MEMS Inertial Sensor with Weakly Coupled Resonant Elements
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Solution Overview
Problem
Microscopic mechanical inertial sensors, such as MEMS resonant accelerometers and gyroscopes, have lower resolution than required for inertial grade navigation systems, limiting their effectiveness in applications that demand higher sensitivity and accuracy.
Innovation Solution
The development of an inertial sensor comprising a proof mass and two weakly coupled resonant elements, where the coupling between the elements is electrostatic or mechanical, allowing for mode localization and enhanced sensitivity by measuring strain modulation through eigenstate variations, rather than conventional frequency shifts, thereby increasing output sensitivity and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional resonant frequency shift measurement is used in MEMS inertial sensors, then the sensor structure is simple, but the resolution and output sensitivity are insufficient for inertial grade navigation systems
Solution Approach 1:
The sensor divides the resonant system into two separate resonant elements (first and second resonant elements) with distinct functions. One element is coupled to the proof mass for sensing, while the other serves as a reference, enabling differential measurement that significantly improves resolution for inertial grade navigation applications.
Solution Approach 2:
The patent transitions from measuring resonant frequency shifts to measuring amplitude ratios at fixed drive frequencies. This parameter change enables higher output sensitivity by utilizing the amplitude response characteristics of the resonant elements, achieving the required resolution for inertial grade navigation without requiring complex frequency tracking circuitry.
2Measurement precision
If resonant frequency shift based measurement is used, then the sensor design is straightforward, but the output sensitivity is orders of magnitude lower than required for navigation systems
Solution Approach 1:
The patent drives both resonant elements at fixed frequencies below their resonant frequencies, rather than operating at resonance. This partial resonance approach simplifies the measurement system while achieving high output sensitivity through amplitude ratio detection, meeting navigation system requirements without excessive measurement complexity.
Solution Approach 2:
The second resonant element acts as an intermediary reference that is not coupled to the proof mass. By comparing the amplitude ratios between the sensing element and this reference element, the system achieves high output sensitivity while canceling out common-mode environmental variations, reducing measurement complexity.
3Object-affected harmful factors
If single resonant element design is used, then the device is simple, but it is highly sensitive to environmental variations such as temperature
Solution Approach 1:
The patent assigns different local qualities to the two resonant elements: one is coupled to the proof mass and experiences strain modulation from inertial forces, while the other remains uncoupled and serves as a stable reference. This local differentiation enables the system to reject environmental variations while maintaining sensitivity to inertial inputs.
Solution Approach 2:
The sensor design introduces asymmetry by coupling only one resonant element to the proof mass while leaving the other uncoupled. This asymmetric configuration creates a differential measurement system where environmental effects appear as common-mode signals that can be rejected, reducing environmental sensitivity while using a relatively simple dual-element structure.
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 approach results in orders of magnitude enhancement in output sensitivity and resolution, making the sensors less sensitive to environmental variations and enabling more precise inertial force measurement without active or passive control techniques.
Implementation Method 1
a drive means coupled to the first and second resonant elements for vibrating the first and second resonant elements; and a sensor assembly for detecting the amplitude of vibration of the resonant elements
Implementation Method 2
the means for coupling the first resonant element to the second resonant element is an electrostatic coupling means
Data Source
AI summary
The invention comprises an inertia! sensor comprising a frame, a proof mass; a first resonant element having a proximal end and a distal end, the first resonant element being fixed to the frame at its proximal end and coupled to the proof mass at its distal end, a second resonant element having a proximal end and a distal end, the second resonant element being fixed to the frame at its proximal end, adjacent to the first resonant element such that there is no coupling between the second resonant element and the proof mass, a means for coupling the first resonant element to the second resonant element; a drive means coupled to the first and second resonant elements for vibrating the first and second resonant elements; and a sensor assembly for detecting the amplitude of vibration of the resonant elements.