Cathodes having carbon nanotube (cnt) fibers wound onto graphite substrates or …
US20250379018A1
Abstract
A field emission (FE) cathode for a vacuum electronic device (VED) includes a graphite substrate or framework in the shape of a hollow cylinder, and at least one continuous carbon nanotube (CNT) fiber in tension or compression around at least a portion of the graphite substrate. The at least one continuous CNT fiber can include a filament, yarn, braided yarn, film, fabric, or combination thereof. The at least one continuous CNT fiber is secured to the electrically conductive substrate by vacuum brazing or any other suitable means.
Description (excerpt)
CROSS-REFERENCE TO RELATED APPLICATIONS Pursuant to 37 C.F.R. § 1.78 (a) (4), this application is a continuation-in-part of U.S. Non-Provisional patent application Ser. No. 18/620,900 filed on Mar. 28, 2024, which in turn is a continuation-in-part of U.S. Non-Provisional patent application Ser. No. 18/436,353 filed on Feb. 8, 2024, now U.S. Pat. No. 12,176,173 issued on Dec. 24, 2024, the contents of which are each expressly incorporated herein in their entireties by reference. RIGHTS OF THE GOVERNMENT The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty. FIELD OF THE INVENTION The present invention relates generally to electrodes and, more specifically, to Field emission cathodes comprising continuous CNT fibers for use in vacuum electronic devices and the like. BACKGROUND OF THE INVENTION Field emission (FE) cathodes for vacuum electronic devices (VEDs) are typically made with high aspect ratio wire or fiber-type structures that are mounted on electrically-conductive substrates such as for example, but not limited to, metallic substrates. The fibers are rigid and vertically-aligned so that they point towards an applied electric field. This type of vertical geometry results in a large concentration of electric field lines at free tips of the fibers which lead to field emission of electrons. This process can be accompanied by intense localized heating and plasma formation at the fiber free tips resulting in erosion of the fiber free tips and eventual breakdown and failure of the FE cathode. The current state of the art material for FE cathodes in VEDs is rigid carbon fiber ( FIGS. 1 A and 1 B ). See Shiffler et al., Review of Cold Cathode Research at Air Force Research Laboratory, IEEE Transactions on Plasma Science , Vol. 36, No. 3, June 2008, the disclosure of which is expressly incorporated herein in its entirety by reference. These FE cathodes are manufactured using a technique called flocking. Flocking is a process of depositing many small fiber particles (referred to as “flock”) onto an electrically-conductive adhesive-coated surface. This process is accomplished with the application of a high-voltage electric field in a flocking machine. The flock is given a negative charge while the substrate is grounded. The flock flies vertically onto the substrate, attaching to a previously-applied electrically-conductive adhesive coating to create a velvet-like surface consisting of vertically-aligned carbon fibers. The diameter of the individual fibers is typically only about a few thousandths of a centimeter, and the length typically ranges from about 0.25 to about 5 mm. Macroscopic carbon nanotube (CNT) fibers may also be vertically mounted onto a horizontal substrate, i.e., the macroscopic CNT fibers are mounted orthogonal to the substrate. These macroscopic CNT fibers have diameters ranging from about 10 to about 100 μm. When vertically mounted for FE cathodes, the macroscopic CNT fibers must be cut to a specific length either mechanically or with a laser. However, since the macroscopic CNT fibers are not stiff, they lean or droop making it difficult to mount multiple macroscopic CNT fibers that are all vertical and of the same height, which is critical for use as a FE cathode. Additionally, mechanically-cut tips usually introduce rough edges with dangling fibrils (see FIG. 2 A ). Laser cutting the macroscopic CNT fibers largely reduces tip roughness, however, the tips of the macroscopic CNT fibers are still spread out at their ends, i.e., frayed ends (see FIG. 2 B ). The tip spread and frayed ends are undesirable because they lead to non-uniform emission, uneven temperature distribution, and hotspots at the tips of the macroscopic CNT fibers. U.S. patent application Ser. No. 16/933,048 filed on Jul. 20, 2020, and entitled “Carbon Nanotube Yarn Cathode Using Textile Manufacturing Methods”, the subject matter of which is expressly incorporated herein in its entirety, discloses using continuous CNT fiber filaments, threads, or yarns, and/or tapes or ribbons that are knitted, woven, sewn, and/or embroidered to form CNT textiles using existing textile manufacturing techniques and equipment. See FIGS. 3 A and 3 B showing an exemplary CNT textile forming emitter loops on a top surface. Each continuous CNT fiber of the CNT textiles is composed of multiple CNTs and exhibits higher specific strength, better flexibility, higher electrical conductivity compared to traditional carbon fibers. The current preparation methods of continuous CNT fibers include, but are not limited to, wet spinning, array spinning, and floating catalyst chemical vapor deposition (FCCVD). FIGS
Filing details
- Inventors
- Steven Fairchild
- Assignee
- Government Of The United States As Represented By The Secretary Of The Air …
- Filed
- May 21, 2025
- Granted
- Application pending
Bibliographic data and excerpted text sourced from Google Patents (public record) as part of IP TechMatch's current-filings monitor. This filing is not part of the 2019 historical archive. For the authoritative full text, drawings, and legal status, see the source links above or consult USPTO records directly.