Patent ID: 7142167

Claim:
A proximity monitoring system capable of accurate detection of a wireless boundary, said proximity monitoring system comprising: a transmitter in electrical communication with a transmitter antenna array including a plurality of antennas, said transmitter antenna array producing a magnetic field, said magnetic field including a digitally modulated magnetic field vector, said digitally modulated magnetic field vector including a plurality of magnetic field components, each of said plurality of magnetic field components being unique and separately identifiable, each of said plurality of magnetic field components respectively produced by a corresponding one of said of plurality of antennas, each of said plurality of antennas having a principal axis direction that is unique and separately identifiable, said transmitter simultaneously exciting each of said plurality of antennas with a plurality of digitally modulated alternating current electrical signals having a common carrier frequency; and a receiver having a receiver antenna array, said receiver responsive to said magnetic field independent of a spatial orientation of said receiver antenna array with respect to said transmitter antenna array, said receiver having a signaling device activation logic circuit responsive to a received magnetic field signal having a received intensity less than a selected threshold value, said selected threshold value corresponding to a selected distance between said transmitter antenna array and said receiver antenna array.