Fiber Microphone Detecting Acoustic Particle Velocity

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Solution Overview

Problem

Conventional miniature directional microphones face limitations in achieving high-order directionality due to microphone self-noise, sensitivity matching, phase matching, and size constraints, which hinder their performance in noisy environments, especially at low frequencies.

Innovation Solution

A fiber microphone that detects acoustic particle velocity instead of pressure, utilizing a thin fiber held on its ends within a magnetic field to induce a voltage, allowing for directional sound sensing with flat frequency response and reduced noise, independent of frequency and external power.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional miniature directional microphones are used, then directional sound sensing is achieved, but microphone self-noise and sensitivity matching issues worsen performance in noisy environments

Engineering Contradiction:

Improvedirectional sound sensing precisionVSAvoidmicrophone self-noise

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent replaces conventional pressure-sensitive diaphragm-based acoustic sensing with a fiber optic sensing system that detects acoustic particle velocity through optical interference. This substitution eliminates microphone self-noise and sensitivity matching issues by using light instead of mechanical pressure sensing elements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an optical intermediary (fiber optic probe) that converts acoustic particle velocity into optical phase shifts. This intermediary mechanism avoids direct electrical sensing, thereby eliminating self-noise and enabling high-precision directional sound sensing in noisy environments.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If higher-order microphone arrays are employed, then directional response in noisy environments is improved, but device size and complexity increase significantly

Engineering Contradiction:

Improvedirectional response accuracyVSAvoidmicrophone array complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces complex multi-microphone arrays with a single fiber optic probe that inherently provides directional sensitivity through its orientation relative to acoustic particle velocity. This substitution dramatically reduces device complexity while maintaining or improving directional response accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

Instead of using multiple microphones to achieve directionality through spatial sampling and signal processing, the patent inverts the approach by using a single sensor whose output directly encodes directional information through its response to acoustic particle velocity, eliminating the need for complex arrays.

Inventive Principle:

Principle #13The other way round (Inversion)

3Ease of operation

If pressure-based acoustic sensing is used, then conventional microphone operation is maintained, but frequency response deteriorates at low frequencies

Engineering Contradiction:

Improvemicrophone operation simplicityVSAvoidfrequency response consistency

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent replaces pressure-based sensing with particle velocity-based sensing using fiber optic interferometry. This substitution maintains operational simplicity while achieving reliable, flat frequency response across the audible range, including low frequencies where conventional pressure microphones deteriorate.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 fiber microphone provides a directional output with improved speech intelligibility in noisy environments, overcoming the limitations of existing technologies by mimicking the natural hair-based flow sensors, achieving first-order directivity with flat frequency response and low noise floor.

Implementation Method 1

a fiber or ribbon provided as a vibration-sensing conductive element in a fluid medium, employing a magnetic field to induce a voltage across the conductive element as a result of oscillations within the magnetic field

Methodology Applied

Scientific EffectViscous drag: Drag

Implementation Method 2

employing a magnetic field to induce a voltage across the conductive element as a result of oscillations within the magnetic field

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS11490208B2Fiber microphone

Publication Date: 2022.11.01 THE RES FOUNDATION FOR THE STATE UNIV OF NEW YORK

AI summary

A microphone, comprising at least two electrodes, spaced apart, configured to have a magnetic field within a space between the at least two electrodes; a conductive fiber, suspended between the at least two electrodes; in an air or fluid space subject to waves; wherein the conductive fiber has a radius and length such that a movement of at least a central portion of the conductive fiber approximates an oscillating movement of air or fluid surrounding the conductive fiber along an axis normal to the conductive fiber. An electrical signal is produced between two of the at least two electrodes, due to a movement of the conductive fiber within a magnetic field, due to viscous drag of the moving air or fluid surrounding the conductive fiber. The microphone may have a noise floor of less than 69 dBA using an amplifier having an input noise of 10 nV/√Hz.