a) General information. To create a constant magnetic field, a number of electrical devices use permanent magnets, which are made of hard magnetic materials that have a wide hysteresis loop (Fig. 5.6).
The work of a permanent magnet occurs in the area from H= 0 to H = - N s. This part of the loop is called the demagnetization curve.
Let us consider the basic relationships in a permanent magnet having the shape of a toroid with one small gap b(Fig. 5.6). Due to the toroidal shape and small gap, leakage fluxes in such a magnet can be neglected. If the gap is small, then the magnetic field in it can be considered uniform.
Fig.5.6. Permanent magnet demagnetization curve
If we neglect bulging, then the induction in the gap IN & and inside the magnet IN are the same.
Based on the total current law with closed loop integration 1231 rice. we get:
Fig.5.7. Permanent magnet shaped like a toroid
Thus, the field strength in the gap is directed opposite to the strength in the magnet body. For electromagnet DC, having a similar shape of the magnetic circuit, without taking saturation into account, we can write: .
Comparing, you can see that in the case of a permanent magnet n. c, creating a flux in the working gap, is the product of the tension in the body of the magnet and its length with the opposite sign - Hl.
Taking advantage of the fact that
, (5.29)
, (5.30)
Where S- pole area; - conductivity of the air gap.
The equation is the equation of a straight line passing through the origin in the second quadrant at an angle a to the axis N. Taking into account the scale of induction t in and tension tn angle a is determined by the equality
Since the induction and magnetic field strength in the body of a permanent magnet are related by the demagnetization curve, then the intersection of the indicated straight line with the demagnetization curve (point A in Fig. 5.6) and determines the state of the core at a given gap.
With a closed circuit and
With growth b conductivity of the working gap and tga decrease, the induction in the working gap decreases, and the field strength inside the magnet increases.
One of the important characteristics of a permanent magnet is the energy of the magnetic field in the working gap Wt. Considering that the field in the gap is uniform,
Substituting the value N b we get:
, (5.35)
where V M is the volume of the magnet body.
Thus, the energy in the working gap is equal to the energy inside the magnet.
Product dependency B(-N) in the induction function is shown in Fig. 5.6. Obviously, for point C, at which B(-N) reaches its maximum value, the energy in the air gap also reaches its greatest value, and from the point of view of using a permanent magnet, this point is optimal. It can be shown that point C, corresponding to the maximum of the product, is the point of intersection with the beam demagnetization curve OK, drawn through a point with coordinates and .
Let's take a closer look at the effect of the gap b by the amount of induction IN(Fig. 5.6). If the magnet was magnetized with a gap b, then after removing the external field, an induction will be established in the body of the magnet corresponding to the point A. The position of this point is determined by gap b.
Reduce the gap to the value , Then
. (5.36)
As the gap decreases, the induction in the magnet body increases, but the process of changing the induction does not follow the demagnetization curve, but along a branch of a private hysteresis loop AMD. Induction IN 1 is determined by the point of intersection of this branch with a ray drawn at an angle to the axis - N(dot D).
If we increase the gap again to the value b, then the induction will drop to the value IN, moreover, dependence V(H) will be determined by branch DNA private hysteresis loop. Typically a partial hysteresis loop AMDNA is quite narrow and is replaced by a straight one A.D. which is called direct return. The inclination to the horizontal axis (+ H) of this straight line is called the coefficient of return:
. (5.37)
The demagnetization characteristics of the material are usually not given in full, and only the saturation induction values are specified Bs, residual induction In g, coercive force N s. To calculate a magnet, it is necessary to know the entire demagnetization curve, which for most hard magnetic materials is well approximated by the formula
The demagnetization curve expressed by (5.30) can be easily plotted graphically if the B s, B r.
b) Determination of flux in the working gap for a given magnetic circuit. In a real system with a permanent magnet, the flux in the working gap differs from the flux in the neutral section (the middle of the magnet) due to the presence of leakage and bulging fluxes (Fig.).
The flow in the neutral section is equal to:
, (5.39)
where is the flow in the neutral section;
Bulging flow at the poles;
Leakage flux;
Work flow.
The scattering coefficient o is determined by the equality
If we assume that the flows 
are created by the same magnetic potential difference, then
. (5.41)
We find the induction in the neutral section by defining:
,
and using the demagnetization curve Fig. 5.6. The induction in the working gap is equal to:
since the flux in the working gap is several times less than the flux in the neutral section.
Very often, the magnetization of the system occurs in an unassembled state, when the conductivity of the working gap is reduced due to the absence of parts made of ferromagnetic material. In this case, the calculation is carried out using direct return. If the leakage fluxes are significant, then it is recommended to carry out the calculation in sections, just as in the case of an electromagnet.
Leakage fluxes in permanent magnets play a much larger role than in electromagnets. The fact is that the magnetic permeability of hard magnetic materials is significantly lower than that of soft magnetic materials from which systems for electromagnets are made. Leakage fluxes cause a significant drop in the magnetic potential along the permanent magnet and reduce n. s, and therefore the flow in the working gap.
The dissipation coefficient of completed systems varies within fairly wide limits. Calculation of the scattering coefficient and scattering fluxes is associated with great difficulties. Therefore, when developing a new design, it is recommended to determine the dissipation coefficient using a special model in which permanent magnet replaced by an electromagnet. The magnetizing winding is selected in such a way as to obtain the required flux in the working gap.
Fig.5.8. Magnetic circuit with a permanent magnet and leakage and bulging fluxes
c) Determining the size of the magnet based on the required induction in the working gap. This task is even more difficult than determining the flow with known dimensions. When choosing the dimensions of a magnetic circuit, one usually strives to ensure that the induction B 0 and tension H 0 in the neutral section corresponded to the maximum value of the product H 0 V 0 . In this case, the volume of the magnet will be minimal. The following recommendations are given for the selection of materials. If it is necessary to obtain a large induction value with large gaps, then the most suitable material is Magnico. If, with a large gap, it is necessary to create small inductions, then Alnisi can be recommended. For small working gaps and high induction values, it is advisable to use alni.
The cross section of the magnet is selected from the following considerations. The induction in the neutral section is chosen equal to At 0. Then the flow in the neutral section
,
where does the cross section of the magnet come from?
.
Induction values in the working gap In p and pole area are given quantities. The most difficult thing is to determine the value of the coefficient scattering. Its value depends on the design and induction in the core. If the magnet cross-section is large, then several magnets connected in parallel are used. The length of the magnet is determined from the condition for creating the necessary n.s. in the working gap at tension in the magnet body H 0:
Where b p - the size of the working gap.
After selecting the main dimensions and designing the magnet, a verification calculation is carried out using the method described earlier.
d) Stabilization of magnet characteristics. During operation of the magnet, a decrease in the flux in the working gap of the system is observed - aging of the magnet. There are structural, mechanical and magnetic aging.
Structural aging occurs due to the fact that after hardening of the material, internal stresses arise in it, and the material acquires a heterogeneous structure. During operation, the material becomes more homogeneous, internal stresses disappear. In this case, the residual induction In t and coercivity N s are decreasing. To combat structural aging, the material is subjected to heat treatment in the form of tempering. In this case, internal stresses in the material disappear. Its characteristics become more stable. Aluminum-nickel alloys (alni, etc.) do not require structural stabilization.
Mechanical aging occurs due to shock and vibration of the magnet. In order to make the magnet insensitive to mechanical stress, it is subjected to artificial aging. Before installation into the apparatus, magnet samples are subjected to the same shocks and vibrations that occur during operation.
Magnetic aging is a change in the properties of a material under the influence of external magnetic fields. A positive external field increases the induction along the direct return, and a negative external field reduces it along the demagnetization curve. In order to make the magnet more stable, it is subjected to a demagnetizing field, after which the magnet operates on the return line. Due to the lower slope of the return line, the influence of external fields is reduced. When calculating magnetic systems with permanent magnets, it must be taken into account that during the stabilization process the magnetic flux decreases by 10-15%.
Switching magnetic flux systems are based on switching magnetic flux relative to removable coils.
The essence of the CE devices reviewed on the Internet is that there is a magnet, for which we pay once, and there is a magnetic field of the magnet, for which no one pays money.
The question is that it is necessary to create conditions in transformers with switching magnetic fluxes under which the magnetic field becomes controllable and we direct it. interrupt. redirect like this. so that the switching energy is minimal or cost-free
In order to consider options for these systems, I decided to study and present my thoughts on new ideas.
To begin with, I wanted to look at what magnetic properties a ferromagnetic material has, etc. Magnetic materials have a coercive force.
Accordingly, the coercive force obtained by cycle, or by cycle, is considered. Designated accordingly and
The coercive force is always greater. This fact is explained by the fact that in the right half-plane of the hysteresis graph the value is greater than , by the amount:
In the left half-plane, on the contrary, it is less than , by an amount . Accordingly, in the first case the curves will be located above the curves, and in the second - below. This makes the hysteresis cycle narrower than the cycle.
Coercive force
Coercive force - (from Latin coercitio - retention), the value of magnetic field strength required for complete demagnetization of a ferro- or ferrimagnetic substance. Measured in Ampere/meter (SI system). Based on the magnitude of the coercive force, the following magnetic materials are distinguished:
Soft magnetic materials are materials with low coercivity that are magnetized to saturation and remagnetized in relatively weak magnetic fields with a strength of about 8-800 a/m. After magnetization reversal, they do not externally exhibit magnetic properties, since they consist of randomly oriented regions magnetized to saturation. An example is various steels. The more coercive force a magnet has, the more resistant it is to demagnetizing factors. Hard magnetic materials are materials with a high coercive force that are magnetized to saturation and remagnetized in relatively strong magnetic fields with a strength of thousands and tens of thousands of a/m. After magnetization, hard magnetic materials remain permanent magnets due to high values of coercivity and magnetic induction. Examples are rare earth magnets NdFeB and SmCo, barium and strontium hard magnetic ferrites.
As the mass of the particle increases, the radius of curvature of the trajectory increases, and according to Newton’s first law, its inertia increases.
With increasing magnetic induction, the radius of curvature of the trajectory decreases, i.e. The centripetal acceleration of the particle increases. Consequently, under the influence of the same force, the change in particle speed will be less, and the radius of curvature of the trajectory will be greater.
As the charge of the particle increases, the Lorentz force (magnetic component) increases, and therefore the centripetal acceleration also increases.
When the speed of motion of a particle changes, the radius of curvature of its trajectory changes, and the centripetal acceleration changes, which follows from the laws of mechanics.
If a particle flies into a uniform magnetic field by induction IN at an angle other than 90°, then the horizontal component of the velocity does not change, but the vertical component under the influence of the Lorentz force acquires centripetal acceleration, and the particle will describe a circle in a plane perpendicular to the vector of magnetic induction and velocity. Due to the simultaneous movement along the direction of the induction vector, the particle describes a helical line, and will return to the original horizontal at regular intervals, i.e. cross it at equal distances.
The braking interaction of magnetic fields is called Foucault currents
As soon as the circuit in the inductor is closed, two counter-directed flows begin to act around the conductor. According to Lenz’s law, the positive charges of the electrogas (ether) begin their screw motion, activating the atoms through which the electrical connection is established. Hence it is impossible to explain the presence of magnetic action and reaction.
By this I explain the inhibition of the exciting magnetic field and the opposition to it in a closed circuit, the braking effect in the electric generator (mechanical braking or the resistance of the rotor of the electric generator to the mechanically applied force and the resistance (braking) of the Foucault current to the falling neodymium magnet falling in the copper tube.
A little about magnetic motors
The principle of switching magnetic fluxes is also applied here.
But it’s easier to move on to drawings.
How is this system supposed to work?
The middle coil is removable and operates on a relatively wide pulse length, which is created by the passage of magnetic fluxes from the magnets shown in the diagram.
The pulse length is determined by the inductance of the coil and the load resistance.
Once the time has elapsed and the core becomes magnetized, the core itself must be interrupted, demagnetized, or remagnetized. to continue working with the load.
Transgeneration of electromagnetic field energy
Essence of research:
The main direction of research is the study of the theoretical and technical possibility of creating devices that generate electricity through the physical process of transgeneration of electromagnetic field energy discovered by the author. The essence of the effect is that when adding electromagnetic fields (constant and variable), it is not the energies that are added, but the amplitudes of the field. The field energy is proportional to the square of the amplitude of the total electromagnetic field. As a result, with simple addition of fields, the energy of the total field can be many times greater than the energy of all the original fields separately. This property of the electromagnetic field is called non-additivity of the field energy. For example, when three flat disk permanent magnets are stacked, the energy of the total magnetic field increases nine times! A similar process occurs during the addition of electromagnetic waves in feeder lines and resonant systems. The energy of the total standing electromagnetic wave can be many times greater than the energy of the waves and the electromagnetic field before addition. As a result, the total energy of the system increases. The process is described by a simple field energy formula:
When three permanent disk magnets are added, the volume of the field decreases three times, and the volumetric energy density of the magnetic field increases nine times. As a result, the energy of the total field of three magnets together turns out to be three times greater than the energy of three separated magnets.
When electromagnetic waves are added in one volume (in feeder lines, resonators, coils, the energy of the electromagnetic field also increases compared to the original one).
The theory of the electromagnetic field demonstrates the possibility of generating energy through the transfer (trans-) and addition of electromagnetic waves and fields. The theory of transgeneration of electromagnetic field energy developed by the author does not contradict classical electrodynamics. The idea of the physical continuum as a super-dense dielectric medium with enormous latent mass energy leads to the fact that physical space has energy and transgeneration does not violate the full law of conservation of energy (taking into account the energy of the medium). The non-additivity of the energy of the electromagnetic field demonstrates that for the electromagnetic field the law of conservation of energy does not simply apply. For example, in the Umov-Poynting vector theory, the addition of Poynting vectors leads to the addition of electric and magnetic fields simultaneously. Therefore, for example, when adding three Pointing vectors, the total Pointing vector increases by nine times, and not three, as it seems at first glance.
Research results:
The possibility of obtaining energy by combining electromagnetic waves was studied experimentally in various types of feeder lines - waveguides, two-wire, stripline, coaxial. The frequency range is from 300 MHz to 12.5 GHz. Power was measured both directly - with wattmeters - and indirectly - with detector diodes and voltmeters. As a result, when certain adjustments were made in the feeder lines, positive results were obtained. When adding field amplitudes (in loads), the power released in the load exceeds the power supplied from different channels (power dividers were used). The most simple experience, illustrating the principle of adding amplitudes, is an experiment in which three highly directional antennas operate in phase with one receiving receiver, to which a wattmeter is connected. The result of this experiment: the power recorded at the receiving antenna is nine times greater than that provided by each transmitting antenna separately. At the receiving antenna, the amplitudes (three) from the three transmitting antennas are added, and the receiving power is proportional to the square of the amplitude. That is, when adding three in-phase amplitudes, the reception power increases nine times!
It should be noted that interference in air (vacuum) is multiphase and differs in a number of ways from interference in feeder lines, cavity resonators, standing waves ah in coils, etc. In the so-called classical interference pattern, both addition and subtraction of the amplitudes of the electromagnetic field are observed. Therefore, in general, with multiphase interference, the violation of the law of conservation of energy is local in nature. In a resonator or in the presence of standing waves in feeder lines, the superposition of electromagnetic waves is not accompanied by a redistribution of the electromagnetic field in space. In this case, in quarter- and half-wave resonators only the addition of field amplitudes occurs. The energy of the waves combined in one volume is the energy passed from the generator to the resonator.
Experimental studies fully confirm the theory of transgeneration. It is known from microwave practice that even with ordinary electrical breakdown in feeder lines, the power exceeds the power supplied from the generator. For example, a waveguide designed for a microwave power of 100 MW is pierced by adding two microwave powers of 25 MW each - by adding two counter-propagating microwave waves in the waveguide. This can happen when microwave power is reflected from the end of the line.
A number of original circuit diagrams to generate energy using various types interference. The main frequency range is meter and decimeter (microwave), up to centimeter. Based on transgeneration, it is possible to create compact autonomous sources of electricity.
What is a permanent magnet? A permanent magnet is a body that can maintain magnetization for a long time. As a result of repeated research and numerous experiments, we can say that only three substances on Earth can be permanent magnets (Fig. 1).
Rice. 1. Permanent magnets. ()
Only these three substances and their alloys can be permanent magnets, only they can be magnetized and maintain this state for a long time.
Permanent magnets have been used for a very long time, and first of all they are devices for orientation in space - the first compass was invented in China in order to navigate in the desert. Today, no one argues about magnetic needles or permanent magnets; they are used everywhere in telephones and radio transmitters and simply in various electrical products. They can be different: there are strip magnets (Fig. 2)
Rice. 2. Strip magnet ()
And there are magnets that are called arc-shaped or horseshoe-shaped (Fig. 3)
Rice. 3. Arc magnet ()
The study of permanent magnets is exclusively related to their interaction. A magnetic field can be created by an electric current and a permanent magnet, so the first thing that was done was research with magnetic needles. If we bring a magnet close to the arrow, we will see interaction - like poles will repel, and unlike poles will attract. This interaction is observed with all magnets.
Let's place small magnetic arrows along the strip magnet (Fig. 4), the south pole will interact with the north, and the north will attract the south. The magnetic needles will be located along the magnetic field line. It is generally accepted that magnetic lines are directed outside a permanent magnet from the north pole to the south, and inside the magnet from the south pole to the north. Thus, the magnetic lines are closed in exactly the same way as those of electric current, these are concentric circles, they close inside the magnet itself. It turns out that outside the magnet the magnetic field is directed from north to south, and inside the magnet from south to north.
Rice. 4. Magnetic field lines of a strip magnet ()
In order to observe the shape of the magnetic field of a strip magnet, the shape of the magnetic field of an arc-shaped magnet, we will use the following devices or parts. Let's take a transparent plate, iron filings and conduct an experiment. Let's sprinkle iron filings on the plate located on the strip magnet (Fig. 5):
Rice. 5. Shape of the magnetic field of a strip magnet ()
We see that the magnetic field lines leave the north pole and enter the south pole; by the density of the lines we can judge the poles of the magnet; where the lines are thicker, the magnet poles are located there (Fig. 6).
Rice. 6. Shape of the magnetic field of an arc-shaped magnet ()
We will carry out a similar experiment with an arc-shaped magnet. We see that magnetic lines start at the north and end at the south pole throughout the magnet.
We already know that a magnetic field is formed only around magnets and electric currents. How can we determine the Earth's magnetic field? Any needle, any compass in the Earth's magnetic field is strictly oriented. Since the magnetic needle is strictly oriented in space, therefore, it is affected by a magnetic field, and this is the Earth’s magnetic field. We can conclude that our Earth is a large magnet (Fig. 7) and, accordingly, this magnet creates a fairly powerful magnetic field in space. When we look at the needle of a magnetic compass, we know that the red arrow points south and the blue arrow points north. How are the Earth's magnetic poles located? In this case, it is necessary to remember that the south magnetic pole is located at the north geographic pole of the Earth and the north magnetic pole of the Earth is located at the south geographic pole. If we consider the Earth as a body located in space, then we can say that when we go north along the compass, we will come to the south magnetic pole, and when we go south, we will end up at the north magnetic pole. At the equator, the compass needle will be located almost horizontally relative to the surface of the Earth, and the closer we are to the poles, the more vertical the needle will be. The Earth's magnetic field could change; there were times when the poles changed relative to each other, that is, the south was where the north was, and vice versa. According to scientists, this was a harbinger major disasters on Earth. This has not been observed for the last few tens of millennia.
Rice. 7. Earth's magnetic field ()
Magnetic and geographic poles do not coincide. There is also a magnetic field inside the Earth itself, and, like in a permanent magnet, it is directed from the south magnetic pole to the north.
Where does the magnetic field in permanent magnets come from? The answer to this question was given by the French scientist Andre-Marie Ampère. He expressed the idea that the magnetic field of permanent magnets is explained by elementary, simplest currents flowing inside permanent magnets. These simplest elementary currents reinforce each other in a certain way and create a magnetic field. A negatively charged particle - an electron - moves around the nucleus of an atom; this movement can be considered directed, and, accordingly, a magnetic field is created around such a moving charge. Inside any body, the number of atoms and electrons is simply enormous; accordingly, all these elementary currents take an ordered direction, and we get a fairly significant magnetic field. We can say the same about the Earth, that is, the Earth's magnetic field is very similar to the magnetic field of a permanent magnet. A permanent magnet is a fairly bright characteristic of any manifestation of a magnetic field.
In addition to the existence of magnetic storms, there are also magnetic anomalies. They are associated with the solar magnetic field. When sufficiently powerful explosions or ejections occur on the Sun, they occur not without the help of the manifestation of the Sun's magnetic field. This echo reaches the Earth and affects its magnetic field, as a result we observe magnetic storms. Magnetic anomalies are associated with iron ore deposits in the Earth, huge deposits are magnetized by the Earth’s magnetic field for a long time, and all bodies around will experience the magnetic field from this anomaly, compass arrows will show the wrong direction.
In the next lesson we will look at other phenomena associated with magnetic actions.
References
- Gendenshtein L.E., Kaidalov A.B., Kozhevnikov V.B. Physics 8 / Ed. Orlova V.A., Roizena I.I. - M.: Mnemosyne.
- Peryshkin A.V. Physics 8. - M.: Bustard, 2010.
- Fadeeva A.A., Zasov A.V., Kiselev D.F. Physics 8. - M.: Enlightenment.
- Class-fizika.narod.ru ().
- Class-fizika.narod.ru ().
- Files.school-collection.edu.ru ().
Homework
- Which end of the compass needle is attracted to north pole Earth?
- In what place on Earth can you not trust the magnetic needle?
- What does the density of lines on a magnet indicate?
There are two main types of magnets: permanent and electromagnets. You can determine what a permanent magnet is based on its main properties. A permanent magnet gets its name because its magnetism is always “on.” It generates its own magnetic field, unlike an electromagnet, which is made of wire wrapped around an iron core and requires current to flow to create a magnetic field.
History of the study of magnetic properties
Centuries ago, people discovered that some types of rocks have an original property: they are attracted to iron objects. Mention of magnetite is found in ancient historical chronicles: more than two thousand years ago in European and much earlier in East Asian. At first it was regarded as a curious object.
Later, magnetite was used for navigation, finding that it tends to occupy a certain position when given the freedom to rotate. Research conducted by P. Peregrine in the 13th century, showed that steel could acquire these characteristics after rubbing with magnetite.
Magnetized objects had two poles: “north” and “south,” relative to the Earth’s magnetic field. As Peregrine discovered, isolating one of the poles was not possible by cutting a fragment of magnetite in two - each individual fragment ended up with its own pair of poles.
In accordance with today's concepts, the magnetic field of permanent magnets is the resulting orientation of electrons in a single direction. Only some types of materials interact with magnetic fields; a much smaller number of them are capable of maintaining a constant magnetic field.
Properties of permanent magnets
The main properties of permanent magnets and the field they create are:
- the existence of two poles;
- opposite poles attract, and like poles repel (like positive and negative charges);
- magnetic force imperceptibly spreads in space and passes through objects (paper, wood);
- An increase in MF intensity is observed near the poles.
Permanent magnets support the MP without external assistance. Depending on their magnetic properties, materials are divided into main types:
- ferromagnets – easily magnetized;
- paramagnetic materials – are magnetized with great difficulty;
- Diamagnets - tend to reflect external magnetic fields by magnetizing in the opposite direction.
Important! Soft magnetic materials such as steel conduct magnetism when attached to a magnet, but this stops when it is removed. Permanent magnets are made from hard magnetic materials.
How does a permanent magnet work?
His work deals with atomic structure. All ferromagnets create a natural, albeit weak, magnetic field, thanks to the electrons surrounding the nuclei of atoms. These groups of atoms are able to orient themselves in the same direction and are called magnetic domains. Each domain has two poles: north and south. When a ferromagnetic material is not magnetized, its regions are oriented in random directions, and their magnetic fields cancel each other out.
To create permanent magnets, ferromagnets are heated at very high temperatures and exposed to strong external magnetic fields. This leads to the fact that individual magnetic domains inside the material begin to orient themselves in the direction of the external magnetic field until all domains are aligned, reaching the point of magnetic saturation. The material is then cooled and the aligned domains are locked into position. Once the external MF is removed, hard magnetic materials will retain most of their domains, creating a permanent magnet.
Characteristics of permanent magnet
- Magnetic force is characterized by residual magnetic induction. Designated Br. This is the force that remains after the disappearance of the external MP. Measured in tests (T) or gauss (G);
- Coercivity or resistance to demagnetization - Ns. Measured in A/m. Shows what the external magnetic field strength should be in order to demagnetize the material;
- Maximum energy – BHmax. Calculated by multiplying the remanent magnetic force Br and coercivity Hc. Measured in MGSE (megaussersted);
- Temperature coefficient of residual magnetic force – Тс of Br. Characterizes the dependence of Br on the temperature value;
- Tmax – the highest temperature value, upon reaching which permanent magnets lose their properties with the possibility of reverse recovery;
- Tcur is the highest temperature value at which the magnetic material irreversibly loses its properties. This indicator is called the Curie temperature.
Individual magnet characteristics change depending on temperature. At different temperatures different types magnetic materials work differently.
Important! All permanent magnets lose a percentage of their magnetism as the temperature rises, but at different rates depending on their type.
Types of permanent magnets
There are five types of permanent magnets, each of which is made differently based on materials with different properties:
- alnico;
- ferrites;
- rare earth SmCo based on cobalt and samarium;
- neodymium;
- polymer.
Alnico
These are permanent magnets consisting primarily of a combination of aluminum, nickel and cobalt, but may also include copper, iron and titanium. Due to the properties of alnico magnets, they can operate at the highest temperatures while retaining their magnetism, but they demagnetize more easily than ferrite or rare earth SmCo. They were the first mass-produced permanent magnets, replacing magnetized metals and expensive electromagnets.
Application:
- electric motors;
- heat treatment;
- bearings;
- aerospace vehicles;
- military equipment;
- high temperature loading and unloading equipment;
- microphones.
Ferrites
To make ferrite magnets, also known as ceramic, strontium carbonate and iron oxide are used in a ratio of 10/90. Both materials are abundant and economically available.
Due to their low production costs, resistance to heat (up to 250°C) and corrosion, ferrite magnets are one of the most popular magnets for everyday use. They have greater internal coercivity than alnico, but less magnetic strength than their neodymium counterparts.
Application:
- sound speakers;
- security systems;
- large plate magnets for removing iron contamination from process lines;
- electric motors and generators;
- medical instruments;
- lifting magnets;
- marine search magnets;
- devices based on the operation of eddy currents;
- switches and relays;
- brakes
Rare Earth SmCo Magnets
Cobalt and samarium magnets operate over a wide temperature range, have high temperature coefficients and high corrosion resistance. This type retains magnetic properties even at temperatures below absolute zero, making them popular for use in cryogenic applications.
Application:
- turbo technology;
- pump couplings;
- wet environments;
- high temperature devices;
- miniature electric racing cars;
- radio-electronic devices for operation in critical conditions.
Neodymium magnets
The strongest existing magnets, consisting of an alloy of neodymium, iron and boron. Thanks to their enormous power, even miniature magnets are effective. This provides versatility of use. Each person is constantly near one of the neodymium magnets. They are, for example, in a smartphone. The manufacture of electric motors, medical equipment, and radio electronics rely on ultra-strong neodymium magnets. Due to their ultra-strength, enormous magnetic force and resistance to demagnetization, samples up to 1 mm are possible.
Application:
- hard drives;
- sound reproducing devices – microphones, acoustic sensors, headphones, loudspeakers;
- dentures;
- magnetically coupled pumps;
- door closers;
- engines and generators;
- locks on jewelry;
- MRI scanners;
- magnetic therapy;
- ABS sensors in cars;
- lifting equipment;
- magnetic separators;
- reed switches, etc.
Flexible magnets contain magnetic particles inside a polymer binder. Used for unique devices where installation of solid analogues is impossible.
Application:
- display advertising – quick fixation and quick removal at exhibitions and events;
- vehicle signs, educational school panels, company logos;
- toys, puzzles and games;
- masking surfaces for painting;
- calendars and magnetic bookmarks;
- window and door seals.
Most permanent magnets are brittle and should not be used as structural components. They are made in standard forms: rings, rods, disks, and individual: trapezoids, arcs, etc. Neodymium magnets, due to their high iron content, are susceptible to corrosion, so they are coated with nickel, stainless steel, Teflon, titanium, rubber and other materials.
Video