MEMS Mirror Position Sensing via Capacitive Circuit

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Solution Overview

Problem

Existing optical interferometers face challenges in determining the position of a moveable mirror with reduced size, cost, and complexity, as traditional methods require bulky laser sources and additional interferometers.

Innovation Solution

A Micro Electro-Mechanical System (MEMS) apparatus with a moveable mirror and a MEMS actuator having variable capacitance, coupled with a capacitive sensing circuit to determine the mirror's position based on current capacitance, using an electrostatic actuator and capacitive sensing circuit, and an application-specific integrated circuit for processing the capacitance data.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a laser and auxiliary interferometer are used to measure the moving mirror position, then the measurement precision is improved, but the device complexity and size increase

Engineering Contradiction:

Improvemirror position measurement precisionVSAvoidinterferometer system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts the position measurement function from the complex laser interferometer system and implements it through a simplified capacitive sensing circuit that directly measures the displacement of the MEMS mirror, eliminating the need for bulky laser sources and auxiliary interferometers while maintaining measurement capability

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the optical measurement system (laser and interferometer) with an electrical measurement system (capacitive sensing circuit), where the mechanical displacement of the MEMS mirror is converted into an electrical signal through capacitance changes, simplifying the overall system architecture

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If a laser and auxiliary interferometer are used to measure the moving mirror position, then the measurement precision is improved, but the system size increases

Engineering Contradiction:

Improvemirror position measurement precisionVSAvoidinterferometer system size

Core Design Contradiction:

Measurement precisionVSVolume of moving object

Solution Approach 1:

The patent removes the large-volume laser source and auxiliary interferometer components from the system, retaining only the essential capacitive sensing elements that can be integrated onto the MEMS chip itself, thereby dramatically reducing the overall system volume

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent integrates the capacitive sensing circuitry directly within the MEMS device structure, nesting the measurement function inside the actuator assembly, which allows the sensing elements to occupy the same space as the actuating elements rather than requiring separate external components

Inventive Principle:

Principle #7Nested doll (Nesting)

3Measurement precision

If a laser and auxiliary interferometer are used to measure the moving mirror position, then the measurement precision is improved, but the manufacturing cost increases

Engineering Contradiction:

Improvemirror position measurement precisionVSAvoidinterferometer system cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent eliminates the expensive laser source and auxiliary interferometer components, replacing them with a capacitive sensing approach that uses standard MEMS fabrication processes and integrated circuits, which are significantly cheaper to manufacture

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent employs inexpensive capacitive sensing elements that can be fabricated using standard semiconductor manufacturing techniques, replacing the costly optical components with affordable electrical measurement components that achieve the required precision at a fraction of the cost

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 solution enables precise determination of the moveable mirror's position, reducing system size, cost, and complexity while maintaining accuracy, facilitating integration into compact devices like handheld spectrometers and interferometers.

Implementation Method 1

The MEMS actuator 110 is an electrostatic actuator, such as a comb drive actuator, parallel plate actuator or other type of electrostatic actuator

Methodology Applied

Scientific EffectElectrostatic force: Electrostatics

Implementation Method 2

the MEMS actuator has a variable capacitance. A capacitive sensing circuit 130 is coupled to the MEMS actuator to sense a current capacitance of the MEMS actuator and determine a position of the moveable mirror based on the current capacitance

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentEP2545406B1A technique to determine mirror position in optical interferometers

Publication Date: 2015.02.11 SI WARE SYSTEMS INC(US)

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AI summary

A Micro Electro-Mechanical System (MEMS) interferometer system utilizes a capacitive sensing circuit to determine the position of a moveable mirror. An electrostatic MEMS actuator is coupled to the moveable mirror to cause a displacement thereof. The capacitive sensing circuit senses the current capacitance of the MEMS actuator and determines the position of the moveable mirror based on the current capacitance of the MEMS actuator.