Nanoparticle-Epoxy Composite Molding for Undeformed Acoustic Holograms with Tailored Acoustic Properties.

Abstract

Acoustic hologram lenses were typically produced by high-resolution 3D printing methods, such as stereolithography (SLA) printing. However, SLA printing of thin, plate-shaped lens structures has major limitations including vulnerability to deformation during photo-curing and limited control of acoustic impedance. To overcome these limitations, we demonstrated a nanoparticle epoxy composite (NPEC) molding technique, and we tested its feasibility for acoustic hologram lens fabrication. The characterized acoustic impedance of the 22.5% NPEC was 4.64 MRayl which is 55% higher than the clear photopolymer (2.99 MRayl) used by SLA. Simulations demonstrated that the improved pressure transmission by the higher acoustic impedance of the NPEC resulted in 21% higher pressure amplitude in the region of interest (ROI, -6 dB pressure amplitude pixels) than the photopolymer. This improvement was experimentally demonstrated after prototyping NPEC lenses through a molding process. The NPEC lens showed no significant deformation and 72% lower thickness profile errors than the photopolymer which otherwise experienced deformed edges due to thermal bending. Beam mapping results using the NPEC lens validated the predicted improvement, demonstrating 24% increased pressure amplitude on average and 10% improved structural similarity with the simulated pressure pattern compared to the photopolymer lens. This method can be used for acoustic hologram lens applications with improved pressure output and accurate pressure field formation.