EAGER: Understanding and Leveraging Nonlinear Effects in Acoustic Holograms

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Ultrasound waves, which can travel through human tissues and fluids, have been used in acoustic sensing, ultrasound therapy, and imaging. The spatial control over the propagation of ultrasound waves can significantly improve noninvasive ultrasound techniques. This EArly-concept Grant for Exploratory Research (EAGER) project will explore acoustic holograms for shaping ultrasound waves in high-intensity fields. Recent studies suggest that passive acoustic holograms can be used for projecting an arbitrary acoustic pattern when illuminated with only a single acoustic source. However, for high-intensity ultrasonic manipulations, where nonlinear effects set in, the hologram technology is in its early stage on untested approaches. This project applies new expertise in volume acoustic holography in nonlinear regimes and contributes to the key elements needed for the novel field of wavefront engineering.The research goal of this EAGER project is to understand how the nonlinear effects influence the general picture of the reflection and transmission phenomena in acoustic holograms, which are characterized by the constructed acoustic fields in the target plane. At higher excitation amplitudes, the nonlinear effects are exhibited by the generation of harmonics, distortion of the acoustic waveform, and possibly the formation of shock fronts. These effects can be responsible for amplitude as well as phase distortions of the primary interfering waves that give rise to extra acoustic images and ambiguity functions of the reconstructed acoustic field. This award will explore an untested nonlinear volume holography approach based on experimental measurements and modeling. The method will help to answer fundamental scientific questions in wavefront engineering research including: (1) What are the dominant origins of nonlinearity in acoustic holograms? (2) Is the enhancement and engineering of nonlinear effects can increase the efficiency of controlling sound waves? (3) What are the effects of the intensity level and frequency of the sound wave as well as nonlinear harmonics on reconstructed acoustic fields?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.