Knudsen Thermal Force MEMS Gas Sensor for Low-Pressure Environments
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Solution Overview
Problem
There is a need for a microelectromechanical (MEMS) pressure sensor system that can effectively operate at low pressures, as existing technologies using mono-crystalline or polycrystalline silicon struggle due to mean-free paths that are larger than typical micro-scale dimensions at lower pressures.
Innovation Solution
A MEMS gas sensor based on Knudsen thermal force, featuring a substrate with stationary and moveable assemblies, actuation and sensing mechanisms, and capacitors that utilize electrostatic forces to move the assemblies and sense pressure changes, allowing for high sensitivity pressure readings and relative species concentration measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional piezoresistive pressure sensors using mono-crystalline or polycrystalline silicon are used, then the sensor structure is simple and manufacturing is straightforward, but the sensor cannot effectively operate at low pressures because the mean-free path becomes larger than the typical micro-scale dimensions
Solution Approach 1:
The patent changes the operating principle parameter from piezoresistive measurement to Knudsen thermal force measurement. By utilizing the Knudsen effect where gas molecules directly impinge on heated surfaces at low pressures, the sensor becomes adapted to low-pressure environments where the mean-free path exceeds micro-scale dimensions, resolving the adaptability issue while maintaining reliability
2Measurement precision
If the sensor operates at low pressures where mean-free paths are larger than micro-scale dimensions, then the sensor can detect low pressure environments, but conventional sensor technologies fail to provide accurate measurements
Solution Approach 1:
The patent replaces the mechanical piezoresistive sensing mechanism with a thermal-based Knudsen force mechanism. The stationary assembly with heated elements generates thermal forces that act on gas molecules, and the resulting movement of the moveable assembly provides a measurable signal that correlates to pressure, enabling accurate measurements in low-pressure environments where conventional mechanical sensors fail
3Measurement precision
If a moveable assembly is introduced to detect Knudsen forces, then pressure and gas composition can be detected with high sensitivity, but the device complexity increases
Solution Approach 1:
The patent divides the sensor into distinct functional segments: a stationary assembly containing heated elements that generate Knudsen forces, and a moveable assembly that responds to these forces. This segmentation allows each component to perform its specific function efficiently while maintaining overall system manageability despite the increased complexity
Solution Approach 2:
The patent introduces a moveable assembly as an intermediary element between the stationary heated assembly and the detection system. This intermediary converts the invisible Knudsen forces into measurable mechanical displacement, enabling sensitive detection of pressure and gas composition while providing a clear signal transduction pathway
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 MEMS sensor provides high sensitivity pressure readings and relative species concentration measurements, suitable for applications like pharmaceutical lyophilization, high-altitude UAVs, and spacecraft, by leveraging Knudsen thermal forces and capacitance changes to detect pressure and gas composition at low pressures.
Implementation Method 1
the at least one stationary assembly terminating at corresponding pads configured to receive an electrical current for heating the at least one stationary assembly
Implementation Method 2
pressure applied to the at least one stationary assembly in the heated state and the at least one moveable assembly forms Knudsen forces applied to the at least one moveable assembly causing active movement of the at least one moveable assembly substantially along the main axis
Implementation Method 3
The actuation mechanism includes an actuation capacitor coupled to actuation pads, such that applying a voltage to the actuation pads results in the selective movement of the moveable assembly due to electrostatic forces
Implementation Method 4
the sensing mechanism includes a sensing capacitor coupled to sensing pads, such that the active movement of the moveable assembly results in changes in capacitance of the sensing capacitor
Data Source
AI summary
A microelectromechanical (MEMS) gas sensor operating based on Knudsen thermal force is disclosed. The sensor includes a substrate, at least one stationary assembly that is fixedly coupled to the substrate, and at least one moveable assembly that is positioned above the substrate which is biased to move substantially according to a main axis and juxtaposed with the at least one stationary assembly.