MEMS Interferometer Self-Calibration via Capacitive Sensing
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Solution Overview
Problem
Existing optical interferometers face challenges in accurately determining the position of a movable mirror without increasing system size, cost, and complexity, as traditional methods require a bulky laser source and additional interferometer.
Innovation Solution
A Micro-Electro-Mechanical System (MEMS) apparatus with a movable mirror and a MEMS actuator having variable capacitance, coupled with a capacitive sensing circuit and digital signal processor, enables self-calibration by mapping capacitance to mirror position and applying correction factors, reducing the need for external lasers and complex systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser and auxiliary interferometer are used to measure the moving mirror position, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines the measurement function and actuation function into a single capacitive sensor that serves both purposes. The capacitive sensor measures mirror position while also providing the actuation signal, eliminating the need for separate laser and auxiliary interferometer systems.
Solution Approach 2:
The capacitive sensor serves itself by providing both measurement and actuation functions. The sensor measures the mirror position and simultaneously generates the actuation signal needed to control the mirror, making the system self-sufficient without external laser equipment.
2Measurement precision
If a laser and auxiliary interferometer are used to measure the moving mirror position, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent merges the measurement and actuation functions into one capacitive sensor component, eliminating the need for expensive laser sources and auxiliary interferometer equipment, thereby significantly reducing manufacturing costs.
Solution Approach 2:
The capacitive sensor provides a low-cost alternative to expensive laser-based measurement systems. By using standard capacitive sensing technology rather than precision optical equipment, the manufacturing cost is dramatically reduced.
3Measurement precision
If a laser and auxiliary interferometer are used to measure the moving mirror position, then measurement precision is improved, but the system size increases
Solution Approach 1:
The patent combines multiple functions into a single compact capacitive sensor, eliminating the need for bulky laser sources, beam splitters, and auxiliary interferometer components, thereby reducing the overall system size.
Solution Approach 2:
The patent extracts and removes the unnecessary laser and auxiliary interferometer components from the system, keeping only the essential capacitive sensor that provides both measurement and actuation in a compact form.
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 allows for precise determination of the movable mirror's position within the MEMS interferometer, integrating the system on a small chip, thereby reducing size, cost, and complexity while maintaining accuracy.
Implementation Method 1
a MEMS actuator having a variable capacitance that is coupled to the moveable mirror to cause a displacement thereof
Implementation Method 2
by using MEMS actuation (electrostatic, magnetic or thermal) to control a movable mirror of a Michelson Interferometer
Data Source
AI summary
A Micro-Electro-Mechanical System (MEMS) interferometer provides for self-calibration of mirror positioning of a moveable mirror. The moveable mirror is coupled to a MEMS actuator having a variable capacitance. The MEMS interferometer includes a capacitive sensing circuit for determining the capacitance of the MEMS actuator at two or more known positions of the moveable mirror and a calibration module for using the actuator capacitances at the known positions to compensate for any drift in the capacitive sensing circuit.