In-Plane MEMS Accelerometer Using L-Shaped Proof Mass
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Solution Overview
Problem
Traditional in-plane monolithic MEMS accelerometers require separate lever arms for mechanical amplification, leading to complexity and increased error in acceleration measurement, while existing vibrating beam accelerometers sense only out-of-plane displacement and are expensive to produce.
Innovation Solution
A monolithic, planar vibrating beam accelerometer with an in-plane pendulous proof mass that rotates within the support base plane, using double-ended tuning forks and electrodes to convert rotational force into frequency changes, eliminating the need for separate leveraging elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate lever arms are used for mechanical amplification in traditional in-plane monolithic MEMS accelerometers, then the amplification of proof mass displacement is achieved, but the device complexity and measurement error increase
Solution Approach 1:
The patent merges the lever arm function directly into the proof mass structure by creating an L-shaped proof mass where the vertical portion acts as both the suspended mass and the lever arm. This integration eliminates separate lever arm components while maintaining the mechanical amplification function, thereby reducing device complexity and potential error sources from additional joints.
Solution Approach 2:
The vertical portion of the L-shaped proof mass serves multiple functions simultaneously: it acts as the suspended proof mass, provides the lever arm for mechanical amplification, and serves as the support structure for mounting resonators. This multi-functionality reduces the number of separate components needed in the accelerometer structure.
2Ease of manufacture
If out-of-plane displacement sensing is used in existing vibrating beam accelerometers, then the sensing mechanism is simplified, but the ability to sense in-plane displacements is lost and production cost increases
Solution Approach 1:
The patent employs double-ended tuning fork resonators that vibrate in the out-of-plane direction (perpendicular to the substrate) to sense in-plane displacement of the proof mass. The resonators are mounted on the vertical portion of the L-shaped proof mass, and their vibration frequency changes in response to the proof mass displacement caused by in-plane acceleration, enabling cost-effective in-plane sensing through out-of-plane vibration.
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 design results in more accurate, cost-effective, and reliable accelerometers with a smaller profile and digital output, capable of sensing in-plane displacements without additional mechanical joints.
Implementation Method 1
The DETF is a resonator, which is specifically designed to change frequency proportional to the load applied by the proof mass under acceleration. The at least two resonators resonate at a respective resonant frequency.
Implementation Method 2
The tines of the DETF may be composed of a piezoelectric or a silicon material.
Data Source
AI summary
A device is described that includes a pendulous proof mass, a support base, a flexure, and at least two resonators. The support base defines a plane and supports the pendulous proof mass. The flexure flexibly connects the pendulous proof mass to the support base, suspends the pendulous proof mass within the support base, and in response to an acceleration of the device, the pendulous proof mass rotates about the flexure in the plane defined by the support base. The at least two resonators flexibly connect the pendulous proof mass to the support base and flex based on the rotation of the pendulous proof mass about the flexure, wherein each of the at least two resonators resonate at a respective resonant frequency.