Title :
Humidity sensor using surface acoustic waves propagating along layered structures
Author :
Nomura, T. ; Yasuda, T. ; Furukawa, S.
Author_Institution :
Shibaura Inst. of Technol., Tokyo, Japan
Abstract :
A surface acoustic wave (SAW) sensor for measurement of humidity in ambient atmosphere is presented. The majority of the SAW sensors have utilized the effect of mass loading. In this paper, we propose a new SAW humidity sensor 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 substrate which is coated with a hygroscopic conductive polymer. In experiments, a 30 MHz dual SAW delay line fabricated on 128/spl deg/ YX LiNbO/sub 3/ was coated with the sodium salt of polystyrene sulfonate. This hygroscopic polymer coating caused the SAW velocity change of 20 m/s per 10% in the relative humidity. The response was quite linear in the range from 40 to 80%RH.<>
Keywords :
humidity measurement; lithium compounds; piezoelectric transducers; surface acoustic wave devices; ultrasonic transducers; 30 MHz; LiNbO/sub 3/; LiNbo/sub 3/; SAW sensor; SAW velocity change; ambient atmosphere; dual SAW delay line; film conductivity; humidity sensor; hygroscopic conductive polymer; layered structures; phase velocity; piezoelectric substrate; polystyrene sulfonate; propagation loss; surface acoustic waves; Acoustic measurements; Acoustic propagation; Acoustic sensors; Acoustic waves; Atmosphere; Atmospheric measurements; Conductive films; Humidity measurement; Polymer films; Surface acoustic waves;
Conference_Titel :
Microwave Symposium Digest, 1994., IEEE MTT-S International
Conference_Location :
San Diego, CA, USA
Print_ISBN :
0-7803-1778-5
DOI :
10.1109/MWSYM.1994.335446
