JPH05235582A - Magnetic shielding material - Google Patents

Abstract

PURPOSE:To make it possible to provide a magnetic shielding material which is thin in thickness and low in weight and cost and obtain a larger magnetic shielding effect compared with the case of a magnetic substance material layer alone by laying a conductive material on the magnetic substance material layer or the conductive material layer on the opposite side of the conductive material of the magnetic substance material layer. CONSTITUTION:A magnetic substance material layer 11 is placed into contact with a conductive material layer 12, thereby constituting a magnetic shielding material 13. A 0.35mm thick permalloy sheet is adopted for the magnetic substance layer 11 while a 0.3mm thick phosphor bronze sheet is adopted for the conductive material layer. A conductive material layer 32 is placed into contact with and laid upon the magnetic substance material layer of the magnetic shielding layer the opposite side of the conductive material layer 12, thereby constituting a magnetic shielding material 33. A 0.35mm thick permalloy sheet is the adopted for the magnetic substance sheet 11 while a 0.1mm thick aluminum sheet is adopted for the conductive material layers 12 and 33. The output of a receiver when the magnetic shielding materials 13 and 33 are used, will be lowered by about 18dB than when a single permalloy sheet is adopted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic shield material suitable for shielding a magnetic field having a relatively low frequency.

[0002]

2. Description of the Related Art For example, in a tomographic diagnostic apparatus utilizing nuclear magnetic resonance, a relatively strong magnetic field is generated, but it is necessary to provide a magnetic shield in order to prevent the magnetic field from affecting other parts. Further, it is necessary to magnetically shield the X-ray tomography diagnostic apparatus so as not to be affected by other magnetic fields. All of these magnetically shield a large volume. In addition, in various electronic devices,
May require magnetic shield.

In any case, conventionally, a magnetic material plate having a high magnetic permeability such as permalloy is usually used for the magnetic shield. In order to enhance the effect of the magnetic shield, a number of magnetic material plates are stacked or the thickness of the magnetic material plates is increased. In other words, in order to double the shielding effect, it was necessary to use two magnetic material plates or double the thickness.

[0004]

The lower the frequency of the magnetic field to be shielded, the more expensive a magnetic material is required as a magnetic shield material. For example, a permalloy plate is usually used to magnetically shield a low frequency of about 9 kHz. However, the permalloy plate is expensive, and it is necessary to use a large amount of permalloy plate in order to increase the shielding effect, which is extremely expensive, and the thickness and weight are also large. There was a huge problem.

[0005]

According to the invention of claim 1, it is composed of a magnetic material layer and a conductive material layer laminated on the magnetic material layer. According to the invention of claim 2, a conductive material layer is laminated on the side opposite to the conductive material layer of the magnetic material layer of the invention of claim 1.

[0006]

Embodiment 1 FIG. 1A shows an embodiment of the present invention. The magnetic material layer 11 and the conductive material layer 12 are in contact with each other to form a magnetic shield material 13. In this example, the magnetic material layer 11 has a thickness of 0.
A 35 mm permalloy plate is used, and as the conductive material layer 12, a phosphor bronze plate having a thickness of 0.3 mm is used in this example.

As shown in FIG. 1A, a loop antenna 14 is arranged on one side of this magnetic shield material 13 with its loop surfaces closely opposed to each other, and a 1 mW sine wave signal is output from the signal generator 15 to the loop antenna 14. The magnetic field was supplied and an alternating magnetic field was applied from the loop antenna 14 to one surface of the magnetic shield material 13, that is, the magnetic material layer 11 side in the figure. The loop antenna 16 on the other surface side of the magnetic shield material 13 was arranged with its loop surface closely opposed to each other, and a receiver (actually a spectrum analyzer) 17 was connected to the loop antenna 16 to measure the reception output. The ratio P1 of the output power P1 of the receiver 17 when the loop antennas 14 and 16 are opposed to each other without the magnetic shield material 13 interposed and the output power P2 of the receiver 17 when the magnetic shield material 13 is interposed. / P2 is the shield effect of the magnetic shield material 13.

A curve 21 in FIG. 2 shows an output P2 when the magnetic shield material 13 made of the permalloy plate and the phosphor bronze plate is interposed. In FIG. 2, the horizontal axis is the frequency axis, that is, the frequency of the sine wave signal generated by the signal generator 15 is 50 kHz.
It was changed in the range of z to 150 kHz. The receiver output P1 without the magnetic shield material 13 is a curve 22, and the receiver output with a 0.3 mm thick phosphor bronze plate in place of the magnetic shield material 13 is a curve 23.
1 permalloy plate with a thickness of 0.35 mm is used as a magnetic shield material 1
The output of the receiver when intervening in place of No. 3 is curve 24, and the output of the receiver when interposing two of the permalloy plates in place of the magnetic shield material 13 is curve 25. The curve 26 represents the noise of the receiver 17, that is, the receiver 17 has a measurement limit of about -80 dB for 1 mW, which indicates a level at which a weaker received signal cannot be measured. With this, it is impossible to measure even if a magnetic shield is used.

Conventionally, a permalloy plate has been used as a magnetic shield material, and the curve 25 has a receiver output reduced by about 3 dB (to about 1/2) compared to the curve 24, and the magnetic field is proportional to the number of permalloy plates. It has been shown that the shield effect is increased. The phosphor bronze plate is a non-magnetic material, and its magnetic shielding effect is almost zero (especially at low frequencies).
Therefore, based on this idea, the magnetic shield material 1 of this example
The output of the receiver when 3 is used should be almost the same as the curve 24, but actually it becomes the curve 21, which is about 18 dB lower than that of one permalloy plate, and when 64 permalloy plates are stacked. It can be seen that there is a magnetic shielding effect similar to. There is a small variation in curves 24 and 25,
The reason why there is a considerably large fluctuation in is that the reception level is too low to measure, and noise appears because the gain of the receiver 17 is increased. Example 2 In place of the magnetic shield material 13, a copper plate having a thickness of 0.1 mm is used, and the output of the receiver 17 is a curve 27 in FIG. When the copper plate having a thickness of 0.1 mm is used as the conductive material layer 12 and the magnetic shield material 13 using a permalloy plate having a thickness of 0.35 mm is interposed as the magnetic material layer 11, the output of the receiver 17 is a curve 28. Therefore, the output is reduced by about 13 dB as compared with the case of one permalloy plate (curve 24), and it is understood that in this case as well, a significantly higher shielding effect can be obtained than with a simple permalloy plate. Example 3 The output of the receiver 17 when the aluminum plate having a thickness of 0.8 mm is inserted in place of the magnetic shield material 13 is a curve 29 in FIG. This aluminum plate is used as the conductive material layer 1
2 and a magnetic shield material 13 with a 0.35 mm permalloy plate as a magnetic material layer 11 is interposed, a receiver 17
Output is curve 31 and one permalloy plate (curve 2
4), which is about 22 dB lower than the noise level (curve 2)
It is quite close to 6), and a significantly large shielding effect is obtained.

In each of the above-mentioned embodiments, the shielding effect is the same even if the transmitting side and the receiving side are replaced. Further, even if a gap of 1 to 2 mm was provided between the magnetic material layer 11 and the conductive material layer 12, the output of the receiver 17 did not change.
A stack of two 0.1 mm copper plates was used as the conductive material layer 12, and one 0.35 mm permalloy plate was used as the magnetic material layer 11.
Then, the output of the receiver 17 was almost the same as the curve 28 of the second embodiment. In the case where two 0.35 mm permalloy plates are stacked as the magnetic material layer 11 and one 0.3 mm phosphor bronze plate is used as the conductive material layer 12, the output of the receiver 17 is the curve of the first embodiment. It was almost the same as 21. From these, the thickness of the magnetic material layer 11 is 0.35 in the case of permalloy.
It is understood that the shielding effect is not improved so much when the thickness is more than 0.1 mm, and the shielding effect is not improved when the thickness of the conductive material layer 12 is copper is more than 0.1 mm. Embodiment 4 Next, an embodiment of the invention of claim 2 will be described. As shown in FIG. 1B, the conductive material layer 3 is in contact with the surface of the magnetic material layer 11 of the magnetic shield material shown in FIG. 1A opposite to the conductive material layer 12.
The magnetic shield material 33 is formed by stacking the two. In this example, a permalloy plate having a thickness of 0.35 mm is used as the magnetic material layer 11, and an aluminum plate having a thickness of 0.1 mm is used as each of the conductive material layers 12 and 32. The magnetic shield effect of this magnetic shield material 33 is shown in FIG.
Curve 34. This curve was measured by the same measurement method as described with reference to FIG. 1A. However, the signal frequency is 30 kHz
The receiver 17 has a measurement limit of -100 dB with respect to 1 mW. Further, in FIG. 5, the reference level, that is, 0 dB is the receiver output (curve 22 in FIG. 2) when nothing is interposed between the loop antennas 14 and 16. In the following examples, the receiver output when measured by all the measuring methods is shown in FIGS. 37 dB for one 0.35 mm permalloy plate from curve 34 in FIG.
It is understood that the degree is large, the receiver output is reduced, and a significantly large shielding effect is obtained.

Curve 35 in FIG. 5 is the aluminum plate 12
-Permalloy plate 11-The receiver output when one aluminum plate of the magnetic shield material 33 of the aluminum plate 32 is removed is shown, and it can be seen that the output is greatly reduced with respect to the curve 24. Further, by comparing the curves 31 and 35 in FIG. 4, it is understood that the thickness of the aluminum plate has little influence. The curve 34 is shown in FIG.
The reason why the fluctuation is smaller than the curves 21, 28 and 31 in FIG. 4 is that the measured dynamic range of the receiver is wider in FIG. 5 as described above. Example 5 The magnetic material layer 11 of the magnetic shield material 33 has a thickness of 0.
Conductive material layers 12, 3 using 35 mm permalloy plate
As the No. 2, a copper plate having a thickness of 0.05 mm was used.
The receiver output in that case is the curve 36 in FIG. It is understood that in this case also, a remarkably large shield effect can be obtained as compared with the case where one 0.35 mm permalloy plate is used. The output of the receiver becomes a curve 37 when one of the copper plates of the magnetic shield material 33 composed of the copper plate-permalloy plate-copper plate is removed. From this, it is understood that the output of the curve 37 is larger than that of the curve 34 and the output of the curve 36 is much smaller than that of the curve 34. Also, curves 28 and 37 in FIG.
Comparing with, it can be seen that the thickness of the copper plate does not significantly affect the shielding effect. Example 6 As shown in FIG. 1C, a magnetic material layer 38 is laminated on the surface of the conductive material layer 12 of the magnetic shield material shown in FIG. 1A opposite to the magnetic material layer 11 to form a magnetic shield material 39. .. In this case, as the magnetic material layers 11 and 38, a permalloy plate having a thickness of 0.35 mm was used, and as the conductive material layer 12, an aluminum plate having a thickness of 0.1 mm was used. The shielding effect in this case was measured in the same manner as described in Example 4. As a result, the receiver output became the curve 41 of FIG. From this, it can be seen that the curve 41 is about 3 dB lower than the receiver output (curve 24) when only two 0.35 mm permalloy plates are used. That is, it is understood that the same effect as when four 0.35 mm permalloy plates are used can be obtained by interposing a thin aluminum plate between the two permalloy plates. Example 7 In FIG. 1C, as the magnetic material layers 11 and 38, 0.3
Using a 5 mm permalloy plate as a conductive material layer 0.0
A 5 mm copper plate was used. The receiver output in this case is the curve 42 in FIG. In this case as well, it is about 3 dB for curve 25
The magnetic shield effect is improved. Example 8 In the configuration of FIG. 1A, the thickness of the magnetic material layer is 0.8 mm.
Of stainless steel, and a copper plate having a thickness of 0.05 mm was used as the conductive material layer 12. The shield effect was measured by the measuring method described in Example 4. As a result, the receiver output is the curve 43 of FIG. Instead of this magnetic shield material, a stainless steel plate having a thickness of 0.8 mm was used to measure the shield effect, and the result was as shown by the curve 44 in FIG. The magnetic shield effect obtained when two stainless steel plates having a thickness of 0.8 mm is shown by the curve 45 in FIG. 9, which is about 3 dB higher than that of one stainless steel plate. On the other hand, the curve 43 has an output lower than that of one stainless plate by about 19 dB, and it is understood that the magnetic shield material 13 made of the stainless plate and the copper plate also has a remarkable effect. Further, comparing the curve 43 with the curve 37 of FIG. 6, the magnetic material layer 11
It is understood that a shield effect of about 5 dB is better when a permalloy plate is used than as a stainless steel plate. However, comparing the curves 24 and 44, it is possible to stack a conductive material layer on a magnetic material layer. It is understood that the improvement of the shield effect is almost the same for both the stainless plate and the permalloy plate.

In the magnetic shield material layer shown in FIG. 1B, a stainless steel plate having a thickness of 0.8 mm is used as the magnetic material layer 11, and the conductive material layers 12 and 32 have a thickness of 0.
A 05 mm copper plate was used. The receiver output in this case is the curve 46 in FIG. From this, it is understood that the shield effect is further improved with respect to the curve 43. Further, from the difference between the curve 43 and the curve 46, and the difference between the curve 37 and the curve 36 in FIG. 6, the magnetic shield material 33 shown in FIG. 1B is the material of the magnetic material layer 11 in contrast to the magnetic shield material 13 shown in FIG. 1A. It is understood that a large shielding effect can be obtained regardless of the above.

In the magnetic shield material 39 shown in FIG. 1C, 0.8 mm thick stainless steel plates are used as the magnetic material layers 11 and 38, and a 0.05 mm thick copper plate is used as the conductive material layer 12. Was used. The receiver output in this case is curve 47 in FIG. From this, it was found that the shield effect was improved by about 3 dB with respect to the curve 45. Example 9 As shown in FIG. 1D, the magnetic shield material 39 shown in FIG. 1C is used.
A conductive material layer 48 is laminated on the outer side of the magnetic material layer 38 to form a magnetic shield material 49. A 0.35 mm permalloy plate is used for each of the magnetic material layers 11 and 38, and 0.05 mm for each of the conductive material layers 12 and 48.
The copper plate of was used. The receiver output in this case becomes the curve 51 in FIG. 10, and the shield effect is improved by about 5 dB as compared with the curve 37 in FIG. Example 10 As shown in FIG. 1E, a conductive material layer 32 is laminated on the outside of the magnetic material layer 11 of the magnetic shield material 49 shown in FIG. 1D to form a magnetic shield material 52. In this magnetic shield material 52, 0.05 mm copper plates were used as the conductive material layers 12, 32 and 48, and 0.35 mm permalloy plates were used as the magnetic material layers 11 and 38. The receiver output at this time is the curve 53 in FIG. From this, it can be seen that the shield effect is considerably improved with respect to the curve 51, and is substantially equivalent to the curve 36 of FIG. Since these curves 36 and 53 are close to the measurement limit, that is, close to the noise level, it is considered that they cannot be distinguished from each other. Further, it can be understood from the curves 36 and 53 that a particularly large shield effect can be obtained when the both outer surfaces of the magnetic shield material are conductive material layers. Example 11 In the configuration of FIG. 1B, 0.35 is used as the magnetic material layer 11.
A permalloy plate having a thickness of mm was used, and copper plating was applied to both surfaces of the permalloy plate so that the thickness was about 15 μm to form the conductive material layers 12 and 32. The receiver output in that case is the curve 54 in FIG. In this case, the measurement frequency is 9
The frequency was changed from kHz to 150 kHz. Others are the same as those in FIGS. It is understood that in this embodiment too, a very large magnetic shield can be obtained. It seems that the magnetic shield is lowered near 9 kHz, but this is indistinguishable from noise due to the noise of the measurement system. Example 12 0.35 mm as the magnetic material layer 11 in the configuration of FIG. 1A
15μ as the conductive material layer 12 using the permalloy plate of
m aluminum foil was used. The output of the receiver is the curve 55 in FIG. 12, and a large magnetic shield effect is obtained.

In the structure of FIG. 1B, a 0.35 mm permalloy plate is used as the magnetic material layer 11, and the conductive material layer 1 is used.
Aluminum foils of 15 μm were used as 2 and 32, respectively. The receiver output was curve 56 in FIG. Curve 5
A shield effect greater than 5 can be obtained. Curve 5
Reference numeral 7 is the noise of the measurement system, which indicates the measurement limit. As is apparent from the above description, the number of superposed magnetic material layers and conductive material layers may be increased. The conductive material layer may be a fairly thin layer, for example, a metal plating layer. The conductive material may be a good conductive metal material layer other than the above-mentioned metal plate, a conductive resin material layer, a conductive adhesive material layer, or the like. Similarly, a magnetic material layer other than those described above may be used.

[0015]

As described above, according to the present invention, by superposing the magnetic material layer and the metal material layer, a magnetic shield effect significantly larger than the magnetic shield effect obtained by only the magnetic material layer is obtained. In particular, when the conductive material layers are formed on both outer sides, a particularly large magnetic shield effect can be obtained.

Therefore, by using the magnetic shield material according to the present invention, it is possible to make the magnetic shield much thinner, lighter and cheaper than the conventional one, which is very convenient when magnetically shielding a large volume. It was also confirmed that the magnetic shield material of the present invention can effectively shield a magnetic field at a considerably low frequency, for example, 9 kHz.

[Brief description of drawings]

FIG. 1 is a sectional view showing various examples of a magnetic shield material according to the present invention.

FIG. 2 is a diagram showing an effect of the first embodiment.

FIG. 3 is a diagram showing the effect of Example 2;

FIG. 4 is a diagram showing an effect of Example 3;

FIG. 5 is a diagram showing an effect of Example 4;

FIG. 6 is a diagram showing the effect of Example 5;

FIG. 7 is a diagram showing the effect of Example 6;

FIG. 8 is a diagram showing an effect of Example 7.

FIG. 9 is a diagram showing the effect of Example 8;

FIG. 10 is a diagram showing effects of Example 9 and Example 10.

FIG. 11 is a diagram showing the effect of Example 11;

FIG. 12 is a diagram showing the effect of Example 12;

Claims (2)

[Claims] 1. A magnetic shield material comprising a magnetic material layer and a conductive material layer laminated on the magnetic material layer. 2. The magnetic shield material according to claim 1, wherein a conductive material layer is also laminated on a side of the magnetic material layer opposite to the conductive material layer.