This phenomenon is called dielectric polarization. Dielectrics and their power, polarization and the disruptive voltage of dielectrics. In strong fields

It is important, depending on the concentration of strong body charges, to be divided into conductors (n 0 ~10 28 ÷ 10 29 m -3), conductors (n 0 ~10 17 ÷ 10 19 m -3) and dielectrics (n 0 ~10 9 ÷ 10 13 m - 3).

Dielectrics, like any other substance, are made up of neutral atoms and molecules. If we replace the entire positive charge of the molecule with one point charge placed at the center of its section and in a similar manner with electrons, then the skin molecule in this situation can be seen as an electric dipole. For this reason, all dielectrics can be divided into three groups:

The first group creates words with a symmetrical division as positive and negative charges in the molecule. For such molecules, the centers of positive charges and electrons are combined. The stench is called non-polar. This is the dipole moment. Under the influx of an external field, the differential charges of such molecules are displaced along the lines of force on the opposite side. In this case, the dipole moment is responsible for rectification along the field (N 2 H 2 O 2 CO 2 CH 4).

Another group consists of materials whose molecules carry an asymmetrical distribution of charges. Such molecules are called polar. The stench of the powerful electric dipole moment looms. In ordinary minds, the vectors of dipole moments of neighboring molecules through the thermal flow are oriented chaotically. Therefore, the total moment of the body is equal to zero. The external electric field orients the dipole moments of such molecules along the force lines of the field. This will cause the guilt of the resulting, not equal to zero, electric moment of every dielectric. Apply: N 2 Pro, NH 3. SO 2 CO.

Before the third type there are dielectrics who create a crystalline structure with the correct drawing of ions of different signs. Their structure can be considered as a system of two sublattices inserted one into another. Under the influx of the field, small sharp displacements of the crystallographic surfaces are observed: the areas that accommodate positively charged ions are displaced by the field, and the areas created by negative ions are moved against the field. This is to bring about the resultant dipole moment of the crystal.

The process of orientation of dipole moments or their appearance under the influx of an external electric field, which leads to the reduction of the electrical moment of the skin element to the volume of the dielectric, is called polarization of dielectrics.

There are three types of such polarization:

1. Electronic deformation - The induced dipole moments of atoms are due to the deformation of the electronic shells, then. displacement of electron orbitals of nuclei.

2. Orientation and dipole - Ordering in the arrangement of the most important dipole moments.

3. Ionna - It arises as a result of the constrictive displacement of crystalline burrs: what is formed by positively charged ions along the field, and created by negative ions - against the field. Polarization is simply characterized by polarization (polarization vector) – a vector quantity, which is defined as the total dipole moment per unit volume of the dielectric:

, (21)

de r i– dipole moment of one molecule; р v - Total dipole moment of any dielectric.

It is clear that for the great class of dielectrics (except for ferroelectrics), the polarization linearly depends on the strength of the external field:

de - Electric field strength at the point for which it is measured; χ (хі) - dielectric responsiveness of speech;

- is always a positive, dimensionless quantity. Most dielectrics (solid and rare) become less than one (though, for example, alcohol χ ≈ 25, and water χ = 80).

To establish similar field patterns in the dielectric, up to a uniform external electrostatic field E 0 is introduced (Creates two parallel differently charged planes) a plate made of a single-core dielectric, extended perpendicularly to the field lines. Under the influx of field, the dielectric becomes polarized. There is a displacement of charges: positive ones are displaced by the field, negative ones are displaced against the field. As a result, on the borders of the dielectric, reduced to a negative surface, there will be an excess of positive charge with surface thickness +σ, on the left - a negative charge with surface thickness –σ. These uncompensated charges, which appear as a result of the polarization of the dielectric, are called bound. So because their surface thickness is less thick

As a result of polarization, charge bonds appear on the surface of the dielectric (Fig.). The vector of the field strength of the connected charges of rectification in the middle of the dielectric is parallel to the vector of the external field strength, which causes polarization (Fig.). Now, in accordance with the principle of superposition, the field strength is in the middle of the dielectric.

Either way, regardless of the aggregate state of the parts of your atomic-molecular structure, for example, an atomic, molecular or ionic crystal, etc., it consists of positively charged nuclei and negatively charged electrons.

Therefore, there is only one mechanism of polarization - the displacement of positive charges along the polarizing field and negative charges against the polarizing field (Fig. 3.14). Here it is correct to point out that the speech is polarized not by the external field (div., for example, (3.2) above), but by the total field created both by external charges (do not rely on the dielectric), and by the polarized speech itself. We don’t have anyone in particular to highlight.

Small 3.14. Displacement of positive charges along the polarizing field
and negative charges against the polarizing field

When studying the polarization of specific speeches, it is reasonable and clear to see the main features of a single mechanism for moving charges under the action of a polarizing field, which indicate the result: the stage and nature of the polarization of the speech. This is to bring to the attention of the whole low “private” mechanisms of polarization, such as:

and many others.

The decal to the left of the drive is a known higher ionic polarization, which plays a role in crystals like kitchen salt NaCl. Under the action of the field, the positively charged sodium ion Na + and the negatively charged chlorine ion Cl – shift on different sides from their equal positions, through which the elementary center of the crystal develops an electric dipole moment. This butt is brown in such a sense: although it is easy to use a damped dielectric - it has an ion crystal - its polarization is determined by the displacement of positive and negative charges on the opposite side. The power lies in the fact that they carry a charge before such a movement: free electrons in metal, strongly associated with the nuclei of the electron shell of neutral atoms or molecules in gas or radium, they are at the nodes of the crystal lattice, and so on. . This means that it is a powered dielectric.

The processes that occur in dielectricity during its polarization can be understood from the statement about dielectricity as a medium that consists of pairwise connected different charges. In addition to conductors, electricians do not have large charges, which, under the influence of an external field, can crumble throughout the entire volume of the image. The charges that enter the warehouse of dielectric molecules are intimately connected with each other and continuously move between their molecules (or atoms), so that at a distance of about 50 cm.

In almost all cases, if the dielectric consists of electrically neutral particles (atoms and molecules), regardless of its aggregate state, it is possible to reduce all “submechanisms” of polarization to two types. For this purpose it is customary to divide all atoms, molecules and dielectrics that are composed of them into two classes:

Small 3.15. Polarization of a non-polar dielectric

Small 3.16. Orientation mechanism of polarization of a polar dielectric

Here is the vector of the dipole moment of one molecule, which is assumed to apply to all molecules that are located in the middle of a physically infinitely small space. For example, let’s look at a uniformly polarized core (Fig. 3.17).

Small 3.17. Polarization and electric field of a uniformly polarized coulee

When a nonpolar dielectric is polarized, the electron shell of an atom or molecule is deformed - electrons move against the polarizing field, nuclei move along the field. The problem lies between the centers of positive and negative charges (without a polarizing field). As a result, the atom or molecule swells guidance dipole moment.

It is more obvious that the induced dipole moment will be proportional to the magnitude of the external electric field. It is possible to understand by looking at the behavior of potential energy P( x) interaction between two particles, de X- Stand between them. Let the same point correspond to the position (often the parts are located at the same point and the dipole moment is daily). With small changes in the position of equality in the unfolded potential energy up to the Taylor series, you can share a few first members

Doctors who are similar in the point of equal zero and the other are similar in this point are positive , it is obvious that near the point of stable equal potential energy is generated as

Evidently, when this situation is exhilarated, strength arises

,

similar to the force of spring when the spring is stretched. Since the charge in the molecule is “connected” by such a “spring”, then when the field is applied E It is again equally important to stand between the parts and to be in a relationship

As a result, we know the value of the dipole moment that is under the influence of the field

Multiplying the dipole moment by the concentration of polarized molecules N/V (N- There is no external number in communication V), the polarization of the dielectric is eliminated

How to write down the polarization (3.16) of a view

de constant (for this speech) behind the meanings є dielectric responsiveness speech, then for, then within the framework of this model, dielectric responsiveness can be calculated using the following formula

In molecules called polar, the centers of positive and negative charges are destroyed, because such a molecule has a dipole moment. When such a molecule is placed in an electric field, its electron shell is deformed, the distance between the charge centers increases, and until the end of the dipole moment, a certain induced dipole moment is added. However, it can be shown that this additional induction dipole moment is much less powerful. It is understandable, and rightly so, that the polarizing fields are much smaller than the field that exists in the middle of the molecule. In order of magnitude, the internal molecular field is the traditional atomic unit of electric field strength: V/m. The written atomic unit of electric field strength has the mass of an electron, its charge, the Planck constant. Vrahovuychi, for example, “breakthrough” - what to lead to a spark discharge - the field strength for a dry wind should be set to V/m, so that it is five orders of magnitude less, it can be confirmed that in the most important part of experiments we induced a dipole moment, for the obviousness of the powerful , you can know. Further, when considering the polarization of dipole dielectrics, this effect (induced by an additional moment) is not correct.

The vectors of the power dipole moments of the adjacent molecules are chaotically oriented through the thermal flow. Therefore, due to the absence of the external electric field, the average total dipole moment of any physically infinitely small dielectric is equal to zero. In other words, the dielectric has no polarizations: its polarization is equal to zero.

The external electric field orients the dipole moments of molecules parallel to the vector, and the thermal collapse of which crosses, the dielectric is polarized, in which case the polarization is due to the temperature, and due to the increase in temperature, it is due to change Xia. The lower deposits are calculated, and it will also be shown that for different polar dielectrics, their polarization is proportional to the strength of the polarizing field. This polarization is called orientation(Fig. 3.18).

Small 3.18. Orientational polarization of a dielectric

Extended to formula (3.8) is the potential energy of the dipole in the external field E lie in the direction of the dipole

According to Boltzmann’s statistical law (Fig. 3.19), which describes the distribution of particles behind the energies in the external field in the minds of the thermodynamic balance, the number of molecules, the dipole moment of each orientation under the cut to the external field, is determined as

Here Z- has become normal, the meanings of which will be known later, T- Absolute temperature, constant Boltzmann - k B = 1.38 · 10 -23 J/K. Due to the smallness of the dipole moment of molecules, for extreme (not very low) temperatures the exponential is small, and we can expand the exponential to a Taylor series, excluding the first two terms

Small 3.19. L. Boltzmann (1844–1906) – Austrian physicist

It is important to note that the recovery of the nearby virus (3.18) and all the elements that flow from it is true at not very low temperatures, if . It doesn’t matter more precisely the payment of wages (3.17) or the replacement of a loved one (3.18), since the reader can earn on his own.

Integral over the total solid value of a date outside the number N molecules in the system. If the middle value of the cosine remains equal to zero, then the first addition (3.18) is integrated. So, since the meaning of complete bodily cover is ancient, it can be removed

Now we know the situation Z and we can write expression (3.18) in the form

It is necessary to calculate the value of the projection of the total dipole moment onto the field direction (other projections are likely to reach zero through the axial symmetry of the field). Projection of the dipole moment of one molecule is the old pcosa, also the new dipole moment R all molecules in one unit are ancient

The integral with respect to the original, and the integral with respect to is calculated after the additional replacement of the variable

We know then

From (3.21) it follows that for different dipole orientational polarizations of speech, the polarization is proportional to the strength of the electric field. Moreover, we discovered that polarization depends on temperature. This is Curie's law, which is confirmed by evidence (Fig. 3.20).

Small 3.20. The degree of polarization of a polar dielectric depending on temperature (more precisely, the solution)

While supporting this section, we will briefly repeat the main principles. The external electric field either creates dipole moments oriented along the field, or orients the dipole moments of neighboring molecules, and the dielectric produces a small macroscopic dipole moment. The vector is called the polarization of the dielectric. It is proportional to the strength of the external electric field, and this connection can be applied to the eye

then the polarization vector CI appears in C/m 2 . This dimension is avoided by the dimension of the surface thickness of the charges. This suggests that the polarization vector is due to the strength of the polarization charges that appear on the surface in connection with the dielectric placed near the external field (Fig. 3.21).

Small 3.21. Vector of polarization and strength of polarization charges

Proportionality between polarization R and tension E the external electrostatic field is explained by different electronic and ion polarizations in that they increase E dipole moments of multiple atoms grow p i. With dipole polarization, the degree of vector orientation increases proportionally to the increase in the strength of the external electrostatic field. p i. Most of all, we have discovered scientific formulas for dielectric responsiveness in various types of polarization. It should be noted that the smell is true for gases: we did not rely on the influx of molecules one on one, which is acceptable for systems where the particles are not tightly packed. However, this principle is no longer valid for condensed media (solids and solids): under the influence of an external electric field, a unit volume of the dielectric develops a dipole moment R ; In the simplest cases there is a linear position

The increased dielectric responsiveness of the dielectric is given by all three considered mechanisms:

It rarely happens that all parts of the dielectric sensitivity are however great. Let's say that in ionic crystals the dipole part is burnt out. Experimentally, by applying skin patches, it is possible to determine the vibrating dielectric penetrations at different frequencies of the electromagnetic field. At low frequencies (static field, which we are immediately occupied with), the inserts are given all three parts of dielectric agility (Fig. 3.22).

Small 3.22. Dependency of full dielectric flexibility
Type of electromagnetic frequency Specifies frequency ranges:
I - microradio region, II - infrared region, III - ultraviolet region

When the frequency is increased, the dipole part is first introduced: the molecules cannot rotate, following the electric field, which changes rapidly. The transition to a new mode depends on the frequency of the radio range. With a further increase in frequency, the introduction of the ion part begins to appear: ions are inertial, lower electrons. The optical frequency range is dominated by the portion of electronic polarization. When moving to even higher frequencies - beyond the ultraviolet region - electronic distortions cannot be detected, follow changes in the electric field, and the polarization of the dielectric decreases.

Let's point it out: kitchen salt NaCl has a dielectric penetration in the static field of 5.62, and the electromagnetic field in the optical range is less than 2.25. The dipole polarization in such crystals is daily, and the difference can be attributed to ionic polarization.

additional information

http://science.hq.nasa.gov/kids/imagers/ems/index.html - electromagnetic fluxes, scale of electromagnetic fluxes;

http://science.hq.nasa.gov/kids/imagers/ems/radio.html - radiokhvili;

http://www.nrao.edu/index.php/learn/radioastronomy/radiowaves - radiokhvili, dzherela radiokhvil.

The main electrical processes that occur in dielectrics under the injection of applied voltage are the processes of polarization, electrical conductivity and breakdown of dielectrics.

Polarization is the reverse displacement of electrically charged particles that enter the dielectric store. There are the following main types of polarization: electronic, ionic, dipole, spontaneous and others.

The process of polarization of dielectrics is described by the comrades of Clausius - Mosotti

de – dielectric penetration of electrical insulating material; - Number of particles (molecules, ions) in 1 cm3 of material; - Polarization of the particle (molecule, ion); P is the polarization of the dielectric.

The Clausius-Mosotti theory establishes a connection between the practical characteristics of the material - dielectric penetration, physical stability of the material and the number of particles that are polarized in one dielectric.

Electronic polarization is the process of spring displacement of electrons (electron orbits) from the nucleus of all dielectric atoms. The process of electronic polarization is a mitigation process. It will be up in an hour. Electronic polarization occurs in all electrical systems.

Electronic polarization lies in the structure of the particle. The greater the radius of a molecule or ion, the greater the magnitude of its dielectric.

The proportional distribution of the number of particles per unit volume of the dielectric has a value. When heated, when the thickness of the dielectric changes, there is a change in the neutral dielectric ε (Fig. 5-1, curve 1).

In dielectrics with pure electronic polarization, the value is numerically equal to the square of the light bending indicator.

The process of ion polarization involves external displacements under the influence of the electric field of ions along the centers of their equalities. The polarization of the ion displacement is achieved in an hour, which can be equalized with the hour of the intense vibration of ions, and become with.

The intensity of the ion polarization process in the Clausius-Mosott equation is determined by the value of the ion polarizability:

where e is the charge of the ion; b – coefficient of spring coupling between ions.

With changes in the temperature of the ion dielectric, the value of ai increases due to the weakening of the spring forces in the ion dielectric and the increased amplitude of ion injection. Therefore, the intensity of the ion polarization process increases with temperature changes. In ion dielectrics, simultaneously with the polarization of ion displacement, the same process of electronic polarization develops - a phenomenon that, with heating and expansion of the dielectric, decreases, but the overall effect of polarization is greater Their dielectrics increase (Fig. 5-2) with changes in temperature.

Small 5.2 Deposit and temperature of ionic crystalline dielectric.

Electronic and ion polarization are types of deformation polarization that do not result in energy consumption in dielectrics. Dipole (dipole-relaxation) polarization occurs in polar dielectrics under the influence of an electric field. This type of polarization is orientation - the rotation of polar molecules in the direction of the current electric field.

The polarization of polar ao molecules is determined by the virus

de - Cob electric moment of a polar molecule; k – Boltzmann constant; T – absolute temperature.

At an increased temperature of the dielectric, the intensity of dipole polarization increases due to weakening of intermolecular forces and a decrease in the coefficient of internal friction. Therefore, with temperature increases, the polar dielectrics become larger (Fig. 5-1). With further increases in temperature, the intensity of the chaotic thermal disturbance of polar molecules begins to prevail over the orientational effect of the electric field and the effect of dipole polarization It is decreasing. This is evident from the change in polar dielectrics.

For the orientation of polar molecules in the process of dipole polarization, the required intervals of hours are significantly longer than those for deformation polarizations. Initially, the dielectric penetration of polar dielectrics is highly dependent on the frequency of the electric field (Fig. 5-3).

Small 5.3 Depth of e type of frequency of electrical insulating ranges.
1-neutral; 2-polar region.

In the coarse frequency range, polar molecules begin to complete their rotation one hour at a time. Therefore, it is practically equivalent to a constant voltage. With further increases in frequency, the hour speeds up and a number of molecules drop out due to the process of dipole polarization. In this case, the dielectric penetration of the dielectric decreases sharply, reaching (at even high frequencies) the value of the electronic polarization of the dielectric molecules. The critical frequency at which the dipole polarization effect begins to decrease sharply can be determined by the formula

de – radius of a polar molecule; - Absolute viscosity; - Boltzmann postion; - Absolute temperature.

Dipole polarization is clearly visible in polar gases and liquids (castor oil, sovola and in). In solid polar dielectrics, dipole polarization is not the orientation of the polar molecules themselves, but the rotation of polar radicals present in the molecules, for example, hydroxyl groups in cellulose molecules, bakelite, etc. This type of dipole-relaxation polarization of the inode is called structural polarization. In Fig. Figure 5-4 shows the density of a solid polar dielectric - galaxy as a function of temperature at different frequencies.

Small 5.4 Deposit of halovax depending on temperature at different frequencies.

The values ​​of the dielectric penetration of polar dielectrics depend on the dimensions of polar molecules and their initial electrical moment. The smaller the size of the polar molecule - dipole and the larger the magnitude of the cobalt moment, the greater the dielectric. In polar dielectrics, dipole and electronic polarization simultaneously occur. As a result, the overall effect of polarization of polar dielectrics, therefore, and the value of their dielectric penetrations is much higher than in neutral dielectrics (Table 5-1).

Dipole-relaxation polarizations cause energy loss in dielectrics, since the electric field loses energy to rotate polar molecules (dipoles). This energy dissipates in the polar dielectrics in the form of heat, which causes the others to heat up. The expenditure of power in dielectrics that operate in the alternating field is assessed by the tangent of the electrical expenditure. In Fig. 5-5 shows the temperature characteristics for neutral and central temperatures.

Small 5.5 Temperature range for electrical insulation areas.
1-neutral;
2-polar region.

In reliably cleaned neutral dielectrics, the electrical losses of the equipment are important due to conductivity, the values ​​of which increase due to changes in the temperature of the dielectric. The connection with the cym grows. In polar dielectrics, a maximum of such dielectric viscosity is avoided if the largest number of polar molecules are involved in the process of polarization of the dipole. The decrease in value with further increases in temperature is due to an increase in the intensity of the cold thermal movement of polar molecules. The second presentation of the signal results in an increased flow of conductivity in the dielectric.

In Fig. 5-6 shows the frequency depth for the polar region. The maximum here represents the frequency at which the value begins to decrease (Fig. 5-3) and . We mean that more polar molecules come out of the process of dipole polarization in connection with a change in time one at a time with a further increase in the frequency of the electric field.

Small 5.6 Frequency range for polar electrical insulation range.

Another type of relaxation polarization occurs in inorganic errors, as well as in ionic crystalline dielectrics with loose packing of ions (mullet in porcelain, etc.). In these dielectrics, the ions are weakly bound, so that in the presence of chaotic thermal fluctuations, they are transferred by an electric field. This process is called ion-relaxation polarization. The transfer of weakly bound ions results in additional energy consumption.

Mimovile (spontaneous polarization) is a process of migrating orientation of dipoles that occurs in the middle of adjacent regions (domains) of a dielectric without an electric field. Mimic polarization occurs in materials called ferroelectrics.

Without an electric field, the electric moments of adjacent regions (domains) of the dielectric are straightened smoothly, but they are mutually equal to each other. The application of an electric field to the dielectric influences the orientation of the dipoles near the field. In this case, the intensity of polarization increases sharply, as a result of which a strong increase in the dielectric penetration of the ferroelectric is avoided. This process continues until the electric field reaches a certain intensity, and then saturation occurs (Fig. 5-7).

Small 5.7 Deposit of ferroelectrics depending on the electric field strength

Further increase in tension does not increase the intensity of polarization and increases. The dielectric penetration of ferroelectric materials also manifests itself clearly at a maximum temperature (Fig. 5-8).

Small 5.8 Deposit of ferroelectric (BaTiO3) depending on temperature.

This temperature is called the ferroelectric Curie temperature (). The presence of spontaneous polarization results in anomalously higher values ​​for ferroelectrics (Rochelle salt, barium titanate, etc.). The process of momentary polarization is accompanied by wasted energy, which dissipates in dielectrics as heat.

Basic concepts

Electric polarization call the process of the removal of tightly connected electric charges or the orientation of dipoles in a directly applied electric field. Otherwise, it seems, electric polarization is the center of speech, in which the electric moment of the action of speech is subtractive from zero.

When describing electrical phenomena (including polarization), consider the system that consists of electrodes, among which there is a dielectric. Voltage is supplied to the designated electrodes, then. One can see a piece of structure, which could be an electrical capacitor, a cable, a winding of an electrical machine or a transformer, etc., as well as a piece of dielectric material, specially prepared for the modification of parameters in the laboratory. In any case, regardless of the visibility or presence of strong electric charges (carrying a charge), there are always associated charges: electrons of the shells of atoms, ions.

Under the current electric field, the associated charges in the dielectricity shift from their equal positions: positive charges - in the direction of the field strength vector E, negative charges - in the reverse direction (Fig. 4.8). As a result, the elementary volume of the dielectric (dV) increases the induced electric moment (dP). Light induced electric moment (P) in dielectricity and is a phenomenon of polarization.

By world polarization of the dielectric polarization vector (polarization, intensity of polarization), which is the traditional relationship of the induced electric moment to the dielectric until it reaches zero:

For a homogeneous dielectric with nonpolar molecules located in a uniform electric field, polarization vector:

de – induction moment of one molecule (atom); N 0 - Number of molecules (atoms) per unit volume.

The value of the induced electric torque () depends on the strength of the external electric field:

de F/m – became dielectric; - Polarization of the particle (characterizes the size of the particle before polarization), m 3 .

Vikoristic expressions (4.20) and (4.21) are eliminated:

, (4.22)

de – dimensionless parameter – dielectric responsiveness speech, or the unit of volume of the dielectric is polarized.

For a homogeneous dielectric with polar molecules placed in a uniform electric field:

de - Average value of the storage field of the vector of the stationary dipole moment of the molecule; calculated using the Boltzmann division for particles in the force field:

, (4.24)

de-classical Langevin function.

When a<< 1 имеем . Но в этом случае вычисляется по формуле Дебая-Ланжевена:

de K - Boltzmann's constant (J/K at K); N 0 - Number of molecules per unit volume; µ =3∙10 29 C∙m – electric (dipole) moment of the Debye molecule.

Powerful electric moment of an ancient molecule:

where q is the total positive (and numerically equal to the total negative) electric charge of the molecule; l – stand between the centers of gravity of the total positive (+q) and negative (-q) charges (dipole arm) (Fig. 4.9).

One of the most important characteristics of a dielectric, which is of particular importance for technology, is its dielectric penetration (ε). The value of ε represents the ratio of the charge (Q) withdrawn at the same voltage on the capacitor with a given dielectric, to the charge (Q 0) that can be obtained in a capacitor of the same geometric dimensions and at the same voltage, which is between the electrodes and all vacuum:

. (4.27)

Z virazu (4.27) vilips, which is significant ε cannot buti less than 1 .

The values ​​of the current dielectric penetration of any dielectric depend on the choice of the unit system. Further, the assessments of the power of the electricians show the most evident electrical penetration, and the word “permeable” for consistency is omitted.

The magnitude of the charge (Q) can be found from the virus:

de Z – capacitance of the capacitor; U – applied to a new voltage.

Viraz (4.28) can give you the following:

where 0 is the capacity of the vacuum capacitor (geometric capacity).

By analyzing the expression (4.29), it is possible to date such a value of the conductive dielectric penetration. The value of the aqueous dielectric

penetration (ε) shows how many times the capacitance of a capacitor with a dielectric is greater than the capacitance of a capacitor of the same geometric configuration, which has a vacuum between the plates .

Also, the value of the dielectric ε means the value of the capacitance (C) of electrical and radio engineering structures:

de - geometric factor.

Between dielectric penetration (ε), polarization (α) and dielectric responsiveness () there is a following:

ale so yak

The behavior of a dielectric in an electric field can also be characterized by absolute dielectric penetration:

de - Absolute dielectric penetration, F/m; D – electrical induction (electrical induction). For vacuum D = E; for dielectrician.

At this time of illegal adoptions, the majority of electricians are divided into two classes:

1) non-polar dielectrics;

2) polar dielectrics.

For non-polar molecules, l = 0 for viras (4.26) also, i µ = 0, then. Non-polar molecules do not produce any electrical power. That's the same hour for polar molecules. The presence of electrical energy in molecules can be judged from the chemical nature of these molecules.

The constant electric moment of a polar molecule, like any electric moment, is a vector quantity. We take it as a direct vector from a negative charge to a positive charge (div. Fig. 4.9).

Regardless of the results that can be taken away from the electrical powers of speech, the presence of electrical power in the molecules of speech can be judged from the chemical nature of its molecules. Moreover, the experimental measurement of the dipole moment (µ) makes it possible to work out very important insights about the structure of the molecules of speech. It is obvious that molecules that are symmetrically formed (due to the center of symmetry) and non-polar, in which case the centers of gravity of both positive and negative charges of the molecule converge with the center of symmetry of the molecule, and therefore, one after another (in which case we can o However, it does not indicate the charge of the surrounding atoms and ions from which the molecule is formed). However, asymmetrical molecules are solid dipoles.

Thus, monoatomic molecules (He, Ne, Ar, Kr, Xe) and molecules that are composed of two atoms connected to one homeopolar bond (H 2, N 2, Cl 2, etc.) non-polar. And the molecules of such a typical ionic (with a heteropolar linkage) connection, such as potassium iodide KI (Fig. 4.10, a), are polar and can be even more

stable electrical moment Klm. This moment is directed from a negatively charged ion () to a positively charged ion ().

The more one type of electronegativity of the atoms that form a diatomic molecule increases, the more strongly the electron pair of one of their atoms is displaced, the greater the electrical moment of such a molecule. For example, as the electronegativity of halogens changes in the range from fluorine to iodine, the dipole moment of the hydrogen halide molecules changes:

It is important to remember that when discussing the polarity of a molecule behind it, it is necessary to rely not only on the mental writing of the chemical formula of the speech, but on the actual distribution of charges in space. Thus, the formulas of carcoal anhydride and water in the notations CO 2 and H 2 are similar, but in fact the carcoal anhydride molecule is symmetrical with a center of symmetry (Fig. 4.10, 6) and therefore carcoal anhydride is non-polar. And a water molecule has the appearance of a rib cage (Fig. 4.10, c) and therefore water has a sharp expression of polar power (for a water molecule µ = 6.1·1030 C m).

All carbohydrate speech is non-polar or weakly polar (µ = 0 or even less). However, when replacing water atoms with halogen atoms F, Cl, Br or I or groups -OH, -N0 2 and etc. (This is a Walden dielectrophore) asymmetrical molecules are created, so that the voltage µ > 0.

Let's take a look at the simplest carbohydrate - methane CH 4 and products of replacement of water with chlorine: methyl chloride (CH 3 C1), methylene dichloride (CH 2 Cl 2), chloroform (CH 1 3) and carbon dioxide (tetraform) (CC 1 4). The methane molecule has the appearance of a tetrahedron, with a C atom at the center, and an H atom at the vertices (div. Fig. 4.10, d). Obviously, for methane µ = 0.

The molecules СНС13, СН2С12 and СНС13 are asymmetric and similar to them; 5.17 · 10 -30 and 3.8 · 10 -30 C · m. The CCl 4 molecule is again symmetrical and has µ = 0.

Benzene C6H6 - rechovina is non-polar; when one atom of water in benzene is replaced by another element or by a group of polar compounds:

1) monochlorobenzene (µ = 5.17 10 -30 C m);

2) monoiodobenzene (µ = 4.3 10 -30 C m);

3) phenol (µ = 5.2 10 -30 C m);

4) aniline (µ = 5.1 10 -30 C m);

5) nitrobenzene (µ = 13.2 · 10 -30 C m) etc.

Acetone due to the fact that the molecule has a polar CO group; for new, µ = 9.7 10 -30 C m.

Inorganic speeches with high meanings are considered:

· aluminum iodide AlI 3 (µ = 16.5 · 10 -30 C m);

· Tin chloride SnCl 4 (µ = 17.0 · 10 -30 C · m).

In addition to the organic materials contained in electrical insulation technology, they are practically non-polar, and there are also carbohydrate-based substances such as polyethylene - a polymer that can look like this (simplified):

,

as well as paraffin, ceresin, polyisobutylene, polypropylene, polystyrene, unvulcanized rubber, escapon, naphtha electroisolating oils, etc.

Strongly polar: polyvinyl chloride, which is like this:

,

polyvinyl alcohol and other materials, cellulose and other materials, phenol-formaldehyde resins, etc.

Polytetrafluoroethylene (fluorolon-4), which can cause such harm:

,

can be seen as a polymeric carbohydrate (polyethylene), in which water atoms are replaced on the surface by fluorine atoms, which is completely symmetrical to the structure of the skin of the molecular lantern of non-polarity; Prote polytrifluorochloroethylene (fluorlon-3) is asymmetrical and therefore polar.

Main types of polarization

Based on the aggregate state, the structures of dielectrics are divided into the following main types of polarization: electron, ion, ion-relaxation, dipole-relaxation, migration, migratory.

Induction under the infusion of an applied electric field, the total electric charge is formed by a sum of different types of polarization. Polarization mechanisms can occur in different dielectrics, and several polarization mechanisms can occur simultaneously in one dielectric. A hypothetical dielectric that drives all polarization mechanisms, perhaps

representations by an equivalent circuit, in which the skin mechanism of polarization is connected in parallel with the voltage (U) capacitance (C) (Fig. 4.11).

Capacity C 0 and charge Q 0 indicate a geometric capacity and charge when there is a vacuum between the electrodes. The capacity C e and charge Q e (Fig. 4.11) characterize electron polarization . Electronic polarization is a displacement of the electron charge center from the positively charged nucleus of an atom under the influence of an external electric field (Fig. 4.12). The displacement counteracts the Coulomb gravity of electrons to the nucleus. The time for establishing electronic polarization is very short (about 10 -15 s), so it is practically impossible to depend on the frequency of the electromagnetic field (Fig. 413), otherwise it is associated with the loss of energy and does not depend on temperature. However, the value of ε of dielectrics, which are subject to electronic polarization, changes with temperature increases due to thermal expansion of the dielectric and changes in the number of polarized particles per volume (Fig. 4.14).

Electronic polarization is avoided in all types of dielectrics. With an increase in the size of atoms, the electronic polarization increases, as the bonds of the external electron shells with the nucleus of the atom weaken and the displacement of the shell (l) increases, and the charge (q) increases.

For manual and scientific assessment of the electronic polarization of an atom or ion (α), the concept geometric polarization , which extends α to constant dielectricity (ε 0), which is measured in units of volume. The geometric polarizability (α/ε 0) is on the order of that of an atom, then. 10 -30 ... 10 -29 m3. For example, the values ​​of α/ε 0 halogen atoms (in the order of increasing their atomic mass) are equal to:

· For F - 0.4 · 10 -30;

· For Cl - 2.4 · 10 -30;

· For Br - 23.6 · 10 -30;

· For J - 5.8 · 10 -30 m3.

For speech, the ionic source is the polarization not of atoms, but of ions. They vary in value, which differs significantly depending on the electronic geometric polarizability () to the cube of the ion radius ().

For example, the relationship for advancing ions is ancient:

		4) for Zr++++
5) for Ca++		6) for Рb++
7) for Ti++++

The presence of ions of great significance is associated with polarization. The values ​​that counteract such ions are even higher, for example, for rutile (TiO 2) ε = 110.

The capacity C and charge Q u (Fig. 4.15) characterize ion polarization. Ionic polarization It results from the spring displacement of the bound ions from their equal position on the riser, so as not to outweigh the constant crystal loss. As the temperature increases, the polarization increases, as the thermal field changes, the forces of interion interaction weaken, and thermal expansion occurs at the same time (Fig. 4.14). The hour for setting ion polarization is approximately 10-13 s. It is also electronic, it is not associated with energy consumption and does not lie at a frequency, even up to the frequencies of the infrared range (Fig. 4.13). Ionic polarization is characteristic of crystalline ionic dielectrics due to dense packing of ions (NaCl and others).

The capacity C and charge Q in (div. Fig. 4.11) characterize the dipole-relaxation polarization. Dipole-relaxation polarization lies at the rotation (orientation) of dipole molecules in the direction of the external electric field. Dipole molecules, which in chaotic thermal conditions, are oriented towards the external electric field, creating the effect of polarization of the dielectric (Fig. 4.16).

Dipole-relaxation polarization is possible because molecular forces do not allow dipoles to be oriented along the same field. With increased temperatures, the molecular forces are weakened, which may enhance dipole-relaxation polarization; However, at the same time, the energy of the thermal flow of molecules increases, which changes the influx of the field that is oriented. In connection with this, the dipole-relaxation polarization with increasing temperature initially increases until the weakening of the forces of intermolecular interaction outweighs the increase in the chaotic thermal disturbance of molecules. Then, if the intensity of the thermal disturbance of molecules is greater (thermal energy “spreads” the dipoles), the dipole-relaxation polarization will change (Fig. 4.14). When the applied electric field is removed, the dipole-relaxation polarization is destroyed by the chaotic thermal flow of molecules, and the polarization (P) decreases according to the exponential law:

de P 0 - Polarization at the moment of voltage release; - It is a constant process, which is called the hour of relaxation of dipole polarization.

Relaxation is a period of time during which the polarization of the dielectric after the removal of the field changes due to the thermal movement of molecules at the same time. Between the hour of relaxation (), the energy of activation (W) and the frequency of the vibrations of the relaxing particle (f), the following is true:

(4.34)

It is on the order of 10 -6 ...10 -10 Hz, therefore, dipole polarization only appears at frequencies lower than 10 6 ...10 10 Hz. Dipole-relaxation polarization is associated with the loss of energy, since the rotation of the dipoles at the direction of the field exerts a heel support. This is shown (div. Fig. 4.11) in the form of a sequentially connected circuit and an active support R d p . As the frequency increases, the value of ε decreases, as a result of which the orientation process exhibits inertia. During the ionization phase of the voltage change, dipole molecules do not completely reorient in the direction of the field.

Dipole-relaxation polarization manifests itself in polar gases and regions. Polarization of this type can also be prevented in solid dielectrics. However, in many solid, highly organic, dielectrics, the dipole-relaxation polarization is primarily determined not by the orientation of the molecule itself, but by the orientation of the polar radicals present in it. Such polarization is called dipole-radical. An example of polarization of this type is cellulose, the polarity of which is explained by the presence of hydroxyl groups (OH) and acidity. Crystals with molecular graters and weak Van Der Wals bonds may have an orientation of larger particles.

The capacity Cyr and charge Q up (div. Fig. 4.11) characterize ion-relaxation polarization. Ion-relaxation polarization is caused by the suppression of weakly bonded ions under the influence of the external electric field on the surface, which exceeds the amplitude of anharmonic thermal waves. Polarization will noticeably increase due to temperature shifts (div. Fig. 4.14) due to the weakening of the interaction forces. As the frequency increases, the value of ε ir decreases due to the inertia of the reorientation process (div. Fig. 4.13). Polarization of this type is associated with energy expenditure, which is shown (div. Fig. 4.11) in the form of a sequentially connected circuit of the active support R up.

Ion-relaxation polarization is avoided in ionic dielectrics of amorphous solids (glass, ceramics, etc.), as well as in inorganic crystalline dielectrics with non-crystalline packaging of ions (fluffy solids).

The viscosity C er and the charge Q е p (div. Fig. 4.11) characterize the electron-relaxation polarization. Electron-relaxation polarization It is due to the connection with the orientation of excess “defective” electrons and “defects” awakened by thermal energy. Electron-relaxation polarization is characteristic of dielectrics with a high degree of bending, a large internal electric field and the presence of electronic storage conductivity. A characteristic representative of this group of materials is: titanium dioxide “contaminated” with a house Nb+5; Ca+2; +2; titanium dioxide with anion vacancies and a home of Ti+3 ions. as well as a number of compounds based on metal oxides with variable valence – titanium, niobium, bismuth.

These dielectrics can have high dielectric penetration values ​​(CaTiO 2 – calcium titanite has ε = 150; etc.). In addition, these electricians are careful about the maximum temperature range. This type of polarization is due to energy consumption, which is shown in Fig. 4.11 it looks like the active support R e p is connected in series.

Moisture C m and charge Q m (Fig. 4.11) characterize migratory polarization. Migration (structural ) polarization It is designed for use in technical dielectrics of conductor and non-conductor switches, balls with different conductivity, and also in composite dielectrics. When heterogeneous materials are introduced into the electric field, the free electrons and conductive and conductive switches begin to move between the skin inclusions, creating polarized areas between the sections of the middle (Fig. 4.17). The process of installing and removing migratory polarization is usually longer and can take three seconds, or even a year. Polarization of this type is especially possible at low frequencies.

Polarization of this type is associated with energy expenditure, which is shown (div. Fig. 4.11) in the form of an active support R m connected in series with the amplitude m.

Resiliency C res and charge Q pe z (div. Fig. 4.11) characterize resonant polarization. Resonance polarization appears in dielectrics at optical frequencies. It depends on the physical and chemical characteristics of dielectrics, which can be carried up to the high frequency of electrons or ions (beyond very high frequencies) or to the characteristic frequency of defective electrons (beyond low frequencies). Resonance changes are shown in Fig. 4.18.

Resonant electronic polarization is associated with anomalous light dispersion and is also insufficiently treated. With anomalous dispersion, the indicator of a broken speech for the singing frequency increases due to the fact that due to the resonance with the vibrations of the particles, the phase fluidity of the broadened voice changes and the material for this sound becomes “viscous”:

de – indicator of the bending of the singing frequency; – phase flexibility of the broadened frequency of the dielectric; з = 3·10 8 m/s – the fluidity of all frequencies in vacuum.

With resonance, the clay energy of the needle increases. Zi bolshennyam

frequency, the value of ε drops sharply through the “victimization” of this polarization mechanism.

All capacitances of the equivalent circuits (div. Fig. 4.11) are shunted R and support the dielectric flow through the through conductivity. The capacity Z n and the charge Q cn and the active support R cn (div. Fig. 4.11) characterize spontaneous polarization. Spontaneous (fleeting ) polarization - Polarization that occurs due to the influx of internal processes in electricians without external infusions. Polarization of this type is nonlinearly dependent on the strength of the electric field (Fig. 4.19) and during cyclic change it looks like a characteristic closed curve - a hysteresis loop (Fig. 4.20).

Dielectrics, which cause spontaneous polarization, have been given the name ferroelectrics (Segnet salt NaKC 4 H 4 O 6 ·4H 2 O; barium titanate BaTiO 3, sodium nitrite NaNO 2, etc.). A special feature of ferroelectrics is that they have a domain structure (similar to the structure of ferromagnets). Furthermore, the superposition of an external electric field combines the important orientation of the electric moments in the direct field, which gives the effect of even strong polarization.

One of the main parameters of ferroelectrics is ferroelectric Curie point (Displayed as magnetic). This is the temperature when it rises (when cooled) and spontaneous polarization occurs (when heated). After reaching the Curie point, when the temperature rises or decreases, a phase transition occurs from the ferroelectric state to the steam electric state (Fig. 4.21). Spontaneous polarization is accompanied by significant energy dissipations.

Like other electrical parameters of dielectrics, dielectric penetration (ε) depends on external factors that change: the frequency of the electric field applied to the dielectric, temperature, pressure, moisture, etc.

Depth depending on frequency ε

As it was assumed, the hour of installation of electronic and ion polarization is very short, and the hour of change in the sign of the voltage (that is, with the opposite change of voltage) will lead to the highest practical stagnation in electrical engineering and rad Frequency technology. Therefore, the polarization of dielectrics, which is characterized by a deformation mechanism of polarization, can be fully established in an hour, which is extremely small for the voltage equal to the current, and there is no basis for this to occur. There is practically no difference in the frequency ε of such dielectrics.

The dielectric penetration of non-polar dielectrics does not lie within very wide frequency ranges (Fig. 4.22). The other one on the right has dipole polarization. When the frequency of the alternating voltage is increased, the value of the polar dielectric ε of the retin is also lost unchanged, but, starting from the critical frequency (f 0), if the polarization is no longer able to completely set in one step. Iodine, ε decrease, approaching at very high frequencies to the values ​​characteristic of non-polar dielectrics The value of f 0 can be approximated from the expression:

de – dynamic viscosity of the liquid; r is the radius of the molecule.

So, for water, for which the value f 0 was found to be approximately 10 11 Hz, then. 100 GHz. With increased temperature, in addition to the increase in T in the numerical operator of formula (4.36), it also changes in the symbol, so f 0 may increase. This is illustrated by Fig. 4.24.

In sharply heterogeneous dielectrics, close to dielectrics when water is turned on, beware of the phenomenon of migratory polarization. Migration polarization (other, non-standard names: high-voltage, interspherical, volumetric) and the accumulation of electrical charges at the interfaces of various dielectrics (in the case of a folded dielectric - turn on the surface water). The processes of establishing migratory polarization are even more advanced and can proceed for several weeks and years. Therefore, the insulation capacity increases as a result of the remaining charge, the lower the frequency of the alternating voltage applied before insulation.

The above provides a framework for assessing the stage of decomposition of various types of insulation, including fibrous, using the “capacity - frequency” method: the insulation capacity varies at the same temperature, and at different frequencies x – very low (2Hz) and extreme frequency (50Hz). The relationship between these two capacity values ​​(Fig. 4.25) is a criterion for the moisture content of the insulation: in whole dry insulation the ratio is close to one, and the more wear, the greater the moisture There are isolations. The “capacity-frequency” method can soon be used as a reliable way to assess the density of insulation, but the very fact of the presence of different frequency deposits of the dielectric ε at different volumes is of significant interest.

As a rule, we do not see the phenomenon of resonant polarization here, which leads to the appearance of maxima at deposits at very high frequency values ​​(f), with elevated f we can be careful because it is practical independence of the frequency or a decrease in it, rather than advancement.

With the instantaneous appearance of a complete (relaxation) polarization in the dielectricity of several physical mechanisms (dipole - for the orientation of different groups of molecules or the orientation of molecules of different components of mixed dielectric, migratory etc.) with different hours of relaxation (a set of hours of relaxation), the picture of bedtime may be complicated. So, in this case, if you move the chart, you can avoid not just one, but a number of decreases.

Deposit in analogy with the dispersion of light, then. the manifestation of the persistence of the indicator of bending in relation to the frequency of ringing is called dispersion of dielectric penetration . The difference in the value of dielectric penetration, measured (with an increase in f) on the beginning of the decline, caused by this or another mechanism of relaxation polarization, and after this decline is called depth of relaxation for which polarization mechanism. Obviously, the greatest value of ε dielectricity is ε, in the case of constant voltage (or at infra-low frequency); tse - so called static dielectric penetration (ε s), and least of all – ε, Vimirians at an extremely high frequency, which is approaching the frequency of light kolivans; tse – optical dielectric penetration (). The difference in these values ​​is called the increment of electrical penetration.

DIELECTRIC MATERIALS.

Classification and hidden power of electricians. Temperature range.

DIELECTRIC MATERIALS.

Speeches that are produced are polarized in an electric field. They have an internal electric field and an equal distribution of potentials.

Nose charge in dielectrics:

1. In gases

1) Positive and negative ions. Reason: ionization of gas molecules.

2) Electronics in strong fields.

2. At home

1) Ioni. Reason: dissociation of redini molecules.

2) Coloidal charging of particles in emulsions and suspensions.

3. In the firmaments

2) Defects of crystal mounts.

3) Electronics and conductivity holes.

There are polar and non-polar.

Malyunok 50.

The main electrical powers of electricians:

1. Polarization

2. Electrical conductivity

3. Dielectric spending

4. Electricity

In case of deterioration of a permanent struma, take care of the draining struma.

Polarization of dielectrics. Types of polarization.

Polarization is the process of displacement and ordering of charges in a dielectric under the influence of an external electric field. In numerical terms, polarization is the polarization of the dielectric - the amount of electric moment per unit volume of the dielectric:

	(1.2)
	(1.2)

de dp- Electrical moment of the dielectric element;

dV – volume of the dielectric element

External electric field strength, V/m,

- dielectric constant,

Vibrant dielectric penetration.

Polarization signifies the power of electricians to create electrical capacity. At the same time, the polarization of dielectrics, which is caused by the loss of energy and heat, leads to the loss of electrical energy in insulating materials, especially at high frequencies, when the process of polarization of the dielectric is repeated There are more than one cycle per hour. Therefore, polarization is described by dielectric parameters.

There are several types of polarization.

2.2.1. Spring polarization is generated by dielectricity without visible energy and dissipation of heat. Separate electron and ion spring polarization

Electronic polarization is a spring displacement and deformation of the electron shells of atoms, which leads to the sub-geometric centers of positive and negative charges in the atom. Installation requires a minimum hour - 10 -15 s. it's practically mittevo. Polarization during electronic polarization does not depend on temperature, and dielectric penetration smoothly changes with temperature increases due to thermal expansion of the dielectric and changes in the number of atoms per volume (Fig. 2.2). Electronic polarization is observed in all dielectrics, regardless of their chemical composition and internal structure.

Ionic polarization - spring displacement of ions - nodes of crystalline mounts, is characteristic of materials with ion cylinders. With the increase in temperature there will be a further weakening of inter-regional forces. The hour of installation of polarization is 10 -13 s – longer, lower in electronic polarization, the fragments are more massive.

Since the processes of electronic and ion polarization are carried out practically by mititation, the value of the dielectric penetration of materials with external polarization has become independent of the frequency.

2.2.2. Relaxation (non-spring) polarization – more types of polarization. To make them work, it is necessary to expend the energy that is then seen in the form of heat when the dielectric is turned at the output position. They differentiate dipole-relaxation, ion-relaxation, electron-relaxation, resonance and migration types of polarization.

Dipole-relaxation polarization is characteristic of speech with a dipole structure and is caused by a reorientation of dipole molecules in the external electric field added to the dielectric. Depending on the mass, packing thickness and dimensions of dipoles, the hour of installation of polarization becomes 10 -10 ..10 -2 s. After removing the field that caused polarization, they spin around in a chaotic state under the influence of the thermal collapse of particles, in which the polarization of the material changes according to the law

(1.2)

de - polarization of the dielectric at the moment of removal of the external field, C/m 2

Hour of relaxation (an hour during which the number of ordered dipoles changes times), h.

The extent of dipole polarization as a function of temperature is shown in Fig. 2.3. The decline in the graph in the region of low temperatures is due to the dense packing of ions and the difficulties of the current reorientation, and in the region of high temperatures - to the small number of dipoles that fall per unit volume of the dielectric.

Small 2.3. Duration of dipole-relaxation polarization as a function of temperature

Dipole-relaxation polarization is avoided in all polar rivers. In solid dielectrics, polarization is caused not by the rotation of the molecule itself, but by the displacement of polar radicals that are in it, for example, Na + and Cl - in a kitchen salt molecule.

With higher frequencies, dipole polarization and dielectric penetration change, so polar dielectrics are frequency-dependent and do not stagnate at high frequencies.

Ion-Releksatsyina Polyarizatsya, to the mother-in-law of the unbearable packaging ioniv, the vicclican fіzichchimovsi ionivs at the Vacancas of the crystal of the crystal. After the field is removed, the polarization gradually weakens. Be careful not to remove solid particles (Fig. 3.x), the fragments become free when melted and the material becomes a conductor with electrolytic conductivity.

Small 3.x. Degree of ion-relaxation polarization

type of temperature

Electron-relaxation polarization is a result of displacements from one ion to another (at the direct field) of excess (defective) electrons and cores. Characteristic of speeches with electronic conductivity, the central maximum is constant and changes with increasing frequency.

Resonant polarization. Be careful in dielectrics at light frequencies, which is caused by the resonance of the powerful vibrations (wrapping) of electrons and ions and the frequency of the external electromagnetic field (light). In reality, there is no stagnation and little infusion of the power of the dielectric in the sphere of frequencies, dominated by electronics and microelectronics.

Migration polarization – manifests itself in solids of heterogeneous structure with macroscopic inhomogeneities and the appearance of houses. The causes of polarization are the presence of conductive and conductive elements in real technical dielectrics (paper, fabric). During migratory polarization, electrons and ions move between the wires, creating large polarized areas. This polarization is associated with great expenditures of energy and occurs even at low frequencies; the hour of relaxation of such dielectrics is only a few seconds.

In real dielectrics, a number of types of polarization appear simultaneously, and therefore the frequency and temperature range of polarization, dielectric penetration and the tangent of dielectric losses are complicated. Based on the type of polarization, there are four groups of dielectrics:

1. Dielectrics are important with electronic polarization. These are non-polar and weakly polar substances in crystalline and amorphous substances (paraffin, polystyrene, polyethylene). Vikorists act as high-frequency dielectrics - insulators.

2. Dielectrics with electronic and dipole-relaxation polarization. These are polar organic, unlike solid materials (resins, cellulose). Vikors are used as low-frequency dielectrics - insulators and in low-frequency capacitors.

3. Solid inorganic dielectrics with electronic, ion and relaxation polarization (mica, quartz, glass, ceramics, sita). They are used as dielectrics in high-frequency capacitors and as insulators.

4. Ferroelectrics that are subject to various types of polarization. Vikoristovuyutsya as active (kerovani) dielectrics.

When polarization changes, the electric field in the middle of the dielectric changes. Dielectric penetration characterizes the weakening of the external field by the internal one:

	(1.2)

de - external electric field, V/m,

Internal electric field, V/m,

Electrical displacement, C/m 2,

Surface strength of bonded charges on the capacitor plates due to the presence of a dielectric, C/m 2,

Additional surface strength of the charge, which is due to the polarization of the dielectric, C/m 2

Surface density of charge on the plates of a surface capacitor, C/m 2

To remove the necessary power, for example, to a minimum of the temperature coefficient of the TKE capacity, electric capacitors can be assembled into a folding dielectric, which is formed from a mixture of simple materials with different values ​​dielectrically ї penetration. When such a dielectric is present, its effective dielectric penetration is determined by the Lichtenecker formula: for a chaotic distribution of components:

,

de q 1і q 2- Volume concentration (parts) of components.

POLARIZATION OF DIELECTRICS.

The process of displacement and ordering of charge carriers under the influence of an electric field

The camp of speech, with which the elementary yogo obsessive rises to the electric moment.

Reasons: external electric field, mechanical stress, brightness and other dowkill factors, spontaneous polarization.

Malyunok 51.

Polarization is the reason for the appearance of electrical capacitance.

Dielectrics:

1) linear – insulation, permanent capacity condenser

2) nonlinear – sensors, copper voltage condensers

Malyunok 52.

Polars are made up of polar molecules (water). Non-polar - from non-polar, which has an electrical moment = 0 (gases, kitchen salt).

Types of polarization:

1. Direct polarization (spring) is generated without dissipation of energy.

1) Electronic polarization - the reduction of electron radiation to the center of the atomic nucleus. The hour of guilt and liquidation is 10^-14…10^-15 s. Polarizability does not depend on temperature, but dielectric penetration does. Malyunok 53.

2) Resonant polarization - occurs when the frequencies of electron wrapping decrease due to a change in the magnetic field.

3) Ionic polarization – displacement of one or more positive and negative ions. Installation hour – 10^-11 s. Stock: kitchen salt. As the temperature increases, the parameters grow.

2. Relaxation

Energy is wasted on it, which can be seen in the form of heat, electrical energy is wasted on the alternating stream.

Riznovidi:

1) Dipole relaxation polarization – rotation and orientation of dipole molecules in the direct field.

Malyunok 54.

Installation hour: 10^-2…10^-10 s.

Tau – an hour of relaxation.

2) Ion-relaxation polarization - movement of ions from one atom to another in molecules with irregular packing of electrons. butt: slope

Malyunok 55.

Rarely, they have conductors with electrolytic conductivity.

3) Electron-relaxation – transfer of an electron to another atom during polarization.

Installation hour: 10^-2…10^-5 C for room temperature.

4) Migration – beware of non-homogeneous dielectrics with wired connections. stock: papier.

Malyunok 56.

Low frequency polarization. An hour of relaxation: hvilini and godini.

5) Spontaneous polarization. Phase – camp of crystalline horates, її structure.

In different rivers, it is possible to change the phase without changing the aggregate state. A phase change in dielectrics can lead to spontaneous polarization – ferroelectrics. Dielectric penetration – up to 10^5. The view of dielectrics is nonlinear. Vikoristavuyutsya at the sensors.

The dielectric penetration of madness.