Method, apparatus and article for detection of transponder tagged objects, for example during surgery
The presence or absence of objects is determined by interrogating or exciting transponders coupled to the objects using pulsed wide band frequency signals. Interrogation is broken down into a number of subsample scan cycles each having interrogation cycles a start time forward in time by a fraction of a period of an expected transponder response signal. Ambient or background noise is evaluated and a threshold adjusted based on the level of noise. Adjustment may be based on multiple noise measurements or samples. Noise detection may be limited, with emphasis placed on interrogation to increase the signal to noise ratio. Matched filtering may be employed. Presence/absence determination may take into account frequency and/or Q value to limit false detections. Appropriate acts may be taken if detected noise is out of defined limits of operation, for example shutting down interrogation and/or providing an appropriate indication.
1. A method of operating a transponder detection device that includes at least one processor, at least one nontransitory processor-readable medium communicatively coupled to the at least one processor and which stores at least one of instructions or data executable by the at least one processor, the method comprising:
during each of a number of successive interrogation cycles, the number of successive interrogation cycles being greater than one,
emitting a periodic electromagnetic interrogation signal during a transmit portion of the interrogation cycle;
receiving electromagnetic signals during a receive response portion of the interrogation cycle that follows the transmit portion of the interrogation cycle; and
waiting a respective delay period before a respective start of each of the successive interrogation cycles of the number of interrogation cycles, each respective delay period for the number of interrogation cycles equal to a respective fraction of a nominal tag response signal period, and, for each one of the successive interrogation cycles of the number of interrogation cycles, the respective delay period of the one of the successive interrogation cycles being less than a respective delay period of an immediately subsequent interrogation cycle of the number of successive interrogation cycles by a duration equal to the nominal tag response signal period divided by the number of successive interrogation cycles.
2. A method of operating a transponder detection device that includes at least one processor, at least one nontransitory processor-readable medium communicatively coupled to the at least one processor and which stores at least one of instructions or data executable by the at least one processor, the method comprising:
obtaining a number of subsamples, each of the subsamples associated with a respective delay period equal to a respective fraction of a nominal tag response signal period, the respective fractions different from one another, each of the number of subsamples obtained by:
during each of a plurality of successive interrogation cycles associated with each of the number of subsamples,
emitting a periodic electromagnetic interrogation signal during a transmit portion of the interrogation cycle;
receiving electromagnetic signals during a receive response portion of the interrogation cycle that follows the transmit portion of the interrogation cycle; and
waiting the delay period of the one of the number of subsamples to which the interrogation cycle is associated before a start of each of the successive interrogation cycles of the plurality of interrogation cycles, wherein waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles comprises waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles and, for each successive pair of subsamples, the delay period associated with a first successive one of the pairs of subsamples is less than the delay period associated with a next successive one of the pairs of subsamples by a duration approximately equal to the nominal tag response signal period divided by the number of subsamples.
3. The method of claim 2 wherein waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles comprises waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles, the delay period for each of the number of subsamples between zero seconds and the nominal tag response signal period.
4. The method of claim 2 wherein waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles comprises waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles, the delay period for at least one of the number of subsamples being a duration between the nominal tag response signal period and twice the nominal tag response signal period.
5. The method of claim 2 wherein waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles comprises waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles and, for each successive pair of subsamples, the delay period associated with a first successive one of the pairs of subsamples is less than the delay period associated with a next successive one of the pairs of subsamples.
6. The method of claim 2 wherein waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles comprises waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles, and the delay period associated with each subsample differs from the delay period for the other subsamples by less than the nominal tag response signal period.
7. The method of claim 2 wherein waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles comprises waiting a delay period before a start of each of the successive interrogation cycles of the plurality of interrogation cycles, and the delay period associated with each subsample is approximately an integer multiple of the nominal tag response signal period divided by the number of subsamples.
8. The method of claim 2 , further comprising:
during each of the plurality of interrogation cycles, before the receive response portion of the interrogation cycle, waiting a fixed recovery time after the transmit portion of the interrogation cycle, the fixed recovery time having a duration determined to provide synchronization between the transmit portion and the receive response portion of each interrogation cycle.
9. The method of claim 2 wherein the transponder detection device includes a plurality of antennas, the method further comprising:
obtaining a number of subsamples for each of the plurality of antennas.
10. The method of claim 2 , further comprising:
determining the presence or absence of a transponder based at least in part on a number of measurements of the electromagnetic signals received during the plurality of interrogation cycles of at least one of the number of subsamples.
11. A method of operating a transponder detection device that includes at least one processor, at least one nontransitory processor-readable medium communicatively coupled to the at least one processor and which stores at least one of instructions or data executable by the at least one processor, and one or more antennas, the method comprising:
for each of the one or more antennas,
obtaining a set of subsamples, the set of subsamples comprising a number of subsamples, each of the subsamples associated with a respective delay period equal to a respective fraction of a nominal tag response signal period, the respective fractions different from one another, each of the subsamples in the set of subsamples obtained by:
during each of a plurality of successive interrogation cycles associated with each subsample in the set of subsamples,
emitting a periodic electromagnetic interrogation signal during a transmit portion of the interrogation cycle, the electromagnetic interrogation signal having an interrogation signal frequency;
receiving electromagnetic signals during a receive response portion of the interrogation cycle that follows the transmit portion of the interrogation cycle; and
waiting the respective delay period of the one of the number of subsamples in the set of subsamples to which the interrogation cycle is associated before a start of each of the successive interrogation cycles of the plurality of interrogation cycles, wherein, for each successive pair of subsamples in the set of subsamples, the delay period associated with a successive one of the pairs of subsamples is less than the delay period associated with an immediately next successive one of the pairs of subsamples by a duration equal to the nominal tag response signal period divided by the number of subsamples.