Interdigital Micro Accelerometer Coupled Field Analysis

The principle of electrostatic servo-microaccelerometer is based on the equilibrium between electrostatic feed-moment, elastic moment of elastic beam and inertial moment. It is necessary to develop a coupled electrostatic-mechanical analysis . method for precise design, and it can be used to analyze the solid model.A coupled-field analysis approach has been developed to solve the problem of one kind of micro-accelerometer, and it uses a FEM software, ANSYS. The analysis subroutine has been programmed using APDL language. The subroutine can be used to calculate the deformation of structures subjected to electric field, and the output voltage of micro-accelerometer subjected to acceleration.Through the analysis with the subroutine and theory analysis, we have had the following conclusions:(1) The structural parameter of comb-fingers , 77 .should be greater than three, orequal to three.(2) The deformation of the fingers because of acceleration can be ignored. The deformation because of electrostatic force is larger, but the fingers are not to touch each other when subjected to electrostatic field. The width of the finger can be increased to reduce its deformation.(3) The effect of elastic beam geometry on mode frequency is analyzed. The influence of wbl on the first mode frequency is biggest, and the influence of Ib2 onthe first mode frequency is quite small.(4) Six mode frequencies and mode shapes have been calculated. The first mode is main along the sensing axis.(5) Finally, we selected two accelerometers with different geometry ,and analyzed their range, sensitivity and the least measurable acceleration .The numerical result is basically agreed with the theory estimation. The results prove that this method is correct, and it also can be used for studying some other MEMS structures.