ... ... Encyclopedia of technology

Hysteresis is a complex concept of processes occurring in systems and substances that are capable of accumulating various energies in themselves, while the rate and intensity of its increase differs from the curve of its decrease when the impact is removed. In translation from Greek the concept of hysteresis is translated as a lag, and therefore it should be understood as a delay of one process in relation to another. In this case, it is not at all necessary that the hysteresis effect be characteristic only of magnetic media.

This property shows up in many other systems and environments:

• hydraulics;
• kinematics;
• electronics;
• biology;
• economy.

The concept is especially often used in the implementation of temperature control in heating systems.

Features of a physical phenomenon

We will focus on hysteresis in electronic engineering associated with magnetic processes in various substances. It shows how one or another material behaves in an electromagnetic field, and this thereby allows you to build dependency graphs and take some readings of the environments in which these same materials are located. For example, this effect is used in the operation of a thermostat.

Considering in more detail the concept of hysteresis and the effect associated with it, one can notice such a feature. A substance with this property is capable of becoming saturated. That is, this is the state in which it is no longer able to accumulate energy in itself. And when considering the process on the example of ferromagnetic materials, energy is expressed by magnetization, which arises due to the existing magnetic bond between the molecules of a substance. And they create magnetic moments - dipoles, which are randomly directed in the normal state.

Magnetization in this case is the adoption of a certain direction by the magnetic moments. If they are directed randomly, then the ferromagnet is considered demagnetized. But when the dipoles point in the same direction, the material is magnetized. By the degree of magnetization of the core of the coil, one can judge the magnitude of the magnetic field created by the current flowing through it.

Physical process with hysteresis

To understand the hysteresis process in detail, it is necessary to thoroughly study the following concepts:

As for the materials in which the hysteresis effect is best observed, ferromagnets are those. It's a mixture chemical elements, which is capable of being magnetized due to the directionality of magnetic dipoles, therefore usually in the composition there are metals such as:

• iron;
• cobalt;
• nickel;
• compounds based on them.

To see the hysteresis, on a coil with a ferromagnet core, it is necessary to apply AC voltage. At the same time, the magnetization graph will not strongly depend on its value, because the effect depends directly on the properties of the material itself and the magnitude of the magnetic bond between the elements of the substance.

The fundamental point when considering the concept of hysteresis in electronics is just the magnetic induction B created around the coil when voltage is applied. It is determined by the standard formula as the product of the magnetic permittivity of a substance and the sum of the field strength and magnetization.

To understand general principle hysteresis effect , you need to use the chart. It shows the magnetization loop from the state of complete demagnetization. The area can be designated by the numbers 0-1. With a sufficient voltage and duration of the magnetic field on the material, the graph reaches its extreme point along the indicated trajectory. The process is carried out not in a straight line, but along a curve with a certain bend, which characterizes the properties of the material. The more magnetic bonds between molecules in a substance, the faster it goes into saturation.

After removing the voltage from the coil, the magnetic field strength drops to zero. This is the area on the graph 1-2. In this case, the material remains magnetized due to the direction of the magnetic moments. But the magnitude of the magnetization is somewhat lower than at saturation. If such an effect is observed in a substance, then it refers to ferromagnets that are capable of accumulating a magnetic field in themselves due to strong magnetic bonds between the molecules of the substance.

With a change in the polarity of the voltage supplied to the coil, the demagnetization process continues along the same curve to saturation. Only in this case the magnetic moments of the dipoles will be directed in reverse side. With the frequency of the network, the process will be periodically repeated, describing a graph called the magnetic hysteresis loop.

With repeated magnetization of a ferromagnet with a lower strength than with saturation, it is possible to obtain a family of curves from which one can construct general schedule, which characterizes the state of matter from fully demagnetized to fully magnetized.

Hysteresis is a complex concept, which characterizes the ability of a substance to accumulate the energy of a magnetic field or other value due to the existing magnetic bonds between the molecules of the substance or the features of the system. But not only alloys of iron, cobalt and nickel can have such an effect. Barium titanate will give a slightly different result when placed in a field with a certain intensity.

Since it is a ferroelectric, a dielectric hysteresis is observed in it. The reverse hysteresis loop is formed with the opposite polarity of the voltage applied to the medium, and the magnitude of the opposite field acting on the material is called the coercive force.

In this case, the magnitude of the field may precede different intensities, which is associated with the features of the actual state of the dipoles - magnetic moments after the last magnetization. Various impurities also affect the process. contained in the material. The more of them, the more difficult it is to move the walls of the dipoles, so the so-called residual magnetization remains.

What affects the hysteresis loop?

It would seem that, hysteresis is more of an internal effect, which is not visible on the surface of the material, but it strongly depends not only on the type of material itself, but also on the quality and type of it machining. For example, iron saturates at a strength of 1 Oe, and a magnico alloy reaches its critical point only at 580 Oe. The more defects on the surface of the material, the greater the magnetic field strength is required to bring it to saturation.

As a result of magnetization and demagnetization, the material releases thermal energy, which is equal to the area of ​​the hysteresis loop. Also, the effect of eddy currents and the magnetic viscosity of a substance can be attributed to losses in a ferromagnet. This is usually observed when the frequency of the magnetic field changes upwards.

Depending on the nature of the behavior of a ferromagnet in a medium with a magnetic field, there are static and dynamic hysteresis. The first is observed at the nominal voltage frequency, but with its growth, the area of ​​the graph increases, which leads to an increase in losses.

Other properties

In addition to magnetic hysteresis, there are also galvomagnetic and magnetostrictive effects. These processes show a change electrical resistance due to mechanical deformation of the material. Ferroelectrics under the action of deformation forces are capable of generating electricity, which is explained by piezoelectric hysteresis. There is also the concept of electro-optical and double dielectric hysteresis. The latter process is usually of the greatest interest, since it is accompanied by a double graph in zones approaching saturation points.

The definition of hysteresis does not only apply to ferromagnets used in electronics. This process can also take place in thermodynamics. For example, when organizing heating from a gas or electric boiler. The regulating component in the system is the thermostat. But the only controlled value is the temperature of the water in the system.

When it drops to a predetermined level, the boiler turns on, starting heating to a predetermined value. Then it turns off and the process repeats in a cycle. If you take temperature readings during heating and cooling of the system at each cycle of turning the heating on and off, you get a graph in the form of a hysteresis loop, which is called the boiler hysteresis.

In such systems hysteresis is expressed in temperature. For example, if it is 4°C, and the temperature of the coolant is set to 18°C, then the boiler will turn off when it reaches 22°C. So you can customize any acceptable temperature regime in the premises. And the thermostat is, in fact, a temperature sensor or a thermostat that turns on or off the heating when the lower and upper thresholds are reached, respectively.

Consider the process of variable magnetization of a ferromagnetic material. For this purpose, we wind a winding on a steel core and pass through it D.C.. Let us assume that the core of the electromagnet was not previously magnetized.

By increasing the current passing through the turns of the winding I from zero, we will thereby increase the magnetizing force and field strength H. The magnitude of the magnetic induction B in the core will also increase. Magnetization curve 0a in figure 1 has a rectilinear part, and then, due to saturation, the curve rises slowly, approaching the horizontal. If now, having reached the point a, decrease H, then it will decrease and B. However, the decrease B when decreasing H, that is, during demagnetization, will occur with a delay in relation to the decrease H. The amount of residual induction at H= 0 is characterized by a segment 0b.

In order for the magnetic induction in the core to become equal to zero, it is necessary to magnetize the material in the opposite direction, that is, remagnetize it. For this purpose, the direction of the current in the winding is reversed. The direction of the magnetic lines and the magnetic field strength also changes. At field strength H = 0v the induction in the core is zero and the core material is completely demagnetized. Field strength value H = 0v at B= 0 is a certain characteristic of the material and is called the retarding (coercive) force.

By repeating the magnetization reversal process, we obtain a closed curve a b c d e f a, which is called a hysteresis loop or a magnetic hysteresis loop. Hysteresis from the Greek - lagging, lagging. Using this experiment, it is easy to verify that the magnetization and demagnetization of the core (the appearance and disappearance of poles, magnetic induction or magnetic flux) lag behind the moment of appearance and disappearance of the magnetizing and demagnetizing force (current in the electromagnet winding). The phenomenon of hysteresis can be characterized in other words as the lag of changes in magnetic induction from changes in field strength. The remagnetization of the material is associated with the expenditure of a certain amount of energy, which is released in the form of heat, heating the material.

The magnetic hysteresis is especially strong if the core material has a high residual magnetism (eg hard steel). The phenomenon of hysteresis is in most cases harmful. It causes hysteresis losses expressed in heating of the core and extra costs power of the voltage source, and is also accompanied by a buzzing of the core due to a change in polarity and rotation of the elementary particles of the core material.

The first serious study of the processes of steel magnetization was carried out by Alexander Grigoryevich Stoletov (1839 - 1896) in 1872 and published in the work "On the function of magnetization of soft iron".

A. G. Stoletov, in addition, investigated and explained the nature of the external photoelectric effect and made the first photocell.

Video 1. Hysteresis

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