Sapphire Capacitive Pressure Sensor for High Temperature
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Solution Overview
Problem
Current capacitive pressure sensors face challenges in high-temperature applications due to susceptibility to stray capacitance, temperature hysteresis, and unreliable electrical connections, limiting their use in harsh environments like gas turbine engines.
Innovation Solution
The development of capacitive pressure sensors utilizing a sapphire diaphragm and substrate with platinum electrodes, fused using plasma activation and brazing, and a hermetic seal with Alumina or HTCC substrates, along with a guard ring to shield from signal line parasitic capacitance, providing a robust and accurate pressure sensing solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If traditional capacitive pressure sensors are used at elevated temperatures, then they can operate in high-temperature environments, but they suffer from susceptibility to stray capacitance and unreliable electrical connections
Solution Approach 1:
A guard ring structure is introduced as an intermediary element between the sensing electrode and the signal line. The guard ring is held at the same potential as the sensing electrode, which eliminates the electric field between them and prevents parasitic capacitance from affecting the measurement signal.
Solution Approach 2:
The patent replaces traditional metal diaphragms with sapphire diaphragms. This substitution eliminates temperature hysteresis and improves thermal stability, as sapphire is a ceramic material that maintains its mechanical properties at high temperatures without the hysteresis effects characteristic of metals.
2Strength
If metal diaphragms are used in high-temperature applications, then they provide structural integrity, but they exhibit temperature hysteresis and pressure hysteresis
Solution Approach 1:
The patent changes the material parameter of the diaphragm from metal to sapphire (a ceramic material). This parameter change fundamentally alters the thermal and mechanical behavior, eliminating temperature hysteresis and pressure hysteresis while maintaining the required structural integrity for high-temperature applications.
3Ease of operation
If DC signal detection is used at high temperatures, then it provides simple measurement, but the dielectric material resistance decreases making DC signal difficult to detect
Solution Approach 1:
The patent employs frequency modulation (FM) capacitive measurement technology, which uses periodic AC signals instead of DC signals. The capacitive signal is modulated onto a carrier frequency, allowing the measurement system to detect changes in capacitance through frequency variations rather than direct voltage measurements, thereby overcoming the low resistance issue at high temperatures.
4Reliability
If electrical connections are made at high temperatures, then connectivity is established, but the connections degrade over time leading to sensor failure
Solution Approach 1:
The patent uses a composite structure combining sapphire diaphragm with sapphire substrate, both fused together. This composite ceramic structure provides thermal stability and mechanical strength throughout the assembly, eliminating the thermal mismatch and degradation issues that occur with traditional metal-to-metal or metal-to-ceramic connections at high temperatures.
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 enables reliable and accurate pressure sensing at elevated temperatures up to 1000°C, minimizing hysteresis effects and ensuring durable electrical connections, thus overcoming the limitations of existing sensors in high-temperature environments.
Implementation Method 1
fused using plasma activation and brazing
Implementation Method 2
fused using plasma activation and brazing
Implementation Method 3
a guard ring to shield from signal line parasitic capacitance
Implementation Method 4
capacitive pressure sensors
Data Source
AI summary
Disclosed are capacitive pressure probes or sensors for high temperature applications. The capacitive pressure sensors of the present invention include, inter alia, a sapphire diaphragm which is disposed within an interior sensing chamber of the probe housing and has a first electrode formed on a central portion thereof. The central portion of the diaphragm and the first electrode are adapted and configured to deflect in response to pressure variations encountered within an interior sensing chamber and by the pressure sensor. A sapphire substrate which has a second electrode formed thereon is fused to the sapphire diaphragm about its periphery to form a sapphire stack and to define a reference chamber therebetween. Prior to fusing the sapphire diaphragm to the sapphire substrate, all contact surfaces are chemically treated and prepared using plasma activation, so as to create a bonding layer and to reduce the temperature required for the fusion.