A magnetic field generating assembly, configured to be associated with a table supporting a body, the assembly comprising: a plurality of elongate conductive elements arranged in a first plane, wherein each conductive element winds in a spiral around a central axis thereof for forming a coil having a first layer and a second layer lying in separate planes, each central axis extending perpendicular to the first plane, each successive turn of the spiral being located at an increased distance from the central axis to an outer periphery of the conductive element; wherein the plurality of conductive elements forms the first layer of the assembly, the first layer lies in the first plane, the plurality of conductive elements further forms the second layer of the assembly, and the second layer lies in a second plane; wherein for each conductive element, the first layer comprises a first inner perimeter and a first outer perimeter, the first outer perimeter defining a first exit point of the conductive element; wherein, for each conductive element, the second layer comprises a second inner perimeter and a second outer perimeter, the second outer perimeter defining a second exit point of the conductive element; and wherein the first exit point and the second exit point are adjacent to each other, so that a single thread of the conductive element begins at the first exit point and forms the first layer, then at the center begins the second layer retracing the path of the first layer, and finally ends at the second exit point, wherein the first and second layers spun in the same direction so as to transmit the magnetic field in a single direction. a plurality of elongate conductive elements arranged in a first plane, wherein each conductive element winds in a spiral around a central axis thereof for forming a coil having a first layer and a second layer lying in separate planes, each central axis extending perpendicular to the first plane, each successive turn of the spiral being located at an increased distance from the central axis to an outer periphery of the conductive element; wherein the plurality of conductive elements forms the first layer of the assembly, the first layer lies in the first plane, the plurality of conductive elements further forms the second layer of the assembly, and the second layer lies in a second plane; wherein for each conductive element, the first layer comprises a first inner perimeter and a first outer perimeter, the first outer perimeter defining a first exit point of the conductive element; wherein, for each conductive element, the second layer comprises a second inner perimeter and a second outer perimeter, the second outer perimeter defining a second exit point of the conductive element; and wherein the first exit point and the second exit point are adjacent to each other, so that a single thread of the conductive element begins at the first exit point and forms the first layer, then at the center begins the second layer retracing the path of the first layer, and finally ends at the second exit point, wherein the first and second layers spun in the same direction so as to transmit the magnetic field in a single direction.