Acoustic Sensor Diaphragm Segmentation for Noise Cancellation
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Solution Overview
Problem
Conventional acoustic sensors face challenges in improving the signal-to-noise (S/N) ratio without compromising sensor size, as methods to increase sensitivity often lead to reduced durability or increased noise, and existing microphone designs struggle with parasitic capacitance and variations in sensitivity and frequency characteristics among multiple sensors.
Innovation Solution
The acoustic sensor features a diaphragm divided by a slit into multiple areas, allowing independent displacement and noise cancellation, maintaining sensitivity and preventing air leakage, which enhances the S/N ratio while maintaining sensor size and low-frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the area of the diaphragm is widened to increase sensitivity, then the sensitivity of the acoustic sensor is improved, but the size of the acoustic sensor increases
Solution Approach 1:
The diaphragm is divided into multiple independent vibration regions by forming grooves or slits, allowing each region to vibrate independently. This segmentation enables the diaphragm to achieve higher effective sensitivity through coordinated vibration of multiple regions without requiring a proportional increase in overall sensor area, thus resolving the contradiction between sensitivity improvement and size control
2Measurement precision
If the spring properties of the diaphragm are reduced to increase displacement amount, then the sensitivity of the acoustic sensor is improved, but the durability of the acoustic sensor decreases
Solution Approach 1:
By dividing the diaphragm into multiple independent vibration regions through grooves or slits, each segmented region can vibrate with appropriate displacement amplitude. This segmentation allows the diaphragm to achieve sufficient total displacement for high sensitivity while maintaining the structural integrity and spring properties of each individual region, thereby preserving durability
Solution Approach 2:
The grooves or slits are strategically positioned to create local variations in the diaphragm structure, with each segmented region having optimized local properties. This allows different parts of the diaphragm to have different displacement characteristics while maintaining overall durability, resolving the contradiction between sensitivity and reliability
3Object-generated harmful factors
If the opening ratio of the acoustic hole is increased to reduce thermal noise, then the thermal noise is alleviated, but the capacitance of the capacitor decreases and sensitivity deteriorates
Solution Approach 1:
The diaphragm is divided into multiple independent vibration regions, which allows for optimized acoustic hole configuration. The acoustic holes can be positioned to serve specific segmented regions, enabling effective thermal noise reduction through increased opening ratio in critical areas while maintaining sufficient capacitance in other areas, thus resolving the contradiction between noise reduction and sensitivity preservation
4Object-generated harmful factors
If the air gap between the diaphragm and back plate is widened to reduce thermal noise, then the thermal noise is alleviated, but the capacitance of the capacitor decreases and sensitivity deteriorates
Solution Approach 1:
By segmenting the diaphragm into multiple independent vibration regions, the air gap can be optimized for each region. This allows sufficient air gap width to be provided in regions where thermal noise reduction is critical, while maintaining smaller air gaps in regions where capacitance and sensitivity are prioritized, thus resolving the contradiction between noise reduction and sensitivity
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 improves the S/N ratio by canceling thermal noise and maintaining sensitivity, while preventing deterioration in low-frequency characteristics and reducing sensor size, achieving a 3 dB improvement in S/N ratio without increasing parasitic capacitance.
Implementation Method 1
thermal noise generated in an air gap formed between the diaphragm (movable electrode plate) and a back plate (fixed electrode plate) are problematical
Implementation Method 2
a capacitance of a capacitor configured by the diaphragm 11 and the back plate 12 decreases
Data Source
AI summary
Provided is an acoustic sensor capable of improving an S/N ratio of a sensor without preventing reduction in size of the sensor. A back chamber 45 is vertically opened in a silicon substrate 42. A thin film-like diaphragm 43 to serve as a movable electrode plate is formed on the top surface of the substrate 42 so as to cover the back chamber 45. The back plate 48 is fixed to the top surface of the substrate 42 so as to cover the diaphragm 43, and a fixed electrode plate 49 is provided on the under surface of the back plate 48. Further, the diaphragm 43 is divided into a plurality of areas by the slit 47, and the respective plurally divided diaphragms 43a, 43b and the fixed electrode plate 49 constitute a plurality of parallelly connected capacitors (acoustic sensing sections 60a, 60b).