This paper mainly presents the design and fabrication of a TDMA (time division multiple access) passive wireless pressure sensor using 2.45 GHz surface acoustic wave (SAW) delay lines. The SAW pressure sensor consists of two LiNbO3 substrates. The first layer is a pressure-detective thin substrate, on which an interdigital transducer (IDT) and reflectors are fabricated. The second layer is a support substrate, in which a reference pressure cavity is etched. These two substrates are directly bonded. The pressure measurement was successfully demonstrated in a pressure range of 20-280 kPa with good repeatability. In addition, the influence of a tire on the wireless interrogation of the sensor was investigated. Automobile tires have little negative influence on wireless communication, at least if they do not rotate.
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