Liquid Crystal Polymer X-Ray Window Seal for Vacuum Integrity
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Solution Overview
Problem
X-ray windows face challenges such as light penetration, x-ray fluorescence interference, high-temperature activation of getters, outgassing, and stress relief due to thermal expansion mismatch, along with the need for a hermetic seal that is opaque, low-leakage, and compatible with various materials.
Innovation Solution
A hermetic seal using a thermotropic liquid crystal polymer adhesive layer that is opaque, low outgassing, and capable of withstanding high temperatures, while providing stress relief and bonding to diverse materials, with properties like low light transmission and low thermal expansion mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the hermetic seal is made opaque to block light penetration, then light interference with x-ray signals is reduced, but the material selection becomes more constrained
Solution Approach 1:
The patent employs a composite hermetic seal structure consisting of a metal seal ring (providing mechanical strength and vacuum sealing) combined with an opaque adhesive layer (blocking light while bonding components). This composite approach allows each material to fulfill its specific function without compromising overall performance.
Solution Approach 2:
Different regions of the hermetic seal assembly have different optical properties - the metal seal ring and mounting structure are opaque, while the x-ray window thin film remains transparent. This local differentiation resolves the contradiction by applying opacity only where needed for light blocking.
2Object-affected harmful factors
If low atomic number elements are used in the hermetic seal to reduce x-ray fluorescence interference, then x-ray signal quality improves, but bonding strength and seal reliability may be compromised
Solution Approach 1:
The hermetic seal combines low atomic number materials (such as aluminum or polymer adhesives with Z<10) for the bonding and sealing function with the metal seal ring for structural integrity. This composite structure maintains seal reliability while minimizing x-ray fluorescence.
Solution Approach 2:
An intermediate adhesive layer serves as a mediator between the metal seal ring and the x-ray window thin film. This adhesive layer uses low atomic number elements to provide both bonding functionality and reduced x-ray fluorescence, while the metal ring provides the primary sealing mechanism.
3Productivity
If the hermetic seal can withstand high temperatures for quick getter activation, then vacuum pump-down time is reduced, but thermal stress and material compatibility challenges increase
Solution Approach 1:
The adhesive layer is formulated to undergo controlled parameter changes at elevated temperatures, including increased flexibility and adjusted coefficient of thermal expansion. This allows the seal to accommodate thermal stress during high-temperature getter activation while maintaining bonding integrity.
Solution Approach 2:
The hermetic seal design accounts for differential thermal expansion between the metal seal ring, adhesive layer, and x-ray window thin film. The adhesive layer is selected or formulated to have intermediate thermal expansion properties, reducing thermal stress concentration during high-temperature operation.
4Reliability
If the hermetic seal material has low outgassing properties to maintain vacuum integrity, then vacuum stability improves, but material selection and bonding capability are limited
Solution Approach 1:
The hermetic seal system uses a composite structure where the metal seal ring provides the primary vacuum barrier with excellent low outgassing properties, while the adhesive layer provides bonding capability. This composite approach allows each material to optimize its specific function.
Solution Approach 2:
The adhesive layer is designed as a thin, low-mass component that, while having higher outgassing potential per unit volume, contributes minimally to overall outgassing due to its small quantity. The primary vacuum sealing function is performed by the metal ring with superior vacuum properties.
5Reliability
If the hermetic seal has low leak rate to prevent pressure rise, then device reliability improves, but manufacturing precision requirements increase
Solution Approach 1:
The adhesive layer is formulated with viscoelastic properties that allow it to conform to surface irregularities and self-heal minor defects during bonding. This flexibility compensates for variations in manufacturing precision while maintaining low leak rate performance.
Solution Approach 2:
The hermetic seal design incorporates a redundant sealing mechanism where the metal seal ring provides the primary seal and the adhesive layer provides a secondary sealing barrier. This redundancy cushions against potential leakage paths, allowing greater tolerance in manufacturing precision.
6Duration of action of stationary object
If the hermetic seal relieves stress in the x-ray window thin film from thermal expansion mismatch, then window durability improves, but the seal structure becomes more complex
Solution Approach 1:
The adhesive layer is specifically formulated or selected to have a coefficient of thermal expansion that intermediates between the metal seal ring and the x-ray window thin film. This thermal expansion matching reduces differential stress and prevents window deformation or delamination during temperature cycling.
Solution Approach 2:
The adhesive layer undergoes parameter changes with temperature, becoming more compliant at elevated temperatures when thermal expansion differences are greatest. This dynamic parameter adjustment allows the seal to relieve stress without requiring complex mechanical stress relief structures.
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 provides a robust hermetic seal that minimizes interference, maintains vacuum integrity, and ensures reliable operation of x-ray devices by reducing stress and leakage, while being compatible with a wide range of materials.
Implementation Method 1
internal stress during manufacture or use due to coefficient of thermal expansion mismatch between the x-ray window thin film and a housing to which it is bonded
Implementation Method 2
an adhesive layer made at least partially from a liquid crystal polymer that is sandwiched between and provides a hermetic seal between the thin film and the housing
Implementation Method 3
a liquid crystal polymer that transitions from a solid state to a liquid crystal state at an elevated temperature
Implementation Method 4
the liquid crystal polymer can be main chain, side chain, linear, cyclic, branched, crosslinked, or combinations thereof
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An x-ray window comprising: a thin film configured for transmission of x-rays; a housing; and an adhesive layer sandwiched between and providing a hermetic seal between the thin film and the housing, the adhesive layer including liquid crystal polymer.