P4J-1 Design Parameters for SAW Multi-Tone Frequency Coded Reflectors

The purpose of this work is to study multi-tone frequency coded reflectors which can provide lower loss, higher reflectivity, chip reflector orthogonality and greater code diversity than the previously published orthogonal frequency coded (OFC) SAW devices [1]. Multiple frequencies are used to spread the signal bandwidth, and act as an identification for a given tag or sensor and to provide signal processing gain. These attributes make this approach very useful in a multi-sensor environment allowing for better coding and lower loss SAW tags and sensors. The use of long reflector banks increases reflectivity and decreases the tag insertion loss; however, this also results in a time response that is much longer than the nominal chip grating time length. With the use of longer gratings the inter-symbol interference is increased thus resulting in distortion of adjacent frequency reflector responses. The multi-tone frequencies presented here, reduce the inter-symbol interference for long reflectors by design, such that the nulls of adjacent chip frequencies coincide. The chip lengths can be modulated to adjust for the decreased transition bandwidths thus resulting in pulse width modulation within the bit. In this paper the optimization of tag design parameters, such as number of electrodes in each reflector chip, reflectivity per strip, tag bandwidth, chip orthogonality conditions and correlation properties will be discussed.