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From modal analysis of this design we found the shapes and natural frquencies for
first three modes, Fig. 5 shows the first mode natural frequency.
The natural frequencies for first three modes are 2.7243, 4.5759 and 4.5766 kHz,
respectively. Fig. 6 (a) shows variation of displacement and that of maximum stress
against the acceleration (1g to 10g) for analytical as well as simulated results.
Wheatstone bridge output voltage for applied acceleration is shown in Fig. 6 (b).
From Fig. 6 (a), we observe that analytical results are in close agreement with the
simulated results. For a fixed bias of 5 V the output is 18.29 mV for 10g applied
acceleration. Sensitivity of this accelerometer is 0.366 mV/V/g.
(a) (b)
Fig. 6. (a) Comparison of analytically calculated and FEM simulated results for acceleration vs.
displacement and acceleration vs. von-Misses stress (b) Acceleration vs. Output voltage.
5
Conclusions
Design and simulation of an out-of-plane Z-axis bulk micromachined accelerometer
has been presented and discussed. In the present design polysilicon piezoresistors are
placed on the top of the beams at maximum stress regions which have higher
sensitivity than the embedded diffused silicon piezoresistors. The proposed
accelerometer design can be fabricated using a combination of wet and dry bulk
micromachining technology. A comparison between analytical and simulated results
using COMSOL software tool have been carried out and results are found to be in
close agreement.
Acknowledgments. Authors would like to acknowledge the generous support of the
Director, CSIR-CEERI, Pilani. The authors would also like to thank all the scientific
and technical staff of MEMS and Microsensors Group at CSIR-CEERI, Pilani. The
financial support by CSIR, New Delhi through PSC-201: MicroSensys project is
gratefully acknowledged.
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