Discussion Forum

Hi,

I'm trying to model a Capacitive Micromachined Ultrasonic Transducer (CMUT) in collapse mode.
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A CMUT is basically formed of 2 membranes, separated by a vacuum gap, and each of them are covered by electrodes; when a potential is applied to one of the electrodes while the other is grounded, they will be attracted to each other by electrostatic force and the membranes will therefore deflect depending on the potential applied - collapse mode is when these membranes finally touch one another).
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To model this collapse, I implement a contact region in the geometry. The geometry is created with a 2D axisymetric model. The first file attached (see "Contact.PNG") describes the geometry used. I parametered the contact region. Regarding the physics, I used Electrostatics (es), Solid Mechanics (solid) and Moving Mesh (ale) to simulate a fixed, grounded membrane, attracting another membrane (already collapsed), which has a high potential. I also use the muliphysic effect Piezoelectic effect (pze).

My problem is that when I try to simulate the displacement of the membranes due to the electrostatic force, COMSOL gives me very odd results, actually out of the meshing area (see "Collapsed_displacement.PNG"). In this situations, only the "ring" (thinking 3D) not touching the lower membrane should be able to move. I'm far from being a pro with this software, so I don't have a clue about whats going on.
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jpletendre