A magnetic field inductor comprising a first plate of insulating material provided with a first face on which a first trace of electroconductive material is formed, said first trace presenting a spiral shape extending about an axis. A second face of said first plate presents a second trace of electroconductive material, the second trace also presenting a spiral shape extending about an axis, the first and second trace being connected together electrically such that, when a current passes therethrough, the first and second trace generate magnetic fields which are added together on said axis.