GB2470060A

GB2470060A - Improved screen assembly for an electrodeless UV lamp

Info

Publication number: GB2470060A
Application number: GB0907901A
Authority: GB
Inventors: Richard Little; David Briggs
Original assignee: Jenact Ltd
Current assignee: Jenact Ltd
Priority date: 2009-05-08
Filing date: 2009-05-08
Publication date: 2010-11-10
Also published as: GB0907901D0

Abstract

The lamp housing includes a chamber 16 having an opening and is configured to contain an electrodeless lamp which is energised by radio frequency energy such as microwaves. The opening is covered with an apertured member 20 dimensioned to be beyond cut-off and, therefore, opaque to the selected radio frequency energy but allow the light emitted by the electrodeless lamp to pass through.

Description

IMPROVED SCREEN ASSEMBLY FOR AN ELECTRODELESS UV LAMP

This invention relates to an apertured member for preventing microwave radiation exiting a chamber including an electrodeless lamp Electrodeless UV lamps have been used industrially since the I 970s and in the majority of applications are situated in a resonant or semi resonant cavity. An example of such a cavity is illustrated in US Patent No. 4,042,850. An outer housing includes a chamber forming a cavity in which a UV lamp is situated. The chamber is provided with an opening so that UV light generated by the lamp can exit the housing. The opening is covered with a metallic mesh to prevent microwave energy exiting the chamber. It should be noted that the two largest current manufacturers of such systems, Fusion Systems Inc. and Nordson Corporation both still supply such UV curing systems exclusively with fine tungsten wire mesh broadly as shown in US 4,042,850. Other patent applications illustrating the use of metallic mesh are: US 6,323,601 Col 4, line 60: US 6,646,384 Ccl 1, lines 25-30 In order for the metallic mesh to prevent microwave energy exiting the chamber but allow UV light to exit the chamber the holes in the mesh must be small. Hence, the wire making up the mesh has a small diameter so that sufficient UV light can exit the housing. Additionally, cooling air is often required to leave the housing via the mesh.

However, there are multiple problems associated with the use of this mesh. Firstly, the wire in the mesh is fragile and can be damaged by movement, such as lifting activity or by impact from items passing underneath the lamp during normal use. Such damage necessitates the change of an expensive component and also potential danger from leakage of radio frequency waves through the damaged mesh screen. Secondly, the lamp generates a large amount of heat in use. This means that any deposits on the wire can heat up the wire sufficiently for it to degrade and fail. Thirdly, air resistance due to the small size of the mesh necessitates a more powerful and noisy cooling air fan than would otherwise be required.

In accordance with an aspect of the present invention there is provided an apertured member arranged for use with a chamber, the chamber having an electrodeless discharge lamp arranged to radiate in the ultraviolet spectrum disposed within it, the apertured member comprising means to engage with the housing and a plurality of elongate tubes, the tubes having a length and width in relation to the operating microwave wavelength which prevents microwave energy passing through the tubes. The inherent structural strength, lack of resistance to airflow and high % of open section to structural cross section overcome the three major problems associated with current mesh systems as outlined above as the apertured member is used as a direct alternative to a mesh screen as used in existing system.

The apertured member may be dimensioned, when used with a 2.54GHz microwave source, so that the maximum cross-sectional internal dimension of each tube is less than � wavelength (approx 30mm) and where the length of each tube forming the structure of the apertured member is dimensioned so that microwaves of an intensity at the inner face of the structure of up to 20w/cm2 are attenuated to a maximum of 5mw/cm2 at the outer surface.

For example, a structure constructed of tubes with 10mm cross sectional internal dimension require a length of at least 11mm to achieve such attenuation.

Preferably, the tubes are arranged at 90 degrees to the planar face of the apertured member.

Optionally, the wall of the chamber is provided with a gasket or plurality of chokes around its edge to permit effective mounting and radio frequency sealing of the apertured member.

Optionally, the apertured member is provided with a gasket or plurality of chokes around its edge to permit effective mounting and rf sealing to the wall of the chamber According to another aspect of the present invention there is provided a housing comprising a chamber including an opening and configured to receive at least one electrodeless discharge lamp arranged to radiate in the ultraviolet spectrum and an apertured member.

The chamber may be dimensioned and arranged to form a non-resonant cavity at the operating wavelength. Optionally, the housing may be arranged to operate generally at a frequency in the range of 2-3GHz and more particularly at about 2.45GHz.

According to a further aspect of the present invention there is provided a UV light system comprising at least one electrodeless discharge lamp arranged to radiate in the ultraviolet spectrum and a housing comprising a chamber and an apertured member.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

Figure 1 illustrates a cross-section of a UV light system; Figures 2A to 2D illustrate perspective views of alternative embodiments of the UV light system; and Figure 3 is a detailed view of a portion of Figure 1.

With reference to Figures 1 and 2 a UV light system 10 is shown. The UV light system includes a microwave source 12, a chamber 16 and a waveguide 14 arranged to convey microwaves to a chamber 16. The chamber 16 forms a cavity 1'7 in which an electrodeless UV lamp 18 is situated such that at least some of the microwaves can energise the lamp 18.

The chamber 16 includes an opening. An apertured member 20 is placed across the opening. The apertured member 20 comprises a number of relatively thin members 22 interlocking to form generally square, round or rectangular section tubes 24. For example in the form of a reticulated reflector for a fluorescent luminaire. The tubes 24 are dimensioned such that the tubes 24 are beyond cutoff, and thus prevent microwave leakage without requiring the fineness of wire.

Generally, the length of the tubes 24 should be greater than the maximum diameter or maximum cross-sectional dimension. Furthermore, the internal cross-sectional maximum dimension of each tube 24 should be less than one quarter of the operating wavelength.

Thus, for a frequency of approximately 2.45 GHz, the maximum cross-sectional dimension of each tube 24 should be not more than approximately 3cm and each tube 24 should preferably be at least 3 cm long. This, as is known to those skilled in the art, will create a tube 24 which is approx beyond cutoff and which will attenuate sufficient microwave energy.

The skilled person will appreciate that many different constructions for the tubes may be suitably manufactured. For example, the tubes may be angled so that they better align with the direction of light emitted from the lamp. The critical features being the length and other dimensions relative to the operating wavelength, being chosen to ensure that the tubes (which operate according to waveguide theory) are beyond cutoff.

The apertured member may be made to be integral with the housing. If the apertured member 20 is not integral with the housing; the end of the wall of the chambers, optionally, may be formed into chokes as illustrated in Figure 3. The chokes act to prevent the transmission of microwaves. Alternatively gaskets may be employed.

Additionally the apertured member may be provided with a hinge connection to the chamber thereby aliowing the bulb within the chamber to be readily replaced.

As will be understood by the skilled person any suitable radio frequency wave may be used to energise the UV lamp. The microwave source may be a magnetron or any other suitable source of microwaves.

The cavity formed by the chamber and apertured member may be resonant or non-resonant.

Additionally, the chamber walls may be formed in any suitable shape and may be shaped to reflect emitted light towards the opening thereby maximising the amount of light emitted from the UV light system.

Claims

CLAIMS1. An apertured member arranged for use with a chamber, the chamber having an electrodeless discharge lamp arranged to radiate in the ultraviolet spectrum disposed within it, the apertured member comprising means to engage with the housing and a plurality of elongate tubes, the tubes having a length and width in relation to the operating microwave wavelength which attenuates microwave energy passing through the tubes.
2. An apertured member according to claim 1, wherein the maximum cross-sectional internal dimension of each tube is less than X/4 where A. is the operating microwave wavelength, and wherein the length of each tube is greater than the maximum cross-sectional internal dimension.
3. An apertured member according to claim 1 or claim 2 wherein the wall of the chamber is provided with a plurality of chokes around its edge.
4. A housing comprising: a) a chamber including an opening and configured to receive at least one electrodeless discharge lamp arranged to radiate in the ultraviolet spectrum; and b) an apertured member as claimed in any one of Claims 1 to 3
5. A housing according to claim 4 wherein the chamber is dimensioned and arranged to form a non-resonant cavity at the operating wavelength.
6. A housing according to any one of claims 4 and 5 arranged to operate generally at a frequency in the range of 2-3GHz and more particularly at about 2.45GHz.
7. A UV light system comprising: a) at least one electrodeless discharge lamp arranged to radiate in the ultraviolet spectrum, and b) a housing as recited in any one of claims 4 to 6.
8. An apertured member substantially as herein described with reference to and as shown in any combination of the accompanying drawings.
9. A housing substantially as herein described with reference to and as shown in any combination of the accompanying drawings.
10. A UV light system substantially as herein described with reference to and as shown in any combination of the accompanying drawings.