Ultra-wide-band SAW sensors and tags

Abstract

SAW tags and sensors often operate in 2.45 GHz ISM band using relatively narrow frequency Band = 82.5 MHz available there. The characteristics of these devices can be improved using the ultra wide band (UWB) technology. We have developed prototype devices operating in 200 MHz-400 MHz and 2000 MHz -2500 MHz UWB frequency ranges. The UWB reader operating in continuous wave radar mode for 2 GHz range was developed and manufactured. The first remote measurements have shown that we get compressed RF pulses of about 2 ns duration, which include unique RF filing of a few sinusoids with amplitude modulation. The precise measurement of the pulse position is possible by correlation methods, avoiding the phase ambiguity problem.The temperature is measured with a precisions of about 0.1 • C degree Celsius. Only 2 reflectors are necessary for such a sensor. The correlation method works even in multi-path environment with strong reflections form metal objects. The short compressed pulses allow measuring a number of sensors simultaneously just separating them in time. For tag application, we measure and identify three different tags at the same time without collision problem, this number can easily be increased. For such limited number of tags there is no "collision" problem.

Chipless RFID tags and sensors: a review on time-domain techniques

“…As the frequency bandwidth is one of the key parameters in identifying the coding capacity according to Shannon's equation [54], increasing the bandwidth leads to time decrease. For example, a bandwidth of 400 MHz in UWB technology instead of 80 MHz in 2.45 GHz ISM band will reduce the coding duration to hundreds of ns instead of few ms [66]. Additionally, by designing a chirp transducer it is possible to compress the incoming pulse and retransmit it in the timereverse situation of the interrogation signal.…”