Development of 15Â MHz 2-2 piezo-composite ultrasound linear array transducers for ophthalmic imaging

High frequency (>15 MHz) ultrasound imaging is capable of producing high spatial resolution B-mode and color Doppler images for the efficient diagnosis of ocular diseases. However, commercial high frequency ultrasound imaging systems cannot currently provide its full capability for ophthalmic applications because either single element or annular array transducers are used in conjunction with mechanical scanning. To overcome the current limitations, 15 MHz 128-element linear array transducers were developed, which are suitable to cover the whole eye from the eyelid in anterior segment to orbital fundus in posterior segment. To achieve the highest electromechanical coupling coefficient, 2-2 piezo-composite was designed and fabricated as an active layer. For the design, the simple model of the thickness-mode oscillation was derived and used in the 1-D model simulator such as PiezoCAD. Also, the usability of the simple model was verified by comparing its simulation results with those by finite element model-based PZFlex. In addition, easy fabrication procedure for the high frequency 2-2 piezo-composite arrays was proposed. In performance evaluation, the pulse-echo response of a representative composite element showed the center frequency of 14.4 MHz and the −6 dB fractional bandwidth of 69.4%. Measured insertion loss was achieved higher than −33.9 dB and crosstalk level between elements less than −30 dB. From the evaluation results, it is expected that the linear array transducer developed using the proposed design and fabrication methods can provide a potential alternative for high frequency ophthalmic imaging with the desired capability.