SHIELDED SOLENOID COIL FOR WELL-LOGGING

A shielded solenoid for use in well logging is disclosed in which a cylindrical or solenoidal coil 44 is provided in a support member 41',41''. A shield 45 is spirally wrapped about the wall of the support member and the coil. The resulting toroidally shaped shield has its individual turns cut 46 so that no complete electrical path exists in each loop of the shield. Each loop of the coil is electrically connected to a ground ring 50. The shielded solenoid is capacitively shielded from the borehole environment. The shielding is effective because the shielding conductors are effectively transparent to TE electromagnetic fields generated by alternating current flow in the cylindrical coil and substantially eliminate TM electromagnetic fields generation by such current flow. Preferably the ground ring 50 is provided with a gap.