A stroboscopic approach to surface acoustic wave delay line interrogation

A pulsed RADAR approach is investigated to probe acoustic delay lines used as passive sensors. In order to comply with the requirements of compact, low power receiver electronics, a stroboscopic equivalent time sampling approach is demonstrated. A strategy for generating high resolution time delays while allowing for long interrogation durations (up to 5 μs) is implemented by combining an FPGA-based delay generator with commercially available programmable digital delay lines. The measurement sequence of generating interleaved combs is due to the long delay line reconfiguration duration (SPI communication) with respect to the coarse comb (FPGA based counter). The response of the sensor is recorded and processed to acquire the coarse acoustic velocity information through magnitude measurement, and an accurate physical quantity estimate is computed thanks to the phase information. We demonstrate an improved software measurement strategy which prevents the slow process associated with a stroboscopic approach and allows to reach refresh rates of up to 20 kHz when probing an acoustic tag for a physical property measurement, while keeping the hardware to a bare minimum.