EP0496388A2

EP0496388A2 - Carbon-fiber based device for heating antennas, preferably for use in space

Info

Publication number: EP0496388A2
Application number: EP92101035A
Authority: EP
Inventors: Giovanni Pellegrineschi
Original assignee: Selenia Spazio SpA
Current assignee: Alenia Spazio SpA
Priority date: 1991-01-23
Filing date: 1992-01-23
Publication date: 1992-07-29
Also published as: IT1244904B; EP0496388A3; ITRM910047A1; ITRM910047A0

Abstract

Heating device for reflecting surfaces of antennas based on carbon fiber, which besides performing a structural function and reflecting electromagnetic waves also provides the heating of the same surfaces in order to melt ice or snow, and is also capable of controlling thermal deformations. This consists essentially of one or more layers of carbon fiber (5), immersed in a resin wherein the electrodes (A), (B) are located, which connected to a generator (G) allow the current to pass into the fabric of carbon fibers providing the heating to a desired temperature depending on the applied voltage, the characteristics of the fiber layer and the shape and arrangement of the electrodes (A), (B).

The invention relates to the technical field of reflectors for microwave antennas and finds its preferred application in the field of satellite communications.

Description

The invention relates to a heating device to be applied to the reflecting surfaces of antennas and based on the use of carbon fibers.
The main objective pursued by the solution proposed by the invention is to achieve with the use of the mentioned carbon fibers the possibility of performing several functions at the same time, namely:

to heat the reflecting surfaces in order to prevent the deposition of snow or ice;
to constitute in itself the structural part (which is reinforced by carbon fibers);
to reflect the electromagnetic waves;
to keep thermal deformation under control.

As known, the large reflector antennas (paraboloidal or similar) have almost always a need for a deicing system, generally based on heaters which prevent the snow and ice from sticking. In fact, if such elements are allowed to accumulate on the reflecting surfaces, the performance of the antenna is impaired.
A thermal control either of these reflecting surfaces or of other structural elements can also be required in other types of antennas such as the ones provided on the board of satellites, in order to insure dimensional stability.
Normally, the reflecting surfaces or the other thermally controlled parts are heated by means of electric resistors made of metallic wire and electrically insulated on the antenna structure, connected with the surfaces to be heated, generally on the side which is opposite to the one upon which the waves reflect.
Other heating method are based on hot-air emission, blown onto the surfaces or on the irradiation of the latter by means of infrared rays.
These alternate methods are much too involved, and in fact the method which is generally preferred is the one based on metallic wire resistors. When the surfaces to be heated are made of composite materials (vitreous resin, carbon fiber) the immersion of metallic conductors in these surfaces can present several inconveniences for the following reasons:

High temperatures in the proximity of the wires because of the poor thermal conductivity of the material and of the distance of the wires from the surfaces to be heated;
Temperature irregularities due to the localized heat generation (high thermal gradients) with subsequent inner tensions, therefore an uneven distribution on the heated surfaces;
Vulnerability of the entire heater network with localized mechanical damage (for instance if the wire is interrupted in one point the entire heater ceases to function and is difficult to repair);

The heating system which is object of the present patent application is based on the use of carbon fiber.
This fiber can:

be a part of the composite material as a structural component;
assume the function of reflecting surface for electromagnetic waves;
assume the function of heating element.

Further, the invention will be described in an illustrative but non-limitative manner with reference to the enclosed Figure. Fig. 1 shows schematically the panel consisting of composite material to be applied to the surfaces to be heated.
The Figure shows in plan and in section an example of a panel with carbon fibers. The following elements can be discerned therein:

1 generator
2 terminal
3 terminal
4 conductive metallic layer
5 carbon fiber
6 conductive metallic layer
7 reflecting surface
8 structural material of various types, for instance vitreous resin.

The binding material of carbon-fiber element 5 can be an epoxy polyester resin or another material. Further, the operation of the device of the invention is described, with reference to the attached drawing in an illustrative but non-limitative manner, taking into account that the description of either the physical-structural composition of the invention device or its operation refer to a solution which is actually preferred by the inventor, but nothing prevents variations in its configuration as long as the results pursued by the invention are not altered.
By applying an electric voltage to the conductors through two or more terminals (2), (3) made accessible from the outside of the panel, the current will traverse the carbon fiber (5), heating the panel surface.
The value of the voltage is selected in accordance with the superficial resistivity of the carbon fabric, the manufactured shape of the electrodes, and also the specific power (W/m²) which will dissipate according to the formula:
By arranging the electrodes suitably and/or by varying the thickness of the layers, it is possible to insure that W will be approximately constant on panels whose shape is not rectangular, for instance on trapezoidal, triangular shapes, etc, and also on shapes with double curvature.
When compared with the traditional use of metallic conductors, the system proposed by the patent application presents the following advantages:

It uses the carbon fibers either as a means for heating or as a structural support element, or as reflecting surfaces: this way, with the use of carbon fibers one achieves three functions at the same time, which results in economic advantages and considerable savings through major ease of manufacturing.
It uniformly and directly heats the surfaces, exactly where the heating has to occur,so that no temperature rise is required in order to transmit the heat from the point where it is generated, e.g. through a metallic wire, to the point where it is used, namely the reflecting surfaces of the panel.
it is only slightly vulnerable to local injuries, in fact any possible local interruptions in the fabric, e.g. a cut, will not prevent the flow of current through its remaining parts. The inconvenience of negligible magnitude which can result from this is a slight overheating around the damaged area, an overheating which is certainly lower than the one occurring under normal conditions around the wires.

The expansion coefficient of carbon fiber is, as known, much lower (ranging from one hundredth to one thousandth of the expansion coefficient of metal), therefore the deformations caused by temperature are minor.

Claims

Heating system to be used in its optimal application in the field of antennas, in order to prevent snow or ice deposits on the surfaces exposed to low temperatures, characterized by the fact that it consists of a composite panel (Fig. 1) with inserted terminals (2), (3) which allow the supply of current coming from the generator (1) to the panel in question.
Heating system to be used in its optimal application in the field of antennas in order to prevent snow and ice deposits on surfaces exposed to low temperatures according to claim 1, characterized by the fact that said composite panel consists essentially of carbon fibers in a polyester or epoxy resin and/or another binding material, having a superficial conductor (4), (6), e.g. carbon fiber, in coincidence with the surfaces to be heated (e.g. the reflecting surfaces of an antenna).
Heating system to be used in its optimal application in the field of antennas in order to prevent snow and ice deposita on surfaces exposed to low temperatures, according to claims 1 and 2, characterized by the fact that said composite panel is essentially capable of functioning as:
- structural support element;

- element capable to evenly heat the surface which is supposed not to freeze;

- reflecting surface for electromagnetic waves.