To obtain a coil which emits a low electric field by forming a conductive screen substantially in the same shape as a winding and forming an open loop circuit having a shield zone.

The coil 30 has a metal screen 35, coupled fixedly with a plate 33, on its reverse surface 30-2. The screen 35 is in the same shape as the winding 31 and its position on the reverse surface 30-2 is aligned with the position of the winding 31 on the front 30-1. The screen 35 is shaped in a frame having external dimensions L1 and I1 and internal dimensions L2 and I2. Further, the screen 35 has the shield zone 36 and therefore forms the open loop conductive circuit including two ends 37 and 38 which never meet each other. The screen 35 never disturbs an effective magnetic field B which is directed along the axis and makes ineffective a parasitic electric field radiated by the winding 31. Consequently, a main feature which can be obtained is the shield zone and in the absence of this, the screen 35 forms the open loop circuit to short-circuit the magnetic field B.