EP3361571A1 - Isolant multicouche thermique et couverture absorbante de radiofréquence - Google Patents

Isolant multicouche thermique et couverture absorbante de radiofréquence Download PDF

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Publication number
EP3361571A1
EP3361571A1 EP17156431.3A EP17156431A EP3361571A1 EP 3361571 A1 EP3361571 A1 EP 3361571A1 EP 17156431 A EP17156431 A EP 17156431A EP 3361571 A1 EP3361571 A1 EP 3361571A1
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EP
European Patent Office
Prior art keywords
layer
patterned
mli
thermal
fss
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
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EP17156431.3A
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German (de)
English (en)
Inventor
Nuno Miguel Santos
Celeste Margarida Correia Pereira
Mário Rui Silveira Pereira
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Hps - High Performance Structures Gestao E Engenharia Lda
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Hps - High Performance Structures Gestao E Engenharia Lda
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Priority to PCT/IB2018/050858 priority Critical patent/WO2018146651A1/fr
Publication of EP3361571A1 publication Critical patent/EP3361571A1/fr
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H01Q17/007—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems with means for controlling the absorption
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
    • H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
    • H01Q15/0013—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
    • H01Q15/0026—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective said selective devices having a stacked geometry or having multiple layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H01Q17/004—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems using non-directional dissipative particles, e.g. ferrite powders

Definitions

  • the present disclosure relates to a multi-layer insulation (MLI) and radio-frequency (RF) absorber blanket having a frequency-selective structure (FSS) for blocking thermal radiation and managing electromagnetic interference (EMI), in particular for use in space (e.g. space telecommunications).
  • MMI multi-layer insulation
  • RF radio-frequency
  • EMI electromagnetic interference
  • MLI blankets are essential to the current space technology, and have been in use since the first days of space exploration.
  • a prior art MLI is composed of metalized polymer layers, the purpose of which is to block radiation concentrated in the infrared (IR) and visible spectral ranges.
  • IR infrared
  • MW microwave
  • MLI causes unwanted interference and even passive intermodulation (PIM) problems due to its high RF reflectivity in the specular direction.
  • PIM passive intermodulation
  • the present subject-matter relates to a RF absorber which built upon readily available and space qualified materials. This absorber proves to be capable of producing very low reflectivity values for very large bandwidths. Electrically speaking the final blanket assembly is a RF structure comprising "resonant cavities" in between several resistive layers. The resistive layers act so as to dissipate the energy "trapped" within the cavities. The more layers are added to the blanket stack, the higher the bandwidth that can be achieved.
  • MLI multi-mission satellites where several antennas are foreseen with different transmit (TX) and receive (RX) frequencies.
  • Embodiments of said RF absorber are disclosed for Ka-band but that the disclosed absorber can be easily customized for other bands as for instance, for C/Ku-bands, Ku-band, or Ku/Ka-bands.
  • the disclosed MLI is able to manage such RF reflections, and minimize them to an insignificant level, with reflectivity simulation for TE/TM polarized waves for incidence angles up to 30° below -25 dB, for entire Ku/K/Ka-bands, validated by experimental tests with absorption below -20 dB for normal incidence for Ka-band (see Fig. 8A ). The results are also validated for 30° incidence, even taking into account the thermal cycle (see fig. 8A' ).
  • the disclosed MLI can be easily tailored to Ku, K and Ka bands, with both narrow (see Fig. 8B ) and wide band performances (see Figs. 8C and 8D ), others frequencies are also possible and, other angles of incidence too, for example 45° or 60°.
  • the disclosed MLI is constructed using the available and space qualified materials typically used in standard MLI, therefore, the standard MLI properties, i.e., optical properties, thermal performance (was validated in TVAC at cycles up to 200 oC during 80 h), grounding, attachment, venting and outgassing are also fulfilled as typical MLI.
  • the standard MLI properties i.e., optical properties, thermal performance (was validated in TVAC at cycles up to 200 oC during 80 h), grounding, attachment, venting and outgassing are also fulfilled as typical MLI.
  • the disclosed RFMLI is from a thermal and mechanical point of view, performing similarly to a typical MLI, thus also achieving its original purpose.
  • the disclosed blanket can be correctly tuned to specific requirements (frequencies, absorption level, incidence angle%) keeping its very low RF reflectivity.
  • thermo multi-layer insulation (MLI) and radio-frequency (RF) absorber blanket comprising:
  • the upper layer comprises a polymeric film and a patterned metallic coating, said patterned metallic coating being a frequency-selective structure.
  • the polymeric film is polyimide film or polyester film, in particular a poly (4,4'-oxydiphenylene-pyromellitimide) or a poly (5,5'-Bi-2-benzofuran-1,1',3,3'-tetrone), or in particular a Kapton(tm) and Upilex(tm), or Mylar(tm) commercial film, respectively.
  • the metallic coating is vacuum deposited aluminium (VDA) on a polymeric substrate, in particular the upper layer is Kapton(tm) with VDA, or Mylar (tm) with VDA, or on Upilex (tm) with VDA, or on other substrate.
  • VDA vacuum deposited aluminium
  • the upper layer comprises a patterned polyimide film loaded with inorganic carbon, which is said patterned frequency-selective structure.
  • the upper layer comprises a patterned Black Kapton(tm) film as the frequency-selective structure and a polymeric film as a substrate of the Black Kapton(tm).
  • Black Kapton(tm) is a carbon filled polyimide film made by DuPont, having high absorptance, high emittance and surface resistivity. Other similarly conductive materials may be used, alternatively.
  • said patterned frequency-selective structure is obtainable by local tailored deposition or laying, followed by etching said pattern, in particular by laser etching.
  • said patterned frequency-selective structure is obtainable by cutting said pattern, in particular by laser cutting.
  • the patterned FSS sheet has a pattern of square, rectangular, hexagonal or circular patches arranged in a grid, in particular a pattern of unconnected patches arranged in a grid, further in particular a pattern of groups of in-group unconnected patches arranged in a grid.
  • the one or more intermediate resistive layers for RF attenuation are 1 to 5.
  • an intermediate resistive layer comprises a polyimide film loaded with inorganic carbon, in particular Black Kapton(tm).
  • an intermediate resistive layer further comprises a spacer layer.
  • a spacer layer is a polymeric layer, in particular a Upilex(tm) foam layer, a Dacron(tm) mesh layer, Beta Cloth scrim layer, Glass Fabric scrim layer, Ceramic Fabric scrim layer or a Nomex(tm) scrim layer.
  • An embodiment comprises one or more adhesive layers between any said contiguous layers and/or sheets.
  • an adhesive layer comprises transfer tape, in particular transfer tape 3M(tm) 9460 or 3M(tm) 966, or any other suitable adhesive, preferably space qualified when space applications are targeted.
  • said ground layer is a typical MLI or the first layer of a typical MLI comprising a deposited metallic coating, in particular a vacuum deposited aluminium (VDA) coating.
  • VDA vacuum deposited aluminium
  • Absorbing layers of carbon-loaded films in particular Black Kapton(tm) are well-proven materials and facilitate integration with the rest of the blanket (i.e., same manufacturing processes and techniques).
  • Black Kapton(tm) provides reason that an absorbing, thin film, is an achievable reality.
  • a somewhat thick layer or multiple layers.
  • FSS frequency selective surfaces.
  • These FSS act not only as RF filters per se, but also as focusing mechanisms that enhance the electric field on the lossy layers, thus maximizing absorption. This allows for less layers, thus reducing overall thickness.
  • this may come at a cost in terms of complexity and optimization effort; moreover, numerical modelling indicates that the efficacy of this architecture is somewhat dependent on the angle of incidence and the relative position of the layers (which is somewhat a problem, taking into account the mechanical nature of the MLI).
  • Resistive capacitive FSS layers can be constructed using Black Kapton(tm), whereas the capacitive FSS can be constructed using Kapton 1-side VDA (opaque to IR). Furthermore, the layer spacing can be assumed to be vacuum for any material with unitary relative permittivity.
  • FSS Frequency Selective Surfaces
  • a structure can be formed by a number of FSS structures interspersed by dielectric (or, in general, magneto-dielectric) layers (the FSS formed by square patches at the top of the structure).
  • the total thickness of the structure at the lowest operational frequency is a small fraction of the wavelength, while at its highest operational frequency it may be on the order of a wavelength or greater.
  • the period of the FSS structures must be significantly smaller than their operation wavelengths.
  • the structure can be modelled as a chain connection of low-pass LRC filters, i.e. as a simple RLC ladder network.
  • the stages in this chain filter circuit are tuned in such a manner that the first stage (the outermost layer) passes through the signals with frequencies below f1 (highest frequency), the second stage does the same for frequencies up to f2 which is smaller than f1, the third stage passes the signals up to f3 ⁇ f2, etc.
  • the waves with frequencies outside of the passband of a given stage are reflected.
  • the passing signals are absorbed in the resistive elements of the circuits they pass through.
  • the equivalent circuit is used as an RF absorber model to which optimization algorithm can be easily applied in order to achieve the desired frequency response, i.e., the desired RF absorptivity.
  • the physical dimensions and properties for the FSS layers and dielectric spacers can be readily obtained.
  • the final frequency response prediction for the RF absorber is then obtained by means of a 3D electromagnetic simulation.
  • the majority of materials considered for the absorber are readily available materials and most importantly they are space-qualified materials, which are usually used in the manufacturing of standard MLI blankets. Namely, the dielectric spacers which are composed by polyimide-based foams (or any other material RF transparent) and the resistive material, which is Black Kapton(tm).
  • a wideband RF absorbing MLI blanket can in fact be constructed as a stack of patterned metallic or resistive sheets, i.e., Frequency Selective Surfaces placed in between (or embedded into) layers of dielectrics.
  • a possible application could be the Gregorian type antenna, since the RF performance of the antenna is somewhat degraded by the use of standard MLI blankets due to their high RF reflectivity. It is one of the main objectives of this RF absorber blanket to mitigate these RF issues, whilst still maintaining the same properties of the standard MLI, i.e., thermal and optical properties as well as electrical grounding properties. In addition, due to its characteristics, it can also be used to mitigate for instance Passive Intermodulation (PIM).
  • PIM Passive Intermodulation
  • the RF absorber must also be capable of handle with the infrared (IR) energy, i.e., it must behave as an IR filter/shield.
  • the overall blanket must fulfil standard grounding requirements.
  • Ka-band was selected to be the operational frequency band for the RF absorbing MLI to be constructed as an embodiment. This is due to the ever-growing interest on this frequency band for satellite communications. In addition, the possible application, STANT antenna, has also previously undergone testing in this frequency band, hence, providing a good base for comparison, and consequently avoiding further testing/measurements.
  • the main RF specifications for an embodiment of the RF absorbing blanket are: Frequency band: 19 to 30 GHz; Return loss higher than 20 dB; Incidence angles up to 60o.
  • the multi-layer FSS structure according to the disclosure has indeed the potential to easily cover the Ka-band with RF reflection values well below -20 dB. Ka-band is being widely spread among telecom satellites.
  • AMC absorber Because its working principle is based on that of an Artificial Magnetic Conductor, i.e., AMC, composed by a single metallic FSS (aluminum) structure, a resistive layer (Black Kapton) and a dielectric spacer, which can be considered to be equivalent to vacuum.
  • AMC Artificial Magnetic Conductor
  • the metallic FSS can be constructed by etching the aluminum coating of a polymeric sheet. Due to the very small aluminum thickness, this metallic FSS construction is considerably faster than that of resistive FSS (Black Kapton) needed for the wideband concept discussed before.
  • the metallic FSS acts as an IR shield.
  • the FSS is composed by an array of relatively large aluminum squares with very small spacing in between, resulting in a practically opaque layer to the infrared spectrum.
  • the dielectric spacers may consist on polyimide based foams
  • the resistive sheets can be standard Black Kapton foils
  • the metallic FSS that sits on top of the absorber can be constructed by laser etching of the aluminum deposited on a polymeric foil.
  • the layup also contemplates several adhesive layers.
  • the main purpose of these layers is to enable a tight fitting of the remaining layers that compose the absorber, hence avoiding "air gaps" on the layers interface.
  • improved assembling methods without using the adhesive layers are also possible so as to mitigate the effect of the air gaps.
  • the impact of the adhesive layers on the RF performance of the absorber can be easily taken into account. However, the impact of the adhesive layers on frequency response is minimum and the performance of the RF absorber with adhesive layers is still well within the specifications.
  • the RFMLI performance was tested for different angles of incidence, namely normal, 5o, 10o, 20o, 30o, 40o, 45o, 50o and 60o for TE polarized waves and for TM polarized waves.
  • the absorber reflection response is still very acceptable for incidence up to 30o as the reflection coefficient is below -20 dB.
  • the reflection response is not so good for 60o, nevertheless a significant absorption level is still verified for the entire frequency band.
  • an alternative embodiment may be tuned to have the same reflection coefficient (below -20 dB) at 60° incidence or almost any other angle.
  • the disclosed absorbers work by transforming RF Power into heat. This power exchange occurs on the resistive sheets located in between the dielectric layers.
  • One of the primary functions of a standard MLI blanket is to control/deal with temperature gradients, thus, it is of utmost importance to analyze how much heat is generated within the RF absorber so that the remaining MLI blanket can be designed accordingly.
  • One way of accomplish this is by identifying the percentage of RF power dissipated by the different resistive sheets within the RF absorber. The outermost resistive sheet dissipates the most RF power within the operational frequency band, hence, this becomes the most critical sheet, as it is the one that generates more heat.
  • the outmost layer of the absorber can be a metallic FSS, which by itself acts as a natural IR filter/shield.
  • the metallic FSS structure consists on a metallic pattern etched on aluminum.
  • the FSS pattern considered within the scope of this work is that of a simple array of metallic rectangles. This choice was motivated due to the symmetry of the square array structure and mainly because cause this type of pattern has a capacitive behaviour (equivalent circuit capacitor) which can be predicted analytically.
  • the FSS structure is completely defined by its period and by the spacing between the rectangles, i.e., the gap. As expected (parallel plate capacitor) the FSS capacitance increases by decreasing the gap between the rectangles.
  • the capacitance is higher when considering larger period values (for the same gap).
  • the effective capacitance is practically independent of frequency (e.g. considering a gap of 30 ⁇ m).
  • the FSS performance we intuitively see that the smaller the gap, the better IR shield the FSS shall be.
  • standard MLI blankets are usually featured with grounding pads which are connected to the frame of the spacecraft by grounding cables so as to discharge the static charges.
  • the top layer of standard MLI blankets is usually composed by a continuous sheet of aluminum, which facilitates the flow of charges.
  • the top layer of the absorber is a surface of metallic squares which are not electrically connected with each other.
  • the inclusion of a grounding mesh on the FSS pattern can be used.
  • the grounding mesh period can be large enough so it does not interfere with the operation of the FSS structure. This can in principle be accomplished by ensuring that the grounding mesh period is relatively larger than the longest wavelength on the FSS operational frequency band.
  • the grounding path must provide a low DC resistance.
  • PIM Passive Intermodulation
  • an RF absorber blanket was designed by running an optimization algorithm for all the relevant parameters on the equivalent circuit, so as to achieve minimal reflectivity.
  • the preliminary tests for this absorber did not produce acceptable results.
  • the theoretical (equivalent circuit) results were in fairly good agreement with those of the 3D electromagnetic simulations indicating that the problem was on the electric properties considered for the several materials constituting the blanket, which are the same for both the theoretical and 3D simulation models.
  • further characterization for the materials, more specifically the Black Kapton material was needed in order to accurately model the RFMLI for synthesis design of said absorbers.
  • the actual values of permittivity for the Black Kapton are many times higher than those initially considered. Hence, the equivalent circuit model must be modified accordingly.
  • the Black Kapton film cannot be considered as a simple resistor within the equivalent circuit. With such high permittivity values, and for the considered operational frequency band, we must also contemplate the electrical length for these resistive films, i.e., we must account the electromagnetic propagation of the RF waves through the Black Kapton films. Notice that the adhesive layers may now be taken into consideration within the equivalent circuit in order to obtain the best possible agreement between the equivalent circuit results and those from the 3D electromagnetic model.
  • ⁇ and ⁇ are the attenuation and propagation constants respectively, and ⁇ and ⁇ are the permittivity and conductivity values.
  • ⁇ is the complex propagation constant referred above. From the values of complex propagation constant and complex medium impedance, an admittance matrix can be created and introduced in the equivalent circuit.
  • the electric field due to the gaps between the FSS squares extends beyond the Kapton and adhesive layers.
  • the electric field extends to these adjacent layers, consequently, the total capacitance for the FSS structure will be different.
  • these extra layers have relatively high permittivity, we shall see that the capacitance values for the FSS, when placed on top of these layers, shall be higher than what was previously considered.
  • Figure 1 illustrates an embodiment comprising the following layers: FSS on top VDA coating of Kapton 25 ⁇ m layer, Black Kapton layer, spacer layer and ground layer.
  • Figure 2 illustrates an embodiment comprising the following layers: FSS on bottom VDA coating of Kapton 25 ⁇ m layer, Kapton 25 ⁇ m layer, Black Kapton layer, spacer layer and ground layer.
  • This embodiment is very similar to the previous embodiment, except for the optical properties of the top layer are thus correspondingly altered.
  • FIG. 3 illustrates an embodiment comprising the following layers: FSS on Black Kapton layer, Kapton layer, spacer layer and ground layer.
  • the FSS is obtained from the Black Kapton layer itself and including a support layer which is Kapton layer. Additionally, a top RF transparent layer for obtaining specific optical properties can be added.
  • Figure 4 illustrates an embodiment comprising the following layers: FSS on Black Kapton layer, Kapton layer, spacer layer, FSS on Black Kapton layer, Kapton layer, spacer layer and ground layer.
  • the FSS is obtained from the Black Kapton layer itself and including a support layer which is Kapton layer.
  • This embodiment is very similar to the previous embodiment except for a repetition of the FSS of the Black Kapton and spacer layers. Depending on the number of layers, this configuration can be considered a broadband configuration. Additionally, a top RF transparent layer for obtaining specific optical properties can be added.
  • Figure 5 illustrates an embodiment comprising the following layers: FSS on top VDA coating of Kapton 25 ⁇ m layer, spacer layer, Black Kapton layer, spacer layer, Black Kapton layer, spacer layer and ground layer. This is a wideband structure which may comprise additional layers.
  • Figure 6 illustrates an embodiment comprising the following layers: FSS on bottom VDA coating of Kapton 25 ⁇ m layer, spacer layer, Black Kapton layer, spacer layer, Black Kapton layer, spacer layer and ground layer.
  • This embodiment is very similar to the previous embodiment except the optical properties of the top layer are thus correspondingly altered.
  • This is a wideband structure which may comprise additional layers.
  • Figure 7 illustrates an embodiment of a RF transparent layer to be used as an IR filter top layer. It comprises two complementary FSS layers obtained from VDA. It is necessary a substrate for the VDA, for example a Kapton layer. This embodiment is designed such that it does not interfere with the layers below and is thus 'RF transparent'.
  • Figure 8 illustrates experimental results of RF absorption for (A) Ka-band, (B) for Ku-band, (C) for C/Ku-Bands, (D) RF absorption for Ku/Ka-bands.
  • FIG. 9 illustrate equivalent circuit of embodiment according to the present disclosure.

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EP17156431.3A 2017-02-10 2017-02-16 Isolant multicouche thermique et couverture absorbante de radiofréquence Withdrawn EP3361571A1 (fr)

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CN109638448A (zh) * 2018-12-12 2019-04-16 航天科工武汉磁电有限责任公司 一种超材料天线罩及天线系统
CN110600885A (zh) * 2019-09-04 2019-12-20 北京理工大学 一种具有吸收-反射-吸收特性的频率选择表面
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CN111029788A (zh) * 2019-12-11 2020-04-17 中国电子科技集团公司第十四研究所 具有角度与极化不敏感性的宽带超材料吸波结构
WO2021000732A1 (fr) * 2019-06-30 2021-01-07 Oppo广东移动通信有限公司 Ensemble boîtier, ensemble antenne et dispositif électronique
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CN109449601A (zh) * 2018-10-31 2019-03-08 宋应龙 一种基于低通和带通多层耦合的超宽带频率选择表面单元
CN109449601B (zh) * 2018-10-31 2020-10-02 宋应龙 一种基于低通和带通多层耦合的超宽带频率选择表面单元
CN109638448A (zh) * 2018-12-12 2019-04-16 航天科工武汉磁电有限责任公司 一种超材料天线罩及天线系统
WO2021000732A1 (fr) * 2019-06-30 2021-01-07 Oppo广东移动通信有限公司 Ensemble boîtier, ensemble antenne et dispositif électronique
CN110600194A (zh) * 2019-08-24 2019-12-20 泉州柔丝蓝新材料科技有限公司 一种柔性透明导电膜制备工艺
CN110600885A (zh) * 2019-09-04 2019-12-20 北京理工大学 一种具有吸收-反射-吸收特性的频率选择表面
CN112803171A (zh) * 2019-11-14 2021-05-14 南京理工大学 采用小型化频率选择表面的电磁透镜
CN112803171B (zh) * 2019-11-14 2022-08-12 南京理工大学 采用小型化频率选择表面的电磁透镜
CN111029788A (zh) * 2019-12-11 2020-04-17 中国电子科技集团公司第十四研究所 具有角度与极化不敏感性的宽带超材料吸波结构
CN113224511A (zh) * 2021-04-23 2021-08-06 华南理工大学 一种基于混合谐振模式谐振腔的波导滤波天线阵列
CN113329607A (zh) * 2021-05-31 2021-08-31 中国人民解放军空军工程大学 一种新型超宽带吸波单元及其吸波结构
CN113329607B (zh) * 2021-05-31 2022-08-02 中国人民解放军空军工程大学 一种新型超宽带吸波单元及其吸波结构

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