UHF Sensor Antenna Protection from Polyurethane Injection
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Solution Overview
Problem
The presence of polyurethane on ultra-high-frequency antennas in sensors for 'hands-free' vehicle access systems leads to antenna mismatching, signal attenuation, and variability in signal power due to heterogeneity, affecting performance and reproducibility.
Innovation Solution
A method involving a seal and compression element to prevent polyurethane from covering the antenna, using a housing structure with injection of polyurethane into separate spaces to ensure impermeability and protect the antenna, while using a piece of foam to prevent polyurethane penetration through holes in the printed circuit board.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyurethane is injected to ensure impermeability and protect the sensor, then the sensor achieves water resistance and structural strength, but the polyurethane covers the ultra-high-frequency antenna causing mismatching and signal attenuation
Solution Approach 1:
The housing is divided into a first housing portion and a second housing portion with a receiving area in between. The seal divides the internal space into a first space (where polyurethane is injected) and a second space (where the antenna is located and protected from polyurethane). This segmentation allows the antenna to be protected while still achieving water resistance through polyurethane injection.
Solution Approach 2:
A seal acts as an intermediary barrier between the polyurethane injection zone and the antenna zone. The seal prevents polyurethane from reaching the antenna while allowing the polyurethane to provide water resistance to the housing structure. The compression element works with the seal to maintain this protective barrier.
2Strength
If polyurethane is injected into the housing to provide structural strength and impermeability, then the sensor becomes more robust, but signal power varies due to heterogeneity of polyurethane coverage
Solution Approach 1:
The housing interior is segmented into a first space for polyurethane injection and a second space protected by the seal. This ensures that the antenna is always in a polyurethane-free zone, eliminating variations in signal power caused by heterogeneous polyurethane coverage. The structural strength is maintained through polyurethane injection in the first space.
3Manufacturing precision
If the housing is sealed to prevent polyurethane penetration, then antenna performance is protected, but the manufacturing process becomes more complex
Solution Approach 1:
The housing is segmented into two portions with a defined receiving area between them. This segmentation provides a clear manufacturing pathway: insert the PCB with antenna into the receiving area, seal the space with a seal and compression element, then inject polyurethane into the first space. The segmented design simplifies the manufacturing process compared to attempting to create a fully enclosed complex seal.
Solution Approach 2:
The seal and compression element are positioned in the first housing portion before polyurethane injection. This preliminary action creates the protective barrier in advance, ensuring the antenna is protected from polyurethane penetration during the injection process. The PCB is also positioned in the receiving area before injection, preliminarily protecting the antenna.
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 approach enhances the transmission and reception capabilities of the ultra-high-frequency antennas by preventing polyurethane coverage, reducing signal absorption, and ensuring consistent performance across sensors.
Implementation Method 1
a compression element for the seal (7) being located within the first housing portion (5) in a manner secured to a face (5a) of the first housing portion (5) opposite the printed circuit board (4)
Implementation Method 2
injecting a layer of polyurethane into the first and second spaces, the seal preventing the polyurethane from penetrating into its interior in the receiving area that the seal delimits
Data Source
AI summary
A method for manufacturing a sensor having an ultra-high-frequency antenna printed on a receiving area on a first face of a printed circuit board. The first face of the board is inserted into a first housing portion with a seal and a compression element, the seal surrounding the receiving area while a first space remains free in the portion. A second face of the board is inserted into a second housing portion and the portions are pressed together, a second space remaining free. Then, polyurethane is injected into the first and second spaces, the seal preventing the polyurethane from penetrating into the receiving area.