GB2469186A

GB2469186A - A delay line for applicators of electrodeless gas discharge lamps

Info

Publication number: GB2469186A
Application number: GB1005107A
Authority: GB
Inventors: Rainer Kling; Michael Meisser; Klaus Stockwald
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2009-03-31
Filing date: 2010-03-26
Publication date: 2010-10-06
Anticipated expiration: 2030-03-26
Also published as: GB201005107D0; GB2469186B

Abstract

An electrodeless high intensity discharge lamp (EHID) comprises a bulb 401 containing a fill mixture for generating a light emission when excited by microwave energy, at least two applicator arms 403 for coupling the microwave energy to the fill mixture and a delay line for creating a phase delay between the applicator arms. The delay line comprises a stripline structure 405 to reduce the size of the lamp. The stripline structure may comprise a pair of parallel ground planes separated by a dielectric layer, and at least one conductor embedded within the dielectric layer. The base 407 of the stripline structure may be mounted on a PCB 409 and a reflector 411 may be mounted and connected to the PCB.

Description

A DELAY LINE FOR APPLICATORS OF ELECTRODELESS

GAS DISCHARGE LAMPS

Technical area The invention relates to the field of electrodeless high intensity discharge lamps (EHID). In particular, but not exclusively it relates to delay line for applicators of EHID intended for general illumination or photo-optical applications.

Background art

Plasma lamps are well known, for example US 2009 146543. These plasma lamps are based on electrodeless high pressure discharge lamps or electrodeless high intensity discharge lamps (EHID).

Other types of plasma lamps are disclosed by Koch, B. (2002). Experimentelle Untersuchungen an neuartigen kompakten Mikrowellenresonatoren zur elektrodenlosen Anregung von Hochdruckentladungslampen. Uchttechnisches Institut.

Karlsruhe, Universitat Karlsruhe; Dissertation.

A device for plasma excitation by means of microwaves is disclosed by DE-A 103 35 523.

Details for EHID Lamps with a Microwave Power Coupler are disclosed by CA-A 2 042 258 and CA-A 2042251.

For operating these conventional EHID lamps, high electric field densities must be coupled into the lamp volume, containing a fill mixture, to excite the fill and generate high intensity light output. The electric field is applied across the lamp volume (or bulb) by applicator arms. To allow high field strengths between the different field applicators, a phase delay between the applicator arms must be generated.

However, at operation frequencies below 1 GHz the geometric length of the delay lines is quite long, in the range of 30 cm. The use of dielectric materials such as aluminium oxide reduces this geometric length only by a factor of JI7 Typical values forsr of low loss materials are 5 to 10 and therefore the length is reduced by approximately a factor of 3.

The relatively large dimensions of the delay lines, thus, make it difficult to make lamps of reduced size and costs and due to the conventional arrangement, EMI is not well damped.

Referring to CA-A 2 042 258 and CA-A 2 042 251 delay lines for EHID lamps can be built using delay lines on a substrate. These structures use only two dimensions and therefore require a lot of space. The applicator structures of (Koch 2002) and OF-A 103 523 use four applicator arms, using four delay lines. At frequencies above 1 GHz delay lines in air are used. Therefore, it remains difficult to reduce the size and costs of such lamps and reduce EMI.

Summary of the invention

The invention seeks to provide an improved more compact EHID lamp.

This is achieved according to an aspect of the present invention by an electrodeless high intensity discharge lamp (EHID) comprising a bulb containing a fill mixture for generating a light emission when excited by microwave energy and at least two applicator arms for coupling the microwave energy to the fill mixture, the at least two applicator arms being separated by at least one delay line, the at least one delay line comprising a stripline structure.

The stripline structure provides reduced dimensions for the delay line even at longer wavelengths.

To further reduce the size of the delay line, the stripline structure may be stacked with conductors of different layers being connected using vias. The stripline structure may be flexible so that the structure can be curved to reduce dimensions of the delay lines even further.

At least a part of at least one side wall of the stripline structure may be metallised to improve shielding against EMI.

The applicator arms may be connected to the delay line in the plane of the layers of the stripline structure. This helps to reduce the size further as well as maximise creepage distances in order to prevent electric flashover. This also enables a compact design in fitting a reflector, a PCB etc. For example, the reflector may be mounted onto the PCB and surround the stripline structure, applicator arms and bulb. The reflector may be partially electrically conductive to provide EMI shielding and/or partially thermally conductive to act as a heat sink for the lamp.

Description of the drawings

For a more complete understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings, wherein: Figures 1 a to 1 c are a simple schematic of examples of lamp arrangements; Figures 2a and 2b are simple schematics a delay line according to embodiments of the present invention; Figure 3 is a simple schematic of a stacked stripline structure according to an embodiment of the present invention; Figures 4a to 4c are simple schematics of assembly of a EHID lamp according to an embodiment of the present invention; Figure 5 is an example of a stripline structure according to an embodiment of the present invention; and Figure 6 is an example of a stacked stripline structure according to another embodiment of the present invention.

Detailed Description of Embodiments

Figures la to lc show different examples of arrangements of EHID lamps. In figures la to I c the bulb 101 contains a fill mixture and is coupled to 4 virgate applicator arms 103_i, 103_2, 103_3, 103_4 over a ground plane 107. The applicator arms 103_I, 103_2, 103_3, 103_4 are coupled to a microwave probe 105 (shown in Figure ic only).

The microwave probe 105 supplies microwave energy to the applicator arms 103_i, 103_2, 103_3, 103_4 to create an electric field within the bulb 101 to excite the fill mixture of the bulb 101 to cause itto emit light.

In Figure la, the applicator arms 103j1, 1032, 103_3, 103_4 are in a single plane surrounding the bulb 101. In Figures lb and icthe applicator arms 103_I, 103_2, 1 03_3, 1 03_4 extend downwardly and outwardly from the bulb 101.

Embodiments of the delay line of the present invention are shown in Figures 2a and 2b.

The delay line is connected to a bulb 201, as shown here, is spherical but it can be appreciated that any shape bulb may be incorporated for example pill or pillow-shaped.

The bulb 201 is filled with a mixture, for example, organic compounds including at least one of acetylene, methane, propane, butane and acetylides. The bulb 201 is coupled to the delay line via at least two applicator arms 203-1, 203, 203_3, 203_4. Although 4 applicator arms are shown here, it can be appreciated that any number of 2 or more applicator arms may be utilised.

The applicator arms 203-1, 203_2, 203_3, 203_4 extend outwardly and downwardly.

The distal end of each applicator arm 203-1, 203_2, 203_3, 203_4, remote from the bulb 201 are interconnected via a delay line. The delay line comprises a stripline structure, for example, as shown in Figure 5. The stripline structure 500 comprises a central conductor 501 embedded in a dielectric layer 503. The dielectric constant of the dielectric layer 503 is greater than 2, less than 11. The dielectric layer 503 is sandwiched between ground planes 505. At least one sidewall 507 may be metallised to improve EMI shielding of the stripline structure 500.

To further reduce the size of the delay line, the stripline structure may be stacked as shown in Figures 3 and 6. Figure 6 shows 3 striplines 601, 603, 605 stacked to form the stripline structure 600. Although 3 striplines are illustrated here, it can be appreciated that any number of striplines may be stacked as required. The first stripline 601 comprises a first ground plane 607 and a second ground plane 609 either side of a dielectric layer 611 in which the conductor 613 is embedded. A via 615 connects the conductor 613 and the ground plane 607. The second stripline 603 shares the ground plane 609 of the first stripline 601. The second stripline 603 comprises a conductor 617 in a dielectric layer 619 and a second ground plane 620.

The via 621 connects the conductor 613 of the first stripline 601 to the conductor 617 of the second stripline 603. The third stripline 603 shares a ground plane 620 with the second stripline 603. The third stripline 603 further comprises a conductor 623 embedded in a dielectric layer 625 and a ground plane 627. A via 629 connected the conductor 617 of the second stripline 603 and the conductor 623 of the third stripline 605.

The sidewalls, or at least part of the sidewalls 631, 633 of the structure 600 are metallised.

As shown in Figures 2a, 2b and in more detail in Figure 3, the conductors 301, 303 of first and second stripline 307, 309 are connected by a via 305, The conductors 3011 303 are extended to the base 311 of the stripline structure 300 to connect to a PCB (not shown here). The top surface 313 of the stripline structure 300 has four points 315_I, 315_2, 315_3, 315_4 atwhich the conductors 301, 303 extend to the top surface 313 of the stripline structure 300 to couple with the distal end of each applicator arm 203-1, 203_2, 203_3, 203_4. The applicator arms are therefore connected in the plane of the layers of the stripline structure 300 providing a compact design having the required delay with low optical shadowing causing a resonant mode having at least one electric field maximum to excited the plasma for light emission.

As shown in Figure 2a, the dielectric materials may be flexible to provide a curved structure or rigid, as shown in Figure 2b, for a more cubic arrangement.

Figures 4a and 4c show assembly of a EHID lamp according to an embodiment of the present invention.

As described in detail above, the lamp comprises a bulb 401 coupled to applicator arms 403 to a stripline structure 405. The base 407 of the stripline structure 405 is mounted and connected to a PCB 409. A reflector 411 is mounted on the PCB 409 substantially surrounding the bulb 401, applicator arms 403 and stripline structure 405.

The reflector 411 is at least partially conductive coated or is made of electrical and thermal conductive material and connected with the (lamp's) ground to obtain a shielding effect, cancelling EMI noise. The reflector 411 is at least partly made of thermally conductive material which serves as a heat sink for the bulb 401, stripline structure 405 and power electronics on the PCB 409. The reflector 411 has a good thermal connection with the FOB 409 and the stripline structure 405.

The whole lamp may comprise the following features: (a) a waveguide having a body of a preselected shape and dimensions, the body comprising at least one dielectric material and having at least one surface determined by a waveguide outer surface, each said material having a dielectric constant greater than approximately 2; (b) a first microwave probe positioned within and in intimate contact with the body, adapted to couple microwave energy into the body from a microwave source having an output and an input and operating within a frequency range from about 0.25 GHz to about 30 GHz at a preselected frequency and intensity, the probe connected to the source output, said frequency and intensity and said body shape and dimensions selected so that the body resonates in at least one resonant mode having at least one

electric field maximum;

(c) the body having a lamp chamber depending from said waveguide outer surface and determined by a chamber aperture and a chamber enclosure determined by a bottom surface and at least one surrounding wall surface; (d) a transparent, dielectric bulb within the lamp chamber; and (e) a fill mixture contained within the bulb which when receiving microwave energy from the resonating body forms a light-emitting plasma.

Although embodiments of the lamp of the present invention have been illustrated in the accompanying drawings and described in the foregoing description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous variations, modifications without departing from the scope of the invention as set out in the following claims.