Capacitive Volatile Sensor With Integrated Electrode Heater
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Solution Overview
Problem
Capacitive humidity sensors face limitations in response time due to small exposed surface area of the sensitive layer and hysteresis issues, which are exacerbated by the need for a thick insulating layer to prevent electrical contact between the heater and detection electrodes, reducing thermal coupling and sensor performance.
Innovation Solution
A capacitive sensor for volatile substances with a substrate, a sensitive layer, coplanar electrodes, and a supply device that heats the sensitive layer through the electrodes, allowing for faster evaporation and reduced hysteresis without the need for dedicated electrical components or additional machining steps, enhancing sensitivity and response time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick insulating layer is used to prevent electrical contact between heater and detection electrodes, then electrical isolation is improved, but thermal coupling between heater and sensitive layer deteriorates
Solution Approach 1:
The detection electrodes are configured to serve dual functions: as detection electrodes for measuring capacitance and as heating elements for thermal coupling with the sensitive layer. By merging the heater and detection electrode functions into a single structure, the patent eliminates the need for a separate thick insulating layer, thereby maintaining both electrical isolation and thermal coupling effectiveness.
2Loss of time
If the exposed surface area of the sensitive layer is increased to improve response time, then response time is improved, but the capacitance of the sensor deteriorates
Solution Approach 1:
The patent transitions from planar parallel plate electrodes to three-dimensional comb-shaped electrodes that extend vertically and horizontally. This dimensional change allows the sensitive layer to be exposed on multiple surfaces (top, bottom, and sides of the comb fingers), dramatically increasing the effective exposed surface area without compromising the capacitance structure.
3Reliability
If a separate heater structure is added to reduce hysteresis, then hysteresis is reduced, but device complexity increases
Solution Approach 1:
The detection electrodes are designed to perform multiple functions: detection of volatile substances through capacitance measurement and heating to reduce hysteresis. This multi-functionality eliminates the need for separate heater structures, maintaining device simplicity while achieving hysteresis reduction through controlled heating of the sensitive layer.
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 improves the accuracy of humidity measurements above 80% with faster and more uniform heating, reducing hysteresis and response time while maintaining sensitivity, without increasing manufacturing complexity.
Implementation Method 1
a supply device, configured to supply a heating current through one of the first electrode structure and the second electrode structure in a first operating condition, so as to heat the sensitive layer
Implementation Method 2
the sensitive layer being of a sensitive material that is permeable to a volatile substance and has electric permittivity dependent on a concentration of the volatile substance absorbed by the sensitive material
Data Source
AI summary
A sensor of volatile substances including: a sensitive layer, of a sensitive material that is permeable to a volatile substance and has an electrical permittivity depending upon a concentration of the volatile substance absorbed; a first electrode structure and a second electrode structure capacitively coupled together and arranged so that a capacitance between the first electrode structure and the second electrode structure is affected by the electrical permittivity of the sensitive material; and a supply device, configured to supply a heating current through one between the first electrode structure and the second electrode structure in a first operating condition, so as to heat the sensitive layer.