X-ray source voltage shield

A shield around an x-ray tube, a voltage multiplier, or both can improve the manufacturing process by allowing testing earlier in the process and by providing a holder for liquid potting material. The shield can also improve voltage standoff. A shielded x-ray tube can be electrically coupled to a shielded power supply.

FIELD OF THE INVENTION

The present application is related generally to x-ray sources.

BACKGROUND

Small size and light weight are important characteristics of x-ray sources in order to allow portability and insertion into small spaces. High power, as indicated by bias voltage differential, can also be important. As power requirements increase, x-ray source size and weight must normally be increased due to increased electrical insulation needed for voltage isolation. It would be beneficial to provide high power x-ray sources with reduced size and weight.

Much of the cost of x-ray sources is the result of difficult manufacturing processes. It would be beneficial to improve the manufacturing process in order to reduce the cost of the x-ray source.

Users of x-ray sources can be injured by stray x-rays. X-ray sources can fail due to arcing of high voltage. Electromagnetic waves from some x-ray source components can interfere with other components. Blocking x-rays, reducing arcing failure, and reducing unwanted electromagnetic interference can also be useful x-ray source characteristics.

SUMMARY

It has been recognized that it would be advantageous to provide small, light x-ray sources which are relatively easy to manufacture. It has been recognized that it would be advantageous to block stray x-rays, reduce x-ray source arcing failure, and reduce unwanted electromagnetic interference. The present invention is directed to various embodiments of x-ray sources, x-ray source components, and methods of manufacturing x-ray sources and components that satisfy these needs. Each embodiment may satisfy one, some, or all of these needs.

An x-ray tube shield can wrap at least partially around, and can be spaced apart from, an x-ray tube. X-ray tube insulation, comprising a solid, electrically-insulative material, can separate the x-ray tube shield from the x-ray tube. A material composition of the x-ray tube insulation can be different than a material composition of the x-ray tube shield.

A power supply shield can wrap at least partially around, and can be spaced apart from, a voltage multiplier. Power supply insulation, comprising a solid, electrically-insulative material, can separate the power supply shield from the voltage multiplier. A material composition of the power supply insulation can be different than a material composition of the power supply shield.

DEFINITIONS

As used herein, the term “adjoin” means direct and immediate contact.

As used herein, the term “GPa” means gigaPascal.

As used herein, the term “kV” means kilovolt(s).

As used herein, the term “mm” means millimeter(s).

As used herein, the term “parallel” means exactly parallel, or within 30° of exactly parallel. The term “parallel” can mean within 0.1°, within 1°, within 5°, within 10°, within 15°, or within 20° of exactly parallel if explicitly so stated in the claims.

As used herein, the term “x-ray tube” means a device for producing x-rays, and which is traditionally referred to as a “tube”, but need not be tubular in shape.

DETAILED DESCRIPTION

As illustrated inFIGS. 1-10, high voltage components10,20a,20b,30,40,50,60,70,80,90, and100can include a shield11spaced apart from a high voltage device13by a gap, which can be an annular gap. The high voltage device13can be operable at a high voltage such as for example ≥1 kV, ≥5 kV, ≥10 kV, ≥20 kV, or ≥40 kV.

The shield11can be electrically insulative to improve high voltage standoff, reduce amount and weight of electrical insulation, or both. For example, an electrical resistivity of the shield11can be ≥106ohm*m, ≥108ohm*m, ≥1010ohm*m, or ≥1012ohm*m. Sometimes, an electrically conductive shield is desirable to help mitigate unwanted electromagnetic interference. For example, an electrical resistivity of the shield11can be ≤10−4ohm*m, ≤0.01 ohm*m, ≤0.1 ohm*m, or ≤1 ohm*m. It can be helpful, for blocking electromagnetic interference, for the shield to have some electrical resistance. Therefore, the shield11can have electrical resistivity of ≥10−8ohm*m, ≥10−7ohm*m, 10−6ohm*m, or ≥10−5ohm*m. All resistivity values herein are at 20° C.

The shield can include high atomic number (Z) materials for blocking stray x-rays. For example, the shield can include material(s) with Z≥24, Z≥40, or Z≥73.

Some high voltage components, including x-ray sources, may need high temperature processing during manufacture. Thus, high temperature resistance can be important. For example, the shield11can have a melting point of ≥250° C., ≥400° C., ≥500° C., or ≥600° C.

Example materials of the shield11, which can meet the above criteria, include ceramic, plastic, glass, polymer, polyimide or combinations thereof. These materials can be impregnated with other materials such as metals or metalloids to provide the desired properties as described above.

As illustrated inFIG. 2a, the shield11can be spaced apart from the high voltage device13by high voltage potting compound21. The high voltage potting compound21can be a liquid. The shield11can be a holder for containing the high voltage potting compound21while it cures, thus providing an easier manufacturing process. As illustrated inFIGS. 2b-10, the shield11can be spaced apart from the high voltage device13by high voltage insulation22, which can be a solid. The high voltage insulation22can be cured high voltage potting compound21. Alternatively, the high voltage insulation22can be a gaseous standoff material or an insulative oil. The high voltage insulation22can partially or completely fill the gap between the shield11and the high voltage device13.

As illustrated inFIGS. 2a-2b, the high voltage device13can have a longitudinal axis13Aextending from a location on the high voltage device13with a lowest absolute value of voltage13Lto a location on the high voltage device13with a highest absolute value of voltage13H. The shield11can have two open ends11olocated opposite of each other and a longitudinal axis11Aextending through a center of one open end110and through a center of the other open end11o. The longitudinal axis13Aof the high voltage device13can be aligned or coaxial with and/or can be parallel to the longitudinal axis11Aof the shield11. Such alignment can provide improved shaping of electrical field gradients.

As shown inFIG. 3, the shield11can encircle or wrap completely around the high voltage device13or can encircle or wrap completely around the longitudinal axis11Aof the shield11. Also illustrated inFIG. 3, the shield11can have a cylindrical shape and can have two open ends11olocated opposite of each other. The shield11can have other shapes. For example, as illustrated inFIG. 4, the shield11can wrap partially around the high voltage device13along the longitudinal axis13Aor partially around the longitudinal axis11Aof the shield11. For example, the shield11can wrap ≥50%, ≥75%, ≥90%, ≥95%, or ≥98% of a circumference around the high voltage device13. An opening or channel in the shield11can extend from one open end11oto the other open end11o. A choice between different shapes of the shield11can be based on availability, ease of encasing the high voltage device13in the shield11, voltage standoff, and desired shaping of electrical field lines.

Another possible shape of the shield11, illustrated inFIGS. 5-6, is a conical frustum shape. A conical frustum shape can be used for shaping the electrical field and improving voltage standoff. The conical frustum shape can have two open ends11olocated opposite of each other, including a larger or wider end11wand a smaller end11s. For example, the wider end11wcan be ≥1.1, ≥1.2, ≥1.6, or ≥2 times larger than the smaller end11s. As another example, the wider end11wcan be ≤3 or ≤10 times larger than the smaller end11s. Example distances between an inner surface of the shield11and the high voltage device13include a shortest distance Dsof between 1.5 mm and 15 mm and a longest distance DLof between 3 mm and 50 mm. For voltage standoff, the wider end11wcan be closer to a location on the high voltage device13with a highest absolute value of voltage and the smaller end can be closer to a location on the high voltage device13with a lowest absolute value of voltage.

As illustrated inFIGS. 7-8, the shield11can partially wrap or fully encircle the high voltage device13along some or all of the longitudinal axis13A, such as for example ≥30%, ≥50%, ≥80%, ≥90%, ≥95%, or 100% of a length L13of the high voltage device13. The high voltage device13can be longer than the shield11, as shown inFIG. 7(L13>L11), about the same length, as shown inFIGS. 1-2band5-6, or shorter than the shield11as shown inFIG. 8(L13<L11).

The shield11can have sufficient thickness Ths(FIGS. 1-2b) to provide structural support. For example, the thickness Thsof the shield can include: Ths≥0.1 mm, ≥0.5 mm, ≥1 mm, or ≥3 mm. This thickness Thscan be a minimum thickness of the entire shield11if explicitly so stated in the claims.

The shield11can be thin to avoid unnecessary added weight. For example, the thickness Thsof the shield can include: ≤5 mm, ≤10 mm, or ≤25 mm. This thickness Thscan be a maximum thickness of the entire shield11if explicitly so stated in the claims.

As illustrated inFIGS. 9-11, an internal surface11iof the shield11, an external surface11eof the shield11, or both, can be corrugated. The corrugated surface(s) can improve high voltage standoff by increasing the distance for an electric arc to travel.

As illustrated on high voltage component100inFIGS. 10-11, the corrugated external surface can include a ridge103and a furrow104extending in a continuous spiral. The continuous spiral can extend between one open end11oof the shield11and the opposite open end11o. This continuous spiral can allow easier application of a coating121on the ridge103. The coating121can extend continuously in a line of material111on the continuous spiral. The line of material111can have electrical resistance optimized for shaping of electrical field lines, optimized to be a voltage sensing resistor, or both. The voltage sensing resistor can be electrically-coupled across and configured for measurement of voltage across the high voltage device13. For example, electrical resistance from one end111eto an opposite end111eof the line of material111can be ≥1 megaohm, ≥10 megaohms, or ≥100 megaohms and ≤10,000 megaohms, ≤100,000 megaohms, or ≤1,000,000 megaohms.

As illustrated on high voltage component120inFIG. 12, the continuous line of material111can wrap multiple times around the shield11, can be arranged in a serpentine pattern, or both. Examples of a relationship between a length L111of the continuous line of material111compared to a shortest distance L11between the two open ends11oof the shield11include: L111/L11≥3, L111/L1110, L111/L11≥20, L111/L11≥50, and L111/L11≥100.

Alternatively, as illustrated on high voltage component130inFIG. 13, instead of a line of material111, the coating121on the surface of the shield11can be sheet of material or a continuous layer of coating131. The continuous layer of coating131can coat all or most (e.g. ≥50%, ≥75%, ≥90%, or ≥95%) of the internal surface11i(FIGS. 9-10) of the shield11, the external surface11, (FIGS. 9-10) of the shield11, or both. The continuous layer of coating131can have electrical resistance optimized for shaping of electrical field lines. For example, electrical resistance between the continuous layer of coating131nearest one open end11oof the shield11and the continuous layer of coating131nearest the opposite open end11oof the shield11can be ≥1 megaohm, ≥10 megaohms, or ≥100 megaohms and ≤10,000 megaohms, ≤100,000 megaohms, or ≤1,000,000 megaohms. The continuous layer of coating131can be a voltage sensing resistor electrically-coupled across and configured for measurement of voltage across the high voltage device13.

As illustrated on inFIGS. 14-15, the high voltage component as described above can be a shielded power supply140. The high voltage device13described above can be a voltage multiplier143with electronic components144, the high voltage insulation22described above can be power supply insulation142, and the shield11described above can be a power supply shield141. The voltage multiplier143can be configured to generate a high voltage, such as for example ≥1 kV, ≥5 kV, ≥10 kV, ≥20 kV, or ≥40 kV. The voltage multiplier143can be a Cockroft-Walton voltage multiplier. A longitudinal axis143Aof the voltage multiplier143can extend from a location on the voltage multiplier with a lowest absolute value of voltage to a location on the voltage multiplier with a highest absolute value of voltage. The longitudinal axis143Aof the voltage multiplier143can be parallel to or aligned or coaxial with the longitudinal axis11Aof the shield11.

As illustrated inFIGS. 16-17, the high voltage component as described above can be a shielded x-ray tube160. The high voltage device13described above can be an x-ray tube163, the high voltage insulation22described above can be x-ray tube insulation162, and the shield11described above can be an x-ray tube shield161. The x-ray tube163can include a cathode165and an anode164electrically insulated from one another. The cathode165can be configured to emit electrons in an electron beam towards the anode164, and the anode164can be configured to emit x-rays out of the x-ray tube in response to impinging electrons from the cathode165. A longitudinal axis163Aof the x-ray tube163can extend along a center of the electron beam and between the cathode165and the anode164. The longitudinal axis163Aof the x-ray tube163can be parallel to or aligned or coaxial with the longitudinal axis11Aof the shield11.

As illustrated inFIGS. 18-20, a voltage multiplier143can be electrically coupled to an x-ray tube163by an electrical connection182. The voltage multiplier143can be part of a shielded power supply140as described above, the x-ray tube163can be part of a shielded x-ray tube160as described above, or both. The x-ray tube shield161can be separate from and spaced apart from the power supply shield141. The shielded power supply140can be spaced apart from the shielded x-ray tube160.

An enclosure181can at least partially surround the electrical connection182, the x-ray tube163(or shielded x-ray tube160), and the voltage multiplier143(or shielded power supply140). An outer insulation202can electrically insulate the enclosure181from these components located therein. The outer insulation202can be solid and electrically insulative material. The outer insulation202can be sandwiched between the enclosure181and the electrical connection182, the shielded x-ray tube160, and the power supply140. The enclosure181can be electrically conductive.

Following are characteristics of materials of the components of the various embodiments of the inventions described herein. A material composition of the shield11, the high voltage insulation22, and the outer insulation202can be selected for optimal insulation of the high voltage device(s)13from the enclosure181or other grounded components. For example, a material composition of the shield11can be different than a material composition of the high voltage insulation22, different than a material composition of the outer insulation202, or both.

Further, for optimal insulation of the high voltage device(s)13, a relative permittivity of the shield11can be greater than a relative permittivity of the outer insulation202, greater than relative permittivity of the high voltage insulation22, or both. For example, relative permittivity of the shield11divided by relative permittivity of the high voltage insulation22can be ≥1.5, ≥2, ≥2.5, ≥3, or ≥5. The relative permittivity of the outer insulation202can be greater than a relative permittivity of the high voltage insulation22. For example, relative permittivity of the outer insulation202divided by relative permittivity of the high voltage insulation22can be ≥1.3, ≥1.5, ≥2, ≥2.5, or ≥3.

Also, for optimal insulation of the high voltage device(s)13, material composition of the shield11can be inorganic, material composition of the high voltage insulation22can be organic, material composition of the outer insulation202can be organic, or combinations thereof. Material composition of the high voltage insulation22, material composition of the outer insulation202, or both, can include a polymer. The shield11can be harder than the high voltage insulation22, harder than the outer insulation202, or both. For example, the high voltage insulation22, the outer insulation202, or both, can have a Shore hardness of ≥10A, ≥20A, ≥30A, ≥40A, or ≥45A and ≤65A, ≤70A, ≤80A, or ≤90A. For example, the shield11can have a Vickers hardness of ≥2.5 GPa, ≥5 GPa, ≥10 GPa, or ≥13 GPa and ≤17.5 GPa, ≤20 GPa, or ≤22 GPa.

A method of manufacturing a high voltage component can comprise some or all of the following steps, which can be performed in the following order. There may be additional steps not described below. These additional steps may be before, between, or after those described.

As illustrated inFIG. 1, one step can include inserting a high voltage device13inside of a shield11, the shield11wrapping at least a portion of the high voltage device13with a gap between the shield11and the high voltage device13. The gap can be an annular gap. The shield11and the high voltage device13can have properties as described above.

As illustrated inFIG. 2a, another step can include inserting a high voltage potting compound21into the gap. The high voltage potting compound21can be a liquid. The high voltage potting compound21can be adjacent to both the shield11and the high voltage device13.

The shield11can have various shapes for holding the liquid, such as for example a cube or a cylinder. Alternatively, the shield11can have a partially open shape such as shown inFIG. 4. Any openings other than the top can be sealed with Kapton tape or other similar material until the high voltage potting compound21has cured into a solid.

As illustrated inFIG. 2b, another step can include curing the high voltage potting compound21into a solid, electrically insulative material, defining high voltage insulation22. Various curing methods can be used, including curing with heat, x-rays, or ultraviolet rays.

Another step can include testing performance of the high voltage device13. For example, if the high voltage device13is a voltage multiplier143, its voltage output capabilities can be tested now that it is embedded in the power supply insulation142. As another example, if the high voltage device13is an x-ray tube163, a bias voltage of several kilovolts can be applied between the cathode165and the anode164, its electron emitter can be activated, and its x-ray output can be analyzed. It can be advantageous to test at this stage, before connecting the voltage multiplier143to the x-ray tube163, and adding outer insulation202around both devices, because after this latter step, both devices may need to be scrapped if one is defective. Thus, it is helpful to know earlier in the process whether one of the high voltage devices13is functional.

Some or all of the above steps can be performed on a voltage multiplier143, on an x-ray tube163, or each of these two devices separately. As illustrated inFIG. 18, an electrical connection182can be made between the voltage multiplier143and the x-ray tube163. The shielded power supply140, the shielded x-ray tube160, or both can be placed at least partially inside of an enclosure181. The electrical connection182made between the voltage multiplier143and the x-ray tube163. The enclosure181can be electrically conductive.

As illustrated inFIG. 19, another step can include inserting an outer potting compound191into the enclosure181. The outer potting compound191can be a liquid and can at least partially or can completely surround the electrical connection182, the shielded power supply140, the shielded x-ray tube160, or combinations thereof.

As illustrated inFIG. 20, another step can include curing the outer potting compound191into an outer insulation202. Various curing methods can be used, including curing with heat, x-rays, or ultraviolet rays. The outer insulation202can be solid and electrically insulative and can have a material composition different from a material composition of the shield(s)11. The outer insulation202can have properties of the high voltage insulation22as described above.

The above method can allow a relatively easier method for manufacture of x-ray sources with reduced scrap parts. The above method can also provide relatively small, light x-ray sources with high voltage standoff capabilities relative to size.