GB2372899A

GB2372899A - Portable communications terminal incorporating a radio signal attenuation devi ce

Info

Publication number: GB2372899A
Application number: GB0105158A
Authority: GB
Inventors: Andrew Beaton Hannigan
Original assignee: Matsushita Communication Industrial UK Ltd
Current assignee: Matsushita Communication Industrial UK Ltd
Priority date: 2001-03-01
Filing date: 2001-03-01
Publication date: 2002-09-04
Anticipated expiration: 2021-03-01
Also published as: GB0105158D0; GB2372899B

Abstract

A shield within the housing 9 of a radio telephone causes local attenuation of transmissions from the terminal in the area of the user interface. Metallic coating 8 of a portion of the inside of the housing of the terminal is connected to a conductive plating on a non-conducting sheet positioned adjacent the display 10 of the terminal. The non-conducting sheet with conductive plating 12 may be incorporated as part of the display 10 and connected to the metallic coating 8 of the housing during assembly of the terminal. The shield is isolated from equipment ground. A PCB 11 may be used to carry the conductive plating.

Description

Portable communications terminal incorporating a radio signal attenuation device This invention relates to portable communications terminals such as radiotelephones and in particular it relates to a means for local attenuation of the radio signals transmitted by communications terminals.

The effectiveness of radio transmissions from portable communications devices is degraded by the proximity of the user of the equipment.

Previous attempts to reduce the interaction with the user have tended to reduce also the effectiveness of the transmissions at a distance from the equipment. The loss in effectiveness is manifest as a distortion of the far field and a reduction in signal power at the receiver.

Use of a shield to protect against radiation is a standard technique. Many types of shielding arrangements have been proposed in the prior art to provide for absorption, blocking and reflection of radiation emanating from radiotelephone terminals and the like. Some of the shields that have been proposed are placed within the housing of the terminal. The absorptive screen described in US 5 493 704 and the ground electrode pattern on a PCB used for shielding in EP 648 023 for example, are both provided inside the terminal. Metallic shields within the housing are suggested also in WO 00/45461.

The portable radio communication apparatus ofEP 522 538 has a conductive film on the inside of the housing of a phone and connects the conductive film on the housing with the PCB ground via the conductive shield parts of the internal components.

The screen of US 5 493 704 is interposed between a user and a high emission region within the phone and is concerned with the distances between the high emission region and the user. No interconnections to the screen are suggested and the effect of the plane or curved metal strip is not discussed. A curved or corrugated metallic surface is proposed in WO 00/45461 as interposed between a user and a transmission antenna but there is no mention of interconnections.

The thin film applied to the phone housing of US 5 731 963 protects the internal components from electromagnetic interference and thereby avoids the use of an additional internal cover for this purpose. The thin film is connected to equipment ground.

EP 522 538 also seeks to avoid the use of an additional internal cover to protect the components from interference by making use of a conductive film on the housing to connect with the metallic covers of the components and subsequently to equipment ground.

It is common for radiotelephones and other communications devices to use a single multi-layer PCB having typically one layer forming a reference potential as equipment ground. Prior art disclosures of radiation shields, where interconnections are mentioned, have radiation shields connected to equipment ground.

Connection of the radiation shield to equipment ground requires additional components and can cause problems through alteration of the characteristics of the antenna.

There remains a requirement for an inexpensive and lightweight but effective radiation shield of simple construction and easy installation without the need for it to be connected to equipment ground. The shield should be able to attenuate locally i. e. alongside or nearby to the equipment the radio transmissions from the equipment.

According to the invention there is provided a portable communications terminal with display means and a housing incorporating a shield, to attenuate locally radio transmissions from said terminal, comprising a metallic coating formed on a portion of the inner surface of said housing adjacent said display means in combination with a member carrying a conductive plating wherein said shield is isolated electrically from equipment ground.

Examples of the invention will now be described with reference to the accompanying figures in which: figure 1 is an external view of a mobile telephone, figure 2 illustrates schematically the components of a radiotelephone, figure 3 is a plan view of the inside of the front cover, figure 4 is a cross-section through A-A'of figure 3, figure 5 is a cross-sectional view for a first embodiment, figure 6 is a plan view of PCB 11 of figure 5, figure 7 is a cross-sectional view for a second embodiment, figure 8 is a plan view of the carrier member of the second embodiment, figure 9 is a side view of the carrier member of the second embodiment.

A radiotelephone terminal configured for use with the GSM system is shown in figure 1. The main housing of the phone is a two-part moulding of a plastic material such as PC/ABS. The two-part main housing comprises a front part and a rear part. The main housing contains all of the components of the phone.

The main components are shown schematically in figure 2. A controller 20, coupled to a memory 22, controls the overall operation of the phone in compliance with the GSM specifications in conventional manner.

A microphone 5 and a loudspeaker 6 enables the user to input voice and to hear audio output. The user can input numbers to be called and other information and instructions for controlling various features of the phone via a keyboard 4. The telephone numbers relating to incoming or outgoing calls or other information can be monitored via display 10. A radio transmitter and receiver 21 coupled to an antenna 7 transmits and receives radio communications over the radio link.

The user interface elements are the display 10, keyboard 4, microphone 5 and loudspeaker 6 and are presented to the user at the front of the phone as viewed in figure 1. The radiation shield acts to attenuate, in the region of the user interface, radio signals emanating from the phone.

The display for these examples is a liquid crystal display (LCD) such as may be obtained from Philips Electronics N. V. as model number LPH 7928. A protective window 14 made from polycarbonate protects the LCD assembly from damage. The main source of radiated transmissions, the antenna 7, is attached to the rear housing. The antenna 7 shown in figure 1 is an external antenna, which is supported and contained by the rear part of the main housing and is connected electrically to the PCB within the housing.

The invention may be used also when an internal antenna is fitted to the phone in addition to, or instead of an external antenna. Antennas suitable for use with this invention are described and referred to in our co-pending application GB0009146. 2.

The figures 3 and 4 give plan and sectional views respectively of parts of the inner front cover and illustrate the areas of the phone to which the metallic coating forming part of the shield is applied. The inside surface of a portion of the front cover indicated at 8 carries a metallic coating. The metallic coating may be aluminium and may be deposited by known techniques such as vacuum deposition.

Metallic coating 8 surrounds the aperture 3 wherein the display 10 is inserted. Ribs 15 and 16 are an integral part of the front cover moulding 9.

The distal end of rib 15 is covered by the metallic coating 8 but the distal end of rib 16 is not covered by metallic coating 8.

With reference to figure 5, which shows a simplified cross-sectional view of part of the phone in a first embodiment, the front part of the two-part main housing is shown at 9 and the LCD display assembly at 10. Typically, as is the case for this embodiment, the majority of electronic components of the phone are carried by and interconnected on a single printed circuit board (PCB). For clarity the single PCB 11 in figure 5 is shown unencumbered by components other than those under discussion. The electronic components are mounted on the surface of PCB 11 opposite the LCD 10 and these surface mounted components are enclosed by a metallised plastic moulding (not shown). The metallised plastic moulding forms part of the equipment ground, protects the mounted components from electromagnetic interference and provides additional mechanical strength to the radiotelephone.

The PCB 11 is, in this example of the invention, the member carrying the conductive plating. The conductive plating is a thin metal plating 12 formed on PCB 11 and has dimensions of 32*10-3 X 32*10-3 X 40 * 10-6 metres with easement at the comers and is positioned so as to be secured adjacent the LCD assembly 10 when PCB 11 is fitted. The conductive metal plating 12 is isolated from equipment ground. The metal plating 12 may be produced as part of the normal PCB fabrication e. g. using copper as the plating material.

The thickness of the plating needs to be sufficient to account for the range of frequencies of the transmissions. The skin depth in respect of the plating materials used needs to be considered. For example with a copper film and a (GSM) transmission frequency of 900 MHz the depth into the

film at which the radiation level falls to 1% of its surface value is 10. 1 * 10-6 metres. At a GSM transmission frequency of 1800 MHz the 1% level is calculated as 7. 2 * 10-6 metres.

A convenient thickness of plating on a PCB or on a sheet of insulating material used as a carrier member would be of the order of 40 * 10-6 metres to allow for manufacturing variations. The conductive coating on the inside of the housing may be reduced in thickness to a few microns e. g. 4 * 6 metres without a significant deterioration in performance.

Springs 13 connect the metallic coating 8 with conductive plating 12. The springs 13 are y-shaped and attached to rib 15 at the upper part of the y with the lower part of the y making spring contact with conductive plating 12. The position of the conductive plating 12 on PCB 11 is illustrated in figure 6.

As it may not always be convenient to use the part of the PCB adjacent to the display to provide the conductive plating, alternative arrangements can be implemented. One such alternative is now described as a second embodiment with reference to the figures in which like numerals refer to identical elements and in which the numerals remain consistent with the foregoing description.

With reference to figure 7, which is a cross sectional view of part of the phone around the display, the front part of the main housing is shown at 9.

The inside surface of a portion of the front cover indicated at 8 carries a metallic coating. This metallic coating is the same as described previously for the first embodiment.

A thin carrier member 17 is included in figure 7 and is shown also in plan and side views in figures 8 and 9 respectively. This carrier member 17 is made of polyester and is screen printed on one side only with a silverbased paint to produce the conductive plating 18. One complete side of the carrier member therefore is a conductor and the opposing side of the carrier member remains as an insulator. It has been found that it is possible for the conductive plating 18 to be perforated to reduce weight without significantly degrading the level of local radio signal attenuation or affecting far field performance.

Pads 19 made from compliant material are adhered to one end of the plate on the non-conducting side as shown in the figure. A compliant material suitable for use as pads 19 is Poron 4701-30-25034-04 available from Rogers Corporation.

The disposition of carrier member 17 within the phone is shown in figure 7.

On assembly of the phone the metallised rib 15 bears down on the top end of the conductive plating 18 opposite the pads 19. The gap between the edge of rib 15 and the surface of PCB 11 is less than the width of the pad 19 and carrier member 17 combined, such that the compliant pads 19 are compressed. Compression of the compliant pads 19 assures a good contact between the conductive plating 18 on one side of carrier member 17 and metallic coating 8 of the cover. The carrier member 17 is secured in position by adhesive tab 23.

Electrical contact between the metallic coating 8 and the conductive plating 18 is via a single strip at on end of the member 17. Similarly the contact between the metallic coating 8 and the thin metal plating 12 formed on PCB 11 is via a single spring or a number of co-located springs making a continuous or piecewise continuous linear contact close to one end of the plating 12. Therefore, conveniently, the electrical contact between the metallic coating 8 and the conductive plating 18 is via a single contact area further reducing component count and assembly time. In some instances the rib 15 may not extend across the whole width of the front cover as is shown in figure 3 and there will be a gap in the line of contact between the metallic coating and the conductive plating. In these cases there will be two or more contact areas towards one end of the conductive plating.

Although described herein as a carrier member, the insulating sheet 17 carrying the conductive plating 18 may be thin enough to become a flexible sheet so as more easily to be attached to the display as part of the display assembly. Implementation of the shield will then require only that the flexible sheet attached to the display as part of the display assembly is connected electrically to the metallic coating 8 formed on a portion of the inner surface of housing 9 adjacent the display. By this means the constituent parts of the shield can be incorporated into standard component parts to minimise the manufacturing task associated with provision of the shield.

Whilst a theoretical analysis of the invention remains incomplete, practical tests have demonstrated a beneficial local distortion of the radiation pattern.

The local distortion of the radiation pattern serves to attenuate the peak level of radiation in the region of the user interface from the levels produced when no shield is in place.

The performance of the transmissions at a distance i. e. at a remote receiver is not affected significantly by the local attenuation provided by the shield.

Claims

Claims 1. A portable communications terminal with display means and a housing incorporating a shield, to attenuate locally radio transmissions from said terminal, comprising a metallic coating formed on a portion of the inner surface of said housing adjacent said display means in combination with a member carrying a conductive plating wherein said shield is isolated electrically from equipment ground
2. A portable communications terminal as in claim 1 in which said member carrying a conductive plating is a PCB.
3. A portable communications terminal as in claim 1 in which said member carrying a conductive plating is a sheet of insulating material.
4. A portable communications terminal as in claim 1 to 3 in said conductive plating is perforated.
5. A portable communications terminal as in claims 3 and 4 in which said member carrying a conductive plating is adhered to the display assembly
6. A portable communications terminal as in any previous claim in which the portion of the inner surface of the housing having an electrically conductive coating is less than one quarter of the whole.
7. A portable communications terminal as in any previous claim wherein electrical contact between said metallic coating and said conductive plating is via a single contact area.
8. A portable communications terminal substantially as hereinbefore described in relation to or as illustrated in the accompanying drawings