Stacked MEMS Microphone Wind Noise Cancellation

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Solution Overview

Problem

Microelectromechanical systems (MEMS) microphones are prone to signal distortion and damage from high sound pressure levels, particularly wind noise, which introduces non-linearity and limits the signal-to-noise ratio (SNR), making it difficult to achieve SNR greater than 66 dB and requiring effective wind noise rejection.

Innovation Solution

A microphone design featuring two stacked MEMS structures with membranes and backplates, where movement of one membrane away from its backplate corresponds to the other membrane's movement towards its backplate, generating signals 180 degrees out of phase, allowing for improved wind noise cancellation and increased SNR through signal processing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a single MEMS microphone structure is used, then the device size is minimized, but the signal-to-noise ratio is limited and wind noise causes non-linearity

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidmicrophone structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The single microphone structure is segmented into two separate microphone structures, each with its own membrane and backplate assembly. These two structures process sound signals independently and then combine their outputs, allowing each structure to operate in a more linear range and reject wind noise more effectively, thereby improving the signal-to-noise ratio without requiring a single complex structure

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Two separate microphone structures are merged into a single integrated device with shared components such as the sound inlet and housing. The electrical outputs of both microphone structures are combined through signal processing circuits, achieving improved wind noise rejection and higher signal-to-noise ratio while maintaining a compact form factor that does not significantly increase overall device complexity

Inventive Principle:

Principle #5Merging (Combining)

2Object-affected harmful factors

If mechanical pop and wind noise shields are added, then wind noise rejection is improved, but the device size increases

Engineering Contradiction:

Improvewind noise rejectionVSAvoidmicrophone volume

Core Design Contradiction:

Object-affected harmful factorsVSVolume of moving object

Solution Approach 1:

The wind noise rejection function is extracted from the mechanical domain and implemented in the electrical signal processing domain. By using two microphone structures whose outputs are combined through electronic processing, wind noise is rejected algorithmically without requiring physical shields, thereby maintaining a compact microphone volume while achieving effective wind noise rejection

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The mechanical wind noise shielding system is replaced with an electrical signal processing system. Instead of using physical barriers to block or diffuse wind noise, the invention uses electronic processing of signals from two microphone structures to achieve wind noise rejection, substituting mechanical complexity with electrical processing and maintaining a smaller overall device volume

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If algorithmic wind noise suppression is used, then the device complexity is minimized, but effectiveness is limited when transducers operate non-linearly

Engineering Contradiction:

Improvesignal processing complexityVSAvoidwind noise suppression effectiveness

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Linearity is preserved in advance by designing two microphone structures that both operate within their linear ranges before signal processing occurs. By ensuring that neither transducer experiences severe non-linearity from wind noise, the subsequent algorithmic combination of signals remains effective, allowing simple signal processing to achieve reliable wind noise suppression without requiring complex non-linear compensation algorithms

Inventive Principle:

Principle #10Preliminary action

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 design enhances SNR, reduces total harmonic distortion, and enables dynamic range augmentation, effectively addressing the limitations of MEMS microphones by detecting non-linearities and adapting to high sound pressure levels.

Implementation Method 1

Loudspeakers and microphones essentially comprise a movable diaphragm or other member which provides conversion between a sound pressure wave and an electrical signal

Methodology Applied

Scientific EffectCapacitive transduction: Capacitance

Data Source

PatentUS9609429B2Microphone

Publication Date: 2017.03.28 KNOWLES IPC M

AI summary

A microphone comprises a sound inlet, a first MEMS microphone structure comprising a first membrane and associated backplate in the path of the sound inlet and a second MEMS microphone structure comprising a second membrane and associated backplate stacked with respect to the first microphone membrane, with an enclosed space between the first and second membranes.