MEMS Accelerometer Torsional Oscillator Linearization
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Solution Overview
Problem
MEMS accelerometers with existing resonant pick-off structures suffer from high noise and scale factor errors due to non-linear effects in beam deformation, making it difficult to accurately measure acceleration.
Innovation Solution
A MEMS inertial sensor with a resonant pick-off structure featuring a torsional oscillatory mechanism where the moment of inertia varies linearly with the displacement of upper and lower masses, reducing non-linear effects and scale factor errors by using a resonant mechanical structure with oscillating upper and lower masses about an oscillation axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resonant pick-off structure is used in MEMS accelerometer, then the sensitivity is improved, but the noise and scale factor errors increase due to non-linear beam deformation
Solution Approach 1:
The patent applies the Dynamics principle by making the moment of inertia of the resonant mechanical structure variable rather than constant. The moment of inertia is modulated in sync with the drive signal at the resonant frequency, creating a dynamic system that actively compensates for non-linear effects. This dynamic modulation allows the structure to maintain linear response characteristics despite the inherent non-linearity of beam deformation, thereby reducing noise and scale factor errors while preserving sensitivity.
Solution Approach 2:
The patent implements Parameter changes by modulating the moment of inertia parameter of the resonant mechanical structure. By varying the moment of inertia in synchronization with the drive signal, the system changes its dynamic parameters to counteract non-linear deformation effects. This parameter modulation transforms the fixed-moment-of-inertia system into a variable-moment-of-inertia system, enabling linearization of the response and reduction of measurement errors.
2Ease of manufacture
If the moment of inertia of the resonant mechanical structure is constant, then the structure is simple to manufacture, but the response to applied forces becomes non-linear causing scale factor errors
Solution Approach 1:
The patent transitions from a static moment of inertia to a dynamic, variable moment of inertia. The resonant mechanical structure is designed with movable masses that can be positioned to change the moment of inertia in sync with the drive signal. This dynamic approach maintains manufacturing feasibility while achieving linear response characteristics, as the variable moment of inertia is controlled through actuation rather than complex structural design.
Solution Approach 2:
The patent applies Periodic action by modulating the moment of inertia at the resonant frequency of the mechanical structure. The moment of inertia varies periodically in sync with the drive signal, creating a rhythmic adjustment that counteracts non-linear effects during each oscillation cycle. This periodic modulation ensures that the linearizing effect is continuously applied during measurement operations.
3Ease of manufacture
If a capacitive pick-off is used in MEMS accelerometer, then the manufacturing is simplified, but the signal-to-noise ratio becomes unacceptably low
Solution Approach 1:
The patent replaces the capacitive pick-off mechanism with a resonant mechanical pick-off structure. Instead of using capacitive sensing elements that suffer from low signal-to-noise ratios, the invention employs a resonant mechanical structure with variable moment of inertia that provides enhanced sensitivity. This substitution maintains the simplicity of manufacturing while dramatically improving the signal-to-noise ratio through resonant amplification and linearized response.
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 significantly reduces noise and scale factor errors by linearizing the response to applied forces, enhancing the accuracy of acceleration measurements.
Implementation Method 1
a resonant mechanical structure configured to oscillate upper and lower masses about an oscillation axis
Implementation Method 2
The body has a moment of inertia when the upper and lower masses are oscillating about the oscillation axis
Implementation Method 3
When the body accelerates, the reference mass moves relative to the housing
Data Source
AI summary
A resonant mechanical structure, such as one for use in a torsional oscillator MEMS accelerometer that includes a mounting substrate and a reference mass configured to move within a reference mass plane, the resonant mechanical structure being connected to the mounting structure and the reference mass, and the resonant mechanical structure including a body, a center of mass, and an aperture, wherein the aperture is surrounded and defined by the body, and wherein the body includes a first mass portion and a second mass portion that are configured to oscillate about an oscillation axis located within the reference mass plane, wherein the center of mass is located on the oscillation axis, and wherein a movement of the reference mass within the reference mass plane varies a moment of inertia of the body while the center of mass of the body remains located on the oscillation axis.