ELECTROMAGNETIC WAVE SHIELDING FILTER

Abstract

An electromagnetic wave shielding filter is configured in a magnetic field transmission scheme, not in a low pass filter or band pass filter scheme, and thus allows a desired signal to pass, while maintaining unintended electromagnetic waves shielded.

The present embodiment relates to an electromagnetic wave shielding filter for high-frequency communication, having a structure in which an elliptical ferrite magnetic core is formed inside the filter, a primary coil and a secondary coil are installed at both ends of the magnetic core, and then a shielding and penetration unit is formed of a shielding material on the elliptical magnetic field core, so that a signal from the primary coil is transmitted in the form of a magnetic field to the secondary coil, and the other unintended common-mode components are eliminated.

Claims

1. An electromagnetic wave shielding filter comprising: an elliptical (circular) ferrite magnetic core installed at the center of the electromagnetic wave shielding filter; a primary coil and a secondary coil disposed to oppose each other symmetrically with respect to the elliptical ferrite magnetic core, and wound around the elliptical (circular) magnetic core; a core shielding and penetration unit surrounding the elliptical magnetic core; and an electromagnetic wave shielding filter outer enclosure surrounding the primary coil, the secondary coil, the elliptical ferrite magnetic core, and the magnetic core in surface contact, and containing the core shielding and penetration unit in close contact with an inner surface of the shielding filter.

2. The electromagnetic wave shielding filter according to claim 1, wherein a signal transmission is maintained in the form of a magnetic field by applying a core having good high frequency characteristics and a high magnetic permeability through the elliptical magnetic core to, and electromagnetic shielding between the primary coil and the secondary coil is maintained by electromagnetically shielding around the elliptical magnetic core, using the core shielding and penetration unit.

3. The electromagnetic wave shielding filter according to claim 2, wherein an elliptical (circular) ferrite core is applied as the magnetic core.

4. The electromagnetic wave shielding filter according to claim 2, wherein the core shielding and penetration unit grounded and shielded by an inner wall and surface of the electromagnetic wave shielding filter around the center of the elliptical magnetic core is formed of a high conductivity (low resistance) material including iron, copper, or aluminum.

5. The electromagnetic wave shielding filter according to claim 2, wherein the core shielding and penetration unit is formed of a low-density, high-conductivity material including iron wool or copper wool being a high conductivity (low resistance) material.

6. The electromagnetic wave shielding filter according to claim 2, wherein the primary coil and the secondary coil are wound around the elliptical (circular) magnetic core once or more times to enable transmission of a radio frequency (RF) signal from a primary end to a secondary end.

7. The electromagnetic wave shielding filter according to claim 2, wherein instead of the primary coil and the secondary coil, coaxial cables are wound around the elliptical (circular) magnetic core once or more times to enable transmission of an RF signal from a primary end to a secondary end.

8. The electromagnetic wave shielding filter according to claim 2, wherein the elliptical (circular) core is replaced with an air core, and coaxial cables are wound once or more times, instead of the primary coil and the secondary coil, to apply loop antennas at ends thereof with surfaces of the loop antennas facing each other and enable transmission of an RF signal from a primary end to a secondary end.

9. The electromagnetic wave shielding filter according to claim 2, wherein the magnetic core is in a structure in which an elliptical (circular) stacked iron core is applied.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0012] FIG. 1 is a diagram illustrating an electromagnetic wave shielding filter including an elliptical (circular) magnetic core and a magnetic core shielding and penetration unit according to the present embodiment;

[0013] FIG. 2 is a diagram illustrating an example of applying the electromagnetic wave shielding filter including the elliptical magnetic core and the magnetic core shielding and penetration unit according to the disclosure to an electromagnetic wave shielding facility;

[0014] FIG. 3 is a diagram illustrating a longitudinal cross-section and a latitudinal cross-section of the electromagnetic wave shielding filter including the elliptical magnetic core according to the present embodiment;

[0015] FIG. 4 is a diagram illustrating an electromagnetic wave shielding filter including double elliptical magnetic cores and primary and secondary coil sets to simultaneously transmit and receive high-frequency signals according to the present embodiment;

[0016] FIG. 5 is a diagram illustrating an example of applying an electromagnetic wave shielding filter including a magnetic core shielding and penetration unit, in which a primary loop antenna and a secondary loop antenna are configured using a coaxial cable, instead of a primary coil and a secondary coil according to the present embodiment;

[0017] FIG. 6 is a diagram illustrating a filter using a coaxial cable as illustrated in FIG. 5 according to the present embodiment, in which the core of an input coaxial cable is not connected to the ground to allow a differential-mode high-frequency signal to pass, and a part of an external ground of the coaxial cable is cut to serve as an antenna for forming a magnetic field, while maintaining electromagnetic wave shielding, and to effectively dissipate the magnetic field by the configured primary and secondary loop antennas;

[0018] FIG. 7 is a diagram illustrating an electromagnetic wave shielding filter using a coaxial cable, for allowing a GHz-band signal to pass according to the present embodiment, in which large surfaces of small loop antennas in the coaxial structure come into contact with each other by removing a ferrite core and applying an air core to allow a GHz-band radio frequency (RF) signal to pass;

[0019] FIG. 8 is a diagram illustrating the shape of a honeycomb used for air exhaust of an electromagnetic wave shielding facility; and

[0020] FIG. 9 is a diagram illustrating a general low pass filter-type electromagnetic wave shielding filter.

DETAILED DESCRIPTION

[0021] An embodiment of the disclosure will be described in detail with reference to the accompanying drawings.

[0022] FIG. 1 is a diagram illustrating an electromagnetic wave shielding filter including an elliptical magnetic core according to the present embodiment.

[0023] An electromagnetic wave shielding filter including an elliptical (circular) magnetic core according to the present embodiment includes an electromagnetic wave shielding enclosure 101, an elliptical (circular) magnetic core 104, a primary coil 102, a secondary coil 103, and a magnetic core shielding and penetration unit 105, to which the electromagnetic wave shielding filter is not necessarily limited.

[0024] As illustrated in FIG. 1, when the electromagnetic wave shielding filter including the elliptical magnetic core is installed on one shielding wall of an electromagnetic wave shielding facility, the primary coil 102 and the secondary coil 103 are installed at both ends of the elliptical magnetic core 104. As the elliptical magnetic core 104 is formed of a material with excellent high frequency characteristics and a high magnetic permeability, a magnetic field formed by a desired signal to be transmitted through the primary coil 102 is transferred to the opposite core via the elliptical magnetic core 104 and converted again to a voltage at the secondary coil 103. The opposite case from the secondary coil 103 to the primary coil 102 is also possible.

[0025] When a signal for communication is applied to the primary coil 102, the signal is changed into a magnetic field and induced and transmitted to the secondary coil via the elliptical magnetic core 104. The magnetic field transferred to the secondary coil may be converted into a voltage by the secondary coil, thereby restoring the received signal. In this state, however, the electromagnetic wave shielding filter is simply a transformer with no electromagnetic wave shielding function. When the inner walls of the shielding filter are filled with a material 105 with high electrical conductivity (low resistance) around the elliptical magnetic core 104, a tunnel-shaped structure surrounding the magnetic core 104 is formed, satisfying a condition for electromagnetic wave shielding.

[0026] Further, since the physical durability of an elliptical ferrite tile is weak, use of a material such as iron wool or copper wool may facilitate manufacture of the shielding and penetration unit for the elliptical magnetic core, and lead to a significant protective effect against external impact. When the filter enclosure and the core are filled with a high-density metal, external shock is transferred as it is. In contrast, when the filter enclosure and the core are filled with a low-density material such as iron wool or copper wool, a physical impact may be absorbed by the low-density (sponge-like structure) material, and thus its transmission is limited.

[0027] A low pass filter-type electromagnetic wave shielding filter illustrated in FIG. 9 includes inductors 920 and 921, capacitors 923, 924, and 925, and an arrestor 927. Because the electromagnetic wave shielding filter has a structure that passes a frequency equal to or lower than a shielding frequency and a frequency equal to higher than the shielding frequency, it is difficult to pass a high frequency higher than the shielding frequency of the low pass filter into the shielding facility, and thus the electromagnetic wave shielding filter may be applied based on band pass filtering to pass only a specific band. However, since frequency shielding characteristics in the vicinity of the pass band of the band pass filter have a band stop attenuation of about 60 dB, it is difficult to secure perfect blocking characteristics. Moreover, when a high-output electromagnetic pulse (EMP) signal is input in the band of the band pass filter, the electromagnetic wave shielding filter may not function to shield electromagnetic waves.

[0028] In contrast, the electromagnetic wave shielding filter (FIG. 1) according to the present embodiment transmits a high-frequency signal induced in the elliptical magnetic core 104 only in a differential-mode structure according to an electromagnetic induction law in Maxwell equations (Equation 1). Therefore, common-mode electromagnetic waves that are radiated, such as high-output electromagnetic waves or external electromagnetic wave noise may not pass through the elliptical magnetic core 104 at the primary coil 102 and transmitted to the secondary coil 103.

[00001]$\begin{array}{cc}{\oint }_{C}E.Math.d1=-\frac{d}{\mathrm{dt}}{\int }_{S}B.Math.\mathrm{dA}& \left[\mathrm{Equation}1\right]\end{array}$

[0029] In addition, the diameter of the elliptical magnetic core applied in the present embodiment is about 3 to 10 mm. Therefore, when a high-output electromagnetic wave of a certain value or higher is input, the magnetic flux of the elliptical magnetic core 104 is saturated, and thus energy at or above a certain level may not be transmitted to the secondary coil. Accordingly, a receiving end and a transmitting end of communication equipment connected to a secondary output of the elliptical magnetic core may be protected.

[0030] In addition, despite the fact that the components of the electromagnetic wave shielding filter are high-frequency devices, they are all passive devices and thus have a low possibility of damage. This is because the components do not include a material that is oxidized or chemically changed over time.

[0031] Moreover, elements included in the low pass filter (FIG. 9), particularly the arrestor 927 and the capacitors 926, 920, and 921 have limited lifetimes and thus may not be used permanently. These elements are components requiring replacement periodically or when damaged. However, the use of the electromagnetic wave shielding filter (FIG. 1) according to the present embodiment obviates the need for the components, which enables continuous use of equipment inside the shielding facility and almost prevents impact-caused breakage of the ferrite core 104 or overcurrent-incurred damage to the primary coil 102 and the secondary coil 103. Accordingly, the electromagnetic wave shielding filter according to the present embodiment may have a permanent lifetime.

[0032] The elliptical magnetic core 104 applied to the electromagnetic wave shielding filter according to the present embodiment may be formed of a ferrite material with good high frequency characteristics and high magnetic permeability. A ZnMn-type ferrite may be used in a relatively low frequency band due to its high conductivity (several tens of ohms), whereas an NiMn-type ferrite may be more effective in a higher frequency band due to its low electrical conductivity (several tens of M ohms) and high magnetic permeability.

[0033] Additionally, although the electromagnetic wave shielding filter described in this example is designed as an electromagnetic wave shielding filter for high-frequency signals, it may also be used as an electromagnetic wave shielding filter for a 50 Hz or 60 Hz power line by applying a stacked iron core instead of the ferrite core. In view of the elliptical magnetic core structure, the primary coil and the secondary coil are far from each other, thereby lowering transmission efficiency. Nonetheless, the electromagnetic wave shielding filter is applicable when needed, because it may secure electromagnetic wave shielding characteristics.

[0034] It is difficult to shield electromagnetic waves with the electromagnetic wave shielding filter illustrated in FIG. 2 alone. With an enclosure 201 in close contact with a wall or the ceiling of a shielding facility 207, the electromagnetic wave shielding filter may be used in the shielding facility with all sides of its cubic structure blocked. All of current shielding facilities are built in this structure, and the electromagnetic wave shielding filter is applied to these facilities.

[0035] When a hole is formed in the elliptical (circular) magnetic core shielding and penetration unit, and a ZnMn-type ferrite is used for the elliptical magnetic core, the electrical conductivity of the ferrite tile is high (with a low resistance of several tens of ohms), which maintains a blocked shape in terms of electromagnetic waves in spite of the existence of the magnetic core hole. When a NiMn-type ferrite is applied to the elliptical magnetic core, the hole through which the magnetic core passes may be regarded as a structure that impairs electromagnetic wave shielding from the perspective of electromagnetic waves. However, this problem may be overcome by adjusting a hole diameter d 306 and a hole depth g 307 as illustrated in Table 1. Further, because the ferrite material itself has a function of absorbing electromagnetic waves, the ferrite does not affect much in terms of the presence or absence of electromagnetic wave shielding damage.

[0036] FIG. 8 is diagram illustrating a honeycomb used in a ventilator of an electromagnetic wave shielding facility. The honeycomb is a component that allows air to pass, while shielding electromagnetic waves. Although there is a physical hole (FIG. 8), electromagnetic waves may be shielded within the shielding frequency of the honeycomb.

[0037] The following table lists formulas for calculating an electromagnetic wave shielding effect determined by the diameter and depth of a honeycomb in an electromagnetic shielding facility. It may be noted that although different electromagnetic shielding effects may be achieved depending on whether the shape of the physical through hole is square, circle, or cube, electromagnetic wave shielding is basically possible at or below the shielding frequency by adjusting the diameter d and depth g of the through hole (see FIGS. 3 and 8) despite the presence of the hole that may impair electromagnetic wave shielding.

TABLE-US-00001 TABLE 1 SE.sub.dB SE.sub.dB(fc/f > 3) square [00002]${\mathrm{SE}}_{\mathrm{dB}}=27.3\frac{d}{g}\sqrt{1-{\left(\frac{\mathrm{gf}}{150000}\right)}^2}$ [00003]${\mathrm{SE}}_{\mathrm{dB}}=27.3\frac{d}{g}$ circle [00004]${\mathrm{SE}}_{\mathrm{dB}}=31.95\frac{d}{g}\sqrt{1-{\left(\frac{\mathrm{gf}}{175800}\right)}^2}$ [00005]${\mathrm{SE}}_{\mathrm{dB}}=31.95\frac{d}{g}$ hexagon [00006]${\mathrm{SE}}_{\mathrm{dB}}=17.5\frac{d}{g}\sqrt{1-{\left(\frac{\mathrm{gf}}{96659}\right)}^2}$ [00007]${\mathrm{SE}}_{\mathrm{dB}}=17.5\frac{d}{g}$

[0038] For example, the shielding effect is maintained at 96 dB at 18 GHz in a hexagonal honeycomb with a depth d of 20 mm and a largest diameter of 3 mm. Therefore, even when there is a hole, electromagnetic wave shielding is possible at or below a shielding frequency determined by the depth and diameter of the hole.

[0039] Accordingly, even when the NiMn-type ferrite is applied, electromagnetic waves may be kept shielded despite the presence of a hole in terms of electromagnetic waves because the ferrite has a low electrical conductivity (with a high resistance).

[0040] The electromagnetic wave shielding filter (FIG. 1) according to the present embodiment does not need a capacitive element (capacitor) and an inductive element (inductor) required for the configuration of the existing low pass filter or band pass filter, and particularly, an arrestor or an EMP protector 926 which is a protection device against an external strong impulsive shock. The elements inside the electromagnetic wave shielding filter (FIG. 9) have limited lifetimes and thus require periodic replacement, resulting in time and cost loss. Compared to the low pass filter, the magnetic field transmission filter advantageously has a high electromagnetic wave shielding effect of 100 dB or more across the entire frequency band. What is better, the magnetic field transmission filter has no separate pass band of the electromagnetic wave shielding filter, and maintains electromagnetic shielding even in the pass band through which a signal passes. In addition, since the part surrounding the primary coil, the secondary coil, and the elliptical core forms an electrically short-circuited and shielding structure inside this structure, the phenomenon of electric field emission or coupling is minimized, thereby maintaining electromagnetic wave shielding between the primary and secondary coils.

[0041] FIG. 3 is a diagram illustrating a longitudinal cross-section and a latitudinal cross-section of the electromagnetic wave shielding filter including the elliptical (circular) magnetic core according to the present embodiment. In FIG. 3, the diameter and depth of the magnetic core through hole are marked.

[0042] The electromagnetic wave shielding filter (FIG. 3) including an elliptical (circular) magnetic core 304 according to the present embodiment includes the elliptical magnetic core 304, a primary coil 302, a secondary coil 303, a magnetic core shielding and penetration unit 305, and an outer enclosure 301. The components of the electromagnetic wave shielding filter (FIG. 3) are not necessarily limited to the above components.

[0043] FIG. 4 is a diagram illustrating an electromagnetic wave shielding filter including double elliptical (circular) magnetic cores according to the present embodiment.

[0044] The electromagnetic wave shielding filter (FIG. 4) including an elliptical core according to the present embodiment includes two elliptical magnetic cores, two primary coils 402, three secondary coils 403, and a magnetic core shielding and penetration unit 405. To transmit a high frequency signal into a shielding facility in digital communication such as Ethernet signals, the electromagnetic wave shielding filter includes a transmitter and a receiver which are configured individually, for simultaneous transmission and reception. The components of the electromagnetic wave shielding filter (FIG. 4) are not necessarily limited to the above components.

[0045] FIG. 5 is a diagram illustrating an electromagnetic wave shielding filter including an elliptical (circular) magnetic core according to the present embodiment.

[0046] The electromagnetic wave shielding filter (FIG. 5) including an elliptical (circular) core according to the present embodiment includes 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 an end of a coaxial cable 509, serving as a secondary coil, and a magnetic core shielding and penetration part 505. Despite deteriorated transmission characteristics at a low frequency, transmission efficiency may be expected in a higher frequency band than a coil. The loop antennas 502 and 503 may be formed by winding the coaxial cables 508 and 509 around the magnetic core and electrically connecting the cores of the coaxial cables 508 and 509 to the shielding surfaces of the coaxial cables 508 and 509, and thus may play the same role as the primary and secondary coils. Further, since a handled frequency has a bandwidth of several hundreds of MHz to several GHz, SMA- or N-type RF connectors 506 and 507 and the cables 508 and 509 are applied and connected to the loop antennas 502 and 503. Components included in the electromagnetic wave shielding filter (FIG. 5) are not necessarily limited thereto.

[0047] FIG. 7 is a diagram illustrating a case in which a ferrite core is replaced with an air core among the afore-mentioned characteristics. Because the ferrite material is easy to operate in a frequency band at or below 1 GHz but it is difficult to satisfy the magnetic field transfer characteristics at or above 1 GHz, the magnetic core is replaced with the air core. In this case, characteristics of a much higher frequency such as a GHz band may be obtained. This structure may be used to shield electromagnetic waves across a total frequency band, while allowing a signal in a specific GHz band to pass. External electromagnetic waves may be shielded even in an RF pass band, and common-mode external electromagnetic noise being radiated electromagnetic waves may not be transmitted from the primary side to the secondary side in view of the magnetic field transfer structure as described in Equation 1. The primary coaxial cable 708 and the secondary coaxial cable 709 connected to the connectors 706 and 707 outside an electromagnetic wave shielding filter enclosure 701 are configured as a small loop antenna structure in which the cores and outer ground parts of the coaxial cables contact each other in the middle of the cables. The primary loop antenna 702 and the secondary loop antenna 703 are arranged to face each other without being electrically short-circuited to each other, and an input RF signal is transmitted in the form of a magnetic field generated through the primary loop antenna 702 and transferred to the secondary loop antenna 703. A core shielding part surrounding the primary and secondary loop antennas, and a small loop antenna part are electrically separated from each other. In addition, since the loop antennas are short-circuited in terms of an electric field in this space, the electric field may not be radiated, and there is no coupling. Accordingly, a primary end and a secondary end that determine the inside and outside of a shielding room are electrically short-circuited, and thus completely separated from each other across the total frequency band. However, although electromagnetic wave loss may partially occur to the primary side and the secondary side, in the form of a magnetic field only in a specific frequency band responsive to the primary loop antenna 702 and the secondary loop antenna 703, the primary end and the secondary end are connected (within 3 dB).

[0048] FIG. 8 is a simplified diagram illustrating the shapes of honeycombs installed in a ventilator of the electromagnetic shielding facility. In FIG. 8, a diameter g 802 and a depth d 803 of a hole are shown. FIG. 8 is intended to illustrate that an electromagnetic wave shielding effect is determined by a function of the two terms, and electromagnetic waves are shielded at or below a specific shielding frequency even when there is an electromagnetic hole.

[0049] FIG. 9 is a diagram illustrating a general low pass filter-type electromagnetic wave shielding filter for a high-frequency signal line in current use. The electromagnetic wave shielding filter includes inductors 920 and 921, capacitors 923, 924, and 925, and a surge protector 925. A signal input to a filter input end passes only at or below a specific shielding frequency, while being blocked above specific shielding frequency. Although the low pass filter-type electromagnetic wave shielding filter is used in combination with a band pass filter or a high pass filter, when an interference signal or a high-output signal is input into the pass band of the shielding filter, the signal is transmitted to the output through the shielding filter, thereby increasing a possibility of damaging equipment in the shielding facility.

[0050] The above description is merely illustrative of the technical idea of the present embodiment, and those skilled in the art will understand that various modifications and variations can be made without departing from the essential features of the present embodiment. Accordingly, the present embodiments are intended to describe rather than limit the technical spirit of the present embodiment, and the scope of the present embodiment is not limited by these embodiments. The protection scope of the present embodiment should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be interpreted as being included in the scope of the present embodiment.

[0051] As is apparent from the foregoing description, according to the present embodiment, a magnetic path is made of a material having high magnetic permeability on an electromagnetic wave shielding interface that determines the outside and the inside of a filter, so that a high-frequency electromagnetic wave signal in an RF or differential mode is transferred in the form of a magnetic field from the outside to the inside via an elliptical (or circular) magnetic core, and an electromagnetic shielding structure is formed by filling a material having a high conductively (low resistance) around the elliptical magnetic core and the inner surface of a shielding filter enclosure, for shielding an electrical filed and a magnetic field inside and outside an electromagnetic wave shielding facility. Therefore, the filer allows high-frequency radio signals to pass, while shielding the other radiated common-mode electromagnetic waves across a total frequency band.

[0052] Further, although a high-frequency signal itself has a differential mode structure and thus passes, high-output electromagnetic waves such as external noise are in a common mode and it is impossible for the high-output electromagnetic waves to pass through the elliptical magnetic core. Accordingly, noise except for a desired signal is blocked across the total band. This is a distinctive feature that differentiates the electromagnetic wave shielding effect from the existing band pass filter-type or low pass filter-type electromagnetic wave shielding filter.