PLASMA SURFACE SANITIZER AND ASSOCIATED METHOD

Abstract

The plasma rail device of the invention is a novel method and device to generate plasma right at the surface or slight above the surface for surface treatment, specifically for surface sanitization. The device generally comprises pairs of electrodes held together by a frame. The device features a fame that holds and positions the electrodes in a close proximity towards the surface under treatment. Discharges are created in the space bounded by the electrodes to generate plasma on the surface and above the surface for treatment so that the device can be positioned outside the object under treatment.

Claims

1. A device for treating surfaces, comprising: (a) at least one pair of electrodes, separated by a distance between 1-20 mm and capable of generating plasma; (b) a frame holding and positioning the electrodes towards a surface under treatment in a distance between 0-20 mm; (c) a power supply for supplying high voltage alternating current to the electrodes; and (d) a controller controlling generation of the plasma and treatment process.

2. The device according to claim 1, wherein one electrode is of a higher voltage and is insulated with a dielectric material and another electrode is of a lower voltage and insulated or bare.

3. The device according to claim 1, wherein one electrode has a conductor in the form of conducting sheets, mesh, wire or deposits.

4. The device according to claim 1, wherein the frame has a flat surface which is parallel to an plan formed by the electrodes and has a vertical distance towards the plan between 0 mm to 20 mm, which determines an distance between the electrodes and a surface under treatment.

5. The device according to claim 1, wherein the frame has a curved surface which conforms to a surface under treatment.

6. The device according to claim 1, wherein the frame has a flexible surface which can change shape to suit to a surface under treatment.

7. The device according to claim 1, wherein the frame housing a fan or fanning device to direct air towards a surface under treatment.

8. The device according to claim 1, wherein the frame has a sliding surface to facilitate movement of the device on a surface under treatment.

9. The device according to claim 1, wherein the frame has a plurality of wheels to facilitate movement of the device over a surface under treatment.

10. The device according to claim 1, wherein the power supply can supply electricity of a voltage between 10 kv and 50 kv.

11. The device according to claim 1, wherein the controller can adjust the power supply and control amplitude, waveform period and shape of a voltage applied to the electrodes so as to maximize plasma treatment and minimize generation of unwanted bi-product gases.

12. The device according to claim 11, wherein the waveform period is in a range of 10.sup.−1 ms to 10.sup.2 ms.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings wherein:

[0038] FIG. 1 illustrates the components of a surface treatment device of the present invention;

[0039] FIG. 2 illustrates the electrode and the frame assembly according to a preferred embodiment;

[0040] FIG. 3 illustrates the electrode construct according to a preferred embodiment;

[0041] FIG. 4 illustrates the electrode assembly according to an another embodiment;

[0042] FIG. 5 illustrates an another embodiment of the electrode assembly with insulated electrodes placed within the circular cut-outs of the ground plate;

[0043] FIG. 6 illustrates an another embodiment of the electrode assembly with insulated electrodes placed within the hexagon cut-outs of the ground plate;

[0044] FIG. 7a, 7b illustrate an another embodiment with adjustable electrode positions;

[0045] FIG. 8 shows a prototype device constructed according to the present invention to demonstrate the effects of surface treatment;

[0046] FIG. 9 shows the experiment results using the prototype of FIG. 8

DETAILED DESCRIPTION OF THE INVENTION WITH EMBODIMENTS

[0047] Reference will now be made in detail to a preferred embodiment of the invention. Referring now to the drawings, FIG. 1 generally shows system components of a surface treatment system 1 comprising the electrode assembly 10 with the high voltage electrodes 20, the low voltage electrodes 30 and its associated power supply 4 and controller 5. The power supply and controller create and sustain discharges with specific plasma parameters predetermined and controlled by the high-voltage alternating current power source. As illustrated in the FIG. 1, the electrodes 20, 30 may be connected to a high-voltage alternating current power supply 4 having an electronic control unit 5. The power supply 4 can provide sufficient voltage to cause breakdown and to generate plasma directly on or above the surface of the object to be treated (including sanitized) without the need for delivering the charged ions and reactive species. The voltage applied to the electrodes 20, 30 may be controlled within a range of 10 kilovolts to 50 kilovolts. The waveform period may be controlled within a range of 10.sub.−1 ms to 10.sub.2 ms.

[0048] FIG. 2 shows a preferred embodiment of the electrode assembly 10 comprising the high voltage electrodes 20, the low voltage electrodes 30. The electrodes are held in place by the holders 11 and 12. Besides the planar form, the assembly can take on other forms, such as a cylinder or sphere. As illustrated in FIG. 3, the high voltage electrode 20 has a conductor 21 covered by an insulator 22 and a wire connection 23 to the power supply. The low voltage electrode 30 has a conductor 31 which can be bare or covered by an insulator 32, and a wire connection 33 to the power supply. The insulators can be made of dielectric materials such as glass or ceramic in the form a cylindrical tube as in this preferred embodiment. They may also be in the form of plates or made from any insulating or dielectric material. The insulators can also be in the form of a dielectric coating. The electrode conductors 21, 31 of the electrodes 21, 31 may be made of conducting sheets, mesh or deposits. The distance between a pair of electrodes 20, 30 may be in the range of about 1 mm to about 20 mm. Electrical discharges are created in the space bounded by the electrodes to generate plasma on the surface and above the surface for treatment.

[0049] The electrodes can take on other shapes, for example, in the wavy shaped the voltage electrodes 120, the low voltage electrodes 130 as shown in FIG. 4. The electrode assembly is not limited to the form of a rail. In the embodiment shown in FIG. 5, the ground electrode 230 is a conducting sheet with circular cut-outs to accommodate the insulated high-voltage electrodes 220. FIG. 6 shows another embodiment with the insulated high-voltage electrodes 320 placed in the hexagon cut-outs of the ground electrode plate 330. Although the embodiments are shown in the planar form, the assembly can take on other forms, such as a cylinder or sphere. As an additional feature illustrated in FIGS. 7a and 7b, the high voltage electrodes 220 mounted on a support 221 can be recessed behind the ground electrode plate 230 when not in use as shown in FIG. 7a and can be moved into the operating position when they are used for surface treatment and sanitization as shown in FIG. 7b. An alternate embodiment is to have the ground electrode plate 230 moved to become flushed with the high-voltage electrodes during surface treatment usage.

[0050] The superior surface sanitization performance of a prototype device of this invention (see FIG. 8) than a prototype device according to a prior art is confirmed in a comparison test. In this test, the petri dishes were pre-loaded with bacteria, treated by the corresponding devices operating at comparable plasma conditions. In the photos of FIG. 9, each ‘dot’ on the petri dish represents a colony of bacteria. FIG. 9c is the ‘control’ in which the petri dish has not been treated by any of the devices, showing the initial concentration of the bacteria. FIG. 9a shows the outcome of a petri dish treated by the device of this invention (device shown in FIG. 8). FIG. 9b shows the outcome of a petri dish treated by a device according to a prior art. There are much fewer colonies of bacteria in FIG. 9a than in FIG. 9b, indicating the device of this invention is more effective in surface sanitization.

[0051] The electrode and frame assembly (for example according to a preferred embodiment in FIG. 2) can be applied to a smooth surface with the surface of the electrodes (20, 30) either resting on the surface to be treated or above the surface to be treated with a distance not larger than the separation between the electrodes (20, 30). In the preferred embodiment shown in FIG. 2, the separation between the electrodes (20, 30) may be in the range from 1 mm to 20 mm. The distance between the electrode surface and the surface to be treated may be in the range of 0 mm to 20 mm. Typical treatment time is a fraction of a second to a few seconds. By moving air (for example using a fan) though the gap space between the electrode surface and the surface to be treated, the device of this invention can simultaneously sanitize air.

[0052] In an alternative embodiment as shown in FIG. 5, the high voltage electrodes 220 can be mounted on a movable support 221 to optimize the distance between the electrode tips and the surface to be treated.

[0053] The surface treatment is not limited to a surface of size smaller than the electrode assembly. The electrode assembly can be used to treat a large surface by sliding or moving the electrode assembly over the surface to be treated. Alternatively, the surface to be treated can be moved under the electrode assembly, for example, the electrode assembly can be positioned above the rubber handrail of an escalator which moves continuously underneath the electrode assembly. As the electrodes are positioned above the moving surface, thereby avoiding physical contact and eliminate mechanical wear and tear.

[0054] With a treatment time of seconds to sanitize a surface under the electrode assembly, an electrode assembly of the size of a small notebook computer can effectively disinfection the surface of a desk within minutes. By attaching the electrode assembly to a mobile device (a robot or a drone), a mobile electrode assembly can sanitize surface of a room in minutes. By allowing air to flow (for example, via the movement of the mobile device or by using a fan) through the gap space between the electrode surface and the surface to be treated, the device can simultaneously sanitize air.

[0055] In the case of a curved surface, the frame holding the electrodes (11, 12 in FIG. 2) may be made in a curved shape to match the curvature of the surface to be treated. Furthermore, the holder of the preferred embodiment (11, 12 in FIG. 2) may be made of flexible materials or be constructed in the form of a flexible chain to enable the electrodes to conform to an arbitrarily curved surface. For the alternative embodiment as shown in FIG. 5, the high voltage electrodes 220 can be mounted on a flexible support 221 together with a flexible ground electrode 230 to enable the electrode tips to conform to an arbitrarily curved surface and an optimal distance between the electrode tips and the surface to be treated.

[0056] In this invention, the distance between the electrode surface and the surface to be treated is not required to be fixed but can be varied within a reasonably range of 0 mm to 20 mm. The device is therefore able to sanitize not only smooth surface but also non-flat surface with surface irregularities up to 20 mm.

[0057] For the device of this invention, the construct and arrangement of the electrodes allow the sanitizer to be easily applied above the surface of the object to be treated. In comparison with the prior art devices, the device of the present invention is simple to construction and yet is flexible and more effective in terms of treating surfaces. There is no specific requirement to ground the surface of the object, i.e., the object to be treated effectively become part of the electrical circuit. For the frame, the basic requirement is that it can hold and position the electrodes in a required close distance towards the treatment surface. So long the frame can accomplish such requirement, it can be constructed in various way in various shape and material. For example, it may be made a flexible material for treating curved or irregular surfaces. It may also embed a fan mechanism for directing the air to the treatment surface. It may also have wheel or sliding mechanism for facilitating moving over the surface under treatment. This invention allows application of plasma treatment to various objects, for example, treating the elevator button panel and other construction surfaces in common areas to reduce virus and bacterial infection and transmission in community. This is because, unlike prior art devices, there is also no requirement to put the object in between the electrodes. Beside the uniqueness of the invention to overcome some of the deployment complexity of prior arts, the device of this invention is able to sanitize a surface better than the device of prior arts.

[0058] It is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. While there have been described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes, in the form and details of the embodiments illustrated, may be made by those skilled in the art without departing from the spirit of the invention. The invention is not limited by the embodiments described above which are presented as examples only but can be modified in various ways within the scope of protection defined by the appended patent claims. It is further under- stood that the present invention can be practiced even without referring to these specific examples because the essence of the present invention does not lie in technical difficulty or complexity but in the novel ideas itself. Once the idea is known, the practice of it is within ordinary skill in the art.