HK1082998B - Radio frequency driven ultra-violet lamp - Google Patents

Description

RF driven ultraviolet lamp

Technical Field

The present invention relates to electrodeless lamps excited with a Radio Frequency (RF) field.

Background

A number of patents disclose electrodeless bulbs excited with RF power using an electrically conductive coupler comprising a coil wound with one or more electrically conductive turns around the periphery of the bulb. See U.S. patents 4204834, 4792725, 5063333, 5070277, 5072157, 5130612, 5280217, 5306987, 5886478, 5923116, 5990632, 6046545, 6107752, 6137237, 6145979, 6248805, and 6249090. The one or more turns of the coil in the electrically conductive coupling means of the excitation bulb function on the basic principle of inductive and/or capacitive coupling to the electrodeless bulb, depending on the design of the RF excitation system.

Electrodeless lamp assemblies comprising electrically conductive coupler excitation with one or more coils of electrically conductive turns wound around the periphery of the bulb are advantageous in view of their ability to produce substantial light output in either the visible or Ultraviolet (UV) range in a compact envelope. However, cooling of the lamp bulb and the one or more turns of the electrically conductive coupler in a fixed relationship with the lamp bulb may deteriorate. Furthermore, in order to produce the maximum amount of light output with the minimum RF power input, it is desirable to prevent RF power from being coupled from the electrically conductive coupler through parasitic capacitance or inductance to the housing containing the electrodeless bulb.

Furthermore, in applications where a small UV light generator is employed, such as for the purpose of reproducing digitally stored photographs, a low operating temperature of the outer sidewall of the UV lamp assembly housing is desirable. In most applications requiring small light sources, the light source is a component in a large device. Thus, the small size and low operating temperature on the lamp surface are valuable because it enables many large equipment components to be made from inexpensive heat sensitive materials such as plastic and many components to be mounted in close proximity to the UV lamp, contributing to the efficient utilization of the overall design.

Disclosure of Invention

The present invention provides a compact electrodeless lamp assembly having high output in selected portions of the spectrum which can be used for a wide variety of applications. The outer side walls of the miniature housing are kept at a temperature at which they will not burn during operation.

The present invention further provides a light reflecting enclosure that houses an electrodeless bulb and minimizes absorption of light generated therein.

The lamp assembly according to the present invention utilizes an electrically conductive coupler for exciting an electrodeless bulb that includes a plurality of turns defining a volume at least partially enclosing the electrodeless bulb. An electrical conductor is connected to a central portion of the electrically conductive coupler, the electrical conductor positioning the coupler relative to the bulb.

The electrically conductive coupler provides efficient coupling of the RF electric field to the electrodeless bulb. The connection of the electrical conductor to the electrical coupling results in a symmetrical transfer of electrical power from the RF electric field to the electrodeless bulb, which ensures uniform dissipation of power within the electrodeless bulb and thus improved efficiency and life of the electrodeless bulb.

A lamp assembly according to the present invention comprises an electrodeless bulb, the electrodeless bulb being axisymmetric and containing a light-emitting fill which emits light when the bulb is excited by a radio frequency electric field coupled to the fill; an electrically conductive coupler comprising a plurality of turns of wire axially symmetric about the coupler, the plurality of turns of wire defining a volume at least partially containing the lamp; and a conductor connected to a central portion of the electrically conductive coupler, the conductor conducting a radio frequency current that produces a radio frequency potential on the electrically conductive coupler so as to produce a radio frequency electric field that couples with the fill when the conductor is connected to the coupler to form a position of the coupler relative to the bulb. The bulb outer surface may comprise a cylindrical portion and the volume may also comprise a cylindrical portion. The axes may be substantially parallel to each other and/or proximate to each other. The electrical conductor may be connected to one turn of the coil at a central portion of the electrically conductive coupler opposite the ends thereof. The rf power may be coupled to the filler symmetrically with respect to the center portion of the electrically conductive coupler. The plurality of turns of the coil may be a wire having a polygonal cross-section which may be a triangle, a quadrilateral such as a square, or an equilateral polygon having more than four sides.

A lamp assembly according to the present invention comprises an electrodeless bulb having an axisymmetric outer surface and containing a light-emitting fill which emits light when the bulb is excited by a radio frequency electric field coupled to the fill; an electrically conductive coupler comprising a plurality of turns of wire axially symmetric about the coupler, the plurality of turns of wire defining a volume at least partially containing the lamp; a conductor connected to a central portion of the electrical coupling device, the conductor conducting a radio frequency current that generates a radio frequency potential on the electrically conductive coupling device when the conductor is connected to a source of radio frequency voltage so as to generate a radio frequency electric field that couples with the fill material, in a condition in which the conductor is connected to the coupling device to configure the coupling device to be positioned relative to the bulb; and a light reflecting box housing the bulb, the electrically conductive coupling device and the electrical conductor, the box including a central portion, an upper portion and a lower portion that reflect light emitted by the bulb from an opening in the box, and each of the upper portion and the lower portion reflecting light emitted by the bulb and light reflected from the other of the upper portion and the lower portion. The upper and lower portions may each include a curved light reflecting groove that mounts the end of the bulb and is recessed in an outward manner relative to the case so that the groove surfaces are spaced further apart than the remaining surfaces of the upper and lower portions that are not recessed, and the curved groove reflects light emitted from the bulb. The lamp assembly may further comprise a housing containing the enclosure and at least one fan positioned at one end of the housing to draw air from one end of the housing and blow the drawn air into contact with the outside surfaces of the portions of the enclosure and the inside surfaces of the housing and then outwardly from the housing to blow air into the enclosure past the light bulb and the electrical coil and outwardly from an opening in the enclosure. The housing may include portions which are joined together to define one end and include another end surrounding the opening in the box and each portion may include at least one opening provided at the one end where the air is blown outwardly by the fan after the portions in the box and housing are cooled. The housing may comprise a plastic. A plurality of fans may be provided at one end face of the housing. The electrical conductor may be connected to a turn of the coil substantially at the central portion of the electrically conductive coupler opposite the end thereof. The rf power may be coupled to the filler symmetrically with respect to the center portion of the electrically conductive coupler. The plurality of turns may be wires having a polygonal cross-section, which may be a triangle, a quadrilateral such as a square, or an equilateral polygon having more than four sides.

A lighting system according to the present invention may comprise a plurality of lamp assemblies connected together, each lamp assembly comprising an electrodeless lamp having an axisymmetric outer surface and containing a light-emitting fill which emits light when excited by a radio frequency electric field coupled to the fill, an electrically conductive coupler comprising a plurality of turns of wire axially symmetric about the coupler, the plurality of turns of wire defining a volume at least partially containing the lamp, an electrical conductor connected to a central portion of the electrically conductive coupler, the electrical conductor conducting a radio frequency current which generates a radio frequency electric potential on the electrically conductive coupler when the electrical conductor is connected to a source of radio frequency voltage so as to generate a radio frequency electric field which couples to the light-emitting fill, the electrical conductor being connected to the electrically conductive coupler to form a position of the coupler relative to the lamp; and a light reflecting box housing the bulb, the electrically conductive coupling means and the electrical conductor, the box comprising a central portion, an upper portion and a lower portion which reflect light emitted by the bulb out of an opening in the box, and each of the upper and lower portions reflecting light emitted by the bulb and light reflected from the other of the upper and lower portions.

Drawings

Fig. 1 shows a side elevation view of a first embodiment of the present invention.

Fig. 2 shows a top view of the embodiment of fig. 1.

Fig. 3 shows a view of a conductor connected to an electrically conductive coupler for exciting an electrodeless bulb in accordance with the present invention.

Fig. 4-7 illustrate different cross-sections of the conductive lines of fig. 3, respectively, that may be used to form the electrically conductive coupler.

Figure 8 shows a front elevational view of the first embodiment with the electrodeless bulb and electrically conductive coupler and electrical conductors removed.

Fig. 9 shows a front elevational view of the first embodiment with the electrodeless bulb and electrically conductive coupler installed.

Fig. 10 is a graph illustrating the transfer of electrical power from the electrically conductive coupler to the electrodeless bulb along the length of the electrodeless bulb.

Fig. 11 illustrates a second embodiment of the invention in which a set of lamp assemblies according to the first embodiment are connected together to illuminate an object.

Fig. 12 shows a third embodiment of the present invention, which is similar to the second embodiment except that adjacent lamp assemblies are in contact with each other.

Like reference numerals refer to like parts throughout the several views of the drawings.

Detailed Description

Fig. 1-9 show a first embodiment 10 of a lamp assembly according to the invention. The lamp assembly of fig. 1-9 provides high light output from the electrodeless bulb 14, the electrodeless bulb 14 is energized with an RF voltage source 42, and the three-dimensional miniature enclosure 12 encloses the RF voltage source 42, and the three-dimensional miniature enclosure 12 can be made of plastic in view of the provision of the efficient cooling mechanism of the present invention described below during operation of the lamp assembly. The electrodeless bulb 14, which is symmetrical about an axis 16, is described in more detail below. The electrodeless bulb 14 is excited by an RF electric field provided from an electrically conductive coupler 18 shown in detail in fig. 3. The electrically conductive coupling device includes a plurality of wire turn coils 20 defining a cylindrical shape 19, the cylindrical shape 19 also being symmetrical about the axis 16. Generally, the electrodeless bulb 14 and the cylindrical shape 19 are preferably coaxial and desirably substantially coincident and or parallel so that the volume of the cylindrical shape 19 at least partially encloses the electrodeless bulb as shown, thereby substantially coupling the RF electric field along the major axis of the electrodeless bulb.

A light reflecting and electrically conductive case 24, which may be made of aluminum or another metal such as stainless steel, houses the electrodeless bulb 14, the electrically conductive coupler 18 and the electrical conductor 26, the electrical conductor 26 being connected to a central portion of the electrically coupler 18 at a connection point 70'. The joint 27 comprises an insulating sleeve 29 preventing RF current from flowing at the location where the electrical conductor 26 passes through the end face wall of the central portion of the electrically grounded tank 24. The connector 29' is used to connect to the RF power source 42. The connection point 70' of the electrical conductor 26 to the electrically conductive coupler 18 positions the coupler relative to the electrodeless bulb 14. The center portion 26' in the electrically grounded and conductive box 24 reflects light 28 emitted by the electrodeless bulb 14 out of the opening 30. The upper and lower portions 32, 34 of the box 24 are connected to the central portion 26' to complete the light-reflecting chamber in the reflective box. The upper and lower sections 32, 34 may be parallel or inclined to each other so that the relative spacing expands toward the tank opening. Each of the upper and lower sections 32, 34 is provided with a recess 36 and an aperture 38, respectively, for increasing reflection, and the end 40 of the electrodeless bulb 14 passes through the aperture 38 to retain the bulb in a position located relative to the chamber 24. The inner side surface 41 of the groove 36 reflects light emitted from the end portion of the electrodeless bulb 14 and light reflected from the other of the upper portion and the lower portion.

Tests have shown that the notch 36 increases the optical output power by about 5% for a constant RF input power of the RF power supply 42 compared to the optical output power when the notch 36 is not used. Moreover, since the excitation of the electrodeless bulb 14 depends on the capacitive coupling of the RF electric field from the electrically conductive coupler to the fill inside the electrodeless bulb, the feasible spacing of the recess 36 away from the inner shell 44 of the electrodeless bulb reduces parasitic capacitance and reduces undesirable RF power coupling to the ground box 24. Preventing the direct coupling of RF power to the ground box 24 allows the RF power to be more efficiently converted to radiation of the visible light 28 than would occur without the notch 36.

At least one fan 22 is disposed at one end face 48 of the housing 12. At least one fan draws air 50 into the housing 12, blows air 50 into the space between the inner side walls of the housing 12 and the outer side walls of the enclosure 24 and blows air 50 into the enclosure through the electrodeless bulb 14 and the electrically conductive coupler. The air 56 exits the other end face 49.

Splitting the incoming air 50 into separate air paths. The first air path flows into the interior of the light reflecting box 24 as indicated by arrow 52 and through the turns 20 in the electrically conductive coupler 18 and the outer side surface 54 of the electrodeless bulb 14 to achieve substantial cooling. The first path of air exits the interior of the box 24 from the distal end 53 with the air flow. A second path for the intake air 50 passes through small holes 60 in the upper and lower portions 32, 34 of the box 24. The air flow 62, as it passes through the apertures 60, cools the outside surfaces of the upper and lower sections 32, 34 and the inside surface 64 of the plastic housing to cool the outside wall of the plastic housing 12 to a temperature that does not cause scalding to a person touching the wall. The third path (fig. 2) for the intake air 50 is against the outer side wall 66 of the central portion 26' of the box 24 and then exits with the air flow 70 through the small holes 68. By the air flow, the electrodeless bulb 14 and the associated electrically conductive coupler 18, the walls of the reflector box 24 and the walls of the compact housing 12 in which the box is mounted are cooled very efficiently.

Fig. 3-7 show more detailed views of the electrically conductive coupler 18 and the connected electrical conductor 26, the electrically conductive coupler 18 and the electrical conductor 26 including possible cross-sectional shapes of the wire turns shown in fig. 4-7. While the connection point 70' of the electrical conductor 26 to the wire turns 20 is shown in fig. 3 as being optimally symmetrical with respect to the ends, it should be understood that the invention is not limited to connection to the center of the cylinder defined by the turns 20, but may be connected at such a location, for example, outside the center but away from the ends, for the desired application, so long as the RF electric field provides sufficient excitation to the electrodeless bulb 14. The closer the location of the connection point 70' is to the center of the conductor 26, the more symmetrical is the power flow from the hottest central operating portion to the coolest end to the electrodeless bulb 14, which is the operating characteristic curve most desired in the case of the lamp assembly of the present invention.

Some of the non-circular cross-sections of fig. 5-7 that may be used to fabricate the electrically conductive coupler 18 have two advantages over circular cross-sections. First, the ribs 80 concentrate the electric field, which may facilitate the electrical coupling of the electric field from the electrically conductive coupler 18 to the electrodeless bulb 14. Furthermore, the non-circular cross-section may increase the overall mechanical stability of the wire.

Fig. 10 shows a graph of the power generated by the RF power source 42 coupled to the electrodeless bulb 14 by the electrically conductive coupler 18 during conduction. The Y-axis represents the input RF power value applied to the axis 16 of the electrodeless bulb 14. The origin of coordinates is on one end face of the electrodeless bulb 14 and "L" is on the other end face of the electrodeless bulb. Connecting the RF voltage substantially at the midpoint, such as point 70' in fig. 3, results in a gradient of power absorption along the length of the bulb from a maximum at the midpoint to a minimum at the end operating at cooler temperatures.

The coupling of the RF electric field at substantially the midpoint of the electrically conductive coupler 18 results in the most uniform dispersion of power along the electrodeless bulb 14, which extends the life of the bulb. For example, if a potential is coupled from an RF power source to one end of the bulb, the result is that the end coupled with the RF potential operates at the highest temperature and the distal end operates at the lowest temperature. Therefore, there is a large temperature difference between the hottest point on the electrodeless bulb 14 and the coldest point on the electrodeless bulb 14, which may be detrimental to bulb life.

Fig. 11 shows a second embodiment 100 of the invention, which is an illumination system. The lighting system includes a set of individual lamp assemblies of fig. 1-9 connected together by a connection mechanism 101. the connection mechanism 101 may be designed as desired. The spacing 102 of the individual lamp assemblies 10 allows a stream of cold air, as described above, to flow between adjacent lamp assemblies to accelerate cooling of the adjacent wall 106. As shown, the set of individual light assemblies when coupled together with the attachment mechanism 101 can illuminate a target 104 containing an object requiring UV treatment, such as an object moving along a conveyor belt.

Fig. 12 shows a third embodiment 200 of the present invention, the third embodiment 200 being similar to the second embodiment. Unlike the second embodiment 100, the adjacent walls 106 of the third embodiment 200 are touching, which positions the walls 106 as the interior walls 108. It is permissible to configure adjacent walls 106 in contact with the joining mechanism 101', so long as the material from which the walls are made is selected to be thermally stable in the application.

The electrodeless bulb 14 in the exemplary embodiment is constructed from technically standard materials.

The following is an example of an embodiment of the present invention that may be used in commercial applications to generate UV light in structures such as those of fig. 1-3 and 6-12.

The electrodeless bulb 14 has an outer diameter of 9mm and an overall length of approximately 0.8 inch. The electrically conductive coupler 18 is preferably formed of nickel, and the electrically conductive coupler 18 may be formed of any other material capable of withstanding high temperature operation, such as stainless steel, titanium, or industrial alloys. The cross-section of the electrically conductive coupler is preferably square, but may be triangular, polygonal or circular. The electrically conductive coupling means is in the form of a substantially six turn coil with an internal diameter of approximately 12.5 mm. The total height of the electrically conductive coupler is about 0.75 inch. The electrically conductive coupler 18 and electrodeless bulb are placed in position within the light reflecting chamber 24. The upper and lower portions 32, 34 of the light-reflecting box 24 are parallel and spaced about 1inch apart at the box opening.

In this embodiment, the electrically conductive coupler couples RF power to the electrodeless bulb at about 600 MHz. Increasing the number of turns or increasing the turn pitch on the electrically conductive coupler tends to result in efficient coupling of RF power to the bulb at lower RF frequencies. Increasing the diameter of the electrically conductive coupling device comprising a turn coil tends to reduce the frequency at which RF power is coupled to the bulb, and also reduces the coupling efficiency. Reducing the diameter of the electrically conductive coupling device can increase the coupling efficiency. However, manufacturing concerns must be taken into account since the electrically conductive coupling means cannot be allowed to contact the bulb, which causes local overheating at the contact location and rapid bulb burn-out.

The structure in the embodiment can be scaled for longer bulbs, a few inches; up to a bulb diameter of at least 15mm or more and modifying the electrically conductive coupling means to a frequency in the range from 100MHz to over 1000 MHz.

While a particular application of the present invention is the generation of UV light, it should be understood that the present invention is not so limited. For example, the fill within the electrodeless bulb 14 may be varied in order to vary the light emission characteristics in order to accommodate the particular frequency of light required for a particular application.

Claims (22)

1. A lamp assembly, comprising:

an electrodeless bulb which is axisymmetric and contains a luminescent filling which emits light when excited by a radio frequency electric field coupled to the filling;

an electrically conductive coupler comprising a plurality of turns of wire axially symmetric about the electrically conductive coupler, the plurality of turns of wire defining a volume at least partially enclosing the electrodeless bulb; and

a conductor secured to the center portion of the electrically conductive coupler by an electrically conductive connection, the electrically conductive connection with the electrically conductive coupler providing positioning of the electrically conductive coupler relative to the electrodeless bulb, the conductor conducting radio frequency current producing a radio frequency potential on the electrically conductive coupler when the conductor is connected to a radio frequency voltage source, the radio frequency current producing a radio frequency electric field coupled to the fill.

2. The lamp assembly of claim 1, wherein:

an outer surface of the electrodeless bulb includes a cylindrical portion; and

the volume includes a cylindrical portion.

3. The lamp assembly of claim 1, wherein:

the axes are parallel.

4. The lamp assembly of claim 1, wherein:

the electrical conductor is secured to one turn of the multi-turn coil by the conductive connection at a central portion opposite the ends of the electrically conductive coupler.

5. A lamp assembly in accordance with one of claims 1-4 wherein:

radio frequency power is coupled to the filler symmetrically with respect to the center portion of the electrically conductive coupler.

6. The lamp assembly of one of claims 1 and 4, wherein:

a multi-turn coil is a wire with a polygonal cross-section.

7. The lamp assembly of claim 6, wherein:

the polygonal cross-section is triangular.

8. The lamp assembly of claim 6, wherein:

the polygonal cross-section is quadrilateral.

9. The lamp assembly of claim 6, wherein:

the polygonal cross-section is an equilateral polygon having more than four sides.

10. A lamp assembly, comprising:

an electrodeless bulb having an outer surface which is axisymmetric and contains a luminescent fill which emits light when excited by a radio frequency electric field coupled to the fill; an electrically conductive coupler comprising a plurality of turns of wire axially symmetric about the electrically conductive coupler, the plurality of turns of wire defining a volume at least partially enclosing the electrodeless bulb; a conductor secured to the center portion of the electrically conductive coupler by an electrically conductive connection, the electrically conductive connection with the electrically conductive coupler providing positioning of the electrically conductive coupler relative to the electrodeless bulb, the conductor conducting radio frequency current producing a radio frequency potential on the electrically conductive coupler when the conductor is connected to a radio frequency voltage source, the radio frequency current producing a radio frequency electric field coupled to the fill; and

a light reflecting case containing the electrodeless bulb, the electrically conductive coupler and the electrical conductor, the case comprising a central portion reflecting light emitted from the electrodeless bulb out of an opening in the case, an upper portion and a lower portion, each of the upper portion and the lower portion reflecting light emitted from the electrodeless bulb and light reflected from the other of the upper portion and the lower portion.

11. The assembly of claim 10, wherein:

the upper and lower portions include curved light reflecting grooves which fit the ends of the electrodeless bulb and are recessed in an outward manner with respect to the case so that groove surfaces are spaced apart from each other by a further distance than the remaining surfaces of the upper and lower portions which are not recessed, and the curved grooves reflect light emitted from the electrodeless bulb.

12. Assembly according to one of claims 10 and 11, comprising:

a housing in which the tank is mounted, and

at least one fan placed on one end surface of the housing, the fan sucking air from the one end surface of the housing and blowing the sucked air into contact with the outer surfaces of the portions of the case and the inner surface of the housing, and then blowing the air outward from the housing to blow the air into the case through the electrodeless bulb and the electrically conductive coupler and outward from the opening in the case.

13. The lamp assembly of claim 12, wherein:

the housing includes portions connected together to define said one end and includes another end surrounding the box opening, and each portion includes at least one opening located away from said one end, air being blown outwardly by the fan out of the opening after cooling said portions of the box and housing.

14. The lamp assembly of claim 13, wherein:

the housing comprises plastic.

15. The lamp assembly of claim 10, wherein:

the electrical conductor is secured to one turn of the multi-turn coil by the conductive connection at a central portion opposite the ends of the electrically conductive coupler.

16. The lamp assembly of claim 15, wherein:

radio frequency power is coupled to the filler symmetrically with respect to the center portion of the electrically conductive coupler.

17. A lamp assembly in accordance with claim 10 or 15 wherein:

the multi-turn coil is a wire having a polygonal cross-section.

18. The lamp assembly of claim 17, wherein:

the polygonal cross-section is triangular.

19. The lamp assembly of claim 17, wherein:

the polygonal cross-section is a quadrilateral.

20. The lamp assembly of claim 17, wherein:

the polygonal cross-section is an equilateral polygon having more than four sides.

21. The lamp assembly of claim 12, wherein:

a plurality of fans are located at one end.

22. An illumination system, comprising:

a plurality of lamp assemblies connected together, each lamp assembly comprising an electrodeless bulb having an axisymmetric outer surface and containing a light-emitting fill material which emits light when excited by a radio frequency electric field coupled to the fill material, an electrically conductive coupler comprising a plurality of turns of a coil axisymmetric along the electrically conductive coupler, the plurality of turns of the coil defining a volume at least partially containing the electrodeless bulb, an electrical conductor secured to a central portion of the electrically conductive coupler by an electrically conductive connection, the electrically conductive connection to the electrically conductive coupler providing positioning of the electrically conductive coupler relative to the electrodeless bulb, the electrical conductor conducting a radio frequency current producing a radio frequency electric potential on the electrically conductive coupler when the electrical conductor is connected to a radio frequency voltage source, the radio frequency current producing a radio frequency electric field coupled to the light-emitting fill material; and a light reflecting case containing the electrodeless bulb, the electrically conductive coupler and the electrical conductor, the case including a central portion, an upper portion and a lower portion, the central portion reflecting light emitted from the electrodeless bulb out of an opening in the case, and each of the upper portion and the lower portion reflecting light emitted from the electrodeless bulb and light reflected from the other of the upper portion and the lower portion.