Miniaturized Sensor Bridges for High-Speed Flow Measurement
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Solution Overview
Problem
Existing miniaturized sensors with heater elements are fragile and limited in measuring high flow speeds due to their small hydraulic diameter and high aspect ratio, making them unsuitable for applications beyond low-speed wall shear friction measurements.
Innovation Solution
A miniaturized sensor design featuring a substrate with a cavity and a thermally insulating structure supported by bridges, where the heater element is transversely extended over the bridges, allowing for a thicker and more robust configuration with optimized geometrical parameters to enhance sensitivity and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the hot wire is made with small hydraulic diameter and high aspect ratio to improve sensitivity and bandwidth, then the sensor can measure low-speed flow and wall shear friction, but the wire becomes fragile and cannot withstand high flow speeds
Solution Approach 1:
The sensor is divided into functionally distinct zones: a measurement zone with a thin hot wire for high sensitivity, and support zones with thicker structural elements for mechanical strength. The transition zones connect these regions, allowing the wire to be thin where needed for measurement while being supported by thicker regions that prevent breakage at high speeds.
Solution Approach 2:
The wire thickness is varied along its length, with the central measurement portion having minimal thickness for maximum sensitivity, while the end portions near the supports have increased thickness for mechanical strength. This local variation in quality allows simultaneous optimization of both sensitivity and robustness in different regions of the same component.
2Loss of energy
If the hot wire is suspended over a cavity with air insulation to reduce heat loss and improve bandwidth, then thermal insulation is enhanced, but the wire becomes more vulnerable to mechanical damage
Solution Approach 1:
The support structure is segmented into multiple discrete support points rather than continuous contact with the substrate. This creates isolated suspension zones where thermal insulation is maximized, while the support points themselves provide mechanical reinforcement without creating continuous thermal conduction paths.
Solution Approach 2:
The air cavity acts as an intermediary medium that provides thermal insulation between the hot wire and the substrate. This intermediate layer reduces direct thermal conduction while the wire remains mechanically suspended, allowing thermal and mechanical functions to be decoupled.
3Loss of energy
If the thermally insulating structure is made of silicon nitride with low thermal conductivity to minimize heat conduction, then thermal insulation is improved, but the structural strength may be compromised
Solution Approach 1:
The support structure utilizes composite construction combining silicon nitride layers with other materials that have complementary properties. This allows the structure to achieve both low thermal conductivity from the silicon nitride and adequate mechanical strength from the composite architecture, resolving the trade-off between thermal insulation and structural integrity.
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 sensor achieves improved robustness and sensitivity, enabling measurements of high flow speeds exceeding 20 m/s while maintaining a wide bandwidth, suitable for various applications including speed and pressure measurements.
Implementation Method 1
The electrical contacts are arranged on the thermally insulating structure and they are connected to the ends of the hot wire, so that the hot wire can be electrically powered to perform heating by the Joule effect.
Data Source
AI summary
The invention relates to a miniaturized sensor having a heating element, and to an associated production method. The sensor includes a substrate, a cavity and a heat-insulating structure suspended above the cavity by areas connecting to the substrate. The heat-insulating structure includes at least two bridges extending above the cavity, the heating element being supported by said bridges, extending transversely thereto.