Communications: radio wave antennas – Antennas – With electrical shield
Reexamination Certificate
1999-06-02
2001-04-10
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With electrical shield
C343S741000, C343S788000, C343S866000
Reexamination Certificate
active
06215455
ABSTRACT:
The present invention relates to a shielded magnetic-field antenna of the type having at least one turn of a metallic element and a metallic tubular shielding disposed around the said element.
It relates in particular to an antenna intended to be used in association with a chip card reader of the contactless type.
Two kinds of antenna of the above type are notably known. One, usually referred to as a coaxial cable, is flexible, the shielding consisting of a metallic braid disposed around a conducting wire sheathed with plastic; the other comprises shielding consisting of a rigid metallic tube, made from copper for example, disposed around a conducting wire also sheathed with plastic.
Producing these antennas has the drawback of requiring manual operations which are expensive and cannot be faithfully reproduced, such as an operation of cutting the coaxial wire or copper tube to the correct length, cutting the shielding in the middle of the loop opposite the location of a connection to an appliance, and then operations of soldering the antenna to a connector and to a frequency tuning system.
In addition, because of their design and the manual operations which they require, it has been found that such antennae exhibit disparities in magnetic characteristics compared with each other. The inventors deduced therefrom that they were not sufficiently reproducible geometrically.
Disparities in characteristics can also exist in an antenna when it is subjected to impacts or mechanical vibrations which cause it to change geometrically.
The consequence of these disparities, in the first case, is to make unsuitable a frequency tuning system with very fine adjustment designed to equip a series of antennae.
In the other case, the consequence of these disparities is to disturb the antenna with respect to a frequency adjustment made during the manufacture or after this by means of an associated frequency tuning system.
This type of antenna used in a metallic environment requires the association of a ferrite element and a metallic screen disposed underneath so as to give it immunity against surrounding magnetic field interference.
Because of its fragility, the ceramic element must be protected from vibrations and impacts which may occur against the antenna or screen. It is therefore necessary to provide an assembly of the whole which protects the breakable element.
At the present time, the antenna and ceramic element are embedded in resin. This has the drawback of being inconvenient and expensive to implement. In addition, the antenna obtained is not geometrically reproducible.
The present invention aims to mitigate the drawbacks set out above.
The objective of the invention is therefore to design an antenna which is reproducible, geometrically stable and of low cost.
Another objective of the invention is to design an antenna able to be used in a metallic environment which is insensitive to vibration and shock and whose design affords easy, reproducible and economical manufacture.
To this end, according to a preferred embodiment, the object of the invention is a shielded magnetic-field antenna having at least one turn of a metallic element and metallic tubular shielding disposed around the said element.
It is characterised in that the turn is produced in a printed circuit on a card made of insulating material, such as a printed-circuit card, and in that the said shielding consists on the one hand of two open rings, produced in a printed circuit, and disposed respectively on a bottom card and a top card made of insulating material, the said cards being connected by clamping the turn, and on the other hand a plurality of metallic vias distributed on each side of the turn, the said vias connecting the edges of the two rings through the said cards. These vias are preferably uniformly distributed.
By virtue of such a design, the antenna is very rigid, and therefore very stable geometrically compared with the antennae of the prior art.
According to another embodiment, for reasons of efficiency at low frequencies, the said shielding consists on the one hand of two open rings, produced in a printed circuit, and disposed respectively on a bottom annular support and a top annular support made of insulating material, the said supports gripping the turn, and on the other hand two metallic films connecting the edges of the two rings on each side of the turn, the said films being deposited on the edges of the annular support.
By virtue of the characteristics of the above two embodiments, the antenna can be manufactured on an industrial scale by the printed-circuit technique. This technique, perfectly mastered, ensures good reproducibility of its geometric characteristics. This can be effected at lesser cost since the manufacture uses production tools which are generally standardised and automated.
In addition, this design makes it possible to change the format of the antenna very easily since the majority of the operations are automated.
Another object of the invention is a device with a magnetic-field antenna including a printed-circuit antenna according to the invention, a ferrite layer, a metallic screen, two flexible leaves disposed respectively between the antenna and the ferrite layer on the one hand and between the ferrite layer and the metallic screen on the other hand. These leaves can have an adhesive on their faces in order to facilitate assembly.
The design of this device by assembling diverse layers has the advantage of adapting the antenna very easily to a metallic environment subjected to mechanical impacts or vibrations.
According to other preferred characteristics, the device can include clamping means for assembling and clamping together the ferrite layer, the flexible leaves and the metallic screen.
By virtue of these provisions, the elements can easily be connected together and if necessary dismantled, and the distance separating them checked.
According to other preferred characteristics, the device has means for keeping the ferrite at a distance from the antenna and keeping the screen at a distance from the ferrite.
By virtue of these provisions, the reproducibility of the geometric parameters of the device is also ensured.
REFERENCES:
patent: 4083006 (1978-04-01), Yokoshima
patent: 4288794 (1981-09-01), Osborne
patent: 5248989 (1993-09-01), Murdoch
patent: 5257033 (1993-10-01), Roche
patent: 2745928 (1997-09-01), None
Collet Pierre Andre
Lamata D'Angelo Patricia
Le Nevez Yves
Porte Philippe
Gemplus S.C.A.
Nguyen Hoang
Plottel Roland
Wong Don
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