Spherically Steerable Microphone Array for 3D Beamforming

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Solution Overview

Problem

Existing microphone arrays face limitations in achieving spherically steerable, direction-invariant directivity patterns across a wide range of frequencies, particularly due to axial or circular symmetry and noise amplification issues, which restrict their application in three-dimensional sound fields.

Innovation Solution

A Spherically Steerable Vector Differential Microphone Array is designed with a circular arrangement of pressure and acoustic particle velocity sensors, enabling arbitrary beam selection and three-dimensional steering, achieving up to third-order spherical harmonic decomposition for direction-invariant steered beams.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a linear configuration of microphones is used, then the device complexity is reduced, but the beam can be steered only in two directions, limiting adaptability

Engineering Contradiction:

Improvemicrophone array configurationVSAvoidbeam steering capability

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent transitions from linear (1D) or planar (2D) microphone configurations to a three-dimensional spherical configuration. The microphones are positioned on the surface of a sphere, enabling beam steering in all three spatial dimensions while maintaining relatively simple omnidirectional microphone elements.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Measurement precision

If a rigid spherical microphone array is used, then spherical harmonic decomposition capability is improved, but the array interacts with the sound field being recorded, causing harmful effects

Engineering Contradiction:

Improvespherical harmonic decompositionVSAvoidsound field interaction

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent removes the rigid spherical baffle from the microphone array design. Instead of mounting microphones on a rigid spherical surface that interacts with sound waves, the invention uses a virtual or software-defined spherical geometry, extracting the spherical harmonic decomposition capability from the physical rigid structure.

Inventive Principle:

Principle #2Taking out (Extraction)

3Measurement precision

If differential microphone arrays are used, then directivity pattern control is improved, but noise amplification occurs, especially at low frequencies

Engineering Contradiction:

Improvedirectivity pattern controlVSAvoidnoise amplification

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent changes the operational parameters of the microphone array by using omnidirectional microphones with specific polar patterns and applying frequency-dependent weighting in the spherical harmonic decomposition process. This approach maintains directivity control while reducing noise amplification through optimized signal processing parameters.

Inventive Principle:

Principle #35Parameter changes

4Measurement precision

If microphones are positioned on a rigid spherical baffle, then spherical harmonic decomposition up to given order is achieved, but the form factor increases, increasing interaction with sound field

Engineering Contradiction:

Improvespherical harmonic decompositionVSAvoidarray form factor

Core Design Contradiction:

Measurement precisionVSVolume of stationary object

Solution Approach 1:

The patent replaces the rigid spherical baffle with a flexible or minimal physical structure. The spherical geometry is maintained through software-defined positions and signal processing rather than a rigid physical shell, dramatically reducing the form factor while preserving spherical harmonic decomposition capability.

Inventive Principle:

Principle #30Flexible shells and thin films

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

The array provides a spherically direction-invariant steered beam that maintains consistency across a wide frequency range, minimizing interaction with the sound field and overcoming noise amplification issues, allowing for more versatile applications in sound field recording and analysis.

Implementation Method 1

comprise P pressure sensors, wherein P is greater than or equal to 1

Methodology Applied

Scientific EffectAcoustic pressure detection: Acoustics

Implementation Method 2

Q uniaxial, biaxial or triaxial acoustic particle velocity sensors

Methodology Applied

Scientific EffectAcoustic particle velocity detection: Acoustics

Data Source

PatentUS11832052B2Spherically steerable vector differential microphone arrays

Publication Date: 2023.11.28 ORTA DOGU TEKNIK UNIVERSITESI

AI summary

A spherically steerable microphone array structure is provided. The spherically steerable microphone array structure uses pressure and acoustic particle velocity signals obtained from sensors positioned co-planarly on a circular arc. The spherically steerable microphone array structure allows a calculation of all spatial partial derivatives of a sound field up to a given order. The spatial partial derivatives are used to obtain a spherical harmonic decomposition of a recorded sound field. Spherical harmonic decomposition coefficients are used in a spherically direction-invariant acoustic mode beamforming.