Note: Descriptions are shown in the official language in which they were submitted.
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CONCENTRATOR
FIELD OF INVENTION
The present invention relates to magnetic field
concentration apparatus, particularly signal enhancement
5 and/or apparatus for confining magnetic flux within an
aperture, and/or to shield magnetic flux from components,
and/or to means for improving signal reception. The present
invention has a particular application to passive devices,
such as tokens, transponders or smart cards.
10 PRIOR ART
It is well known that metal placed in the proxi~ity
of a magnetic field receiving coil will substantially reduce
the amount of magnetic field received by the coil. For
example, metal placed between a source of the magnetic field
15 and the coil can operate to prevent any magnetic field from
being picked up by the coil as shown in Figure 1. The metal
sheet serves to absorb and deflect the flux radiated from
the driver coil or magnetic field source.
Figure 2 shows another situation where a metal
20 sheet serves to reduce signal reception. The metal sheet is
placed behind the coil. The metal sheet acts to reduce the
amount of flux received by the coil by radiating an opposing
flux field. The closer the metal sheet, to the coil, the
larger the opposing flux field and the less signal flux is
25 received by the coil. In effect the metal sheets serve to
proportionately nullify the driver coil radiated flux.
U.S. Patent 4,373,163 discloses an electrostatic
shield with an antenna loop therein (Figure 1). The antenna
is surrounded by a metal shield. The specification does not
30 disclose a conductor plate proximate and in substantially
the same plane as an antenna to enhance signal reception, in
accordance with the present invention as will be described
in more detail hereinafter.
U.S. Patent 4,486,731 discloses a signal
35 enhancement apparatus in the form of a coil having
magnetically permeable material disposed in overlapping
relationship with a coil. The coil is influenced by strips
23 and 24 when the coil is oriented parallel to the
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direction of impinging flux (column 2, lines 23 to 41).
However, U.S. Patent 4,486,731 relates to the problem of
coil reception when the coil is in the same plane as the
impinging flux, whereas the present invention relates to
increasing the reception of flux by a coil by providing a
concentrator in juxtaposition to and in substantially the
same plane as the coil.
U.S. Patent 4,754,284 discloses an automobile
antenna system for use in receiving high frequency bands in
excess of 50 MHz.
SUMMARY OF INVENTION ~`
An object of the present invention is to provide a
concentrator which can be associated or juxtaposed a coil
without deleterious effect on the coil's ability to receive
signals or magnetic fields.
Another object of the present invention is to
provide improved concentrator performance.
The present invention in one form provides a
concentrator adapted to concentrate signals for reception by
a receiver means, said concentrator comprising an
electrically conductive portion juxtaposed said receiver
means, said concentrator being aligned so as to receive said
signals and cause further signals to impinge on said
receiver means, and thereby enhance reception of said
signals by said receiver means.
The present invention further provides a magnetic
field concentrator comprising an electrically conductive
portion, said concentrator being orientated to receive a
magnetic field and cause flux to be radiated from said
portion, the concentrator being juxtaposed a receiver means,
adapted to also receive said field, such that said receiver
means operates to receive said flux in addition to said
field.
The electrically conductive portion is preferably
made of metal, for example aluminium or copper.
The present invention also provides a magnetic
field concentrator adapted to surround a receiver means, the
concentrator comprising a loop having first and second
interconnected portions, wherein :
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the first portion has first and second regions, the
first portion being continuous between said first and second
regions, the first region being juxtaposed and spaced from
said second region, the first portion being adapted to
surround said receiver means,
the second portion having third and fourth regions,
the second portion being continuous between said third and
fourth regions, the third region being juxtaposed and spaced
from said fourth region, the second portion being adapted to
10 substantially encircle said first portion,
first and second interconnection portions, the ~
first interconnection portion being adapted to couple said
first region to said third region, the second
interconnection portion being adapted to couple said second
region and said fourth region,
the loop being formed in a continuous manner and
having a space provided between said first and second
interconnection portions.
The concentrator described above may, upon being
incident with a magnetic field, have substantially no
magnetic field pass between said first and second portions,
the field being diverted through said first portion and
incident said receiver means.
The present invention also provides a magnetic
field concentrator adapted to enhance field reception by a
receiver means, the concentrator being juxtaposed and
adapted to influence said receiver means, wherein the
concentrator comprises a metal portion adapted to
substantially surround said receiver means in one plane, the
metal portion being further adapted to encircle the receiver
means in the plane in a discontinuous manner, wherein, upon
radiation by said field, the concentrator generates flux
which is received by the receiver means in addition to said
field.
The present invention may provide a shield for
alleviating radiation from magnetic fields within a
predetermined area, the shield comprising a loop having
first and second portions and third and fourth
interconnecting portions,
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the first portion having first and second regions,
the first portion being continuous between said first and
second regions, the first region being substantially
opposingly juxtaposed and spaced from said second region,
the first portion substantially encircling said
predetermined area,
the second portion having third and fourth regions,
being aligned with the first and second regions
respectively, the second portion being continuous between
10 said third and fourth regions, the third region being
substantially opposingly juxtaposed and spaced from said~
fourth region, the second portion being adapted to
substantially encircle said first portion,
the first interconnection portion being adapted to
15 couple said first and fourth regions and the second
interconnecting portion being adapted to couple said second
and third regions,
wherein said magnetic fields are substantially
excluded from the area bounded by the first portion.
The portions of the shield and concentrators
described above may in one form be substantially "C" shaped
in configuration.
The present invention also provides a shield for
substantially eliminating magnetic field radiation from
25 within a predetermined area comprising a first conductive
portion substantially encompassing said area and a second
conductive portion substantially encompassing and being
spaced from said first portion, end regions of said first
and second portions being coupled in an overlapping
30 arrangement so as to form one continuous strip, whereby,
upon radiation by a magnetic field, the field is
substantially diverted from said area.
The present invention may also provide a magnetic
field concentrator which may be used to confine an
35 alternating magnetic flux within an aperture and/or
concentrate a magnetic flux in a coil and/or shield
components from the flux. The concentrator may be useful
where a large coil for collecting flux is more expensive
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than a concentrator and smaller coil or where the coil size
presents problems. The concentrator may preferably be made
from a material with good electrical conductivity which
thereby improves the concentrator's performance. The degree
of conductivity may determine the amount of flux radiated
from the concentrator. Non-magnetic or magnetic conductors
may also be contemplated.
Preferred embodiment(s) of the present invention
will now be described with reference to the accompanying
10 drawings, wherein :
Figures 1 and 2 show prior art arrangements. ~
Figures 3 to 14 show various exemplary (only) forms
of concentrator according to the present invention.
Throughout this document, the term "coil" should be
15 construed in a non-limiting way. The term "coil" may
include, for example, any signal receiving apparatus or
magnetic field receptor as the present invention has many
applications. As can be appreciated, the shape of the metal
herein described should not be limited to a particular
20 configuration. The shape of metal is dependent on its
application or use.
Also, throughout this document, the terms "signal"
or "signals" include within their scope any form of
electromagnetic radiation. The signal may, for example, be
25 a powering signal or a data or informational signal.
Although metal placed proximate a receiving coil is
known to reduce the coil's receptive ability, a metal sheet
placed in juxtaposition and/or in substantially the same
plane as the coil as will be hereinafter detailed will not
30 have a negative effect on the coil's receptive ability.
Figure 3 shows a metal sheet placed in the same plane as the
coil. The metal serves to increase the amount of flux,
impinging the coil. The increase of flux on the coil due to
the metal is inversely proportional to the spacing between
35 the metal and the coil.
Figure 4 shows a coil surrounded in the coil's
plane by metal. As can be seen, the additional fluxes
produced by circulating currents, opposes and reduces the
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applied currents. Accordingly, no flux enhancement is
produced for the coil the metal surrounds.
Figure 5 shows metal similar in shape to that
previously mentioned, however, a slot or gap is provided in
the metal so that the metal surrounds the coil in a
discontinuous manner.
The gap in the metal surrounding the coil causes
the eddy currents (produced in response to impinging flux) to
produce a field that serves to increase the flux impinging
the coil.
Figure 6 shows a concentrator similar to that
hereinbefore described.
The concentrator may be preferably constructed in
two forms :-
15 (i) A metal plate with a hole cut to allow the magnetic
flux to pass through. A slot of slots are cut from
the hole out to the perimeter to alleviate
circulating currents, which causes a drastic
reduction in flux, from encircling the hole. The
slot(s) may overlap, as long as there is
substantially no continuous conduction path around
the central hole (Figures 5, 6 and 7). Co-pending
Canadian Applications SN 585,702 filed Dec. 12,
1988 ANTENNA STRUCTURE AND METHOD OF MANUFACTURE
and SN 593,519 filed March 13, 1989 INDUCTIVE
ELEMENT FOR USE AS AN ANTENNA IN TRANSPONDERS filed
in the name of Magellan Corporation (Australia)
Pty. Limited disclose a method of simultaneously
fabricating electrical coils and capacitors, and
now forming PCT specification No. PCT/AU89/00095.
Transponders, identification devices or the like
employ resonant circuits which comprise
interconnected inductors or coils and capacitors,
and optionally include interconnected active
circuitries embodied in VLSI integrated circuit
chips. The resonant circuits are adapted to
receive electrical power from an external
electromagnetic field generated by some
,~
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interrogators or like apparatus. Optionally, the
resonant circ~its supply the power so received and
collected to the active circuitries which may then
generate the appropriate electrical signals as
predetermined. Such signals may further be sent
to other inductors, preferably the same power
receiving inductors, functioning as antennae for
transmission of the signals, to be received by
some external receptors, preferably the same
interrogators.
Accordingly, it is of significance that in the
construction and fabrication of the complete
electronic circuits of the transponders,
identification devices or the like, the capacitors
and inductors or coils should be conveniently
interconnected.
The circuit for use in a transponder,
identification device or the like, can comprise at
least one inductive element or coil wherein said
at least one generally elongate or serpentive
conductive strip is arranged on the one and same
insulative substrate. The electronic circuit may
further comprise at least one capacitive element,
each capacitive element comprising a plurality of
conductive members arranged on one or both sides
of the one and same insulative substrate such that
said plurality of conductive members superpose
each other by folding of the substrate to form at
least one capacitor.
Conveniently, the plates of capacitors so
fabricated may take a substantially "C" shaped
- configuration and be disposed to surround the
associated coils as hereinbefore described. This
technique permits the area consumed by said
capacitor plates to contribute towards the flux
gathering ability of said coils.
(ii) A wire loop concentrator using high conductivity
X
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wire, for example bent to follow the perimeter of
the metal plate shown in Figures 7, 9 and 10, may
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perform the same concentrating function provided
the wire forms a continuous conducting path.
The operation of both exemplary forms as shown in the
drawings can be described thus :-
5 (i) Circulating currents induced on the surface of a
metal plate prevent an alternating magnetic flux
from penetrating below the skin depth. For lOOKHz
on copper, this is about 0.18mm. Consequently, an
alternating flux cannot penetrate thick metal
plates and flows around the conducting obstacle.
With a hole cut in the metal plate, some of the~
flux interrupted by the plate is diverted through
the hole increasing the flux density in that area,
while the balance goes around the outer edge of the
plate (Figure 8). Without the slot, the metal
plate acts as a one turn short circuit. This may
maintain an almost equal in magnitude, oppositely
directed flux in the central hole cancelling most
of the flux trying to pass through it. This may
have a negative effect for magnetic field
concentration purposes, but may be used to
substantially exclude flux from an area.
(ii) The wire loop acts as a one turn short circuit.
The back emf generated in the wire loop ensures
that the total flux passing through the space
between the inner and outer loops is very small,
only enough to account for ohmic losses. The flux
intercepted by the loop configuration is
concentrated in the inner loop in substantially the
same manner as for the metal plate (Figure 9).
The wire loop concentrator may also be used to
substantially exclude flux from an area. By crossing the
wire connections between the inner and outer loops, without
allowing them to touch, the flux passing through the inner
35 loop is drastically reduced. Figure 10 shows an example ofthis configuration.
Figure 11 shows an example of a field concentrator
acting as an electrostatic Faraday shield. The coil is
1 3342 1 5
shown partially surrounded by a conventional Faraday shield.
The Faraday shield is extended to form a field concentrator,
or may be coupled to an existing concentrator.
Electrostatic shielding reduces the capacitive
sensitivity of the coil to objects in the vicinity of the
coil. The Faraday shield may extend only part way around
the coil in order to adjust capacitive sensitivity.
Alternatively, field concentration and
electrostatic shielding can be achieved using two field
10 concentration plates. One placed in front of the coil, the
other behind the coil as shown in Figure 12.
Figure 13 shows a cross-section of this
arrangement. Connection between the front and back plates
can be made anywhere along the plates, however, preferably
15 this is done on the inside and/or the outside of the coil.
See Figures 14A, B and C.
