Long-distance SAW Sensor Interrogation

Wirelessly interrogated SAW sensors are an attractive option for sensing temperature, chemical environment, pressure, etc. However, the interrogation range in free space is severely limited due to the 1/R
⁴
decline in signal strength, where R is the distance between the interrogator and the sensor. The use of waveguides, especially waveguides that are already part of the sensed environment, would greatly increase the useful interrogation distance. We report here on the use of pipes as a circular waveguide for SAW interrogation.