ePTFE Membrane Water Detector for Wearable Sensors
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Solution Overview
Problem
Wearable devices with gel-filled pressure sensors are vulnerable to orientation sensitivity and capillary pressure errors due to water, leading to feature-level errors in altitude changes and exercise metrics, necessitating a robust water detection mechanism.
Innovation Solution
A stand-alone water detector using an expanded polytetrafluoroethylene (ePTFE) membrane architecture, which forms a parallel plate capacitor with metal electrodes, detects water occlusion by measuring capacitance changes between the ePTFE membrane and electrodes, allowing for alerting the system and potentially eliminating water through resistive heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gel-filled sensors are used to survive dust and debris exposure, then environmental robustness is improved, but orientation sensitivity and capillary pressure errors occur due to water in the gel surface
Solution Approach 1:
The patent removes the gel filling from the pressure sensor assembly and replaces it with an ePTFE membrane. This extraction eliminates the source of capillary pressure errors and orientation sensitivity while maintaining environmental protection through the membrane's inherent properties.
Solution Approach 2:
The patent employs an expanded polytetrafluoroethylene (ePTFE) membrane as a porous material that allows air passage for pressure sensing while providing hydrophobic protection against water ingress. The porous structure enables environmental robustness without the harmful capillary effects of gel materials.
2Measurement precision
If ePTFE membrane is used to eliminate gel and provide environmental robustness, then orientation sensitivity and capillary pressure errors are reduced, but water occlusion of the membrane occurs
Solution Approach 1:
The patent introduces a hydrophobic coating as an intermediary layer on the ePTFE membrane surface. This coating acts as a mediator that enhances water repellency while maintaining the membrane's air permeability, preventing water occlusion without compromising pressure sensing functionality.
Solution Approach 2:
The patent modifies the surface properties of the ePTFE membrane by applying a hydrophobic treatment that changes the surface energy parameters. This parameter change increases the contact angle with water, enhancing water repellency and preventing water occlusion while preserving the membrane's inherent air passage capabilities.
3Reliability
If water detection capability is added to detect water occlusion, then water occlusion can be detected and system alerted, but device complexity increases
Solution Approach 1:
The patent integrates water detection functionality into the existing ePTFE membrane assembly by utilizing the same membrane structure for both pressure sensing and water detection. The membrane's response to water occlusion provides dual functionality, eliminating the need for separate water detection components and reducing overall device complexity.
Solution Approach 2:
The patent combines pressure sensing and water detection functions into a single integrated assembly. The ePTFE membrane serves dual purposes: as the pressure-sensitive element and as the water detection indicator, merging multiple functions into one component to minimize device complexity.
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 ePTFE membrane-based water detector provides environmental robustness and prevents feature-level errors by accurately detecting water occlusion, enabling reliable barometric pressure measurements and exercise tracking in wearable devices.
Implementation Method 1
The ePTFE membrane and the metal electrodes form a parallel plate capacitor that detects water occlusion
Implementation Method 2
The sensor assembly further includes a resistive heating element that, when activated, eliminates water
Data Source
AI summary
According to some aspects of the subject technology, an apparatus includes a first electrode, a second electrode and a dielectric membrane disposed between the first electrode and the second electrode. The first electrode and the second electrode include a number of pores within a region of an input port of the apparatus. The first electrode, the second electrode and the dielectric membrane form a capacitor that is configured to enable detection of occlusion of the input port by water.