MEMS Microphone Electrostatic Force Feedback for Acoustic Pressure

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Solution Overview

Problem

Existing MEMS microphones face accuracy issues due to aging and non-linearities, which affect the measurement of acoustic pressure, and are limited by mechanical displacement and resonance, leading to measurement inaccuracies.

Innovation Solution

A microelectromechanical systems microphone design featuring a backplate and diaphragm with multiple electrodes, where the first capacitor senses mechanical displacement and the second capacitor applies an electrostatic force to return the diaphragm to its original position, independent of mechanical parameters, using digital or analog-based electrostatic force feedback systems.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional MEMS microphone designs are used, then the device structure is simple, but measurement precision deteriorates due to aging and non-linearities

Engineering Contradiction:

Improveacoustic pressure measurement accuracyVSAvoidmicrophone structure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The backplate is divided into multiple electrodes (first electrode, second electrode, third electrode, fourth electrode) that are electrically isolated from one another. These electrodes form separate capacitors (first capacitor, second capacitor) that can independently sense displacement and apply electrostatic force, enabling precise measurement and feedback control while maintaining a relatively simple overall structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements electrostatic force feedback by using the second capacitor to apply an electrostatic force to the diaphragm based on displacement sensed by the first capacitor. This feedback mechanism compensates for non-linearities and aging effects, improving measurement precision without requiring complex external correction systems.

Inventive Principle:

Principle #23Feedback

2Reliability

If mechanical displacement sensing is used, then the device structure is simple, but reliability deteriorates due to mechanical limitations and resonance

Engineering Contradiction:

Improvemeasurement consistency over timeVSAvoidsensing system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces purely mechanical displacement sensing with an electrostatic sensing mechanism. The first capacitor senses diaphragm displacement through changes in electrical capacitance rather than mechanical contact, eliminating mechanical wear and resonance issues. The second capacitor applies electrostatic force for feedback, further reducing mechanical limitations and improving long-term reliability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If electrostatic force feedback is applied, then measurement precision improves, but energy consumption increases

Engineering Contradiction:

Improvedisplacement measurement accuracyVSAvoidelectrostatic force feedback energy

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The electrostatic force feedback is applied selectively through the second capacitor only when needed for compensation, rather than continuously. The feedback mechanism activates based on displacement sensing from the first capacitor, providing precise measurement accuracy only when required, thereby reducing unnecessary energy consumption while maintaining measurement precision.

Inventive Principle:

Principle #16Partial or excessive 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 the accuracy and dynamic range of acoustic pressure measurement by decoupling it from mechanical limitations, improving performance and reducing errors caused by aging and non-linearities, while canceling in-band resonance.

Implementation Method 1

The first electrode and the third electrode may form a first capacitor having a first capacitance... configured to sense a mechanical displacement of the diaphragm

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

the second capacitor may be configured to apply an electrostatic force to the diaphragm to return the diaphragm to an original position

Methodology Applied

Scientific EffectElectrostatic force: Electrostatics

Data Source

PatentUS10356543B2Microelectromechanical systems microphone with electrostatic force feedback to measure sound pressure

Publication Date: 2019.07.16 CIRRUS LOGIC INC

AI summary

A MEMS may include a backplate comprising first and second electrodes electrically isolated from one another and mechanically coupled to the backplate in a fixed relationship relative to the backplate, and a diaphragm configured to mechanically displace relative to the backplate as a function of sound pressure incident upon the diaphragm. The diaphragm may comprise third and fourth electrodes electrically isolated from one another and mechanically coupled to the diaphragm in a fixed relationship relative to the diaphragm such that the third and fourth electrodes mechanically displace relative to the backplate as the function of the sound pressure. The first and third electrodes may form a first capacitor, the second and fourth electrodes may form a second capacitor, and the first capacitor may be configured to sense a displacement of the diaphragm responsive to which the second capacitor may be configured to apply an electrostatic force to the diaphragm to return the diaphragm to an original position.