Nonlinearity analysis of piezoelectric micromachined ultrasonic transducers based on couple stress theory |
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Authors: | Xin Kang Fu-Jun Yang Xiao-Yuan He |
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Institution: | 1. Department of Applied Mechanics, Nanjing University of Science and Technology, 210094, Nanjing, China 2. Department of Mechanical and Aeronautical Engineering, University of California, Davis, 95616, USA 3. Institute of Engineering Mechanics, Southeast University, 210096, Nanjing, China
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Abstract: | This paper studies the static deformation behavior of a piezoelectric micromachined ultrasonic transducer (PMUT) actuated
by a strong external electric field. The transducer membrane consists of a piezoelectric layer, a passive layer and two electrode
layers. The nonlinearities of the piezoelectric layer caused by electrostriction under a strong electric field are analyzed.
Because the thickness of the transducer membrane is on the microscale, the size dependence of the deformation behavior is
evaluated using the couple stress theory. The results show that the optimal ratio of the top electrode diameter and the membrane
diameter is around 0.674. It is also found that this optimal value does not depend on any other parameters if the thicknesses
of the two electrodes are negligible compared with those of the piezoelectric and passive layers. In addition, the nonlinearities
of the piezoelectric layer will become stronger along with the increase of the electric field, which means that softening
of the membrane stiffness occurs when a strong external electric field is applied. Meanwhile, the optimal thickness ratio
for the passive layer and the piezoelectric layer is not equal to 1.0 which is usually adopted by previous researchers. Because
there exists size dependence of membrane deformation, the optimal value of this thickness ratio needs to be greater than 1.0
on the microscale. |
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Keywords: | Piezoelectric micromachined ultrasonic transducer (PMUT) · Couple stress theory · Static deformation · Nonlinearity analysis |
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