Field Emitter Array with Meshed Grid for X-ray Generation
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Solution Overview
Problem
Field emitter arrays in x-ray tubes are susceptible to arcing and structural wear due to electrical overvoltage, leading to operational failures and beam quality degradation, and require numerous activation lines and connections that increase vacuum leak rates and inhibit performance.
Innovation Solution
A field emitter unit with a protection and focusing scheme that includes a meshed grid to enhance the electric field and a focusing electrode to minimize beam degradation, along with a control system that reduces the number of activation connections by using a matrix configuration with shared activation lines to control multiple emitters efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a field emitter array is used in an x-ray tube, then electron beam generation is achieved, but the system becomes susceptible to arcing and operational failures
Solution Approach 1:
A meshed grid structure is introduced as an intermediary component between the gate electrode and the emitter elements. This grid acts as a mediator that distributes the electric field more uniformly across the emitter array, preventing localized field concentration that would cause arcing. The grid structure with its multiple interconnected elements provides a gradual field transition, eliminating the direct high-voltage stress on individual emitters.
Solution Approach 2:
The invention changes the electric field distribution parameter by transforming the conventional uniform gate voltage application into a spatially distributed field through the meshed grid. By modifying how the electric field is applied (from direct to distributed), the system achieves lower local field intensities that prevent breakdown while maintaining overall emission functionality.
2Ease of operation
If numerous activation lines are used to control each emitter individually, then precise emitter control is achieved, but the number of vacuum connections increases leading to higher leak rates
Solution Approach 1:
Multiple emitter control functions are merged into shared activation lines. Instead of dedicating one activation line per emitter, the invention groups emitters and uses common activation lines that can selectively activate groups of emitters. This merging reduces the total number of vacuum feedthrough connections while maintaining the ability to control different emitter regions independently through combinatorial addressing schemes.
Solution Approach 2:
The activation lines are designed to serve multiple functions and multiple emitter groups simultaneously. A single activation line can address different sets of emitters at different times, and combinations of activation lines can selectively enable specific emitter patterns. This multi-functionality allows precise emitter control with fewer physical connections.
3Power
If high voltage is applied to extract electron beams, then electron emission current is increased, but beam quality degrades due to increased emittance
Solution Approach 1:
The electron extraction process is segmented into multiple stages through the meshed grid structure. Instead of applying the full extraction voltage directly at the emitter tip, the voltage application is divided across multiple grid elements, creating a progressive field acceleration. This segmented approach reduces the instantaneous field intensity at the emitter surface, lowering emittance while still achieving the required extraction current through cumulative acceleration.
Solution Approach 2:
The meshed grid serves as an intermediary acceleration structure between the emitter and the final extraction point. Electrons are first emitted with low energy, then gradually accelerated through the grid's electric field distribution before reaching full extraction energy. This intermediary acceleration path preserves beam quality by avoiding direct high-field emission.
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 effectively suppresses arcing, improves beam focusing, and reduces the number of activation lines, enhancing the stability and performance of field emitter arrays by minimizing beam degradation and vacuum leaks, thereby enabling robust operation and high-quality tomographic imaging.
Implementation Method 1
a meshed grid disposed adjacent each emitter element to enhance an electric field at a surface of the emitter element
Implementation Method 2
a focusing element positioned to receive the electron beam from each of the emitter elements and focus the electron beam to form a focal spot on the target anode
Implementation Method 3
Each emitter device, when properly driven, can emit a beam or current of electrons from the tip portion of the emitter device. Field emitter arrays have many applications, one of which is in field emitter displays
Data Source
AI summary
A multiple spot x-ray generator is provided that includes a plurality of electron generators. Each electron generator includes an emitter element to emit an electron beam, a meshed grid adjacent each emitter element to enhance an electric field at a surface of the emitter element, and a focusing element positioned to receive the electron beam from each of the emitter elements and focus the electron beam to form a focal spot on a shielded target anode, the shielded target anode structure producing an array of x-ray focal spots when impinged by electron beams generated by the plurality of electron generators. The plurality of electron generators are arranged to form an electron generator matrix that includes activation connections electrically connected to the plurality of electron generators, wherein each electron generator is connected to a pair of the activation connections to receive an electric potential therefrom.