Electrostatic comb-drive actuators feature easy design, fabrication and implementation. They are used in for different applications, such as optical communication, biomedical engineering, wireless communication and nanotechnology. Increase in traveling distance and force output are two major concerns in developing comb-drive actuators.
The actuator consists of two interdigitated structures; one is fixed and the other is connected to a compliant suspension.The moving part consists of four fingers, whereas the fixed one is formed by five fingers.
The driving voltage between the comb structures causes the displacement of the movable fingers towards the fixed fingers by an attractive electrostatic force.
EMS electro-structural module aims at finding the resultant deflection of the moving finger under an applied dc voltage.
In our analysis, we are not accounting for forces other than the electric force; gravity acceleration is ignored.
Material Name | Relative permittivity | Electrical conductivity (Mho/m) | Elastic modulus (N/m2) | Poisson’s Ratio |
PolySilicon | 4.5 | Not required | 160e+09 | 0.22 |
Air | 1 | 0 | Not required | Not required |
The movable part of the actuator is assigned a positive voltage. Figure 3 shows the where the voltage is applied.
Figure 3 - Fixed voltage applied on the lower finger
The model geometry doesn’t contain very complicated shapes. A mesh control to refine the lower finger would be sufficient to get accurate electrical and structural results.
As given in figure 4, the mesh is quite fine in the movable part compared to the other parts. The beam connecting the lower finger to its anchor does not need a fine mesh.
The upper finger (the body colored in blue in figure 5) is coarsely meshed as it will not experience any deflection.
EMS Result | Simulation Result | |
Resultant Displacement under 30V (in meters) | 4.16e-08 | 5e-08 |
Resultant Displacement plot
Electro-structural analysis of a comb drive actuator is done inside EMS. EMS results have shown to be in good agreement with numerical (given in [1]) and analytical results.
[1]: S. Gupta, T Pahwa, R Narwal, B.Prasad and D. Kumar. Optimizing the Performance of MEMS Electrostatic Comb Drive actuator with different Flexure Springs.