Control grids are indispensable in high-power microwave systems used in the defense and aerospace industries.
Commonly used in traveling wave tubes (TWTs), radio frequency (RF) power amplifiers, and medical devices such as electron guns (often used for radiation therapy), control grids amplify RF signals and control the flow of electrons through the devices.
Over 30 years ago, Elcon Precision first started the process of photochemical etching and forming for 3D hemispherical and flat grids.
We continue to be leaders in the area, investing in equipment and inspection tools to meet increasingly tighter tolerances on smaller and smaller parts.
In this article, we discuss the importance of precision and customization in manufacturing control grids and how Elcon's photochemical etching process delivers expertly crafted control grids.
The Role of Control Grids
A traveling wave tube (TWT) is a specialized vacuum tube that amplifies radio frequency (RF) signals in the microwave range. A vacuum tube controls electric current flow between electrodes to which a differential electric potential has been applied.
An electron gun uses a heated cathode to emit electrons. When positive voltage is applied across the cathode and anode, it drives the electrons toward the far end of the gun tube where the electrons are focused into a beam.
The control grid is an electrode used in amplifying vacuum tubes and is used to control the flow of electrons from the cathode to the anode.
The control grid within a TWT plays a crucial role in managing the flow of electrons through the device. It directs the electrons toward a specified area or point with high precision. In fact, it can control, shape and focus the electron beam inside TWTs or electron guns.
The electron beam can be controlled precisely by varying the voltage to the control grid. Efficient amplification or focusing of electron beams inside a device is crucial for it to function optimally.
At Elcon, we design and manufacture customized control grids to meet each application's unique requirements.
By customizing the dimensions of the grid structure and the patterns or apertures etched on it, our customers optimize the performance of the device.
This customization is pivotal as it ensures that the control grid fulfills the intended functionality and performance requirements of the TWT or electron gun.
For example, high-power RF amplification is a critical function in defense and aerospace applications. Similarly, precise and efficient electron beam delivery is vital for medical devices to deliver proper treatment protocols.
High precision in design and manufacturing is essential for producing control grids. Control grid etching processes must be designed and tested for high accuracy and repeatability. This level of precision is essential for high-performance devices to meet stringent quality control standards and reduce variations between devices.
Photochemical etching allows us to create intricate patterns and apertures on the control grid with tight tolerances.
At Elcon, we follow a well-developed Design for Manufacturability (DFM) practice to evaluate and test the control grid design at the prototyping stage to ensure that it can be consistently produced to the required specifications once it goes into full production.
Etching Process for 3D Hemispherical and Flat Control Grids
Photochemical etching involves precisely removing or etching material from the control grid structure to achieve specific performance characteristics.
Advanced photochemical etching techniques allow us to create complex patterns or structures, such as slots or meshes on the grid, which ultimately determine the functionality and performance of the device.
These are the basic steps we follow in the etching process:
- We start by coating the control grid material (substrate) with a photosensitive resist film.
- A digital artwork defines the pattern or shape for the etching and is transferred to the substrate using a digital imager tool.
- The substrate is then exposed to light, and the unexposed areas of the pattern are developed.
- The substrate is then sprayed with a chemical etchant at high-pressure and high temperature.
- The mask protects certain areas of the grid from coming into contact with the etchant.
- The remaining exposed areas come into contact with the corrosive chemicals, selectively removing material based on the pattern defined by the mask.
- The amount of etchant used, the duration of the chemical bath, and the etching depth must be precisely controlled to achieve the desired results.
- For 3D hemispherical grids, the etching process must also be carefully controlled to maintain the shape of a 3D hemispherical structure.
There are several benefits to using photochemical etching for fabricating control grids:
- Photochemical etching produces a burr-free, stress-free surface, unlike other fabrication methods that use stamping or lasers to create the desired shape.
- It creates straight sidewall surfaces and annular ring walls aligned to the radius of curvature, which are important for the integrity of the grid structure, for a consistent flow of electrons through the tube, and for the efficient amplification of RF waves.
- Photochemical etching also delivers a superior finish not available from electrical discharge machining.
While photochemical etching has clear benefits, it also has some limitations:
- Misalignment of the mask during the etching process can cause variations and defects in the control grid.
- It can be challenging to etch very deep or narrow patterns on a 3D hemispherical grid as this can affect its structural integrity.
However, these challenges can be addressed with careful process design and optimization. That's why working with a competent and experienced partner is crucial.
Elcon invented the photochemical etching process for custom grids—so we know all there is to know about the process. We have developed proprietary etchants, and our team works with you to select the appropriate materials. We use DFM best practices to evaluate at the prototyping stage, which is the suitable material and etchant ideally suited for your application's specific needs and requirements.
Reach out to our experts if you have any clarifications on design guidelines or specifications for your custom control grids.
What To Consider When Creating Control Grids
There are several considerations to keep in mind when creating control grids. These factors help ensure that the custom control grid will perform as intended and meet the rigorous demands of critical applications.
It is essential to choose the right material for your control grid requirement. The material you choose (Usually a refractory metal) should have mechanical strength to maintain the grid's structural integrity. It must have the correct electrical conductivity required for efficient electron flow and heat resistance to function properly even if the device gets overheated during operation.
DFM is critical before we run into the production of control grids. The dimensions of the piece to be produced, the pattern of slots, meshes, or apertures, and the tolerances expected must all be clearly defined.
Finally, control grid etching is a repeatable and consistent process and must conform to quality standards and industry-mandated compliances. Elcon adheres to stringent quality standards. We are AS9100D-certified, ISO 9001:2015-certified, ITAR-registered, and RoHS-compliant.
Receive Expertly Crafted Custom Grids With Elcon Precision
Elcon Precision uses advanced photochemical etching techniques to manufacture high-precision parts for industries ranging from aerospace to medicine, and from electronics to renewable energy.
We are one of the few manufacturers in the world specializing in the manufacture of focus and control grids for traveling wave tubes (TWT) and other mission-critical devices and systems.
We have the requisite experience and state-of-the-art equipment to produce high-precision, customized control grids for defense, aerospace, and medical applications while ensuring precise control over key production steps.
Connect with our experts to learn more about Elcon's photochemical etching process for custom control grids.