The NASA project achieves major advances in controlling how sound waves behave in complex environments. By combining active electroacoustics, innovative material design, and concepts from modern wave physics, the research reveals new ways to absorb, direct, and manipulate intense sound with high precision.
1. Active and One-Way Control of Sound
A central achievement is the experimental creation of a compact device that allows sound to travel in only one direction. Using two loudspeakers connected through electronically tuned feedback loops, the team demonstrates striking effects:
• Directional amplification: waves arriving from one side are amplified, while those from the opposite direction are blocked (up to 42 dB isolation).
• One-sided absorption: sound coming from one direction is almost fully absorbed (up to 96%), while waves from the other are reflected.
These experiments link acoustics with topological physics, showing that sound can mimic exotic wave behaviors previously observed only in quantum and optical systems.
2. Nonlinear sound
The project investigates how acoustic geometry and resonant design influence nonlinear sound propagation in air. Engineered structures composed of air-filled cavities, ducts, and subwavelength resonators exhibit strong amplitude-dependent responses, enabling the formation of stable, reshaped waveforms that maintain their structure even at high sound levels. In two-dimensional acoustic networks, the inclusion of tuned resonators produces nearly isotropic propagation, allowing circular and ring-shaped wave fronts to emerge. Theoretical developments further introduce strategies for designing customized perfect absorbers capable of capturing all incoming low-frequency sound through tailored incident wave profiles.
The project investigates how acoustic geometry and resonant design influence nonlinear sound propagation in air. Engineered structures composed of air-filled cavities, ducts, and subwavelength resonators exhibit strong amplitude-dependent responses, enabling the formation of stable, reshaped waveforms that maintain their structure even at high sound levels. In two-dimensional acoustic networks, the inclusion of tuned resonators produces nearly isotropic propagation, allowing circular and ring-shaped wave fronts to emerge. Theoretical developments further introduce strategies for designing customized perfect absorbers capable of capturing all incoming low-frequency sound through tailored incident wave profiles.
Together, these breakthroughs redefine how intense air-borne sound can be controlled and absorbed, paving the way for smarter, more efficient technologies in noise reduction, acoustic metamaterials, and advanced wave-control systems.
