Inclined electrode surface acoustic wave substance sensor

Abstract

A chemical sensor for detecting a plurality of different chemical substances. A chemical sensor (100, 200) includes a substance sensitive SAW device (102, 202) and a reference SAW device (104, 204) formed on the same substrate (106). A plurality of interlaced fingers (112 and 114, 120 and 122; or 206 and 208, and 210 and 212) extend outwardly from the inclined source and output electrodes in parallel relationship with reach other. An RF pulse signal is applied to the inclined source electrodes in both the substance sensitive and reference SAW devices, causing surface acoustic waves to be generated that propagate perpendicularly away from the interlaced fingers toward the inclined output electrodes. A plurality of polymer coatings are applied in regions between the inclined source and output electrodes so that the surface acoustic waves generated by successive overlapped interlaced fingers propagate through different regions and coatings. In the substance sensitive SAW device, each polymer coating has a characteristic affinity to absorb a different chemical substance or substances, such absorption changing the phase, delay, and amplitude of a surface acoustic wave propagating through the region in which the coating is applied. In the reference SAW device, corresponding coatings are applied that do not absorb any of the chemical substances. Time multiplexed output signals from the substance sensitive SAW device and reference SAW device are compared in a mixer (134) to determine the differences in phase or delay, and in a differential amplifier (150), to determine differences in amplitude of the surface acoustic waves passing through corresponding regions.