Inductive Acoustic Filters for Microphone Liquid Ingress Protection
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Solution Overview
Problem
Integrating acoustic components, such as microphones, into compact electronic devices poses challenges due to the difficulty in preventing liquid ingress while maintaining acoustic functionality, especially under high ingress pressures, and existing solutions like porous membranes are not robust enough.
Innovation Solution
A non-porous membrane is used to prevent liquid ingress, and a leak port with resistive or inductive vents is implemented to allow airflow while preventing sound from reaching the microphone, ensuring the device remains functional and resistant to deep water immersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous membrane is used to allow airflow, then acoustic functionality is maintained, but liquid ingress protection is insufficient under high ingress pressures
Solution Approach 1:
The acoustic opening is segmented into multiple smaller openings rather than a single large opening, allowing the use of non-porous membranes that can effectively block liquid while still permitting airflow and acoustic signals to pass through collectively
Solution Approach 2:
A non-porous membrane is introduced as an intermediary component between the acoustic opening and the microphone element, serving as a mediator that allows acoustic energy to pass while blocking liquid ingress, thus resolving the contradiction between protection and functionality
2Reliability
If a non-porous membrane is used to prevent liquid ingress, then liquid resistance is improved, but airflow restriction increases
Solution Approach 1:
The single acoustic opening is divided into multiple smaller openings in the non-porous membrane, collectively providing sufficient airflow pathways while each individual opening remains small enough to maintain effective liquid ingress protection under high pressure
3Reliability
If the acoustic opening is reduced to prevent liquid ingress, then liquid ingress protection is improved, but acoustic signal transmission is weakened
Solution Approach 1:
The acoustic opening is divided into multiple smaller openings that collectively maintain adequate acoustic signal transmission while each individual opening remains small enough to provide effective liquid ingress protection
Solution Approach 2:
The solution transitions from considering only the size of a single opening to considering the collective effect of multiple openings across a two-dimensional membrane surface, allowing adequate total acoustic transmission area while maintaining small individual opening dimensions for liquid protection
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 solution effectively prevents liquid ingress while allowing airflow, maintaining the microphone's functionality and robustness against high water pressures, ensuring the device's reliability in wet environments.
Implementation Method 1
an inductive filter having a first port coupled to the front volume, a second port coupled to the second opening in the substrate, and a serpentine fluid pathway from the first port to the second port
Data Source
AI summary
Aspects of the subject technology relate to inductive acoustic filters for acoustic devices. An inductive filter may include a substrate, an etched serpentine channel in a surface of the substrate and extending within the substrate from a first port in the substrate to a second port in the substrate. The inductive filter may also include a polymer cover layer adhesively attached to the surface of the substrate over the etched serpentine channel. The inductive filter may be positioned over an opening in a substrate of an acoustic module, such as a microphone module or a speaker module.