Wide range beam steering capability of a 1-D MEMS transducer imager array with directional beam pattern

Abstract

A linear array of capacitive micromachined ultrasonic transducer (CMUT) has been designed as an alternative to conventional piezoelectric transducers. The proposed array is favorable for imaging applications where there is a need for high resolution detection in directions with an angle other than that perpendicular to the axis of the transducer array. The transducer array cells include a thin silicon nitride membrane that is suspended over a bottom electrode, fabricated on a silicon wafer. In immersion mode, the transducer cell shape and dimensions are optimized for an operating frequency of 10MHz. The proposed imager array is shown to be able to generate a pencil shape beam with a ∼1.5° half beam width for enhancing the detector resolution. A phased array technique is employed to excite multiple cells using time-delayed signals to steer the acoustic beam toward the object. Therefore, the need for mechanically moving the transducer array or the cell membrane is eliminated, which results in simplifying the transducer driving system. Moreover, unlike conventional transducers, the pencil beam can be effectively steered over a wide range of angles without producing grating lobes or degrading the power difference between the main lobe and side lobes. Consequently, in transmitting mode the power loss in any undesired directions is minimized and in receiving mode the noise level from other angles interfering with the data collection is suppressed, which improves the signal to noise ratio of the imager CMUT array.