MEMS Microphone Package with Sound-Absorbing Helmholtz Cavity
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Solution Overview
Problem
MEMS microphones have a limited operation bandwidth due to a sharp increase in high-frequency output amplitude, which restricts their frequency response and sensitivity.
Innovation Solution
A package structure for MEMS microphones incorporating a Helmholtz resonant cavity with a sound-absorbing layer on its inner walls, which absorbs high-frequency sound waves, acting as a low-pass filter to suppress high-frequency response and widen the operational bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Helmholtz resonant cavity is used in the MEMS microphone package structure, then the sensitivity is improved at resonant frequency, but the operation bandwidth is limited due to sharp increase in high-frequency output amplitude
Solution Approach 1:
A sound-absorbing layer with porous structure is introduced on the inner wall of the Helmholtz resonant cavity. This porous material absorbs high-frequency sound waves through viscous losses and thermal conduction within the porous structure, suppressing the sharp high-frequency resonance peak while preserving the desired sensitivity enhancement at the resonant frequency, thereby expanding the operation bandwidth
Solution Approach 2:
The physical parameters of the sound-absorbing layer (such as porosity, thickness, and flow resistivity) are optimized to achieve the desired frequency-dependent absorption characteristics. By adjusting these parameters, the sound-absorbing layer selectively absorbs high-frequency waves while allowing the resonant frequency response to be maintained, thus resolving the bandwidth limitation
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 sound-absorbing layer effectively reduces high-frequency amplitude, increasing the high-frequency cut-off frequency and expanding the microphone's operation bandwidth while maintaining resonance characteristics.
Implementation Method 1
at least part of an inner wall of the Helmholtz resonant cavity is provided with a sound-absorbing layer... The sound-absorbing layer has a certain absorption capacity to high-frequency sound waves
Implementation Method 2
The package shell, the package substrate and the sound hole together constitute a Helmholtz resonant cavity... When a sound wave frequency is the same as a resonant frequency of the Helmholtz resonant cavity, a resonance phenomenon appears
Data Source
AI summary
The present invention discloses a package structure of a MEMS microphone. The package structure comprises a package substrate and a package shell, wherein the package shell is provided on the package substrate and forms a closed cavity with the package substrate. In the package structure provided by the present invention, the sound-absorbing layer is arranged on the inner wall of the Helmholtz resonant cavity. The sound-absorbing layer has a certain absorption capacity to high-frequency sound waves, but has a very low absorption to low-frequency sound waves, so it may be equivalent to a “low-pass filter”. Through the absorption of the high-frequency sound waves, a high-frequency amplitude value of sound waves can be suppressed, reducing high-frequency response of the Helmholtz resonant cavity. That is, a high-frequency cut-off frequency of the sound waves is improved, widening operation bandwidth of the MEMS microphone.