Z-axis MEMS Accelerometer with Tilting Masses for Sensitivity
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Solution Overview
Problem
Existing z-axis MEMS structures face limitations in scalability and sensitivity due to reduced dimensions, which result in decreased moment of inertia and limited rotation angle variation in response to external accelerations.
Innovation Solution
The MEMS detection structure incorporates a substrate with a translating mass and tilting masses connected by elastic elements, allowing for increased distance between the centroid and rotation axes, enhancing the equivalent arm length and sensitivity through dual-rotating tilting masses and a translating mass configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the dimensions of the MEMS structure are reduced, then the device size is minimized, but the moment of inertia decreases and sensitivity is reduced
Solution Approach 1:
The detection mass is divided into multiple segments (first detection mass portion, second detection mass portion, third detection mass portion) connected by elastic anchorage elements. This segmentation allows the structure to achieve both compact dimensions and sufficient moment of inertia through the distributed mass arrangement and the mechanical leverage provided by the elastic elements acting as force multipliers.
2Length of moving object
If the detection mass is positioned closer to the rotation axis, then the structure is more compact, but the rotation angle variation in response to acceleration is limited
Solution Approach 1:
Elastic anchorage elements are introduced as intermediary components between the detection mass segments and the substrate. These elastic elements act as mediators that amplify the rotational motion through their compliance and elastic deformation, allowing the detection mass to achieve larger rotation angle variations even when positioned closer to the rotation axis, thereby maintaining sensitivity in a compact configuration.
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 configuration significantly improves sensitivity by allowing twice the rotation angle variation per external acceleration, enabling better detection capabilities while maintaining or reducing mass and dimensions, and allowing for independent adjustment of damping coefficients.
Implementation Method 1
The elastic connection elements 8 are configured to be compliant to torsion about their extension direction, thus enabling rotation of the detection mass 3 out of the plane xy, about the rotation axis A
Implementation Method 2
In use, in response to an acceleration acting in the orthogonal direction z, the detection mass 3, due to its eccentricity with respect to the rotation axis A, turns about the latter, by an inertial effect
Implementation Method 3
the first and second fixed electrodes 5a, 5b are positioned, respectively, underneath the first and second portions 3a, 3b of the detection mass 3... define, together with the detection mass 3, a first a second sensing capacitors with plane and parallel faces, designated as a whole by C1, C2
Data Source
AI summary
A z-axis micro-electro-mechanical detection structure, having a substrate defining a plane and a suspended mass carried by two anchorage elements. The suspended mass includes a translating mass, suspended over the substrate, mobile in a transverse direction to the plane and arranged between the anchorage elements and two tilting masses, each of which is supported by the anchorage elements through respective elastic anchorage elements so as to be able to rotate with respect to respective oscillation axes. The oscillation axes are parallel to each other to enable a translation movement of the translating mass. Fixed electrodes face at a distance the tilting masses or the translating mass so as to be able to detect displacement of the suspended mass as a result of external forces. Elastic supporting elements are arranged between the translating mass and the tilting masses to enable relative rotation between the translating mass and the tilting masses.