Pulse Ultrasound-Based Response Enhancement of a MOX Gas Sensor

In this work, a new method to enhance the sensing response of an ultrasonically catalyzed metal oxide gas sensor has been proposed and developed, in which pulse ultrasound is employed to enhance the redox reaction at the sensing surface. It is experimentally confirmed that with a proper pulse width, the negative effect of acoustic streaming on the ultrasonic enhancement process can be effectively suppressed. Comparing the steady responses of five target gases under the pulse and continuous ultrasound, respectively, it is found that the pulse ultrasound causes a better catalysis effect, and response enhancement (RE) by the pulse ultrasound with an optimal pulse width depends on the ultrasonic strength as well as the species and concentration of the target gas. For 2 ppm methanol, the RE by the pulse ultrasound is 50%, relative to the continuous ultrasound, when the pulse width, duty ratio, and working frequency are 0.4 ms, 50%, and 110.1 kHz, respectively. The optimal pulse width decreases when the ultrasonic strength increases and is not affected by the target gas species and concentration. The lower the target gas concentration, the larger the optimal RE caused by pulse ultrasound. Moreover, for a given pulse width, the interpulse time also affects the RE.