A novel identification method of multiple OFC SAW sensor tags

In order to identify more surface acoustic wave (SAW) sensor tags simultaneously, the characteristics of superposed signals reflected from multiple orthogonal frequency coded (OFC) SAW tags are analyzed. Although these signals arriving at a reader are asynchronous, the different central frequency signals still keep orthogonal in an appropriate time window range as long as all tags are within a certain distance. The amplitudes and phases of the superposed signals with same central frequency from the identical reflector positions of different sensor tags can be measured. The matrix relational expression between the measurable values and the amplitudes, delay of signals from each tag is found out. Then, tags identification is converted into solving this equation. The relation between the maximum number of simultaneous identifiable tags and the number of optional central frequencies of reflectors is obtained with the assumption that all reflected signals arrive at a reader synchronically. The simultaneous identifiable OFC SAW tags set is selected with the above assumption. It is explained that the selected tags set can also be identified simultaneously on condition that reflected signals arrive at a reader asynchronously. The above theoretical analysis is verified by iterative method in MATLAB software.