JP3122439U - Leakage magnetic shielding plate - Google Patents

Abstract

A leakage magnetic field shielding plate for preventing a failure due to a leakage magnetic field radiated from a power transformer built in an audio device is provided.
A leakage magnetic field shielding plate, wherein a plurality of small blade-shaped or strip-shaped phase adjusting plates made of a ferromagnetic thin plate are attached to a ferromagnetic substrate.
[Selection] Figure 2

Description

  The present invention relates to a leakage magnetic field shielding plate for preventing a failure caused in an internal electronic circuit by a leakage magnetic field radiated from a power transformer built in an audio device.

  The leakage magnetic field radiated from the power transformer of the CD player or amplifier is applied to the internal circuit board to generate an induced voltage. The main component of the magnetic field is that which vibrates at 50 to 60 hertz, but there is also a high frequency component based on the noise generated in the rectifier circuit and fed back to the power transformer. The voltage is superimposed on the signal voltage and its waveform is disturbed, so that the sound quality is significantly impaired.

The leakage magnetic field is attenuated when the iron plate is applied. Therefore, in the electronic industry, a means for attenuating the leakage magnetic field by covering the power transformer inside the device with an iron plate cover and surrounding the iron plate is used. Yes. The thicker the iron plate, the greater the attenuation of the leakage magnetic field, so there is an idea that a thick iron plate may be used to improve sound quality. However, in the process in which the changing magnetic flux penetrates the iron plate, fine vibration is added to the magnetic flux inside the iron plate, and as the thickness of the iron plate increases, the added components increase and the sound quality deteriorates. I must think.
In short, it is indispensable to attenuate the leakage magnetic field as much as possible, but with the countermeasures using the iron plate considered to be the only means for that, even if the leakage magnetic field becomes weak, fine vibrations are added inside the iron plate, which in turn It becomes a cause, and how to overcome such contradiction becomes a problem.

  The problem can be solved by using the leakage magnetic field shielding plate of the present invention. It uses the attenuation of the magnetic field by the iron plate first, and then the surface shape is devised so that a phase difference occurs in the vibration of the magnetic flux generated inside the iron plate, and the vibration component is reduced by its canceling action. It is characterized in that it is suppressed. Next, the theoretical explanation to support the structure or shape and the action of such a leakage magnetic field shielding plate will be shown. However, there are a variety of leakage magnetic field shielding plates for solving the problems, and the following four types (1), (2), (3), and (4) are considered.

(Four kinds of leakage magnetic shielding plates)
{Circle around (1)} A plurality of small blade-shaped phase adjustment plates made of thin iron plates are mounted vertically and horizontally on a substrate made of iron plates to form a leakage magnetic field shielding plate. However, it is appropriate that the small blade-shaped phase adjusting plate is attached with an inclination of 45 degrees with respect to the substrate. This shielding plate is used in a direction perpendicular to the direction of the leakage magnetic field. (Figure 1)
(2) A leakage magnetic field shielding plate in which a coil which is short-circuited by connecting both ends to the small blade-shaped phase adjustment plate of the leakage magnetic field shielding plate of (1) is wound. The coil is an auxiliary means for obtaining a larger phase difference. (Figure 2)
{Circle around (3)} A plurality of strip-shaped phase adjustment plates made of a thin iron plate are attached in parallel to each other on a substrate made of an iron plate to form a leakage magnetic field shielding plate. The angle formed by the rectangular phase adjusting plate and the surface of the iron plate is appropriately 45 degrees. (Figure 3)
(4) A leakage magnetic field shielding plate in which a coil which is short-circuited by connecting both ends to the strip-shaped phase adjusting plate of the leakage magnetic field shielding plate of (3) is wound. The coil is auxiliary means for increasing the phase difference. (Fig. 4)
Even if the material of the leakage magnetic field shielding plate is not iron, the same effect can be obtained if it is a ferromagnetic material such as stainless steel or permalloy. However, because the material is easily available, the present invention is described as using an iron plate. Proceed.

(Theoretical explanation of leakage magnetic field shielding plate (1) (2))
As shown in FIG. 5, a small blade-shaped phase adjusting plate made of a thin iron plate is magnetized in the direction of the surface by a leakage magnetic field, and a high-density magnetic flux is generated inside. Moreover, since the magnetic flux changes, an eddy current flows through the small blade-shaped plate in a form surrounding the magnetic flux. Due to the eddy current, a new magnetic flux delayed by 90 degrees is generated and combined with the original magnetic flux, resulting in a magnetic flux slightly delayed in phase. The magnetic flux delayed in phase passes through the back substrate (iron plate). On the other hand, a magnetic flux due to the original leakage magnetic field is also generated on the substrate and passes through it, but a fine vibration specific to the iron plate is added to each of these two types of magnetic fluxes having different phases. However, the added oscillating magnetic flux should also have a phase difference, and when they are combined, they will cancel each other. FIG. 6 shows a situation where fine vibrations are canceled if the phase is different, but the fine vibrations added in the substrate are canceled as shown in this figure. Eventually, the magnetic field behind the thick iron plate serving as the substrate is attenuated, and the amplitude of the fine vibration component is small.
Note that (2) is essentially the same as (1). However, letting the current flow in the same direction through the coil in addition to the eddy current, further increase the phase lag and obtain a further cancellation effect. It is what.

(Theoretical explanation of leakage magnetic field shielding plate (3) (4))
In {circle over (1)}, small blade-shaped phase adjusting plates are arranged vertically and horizontally, but the strip-shaped phase adjusting plate of {circle around (3)} is equivalent to a small blade-shaped plate connected horizontally. However, in order to obtain a remarkable effect, the direction of the magnetic field lines to be applied must be oblique to the shielding plate. In that case, the magnetic flux inside the strip-shaped plate is in a direction penetrating the plate diagonally, and the eddy current flows around the magnetic flux to delay the phase of the magnetic flux. In (4), a current also flows through the coil, and the phase delay of the changing magnetic flux is further increased.

Whether or not the leakage magnetic field shielding plate of the present invention is effective is first determined by whether or not the leakage magnetic field is sufficiently attenuated and fine magnetic field vibrations generated in the iron plate have disappeared. This is the determination of the effect of the first stage. Next, the leakage magnetic field shielding plate is used for an audio device, and it is determined whether or not a clear sound quality improvement effect is confirmed for stereo reproduction sound. This is determined as the effect of the second stage.
In the following, a method for determining the presence or absence of these effects and the results are shown.

(First stage effect assessment method and results)
Using a commercially available CD player as an audio device, install the leakage magnetic field shielding plate of type (2) of the present invention so as to block the magnetic field lines radiated from the power transformer, and place a detection coil behind it. The induced voltage was observed with an oscilloscope. FIG. 9 is a waveform recording at that time. For comparison, we recorded the ones that detected the leakage magnetic field directly and the ones that detected the magnetic field behind it by blocking it with an iron plate. This is shown in FIGS. Examining the waveforms in detail, FIG. 8 and FIG. 9 both show that the original magnetic field is significantly attenuated, but FIG. 9 shows that the fine vibrations as seen in FIG. 8 are removed. . Focusing on some of the corresponding peaks of both, and confirming the presence or absence of fine vibrations in the vicinity, it can be seen that the target has been achieved. Since similar results can be obtained with shielding plates other than (2), their data are omitted.

(Method for judging the effect of the second stage and its concept)
Among audio devices, CD players have a low level of signal voltage to be processed and are susceptible to leakage magnetic fields, so the sound quality is improved by using the leakage magnetic field shielding plate of type (2) of the present invention for the CD player. I confirmed whether or not. In this case, the place where this shielding plate is installed is the upper part and the side of the power transformer.

As a CD for confirming the effect, a CD recorded with orchestral music was used. It is generally known that the width of the sound field spreading between the left and right speakers differs depending on the presence or absence of power supply noise, so the width of the sound field can be reduced by adding a countermeasure against leakage magnetic fields that are another type of noise source. It is to test whether it spreads further. It is also to determine how clearly the sound of individual instruments in the orchestra can be heard.
The difference in stereo sound due to noise is due to the fact that the noise is fundamentally random, the way in which the left and right channel signals are disturbed, and the phase difference between the left and right signals at the moment is fluctuated. Is.

(Results of judging the effects of the second stage)
In consideration of the above, the orchestra music recorded on the CD was reproduced and listened carefully to see how the reproduced sound changed by using the leakage magnetic field shielding plate. As a result, the following sound quality improvement effects were confirmed.
(A) The width of the sound field spreads greatly. 10 shows the expansion of the sound field when there is no shielding plate, and FIG. 11 shows the expansion of the sound field when the shielding plate is placed, but the width of the expansion of the sound field is greatly increased by the shielding plate as shown in this figure. By removing the power supply noise, the width of the sound field is somewhat widened, but the use of a leakage magnetic field shielding plate means that the width of the left and right speakers is full.
(B) The sound image of each instrument becomes clearer.

(Supplementary explanation 1: Why is the width of the sound field widened by reducing noise?)
In the theory of stereophonic sound, the position of a sound image is primarily recognized by detecting the phase difference between sound waves heard from left and right speakers. And as the phase difference between the left and right sound waves is not constant due to noise and it becomes more difficult to detect the phase difference, the difference in sound intensity between the left and right sounds can be used to recognize the position of the sound image to compensate for it. It is considered a characteristic of human hearing. Now, since the distance between the stereo microphones during recording is smaller than the distance to each instrument on the stage, the difference in sound intensity between the instruments captured by the left and right microphones is small. Therefore, if it is assumed that the position of the sound image is recognized only by detecting the difference in sound intensity, the sound images of all musical instruments are collected at the middle position between the speakers. Therefore, the stronger the influence of noise, the stronger the tendency of the sound image to gather in the middle and the width of the sound field becomes narrower.On the contrary, the weaker the influence of noise and the more reliable the phase difference is, the more reliable the instrument located at the left or right end of the stage. It is also explained that the sound image is recognized as a position close to the original left end or right end, and therefore the width of the sound field is widened.

(Supplementary explanation 2: Why is the sound image clearer due to noise reduction)
When the induced voltage due to noise is added and the signal voltage is disturbed, the phase difference between the left and right waveforms related to the recognition of the sound image of each instrument is blurred, so the position of the sound image is also widened from side to side. That is, the sound image is blurred. Therefore, it can be said that if there is no noise, the position of the sound image of each musical instrument becomes less blurred and clearer.

  An example of a leakage magnetic field shielding plate manufactured using an iron plate is shown.

Example 1: Example of a leakage magnetic field shielding plate in which a plurality of small blade-shaped phase adjusting plates made of a thin iron plate are attached to one surface of a substrate made of an iron plate (FIG. 1)
A small blade-shaped phase adjusting plate (2) made by cutting an iron plate having a thickness of 0.3 mm is bonded to an iron plate (1) having a thickness of 1.0 mm and a size of 100 × 120 cm with an adhesive. However, the size of the small blade-shaped plate is 20 mm × 20 mm, and one end is bent by 45 degrees with a width of 2 mm to obtain a paste margin. These are arranged in 3 columns, and the number per column is 7. In principle, the side with the small blade-shaped plate is used facing the power transformer, but it is installed on the top and side of the power transformer.
This is an embodiment of the shielding plate (1) shown as means for solving the problem.

Example 2: A leakage magnetic field shielding plate having a structure in which a coil is wound around a small blade-shaped phase adjusting plate of the leakage magnetic field shielding plate of Example 1 (FIG. 2).
A small-blade phase adjusting plate of the leakage magnetic field shielding plate of Example 1 is coated with a coated conductor having a diameter of 0.5 mm 20 times to form a coil (3), and both ends thereof are short-circuited. This is the embodiment (2).

Example 3: A leakage magnetic field shielding plate in which a plurality of strip-shaped phase adjusting plates made of a thin iron plate are attached to one surface of a substrate made of an iron plate (FIG. 3).
A rectangular phase adjusting plate (4) made by cutting an iron plate having a thickness of 0.3 mm is attached to an iron plate (1) having a thickness of 1.0 mm and a size of 100 × 120 mm. However, the length of the strip-shaped plate is 70 mm. The width is 8 mm. The strip-shaped plates are arranged so as to be parallel to each other at intervals of 10 mm, and one end of each of the strip-shaped plates is fixed to the iron plate with a mounting bracket. This is the embodiment (3).

Example 4: A leakage magnetic field shielding plate having a structure in which a coil is wound on a strip-like phase adjusting plate of Example 3 (FIG. 4).
30 times so that a 0.5 mm diameter coated conductor is parallel to the shorter side of the strip and along the longer side of the rectangular phase adjusting plate of the leakage magnetic field shielding plate of Example 3 The coil (5) is rolled up and both ends thereof are short-circuited. This is the embodiment (4).

  Perspective view of leakage magnetic field shielding plate using small blade phase adjustment plate   A perspective view of a leakage magnetic field shielding plate using a small blade-shaped phase adjusting plate in which a coil is wound   Perspective view of leakage magnetic field shielding plate using strip-shaped phase adjusting plate   Perspective view of leakage magnetic field shielding plate using strip-shaped phase adjusting plate with coiled coil   A figure showing the situation where the magnetic flux passing through the small blade and the magnetic flux due to the original leakage magnetic field are combined   The figure which shows the situation where the minute vibration of magnetic flux is canceled by the phase difference   Diagram showing the waveform of induced voltage due to leakage magnetic field   The figure showing the waveform of the induced voltage by the leakage magnetic field that passed through the iron plate   A diagram showing the waveform of the induced voltage due to the leakage magnetic field that has passed through the shielding plate   Diagram showing the expansion of the sound field of stereo sound without using a shielding plate   Diagram showing the expansion of the sound field of stereo sound when a shielding plate is used

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Small blade-shaped phase adjusting plate 3 Coil wound on small blade-shaped plate 4 Strip-shaped phase adjusting plate 5 Coil wound on a strip-shaped plate

Claims (4)

  It consists of a substrate made of a ferromagnetic plate and a plurality of small blade-shaped phase adjusting plates made of a ferromagnetic thin plate, and a plurality of small blade-shaped phase adjusting plates are arranged on one side of the substrate. And a leakage magnetic field shielding plate characterized in that each is attached to be inclined with respect to the surface of the substrate.   A leakage magnetic field shielding plate characterized in that each of the small blade-shaped phase adjusting plates in the leakage magnetic field shielding plate according to claim 1 is coiled with a short-circuited coil.   A substrate made of a ferromagnetic plate and a plurality of strip-shaped phase adjusting plates made of a ferromagnetic thin plate, wherein the plurality of strip-shaped phase adjusting plates are arranged on one surface of the substrate; and A leakage magnetic field shielding plate characterized in that each is attached to be inclined with respect to the surface of the substrate.   A leakage magnetic field shielding plate, characterized in that a coil which is short-circuited by connecting both ends to each strip-shaped phase adjustment plate in the leakage magnetic field shielding plate of claim 3 is wound.

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