Acoustic Diode Using Rotating Cavity for Non-Reciprocal Sound
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Solution Overview
Problem
Current acoustic devices for non-reciprocal sound propagation are either bulky, require high input powers, or are limited to specific wave types, making them unsuitable for compact, efficient sound isolation in linear systems, particularly for longitudinal waves in gases like air.
Innovation Solution
A non-reciprocal acoustic device utilizing an azimuthally symmetric acoustical cavity with angular momentum bias, achieved through circular motion of the filling medium, inducing total transmission in one direction and zero transmission in another, effectively creating a compact acoustic diode or circulator for longitudinal waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnetic bias is used to induce non-reciprocity (acoustic Faraday effect), then non-reciprocal propagation is achieved, but the device becomes very bulky and larger than the wavelength
Solution Approach 1:
The patent replaces magnetic bias (acoustic Faraday effect) with mechanical rotation of the cavity. The rotating cavity walls directly impart angular momentum to the acoustic waves, eliminating the need for magnetic fields and the associated bulky device structure. This mechanical substitution achieves the same non-reciprocal effect in a compact geometry.
Solution Approach 2:
The patent introduces dynamic rotation of the cavity as the biasing mechanism. The rotating cavity creates time-varying boundary conditions that break time-reversal symmetry, enabling non-reciprocal propagation. This dynamic approach allows compact device design compared to static magnetic biasing methods.
2Reliability
If non-linear media are used to achieve acoustic non-reciprocity, then isolation is achieved, but very high input powers are required and the frequency of the signal is drastically modified
Solution Approach 1:
The patent changes the system parameter from non-linear medium to linear rotating cavity. By using a linear acoustical system with rotational bias, the device achieves non-reciprocity without requiring high input powers or frequency conversion. The rotation speed and cavity geometry are the controlling parameters, not input power levels.
3Reliability
If mechanical motion is used to realize an acoustic gyrator, then non-reciprocal phase shifting is achieved, but the device is very bulky and limited to transverse waves on pipes
Solution Approach 1:
The patent creates a universal non-reciprocal device that works for both longitudinal and transverse waves, unlike acoustic gyrators limited to transverse waves. The rotating cavity configuration supports multiple wave types, making the device more versatile and applicable to different acoustic scenarios without requiring separate specialized structures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables efficient, compact, and low-power non-reciprocal sound propagation without distorting input signals, achieving significant acoustic isolation (>30 dB) and tunable operation, suitable for audible sound isolation and wave manipulation.
Implementation Method 1
angular momentum bias, achieved through circular motion of the filling medium
Implementation Method 2
angular momentum bias, achieved through circular motion of the filling medium
Data Source
AI summary
A non-reciprocal acoustic device that accomplishes non-reciprocity via linear or angular-momentum bias. The non-reciprocal acoustic device includes an azimuthally symmetric or planar acoustical cavity (e.g., ring cavity), where the cavity is biased by imposing a circular or linear motion of a gas, a fluid or a solid medium filling the cavity. Acoustic waveguides are connected to the cavity or the cavity is excited from the surrounding medium. A port of this device is excited with an acoustic wave. When the cavity is biased appropriately, the acoustic wave is transmitted to one of the other acoustic waveguides while no transmission of the acoustic wave occurs at the other acoustic waveguides. As a result, linear non-reciprocity is now realized in acoustics without distorting the input signal or requiring high input power or bulky devices.