WO2011146003A1

WO2011146003A1 - Member and system for electromagnetic shielding

Info

Publication number: WO2011146003A1
Application number: PCT/SE2011/050617
Authority: WO
Inventors: Tore Nilsson
Original assignee: Nolato Silikonteknik Ab
Priority date: 2010-05-18
Filing date: 2011-05-17
Publication date: 2011-11-24
Also published as: SE1050492A1; SE534851C2; SE534851E; CN102511206A; CN102511206B

Abstract

An element for electromagnetic shielding, which element has a longitudinal extent and which element, along its longitudinal extent, is coextruded to form a first portion consisting of an electrically conductive material and a second portion consisting of an electrically non-conductive material. In the element, viewed in a cross section transverse to the longitudinal extent of said element, the first portion and the second portion are arranged side by side, and wherein, when the element is fitted between a first and a second, oppositely situated component, the first portion is contrived such that it forms an electrical connection between the first and second component. The element has at least one protrusion along its longitudinal extent, which protrusion is intended to secure the element when this is fitted into a groove made in said first and/or second component.

Description

ELEMENT AND SYSTEM FOR ELECTROMAGNETIC SHIELDING

TECHNICAL FIELD

The present invention relates to an element for electromagnetic shielding and to a system containing such an element.

PRIOR ART

Electrical equipment normally needs to be shielded from electromagnetic radiation in order to be able to purposefully function and avoid interference to the electronics from, for example, unwanted radio signals. The shielding is normally realized by enclosing the electrical equipment with an electrically conductive casing. Since in certain cases, for example in a repair situation, access is needed to the electrical equipment, the casing is made openable. In order to achieve a tightly enclosing casing, elastic and electrically conductive elements, also referred to as packings, are used in the contact surfaces which are formed between, for example, a housing and a lid.

These elements can be made of an electrically conductive material and a non-conductive material. The former material is used to obtain an electrical contact, i.e. a shielding, between the openable parts when they are closed, and the latter material is used to effect a seal against the environment in order to prevent moisture, dirt and the like from penetrating into the electrical equipment.

In the assembly of these elements, use is often made of an adhesive which has been applied to said elements. With the aid of the adhesive, the elements can be placed on an electrical casing and remain in their position during assembly and maintenance.

A problem with the use of adhesive is that it involves an extra step in the production of the element and that, when joining by vulcanization at elevated temperature, it is difficult to obtain a satisfactory joint, since the adhesive does not tolerate as high a temperature as the materials of which the elements are otherwise made. The use of adhesive also makes disassembly and repair more difficult, since the element can fracture and leave unwanted remnants in the element groove. SUMMARY OF THE INVENTION

One object of the present invention is to solve the above problems and provide an element for shielding which allows assembly without the use of adhesive.

One particular object is to provide an element which allows simpler and more reliable assembly of elements for electromagnetic shielding.

In order to achieve these objects, and also other objects emerging from the following description, an element for electromagnetic shielding, as well as a system, are provided according to the present invention. Alternative embodiments of the invention are described in the independent patent claims.

More precisely, an element for electromagnetic shielding is provided according to the present invention, which element has a longitudinal extent and which element, along its longitudinal extent, is coextruded to form a first portion consisting of an electrically conductive material and a second portion consisting of an electrically non-conductive material, and in which element, viewed in a cross section transversely to the longitudinal extent of said element, the first portion and the second portion are arranged side by side, and wherein, when said element is fitted between a first and a second, oppositely situated component, the first portion is contrived such that it forms an electrical connection between the first and second component and the second portion forms an environmental seal between the first and second component, and wherein said element has at least one protrusion along its longitudinal extent, which protrusion is intended to secure the element when this is fitted into a groove made in said first and/or second component.

An advantage of the present invention is that the element, by virtue of the protrusion, can be fixed in the groove without use of an adhesive. Adhesive normally has the task of ensuring that an element remains in its groove during assembly and disassembly. By virtue of the elasticity which the element exhibits with the aid of protrusion(s) in the longitudinal extent of the element, both assembly and fastening can be realized without adhesive.

The resilient properties of the inventive element further ensure that the contacting pressure is always present and that the desired shielding is achieved along the entire longitudinal extent of the element.

By component is meant, for example, a housing or a lid which is arranged to enclose a piece of electrical equipment. It can also be two other types of parts which, when brought together, form contact surfaces facing each other.

According to one embodiment, when the element is fitted into a groove made in said first and/or second component, said first portion can form an electrically conductive contact surface between said first and second mutually opposing components, which contact surface extends at least over a dividing plane between these components.

By virtue of the fact that the first portion, which contains an electrically conductive material, forms a contact surface extending over the dividing plane, an electrically conductive contact therebetween, and hence also an electromagnetic shielding between the components when these are brought together, is ensured.

According to another embodiment, the first portion of the element, viewed in a cross section transversely to the longitudinal extent of said element, has a geometry which at least partially circumferentially encloses said second portion.

By the term "partially circumferentially enclosing geometry" is meant a portion which extends past the dividing plane between the first and second component when these are brought together and which thereby provides a large contact surface against the components. This contact surface is maintained regardless of the transformation of the element which occurs when the two components are brought together.

It will be appreciated that the geometry of the contact surface and its extent in the groove, as well as over the dividing plane, is dependent on parameters such as the cross-sectional geometry of the element, the geometry of the groove, the geometry of the components and the elasticity in the materials of the first and second portion.

The advantage with a partially enclosing first portion is that the quantity of material in this part of the element can be optimized both with regard to electrical conductivity and in terms of cost.

According to a further embodiment, when the element is fitted into a groove made in said first and/or second component, said second portion can form an environmental seal between said first and second mutually opposing components, which environmental seal extends at least over a dividing plane between these components.

The environmental seal prevents unwanted material, such as moisture and dirt, from penetrating into the electrical equipment. In one embodiment of the element for electromagnetic shielding, said at least one protrusion can have a geometry which is resilient in a direction transverse to the longitudinal extent of the element.

With the aid of the resilient geometry, the element can be fitted by being pressed in place in a groove, whereupon the element, by means of the resilient geometry, secures the element such that it is not moved in the course of assembly and disassembly. In addition, the effect of the environment-sealing action of the second portion is improved. A further effect is that the first portion, as an effect of the transformation of the second portion, will also be pressed closer with its contact surfaces against the components and over the dividing plane and will thus enhance the shielding action.

Said first portion of the element for electromagnetic shielding can comprise an elastic material accommodating electrically conductive particles.

Said first portion can comprise an electrically conductive particles component amounting to 10-80 percent by weight, and more preferably 50- 70 percent by weight.

Said second portion of the element for electromagnetic shielding can comprise an elastic material. The elasticity allows the transformation of the second portion when the element is installed and thereby helps to secure the element when this is installed. The element can hence be installed without the use of an adhesive.

According to one embodiment, the element, viewed in a cross section transversely to its longitudinal extent, can comprise a hole. The advantage with a hole in the longitudinal extent is that the element can be further compressed when said first and second components are brought together.

In addition, a system comprising an element for electromagnetic shielding, as well as a first and a second component, is provided according to the present invention, which components in brought-together state, in their contact surfaces, delimit between them a groove, and which element has a longitudinal extent and is coextruded to form a first portion consisting of an electrically conductive material and a second portion consisting of an electrically non-conductive material, and in which element, viewed in a cross section transverse to its longitudinal extent, the first portion and the second portion are arranged side by side, and the element has at least one protrusion along its longitudinal extent, which protrusion is intended to secure the element when this is fitted into said groove, wherein, in the fitting of the element into said groove, the first portion is contrived such that it forms an electrical connection between the first and the second component and the second portion forms an environmental seal between the first and second component.

The inventive system has in all respects essentially the properties and advantages which have been discussed above, whereby reference is made to the above discussion. DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The figures should not be regarded as a limitation of the present invention, but instead the figures should be used to illustrate and gain a better understanding of the invention.

Figure 1a shows in schematic representation a cross-sectional view with two component parts and an uninstalled element.

Figure 1 b shows in schematic representation a cross-sectional view with two component parts and an installed element. For illustrative reasons, the two components are not fully brought together.

DETAILED DESCRIPTION

In figure 1a and b, to which reference is made, is illustrated an element 1 for electromagnetic shielding according to the present invention. The figures are also representative for illustration of the inventive system.

The element 1 is arranged to be fitted between two components 7, 8, which can be constituted, for example, by a lid and a housing in which electrical equipment is intended to be placed. The element 1 is arranged to be fitted into a groove 6 which can be made in a contact surface of either of the first and second components 7, 8 or in both components 7, 8. In the brought-together state, when the two components 7, 8 are in contact with the element 1 , the two components 7, 8 are intended to form an electrically shielded enclosure for, for example, a piece of electrical equipment. It will be appreciated that, even though the description is based on two components 7, 8, they can constitute more parts.

The element 1 can be produced by extrusion, and then, above all, coextrusion. Coextrusion allows the use of two or more different materials in the element 1 in order thereby to obtain different properties viewed in a cross section. The coextruded element 1 can be extruded in an infinite length, which is then cut up into suitable lengths according to the field of application.

Viewed in a cross section transverse to the longitudinal extent of the element, the element has two portions 2, 3, which are oriented side by side: a first portion 2, consisting of an electrically conductive material, and a second portion 3, consisting of an electrically non-conductive material. In its simplest embodiment (not shown), the element 1 can be constituted, for example, by two geometrically uniform portions consisting of a first and a second material which are coextruded side by side.

In the illustrated embodiment, the first portion 2 is arranged however as a layer, which partially circumferentially encloses the second portion 3. The degree of partial enclosure can vary in dependence on the cross- sectional geometry. For example, an element 1 of substantially square cross section can, as illustrated, have a first portion 2 which partially encloses the second portion 3 by virtue of the fact that the first portion 2, when the element 1 is arranged between two components 7, 8, extends over and past the dividing plane between the two components 7, 8, and over at least a corner portion of the groove 6 in which the element 1 is intended to be installed.

Depending on the geometry of the groove 6, the enclosing portion 2 can extend over the dividing plane between the two components 7, 8 and over and past two corner portions, which are formed once the components 7, 8 have been brought together. This variant is shown in figure 1a and 1b.

It will be appreciated that the enclosure is dependent on the element

1 and the geometry of the components 7, 8, and that alternative embodiments are possible for ensuring a contact surface between the components 7, 8 and the element 1.

As will be appreciated, the geometric cross section of the element 1 can be virtually infinitely varied on condition that the element 1 , when it is installed between two components 7, 8, forms an electrical connection and an environmental seal between the components 7, 8.

In the shown embodiment, viewed in a cross section transverse to the longitudinal extent of the element 1 , two protrusions 5 are arranged in the second portion 3. The protrusions have a resilient function which depends on both material choice and geometry.

By choosing an elastic material in the protrusions 5, the resilient properties are obtained, which are then used to secure the element 1 in a groove 6 made in a component. In addition, the geometry of the protrusions

5 is configured such that the protrusions 5, when subjected to a force in the course of assembly, can change shape, for example by bending in toward the element 1.

The number of protrusions 5 can vary in dependence on the size of the element 1 , but a preferred number can be up to three protrusions. The number of protrusions 5 and the geometry thereof are dependent on the force which it is wished to produce between the element 1 and the groove

6 when the element 1 is installed in the groove 6. The number of protrusions 5 is also dependent on the size of the element 1 , i.e. on how many are practically possible and appropriate.

It will be appreciated that the choice of material and geometry can be determined on the basis of a number of variations and combinations, as long as a resilient function can be obtained.

As an alternative to being a part of the second portion 3, the protrusions 5 with maintained function can be shaped from the first portion 2 or be coextruded with the first portion 2 or second portion 3 and thus form a third or even fourth portion. The material in the protrusions 5 does not need to be the same as in the first portion 2, or alternatively the second portion 3.

The protrusions 5 of the element 1 can have a continuous extent, or alternatively have an intermittent extent, that is to say that protrusions 5 are present on the element 1 along a part of the element 1 viewed in its longitudinal extent, followed by a part which has no protrusions 5 along its longitudinal extent. For principally production engineering reasons, the preferred embodiment has a continuous extent.

In the shown embodiment, the element 1 has a continuous hole 4 made in the longitudinal extent. The hole 4, which forms a channel, enables the element 1 to be further compressed when the two components 7, 8 are brought together. One effect of the hole 4 in the element 1 is that, compared with an element 1 without hole 4, material and hence cost savings can be made. In the shown embodiment the shape of the hole 4 is circular, but other shapes, for example triangular or square, are also possible.

In the shown embodiment, the geometry of the element 1 , viewed in a cross section transverse to the longitudinal extent of the element 1 , is substantially square, with at the top a double bulge in which each portion 2, 3 forms a bulge. The object of the bulges is to make the element 1 more flexible and increase the contact pressure in the installed state.

The shown embodiment has a double bulge toward the part facing the component 7 which acts as a lid. It will be appreciated that a double bulge is not a requirement for achieving a tight contact between the components 7, 8. Alternative geometries are, for example, a single bulge, or even a flat surface.

The first portion 2 in the element is arranged as an electrically conductive material, which can comprise an elastic material such as silicone rubber, polyurethane, TPE or the like. Alternatively, the first portion 2 can be constituted by an electrically conductive silicone. The electrical conductivity can be realized or enhanced by mixing electrically conductive particles with the elastic material.

The particles can be constituted by a pure material such as Ag or Ni or the like, but also by metal-coated particles such as Ag/Cu, Ag/glass, Ag/Ni, Ag/AI, Ni/C or the like. Alloys of these materials are also possible. The particles component can be 10-80 percent by weight, and preferably 50-70 percent by weight. The size of the particles can be between 10 and 200 micrometers in diameter, with a mean particle size of around 40-80 micrometers in diameter. The particles are preferably mixed in to form a homogeneous mixture.

The second portion 3 in the element is preferably an elastic material of the silicone rubber type and which is not electrically conductive. For example, the second portion 3 can be constituted by a silicone, polyurethane, TPE or the like.

The element 1 can be extruded in an infinite length, even though lengths of several hundreds to thousands of meters are commonly found. Prior to use, the element 1 is cut to suitable lengths and, where elements 1 are used in, for example, base stations within the telecommunications industry, lengths of between 0,3 and 2 meters are typical. A typical height and width of the element 1 is 1-10 mm, preferably between 2 and 5 mm. In certain applications, the element 1 , in conjunction with or prior to assembly, can be joined together/joined into a closed loop by vulcanization or gluing.

When the element 1 is fitted into a groove 6 of a component 8, it is forced down into the groove, whereupon the protrusions 5 yield due to their elasticity. Placed in the groove 6, the element 1 and its protrusions 5 endeavor to spring back into its/their original positions, thereby engendering a contacting pressure which results in the electrically conductive side, i.e. the first portion 2, being always in contact with the component 8. The same applies to the environment-sealing action of the second portion 3. A corresponding effect occurs also when a second component 7 is arranged on top of the first component 8 to form a lid. The element 1 with its first and second portions 2, 3 respectively will then extend at least over the dividing plane between these components 7, 8 to achieve shielding or sealing against the environment.

If an adhesive is used, a gap must be present between the wall of the groove 6 and the element 1 , which means that a contact between the element 1 and the wall of the component 8 is not always achieved. The adhesive also makes the electrical contact against the bottom of the groove more difficult. By contrast, the resilient properties of the inventive element 1 ensure that the contacting pressure is always present and that the desired shielding is achieved along the entire longitudinal extent of the element 1.

At a rough estimate, the shielding can be improved by up to 40 dB, depending on frequency, compared with the use of an adhesive.

Many variants and modifications are possible, so that the scope of the invention is exclusively defined by the patent claims.

Claims

PATENT CLAIMS

1. An element (1) for electromagnetic shielding, which element (1) has a longitudinal extent and

which element (1), along its longitudinal extent, is coextruded to form a first portion (2) consisting of an electrically conductive material and a second portion (3) consisting of an electrically non-conductive material, and in which element (1), viewed in a cross section transverse to the longitudinal extent of said element (1), the first portion (2) and the second portion (3) are arranged side by side, and

wherein, when said element (1) is fitted between a first and a second, oppositely situated component (7, 8),

the first portion (2) is contrived such that it forms an electrical connection between the first and second component (7, 8) and the second portion (3) forms an environmental seal between the first and second component (7, 8), and

wherein said element (1) has at least one protrusion (5) along its longitudinal extent, which protrusion (5) is intended to secure the element (1) when this is fitted into a groove (6) made in said first and/or second component (7, 8).

2. The element (1) for electromagnetic shielding as claimed in claim 1 , wherein, when the element (1) is fitted into a groove (6) made in said first and/or second component (7, 8),

said first portion (2) forms an electrically conductive contact surface between said first and second mutually opposing components (7, 8), which contact surface extends at least over a dividing plane between these components (7, 8).

3. The element (1) for electromagnetic shielding as claimed in any one of the preceding claims, in which said first portion (2), viewed in a cross section transverse to the longitudinal extent of said element (1), has a geometry which at least partially circumferentially encloses said second portion (3).

4. The element (1) for electromagnetic shielding as claimed in claim 1 , wherein, when the element (1) is fitted into a groove (6) made in said first and/or second component (7, 8),

said second portion (3) forms an environmental seal between said first and second mutually opposing components (7, 8), which environmental seal extends at least over a dividing plane between these components (7, 8).

5. The element (1) for electromagnetic shielding as claimed in any one of the preceding claims, wherein said at least one protrusion (5) has a geometry which is resilient in a direction transverse to the longitudinal extent of the element (1).

6. The element (1) for electromagnetic shielding as claimed in any one of the preceding claims, wherein said first portion (2) comprises an elastic material accommodating electrically conductive particles.

7. The element (1) for electromagnetic shielding as claimed in claim 6, wherein said first portion (2) comprises an electrically conductive particles component amounting to 10-80 percent by weight, and more preferably 50- 70 percent by weight.

8. The element (1) for electromagnetic shielding as claimed in any one of the preceding claims, wherein said second portion (3) comprises an elastic material.

9. The element (1) for electromagnetic shielding as claimed in any one of the preceding claims, wherein the element (1), viewed in a cross section transversely to the longitudinal extent of said element (1), further comprises a hole (4).

10. A system comprising an element (1) for electromagnetic shielding, as well as a first and a second component (7, 8),

which components (7, 8) in brought-together state, in their contact surfaces, delimit between them a groove (6), and

which element (1) has a longitudinal extent and is coextruded to form a first portion (2) consisting of an electrically conductive material and a second portion (3) consisting of an electrically non-conductive material, and in which element (1), viewed in a cross section transverse to its longitudinal extent, the first portion (2) and the second portion (3) are arranged side by side, and the element (1) has at least one protrusion (5) along its longitudinal extent, which protrusion (5) is intended to secure the element (1) when this is fitted into said groove (6),

wherein, in the fitting of the element (1) into said groove, the first portion (2) is contrived such that it forms an electrical connection between the first and the second component (7, 8) and the second portion (3) forms an environmental seal between the first and second component (7, 8).