Physical principle of enhancing the sensitivity of a metal oxide gas sensor using bulk acoustic waves

Abstract

The bulk acoustic wave (BAW) assisted gas sensor utilizes the BAW to raise the sensitivity of a gas sensor, which provides a new and universal physical strategy to greatly improve the sensitivity of gas sensors. However, the physical principle of this type of gas sensor has not been clarified yet. In this work, the physical principle of the BAW assisted gas sensor is investigated experimentally and theoretically, and the effects of sound pressure and acoustic streaming on the sensing process are directly verified. It indicates that the transfer of target gas molecules onto the sensing surface can be enhanced by sound pressure on the sensing surface, which results in a significant increase of both the sensing response and sensitivity. Also, it is found that the sensing surface can be cooled down by acoustic streaming, which causes a sensing response change opposite to the change direction caused by the sound pressure, and little change of the sensitivity. It is predicted and experimentally verified that when both acoustic streaming and sound pressure exist on the sensing surface, the sensing characteristics should be between those of the two extreme working modes in which there is only sound pressure or acoustic streaming on the sensing surface.

Recent trends in ozone sensing technology

“…However, acoustic streaming had a more negligible effect on the sensitivity of the sensor. 73 Tin oxide lms were fabricated on an SiO 2 substrate for use as ozone sensors with illumination using ultraviolet radiation emitted by a light-emitting diode. The light-emitting diode saved power and helped the sensor to operate at room temperature compared to other chemical sensors.…”

A high-performance structure for the bulk acoustic wave metal oxide semiconductor gas sensor

“…This phenomenon can be explained by the enhanced desorption of oxygen species from the sensing layer by the ultrasound. The ultrasonic field within the metal case can generate the acoustic streaming which is a 2nd order effect of ultrasound field [37]. The acoustic streaming cools down the sensing surface, and strengthens the desorption capability of oxygen species from the sensing surface.…”

“…Based on our experiments [36,37], it is known that the BAW ultrasound can be used to enhance the sensing performance of a metal oxide semiconductor gas sensor for the reducing gas (such as VOCs, CH 4 , C 2 H 5 OH, NH 3 , CO, H 2 , etc) and oxidizing gases (such as O 3 ). In existing BAW metal oxide semiconductor gas sensors, the working frequency of ultrasound field is less than 150 kHz, and sound pressure on the sensing surface is in the range of 0-700 Pa (0-p) [36,37].…”

Ultrasonic trapping and collection of airborne particulate matter enabled by multiple acoustic streaming vortices

“…When the air gap thicknesses are 0.5λ, λ, and 1.5λ, the mass of collected particulate matter reaches the local maximum values, respectively. This is because when the air gap thickness equals integral multiples of the half wavelength of acoustic field, the acoustic field in the air gap is in resonance, under which the intensity of acoustic field reaches locally strongest [26,28,29]. Therefore, the consequent acoustic streaming field resulting from the acoustic field is also locally strongest, and the peak values of mass of collected particulate matter occur at these state points.…”