Gas Sensor Element Oxygen Barrier Design
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Solution Overview
Problem
Sensor elements used to detect NOx concentrations in gases face accuracy degradation due to oxygen reaching the electrodes from outside paths, such as fine spaces or cracks, which are not derived from the specific gas, leading to incorrect detection readings.
Innovation Solution
A sensor element configuration with a hermetic layer surrounding the end region of the measurement electrode lead and a lead insulating layer with higher oxygen permeability than the hermetic layer, preventing external oxygen from reaching the measurement area, and using a hermetic bonding layer that can also serve as a solid electrolyte layer for easier production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous insulating layer is used to insulate the lead, then electrical insulation is achieved, but oxygen can penetrate through the porous structure and reach the electrode, degrading detection accuracy
Solution Approach 1:
The patent divides the protective structure into two distinct layers: a hermetic layer (with porosity 0-20%) and a lead insulating layer (with porosity 30-70%). The hermetic layer serves as the primary barrier against oxygen penetration, while the lead insulating layer provides electrical insulation. This segmentation allows each layer to optimize its function without compromising the other, resolving the contradiction between insulation and oxygen blocking.
Solution Approach 2:
The patent employs a composite structure combining materials with different properties: the hermetic layer uses low-porosity material (such as alumina or zirconia) to block oxygen, while the lead insulating layer uses high-porosity material to ensure electrical insulation. This composite approach allows the system to simultaneously achieve both oxygen barrier functionality and electrical insulation, resolving the technical contradiction.
2Measurement precision
If the hermetic layer has very low porosity to block oxygen, then detection accuracy is maintained, but oxygen permeability becomes too low for necessary gas transport
Solution Approach 1:
The patent segments the gas transport and oxygen blocking functions into different layers. The hermetic layer (porosity 0-20%) maintains detection accuracy by blocking external oxygen, while the lead insulating layer (porosity 30-70%) facilitates gas transport to the electrode. This segmentation resolves the contradiction between oxygen blocking and gas transport efficiency.
Solution Approach 2:
Different regions of the sensor structure are assigned different porosity characteristics tailored to their specific functions. The hermetic layer has low porosity locally optimized for oxygen blocking, while the lead insulating layer has high porosity locally optimized for gas transport. This local quality differentiation allows the system to simultaneously achieve both requirements.
3Measurement precision
If a hermetic layer with low porosity is added to surround the lead, then oxygen penetration is reduced and detection accuracy improves, but device complexity increases
Solution Approach 1:
The hermetic layer is designed to serve multiple functions: it provides oxygen blocking to protect the electrode, maintains structural integrity of the sensor element, and works in conjunction with the lead insulating layer for comprehensive protection. This multi-functionality justifies the added structural complexity by delivering multiple benefits from a single component.
Solution Approach 2:
The patent merges the hermetic layer and lead insulating layer into an integrated protective structure surrounding the lead. Rather than treating them as separate, independent components, they are combined into a unified system where the hermetic layer and insulating layer work together to provide both oxygen blocking and electrical insulation, reducing overall system 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
This configuration effectively suppresses the degradation of detection accuracy by preventing external oxygen from affecting the measurement, ensuring reliable NOx concentration detection and reducing the time required for signal stabilization.
Implementation Method 1
a hermetic layer that is part of the element main body and that surrounds an end region of the second portion including the border with the first portion
Implementation Method 2
a lead insulating layer that is part of the element main body and that surrounds at least part of the second portion excluding the end region. In the sensor element, the measurement electrode lead has the first portion that is disposed in the flow portion of a measurement-object gas and the second portion that is connected to the first portion and that is embedded in the element main body
Implementation Method 3
an element main body which has a plurality of oxygen-ion-conductive solid electrolyte layers stacked
Data Source
AI summary
A sensor element includes an element main body in which a flow portion of a measurement-object gas is disposed, a measurement electrode disposed in the flow portion of a measurement-object gas, a measurement electrode lead having a first portion that is connected to the measurement electrode and that is disposed in the flow portion of a measurement-object gas and a second portion that is connected to the first portion and that is embedded in the element main body, a hermetic layer that is part of the element main body and that surrounds an end region of the second portion including the border with the first portion; and a lead insulating layer that is part of the element main body and that surrounds at least part of the second portion excluding the end region.