Patent Grant
9824787
The present application is related generally to x-ray sources.
X-ray sources have many uses, such as for example, imaging, x-ray crystallography, electrostatic dissipation, electrostatic precipitation, and x-ray fluorescence.
Some uses can be limited due to the high cost of the x-ray source. It would be beneficial to reduce the cost of x-ray sources while maintaining their functionality.
For some applications, a narrow beam of x-rays is desired. Other applications, however, require a wide angle beam to emit the x-rays over a large area.
X-ray tubes can be fragile, but are sometimes used in rough environments, so it can be important to protect x-ray sources from damage due to bumping against other devices or from chemical corrosion. It would be beneficial to make a more robust x-ray source.
One fragile x-ray tube component is the x-ray window through which x-rays are transmitted. If a protective structure is placed in front of or surrounds the window then it can be important, especially for low energy x-ray sources, to select materials for the protective structure that have high x-ray transmissivity in order to avoid excessive x-ray attenuation.
It has been recognized that it would be advantageous to: (1) reduce the cost of x-ray sources while maintaining their functionality, (2) provide a more robust x-ray source, and/or (3) provide an x-ray source with a wide angle beam of x-rays. The present invention is directed to various embodiments of x-ray sources, and methods of using such x-ray sources, that satisfy these needs. Each embodiment or method may satisfy one, some, or all of these needs.
In one embodiment, the x-ray source can comprise a cathode with a an elongated blade pointed towards an anode. There can be a gap between the blade and the anode.
In another embodiment, the x-ray source can include a window having an annular-shape, forming a hollow-ring. The window can be electrically-conductive and substantially transmissive to x-rays. The x-ray source can also include a half-ball-shaped anode.
In another embodiment, the x-ray source can include an anode having a dome shape with a concave side facing an electron emitter, the concave side including a target material configured to emit x-rays in response to impinging electrons from the electron emitter.
As used herein, the term “half-ball-shape” means that the shape includes a portion that is curved like approximately half of a ball, but not necessarily a shape with all points equidistant from the center. A half-ball-shape can be hollow or solid, as some balls are hollow (e.g. tennis balls) and some balls are solid (e.g. baseball). The entire shape can be “half-ball-shaped” or, in addition to the “half-ball-shaped” portion, there can be another portion having a shape (e.g. a matching half-ball shape, a cube-shape, etc.).
As used herein, the term “bowl-shaped” means that the shape includes a convex portion (bulging outwards but not necessarily rounded) and a concave portion (extending inwards but not necessarily rounded). For example, a “bowl-shaped” structure can have a triangular, square, or rounded cross-sectional profile.
As used herein, the term “pointed end” means a tapering end such as on a dagger, a needle, or an end of a ball-point pen.
As used herein, “evacuated” or “substantially evacuated” means a vacuum such as is typically used for x-ray tubes.
As illustrated in
A power supply 8 can be electrically connected to the anode 14 and to the cathode 11. In one embodiment, the power supply 8 can provide pulses of voltage between the anode 14 and the cathode 11. These pulses can have a magnitude sufficiently high to cause periodic arcs between the cathode 11 and the anode 14. Electrons 18 in the arc, impinging on the anode 14, can cause an emission of x-rays 19 outward from the x-ray source. Examples of voltage differentials between the anode 14 and the cathode 11, at the time of the arcs, include between 1 kilovolt and 20 kilovolts in one aspect or between 10 kilovolts and 200 kilovolts in another aspect. For example, the periodic pulses of voltage can be created by an induction coil.
A size of the gap G, an angle A1 of the pointed end 9 of the cathode 11, and a diameter D of the cathode 11 at a location where the cathode 11 begins to taper towards the pointed end 9, can be modified for desired electric field gradients and desired voltage at which arcing occurs. For example, the internal angle A1 of the pointed end 9, can be less than 90° in one aspect, between 60° and 90° in another aspect, or between 30° and 65° in another aspect. The diameter D of the cathode 11 can be less than 0.5 millimeters in one aspect. The gap G can be between 3-5 millimeters in one aspect. In one embodiment, the pointed end 9 can have an angle of sharpness and the gap G can be sized for a voltage gradient at the pointed end 9 of at least 500 volts/mil just prior to arcing.
An electrically-conductive window 16 can be associated with and can be connected to the anode 14. The window 16 can be electrically connected to the anode 14. The window 16 can be substantially transmissive to x-rays 19. The window 16 can include some or all of the properties (e.g. low deflection, high x-ray transmissivity, low visible and infrared light transmissivity) of the x-ray window described in U.S. patent application Ser. No. 14/597,955, filed on Jan. 15, 2015, which is incorporated herein by reference in its entirety. The window 16 can form at least part of a wall of the enclosure 4 and can separate at least a portion of the cavity 17 from an exterior of the enclosure 4.
The cavity can have a high vacuum, a low vacuum, or can be at or near atmospheric pressure, depending on the application. A benefit of a high vacuum in the cavity 17 is that electrons 18 emitted from the cathode 11 towards a target material 15 on the anode 14 or window 16 are not, or are minimally, impeded by the gas. Evacuated x-ray tubes can be more efficient and can have less variation in output. On the other hand, evacuated x-ray tubes can have a substantially higher manufacture cost.
Some applications might not require the high efficiency with use of an evacuated x-ray tube and can use a lower cost x-ray tube with a relatively higher internal pressure. A power supply 8 that is pulsed can provide, sufficient voltage for pulses of electrons 18 from the cathode 11 to the anode 14.
The x-ray sources described herein can be evacuated or can have a gas disposed in the cavity 17. The gas in the cavity 17 can have a pressure of at least 0.0001 Torr in one aspect or a pressure of between 1 Torr and 900 Torr in another aspect. The gas can comprise a low atomic number element (e.g. Z<11), such as nitrogen or helium for example. The gas can comprise at least 85% helium. Helium can be beneficial due to its relatively low cost, high thermal conductivity, low atomic number, and because it is inert. For simplicity of manufacture, the gas can be or can comprise air. The cavity 17 can be hermetically sealed to maintain the desired pressure and type of gas in the cavity 17. Reduced vacuum requirements can allow the x-ray source to be more robust because minor leaks or outgassing might have a negligible effect on performance.
As shown in
X-ray sources 10 and 50 in
X-ray sources 20, 30, 40, and 60 in
As shown on x-ray source 20 in
It can be beneficial for imaging applications for the x-rays 19 to emit from a point source. Emission of x-rays from a point source, rather than from a broad surface of the anode 14, may be accomplished by a protrusion 32 extending from a face 31 of the anode 14 (see
As shown on x-ray source 50 in
As shown on x-ray source 60 in
The half-ball-shape of the anode 14 can be made of or can comprise various materials, such as for example refractory metals, tungsten, metal carbide, metal boride, metal carbon nitride, and/or noble metals. The half-ball-shape 64 of the anode 14 can have a hollow, concave portion opposite of the convex portion like half of a tennis ball (see
The annular-shape 66 of the window 16 can be made of or can comprise various materials, such as for example carbon fiber composite, graphite, plastic, glass, beryllium, and/or boron carbide. Advantages of using carbon-based materials include low atomic number and high structural strength. An advantage of a window 16 that comprises an annular-shape 66 is a 360° ring-like (wide angle) emission of x-rays 19 around the longitudinal axis 6. For some applications, a hemispherical-shaped emission of x-rays 19, as shown in
As shown in
A portion of the support 71 can extend out of the concave hollow of the half-ball-shape 64. The support can have a substantially flat portion 72 facing away from the anode 14. The flat portion 72 can be configured to bear against the device (e.g. flat panel display 83).
As shown in
As shown in
X-rays 19 can smoothly or gradually dissipate the electrostatic charges, without rapid, harmful electrostatic discharge, by forming ions in the fluid 86 (e.g. air) between the flat panel display 83 and the table 84. The ions can smoothly and gradually reduce the electrostatic charges on the flat panel display 83. It can be difficult, however, to emit x-rays 19 throughout the entire region between the flat panel display 83 and the table 84. Embodiments of the present invention include associating, the x-ray sources 85 or 95, such as those described above, with the lift pin 82. The x-ray sources 85 or 95 can be movable with the lift pin 82. The x-ray sources 85 or 95 can emit x-rays 19 between the flat panel display 83 and the table 84 while the flat panel display 83 is lifted off of the table 84 and/or soon thereafter. Because the lift pins 82 can be distributed at various locations, associating the x-ray sources 85 or 95 with the lift pins 82 can provide effective emission of x-rays 19 into a large portion or all of the region between the flat panel display 83 and the table 84.
As shown on manufacturing system 80 in
As shown on manufacturing system 90 in
As shown in
X-ray source 110, with an elongated blade 113 of the cathode 111, can be beneficial for emission of an elongated line or curtain of x-rays 19 in order to cover a large area, such as for example a top side 83t of a flat panel display 83 during manufacture of the flat panel display 83. The blade 113 can have a length of at least 10 centimeters in one aspect, at least 20 centimeters in another aspect, or at least 80 centimeters in another aspect.
Shown in
A window 16 can form a hollow-ring as one section of the enclosure 4. The window 16 can be electrically-conductive, can include an annular-shape 66, and can be substantially transmissive to x-rays 19. The window 16 can separate at least, a portion of the cavity 17 from an exterior of the enclosure 4. In one embodiment, the window 16 can comprise tungsten, carbon fiber composite, and/or graphite.
The anode 14 can include a half-ball-shape 64 having a convex portion extending into the cavity 17 and into a hollow of the annular-shape 66. The electron emitter 224 can emit electrons 18 towards the anode 14. The convex portion of the anode 14 can include a target material 15 configured to emit x-rays 19 in response to impinging electrons 18 from the electron emitter 224. In one embodiment, the x-ray source 140 can emit x-rays 19 in a 360° circle 145 outward from the x-ray source 140.
Illustrated in
The x-ray tube 225 can include a cathode 214 and an anode 212. The cathode 214 can be electrically insulated from the anode 212 and can be separated from the anode 212 by an electrically insulative enclosure 211. For example, the electrically insulative enclosure 211 can have an electrical resistivity of at least 1×1012 in one aspect, at least 7×1012 in another aspect, or at least 1×1013 in another aspect.
The cathode 214 can be configured to emit electrons 18 towards the anode 212 (e.g. due to cathode 214 heat and a large bias voltage differential between the cathode 214 and the anode 212). The anode 212 can be configured to emit x-rays 19 (e.g. due to target material of or on the anode 212) outward from the x-ray tube 225 in response to impinging electrons 18 from the cathode 214. Transmission target x-ray sources 210, 260, and 270 are shown in the figures, but the invention described herein is also applicable to a side-window type of x-ray source.
A shell 215 can circumscribe at least a portion of the x-ray tube 225. The shell 215 can be electrically coupled to the anode 212 and can be electrically insulated from the cathode 214. The shell 215 can conveniently be used as an electrical current path for removing electrical charge from the anode 212. If the shell 215 is used as a primary or sole electrical path for electrical current flow away from the anode 212, and/or there is limited means of conducting heat away from the x-ray source 210, 260, or 270, then it can be important for the shell 215 to have a relatively high electrical conductivity because electrical resistance of the shell 215 can result in increased shell 215 temperature, which can lead to heat damage of the x-ray source 210, 260, or 270, power supply 219, and/or surrounding materials. For example, the shell 215 can have an electrical resistivity less than 0.02 ohm*m in one aspect, less than 0.05 ohm*m in another aspect, less than 0.15 ohm*m in another aspect, or less than 0.25 ohm*m in another aspect.
The power supply 219 can provide electrical power (e.g. through electrical connectors 222) to an electron emitter 224 (e.g. to cause electrical current, to flow through a filament to heat the filament). The power supply 219 can provide a voltage differential (e.g. a few to tens of kilovolts) between the electron emitter 224 and the anode 212. The power supply can maintain the cathode 214 at a low voltage (e.g. −10 kV) and the anode 212 at a higher voltage (e.g. ground voltage). Electrical connections for transferring electrical power from the anode 212 can be through the shell 215 and from the shell 215 through electrical connection 223 to the power supply 219 or to a separate ground. The shell 215 can conveniently be used as an electrical current path, thus avoiding the expense and space required of an added component.
The shell 215 can substantially circumscribe the anode 212. The shell 215 can circumscribe (or substantially circumscribe if the shell 215 includes holes) a length L225 of the x-ray tube 225. The shell 215 can have a length L215 longer than the length L225 of the x-ray tube 225. The shell 215 can have a distal end 215d closer to the anode 212 and a proximal end 215p closer to the cathode 214. The x-ray tube 225 can have a distal end 225d closer to the anode 212 and a proximal end 225p closer to the cathode 214. The distal end 215d of the shell 215 can extend beyond the distal end 225d of the x-ray tube 225 away from the x-ray tube 225.
There can be a hollow region 226 disposed within the shell 215 between the distal end 225d of the x-ray tube 225 and the distal end 215d of the shell 215. This hollow region 226 can provide a protective region for the x-ray tube 225 and/or a region to allow x-rays 19 to expand outward. A region to allow x-rays 19 to expand outward can be important if the distal end 215d of the shell is used to press against a device (e.g. flat panel display) and space is needed for x-rays 19 to emit out between the device and the x-ray tube 225. A proper length Le of this extension of the shell 215/protective region 226 can be important for proper angle of distribution of x-rays 19, and can vary, depending on the application of use. For example, the distal end 215d of the shell 215 can extend beyond the distal end 225d of the x-ray tube 225, away from the x-ray tube 225, for a distance of between 3 and 10 millimeters in one aspect or between 2 and 20 millimeters in another aspect.
A sheath 216 can circumscribe at least a portion of the shell 215 and the anode 212. The sheath 216 can be electrically resistive in order to avoid creating undesirable electrical current paths away from the shell 215. For example, if the x-ray source 210, 260, or 270 is used as a lift pin for lifting a flat panel display off of a table during manufacture of the flat panel display, it can be desirable to avoid the shell 215 discharging electrical current through the table. The sheath 216 can thus be used to avoid such undesirable electrical current paths. As an example of electrical resistivity of the sheath 216, the sheath 216 can have an electrical resistivity of greater than 100 ohm*m in one aspect or greater than 500 ohm*m in another aspect.
A distal end 216d of the sheath 216 can extend beyond the distal end 225d of the x-ray tube 225 away from the x-ray tube 225 (for example, for a distance of between 3 and 10 millimeters in one aspect or between 2 and 20 millimeters in another aspect). The sheath 216 can substantially surround a length L215 of the shell 215. The sheath 216 can have a length L216 that is the same as the length L215 of the shell 215. The sheath 216 can have a distal end 216d that terminates at the distal end 215d of the shell 215 and/or a proximal end 216p that terminates at the proximal end 215p of the shell 215.
Referring to
In one aspect, the cap 218 can be used to provide an electrically insulative barrier between the shell 215 and a flat panel display when lifting the flat panel display off of a table during manufacture. The cap 218 can include or can be a polymer, such as polyether ether ketone (PEEK) for example. PEEK can be useful due to relatively high electrical resistivity. For this application, it may be preferred for the cap 218 to have two open ends 231, forming a hollow within the cap, to allow convective heat transfer away from the x-ray tube 225. It can also be preferable for the cap 218 to have openings 232 around a perimeter to allow improved x-ray 19 transmissivity away from the x-ray source 210, 260, or 270. The cap 218 can fit over the distal end 215d of the shell 215 with a flange inserted inside or outside of the shell 215 or can be flat like a washer and can be attached to the shell 215 with an adhesive.
In another aspect, the cap 218 and the shell 215 surrounding the hollow region 226 can be made of materials and thicknesses capable of protecting the anode 212 from corrosive chemicals. The cap 218 can cover the distal end 215d of the shell 215, thus enclosing the hollow region 226 between the anode 212 and the cap 218. The cap can be sealed to the shell 215 to prevent chemical damage to the x-ray tube 225. Thus, a trade-off may be needed between (1) protecting the x-ray tube 225 from chemical damage and (2) improved convective cooling of the anode plus improved x-ray 19 transmissivity out of the cap 218. The cap can be made of various materials, including polymers and composites. If electrical resistivity of the cap 218 is not important, then the cap can be made of carbon fiber composite and/or can be integrally connected to or formed with the shell 215.
Proper selection of materials for the shell 215, the sheath 216, and/or cap 218 can allow for a relatively high transmission of x-rays 19 out into regions outside the x-ray source 210, 260, or 270 where such x-rays can be useful (e.g. for electrostatic dissipation). At x-ray 19 energy of 10 keV, the shell 215, the shell 215 and the sheath 216 combined, and/or the cap 218 can have x-ray transmissivity of greater than 40% in one aspect, greater than 45% in another aspect, greater than 50% in another aspect, greater than 60% in another aspect, or greater than 70% in another aspect. The x-ray 19 energy just described refers to energy of electrons 18 hitting a target material, energy of x-rays 19 emitted from the x-ray tube 225, and a bias voltage between the cathode 214 and the anode 212. For example, a 10 kV bias voltage between the cathode 214 and the anode 212 can result in 10 keV electrons 18 hitting the target and 10 keV x-rays 19 emitting from the x-ray tube 225.
In order to allow high x-ray 19 transmissivity, low atomic number materials can be selected. For example, a maximum atomic number of any or all material of the shell 215, the sheath 216, and/or the cap 218 can be 8 in one aspect or 16 in another aspect. Materials with a relatively large mass percent of carbon can be useful due to the low atomic number of carbon (6). Beryllium is also useful due to its low atomic number of 4, but beryllium can be expensive and hazardous.
It can be important for the shell 215 to be strong or durable to protect the x-ray tube 225 from damage and to provide sufficient mechanical strength (e.g. for lifting a flat panel display). The shell 215 and the x-ray tube 225 can be tube-shaped for ease of manufacturing and improved strength.
The shell 215 can include or can be made substantially or entirely of a composite material. Some composite materials can be strong and can also have relatively high x-ray 19 transmissivity and/or relatively high electrical conductivity. The term “composite material” typically refers to a material that is made from at least two materials that have significantly different properties from each other, and when combined, the resulting composite material can have different properties than the individual component materials. Composite materials typically include a reinforcing material embedded in a matrix. Typical matrix materials include polymers, bismaleimide, amorphous carbon, hydrogenated amorphous carbon, ceramic, silicon nitride, boron nitride, boron carbide, and aluminum nitride.
The shell 215 can include or can be made substantially or entirely of a carbon fiber composite material. Electrical conductivity of the shell 215 can be improved by a relatively high percent of carbon fibers. For example, the shell 215 can include at least 60% volumetric percent carbon fibers in one aspect, at least 70% volumetric percent carbon fibers in another aspect, or at least 90% volumetric percent carbon fibers in another aspect.
An electrically-insulative material 217 can be disposed between the cathode 214 and the shell 215 to insulate the cathode 214, which will typically be maintained at a large negative voltage (e.g. negative 5-20 kV), from the shell 215, which will typically be maintained at a more positive voltage (e.g. ground). Examples of electrical resistivity of the electrically-insulative material 217 are greater than 1×1012 ohm*m in one aspect or greater than 7×1012 ohm*m in another aspect. It can also be beneficial for the electrically-insulative material 217 to have a relatively high thermal conductivity in order to allow heat transfer away from the x-ray tube 225. For example, the electrically-insulative material 217 can have a thermal conductivity of greater than
Emerson and Cuming SYYCASE 2850, with thermal conductivity of about
and electrical resistivity of about 1×1013 ohm*m, is one example of an electrically-insulative material 217.
The x-ray sources 210, 260, and 270 can be configured to or can be capable of electrostatic dissipation. For example, the x-ray source 210, 260, and 270 can be operated at a relatively low voltage and/or can emit x-rays 19 across a broad angle (instead of a narrow x-ray beam). As an example of relatively low voltage, the power supply 219 can be configured to or capable of providing a voltage between the cathode 214 and the anode 212 that is at least 1 kilovolt but no greater than 21 kilovolts. A broad angle of x-ray 19 emission, as shown in
The anode 212 can include a dome-shape 262 for a broad angle of x-ray 19 emission. As shown in
Method of Electrostatic Dissipation
The x-ray sources described above can be beneficial for electrostatic dissipation due to their relatively low cost, robustness, and/or wide angle beam of x-rays 19. A method of electrostatic dissipation can comprise some or all of the following steps. See
Note that in step 6 above, a fan or other source of forced air can cause the flow of air. The air flow typically would be from a base of the lift pin 82 (closer to the actuator 81) towards the flat panel display 83.
Method of Electrostatic Precipitation
The x-ray sources described above can be beneficial for electrostatic precipitation due to their relatively low cost, robustness, and/or wide angle beam of x-rays 19. A method of electrostatic precipitation can comprise some or all of the following steps (see
This is a continuation of U.S. patent application Ser. No. 14/739,712, filed on Jun. 15, 2015, which claims priority to U.S. Provisional Patent Application Nos. 62/028,113, filed on Jul. 23, 2014, and 62/079,295, filed on Nov. 13, 2014, which are incorporated herein by reference in their entirety.
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| Child | 15618458 | US |
