GB2488150A

GB2488150A - EMI screen with isolated conductive elements on or in a lossy dielectric substrate

Info

Publication number: GB2488150A
Application number: GB201102805A
Authority: GB
Inventors: Andrew Ian Briggs
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-02-17
Filing date: 2011-02-17
Publication date: 2012-08-22
Anticipated expiration: 2031-02-17
Also published as: GB201102805D0; GB2488150B

Abstract

A screen for blocking high frequency electromagnetic emissions EMI from electromagnetic devices is formed of conductive elements 3 separated by a supporting dielectric substance 4 with high Dielectric Constant and High Dissipation factor. Preferably the loss factor and/or the dissipation factor of the dielectric is above 0.1 at 1 Mhz; the dielectric constant is above 4. The dielectric may be a composite of a ferro-electric polymer, such as PVDF, and a mineral such as Barium titanate (BaTiO3) to give loss factors above 3 and dielectric constants above 15. The Screen may comprise islands 3 on the surface or within the dielectric 4 and may comprise an array of regular hexagonal elements with an edge length of 1mm (see figures 3a, 3b and 5) The screen may also comprise straight or zig-zag strips, granular islands and other shapes (figures 2a, 2b) The screen may be formed as a corrugated sheet E1, or a plane E3 for using in a mobile phone. The screen may also be used in the construction of cables to reduce interference (figures 4a, 4b ) between conductors, such as sets of twisted pairs (7,8).

Description

Method and design for screening or reducing electromagnetic emissions from electrical or electromagnetic devices.

Introduction

1. This invention relates to a novel method and design for screening or reducing unwanted electromagnetic radiation or noise from electrical or electromagnetic equipment operating within the kHz, MHz and (3Hz frequency ranges.

2. External to a conductor or device conveying or transmitting an electromagnetic signal, unwanted electromagnetic radiation or noise may originate from several sources including the device itself, adjacent machinery, communication equipment, power equipment, 1{F systems, microwave systems and wave-guides.

3. Electrical equipment may generate electromagnetic radiation from many internal parts in many directions. Said radiation may be absorbed by other equipment or by a user. Said equipment is often required to comply with limits of Electromagnetic Interference (EMIl) or regulations for Electromagnetic Compatibility (EMC).

4. Portable equipment presents difficulties in achieving a connection to electrical earth. A conductive screen floating' in relation to earth may exacerbate the problem of unwanted radiation in any given direction.

5. A typical electrical screening solution for an object or work area employs a metallic plate, foil or mesh separating the object or area from the source of the problem. Said screen is usually earthed. If not earthed then the screen is often made up of a bulk of continuous or granular conductive material where the intention is to dissipate noise within the bulk of the conductive material by scattering the noise in different directions or by causing electrical losses due to resistance during passage of the noise signal therein. For example U5565 7386 discloses a screen for mobile telephones made up of composite material with carbon fibres held within plastic. Often such filler materials are expensive and require high concentrations to be effective.

6. In an example where equipment is simply patched' with conductive material, and this material is earthed or un-earthed, noise may transfer to other areas within the same equipment or to an adjacent device. Voltage or currents signals may flow along large lengths of the conductive material inducing voltage or current signals in other areas of the equipment.

7. Typical applications: 8. The preferred application of this invention takes the form of a novel screen (1). This screen (1) offers a solution for shielding electromagnetic radiation without the requirement to earth the screen (1). Such a system is simpler to install than a conventional shielded system and may be used on areas where connecting to earth is not practical, for example portable equipment & handsets or where no suitable earth is available nearby. For the proposed type of shielding, when used as a screen (1) for an object (2) there is no requirement to earth at any point along the length of said object (2).

9. In a first embodiment (El) depicted in Figure IA the screen (1) may be used to shield one work-area from another for example a barrier curtain between two manufacturing bays.

10. In a second embodiment (E2) the screen (1) may be attached to an object (2) as an integral part of that object (2) or an adhesive patch to shield said object (2) from external electromagnetic interference or to stop said object (2) itself emitting electromagnetic interference. For example a directional emission barrier for installed communication equipment or a screen for communications cable.

11. In a third embodiment (E3) the screen (I) may be used within an object (2) or piece of equipment at a location considered a problem area regarding emissions, to screen the internal parts of an object (2) or piece of electrical equipment where said parts are difficult to earth or are assembled within a polymer case, for example the circuits or earpiece of a mobile telephone.

12. Detailed description

13. The invention will now be described with reference to the following drawings: 14. Figure 1A) depicts a variety of objects (2) on which the screen (1) may be employed; and Figure lB) depicts a close-up of two conductive islands (3) separated by a dielectric substance (4).

15. Figures 2A) and 2B) depict alternative designs for the conductive islands (3) and dissipative substance (4).

16. Figure 3A): depicts an arrangement of six-around-one' islands (3) and Figure 3B) shows the electrical relationship' between islands (3) regarding capacitance.

: 17. Figure 4A): depicts examples of the use of the screen (I) within cabling * systems; and Figure 4B) depicts the screen (1) formed as a tape.

S.....

* 18. Figure 5 depicts an example of preferred dimensions of conductive islands (3) and dissipative substance (4).

* . 19.

20. The invention when in use consists of a screen (1) made from a plurality of conductive islands' (3) arranged to extend in directions within a volwne or : ... surface of the screen (1), the islands (3) proximal to and preferably separated *....: by at least one region of substance (4) where said substance (4) possesses the * dual properties of high relative Dielectric Constant' and high Dissipation Factor' along said directions.

21. Preferably the conductive islands (3) and dissipative substance (4) conjoin in a manner allowing immediate interaction between them with regard to electrical charge, electrical fields or electromagnetic radiation emanating from one or the other.

22. It is most preferred to employ many discontinuous conductive islands (3) along any direction in relation to an object (2). This arrangement necessitates that any signal flowing along the screen (I) substantially in any direction with respect to an object (2) will follow a path across at least one and probably several interfaces of the conductive islands (3) and dissipative substance (4).

23. It is preferred the islands (3) and gaps (4) are of small dimension with respect to the total volume or surface area of the screen (1) so there are many abutments between the dissipative substance (4) and islands (3). For example a preferred arrangement would be fifty hexagon shaped islands (3) each of dimension 1mm width measured across the flats per square centimeter surface area of screen (1).

24. It is further preferred the majority of islands (3) are held with their faces substantially within a similar plane and in close proximity to one another with respect to the edges of those islands (3). For example, gaps (4) between edges of islands may be 0.2mm. In this way the islands (3) may form a ground plane' to electromagnetic fields or noise signals incident from directions forming an acute or normal angle with said plane of the islands (3) and gaps (4) encouraging the noise signals to travel along said plane without penetrating through said gaps (4) in a direction normal to said plane or traveling normal to the face of the islands (3). Once the noise signals reside within said plane the high conductivity of the islands together with the high dielectric constant substance (4) between the islands (3) may encourage the noise signals to flow along said plane through the conductors (3) and from one conductor (3) to another via the substance (4) within said plane. The desired paths (P) for propagation of a noise signal are depicted in figure lB.

25. Particularly preferred is an arrangement where the islands (3) are much larger in surface area than the intermittent gaps (4), so the ground plane is better established by the conductive elements (3) and has higher conductivity per length of screen (I). This arrangement may be cheaper regarding material costs compared to one where smaller islands (3) of conductor are mixed within the substrate (4) as depicted in Figure 2A.

26. Comparing the preferred arrangement in Figure lB to the one depicted in Figure 2A where in the latter a relatively thick sheet of screen (1) contains islands (3) of a granular nature within the volume of substance (4); in the Figure 2A example, at any position within the volume of substance (4) there is little control' over the direction the noise signal travels within the volume. In Figure lB the thin sheet of screen (1) having only islands (I) in one plane may prove beneficial in establishing a path of least resistance along said plane and discourage noise signals from exiting said plane and becoming a noise hazard to external equipment by exiting the volume of the screen (1).

27. lslands (3) shaped as hexagons are further preferred as these may be arranged in a symmetrical six round one' matrix on a surface or substrate (4). With islands (3) arranged in close proximity such as 0.2mm apart, such spacing allows a relatively strong electric field to be established between islands (3).

28. Many other patterns of conductive islands (3) may be used for example a helix or herringbone pattern. Some are depicted in Figure 2B. Many different shapes and interfaces may be used for the lengths of conductive islands (3) and dissipative substance (4). They may be in bands around the circumference of the object (2), staggered longitudinal strips, meshed, chequered or zig-zag'.

The conductive (3) or dissipative (4) materials may be granular within a conductive or non-conductive substrate (4).

29. The screen (1) may be made up of at least two conductive islands (3) and one intermediary substance (4) forming a sandwich (5) where all three parts of the sandwich (5) are located substantially within the same plane and the largest dimension of the conductive islands (3) is within said plane.

30. When used on a screen (1) for objects (2) it is preferred the islands (3) are constructed of metal foil. Particularly preferred is copper foil of thickness 0.05mm to match the maximum penetration depth of a 30MHz signal through said metal. Above this frequency noise is less likely to penetrate the foil due to skin effects.

31. The screen (1) may be manufactured by etching metal foil to create conductive islands (3) held on a substrate (4); by electro-less deposition of silver ink on a substrate then plating with metal (3), by laser cutting of metal foil (3), by sputtering metal (3) on to a substrate (4) or by moulding a substrate (4) with islands (3) held within the volume of the substrate (4).

32. Definitions of terms used in the following text: 33. Relative Dielectric constant' (or relative electrical permittivity) is a measure of the electrostatic energy (concentration of electrostatic flux) that may be stored within the volume of the dielectric.

34. Dissipation factor' (also known as dielectric absorption or loss tangent) is the d4fference in phase of the capacitor voltage and capacitor current with respect to a theoretical 90 degree phase dfference. In high frequency circuits dissipation of charge within a dissipative substance (4) mainly is due to a change in molecular alignment of the molecules in the dissipative substance (4) absorbing energy from the electrical potential and converting it to heat (the rotation ofpolarised atoms within the electrostatic field). Movement of molecules lags the EMfield so there is a phase sh/i. Put another way this is the ratio of resistive power loss in the equivalent resistance to the reactive power oscillating in the capacitor. Energy is used to overcome inertial

resistance in an alternating electricalfield.

35. Loss Factor' DC x DF. A high Loss Factor substance (4) may have both high Dielectric Constant and high Dissipation Factor.

36. Aferroelectric polymer is a substance (4) that may be electrically polarized permanently' similar to an Electret' but without requiring application of heat This effect may be reversed repeatedly, by an opposing electric field.

Application of an electric field may align dipoles in the substance (4).

37. It is especially preferred the dissipative substance (4) is one of loss factor> 0.1 at 1MHz electrical frequency. Jt is more preferred the substance (4) has a relative Dielectric Constant > 4 and Dissipation Factor> 0.1 at 1MI-Iz electrical frequency. It is further preferred the substance (4) is a thermo-polymer of relative Dielectric Constant> 4 and Dissipation Factor> I at 1MHz electrical frequency. It is most preferred the substance (4) is a ferroelectric polymer such as Polyvinylidenefluoride (PVDF). Yet more preferentially the dissipative substance (4) is a composite of ferroelectric polymer (such as PVDF) interspersed with Barium Titanium Oxide BATiO3 powder or material with similar high relative Dielectric constant such as CaCu3TiO4, TiO2 or A12O3 where the relative Dielectric Constant preferably is> 15 at 1MHz electrical frequency. Most preferred the substance (4) is a composite of loss factor> 3 at 1M}{z electrical frequency.

38. From Tables 1A and lB it may be seen the loss factor for a typical grade of PVDF is typically 1609 times greater than that for Polypropylene, a polymer commonly used in electrical systems. At a frequency of 1 MHz the loss factor of PVDF / BaTiO3 composite is 6736 greater than that for Polypropylene.

39. Note: The ideal storage capacitor would have high Dielectric Constant like BaTiO3 and low Dissipation Factor like Polypropylene. The ideal PCB material where losses from the signal were to be discouraged would have low Dielectric Constant and low Dissipation Factor.

40. A screen (1) may be deliberately employed to attenuate emissions of electromagnetic noise by encouraging the noise signals to traverse the screen (1) within the screen (1) across sandwiches (5) of the conductor (3) and dielectric (4) behaving in the manner of the interfaces (Ii and 12) of a capacitor (C). The high Dissipation Factor dielectric (4) causes the noise signal attenuation. Digital noise signals may further be disrupted by propagation delay due to the dielectric.

41. Regarding Figure lB consider a sandwich' (5) of dissipative substance (4) between two conductive islands (SI and S2). Charge accumulation on the first island (Si) induces charge (opposite polarity) accumulation on the second island (S2). This effect is enhanced by the location of the substance (4) of high dielectric constant between the islands (Si & S2). Thus the arrangement encourages the generation of potential difference between the conductive islands (Si and S2) when a first island (Si) is subjected to an accumulation of electrical charge. The electric field is encouraged to concentrate in the direction of the dielectric and towards an adjacent island (Si towards 52) rather than in other directions away from the plane of the screen (I). In other words the noise signal is encouraged to transfer between islands SI and S2 parallel to the plane of the face of the islands Si and S2.

42. Substance (4) is chosen to be dissipative in nature, so during an oscillating transfer process it may reduce the potential of the charge that minors' across between islands Si and S2 by turning some of the charge potential to heat.

Thus the screen (1) functions in the manner of multiple sandwiches (5) behaving in the manner of high electrical permittivity, high dissipative loss capacitors' (C)connected in parallel and series.

43. Regarding Figures 3A and 3B: consider a noise source originating at hexagon marked HI. From Hi via the six adjacent hexagons (H2) there are in effect six virtual' capacitors(C) connected in parallel to hexagon 111. Capacitance is increased six-fold compared to a single capacitor of the same dimensions.

Thus higher capacitance is achieved without the need to increase the depth of the screen (I). A smaller separation gap (4) between islands (3) than the 0.2mm gap (4) shown may enhance capacitance but such a gap (4) may be more difficult to manufacture. The available charge is spread between the six capacitors(C) reducing the charge density per volume of substance (4) at each capacitor(C). The next hexagon in turn H3 has 6 virtual capacitors(C) around said hexagon. In this way as a noise signal moves between hexagons it is rapidly dissipated within a relatively small distance from the source.

44. Consider an example where all islands (3) are in a regular pattern on a flat surface. From a source of noise at any given location, the same potential, charge or current may be induced on any two different islands (3) within the electromagnetic field generated by the noise. In such a case it may be less likely that an electrical field will be established between two proximal islands (3). Therefore it is preferred that an arrangement to screen (1) an object (2) uses a screen (1) with the plane of the screen (1) folded into a corrugated cross section for example in the form of a pleated curtain (arrangement El).

45. It is especially preferred that some areas (6) of conjdined conductive (3) and dissipative substance (4) are discontinuous along the length of the object (2) with respect to other areas (6) of conjoined conductive (3) and dissipative substance (4). Thus noise signals are substantially kept' within each area (6) looping in the manner of a standing wave and dissipated therein around the area (6). In this way noise may only affect localised areas (6) until said noise is dissipated.

46. Regarding conventional shielded objects (2) the signals at high frequencies often produce a skin effect' where the signals undulate near a layer of insulation or under the shield. High frequency noise may also travel in this location. Generally in shielding systems the requirement is to have the lowest resistance I impedance possible conducting to ground from the shielding to carry noise away with the minimum effect on the signal channels. In respect of the screen (1) enclosing the object (2), the proposed system will pose higher impedance to electrical currents passing within the screen (1) along the length of the object (2) compared to a continuous single metal screen (which may be earthed). However, this may be advantageous in that the noise will be destroyed as it crosses the boundaries of the conductor (3) and dissipative substance (4).

47. It may be advantageous to employ a continuous shield () offering total optical' coverage in some portions of the object (2) as more protective alternative. However, by shielding in this way compared to the former arrangements more conductor (3) would be used and the cost would increase.

Using a larger amount of conductor (3) within the object (2) may have an adverse effect on electrical transmission parameters within the object (2) such as Nominal Propagation Velocity (NPV) or Return Loss (RL).

48. In Figure 2A example (X) where the conductive islands (3) are arranged on a substrate of dissipative substance (4) it is preferred when the screen (1) is in use around an object (2) that the screen (1) is oriented with the islands (3) facing towards the object (2) and the substrate (4) presented away from the object (2). In this way the islands (3) will substantially form a ground-plane', screening the object (2) from the dissipative substance (4) so that any (desired) electromagnetic signal within the object (2) may be less likely to suffer from dissipation by the dissipative substance (4).

49. Similarly if the screen (1) in example (X) is to be used within an object (2) it is preferred that the screen (1) is presented with the islands (3) facing the component from which the electromagnetic radiation is to be shielded.

50. Considering example X, a rupture within the material structure of an island (3) perhaps due to mechanical stress will not be as critical regarding shielding performance compared to some conventional shielded methods. Such a rupture will simply add a small extra area that is not covered with conductor (3) to the existing gaps (4) in the conductor islands (3) and create a different length of dissipation substance (4) in the gap (4) than existed before the rupture.

51. It is most preferred the islands (3) are fully encased within the dissipative substance (4) as depicted by arrangement (Y) so that any field from any island (3) cuts through dissipative substance (4) in every direction it emanates. This may increase the dissipation compared to an example where the dissipative substance (4) is only located between the islands (3).

52. In an example where the screen (1) is oriented on the outside of an object (2) with the islands (3) facing away from the object (2) it is preferred that a layer of insulating material (not shown) covers the outer face of the islands (3) in relation to the centre of the object (2) to prevent the islands (3) becoming an electrical hazard by bridging electrical contacts on other equipment.

53. The screen (1) may be used to shield or reduce noise between two components (K) within an object (2) for example one component (K) on a PCB from another component (K).

54. Similarly the screen (1) may be used on or within a cable (7) to shield one cable (7) from electromagnetic interference caused by a second cable (7) or shield one pair of twisted wires (8) from a second pair of twisted wires (8).

55. In the case of cable (7) used for conimunications, with the advent of the latest (100) Ethernet cabling standard Augmented Category 6 (Cat 6A)' there is a particular focus on reducing the noise transmitted between different cables.

This noise is known as alien crosstalk (AXT)'.

56. The AXT problem is generally confined to unshielded twisted pair (UT?) cables. Shielded systems have been shown to eliminate AXT but the extra materials needed may add complexity and expense.

57. Where the object (2) is a cable (7) made up of four pairs of twisted wires (8) it is preferred to use one overall cable (7) screen (1) enveloping all the wire pairs (8). However, each individual wire pair (8) may be wrapped within it's own screen (1) held within the body of the cable (7). This may be in addition to an overall cable (7) screen (1). Similarly a separator (9) between different twisted pairs (8) such as an insulator material formed in cruciform cross-section may be constructed from, or lined with the proposed shielding screen (1).

58. Furthermore, when used as a screen (1) for an Ethernet signal cable (7) the preferred arrangement is a hexagon pattern of conductive islands (3) formed on a tape (10) of dissipative substance (4) wrapped around the twisted wires (8) with the centre (11) of the tape (10) parallel to the axis of the cable (7).

The difference in angle of presentation at many locations along the length of the cable (7) between areas (6) of the conductive islands (3) offers a different angle of presentation in relation to the source of noise, thus increasing the chance of different levels of inductive and capacitive coupling on different islands (3), in turn increasing the chance of a different charge accumulation being established on different islands (3) at any instant. If the islands (3) are positioned at a given radial distance from the centre of the cable (7) in a layer concentric with the circumference of the cable (7) then the natural curvature of the cable (7) will create different angles of presentation and spatial positions in relation to external and internal noise signals.

59. When the screen (1) is used within an Ethernet cable (7) at a location closer to the axis (12) than the outer sheath (13) or placed on a cruciform separator (9) it is preferred that the screen (1) is presented with the islands (3) facing the axis (14) of each wire pair. This arrangement also encourages any unwanted signal emanating in a radial direction from the pairs (8) to travel longitudinally long the cable (7) via the ground-plane or planes within the cable (7).

60. Further considering the example of an Ethernet cable (7) it is preferred the conductive islands (3) are hexagons of size measuring less than 1mm across the flats. This ensures a noise signal traveling axially around the cable (7) will have to cross at least one pair of hexagon islands (3) to go from the proximity of one pair of twisted wires (8) to the proximity of a second pair of twisted wires (8).

61. Again regarding Ethernet cable (7) most AXT coupling occurs within the first 20m of the near-end (both ends) of the cabling (7) so it may be that some part of the length of a long cable (7) could be left without any screen (1), for example in the middle section. The main vulnerability to AXT is felt' at the ends of the cable (7) so it may be advantageous to simply use patch cords with the screen (1) matched to cable with other more traditional AXT mitigation methods. This may reduce cost and the effects of screening (I) on return loss, NPV and insertion loss.

62. When using the screen (1) as a screen (1) for a communications cable (7) it is not necessary to maintain shielding continuity through connectors and panels within the cable (7) channel. This speeds up the time required for installation compared to conventional shielded systems.

63. Amongst the cable conduits installed within a building it is possible that an Ethernet CAT6A victim' cable (7) is subject to noise from a transmitting disturber' cable carrying any signal or communication protocol (s) such as mains power cable, CAT6A, CATS or CAT6. Some disturber' cables may generate noise signals of a longer duration and greater voltage than a CAT6A disturber cable.

64. In any of the above cases regarding communications protocols the heat generated within a cable (7) by dissipative loss within the dissipative substance (4) should not cause a problem because the signal currents and voltages are very low meaning low available power (heat) output.

65. Where the screen (1) is employed on an Ethernet cable (7) the internal characteristics of the cable (7) may be tuned to the particular impedance properties of the arrangement of conductive islands (3) and dissipative material (4). The screen (1) arrangement may have an effect on impedance, Return Loss, NPV and insertion loss.

66. The screen (1) may benefit internal' as well as external crosstalk. The screen (I) may aJlow the reduction of the number of twists within the twisted pairs (7), allow reduced spacing in the cable (7) and allow reduction of the cross-sectional area of copper used in the wires (8). The skin effect may be less important if a wire pair (8) or cable (7) is wrapped in the proposed screen (1).

Better noise reduction in the cable (7) may allow less concern regarding the consistency of termination at the interface of the wires (8) with connectors.

67. Use of the screen (1) may allow manufacture of cable (7) with fiexural properties similar to that of Foiled Twisted Pair (FTP) cable with a similar resultant bend radius. The screen (I) may be advantageous over other systems as regards cable (7) size due to the small contribution of the screen (1) to the overall diameter of the cable (7) to achieve the packing density exhibited by existing cables and to offer favourable cost of manufacture. The screen (1) may be less compromised by ruptures in the conductive islands (1) compared to ruptures in the conductive layer (3) of other cables with an overall screen for example coaxial signal cable.

**.Se. * I

I..... * * ** ** * * * * * 4. * fl * II. 1.1.4 * *

Substance Frequency Temp --DC --DF -Loss factor ________ _______ _____ ______ _______ DC x DF Polypropyene 1MHz -20C -2.2 0.0005 0.0011 PVDF 1MII-Iz 20 C 7.7 0.23 1.77 BaliO3pure 1MHz -20C -1143.0 0.0! 11.43 PVDF/ mixed 1MHz 20C 57.0 0.13 7.41 with BaTiO3 powder 40% by vol (70% byweight) ________ ______ _______ ________ _______

Table 1A

Typical values for PVDF at other frequencies: Substance Frequency 1 Temp DC DF Loss factor I DCxDF PVDF 100Hz 120C 8.5 0.16 1.36 PVDf 100MHZ _j9C 5.5 0.30 1.65

Table lB

Table 1A and 1B: Examples of typical Dielectric Constant and Dissipation Factor for some materials

Claims

Claims 1. A screen consisting of a plurality discrete conductive islands within a volume or surface where the islands are proximal to one another and proximal to and separated by a dielectric substance of Loss Factor> 0.1 at 1MI-iz electrical frequency.
2. A screen as claimed in Claim 1 where the dielectric substance has a Relative Dielectric Constant of >4 and Dissipation Factor >0.1 at 1MHz electrical frequency.
3. A screen as claimed in Claim 2 where the dielectric substance is a thermo-polymer
4. A screen as claimed in any of Claims 1 to 3 where the dielectric substance is a ferroelectric polymer.
5. A screen as claimed in Claims 3 or 4 where the dielectric substance is PVDF.
6. A screen as claimed in Claims 4 or 5 where the dielectric substance is a composite of a ferroelectric polymer and a mineral with Relative Dielectric Constant >l5.
7. A screen as claimed in Claim 6 where the dielectric substance is a composite of PVDF and a mineral with Relative Dielectric Constant >15.
8. A screen as claimed in any of Claims 1 to 7 where the dielectric substance is a composite with loss factor> 3 9. A screen as claimed in Claim 8 where the composite is one of a mixture of PVDF and BaTiO3.10. A screen as claimed in Claim I where the screen is made up of at least two conductive islands and one intermediary substance forming a sandwich where all three parts of the sandwich are located substantially within the same plane and the largest dimension of the conductive islands is within said plane 11. A screen as claimed in Claim 10 where the conductive islands have a largest dimension of 1.5mm within the plane of the screen.12. A screen as claimed in Claim 11 where the conductive islands are hexagons of 1mm measured across the flats 13. A screen as claimed in any of Claim 10 to 12 where the islands are hexagons arranged in a symmetrical 6-round-one pattern within a plane 14. A screen as claimed in any of Claims 10 to 13 where this plane is subsequently formed into a corrugation 15. A screen as claimed in any of Claims 10 to 13 where this plane is subsequently formed into a cylinder 16. A screen as claimed in Claim 1 where the conductive islands are encased within the dielectric substance 17. A screen as claimed in any of claims ito 16 where the conductive islands are shaped as strips.18. A screen as claimed in any of claims 1 to 16 where the conductive islands are shaped as zig-zag patterns.19. A screen as claimed in any of claims ito 16 where the conductive islands are manufactured from metal foil.20. A screen as claimed in any of claims ito 19 where the screen is integral to a mobile telephone.21. A screen as claimed in any of claims I to 19 where the screen is integral to an electronic instrument.22. A screen as claimed in any of claims 1 to 19 where the screen is used as a circumferential screen for a cable.23. A screen as claimed in any of claims I to 19 where the screen is used as a circumferential screen for a pair of twisted wires within a cable.24. A screen as claimed in Claim 23 where the screen is used as a circumferential screen for each pair of twisted wires within a cable where the cable is made up of four pairs of twisted wires.25. A screen as claimed in any of Claims 1 to 19 where the screen is used on a separator positioned between pairs of twisted wires within a cable.26. A screen for shielding formed from at least one sandwich of an intermediary dissipative substance between two conductive islands forming a capacitor of loss factor >0.1 27. A screen as claimed in Claim 26 where the sandwiches are arranged in a six-around-one arrangement forming six capacitors connected in parallel where each capacitor has loss factor> 0.1.28. A screen as claimed in any of claims 1 to 28 where the islands are formed on the surface of a substrate of dielectric substance.29. A screen as claimed in claim 28 where the screen is in the form of a tape.30. A screen as claimed in Claims 28 or 29 where the islands are oriented to face a source of noise 31. A screen as herein described and or depicted in any one or more of the accompanying drawings.Amendments to the daims have been Wed as follows Claims 1. A screen consisting of at least two discrete conductive islands where the largest dimension of the islands is located within a substantially planar surface where the face of the islands encompassing the largest dimension is substantially parallel to the planar surface, where the islands are proximal to one another separated within said planar surface along adjacent edges by a gap of width less than or equal to 0.2mm where within said gap wIthin said planar surface is a dielectric substance having a Loss Factor> 0.1 at 1MHz electrical frequency.2. A screen as claimed in Claim I where the dielectric substance has a Relative Dielectric Constant of>4 and Dissipation Factor >0.1 at 1MHz electrical frequency.3. A screen as claimed in Claim 2 where the dielectric substance is a thermo-polymer 4. A screen as claimed in any of Claims I to 3 where the dielectric substance is a ferroelectric polymer.5. A screen as claimed in Claims 3 or 4 where the dielectric substance is PVDF.6. A screen as claimed in Claims 4 or 5 where the dielectric substance is a composite of a ferroelectric polymer and a mineral with Relative Dielectric Constant >15.7. A screen as claimed in Claim 6 where the dielectric substance is a composite of PVDF and a mineral with Relative Dielectric Constant >15.8. A screen as claimed in any of Claims I to 7 where the dielectric substance is a composite with loss factor> 3 at 1MHz electrical frequency.
9. A screen as claimed in Claim 8 where the composite is one of a mixture of PVDF and BaTiO3.
10. A screen as claimed in any of claims I to 9 where the conductive islands have a largest dimension of! .5mm within the plane of the screen.
11. A screen as claimed in Claim 10 where the conductive islands arc hexagons of 1mm measured across the flats ". :
12. A screen as claimed in any of Claim 10 to 11 where the islands are hexagons arranged in a symmetrical 6-round-one pattern within the plane of the screen.
13. A corrugated screen where at least one face of the corrugation is formed from the screen as claimed in any of Claims 10 to 12.
14. A cylindrical screen where the cylinder is formed from bending the planar screen claimed in any of Claims 10 to 12.
15. A screen as claimed in any of claims 1 to 12 where the conductive islands are encased within the dielectric substance
16. A screen as claimed in any of claims I to 15 where the conductive islands are * shapedasstrips.
17. A screen as claimed in any of claims I to 15 where the conductive islands are shaped as zig-zag patterns.
18. A screen as claimed in any of claims I to IS where the conductive islands are manufactured from metal foil.
19. A mobile telephone having integral to it a screen as claimed in any of claims 1 to 18.
20. An electronic instrument having integral to it a screen as claimed in any of claims ito 18.
21. A cable having integral to it a screen as claimed in any of claims I to 18 where the screen is circumferential to the wires of the cable.
22. A pair of twisted wires having a screen as claimed in any of claims ito 18 where the screen is circumferential to the twisted wires.
23. Four pairs of twisted wires as claimed in Claim 22 where the screen is used as a circumferential screen for each pair of twisted wires.
24. A separator positioned between pairs of twisted wires having an integral screen as claimed in any of Claims ito 18.
25. A screen as claimed in any of claims I to 18 where the islands are formed on the surface of a substrate of dielectric substance.
26. A tape formed from the screen as claimed in claim 25.27 A screen as herein described and or depicted in any one or more of the accompanying drawings. S. S * . S * *S* S....S 0* S. * S..SS -* S)t *S iS S