A Novel Dual Track SAW Gas Sensor Using Three-IDT and Two-MSC

In this paper, a sensor architecture of a dual track surface acoustic wave (SAW) gas sensor using three-interdigitated transducers (IDTs) and two-multistrip couplers (MSCs) is proposed. The dual track SAW gas sensor consists of three IDTs and two MSCs fabricated on 128degY-X LiNbO₃ piezoelectric substrate. Dual track structure and MSCs are incorporated into the sensor, thus the perturbations of the measurement signal from external environment are eliminated, and spurious responses caused by bulk acoustic waves (BAWs) are suppressed. Furthermore, the side lobe rejection is better than that of SAW sensors with uniform IDTs due to input IDT apodized by Morlet wavelet function. An experiment of dual track SAW gas sensor coated with polyaniline film sensitive to SO₂ gas is presented. Experiment results confirm that the sensor has good reproducibility and response properties to SO₂ gas at different concentrations. In the measurement ranging from 312 ppb to 20 ppm, the sensor has good linearity, and its sensitivity is approximately 6.8 KHz/ppm.