2F-3 Design of 20 MHz Convex Array Transducers for High Frequency Ophthalmic Imaging

20 MHz 192 element convex array transducers are proposed for high frequency ophthalmic imaging. A convex array can cover the whole eye within a single image, achieve higher frame rate, create multiple focal zones with dynamic aperture and implement Doppler or color flow mapping whereas other types of arrays are limited to implement those features. A 1.5 wavelength pitch, 24 mm radius of curvature and 52deg maximum view angle were chosen to provide adequate spatial sampling and resolution along with minimal image aliasing. A 7.0 mm elevation width and 30 mm geometric focus was chosen as a compromise between depth of field and resolution. The number of channels used to acquire one scan line was 64. From the Field II simulation, with a single transmit focus and dynamic receive focusing, the -6 dB lateral and axial beamwidth were 200 mum and 50 mum, respectively. The -6 dB depth of field was 4.8 mm. The grating lobe level was -75 dB at 20deg at a range of 30 mm. For the KLM modeling of a single array element, 1-3 composite with a high dielectric constant piezo ceramic was chosen as the active material along with two matching layers and a lossy low impedance backing layer. KLM modeling showed an echo fractional bandwidth above 70% and sensitivity above -50 dB. Images of the wire phantom and the dog eye were simulated and compared with those of a linear array with similar specifications.