Radio frequency identification (RFID) technology has been used in a variety of applications such as tracking, security, transportation, retailing, industrial, and individual identification. Data communication via RFID technology may be used for detecting the presence of an object, identifying the object, or obtaining data associated with the object. In an RFID system, an RFID tag is attached to an object and communicates wirelessly with an RFID reader. The RFID reader typically drives a plurality of RF antennas to detect and identify RFID tags at different locations.
In passive RFID systems, the antenna of the RFID reader emits RF signals to activate passive RFID tags within a reading range. Once activated by the RF energy, the passive RFID tags are configured to transmit a responding signal to the RFID reader. The RFID tag obtains its energy through electromagnetic induction with the EM field generated by the RF antenna, and the communication range of the RFID tag is dependent on the intensity of the EM field. For an RF antenna in the shape of a square, since the electromagnetic wave radiates less effectively around its four corners, the intensity of the EM field is weak around the corners, and thus the RFID tag will be difficult to be detected and identified if it is placed in close proximity to any corners of the RF antenna.
Therefore, for an RF antenna array with multiple antennas, a “blind spot” is formed as a result at the area encompassing borders of multiple RF antennas in the array. The blind spot refers to an area on the surface of the RF antenna array, where an RFID tag fails to be detected. At the same time, an RFID tag placed elsewhere outside the blind spot within the effective communication range of the RF antenna array is detectable to the antenna array. Practically, there is usually a distance between the surface where the RFID tag is placed and the surface of the RF antenna array. Typically the bigger the distance is, the bigger the blind spot is.
The present invention provides to an apparatus and method for eliminating the blind spot in high frequency (13.56 MHz) RF antenna arrays.