Formation resistivity measurement while drilling, utilizing physical conditions representative of the signals from a toroidal coil located adjacent the drilling bit

Claim 1

A RESISTIVITY LOGGING SYSTEM WHICH COMPRISES THE COMBINATION OF: (A) A DRILL COLLAR ADAPTED TO RECEIVE A DRILL BIT AT THE LOWER END THEREOF FOR CONTACT WITH BOTTOM HOLE FORMATIONS, (B) A FIRST TOROID ENCIRCLING SAID DRILL COLLAR IMMEDIATELY ADJACENT TO SAID BIT, (C) A SECOND TOROID ENCIRCLING SAID DRILL COLLAR AT A POINT SPACED FROM SAID FIRST TOROID, (D) MEANS FOR ENERGIZING SAID SECOND TOROID WITH ALTERNATING CURRENT AT A PREDETERMINED LEVEL FOR THE PRODUCTION OF CURRENT FLOW THROUGH SAID DRILL COLLAR SAID FIRST TOROID AND SAID BIT INTO SAID FORMATIONS AT THE BIT-FORMATION CONTACT, (E) GENERATING MEANS IN SAID DRILL COLLAR FOR PRODUCING PRESSURE PULSATIONS IN THE DRILLING FLUID FLOWING TO SAID FORMATION THROUGH SAID BIT FOR TRANSMISSION TO THE EARTH''S SURFACE, AND (F) MEANS COUPLED TO SAID FIRST TOROID FOR ENERGIZING SAID GENERATING MEANS AT A RATE PROPORTIONAL TO THE MAGNITUDE OF SAID CURRENT FLOWING THROUGH SAID BITFORMATION CONTACT.