A New Advanced Analytical Model for Bi-Layer Circular CMUT-Based Gas Sensors

Mass Sensors Based on Capacitive and Piezoelectric Micromachined Ultrasonic Transducers—CMUT and PMUT

“…In the proposed analytical models of the CMUT, two different approaches exist which address the device membranes' small and large deflections. The small deflection approach is proposed when the membrane's displacement due to the sensing material's mass change is small in comparison to its thickness, and there is a linear relation between the applied force and the membrane's displacement [10]. Meanwhile, in the large membrane deflections, there is a nonlinearity seen between the membrane's displacement and the applied force [14].…”

“…This, in return, results in enhanced operational properties, and higher sensitivity [15]. When used as a gas sensor, the top membrane is functionalized The CMUT sensor is modeled using a mass-spring-damper in one dimension, as shown in Figure 2, where k and B are the membrane's spring constant and damping factor, respectively [10]. In the proposed analytical models of the CMUT, two different approaches exist which address the device membranes' small and large deflections.…”

“…The device sensitivity is defined by the sensor physical and material properties presented in Equations (1) to (3). Moreover, the sensitivity is influenced by the designed sensing material [10,18]. A frequency shift, from 3.1 to 2.3 MHz, for a simulated CMUT-based sensor was achieved when the sensor absorbed 1.7 fg of the target gas molecules, as illustrated in Figure 5.…”

“…Therefore, in order to design a CMUT-based sensor for a target gas detection application, effective structural parameters should be considered in addition to the sensing component's properties to enhance device sensitivity. These critical parameters consist of the membrane's radius and thickness, the cavity height and the structural material in addition to the sensing component's thickness and its material properties [10,18]. In a CMUT-based sensor, the sensing component and the absorbed mass of gas act together as an added mass to the membrane and spring, as shown in Figure 6.…”

“…CMUTs were introduced as an alternative device for the traditional piezoelectric transducers for non-destructive testing applications as well as medical and underwater imaging [8,9]. Due to the unique structure of the CMUTs, they can also act as a mass resonant sensor [10]. Therefore, in an unconventional approach, they are proposed to be used for volatile organic compound detection applications.…”