An Accurately Steerable, Compact Phased Array System for Narrowbeam Ultrasound Transmission

Abstract

For over more than a decade, ultrasound phased arrays have been playing a leading role in domains such as noninvasive diagnostic examination, nondestructive testing and sonar, and will continue to be indispensable in a wide range of new applications. Unlike the aforementioned traditional scanning systems, many new applications require a transmit-only configuration and work in the low ultrasound frequency range, consequently posing new challenges in low-cost phased array design. However, two sought-after features are still missing in current low-cost ultrasound phased array systems, namely broadband transmission and wide angular beam steering. In this work, a low-cost ultrasound phased array system is presented that enables the transmission of both narrowband and broadband signals. Accurate beam steering is achieved through the concept of Direct Digital Synthesis (DDS). The design features small, wide bandwidth MEMS transducers enabling grating lobe free beam patterns at high frequency and a broad angular beam steering range. The presented prototype supports 64 speaker elements and allows very fine amplitude and phase control over each transducer stage with respectively 10-bit and 12-bit resolution. The beam steering performance is validated for a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1}\times {10}$ </tex-math></inline-formula> calibrated uniform linear array design. In these measurements, an accuracy in the order of just a few degrees was observed, even at a steering angle of 70° off-axis.