Recent developments on surface acoustic wave (SAW) sensors for harsh conditions

The results of research into Surface Acoustic Waves (SAW) devices have been recognized for their efficiency and versatility in the electrical signals processing. Actual progress in the industrial application of piezoelectric materials such as Lithium Niobate (LiNbO 3 ), Langasite (LGS), Lanthanum-Gallium Silicate La 3 Ga 5 SiO 14 and Gallium Orthophosphate (GaPO 4 ), allows the manufacturing of devices with piezoelectric performances, which overcome the limits obtained with quartz crystals. The single crystal materials have a long term high stability - near to infinite – and moreover, some of these have an excellent behavior with temperature variation. Today, GaPO 4 with its properties is by far the best suited piezoelectric material to be used in sensor applications for machine monitoring and pressure measurements, at high temperatures. SAW micro devices based on GaPO 4 operate at temperatures of up to 800 0 C. For a particular case, of harsh-environment applications, additional challenges need to be overcome, relating to substrate integrity and operation, thin film electrode fabrication, device packaging, and sensor interrogation. This paper reviews the novel progres in the area of (SAW) sensors for harsh conditions.