Multistrip couplers for surface acoustic wave sensor application

We present a new surface acoustic wave gas sensor utilizing a multistrip coupler on LiNbO/sub 3/ and LiTaO/sub 3/ substrates and using copper phthalocyanine as a sensor layer for NO/sub 2/. The sensor signal originates from surface conductivity changes induced by the adsorbed NO/sub 2/. This variation in conductivity leads to a changing coupling efficiency of the multistrip coupler and thus to variations in the insertion loss of the device. Rayleigh and shear wave devices with operating frequencies of 170 and 243 MHz have been tested. A sensitivity of better than 1 ppb NO/sub 2/ in air was achieved.