Observation of non-reciprocal harmonic conversion in real sounds

Area of Science:

• Acoustics
• Non-linear physics
• Metamaterials

Background:

• Reciprocity ensures symmetric sound transmission in most media, a fundamental principle.
• Breaking reciprocity typically requires high power, significant losses, and pure tones.
• Previous non-reciprocal acoustics could not handle complex sounds with multiple harmonics.

Purpose of the Study:

• To achieve non-reciprocal sound transmission for complex audio signals, preserving timbre.
• To develop a system that operates with low input power and handles arbitrary audible frequencies.
• To enable tunable control over sound transmission, including non-reciprocal gain.

Main Methods:

• Developed a non-linear, actively reconfigurable, and non-Hermitian acoustic isolator.
• Tested the isolator with complex sound notes containing multiple harmonics, including those from musical instruments.
• Characterized isolation levels and tunable gain across audible frequencies at low input power.

Main Results:

• Achieved large, tunable, and timbre-preserved non-reciprocal transmission of complex sound notes.
• Demonstrated high isolation levels up to 30dB.
• The system operates effectively at arbitrarily low input power across the audible spectrum.

Conclusions:

• Successfully extended non-reciprocal acoustics to handle real-world, complex sounds.
• The developed acoustic isolator offers significant advantages in power efficiency and tunability.
• Potential applications include advanced sound isolation, noise control, and analog audio processing.