DE102008035917B4 - Lightning protection of radomes and transceivers - Google Patents

Abstract

Lightning protection arrangement, in particular for radomes and transceiver devices, comprising:
a protective sheath (14), in particular a radome wall, which surrounds a transmitting / receiving device (12) and is permeable to electromagnetic radiation;
wherein the protective sheath (14) is provided with a coating (16) such that the dielectric strength of the coated protective sheath (14) is at least 100 kV / mm, and
the coating (16) is selected from a material of the group comprising diamond, diamond-like carbon compounds, cubic boron nitride, silicon dioxide and silicon nitride.

Description

FIELD OF THE INVENTION

The The invention relates to a lightning protection arrangement, in particular of radomes and transceivers. The invention further relates an aircraft with an inventive arrangement, the use an arrangement and a method for producing an inventive arrangement.

BACKGROUND OF THE INVENTION

radomes protect known transmission / reception devices, such as antennas, Radar systems or other electromagnetically sensitive systems, from external influences (eg. B. weather conditions) and have a protective sleeve surrounding the transceiver, which is made of dielectric material for electromagnetic radiation permeable to be. In addition, grant Radome a certain privacy, so that external observers are not without further on the technical equipment inside can close.

Radomes can be found, for example, in large-scale systems that are permanently installed on earth, and on ships. Also the bow fairing of aircraft, which have a radar or electromagnetically sensitive systems in the bow nose, is called Radom (see 1 ).

radomes and the transceivers positioned behind the radomes have to known against lightning strikes to be protected, which is especially ensured for aircraft and other aircraft must be to the damage caused by a lightning strike could be as low as possible otherwise the radome will be destroyed and the aircraft will be unable to fly could.

Known lightning protection measures, as introduced, for example, in EP 1 263 648 B1 are mentioned in detail and in FA Fisher et. al. "Lightning Protection of Aircraft", Pittsfield 1990, pages 136 to 143, consist of solid metal diverters or alternatively segmented strips or button strips. to install on the radome surface. The latter consist of a dielectric support on which button-shaped metallic elements (so-called "buttons") are placed at a small distance (see 2 ). The dielectric support may have an electrically slightly conductive substructure which prevents electrostatic charging of the isolated metallic buttons. The buttons differ depending on the design by their shape and size.

The arrester and strip described are arranged on the radome surface, that they have the emergence of catch discharges at their free ends favor, while it the emergence of discharges on metallic parts of the transceiver conditionally hinder by their shielding effect. This way will the electrical breakdown of a flash channel on the transceiver or other metal parts behind the radome. The lightning current instead is over the arresters or strips, due to their electrical connection to a massive metallic structure that is capable of one To survive lightning without damage derived.

The geometric arrangement of the arrester and strip, in particular their Length as well their mutual distance, is determined by the radome and antenna geometry and at the same time determines the dielectric strength of Radomwand.

To something present State of the art, the design of the Radomwand after mechanical and Radar-optical aspects under consideration of other boundary conditions, such as B. the weight load. The design of lightning protection, the Choice of arrester or strip length, their distance and the accurate positioning is done in a second step on the base experience and with the help of high voltage tests in Laboratory.

From Disadvantage is that the above-described known lightning protection arrangements lie in the radiation field of the transmitting / receiving device. Depending on Alignment of the transmitting / receiving device or the main lobe the emission characteristic of the transmitting / receiving device becomes more or less adversely affected by the lightning protection provision. In order to reduce this effect, there is an endeavor to the document density and the length make the arrester or strip as small as possible, without the Lightning protection effect to impair.

The US 3 906 308 A describes lightning protection systems that use dielectric materials in the form of coatings or films applied to critical components comprising graphite or boron epoxy resin composites that have significantly lower electrical conductivity and thermal conductivity than metals. As dielectric materials polyurethane or epoxy coatings or films of Kapton (Kapton is a polyimide) are used.

Venables John D. et al. "Status and Applications of Diamond and Diamond-like Materials: An Emerging Technology "National Research Council, Committee to Superhard Materials, National Academics Press, 1990, ISBN 0309041961, give an overview of materials such as diamond, diamond-like Carbon compounds, cubic boron nitride, silicon dioxide and Silicon nitride and possible Uses of such materials. It is pointed out that diamond due to its large band gap of 5.5 eV and its high Breakdown voltage of 10 V / cm used in the field of electronics could be. Mentioned also the use of diamond as a protective coating for optical components, also for Radome, for protection against influences from dust, rain and attrition as well as high temperatures like those at Radomes of space shuttles occur when re-entering the atmosphere can. In this context, radomes of diamond are beneficial considered.

Consequently the object of the present invention is to provide an improved Lightning protection arrangement, in particular of radomes and transceiver devices, so that the transmission and reception characteristics of the protected transceiver as little as possible disturbed become.

SUMMARY OF THE INVENTION

These The object is achieved by the subject matter of the invention according to the independent claims. advantageous embodiments of the invention are in the dependent claims specified.

in the The following terms are related to this invention used with appropriate meaning.

Under the dielectric strength or Dielectric strength of an insulator is the field strength to understand which in the material at most may prevail without causing a voltage breakdown or a spark discharge comes through the material. The dielectric strength has therefore the dimension of an electric field strength or a voltage per thickness of the insulator. The dielectric strength is not a material constant in the true sense, as it is from a Variety of factors, such as Electrode arrangement, duration of stress, local, microscopic material inhomogeneities and temporal voltage curve depends. For the purpose of comparability Therefore, there are standardized test methods for corresponding values.

"Streamer" and "Leader", terms that are taken from gas-discharge physics, are to be understood as follows, based on Rakov and Uman in "Lightning - Physics and Effects", Cambridge University Press, Cambridge 2003: A corona discharge is on the immediate vicinity of an electrode limited; It consists of many individual streamers, which are unable to expand independently and to leave the area of the electrode proximity. Discharge or plasma channels capable of self-growth, on the other hand, are referred to as leaders. While leaders have an electrical conductivity of about 10 ⁴ S / m, streamer have a much lower conductivity.

With Leitblitz (English: "lightning leader") is the following: From the negative charge center of a Thundercloud pushes a cloud-filled, cylindrical tube with a diameter of some 10 meters and a thin, highly ionized Plasma core with a diameter of about 1 cm jerky to the ground in front. This so-called Leitblitz has a Vorwachsgeschwindigkeit in the order of magnitude of one thousandth of the speed of light, that is 300 km / s. Of the Leitblitz is growing jerky in sections of some 10 m in front, taking the break between the jerk levels is a few tens of microseconds. When the Leitblitz of the earth has approached for a few tens to a few 100 m increases for example, at the Leitblitzkopf the nearby peaks of trees or gables of buildings the electric field strength so strong that finally the electrical strength of the air is exceeded and from there now also a Leitblitz similar, some 10 to some 100 m long so-called Fang discharge (Leader) breaks out, which the Leitblitz grows towards it and finally coincides with the Leitblitzkopf.

The lightning protection arrangement according to the invention comprises a surrounding a transmitting / receiving device, permeable to electromagnetic radiation protective cover, wherein the protective cover with a Beschich tion, which increases the dielectric strength of the protective cover considerably, namely to at least 100 kV / mm.

The cover is typically a radome wall, which is known to be the protected transceiver surrounds and consists of a dielectric material.

Additionally, you can the coated according to the invention cover Ableiterelemente be arranged, which for diverting lightning currents, respectively are connected on one side with a metallic structure. The arrester elements are used to capture a Leitblitzes, and the resulting current is relayed to a metallic structure that is capable is to survive this stream unscathed.

Of the essential core of the invention is the protective cover with to coat a special material that has a high dielectric Has strength with low electrical losses. This leads to the dielectric strength of the coated protective sheath in comparison to an uncoated protective cover significantly higher is, so that a lightning strike through the coated protective cover prevents becomes. In some applications (eg for small radomes) can then even completely on additional Arrangements as known from the prior art (eg. As conductors and strips), be waived so that the transmitting and reception characteristics of the transceiver to be protected not affected. For other applications (eg in large radars) or for safety reasons (eg. B. in passenger aircraft) can or will not usually entirely on additional Dispense arrester elements to ensure safe lightning protection; however, the coating according to the invention causes that by the increase the dielectric strength of the protective cover created the prerequisites are, the density of the protective cover with arrester elements to reduce, causing the disturbing Influencing the transmission and reception characteristics of the concerned Transmitting / receiving device is significantly reduced. With others Words is the number of arrester elements compared to one cover reduced without coating, reducing the transmission and reception characteristics the transmitting / receiving device of a lower disturbance than at conventional Arrangements are exposed.

According to one preferred embodiment is the dielectric strength of the coating is at least 350 kV / mm. Particularly advantageous are coatings with a dielectric Strength of at least 400 kV / mm.

Especially preferred are coatings having a dielectric strength of at least 1000 kV / mm used.

conventional Radom structures have, depending of the respective construction, a dielectric strength, the between 10 to 40 kV / mm. With the coating according to the invention let yourself the dielectric strength by more than 100, depending on the layer thickness increase kV / mm, so that resulting dielectric strengths significantly above 100 kV / mm. As mentioned, the dielectric strength is the coated according to the invention cover at least 100 kV / mm.

According to one embodiment The invention provides the coating applied to the protective cover made of diamond or diamond-like Carbon compounds, wherein for the latter is the predominant sp3 hybridization of the carbon atomic orbitals is essential. Layers of such materials have one Real part of the dielectric constant, that is not too big, and at the same time a sufficiently small electrical loss factor, making them for the desired Application are suitable accordingly. The dielectric strength for diamond is about 1000 kV / mm and is thus by a factor of 25 to 100 greater than the more conventional Radomwände (10 to 40 kV / mm). Consequently, you can even thin Diamond coatings significantly reduce the dielectric strength of the protective cover enlarge.

According to one another embodiment the coating consists of cubic boron nitride (BN cub). boron nitride has a diamond-like Structure and its dielectric properties are comparable with those of diamond-like Carbon. Boron nitride also has a high dielectric strength on (about 400 kV / mm). The real part of the dielectric constant moves in one for This application adequate framework and the loss factor is sufficient small to be used as a coating material for the protective cover to be able to without increasing the transmission losses.

According to a further embodiment, the coating consists of silicon oxide (SiO ₂ ), which has a dielectric strength of about 1000 kV / mm.

According to another embodiment, silicon nitride (Si ₃ N ₄ ) whose dielectric strength is about 1000 kV / mm is used as the material for the coating.

According to one another embodiment they may be additional on the coated protective cover arranged arrester elements of strip-shaped metallic elements, in the prior art as "solid diverters " become.

According to a further embodiment, the arrester elements are in the form of segmented strips with button-shaped metallic elements, which are also known as "segmented strips" or "button strips" (see 2 ).

The Lightning protection arrangement according to the invention especially in aircraft, such as aircraft and helicopters, application.

at an aircraft having the inventive arrangement is the protective cover typically a radome, which is arranged at the nose of the aircraft is. The to be protected Transceiver is usually a radar or another electromagnetic sensitive system. Of course you can the inventive arrangement also be applied in other places.

According to one Another aspect of the invention is a method for the production a lightning protection arrangement, in particular for radomes and transceivers, indicated, with one for electromagnetic radiation transparent protective cover provided which is to surround a transceiver, and on the protective cover a coating is applied, increasing the dielectric strength the shelter at least 100 kV / mm.

ever After application, in addition to the coated protective cover Ableiterelemente arranged to derive lightning currents one-sided with a metallic structure are connected.

Prefers becomes a coating of diamond, diamond-like carbon compounds, cubic boron nitride, silicon oxide or silicon nitride with a applied gas phase bescheidung known, in particular by means of "Chemical Vapor Deposition "CVD method or a plasma assist CVD method. These methods are suitable both for the production of elemental as well as compound coatings.

It It should be noted that the described embodiments and the comments and explanations equally refer to the layout, the procedure and an aircraft. Separate Features can Of course also be combined with each other.

DESCRIPTION OF THE FIGURES

exemplary embodiments are described below with reference to the following figures, which, however, should not be construed as limiting the invention.

1 shows a schematic representation of a front view of an aircraft which has a radome on the aircraft bow;

2a shows a schematic plan view of a conductor element, which is formed in the form of a segmented strip with button-shaped metallic elements, as is known from the prior art; and

2 B shows a cross-sectional view of the in 2a illustrated arrester element; and

3 shows a schematic representation for explaining the physical processes during lightning strikes in radomes or antennas.

In The following figure description will be for the same or similar Elements use the same reference numerals. The representations in the figures are schematic and not to scale.

1 shows a schematic representation of the front view of an aircraft 30 , At the bow of the plane 30 is usually a radome, the underlying antennas, radar systems or others It protects electromagnetically sensitive systems. Since the radome is normally not visible from the outside, it is in 1 only schematically by a circular line 14 indicated.

To lightning protection of the Radome and the behind, in 1 Unrecognizable transceivers are, as is known in the art, on the surface of Radomwand 14 Arrester elements arranged. These arrester elements are in 1 only shown schematically and with reference numerals 18 designated. The electrically conductive arrester elements 18 are strip-shaped, spaced from each other and extend in the direction of Radomspitze 32 , The towards Radomspitze 32 pointing end of a respective arrester element 18 is free, whereas the other end is shorted to the metallic fuselage. When the radome is struck by lightning, the resulting current will be via the arrester elements 18 forwarded to the fuselage, where high current densities can be safely dissipated.

The strip-shaped metallic arrester elements 18 ("Solid diverters") have a substantially rectangular cross-section with a typical cross-sectional area of 0.5 cm ² .

Alternatively, as arrester elements 18 segmented strips with button-shaped metallic elements ("segmented strips" or "button strips") are used, as they are in 2a and 2 B are shown schematically. 2a shows a plan view and 2 B shows a cross-sectional view. As is known, they consist of a dielectric carrier 40 , optionally a resistance strip 42 , and at a small distance from each other on the support 40 arranged button-shaped, electrically conductive elements 44 , the so-called "buttons". The dielectric carrier 40 may be an electrically slightly conductive substructure 42 have an electrostatic charge of the isolated metallic buttons 44 prevented.

The geometric configuration of the arrester elements 18 , in particular the choice of the length and the distance between each other, as well as the exact positioning depends on the geometry of the protective cover and the transceiver as well as on the dielectric strength of the protective cover and is designed according to mechanical and radar optical aspects.

Basically the influence of the antenna diagrams by the segmented Strip ("segmented strips "or" button strips ") less than by the solid diverters. she However, they have the significant disadvantage of their protective effect across from Flashing under unfavorable Weather conditions (water surface and ice formation on the Radomoberfläche or to lose the strip more or less. That's why they will usually not used in safety-critical applications. Besides, they require a larger maintenance effort, since they withstand no multiple lightning exposure.

3 shows a schematic representation for explaining the physical processes during lightning strikes in radomes or antennas. In 3 is with reference number 10 generalized designates a lightning protection arrangement that can be arranged on any object, such as an aircraft or a radar system installed on the ground. To protect a transceiver 12 , which is exemplified here as an antenna, this is dome-like in a known manner of a dielectric protective cover or Radomwand 14 surround. On the surface of the radome wall 14 can, as described above, arrester elements 18 be arranged. For the sake of graphic representation is in 3 only one arrester element 18 shown, one end of which is free, whereas the other end with a metallic structure 20 , z. B. a flange of the fuselage or a ground-based antenna with the reason is shorted.

In a simplified form, one can observe the processes during the lightning strike in the antenna 12 or the arrester elements 18 represent as follows: A Leitblitz 22 approaches the object, for example an airplane. The electric field, this Leitblitz 22 near the Radomwand 14 can cause on the arrester element 18 and / or the antenna 12 so-called streamer 24 cause. One of these streamer 24 can develop into a catch discharge (leader), dealing with the lead lightning 22 connect and a lightning strike on antenna 12 or arrester elements 18 cause.

The preferred path for lightning breakdown is that with the lowest breakdown voltage. For the path to the arrester element 18 the breakdown voltage V _a results from the voltage for the breakthrough in air between the tip of the Leitblitzes 22 and the free end of the arrester element 18 if it is a metallic strip ("solid diverter"). For a segmented strip ("segmented strip" or "button strip"), an additional share is added, but not discussed here will be.

For the path to the antenna 12 the breakdown _voltage results from three parts: the breakdown _voltage V _b1 between the tip of the Leitblitzes 22 and the outer radome wall 14 , the breakdown voltage V _b2 through the radome wall 14 and the breakdown voltage V _b3 from the inner radome wall 14 to the antenna 12 ,

According to the invention the radome wall 14 with a coating 16 provided in 3 simplified represented by a dashed line. The coating 16 has a high dielectric strength (≥ 350 kV / mm) with low electrical losses. By such a coating 16 the breakdown voltage V _b2 through the coated Radomwand 14 substantially increased, which means that in some applications (eg in small radar systems) can be completely dispensed with additional arrester elements and thus the transmission properties of the antenna 12 not be affected by this.

In the event that can not be dispensed with additional arrester elements, such as in large plants or for safety reasons, the coating of the invention causes 16 in that the number or size of the arrester elements 18 compared to a conventional, uncoated Radomwand is significantly reduced. This in turn means that the transmission and reception characteristics of the protected device 12 less affected, ie the radiation characteristics of the antenna 12 is less disturbed.

As a coating according to the invention 16 Suitable are diamond or diamond-like carbon compounds, ie layers with a substantially sp3 hybridization of the carbon atomic orbitals. One of the diamond-like carbon-like substances in terms of properties required here is cubic boron nitride. In addition, silicon oxide and silicon nitride are also suitable. The dielectric strengths of the materials mentioned have the following values: MATERIAL DIELECTRIC STRENGTH [kV / mm] diamond ~ 1000 Cubic boron nitride ~ 400 silica ~ 1000 silicon nitride ~ 1000

Since typical breakdown strengths of conventional radome structures range from 10 to 40 kV / mm, the dielectric strength of one already increases with a thin coating 16 provided radome wall 14 significant.

At the same time, because of its mechanical hardness, crack resistance and high thermal conductivity, the said layer is suitable for protecting the radome wall 14 against environmental influences (eg rain erosion, damage due to electrostatic discharge, thermal shock).

in the Regarding the coating technology for the relevant substances is to be differentiated so that in the case of diamond-like Carbons an element coating, in the case of cubic boron nitride a connection coating is present. Element coatings are procedurally in principle easier to implement than compound coatings.

diamond-like Carbon layers can be deposited via vapor deposition, such as For example, chemical vapor deposition (CVD) or plasma assisted CVD realize. Corresponding methods are known. As precursor In the simplest case, methane can be used. Other precursors (usually hydrocarbons) are also possible (acetylene, Propane / propene mixtures).

Cubic boron nitride is also plating by CVD / plasma assisted CVD using the precursors borane (B ₂ H ₆ ) and nitrogen or nitrogen bearing reactive compounds (eg ammonia directly or corresponding nitrogen / hydrogen mixtures in plasma assisted processes). The same applies to coatings of silicon dioxide and silicon nitride.

The above description of 3 refers to the so-called ungetriggered lightning strike in an airplane. The electric field that a streamer causes on the arrester strip or antenna is generated by the electrical charges in the guide-light approaching the aircraft.

much frequently occurs the case of so-called triggered lightning strikes in airplanes on, in which the aircraft itself triggers the impact. The physical processes differ only insofar as in this case the electric Field that causes the streamer, not from the charges in the Leitblitz, but is generated by the charges in the storm cloud. The Time scales on which the electric fields change, the Lightning rods and antenna see, change also, however, there are no consequences with respect to the discussion the occurring physical processes and the effect of the coating according to the invention.

Finally, it will noted that expressions like "having" or "similar" not to exclude that further elements or steps can be provided. Of Further, it should be noted that "one" or "one" does not exclude a multitude. In addition, in Connection with the various embodiments described features be combined with each other as desired.

10

Lightning protection order

12

Transmitting / receiving device (Antenna)

14

Protective cover (Radomwand)

16

coating

18

arrestor

20

metallic Structure (mass, flange)

22

downward leader

24

Streamer

30

plane

32

radome

40

dielectric substratum

42

resistive material

44

button-shaped metallic Elements (buttons)

V _a

Breakdown voltage between Leitblitz and arrester element

V _b1

Breakdown voltage between Leitblitz and outer Radomwand

V _b2

Breakdown voltage through the Radomwand

V _b3

Breakdown voltage between inner radome wall and antenna

Claims (14)

Lightning protection arrangement, in particular for radomes and transceiver devices, comprising: a transceiver device ( 12 ) surrounding, permeable to electromagnetic radiation protective cover ( 14 ), in particular Radomwand, wherein the protective cover ( 14 ) with a coating ( 16 ), so that the dielectric strength of the coated protective cover ( 14 ) is at least 100 kV / mm, and the coating ( 16 ) is selected from a material of the group comprising diamond, diamond-like carbon compounds, cubic boron nitride, silicon dioxide and silicon nitride. Arrangement according to claim 1, wherein on the protective cover ( 14 ) Arrester elements ( 18 ) arranged to derive lightning currents on each side with a metallic structure ( 20 ) are connected. Arrangement according to claim 1 or 2, wherein the dielectric strength of the coating ( 16 ) is at least 350 kV / mm. Arrangement according to one of claims 2 to 3, wherein the arrester elements ( 18 ) are formed in the form of strip-shaped metallic elements. Arrangement according to one of claims 2 to 4, wherein the arrester elements ( 18 ) are formed as segmented strips with button-shaped metallic elements. Arrangement according to one of claims 2 to 5, wherein the number of arrester elements ( 18 ) compared to a protective cover ( 14 ) without coating ( 16 ), whereby the transmission and reception characteristics of the transceiver ( 12 ) are exposed to less interference. Aircraft with an arrangement according to one of claims 1 to 6th Aircraft according to claim 7, wherein the protective cover ( 14 ) a radome is at the bow of the aircraft ( 30 ) is arranged. Aircraft according to claim 7 or 8, wherein the transceiver device ( 12 ) is a radar system. Use of an arrangement according to one of claims 1 to 6 in an aircraft. Method for producing a lightning protection arrangement, in particular for radomes and transceivers ( 12 ), comprising the steps of: providing a transceiver device ( 12 ) surrounding, electromagnetic radiation permeable protective cover ( 14 ), in particular Radomwand, and applying a coating ( 16 ) on the protective cover ( 14 ), whereby through the coating ( 16 ) the dielectric strength of the coated protective cover ( 14 ) is at least 100 kV / mm, and wherein a coating ( 16 ) is selected from a material of the group comprising diamond, diamond-like carbon compounds, cubic boron nitride, silicon dioxide and silicon nitride. A method according to claim 11, wherein on the coated protective cover ( 14 ) Arrester elements ( 18 ) arranged to derive lightning currents on each side with a metallic structure ( 20 ) are connected. Process according to claim 11 or 12, wherein as coating ( 16 ) a material is used which has a dielectric strength of at least 350 kV / mm. A method according to claim 11, 12 or 13, wherein the coating ( 16 ) by CVD method or plasma assisted CVD method on the protective cover ( 14 ) is applied.