CN111788652A - Electron emission device - Google Patents
Electron emission device Download PDFInfo
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- CN111788652A CN111788652A CN201980015776.1A CN201980015776A CN111788652A CN 111788652 A CN111788652 A CN 111788652A CN 201980015776 A CN201980015776 A CN 201980015776A CN 111788652 A CN111788652 A CN 111788652A
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- electron
- barrier
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- emitting device
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- 230000004888 barrier function Effects 0.000 claims abstract description 46
- 230000005684 electric field Effects 0.000 claims description 5
- 230000005669 field effect Effects 0.000 claims description 4
- 238000010438 heat treatment Methods 0.000 claims description 3
- 238000002360 preparation method Methods 0.000 claims 5
- 238000009826 distribution Methods 0.000 description 10
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 7
- 239000002041 carbon nanotube Substances 0.000 description 7
- 229910021393 carbon nanotube Inorganic materials 0.000 description 7
- 238000010894 electron beam technology Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 5
- QVQLCTNNEUAWMS-UHFFFAOYSA-N barium oxide Chemical compound [Ba]=O QVQLCTNNEUAWMS-UHFFFAOYSA-N 0.000 description 4
- 239000010406 cathode material Substances 0.000 description 4
- 239000000758 substrate Substances 0.000 description 3
- 239000000919 ceramic Substances 0.000 description 2
- 229910052746 lanthanum Inorganic materials 0.000 description 2
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000006978 adaptation Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 238000002059 diagnostic imaging Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 229910003460 diamond Inorganic materials 0.000 description 1
- 239000010432 diamond Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000003698 laser cutting Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 238000004846 x-ray emission Methods 0.000 description 1
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Abstract
The present invention relates to an electron emission device, comprising: at least one electron emitter (2) having at least one emission face (3); and at least one barrier (5) which is spaced apart from the emission surface (3) of the electron emitter (2) and has a predefinable number of individually controllable barrier segments (G)1‑G7，GN). According to the invention, in each gate segment (G)1‑G7，GN) At least one individually presettable gate voltage can be applied to each of them. Such an electron-emitting device allows, in a simple manner, an adjustment of the image quality with as low an anode load as possible.
Description
Technical Field
The present invention relates to an electron emission device.
Background
An electron-emitting device comprising an electron emitter having an emission surface and a barrier rib is known from DE 4100297 a 1. The barrier is spaced apart from the emission surface of the electron emitter and has a predeterminable number of individually controllable gate sections. To this end, a switch and a series resistor are respectively associated with all gate segments. The gate sections can be switched on or off by means of switches, respectively.
Furthermore, US 5,857,883 discloses an electron emitting device having an electron emitter and an emitting surface facing a barrier. The barrier is spaced apart from the emission surface of the electron emitter and has a plurality of individually switchable gate sections.
An electron-emitting device constructed as a heat-emitting device is described, for example, in US 8,374,315B 2. In the known case, the electron-emitting device comprises at least one planar emitter having at least one emission surface which thermally emits electrons when a heating voltage is applied. Furthermore, the known electron emission device comprises at least one barrier grid, which is spaced apart from the emission surface of the planar emitter. In the known case, a barrier is used as a control electrode, since the emission of electrons from the material of the emission surface can be varied by applying a gate voltage. A defined beamlet of electron emissions can thereby be generated.
The possibility of increasing the power by using an asymmetrical focal spot shape is described in US 7,835,501B 2 and DE 102012209089 a 1.
Furthermore, it is known from US 8,054,944B 2 to divert a plurality of electron beams that are deflectable by a deflection device onto an anode.
Furthermore, a so-called "Coded Spot" method is disclosed IN US 7,817,777B 2 and IN 201400992I 2.
Field-effect emission cathodes are described, for example, in US 7,751,528B2 (in particular FIGS. 11B and 8) and in the publication "Multi source inverse-geometry CT.part II.X-ray source design and protocol" (author: V.Bogdan Neculas et al), Medical Physics 43(8), August 2016, p. 4617-4627, in particular FIG. 7. There is a metal grid over the large-area emitting surface of the emitting material (carbon nanotubes or dispenser cathode material, e.g. barium oxide). The dispenser cathode is also referred to as a subsequent delivery cathode or as a spare cathode. By applying a voltage to the entire gate, the emission current intensity over the entire surface is controlled. The current flowing onto the barrier heats the barrier and limits the pulse time and current intensity of electron emission, thereby preventing damage to the barrier.
It is also known from US 7,751,528B2 to switch a plurality of cathodes individually in order to switch the electron beams on and off at a small distance from one another.
Disclosure of Invention
The object of the present invention is to provide an electron-emitting device for an X-ray tube, which in a simple manner allows an adjustment of the image quality with as little anode loading as possible.
Said object is achieved according to the invention by an electron-emitting device according to claim 1. Advantageous embodiments of the invention are the subject matter of the further claims.
The electron-emitting device according to claim 1, comprising: at least one electron emitter having at least one emission face; and at least one barrier which is spaced apart from the emission surface of the electron emitter and has a predeterminable number of individually controllable gate segments. According to the invention, at least one individually predeterminable gate voltage can be applied to each gate segment. The predefinable gate voltage can be between a lower limit value, which does not necessarily have to be zero, and an upper limit value, which can also be lower than the maximum permissible value.
Since in the solution according to the invention at least one individually presettable gate voltage can be applied to each gate segment, a specifically defined beamlet (electron beamlet) of the electron beam can be generated for a presettable number of individually controllable gate segments. The barrier rib thus forms a reliable control electrode in the electron-emitting device according to claim 1.
The segmented barrier ribs are spaced apart from the emission surface of the electron emitter. Since the individually controllable gate segments can generate different voltage patterns, a large number of different electron beams can be generated by means of said different voltage patterns. Within the scope of the invention, it is possible, for example, to achieve electron emission alternately in each case by means of a single gate segment. It is also possible, however, that a plurality of gate segments, which are not necessarily arranged next to one another, are simultaneously able to carry out the emission of electrons from the emission surface of the electron emitter. In this way, the targeted blocking of the individual grid segments makes it possible to specifically vary the electron emission and thus the distribution of the emitted electrons with respect to the position of the defined focal point shape. This reliably achieves an optimum adaptation to the respective application.
The individual gate segments differ in their penetrability for the emitted electrons by means of the respectively applied gate voltages. A correspondingly higher electron emission occurs in the gate region to which the smaller gate voltage is applied. In contrast, a correspondingly low electron emission is obtained at a correspondingly high gate voltage.
The barrier grids or grid sections always have a positive potential with respect to the emission face of the electron emitter. The gate sections in the non-emission region are either at the potential of the emission surface of the electron emitter or at a potential which is negative compared to the potential of the electron emitter. The electron beam can be deflected or focused in the emission region if the potentials are selected accordingly. The distribution of the emitted electrons is thus almost freely selectable.
In X-ray tubes for diagnostic imaging, the property is required by which the focal spot can be dynamically changed at the anode forming the X-ray source area ("Point-Spread-Function", PSF, Point Spread Function, or emission profile). With this function a series of improvements can be achieved:
increasing the electrical power density in the focal spot (by an asymmetric emission distribution),
increasing the continuous power in the switched-on carbon nanotube emitters (by using multiple electron beams),
improved resolution (by encoded point algorithm).
According to a preferred embodiment of the electron-emitting device, the electron emitter is configured as a dispenser cathode (also referred to as "Spindt cathode") that emits electrons when an electric field strength is applied (claim 2). The term "dispenser cathode" is understood to mean a cathode in which the support material is coated with a dispenser cathode material which emits electrons upon application of an electric field strength. Suitable dispenser cathode materials are, for example, barium oxide (BaO) and lanthanum hexaboride (LaB)6)。
In an equally advantageous embodiment of the electron emitter, the electron emitter is designed as a field effect emitter which also emits electrons when an electric field strength is applied (claim 3). Within the scope of the present invention, the field-effect emitters can be configured, for example, as CNT-based field emitters (CNT, Carbon nanotubes) or as Si-based field emitters (Si, silicon). Nanocrystalline diamond is also suitable for the production of cold cathodes according to DE 19727606 a 1.
According to a further advantageous alternative of the electron-emitting device, the electron emitter is designed as a thermal emitter (thermionic emission), which emits electrons when a heating voltage is applied (claim 4). Preferably, the emission surface of the electron emitter is structured. The structuring can be achieved, for example, by slits in the emission surface in planar emitters with rectangular surfaces.
For certain requirements, it may be advantageous to provide a second barrier at a distance from the barrier, the planes of the two barriers running parallel to one another, and the second barrier likewise having a predeterminable number of individually actuatable barrier sections and the barrier sections of the barrier running perpendicular to the barrier sections of the second barrier (claim 5). Thereby, the emission distribution of electrons can be arbitrarily controlled in two spatial directions.
The electron emission device according to the invention or its advantageous embodiments (claims 2 to 5) is suitable for installation in a focusing head (claim 6).
With the aid of the electron emission device (claims 1 to 5) or with the aid of the focusing head provided with an electron emission device (claim 6), it is possible to manufacture in a simple manner an X-ray tube (claims 7 and 8) which makes it possible to adjust the image quality with a small anode load.
The X-ray tube (claims 7 and 8) can be inserted without modification into the emitter housing of the X-ray emitter (claim 9).
Drawings
In the following, schematically illustrated embodiments of the invention are explained in detail on the basis of the drawings, without being restricted thereto. The figures show:
fig. 1 shows a schematic diagram of an electron emission device according to the present invention;
fig. 2 shows a first example of an emission distribution of electrons emitted from the electron-emitting device according to fig. 1;
FIG. 3 shows a second example of emission distribution of electrons emitted from the electron-emitting device according to FIG. 1;
fig. 4 shows a third example of emission distribution of electrons emitted from the electron-emitting device according to fig. 1;
FIG. 5 shows a longitudinal section through one embodiment of an electron emitting device;
fig. 6 shows a top view of the electron-emitting device according to fig. 5.
Detailed Description
The electron-emitting device shown in a schematic representation in fig. 1 comprises an electron emitter 2 having an emission surface 3 and having a barrier 5 spaced apart from the emission surface 3 of the electron emitter 2. The barrier 5 has individually controllable gate sections G1To GN. For illustration purposes, only seven gate segments are shown for overview reasons onlyI.e. N is chosen to be 7 for the number N of gate segments. The invention is furthermore not limited to a single electron emitter 2 and to a single emission surface 3. Depending on the application, a plurality of electron emitters 2 and a plurality of emission surfaces 3 for each electron emitter 2 can be provided. The same applies to the barrier 5. A plurality of barriers 5 may also be provided here. Such limitations have been chosen in the schematic for the sake of overview only.
In each gate region G1To GNCan apply freely selectable gate voltage UG1To UGN(see fig. 6). Thus, in each gate region G1To GNMay also have different gate voltages U applied theretoGN. Thereby, subsequently in the corresponding gate section G1To GNAnd the emission surface 3, which causes different emission of electrons from the emission surface 3 of the electron emitter 1.
The emission profiles shown in fig. 2 to 4 for the electrons emitted from the emission surface 3 can be realized, for example, by means of the solution according to the invention. For viewing, the grid segments G have been plotted on the abscissa in a cartesian coordinate system1To GNAnd the electron emission E is plotted on the ordinate.
In the emission profile shown in FIG. 2, in the gate section G1To GNUpper gate voltage UG1To UGNIs selected so that in the gate section G1And GNTwo equally strong gate voltages U are appliedG1And UGNWhereby the electron emission E is equally strong, respectively. However, the gate section G2To GN-1By applying a higher gate voltage UG2To UGN-1Blocking so that in the gate section G2To GN-1No electrons are emitted.
In contrast, in the emission profile shown in fig. 3, in the gate section G1To GNGate electrode U onG1To UGNIs different. Electron emission E is achieved by applying a desired gate voltage UGNCan be freely chosen, whereby the MTF (modulation-Transfer-modulation) can be influenced accordingly. ByHere, the MTF of the distribution obtained at the anode of the X-ray emission contains high frequency components, whereby the boundary resolution (Coded Spot) of the entire system can be favorably affected. In the case shown, the gate section G2And G4Is completely blocked and passes through the gate region G1、G3And G5To GNAt least partial electron emission E is possible.
The emission distribution according to fig. 4 is an asymmetric emission distribution of electrons passing through the barrier 5. Gate segment G1To G5By means of separately applied gate voltages UG1To UGNThe penetrability for the emitted electrons differs. Gate segment G1With the lowest gate voltage UG1And thus has the highest electron emission E. In contrast, in the gate region G5Is applied with the highest gate voltage UG5Thereby obtaining a correspondingly small electron emission E. The electrons emitted by the electron emitter 2, when they strike a rotating anode, not shown in fig. 4, produce an asymmetrical focal point, which enables a higher electron beam power.
One embodiment of the electron emission device 1 is shown in longitudinal section in fig. 5 and in plan view in fig. 6.
An emitter material 6, which emits electrons in the emission area 3 (electron emission E), is applied to the substrate 4.
The substrate 4 is a basic body made of, for example, an engineering ceramic. The emitter material 6 is for example Carbon Nanotubes (CNT) or a dispenser cathode material, for example barium oxide (BaO) or lanthanum hexaboride (LaB)6)。
Including a gate section G1To GNIs arranged spaced apart from the substrate 4 (basic body) on a ceramic carrier 7.
As can be seen from FIG. 6, the gate section G1To GNRespectively individually by means of corresponding gate voltages UG1To UGNAnd (6) controlling. The gate section G is not shown for the sake of overview3To GN-1. The barrier 5 can be produced, for example, from a tungsten plate from which the gate sections G forming the gate structure are cut out by laser cutting1To GN。
For certain requirements, it may be advantageous to arrange a second barrier (not shown) parallel and perpendicular to and spaced apart from barrier 5. The second barrier likewise has a predefinable number of individually controllable barrier elements. The emission profile E of the electrons can thus be arbitrarily controlled in both spatial directions.
The segmented barrier 5 in the embodiment according to fig. 5 and 6 is also suitable for optimizing the electron-emitting device known from US 8,374,315B 2.
As can be seen from the description of the embodiments shown in fig. 1 to 6, an improvement in image quality with a low anode load can be achieved in a simple manner by the solution according to the invention by adapting the focal spot geometry (shape and size) to the specific application.
Although the invention has been illustrated and described in detail with reference to a preferred embodiment, the invention is not restricted to the embodiment described and other embodiments can be derived therefrom by the person skilled in the art without problems, without departing from the scope of protection of the invention.
Claims (9)
1. An electron emission device, comprising: at least one electron emitter (2) having at least one emission face (3); and at least one barrier (5) which is spaced apart from the emission surface (3) of the electron emitter (2) and has a predefinable number of individually controllable barrier sections (G)1-G7，GN)，
It is characterized in that the preparation method is characterized in that,
in the gate region (G)1-G7，GN) Can be respectively applied with at least one individually preset gate voltage.
2. The electron-emitting device of claim 1,
it is characterized in that the preparation method is characterized in that,
the electron emitter (2) is designed as a distributor cathode which emits electrons when an electric field strength is applied.
3. The electron-emitting device of claim 1,
it is characterized in that the preparation method is characterized in that,
the electron emitter (2) is designed as a field effect emitter which emits electrons when an electric field strength is applied.
4. The electron-emitting device of claim 1,
it is characterized in that the preparation method is characterized in that,
the electron emitter (2) is designed as a heat emitter which emits electrons when a heating voltage is applied.
5. The electron-emitting device of claim 1,
it is characterized in that the preparation method is characterized in that,
a second barrier is arranged at a distance from the barrier (5), wherein the planes of the two barriers run parallel to each other, and wherein the second barrier likewise has a predeterminable number of individually controllable barrier sections and the barrier sections of the barrier (5) run perpendicular to the barrier sections of the second barrier.
6. A focusing head having the electron-emitting device according to any one of claims 1 to 5.
7. An X-ray tube comprising an anode and an electron emitting device according to any one of claims 1 to 5.
8. An X-ray tube comprising an anode and a focusing head according to claim 6.
9. An X-ray radiator having a radiator housing in which an X-ray tube according to claim 7 or 8 is arranged.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP181588989 | 2018-02-27 | ||
| EP15088989 | 2018-02-27 | ||
| PCT/EP2019/051860 WO2019166161A1 (en) | 2018-02-27 | 2019-01-25 | Electron-emission device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN111788652A true CN111788652A (en) | 2020-10-16 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201980015776.1A Pending CN111788652A (en) | 2018-02-27 | 2019-01-25 | Electron emission device |
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1069828A (en) * | 1991-05-13 | 1993-03-10 | 精工爱普生株式会社 | Multipole field-causing electron ballistic device and manufacture method thereof |
| US5259014A (en) * | 1991-01-08 | 1993-11-02 | U.S. Philips Corp. | X-ray tube |
| CN1199914A (en) * | 1997-05-09 | 1998-11-25 | 国际商业机器公司 | Metal/ferrite laminate magnet and process thereof |
| CN105679628A (en) * | 2016-01-20 | 2016-06-15 | 中山大学 | Field electron emission device structure with reverse bias nano junction |
-
2019
- 2019-01-25 CN CN201980015776.1A patent/CN111788652A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5259014A (en) * | 1991-01-08 | 1993-11-02 | U.S. Philips Corp. | X-ray tube |
| CN1069828A (en) * | 1991-05-13 | 1993-03-10 | 精工爱普生株式会社 | Multipole field-causing electron ballistic device and manufacture method thereof |
| CN1199914A (en) * | 1997-05-09 | 1998-11-25 | 国际商业机器公司 | Metal/ferrite laminate magnet and process thereof |
| CN105679628A (en) * | 2016-01-20 | 2016-06-15 | 中山大学 | Field electron emission device structure with reverse bias nano junction |
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