Patent Application
20070290148
The foregoing and additional features and characteristics of the disclosed sensor and system for sensing an electron beam will be described in greater detail below with reference to the accompanying drawing figures, wherein like reference numerals are used to designate like elements.
It should be noted that the thicknesses of the layers shown in the figures have been exaggerated, and that the figures are not drawn according to scale.
The sensor 10 senses the intensity of the electron beam 6 generated by the electron beam generator 8 along a path which irradiates the target area 4. The electron beam generator 8 includes a vacuum chamber 12. The electron beam sensor 10 is formed and located in a way to be able to detect and measure the intensity of the electron beam 6 exiting the vacuum chamber 12.
A support 14 is provided for supporting a target 16 within the target area 4. In the embodiment shown in
The electron beam generator 8, as shown in
The filament 22 can be housed in the vacuum chamber 12. In one disclosed embodiment, the vacuum chamber 12 can be hermetically sealed. In operation, electrons e− from the filament 22 are emitted along an electron beam path 6 in a direction towards the target area 4.
Further, the electron beam generator 8 is provided with an electron exit window 24 through which the electrons exit the vacuum chamber. The window 24 can be made of a metallic foil 25, shown in
The sensor 10 is formed on the exit window 24 and is thereby an integrated portion of the window. It comprises at least one area 26 of at least one conductive layer 28 located within the electron beam path 6. In a first presently preferred embodiment, the sensor 10 comprises a single conductive layer 28.
The conductive layer 28 is made up of several areas 26 of conductive material. Each area 26 is formed as a band placed across the exit window 24 as shown in
A shield 32 of insulating material shields off the bands 26 in the conductive layer 28 from each other, from the surrounding environment and from the foil of the electron exiting the window 24. The function of the shield 32 is to protect the bands 26 from plasma contained in the surrounding environment around the exit window 24, and to help make sure that the bands 26 are not in direct contact with any other conducting material, for example the titanium foil of the exit window 24 and the other bands 26.
The shield 32 according to this first embodiment comprises at least a first and a second insulating layer 32a, 32b. The first insulating layer 32a covers substantially the entire foil of the exit window 24. On top of the insulating layer 32a, the bands 26 of the conductive layer 28 are formed. Over the bands 26 and over the still partly exposed first insulating layer 32a, the second insulating layer 32b is formed. Thereby, the bands 26 of the conductive layer 28 are encapsulated by insulating material.
The sensor 10 is formed on the foil 25 of the exit window 24. This means that the sensor 10 is located outside the vacuum chamber 12 and is facing the environment surrounding the electron beam generator 8.
The layers, both the insulating layers 32a, 32b and the conductive layer 28, are very thin and can be formed using deposition technology. For example plasma vapour deposition technique or chemical vapour deposition technique can be used. Other techniques for forming thin layers of material are of course also possible.
Preferably, the same technique is used for all the layers in the sensor 10. The areas, i.e., the bands 26, of the conductive layer 28 can be deposited by providing a mask to the first insulating layer 32a to cover the portions where any conductive area 26 is not desired.
The thickness selected for the layers can be of any suitable dimension. For example, thin layers can be used. In one example, the layers can be in the range of approximately 0.1-1 micrometers (μm), or lesser or greater as desired. Preferably, the thickness is the same or substantially the same for all layers within the sensor 10.
The insulating layers 32a, 32b can be made of any insulating material that can withstand temperatures in the order of a few hundred degrees Celsius (up to about 400 degrees Celsius). Preferably, the insulating material is an oxide. One oxide that may be used is aluminium oxide (Al2O3). Other insulating materials can of course also be used, for example different types of ceramic material. The term “insulating” refers to the material in the insulating layers being electrically insulating, i.e., non-conductive.
Preferably, the conductive layer 28 is made of metal. One metal that may be used is aluminium. Other conductive materials can of course also be used, for example diamond, diamond like carbon (DLC) and doped materials.
To be able to measure the electron beam intensity each band 26 is connected to a current detector 34. Connectors between the bands 26 and the current detector 34 are preferably located at the outer frame of the window 24.
Electrons from the electron beam 6 will penetrate the exit window 24 and, unlike the prior art sensors mentioned in the introductory portion, also penetrate the thin sensor structure. Hence, the electrons will not be totally absorbed by the conductive material, but only a fraction, in the range of approximately a few percentage, of the energy of the electrons will be absorbed by the conducting material of the sensor. The absorbed energy gives rise to a current in the band 26 and the signal from each conductive band 26 is separately detected and handled by a current detector 34 and provides a measure of the intensity of the electron beam over the band. The current detector 34 can comprise an amplifier and a voltmeter in combination with a resistor, or an ampere meter, or any other suitable device.
In this respect it should be noted that, compared to the prior art sensors discussed above, a larger portion of the exit window 24 can be covered by the sensor 10, but that the signal detected will be much smaller per area unit.
An output from the current detector 34 can be compared with a preset value or be supplied to a controller 36, which in turn can serve as a means for adjusting the intensity of the electron beam in response to an output of the sensor 10. By way of example, the electron beam can be emitted with an energy of, for example, less than 100 keV, e.g. 60 to 80 keV.
Here, the sensor 10′ is of a sandwich structure type and comprises a first and a second conductive layer 28′, 38, each comprising at least one area 26′ for sensing electron beam intensity. In this case, the first and second layers 28′, 38 each comprise several areas 26′ in the form of bands, similar to the bands 26 in the previously described first embodiment. The first and the second layers 28′, 38 are placed on top of each other, but it is of course needed to have insulation to shield them from each other, from the exit window foil 25′ and from the surrounding environment. To encapsulate the conductive layers 28′, 38 the shield 32′ comprises first, second and third insulating layers 32a′, 32b′, 32c. The first layer 32a′ covers, in this case, substantially the entire foil 25′ of the exit window 24′ and carries the first conductive layer 28′, i.e., the bands 26′ of the first conductive layer 28′ are deposited on the first insulating layer 32a′. The second insulating layer 32b′ is deposited on top of the still partly exposed first insulating layer 32a′ and on top of the bands 26′ of the first conductive layer 28′. Thereby, the bands 26′ of the first conductive layer 28′ are encapsulated by insulating material. The second insulating layer 32b′ carries the second conductive layer 38, i.e., the areas, in this case bands 26′, of conductive material deposited on the second insulating layer 32b′. The third insulating layer 32c is deposited on top of the still partly exposed second insulating layer 32b′ and the bands 26′ of the second conductive layer 38. Thereby, the bands 26′ of the second conductive layer 38 are encapsulated by insulating material.
A further embodiment of the sensor 10 may comprise any number of additional layers of conductive material. In such alternatives, the conductive layers are sandwiched one by one between insulating layers. Similar to the first and second embodiment this sandwich structure begins with a first insulating layer formed on the exit window and a last insulating layer covering at least the last conductive layer to protect it from the surrounding environment.
A sensor with several layers of conductive material in a sandwich structure can be used to verify the acceleration voltage, that is the energy output of the electron beam generator. Such information can constitute one parameter used to supervise correct operation of the generator. Moreover, a combination of measurements on both energy output and electron beam intensity can be used to further assure that the packaging material is treated with a sufficient sterilisation dosage.
In a sensor having, for example, three conductive layers, the first conductive layer, being closest to the filament 21, will absorb more energy than the second layer, which in turn will absorb more energy than the third layer. In
To facilitate the measuring, the thickness of the conductive layers and the insulating layers is preferably the same.
As mentioned, one of the functions of the shield is to protect the conductive layer or layers from plasma and secondary electrons. In the following, the term or concept of plasma or secondary electrons will be described. When an electron e− emitted from the filament 22 of
There will possibly be plasma in the surrounding environment, i.e., outside the exit window 24 of the electron beam generator 8, due to the presence of air. However, since plasma has not enough energy to penetrate the outermost insulating layer, which is covering the outermost conductive layer, it will function as a proper plasma shield.
Another previously mentioned function of the shield 32, 32′ is to isolate the bands 26, 26′ of a conductive layer from each other, and where appropriate, isolate conductive layers 28′, 38 from each other. Thus, there will be a separate signal that can be detected from each band 26, 26′, which together can give a clear picture, or map, of the dosage provided to the material 16 which is to be sterilised. Information from each band (e.g., signal amplitudes, signal differences/ratios, band positions and so forth) can be used to produce an emission intensity plot via a processor.
A sensor like the one described may as well be used in connection with irradiation of targets in the form of partly formed packages. Partly formed packages are normally open in one end and sealed to form a bottom or top in the other, and are commonly denoted Ready-To-Fill packages (RTF packages). In
Although the present invention has been described with respect to presently preferred embodiments, it is to be understood that various modifications and changes may be made without departing from the object and scope of the invention as defined in the appended claims.
In the embodiments described, the first insulating layer 32a, 32a′ covers substantially the entire exit window foil 25, 25′ and an overlying insulating layer covers substantially an underlying insulating layer. However, it is to be understood that the insulating layers don't practically need to cover more than necessary of each other and the window foil 25, 25′ to encapsulate each area 26, 26′ of the conductive layers present in the sensor structure.
The areas in the previously described embodiments have been described as bands 26, 26′. However, it is to be understood that the areas can have any shape, such as for example circles, circles segments, ellipses, arcs, wires, rectangular shapes and stripes, suitable for obtaining a sufficient dosage map.
It has also been described that the sensor is formed on the outside of the electron exit window. It should be understood that it is possible to form the sensor on the inside of the window, i.e., on the surface facing the vacuum chamber 12.
Finally, the embodiment described comprises a shield of insulating material. The shield may also comprise further layers or portions of protective nature for physically protecting the sometimes fragile conductive and insulating layers. Such layers or portions may be placed between the first insulating layer and the window foil and can be of any material suitably used together with the material in said foil. An additional protective layer can also be provided on the outside of the outermost insulating layer for protection from the environment.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0601304-9 | Jun 2006 | SE | national |
This application is based on and claims priority under 35 U.S.C. § 119(e) with respect to U.S. provisional application No. 60/814,532 filed on Jun. 19, 2006, the entire content of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60814532 | Jun 2006 | US |
