For shielding magnetic field two methods are used:
Bypass method;
Screen magnetic field method.
Let's take a closer look at each of these methods.
Method of shunting a magnetic field with a screen.
The method of shunting a magnetic field with a screen is used to protect against a constant and slowly changing alternating magnetic field. Screens are made of ferromagnetic materials with high relative magnetic penetration (steel, permalloy). If there is a screen, the lines of magnetic induction pass mainly along its walls (Figure 8.15), which have low magnetic resistance compared to the air space inside the screen. The quality of shielding depends on the magnetic permeability of the shield and the resistance of the magnetic circuit, i.e. The thicker the screen and the fewer seams and joints running across the direction of the magnetic induction lines, the shielding efficiency will be higher.
Method of displacement of a magnetic field by a screen.
The method of displacement of a magnetic field by a screen is used to screen alternating high-frequency magnetic fields. In this case, screens made of non-magnetic metals are used. Shielding is based on the phenomenon of induction. Here the phenomenon of induction is useful.
Let's place a copper cylinder in the path of a uniform alternating magnetic field (Figure 8.16a). Variable EDs will be excited in it, which, in turn, will create alternating inductive eddy currents (Foucault currents). The magnetic field of these currents (Figure 8.16b) will be closed; inside the cylinder it will be directed towards the exciting field, and outside it - in the same direction as the exciting field. The resulting field (Figure 8.16, c) turns out to be weakened near the cylinder and strengthened outside it, i.e. the field is displaced from the space occupied by the cylinder, which is its shielding effect, which will be the more effective, the lower the electrical resistance of the cylinder, i.e. the greater the eddy currents flowing through it.
Thanks to the surface effect (“skin effect”), the density of eddy currents and the intensity of the alternating magnetic field decreases exponentially as one goes deeper into the metal
, (8.5)
Where 
(8.6)
– indicator of the decrease in field and current, which is called equivalent penetration depth.
Here is the relative magnetic permeability of the material;
– magnetic permeability of vacuum, equal to 1.25*10 8 g*cm -1;
– resistivity of the material, Ohm*cm;
- frequency Hz.
The value of the equivalent penetration depth is convenient to characterize the shielding effect of eddy currents. The smaller x0, the greater the magnetic field they create, which displaces the external field of the pickup source from the space occupied by the screen.
For a non-magnetic material in formula (8.6) =1, the shielding effect is determined only by and . What if the screen is made of ferromagnetic material?
If they are equal, the effect will be better, since >1 (50..100) and x 0 will be less.
So, x 0 is a criterion for the shielding effect of eddy currents. It is of interest to estimate how many times the current density and magnetic field strength become lower at depth x 0 compared to what they are at the surface. To do this, we substitute x = x 0 into formula (8.5), then
from which it can be seen that at a depth of x 0, the current density and magnetic field strength drop by e times, i.e. to a value of 1/2.72, which is 0.37 of the density and tension on the surface. Since the field weakening is only 2.72 times at depth x 0 not enough to characterize the shielding material, then use two more values of penetration depth x 0.1 and x 0.01, which characterize the drop in current density and field voltage by 10 and 100 times from their values on the surface.
Let's express the values x 0.1 and x 0.01 through the value x 0; for this, based on expression (8.5), we create the equation
AND 
,
having decided which we get
x 0.1 =x 0 ln10=2.3x 0 ; (8.7)
x 0.01 = x 0 ln100 = 4.6x 0
Based on formulas (8.6) and (8.7) for various shielding materials, the values of penetration depths are given in the literature. For clarity purposes, we present the same data in the form of table 8.1.
The table shows that for all high frequencies, starting from the medium wave range, a screen made of any metal with a thickness of 0.5..1.5 mm is very effective. When choosing the thickness and material of the screen, you should not proceed from the electrical properties of the material, but be guided by considerations of mechanical strength, rigidity, resistance to corrosion, convenience of joining individual parts and making transition contacts with low resistance between them, convenience of soldering, welding, etc.
From the table data it follows that for frequencies greater than 10 MHz, a film of copper, and even more so of silver, with a thickness of less than 0.1 mm gives a significant shielding effect. Therefore, at frequencies above 10 MHz, it is quite acceptable to use screens made of foil getinax or other insulating material with a copper or silver coating applied to it.
Steel can be used as screens, but you need to remember that due to the high resistivity and hysteresis phenomenon, a steel screen can introduce significant losses into the shielding circuits.
Filtration
Filtering is the primary means of reducing structural noise generated in DC power and switching circuits. alternating current ES. Noise suppression filters designed for this purpose make it possible to reduce conducted noise from both external and internal sources. Filtration efficiency is determined by the attenuation introduced by the filter:
dB,
The following basic requirements are imposed on the filter:
Ensuring the specified efficiency S in the required frequency range (taking into account the internal resistance and load of the electrical circuit);
Limitation of the permissible drop in direct or alternating voltage across the filter at maximum load current;
Ensuring acceptable nonlinear distortions of the supply voltage, which determine the requirements for filter linearity;
Design requirements - shielding efficiency, minimum overall dimensions and weight, ensuring normal thermal conditions, resistance to mechanical and climatic influences, manufacturability of the design, etc.;
Filter elements must be selected taking into account the rated currents and voltages of the electrical circuit, as well as the voltage and current surges caused in them, caused by instability of the electrical regime and transient processes.
Capacitors. They are used as independent noise suppression elements and as parallel filter units. Structurally, noise suppression capacitors are divided into:
Two-pole type K50-6, K52-1B, ETO, K53-1A;
Support type KO, KO-E, KDO;
Feed-through non-coaxial type K73-21;
Feedthrough coaxial type KTP-44, K10-44, K73-18, K53-17;
Capacitor units;
The main characteristic of a noise suppression capacitor is the dependence of its impedance on frequency. To reduce interference in the frequency range up to approximately 10 MHz, two-pole capacitors can be used, taking into account the short length of their leads. Reference noise suppression capacitors are used up to frequencies of 30-50 MHz. Symmetrical pass capacitors are used in a two-wire circuit up to frequencies of the order of 100 MHz. Pass capacitors operate over a wide frequency range up to approximately 1000 MHz.
Inductive elements. They are used as independent noise suppression elements and as sequential links of noise suppression filters. Structurally, the most common chokes are special types:
Turning on a ferromagnetic core;
Turn-free.
The main characteristic of a noise suppression choke is the dependence of its impedance on frequency. At low frequencies It is recommended to use magnetodielectric cores of the PP90 and PP250 brands, made on the basis of m-permalloy. To suppress interference in equipment circuits with currents up to 3A, it is recommended to use HF chokes of the DM type, and for higher rated currents - chokes of the D200 series.
Filters. Ceramic pass-through filters of type B7, B14, B23 are designed to suppress interference in circuits of direct, pulsating and alternating currents in the frequency range from 10 MHz to 10 GHz. The designs of such filters are shown in Figure 8.17
The attenuation introduced by filters B7, B14, B23 in the frequency range 10..100 MHz increases from approximately 20..30 to 50..60 dB and in the frequency range above 100 MHz exceeds 50 dB.
Ceramic in-line filters type B23B are built on the basis of disk ceramic capacitors and turn-free ferromagnetic chokes (Figure 8.18).
Turn-free chokes are a tubular ferromagnetic core made of grade 50 VCh-2 ferrite, mounted on a feed-through terminal. The inductance of the inductor is 0.08…0.13 μH. The filter housing is made of UV-61 ceramic material, which has high mechanical strength. The housing is metalized with a layer of silver to ensure low contact resistance between the outer lining of the capacitor and the grounding threaded bushing, which is used to secure the filter. The capacitor is soldered along the outer perimeter to the filter housing, and along the inner perimeter to the feed-through terminal. Sealing of the filter is ensured by filling the ends of the housing with a compound.
For B23B filters:
nominal filter capacitances – from 0.01 to 6.8 µF,
rated voltage 50 and 250V,
rated current up to 20A,
Overall dimensions of the filter:
L=25mm, D= 12mm
The attenuation introduced by B23B filters in the frequency range from 10 kHz to 10 MHz increases from approximately 30..50 to 60..70 dB and in the frequency range above 10 MHz exceeds 70 dB.
For onboard ES, the use of special noise-suppressing wires with ferrofillers having high magnetic permeability and high specific losses is promising. So, for PPE brand wires, the insertion attenuation in the frequency range 1...1000 MHz increases from 6 to 128 dB/m.
The design of multi-pin connectors is known, in which one U-shaped noise suppression filter is installed on each contact.
Overall dimensions of the built-in filter:
length 9.5 mm,
diameter 3.2 mm.
The attenuation introduced by the filter in a 50-ohm circuit is 20 dB at a frequency of 10 MHz and up to 80 dB at a frequency of 100 MHz.
Filtering of power supply circuits of digital electronic devices.
Pulse noise in power buses that occurs during the switching of digital integrated circuits (DIC), as well as penetrating externally, can lead to malfunctions in the operation of digital information processing devices.
To reduce the level of noise in power buses, circuit design methods are used:
Reducing the inductance of the “power” buses, taking into account the mutual magnetic coupling of the forward and reverse conductors;
Reducing the lengths of sections of “power” buses, which are common for currents for various digital information systems;
Slowing down the edges of pulse currents in the “power” buses using noise-suppressing capacitors;
Rational topology of power circuits on a printed circuit board.
Increasing the cross-sectional dimensions of the conductors leads to a decrease in the intrinsic inductance of the buses, and also reduces their active resistance. The latter is especially important in the case of the ground bus, which is the return conductor for signal circuits. Therefore, in multilayer printed circuit boards It is desirable to make the “power” buses in the form of conducting planes located in adjacent layers (Figure 8.19).
The overhead power buses used in printed circuit assemblies on digital ICs have larger transverse dimensions compared to busbars made in the form of printed conductors, and therefore have lower inductance and resistance. Additional advantages of mounted power buses are:
Simplified routing of signal circuits;
Increasing the rigidity of the PP by creating additional ribs that act as limiters that protect the IC with mounted ERE from mechanical damage during installation and configuration of the product (Figure 8.20).
The “power” bars, manufactured by printing and mounted vertically on the PCB, are highly technologically advanced (Figure 6.12c).
There are known designs of mounted busbars installed under the IC body, which are located on the board in rows (Figure 8.22).
The considered designs of the “supply” buses also provide a large linear capacitance, which leads to a decrease in the wave impedance of the “supply” line and, consequently, a decrease in the level of impulse noise.
The power distribution of the IC to the PCB should not be carried out in series (Figure 8.23a), but in parallel (Figure 8.23b)
It is necessary to use power distribution in the form of closed circuits (Fig. 8.23c). This design is close in its electrical parameters to solid power planes. To protect against the influence of an external interference-carrying magnetic field, an external closed loop should be provided along the perimeter of the PP.
Grounding
The grounding system is an electrical circuit that has the property of maintaining a minimum potential, which is the reference level in a particular product. The grounding system in the power supply must provide signal and power return circuits, protect people and equipment from faults in power source circuits, and remove static charges.
The following basic requirements apply to grounding systems:
1) minimizing the overall impedance of the ground bus;
2) the absence of closed grounding loops sensitive to magnetic fields.
The ES requires at least three separate grounding circuits:
For signal circuits with low level currents and voltages;
For power circuits with high level power consumption (power supplies, ES output stages, etc.)
For body circuits (chassis, panels, screens and metallization).
Electrical circuits in the ES are grounded in the following ways: at one point and at several points closest to the grounding reference point (Figure 8.24)
Accordingly, grounding systems can be called single-point and multi-point.
The highest level of interference occurs in a single-point grounding system with a common series-connected ground bus (Figure 8.24 a).
The further away the grounding point is, the higher its potential. It should not be used for circuits with a large spread of power consumption, since high-power FUs create large return ground currents that can affect small-signal FUs. If necessary, the most critical FU should be connected as close as possible to the reference grounding point.
A multipoint grounding system (Figure 8.24 c) should be used for high-frequency circuits (f≥10 MHz), connecting the RES FU at the points closest to the reference grounding point.
For sensitive circuits, a floating ground circuit is used (Figure 8.25). This grounding system requires complete isolation of the circuit from the chassis (high resistance and low capacitance), otherwise it is ineffective. The circuits can be powered by solar cells or batteries, and signals must enter and leave the circuit through transformers or optocouplers.
An example of the implementation of the considered grounding principles for a nine-track digital tape drive is shown in Figure 8.26.
There are the following ground buses: three signal, one power and one body. The analog FUs most susceptible to interference (nine sense amplifiers) are grounded using two separated ground buses. Nine write amplifiers, which operate at higher signal levels than the read amplifiers, as well as control ICs and interface circuits with data products are connected to the third signal bus, ground. The three DC motors and their control circuits, relays and solenoids are connected to the power bus ground. The most sensitive driveshaft motor control circuit is connected closest to the ground reference point. The chassis ground bus is used to connect the chassis and casing. The signal, power, and chassis ground buses are connected together at one point in the secondary power supply. It should be noted that it is advisable to draw up structural wiring diagrams when designing RES.
How can you make two magnets next to each other not feel each other's presence? What material needs to be placed between them to power lines would the magnetic field from one magnet not reach the second magnet?
This question is not as trivial as it might seem at first glance. We need to truly isolate the two magnets. That is, so that these two magnets can be rotated differently and moved differently relative to each other and yet, so that each of these magnets behaves as if there was no other magnet nearby. Therefore, any tricks involving placing a third magnet or ferromagnet nearby to create some special configuration of magnetic fields with compensation of all magnetic fields at any one particular point do not work in principle.
Diamagnetic???
Sometimes they mistakenly think that such a magnetic field insulator can serve diamagnetic. But this is not true. A diamagnetic material actually weakens the magnetic field. But it weakens the magnetic field only in the thickness of the diamagnetic itself, inside the diamagnetic. Because of this, many people mistakenly think that if one or both magnets are immured in a piece of diamagnetic material, then their attraction or repulsion will weaken.
But this is not a solution to the problem. Firstly, the field lines of one magnet will still reach another magnet, that is, the magnetic field only decreases in the thickness of the diamagnetic, but does not disappear completely. Secondly, if the magnets are immured in the thickness of the diamagnetic material, then we cannot move or rotate them relative to each other.
And if you just make a flat screen out of a diamagnetic material, then this screen will transmit a magnetic field through itself. Moreover, behind this screen the magnetic field will be exactly the same as if this diamagnetic screen did not exist at all.
This suggests that even magnets embedded in a diamagnetic material will not experience a weakening of each other’s magnetic field. In fact, where the walled magnet is located, there is simply no diamagnetic material directly in the volume of this magnet. And since there is no diamagnetic material where the walled magnet is located, it means that both walled magnets actually interact with each other in exactly the same way as if they were not walled up in the diamagnetic material. The diamagnetic material around these magnets is as useless as the flat diamagnetic shield between the magnets.
Ideal diamagnetic
We need a material that would not allow magnetic field lines to pass through itself at all. It is necessary that the magnetic field lines be pushed out of such a material. If magnetic field lines pass through a material, then, behind a screen made of such material, they completely restore all their strength. This follows from the law of conservation of magnetic flux.
In a diamagnetic material, the weakening of the external magnetic field occurs due to the induced internal magnetic field. This induced magnetic field is created by circular currents of electrons inside the atoms. When an external magnetic field is turned on, the electrons in the atoms should begin to move around the lines of force of the external magnetic field. This induced circular motion of electrons in atoms creates an additional magnetic field, which is always directed against the external magnetic field. Therefore, the total magnetic field inside the diamagnetic becomes less than outside.
But complete compensation of the external field due to the induced internal field does not occur. There is not enough circular current strength in the diamagnetic atoms to create exactly the same magnetic field as the external magnetic field. Therefore, the lines of force of the external magnetic field remain in the thickness of the diamagnetic material. The external magnetic field, as it were, “pierces” the diamagnetic material through and through.
The only material that pushes magnetic field lines out of itself is a superconductor. In a superconductor, an external magnetic field induces circular currents around the external field lines that create an oppositely directed magnetic field exactly equal to the external magnetic field. In this sense, a superconductor is an ideal diamagnetic.
On the surface of a superconductor, the magnetic field strength vector is always directed along this surface, tangential to the surface of the superconducting body. On the surface of a superconductor, the magnetic field vector does not have a component directed perpendicular to the surface of the superconductor. Therefore, magnetic field lines always bend around a superconducting body of any shape.
Bending of a superconductor by magnetic field lines
But this does not mean at all that if a superconducting screen is placed between two magnets, it will solve the problem. The fact is that the magnetic field lines of the magnet will go to another magnet, bypassing the superconductor screen. Therefore, a flat superconducting screen will only weaken the influence of magnets on each other.
This weakening of the interaction between the two magnets will depend on how much the length of the field line that connects the two magnets to each other has increased. The greater the length of the connecting field lines, the less interaction between two magnets with each other.
This is exactly the same effect as if you increase the distance between the magnets without any superconducting screen. If you increase the distance between magnets, then the lengths of the magnetic field lines also increase.
This means that in order to increase the lengths of the power lines that connect two magnets bypassing the superconducting screen, it is necessary to increase the dimensions of this flat screen both in length and width. This will lead to an increase in the lengths of bypass power lines. And the larger the dimensions of the flat screen compared to the distance between the magnets, the less interaction between the magnets becomes.
The interaction between the magnets completely disappears only when both dimensions of the flat superconducting screen become infinite. This is an analogue of the situation when magnets were separated to an infinitely large distance, and therefore the length of the magnetic field lines connecting them became infinite.
Theoretically, this, of course, completely solves the problem. But in practice we cannot make a superconducting flat screen of infinite dimensions. I would like to have such a solution that can be implemented in practice in the laboratory or in production. (We are no longer talking about everyday conditions, since it is impossible to make a superconductor in everyday life.)
Space division by superconductor
Alternatively, a flat screen of infinitely large dimensions can be interpreted as dividing the entire three-dimensional space into two parts that are not connected to each other. But it’s not just a flat screen of infinite size that can divide space into two parts. Any closed surface also divides space into two parts, the volume inside the closed surface and the volume outside the closed surface. For example, any sphere divides space into two parts: the ball inside the sphere and everything outside.
Therefore, a superconducting sphere is an ideal insulator of a magnetic field. If you place a magnet in such a superconducting sphere, then no instrument can ever detect whether there is a magnet inside this sphere or not.
And, conversely, if you are placed inside such a sphere, then external magnetic fields will not act on you. For example, the Earth's magnetic field cannot be detected inside such a superconducting sphere by any instruments. Inside such a superconducting sphere, it will be possible to detect only the magnetic field from those magnets that will also be located inside this sphere.
Thus, in order for two magnets not to interact with each other, one of these magnets must be placed inside the superconducting sphere, and the second one must be left outside. Then the magnetic field of the first magnet will be completely concentrated inside the sphere and will not go beyond the boundaries of this sphere. Therefore, the second magnet will not feel the presence of the first. Likewise, the magnetic field of the second magnet will not be able to penetrate inside the superconducting sphere. And therefore the first magnet will not sense the close presence of the second magnet.
Finally, we can rotate and move both magnets relative to each other as we please. True, the first magnet is limited in its movements by the radius of the superconducting sphere. But that's just how it seems. In fact, the interaction of two magnets depends only on their relative position and their rotations around the center of gravity of the corresponding magnet. Therefore, it is enough to place the center of gravity of the first magnet in the center of the sphere and place the origin of coordinates there at the center of the sphere. All possible options for the location of magnets will be determined only by all possible options the location of the second magnet relative to the first magnet and their rotation angles around their centers of mass.
Of course, instead of a sphere, you can take any other surface shape, for example, an ellipsoid or a box-shaped surface, etc. If only it divided the space into two parts. That is, there should not be a hole in this surface through which a power line can pass through to connect the internal and external magnets.
Let's consider a regular bar magnet: magnet 1 rests on the North surface with its pole up. Hanging distance y " role="presentation" style="position: relative;"> Y y " role="presentation" style="position: relative;"> y " role="presentation" style="position: relative;">Y above it (supported from side to side by a plastic tube) is a second, smaller bar magnet, magnet 2, with the North pole facing down. The magnetic forces between them exceed the force of gravity and keep magnet 2 suspended. Consider some material, material-X, which moves towards the gap between two magnets with initial speed. v " role="presentation" style="position: relative;"> v v " role="presentation" style="position: relative;"> v " role="presentation" style="position: relative;">v ,
Is there a material, material-X , that will reduce the distance y " role="presentation" style="position: relative;"> Y y " role="presentation" style="position: relative;"> y " role="presentation" style="position: relative;">Y between two magnets, and pass through the gap without changing speed v " role="presentation" style="position: relative;"> v v " role="presentation" style="position: relative;"> v " role="presentation" style="position: relative;">v ?
Amateur physicist
such a strange question
Answers
Jojo
The material you are looking for may be a superconductor. These materials have zero current resistance and can thus compensate for penetrating field lines in the first layers of the material. This phenomenon is called the Meissner effect and is the very definition of a superconducting state.
In your case the plates are between two magnets, this will definitely reduce y " role="presentation" style="position: relative;"> Y y " role="presentation" style="position: relative;"> y " role="presentation" style="position: relative;">Y ,
For speed:
Here, usually eddy currents induced by the magnetic field lead to a loss of power, defined as:
P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> = π P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> 2 P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> IN P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> 2 P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> d P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> 2 P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> e P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> 2 P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> 6 k ρ D P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> , P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation"> P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">п P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">= P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">π P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">2 P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">B P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">п P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">2 P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">d P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">2 P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">е P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">2 P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">6 P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">К P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">ρ P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">D P = π 2 B p 2 d 2 f 2 6 k ρ D , " role="presentation">,
since, however, a superconductor has zero resistance and thus de facto
ρ = ∞ " role="presentation"> ρ = ∞ ρ = ∞ " role="presentation"> ρ = ∞ " role="presentation">ρ ρ = ∞ " role="presentation">= ρ = ∞ " role="presentation">∞
no kinetic energy should be lost and thus the speed will remain the same.
There's just one problem:
A superconductor can only exist at very low temperatures, so this may not be possible in the case of your car... you'll at least need a cooling system that runs at liquid nitrogen to cool it down.
Other than superconductors, I don't see any possible material, because if the material is a conductor, then you always have eddy current losses (thus reducing v " role="presentation" style="position: relative;"> v v " role="presentation" style="position: relative;"> v " role="presentation" style="position: relative;">v) or the material is not a conductor (then y " role="presentation" style="position: relative;"> Y y " role="presentation" style="position: relative;"> y " role="presentation" style="position: relative;">Y will not decrease).
adamdport
Can this phenomenon be observed in a car or somewhere in an experiment?
Jojo
The point, however, is that when a superconductor enters a magnetic field, the lines of force are deflected, which will involve work... so in reality, entering the area between two magnets will cost some energy. If the plate leaves the area afterwards, the energy will be played back.
Lupercus
There are materials with very high magnetic permeability, for example, the so-called µ-metal. They are used to make screens that weaken the Earth's magnetic field in the path of the electron beam in sensitive electro-optical instruments.
Since your question combines two separate parts, I'll split it up to look at each one separately.
1. Static case: Do the magnetic poles get closer to each other when a magnetic shielding plate is placed between them?
Mu materials do not "kill" the magnetic field between your magnetic poles, but only deflect its direction, directing part of it into a metal screen. This will change the field strength greatly B " role="presentation" style="position: relative;"> IN B " role="presentation" style="position: relative;"> B " role="presentation" style="position: relative;">B on the surface of the screen, almost suppressing its parallel components. This leads to a decrease in magnetic pressure p = B 2 8 π μ " role="presentation" style="position: relative;"> p = B p = B 2 8 π μ " role="presentation" style="position: relative;"> p = B 2 8 π μ " role="presentation" style="position: relative;"> 2 p = B 2 8 π μ " role="presentation" style="position: relative;"> p = B 2 8 π μ " role="presentation" style="position: relative;"> 8π p = B 2 8 π μ " role="presentation" style="position: relative;"> p = B 2 8 π μ " role="presentation" style="position: relative;"> μ p = B 2 8 π μ " role="presentation" style="position: relative;"> p = B 2 8 π μ " role="presentation" style="position: relative;">п p = B 2 8 π μ " role="presentation" style="position: relative;">equals p = B 2 8 π μ " role="presentation" style="position: relative;">B p = B 2 8 π μ " role="presentation" style="position: relative;">2 p = B 2 8 π μ " role="presentation" style="position: relative;">8 p = B 2 8 π μ " role="presentation" style="position: relative;">π p = B 2 8 π μ " role="presentation" style="position: relative;">μ in close proximity to the screen surface. What if this decrease in the magnetic field on the screen significantly changes the magnetic pressure at the magnets' location, causing them to move? I'm afraid a more detailed calculation is needed here.
2. Plate movement: Is it possible that the speed of the shielding plate will not change?
Consider the following very simple and intuitive experiment: take copper pipe and keep it upright. Take a small magnet and let it fall into the pipe. The magnet falls: i) slowly and ii) at a uniform speed.
Your geometry can be made similar to that of a falling tube: consider a stack of magnets floating on top of each other, that is, with paired poles, NN and SS. Now take a "multi-plate" shield made from parallel sheets held firmly in place at equal distances from each other (like a 2D comb). This world simulates several falling pipes in parallel.
If you now hold a column of magnets in a vertical direction and pull a multi-plate through them with a constant force (analogous to gravity), then you will achieve a constant speed regime - similar to the falling pipe experiment.
This suggests that a column of magnets, or, more precisely, their magnetic field, acts on the copper plates of a viscous medium:
M p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> m m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> p l a t e m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> v m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> ˙ m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> = - γ m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> IN m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> V+ F m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> p l l m p l a t e v ˙ = − γ B v + F p u l l " role="presentation"> m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">m m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">п m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">L m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">T m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">е m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">v m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">˙ m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">= m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">- m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">γ m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">B m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">v m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">+ m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">F m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">п m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">U m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">L m p l a t e v ˙ = − γ B v + F p u l l " role="presentation">L
Where γ B " role="presentation" style="position: relative;"> γ γ B " role="presentation" style="position: relative;"> γ B " role="presentation" style="position: relative;"> IN γ B " role="presentation" style="position: relative;"> γ B " role="presentation" style="position: relative;">γ γ B " role="presentation" style="position: relative;">B there will be an effective coefficient of friction due to the magnetic field disturbed by the presence of the plates. After some time, you will eventually reach a state where the friction force will compensate for your effort and the speed will remain constant: v = F p u l l γ B " role="presentation" style="position: relative;"> v = F v = F p u l l γ B " role="presentation" style="position: relative;"> v = F p u l l γ B " role="presentation" style="position: relative;"> p l l v = F p u l l γ B " role="presentation" style="position: relative;"> v = F p u l l γ B " role="presentation" style="position: relative;"> γ v = F p u l l γ B " role="presentation" style="position: relative;"> v = F p u l l γ B " role="presentation" style="position: relative;"> IN v = F p u l l γ B " role="presentation" style="position: relative;"> v = F p u l l γ B " role="presentation" style="position: relative;"> v v = F p u l l γ B " role="presentation" style="position: relative;"> = v = F p u l l γ B " role="presentation" style="position: relative;"> F v = F p u l l γ B " role="presentation" style="position: relative;"> P v = F p u l l γ B " role="presentation" style="position: relative;"> U v = F p u l l γ B " role="presentation" style="position: relative;"> L v = F p u l l γ B " role="presentation" style="position: relative;"> L v = F p u l l γ B " role="presentation" style="position: relative;"> γ v = F p u l l γ B " role="presentation" style="position: relative;"> IN ,
If that speed is the same as the speed you had before you pulled the plates into the magnetic field, it's a matter of how you control the force of gravity. Note: If there is no thrust, then the plate will simply be stopped by the magnetic brake effect. So you have to pull accordingly if you want to have a consistent speed.