Optical Microphone Assembly With Acoustic Cavity Vibration Isolation
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Solution Overview
Problem
Existing optical microphones face limitations in achieving high signal-to-noise ratio (SNR) and sensitivity due to restrictions on membrane compliance, primarily from housing and substrate vibrations, which degrade performance, especially with high compliance membranes.
Innovation Solution
An optical microphone assembly with a rigid substrate and a large acoustic cavity volume, defined by a membrane diameter squared multiplied by 3mm, combined with apertures for air passage, to reduce substrate vibrations and minimize membrane stiffening, allowing high compliance membranes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high compliance membrane is used to increase sensitivity, then the membrane displacement increases, but substrate vibrations and housing restrictions degrade the performance
Solution Approach 1:
The patent separates the substrate into two functional parts: a rigid support structure that provides stable mounting for optical components, and a localized compliant region (acoustic cavity) that allows membrane displacement without transmitting vibrations to the entire substrate. This segmentation enables the membrane to move freely for high sensitivity while the rigid substrate maintains stability.
Solution Approach 2:
The patent introduces an acoustic cavity as an intermediary between the membrane and the substrate. This cavity acts as a vibration isolation medium, allowing the membrane to displace with high compliance while preventing substrate vibrations from coupling to the membrane. The cavity volume is specifically designed to be at least 3mm×d² to provide sufficient isolation.
2Measurement precision
If the membrane compliance is increased for better signal-to-noise ratio, then the displacement increases, but the housing and substrate restrictions limit the maximum displacement
Solution Approach 1:
The patent extracts the acoustic cavity from the traditional rigid housing structure, creating a dedicated vibration isolation zone. By removing the restrictive housing constraints from the membrane region and replacing them with a compliant acoustic cavity, the membrane can achieve greater displacement ranges without compromising overall device stability or increasing complexity.
3Stability of the object's composition
If a rigid substrate is used to reduce vibrations, then the substrate stability improves, but the membrane stiffening may occur
Solution Approach 1:
The patent applies local quality by creating a localized compliant region (acoustic cavity) within the rigid substrate. The substrate maintains its rigid, stable properties in regions supporting optical components, while the acoustic cavity region provides local compliance to prevent membrane stiffening. This spatial differentiation of mechanical properties allows both substrate stability and membrane flexibility to coexist.
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 combination of a rigid substrate and large acoustic cavity enhances microphone sensitivity and SNR by reducing substrate vibrations and membrane stiffening, enabling high compliance membranes to achieve greater deflections and improved performance.
Implementation Method 1
a first portion of said light propagates along a first optical path via said interferometric arrangement and a second portion of said light propagates along a second different optical path via said interferometric arrangement, thereby giving rise to an optical path difference between the first and second optical paths which depends on a distance between the membrane and the optical element
Implementation Method 2
at least one photo detector arranged to detect at least part of an interference pattern generated by said first and second portions of light dependent on said optical path difference
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
An optical microphone assembly (38) comprises a rigid substrate (42); an interferometic arrangement, a light source (48), at least one photo detector (50) and an enclosure (74). The interferometric arrangement comprises a membrane (46) and at least one optical element (62) spaced from the membrane (46), wherein the at least one optical element comprises a surface (60) of the substrate (42) and/or is disposed on a surface (60) of the substrate (42). The light source (48) is arranged to provide light to the interferometric arrangement such that a first portion of the light propagates along a first optical path via the interferometric arrangement and a second portion of the light propagates along a second different optical path via the interferometric arrangement, thereby giving rise to an optical path difference between the first and second optical paths which depends on a distance between the membrane (46) and the optical element (62). The photo detector(s) (50) are arranged to detect at least part of an interference pattern generated by said first and second portions of light dependent on said optical path difference. The enclosure (74) is arranged to form an acoustic cavity (76) in fluid communication with one side of the membrane (46). The volume of the acoustic cavity (76) is at least 3mm multiplied by d2, where d is a diameter of the membrane (46).