Multiple Wireless SAW Interrogators Based on Software-Defined Radios

Multiple SAW sensors working in separate frequency bands can encode multiple measurands in the frequency domain during a single interrogation. In such applications, software-defined radio is the most convenient platform to transceive wideband RF signals and process them in digital mode. This paper introduces a novel SDR platform that can interrogate a large number of resonant SAW sensors simultaneously. These sensors can be distributed in a frequency range from 70 MHz to 6 GHz, with an instantaneous bandwidth of 56 MHz. The 56 MHz wideband excitation signal is transmitted and received without frequency sweeping, so sensors operating at different resonant frequencies can be stimulated simultaneously, which is critical for accurate frequency-based measurement in multi-sensor applications. Five-sensor interrogation is described as an example, with an interrogation period of 15.12 μs. As the transceiver operates in time-division mode, the delay before reception and the listen-window width are designed to be parameter-adjustable to fit diverse applications, thereby improving system performance. The described SDR platform is based on USRP-B210 hardware and GNU Radio software. The USRP-B210 operates at its maximum sampling rate of 61.44 MHz with a bandwidth of 56 MHz. For decay-time-limited resonant sensors, the maximum sampling rate captures the most samples of the response signal, resulting in improved SNR performance.