METHOD, APPARATUS AND ARTICLE FOR DETECTION OF TRANSPONDER TAGGED OBJECTS, FOR EXAMPLE DURING SURGERY

• US 20080272913A1
• Filed: 05/01/2007
• Published: 11/06/2008
• Est. Priority Date: 05/01/2007
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: RF Surgical Systems, Incorporated (Medtronic Plc)
• Inventors: Blair, William A., Poirier, David A., Barnes, Bruce E.
• Granted Patent: US 7,696,877 B2
• Time in Patent Office: Days
• US Class Current: 340/572.1
• CPC Class Codes: G08B 21/0225 Monitoring making use of different thresholds, e.g. for different alarm levels
• CPC Class Codes: G08B 21/24 Reminder alarms, e.g. anti-loss alarms
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

The presence or absence of objects is determined by interrogating or exciting transponders coupled to the objects using pulsed wide band frequency signals. 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. Match filtering may be employed. 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.

Claims

1. A method of operation of a transponder detection device, the method comprising:

during each of a plurality of detection cycles,

receiving unmodulated electromagnetic signals during a noise detection portion of the detection cycle;

determining a value indicative of a noise level based at least in part on the unmodulated electromagnetic signals received during the noise detection portion of the detection cycle;

adjusting a detection threshold based at least in part on at least one determined value indicative of the noise level;

emitting at least one electromagnetic interrogation signal during a transmit portion of the detection cycle;

receiving unmodulated electromagnetic signals during a receive response portion of the detection cycle that follows the transmit portion of the detection cycle; and

determining the presence or absence of a transponder based at least in part on the unmodulated electromagnetic signals received during the detection cycle and the adjusted detection threshold.

2. The method of claim 1 wherein determining a value indicative of a noise level based at least in part on the unmodulated electromagnetic signals received during the noise detection portion of the detection cycle includes averaging the values indicative of the noise level over each of the detection cycles, and wherein adjusting a detection threshold based at least in part on the determined value indicative of the noise level includes adjusting the detection threshold based at least in part on an average of the values indicative of the noise levels over multiple samples or measurements of at least one of the detection cycles.

3. The method of claim 1 wherein determining a value indicative of a noise level based at least in part on the unmodulated electromagnetic signals received during the noise detection portion of the detection cycle includes averaging a sufficient number of the values indicative of the noise level over each of the detection cycles to provide a signal to noise ratio greater than approximately 1.93, and wherein adjusting a detection threshold based at least in part on the determined value indicative of the noise level includes adjusting the detection threshold based at least in part on an average of the values indicative of the noise levels over multiple samples or measurements of at least one of the detection cycles.

4. The method of claim 1, further comprising:

ignoring any unmodulated electromagnetic signals received during a recovery portion of the detection cycle that precedes the receive response portion of the detection cycle.

5. The method of claim 1, further comprising:

dumping energy from an antenna circuit during a dump portion of the detection cycle that precedes the recovery portion of the detection cycle.

6. The method of claim 1, further comprising:

for each successive pair of detection cycles, varying a time between a start of a first one of the successive pairs of the detection cycles and a start of a next successive one of the pairs of the detection cycles.

7. The method of claim 1 wherein the transmit and the receive response portions each occur during an interrogation portion of the detection cycle, which follows the noise detection portion of the detection cycle.

8. The method of claim 1 wherein emitting at least one electromagnetic interrogation signal during a transmit portion of the detection cycle includes emitting at least one wide band electromagnetic interrogation signal.

9. The method of claim 1 wherein emitting at least one electromagnetic interrogation signal during a transmit portion of the detection cycle includes emitting a first wide band electromagnetic interrogation signal during a first transmit portion of the detection cycle and emitting at least a second wide band electromagnetic interrogation signal during a second transmit portion of the detection cycle.

10. The method of claim 1 wherein emitting at least one electromagnetic interrogation signal during a transmit portion of the detection cycle includes emitting a first wide band electromagnetic interrogation signal centered about a first center frequency during a first transmit portion of the detection cycle and emitting a second wide band electromagnetic interrogation signal centered about a second center frequency during a second transmit portion of the detection cycle, the second center frequency different than the first center frequency.

11. The method of claim 1 wherein emitting at least one electromagnetic interrogation signal during a transmit portion of the detection cycle includes emitting a first wide band electromagnetic interrogation signal centered about a first center frequency and emitting a second wide band electromagnetic interrogation signal centered about the first center frequency.

12. The method of claim 1 wherein adjusting a detection threshold based at least in part on at least one determined value indicative of the noise level includes adjusting the detection threshold based at least in part on a number N of noise measurements or samples, and determining the presence or absence of a transponder based at least in part on the unmodulated electromagnetic signals received during the detection cycle and the adjusted detection threshold includes determining the presence or absence of the transponder based at least in part on a number M of response measurements or samples received an interrogation portion of the detection cycle, wherein a square root of a ratio of M/N is equal or greater than approximately 1.93.

13. The method of claim 1 wherein adjusting a detection threshold based at least in part on at least one determined value indicative of the noise level includes adjusting the detection threshold based at least in part on a number N of noise measurements or samples, and determining the presence or absence of a transponder based at least in part on the unmodulated electromagnetic signals received during the detection cycle and the adjusted detection threshold includes determining the presence or absence of the transponder based at least in part on a number M of response measurements or samples received an interrogation portion of the detection cycle, wherein a square root of a ratio of M/N is equal or greater than approximately 1.1.

14. The method of claim 1 wherein determining the presence or absence of a transponder based at least in part on the received unmodulated electromagnetic signals and the adjusted detection threshold includes match filtering an accumulated response signal with at least one in-phase reference signal and at least one quadrature reference signal to determine a magnitude of the accumulated response signal, where the accumulated response signal is indicative of the unmodulated electromagnetic signals received during the receive response portion of at least two of the detection cycles.

15. The method of claim 1, further comprising:

accumulating the unmodulated electromagnetic signals received during the noise detection portion of at least two of the detection cycles into an accumulated noise signal;

comparing the accumulated noise signal against an ambient noise threshold; and

taking a fault action if the accumulated noise signal exceeds the ambient noise threshold.

16. The method of claim 1, further comprising:

comparing a transmit voltage to a transmit voltage threshold; and

taking a fault action if the transmit voltage is below the transmit voltage threshold.

17. A transponder detection system, comprising:

transmitting means for transmitting electromagnetic interrogation signals during at least one transmit portion of each of a plurality of detection cycles;

receiving means for receiving unmodulated electromagnetic signals during a noise detection portion and a receive response portion of each of the detection cycles;

noise level determination means for determining a noise level during the noise detection portion of the detection cycles, the noise detection portion temporally spaced from the transmit portions such that transponders are not responding to the electromagnetic interrogation signals;

detection threshold adjustment means for adjusting a detection threshold of the transponder detection system based at least in part on at least one value indicative of at least one of the noise levels; and

means for determining the presence or absence of the transponders based at least in part on the received unmodulated electromagnetic signals and the adjusted detection threshold.

18. The transponder detection system of claim 17 wherein the detection threshold adjusting means adjusts the detection threshold based at least in part on at least one of an average or an integration of the determined noise levels over multiple samples or measurements of at least one of the detection cycles.

19. The transponder detection system of claim 17, further comprising:

averaging means for movingly averaging a plurality of the determined noise levels over the plurality of detection cycles, and wherein the detection threshold adjusting means adjusts the detection threshold based at least in part on the determined noise level includes adjusting the detection threshold based at least in part on average of the determined noise levels over multiple samples or measurements of at least one of the detection cycles.

20. The transponder detection system of claim 17, further comprising:

recovery means for ignoring any unmodulated electromagnetic signals received during a recovery portion of the detection cycle that precedes the receive response portion of the detection cycle;

dumping means for dumping energy from an antenna circuit during a dump portion of the detection cycle that precedes the recovery portion of the detection cycle; and

dithering means for varying a time between a start of a first one of the successive pairs of the detection cycles and a start of a next successive one of the pairs of the detection cycles.

21. The transponder detection system of claim 17 wherein the transmitting means includes frequency adjustment means adjusting a center frequency of the electromagnetic interrogation signals between successive transmit portions of the detection cycle.

22. The transponder detection system of claim 17 wherein the nose level determination means captures a number N of noise measurements or samples are captured during the noise detection portion of the detection cycles and wherein the transponder detection system captures a number M of response measurements or samples during an interrogation portion of the detection cycle and a square root of a ratio of M/N is at least equal to approximately 1.93.

23. The transponder detection system of claim 17 wherein the nose level determination means captures a number N of noise measurements or samples are captured during the noise detection portion of the detection cycles and wherein the transponder detection system captures a number M of response measurements or samples during an interrogation portion of the detection cycle and a square root of a ratio of M/N is equal to or greater than approximately 1.1.

24. A transponder detection system, comprising:

a receiver configured to receive unmodulated electromagnetic signals during a noise detection portion and at least one receive response portion of each of a plurality of detection cycles;

a transmitter configured to transmit at least one electromagnetic interrogation signal during at least one transmit portion of each of the detection cycles;

a controller configured to adjust a detection threshold of the transponder detection system based at least in part on at least one determined value indicative of a noise level and to determine whether the unmodulated electromagnetic signals received during the at least one receive response portion of the detection cycles were received from a transponder in response to the electromagnetic interrogation signals based at least in part on the adjusted detection threshold, wherein the controller is configured to employ a number N of noise measurements or samples captured during the noise detection portion of the detection cycles and a number M of response measurements or samples captured during an interrogation portion of the detection cycle, and a square root of a ratio of M/N is at least equal to approximately 1.93.

25. The transponder detection system of claim 24 wherein the controller is further configured adjust the detection threshold based at least in part on an average or an integration of the determined noise levels over multiple samples or measurements of at least one of the detection cycles.

26. The transponder detection system of claim 24 wherein the controller is further configured to movingly average a plurality of determined noise levels over at least two of detection cycles, and to adjust the detection threshold based at least in part on the average of the determined noise levels over multiple samples or measurements of at least one of the detection cycles.

27. The transponder detection system of claim 24 wherein the controller is further configured to determine a noise level value indicative of a noise level based at least in part of the unmodulated electromagnetic signals received during the noise detection portion of the detection cycles.

28. The transponder detection system of claim 24 wherein the controller is further configured to ignore any unmodulated electromagnetic signals received during a recovery portion of the detection cycles that precedes the receive response portion of the detection cycles, and to dump energy from an antenna circuit during a dump portion of the detection cycles that precedes the recovery portion of the detection cycles.

29. The transponder detection system of claim 24 wherein the controller is further configured to vary a time between a start of a first one of a successive pair of the detection cycles and a start of a next successive one of the pair of the detection cycles, for each successive pair of detection cycles.

30. The transponder detection system of claim 24 wherein the controller is further configured to adjust a frequency of the electromagnetic interrogation signals during at least two transmit portions during each of the detection cycles.

32. The transponder detection system of claim 24 wherein the square root of the ratio of M/N is at least equal to approximately 1.1.

33. The transponder detection system of claim 24, further comprising:

an antenna removably coupled to a transmission line to form a low Q tuned LC circuit with the number of switch capacitors.

34. The transponder detection system of claim 24 wherein the controller is further configured to determine a presence or absence of a transponder by match filtering an accumulated response signal with at least one in-phase reference signal and at least one quadrature reference signal to determine a magnitude of the accumulated response signal, where the accumulated response signal is indicative of the unmodulated electromagnetic signals received during the receive response portion of at least two of the detection cycles.

35. The transponder detection system of claim 24 wherein the controller is further configured to accumulate the unmodulated electromagnetic signals received during the noise detection portion of at least two of the detection cycles into an accumulated noise signal, compare the accumulated noise signal against an ambient noise threshold, and take a fault action if the accumulated noise signal exceeds the ambient noise threshold.

36. The transponder detection system of claim 24 wherein the controller is further configured to compare a transmit voltage to a transmit voltage threshold, and take a fault action if the transmit voltage is below the transmit voltage threshold.

31. (canceled)