Embedded Passive RF Tags towards Intrinsically Locatable Buried Plastic Materials

This paper demonstrates the use of passive harmonic tags (transponder) as markers for buried plastic pipes. The tag design is based on a double slot antenna that can be buried in the plastic pipes during manufacturing. Design and measurement results are presented for two tag designs: one with a metal backing and one without. The tags are embedded in a plastic casing representing the walls of the plastic pipes. The tag operates at a fundamental frequency (fo) of 2.5 GHz with a return signal (2fo) of 5 GHz. Use of harmonic tags eliminates the clutter from the surface of the ground and thus enhances signal to noise (S/N) ratio of the return signal without the use of filters. The antenna is linearly polarized and polarization can be used as a marker for the direction of the buried pipes. The tag design is compact and can also readily be interrogated using simple hand-held radar units.