The present application relates to field emission cathode devices and, more particularly, to a field emission cathode device and method of forming a field emission cathode device.
A typical field emission cathode assembly includes a field emission cathode and an extraction gate structure with certain gap distance in between, an example of which is shown in
A field emission cathode, in a typical scenario, only operates stably under a certain maximum current density. As such, in order to achieve a stable high current, a cathode with a large area is generally required. The electron emission area (e.g., corresponding to the electron beam cross-section) is defined by the corresponding cathode area, as illustrated in
Thus, there exists a need for a device and formation method for a field emission cathode assembly having a large-area cathode for achieving stable high current that is also capable of forming a small and focused electron beam cross-section from the field emission electrons. That is, it would be desirable to achieve a field emission cathode assembly capable of increasing the total amount of field emission electrons (e.g., current) emitted from a given area (e.g., gate size), without significantly increasing the electron beam cross section, and while protecting the cathode from ion bombardment.
The above and other needs are met by aspects of the present disclosure which includes, without limitation, the following example embodiments and, in one particular aspect, provides a field emission cathode device, comprising a field emission cathode including a cylindrical substrate having a field emission material deposited on a cylindrical surface thereof, the field emission cathode defining a longitudinal axis; a solenoid extending concentrically about the cylindrical surface of the field emission cathode, and defining a gap therebetween, the solenoid defining opposed first and second open ends extending perpendicularly to the longitudinal axis; a current source (VI) electrically connected to the solenoid and arranged to direct a constant polarity (DC) current (I) thereto, the DC current (I) in the solenoid forming a magnetic field (B) along the solenoid; and a gate voltage source (VG) electrically connected to the solenoid or the field emission cathode and arranged to interact therewith to generate an electric field (E) inducing the field emission cathode to emit electrons (e) from the field emission material into the gap, the emitted electrons being responsive to the magnetic field to spiral within the gap and about the longitudinal axis, in correspondence with the current flow in the solenoid, through the first open end of the solenoid.
Another example aspect provides a method of forming a field emission cathode device, comprising inserting a cylindrical substrate of a field emission cathode into a solenoid such that the solenoid extends concentrically about a cylindrical surface of the substrate and defines a gap therebetween, the field emission cathode defining a longitudinal axis and the solenoid defining opposed first and second open ends extending perpendicularly to the longitudinal axis; directing a constant polarity (DC) current (I) to the solenoid from a current source (VI) electrically connected thereto, the DC current (I) in the solenoid forming a magnetic field (B) along the solenoid; and generating an electric field (E) with a gate voltage source (VG) electrically connected to the solenoid or the field emission cathode, the electric field (E) inducing the field emission cathode to emit electrons (e) from the field emission material into the gap, the emitted electrons being responsive to the magnetic field to spiral within the gap and about the longitudinal axis, in correspondence with the current flow in the solenoid, through the first open end of the solenoid.
The present disclosure thus includes, without limitation, the following example embodiments:
Example Embodiment 1: A field emission cathode device, comprising a field emission cathode including a cylindrical substrate having a field emission material deposited on a cylindrical surface thereof, the field emission cathode defining a longitudinal axis; a solenoid extending concentrically about the cylindrical surface of the field emission cathode, and defining a gap therebetween, the solenoid defining opposed first and second open ends extending perpendicularly to the longitudinal axis; a current source electrically connected to the solenoid and arranged to direct a constant polarity (DC) current thereto, the DC current in the solenoid forming a magnetic field along the solenoid; and a gate voltage source electrically connected to the solenoid or the field emission cathode and arranged to interact therewith to generate an electric field inducing the field emission cathode to emit electrons from the field emission material into the gap, the emitted electrons being responsive to the magnetic field to spiral within the gap and about the longitudinal axis, in correspondence with the current flow in the solenoid, through the first open end of the solenoid.
Example Embodiment 2: The device of any preceding example embodiment, or combinations thereof, comprising an anode disposed in spaced-apart relation to the first open end of the solenoid; and a high voltage source electrically connected to the anode and arranged to apply a voltage of at least about 10 kV to the anode, the anode being responsive to the application of the voltage thereto to attract the electrons emitted from the first open end of the solenoid.
Example Embodiment 3: The device of any preceding example embodiment, or combinations thereof, wherein a velocity of the electrons attracted to the anode is proportional to the voltage applied to the anode.
Example Embodiment 4: The device of any preceding example embodiment, or combinations thereof, wherein an amount of the electrons emitted through the first open end of the solenoid is proportional to a voltage applied by the gate voltage source to generate the electric field.
Example Embodiment 5: The device of any preceding example embodiment, or combinations thereof, wherein a focus of the electrons emitted from the first open end of the solenoid is proportional to a diameter of the first open end.
Example Embodiment 6: The device of any preceding example embodiment, or combinations thereof, wherein a focus of the electrons emitted from the first open end of the solenoid is proportional to a dimension of the gap between the solenoid and the cylindrical surface of the field emission cathode at the first open end.
Example Embodiment 7: The device of any preceding example embodiment, or combinations thereof, wherein the cylindrical substrate is comprised of an electrically conductive material or a metallic material.
Example Embodiment 8: The device of any preceding example embodiment, or combinations thereof, wherein the field emission material deposited on the cylindrical surface comprises nanotubes, nanowires, graphene, amorphous carbon, or combination thereof.
Example Embodiment 9: The device of any preceding example embodiment, or combinations thereof, wherein the cylindrical substrate has a diameter of between about 1 mm and about 5 cm, and the gap is between about 100 µm and about 1 mm.
Example Embodiment 10: The device of any preceding example embodiment, or combinations thereof, wherein the first and second open ends of the solenoid have a diameter of between about 1 mm and about 5 cm.
Example Embodiment 11: A method of forming a field emission cathode device, comprising inserting a cylindrical substrate of a field emission cathode into a solenoid such that the solenoid extends concentrically about a cylindrical surface of the substrate and defines a gap therebetween, the field emission cathode defining a longitudinal axis and the solenoid defining opposed first and second open ends extending perpendicularly to the longitudinal axis; directing a constant polarity (DC) current to the solenoid from a current source electrically connected thereto, the DC current in the solenoid forming a magnetic field along the solenoid; and generating an electric field with a gate voltage source electrically connected to the solenoid or the field emission cathode, the electric field inducing the field emission cathode to emit electrons from the field emission material into the gap, the emitted electrons being responsive to the magnetic field to spiral within the gap and about the longitudinal axis, in correspondence with the current flow in the solenoid, through the first open end of the solenoid.
Example Embodiment 12: The method of any preceding example embodiment, or combinations thereof, comprising depositing a field emission material on the cylindrical surface of the substrate.
Example Embodiment 13: The method of any preceding example embodiment, or combinations thereof, comprising applying a voltage of at least about 10 kV from a high voltage source to an anode disposed in spaced-apart relation to the first open end of the solenoid, the anode being responsive to the application of the voltage thereto to attract the electrons emitted from the first open end of the solenoid.
Example Embodiment 14: The method of any preceding example embodiment, or combinations thereof, comprising varying a diameter of the first open end of the solenoid to proportionally vary a focus of the electrons emitted from the first open end.
Example Embodiment 15: The method of any preceding example embodiment, or combinations thereof, comprising varying a dimension of the gap between the solenoid and the cylindrical surface of the field emission cathode at the first open end of the solenoid to proportionally vary a focus of the electrons emitted from the first open end.
Example Embodiment 16: The method of any preceding example embodiment, or combinations thereof, comprising forming the cylindrical substrate of an electrically conductive material or a metallic material, and depositing the field emission material comprised of nanotubes, nanowires, graphene, amorphous carbon, or combinations thereof on the cylindrical surface of the cylindrical substrate.
Example Embodiment 17: The method of any preceding example embodiment, or combinations thereof, wherein inserting the cylindrical substrate into the solenoid comprises inserting the cylindrical substrate having a diameter of between about 1 mm and about 5 cm into the solenoid, such that the gap is between about 100 µm and about 1 mm.
Example Embodiment 18: The method of any preceding example embodiment, or combinations thereof, comprising forming the solenoid such that the first and second open ends of the solenoid have a diameter of between about 1 mm and about 5 cm.
These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying drawings, which are briefly described below. The present disclosure includes any combination of two, three, four, or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined or otherwise recited in a specific embodiment description herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and embodiments, should be viewed as intended, namely to be combinable, unless the context of the disclosure clearly dictates otherwise.
It will be appreciated that the summary herein is provided merely for purposes of summarizing some example aspects so as to provide a basic understanding of the disclosure. As such, it will be appreciated that the above described example aspects are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. It will be appreciated that the scope of the disclosure encompasses many potential aspects, some of which will be further described below, in addition to those herein summarized. Further, other aspects and advantages of such aspects disclosed herein will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described aspects.
Having thus described the disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all aspects of the disclosure are shown. Indeed, the disclosure may be embodied in many different forms and should not be construed as limited to the aspects set forth herein; rather, these aspects are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
In particular aspects, the cylindrical substrate 225 defining the cathode 200 is comprised of an electrically conductive material or a metallic material. In such aspects, the field emission material 250 deposited on the cylindrical surface of the substrate 225 comprises a layer of nanotubes, nanowires, graphene, amorphous carbon, or combinations thereof. The solenoid 300 is comprised, for example, of a coil of a suitable dimension of wire. Further, in some aspects, the first and second open ends 300A, 300B of the solenoid 300 have a diameter (e.g., the inner dimension of the coil) of between about a few millimeters (e.g., 1 mm) and about a few centimeters (e.g., 5 cm). In some aspects, the cylindrical substrate 225 has a diameter of between about a few millimeters (e.g., 1 mm) and about a few centimeters (e.g., 5 cm), and the gap 150 defined between the solenoid 300 and the cylindrical surface of the substrate 225 is between about 100 µm and about 1 mm.
As shown, for example, in
As shown in
In such an arrangement, the amount of the electrons emitted through the first open end 300A of the solenoid 300 are the electrons emitted from the cylindrical surface (e.g., the layer of the field emission material 250) of the cathode 200, and the amount of electrons is thus proportional to the DC voltage (continuous or pulsed) applied to the solenoid 300. Further, the induced spiral motion of the emitted electrons within the gap 150 continues upon the electrons exiting through the first open end 300A of the solenoid 300. The cross-section of the resulting electron beam (the spiral projection of the emitted electrodes - see, e.g., element 900 in
One application of the aspects of the field emission cathode device disclosed herein include, for example, an X-ray tube 700. In such an application, as shown, for example, in
That is, the anode 800 having the high voltage (HV) applied thereto is disposed in spaced apart relation with respect to the field emission cathode device 100. Under the influence of the anode 800 having the high voltage applied thereto, the electrons going through spiral motion within the gap 150 are attracted by and toward the anode 800. Since the electrons are confined within the gap 150 by the magnetic field generated by the solenoid 300, the cross-section of the electron beam 900 exiting the first open end 300A of the solenoid 300 is proportional to and at least partially determined by the dimension of the first open end 300A of the solenoid 300. However, since the electrons forming the electron beam 900 are emitted from the side of the cathode 200 (e.g., the cylindrical surface of the substrate), the overall emitting area of the field emission cathode device 100 is larger than the dimension of the first open end 300A of the solenoid 300, and is not limited by the cross-section (dimensions) of the emitting area of the cathode itself. Such aspects of the present disclosure thus provide a field emission cathode device 100 capable of achieving stable high current, while also forming a small and focused electron beam cross-section from the field emission electrons, with the field emission current directed through the first open end of the solenoid providing additional protection of the cathode from ion bombardment.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these disclosed embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that embodiments of the invention are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the invention. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the disclosure. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated within the scope of the disclosure. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
It should be understood that although the terms first, second, etc. may be used herein to describe various steps or calculations, these steps or calculations should not be limited by these terms. These terms are only used to distinguish one operation or calculation from another. For example, a first calculation may be termed a second calculation, and, similarly, a second step may be termed a first step, without departing from the scope of this disclosure. As used herein, the term “and/or” and the “/” symbol includes any and all combinations of one or more of the associated listed items.
As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Therefore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2021/058933 | 9/29/2021 | WO |
Number | Date | Country | |
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63085309 | Sep 2020 | US |