Capacitance Vibration Sensor Air Escape Portion Thermal Noise
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitance type vibration sensors face challenges in reducing thermal noise in the vent hole while maintaining satisfactory low frequency characteristics, as widening the vent hole gap to reduce noise leads to decreased acoustic resistance and degraded low frequency performance, and narrowing it increases noise, making it difficult to achieve both low noise and good low frequency characteristics simultaneously.
Innovation Solution
Incorporating an air escape portion, such as a through-hole or groove, in the vibration electrode plate or substrate to facilitate the escape of thermal noise air molecules, thereby reducing noise and maintaining adequate acoustic resistance to preserve low frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the vent hole gap is widened to reduce thermal noise, then the signal-to-noise ratio is improved, but the acoustic resistance decreases and low frequency characteristics are degraded
Solution Approach 1:
The vent hole is divided into multiple smaller holes instead of one large hole. This segmentation allows the total open area to be maintained for noise reduction while each individual small hole preserves acoustic resistance, thus maintaining low frequency characteristics.
Solution Approach 2:
Different regions of the vent hole structure are given different properties - the overall gap is widened in certain areas to reduce thermal noise, while specific localized regions maintain smaller dimensions to preserve acoustic resistance. This creates non-uniform quality distribution to simultaneously achieve both goals.
2Reliability
If the vent hole gap is narrowed to maintain acoustic resistance, then low frequency characteristics are preserved, but thermal noise increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The vent hole structure is segmented into multiple small holes distributed across the substrate. This allows the cumulative open area to be sufficient for noise reduction while each segment maintains small dimensions to preserve acoustic resistance and low frequency response.
Solution Approach 2:
Instead of adjusting the gap width in one dimension, the solution transitions to controlling the number, size, and distribution of multiple holes in two dimensions. This dimensional shift allows independent optimization of noise reduction and acoustic resistance preservation.
3Ease of manufacture
If the hollow portion is blocked to simplify structure, then manufacturing is easier, but pressure difference causes vibration electrode plate bending and measurement error
Solution Approach 1:
The vent hole acts as an intermediary structure that connects the hollow portion to the external environment. This intermediary allows pressure equalization to prevent measurement errors while maintaining the blocked hollow portion structure for manufacturing simplicity.
Solution Approach 2:
The vent hole extracts the pressure equalization function from the hollow portion structure. By providing a dedicated pressure relief path separate from the main structural elements, the solution achieves both manufacturing simplicity and measurement accuracy.
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 air escape portion effectively reduces thermal noise and enhances the signal-to-noise ratio while minimizing the degradation of low frequency characteristics by allowing air molecules to escape, thus achieving a vibration sensor with low noise and satisfactory low frequency performance.
Implementation Method 1
the noise generated in the vibration sensor originates from the thermal noise (fluctuation of air molecules) in the air gap between the vibration electrode plate and the fixed electrode plate
Implementation Method 2
the acoustic vibration 19 (air vibration) can be converted to an electric signal for output by detecting the change in electrostatic capacitance between the vibration electrode plate 14 and the fixed electrode plate 15
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3
AI summary
A vibration electrode plate (34), which performs film vibration upon receiving vibration, is arranged on an upper surface of a silicon substrate (32) including a hollow portion (37). A fixed electrode plate (36) in which a plurality of acoustic perforations (43) passing therethrough in the thickness direction is opened is arranged on an upper side of the vibration electrode plate (34), and the vibration electrode plate (34) and the fixed electrode plate (36) are faced to each other. A vent hole (45) for communicating an air gap (35), which is between the vibration electrode plate (34) and the fixed electrode plate (36), to the hollow portion (37) is arranged between the upper surface of the silicon substrate (32) and the lower surface of the vibration electrode plate (34) at the periphery of the hollow portion (37). An air escape portion (42) in the form of a plurality of through-holes is opened in the vibration electrode plate (34) in the region corresponding to the vent hole (45).