Directional MEMS Microphone Tuning Cavity Design
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Solution Overview
Problem
Existing directional MEMS microphones face challenges in achieving high sensitivity and directivity due to small back volume and cavity size, leading to minor sound pressure differences and inability to effectively eliminate background noise from various directions.
Innovation Solution
The introduction of a tuning cavity with varying dimensions and mesh structures in the acoustic ports, which increases sound pressure differences by altering sound transmission distances and paths, enhancing sensitivity and directivity by connecting internal and external acoustic ports through these cavities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the back volume and cavity size are increased to improve sound pressure difference and sensitivity, then the directivity and noise rejection improve, but the device size and complexity increase
Solution Approach 1:
The patent implements a nested cavity structure where a first tuning cavity and a second tuning cavity are positioned at different levels, with the second cavity nested within or adjacent to the first cavity structure. This nested arrangement allows sound waves to traverse through multiple cavity levels, effectively increasing the sound transmission distance and sound pressure difference without proportionally increasing the overall device volume, thereby resolving the contradiction between sensitivity enhancement and compact size.
Solution Approach 2:
The patent utilizes vertical stacking of multiple tuning cavities (first cavity and second cavity at different levels) to extend the sound transmission path in the vertical dimension. This dimensional approach allows the sound pressure difference to be enhanced through multi-level cavity traversal rather than relying solely on horizontal expansion, achieving improved directivity while maintaining a compact footprint.
2Measurement precision
If the acoustic port channels are lengthened to increase sound pressure difference, then the sensitivity and directivity improve, but the device volume and structural complexity increase
Solution Approach 1:
The patent employs nested tuning cavities where sound waves pass through multiple cavity levels sequentially. This nesting approach effectively extends the acoustic path length by forcing sound to traverse through the first cavity and then the second cavity, achieving enhanced sound pressure difference and sensitivity without requiring a single excessively long acoustic port channel, thus avoiding excessive device elongation.
Solution Approach 2:
The patent divides the acoustic transmission path into multiple segments through the first tuning cavity and the second tuning cavity. Instead of using one long continuous channel, the sound transmission is segmented into multiple shorter cavity passages, each contributing to the overall sound pressure difference. This segmentation achieves the desired sensitivity enhancement while keeping individual channel lengths manageable and device compact.
3Reliability
If multiple tuning cavities are added to enhance sound pressure difference, then the directivity improves, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent implements a nested cavity configuration where the first tuning cavity and second tuning cavity are positioned at different levels with a nested spatial relationship. This nested structure, while adding functional complexity for enhanced directivity, optimizes space utilization and can be integrated into existing microphone housing designs, thereby managing manufacturing complexity more effectively than completely separate cavity structures.
Solution Approach 2:
The tuning cavities serve multiple functions: they enhance sound pressure difference, improve directivity, and can be integrated into the existing microphone housing structure. The cavities may also serve as structural support elements or be used for acoustic tuning of different frequency ranges, making the added structural elements multi-functional and justifying the increased complexity through enhanced overall performance.
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 significantly improves the directivity and noise rejection capabilities of the directional MEMS microphone by increasing sensitivity differences and optimizing sound pressure distribution, effectively eliminating background noise from specific angles.
Implementation Method 1
The introduction of a tuning cavity with varying dimensions and mesh structures in the acoustic ports, which increases sound pressure differences by altering sound transmission distances and paths
Implementation Method 2
The MEMS die contains a rigid perforated back electrode and an elastic silicon diaphragm serving as a capacitor which can transform the sound wave into the capacitance changes
Data Source
AI summary
The present invention provides a directional MEMS microphone and a receiver device wherein MEMS microphone comprises a microphone cover, a printed circuit board (PCB), a application specific integrated circuit (ASIC) chip, a MEMS die, a diaphragm, a damping, a metal wire(s), at least two internal acoustic ports and at least two external acoustic ports corresponding to the internal acoustic ports. The microphone further comprises a tuning cavity which includes a first tuning cavity by which a first internal acoustic port is communicated with a first external acoustic port, or by which a second internal acoustic port is communicated with a second external acoustic port. Compared with the prior art, the directional MEMS microphone including the tuning cavity to form a sound transmission channel by connecting the internal acoustic port and the external acoustic port expands the sound transmission distance, thereby increasing the sensitivity the directivity of the MEMS microphone.