WO2014141184A1

WO2014141184A1 - Packed microwave powered lamp

Info

Publication number: WO2014141184A1
Application number: PCT/IB2014/059814
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: ITRM20130160A1

Abstract

A microwave powered lamp (1 ), having a simple structure is provided, allowing a flexible operation of the lamp assembly, taking advantage of the light emitted by the excitation due to the so called microwave near field, includes: one or more transparent tubular bulbs (2) containing, in an inner space thereof, a material apt to be excited by microwave irradiation thereby emitting an electromagnetic radiation; one or more microwave coaxial antennas (3) respectively connected to a microwave source via corresponding antenna leads (4), said bulbs (2) and said microwave antennas (3) being displaced in a close relationship to each other to allow the microwave excitation of said material, wherein one or more bulb (2) and/or one or more microwave coaxial antenna (3) are present in a single assembly of bulb(s) and antenna(s) packed together, wherein coaxial antenna(s) (3) and bulb(s) (2) are placed adjacent to each other, the coaxial antenna(s) (3) being placed in an outer space with respect to the bulbs (2) and being operated to excite the material apt to be excited along the overall length of the bulb(s) (2) and the coaxial antenna(s) being kept at a minimum distance from the respective bulb(s) so as the excitation is started and sustained by the near field region of the coaxial antenna(s).

Description

PACKED MICROWAVE POWERED LAMP

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a packed 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.

This kind of lamp includes an assembly of coaxial microwave antenna(s) and related tubular bulb(s) packed together to form a lamp.

2. Description of the prior art

This kind of electrodeless lamp is generally known from US 5,013,976 A, US 4,189,661 A and US 4,266,167 A.

A lamp of this kind was described in US 4,586,115 A (Zimmerman et al.), wherein a lighting system includes tubular transparent enclosures 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. The gas is excited through a coaxial antenna supplied by generating means for generating radio frequency electromagnetic energy; the antenna is put inside the housing at a certain distance from the respective enclosure, so as to form a lamp unit in said lighting system.

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 one or two antennas energized by an antenna lead connected to means for exciting the microwave source.

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. Said antennas are located at the ends of an elongated bulb, therefore acting only on one end portion of the bulb itself. Further disclosures, see for instance US 8,258,687B, US 7,566,890 B, US 5,216,322 A, US 5,113,121 A, US 2009/045750 A and US 3,911 ,318 A show device wherein microwaves are driven at a bulb through a waveguide, i.e. without using a coaxial antenna in relationship with at least one bulb but outside the bulb itself. 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.

It should be noted that, in the last example of prior art, it is not possible to obtain a flexible operation lamp having a simple configuration.

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 microwave excited lamp as above specified, comprising one or more transparent tubular bulbs containing, in an inner space thereof, a material apt to be excited by microwave irradiation thereby emitting an electromagnetic radiation; and one or more microwave coaxial antennas respectively connected to a microwave source via corresponding antenna leads, wherein said bulbs and said microwave antennas are displaced in a close relationship to each other to allow the microwave excitation of said material, and wherein one or more bulb and/or one or more microwave antenna are present in a single assembly of bulb(s) and antenna(s) packed together, antenna(s) and bulb(s) being placed adjacent to each other, the antenna(s) being placed in an outer space with respect to the bulbs and being operated to excite the material apt to be excited along the overall length of the bulb(s), and the antenna(s) being kept at a minimum distance from the respective bulb(s) so as the excitation is started and sustained by the near field region of the antenna(s)

In the above lamp, a simple structure is provided allowing a flexible operation of the lamp assembly, possibly taking advantage of the light emitted by the excitation due to the so called microwave near field.

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.

The antenna may be straight or wound around one or more bulbs according to a helical path.

According to preferred embodiments of the invention, the lamp comprises more than one bulb and/or more than one microwave antenna are present in a single assembly of bulb(s) and antenna(s) packed together. Namely, at least two bulbs and one antenna are present and the bulbs may be arranged so as to surround the antenna and/or have transverse sections of different area.

Here and in the following, bulb means a single transparent enclosure delimited by walls, defining a single chamber. Many bulbs may be packed together or be formed by common walls separating each other within a container having outer walls.

Otherwise, at least two antennas and one bulb are present, the antennas being arranged so as to surround the bulb.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows three different embodiment of a lamp according to the invention, namely: (a) a simpler embodiment with one bulb and one Microwave antenna, (b) a further embodiment with a dual bulb and one microwave antenna; and (c) a single bulb lamp with a helicoidal microwave antenna;

Figure 2 shows a schematic transverse view of a fourth embodiment of a lamp according to the present invention, with a multiple bulb configuration;

Figure 3 shows a schematic transverse view of a fifth embodiment of a lamp according to the present invention, with a multiple MW antenna configuration;

Figure 4 shows a schematic sectional view of said first embodiment of including a MW reflecting mirror;

Figure 5 shows a schematic sectional view of said first embodiment of including a partially shielded MW antenna; and

Figure 6 illustrates the effect of a dipole acting as MW antenna in the near field and in the far field regions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawings and for all the embodiments herein described, a microwave energized lamp is generally indicated as 1. According to a simpler embodiment, it comprises (Figure 1(a)) an elongated tubular bulb 2 defined by a continuous external thick wall 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 elongated bulb 2 generally has a straight and tubular shape.

The elongated bulb 2 defines a single 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.

A possible bulb filling may be made with Argon at low pressure (2÷3 mmHg) and vapours of Mercury (Hg).

The lamp 1 of Figure 1 (a) then comprises one microwave antenna 3, which is connected to a corresponding microwave source (not shown) via a respective antenna lead 4.

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 made of a dielectric material placed between the inner wire conductor and the outer tubular conductor to electrically separate them. Usually, this kind of cable is flexible or semi-rigid 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 coaxial antenna is formed by stripping off a section of the external conductor, the inner conductor possibly being covered by a protection layer transparent to the generated electromagnetic waves, namely microwaves; the tubular insulator layer can be seen as a good protection layer. In a typical coaxial dipole antenna configuration the length of the stripped-off section is λ/2, λ being the wavelength of the working microwaves.

The respective antenna lead is instead embodied by a section of coaxial cable connected to said microwave source, comprising both the inner and the outer conductors. The coaxial antenna is placed outside the bulb. The coaxial antenna could have in principle any length to cope with different shapes and lengths of the bulb or bulbs 2. Here and in all the embodiments of the present invention, a single coaxial antenna or more coaxial antennas are placed in an outer space with respect to one or more bulb.

In the embodiment of Figure 1(a), the coaxial antenna 3 has a straight profile, and it is kept adjacent to the bulb 2, having substantially the same length, i.e. the coaxial antenna 3 can be operated to excite the material apt to be excited along the overall length of the bulb 2.

According to Figure 1(b), two different bulbs 2 are kept adjacent to one antenna 3; and according to Figure 1 (c) one antenna 3 is wound around one bulb 2 according to a helical path.

In this invention, the or each bulb 2 is excited by the external coaxial antenna 3 at microwave frequencies, arranged near or around the bulb. The plasma discharge in the gas filling is produced and sustained by the electromagnetic field surrounding the dipole coaxial antenna in the so called near field region. It is well known that in the near field region the amplitude of the quasi stationary microwave electric field of the half wave dipole antenna depends on the radial distance as r^"2 and r^"3. Accordingly, working with a few tens W at 2450 MHz, the amplitude of the electric field at e.g. 4 mm of distance is of the order of 10² V/cm, i.e. sufficient to produce and sustain a plasma discharge in a low pressure Ar + Hg bulb.

As explained in the electromagnetism theory regarding the operation of thin dipole radiating coaxial antennas, i.e. having a diameter d « λ, wherein λ is the wavelength of the exciting radiation, the electromagnetic field in the active region surrounding the antenna, according to a spherical coordinate system with centre at the radiating excitation point, is the described by the following formulae (see Ramo S. et al, Fields and Waves in Communication Electronics, J Wiley & NY 1993, 3^rd Ed., p 590):

kh

Ε _θ 4 + where k = 2π/λ is the wave vector, r is the radial coordinate, ω is the microwave angular frequency, η = 120π is the space impedance, ε and μ represent the magnetic permittivity and the permeability of the medium, l₀ is the electric current in the antenna and h (h « λ) is the coaxial antenna length.

For the description of the interaction between field emitted by the coaxial antenna and gas (plasma) inside the bulb, the space around the coaxial antenna can by splitted into two regions (Figure 6).

The region near the coaxial antenna, the so-called near field region, is a cylinder with radius r « λ/2π. In this region, the electromagnetic field is not irradiated and it may be describe as a quasi-stationery wave system, the waves moving to and from parallel to the antenna axis, with a high energy density (energy per volume unit). In this region, the electric field, in the spherical coordinate system (r, θ, cp) of the above formulae, has only two components (r, Θ), the magnetic field has only the azimutal component (φ) and the field polarization is generally elliptical in function of the place.

The electric field amplitude in this near field region, i.e. immediately outside the antenna, is very high, depending upon the quadratic or cubic terms r^"2, r^"3, and rapidly decreasing at the rise of r. Passing from the near field region to the far field region, i.e. at distance r » λ/2ττ, the radial component of the electric field vanishes, and the dependence of the amplitude of E and H field, which are perpendicular to each other in this region and perpendicular to the propagation direction, is that of a transverse plane electromagnetic wave, with field amplitudes decreasing in inverse relation to the distance.

The separation between these regions is not clear, but an intermediate region exists wherein the near field is no more stable and wherein the irradiation starts.

According to the above considerations, with a quartz bulb (e_rei ~ 3,78) with thin walls (~ 1 mm), within a radial distance of few mm from a thin antenna configured as a dipole λ/2 and supplied with 1 W at 2,45 GHz, a filed E~10² V/cm is found, sufficient to start and sustain a lighting plasma in a Ar and Hg vapour mixture at low pressure. Otherwise, with the bulb placed far from the near field region and operating at 2,45 GHz, at few cm of distance from the antenna, a very larger power would be required to start and sustain the plasma discharge.

Each coaxial antenna lead 4 has a microwave choke 14 or trap applied onto the outer conductor, blocking the propagation of microwaves reflected back from the respective coaxial antenna, 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 microwaves) and a diameter greater than the cable diameter.

The choke 14 is mounted outside the outer conductor near and comprises a co-axial 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 in the choke A_e/r being in this case

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

According to Figure 2, several bulbs 2 having a circular transverse section with different diameters, i.e. a transverse section having a different area, surround a single antenna 3. The bulbs may be filled with gases with different parameters to produce different kinds of light. It is understood that this configuration is only one among the many possible configurations which can be used to achieve this multi- bulb lamp.

According to Figure 3, several (three) antennas 3 surround only one bulb 2: each coaxial antenna 3 determines a plasma lighting region 10 close to the coaxial antenna 3 inside the bulb 2; the antennas 3 may be simultaneously or alternatively operated.

According to Figure 4, a configuration already shown at Figure 1 (a) further has a concave mirror shield 5 surrounding both the bulb 2 and the coaxial antenna 3, the bcoaxial antenna 3 being placed between the bulb and the mirror shield. In this configuration, both the near field region and the far field region may be alternatively used. In any case all the microwaves are blocked by the shield 5 and a metallic network 6 may close the open side of the shield 5 to block the microwaves but not the generated light. The coaxial antenna 3 is powered by a microwave source 7 through an antenna lead 4. According to Figure 5, in a configuration already shown at Figure 1 (a), the coaxial antenna is very long and has spaced holes 9 formed through the outer conductor 8 thereof (shown enlarged), the holes 9 being positioned so as to face the bulb 2.

In this embodiment, microwaves leak from the holes 9 to excite the material inside the bulb 2, each determining a plasma lighting region 10. The coaxial antenna 3 is powered by a microwave source 7 through an antenna lead 4.

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:

• one or more transparent tubular bulbs (2) containing, in an inner space thereof, a material apt to be excited by microwave irradiation thereby emitting an electromagnetic radiation;

• one or more microwave coaxial antennas (3) respectively connected to a microwave source via corresponding antenna leads (4),

said bulbs (2) and said microwave coaxial antennas (3) being displaced in a close relationship to each other to allow the microwave excitation of said material, wherein one or more bulb (2) and/or one or more microwave antenna (3) are present in a single assembly of bulb(s) and coaxial antenna(s) packed together,

wherein antenna(s) (3) and bulb(s) (2) are placed adjacent to each other, the coaxial antenna(s) (3) being placed in an outer space with respect to the bulbs (2) and being operated to excite the material apt to be excited along the overall length of the bulb(s) (2) and the antenna(s) being kept at a minimum distance from the respective bulb(s) so as the excitation is started and sustained by the near field region of the coaxial antenna(s).

2. Microwave powered lamp (1) according to claim 1 , wherein more than one bulb (2) and/or more than one microwave coaxial antenna (3) are present in a single assembly of bulb(s) and coaxial antenna(s) packed together.

3. Microwave powered lamp (1) according to claim 2, wherein at least two bulbs

(2) and one microwave coaxial antenna (3) are present.

4. Microwave powered lamp (1) according to claim 3, wherein the bulbs (2) are arranged so as to surround the microwave coaxial antenna (3).

5. Microwave powered lamp (1 ) according to claim 2, wherein the bulbs (2) have transverse sections of different area.

6. Microwave powered lamp (1) according to claim 1 , wherein one microwave coaxial antenna (3) is wound around one or more bulbs (2) according to a helical path.

7. Microwave powered lamp (1 ) according to claim 2, wherein at least two microwave coaxial antennas (3) and one bulb (2) are present, the coaxial antennas

(3) being arranged so as to surround the bulb (2).

8. Microwave powered lamp (1) according to claim 7, wherein each microwave coaxial antenna (3) determines a plasma lighting region (10) close to the coaxial antenna (3) inside the bulb (2); the coaxial antennas (3) being simultaneously or alternatively operated.

9. Microwave powered lamp (1) according to claim 1 , further having a concave mirror shield (5) surrounding both the bulb (2) and the coaxial antenna (3), the coaxial antenna (3) being placed between the bulb (2) and the mirror shield (5) so as to block all the microwaves.

10. Microwave powered lamp (1) according to claim 1 , wherein one microwave coaxial antenna (2) has spaced holes (9) formed through the outer conductor (8) thereof and facing the bulb (2).