Patent ID: 6750771
Filing Date: 2004-06-15
Classification: G06K

Abstract:
A method of reading an identifier of a tag being conveyed by a conveyor, the tag having an antenna having any orientation in the plane of the conveyor, comprising the steps of:generating a first circularly polarized field having a first rotation and a null; generating a second circularly polarized field having a second rotation opposite the first rotation and a peak, the peak of the second field covering the null of the first field; powering the tag with the first or second field responsive to the first or second field aligning with the orientation of the tag's antenna, wherein the powered tag changes a load on the tag's antenna responsive to data stored in the tag; detecting impedance changes caused responsive to the load on the tag's antenna; determining the tag's identifier responsive to the detected impedance changes: and wherein there are a plurality of first fields and a plurality of second fields, the first fields are generated by a first linear array of antennas, the second fields are generated by a second linear array of antennas, adjacent antennas in the first and second arrays generate fields having opposite rotation, and the first and second linear arrays are linearly interleaved such that the peaks of the second fields cover the nulls of the first fields.