JP2003507903A - Method and apparatus for attenuating electromagnetic interference - Google Patents

Abstract

The EMI attenuator has at least two substrates (36, 37) and the spacing (D1) between these substrates is selected to maximize shielding performance at a particular frequency. The device further comprises an additional substrate (38) positioned a predetermined distance from the first two substrates to optimize shielding performance.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electromagnetic interference (EMI) shielding. More specifically, it relates to the use of a multilayer shield substrate to optimize EMI attenuation at frequencies above 100 megahertz (MHz), and especially at much higher frequencies, using transparent structures.

BACKGROUND OF THE INVENTION The environment of industrialized societies is constantly under attack by electromagnetic radiation. Such radiation exists in a wide frequency band and is generally emitted from an electric appliance as an electromagnetic wave. While currently mild levels of electromagnetic radiation are considered to be relatively harmless to living tissue, this same radiation causes significant damage to the operation of any appliances and devices.

Shielded enclosures are needed to isolate sensitive equipment from electromagnetic radiation in a variety of environments including nuclear magnetic resonance (NMR) imaging, electrical testing of communications equipment, and sensitive data communications. Frequently, it is often necessary to suppress radiation from electrical equipment. EMI shielding is often achieved by coating the walls of the enclosure with one or more electrically continuous layers of metallic conductive material (eg, copper, aluminum, bronze or steel). . The shield layer is usually grounded at one point and conducts the electromagnetic energy absorbed by the shield to the ground. It is very important that there is no gap in this conductive shield even in the place where holes such as doors and windows are provided.

[0004] While visually observing the effects occurring within an enclosure in a variety of shielded enclosures, many observers, administrators, and operating technicians are able to remain outside the enclosure, so many If, windows are needed. NMR imaging, also known as magnetic resonance imaging (MRI), allows patients and extremely precise M
The RI device is located inside the EMI shielded enclosure. This is to provide an unobstructed environment so as to avoid artifacts and visual defects in the final image. Typical examples of screens and windows designed in EMI attenuators are US Pat. No. 4,701,801 and US Pat. No. 5,012,04.
1, US Pat. No. 5,017,419, US Pat. No. 5,239,125 and US Pat. No. 5,295,046.

Windows for EMI / RFI enclosures must be shielded and in continuous electrical contact with the walls that shield the enclosure. In addition, the window substrate must provide transparency with sufficient "transparency" and in some cases "audibility" to allow external monitoring by an administrator. Therefore, it is desirable to minimize optical distortion due to the window substrate.

[0006] Single-layer and double-layer screen windows of optically transparent metallized glass, transparent plastic, other conductive materials or combinations of the above materials are optically transparent and attenuate EMI. It is used to The effectiveness of the shield depends on variables including screen mesh, wire diameter, grid number and thickness and type of conductive material.

When a screen is used, one determinant of the shielding effect (SE) is a function of the distance (g) between the grid wires of each individual screen, translated into the following equation: SE = f ( g) As the value of g approaches 0 (g → 0), the attenuation of the electromagnetic field (E-field) improves at higher frequencies. However, this has the undesirable effect of reducing the desired "transparency" and "audibility" properties of the resulting substrate.

While a single screen window provides some EMI attenuation, White Donald R.A. J. (White Donald R.J.) “Ele
ctromagnetic Shielding Materials and
Performance. 2nd Ed, 1980 "(Don White Consultants, Inc., Gainesville, VA), this attenuation is about 20d as frequencies above 1MHz increase tenfold (" decimal ").
B decreases. As a result, a significant amount of electromagnetic radiation penetrates one screen structure as the frequency increases significantly.

US Pat. No. 5,012,041 (hereinafter “'), which is incorporated herein by reference.
No. 041) and shown with a typical dual screen EMI window, a window consisting of two parallel screens provides some improvement in damping. '041
The U.S. Patent teaches the use of two parallel screens of relatively different wire size and spacing to attenuate EMI and further reduce moire patterns.

However, the inventor has found that the two parallel screen structures exceed 100 MHz,
In particular, it has been discovered that an abnormality occurs in the frequency attenuation performance in the frequency band of 1 GHz (GHz) to 10 GHz. These anomalies occur as a function of screen separation, and the distance separating two flat screens depends on the wavelength of the impinging electromagnetic wave (λ
) Is especially serious whenever it is equal to a multiple of half. Where c is the speed of light and f is the frequency of the wave, it is defined by the equation c = fλ. In these cases, the spacing between the screens forms resonant cavities at their respective frequencies and their integer multiples. This results in a significant reduction in EMI attenuation at or near the resonant frequency and its harmonics. The presence of such resonant transmission results in image problems, one of which is that the resulting transmitted radiation can be mistaken for a signal generated from the target under consideration. Moreover, the inventor has discovered that resonant transmission can occur at other frequencies. As a result of such a phenomenon of resonance generation, the double screen structure has poor attenuation characteristics at a specific frequency as compared with the single screen structure.

Since the additional screens provide an additional resonant frequency that is a function of the spacing between the screens, an additional screen layer is added to the dual screen structure without considering the relative separation between the screens. Simply adding can be counterproductive.

There is a need in the art for a method and apparatus for providing improved attenuation of EMI at frequencies above 10 MHz, especially in the frequency range 1 GHz to 10 GHz, while retaining sufficient transparency and audibility properties. Exists. The method and the device should use commercially available materials, further facilitating easy maintenance and replacement.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an EMI shielding method and a device with the best attenuation performance that overcomes many of the disadvantages of the prior art. Another object of the present invention is to provide a method for attenuating EMI at multiple frequencies. A feature of the method is that the first set of materials attenuates the incident EMI and the second set of materials further attenuates the attenuated EMI described above, and is transparent and audible with a predetermined structure. The relatively parallel arrangement of the surfaces of the lightweight conductive material. An advantage of the present invention is that at specific electromagnetic radiation frequencies above 10 MHz, it reduces the transmission of resonant electromagnetic radiation through the multilayer material so as to tune or optimize the performance of the method.

Another object of the present invention is to provide a device having an EMI shielding property with an attenuation level of 100 decibels (dB) or more for frequencies of 100 MHz to 10 GHz. A feature of the invention is the combination of multiple screens of conductive material. An advantage of the present invention is that it progressively achieves higher levels of EMI / RFI shielding performance under either transparency or audibility conditions.

Yet another object of the present invention is to provide an EMI attenuator consisting of a lightweight screen or other electrically conductive material that is an optically transparent material. A feature of the invention is the particular juxtaposition of the screen surfaces relative to each other. The advantages of the present invention are:
A combination of cavities that interfere with radiated resonances and harmonics of the EMI frequency of interest, thus reducing EMI transmission through the substrate.

Briefly, the invention comprises a first electrically conductive means arranged spatially adjacent to a second electrically conductive means and a first electrically conductive means arranged spatially adjacent to a second electrically conductive means. An EMI shield device comprising three conductive means. The first conductive means is spatially separated from the second conductive means at a specific distance different from the distance that the second conductive means is spatially separated from the third conductive means.

The present invention further provides a method of reducing the transmission of electromagnetic radiation, comprising impeding the passage of electromagnetic radiation and applying the electromagnetic radiation to an area that impedes the generation and passage of resonant frequencies of the electromagnetic radiation.

Further provided is a method of attenuating electromagnetic radiation that includes directing radiation to a plurality of resonant cavities of different magnitudes and resonant frequencies so that radiation resonances within a particular cavity are shielded by other cavities.

A window for use in combination with an EMI shielding enclosure is provided by a window consisting of at least two conductive surfaces whose two surfaces are not adjacent in parallel. The present invention causes electromagnetic radiation to impinge on a first conductive substrate such that a first portion of electromagnetic radiation does not pass or pass through the first substrate and a second portion of electromagnetic radiation passes through and passes through the first substrate. A method for attenuating electromagnetic radiation is provided that comprises applying a means to prevent the generation of resonant frequencies of the radiation transmitted therethrough.

In another embodiment, the invention comprises a first predetermined space having a plurality of walls formed of first and second conductive shields, and a second conductive shield and a third conductive shield. The second predetermined space having a plurality of walls and the distance between the adjacent walls of the first and second shielding means are the same collinear distance between the adjacent second and third shielding means. And a means for attenuating electromagnetic interference comprising means for arranging the first, second and third shielding means.

Yet another embodiment of the present invention is an EMI attenuator consisting of conductive surfaces separated by an average distance so that the average distance provides maximum attenuation at a given frequency. It is selected.

The invention according to the above and other objects and advantages can best be understood from the following detailed description according to the embodiments of the invention shown in the drawings. Detailed Description of the Preferred Embodiments Methods and apparatus are provided for attenuating EMI using lightweight materials. The invention is characterized by providing satisfactory "transparency" and / or "audibility" in a lightweight construction and also by providing excellent attenuation levels at frequencies above 100 MHz. The present invention can be used to provide shielding protection over large surface areas. The present invention can further be used to provide windows to shielded enclosures without the shielding performance of the enclosure adversely impacting to the same extent as found in conventional two-layer screen constructions.

In general, the methods and apparatus of the present invention provide a means for generally attenuating incident and / or radiated EMI, and then suppressing the oscillations of the remaining EMI and generally attenuating the remaining resonant electromagnetic radiation. Incorporate. At EMI frequencies below 10 GHz, an attenuation of around 100 dB can be achieved. The present invention is particularly useful in providing these high levels of attenuation at frequencies between 1 GHz and 4 GHz.

The present invention is particularly useful in optimizing shielding performance at specific wavelengths. This "optimization" occurs by changing the relative shape and / or distance of adjacent shielding surfaces forming the device.

The damping means generally comprises conductive screens placed parallel to each other in a parallel or non-parallel structure at a predetermined distance to provide improved damping through the plurality of compartments and cavities. It consists of multiple surfaces such as: The pre-positioned screen not only attenuates the impinging EMI first, but also causes the remaining EMI not initially attenuated by the screen to be incompletely transmitted (ie, transmitted, reflected or re-reflected out of phase). , Further minimizes the occurrence of any resonant induction or resonance of impinging EMI. This transmission occurs within the cavity formed by the multiple conductive substrate structure. In essence, the screens arranged in a predetermined manner first shield some of the colliding EMI and prevent coherent overlap of the remaining EMI.

For example, in a structure including three or more conductive substrates, the first and second substrates close to the source of EMI serve to attenuate EMI, and one or more other substrates serve as the remaining EMI.
Promotes further attenuation of the. This structure optimizes the performance of the invention at specific frequencies. With one or more target frequencies, the distance between the substrates and the shape / microstructure of each surface are used experimentally to ensure these best damping performances.

An exemplary EMI attenuator incorporating features of the present invention is shown in FIG. 1 as provided in the wall 14 of a shielded enclosure 16 such as a room. Mounted on the wall 14 is the damping device of the present invention, generally indicated at 18, constructed in accordance with the principles of the invention. The attenuator 18 is provided with an improved multi-substrate structure 19 in order to achieve a high degree of EMI shielding in the frequency band 1 GHz to 10 GHz.

The walled enclosure 16 may be of any suitable type of construction. The wall has an opening 20 for receiving either a window incorporating a multi-substrate structure according to the present invention or a modular panel incorporating a multi-substrate structure according to the present invention. The metal shielding layer 17 on the outer surface of the wall 14 is shown in FIG. 2A, which is a cross-sectional view taken along line 2-2 of FIG. 1, with the shielding module 18 and the shielding layer 17 arranged in the opening. In order to provide a continuous electrical contact there between, it is continuous around the entire chamber 16 by means of the ends of the shielding layer 17 which extend to the openings 20. Module 1
8 is fixed to the window by means of fasteners 21.

The multi-screen substrate according to the present invention is an EM for large enclosure surfaces.
It may be applied on a large sheet to provide I damping. The smaller module substrate may be provided assembled in the same position on the screen means.

Details of Triple Substrate Module Structure The shielding system according to the present invention comprises a plurality of shielding substrates. The substrate is microstructurally generally flat, but need not be flat or planar. Further, the substrates are collinearly positioned relative to each other such that one substrate is present as a reference point indicating whether another substrate is proximally or distally positioned.

As shown schematically in FIGS. 2A, 2B, 2C and 2D, the exemplary shield system covers the entire opening 20, a first shield substrate 36, a second shield substrate 37 and a third shield substrate. 38. Any means of maintaining electrical contact with the enclosure of the room and mounting or placing the substrates relative to each other in a predetermined structure is suitable.

The structure shown in FIG. 2A provides a rigid conductive substrate, a flexible conductive substrate or a combination of rigid and flexible substrates. As shown, the triple substrate module has structural frames 26 and 27 received in the openings and adapted to contact substantially the entire perimeter of the openings. The frame may have the same cross-sectional shape throughout. One embodiment of frames 26 and 27 is a protruding metal with corners mitered. Suitable metals include, but are not limited to, tinned brass, other alloys, aluminum or steel. Optionally, the corners are formed with resilient conductive strips thereon to ensure a more intimate electrical contact between the module frame means 26, 27 and the window perimeter. The frame support 41 itself makes electrical contact with the wall 14 of the enclosure and is embedded within the wall 14 and serves to form a perimeter.

Generally, any material that is or can be electrically conductive is a suitable frame support material or frame material. Therefore, the frame is made of solid material (ie,
It may be uniformly conductive) or may be formed from a non-conductive material coated with a conductive material. A suitable coating thickness is about 0.0254 mm (1 mil) or greater. Therefore, the frame supporting means 41 can be covered with a metal such as tin having a high conductivity and being substantially non-oxidizing.

If either a rigid conductive substrate or a flexible conductive substrate is used or combined, a substrate clamping means of the type shown in FIG. 2A is applicable. In general, the wrap plate 15 allows the frame means 26, 27 to be attached to each other or to conductive substrates 36, 3
Used to clamp or tighten against 7,38. The tightening action directed towards the mid-plane of the opening is achieved by fasteners and tightening means such as bolts 21, which plane is parallel to the EMI damping module to be mounted. The bolt 21 is received by a particular area of the window frame support means 41 forming a complementary mating surface such as a threaded hole 22. The frame support 41 further has a lip 43 that extends inward toward the center of the opening and extends at a right angle to the plane of the module. The lip acts as a stiffener for pressing the substrate support frames 26 and 27 together against the lip by the lap plate 15. Reinforcing means for fixing the wrap plate 15 to the wall shield 17 are also suitable. For example, another bolt hole structure provided inside the first bolt hole structure, such as tightening the lap plate directly to the frame means 26, provides additional stability to provide the frame means 26 with the plate 1.
To further improve the electrical contact with 5.

If only flexible substrates are used (eg screens), then alternative frame structures 28, 29 may be used, as shown in FIG. These structures were first constructed with arched channel portions 46, 47 and 4 for receiving the ends of the flexible screen.
Have eight. Flexible beads or splines 44, adapted to receive channels 46, 47 and 48, are then firmly pressed into these channels to ensure additional electrical contact between the screen and frame. To Such a screen locking mechanism is disclosed in detail in US Pat. No. 5,012,041 owned by the current assignee and previously incorporated by reference herein.

Frame members 28 and 29, like frame members 26 and 27 of FIG. 2A,
It is possible to stack and crimp. FIG. 2B provides another embodiment, in which one frame member 29 allows the conductive substrates 36, 37 and 38 to be installed separately.
It is located inside the other frame member 28 and inside the center of the opening of the window.

The frame members 28 and 29 are detachably attached to the window frame support portion 41 by a normal male and female screw structure 30. In this case, fasteners such as bolts are slidably received by the region of the frame member forming the lateral hole. The ends of the bolts are fixed in the area of the window frame support that forms the threaded holes 22. Any cam device or (
A "pull-up" pin that functions in addition to or in combination with the male and female coupling means 30 described above) is placed around the screen to be installed and used to adjustably extend each screen. obtain. The stretching or relaxation of such a screen surface is
As an auxiliary “adjustment” mechanism, it can be achieved during initial installation or after installation. In order to improve the mechanical and electrical contact, the screen is a frame member 2
Surround 8 and 29.

Yet another alternative substrate mounting method is shown in FIG. 2C. In this embodiment, the screens 36, 37 and 38 or any other electrically conductive substrate are maintained in electrical contact with each other and with the enclosure shield 17 by simple fastening and fastening means. In this case, the screen is sandwiched between the conductive wrap plates 50. That is, the lap plate 50 includes the wall shield 17 and the screens 36, 37 and 3.
8 is in electrical contact. As long as close electrical contact is achieved and maintained
Any means of fastening the lap plate 50 to the wall shield 17 is suitable. Such tightening means include, but are not limited to, cap screws 54, welding and friction fitting.

Adapted to receive or secure a cap screw or to cooperate with a cap screw to keep the opposing surfaces of adjacent conductive substrates spaced apart from each other by a predetermined distance D1 and D2. Filling material 52 may be used.

Yet another substrate mounting structure is shown in FIG. 2D. This structure has a frame supporting surface 61,
It makes it possible to mount the frames 64, 65 and 66 separately on 62 and 63 respectively, the frame supporting surfaces being arranged in a tilted stepped structure. The stepped frame support surfaces may be integrally formed with each other to form one frame mounting structure 68, but are formed separately and together by a plurality of fasteners or bolt means as described above. It may be connected. Similarly, individual frames 64, 64 and 6
The 6 is reversibly attached to the frame support surface by screws, bolts or other fasteners 71. A salient feature in this mounting structure allows the individual frame boards to be installed separately, thereby facilitating the installation, maintenance, replacement and cleaning of all selected boards from one side of the enclosure. .

One or more conductive substrates may be used to provide the multiple conductive surfaces described herein. For example, a typical mounting structure readily accepts a discrete conductive substrate, while a flexible conductive substrate can be folded or arranged to provide the surface described above. The use of one such flexible conductive substrate is shown in FIG.
2C, surfaces 36, 37 and 38 are formed from a single flexible substrate that curves through the mounting assembly and fill substrate.

Substrate Distance Details A myriad of distances between screens have been discovered that provide excellent attenuation. Under some circumstances, screen separation of less than about 76.2 centimeters (30 inches), typically about 0.86 to about 30.48 centimeters (1 / 3-12 inches) may result in EMI shielding. Can be applied to optimize Generally, about 1.5 inches to about 5.0 inches separating the first and second screens.
A distance between 8 cm (2.0 inches) and about 1.27 cm (0.5 inches) to about 1.905 cm (0.75 inches) separating the second and third screens. The distance between gives excellent results. In some cases
Depending on the target EMI frequency, the distance D1 between the substrates is another distance D2. ． ． Must not be equal to an integer multiple of Dx. In an exemplary embodiment, the distance between the first screen 36 and the second screen 37 is approximately but not exactly half the distance between the second screen 37 and the third screen 38. In addition, the third screen 38 is arranged in relation to the first screen 36 and the second screen 37. Depending on the frequency of the EMI, the preferred maximum distance separating the second screen 37 and the third screen 38 is about 5.08 centimeters (2 inches).

As mentioned above, when the first and second screens form what may be considered as resonant cavities, three different non-integer multiples are provided, such that the third screen blocks the transmission of its resonant radiation. The distance between the screens is incorporated into the present invention. Conversely, when the second and third screens form a resonant cavity, the first screen blocks the transmission of resonant radiation.

(Details of Material of Conductive Substrate) The shielding substrates 36, 37 and 38 are processed from a conductive material. 12 per square
Materials with a resistivity below ohms are suitable. Therefore, if this resistivity is measured across two parallel sides of the square, then the square EMI
The damping module should not have a resistance greater than 12 ohms. If a larger area conductive substrate is selected, a correspondingly thicker conductive layer is required. In many cases, the thickness of the conductive layer is determined by the required transparency, not the resistivity. Generally, the conductivity is from 0.10 × 107 mhos / meter to 6.2.
It is preferable to select a substrate that has dropped to the range of 5 × 10 7 mhos / meter.

Many types of conductive materials can be used, including gold, silver, bronze,
Includes, but is not limited to, copper, aluminum, stainless steel and combinations thereof. The inventor has found that certain materials (such as bronze, copper and stainless steel) that are relatively highly reflective (ie, conductive) for use in the intermediate screen 37.
Have been found to give high damping characteristics.

Other embodiments are also suitable as the conductive substrate, where the conductive substrate is a rigid or flexible transparent structure coated with a highly conductive, optically transparent metal or grid coating. Includes, but is not limited to, composite materials made of (eg, plastic or glass). The conductive material can be applied by flame spraying through electro-deposition (such as plasma spraying) means or other means. This method
It allows the use of optically transparent and electrically conductive coatings, which, when used in a grid pattern, are more than a few angstroms thick. As a result, such optically transparent materials have the advantage of superior optical transparency over freestanding screens. Suitable optically transparent materials are available from Tempest Security Systems, Inc. of Troy, Ohio.
tems Inc. , Troy, OH), located in St. Helen, United Kingdom, through the Pilkington United Kingdom,
Ltd of St. Helens, England).

As mentioned throughout, the substrate may be used in a flat planar sheet-like structure, a curved sheet structure or a structure with both flat and curved. For example, FIG. 2A shows generally planar substrates 37 and 38, the perimeters of which form upwardly angled portions 39 and 40, respectively. These angled areas are
It is optionally provided to further improve the electrical contact between the substrate and the frame support member 41.

Details of Screen Substrate When the screen is used as a conductive substrate, several different mesh numbers are suitable. The mesh pattern is defined as the number of openings that are within a length of about 2.54 centimeters (1 inch) along a given straight line or orthogonal thereto. As mentioned above, the size of the mesh varies between screens. Generally, 14 (
A mesh number between coarse and 60 (fine) provides excellent damping results. In one embodiment where maximum damping is desired and less emphasis is placed on minimizing moiré patterns, the first screening screen 36 may have a relatively coarse mesh and the second screen 37 may be compared. The innermost screen 38 may have the finest mesh of all three screens. However, the screens may be installed in any order to obtain the desired damping performance. If a screen is used, it is often advantageous for the screen to have a separately removable assembly for easy cleaning, maintenance and replacement, as shown in FIGS. 2B and 2D.

In addition to the three screens having different screen patterns, the three screens can be further oriented such that the wire array of each screen offsets angularly with respect to each wire array of the other two screens. . Offset angles of 15 to 45 degrees provide the best performance. The offset arrangement minimizes the moire effect.

The screen can be formed from a variety of structures. Suitable screens consist of conductive strands arranged in a triangular, rectangular or other polygonal array. In addition, the actual diameter of the screen wires may differ in that they are thicker than usual, which provides greater rigidity.

In addition to knitted cross wires, other structures such as grids, stretched grids, perforated sheets, and conductive grids vacuum-bonded to non-metallic substrates (such as glass sheets for windows) are also suitable. However, it is not limited thereto. Often, a continuous film is affixed and then excess metal is etched. If a metallized pattern on a transparent substrate is used, the stiffness of the surface depends on the width and thickness of the metal elements of the grid fixed to the substrate.

Example of Shielding Performance Referring to FIGS. 3 and 4, a graph is displayed, showing a structure with three flat screens and two separated by about 4.445 cm (one and a third quarter inch). Improved EMI shielding in the frequency band of 1 GHz to 11 GHz in the structure with a flat screen, the structure with two flat screens separated by about 1,905 cm (third inch), and the structure with one screen. Shows.

FIGS. 3 and 4 show the excellent damping characteristics of the triple screen system according to the invention in which damping of 100 decibels or more is achieved. The superior attenuation characteristics of the triple screen system are EM especially when compared with the double screen system exceeding 10 MHz.
It is further shown to be due to the reduction of resonance. For example, when two screens are used, the EMI attenuation is a certain value when comparing the resonance point of, for example, 3.3 GHz (point A in FIG. 3) and its multiple 6.6 GHZ (point B in FIG. 4). There is a general decrease in initial frequency and resonance / harmonic frequencies. The other resonance point of interest is C in the two graphs,
Designated as D and E. Significant resonant or harmonic effects at those frequencies are
Not seen on the triple screen system. Therefore, the present invention not only improves the shielding performance generally, but also optimizes the shielding performance at the selected frequency.

The method described above can be scaled up by the use of four or more appropriately spaced screens. Non-Parallel Substrates Referring to FIGS. 5A, 5B and 5C, side views are provided illustrating another structure according to the present invention. As mentioned above, the three screens are arranged to attenuate EMI. However, these structures also use non-parallel cavity surfaces to further enhance the imperfect phase reflection of the cavity-confined EMI. One way to obtain non-parallel surfaces is to use a first screen 36 and a third screen 38, as shown in FIG. 5A.
The central portion 39 of the cavity 15 is pulled inward or moved laterally so that the inner wall 1 of the cavity 15
Part of 9 is projected. The structure of a horizontal screen with low protrusion is shown in FIG. 5B. Alternatively, the central portion may be moved outward by recessing the inner wall, in other words, the first screen 36 and the third screen 38 are generally such that their respective arcuate portions are arranged facing each other. It may be formed in a curved structure. Instead, two of the three screens are arranged in a "V" shaped structure, as shown in Figure 5C.

As a result, the first and third screens may be arranged, for example, with the first screen 36 laterally or outwardly from the center to provide a more concave surface and the second screen to provide a more protruding surface. By arranging the three screens 38 inside or inside, they may be processed to have differently shaped surfaces facing each other. Another suitable screen construction is two lateral screens 36, such as to form a "V" shape with an intermediate screen 37 that substantially (uniformly or unevenly) divides the acute angle formed between the side screens. And 38.

One method for providing a non-parallel cavity surface is to attach one end of a simple wire to the center 39 of the first screen 36 and the other end of the wire to the third screen 38.
Of the outermost screen is pulled inward toward the intermediate screen or moved laterally so as to project a portion of the inner wall 19 of the cavity. Another method of providing a curved cavity surface is to first process a hard conductive material into a desired shape, then "details of the substrate material" for a flat conductive substrate.
Metallize these uneven surfaces using the same method described above in.

As in the structure described above, the distance between any two adjacent substrates should not be equal to an integer multiple of the distance corresponding to another screen. FIGS. 6 and 7 compare frequency and EMI attenuation values for a structure with three screens having a depressed center, three flat screens, and one screen. What is written in the legend of coordinates as 14 × 18 is the mesh number.

FIG. 6 and FIG. 7 clearly show that the structure in which the central portion is formed by the triple screen is excellent in attenuation at a specific resonance frequency as compared with the structure by the three flat screens (point F, See also G and H). For example, at 7.9 GHz (point G in FIG. 7), the parallel structure of the three-layer screen is less damped (down to 31 dB) due to the resonance created by the distance between the inner screen 36 and the outer screen 38. To do. This is comparable to the high damping values above 50 decibels provided by the depressed center structure.

However, as shown in FIG. 7, at some high frequencies, the three parallel screen structures have better EMI attenuation (at other than resonant frequency) compared to the center recessed structure. Show.

The excellent attenuation properties of the triple screen embodiment prevent resonance and harmonics of the impinging radiation and are thus a non-parallel side-by-side arrangement (eg, “recessed center”). However, it can also be used in a double screen construction to achieve some improvement. Proper selection of screen separation and shape can ensure sufficient shielding at specific frequencies. Furthermore,
Non-parallel screens can also be applied to structures incorporating more than three screens.

The present invention is particularly useful for moving or changing the resonance point from the frequency of interest. The operation of the present invention causes electromagnetic radiation to impinge on a first conductive planar substrate such that a first portion of the electromagnetic radiation passes through the substrate and a second portion of the electromagnetic radiation does not pass through the first substrate and thereafter. Can be described as a method for attenuating electromagnetic radiation by applying it to a means for preventing the generation of resonant frequencies of the transmitted radiation.

The anti-resonance means comprises a first conductive plane substrate and a plurality of additional conductive plane substrates arranged in parallel with the first conductive plane substrate in the periphery in the opposite direction from the position of the electromagnetic radiation source. It consists of a cavity formed by.

In summary, the present invention provides the best shielding substrate and method for optimizing EMI shielding performance in many applications. The method and substrate according to the present invention are useful for a variety of purposes and may therefore be used in the construction of walls, ceilings, windows and compartments of enclosures, in addition to the manufacture of electrical appliances, the manufacture of electric vehicles, and It can be used to facilitate shielding in military and industrial applications where tampering is a concern.

As such, typical conductive substrates (screens and metallized grids described above) and irregular conductive substrates may be used, such irregular substrates including triangles, honeycombs and It includes, but is not limited to, conductive materials arranged in non-orthogonal patterns such as circular patterns. The pattern elements can be arranged concentrically or in the same size and in the same plane to form a continuous substrate. By choosing the appropriate material, the method and substrate can add transparency and audibility elements to any shielding attempt.

Although the present invention is described with reference to details of the illustrated embodiments, these details do not limit the scope of the invention, as defined in the appended claims. For example, as mentioned above, two, three or more substrates may be placed relative to each other and their surfaces individually modified and shaped to achieve the best performance of EMI attenuation at the target frequency.

[Brief description of drawings]

1 is a front view of a part of a damping device according to the invention.

2A is a cross-sectional view taken along line 2-2 of FIG. 1 showing exemplary means for mounting a conductive substrate on a frame in accordance with features of the invention.

FIG. 2B is a cross-sectional view showing another exemplary means for mounting a conductive substrate in accordance with features of the invention.

FIG. 2C is a cross-sectional view showing another exemplary means for mounting a conductive substrate in accordance with features of the invention.

FIG. 2D is a cross-sectional view showing another exemplary means for mounting a conductive substrate in accordance with features of the invention.

FIG. 3 is a graph showing EMI shielding in the frequency band of 1.5 GHz to 5 GHz when one, two and three conductive substrate layers are used according to the present invention.

FIG. 4 is a graph showing EMI shielding in the frequency band of 6 GHz to 11 GHz when one, two and three conductive substrate layers are used according to the present invention.

FIG. 5A is a side view showing a window comprised of non-parallel conductive surfaces in accordance with features of the present invention.

FIG. 5B is a side view of a window made of an alternative non-parallel conductive surface in accordance with features of the present invention.

FIG. 5C is a side view of another alternative form of a window comprised of non-parallel conductive surfaces in accordance with features of the present invention.

FIG. 6 is a graph showing EMI shielding in the frequency band of 1.5 GHz to 5.1 GHz when parallel and non-parallel conductive substrates are used according to the present invention.

FIG. 7 is a graph showing EMI shielding in the frequency band of 7 GHz to 11 GHz when parallel and non-parallel conductive substrates are used according to the present invention.

[Procedure for Amendment] Submission for translation of Article 34 Amendment of Patent Cooperation Treaty

[Submission date] July 20, 2001 (2001.7.20)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Contents of correction]

[Claims]

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE), OA (BF, BJ , CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, K E, LS, MW, SD, SL, SZ, UG, ZW), E A (AM, AZ, BY, KG, KZ, MD, RU, TJ , TM), AE, AL, AM, AT, AU, AZ, BA , BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GD, G E, GH, GM, HR, HU, ID, IL, IN, IS , JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, M N, MW, MX, NO, NZ, PL, PT, RO, RU , SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, US, UZ, VN, YU, Z A, ZW (72) Inventor Egan, Michael T.             United States 60137 Gu, Illinois             Ren Erin Kenilworth Avenue               2 S476 F term (reference) 5E321 AA11 AA46 BB41 BB44 CC21                       CC22 GG05 GG12 GH01

Claims (43)

[Claims] 1. An EMI attenuator, comprising: a) a first conductive planar member spatially adjacent to a second conductive planar member and disposed at a first distance; b). An EMI attenuator comprising: a third conductive planar member spatially adjacent to the second member and disposed at a second distance. 2. The first distance and the second distance are equal to each other.
The device according to. 3. The device of claim 1, wherein the first distance and the second distance are different. 4. The device of claim 1, wherein adjacent surfaces are parallel to each other. 5. The device of claim 1, wherein at least two adjacent surfaces are non-parallel to each other. 6. The apparatus of claim 1, further comprising a fourth planar member located proximal to the third planar member and distal to the first planar member. 7. The apparatus of claim 1, wherein the conductive planar members are of materials arranged in an orthogonal array. 8. The device according to claim 1, wherein the attenuation value is about 90 to 120 dB. 9. The apparatus according to claim 1, wherein the flat member is a screen configured by a knitting pattern, and each of the knitting patterns is a lattice and has a specific mesh number. 10. The apparatus according to claim 9, wherein the mesh number of the first member is less than the mesh number of the second member. 11. The apparatus according to claim 10, wherein the mesh number of the second member is less than the mesh number of the third member. 12. The apparatus of claim 10, wherein the mesh size of the member is from 8 to 200 per inch. 13. The distance separating the first surface from the second surface is about 0.
． 847 centimeters (third inch) to about 76.2 centimeters (3
The device of claim 1 which is between 0 inches). 14. The distance separating the first surface from the second surface is about 0.
． 847 centimeters (third inch) to about 30.48 centimeters (
The device of claim 1, wherein the device is between 12 inches). 15. The device of claim 1, wherein the conductive material is optically transparent. 16. The device of claim 1, wherein the conductive material is a metallized optically transparent substrate. 17. The apparatus of claim 16, wherein the optically transparent substrate is selected from glass, plastic, knitted material, lattice material, or combinations thereof. 18. The device of claim 1, wherein the conductive planar member has a resistance of less than 12 ohms per square. 19. The apparatus of claim 1, wherein adjacent planar members are not parallel to each other. 20. The apparatus of claim 1, wherein the first distance and the second distance are selected to maximize EMI attenuation at a given EMI frequency. 21. The first distance is selected to achieve a first attenuation level at a particular EMI frequency, and the second distance is to achieve further attenuation of EMI at the particular frequency. The apparatus of claim 1 selected. 22. The apparatus of claim 1, wherein the first distance and the second distance are selected to maximize EMI attenuation over a predetermined frequency band. 23. A method for attenuating electromagnetic radiation comprising subjecting radiation to a plurality of resonant cavities having different dimensions and different resonant frequencies so that the radiation resonances in a particular cavity are shielded by other cavities. . 24. The cavity comprises: a) a first conductive planar surface; and b) a first predetermined space including a first distance separating the first surface and the second surface. A second electrically conductive planar surface disposed proximate to the first surface; and c) forming a first predetermined space that includes a second distance separating the second surface and the third surface. 24. The method of claim 23, comprising a third conductive planar surface disposed distal to the one surface. 25. The method of claim 23, further comprising a fourth conductive surface disposed proximal to the third surface and distal to the first surface so as to form a third defined space. The described device. 26. The first distance and the second distance are different from each other.
The device according to. 27. The device of claim 23, wherein the surface is a conductive screen. 28. The device of claim 23, wherein the surface is an optically transparent conductive surface. 29. A window for use in combination with an EMI shielding enclosure, the window comprising at least two conductive surfaces in which two adjacent surfaces are not parallel. 30. a) a first conductive surface attached to a conductive window frame, b) a second conductive surface located adjacent to the first surface on the frame, and c) the first conductive surface. 30. The window of claim 29, further comprising a third conductive surface disposed proximal to two surfaces and distal to the first screen on the frame. 31. The window of claim 30, further comprising a fourth electrically conductive surface located proximal to the third surface and distal to the first surface. 32. The window of claim 29, wherein at least one said surface is not flat. 33. The window of claim 29, wherein the surface is a screen. 34. The window of claim 29, wherein the surface is optically transparent. 35. A method for attenuating electromagnetic radiation comprising: a) impinging the electromagnetic radiation on a first conductive planar substrate, the first portion of the electromagnetic radiation not passing through the substrate and the electromagnetic radiation passing through the substrate. And b) applying the passed radiation to a means for reducing further passage of the passed radiation. 36. The reducing means comprises a plurality of additional conductive planar substrates arranged in parallel along a line orthogonal to the plane of the first substrate and in the opposite direction from the position of the electromagnetic radiation source. 36. The method of claim 35, comprising a formed area. 37. The method of claim 36, wherein at least one of the additional planar substrates is not parallel to the first planar substrate. 38. The method of claim 35, wherein the substrate is a screen. 39. The method of claim 35, wherein the substrate is optically transparent. 40. A device for attenuating electromagnetic interference, comprising: a) a first defined space having a plurality of walls formed by first and second conductive shielding means, and b) the second conductive material. A second defined space having a plurality of walls formed by the shielding means and the third conductive shielding means, and c) the distance between the adjacent walls of the first and second shielding means is the second and third. Means for arranging said first, second and third shielding means different from the corresponding collinear distance between adjacent walls of the shielding means. 41. An EM comprising two conductive surfaces separated by a mean distance, said mean distance being selected to provide maximum attenuation at a given frequency.
I attenuator. 42. The two conductive surfaces have a non-planar shape, the surfaces are separated by an average distance, and the non-planar shape and the average distance are selected to provide maximum attenuation at a given frequency. 42. An EMI attenuator according to claim 41. 43. The EMI attenuator of claim 41, wherein at least one of the surfaces further comprises a screen.