WO2014141182A1

WO2014141182A1 - Microwave powered lamp

Info

Publication number: WO2014141182A1
Application number: PCT/IB2014/059812
Authority: WO
Inventors: Iginio Longo
Original assignee: Consiglio Nazionale Delle Ricerche
Priority date: 2013-03-15
Filing date: 2014-03-14
Publication date: 2014-09-18
Also published as: ITRM20130158A1

Abstract

A microwave powered lamp (1 ) provides an efficient and reliable heat removal while keeping the lamp compact, and includes: at least one transparent bulb (2) containing, in an inner space thereof, a material apt to be excited by microwave irradiation thereby emitting an electromagnetic radiation; at least one microwave coaxial antenna (7), placed outside said bulb (2), connected to a microwave source via a respective antenna lead (9), said bulb and said microwave coaxial antenna (7) being displaced in a close relationship to each other to allow the microwave excitation of said material, wherein the bulb is shaped so as to form an open channel (4) housing said at least one microwave coaxial antenna (7) and a refrigeration circuit wherein a refrigerating fluid is circulated, said open channel (4) defining a bulb refrigeration path, which is part of said refrigeration circuit, wherein the refrigerating fluid is allowed to circulate, and wherein said refrigeration fluid is a MW absorber liquid, namely water.

Description

MICROWAVE POWERED LAMP

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a microwave powered lamp, generally described as an electrodeless lamp wherein a plasma material is excited by radio frequencies, namely in the microwave frequency range, to emit light.

2. Description of the prior art

A lamp of this kind was described in US 4,586,115 A (Zimmerman et al.), wherein a lighting system includes a tubular transparent enclosure filled with a radiation responsive fluorescent material on its interior wall surface, and containing a gas responsive to radio frequency electromagnetic radiation to activate said fluorescent material. Generating means for generating radio frequency electromagnetic energy were provided, transmitting said radio frequency electromagnetic energy through waveguide conduits connected to resonant horns of said generating means.

US 6,445,138 B1 (Barry et al.) is related to a microwave powered lamp wherein a water cooled magnetron provides an air cooled microwave excited bulb with microwave energy through a wave guide.

US 6,608,443 B1 (Bae) describes a lighting apparatus using microwave energy, including a magnetron for generating microwave energy, a transparent bulb for generating lights by the microwave energy and a wave guide for connecting the magnetron and the bulb and transmitting the microwave energy generated in the magnetron to the bulb. Here, the magnetron is passively cooled through a finned case.

US 6,731 ,074 B2 (Suzuki) discloses an electrodeless lamp equipment comprising a microwave-generating source and a microwave chamber receiving the microwaves from antennas energized through appropriate and respective waveguides connecting the generating source and an antenna end.

US 7,095,163 B2 (Longo) is referred to a lamp without electrodes comprising one bulb having inside a material capable of being excited by means of microwaves irradiation, a recess formed in walls of the bulbs, accessible from the outside and a source of microwaves radiation inserted into said recess, namely an antenna energized by an antenna lead connected to means for exciting the microwave source.

It should be noted that, in the last example of prior art, neither a waveguide nor a cavity is used to excite the plasma material inside the bulb, thereby providing very compact lighting solutions. However, said recess is formed by a separate and isolated chamber, thus establishing an enclosure from which residual heat may be removed only through irradiation, a mechanism not completely reliable in case of huge powers involved, i.e. for having high lighting powers such as in the massive curing or for sterilization purposes.

WO 2007/048417 is related to a gas discharge device used for cleaning materials and equipments by a gas-discharge UV radiation, wherein air is used to cool the UV radiation source.

In DE 195 03 205 A, a device for emitting irradiating an alternate electromagnetic field has a wire electrode refrigerated by an air flow. Also in DE 198 52 524 A a device for emitting UV light and microwaves has a bulb which is externally refrigerated by an air flow generated through an enclosure chember.

However, in these examples, the refrigeration may be hampered by the poor thermal capacity of air, which is used because of the MW transparency thereof. For this reason, air or gas refrigeration can be used only to a limited extent, and wide passages and ducts should be provided, so as to exploit large volumes or high mass frlow rate of gaseous refrigerant.

SUMMARY OF THE INVENTION

The technical problems underlying the present invention is to provide a microwave energized lamp allowing to obviate to the drawbacks mentioned with reference to the prior art.

Such problem is solved by a lamp as above specified, including a transparent bulb filled with a material apt to be excited by microwave irradiation, thereby emitting an electromagnetic radiation; at least one microwave coaxial antenna, placed in an outer space with respect to the bulb, connected to a microwave source via a respective antenna lead, said bulb and said microwave antenna being displaced in a close relationship to each other to directly allow the microwave excitation of said material, wherein the bulb is shaped so as to form an open channel housing said at least one microwave antenna and a refrigeration circuit wherein a refrigerating fluid is circulated, said open channel defining a bulb refrigeration path, which is part of said refrigeration circuit, wherein the refrigerating fluid is allowed to circulate, and wherein said refrigeration fluid is a refrigerating liquid.

Preferably, the microwave antenna is a thin coaxial antenna, and the lead is a coaxial cable. The preferred refrigerant liquid is water, and the lamp may be also operated to water sanitization purposes.

It is understood that, although a refrigerant liquid basically is a MW absorber medium but considering the higher thermal capacity of a liquid and the improved heat transfer coefficient thereof, in the above defined lamp the refrigerant liquidi passage volumes can be substantially reduced without decreasing the refrigeration power and minimizing the thicknesses of the refrigerant layers passed through by electromagnetic radiations. In any case, the refrigerant liquid can be a MW absorber liquid.

This kind of lamp may be arranged for the production of a visible, UV, or IR, pulsed or continuous radiation, within either a spectral or wide band wavelength range, especially with high lighting or heating powers in a safe and reliable way, without losing the compactness and the efficiency of the microwaves lamps directly excited by a microwave antenna.

According to a preferred embodiment of the lamp according to the invention, the bulb is shaped so as said open channel is delimited by walls of the bulb itself, defining an enclosure of the open channel housing the microwave antenna and said inner space. In particular, the antenna and the open channel may have an elongated shape, with the antenna placed substantially coaxial to the open channel so as to leave a toroidal and an elongated space, as thin as possible, surrounding the microwave antenna wherein the MW absorber liquid is flown or injected.

The open channel can be a passing through hole within the bulb preferably having an elongated shape with two opposite ends, the passing through hole extending end-to-end along the bulb profile, with two apertures arranged as inlet and outlet of said refrigeration path. In particular, the bulb may be shaped so as to show an open duct passing through its body, i.e. it may have a tubular and toroidal shape.

With this configuration, the refrigerating liquid circulation may be either forced, with a pump, or natural, the open channel being arranged so as to operated as a chimney, e.g. in a vertical position, possibly immersed in a bath of refrigerating liquid.

In the passing through configuration, the open channel may house two microwave antennas respectively connected to a microwave source via corresponding antenna leads, said antennas being displaced head-to-head to form a continuous line, with said antenna leads being placed at the opposite ends of said open channel respectively, so as to save more space in realizing a more powerful lamp, having an increased length.

It is understood that the refrigerating liquid may be water, and the lamp as defined above, arranged to emit light in the UV field, can be used in a water sterilization device wherein infected water is continuously flown inside a chamber also housing one or more of the above lamps, the water acting as refrigerating fluid while it is sterilized by the UV light.

The energy supply of the above described lamp can be electronically controlled both in power and in frequency.

The above microwave energized lamp can be used both for illumination of closed or open spaces and as spectral or power lamp, for the treatment, e.g. the curing, of non-metal material, polymers or other biologically interesting material, for sterilization, for processes of chemical and photochemical catalysis, for photographic processes, for laser triggering, for spectroscopic applications and so on.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic sectional view of a first embodiment of a lamp according to the present invention;

Figure 2 shows a schematic sectional view of a second embodiment of a lamp according to the present invention;

Figure 3 shows a schematic sectional view of a third embodiment of a lamp according to the present invention;

Figure 4 shows a schematic sectional view of a fourth embodiment of a lamp according to the present invention; and

Figure 5 shows a schematic sectional view of a water sterilizer using a lamp according to the present invention

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawings and for all the embodiments herein described, a microwave energized lamp is generally indicated as 1. It comprises a bulb 2 defined by a continuous external thick wall 3, of a material substantially transparent to the visible, UV, IR radiation, and to the MW radiation as well, e.g. glass, possibly a heat resistant glass suitable for lamp bulbs.

The bulb 2 defines a closed chamber containing a microwaves irradiation excitable material, which may be a gas, a vapor, a dust, or a liquid, capable of emitting radiation by activation with other electromagnetic radiation and/or owing to hits between neutral or ionized particles (plasma atoms or molecules). The material can be put in with either a certain rate of vacuum or at a pressure higher than the atmospheric. A mixture of gases or vapors, or only a single atomic or molecular species can be used.

The bulb 2 generally has an elongated and tubular shape and it is shaped so as to form an open channel 4, in the embodiment of Figure 1 a blind hole coaxial to the bulb 2 with an aperture 5 at one end 6 of the bulb 2 and a blind hole 13 at the opposite end 6'.

Anyway, it is intended that the bulb 2 may have any other shapes, e.g. ellipsoidal, spherical and so on.

The lamp 1 then comprises one microwave coaxial antenna 7, which is connected to a microwave source 8 via a respective antenna lead 9.

This kind of antenna is substantially obtained from a coaxial cable having an inner wire conductor forming the core of the cable, an outer tubular conductor surrounding the inner wire conductor, a tubular insulator layer placed between the inner wire conductor and the outer tubular conductor to electrically separate them, and an external sheath covering the outer tubular conductor. Conventionally, this kind of cable is flexible and it can be bent or curved.

Both the active part of the coaxial cable, i.e. that part acting as antenna, and the antenna lead are made from said coaxial cable. The active coaxial antenna 7 is formed by the inner wire conductor possibly covered by a protection layer transparent to the generated electromagnetic waves, namely microwaves, i.e. for example by stripping off a section of the external conductor of a semi-rigid coaxial cable; the tubular insulator layer can be seen as a good protection layer. This arrangement is conventionally known as coaxial antenna and the coaxial antenna is placed outside the bulb. The antenna lead 9 is instead embodied by a section of coaxial cable connected to said microwave source, therefore comprising both the inner and the outer conductors.

The coaxial antenna 7, i.e. the active parte of said coaxial cable, could have in principle any length to cope with different shapes and lengths of the bulb 2. It is noted that, in all the embodiments of the invention, the coaxial antenna 7 is placed outside the bulb 2, i.e. in an outer space with respect to the bulb 2.

In general, the bulb 2 and said microwave coaxial antenna 7 are displaced in a close relationship to each other, so as to allow the direct microwave excitation of the target material inside the bulb chamber. As close relationship it is understood to be a closed configuration wherein the antenna lies adjacent to the bulb. Since both the bulb and the coaxial antenna may have an elongated shape, they may be placed the one inside the other. In this configuration, the microwave radiations emitted by the coaxial antenna directly irradiate the target material inside the bulb, with no interposition of any kind of further waveguide or cavity.

According to the present invention and in this first embodiment, the coaxial antenna 7 and a partial section of the antenna lead 9 are inserted inside the open channel 4, with spacers (not shown) arranged so as to leave a toroidal channel between the bulb walls and the coaxial antenna 7. A further protection sheath 10 made of a material transparent to the microwaves, envelopes the coaxial antenna 7 inside the open channel 4. The protection sheath 10 is obtained from said insulator layer covering the inner wire conductor of the coaxial antenna, and it is preferably made of PTFE.

In this configuration the target material inside the bulb 2 may be excited by microwaves at a continuous power of about 1 kW, at a frequency of 2.45 GHz. With these parameters, the temperature of the section inserted inside the open channel may destroy an ordinary coaxial cable, but costly special cable would not be operated in optimal temperature conditions. According to a rough estimation, given a microwave efficiency of 70% and an open channel of 8.0 cm and 8 mm inner diameter, the heat to remove is about 15 W/cm².

The lamp is then equipped with a heat removal system wherein a refrigeration circuit is flown with a refrigerating fluid, and said open channel is arranged to define a bulb refrigeration path, which is part of said refrigeration circuit, wherein the refrigerating fluid is allowed to circulate. In present embodiment, as shown in Figure 1 , in which the open channel 4 is a blind hole with one aperture 5, the refrigerating fluid is a refrigerating liquid, usually being a MW absorber medium and having a higher thermal capacity than that typical of gases (air etc.), the latter usually being transparent or quasi-transparent to MW.

In this embodiment and in the following ones, such a refrigerant liquid is water, which is injected at said aperture 5 by at least a nozzle, namely a single nozzle 11 formed at the end of a tube 12 inserted in the hollow toroidal space between coaxial antenna 7 and bulb 2. It is understood the nozzle may be positioned also at the aperture 5 itself or in any intermediate position along the open channel 4. In the present embodiment, the nozzle 1 1 is placed at the blind end 13 of the open channel 4. Then, water or any other suitable liquid is let flow outside the open channel 4 from the aperture part uncovered by said at least one nozzle, i.e. by the aperture area not crossed by the tube 12.

At the aperture 5 of the open channel 4, the antenna lead 9 has a microwave choke 14 or trap applied onto the outer conductor, blocking the propagation of microwaves reflected back from the coaxial antenna 7 due to incorrect impedance balancing. The microwave choke 14 substantially is a metallic bushing, preferably made of copper or brass, with a length of λ/4 (λ = wavelength of the microwaves travelling inside the choke) and a diameter greater than the cable diameter.

The choke 14 is mounted outside the outer conductor near and comprises a coaxial conducting portion of diameter higher than the external conductor; a conducting collar for connecting the coaxial conductor to the external conductor, arranged along the coaxial conducting portion. The choke 14 may be filled with a high-temperature resistant dielectric material, e.g. a tubular piece of ceramic, with a complex permittivity ε= e₀(e'-je") with ε"«1 and ε' » 1 - allowing the construction of a compact, i.e. short, choke 14, the effective wavelength A_eff being in this case

with λοο = wavelength of microwaves in vacuum, and the length of the choke 14, being equal to A_eff/4, is lower than λ₀₀ /4.

With reference to Figure 2, a second embodiment of the lamp 1 has a bulb 2 containing, in an inner space thereof, a material apt to be excited by microwave irradiation thereby emitting an electromagnetic radiation. The bulb 2 generally has an elongated and tubular shape and it is shaped so as to form a coaxial open channel 4 that, in the present embodiment, is a passing through hole extending end- to-end inside the bulb 2, with two opposite apertures 5, 5' at the opposite respective ends 6, and 6' of the bulb 2.

The lamp 1 then comprises one microwave coaxial antenna 7, which is connected to a microwave source 8 via a respective antenna lead 9. Preferably, both the coaxial antenna 7 and the lead 9 are made by a coaxial cable comprising an inner conductor, an insulator, and an outer conductor, while the active antenna section has further protection sheath 10, made of a material transparent to the microwaves, enveloping the coaxial antenna 7. The protection sheath 10 is preferably made of PTFE.

According to the present invention and in this second embodiment, the coaxial antenna 7 is inserted inside the open channel 4, with spacers (not shown) arranged so as to leave a toroidal channel between the bulb walls and the coaxial antenna 7.

The lamp is then equipped with a heat removal system wherein a refrigeration circuit is flown with a refrigerating liquid, namely water, and said open channel is arranged to define a bulb refrigeration path, which is part of said refrigeration circuit, wherein the refrigerating liquid is allowed to circulate.

In the present embodiment, in which the open channel 4 is arranged as a duct of said refrigeration circuit and the apertures 5, 5' thereof act as inlet and outlet of said refrigeration path.

Therefore, said apertures 5, 5' may be connected to a tubing of the heat removal system, in which a refrigerating liquid, preferably water, is circulated to remove the excess of heat at the antenna, possibly due to a forced circulation rather than a natural circulation.

With reference to figure 2, the whole bulb is immersed in a bath 21 of refrigerating water inside a transparent container 22, which is part of the refrigeration circuit. The coaxial antenna 7 and its protection sheath 10 are inserted through the container with an appropriate sealing 20. The container 22 is provided with a supply tube 23 comprising a circulation pump 24, an exhaust tube 25 and an external water reservoir 26 and/or a heat exchanger (not shown).

With reference to figure 3, a similar arrangement is disclosed, wherein the bulb 2 and the heat removal system are substantially the same than in second embodiment. However, this lamp 1 has two coaxial antennas 7 and 7' as previously described, respectively inserted into the open channel 4 through opposite aperture 5, 5'. The two microwave coaxial antennas 7, T are respectively connected to a microwave source 8, 8' via corresponding antenna leads 9, 9', said coaxial antennas 7, T being displaced head-to-head to form a continuous line, with said antenna leads 9, 9' being placed at the opposite ends 6, 6' of the bulb 2 and entering the container 22 at opposite side thereof, provided with corresponding sealing 20, 20'. It should be noted that the respective distal ends of said coaxial antennas 7, 7', facing to each other, leave a gap therebetween.

The fourth embodiment of Figure 4 is similar to the preceding second embodiments. However, the container 22 of the heat removal system is an open container filled with refrigerating liquid, preferably water. The tubular bulb 2, the coaxial antenna 7 and the open channel 4 are all vertically placed inside the bath 21.

In this way, the water circulation is promoted by a natural convection inside the bath and the open channel 4 is placed so as to be operated substantially like a chimney, achieving a chimney effect from the bottom aperture 5' and the top aperture 5 of the open channel 4.

With reference to Figure 5, the use of a lamp 1 according to the invention and substantially corresponding to the second embodiment is illustrated.

In a sterilization device 30, a reservoir 32 is supplied with infected water through an inlet port 33. The reservoir is also fed with air or oxygen through a nozzle 34. Then, the reservoir has an outlet port 35 for the outlet of purified water and an upper vent 36, for the discharge of gases from the reservoir 32.

At the inlet port 33, the sterilization device has a filter 37, for the capture of all the solid residues. The sterilization device 30 also includes a UV lamp 1 , immersed in the water coming from the inlet port 33.

The lamp 1 is substantially that described in connection with the second embodiment, but the heat removal system is simply replaced by the water circulation inside the reservoir 32. Therefore, the lamp 1 includes a tubular bulb 2 with a passing through open channel 4 housing a microwave an inner conductor, an insulator, and an outer conductor, with a sheath covering coaxial antenna 7 connected to a microwave source 8 via a microwave lead 8. The coaxial antenna 7 in inserted within the open channel 4, leaving a toroidal space sufficient for the water circulation.

The lamp 1 is arranged so as to irradiate both the filter 37 and the bath 31 , thus operating a sterilization process for the filter renovation and for obtaining sterilized water. Further, if oxygen is injected in the bath 31 , the lamp 1 also operates as an ozonizer and produce free radicals, increasing the sterilization effect.

From the above described embodiment, it can be understood that the open channel need not to be coaxial to the bulb. It should be further noted that the passing- through open channel improves the mechanical strength of the bulb and allows an effective circulation of the refrigerating liquid.

Further, the water refrigeration can be used with a phase transition, which should keep the temperature of the hot surface at 100°C. Then, a thick water layer can improve the so called impedance-matching between antenna and bulb, since the water can eliminate or mitigate possible residual electromagnetic resonances.

The lamp is capable of emitting radiation with a line spectrum, a band spectrum or mixed spectrum, in a wide range of wavelengths. It works without any electrodes in contact with the particles that emit the radiation, in a continuous or pulsed way. The spectral composition of the radiation as emitted depends from the substances used for filling the bulb, their quantity ratio, as well as the power and the frequency of the microwaves used for excitation.

To the above described microwave powered lamps a man skilled in the art, in order to meet specific requirements and contingencies, may bring further modifications, all falling within the scope of protection of the present invention, as defined by the annexed claims.

Claims

1. Microwave powered lamp (1 ), including:

• at least one transparent bulb (2) containing, in an inner space thereof, a material apt to be excited by microwave irradiation thereby emitting an electromagnetic radiation;

• at least one microwave coaxial antenna (7) connected to a microwave source via a respective antenna lead (9) , placed outside the bulb (2), said bulb (2) and said microwave coaxial antenna (7) being displaced in a close relationship to each other to allow the microwave excitation of said material, wherein the bulb (2) is shaped so as to form an open channel (4) housing said at least one microwave coaxial antenna (7) and a refrigeration circuit wherein a refrigerating fluid is circulated, said open channel (4) defining a bulb refrigeration path, which is part of said refrigeration circuit, wherein the refrigerating fluid is allowed to circulate, and wherein said refrigeration fluid is a refrigerating liquid.

2. Microwave powered lamp (1 ) according to claim 1 , wherein said at least one bulb (2) is shaped so as said open channel (2) is delimited by walls of the bulb (2) separating an enclosure of the open channel (4) housing the microwave coaxial antenna (7) and said inner space.

3. Microwave powered lamp (1 ) according to claim 2, wherein both said at least one microwave coaxial antenna (7) and the respective open channel (4) have an elongated shape, the microwave coaxial antenna (7) being substantially coaxial to the open channel (4) leaving a toroidal elongated space surrounding the microwave coaxial antenna (7).

4. Microwave powered lamp (1 ) according to claim 3, wherein said open channel (4) is a blind hole with one aperture (5), the refrigerating liquid being injected at said aperture by at least a nozzle, and being let to flow outside the open channel (4) from the aperture part uncovered by said at least one nozzle (11).

5. Microwave powered lamp (1) according to claim 3, wherein said open channel (4) is a passing through hole, the bulb having an elongated shape with two opposite ends (5, 5'), the passing through hole extending end-to-end inside the bulb (2).

6. Microwave powered lamp (1) according to claim 5, wherein said open channel (4) has two apertures (5, 5') at the opposite respective ends of the bulb (2), arranged as inlet and outlet of said refrigeration path.

7. Microwave powered lamp (1) according to claim 6, wherein said open channel (4) is arranged as a duct of said refrigeration circuit.

8. Microwave powered lamp (1 ) according to claim 7, wherein the refrigerating liquid is flowed into the open channel (4) by forced circulation.

9. Microwave powered lamp (1 ) according to claim 8, wherein the open channel (4) houses two microwave coaxial antennas (7, 7') respectively connected to a microwave source via corresponding antenna leads (9, 9'), said microwave coaxial antennas (7, 7') being displaced head-to-head to form a continuous line, with said microwave coaxial antenna leads being placed at the opposite ends of said open channel (4) respectively.

10. Microwave powered lamp (1 ) according to claim 7, wherein the refrigerating liquid is flowed into the open channel (4) by natural circulation, the open channel being arranged so as to operate as a chimney.

11. Microwave powered lamp (1) according to any of the preceding claims, wherein the refrigerating liquid is water.

12. Use of the microwave powered lamp (1) of claim 11 in a sterilization device, wherein the water used as refrigerating liquid is the same water to be sterilized.