MEMS Gravimeter Using Negative-Stiffness Spring for High-Sensitivity Gravity Measurement
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Solution Overview
Problem
Current gravimeters, both absolute and relative, are large, expensive, and have limitations in measurement accuracy and portability, with MEMS accelerometers falling short of the requirements for high-precision gravity measurement.
Innovation Solution
A MEMS gravimeter with a spring-mass system comprising negative-stiffness and positive-stiffness springs, a proof mass, and an outer frame, integrated using MEMS technology, which reduces equivalent stiffness and resonant frequency, allowing for high sensitivity and accuracy while minimizing size and cost through symmetric spring placement and vacuum module integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional spring-mass system with zero-length spring is used to achieve high sensitivity to acceleration change, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent changes the stiffness parameter of the spring from traditional positive stiffness to negative stiffness, fundamentally altering the mechanical characteristics of the spring-mass system. This parameter change enables the system to achieve ultra-low resonant frequency (below 1 Hz) without requiring complex zero-length spring structures, thereby improving acceleration sensitivity while simplifying the overall system design
Solution Approach 2:
The patent replaces the mechanical zero-length spring structure with an equivalent stiffness mechanism that combines negative stiffness and positive stiffness springs. This substitution eliminates the need for complex mechanical arrangements while achieving the same sensitivity enhancement effect through controlled spring deformation characteristics
2Measurement precision
If proof mass is increased to improve acceleration sensitivity, then measurement precision is improved, but device weight increases
Solution Approach 1:
The patent changes the resonant frequency parameter of the spring-mass system to below 1 Hz by using negative stiffness springs, which dramatically increases acceleration sensitivity according to the relationship Δx=Δa/ω02. This allows the use of smaller proof masses while maintaining high sensitivity, thereby reducing the overall weight of the gravimeter
3Measurement precision
If spring stiffness is reduced to improve acceleration sensitivity, then measurement precision is improved, but device stability deteriorates
Solution Approach 1:
The patent introduces asymmetric spring configuration with different stiffness characteristics - negative stiffness springs for sensitivity enhancement and positive stiffness springs for stability. This asymmetric design allows the system to achieve ultra-low resonant frequency while maintaining structural stability through the complementary roles of the two spring types
Solution Approach 2:
The patent creates a composite spring system combining negative stiffness and positive stiffness elements, where the negative stiffness component provides enhanced acceleration sensitivity and the positive stiffness component ensures system stability. This composite approach allows the system to simultaneously achieve both sensitivity and stability that cannot be obtained with single-type springs
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 MEMS gravimeter achieves high-precision and high-stability gravity measurement with reduced volume and weight, enhanced portability, and lower production costs, while maintaining or exceeding the accuracy of existing systems.
Implementation Method 1
a negative-stiffness spring and a positive-stiffness spring... matching of the positive-stiffness spring and the negative-stiffness spring effectively reduces equivalent stiffness, so that a resonant frequency of the spring-mass system is less than 5 Hz
Implementation Method 2
a resonant frequency of the spring-mass system is required to be as low as possible... matching of the positive-stiffness spring and the negative-stiffness spring effectively reduces equivalent stiffness, so that a resonant frequency of the spring-mass system is less than 5 Hz
Implementation Method 3
Gravimeter is an instrument for measuring gravity acceleration... the gravity of the proof mass is balanced with the elastic force generated by the spring deformation... when the gravity acceleration in the environment where the gravimeter is located is changed, the spring deformation is changed accordingly
Data Source
AI summary
The present invention discloses a MEMS gravimeter comprising: a spring-mass system, a displacement sensing structure, a displacement detecting circuit, a cavity body and a level adjustment base; the spring-mass system is disposed inside the cavity body and includes: a negative-stiffness spring, a positive-stiffness spring, a proof mass and an outer frame; the proof mass is connected to the outer frame by the negative-stiffness spring and the positive-stiffness spring, the negative-stiffness spring and the positive-stiffness spring are symmetrically disposed with respect to the proof mass, and the outer frame is fixedly connected to the cavity body; the displacement sensing structure is located on a surface of the proof mass, and the displacement detecting circuit is configured to detect a displacement signal from the displacement sensing structure; the spring-mass system realizes reduction in resonant frequency by matching of the positive and negative stiffness springs; and change in gravitational acceleration is detected by detecting a displacement of the proof mass. The MEMS gravimeter has high stability, small size and light weight, and thus can effectively reduce the production cost as well as the development difficulty of the signal detection unit and stable platform.