Asymmetric Seismic Mass for Low-Frequency Acceleration Sensor
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Solution Overview
Problem
Micromechanical lateral acceleration sensors face challenges in achieving low natural frequencies while maintaining sensitivity and avoiding resonance exaggeration, especially in the automotive sector, where high vibration robustness and low deflection amplitudes are required, due to the constrained correlation between natural frequency and mechanical sensitivity.
Innovation Solution
A micromechanical structure with a seismic mass asymmetrically positioned relative to the rotational Z axis, coupled with spring elements fastened on the seismic mass and a fastening element, allowing rotational motion only in a defined sensing direction within a plane orthogonal to the Z axis, thereby reducing natural frequency and enhancing vibration resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the natural frequency is reduced to increase vibration resistance, then the deflection amplitude increases, but the sensor may mechanically hit or clip
Solution Approach 1:
The seismic mass is positioned asymmetrically with respect to the rotational Z axis, creating a defined asymmetry that enables rotational motion while maintaining structural integrity. This asymmetric positioning allows the mass to rotate around the Z axis without requiring large linear deflections, thus maintaining overload robustness while achieving low natural frequency for vibration resistance
Solution Approach 2:
The invention transitions from linear deflection to rotational motion around the Z axis. By allowing the seismic mass to rotate rather than deflect linearly, the sensor achieves low natural frequency (1 kHz or lower) through rotational inertia while maintaining small deflection amplitudes, preventing mechanical clipping even at high overloads
2Speed
If the spring constant is reduced to lower natural frequency, then the deflection increases, but the sensitivity decreases due to larger gap requirements
Solution Approach 1:
The invention utilizes rotational vibration around the Z axis as the primary sensing mechanism. The asymmetric seismic mass creates a rotational moment of inertia that, combined with the spring elements, produces a low natural frequency rotational oscillation. This rotational vibration mode maintains high sensitivity because the seismic mass remains close to the electrode assembly, avoiding the sensitivity loss associated with large linear gap increases
Solution Approach 2:
The asymmetric positioning of the seismic mass relative to the rotational Z axis creates a rotational lever arm that amplifies the sensing effect. The asymmetry generates a torque when acceleration occurs in the sensing direction, producing measurable rotational motion while keeping the mass centered near the electrodes, thus maintaining high capacitive sensitivity
3Stability of the object's composition
If damping is increased to suppress resonance, then the mechanical low-pass behavior improves, but the amplitude suppression remains weak at most 20 dB per frequency decade
Solution Approach 1:
By transitioning to rotational motion around the Z axis, the system achieves a different damping characteristic. The rotational degree of freedom with asymmetric mass distribution creates a low natural frequency (1 kHz or lower) that provides stronger natural amplitude suppression. The rotational inertia and asymmetric configuration enable more effective vibration suppression beyond the 20 dB per decade limit of conventional linear damping
Solution Approach 2:
The invention changes the fundamental operating parameter from linear deflection to rotational angle. The asymmetric seismic mass configuration creates a rotational moment of inertia that, when combined with the spring elements, produces a low natural frequency rotational system. This parameter change enables the sensor to achieve both low natural frequency for vibration resistance and effective amplitude suppression through rotational damping mechanisms
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 structure achieves a natural frequency of 1 kHz or lower while maintaining low mechanical sensitivity, effectively suppressing unwanted vibrations and preventing signal mixing from perpendicular directions, thus enhancing the sensor's robustness and accuracy in detecting lateral accelerations.
Implementation Method 1
spring elements that are fastened on the seismic mass and on at least one fastening element, a motion of the seismic mass being generatable by way of the spring elements
Implementation Method 2
a seismic mass that is constituted definedly asymmetrically with reference to the rotational Z axis of the structure of the acceleration sensor
Implementation Method 3
a seismic mass that is constituted definedly asymmetrically with reference to the rotational Z axis
Implementation Method 4
The enclosed gas ensures a high degree of damping of the micromechanical structure
Data Source
AI summary
A micromechanical structure for an acceleration sensor, including a seismic mass that is constituted definedly asymmetrically with reference to the rotational Z axis of the structure of the acceleration sensor, spring elements that are fastened on the seismic mass and on at least one fastening element, a rotational motion of the seismic mass being generatable by way of the spring elements substantially only upon an acceleration in a defined sensing direction within a plane constituted substantially orthogonally to the rotational Z axis.