Ceramic Capacitive Probe Bonding to Cut Thermal Stress and Capacitance
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Solution Overview
Problem
Existing non-contact capacitive probes for monitoring moving engine elements in gas turbines and compressors face issues with differential thermal expansion, high internal capacitance, and complex, costly manufacturing processes due to multiple metal and ceramic components and interfaces.
Innovation Solution
A probe design featuring a ceramic housing and core bonded with an electrically conductive sensing electrode, which also serves as a braze filler material, minimizing interfaces and internal capacitance, and using an active braze filler material to simplify manufacturing and reduce thermal stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If multiple metal and ceramic components are used in the probe, then the probe can function in high-temperature environments, but differential thermal expansion causes unwanted stresses and reduces reliability
Solution Approach 1:
The patent merges the housing and core into a single integral ceramic component, eliminating the interface between separate housing and core components. This eliminates differential thermal expansion stresses at the housing-core interface, resolving the contradiction between high-temperature operation and measurement reliability.
Solution Approach 2:
The patent uses the same ceramic material for both the housing and core, ensuring homogeneous material properties and matching thermal expansion coefficients throughout the structure. This homogeneity prevents thermal stresses during temperature changes, maintaining reliability in high-temperature environments.
2Reliability
If multiple metal and ceramic components and interfaces are used in the probe, then the probe can achieve sensing functionality, but manufacturing complexity and cost increase
Solution Approach 1:
The patent combines multiple components (housing, core, and braze filler material) into an integral structure that is formed in a single manufacturing process. This eliminates the need for separate assembly steps and reduces manufacturing complexity while maintaining sensing functionality.
Solution Approach 2:
The ceramic material serves multiple functions: it provides the structural housing, forms the core, and the embedded conductive material provides both mechanical bonding and electrical sensing functionality. This multi-functionality reduces the number of separate components needed, simplifying manufacturing.
3Reliability
If multiple metal and ceramic components are used in the probe, then the probe can achieve sensing functionality, but internal capacitance increases
Solution Approach 1:
The patent removes unnecessary conductive components and interfaces that contribute to internal capacitance. By using a minimalistic design with only essential conductive elements embedded in the ceramic, the harmful capacitive effects are reduced while maintaining sensing functionality.
Solution Approach 2:
The use of homogeneous ceramic material with minimally embedded conductive material reduces the number of interfaces between different materials. Fewer interfaces mean fewer parasitic capacitances, reducing the harmful internal capacitance while preserving sensing capability.
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 probe experiences reduced thermal stresses and internal capacitance, is easier to manufacture, and maintains reliability in high-temperature environments, enhancing measurement accuracy and operational lifespan.
Implementation Method 1
Capacitive probes generally comprise a sensing electrode that forms one electrode of a capacitor, the other electrode of the capacitor being formed by the tip of a turbine blade as the turbine blade passes over the probe
Implementation Method 2
The extreme high temperature environments within gas turbines impose certain design considerations on non-contact probes, in particular to avoid movement of components within the probes due to differential thermal expansion
Data Source
Figure 1~2
Figure 3
AI summary
A probe (1, 101) for monitoring a moving engine element and a method of forming a probe (1, 101) for monitoring a moving engine element, the probe (1, 101) comprising: a housing (2, 102) formed of electrically insulating ceramic material; a core (14, 114) formed of electrically insulating ceramic material, the core (14, 114) comprising a front face (16, 116); and a sensing electrode (20, 120) formed of electrically conductive material, the sensing electrode (20, 120) being arranged between the housing (2, 102) and the front face (16, 116) of the core (14, 114) and the housing (2, 102) and the front face (16, 116) of the core (14, 114) being bonded together by the sensing electrode (20, 120).