Dynamic Acousto-Caustics in Dual-Optimized Holographic Fields
Koki Nagakura

Tatsuki Fushimi

knag0019@digitalnature.slis.tsukuba.ac.jp
University of Tsukuba
Tsukuba, Japantfushimi@digitalnature.slis.tsukuba.ac.jp
University of Tsukuba
Tukuba, Japan

Ayaka Tsutsui

Yoichi Ochiai

ayakatsutsui1128@digitalnature.slis.tsukuba.ac.jp
University of Tsukuba
Tukuba, Japan(a)wizard@slis.tsukuba.ac.jp
R&D Center for Digital Nature
Tukuba, Japan

(b)

(c)

(d)

(e)

Figure 1: (a) The actual setup used. This setup, from top to bottom, consists of a PAT, mesh, a water tank with silicon oil, aFresnel lens, and a light. The mesh serves as a screen to display the caustics. (b) Top left: target pattern; Top right: soundpressure distribution optimised for the target pattern; Bottom left: focus area before Digital Twin; Bottom right: focus area
after Digital Twin. (c) ‘S’ written by focusing caustics. (d) Cross mark drawn in shadow. (e) A human running. Six frames arelisted here. Top: These serve as the target images. Bottom: The actual animation of these target images as dynamic caustics.

ABSTRACT
We aims to computationally replicate the dynamic caustics observedin nature, such as the captivating light patterns found at the poolor within flowing rivers. Traditional computer science approaches
have only been able to reproduce these light patterns through staticfabrication. We introduce “Dynamic Acousto-Caustics” a methodthat merges acoustofluidics with optics to dynamically manipulate
light caustics by controlling the shape of liquid surfaces. Using
computer-controlled acoustic fields to deform the surface of a liquid medium, we generate dynamic light behaviors in fluid patterns
unachievable with static refractive surfaces. This research not only
extends the understanding and application of controlled caustics
across various technical and creative domains but also exemplifies
the intersections made possible at the convergence of multidisciplinary research. While devices exist to generate waves by vibrating
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SIGGRAPH Emerging Technologies ’24, July 27–August 01, 2024, Denver, CO, USA© 2024 Copyright held by the owner/author(s).
ACM ISBN 979-8-4007-0524-3/24/07
https://doi.org/10.1145/3641517.3664384

water surfaces, they could not produce continuous caustics at specific locations and timings. Employing ultrasonics to deform thewater surface allows us to directly manipulate the surface to create
more continuous animated patterns. We shape caustics throughacoustic field manipulation and optimize the visual outcome emanating from the geometry of these manipulated objects within adynamic system. Our approach leverages the Digital Twin methodology as an optimization strategy to fine-tune the interplay between
sound and light. This enhances the understanding and applicationof controlled caustics in numerous technical, demonstrating thecrossing points enabled by the convergence of interdisciplinary
research streams.
ACM Reference Format:
Koki Nagakura, Tatsuki Fushimi, Ayaka Tsutsui, and Yoichi Ochiai. 2024. Dynamic Acousto-Caustics in Dual-Optimized Holographic Fields. In Special
Interest Group on Computer Graphics and Interactive Techniques Conference Emerging Technologies (SIGGRAPH Emerging Technologies ’24), July
27–August 01, 2024, Denver, CO, USA. ACM, New York, NY, USA, 2 pages.
https://doi.org/10.1145/3641517.3664384

1

INTRODUCTION

Caustics refer to the distinctive patterns that occur when lightreflects or refracts off an object’s surface, casting a projection onto

SIGGRAPH Emerging Technologies ’24, July 27–August 01, 2024, Denver, CO, USA(a)(b)(c)(d)(e)(f)(g)

(h)

(i)

(j)

Figure 2: Comparison of the target image used for the animation and the generated caustics. Here, the caustics arepresented frame by frame rather than in sequence as they
were animated. The actual animation, which is generated
by projecting these frames in succession, is included in theSUPPLEMENTAL MATERIAL. Each frame was created bysuperimposing the sound pressure of 9 frames to optimize
the initial sound pressure distribution, followed by Digital
Twin processing.

another surface. These phenomena exhibit dynamic and alluring
light patterns that captivate observers, commonly witnessed insettings such as pools, flowing rivers, and seas. Our research aims tocomputationally reproduce these dynamic caustics found in naturalenvironments.
We introduce an approach that merges acoustofluidics and optics
to dynamically manipulate light caustics by controlling the shapeof liquid surfaces, which we term “Dynamic Acousto-Caustics”.
Traditional computer science approaches have facilitated the reproduction of caustic light patterns through static fabrication [Papaset al. 2011; Schwartzburg et al. 2014; Yue et al. 2014]. However, thesestudies frequently employed static solid surfaces as refractive media.
The usage of liquid surfaces to form caustics has been proposed
before [Suzuki et al. 2019]. Yet, this has been confined to in silico
and has not been applied to real-world fluid manipulation.
Our research successfully utilizes ultrasonics to directly push
and shape fluid surfaces, creating dynamic caustics capable of depicting text and imagery. Phased Array Transducers (PAT) havebeen enthusiastically adopted in computer graphics for applications such as touch display [Monnai et al. 2014] and aerial displays[Hoshi et al. 2010; Long et al. 2014]. Our approach does not solely

Nagakura et al.

rely on the optimization of acoustic fields using holograms but involves shaping caustics by utilizing an acoustic field to generate themanipulated object and optimizing the resultant light pattern fromthis object’s geometry. We utilized the Digital Twin methodology[Fushimi et al. 2024] as an optimization strategy for fine-tuning theinterplay between sound and light.

2CAUSTICS GENERATION MECHANISM

The ultrasonic waves emitted from the PAT pass through the meshstructure screen and generate sound pressure on the surface of thesilicone oil in the tank. The deformed surface refracts the parallel
light passing through the fresnel lens, forming a pattern on thescreen. In order to further enhance the quality of the generated caustics, we perform experimental optimization. Detailed experimental
setups are available in the Supplemental Material.

3EXPERIENCE

The installation allows visitors to directly observe ’dynamic acoustics’, achieved through the fusion of acoustics and optics. By using acomputer-controlled sound field to deform the surface of the liquidmedium, dynamic light behaviour is generated in the fluid patternthat cannot be achieved with static refractive surfaces. Participants
can view the resulting caustics either directly on the screen of theexperimental setup or on a real-time video displayed on the screen
and captured by a camera. The displayed dynamic caustics include
various animation patterns prepared here (e.g. running stickmen,ripples, etc.) and a demonstration of caustics optimisation using aDigital Twin.

ACKNOWLEDGMENTS
We would like to extend our sincere gratitude to Sony Semiconductor Solutions Corporation for their generous support in lending
us a sensor kit which was instrumental in the completion of ourresearch.

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