Active tag for object sensing
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Abstract
A combined passive and active object sensing system (30; 50; 70) employing electric field sensing is described. An electric field sensing transmission electrode (2) generates a first electric field (11, 12, 13) that induces a current in an electric field sensing reception electrode (4). A passive object (10) is sensed from variation in this current. An active object (31; 51; 71) comprises a further electric field sensing transmission electrode (33; 53; 73) and generates a second electric field (35, 36, 37; 55, 56, 57; 75, 76, 77). This may be generated by the active object (31) coupling with and applying a phase shift to the first electric field (11, 12, 13). Alternatively the second electric field (55, 56, 57) may be generated at a different frequency to the first electric field (11, 12, 13). Alternatively the second electric field (75, 76, 77) may be generated by the active object (71) coupling with an alternating magnetic field generated by a coil (172). The second electric field (35, 36, 37; 55, 56, 57; 75, 76, 77) induces a current in the electric field sensing reception electrode (4) that varies with the position of the active object (31; 51; 71). The separate currents are distinguished by virtue of their different phase or frequency.
31 Citations
9 Claims
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1-5. -5. (Canceled)
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6. An active tag, comprising:
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an electric field sensing transmission electrode;
a reception electrode for coupling with a first electric field to generate a received signal;
means for applying a phase shift to the received signal; and
means for driving the electric field sensing transmission electrode with the phase shifted signal so as to generate a second electric field. - View Dependent Claims (7)
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8. A set of active tags, each tag comprising:
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an electric field sensing transmission electrode; and
means for driving the electric field sensing transmission electrode so as to generate an electric field of a given frequency for each tag;
wherein the given frequency for each of at least some of the tags is different.
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9-18. -18. (Canceled)
Specification