Resonant MEMS Accelerometer Asymmetric Capacitive Gaps
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Solution Overview
Problem
Existing navigational-grade accelerometers face limitations in dynamic range and sensitivity to spurious vibrations, with prior art requiring complex designs and low natural frequencies to achieve high quality factors, which restricts their ability to handle large input ranges while accurately resolving small inertial signals.
Innovation Solution
A resonant MEMS accelerometer with a single proof mass and asymmetric capacitive transduction gaps, utilizing electrostatically-induced frequency shifts and vacuum packaging, allows for high dynamic ranges and reduced sensitivity to spurious vibrations by employing frequency modulation and self-calibration techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If prior art resonant MEMS accelerometers use two independent resonators with in-phase and anti-phase modes to achieve high Q factor, then quality factor is improved, but device complexity increases and spurious vibration sensitivity remains high due to low operating frequency
Solution Approach 1:
The patent extracts and eliminates the anti-phase mode resonator from the prior art design, using only a single in-phase mode resonator. This simplification maintains high Q factor performance while reducing device complexity and removing the need for complicated electronics readout schemes required for dual-mode operation.
Solution Approach 2:
The patent increases the natural frequency of the resonator from the typical 10 kHz in prior art to greater than 10 kHz, which simultaneously improves spurious vibration rejection (by 25 to 2500×) while maintaining high Q factor through vacuum packaging and optimized mechanical design.
2Device complexity
If static MEMS accelerometers use amplitude modulation readout mechanism, then device design is simplified, but dynamic range is limited to 6
Solution Approach 1:
The patent replaces the amplitude modulation (AM) readout mechanism with frequency modulation (FM) readout. This substitution enables dynamic ranges exceeding 10^9 by measuring frequency shifts of the resonator, allowing the system to simultaneously handle large input ranges (>±100 g to ±1000 g) and resolve small inertial signals below 1 μg.
3Reliability
If resonant MEMS accelerometers operate at low natural frequency to achieve high Q factor, then quality factor is improved, but sensitivity to spurious vibrations increases
Solution Approach 1:
The patent changes the operating frequency parameter from low (10 kHz) to high (greater than 10 kHz) through vacuum packaging and optimized mechanical design. This frequency increase provides 25 to 2500× reduced sensitivity to spurious vibration signals while maintaining high Q factor greater than 10,000.
4Reliability
If prior art resonant MEMS accelerometers use two proof masses to create in-phase and anti-phase modes, then quality factor is improved, but available proof mass for sensitivity is reduced
Solution Approach 1:
The patent removes the anti-phase mode resonator and its associated proof mass from the design, utilizing only a single in-phase mode resonator with one proof mass. This extraction maintains high Q factor while preserving maximum proof mass for sensitivity, eliminating the trade-off present in prior art.
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 solution achieves dynamic ranges exceeding 10^9, enabling large input ranges while accurately resolving small signals, with improved resistance to spurious vibrations and simplified device design compared to prior art.
Implementation Method 1
one or more springs connecting the proof mass to an anchor and one or more capacitive transduction gaps (which may comprise a void between the movable proof mass and a corresponding fixed electrode)
Implementation Method 2
by utilizing MEMS design and vacuum packaging technologies, produces silicon accelerometer structures with Q factors greater than 10,000
Implementation Method 3
the presently disclosed technology, by utilizing MEMS design and vacuum packaging technologies, produces silicon accelerometer structures with Q factors greater than 10,000 with natural frequencies greater than 10 kHz
Data Source
AI summary
A resonant accelerometer includes a proof mass, one or more springs connecting the proof mass to an anchor, and one or more capacitive transduction gaps providing a void or space between the movable proof mass and a corresponding fixed electrode, wherein the static displacement of the proof mass in response to acceleration applied to the anchor modifies the electrostatic stiffness imparted by one or more of the capacitive transduction gaps on the proof mass, resulting in a corresponding change in the resonance frequency of the resonant accelerometer.