MEMS Optical Microphone Variable Transmittance Filter
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Solution Overview
Problem
The sensitivity of existing MEMS optical microphones is reduced due to the intensity of light entering the photo detector depending on the location on the optical filter through which the reflected light passes.
Innovation Solution
The MEMS optical microphone incorporates an optical filter with variable transmittance, where the transmittance varies along a linear direction, has a central region with maximum transmittance and edge regions with minimum transmittance, or includes a plurality of gratings with gradient transmittance, to enhance light detection sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional optical filter with uniform transmittance is used, then the structure is simple, but the sensitivity of the MEMS optical microphone is reduced
Solution Approach 1:
The optical filter is designed with spatially varying transmittance properties. The filter includes a first region with first transmittance and a second region with second transmittance, where the transmittance values differ across different locations. This local variation in optical properties allows different portions of the reflected light to be transmitted with different intensities, thereby enhancing the sensitivity of the photo detector to membrane deflections without requiring complex mechanical or optical structures.
2Adaptability or versatility
If the light detection unit uses a single photo detector, then the device structure is simple, but the dynamic range is limited
Solution Approach 1:
The light detection unit is segmented into multiple photo detectors arranged in an array. Each photo detector corresponds to a specific region of the optical filter and detects light transmitted through that region. This segmentation allows the system to simultaneously measure light intensities across multiple transmittance values, thereby expanding the dynamic range of the microphone to accommodate a wider range of sound or pressure signals.
Solution Approach 2:
The solution transitions from a single-point detection (one photo detector) to a spatially distributed detection system (array of photo detectors). By arranging photo detectors in an array that corresponds to different regions of the optical filter, the system adds a spatial dimension to the detection process, enabling simultaneous measurement of multiple light intensity levels and thus expanding the dynamic range.
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 implementation of the optical filter with variable transmittance significantly improves the sensitivity and dynamic range of the MEMS optical microphone, allowing for a wider range of sound or pressure signals to be sensed with higher sensitivity.
Implementation Method 1
a first reflective coating coated on a surface of the membrane facing the light source and configured to reflect the light beam
Implementation Method 2
an optical filter with a variable transmittance hoisted above the photo detector... the transmittance of the optical filter varies along a linear direction between two edges of the optical filter
Implementation Method 3
a photo detector configured to convert light intensity into photo current
Data Source
AI summary
A MEMS optical microphone includes: a housing including an inner cavity and a sound port communicating the inner cavity with outside, a light source configured to emitting a light beam, a MEMS module including a membrane suspended above the sound port, and a first reflective coating coated on a surface of the membrane facing the light source and configured to reflect the light beam; a light detection unit configured to detecting light reflecting from the first reflective coating, including a photo detector configured to convert light intensity into photo current, and an optical filter with a variable transmittance hoisted above the photo detector. The MEMS optical microphone has wider dynamic range and higher sensitivity.