Improved modeling and fabrication techniques for capacitive micromachined ultrasonic Lamb wave transducers

This paper discusses improvements in the theoretical and experimental framework of capacitive micromachined ultrasonic Lamb wave transducers. Theoretically, a new method for the analysis of these Lamb wave devices is proposed using the electro-mechanical capabilities of ANSYS, a commercial finite element package. The model used in these simulations has been verified by comparing its predictions when configured as a clamped transducer to those predicted by the standard equivalent circuit model; the input impedances obtained using the two methods agree to within 1%. This method performs harmonic and transient analyses to predict device performance metrics in the presence of electrostatic forces. Experimentally, this paper introduces a new manufacturing process for the fabrication of Lamb wave devices using CMUT wafer bonding technology. Devices have successfully been built using this technique and preliminary results show significantly improved uniformity in membrane to membrane performance and successful Lamb wave propagation between transducers. The membranes fabricated are 1 cm long and 60 μm wide have an insertion loss of 16.2 dB near 2.6 MHz.