Seminar: Holographic tools in acoustics

Dr. Kai Melde from Heidelberg University will present on acoustic holography and its applications in particle manipulation, as part of the ongoing Physical Acoustics course (https://kurser.lth.se/lot/course-syllabus/23_24/BMEN45). Kai pioneered the development of monolithic acoustic holograms during his Ph.D. studies in Peer Fischer’s group at the Max Planck Institute for Intelligent Systems. This groundbreaking discovery has had a profound impact on the field of physical acoustics and has quickly found applications in medical imaging, particle manipulation, and tissue engineering. In this seminar, Kai will provide an in-depth overview of acoustic holography, from field synthesis to particle manipulation.

Abstract: Over the last decades, ultrasound emerged as a tool for remote manipulation of matter, including microparticles and biological cells. Its biocompatibility and favorable implementation have led to a wide adoption especially in the microfluidics community (e. g. for cell sorting). However, the effects of ultrasound can act over much larger length scales, provided that there is sufficient control over the sound field. In this talk, I will present how ultrasound combined with holographic beamforming enables us to project user-defined sound fields with large extent, which can direct the parallel assembly of matter to arbitrary shapes in 2D and 3D. Since implementations of acoustic holograms are typically limited to phase-only modulation, numerical optimization of the sound field for constrained transducer amplitudes is needed. Therefore, I will present two common algorithms to find optimal phase distributions for a chosen target image: the iterative angular spectrum approach (IASA) and a projected gradient descent algorithm (PGD). The latter allows for more control by choice of different loss functions, which have a significant effect on the outcome. I will demonstrate how these algorithms can be applied to different use cases and show examples how we used them for particle manipulation.

Representative works:

https://www.nature.com/articles/nature19755

https://www.science.org/doi/full/10.1126/sciadv.adf6182

Host: Dr. Wei Qiu, BME