Electric lamp and discharge devices: systems – Pulsating or a.c. supply – Transformer in the supply circuit
Reexamination Certificate
2001-03-15
2003-10-07
Vu, Bao Q. (Department: 2838)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
Transformer in the supply circuit
C315S205000, C315S2090SC, C361S038000
Reexamination Certificate
active
06630799
ABSTRACT:
TECHNICAL FIELD
The present invention relates to x-ray tube design and x-ray tube power supply design. More particularly, the present invention relates to the development of a high efficiency x-ray source consisting of a fluorescent x-ray tube, and resonant power supply, which relies on plasma within the tube. The present invention further relates to the design of a power supply to achieve enhanced efficiency. This x-ray tube design can then be used in applications such as product irradiation, and more particularly the sterilization of materials such as foodstuffs and medical implements.
BACKGROUND OF THE INVENTION
As public demand for greater safety from potentially harmful microorganisms increases, scientists must come up with more effective and efficient ways of providing safe products and environments. One technique that is well suited to the reduction in the quantities of microorganisms and pests is irradiation.
Irradiation uses relatively high doses of one of several forms of radiation, gamma rays, electron beam (e-beam), or x-rays, to kill microorganisms and pests that may be present in or on a given material. The radiation ionizes atoms that are sometimes part of critical molecules such as DNA and RNA. Damaging key cell components such as these causes the cells to die, and if enough cells are killed, then the organism dies. There are two main forms of irradiation in use today. They are gamma irradiation and e-beam irradiation. Gamma irradiation uses a radioisotope source such as cobalt-60 that emits gamma rays measured in the millions of electron volts (MeV), while e-beam uses an accelerator to accelerate electrons to MeV range energies. Although both technologies have performed well in limited situations, significant improvements are required to make this technology more accessible.
Gamma irradiation has the major drawback of using radioisotope sources. Radioisotopes cannot be turned off and therefore create a disposal hazard. Additionally, there is public perception linking all radioisotopes to atomic bombs and various accidental radiation deaths, as well as fear that the object being irradiated will be contaminated or somehow become radioactive, even if it cannot. All this makes it difficult to sell the public on the benefits on gamma irradiation. The high energy MeV range gamma rays also require a significant amount of shielding, leading to the irradiation facilities being very large, usually requiring their own building with elaborate shielding and convoluted conveyor systems to safely move the product through the high radiation area. It should be noted also that the gamma rays mostly go through the material without loosing much energy, i.e., without creating much ionization. On the positive side, irradiation sources are inexpensive, stable and require no power to produce the radiation. But while the source itself is inexpensive, the irradiation facility itself is expensive-often costing a million dollars or more. Further, due to the nature of the shielding requirements for radioisotopes, the use of gamma irradiation usually requires a completely separate facility from the manufacturer or distributor and thus results in additional expenses associated with shipping, loading, and packing the materials being irradiated. On top of all this, add the burden of meeting US Nuclear Regulatory Commission and associated state regulatory bodies rules for handling radioactive material.
E-Beam irradiation has several major drawbacks as well. The accelerators are expensive (usually in the million to several million-dollar range) and are fairly big requiring a large room or separate building. Further, unlike gamma irradiation that can penetrate through fairly thick materials (even metals), electrons only travel a short distance in most products. For example, a typical e-beam may only penetrate ¼ inch (6 mm) in hamburger meat, and is only effective near the surface of materials composed of heavier atoms such as steel. This lack of penetration depth does lead to a benefit in that it may require less shielding if there is not much secondary x-ray production, but the limitations prevent the technology from being useful in many cases. E-beam technology is also usually part of a separate facility as well, creating the same types of transport problems as gamma facilities. Similarly, accelerators must be licensed with the states and are carefully controlled as one of the more dangerous electronic radiation producing products available.
It is also possible to have electrons from an accelerator shine on a heavy metallic target to produce high-energy x-rays or low-energy gamma rays that can in turn be used much in the same way as gamma irradiation from radioisotopes. Unfortunately, the percentage of e-beam energy converted into x-rays energy is only about 1 percent and the overall efficiency is much less than that. Thus, an e-beam x-ray system could be considered the worst of both worlds in that now heavier shielding is required with a much more expensive and inefficient source. A full-scale commercial irradiation facility built on this principle would pretty much require its own separate power plant. With the source being so inefficient that the technique is not economically viable except as an occasionally used add-on feature to an otherwise useful e-beam system.
Therefore, in light of all these problems, a need exists for a device that: (1) is small enough to be integrated into the sites where they are needed; (2) achieves an optimal penetration depth for the product being treated; (3) is safe enough for use by an average person; (4) uses available power efficiently, and (5) is low in cost.
Low energy x-rays appear to meet most of these requirements since they can be tuned so that a maximum amount of x-ray energy is absorbed in a given product. X-ray tubes and power supplies are small and inexpensive and can be made in a wide variety of sizes. Television sets are one example of small economical x-ray producing device since they contain the high voltage supply, vacuum tube and other components that are necessary at very low cost, but use shielding to minimize x-ray emissions.
A traditional x-ray tube is made of a glass or ceramic envelope and is evacuated to a high vacuum. The envelope usually has an x-ray transparent window, typically made of beryllium, aluminum, or glass. The x-ray tube may have x-ray shielding, cooling, and high voltage insulation incorporated into its design as well. The tube has a filament at one end that is intensely heated so that it easily supplies electrons when a high voltage potential is applied between it and the anode. The anode is typically a large block of metal that normally is copper (due to its heat conduction), with a different target material often brazed to the surface that the electrons strike. The vacuum x-ray tube requires two power supplies: a DC power supply for the filament heating which typically operates at low voltage (0-10 volts typical) and a few watts of power; and a second power supply that provides a high voltage (5-200+ kV) DC supply that may range in power from a few watts to 100 kilowatts or more.
Traditional x-ray tubes, however, still suffer from a number of known problems associated with efficiency. When electrons hit the target material of the x-ray tube, they loose the energy they gained from being accelerated by the high voltage electrical potential existing between the filament and the target anode. Through scattering and ionization, the electrons lose energy by transferring some of it to the atoms in the anode target material. For each scattering and ionization event, x-rays and lower energy light are emitted, creating a spectrum of energy that is made up of a continuum of x-rays given up through scattering, and characteristic x-rays of the target material. The efficiency of the conversion of electrical energy to x-ray energy is sometimes expressed by a simple empirically derived formula of the form E
x
=E*kZV
x
where E
x
is the x-ray energy, E is the electrical energy, k is a constant, Z is the atomic nu
Fleming Ray
Popa Constantin
Safe Food Technologies, Inc.
Thompson & Knight L.L.P.
Vu Bao Q.
Weiss Aaron A.
LandOfFree
Resonant power supply and apparatus for producing vacuum arc... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Resonant power supply and apparatus for producing vacuum arc..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Resonant power supply and apparatus for producing vacuum arc... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3152108