Fabrication of a conformal ring-annular ultrasound array

Abstract

This paper presents the fabrication of a conformal, ring-annular ultrasound imaging array. Two-dimensional (2D) ultrasound scanning is possible with ring-annular array transducers in which a number of piezoelectric elements are arranged in a circle. The 2D scanning technique can be realized through time delays, potentially allowing for 3D imaging. Ring-annular array transducers have previously been shown to have increased bandwidth, better signal-to-noise, and uniform scanning in space in contrast to 2D matrix arrays of an equal number elements and aperture size. Conformal, ring-annular transducers have the ability to match the curvature of body surfaces, and have the additional advantage that the flexible array elements can be mechanically focused to provide enhanced focusing capabilities relative to rigid ring-annular arrays. The process developed for the fabrication of conformal, ring-annular ultrasound array is presented. A microfabrication approach is used to produce ring-annular arrays featuring flexible joints with high durability, and capable of scaling in size and element architectures. The fabrication process yields a ring of piezoelectric transducer elements held together with polyimide, which is the basis of the flexible joints that enable conformal ultrasonography. The described fabrication process is used to produce a ring-annular array with a single ring containing piezoelectric elements, but the process can be extended to form arrays with multiple annular-rings of varying sizes. The transducer had a fundamental thickness-mode resonant frequency of 12 MHz, a 6 dB bandwidth of 23%, and an acoustic pulse width of 1.8 μs in water.