DE20304806U1 - Radar reflection damping double glazing - Google Patents

Description

DURM & DURM

PATENT ATTORNEYS
MOLTKESTRASSE 45 76133 KARLSRUHE

B 5692/02-Gbm
June 5, 2003

BGT Bischoff Glastechnik GmbH & Co. KG
EADS Germany GmbH

Radar reflection-attenuating double glazing

Description

The invention generally relates to radar reflection-attenuating double glazing, in particular for buildings.

The ever-increasing air traffic and the increasing height of buildings near airports increase the risk that air traffic safety will be compromised by reflections on building facades. Radar signals reflected from buildings near airports and in flight paths can lead to dangerous phantom targets on air traffic controllers' screens. In order to reduce such reflected radar signals or, if possible, to eliminate them completely, radar reflection-damping glazing is required. The higher the building and the larger the glazed areas of the facade, the greater the requirements for the optical, thermal and electrical properties of the prescribed radar reflection-damping glazing.

Radar reflection-attenuating glazing cannot be produced as standard. The radar situation must be individually examined for each individual building and a radar technical report obtained in order to determine the parameters of the glazing. In particular, the polarization direction and the wavelength of the incident radar beams must be taken into account.

The patent specification DE 42 27 032 Cl describes a radar-absorbing or attenuating double glazing, consisting of an outer pane and an inner pane. The inner pane is provided with a radar-reflecting, optically transparent layer. A layer of wire-shaped electrical conductors arranged parallel to one another is embedded in the outer pane. Radar rays entering from the outside are partially reflected in the area of the outer pane and the rest reflected on the inner pane and thus - according to the functional principle of the so-called Jaumann absorber - caused to be extinguished. The distance between two adjacent conductors is between 10 and 30 mm; the wire diameter is in the range of less than 0.5 mm. The outer pane can also consist of two glass panes joined together, between which the wire-shaped conductors are inserted.

The patent specification DE 43 40 907 Cl describes a radar-absorbing window glazing consisting of double glazing in which the layer in the area of the outer pane consists of parallel, alternating, strip-like first and second partial surfaces. The first partial surfaces can be applied, for example, by vapor-depositing metal layers such as silver or gold. In the simplest case, the second partial surfaces are left free; otherwise, an optically effective layer, such as a sun protection made of metal oxides, can be vapor-deposited.

The patent specification DE 199 29 081 C2 describes a radar-absorbing laminated glass pane which consists of at least three glass panes connected to one another. A first layer of parallel, thread-like electrical conductors is arranged between the outer pane and the middle pane. A second layer of thread-like electrical conductors is provided between the middle pane and the inner pane.

In practice, radar-absorbing double glazing with an outer pane that is designed as a laminated glass pane consisting of two glass panes connected to one another has proven to be effective. Thin tungsten wires are inserted between the two glass panes of the laminated glass pane. The two individual panes are then pressed together to form the laminated glass pane using a transparent plastic adhesive film. Due to the lateral offset of the highly elastic plastic film, uncontrolled lateral distortions of the individual wires occur; in particular, the individual wire-shaped conductors are no longer completely parallel to one another at the end. This affects not only the electrical but also the optical properties of the finished laminated glass pane; the actual radar attenuation falls significantly short of the theoretically achievable values.

If strip-shaped layers of gold or silver are vapor-deposited onto the outer pane, it is difficult to achieve the required precision and reproducibility. The vapor-depositing of gold or silver is also a very complex and expensive technique.

It has not yet been possible to permanently fix thin wires to the surface of a glass pane.

The present invention therefore relates in particular to a radar reflection-damping double glazing in which the outer pane carries a layer of thin electrical conductors arranged parallel to one another which partially reflects radar rays, and the inner pane is provided with a radar-reflecting layer, wherein the arrangement of the conductors on the outer pane and their distance from the radar-reflecting layer on the inner pane is selected depending on the polarization direction and the wavelength of the radar rays such that the respective reflected portions of the radar rays are superimposed on one another in antiphase and the incident radar rays are thereby extinguished.

In view of the disadvantages of the state of the art described above, a structure for radar reflection-attenuating double glazing is to be specified which meets the special manufacturing requirements of an individual object-specific

which takes particular account of the special manufacturing process, which is characterized by high precision and reproducibility of the partially reflective layer on the outer pane, and which is also well suited to the production of curved building glazing.

The task is solved by printing and partially burning in a pattern of stripes of a silver paste with good electrical conductivity onto a surface of the outer pane as a layer that partially reflects the radar rays in the area of the outer pane, whereby the width of the printed stripes is greater than their layer thickness.

The use of a pasty mass allows the application of an exact and easily reproducible pattern of thin parallel conductors to the glass surface using easily controllable printing techniques, such as screen printing in particular. The subsequent firing process bonds the silver paste or the silver particles embedded in it firmly and permanently to the glass. The firing of the printed silver paste preferably takes place at a temperature in the range of the softening point of the glass, i.e. in the temperature range between 640 and 680 degrees Celsius.

Compared to the wire-shaped conductors known from the state of the art, strips that are significantly wider than the layer thickness do show somewhat lower reflection attenuation values; however, when constructed as double glazing, the dependence on the angle of incidence of the incoming radar radiation is significantly reduced. This makes the use of such radar reflection-attenuating glazing on curved facades possible. Especially with strongly curved facades, a uniform reflection-attenuating construction can be implemented over almost the entire facade.

Suitable silver pastes are commercially available. Cerdec AG, Frankfurt am Main, Germany, supplies a silver paste under the trade name SP 509, which contains silver in the form of powder and frits, terpineol as a solvent and small amounts of lead and dibutyl phthalate. Good experiences have also been made with the product AG 2100-85 from Johnson Matthey B.V., Maastricht, Netherlands; this is a

Suspension of silver powder/silver flakes and frits in an organic solvent.

If the strips of silver paste are printed on the inside of the outer pane and then burned in, the resulting partially reflective layer is automatically protected against the effects of the weather by the hermetically sealed gap between the outer pane and the inner pane.

If the strips of silver paste are printed on the outside of the outer pane, this leads to an increase in the distance between the plane of the printed conductors and the radar-reflecting layer on the inner pane, which is entirely desirable; in this case, however, additional weather protection must be provided. According to a particularly advantageous development of the invention, a thin transparent layer of glass ceramic is therefore additionally applied over the strip of silver paste printed and fired onto the outside of the outer pane.

Such a structure results in a particularly thin and light double glazing, which consists of only two panes of glass and is at the same time characterized by optimal radar reflection attenuation.

Alternatively, however, the outer pane can also be designed - in a manner known per se - as a laminated glass pane consisting of at least two connected glass panes. The strips of silver paste are then expediently printed on one of the inner surfaces of one of the connected glass panes.

The printing technology used according to the invention makes it possible to produce curved radar reflection-dampening double glazing in a particularly simple and cost-effective manner, which allows greater freedom in the architectural design of glass facades. Screen printing technology in particular is ideally suited to printing on curved surfaces.

Another advantage of the screen printing process is the relatively cheap production of the printing screen, so that even small batches for smaller objects can be produced according to the in-

individual technical parameters with high precision and yet at reasonable prices.

The manufacture of the double glazing according to the invention can be optimized by pre-drying the printed stripes of silver paste at a temperature of approximately 200 degrees Celsius. The pre-drying removes the solvent components from the silver paste and makes the printed panes ready for transport. The panes with the printed stripe pattern can then be placed in a tempering oven at a later date, in which the required firing process is carried out.

Examples of double glazing according to the invention are explained in more detail below with reference to the accompanying drawings. They show:

Fig. 1 a double glazing in which the radar beams are partially

reflective layer on the outside of the outer pane and a transparent layer of glass ceramic is arranged above it;

Fig. 2 a double glazing in which the partially reflecting layer

is arranged on the inside of the outer pane;

Fig. 3 a double glazing according to Fig. 1, with curvature;

Fig. 4 a double glazing according to Fig. 2, with curvature;

Fig. 5a - Fig. 5d a double glazing with an outer pane designed as a laminated glass pane.

All images show a simplified vertical section through the double glazing. Identical elements are provided with the same reference symbols.

In Fig. 1, the double glazing consists of a flat outer pane 1 and an inner pane 2 arranged parallel to it and at a distance. In between there is an airtight space 3. The thickness of the outer pane

The thickness of the outer pane 1 and the inner pane 2 is approximately 10 mm each. The thickness of the entire double glazing is approximately 50 mm.

The radar radiation R comes in from the outside, in the drawings from the left side. The radar radiation R is characterized by a certain polarization angle with respect to the planes of the outer pane 1 and the inner pane 2 as well as a predetermined fixed wavelength.

On the side of the outer pane 1 facing outwards (on the so-called level 1) a layer is applied which partially reflects the radar beams R that hit it. This partially reflective layer is formed by a pattern of narrow strips 5 of a silver paste with good electrical conductivity, which is printed onto the surface of the outer pane 1 using a screen printing process and then at least partially burned into the glass surface. The width of a strip 5 is e.g. 0.5 mm, the distance between two adjacent strips is approximately 20 mm. The layer thickness of the strips 5 is significantly less than their width. To protect against the effects of the weather, a thin transparent layer of glass ceramic 6 is applied over the strip 5.

On the inner side of the inner pane 2 facing the sealed gap 3, a layer 7 is applied which is designed as a metallic heat protection layer and thus almost completely reflects incident radar beams.

The pattern of the printed parallel stripes 5, in particular the angular position of the individual stripes and the distance between two adjacent stripes, as well as the distance of the plane on which the stripes 5 are arranged to the plane of the radar-reflecting layer 7 is selected depending on the polarization direction and the wavelength of the incident radar radiation R such that the respective reflected portions of the radar beams are superimposed on one another in antiphase and are thereby canceled out.

In the double glazing according to Fig. 2, the partially reflective layer of printed stripes 5 of silver paste is arranged on the inside of the outer pane 1 (on the so-called level 2). No special weather protection is required here. However, the distance between the level of the stripes 5

and the plane of the radar-reflecting layer 7 is smaller by the thickness of the outer pane 1 than in the embodiment of Fig. 1. For the same wavelength of the incident radar radiation R, the gap 3 between the outer pane 1 and the inner pane 2 must therefore be increased by a few millimeters in order to maintain the functional principle of the Jaumann absorber.

The double glazings shown in Fig. 3 and Fig. 4 have a curvature towards the outside. In both cases, the partially reflective layer is provided on the outer pane 1, with the strips 5 of silver paste being printed on the outside in the first case (Fig. 3) and on the inside in the second case (Fig. 4). In the first case (Fig. 3), the printed and fired strips 5 of silver paste are in turn covered with a thin transparent layer of glass ceramic 6.

The double glazings according to Figures 5a to 5d have outer panes 1 which are laminated from two individual glass panes la and 1b to form a composite glass pane by means of a transparent plastic film Ic arranged between them. Strips 5 of silver paste are again printed as a layer which partially reflects the incident radar radiation R, namely on the outside of the first pane (Fig. 5a) or on the inside of the first pane la (Fig. 5b) or on the outside of the second pane Ib (Fig. 5c) or on the inside of the second pane Ib (Fig. 5d). The strips 5 are therefore located on one of the levels 1, 2, 3 or 4 of the glass package, while the radar-reflecting layer 7 is always located on the inside of the inner pane 7 (on the so-called level 5). In the embodiment according to Fig. 5a, an additional thin layer of transparent glass ceramic 6 covers the printed strips 5 of silver paste on the very outside.

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B 5692/02-Gbm 24 March 2003

List of reference symbols

1 outer pane

la First Disc (of 1)

Ib Second Disc (of 1)

Ic plastic film (between la and Ib)

2 inner pane

3 Space (between 1 and 2)

4 Seal

5 strips of silver paste (on 1)

6 Glass ceramic

7 Radar reflecting layer (on 2) R Radar radiation

Claims (8)

1. Radar reflection-attenuating double glazing, especially for buildings, with - an outer pane ( 1 ) carrying a layer of thin electrical conductors arranged parallel to one another which partially reflects radar rays; - an inner pane ( 2 ) provided with a radar-reflecting layer ( 7 ); - an airtight gap ( 3 ) between the outer pane ( 1 ) and the inner pane ( 2 ); - wherein the arrangement of the conductors on the outer pane ( 1 ) and their distance from the radar-reflecting layer on the inner pane ( 2 ) is selected depending on the polarization direction and the wavelength of the radar beams such that the respectively reflected portions of the radar beams are superimposed on one another in antiphase and the incident radar beams are thereby extinguished; characterized in that - a pattern of stripes ( 5 ) of a silver paste with good electrical conductivity is printed and partially burned into a surface of the outer pane ( 1 ) as a partially reflective layer; - the width of the printed strips ( 5 ) is greater than their layer thickness. 2. Radar reflection-attenuating double glazing according to claim 1, characterized in that the silver paste contains 50% to 95% silver. 3. Radar reflection-attenuating double glazing according to claim 1 or 2, characterized in that the silver paste is applied by screen printing. 4. Radar reflection-attenuating double glazing according to one of claims 1 to 3, characterized in that the strips ( 5 ) are printed on the inside of the outer pane ( 1 ). 5. Radar reflection-attenuating double glazing according to one of claims 1 to 3, characterized in that the strips ( 5 ) are printed on the outside of the outer pane ( 1 ). 6. Radar reflection-attenuating double glazing according to claim 5, characterized in that a thin transparent layer of glass ceramic ( 6 ) is applied over the strip ( 5 ). 7. Radar reflection-attenuating double glazing according to one of claims 1 to 6, characterized in that - the outer pane ( 1 ) is designed as a laminated glass pane consisting of at least two connected glass panes ( 1a ) and ( 1b ); - the stripes ( 5 ) are printed on one of the inner surfaces of one of the connected glass panes ( 1a , 1b ). 8. Radar reflection-attenuating double glazing according to one of claims 1 to 7, characterized in that it has a curvature.