Title :
Humidity sensor using surface acoustic waves propagating along polymer/LiNbO3 structures
Author :
Nomura, Tadahiro ; Yasuda, Toshiyuki ; Furukawa, S.
Author_Institution :
Shibaura Inst. of Technol., Tokyo
fDate :
31 Oct-3 Nov 1993
Abstract :
A surface acoustic wave (SAW) sensor for measurement of humidity in ambient atmosphere is presented. The majority of SAW sensors utilize the effect of mass loading. In this paper, we propose a new SAW humidity sensor that is based on the changes in the film conductivity rather than the mass. The phase velocity and propagation loss were computed for the SAW propagating on a piezoelectric (128° YX LiNbO3) substrate, which is coated with a hygroscopic conductive polymer. In experiments, a 30 MHz dual SAW delay line fabricated on 128° YX LiNbO3 was coated with the sodium salt of polystyrene sulfonate. This hygroscopic polymer coating caused a SAW velocity change of 20 m/s per 10% relative humidity. The response was quite linear in the range from 40 to 80% RH
Keywords :
humidity measurement; moisture measurement; piezoelectric devices; piezoelectric thin films; surface acoustic wave devices; ultrasonic delay lines; ultrasonic transducers; ultrasonic velocity measurement; 20 MHz; LiNbO3; LiNbO3 substrate; SAW delay line; SAW sensor; SAW velocity; YX LiNbO3; ambient atmosphere; film conductivity; humidity sensor; hygroscopic conductive polymer; phase velocity; polymer/LiNbO3 structures; polystyrene sulfonate; propagation loss; sodium salt; Acoustic measurements; Acoustic propagation; Acoustic sensors; Acoustic waves; Atmosphere; Atmospheric measurements; Conductive films; Humidity measurement; Polymer films; Surface acoustic waves;
Conference_Titel :
Ultrasonics Symposium, 1993. Proceedings., IEEE 1993
Conference_Location :
Baltimore, MD
Print_ISBN :
0-7803-2012-3
DOI :
10.1109/ULTSYM.1993.339458
