The invention is comprised in the technical field of metamaterials or composites, also covering aspects of electromagnetism, magnetic absorbers and metallurgy.
Multiple applications which require eliminating reflections of electromagnetic radiation are known.
Thus, for example, microwave absorbers are made by modifying dielectric properties, in other words, the dielectric permittivity or the magnetic permeability of determined materials. To that end, it is necessary to disperse small sized metallic elements in a dielectric matrix. Various inventions show these types of solutions, as is the case of U.S. Pat. No. 5,147,718, in which a radar absorber based on the dispersion of carbonyl iron powder into a paint is described. The solution is also shown in patent document WO 03/004202 which shows a method for making an electromagnetic radiation absorber based on the dispersion of flakes of an iron-silicon alloy. The solution is also shown in United States patent U.S. Pat. No. 5,085,931 in which an electromagnetic radiation absorber is formed by dispersing acicular magnetic filaments into a dielectric matrix.
Some absorbers based on amorphous magnetic microwires obtained by the Taylor technique (“The preparation, properties and applications of some glass coated metal filaments prepared by the Taylor-wire process”, W. Donald et al., Journal of Material Science, 31, 1996, pp. 1139-1148) can be included among magnetic type absorbers. This type of absorber can be a dielectric matrix in which amorphous magnetic microwires with high magnetic anisotropy having magnetic resonance properties are randomly distributed, as described in European patent EP-1675217.
The invention relates to a paint with metallic microwires according to claim 1, to a process for integrating metallic microwires in paint according to claim 5, and to a process for applying said paint on metallic surfaces according to claim 10. The preferred embodiments are described in the dependent claims.
A first aspect of the invention relates to a paint with metallic microwires for attenuating the reflectivity of electromagnetic radiation, the paint having a determined dielectric constant εr; the paint comprises:
A second aspect of the present invention relates to a process for integrating metallic microwires in paint for attenuating the reflectivity of electromagnetic radiation, the paint having a determined dielectric constant εr; the process comprises:
The amount of solvent used for liquefying the paint must not be greater than 20%.
The metallic microwire used in the present invention is preferably a metallic filament of high electrical conductivity or of an amorphous magnetic alloy with Pyrex coating, in which the diameter of the core and the total diameter are not greater than 100 and 200 μm, and with a length comprised between 0.1 and 20 mm.
The beating for integrating the microwire in the paint is preferably performed with a mixing rod at a maximum speed of 2500 r.p.m.
Another aspect of the invention relates to the application of said paint with microwires on a metallic surface for the attenuation of the reflectivity of electromagnetic radiation which comprises:
The process preferably includes an additional step of:
The metallic surface can be a composite with high conductivity, or it can also be a plastic metalized, for example, by means of metallic adhesive tapes or with metallic paint.
The paint can be applied by means of a spray gun, roller or airless system.
Preferably, the microwires used in the spray or airless gun application method do not have lengths greater than 5 mm.
Preferably, the microwires used in the roller application method do not have lengths greater than 20 mm.
The following must be considered with regard to the application steps:
The first coat of primer has a dielectric constant, εr1 with a real part preferably comprised between 2 and 4, it is applied on the metallic surface and its thickness can be comprised between 20 and 100 μm.
The second coat of paint can have a thickness between 25 μm and 5000 μm with a real part of the dielectric constant εr2 between 2 and 9 and it is applied on the first coat of primer.
This second coat of paint can contain metallic microwires; in this case, its dielectric constant εr2 can range between 2 and 500.
The values of the real part of the dielectric constant of the second coat εr2 can be modified by varying the percentage by weight of the microwire between 0.5 and 5%.
The active third coat can have a thickness between 75 and 500 μm, and the real part of its dielectric constant εr3 can be between 9 and 1000, and it is modified based on a percentage by weight of the microwire comprised between 0.5 and 10% by weight.
The fourth coat of finish paint can have a thickness between 25 and 100 μm, and the real part of its dielectric constant εr4 can be comprised between 2 and 9.
Preferably, the fourth coat of finish paint does not contain a high density of metallic or carbon particles; otherwise it can reflect electromagnetic radiation.
The thickness of the second coat, which is the coat that mainly determines at what distance the active third coat with the microwires of the metallic surface is located, greatly influences the tuning frequency for the attenuation of electromagnetic radiations.
The tuning frequency can range between 0.1 and 70 GHz for a sum of thicknesses of the second and third coats between 25 and 5000 μm.
To complement the description which is being made and for the object of aiding to better understand the features of the invention according to a preferred practical embodiment thereof, a set of drawings is attached as an integral part of said description in which the following has been depicted with an illustrative and non-limiting character:
A preferred embodiment of the process for integrating metallic microwires in paint is described below. This process includes:
liquefying the paint with a solvent which is suitable for said paint in an amount no greater than 20%;
The process object of the invention has been confirmed as effective for painting on a metallic surface in two cases: both with amorphous microwires with the same composition, Fe89Si3B1C3Mn4 and varying the geometry thereof.
In the first case amorphous microwires with a diameter of the metallic core of 20 μm and a length of 3 mm were used. The microwires were integrated in the paint by beating with a mixing rod at 1700 rpm, the paint having a real part of the dielectric constant, εr, of value 4 lowered with 5% solvent.
A first coat 2 of primer of 30 μm and with a real part of the dielectric constant Cr of value 4 was applied on the metallic surface 1.
A second coat 3 of paint without microwires with a thickness of 700 μm was then applied, resulting in a real part of the dielectric constant εr of 6.5.
A third active coat 4 was then applied on the second coat 3, the third active coat containing microwires in a density of 2% by weight, with a thickness of 300 μm, and resulting in a real part of the dielectric constant εr of 75.
A fourth coat 5 of finish was then applied on the third active coat, this coat having a thickness of 100 μm, and a dielectric constant εr of 6.5.
The paint thus obtained has an attenuation curve of electromagnetic waves centred on 53 GHz with a level of 18 dB and with a level of attenuation greater than 10 dB for a bandwidth of 1.6 GHz centred on 53 GHz, as shown in the graph of
In the second case, amorphous microwires with a diameter of the metallic core of 8 μm and a length of 2 mm were used. The microwires were integrated in the paint by beating paint with a real part of the dielectric constant, εr, of value 4 lowered with 10% solvent with a mixing rod at 1000 rpm.
A 900 μm first coat 2 of primer with a real part of the dielectric constant εr of value 4 was applied on the metallic 1 surface.
A second coat 3′ of paint containing microwires at a density of 4% by weight, with a thickness of 200 μm was then applied, resulting in a real part of the dielectric constant εr of 60.
The active coat 4 is applied on the second coat 3′; this active coat contained microwires at a density of 2% by weight.
The coat 5 of finish applied on the active coat 4 had a thickness of 75 μm and a dielectric constant εr of 4.
In this case, the paint obtained has an attenuation curve of electromagnetic waves centred on 9 GHz with a level of 18 dB and with a level of attenuation greater than 10 dB for a bandwidth of 1 GHz centred on 9 GHz, as shown in the graph of
In view of this description and set of drawings, the person skilled in the art will be able to understand that the embodiments of the invention which have been described can be combined in multiple manners within the object of the invention.