Electromagnetic wave shielding filter

Abstract

To provide an electromagnetic wave shielding filter that is configured to shield electromagnetic waves using a lowpass filter or a bandpass filter, by transmitting a desired high-frequency signal while blocking undesired common-mode-form electromagnetic waves.SOLUTION: An electromagnetic wave shielding filter for high-frequency communication has an elliptical ferrite magnetic core inside the filter, and has a primary coil and a secondary coil installed at both ends. Then, in an elliptical magnetic field core, shielding and penetrating portions are finished with electromagnetic wave shielding material. A signal on the first coil side is transmitted to the secondary coil in a magnetic field form and a common mode component that is not very desired is removed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] One embodiment of the present invention relates to an electromagnetic wave shielding filter, and relates to a filter that allows necessary high-frequency signals to pass through in an electromagnetic wave shielding facility and blocks other interfering frequency components.

Background Art

[0002] The content described below only provides background information related to this implementation, and does not constitute the prior art.

[0003] Generally, in order to verify the shielding effect performance of an electromagnetic wave shielding facility, a shielding test is performed according to standards such as EEEE-std-299 or MIL-STD-188-125-1 / 2, and the shielding performance of the electromagnetic wave shielding facility is confirmed.

[0004] An electromagnetic wave shielding facility is basically a facility designed so that the outside and the inside are electromagnetically separated, and the inside of the facility is not affected by the external electromagnetic wave environment. The inside and outside of the electromagnetic wave shielding facility are connected using a shielding door for the movement of personnel and equipment and an electromagnetic wave shielding filter for power supply and communication inside.

[0005] Conventional general electromagnetic wave shielding filters currently in use use a low-pass filter to block high bands from 10 kHz to 100 kHz or more up to several to 18 GHz bands where electromagnetic wave shielding is desired, and allow low frequencies such as 60 Hz for power supply to pass through. In some cases, it may be configured in a form where only a specific band passes through using a band-pass filter. When the high-frequency communication frequency is a communication band frequency (for example, 500 MHz) higher than the cut-off frequency of the low-pass filter, it is input through an optical cable after optoelectronic conversion, and optoelectronic conversion is performed again, and the signal is transmitted while maintaining electromagnetic wave shielding to connect the inside and outside of the shielding facility.

[0006] Generally, a low-pass electromagnetic shielding filter used as a military (EMP) shielding filter that shields electromagnetic waves up to the lowest frequency has a cut-off frequency with a 3 dB loss of around 10 kHz. If the cut-off frequency is further lowered, it will cause loss of supply power. Therefore, the cut-off frequency of 10 kHz is the normal lower limit. For this reason, when sending frequencies below 10 kHz, frequencies lower than that can pass through the filter, resulting in a situation where the role of the filter is restricted. Thus, in the currently used low-pass electromagnetic shielding filters, there is a limit to blocking the entire frequency band and allowing only the signals in the desired frequency band to pass through. Therefore, in the configuration of the electromagnetic shielding filter, a fundamental structural change is necessary.

Summary of the Invention

Problems to be Solved by the Invention

[0007] In this embodiment, inside the filter, an elliptical magnetic core made of a material with high permeability is arranged at the part that determines the outside and inside of the electromagnetic shielding surface. Through the core shielding and through-hole with appropriate depth and diameter capable of shielding electromagnetic waves, the high-frequency electromagnetic wave signal is changed into a differential mode form by the primary coil, transmitted from the outside to the inside of the shielding facility in the differential mode magnetic field form by the elliptical magnetic core, and the differential mode high-frequency signal is restored again by the secondary coil. While the desired high-frequency signal is transmitted, the unwanted common mode electromagnetic waves are blocked, aiming to configure electromagnetic shielding with a low-pass or band-pass filter.

Means for Solving the Problems

[0008] According to one aspect of the present embodiment, the electromagnetic wave shielding filter installed on one shielding wall surface of the electromagnetic wave shielding facility has a structure in which a primary coil and a secondary coil are wound around both short sides of an elliptical (circular) magnetic core structure having a high magnetic permeability. In the middle of the elliptical magnetic core, it is composed of a material having a high conductivity (low resistivity). By configuring the inside of the electromagnetic wave shielding filter to have a depth and diameter that enable electromagnetic wave shielding in the longitudinal direction, a primary coil arranged symmetrically facing each other around an elliptical magnetic core structure having a high magnetic permeability; the secondary coil, an outer casing including the magnetic core (magnetic path) having the high magnetic permeability; a structure in which a material having a high electrical conductivity (low resistivity) is filled in the longitudinal direction at the center of the core; The electromagnetic wave shielding filter is characterized by including.

Effects of the Invention

[0009] As described above, according to the present embodiment, inside the filter, a magnetic path is formed of a material having a high magnetic permeability at the shielding boundary surface of the electromagnetic wave that determines the outside and the inside. The high-frequency electromagnetic wave signal in the RF or differential mode form is transmitted from the outside to the inside in the form of a magnetic field through the elliptical (or circular) magnetic core. The periphery of the elliptical magnetic core and the inner surface of the shielding filter housing are filled with a material having a high conductivity (low resistivity) to shield electromagnetic waves. It has a structure that shields the electric and magnetic fields outside and inside the electromagnetic wave shielding facility. Therefore, it has the effect of allowing wireless high-frequency signals to pass through while shielding the remaining radioactive common mode electromagnetic waves over all frequency bands.

[0010] In addition, since the high-frequency signal itself has a differential mode structure, it can pass through. However, high-output electromagnetic waves such as external noise are in the common mode, so they cannot pass through the elliptical magnetic core. Therefore, noise other than the signal that is desired to pass through is blocked over the entire band. This is a special feature compared to conventional band-pass filters and low-pass filter type electromagnetic wave shielding filters.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Best Mode for Carrying Out the Invention

[0012] Hereinafter, the present embodiment will be described in detail with reference to the accompanying drawings.

[0013] FIG. 1 is a diagram showing an electromagnetic wave shielding filter including an elliptical magnetic core according to the present embodiment.

[0014] The electromagnetic wave shielding filter including an elliptical (circular) core according to the present embodiment includes an electromagnetic wave shielding housing 101, elliptical (circular) magnetic cores 104, a primary coil 102, a secondary coil 103, and a magnetic core shielding and through portion 105. The components included in the electromagnetic wave shielding filter are not necessarily limited to these.

[0015] As shown in FIG. 1, when installing the filter on the shielding wall surface on one side of the electromagnetic wave shielding facility, the primary coil 102 and the secondary coil 103 are installed at both ends of the elliptical magnetic core. The elliptical magnetic core 104 is made of a material with excellent high-frequency characteristics and high magnetic permeability, and is transmitted from the primary coil 102 to the opposite core via the elliptical core in the magnetic field form formed by the signal desired to pass through, and is changed back to the voltage form by the secondary coil 103 on the opposite side. The opposite case from the secondary coil 103 to the primary coil 102 is also possible.

[0016] If a signal for high-frequency communication is applied to the primary coil 102 side, it is changed to a magnetic field and induced and transmitted to the secondary coil via the elliptical magnetic core 103. The magnetic field transmitted to the secondary coil again is converted to the voltage form by the secondary coil, and the received signal can be restored. However, in this state, it is in the form of a transformer without an electromagnetic wave shielding function. If the inner wall surface of the shielding filter is filled with a material 105 having high electrical conductivity (low resistance) around the elliptical magnetic core 104, a tunnel-shaped structure surrounding the magnetic core is formed, and conditions for electromagnetic wave shielding can be formed.

[0017] In addition, since the physical durability of the elliptical ferrite tiles is relatively low, when forming the elliptical magnetic core shielding and the through portion, if a form such as iron wool or copper wool is applied, it is easy to manufacture and can also have a considerable protective effect against external impacts. When the filter housing and the core part are filled with a metal form with a high density, external impacts are transmitted as they are. However, when filled with a material with a low density such as iron wool or copper wool, the physical impact is absorbed by the material with a low density (a structure similar to a sponge), and the transmission of the impact is restricted.

[0018] The electromagnetic wave shielding filter of the low-pass filter type as shown in FIG. 9 is composed of inductors 920, 921, capacitors 923, 924, 925, a lightning protection device 927, etc. It has a structure that allows frequencies below the cut-off frequency to pass through and blocks frequencies above the cut-off frequency. Therefore, it is difficult to pass frequencies higher than the cut-off frequency of the low-pass filter through the shielding facility and send them. Therefore, in some cases, an electromagnetic wave shielding filter is applied in the band-pass filter type so as to pass only a specific band. However, since the cut-off characteristics of frequencies near the pass band of such a low-pass filter or band-pass filter have a band-stop attenuation of about 60 dB, it is difficult to ensure perfect cut-off characteristics. Moreover, when a high-power electromagnetic wave (EMP) signal is input into the band of the band-pass filter, it is difficult for the electromagnetic wave shielding filter to play its role.

[0019] However, in the electromagnetic wave shielding filter (FIG. 1) according to the present embodiment, the high-frequency signal induced in the elliptical magnetic core 104 is transmitted only in the structure of the differential mode by the law of electromagnetic induction (Equation 1) of Maxwell's equations. Therefore, common-mode electromagnetic waves that are radioactive, such as high-power electromagnetic waves or external electromagnetic wave noises, cannot pass from the primary coil 102 through the elliptical magnetic core 104 and be transmitted to the secondary coil 103.

[0020]

Equation

[0021] In addition, since the diameter of the elliptical magnetic core applied in this embodiment is about 3 to 10 nm, when high-output electromagnetic waves above a certain value are input, the magnetic flux of the elliptical magnetic core 104 is saturated, so that energy above a certain level is not transmitted to the secondary coil. As a result, the receiving end and the transmitting end of the communication equipment connected to the output on the secondary side of the elliptical magnetic core can be protected.

[0022] In addition, although the constituent elements constituting the electromagnetic wave shielding filter are all passive elements despite being high-frequency elements, the possibility of damage is extremely low because they do not contain substances that are oxidized or have their chemical properties changed over time.

[0023] Note that the elements included in the low-pass filter (Figure 9), particularly the lightning protection device 927, capacitors 926, 920, 921, etc., have a lifespan and cannot be used permanently. They are components that need to be replaced when damaged or at regular intervals. However, when the electromagnetic wave shielding filter (Figure 1) according to this embodiment is applied, such components become unnecessary, so the equipment inside the shielding facility can be used without interruption. The phenomenon that the ferrite core is broken by impact or the primary coil 102 and the secondary coil 103 are damaged by overcurrent hardly occurs. Therefore, the electromagnetic wave shielding filter according to this embodiment can have a permanent lifespan.

[0024] Since the material of the elliptical magnetic core 104 applied to the electromagnetic wave shielding filter according to this embodiment has excellent high-frequency characteristics and a high magnetic permeability, a ferrite material may be used. Since the ZnMn type ferrite has a relatively high conductivity (about several tens of ohms), it may be utilized in a relatively low frequency band. Since the NiMn type ferrite material has a low electrical conductivity (about several tens of M ohms) and a high magnetic permeability, it may be more effective in a higher frequency band.

[0025] Furthermore, although the electromagnetic wave shielding filter described in this example is designed as an electromagnetic wave shielding filter for high-frequency signals, if an elliptical magnetic core is applied as the magnetic core of a laminated iron core instead of a ferrite core, it can also be used as an electromagnetic wave shielding filter for a 50 Hz or 60 Hz power line. Due to the structure of the elliptical magnetic core, the distance between the primary coil and the secondary coil may increase and the transmission efficiency may decrease, but since the electromagnetic wave shielding characteristics can be ensured, it can be applied if necessary.

[0026] The electromagnetic wave shielding filter shown in FIG. 2 is difficult to shield electromagnetic waves alone and is configured in a structure where the shielding filter housing 201 is in close contact with the wall surface and ceiling of the shielding facility 207, and can be used in a shielding facility structure where all hexahedrons are blocked. All currently constructed shielding facilities are built in such a structure, and it is a filter applied to such facilities.

[0027] Holes are formed in the part that forms the elliptical (circular) magnetic core shielding and the through portion. When ZnMn type ferrite is used as the elliptical magnetic core, since the electrical conductivity of the ferrite tile itself is high (low resistance, dozens of ohms), even if there are holes in the magnetic core, it can maintain a form that seems to be blocked from the perspective of electromagnetic waves. And when applying NiMn type ferrite as the elliptical magnetic core, the holes through which the magnetic core penetrates can be regarded as a structure in which the shielding of electromagnetic waves can be damaged from the perspective of electromagnetic waves. However, as shown in Table 1, by adjusting the diameter ( g ) 306 and the depth ( d ) 307, this can be solved. Also, since the ferrite material itself has the function of absorbing electromagnetic waves, even if there are holes, there is little influence from the perspective of the presence or absence of damage in electromagnetic wave shielding.

[0028] FIG. 8 is a honeycomb used in the ventilation part of an electromagnetic wave shielding facility, which is a component that allows air to pass through but shields electromagnetic waves. Although there are physical holes (FIG. 8), it can shield electromagnetic waves within the cut-off frequency of the honeycomb.

[0029] The following table shows the calculation formula for the electromagnetic wave shielding effect determined by the diameter and depth of the honeycomb of the electromagnetic wave shielding facility. Although the shielding effect of electromagnetic waves can vary depending on the form of the physical hole of the through-hole, such as casting in a square, circular, or hexagonal shape, basically, by adjusting the diameter ( g ) and depth ( d ) (refer to Figures 3 and 8), it can be seen that even if there are holes that can damage the electromagnetic wave shielding, electromagnetic waves can be shielded below the shielding frequency.

[0030]

Table 1

[0031] For example, in the case of a hexagonal honeycomb, when the depth (d) is 20 mm and the longest diameter is 3 mm, the shielding effect is maintained at 96 dB at 18 GHz. Therefore, even if there are holes, electromagnetic waves can be shielded below the cut-off frequency determined by the depth and diameter of the holes.

[0032] Therefore, even when applying a NiMn type ferrite, since the electrical conductivity is low (a high-resistance material), a structure that can maintain electromagnetic wave shielding without damage to the electromagnetic wave shielding can be achieved even if there are holes from the electromagnetic wave perspective.

[0033] The electromagnetic wave shielding filter according to this embodiment (Figure 1) does not require capacitive (capacitor) elements and inductive (inductor) elements that are necessary in terms of configuration in conventional low-pass filters and band-pass filters. In particular, a lightning protection device and an EMP protection device 926, which are protection devices against strong external impulse shocks, become unnecessary. The elements inside the electromagnetic wave shielding filter (Figure 9) are elements with a lifespan, and periodic alternation is required, resulting in temporal and cost losses. Compared with such a low-pass filter method, the greatest advantage of the magnetic field transmission method filter is that it has the characteristic of a high electromagnetic wave shielding effect of 100 dB or more in the entire frequency band. Furthermore, there is no separate passband for the electromagnetic wave shielding filter, and electromagnetic wave shielding can be maintained even in the passband through which signals pass. Also, the part surrounding the primary coil, secondary coil, and elliptical core creates an internal and electrically short-circuited and shielded structure, minimizing the phenomenon of being emitted or coupled in the electric field form and showing the characteristic of maintaining electromagnetic wave shielding between the primary and secondary coils.

[0034] Figure 3 is a diagram showing the side and longitudinal cross-section of an electromagnetic wave shielding filter including an elliptical (circular) magnetic core according to this embodiment, and the diameter and depth of the through-hole of the magnetic core are shown.

[0035] The electromagnetic wave shielding filter (Figure 3) including the elliptical (circular) magnetic core 304 according to this embodiment includes the elliptical magnetic core 304, the primary coil 302, the secondary coil 303, the magnetic core shielding and through portion 305, and the outer housing 301 of the electromagnetic wave shielding filter. The components included in the electromagnetic wave shielding filter (Figure 3) are not necessarily limited to these.

[0036] Figure 4 is a diagram showing an electromagnetic wave shielding filter including a double elliptical (circular) magnetic core according to this embodiment.

[0037] The electromagnetic shielding filter (Fig. 4) including the elliptical core according to this embodiment is composed of two elliptical magnetic cores, two primary coils 402, three secondary coils 403, a magnetic core shield and a through portion 405. In digital communication such as Ethernet signals, in order to transmit high-frequency signals inside the shielding facility, the transmitting part and the receiving part are configured separately to enable simultaneous transmission and reception. The components included in the electromagnetic shielding filter (Fig. 4) are not necessarily limited to this.

[0038] Fig. 5 is a diagram showing an electromagnetic shielding filter including an elliptical (circular) magnetic core according to this embodiment.

[0039] The electromagnetic shielding filter (Fig. 5) including the elliptical (circular) core according to this embodiment is composed of an elliptical (circular) magnetic core 504, a loop antenna 502 at the end of a coaxial cable 508 serving as a primary coil, a loop antenna 503 at the end of a coaxial cable 509 serving as a secondary coil, a magnetic core shield and a through portion 505. Although the transmission characteristics at low frequencies are poor, higher transmission efficiency in a higher frequency band can be expected compared to coils. After winding the coaxial cables 508, 509 around the magnetic core, loop antennas 502, 503 can be created and made to serve the same role as the primary and secondary coils by electrically connecting the cores of the coaxial cables 508, 509 to the shield surfaces of the coaxial cables 508, 509. Also, since the frequencies to be handled have a bandwidth of several hundred MHz to several GHz, RF connectors 506, 507 and cables 508, 509 such as SMA type or N type are applied for connection. The components included in the electromagnetic shielding filter (Fig. 5) are not necessarily limited to this.

[0040] FIG. 7 shows the case where among the features mentioned in the previous section, the ferrite core is replaced with an air core. The ferrite material is easy to operate in a frequency band of 1 GHz or less, but it is difficult to satisfy the magnetic field transmission characteristics above the 1 GHz band. Therefore, when the ferrite magnetic core is replaced with an air core, much higher frequency characteristics such as those in the GHz band can be obtained. It can be used to shield electromagnetic waves in the entire frequency band while allowing signals in a specific GHz band to pass through. Furthermore, external electromagnetic wave shielding is possible even within the RF passband. Due to the magnetic field transmission structure as shown in [Equation 1], the external electromagnetic wave noise of the common mode, which is a radioactive electromagnetic wave, cannot be transmitted from the primary side to the secondary side. The primary coaxial cable 708 and the secondary coaxial cable 709 connected to the external connectors 706 and 707 of the electromagnetic wave shielding filter housing 701 are configured in a small loop antenna structure where the core and the outer skin ground part of the coaxial cable are in contact at the middle part. The primary loop antenna 702 and the secondary loop antenna 703 are arranged in a structure facing each other and are not electrically short-circuited to each other. The input RF signal operates in a structure where the magnetic field generated while passing through the primary loop antenna 702 is transmitted in the form of a magnetic field to the secondary loop antenna 703 side, and this magnetic field signal is received. The core shielding part and the small loop antenna part surrounding the primary and secondary loop antennas are electrically separated. Also, within this space, since the loop antenna itself is short-circuited on the electric field side surface, no electric field radiation can occur, there is no coupling, and the primary end and the secondary end that determine the inside and outside of the shield room are electrically short-circuited, so they are completely electrically separated for the entire frequency band. However, only the specific corresponding frequency band that reacts with the primary loop antenna 702 and the secondary loop antenna 703 has some electromagnetic wave loss occurring on the primary and secondary sides in the form of a magnetic field, but the primary end and the secondary end are connected. (Within 3 dB)

[0041] FIG. 8 is a schematic diagram showing the shape of a honeycomb installed at the ventilation opening of the present electromagnetic wave shielding facility, showing the hole diameter (g) 802 and the depth (d) 803. The amount of electromagnetic wave shielding effect is determined by a function with two terms, and it is a diagram showing that even if there is an electromagnetic opening surface, electromagnetic wave shielding is possible below a specific cut-off frequency.

[0042] FIG. 9 is a diagram showing an electromagnetic wave shielding filter of a low-pass filter type for a high-frequency signal line currently in general use. It is composed of inductors 920, 921, capacitors 923, 924, 925, a surge protector 925, etc. The signal input to the filter input terminal has the characteristic of passing only below a specific cut-off frequency and being blocked above that. In some cases, it may be used in combination with a band-pass filter or a high-pass filter. However, when an interference signal or a high-output signal is input within the pass band of the shielding filter, it is transmitted as an output after passing through the shielding filter, so there is a high possibility that the equipment in the shielding facility will be damaged.

[0043] The above description is only an illustrative explanation of the technical idea of the present embodiment. Those with ordinary knowledge in the technical field to which the present embodiment belongs can make various modifications and deformations without departing from the essential characteristics of the present embodiment. Therefore, the present embodiment is not for limiting the technical idea of the present embodiment but for explaining it, and the scope of the technical idea of the present embodiment is not limited by such examples. The protection scope of the present embodiment should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of rights of the present embodiment.

Explanation of Reference Numerals

[0044] 101, 201, 301, 401, 501, 601, 701: Electromagnetic wave shielding filter housing 202, 302, 402, 502: Primary coil 104, 204, 304, 404, 504: Elliptical (circular) magnetic core (magnetic path) 203, 303, 403, 403: Primary and secondary coils 105, 205, 305, 405, 505, 605, 705: Magnetic core shielding and through-hole (high conductivity material) 506, 507, 606, 607, 706, 707: RF connector 508, 509, 608, 609, 708, 709: Coaxial cable 502, 503, 602, 603, 702, 703: Termination loop antenna of coaxial cable (serving as primary and secondary coils) 206: Electromagnetic shielding door 801: Honeycomb 802: Diameter of honeycomb (g) 803: Depth of honeycomb (d) 920, 921: Inductor 923, 924, 925: Capacitor 926: Lightning protection device (MOV, Arrestor)

Claims

1. An elliptical ferrite magnetic core installed at the central part of an electromagnetic wave shielding filter, a primary coil and a secondary coil arranged in a form symmetrically facing both sides in the major axis direction of the elliptical ferrite magnetic core, a magnetic core through-shielding part that fills a region surrounded by the inner wall surface of the electromagnetic wave shielding filter along the major axis direction of the elliptical ferrite magnetic core and forms a tunnel-shaped structure having a specific depth and diameter surrounding the elliptical ferrite magnetic core, an outer casing of the electromagnetic wave shielding filter that adheres to the wall or ceiling of the electromagnetic wave shielding facility, and includes the primary coil is wound around the elliptical ferrite magnetic core and is arranged on the primary side of the two sides, the secondary coil is wound around the elliptical ferrite magnetic core and is arranged on the secondary side of the two sides, An electromagnetic wave shielding filter, characterized in that electromagnetic waves are shielded below a cut-off frequency determined by the depth and diameter of the tunnel-shaped structure.

2. While maintaining signal transmission in the form of a magnetic field through the elliptical ferrite magnetic core, the periphery of the elliptical ferrite magnetic core is electromagnetically shielded using the magnetic core through-shielding part, and electromagnetic shielding between the primary coil and the secondary coil is maintained below the cut-off frequency. The electromagnetic wave shielding filter according to claim 1, characterized in that.

3. The electromagnetic wave shielding filter according to claim 2, characterized in that the material of the magnetic core through-shielding part is made of a material such as iron, copper, or aluminum.

4. The electromagnetic wave shielding filter according to claim 2, characterized in that the magnetic core through-shielding part is formed in the form of iron wool or copper wool.

5. The electromagnetic wave shielding filter according to claim 2, characterized in that the primary coil and the secondary coil are each wound around the elliptical ferrite magnetic core only once.

Images