Humidity Sensor Element With Permeable Electrode
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Solution Overview
Problem
Current humidity sensors, especially capacitive ones, are expensive and lack reliability and durability at extreme humidity levels below 20% or above 70% relative humidity, and inexpensive alternatives often fail to perform effectively across the entire humidity range.
Innovation Solution
A humidity sensor element comprising a dielectric substrate, a nonporous conductive electrode, a permeable conductive electrode permeable to water vapor, and a detection layer made of a sulfonated fluoropolymer copolymer, which measures capacitance changes to accurately detect humidity levels over a wide range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional humidity sensors are used, then measurement capability is provided, but reliability and durability deteriorate at extreme humidity levels below 20% or above 70% relative humidity
Solution Approach 1:
The patent changes the chemical parameters of the sensing membrane by using sulfonated fluoropolymer with specific sulfonation levels (30-70%) and controlled molecular weight (10,000-100,000 g/mol). This parameter optimization enables the membrane to maintain dimensional stability and measurement accuracy across the full humidity range including extreme conditions below 20% and above 70% RH, resolving the contradiction between reliability and measurement precision.
Solution Approach 2:
The patent employs a composite material system consisting of sulfonated fluoropolymer as the base polymer combined with specific additives and cross-linking agents. This composite structure provides both the chemical stability needed for reliability at extreme humidity levels and the controlled porosity required for accurate measurement, simultaneously addressing both requirements.
2Measurement precision
If sulfonated fluoropolymer is used as detection layer, then response speed and accuracy are improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent performs preliminary sulfonation of the fluoropolymer chain during the polymerization stage, creating pre-sulfonated polymer that can be directly processed into sensing membranes. This preliminary chemical modification eliminates the need for complex post-polymerization sulfonation steps, reducing manufacturing complexity while maintaining the high measurement precision associated with sulfonated fluoropolymers.
Solution Approach 2:
The patent optimizes the sulfonation degree parameter to a specific range (30-70%) that balances performance and manufacturability. This parameter control ensures sufficient humidity sensitivity and response speed while avoiding the excessive complexity and cost associated with achieving complete or near-complete sulfonation, thus improving ease of manufacture without sacrificing detection accuracy.
3Speed
If conventional polymer membranes are used, then manufacturing is simpler, but response time to humidity changes is slower
Solution Approach 1:
The patent changes the molecular weight parameter of the fluoropolymer to a specific range (10,000-100,000 g/mol) and controls the sulfonation degree (30-70%). These parameter changes create a membrane with optimal free volume and chain mobility that enables rapid water vapor diffusion and response, achieving fast response times while maintaining manufacturing feasibility through controlled polymerization processes.
Solution Approach 2:
The patent creates a controlled porous structure within the sulfonated fluoropolymer membrane through the sulfonation process itself, which generates hydrophilic channels for rapid water vapor transport. This porous architecture significantly accelerates response time compared to conventional non-porous polymer membranes, while the porosity is inherently created during manufacturing, preserving ease of manufacture.
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 provides a cost-effective, reliable, and durable humidity sensor capable of sensitive and accurate measurements across the entire humidity range, suitable for various applications including industrial and household use.
Implementation Method 1
the permeable conductive electrode is permeable by water vapor
Implementation Method 2
Sulfonated fluoropolymers have been used as the humidity-sensitive material because of their excellent thermal and mechanical stability, and the capability of extremely fast and accurate response to change in humidity
Implementation Method 3
a humidity sensor element comprising... a permeable conductive electrode having a second conductive member electrically coupled thereto... an operating circuit in electrical communication with the first and second conductive leads of the humidity sensor element, whereby if the humidity sensor element is connected to a source of electrical power, the operating circuit measures the capacitance of the sensor element
Data Source
AI summary
A humidity sensor element includes a dielectric substrate, a nonporous conductive electrode disposed on the dielectric substrate, a permeable conductive electrode having a thickness in a range of from 4 to 10 nanometers and permeable by water vapor, and a detection layer sandwiched between the nonporous conductive electrode and the permeable conductive electrode. The permeable conductive electrode is parallel to the nonporous electrode. Both conductive electrodes have respective conductive leads attached thereto. The detection layer includes a copolymer having monomeric units comprising wherein M represents H, or an alkali metal. A humidity sensor including the humidity sensor element is also disclosed.