Design of 15 MHz concave array transducers for ophthalmic imaging

15 MHz concave array transducers for effective high frequency ultrasound ophthalmic imaging are proposed and designed in this paper. The concave type, fitting well to the spherical shape of the eye, can keep off refraction and reflection from the anterior segment of the eye, especially the cornea and lens. A 15 mm radius of curvature and a 1.44λ pitch with 128 elements in the array design were chosen for this concave array. Also, geometric focus of 30 mm and a view angle of 72.3° at the center of eyeball were decided, allowing the imaging area to cover the retinal region of interest in the posterior segment. Based on the Field II simulation, a -6 dB lateral beam width was 200 μm and the -3 dB depth of focus was 6.6 mm at the depth of 29.1 mm. In the design, 1-3 composite of PMN-PT was selected due to its high coupling coefficient. From KLM single element modeling, it was learned that the designed concave array can provide the -6 dB fractional bandwidth of 81.8% and the - 20 dB pulse length of 0.127 μm. From those results, the concave array transducer is expected to be a possible alternative to the conventional arrays for imaging the posterior segment of the eye.