Acoustic hologram optimisation using automatic differentiation

Abstract

Acoustic holograms are the keystone of modern acoustics. They encode three-dimensional acoustic fields in two dimensions, and their quality determines the performance of acoustic systems. Optimisation methods that control only the phase of an acoustic wave are considered inferior to methods that control both the amplitude and phase of the wave. In this paper, we present Diff-PAT, an acoustic hologram optimisation platform with automatic differentiation. We show that in the most fundamental case of optimizing the output amplitude to match the target amplitude; our method with only phase modulation achieves better performance than conventional algorithm with both amplitude and phase modulation. The performance of Diff-PAT was evaluated by randomly generating 1000 sets of up to 32 control points for single-sided arrays and single-axis arrays. This optimisation platform for acoustic hologram can be used in a wide range of applications of PATs without introducing any changes to existing systems that control the PATs. In addition, we applied Diff-PAT to a phase plate and achieved an increase of > 8 dB in the peak noise-to-signal ratio of the acoustic hologram.

Theoretical Zero-Thickness Broadband Holograms Based on Acoustic Sieve Metasurfaces

“…If the desired image size is set too large, the paraxial approximation will not be satisfied or the information content [21] of the hologram will be less than that of the image. Therefore, in general, for acoustic holographic imaging, the desired image size is set to be equal to or similar to the hologram size in most research [3,[15][16][17][18][19][21][22][23][24][25][26][27][28].…”

“…Due to its powerful and flexible capability of arbitrary sound beam shaping and predesigned sound field reconstruction, acoustic holography has recently received increased attention in many interdisciplinary fields related to acoustics, including medicine [3][4][5][6], engineering [7,8], and biology [9][10][11], in addition to the pure acoustic field. Many applications have been made possible by acoustic holography, including acoustic fabrication [7], beam shaping [12][13][14][15][16][17][18][19][20], acoustic holographic imaging [3,[15][16][17][18][19][20][21][22][23][24][25][26][27][28], volumetric display [29,30], volumetric haptics [31,32], particle manipulation [11,21,26,33,34], 3D ultrasound imaging [8], cell manipulation [9,10], characterizing medical ultra...…”

“…The algorithms used include the iterative angular spectrum approach [21], the iterative backpropagation algorithm [33], the weighted Gerchberg-Saxton algorithm [20], the pseudo-inverse method [36], the conjugate field method [37], the deep learning method [35], and so on. Physically, these calculated maps are realized by either discrete and independently driven elements of active phasedarray emitters [3][4][5][27][28][29][30][31][32][33][34] (such as loudspeakers in the air or piezoelectric transducers in 2 of 13 water) or meta-pixels of passive acoustic metasurfaces [6][7][8][9][12][13][14][15][16][17][18][19][20][21][22][23][24][25]38], or a combination of both [26]. In the reconstruction process, these acoustic holographic devices with the required phase and/or amplitude distributions diffract sound waves to form the desired real image in the pre-designed image plane.…”

Discrete multi-step phase hologram for high frequency acoustic modulation

“…In addition, acoustic holography can be well scaled to higher information content than commercial phasedarray and self-focusing mechanisms. With its high costeffective and high freedom degree of reconstruction, [20,[26][27][28] which makes it widely applicable to various transmitting and reflecting elements.…”

Bisymmetric coherent acoustic tweezers based on modulation of surface acoustic waves for dynamic and reconfigurable cluster manipulation of particles and cells

“…Therefore, considerable research has been conducted to explore a prospective approach for precise manipulation using acoustic waves. Acoustic holograms can generate arbitrarily specified acoustic pressure fields and phase maps in the target plane, 29 providing significant advances for manipulating submicron particles and biological cells. 30 Melde et al 31 proposed the technique of acoustic holograms, which allows the reconstruction of arbitrary acoustic pressure fields and the precise manipulation of particles in liquids as well as in air.…”