MEMS Force Sensor Noise Reduction via Dynamic Mass Segmentation
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Solution Overview
Problem
Piezoresistive accelerometers suffer from significant 1/f noise at low frequencies, limiting their resolution and causing bias drift, making them unsuitable for certain applications.
Innovation Solution
A MEMS or NEMS sensor design featuring a composite mobile mass with a part excited at high frequency, altering the distance between the pivot axis and the center of gravity, which reduces 1/f noise by converting the low-frequency acceleration signal into a high-frequency dynamic component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If piezoresistive gauges are used for detection, then the sensor is inexpensive and easy to implement, but 1/f noise becomes predominant at low frequencies causing resolution limits and bias drift
Solution Approach 1:
The patent applies the dynamics principle by making the seismic mass movable at high frequency relative to the support. The mobile mass is displaced at a frequency higher than the bandwidth of the sensor, converting the static or low-frequency measurement problem into a high-frequency dynamic measurement, thereby avoiding the 1/f noise region and improving resolution while maintaining piezoresistive gauge simplicity
Solution Approach 2:
The patent changes the frequency parameter of the seismic mass motion from low/static frequency to high frequency (above sensor bandwidth). This parameter change shifts the measurement away from the problematic low-frequency 1/f noise region, allowing piezoresistive gauges to achieve high resolution without bias drift
2Force
If the mobile mass is suspended at the end of a recessed beam with piezoresistive gauges extending parallel to the beam, then a lever arm effect amplifies the force on the gauges, but the structure complexity increases
Solution Approach 1:
The patent segments the mobile mass into two parts: a first part forming the main body and a second part that is movable relative to the first part. This segmentation allows the second part to be displaced at high frequency while the first part provides the main mass for acceleration sensing, enabling force amplification through the lever arm effect without excessive structural complexity
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 effectively reduces 1/f noise, enhancing the sensor's resolution and robustness to environmental vibrations, allowing operation under vacuum conditions with identical electronics to gyroscopes.
Implementation Method 1
the gauges extend parallel to the beam and are deformed during movement of the mass. This structure makes it possible to benefit from a lever arm effect, the force which is exerted on the piezoresistive gauges is then amplified
Implementation Method 2
the mobile mass being in two parts, one of the parts being moved at high frequency by relative to the other part, causing a high frequency variation of the distance between the axis of the pivot link and the center of gravity of the part moved at high frequency, which makes it possible to reduce the noise in 1/f
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3~4
AI summary
MEMS or NEMS force detection device in a given direction, comprising a support (4) and at least one seismic mass (2) capable of moving under the effect of the force to be measured in the direction of said force, and means for detecting (10) the displacement of said seismic mass (2), said seismic mass being articulated with respect to the support by at least one pivot joint, and means capable of varying the distance between the axis (Z) of the pivot joint and the center of gravity (G) of the force exerted on said seismic mass.