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An electromagnetic device has a stator and a rotor rotating between facing surfaces of the stator and bearing a plurality of magnets distributed at regular intervals along its periphery. The magnets are so arranged that they form a sequence of alternately opposite poles on the surfaces of the rotor

An electromagnetic device has a stator and a rotor rotating between facing surfaces of the stator and bearing a plurality of magnets distributed at regular intervals along its periphery. The magnets are so arranged that they form a sequence of alternately opposite poles on the surfaces of the rotor directed towards the stator, and the stator comprises two sets of independently supported magnetic yokes located at both sides of the rotor in front of the magnets. The magnetic yokes have two axially oriented arms, the end surfaces of which, in static conditions of the rotor, at least partly face a pair of successive magnets on a same surface of the rotor.

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1. An electromagnetic device with reversible generator-motor operation, the device comprising: a rotor rotating about an axis and bearing a plurality of magnets distributed at regular intervals there around and with alternate orientations in a substantially ring-shaped pattern;a stator comprising at

1. An electromagnetic device with reversible generator-motor operation, the device comprising: a rotor rotating about an axis and bearing a plurality of magnets distributed at regular intervals there around and with alternate orientations in a substantially ring-shaped pattern;a stator comprising at least one set of individual magnetic yokes each having a pair of projecting arms that extend towards the magnets and bear a respective coil for electrical connection to a utilising device or a power driver, a magnetic yoke in each set being part together with a pair of magnets confronting the yoke arms at a given instant, and an air gap separating the yoke from the magnets, of a same closed magnetic circuit; the individual magnetic yokes being independently mounted on supports that are adjustable by a mechanism under the control of an electronic control unit to dynamically adjust the positions of the individual magnetic yokes relative to the magnets during operation of the device. 2. The device as claimed in claim 1, wherein said supports are axially adjustable through a translational movement. 3. The device as claimed in claim 1, wherein said supports are further adjustable through a pivotal movement about at least one axis. 4. The device as claimed in claim 3, wherein said supports are adjustable through a pivotal movement about three axes. 5. The device as claimed in claim 1, wherein said stator includes a single set of individual magnetic yokes. 6. The device as claimed in claim 5, wherein said rotor is made of ferromagnetic material, and said magnetic circuit comprises a pair of magnets and one yoke facing the magnet pair and it is closed through the rotor and the air gap separates the yoke from the magnets. 7. The device as claimed in claim 5, wherein said rotor (12; 12′), in areas not occupied by the magnets (14; 14′; 14′a, 14′b; 140), is made of non-ferromagnetic material, the magnets (14; 14′; 14′a, 14′b; 140) facing a same yoke are connected by ferromagnetic elements (61), and said magnetic circuit comprises a pair of magnets (14; 14′; 14′a, 14′b; 140) and one yoke (16; 16′) facing the magnet pair, and it is closed through the ferromagnetic elements (61) and an air gap separating the yoke from the magnets. 8. The device as claimed in claim 2, wherein said magnets are glued onto the surface of the rotor facing the yokes. 9. The device as claimed in claim 1, wherein: said rotor (12, 12′), in areas not occupied by the magnets (14; 14′; 14′a, 14′b; 140), is made of non-ferromagnetic material; said stator (16, 20a, 20b, 18, 22a, 22b; 16′, 18′, 20′, 22′) includes a first and a second set of magnetic yokes (16, 18; 16′, 18′; 6) symmetrically arranged relative to the rotor (12, 12′), and said magnetic circuit comprises a pair of adjacent magnets (14; 14′; 14a, 14b; 140) and one magnetic yoke (16, 18; 16′, 18′; 6) in each of the first and the second set. 10. The device as claimed in claim 1, wherein said magnets are magnetised areas in the rotor and they form a succession of alternately opposite poles onto the rotor surfaces facing the individual magnetic yokes. 11. The device as claimed in claim 1, wherein said individual magnetic yokes are arranged in front of one arc or of a number of discrete arcs of magnets in the magnet ring. 12. The device as claimed in claim 1, wherein said individual magnetic yokes are distributed in front of the whole magnet ring. 13. The device as claimed in claim 12, wherein said rotor bears a number M of magnets chosen out of: 2N, N being the number of the magnetic yokes in the or each set;an even number different from 2N. 14. The device as claimed in claim 1, wherein the coil of each yoke arm is individually connected to a utilising device or a power driver. 15. The device as claimed in claim 13, wherein the coils of the yoke arms having a same geometrical phase relationship with a confronting magnet are connected together inside the device and have a common connection to a utilising device or a power driver. 16. The device as claimed in claim 13, wherein the coils of alternate yoke arms having a same geometrical phase relationship with a confronting magnet are connected together inside the device and have respective common connections with opposite phases to a utilising device or a power driver. 17. The device as claimed in claim 14, wherein the coils of at least some yoke arms are connected to a utilising device, and the coils of at least some other arms are connected to a power driver. 18. The device as claimed in claim 1, wherein said individual magnetic yokes bear a first coil for electrical connection to a utilising device or a power driver, and a second coil acting as a feedback detector. 19. The device as claimed in claim 1, wherein said rotor (12′) is a cylindrical body bearing the plurality of magnets (14′a, 14′b) on its side surface and the plurality of magnets are arranged in two parallel rows (14′a, 14′b) on said side surface, a magnet in one row having opposite orientation to an adjacent magnet in the other row and each yoke (16′) being arranged so as to bridge both rows of magnets (14′a, 14′b). 20. The device as claimed in claim 19, wherein each yoke (16′) and the respective pair of magnets (14′a, 14′b) bridged by it are obliquely arranged with respect to the generatrices of the rotor (12′). 21. The device as claimed in claim 1, wherein said arms (17a, 17b, 19a, 19b; 7) and said magnets (14; 14′; 14′a, 14′b; 140) have a cross sectional shape chosen out of the group including: circular cross section; non-circular curvilinear cross section; concave polygonal cross section; convex polygonal cross section, in particular square or rectangular; and wherein facing areas of the magnets (14; 14′; 14′a, 14′b; 140) and the arms (17a, 17b, 19a, 19b; 7) have similar sizes. 22. The device as claimed in claim 21, wherein said yoke arms and said magnets have different cross-sectional shapes. 23. The device as claimed in claim 1, wherein said magnets are magnetic bodies (140) having a shape chosen out of: wedge shape;a polyhedral shape with quadrangular bases connected by inclined side faces, the inclinations of the two pairs of opposite side faces being such that they produce an opposite tapering of the plate;frusto-conical shape. 24. The device as claimed in claim 23, wherein adjacent magnets (140) have located therebetween tapered retaining members having a complementary tapering to that defined by confronting surfaces of said adjacent magnets (140). 25. The device as claimed in claim 23, wherein adjacent magnets (140) have located therebetween tangentially operating resilient or elastomeric retaining members (60). 26. The device as claimed in claim 1, wherein each yoke arm (7) includes a base (7c) for being secured to a support, a stem (7b) extending from the base (7c) towards the magnets (14′; 140) and having the coil (21) wound thereon, and a head (7a) joined to the stem end opposite to the base (7c), and wherein said head has a greater cross sectional size than the overall cross sectional size of the stem (7b) and the coil (21) and is arranged to hide the coil (21) to a confronting magnet (14′; 140). 27. The device as claimed in claim 26, wherein each yoke (6) comprises a pair of individually mounted arms (7) defining an angle open towards the magnets (14′; 140), and wherein a gap (77) is provided between the bases (7c) of two adjacent arms (7) respectively belonging to two adjacent jokes (6). 28. The device as claimed in claim 1, wherein said yoke arms (17a, 17b, 19a, 19b) are connected by a member having a length equal to the transversal size of the arm, and facing sides of adjacent arms in adjacent yokes (16, 18; 16′, 18′) are spaced apart by a distance equal to the transversal size of the arm. 29. The device as claimed in claim 1, wherein said individual magnetic yokes are made of a material chosen out of the group: high permeability, low residual flux and low magnetic reluctance ferrites; iron-silicon sheet; Ni—Zn or Mn—Zn ferrites; Mn—Ni materials. 30. The device as claimed in claim 1, wherein the supports of the individual magnetic yokes are equipped with rolling members arranged to cooperate with the rotor surface to keep the air gaps between the individual magnetic yokes and the magnets constant and to compensate for axial and radial oscillations of the rotor. 31. The device as claimed in claim 1, wherein the individual magnetic yokes are associated with temperature detectors and position detectors connected with processing and control circuitry of said electronic control unit arranged to actuate displacement means on the supports to vary the air gap and/or the degree of overlapping between the magnets and the confronting arms in order to vary the concatenated voltage in the individual coils in response to the detected temperature and/or position. 32. The device as claimed in claim 30, wherein the individual magnetic yokes together with their coils, their supports, support and adjusting units for the rolling members, the detectors and the control and processing circuitry are embedded within a resin layer, possibly charged with powder materials increasing thermal conductivity. 33. The device as claimed in claim 32, wherein said resin layer is provided with heat dissipating members. 34. The device as claimed in claim 1, wherein said device (10) is integrated in an impeller of an apparatus driven by the motion of a fluid. 35. An apparatus having an impeller driven by the motion of a fluid, characterised in that said impeller has integrated therein a device (10) as claimed in claim 1. 36. The apparatus as claimed in claim 35, wherein said apparatus is chosen out of the group including: turbines, in particular for aeronautical or naval engines, screws of propellers for aeronautical or naval applications, pumps for gas pipelines, Aeolian generators. 37. The device as claimed in claim 1, wherein the electronic control unit includes signal processing and control circuits for receiving signals from position detectors provided within the individual magnetic yoke mounting supports to thereby control the dynamic adjustment of the position of individual magnetic yokes.