A Two-Dimensional CMUT Linear Array for Underwater Applications: Directivity Analysis and Design Optimization

Abstract

Capacitive micromachined ultrasonic transducers (CMUTs) are one of the promising MEMS devices. This paper proposed an integrated vibration membrane structure to design a two-dimensional CMUT linear array for underwater applications. The operation frequencies for different medium have been calculated and simulated, which are 2.5 MHz in air and 0.7 MHz in water. The directivity analyses for the CMUT cell, subarray, and linear array have been provided. According to the product theorems, the directivity function of the complex array is obtained using a combination of the directivity functions of certain simple structures. Results show that the directivity of a CMUT cell is weak due to the small size, but the directivity of the designed linear array is very strong. Influential parameters of the linear array have been discussed, including the cell numbers, the adjacent distance, and the operation medium. In order to further suppress the side lobe interference and improve the resolution and the imaging quality of the imaging system, several weighting methods are used for optimization and comparison. Satisfactory side lobe suppression results are obtained, which can meet the actual requirements.

An Analytical Model for Bandwidth Enhancement of Air-Coupled Unsealed Helmholtz Structural CMUTs

“…Referencing from [18], this frequency can be calculated more accurately as the fundamental resonant frequency of a clamped circular membrane as…”

Ultrasound Non-Destructive Evaluation/Testing using Capacitive Micromachined Ultrasound Transducer (CMUT)

“…The membrane deflection increases as the DC input voltage increases because the electrostatic force deflects the flexible membrane, while the mechanical restoring force resists the attraction [10]. At an above-specific voltage (collapse voltage), the flexible membrane collapse to a fixed membrane and does not vibrate because the mechanical restoring force overwhelms the electrostatic force; hence the imbalance of CMUT occurs, and the CMUT breaks [11,12]. The DC bias can be eliminated if the efficiency is not a matter.…”