StreamFog: Using ultrasonic streaming for controlling aerosols in fog-based displays

Paper Title

StreamFog: Using ultrasonic streaming for controlling aerosols in fog-based displays

Publication Info

• Topic area: Dynamic control of aerosols for fog-based projection displays using ultrasonic streaming.
• Keywords: Fog-based displays, ultrasonic streaming, aerosols, optical diffusion, mid-air projection, reach-through interaction, mixed reality, phased-array, acoustic control, multi-layer projection.

Background and Problem

• Problem / challenge: Traditional fog screens are static due to reliance on laminar flows from linear outlets, limiting their speed, shape variability, and interaction capabilities. Existing dynamic systems are constrained in speed, shape complexity, and scalability.
• Significance: Dynamic fog displays could enable novel applications in interactive projection, mixed reality, and multi-layer visualization, enhancing user interaction and display versatility.
• Motivation and related work: Prior research explored fog screens for mid-air projection and interaction, but dynamic capabilities were limited by mechanical or electrostatic methods. Ultrasonic techniques have been used for particle manipulation but lacked applicability to aerosols. This paper addresses these gaps by leveraging ultrasonic streaming for precise and rapid aerosol control.

Solution

• Proposed approach: StreamFog, a system using ultrasonic streaming to dynamically raise, move, and shape fog columns and other aerosol structures for projection and interaction.
• Novelty:
  1. Application of ultrasonic streaming to control aerosol columns with high speed and precision.
  2. Characterization of aerosols (e.g., water mist, glycerine fog) under ultrasonic streaming for optical diffusion.
  3. Development of control mechanisms for generating multiple columns, shapes, and dynamic patterns.
  4. Demonstration of applications in multi-layer projection, reach-through interaction, and mixed reality.
• Procedure and key techniques:
  • Use of a 16×16 ultrasonic phased-array to generate streaming fields for aerosol manipulation.
  • Characterization of aerosol behavior under varying conditions (temperature, focal point distance, ultrasonic amplitude).
  • Implementation of time-multiplexed and single-emission techniques for generating multiple columns and shapes.
  • Evaluation of interaction robustness and projection quality for practical applications.

Results

• Concrete findings:
  • Columns of water mist can be raised in 400 ms, pushed down in 200–400 ms, and moved laterally at speeds up to 200 mm/s.
  • Water mist was preferred over glycerine fog due to better controllability, fewer artifacts, and safety.
  • Multiple columns (up to 9) and shapes (e.g., letters, lines) were successfully generated, with time-multiplexation yielding better results.
  • Columns remained stable under partial occlusion but were sensitive to direct blockage at their base.
• Advantage over baselines:
  • Faster actuation and more versatile shape control compared to prior mechanical or electrostatic methods.
  • Improved projection quality and interaction robustness compared to static fog screens.
• Experiments / evaluation:
  • Tested aerosol types (water mist, glycerine fog) under varying temperatures, focal point distances, and ultrasonic amplitudes.
  • Evaluated optical scattering, reaction times, and shape formation.
  • Demonstrated applications in multi-layer projection, reach-through interaction, and mixed reality.
• Limitations and future work:
  • Columns tilt slightly near the edges of the array; larger arrays or tiling could address this.
  • Display volume height is limited by array power and aperture; future work could explore stacking arrays.
  • Projection collisions occur when multiple columns align; multi-projector setups could mitigate this.
  • Future directions include adding haptics, smell, audio, and more complex aerosol shapes.

Summary

StreamFog introduces a novel approach to dynamically control fog-based displays using ultrasonic streaming, enabling rapid and precise manipulation of aerosol columns and shapes. The system demonstrated superior speed, versatility, and interaction capabilities compared to prior methods, with applications in multi-layer projection, reach-through interaction, and mixed reality. Water mist was identified as the optimal aerosol for its controllability and safety. Limitations in display volume and projection collisions suggest avenues for future research, alongside potential extensions to haptics, smell, and audio integration.