Focused Ultrasound Assistance to the MOS Gas Sensor System

It is known that the ultrasound assisted metal oxide semiconductor (MOS) gas sensor system can improve the sensitivity and lower detection limit (LDL) of a MOS gas sensor. The existing ultrasound assisted MOS gas sensor system employs the standing-wave ultrasonic field. As the size of the sensing element is much smaller than that of the ultrasonic field, energy utilization rate of the ultrasonic subsystem has been very poor. In this work, we propose a method to raise the energy utilization rate and the limit sensing properties of the ultrasound assisted MOS gas sensor system, which utilizes the focused ultrasound generated by a low-frequency ultrasonic transducer with a concave radiation face. By placing the sensing element at the focal region, the electric power input of the ultrasonic transducer can be decreased by about 50% for the same sensing response. Moreover, the maximum sensitivity can be increased by 45%, and the LDL can be decreased by 50% by the new method.