Mechanically-Coupled Diaphragms for MEMS Microphone Sensitivity
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Solution Overview
Problem
MEMS microphones face limitations in dynamic range due to total harmonic distortion at the upper end and noise floor at the lower end, which restricts their acoustic quality and sensitivity.
Innovation Solution
A microphone system with mechanically-coupled primary and reference diaphragms that move inversely to each other, increasing signal sensitivity while maintaining a comparable height profile, by varying the capacitance in response to acoustic signals through a torsion bar and beam mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single diaphragm is used in MEMS microphones, then the device size is small, but the sensitivity and acoustic quality are limited
Solution Approach 1:
The single diaphragm is segmented into two separate diaphragms: a primary diaphragm that directly receives acoustic signals and a reference diaphragm that is mechanically coupled to move inversely. This segmentation allows each diaphragm to contribute to the output signal, effectively doubling the signal strength while maintaining a compact MEMS structure.
Solution Approach 2:
A mechanical coupler acts as an intermediary between the primary and reference diaphragms, transferring mechanical motion from the primary diaphragm to the reference diaphragm in inverse proportion. This intermediary mechanism enables the reference diaphragm to move opposite to the primary diaphragm, creating additive capacitance changes that enhance sensitivity.
2Measurement precision
If the diaphragm area is increased to improve sensitivity, then the acoustic quality improves, but the height profile increases
Solution Approach 1:
Instead of increasing sensitivity by enlarging the diaphragm area in the planar dimension, the invention uses the vertical dimension by stacking two diaphragms with inverse motion. The mechanical coupler transfers motion vertically, allowing both diaphragms to contribute to signal output without increasing the overall height profile significantly.
Solution Approach 2:
The reference diaphragm is made dynamically responsive through mechanical coupling, allowing it to move inversely to the primary diaphragm in response to acoustic signals. This dynamic configuration enables the system to effectively double the signal output without requiring larger static dimensions.
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 system produces an output signal with greater sensitivity than conventional MEMS microphones of similar size, enhancing acoustic quality by effectively increasing the electrical signal from impinging acoustic energy.
Implementation Method 1
the primary diaphragm and the backplate forming a variable primary capacitance across the primary gap, such that the primary capacitance varies in response to the acoustic signal impinging on the primary diaphragm
Implementation Method 2
the reference diaphragm forming a variable reference capacitance with the reference electrode across the variable reference gap; the mechanical coupler is configured to vary the reference gap inversely and proportionately to the variation of primary gap
Implementation Method 3
the mechanical coupler includes a torsion bar supported by at least one anchor coupled to a substrate, the torsion bar between the primary diaphragm and the reference diaphragm
Data Source
AI summary
A microphone system has two diaphragms and are mechanically interconnected such that they respond in antiphase to an acoustic signal impinging on one of the diaphragms. The two diaphragms produce two variable capacitances that vary proportionately but inversely to one another. Voltage signals produced by the two variable capacitances are summed to provide an output signal proportional to the acoustic signal, but with greater sensitivity than a single-diaphragm microphone.