twelve inches or about six inches to about two feet additionally core 32 may have a width of about half an inch to about three inches about one inch to about four inches about two inches to about six inches or about six inches to about twelve inches core 32 may be separated from receiver windings 36 by separation material 34 in embodiments transmitter coils 22 disposed within sonde 14 may be energized simultaneously but with different polarization in embodiments transmitter coils 22 may be manufactured to be identical structures which may allow for the detection of defects and pipe wall thickness within pipe 4 easier as further illustrated in fig3 embodiments include separation material 34 which may completely enclose the outer surface of core 32 in some embodiments not shown separation material 34 may only enclose the sides 39 of core 32 separation material 34 may be made of any suitable material to substantially prevent the transfer of electricity from receiver windings 36 to core 32 suitable separation material 34 may be but is not limited to fabric glass polymer clay and or any combination thereof in embodiments receiver windings 36 may wind around core 32 any suitable number of times and may further be any suitable gauge of wire receiver windings 36 may.