A three-dimensional magnet structure (6) made up of a plurality of individual magnets (4), the magnet structure (6) having a thickness that forms its smallest dimension, the magnet structure (6) incorporating at least one mesh (5a) exhibiting mesh cells each one delimiting a housing (5) for a respective individual magnet (4), each housing (5) having internal dimensions just large enough to allow an individual magnet (4) to be inserted into it, the mesh cells being made from a fibre-reinforced insulating material, characterized in that a space is left between the housing (5) and the individual magnet (4), which space is filled with a fibre-reinforced resin, the magnet structure (6) comprising a non-conducting composite layer coating the individual magnets (4) and the mesh structure (5a).