JPH06224588A - Composite material for electromagnetic shielding - Google Patents

Abstract

PURPOSE:To obtain a shielding material showing a good shielding effect to a DC magnetic field, an AC magnetic field and an electromagnetic wave of scores of KHz or more constituting by laminating one sheet of directional electromagnetic steel plate and one sheet of non-directional electromagnetic steel plates. CONSTITUTION:An AC magnetic shielding property of a directional electromagnetic steel plate decreases up to about 20kHz together with the increasing frequency while in case of a non-directional electromagnetic steel plate, a shielding property in a DC magnetic field is bad, however, the shielding property improves together with the frequency so as to be better than that of the directional electromagnetic steel plate at scores of KHz or more. Then, in a composite substrate of both parties, an excellent shielding characteristic can be obtained ranging over the low to high frequencies as frequency characteristics, the steel plate having high permeability mu effectively acts also to electromagnetic wave shielding in a high frequency region, however, the shielding property extreamly worsens when the junction part has no conductivity deltaso that an excellent electromagnetic shielding property can be obtained when the nondirectional electromagnetic steel plate is conductively jointed. Accordingly, a magnetic shielding material can sharply improve the shielding effect in the DC and high frequency environment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shield material such as a shield container or a shield room for shielding electromagnetic fields, which is used in connection with electric equipment and electronic equipment.

[0002]

2. Description of the Related Art As electric and electronic equipments have advanced in performance and have rapidly expanded in use, the magnetic fields used by these equipments have increased, while protecting operating rooms, test rooms, human bodies, etc. In order to prevent obstacles due to magnetic fields, active shielding that shields the magnetic field emitted from the device and passive shielding that shields the magnetic field entering the device are performed, and magnetic shielding materials are used.

For example, an imaging apparatus using nuclear magnetic resonance (NMR) requires a high magnetic field by a superconducting magnet or the like, so that the leakage magnetic flux outside the measurement region becomes large. Therefore, magnetic shielding is performed to reduce the leakage magnetic field to the environment. Also, superconducting magnetometer (SQUID)
In order to study biomagnetism by et al., A weak magnetic environment is necessary, and a magnetic shield for shielding magnetic noise from the outside is performed. In such a magnetic environment, not only the DC magnetic field but the substantial AC magnetic field shield is important. Furthermore, the equipment used is several tens of MHz, such as a magnetic resonance imaging system (MRI).
When operating in the high frequency range, the electromagnetic wave shield is required.

In order to avoid such magnetic interference, a soft magnetic material such as iron is used as a shield material. For example, magnetic shielding is performed with a thick iron plate or the like using nuclear magnetic resonance (NMR). Further, in the case of shielding a room, in response to a request for reduction in size and weight, magnetic strips such as electromagnetic steel sheets, permalloy, and amorphous have recently been used. A material having a high magnetic permeability is generally used for the magnetic shield. However, in practice, it is necessary to select an appropriate material depending on the type and strength of the magnetic field to be shielded. On the other hand, for the electromagnetic wave shield, a conductive material such as electrolytic copper foil or aluminum plate is used for shielding. Such a conductive material is effective for an AC magnetic field of at least several tens of kHz and cannot shield an AC magnetic field from DC to several tens of kHz. Therefore, for example, MRI
When constructing a shielded room, the magnetic shield construction is performed with a ferromagnetic material such as a pure iron thick plate, and then the electromagnetic copper shield construction is performed with an electrolytic copper foil. In recent years, due to the higher density and higher accuracy of electronic devices, an AC magnetic field called magnetic noise has become a problem, and not only the electromagnetic wave shield but also the AC magnetic field in which the AC magnetic field is superimposed on the DC magnetic field is effectively used. There is a need for an effective and inexpensive method of shielding.

[0005]

The object of the present invention is to show a good shielding effect against alternating magnetic fields such as DC magnetic fields and magnetic noise, and electromagnetic waves of several tens of kHz or more, and is lightweight, easy to handle and inexpensive. To provide a shielding material.

[0006]

The present invention has been made to solve the above-mentioned problems, and its gist is (1) in a composite material of which an electromagnetic shield is made of an electromagnetic steel plate, a single grain-oriented electromagnetic steel plate; A composite material for an electromagnetic shield, which is constructed by laminating one non-oriented electrical steel sheet.

(2) In a composite material of which an electromagnetic shield is made of an electromagnetic steel sheet, at least two grain-oriented electrical steel sheets are laminated so that rolling directions are orthogonal to each other, and at least one non-oriented electrical steel sheet is further laminated. A composite material for electromagnetic shielding, which is characterized by being laminated. (3) An electromagnetic shield structure comprising the composite material for electromagnetic shield according to (1) or (2), characterized in that conductivity is secured at a joint portion of non-oriented electrical steel sheet ends. It is the body.

In order to effectively shield from a DC magnetic field to electromagnetic waves, a feature of the present invention is to use a grain-oriented electrical steel sheet and a non-oriented electrical steel sheet as a multi-layer steel sheet to shield a magnetic field up to several tens of kHz. . When used as a shield panel, use two or more grain-oriented electrical steel sheets with an easy axis of magnetization <1.
It is desirable that the rolling directions having the angle 00> intersect 90 ° with each other to reduce the directional characteristics of the panel.

Another feature of the present invention is to keep the end portions of the non-oriented electrical steel sheet in a conductive state in order to further shield electromagnetic waves in a high frequency range. That is, a non-oriented electrical steel sheet having a cross-section of the end portion is electrically joined at the end portions adjacent to each other to form a shield body. The joining can be performed by welding such as a commonly used TIG licking method, soldering, or a conductive adhesive. The electromagnetic wave shielding can be effectively performed if the surface of the non-oriented electrical steel sheet has a thickness of several tens of μm or more even if it is not the entire thickness of the non-oriented electrical steel sheet. It is necessary to join so that it can be secured. In any case, it is a feature of the present invention that the joint portion of the non-oriented electrical steel sheet is kept in a conductive state. The shield panel may be mechanically tightened to have a conductive joint, and the mechanical tightened portion may be filled with a conductive paint or a conductive substance to form a better joint. At the time of construction, it is desirable to install the shield composite material so that the non-oriented electrical steel sheet is located on the side of the source of electromagnetic waves to be shielded.

Regarding the shielding property of the composite magnetic steel sheet, the inventors of the present invention have found that the grain-oriented electromagnetic steel plate having a large magnetic domain structure exhibits effective shielding property against a magnetic field having a frequency of 1 kHz or less, and the magnetic domain structure has a fine structure. It has been found that the non-oriented electrical steel sheet effectively shields a magnetic field having a frequency of 1 kHz or more. If a composite steel sheet is used for the grain-oriented electrical steel sheet and the non-oriented electrical steel sheet, the magnetic field of DC to several tens of kHz can be effectively shielded. That is, the AC magnetic shielding property of the grain-oriented electrical steel sheet decreases to about 20kHz as the frequency increases, but the non-oriented electrical steel sheet has a poor shielding property in the DC magnetic field, but the shielding property improves with the frequency and is several kHz or more. It is better than grain oriented electrical steel. Both composite steel sheets have good frequency characteristics in the low to high frequency range.

A steel sheet having a high magnetic permeability μ works effectively also for an electromagnetic wave shield in a high frequency range, but the conductivity σ of the joint is
Without it, the shielding property will be extremely poor. Since the skin depth (μσf) ^-1/2 becomes smaller as the frequency f becomes higher, a sufficiently good electromagnetic wave shielding property can be obtained by conductively joining the non-oriented electrical steel sheets. As the grain-oriented electrical steel sheet used in the present invention, a 3% Si steel sheet is usually used, but it is not particularly necessary and Si may be 0 to 7%. The non-oriented electrical steel sheet can be selected from each grade of Si of 0% to 3% depending on the required shielding property, but when considering only high frequency electric field shield, it is not a so-called commercially available electrical steel sheet but a zinc iron sheet. Ordinary steel plate material may be substituted.

[0012]

EXAMPLES The present invention will be specifically described below based on examples. Example 1 A 1,000 mm square shield box was made of a grain-oriented electrical steel sheet and a non-oriented electrical steel sheet. Two 0.23 mm-thickness grain-oriented electrical steel sheets were stacked so that each rolling direction was 90 °. Overlaid on it, 0.5 mm thick 1.0% Si
Non-oriented electrical steel sheets were adhered, and steel sheet ends having no insulating film were joined with a conductive adhesive interposed (ZZN1 = Invention 1) and without (ZZN2 = Invention 2). For comparison, three grain-oriented electrical steel sheets (ZZZ = Comparison A) and three non-oriented electrical steel sheets (NNN = Comparison B)
I made a similar shield. We measured the shield characteristics (magnetic field mode) by putting the receiving antenna inside the shield and changing the frequency from the outside. The results are shown in Table 1.

[0013]

[Table 1]

As can be seen from Table 1, the method according to the present invention is effective in shielding a wide range from DC to high frequencies. Particularly, when the non-oriented electrical steel sheets were electrically conductively bonded, the shielding property was improved in the high frequency range. Example 2 According to the present invention, a shield sheet was made from the grain-oriented electrical steel sheet 23ZH100 and the non-oriented electrical steel sheet 50H700, and the shieldability measurement test was conducted. Copper plate 0.8mm as a comparison material
The plate thickness was measured at the same time. The measurement was performed by applying a magnetic field with a loop antenna from one surface of a shield cube of 300 mm square. The measurement frequency was 1 MHz.

The measurement result shows that the shielding property according to the present invention is 1
It is more than 10 dB, but 85 dB for a copper plate of the same thickness.
Met. In this way, the electromagnetic steel plate shield material showed good shielding properties even in the high frequency region, and showed superior shielding properties to the copper plate having excellent conductivity in the high frequency region above MHz.

[0016]

INDUSTRIAL APPLICABILITY The magnetic shield material of the present invention can greatly improve the shield effect under the environment of direct current and high frequencies. This simplifies the construction without the need to separate the construction for the magnetic shield and the construction for the electromagnetic shield, greatly improves the handleability, and reduces the cost of the shield device.
The weight was reduced.

Claims (3)

[Claims] 1. A composite material for forming an electromagnetic shield made of an electromagnetic steel sheet, which is characterized in that it is formed by laminating one directional electromagnetic steel sheet and one non-oriented electromagnetic steel sheet. material. 2. A composite material comprising an electromagnetic shield made of electromagnetic steel sheets, wherein at least two grain-oriented electrical steel sheets are laminated so that their rolling directions are orthogonal to each other, and at least one non-oriented electrical steel sheet is laminated. A composite material for an electromagnetic shield, characterized by being configured as follows. 3. A structure for electromagnetic shield comprising the composite material for electromagnetic shield according to claim 1 or 2,
A structure for an electromagnetic shield, characterized in that conductivity is secured at a joint portion of the ends of a non-oriented electrical steel sheet.