A field (e.g., a magnetic field) which nutates about a pointing vector is used to both track or locate an object in addition to determining the relative orientation of this object. Apparatus for generating such a field includes mutually orthogonal coils and circuitry for supplying an unmodulated carrier,...http://www.google.com/patents/US4017858?utm_source=gb-gplus-sharePatent US4017858 - Apparatus for generating a nutating electromagnetic field
