SAW RFID with enhanced penetration depth
Some methods to enhance penetration depth further are proposed and demonstrated. A second harmonics SPUDT, new criterion of matching and high reflectivity reflector are utilized to reduce the losses of SAW tag. The enhancement of reading system including high signal processing gain and compensate the center frequency mismatch between reader and SAW tag are achieved. Furthermore, the effect of decreasing working frequency to penetration capability is demonstrated. Mediums such as dry sandy, dry soil and water are compared in the experiments in order to get the achievable penetration depth. In conclusion, the practical penetration depth is superior to the ground penetrating radar with the same center frequency range.
SPUDT filters for the 2.45 GHz ISM band
Filters based on using single-phase, unidirectional transducers (SPUDT) consisting of /spl lambda//4 and wider electrodes are presented. The design variants exploit the significant difference between the reflectivity of short-circuited /spl lambda//4 electrodes and that of floating wide electrodes on 128/spl deg/ lithium niobate (LiNbO/sub 3/). The surface acoustic wave (SAW) devices operating at 2.45 GHz have critical dimensions of about 0.3-0.4 /spl mu/m, accessible to standard optical lithography. When matched, the fabricated SPUDT filters exhibit minimum insertion losses of 5.5-7.9 dB together with 3 dB passbands of 89-102 MHz. The majority of the insertion loss can be attributed to the attenuation on free surface and inside the grating, and to the resistivity of the electrodes.
SAW-RFID enabled temperature sensor
Abstract Wireless sensors based on surface acoustic wave (SAW) technology has its own advantages over its counterparts. In this paper, a novel SAW radio frequency identification (RFID) enabled temperature sensor is proposed for industrial applications, in which short measurement range but high accuracy is usually required. The encoding scheme for the sensor using pulse positions combined with phase information is adopted, and then the relationship between the length of a time slot and the decoding errors is deduced to ensure the sensor can be accurately identified, even though ambient temperature fluctuates. In order to solve the phase ambiguity problem involved in temperature measurements more efficiently and reduce the cost of obtaining the unwrapping temperature characteristic curves in the calibration process, an analytical procedure for calculating the variation of phase delay differences with respect to temperature has been proposed. A self-developed burst transceiver supporting online data analysis is also presented. The experimental results demonstrate the effectiveness and practicality of the proposed SAW-RFID enabled temperature sensing scheme, and the prototype sensor within a temperature-controlled oven 2 m away from the center of the transceiver antenna in a horizontal orientation achieves an accuracy of ±0.3 °C in the temperature range 0–40 °C.