Design and Analysis of Capacitive Micromachined Ultrasonic Transducer

Background: Ultrasound refers to the acoustic energy above the human hearing range (20 Hz to 20 kHz) and finds applications in quality control of food technology, medical imaging, nondestructive testing, distance measuring etc. Ultrasonic transducers are designed to work both as a transmitter to generate ultrasound and as a receiver according to recent patents. Piezoelectric transducers have long dominated the society for generating ultrasound but recent developments in the Micromachining techniques have led to Capacitive Micromachined Ultrasonic Transducer (CMUT). Objective: To simulate a Micromechanical systems (MEMS) based CMUT working as a transmitter with the existing design and provide comparison within the possible architectural geometries. Methods: FEM simulation software COMSOL is used to simulate the 3D model of the transducer radiating in the air. The classical thin-plate theory is employed to solve for CMUT with a circular shape which is sufficient when the ratio of the diameter to thickness of the plate is very large, an aspect common in CMUTs. The Galerkin-weighted residual technique is used to get a solution for thin plate equation with the presumption that the deflections are small in comparison to the thickness of the plate. Results: The resonant frequency of CMUT with different geometries have been calculated. The deflection of membrane with applied DC bias is shown along with collapse voltage calculation. The generated ultrasound is shown with the AC bias superimposed on the DC bias. The capacitance change with the increasing DC voltage is discussed. The deflection of membrane is maximum as the resonance frequency is proved. Conclusion: The review of Capacitive Micromachined Ultrasonic Transducer architectures with different shapes is highlighted. The working behavior of CMUT with suitable dimension is simulated in 3D providing researcher data to wisely choose the CMUT prior to the fabrication. The CMUT is prioritized on various characteristics like wafer area utilization, deflection percentage within the cavity and durability of the transducer.