Microfocus X-ray Tube Cathode Filament Design
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Solution Overview
Problem
Microfocus X-ray tubes with hairpin filaments have a short service life due to high tube currents, leading to frequent replacements and increased service costs, which hinders their use in industrial production.
Innovation Solution
The filament is elongated in two directions perpendicular to the electron beam, significantly increasing the electron-emitting area, allowing for lower filament temperatures and a substantial increase in service life, with the option to maintain a focal spot size of less than 10 μm using multiple wire sections arranged in a helix shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a hairpin filament is used to achieve a fine electron beam, then the focal spot size is reduced to the μm range, but the filament temperature must be increased leading to short service life
Solution Approach 1:
The patent transitions from a punctiform (0D/1D) filament tip to a two-dimensional elongated filament structure. The filament is extended in two directions perpendicular to the electron beam, creating a planar emitting surface that increases the effective area while maintaining fine focal spot dimensions through controlled geometry.
Solution Approach 2:
The filament is divided into multiple wire sections arranged in a helical pattern. This segmentation increases the total electron-emitting surface area while distributing the thermal load across multiple sections, preventing localized overheating and extending service life.
2Productivity
If high tube currents are used to increase productivity, then the electron beam intensity is improved, but the filament temperature increases causing frequent replacements
Solution Approach 1:
By extending the filament into two dimensions perpendicular to the beam direction, the patent creates a larger emitting surface area that can support higher tube currents without requiring proportionally higher temperatures, thus maintaining productivity while extending cathode life.
Solution Approach 2:
The filament is pre-configured with an elongated geometry and helical wire sections before operation. This preliminary structural design ensures that the electron-emitting area is already optimized for high current operation, preventing the need for frequent replacements during the device lifecycle.
3Duration of action of stationary object
If the filament electron-emitting area is increased to reduce temperature, then the service life is extended, but the focal spot size may increase reducing resolution
Solution Approach 1:
The patent carefully controls the two-dimensional extension of the filament, ensuring that while the area increases for lower temperature operation, the dimensions perpendicular to the electron beam remain constrained to maintain the fine focal spot size required for high-resolution imaging.
Solution Approach 2:
The filament structure is designed with specific local geometries where the wire sections are arranged to provide adequate emitting area while maintaining appropriate dimensions in the beam direction. The helical arrangement and spacing are optimized to balance area expansion with focal spot preservation.
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 design extends the filament life by several orders of magnitude, enabling the use of high-resolution microfocus X-ray inspection devices in industrial settings without the need for frequent replacements.
Implementation Method 1
a heatable filament (17) formed from a wire for the glow emission of electrons to form an electron beam
Data Source
Figure 1
Figure 2~4
Figure 5~7
AI summary
The invention relates to a cathode element for a microfocus x-ray tube comprising a heatable filament made of wire for thermionically emitting electrons to form an electron beam. The filament has an elongated extension (11, 12) in each of two directions perpendicular to the electron beam in a source area of the electron beam.