Patent ID: 8358134

Claim:
A marker comprising: a radio receiver having a coil antenna comprising at least two coils electrically connected in series; the radio receiver wherein each coil of the at least two coils comprises a conductor coiled around a central axis to define a coil length extending axially and a coil diameter extending radially; the radio receiver wherein the central axis of one coil of the at least two coils is radially spaced from and parallel to the central axes of all other coils of the at least two coils; and first and second flux detection systems, each comprising a flux sensor, a first flux concentrator positioned on one side of the flux concentrator, and a second flux concentrator positioned on the opposite side of the flux sensor, the first and second flux concentrators formed of magnetically permeable material, the first and second flux concentrators each having a proximal edge and a distal edge, the distal edge being longer than the proximal edge, the first and second flux concentrators each curving and tapering as it extends from the distal edge to the proximal edge, and the first and second flux concentrators each being positioned with respect to the flux sensor such that the proximal edge is positioned directly adjacent the flux sensor.