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`(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
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`(19) World Intellectual Property
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`International Bureau
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`( 43) International Publication Date
`17 March 2005 (17.03.2005)
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`(10) International Publication Number
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`PCT
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`WO 2005/024865 A2
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`(51) International Patent Classification 7: (81) Designated
`HOlF 38/14,
`States (unless otherwise indicated, for every
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`27/36
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`kind of national protection available): AE, AG, AL, AM,
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`AT, AU, AZ, BA, BB, BG, BR, BW, BY, BZ, CA, CH, CN,
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`CO, CR, CU, CZ, DE, DK, DM, DZ, EC, EE, EG, ES, Fl,
`(21) International Application Number:
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`PCT/GB2004/003844
`GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE,
`KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD,
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`MG, MK, MN, MW, MX, MZ, NA, NI, NO, NZ, OM, PG,
`8 September 2004 (08.09.2004)
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`PH, PL, PT, RO, RU, SC, SD, SE, SG, SK, SL, SY, TJ, TM,
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`TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, YU, ZA, ZM,
`English
`zw.
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`(22) International Filing Date:
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`(25) Filing Language:
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`(26) Publication Language:
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`(30) Priority Data:
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`0320960.8 8 September 2003 (08.09.2003) GB
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`English
`(84) Designated States (unless otherwise indicated, for every
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`kind of regional protection available): ARIPO (BW, GH,
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`GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM,
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`ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
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`European (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, Fl,
`(71) Applicant (for all designated States except US): SPLASH­
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`FR, GB, GR, HU, IE, IT, LU, MC, NL, PL, PT, RO, SE, SI,
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`POWER LIMITED [GB/GB]; The Jeffery's Building,
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`SK, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ,
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`Cowley Road, Cambridge CB4 0WS (GB).
`GW, ML, MR, NE, SN, TD, TG).
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`(72) Inventor; and
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`Published:
`(75) Inventor/Applicant (for US only): BEART, Pilgrim,
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`without international search report and to be republished
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`Giles, W illiam [GB/GB]; 35 Royston Road, Harston,
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`upon receipt of that report
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`Cambridge CB2 5NH (GB).
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`(74) Agent: HITCHING, Peter, Matthew; Haseltine Lake,
`For two-letter codes and other abbreviations, refer to the "Guid­
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`Imperial House, 15-19 Kingsway, London WC2B 6UD
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`ance Notes on Codes and Abbreviations" appearing at the begin­
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`ning of each regular issue of the PCT Gazette.
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`!!!!!!!! --iiiiiiii iiiiiiii iiiiiiii
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`(54) Title: INDUCTIVE POWER TRANSFER UNITS HAVING FLUX SHIELDS
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`Q (57) Abstract: An inductive power transfer unit is adapted to be placed when in use on a support surface (200). A flux generating
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`surface of the at or in proximity to a power transfer surface, and generates flux over the support ll) unit (50) extends in two dimensions
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`from the unit. power inductively surface can receive to the power transfer Q unit so that a secondary device placed on or in proximity
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`0 A flux shield (70), made of electrically-conductive material, is interposed between the flux generating unit and the support surface,
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`M the shield extending outwardly
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`Alternatively, the flux shield may have (e1 -e4) beyond at least one edge of the flux generating unit.
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`the side between power transfer unit or which extend of the inductive over one or more side faces 0 one or more portions which extend
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`of the outside as a removable accessory which attaches to the :, face(s) and the flux generating unit. The flux shield may be supplied
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`unit. ;;, inductive power transfer
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`200
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`Momentum Dynamics Corporation
`Exhibit 1009
`Page 001
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`W O 2005/024865
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`PCT/GB2004/003844
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`INDUCTIVE POWER TRANSFER UNITS HAVING FLUX SHIELDS
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`This invention relates to inductive power transfer units having flux shields.
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`applicant's for example in the present units, as described 5 Inductive power transfer
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`published International patent publication no. WO-A-03/096512, the entire contents
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`of which is hereby incorporated into the present application by reference, seek to
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`provide a flat or curved power transfer surface over which a substantially horizontal
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`alternating magnetic field flows. This field couples into any secondary devices
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`10 placed upon the power transfer surface. In some variants this field may rotate in the
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`plane of the surface to provide complete freedom of positioning for any secondary
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`device placed on the surface to receive power. The secondary devices are, for
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`example, built into portable electrical or electronic devices or rechargeable batteries
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`which can be removed from the surface when not receiving power.
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`15
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`Depending on the design of the flux generating unit (magnetic assembly) of such
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`power transfer units, they may also emit flux in directions other than desired
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`horizontal surface field. For example a "squashed solenoid" design of flux generating
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`unit emits flux symmetrically above and below it.
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`into a flat solenoid a coil 10 shaped unit 50 comprises In Figure 1, a flux generating
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`20 is in the form of a thin sheet of magnetic wound around a former 20. The former
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`material. This results in a substantially horizontal field across the upper surface of
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`the flux generating unit, but also an equal field across the lower surface.
`The field
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`over the respective with one another 25 lines of both fields extend generally in parallel
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`surfaces, substantially perpendicularly to the coil windings. A secondary device 60
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`is shown in place over the upper surface.
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`Figure
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`2 shows a similar arrangement to that of Figure 1, but with an additional coil
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`of the coil 10, around direction 30 11 wound, in an orthogonal direction to the winding
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`the former 20. By driving the two coils 10 and 11 in a suitable manner, the flux
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`generating unit may create a field which is substantially horizontal over the power
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`Momentum Dynamics Corporation
`Exhibit 1009
`Page 002
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`transfer surface (upper surface) and which rotates in the plane of that surface. In
`typical usage, the flux above the upper surface provides the functionality that the
`user desires (powering the secondary device 60), but the flux present at other
`surfaces may not be useful� can cause undesired effects.
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`5
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`Figure 3 shows a side view Finite Element analysis of the flux lines generated by the
`flux generating unit 50 in Figure I at an instant in time. The lines travel through the
`centre of the solenoid and then divide to return over and under it through the air. A
`secondary device 60 is shown placed on top of the unit 50.
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`One undesired effect occurs particularly when the primary unit is placed upon a
`ferrous metal surface, for example a mild steel desk or part of a vehicle chassis. The
`permeability of mild steel is sufficiently high that it provides a return path for the
`flux which is of considerably lower reluctance than the alternative path through air.
`15 Therefore the flux is "sucked" down into the metal desk. Figure 4 shows another
`Finite Element analysis view when a metal desk 200 is brought under the flux
`generating unit. The high permeability of the metal offers the flux lines a much
`lower-reluctance path than air to return from one end of the flux generating unit 50 to
`the other, and so they travel within the desk rather than through the air. This is
`undesirable for two reasons:
`• A significant proportion of the flux generated by the inductive power transfer
`unit (primary unit) is flowing into the metal desk instead of flowing into any
`secondary devices on the upper surface of the unit, therefore the system
`becomes less efficient (corisumes the more power) and the power received by
`the secondary device varies.
`• The flux flowing through the metal desk causes core losses, for example via
`hysteresis and / or eddy current loss , which cause it to heat up.
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`It is known that when conductive materials, for example copper or aluminium, are
`placed into an alternating magnetic field, the field induces eddy-currents to circulate
`within them. The eddy currents then act to generate a second field which - in the
`limit of a perfect conductor - is equal and opposite to the imposed field, and cancels
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`Momentum Dynamics Corporation
`Exhibit 1009
`Page 003
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`PCT/GB2004/003844
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`it out at the surface of the conductor. Therefore these conductive materials can be
`seen as "flux-shields" - the lines of flux in any magnetic system are excluded from
`them. This may be used to. shield one part of a system from a magnetic field and
`consequently concentrate tht: field in another part. GB-A-2389720, which is a
`document published after the priority date of the present application but having an
`earlier priority date, discloses a flux generating unit in the form of a printed circuit
`board having an array of spiral conductive tracks for generating flux above the upper
`surface of the unit. A ferrite sheet is placed under the board, and a conductive sheet
`is placed under the ferrite sheet, to provide a flux shield. The ferrite sheet and
`conductive sheet are of the same dimensions, parallel to the sheets, as the board.
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`According to a first aspect of the present invention there is provided an inductive
`power transfer unit, adapted to be placed when in use on a support surface,
`comprising: a flux generating means which, when the unit is placed on the support
`surface, extends in two dimensions over the support surface, said flux generating
`means being operable to generate flux at or in proximity to a power transfer surface
`of the unit so that a secondary device placed on or in proximity to the power transfer
`surface can receive power inductively from the unit; and a flux shield, made of
`electrically-conductive material, arranged so that when the unit is placed on the
`support surface, the shield is interposed between the flux generating means and the
`support surface, the shield extending outwardly beyond at least one edge of the flux
`generating means.
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`According to a second aspect of the present invention there is provided an inductive
`power transfer unit, adapted to be placed when in use on a support surface,
`comprising: a flux generating means which, when the unit is placed on the support
`surface, extends in two dimensions over the support surface, said flux generating
`means being operable to generate flux at or in proximity to a power transfer surface
`of the unit so that a secondary device placed on or in proximity to the power transfer
`surface can receive power inductively from the unit; and a flux shield, made of
`electrically-conductive material, having one or more portions which extend over one
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`Momentum Dynamics Corporation
`Exhibit 1009
`Page 004
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`or more side faces of the unit or which extend between said one or more side faces
`and said flux generating means.
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`In cases where the flux genei:ating unit operates by creating a field which alternates
`back and forth in one linear dimension, the conductive shield will have induced in it
`an equal and opposite alternating linear field, which acts to cancel the field near the
`shield. In cases where the unit operates by creating a rotating field in the plane of its
`laminar surface, the conductive shield has induced in it a field which also rotates,
`again cancelling the field.
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`Such power transfer units are advantageous because they allow the flux to be
`concentrated in directions in which it is useful, improving the flux-efficiency of the
`unit, and to be shielded from directions where it can cause side-effects, for example
`by coupling into a metal desk under the unit.
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`In addition, the flux shield increases the coupling between the flux generating unit
`and the secondary device(s) by forcing most of the flux to go over the power transfer
`surface. Therefore less drive current is needed in the flux generating unit to create a
`given flux density in the secondary device(s). Accordingly, provided that losses in
`the flux shield are minimised, the system as a whole becomes more efficient.
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`To ensure that the apparatus runs cool and is power-efficient, I2R losses (losses
`caused by circulating currents dissipating ·as heat) in the conductive shield must be
`kept small:
`• The conductive shield is advantageously made of a highly conductive
`material, for example copper or aluminium sheet of sufficient thickness to
`ensure that the eddy-currents induced therein do not suffer from excessive
`resistance and therefore create heat. The flux density, and therefore the eddy
`currents, may vary across different parts of the apparatus, and therefore the
`necessary thickness, or material, may also vary.
`• The spacing between the shield and the electrically-driven conductors of the
`flux generating unit can be optimised. The larger it is (i.e. the greater the
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`Momentum Dynamics Corporation
`Exhibit 1009
`Page 005
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`spacing between it and the electrically-driven conductors), the lower the
`current-density induced in the conductive shield, and therefore the lower the
`heating. However this must be traded-off against the larger the overall
`dimensions necessary,:which may be less ergonomic.
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`In addition, the conductive shield must not itself be substantially ferrous, otherwise it
`may provide a low-reluctance path which "shorts" the intended flux path.
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`In one embodiment of the present invention, the conductive shield extends in a
`substantially continuous sheet substantially over all but one face of the flux
`generating unit, such that only the face substantially exposed is the laminar surface
`intended for power delivery to secondary devices. For example, if the generating unit
`is a substantially flat rectangular shape, the shield may extend to cover the bottom
`and four sides of the unit. As another example, if the flux generating unit is a
`substantially flat cylinder, the shield may extend to cover the bottom and cylindrical
`side of the unit. The advantage of such an arrangement is that it increases still
`further, compared to a flat sheet, the path that flux would have to travel in order to
`travel through a metal object underneath.the flux generating unit.
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`In another embodiment of the present invention, the conductive shield may enclose
`all but a part of one or more faces of the flux generating unit. For example, if the flux
`generating unit is a substantially flat rectangular shape, the shield may cover the
`bottom, sides and outer part of the top of the flux generating unit. This may be
`advantageous in controlling the flux pattern at the edge of the top of the flux
`generating unit.
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`The conductive shield may form part of an enclosure of the inductive power transfer
`unit, for example a formed or cast aluminium or magnesium casing. This may be
`advantageous in reducing cost.
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`30
`According to a third aspect of the present invention there is provided an inductive
`power transfer unit comprising: a power transfer surface on or in proximity to which
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`5
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`Momentum Dynamics Corporation
`Exhibit 1009
`Page 006
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`PCT/GB2004/003844
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`a secondary device can be placed to receive power inductively from the unit; flux
`generating means arranged to generate flux at or in proximity to said power transfer
`surface; and flux shield attac,:hment means arranged for attaching a flux shield to the
`unit such that the attached shi�ld is arranged at one or more external surfaces of the
`unit other than said power transfer surface, or is arranged between said one or more
`external surfaces and said flux generating means, so that the shield serves to shield
`objects outside the unit, adjacent to said one or more external surfaces, from flux
`generated by the flux generating means.
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`1 O According to a fourth aspect of the present invention there is provided an accessory,
`adapted to be attached to the outside of an inductive power transfer unit, the unit
`having a power transfer surface on or in proximity to which a secondary device can
`be placed to receive power inductively from the unit and also having flux generating
`means arranged to generate flux at or in proximity to the power transfer surface, and
`15 the accessory comprising: means which co-operate with the unit to attach the
`accessory to the outside of the unit in a predetermined working disposition; and
`a flux shield, made of electrically-conductive material, which, when the accessory is
`in its said working disposition, extends at or in proximity to one or more external
`surfaces of the unit other than said power transfer surface so as to shield objects
`outside the unit, adjacent to said one or more external surfaces, from flux generated
`by the flux generating means.
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`20
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`In the third and fourth aspects of the invention the conductive shield is supplied to
`the user as a separate accessory to be placed under or around the power transfer unit.
`25 Optionally it may be provided as a retainable accessory, for example a clip-on cover.
`This is advantageous as it allows the bill of materials for the power transfer unit to be
`kept to an absolute mi:p.imum, yet allows users to purchase the accessory if the unit is
`to be used in a location where it may be necessary to constrain its field, for example
`on a ferrous metal desk.
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`In one embodiment the flux generating unit comprises at least one means for
`generating an electromagnetic field, the means being distributed in two dimensions
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`Exhibit 1009
`Page 007
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`across a predetermined area in or parallel to the power transfer surface so as to define
`at least one power transfer area of the power transfer surface that is substantially
`coextensive with the predetermined area, the charging area having a width and a
`length on the power transfer-Jmrface. Preferably the means is configured such that,
`5 when a predetermined current is supplied thereto and the primary unit is effectively
`in electromagnetic isolation, an electromagnetic field generated by the means has
`electromagnetic field lines that, when averaged over any quarter length part of the
`power transfer area measured parallel to a direction of the field lines, subtend an
`angle of 45° or less to the power transfer surface in proximity thereto and are
`distributed in two dimensions thereover. Preferably the means has a height measured
`substantially perpendicular to the power transfer area that is less than either of the
`width or the length of the power transfer area. The height is more preferably less
`than one fifth, or less than one tenth, of either the width or height, so that the
`inductive power transfer unit as a whole is in the form of a flat bed or platform.
`15 When a secondary device, including at least one electrical conductor, is placed on or
`in proximity to a power transfer area of the inductive power transfer unit, the
`electromagnetic field lines couple with the at least one conductor of the secondary
`device and induce a current to flow therein. The conductive sheet or shield is
`arranged on or in the power transfer unit at a location other than the side on which
`the power transfer area is located.
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`In the context of the present application, the word "laminar" defines a geometry in
`the form of a thin sheet or lamina. The thin sheet or lamina may be substantially flat,
`or may be curved.
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`It is to be appreciated that the conductive sheet or shield may be generally laminar,
`or may include one or more edge portions that are directed towards the power
`transfer surface.
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`The conductive sheet or shield may be exposed on the side of the power transfer unit
`opposed to the power transfer surface, or may be covered with a layer of dielectric or
`other material, for example by part of a casing of the unit.
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`Exhibit 1009
`Page 008
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`For a better understanding of the present invention and to show how it may be
`carried into effect, reference shall now be made, by way of example, to the
`accompanying drawings, in which:
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`5
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`FIGURE 1 is a perspective view showing an example of a flux generating unit
`suitable for use in embodiments of the present invention.
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`FIGURE 2 is a perspective view showing another example of a flux generating unit
`suitable for use in embodiments of the present invention.
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`FIGURE 3 shows a side view of the flux generating ·unit of Figure 1 for illustrating
`flux lines generated thereby.
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`FIGURE 4 is a view corresponding to Figure 3 but illustrating flux lines generated
`when a metal desk is present under the arrangement.
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`FIGURE 5 is a perspective view showing parts of an inductive power transfer unit
`according to a first embodiment of the present invention.
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`FIGURE 6 shows a side view of the unit of Figure 5 for illustrating flux lines
`generated thereby when the unit is placed on a metal desk.
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`FIGURE 7 is a perspective view showing parts of an inductive power transfer unit
`according to a second embodiment of the present invention.
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`FIGURE 8 shows a side view of the unit of Figure 7 for illustrating flux lines
`generated thereby when the unit is placed on a metal desk.
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`FIGURE 9 is a side view of an inductive power transfer unit and an accessory
`therefor according to a third embodiment of the present invention.
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`Momentum Dynamics Corporation
`Exhibit 1009
`Page 009
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`Figure 5 shows parts of an inductive power transfer unit according to a first
`embodiment of the present invention. In this embodiment, a flux generating unit 50
`has the same general construction as the :fl.1:1x generating unit described in the
`introduction with reference to Figure 1. Of course a flux generating unit 50' as
`shown in Figure 2 can be used in this (and other) embodiments of the invention,
`instead. Similarly, any of the flux generating units described in WO-A-03/096512
`can be used in embodiments of the present invention.
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`The flux generating unit 50 comprises a coil 10 wound around a former 20. The
`10 former 20 is in the form of a thin sheet of magnetic material. When the inductive
`power transfer unit is placed on a support surface 200, the flux generating unit 50
`extends in two dimensions over the support surface.
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`A flux shield 70, made of electrically-conductive material such as copper, is
`interposed between the flux generating unit 50 and the support surface 200. As
`shown in Figure 5, the shield 70 extends outwardly by distances e1 to e4 beyond each
`edge of the flux generating unit 50. The distance e1 is for example 50mm. The
`distance e2 is for example 50mm. The distance e3 is for example 50mm. The distance
`e4 is for example 50mm.
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`In this embodiment, the flux shield 70 is in the form of a flat sheet which extends
`generally in parallel with the support surface. There is a gap of size d between the
`sheet and the electrical conductors of the coil 10 extending over the lower surface of
`the former 20. d is 4mm, for example.
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`Figure 6 shows a Finite Element analysis view of the unit of Figure 5. The support
`surface 200 is assumed to be a metal desk. The shield 70 forces any flux lines
`flowing through the metal desk to travel around the shield, increasing the path length
`and thus the effective reluctance of the "desk" path. As a result, the presence of the
`desk has less effect, since more flux lines travel over the unit instead of going
`through the desk.
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`9
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`Momentum Dynamics Corporation
`Exhibit 1009
`Page 010
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`Although the flux shield 70 has extensions beyond all edges of the unit 50 in the
`Figure 5 example, it will be appreciated that a worthwhile flux-shielding effect can
`also be obtained even if the flux shield extends beyond one edge or only extends
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`beyond a pair of opposite edges.
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`Figure 7 shows parts of an inductive power transfer unit according to a second
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`embodiment of the present invention. In this embodiment a flux shield 80 having 5
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`sides (base 82 and side walls 84, 86, 88 and 90) is provided. The base 82 of the flux
`
`shield 80 extends between the lower surface of the flux generating unit 50 and the
`support surface 200. Because the flux shield 80 has side walls in this embodiment,
`
`10
`
`the base 82 need not extend out beyond the edges of the flux generating unit 50 by as
`far as the distances e1 to e4 in the Figure 5 embodiment. For example, e 1 to e4 may
`each be 4mm. This can enable the overall dimensions of the power transfer unit to
`
`be reduced while keeping the effective reluctance of the desk path high. The height
`
`15
`
`of the side walls 84, 86, 88 and 90 is exaggerated in Figure 7 for clarity. In practice,
`
`the side walls need not extend above the upper surface of the flux generating unit 50.
`
`The flux shield 80 may be formed from a flat sheet of conductive material which is
`
`cut and folded up at the edges to form a tray-form member.
`
`20
`
`Figure 8 shows a finite element analysis view of the unit of Figure 7.
`
`Figure 9 shows parts of an inductive power transfer unit 400 according to a third
`
`embodiment of the present invention. In this embodiment a flux generating unit 50,
`
`25
`
`similar to the flux generating units described with reference to the first and second
`
`embodiments, is contained in a casing 410 of the unit 400. An upper surface of the
`
`casing 410 provides the power transfer surface in this embodiment, and a secondary
`device 60 is placed directly on the surface to receive power inductively from the flux
`generating unit 50.
`
`30
`
`In each of the four side walls of the casing 410 a small circular recess 420 is formed.
`
`Momentum Dynamics Corporation
`Exhibit 1009
`Page 011
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`

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`W O 2005/024865
`
`PCT/GB2004/003844
`
`In this embodiment the flux shield 90 is an accessory which is adapted to be attached
`
`to the outside of the inductive power transfer unit 400. The flux shield 90, which is
`
`similar in form to the flux shield 80 shown in._Figure 7, has circular projections 95
`
`formed on the inner surfaces-of the upstanding side walls of the flux shield 90. The
`
`5
`
`projections 95 engage respectively with the recesses 420 in the casing of the
`
`inductive power transfer unit 400. In this way, the unit 400 can be inserted into the
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`flux shield 90 due to the resilience of the materials of the flux shield 90 and/or casing
`
`410. The projections and recesses serve to hold the flux shield 90 on the outside of
`
`the unit 400 in such a way that the flux shield shields objects outside the unit,
`
`10
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`adjacent to the external surfaces of the unit, from flux generated by the flux
`
`generating unit 50.
`
`The provision of a removable flux shield has several advantages.
`
`In some
`
`applications, the flux shield is unnecessary. For example, the shield is unnecessary if
`
`15
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`the support surface on which the unit will be placed is non-metallic. In this way, the
`
`unit can be made as small as possible and at the lowest possible cost. Any user who
`
`intends to use the unit on a metallic support surface can purchase the flux shield as
`
`an optional accessory.
`
`20 When the flux shield is in the form of a removable accessory, it is not necessary for
`
`the flux shield to have the form of the first embodiment or second embodiment
`
`described above. For example, the flux shield need not extend outwardly beyond the
`
`edges of the flux generating unit 50; it could be coterminous with the planar area of
`
`the flux generating unit 50 or even smaller than the planar area thereof. For example,
`
`25
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`a flat sheet-form conductive shield could be built into the base of a tray-form plastics
`
`housing of the accessory.
`
`Any suitable way of attaching the flux shield to the outside of the inductive power
`
`transfer unit may be used. Although snap-fitting is particularly convenient, the flux
`
`30
`
`shield may be attached to the unit using screws or Velcro ®. Equally, there could
`
`simply be a tight fit between the flux shield and the casing of the unit.
`
`11
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`Momentum Dynamics Corporation
`Exhibit 1009
`Page 012
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`

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`W O 2005/024865
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`PCT/GB2004/003844
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`By way of example only, there now follows a set of test results for embodiments of
`this invention. In the test set up the flux generating unit 50 measured approximately
`175x125x9mm. The flux shield 70 or 80 was_ made .from a 0.6mm thick sheet of
`copper. The metal desk 200 -was a sheet of metal 500mm x 500mm x 0.6mm thick
`(magnetically, this is effectively an infinite plane).
`
`The cunent through the flux generating unit 50 was adjusted so that the power
`delivered to a secondary device 60 was the same at the start of each test. A control
`loop then held the cunent constant during the rest of each test.
`
`The power received by the secondary device was monitored and the extra power
`drawn from the charger was monitored.
`
`The results were as follows:
`
`Test Condition
`
`Power seen by Extra power
`secondary
`needed from
`device charger
`
`1 a. No flux shield
`
`
`1 b. As 1 a with steel under
`
`1 00%
`
`123%
`
`ow
`
`1 1 W
`
`5
`
`10
`
`15
`
`2a. Flux shield sheet (Figure 5 ) immediately under 1 00%
`
`
`
`maqnetic assembly
`
`
`
`2b. Flux shield moved 4mm from assembly 1 00%
`
`2c. As 2b with steel under
`
`1 10%
`
`1 .5W
`
`0.7W
`
`4.6W
`
`3a. Flux shield box (Figure ?)around bottom and
`
`
`
`edges ( 4mm gap )
`3b. As 3a with steel under
`
`1 00%
`
`1 .5W
`
`108%
`
`2.2W
`
`20
`
`25
`
`Test 1 shows the case without any flux shield. The flux lines will initially be
`approximately as shown in Figure 3. Introducing a metal sheet under the assembly
`causes the flux to travel down and through the sheet, in preference to travelling up
`and over the top, as shown in Figure 4. The control loop in the generator is forced to
`expend 11 W to keep its coil current constant, which is not optimal since it is
`inefficient and will cause the metal to warm up. In addition, the secondary device
`sees a rise in the power it receives to 123%, because eddy currents in the metal desk
`do act as a poor flux excluder even as they consume large amounts of generator
`
`12
`
`Momentum Dynamics Corporation
`Exhibit 1009
`Page 013
`
`

`

`W O 2005/024865
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`PCT/GB2004/003844
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`power - and this is not optimal either.
`
`Test 2 shows the case with a flat flux shiel�ing sheet underneath as in the first
`
`embodiment. A large (190mm. x 140mm x 0.6mm) copper sheet flux shield
`
`5
`
`immediately under the magnetic assembly (test 2a) causes the generator to have to
`
`supply an additional 1.5W, presumably because it starts to short the coil turns in the
`
`assembly. Moving this 41mn away from the assembly (i.e. d = 4mm in Figure 5)
`reduces this drain to 0.7W (test 2b). Now introducing a metal sheet only causes the
`
`generator to have to supply 4.6W (i.e. an additional 3.9W), and the power into the
`
`10
`
`secondary device now only changes to 110% (test 2c). This is shown in Figure 6. So
`
`the flux shield has reduced each of the two side-effects by more than half.
`
`Test 3 shows the case where the edges of the flux shield are brought up around the
`
`edges of the magnetic assembly, as in the second embodiment shown in Figure 7.
`
`15 The shield is kept 4mm away from the magnetic assembly on all sides (test 3a) to
`
`avoid the phenomenon seen in Test 2a. The generator must supply an additional
`
`1.5W to overcome the losses of the eddy currents in the shield. Now introducing a
`
`metal sheet (test 3b) only causes the generator to have to supply an extra 2.2W (i.e.
`
`an additional 0.7W), and the power seen by the secondary device now only changes
`
`20
`
`to 108%.
`
`In conclusion, these test results clearly demonstrate the two key advantages of a flux
`
`shield in reducing the side effects of metal objects: less power delivered into the steel
`by the generator, and less variation in the power seen by the secondary device.
`
`25
`
`30
`
`A shield extending completely around the magnetic assembly, except over the
`desired power transfer surface, can reduce the effect of metal desks on the generator
`by more than an order of magnitude, and on the secondary device by more than