Lateral Mode MEMS Microphone with Additive Inverse Outputs
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Solution Overview
Problem
Capacitive microphones suffer from significant mechanical noise due to squeeze film damping, which dominates noise sources and affects audio quality, especially in applications requiring high-fidelity recording.
Innovation Solution
A lateral mode capacitive microphone design is implemented, featuring two capacitors with signal outputs where one is the additive inverse of the other, reducing noise by configuring electrical conductors in a lateral mode to minimize mutual capacitance variation and squeeze film damping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two layers are placed in close proximity to each other in a parallel-plate configuration, then the microphone can convert sound into electrical signal effectively, but squeeze film damping occurs causing significant mechanical noise
Solution Approach 1:
The patent transitions from a conventional parallel-plate configuration (one-dimensional separation) to a lateral mode configuration where electrical conductors are arranged side-by-side in the same plane. This dimensional change eliminates the squeeze film damping effect that occurs when layers are stacked closely together, thereby reducing mechanical noise while maintaining signal output quality.
Solution Approach 2:
The patent employs asymmetric arrangement of electrical conductors in lateral mode, where conductors are positioned adjacent to each other rather than in symmetric parallel layers. This asymmetric configuration prevents the formation of narrow gaps that cause squeeze film damping, effectively reducing mechanical noise generation.
2Measurement precision
If layers are positioned within 5 μm gap, then capacitance sensitivity is improved, but air flow viscosity creates resistance force that dominates noise sources
Solution Approach 1:
The patent eliminates the need for sub-5 μm gap positioning by transitioning to lateral mode configuration. Electrical conductors are arranged side-by-side in the same plane rather than stacked in parallel layers, achieving capacitance sensitivity through lateral proximity instead of vertical closeness, thereby avoiding air flow viscosity issues entirely.
3Measurement precision
If membrane has large surface area to gap length ratio, then acoustic sensitivity is enhanced, but squeeze film damping becomes significant mechanical noise source
Solution Approach 1:
The patent resolves the contradiction between large surface area and noise reduction by implementing lateral mode configuration. Electrical conductors are arranged adjacent to each other in the same plane, allowing large surface area conductors to generate strong acoustic signals without creating narrow gaps that would cause squeeze film damping and mechanical noise.
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 significantly reduces mechanical noise, enhancing audio quality by partially or completely canceling out noise sources, thereby improving the overall performance of capacitive microphones in various applications.
Implementation Method 1
The mutual capacitance can be varied by an acoustic pressure impacting upon ECA1 and/or ECA2 along a range of impacting directions in 3D space, generating the signal output S1 of the first capacitor
Implementation Method 2
Dmin remains greater than zero regardless of that ECA1 and/or ECA2 is (are) impacted by an acoustic pressure along the primary direction or not
Data Source
AI summary
The present invention provides a capacitive microphone such as a MEMS microphone with two capacitors. The signal output from the first capacitor is additive inverse of that from the second capacitor, and a total signal output is a difference between the two outputs. In at least one of the two capacitors, a movable or deflectable membrane/diaphragm moves in a lateral manner relative to the fixed capacitor plate, instead of moving toward/from the fixed plate. The squeeze film damping, and the noise are substantially avoided, and the performances of the microphone is significantly improved.