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

fYear

1994

fDate

23-27 May 1994

Firstpage

509

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;

fLanguage

English

Publisher

ieee

Conference_Titel

Microwave Symposium Digest, 1994., IEEE MTT-S International

Conference_Location

San Diego, CA, USA

ISSN

0149-645X

Print_ISBN

0-7803-1778-5

Type

conf

DOI

10.1109/MWSYM.1994.335446

Filename

335446