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AC magnetic tracking with phase disambiguation

  • US 20090076746A1
  • Filed: 09/10/2008
  • Published: 03/19/2009
  • Est. Priority Date: 09/14/2007
  • Status: Active Grant
First Claim
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1. A magnetic locating system comprising:

  • (a) a transmitter including;

    (i) a plurality of co-located orthogonal transmit coils;

    (ii) a transmitting circuit operable to actuate the coils in alternating sequence so that the coils will emit a time-multiplexed sequence of magnetic fields MB during successive intervals of the sequence, where the subscript B denotes one of the transmit coils, each magnetic field varying at a carrier frequency f, such magnetic fields having a known phase relationship with one another; and

    (b) a receiver including;

    (i) a plurality of orthogonal sensor coils, whereby, when the sensor coils are exposed to the sequence of magnetic fields from the transmit coils, each sensor coil will generate a sensor signal during each transmit interval of the time-multiplexed sequence used by the transmitter;

    (ii) a receiver circuit operative to derive a set of components CAB at frequency f from the sensor signals, wherein the subscript A denotes the particular receiving coil which received such components and the subscript B denotes the transmitter coil active during the transmit interval, each such component CAB having amplitude and phase, the phases of the components being referenced to phase reference times, the phase reference times used in successive transmit intervals being offset from one another by known amounts; and

    (iii) a computation circuit operative to form a matrix of the signal components CAB with each row having the same value of A and each column having the same value of B, compute the determinant of the matrix and;

    (1) if the determinant is positive, calculate the position and orientation of the sensor coils relative to the transmit coils based upon the signal components CAB; and

    (2) if the determinant is negative, derive inverted signal components C′

    AB corresponding to the signal components CAB phase-shifted by π

    radians, and calculate the position and orientation of the sensor coils relative to the transmit coils based upon the inverted signal components.

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