Resonant MEMS Accelerometer with Suspended Sensor Isolation
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Solution Overview
Problem
Existing micro-electro-mechanical systems (MEMS) accelerometers face challenges in providing high sensitivity and stability for low-frequency or quasi-static acceleration measurements, as they are susceptible to thermal stress and have limited dynamic range due to spring hardening effects and stress concentrations.
Innovation Solution
A resonant sensor design featuring proof masses suspended by serpentine flexures and connected to resonant elements via non-inverting and inverting microlevers, which isolates the resonant elements from thermal stress and uses electrode assemblies for drive and sense circuitry to provide enhanced sensitivity and stability, along with optional calibration and damping signals to improve accuracy and robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the resonant element is directly connected to the substrate, then the structural support is simplified, but thermal stress is transferred to the resonant element causing measurement drift
Solution Approach 1:
The connection between the resonant element and substrate is segmented through the introduction of lever arms and suspension mechanisms. The resonant element is not directly connected to the substrate but is instead connected through levers that are suspended by flexures, creating a segmented mechanical path that isolates thermal stress while maintaining structural support.
Solution Approach 2:
Lever arms and suspension flexures are introduced as intermediary elements between the resonant element and the substrate. These intermediaries mechanically decouple the resonant element from direct thermal contact with the substrate while still providing the necessary structural support and force transmission for acceleration sensing.
2Device complexity
If conventional MEMS accelerometer designs are used, then the device structure is simple, but sensitivity and stability for low-frequency measurements are insufficient
Solution Approach 1:
The invention utilizes mechanical resonance by designing a resonant element with specific vibrational characteristics. The resonant element is driven to vibrate at its resonant frequency, and acceleration measurements are derived from changes in this resonant frequency or vibration characteristics, providing enhanced sensitivity for low-frequency and quasi-static acceleration measurements.
Solution Approach 2:
The invention changes the operational parameters of the accelerometer by using resonant frequency as the measurement parameter instead of direct displacement measurement. By monitoring changes in the resonant frequency of the element in response to applied acceleration, the system achieves superior measurement precision and stability.
3Device complexity
If proof masses are rigidly connected to the substrate, then the mounting is simplified, but spring hardening effects and stress concentrations limit dynamic range
Solution Approach 1:
The invention employs flexible suspension elements in the form of serpentine flexures that connect the proof masses to the substrate. These flexible film-like structures provide the necessary mechanical compliance to avoid stress concentrations and spring hardening effects, enabling a larger dynamic range while maintaining a relatively simple mounting 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
The design achieves improved sensitivity and reduced thermal drift, allowing for accurate and robust high-resolution acceleration measurements with enhanced mechanical symmetry and reduced spring hardening effects, enabling better performance in low-frequency applications.
Implementation Method 1
Oscillators based on lightly damped microscopic mechanical resonators are well known for their ability to produce stable, low-noise frequency outputs
Implementation Method 2
The electrode assembly may be used both to drive the resonant element at a resonant frequency using a drive signal and to sense the response of the resonant element to the drive signal
Implementation Method 3
one or more proof masses suspended from the substrate to allow for movement of the one or more proof masses along a sensitive axis
Data Source
AI summary
The invention provides a resonant sensor comprising: a substrate; one or more proof masses suspended from the substrate to allow for movement of the one or more proof masses along a sensitive axis; a first resonant element having a first end and a second end, the first resonant element extending between the first end and the second end along the sensitive axis, wherein the first end is connected to the one or more proof masses through a non-inverting lever and the second end is connected to the one or more proof masses through an inverting lever; and an electrode assembly positioned adjacent to the first resonant element. A resonant sensor in accordance the invention comprises a resonant element that is suspended between two proof masses or between two portions of a single proof mass, and so is not connected directly to the substrate. This isolates the resonant element from thermal stress that might otherwise be transferred from the substrate.