Squeeze film damping and stiffening in circular CMUT with air-filled cavity: Influence of the lateral venting boundary conditions and the bias voltage

Abstract

The present paper deals with the analysis of the squeeze film effects in circular capacitive micromachined ultrasound transducers (CMUT) operating in air, with emphasis on improved bandwidth. Firstly, a 1D analytical approach based on parallel plate approximation is recalled. The opposing influences of the electrostatic softening and the squeeze film stiffening make the resonant frequency dependent on the bias voltage with respect to air spring constant to mechanical spring constant ratio. In a second part, FEM models using COMSOL Multiphysics ® are built to analyze the influences of the plate flexibility and the lateral venting boundary conditions on the squeeze film effects. The associated numerical results show that viscous losses are involved in sealed air-filled cavities. Moreover, the dimensionless elastic and viscous damping forces do not depend on the lateral venting boundary conditions for high squeeze number range, usual for CMUT operation. Finally, 2D full coupled simulations of flexible CMUT are compared with experimental data. Thus, the squeeze film damping increases bandwidth of aircoupled CMUTs with both sealed and laterally vented cavities.

PMMA-Based Wafer-Bonded Capacitive Micromachined Ultrasonic Transducer for Underwater Applications

“…Due to the pressure difference, air flows from higher-pressure regions to lower-pressure regions in the sealed cavity, which consequently results in viscous loss [41,42]. Galisultanov et al investigated the damping effect in CMUTs and revealed that, for a squeeze number higher than 50, CMUTs possess a damping effect as, at a high squeeze number, the viscous damping force is similar for both sealed and open cavities [41,42]. The data in Table A3 show that the proposed CMUT carries a damping effect for the cavity pressure of as low as 300 Pa as per the findings of References [41,42].…”

“…Since the CMUT acts like a flexible plate instead of a rigid piston, the nonuniform deflection of the membrane results in nonuniform distribution of pressure within the cavity. Due to the pressure difference, air flows from higher-pressure regions to lower-pressure regions in the sealed cavity, which consequently results in viscous loss [41,42]. Galisultanov et al investigated the damping effect in CMUTs and revealed that, for a squeeze number higher than 50, CMUTs possess a damping effect as, at a high squeeze number, the viscous damping force is similar for both sealed and open cavities [41,42].…”

Modeling and experimental characterization of squeeze film effects in nonlinear capacitive circular microplates

“…FDM is coupled with the arclength continuation method to determine how the solution of a system varies with respect to a certain parameter [59]. We consider the following algebraic system: F (X, α) = 0 (40) where α is the continuation parameter and X is the unknown parameter. The idea of this method is to avoid varying the parameter α by parametrizing the variables X and α via a new continuation parameter s, X = X(s) and α = α(s).…”

“…The static and dynamic behavior is very sensitive to residual stress, initial imperfection and squeeze film damping [36,37,38,39]. Galisultanov et al [40] developed a 1D equivalent system, based on a rigid piston model, and a 2D FEM model using COMSOL. The model demonstrates the competition between the electrostatic softening, caused by the DC voltage, and the squeeze film stiffening due to the gap change.…”

CMUT sensors based on circular membranes array for SHM applications

“…[7][8][9] They have shown that, in spite of a low signal-to-noise ratio compared to the piezoelectric transducer, the CMUTs are able to detect, for example, acoustic emission events. In our work, the CMUTs of interest have been developed by Galisultanov et al 10 and the technology is presented in the next section. A numerical study to optimize the sensor design is presented.…”