Reflective acoustic holograms for arbitrary pressure patterning and focusing

Abstract

Monolithic passive holographic lenses (MPHLs) are being proposed as an alternative technology to phased array transducers (PATs) and subwavelength structured metamaterials due to their unprecedented spatial control over the sound field. These new capabilities enable precise focusing of acoustic energy or high resolution elaborate pressure patterning without the limitations associated with the aforementioned techniques. In particular, PATs and metamaterials require either an impractical high number of active elements or face fabrication limitations when operated at ultrasonic frequencies, especially underwater or inside the human body. MPHLs do not have such limitations and are being utilized in a wide range of crucial ultrasonic applications such as medical imaging and therapy, ultrasonic contactless energy transfer and nondestructive testing. In this work, we introduce a 3-D-printed metal reflective acoustic hologram. We will present the modeling and design process of such holograms as well as their capabilities for constructing single and multifocal spatial distributions of acoustic energy in a target plane. The effects of operating frequency, hologram material and propagation distance will also be highlighted. The results are verified using finite element multiphysics simulations in COMSOL as well as experimental investigations. [This work was supported by NSF Grant Nos. ECCS—1711139 and IIP-1738689, which are gratefully acknowledged.]