SAW-based radio sensor systems

TLDR

Surface acoustic wave devices act as power‑free, wireless transponders capable of measuring temperature, pressure, torque, acceleration, humidity, and other physical quantities, and together with a local radar transceiver form a complete sensor system whose high delay times typically prevent intersymbol interference. This review examines the operating principles and state‑of‑the‑art performance of such SAW‑based wireless sensor systems, illustrating examples of temperature, pressure, torque, acceleration, tire‑road friction, magnetic field, and soil water content measurements. The system operates by transmitting an RF burst from a radar transceiver to the SAW transponder, which echoes back an RF signal whose amplitude, frequency, phase, and arrival time encode the sensor measurement. Index terms include acceleration, local radar transceiver, magnetic field, passive SAW transponder for sensing, pressure, temperature, tire‑road friction, torque, water content of soil, and wireless measurement.

Abstract

Surface acoustic wave (SAW) devices can be used as identification and sensor elements (SAW transponders) for mea- suring physical quantities such as temperature, pressure, torque, acceleration, humidity, etc., that do not need any power supply and may be accessed wirelessly. The complete wireless sensor system consists of such a SAW transponder and a local radar transceiver. An RF burst transmitted by the radar transceiver is received by the antenna of the SAW transponder. The passive transponder responds with an RF signal—like a radar echo—which can be received by the front-end of the local transceiver. Amplitude, frequency, phase and time of arrival of this RF response signal carry information about the SAW reflection and propagation mechanisms which in many cases can be directly attributed to the sensor effect for a certain measurand. Usually no intersymbol interference (ISI) due to environmental echoes occur, due to the high delay time of the SAW transponder in the order of some s. The present work reviews the operating principles of such sensor systems and their state-of-the-art performance by way of some examples which include the wireless measurement of temperature, pressure, torque, acceleration, tire-road friction, magnetic field, and water content of soil. Index Terms—Acceleration, local radar transceiver, magnetic field, passive SAW transponder for sensing, pressure, temper- ature, tire-road friction, torque, water content of soil, wireless measurement.