Optical Accelerometer Dual-Layer Membrane Proof Mass
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Solution Overview
Problem
Optical accelerometers and microphones based on MEMS technology face challenges in manufacturing due to the small component sizes involved, particularly in achieving large proof masses and maintaining low cross-axis sensitivity, which affects their sensitivity and accuracy.
Innovation Solution
The design incorporates a dual-layer membrane with a proof mass positioned between and attached to both membrane layers, allowing for a larger proof mass and low cross-axis sensitivity, along with a support structure that is static relative to the light source and photo detector, enabling improved sensitivity and manufacturing using surface micromachining.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical interferometry is used to measure proof mass deflection, then sensitivity and signal-to-noise ratio are improved, but manufacturing difficulty increases due to small component sizes
Solution Approach 1:
The patent transitions from planar 2D MEMS components to a 3D configuration by positioning the proof mass between two membrane layers separated by a gap. This vertical stacking approach allows larger effective proof mass volume while maintaining compatibility with surface micromachining processes, resolving the contradiction between sensitivity (requiring larger mass) and manufacturability (constrained by small component sizes).
Solution Approach 2:
The proof mass is nested between the first and second membrane layers, with the second optical element positioned between the membrane layers. This nested configuration maximizes the use of vertical space within the MEMS structure, allowing larger proof masses to be accommodated within the constrained thickness of the device, thereby improving sensitivity without significantly increasing lateral dimensions that would complicate manufacturing.
2Measurement precision
If larger proof masses are used to improve sensitivity, then measurement accuracy is enhanced, but cross-axis sensitivity increases
Solution Approach 1:
The patent employs asymmetric positioning of the proof mass and support structure within the dual-layer membrane configuration. The support structure is positioned to provide differential support that counteracts cross-axis forces, while the proof mass is strategically located to maximize sensitivity to the primary measurement axis. This asymmetric arrangement allows larger proof masses to be used without proportionally increasing cross-axis sensitivity.
Solution Approach 2:
The support structure provides localized support at specific points between the membrane layers, creating regions of different mechanical properties. This local variation in support characteristics allows the proof mass to be larger while maintaining low cross-axis sensitivity, as the support is concentrated in locations that restrain cross-axis motion but allow primary axis deflection.
3Volume of moving object
If dual-layer membrane structure is implemented to accommodate larger proof masses, then device complexity increases, but manufacturing feasibility is maintained through surface micromachining
Solution Approach 1:
The device is segmented into distinct functional layers: a first membrane layer, a second membrane layer, a support structure, and a proof mass. Each layer is manufactured separately using surface micromachining processes and then assembled. This segmentation allows complex 3D structures to be built from simpler 2D layers, maintaining manufacturing feasibility while achieving larger proof mass volumes through vertical stacking.
Solution Approach 2:
The membrane layers and support structure are preliminarily formed using surface micromachining techniques before the proof mass is positioned and attached. This preliminary fabrication of the structural framework enables subsequent integration of larger proof masses without requiring complex in-situ formation processes, thereby managing device complexity while achieving increased proof mass volume.
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 configuration enhances the sensitivity and manufacturing feasibility of optical accelerometers by allowing larger proof masses and reduced cross-axis sensitivity, improving the accuracy and efficiency of acceleration and force measurements.
Implementation Method 1
a first portion of said light propagates along a first optical path via said interferometric arrangement and a second portion of said light propagates along a second different optical path via said interferometric arrangement, thereby giving rise to an optical path difference between the first and second optical paths... and the photo detector is disposed to detect at least part of an interference pattern generated by said first and second portions of light dependent on said optical path difference
Data Source
AI summary
An optical accelerometer including an interferometric arrangement, a light source, a photodetector, a support structure that is static relative to the light source and photo detector, and a dual-layer membrane that is deflectable relative to the support structure. The dual-layer membrane includes first and second membrane layers that are mechanically coupled by a proof mass that is positioned between and attached to or integrally formed with the membrane layers. The interferometric arrangement includes a first optical element which includes or is disposed on a surface of one of the membrane layers and which is moveable relative to a second optical element which includes or is disposed on a surface of the support structure. The second optical element and at least part of the support structure are positioned between the membrane layers. The light source provides light to the interferometric arrangement and the photo detector detects an interference pattern generated by the light that is dependent on a distance between the first and second optical elements.