Design and Characterization of γ-Al₂O₃/PDMS Nanocomposite Acoustic Lenses for Enhanced Acoustic Field Performance of CMUT

In this paper, a novel acoustic lens composed of γ-Al<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>/PDMS nanocomposites is developed to address the mechanical and acoustic deficiencies inherent to conventional PDMS encapsulation materials in capacitive micromachined ultrasonic transducer (CMUT). The filler volume fraction (5-25%) is optimized using the Coherent Potential Approximation (CPA) model to achieve a tailored balance between acoustic impedance (ranging from 1.04 to 2.71 MRayl) and mechanical stiffness. Experimental characterization reveals a substantial enhancement in Young’s modulus to 2.17 MPa, representing a 189% increase compared to pure PDMS and resulting in improved mechanical robustness. The acoustic lens is fabricated via a precision-engineered mold casting technique, effectively minimizing near-field artifacts. Performance evaluation at a 3 MHz operating frequency demonstrates a 63% increase in focal pressure amplitude (from 10.395 kPa to 16.936 kPa), a 25% reduction in main lobe width, and a 10% increase in bandwidth (from 87.7% to 97.4%), all while preserving optimal electromechanical coupling performance. This work introduces a materials engineering strategy for enhancing acoustic field control in CMUT, demonstrating potential applicability in high-resolution medical imaging and advanced nondestructive evaluation.