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Integrated design of component and configuration for a flexible and ultrabroadband radar absorbing composite
Accepted Manuscript Integrated design of component and configuration for a flexible and ultrabroadband radar absorbing composite Qunfu Fan, Yixing Huang, Mingji Chen, Ying Li, Weili Song, Daining Fang PII:
S0266-3538(18)32640-X
DOI:
https://doi.org/10.1016/j.compscitech.2019.04.008
Reference:
CSTE 7616
To appear in:
Composites Science and Technology
Received Date: 31 October 2018 Revised Date:
5 March 2019
Accepted Date: 7 April 2019
Please cite this article as: Fan Q, Huang Y, Chen M, Li Y, Song W, Fang D, Integrated design of component and configuration for a flexible and ultrabroadband radar absorbing composite, Composites Science and Technology (2019), doi: https://doi.org/10.1016/j.compscitech.2019.04.008. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Integrated design of component and configuration for a flexible and ultrabroadband radar absorbing composite Qunfu Fan1, Yixing Huang2, Mingji Chen1,3*, Ying Li1,3*, Weili Song 1, Daining
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Fang1,3 Beijing Key Laboratory of Lightweight Multi-functional Composite Materials and
Structures, Beijing Institute of Technology, Beijing 100081, PR China
School of Civil Engineering and Transportation, South China University of
Technology, Guangzhou 510641, PR China
State Key Laboratory of Explosion Science and Technology, Beijing Institute of
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Technology, Beijing, 100081, PR of China
Corresponding Author: Mingji Chen(E-mail: [email protected]);
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Ying Li (E-mail: [email protected]);
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ACCEPTED MANUSCRIPT Abstract: To achieve ultra-broadband radar absorption at small thickness, the integrated design of component and configuration of a rubber matrix flexible radar absorbing composite (RAC) is performed in the present study. At the material
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component level, hydrogenated acrylonitrile butadiene rubber (HNBR) reinforced by flaky carbonyl iron particles (FCIP) ensures the considerable permeability of RAC, as well as its good flexibility, mechanical strength and elongation to break. At the structure design level, a novel modified step-configuration (MSC) is proposed
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through full-wave calculation. The preparation process of RAC with the modified
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step-configuration includes components mixing in a two-roll mixer and hot-press moulding. Radar reflectivity testing experiment demonstrates that, by integrated design of component and configuration, the absorbing bandwidth corresponding to -10dB can span from 2GHz to 30GHz for a 5mm-thick composite absorber.
absorber 1.
Introduction:
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Keywords: Radar absorbing composite, Rubber matrix, Structure design, Broadband
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With the rapid development of high precision electronic equipment and radar detection technology, the radar target without special design is difficult to avoid being
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detected. Many strategies have been performed to reduce the chances of being detected for radar target, such as the application of radar absorbing materials (RAMs) and radar absorbing structures (RASs)[1-7]. On the whole, the RAMs contain dielectric-loss materials and magnetic-loss
materials. In recent years, many excellent dielectric-loss RAMs, such as dielectric-loss carbon materials and transition metal oxides or chalcogenides, have been fabricated by novel methods. The typical carbon materials include carbon nanotubes (CNT)[8], carbon fibers[9], graphene[10], reduced graphene oxide 2
ACCEPTED MANUSCRIPT (RGO)[11] and so on, while the radar absorbing transition metal oxides or chalcogenides contain nanostructured ZnO[12], MnO2[13], TiO2[14], MnSe2[15], etc. In general, the dielectric-loss mechanism of these RAMs is mainly attributed to the
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conduction loss and dielectric relaxation which are influenced by conductivity and polarization respectively under the altering electromagnetic field[16]. Besides dielectric-loss RAMs, magnetic-loss RAMs has also been widely studied[17]. The magnetic dissipation of magnetic-loss RAMs mainly includes eddy current loss,
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ferromagnetic resonance, and hysteresis loss[18, 19]. As a conventional magnetic
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absorbent, spherical carbonyl iron particles (SCIP), have been used in microwave absorption for many years, due to their large permeability and high Snoek’s limit at high frequency[20-23]. However, compared to SCIP, flaky carbonyl iron particles (FCIP), as another form of carbonyl iron particles, have higher permeability, lower
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permittivity, and better filling characteristics[21-23].
Generally, the absorption bandwidth of RAMs is relatively narrow, though their absorption intensity is strong. In contrast, RASs can be designed to achieve broader
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absorption bandwidth, at the cost of larger thickness. Typical RASs include pyramidal structure[24] which is mainly applied in anechoic chambers, and
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honeycomb structure[25] whose thickness is exceeding 10mm for broadband absorption over 2GHz to 14GHz. For another type of RASs consisting of frequency selective surface (FSS)[1, 26] and load bearing dielectric spacer, typical thickness for broadband absorption is also 5~10mm or even larger, with the absorption band within 4GHz to 18GHz. Recently, the periodic stepped RASs[27, 28] have attracted many attentions, because of the λ/4 resonance and edge diffraction effect which has been proved to be helpful in creating multiple absorption peaks to reduce broadband reflection at relatively small thickness[29-32]. 3
ACCEPTED MANUSCRIPT On the other hand, flexible rubber RASs which possess favorable absorbing performance, could be applied in many special fields because of their large elongation at break and deformation recovery[33]. In this study, hydrogenated acrylonitrile
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butadiene rubber (HNBR), which exhibits high elasticity, good mechanical properties[34] and good processing property was chosen as matrix. The flaky carbonyl iron particles (FCIP) were dispersed into the HNBR matrix to fabricate radar absorbing composites with considerable permeability as well as large elongation and
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flexibility. Then, structure design of the flexible radar absorbing composite (RAC)
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was performed by numerical simulation and a novel modified step-configuration (MSC) for broadband absorption was obtained. Radar reflectivity testing experiment demonstrated that, by integrated design of component and configuration, the absorbing bandwidth corresponding to -10dB can span from 2GHz to 30GHz for a
2.
Experimental
2.1 Materials
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5mm-thick composite absorber.
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Hydrogenated acrylonitrile butadiene rubber (HNBR) was used as raw material (Zetpol 1000L, produced by Zeon Corporation, Japan). The flaky carbonyl iron
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particles (FCIP) were purchased from Gansu Metal Flake Material Technology LTD. China. The vulcanizing agent dicumyl peroxide (DCP) (analytical grade) was supplied by Beijing Chemical Reagents Co., Ltd. China. 2.2 Preparation methods of RAC The matrix material HNBR was dried in drying oven for 24 hours. The cured HNBR and different mass fraction of FCIP were mixed in a two-roll-mixer at 80 for 20min. FCIP in HNBR-FCIP composite were 100phr, 200phr, 300phr, 400phr (parts per hundred rubber by weight) respectively. As vulcanizing agent, 3phr DCP 4
ACCEPTED MANUSCRIPT was added for each composite. The composite was mixed for another 10min in the mixer, and then removed from mixer for curing. The curing approach was hot-pressing for 10min, in the steel mold at 160 , under a pressure of 10Mpa. The
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prepared composites specimens, named as RAC-100, RAC-200, RAC-300, and RAC-400, were cut into different sizes for electromagnetic parameters tests in corresponding frequency band. The electromagnetic parameters of the composite specimens were measured by waveguide transmission line method. The sizes of the
47.55mm*22.15mm*2mm,
34.85mm*15.8mm*2mm,
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72.14mm*34.04mm*2mm,
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specimens suitable for the rectangular waveguide for different waveband, were
22.86*10.16mm*2mm, respectively. The schematic diagram of the manufacturing
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procedures was shown in Fig.1.
Fig.1. The procedures of manufacturing RAC and MSC, and the sketch of measuring 5
ACCEPTED MANUSCRIPT electromagnetic parameter and reflectivity. 2.3 Preparation of MSC As shown in Fig.1, a steel mold with designed periodical structure was prepared
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by computerized numerical control (CNC). The composites with different content of FCIP prepared by two-roll-mixer, were placed on the steel mold, and covered by a steel plate. The composites were shaped and cured in the designed steel mold, and the curing strategy was hot-pressing for 10min at 160
, under a pressure of 10Mpa. The
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as-fabricated absorbing structures with different content of FCIP were named as
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MSC-200, MSC-300 and MSC-400. The reflectivity of the MSC specimens was measured from 2GHz to 40GHz by the arch framing reflection method, and the sizes of the prepared MSC specimens were 300mm*300mm for 2GHz~18GHz measurement and 180mm*180mm for 18GHz~40GHz measurement.
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2.4 Characterization
Micromorphology of the fabricated RAC were studied by Field-emission scanning electron microscopy (FEI QUANTA 450 FEG system). The element
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components of the composites were characterized by energy dispersive spectroscopy (EDS). Mechanical performance of the RAC was investigated with a tensile tester
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(Zwick/roell Z010) according to Chinese national standard GB/T 528-1998. Vector network analyzer (Ceyear AV3672D) was used to measure the electromagnetic parameters of the RAC specimens by waveguide transmission line method and the reflectivity of the fabricated MSC was measured by the arch framing reflection method with Vector network analyzer. CST Microwave Studio software was used to simulate the reflectivity of the RAC and the designed MSC.
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Result and discussion
3.1 Morphology of the RAC The dispersion of fillers in the matrix could affect the electromagnetic
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characteristics of the composites[35]. In this study, Field-emission scanning electron microscopy (FESEM) was used to observe the shape, dimension, and dispersion of FCIP in the fabricated RAC. Fig.2 shows the surface and sheared cross profile morphology of the RAC. In RAC with different mass fraction of FCIP, the FCIP are
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uniformly dispersed in HNBR matrix with no obvious agglomeration, because the
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shearing force provided by the roll-mixer in the mixing process could overcome the van der Waals force between particles[36]. The diameters of FCIP in the RAC, are ranged from 3µm to 10µm, while the thickness from 0.2µm to 0.8µm. As shown in Fig.2 (a), (c), (e), the fillers increase in turn and disperse uniformly in the matrix.
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Fig.2 (b), (d), (f) shows that the dispersion of FCIP in the inner of the RAC is homogeneous. The component of prepared composites can be characterized by energy dispersive spectroscopy (EDS). Fig.2 (h) shows the co-existent elements include
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element carbon (C) and ferrum (Fe) in the composite RAC-400. And all the positions of ferrum (Fe) in Fig.2 (h) is matching with the EDS of pure FCIP[22]. Obviously,
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element carbon (C) is from rubber matrix and ferrum (Fe) is from FCIP. As shown in Fig.2 (g), EDS mapping confirms the homo-disperse of ferrum (Fe) element in RAC-400. The FESEM morphology and EDS suggest that the uniform RAC can be fabricated by this processing procedure.
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Fig.2. FESEM images of the RAC with different content of FCIP. (a), (c), (e) are
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surface morphology of RAC-200, RAC-300, RAC-400 respectively. (b), (d), (f) are the sheared cross profile morphology of RAC-200, RAC-300, RAC-400 respectively, (g) is the mapping of Fe element in RAC-400, (h) is EDS of RAC-400.
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3.2 Mechanical properties of RAC
Fig.3. Tensile strength (a) and Stress-Strain curve (b) of the RAC with different mass fraction of FCIP.
Fig.3 shows the tensile strength (TS) and the stress-strain curve of the RAC with different mixing mass fraction of FCIP. Meanwhile, Table I summarizes tensile properties of RAC, including tensile strength (TS), elongation at break (EB), and Young’s modulus. As shown in Fig.3 (a) (b), the TS of RAC increases with the 8
ACCEPTED MANUSCRIPT increase of FCIP first, and then decreases, while the tendency of the (EB) is similar with that of the TS. The increase in TS and EB may be attributed to the random distribution of FCIP in HNBR matrix, the strong interfacial interaction caused from
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the high specific surface of FCIP[37], and the synergistic effect of macromolecule chain slippage and orientation of FCIP[38]. The TS and EB decrease at higher FCIP loading due to the aggregation tendency of FCIP in rubber matrix[37]. Table I shows that the Young’s modulus increases with the increasing of FCIP in RAC. The increase
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of Young’s modulus, which is likely attributed to the steric hindrance of FCIP itself
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and the strong interaction of filler-matrix[37] reveals that the flexibility of the RAC will reduce. Even so, the RAC-400 is still flexible.
Table I. Tensile properties of the RAC with different mass fraction of FCIP Tensile Strength
Elongation at Break
Young’s Modulus
(MPa)
(%)
(MPa)
HNBR
10.41±1.05
1483
1.23
RAC-100
17.58±1.39
1800
1.16
RAC-200
16.02±0.69
1774
2.50
RAC-300
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Composite type
12.14±0.95
1480
3.06
9.09±0.42
1125
5.02
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RAC-400
3.3 Microwave absorbing properties of the single-layered RAC In order to achieve the electromagnetic characteristic of the RAC with different
mass fraction of FCIP, the specimen RAC-200, RAC-300 and RAC-400 were fabricated. Their electromagnetic parameters including complex permittivity and complex permeability were measured by waveguide transmission line method. The measured electromagnetic parameters would be used to simulate the reflectivity of the 9
ACCEPTED MANUSCRIPT designed MSC and the single-layered RAC with different thickness. Generally, the absorbing properties of magnetic composites are attributed to hysteresis, domain wall resonance, nature ferromagnetic resonance and eddy current
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losses. The domain wall resonance usually does not occur in gigahertz frequency band, while the hysteresis loss can be neglected in weak fields. Contrast to eddy current loss in spherical iron carbonyl particles (SCIP) composite, nature resonance occurs in FCIP composite in gigahertz frequency band[39].
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According to the λ/4 resonance mechanism, the absorbing peak of single-layered
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composite panel exists at the frequency point where standing wave is generated[40]. Base on transmission line theory, the microwave absorption (MA) properties of the prepared composites can be calculated by the reflection loss (RL) as the following formulas[41, 42]:
Zin=(µr/ɛr)1/2tanh[2 fdj(µr/ɛr)1/2]
(1)
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RL=20log10│(Zin-Z0)/(Zin+Z0)│
Zin--- the normalized input impedance of the absorber; Z0---impedance of free space;
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µr---relative complex permittivity of the absorber; ɛr---relative complex permeability of the absorber;
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c---velocity of electromagnetic wave in vacuum; d---thickness of the absorber;
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π
(2)
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Fig.4. 3D plot of the calculated reflectivity of RAC-200 (a), RAC-300 (b), RAC-400 (c) versus frequency and thickness. Frequency dependence of reflectivity of the three
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samples with the thickness of 2mm (d)
The calculated theoretical reflectivity of single-layered RAC with different thickness was presented in the three dimensional (3D) plots in Fig.4. As shown in
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Fig.4(a), (b), (c), all of the single-layered RAC (including RAC-200, RAC-300,
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RAC-400), reveal similar tendency. With the thickness of the RAC increasing, the absorption peaks become stronger, and shift to lower frequency simultaneously till disappear out of the measured frequency band. Generally, when reflectivity -10dB, the materials can be applied for electromagnetic wave absorbing[43]. The frequency region which is below -10dB can be marked “available absorption bandwidth”. Fig.4 (a), (b), (c) suggest that just increasing the thickness of the single-layered RAC cannot extend the “available absorption bandwidth”. Fig.4 (d) shows the frequency dependence of reflectivity of the single-layered 11
ACCEPTED MANUSCRIPT RAC with the thickness of 2mm. In Fig.4 (d), when the thickness of the single-layered RAC is 2mm, the available bandwidth of RAC-200, RAC-300, RAC-400 are 3.8GHz, 2.2GHz, 1.1GHz, while the corresponding peak value are
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-17dB, -16dB, -14dB respectively. With the mass ratio of FCIP increasing, the absorbing properties of the single-layered RAC are weakening in 2GHz-18GHz frequency band. Obviously, when the thickness of the single-layered RAC is fixed, it is difficult to improve their absorbing properties just improving the mass ratio of
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fillers.
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In order to improve the radar absorbing properties of RAC, a modified step-configuration (MSC) will be developed in this research.
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3.4 Microwave absorbing properties of the novel MSC
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Fig.5. The diagram of NTSS (I), and the reflectivity of NTSS with different side length of the top layer (II) Before the MSC is proposed, several normal three layers periodic stepped
structures (NTSS) are investigated with the electromagnetic parameter of RAC-400. As showed in Fig.5 (I), the geometric parameters of the NTSS are marked as “a, b, c and h1, h2, h3”. And a=15mm, b=12mm, c= (0, 4, 8, 10, 12mm respectively), h1=1mm, h2=1mm, h3=3mm. When c is 0 mm, the corresponding NTSS is marked as NTSS-C0, and the reflectivity of NTSS-C0 is depicted in Fig.5 (II). Meanwhile, the 12
ACCEPTED MANUSCRIPT NTSS-C4, NTSS-C8, NTSS-C10, NTSS-C12 represent the NTSS with c= (4, 8, 10, 12mm) respectively, and the corresponding reflectivity of NTSS are depicted in the same graph Fig.5 (II). As shown in Fig.5 (II), with c increases from 0 mm to 12 mm,
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the volume fraction of the NTSS unit increases from 32.8% (NTSS-C0) to 71.2% (NTSS-C12). The absorption properties of the NTSS strengthen first, and weaken subsequently. It reveals that the absorption properties of the NTSS probably reach to a top with the increase of volume fraction of the NTSS unit, and the top might exist
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between NTSS-C8 and NTSS-C10.
Fig.6 The schematic of designed MSC (I), the fabricated MSC (II), the simulated reflectivity of the MSC with different D (III), L, H (IV). The inset is the detail of 2~4GHz in (III). The outline of the proposed MSC is shown in Fig.6 (I). The bottom layer and middle layer are slabs with the side length 15mm (L1=15mm) and 12mm (L2=12mm), 13
ACCEPTED MANUSCRIPT the height 1mm (H1=1mm) and 1mm (H2=1mm). The top layer of the designed MSC is a cube with four cubes surrounded. The geometric parameters of the cubes are marked as D, H and L, W, H. On the premise of retaining the basic outline, the
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influences of size of the top layer cubes on the absorption performance are investigated. As shown in Fig.6 (III), when L, W, H are 8mm, 2mm, 3mm respectively, from 2GHz-2.75GHz, the absorption of MSC improve with the increasing of D, and from 18GHz to 30GHz, the absorption decrease. In order to
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balance the absorption in low frequency band (2~4GHz) and the broadband
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absorption, edge length of the center cube of the top layer is designed as 4mm. The influence of edge length of the four surrounding cubes on the absorption is also studied, and shown in Fig.6 (IV). When D, W, H are 4mm, 2mm, 3mm respectively, with L increasing from 4mm to 8mm, the effective absorbing bandwidth ( -10dB)
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increase gradually in the whole 2GHz-30GHz frequency range. When D, W, L are 4mm, 2mm, 8mm respectively, with H increasing from 1mm to 3mm, the total thickness of MSC increase from 3mm to 5mm. Obviously, the effective absorbing
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bandwidth extends with the increasing of thickness. Integrating the absorption in low frequency stage and effective absorbing
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bandwidth in 2GHz-30GHz frequency range, the best geometrical parameter for MSC is confirmed as D=4mm, L=8mm, W=2mm, H=3mm. Namely the assembly (D=4mm, L=8mm, W=2mm, H=3mm, H1=H2=1mm, L1=15mm, L2=12mm) is selected for fabrication of MSC whose total thickness is 5mm, and the volume fraction of this MSC is 54.13%, falling in between 49.87% (NTSS-C8) and 59.47% (NTSS-10). As an important factor for designed artificial absorbing structure, impedance matching of the designed structure is investigated. The effective input impedance (Zeff) of the designed structure can be obtained from the formula[27, 44]: 14
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Zeff = [
=(
1/2 )
(3)
εeff, µeff are the effective permittivity and permeability respectively. In this paper, the structures are backed by a metallic plane, │S21│= 0. The real
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and imaginary part of complex S11 can be gained from the simulation of the structures by CST Microwave Studio software. The real and imaginary part of Zeff can be calculated according to formula (3). The real part and imaginary part of Zeff are
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marked as Zeff(real) and Zeff(imag) . Generally, if the Zeff(real) is closer to unity and Zeff(imag) is closer to zero, the Zeff of the structure is matched to that of free space
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better, and the reflection is weaker[27]. In order to illustrate the degree of the Zeff(real) close to unity and Zeff(imag) close to zero, the formula “Ʃ[Zeff(real)-1]2/n” and “Ʃ [Zeff(imag)-0]2/n” (“n” is the amount of frequency points in the test frequency range), which are similar with variance in statistics, are introduced in this research, and
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marked as α and β for short. The statistical results are summarized in table II. Table II. The matching degree of Zeff(real) to 1 and Zeff(imag.) to 0 for different
Structure NTSS-C8
β=Ʃ [Zeff(imag.)-0]2/n
49.87%
0.2245
0.2709
54.13%
0.1762
0.2061
59.47%
0.2794
0.3179
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MSC
α=Ʃ [Zeff(real)-1]2/n
Volume Fraction
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structures
NTSS-C10
As shown in table II, “α” and “β” of the MSC are 0.1762 and 0.2061
respectively, which are less than that of NTSS-C8 (0.2245 and 0.2709) and NTSS-C10 (0.2794 and 0.3179). It means that, compared with that of the NTSS-C8 and NTSS-C10, Zeff(real) of the MSC is closer to unity, and Zeff(imag.) of the MSC is closer to zero. It suggests that the impedance of the MSC matches better with the 15
ACCEPTED MANUSCRIPT impedance of free space than that of NTSS-C8 and NTSS-C10 over the test frequency range[27, 44]. The radar absorption property of the designed MSC with different content of
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FCIP is simulated, and the simulated reflectivity of the designed MSC is presented in Fig.7 (I). To aid comparisons with the simulated reflectivity, the measured experimental reflectivity of the fabricated MSC-300 and MSC-400 are also depicted
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in the same graph, as showed in Fig.7 (II).
Fig.7. The comparison of simulated and experimental reflectivity of MSC with different content of FCIP (I, II).
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The simulated reflectivity of MSC-200, MSC-300, and MSC-400 are shown in Fig.7 (I). The former possesses effective bandwidth (
-10dB in general) from
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3.71GHz to 30GHz, the middle one from 2.72GHz-30GHz, while the latter covers 2.38GHz-29.28GHz.
The experimental reflectivity curves in Fig.7 (II) show that the effective
bandwidth of the fabricated MSC-300 is from 2.72GHz to 30GHz, and that of the MSC-400 covers the total frequency range of 2-30GHz. In addition, for the different MSC, the tendency of experimental reflectivity and simulated reflectivity are similar in the frequency range of 2-30GHz. It means that the experiment and the simulation 16
ACCEPTED MANUSCRIPT match well. Therefore, the simulation about the MSC by CST software is credible. 3.5 Absorption mechanism As marked at the simulated reflectivity curve (Fig.7 II), there are four absorption
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peaks corresponding with frequency points 3.24GHz, 7.18GHz, 15.09GHz, 24.85GHz, respectively. The distributions of the electric field, magnetic field, and power loss (PL) of MSC-400 at the four absorption peaks are simulated. As shown in Fig.8, the 3D diagrams and cross sections of the distributions are mapped. At the first frequency
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point 3.24GHz, as shown in Fig.8 (a), the electric field concentrates on the gap of the
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top layer of MSC-400 in the x-z plane and the gap between the top layers of adjacent units in the x-z plane. As for the magnetic field, in the y-z plane, concentration not only takes place on the gap of top layer of MSC-400 and two side edges of the MSC-400 bottom, it also distributes in the gap between the middle layers of adjacent
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units. The PL concentrates on the two side edges of the bottom of MSC-400, overlapping the magnetic field distribution. The result indicates that the power loss of electromagnetic wave on MSC-400 is attributed to magnetic loss. More precisely, the
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field concentration derives from nature resonance[39]. In addition, the power loss distributes in the inner of the MSC-400 bottom layer. Therefore, the power loss at
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3.24GHz may be attributed to the standing wave which is generated in the bottom layer of MSC-400 according to λ/4 resonance[40]. Fig.8 (b) shows that the electric field distribution on the MSC-400 at 7.18GHz shifts to the top gap of the top layer in the x-z plane. The magnetic field distribution concentrates on the inner of the gap of the top layer and the surface of top layer in the y-z plane. The PL at 7.18GHz concentrates on the surface of top layer in the y-z plane. The PL distribution and the magnetic field distribution overlap on the surface of top layer at 7.18GHz indicating that the PL at 7.18GHz is mainly attributed to strong edge diffractions of magnetic 17
ACCEPTED MANUSCRIPT field. Fig.8 (c) gives the electric field, magnetic field, PL distribution at 15.09GHz. The electric field distribution concentrates on the gap of top layers between adjacent units in the x-z plane. The magnetic field distributes on the top of MSC-400 in the y-z
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plane and concentrates on the gap of the adjacent units in the x-z plane. The PL distribution which is similar to that of magnetic field, concentrates on the top of MSC-400 in the y-z plane, and the two sides of MSC-400 in the x-z plane. Strong resonance between adjacent units and strong edge diffraction are two major
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mechanisms for field distortion.
Fig.8. The distributions of electric field, magnetic field, and power loss of the MSC-400 at the different absorption peaks. The corresponding frequency points are (a) 3.24GHz, (b) 7.18GHz, (c) 15.09GHz, (d) 24.85GHz respectively As shown in Fig.8 (d), at 24.85GHz, the electric field distribution is similar with the distribution at 15.09GHz. The difference is that the electric field distributes 18
ACCEPTED MANUSCRIPT in the gap of MSC-400 in the x-z plane at 24.85GHz while is weakened at 15.09GHz. The distribution of magnetic field and PL are nearly identical in the y-z plane. In the x-z plane, the magnetic field concentrates on the bottom of MSC-400 gap and the gap
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between middle layers of adjacent units while the PL concentrates on the two side edges of the bottom layer and the middle layer. This PL distribution suggests that when the electromagnetic wave concentrates on the designed MSC-400, the power loss results from the magnetic loss in the way of edge diffraction and resonance
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between the adjacent units. In a word, the power loss of the electromagnetic wave on
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the designed MSC-400 is mainly attributed to the magnetic loss induced by λ/4 resonance of magnetic field in the bottom layer, the edge diffraction of magnetic field at the edge of top layer, and the resonance of magnetic field between adjacent units. Fig.9 summarizes the bandwidth and corresponding thickness of the typical radar
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absorbing materials and structures. Except that of compressed graphene foam[3], the bandwidth of radar absorbers without structural design are relatively narrow[2, 5, 6, 17]. It is clear that the fabricated MSC with small thickness in this work possesses absorbing
property.
Its
absorbing
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excellent
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2GHz~18GHz, and extends to 30GHz.
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bandwidth
covers
the
whole
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Fig.9. Bandwidth and corresponding thickness for the typical radar absorbing materials and structures Conclusion
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4.
In summary, a broadband flexible MSC with more than 90% absorption ( -10dB) in 2-30GHz is designed and fabricated. The components of the MSC are
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highly resilient HNBR and magnetic FCIP. The total thickness of the MSC is 5mm.
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The incident energy is concentrated at the special designed structure, and dissipated subsequently. At low frequency, the great reflection loss of this MSC is mainly caused by the λ/4 resonance, while the incident energy disspation at high frequency is contributed by the edge diffraction and resonance between the adjacent units. The similar normal stepped stuctures with different volume fraction are investigated. It demonstrates that the excellent absorption property of the MSC also relys on the matching degree of effective impedance. It is shown that the fabricated flexible MSC is a potential practical composite structure in radiation protection and radar stealth. 20
ACCEPTED MANUSCRIPT Acknowledgement This work is supported by the National Natural Science Foundation of China (11872113) and the Project of State Key Laboratory of Explosion Science and
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Technology. References
[1] C.X. Wang, M.J. Chen, H.S. Lei, K. Yao, H.M. Li, W.B. Wen, D.N. Fang, Radar stealth and
mechanical properties of a broadband radar absorbing structure, Compos Part B-Eng 123 (2017) 19-27. [2] Y.C. Qing, D.D. Min, Y.Y. Zhou, F. Luo, W.C. Zhou, Graphene nanosheet- and flake carbonyl iron
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particle-filled epoxy-silicone composites as thin-thickness and wide-bandwidth microwave absorber, Carbon 86 (2015) 98-107.
[3] Y. Zhang, Y. Huang, T.F. Zhang, H.C. Chang, P.S. Xiao, H.H. Chen, Z.Y. Huang, Y.S. Chen,
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Broadband and Tunable High-Performance Microwave Absorption of an Ultralight and Highly Compressible Graphene Foam, Adv Mater 27(12) (2015) 2049-2053.
[4] T. Wang, P. Wang, Y. Wang, L. Qiao, A broadband far-field microwave absorber with a sandwich structure, Mater. Des. 95 (2016) 486-489.
[5] C.Q. Song, X.W. Yin, M.K. Han, X.L. Li, Z.X. Hou, L.T. Zhang, L.F. Cheng, Three-dimensional reduced graphene oxide foam modified with ZnO nanowires for enhanced microwave absorption properties, Carbon 116 (2017) 50-58.
[6] Y.C. Qing, W.C. Zhou, F. Luo, D.M. Zhu, Epoxy-silicone filled with multi-walled carbon nanotubes
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and carbonyl iron particles as a microwave absorber, Carbon 48(14) (2010) 4074-4080. [7] L. Yang, H.L. Fan, J. Liu, Y. Ma, Q. Zheng, Hybrid lattice-core sandwich composites designed for microwave absorption, Mater. Des. 50 (2013) 863-871. [8] Y.C. Qing, X. Wang, Y.Y. Zhou, Z.B. Huang, F. Luo, W.C. Zhou, Enhanced microwave absorption of multi-walled carbon nanotubes/epoxy composites incorporated with ceramic particles, Compos Sci
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Technol 102 (2014) 161-168.
[9] M.S. Cao, W.L. Song, Z.L. Hou, B. Wen, J. Yuan, The effects of temperature and frequency on the dielectric properties, electromagnetic interference shielding and microwave-absorption of short carbon
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fiber/silica composites, Carbon 48(3) (2010) 788-796. [10] B. Wu, H.M. Tuncer, A. Katsounaros, W.P. Wu, T.C. Matthew, K. Ying, L.H. Zhang, W.I. Milne, Y. Hao, Microwave absorption and radiation from large-area multilayer CVD graphene, Carbon 77 (2014) 814-822.
[11] X.J. Zhang, G.S. Wang, W.Q. Cao, Y.Z. Wei, M.S. Cao, L. Guo, Fabrication of multi-functional PVDF/RGO composites via a simple thermal reduction process and their enhanced electromagnetic wave absorption and dielectric properties, Rsc Adv 4(38) (2014) 19594-19601. [12] Y.J. Chen, M.S. Cao, T.H. Wang, Q. Wan, Microwave absorption properties of the ZnO nanowire-polyester composites, Appl Phys Lett 84(17) (2004) 3367-3369. [13] Y. Wang, H.T. Guan, S.F. Du, Y.D. Wang, A facile hydrothermal synthesis of MnO2 nanorod-reduced graphene oxide nanocomposites possessing excellent microwave absorption properties, Rsc Adv 5(108) (2015) 88979-88988. [14] J.L. Xu, X.S. Qi, C.Z. Luo, J. Qiao, R. Xie, Y. Sun, W. Zhong, Q. Fu, C.X. Pan, Synthesis and
21
ACCEPTED MANUSCRIPT enhanced microwave absorption properties: a strongly hydrogenated TiO2 nanomaterial, Nanotechnology 28(42) (2017). [15] J. Zhang, J.W. Liu, C.Y. Liang, F. Zhang, R.C. Che, Highly crystalline manganese selenide nanorods: Synthesis, characterization, and microwave absorption properties, J Alloy Compd 548 (2013) 13-17. [16] J.S. Li, H. Huang, Y.J. Zhou, C.Y. Zhang, Z.T. Li, Research progress of graphene-based microwave absorbing materials in the last decade, J Mater Res 32(7) (2017) 1213-1230.
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[17] Q.H. Liu, Q. Cao, H. Bi, C.Y. Liang, K.P. Yuan, W. She, Y.J. Yang, R.C. Che, CoNi@SiO2@TiO2 and CoNi@Air@TiO2 Microspheres with Strong Wideband Microwave Absorption, Adv Mater 28(3) (2016) 486-+.
[18] Y.X. Huang, W.L. Song, C.X. Wang, Y.N. Xu, W.Y. Wei, M.J. Chen, L.Q. Tang, D.N. Fang, Compos Sci Technol 162 (2018) 206-214.
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Multi-scale design of electromagnetic composite metamaterials for broadband microwave absorption, [19] X.F. Liu, Y.X. Chen, X.R. Cui, M. Zeng, R.H. Yu, G.S. Wang, Flexible nanocomposites with enhanced microwave absorption properties based on Fe3O4/SiO2 nanorods and polyvinylidene fluoride, J Mater Chem A 3(23) (2015) 12197-12204.
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[20] Y.Y. Zhou, W.C. Zhou, Y.C. Qing, F. Luo, D.M. Zhu, Temperature dependence of the electromagnetic properties and microwave absorption of carbonyl iron particles/silicone resin composites, J Magn Magn Mater 374 (2015) 345-349.
[21] B.S. Zhang, Y. Feng, H. Xiong, Y. Yang, H.X. Lu, Microwave-absorbing properties of De-aggregated flake-shaped carbonyl-iron particle composites at 2-18 GHz, Ieee T Magn 42(7) (2006) 1778-1781.
[22] Y.Y. Zhou, W.C. Zhou, R. Li, Y. Mu, Y.C. Qing, Enhanced antioxidation and electromagnetic 637 (2015) 10-15.
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properties of Co-coated flaky carbonyl iron particles prepared by electroless plating, J Alloy Compd [23] Y. Cheng, Y.G. Xu, J. Cai, L.M. Yuan, D.Y. Zhang, Effect of the bio-absorbent on the microwave absorption property of the flaky CIPs/rubber absorbers, J Magn Magn Mater 389 (2015) 106-112. [24] M.J. Park, J.H. Choi, S.S. Kim, Wide bandwidth pyramidal absorbers of granular ferrite and
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carbonyl iron powders, Ieee T Magn 36(5) (2000) 3272-3274. [25] W.H. Choi, C.G. Kim, Broadband microwave-absorbing honeycomb structure with novel design concept, Compos Part B-Eng 83 (2015) 14-20.
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[26] M. Olszewska-Placha, B. Salski, D. Janczak, P.R. Bajurko, W. Gwarek, M. Jakubowska, A Broadband Absorber With a Resistive Pattern Made of Ink With Graphene Nano-Platelets, Ieee T Antenn Propag 63(2) (2015) 565-572. [27] Q. Zhou, X.W. Yin, F. Ye, X.F. Liu, L.F. Cheng, L.T. Zhang, A novel two-layer periodic stepped structure for effective broadband radar electromagnetic absorption, Mater. Des. 123 (2017) 46-53. [28] W.L. Song, Z.L. Zhoup, L.C. Wang, X.D. Cheng, M.J. Chen, R.J. He, H.S. Chen, Y.Z. Yang, D.N. Fang, Constructing Repairable Meta-Structures of Ultra-Broad-Band Electromagnetic Absorption from Three-Dimensional Printed Patterned Shells, Acs Applied Materials & Interfaces 9(49) (2017) 43179-43187. [29] W. Li, T.L. Wu, W. Wang, P.C. Zhai, J.G. Guan, Broadband patterned magnetic microwave absorber, J Appl Phys 116(4) (2014). [30] B.C. Wang, J.Q. Wei, L. Qiao, T. Wang, F.S. Li, Influence of the interface reflections on the microwave reflection loss for carbonyl iron/paraffin composite backed by a perfect conduction plate, J
22
ACCEPTED MANUSCRIPT Magn Magn Mater 324(5) (2012) 761-765. [31] B.C. Wang, J.Q. Wei, Y. Yang, T. Wang, F.S. Li, Investigation on peak frequency of the microwave absorption for carbonyl iron/epoxy resin composite, J Magn Magn Mater 323(8) (2011) 1101-1103. [32] P.J. Joseph, A.D. Tyson, W.D. Burnside, An Absorber Tip Diffraction Coefficient, Ieee T Electromagn C 36(4) (1994) 372-379. [33] H. Zou, S.H. Li, L.Q. Zhang, S.N. Yan, H.G. Wu, S.A. Zhang, M. Tian, Determining factors for high performance silicone rubber microwave absorbing materials, J Magn Magn Mater 323(12) (2011)
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1643-1651.
[34] Y.H. Zhai, Y. Zhang, W.T. Ren, Electromagnetic characteristic and microwave absorbing
performance of different carbon-based hydrogenated acrylonitrile-butadiene rubber composites, Mater Chem Phys 133(1) (2012) 176-181.
[35] F. Nanni, P. Travaglia, M. Valentini, Effect of carbon nanofibres dispersion on the microwave
SC
absorbing properties of CNF/epoxy composites, Compos Sci Technol 69(3-4) (2009) 485-490.
[36] Y.G. Xu, D.Y. Zhang, J. Cai, L.M. Yuan, W.Q. Zhang, Microwave absorbing property of silicone rubber composites with added carbonyl iron particles and graphite platelet, J Magn Magn Mater 327 (2013) 82-86.
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[37] B. Pradhan, S. Roy, S.K. Srivastava, A. Saxena, Synergistic effect of carbon nanotubes and clay platelets in reinforcing properties of silicone rubber nanocomposites, J Appl Polym Sci 132(15) (2015). [38] H. Acharya, S.K. Srivastava, A.K. Bhowmick, Synthesis of partially exfoliated EPDM/LDH nanocomposites by solution intercalation: Structural characterization and properties, Compos Sci Technol 67(13) (2007) 2807-2816.
[39] M.A. Abshinova, S.M. Matitsine, L. Liu, C.R. Deng, L.B. Kong, High Microwave Magnetic Permeability of Composites with Submicron Iron Flakes, J Phys Conf Ser 266 (2011).
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[40] Z.J. Li, Z.L. Hou, W.L. Song, X.D. Liu, W.Q. Cao, X.H. Shao, M.S. Cao, Unusual continuous dual absorption peaks in Ca-doped BiFeO3 nanostructures for broadened microwave absorption, Nanoscale 8(19) (2016) 10415-10424.
[41] H.T. Guan, J.B. Xie, G. Chen, Y.D. Wang, Facile synthesis of alpha-MnO2 nanorods at low temperature and their microwave absorption properties, Mater Chem Phys 143(3) (2014) 1061-1068.
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[42] H.L. Yu, T.S. Wang, B. Wen, M.M. Lu, Z. Xu, C.L. Zhu, Y.J. Chen, X.Y. Xue, C.W. Sun, M.S. Cao, Graphene/polyaniline nanorod arrays: synthesis and excellent electromagnetic absorption properties, J Mater Chem 22(40) (2012) 21679-21685.
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[43] J.Z. He, X.X. Wang, Y.L. Zhang, M.S. Cao, Small magnetic nanoparticles decorating reduced graphene oxides to tune the electromagnetic attenuation capacity, J Mater Chem C 4(29) (2016) 7130-7140.
[44] D.R. Smith, D.C. Vier, T. Koschny, C.M. Soukoulis, Electromagnetic parameter retrieval from inhomogeneous metamaterials, Phys Rev E 71(3) (2005).
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S0266-3538(18)32640-X
DOI:
https://doi.org/10.1016/j.compscitech.2019.04.008
Reference:
CSTE 7616
To appear in:
Composites Science and Technology
Received Date: 31 October 2018 Revised Date:
5 March 2019
Accepted Date: 7 April 2019
Please cite this article as: Fan Q, Huang Y, Chen M, Li Y, Song W, Fang D, Integrated design of component and configuration for a flexible and ultrabroadband radar absorbing composite, Composites Science and Technology (2019), doi: https://doi.org/10.1016/j.compscitech.2019.04.008. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Integrated design of component and configuration for a flexible and ultrabroadband radar absorbing composite Qunfu Fan1, Yixing Huang2, Mingji Chen1,3*, Ying Li1,3*, Weili Song 1, Daining
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Fang1,3 Beijing Key Laboratory of Lightweight Multi-functional Composite Materials and
Structures, Beijing Institute of Technology, Beijing 100081, PR China
School of Civil Engineering and Transportation, South China University of
Technology, Guangzhou 510641, PR China
State Key Laboratory of Explosion Science and Technology, Beijing Institute of
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2
Technology, Beijing, 100081, PR of China
Corresponding Author: Mingji Chen(E-mail: [email protected]);
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Ying Li (E-mail: [email protected]);
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ACCEPTED MANUSCRIPT Abstract: To achieve ultra-broadband radar absorption at small thickness, the integrated design of component and configuration of a rubber matrix flexible radar absorbing composite (RAC) is performed in the present study. At the material
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component level, hydrogenated acrylonitrile butadiene rubber (HNBR) reinforced by flaky carbonyl iron particles (FCIP) ensures the considerable permeability of RAC, as well as its good flexibility, mechanical strength and elongation to break. At the structure design level, a novel modified step-configuration (MSC) is proposed
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through full-wave calculation. The preparation process of RAC with the modified
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step-configuration includes components mixing in a two-roll mixer and hot-press moulding. Radar reflectivity testing experiment demonstrates that, by integrated design of component and configuration, the absorbing bandwidth corresponding to -10dB can span from 2GHz to 30GHz for a 5mm-thick composite absorber.
absorber 1.
Introduction:
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Keywords: Radar absorbing composite, Rubber matrix, Structure design, Broadband
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With the rapid development of high precision electronic equipment and radar detection technology, the radar target without special design is difficult to avoid being
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detected. Many strategies have been performed to reduce the chances of being detected for radar target, such as the application of radar absorbing materials (RAMs) and radar absorbing structures (RASs)[1-7]. On the whole, the RAMs contain dielectric-loss materials and magnetic-loss
materials. In recent years, many excellent dielectric-loss RAMs, such as dielectric-loss carbon materials and transition metal oxides or chalcogenides, have been fabricated by novel methods. The typical carbon materials include carbon nanotubes (CNT)[8], carbon fibers[9], graphene[10], reduced graphene oxide 2
ACCEPTED MANUSCRIPT (RGO)[11] and so on, while the radar absorbing transition metal oxides or chalcogenides contain nanostructured ZnO[12], MnO2[13], TiO2[14], MnSe2[15], etc. In general, the dielectric-loss mechanism of these RAMs is mainly attributed to the
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conduction loss and dielectric relaxation which are influenced by conductivity and polarization respectively under the altering electromagnetic field[16]. Besides dielectric-loss RAMs, magnetic-loss RAMs has also been widely studied[17]. The magnetic dissipation of magnetic-loss RAMs mainly includes eddy current loss,
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ferromagnetic resonance, and hysteresis loss[18, 19]. As a conventional magnetic
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absorbent, spherical carbonyl iron particles (SCIP), have been used in microwave absorption for many years, due to their large permeability and high Snoek’s limit at high frequency[20-23]. However, compared to SCIP, flaky carbonyl iron particles (FCIP), as another form of carbonyl iron particles, have higher permeability, lower
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permittivity, and better filling characteristics[21-23].
Generally, the absorption bandwidth of RAMs is relatively narrow, though their absorption intensity is strong. In contrast, RASs can be designed to achieve broader
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absorption bandwidth, at the cost of larger thickness. Typical RASs include pyramidal structure[24] which is mainly applied in anechoic chambers, and
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honeycomb structure[25] whose thickness is exceeding 10mm for broadband absorption over 2GHz to 14GHz. For another type of RASs consisting of frequency selective surface (FSS)[1, 26] and load bearing dielectric spacer, typical thickness for broadband absorption is also 5~10mm or even larger, with the absorption band within 4GHz to 18GHz. Recently, the periodic stepped RASs[27, 28] have attracted many attentions, because of the λ/4 resonance and edge diffraction effect which has been proved to be helpful in creating multiple absorption peaks to reduce broadband reflection at relatively small thickness[29-32]. 3
ACCEPTED MANUSCRIPT On the other hand, flexible rubber RASs which possess favorable absorbing performance, could be applied in many special fields because of their large elongation at break and deformation recovery[33]. In this study, hydrogenated acrylonitrile
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butadiene rubber (HNBR), which exhibits high elasticity, good mechanical properties[34] and good processing property was chosen as matrix. The flaky carbonyl iron particles (FCIP) were dispersed into the HNBR matrix to fabricate radar absorbing composites with considerable permeability as well as large elongation and
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flexibility. Then, structure design of the flexible radar absorbing composite (RAC)
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was performed by numerical simulation and a novel modified step-configuration (MSC) for broadband absorption was obtained. Radar reflectivity testing experiment demonstrated that, by integrated design of component and configuration, the absorbing bandwidth corresponding to -10dB can span from 2GHz to 30GHz for a
2.
Experimental
2.1 Materials
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5mm-thick composite absorber.
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Hydrogenated acrylonitrile butadiene rubber (HNBR) was used as raw material (Zetpol 1000L, produced by Zeon Corporation, Japan). The flaky carbonyl iron
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particles (FCIP) were purchased from Gansu Metal Flake Material Technology LTD. China. The vulcanizing agent dicumyl peroxide (DCP) (analytical grade) was supplied by Beijing Chemical Reagents Co., Ltd. China. 2.2 Preparation methods of RAC The matrix material HNBR was dried in drying oven for 24 hours. The cured HNBR and different mass fraction of FCIP were mixed in a two-roll-mixer at 80 for 20min. FCIP in HNBR-FCIP composite were 100phr, 200phr, 300phr, 400phr (parts per hundred rubber by weight) respectively. As vulcanizing agent, 3phr DCP 4
ACCEPTED MANUSCRIPT was added for each composite. The composite was mixed for another 10min in the mixer, and then removed from mixer for curing. The curing approach was hot-pressing for 10min, in the steel mold at 160 , under a pressure of 10Mpa. The
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prepared composites specimens, named as RAC-100, RAC-200, RAC-300, and RAC-400, were cut into different sizes for electromagnetic parameters tests in corresponding frequency band. The electromagnetic parameters of the composite specimens were measured by waveguide transmission line method. The sizes of the
47.55mm*22.15mm*2mm,
34.85mm*15.8mm*2mm,
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72.14mm*34.04mm*2mm,
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specimens suitable for the rectangular waveguide for different waveband, were
22.86*10.16mm*2mm, respectively. The schematic diagram of the manufacturing
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procedures was shown in Fig.1.
Fig.1. The procedures of manufacturing RAC and MSC, and the sketch of measuring 5
ACCEPTED MANUSCRIPT electromagnetic parameter and reflectivity. 2.3 Preparation of MSC As shown in Fig.1, a steel mold with designed periodical structure was prepared
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by computerized numerical control (CNC). The composites with different content of FCIP prepared by two-roll-mixer, were placed on the steel mold, and covered by a steel plate. The composites were shaped and cured in the designed steel mold, and the curing strategy was hot-pressing for 10min at 160
, under a pressure of 10Mpa. The
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as-fabricated absorbing structures with different content of FCIP were named as
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MSC-200, MSC-300 and MSC-400. The reflectivity of the MSC specimens was measured from 2GHz to 40GHz by the arch framing reflection method, and the sizes of the prepared MSC specimens were 300mm*300mm for 2GHz~18GHz measurement and 180mm*180mm for 18GHz~40GHz measurement.
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2.4 Characterization
Micromorphology of the fabricated RAC were studied by Field-emission scanning electron microscopy (FEI QUANTA 450 FEG system). The element
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components of the composites were characterized by energy dispersive spectroscopy (EDS). Mechanical performance of the RAC was investigated with a tensile tester
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(Zwick/roell Z010) according to Chinese national standard GB/T 528-1998. Vector network analyzer (Ceyear AV3672D) was used to measure the electromagnetic parameters of the RAC specimens by waveguide transmission line method and the reflectivity of the fabricated MSC was measured by the arch framing reflection method with Vector network analyzer. CST Microwave Studio software was used to simulate the reflectivity of the RAC and the designed MSC.
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Result and discussion
3.1 Morphology of the RAC The dispersion of fillers in the matrix could affect the electromagnetic
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characteristics of the composites[35]. In this study, Field-emission scanning electron microscopy (FESEM) was used to observe the shape, dimension, and dispersion of FCIP in the fabricated RAC. Fig.2 shows the surface and sheared cross profile morphology of the RAC. In RAC with different mass fraction of FCIP, the FCIP are
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uniformly dispersed in HNBR matrix with no obvious agglomeration, because the
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shearing force provided by the roll-mixer in the mixing process could overcome the van der Waals force between particles[36]. The diameters of FCIP in the RAC, are ranged from 3µm to 10µm, while the thickness from 0.2µm to 0.8µm. As shown in Fig.2 (a), (c), (e), the fillers increase in turn and disperse uniformly in the matrix.
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Fig.2 (b), (d), (f) shows that the dispersion of FCIP in the inner of the RAC is homogeneous. The component of prepared composites can be characterized by energy dispersive spectroscopy (EDS). Fig.2 (h) shows the co-existent elements include
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element carbon (C) and ferrum (Fe) in the composite RAC-400. And all the positions of ferrum (Fe) in Fig.2 (h) is matching with the EDS of pure FCIP[22]. Obviously,
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element carbon (C) is from rubber matrix and ferrum (Fe) is from FCIP. As shown in Fig.2 (g), EDS mapping confirms the homo-disperse of ferrum (Fe) element in RAC-400. The FESEM morphology and EDS suggest that the uniform RAC can be fabricated by this processing procedure.
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Fig.2. FESEM images of the RAC with different content of FCIP. (a), (c), (e) are
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surface morphology of RAC-200, RAC-300, RAC-400 respectively. (b), (d), (f) are the sheared cross profile morphology of RAC-200, RAC-300, RAC-400 respectively, (g) is the mapping of Fe element in RAC-400, (h) is EDS of RAC-400.
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3.2 Mechanical properties of RAC
Fig.3. Tensile strength (a) and Stress-Strain curve (b) of the RAC with different mass fraction of FCIP.
Fig.3 shows the tensile strength (TS) and the stress-strain curve of the RAC with different mixing mass fraction of FCIP. Meanwhile, Table I summarizes tensile properties of RAC, including tensile strength (TS), elongation at break (EB), and Young’s modulus. As shown in Fig.3 (a) (b), the TS of RAC increases with the 8
ACCEPTED MANUSCRIPT increase of FCIP first, and then decreases, while the tendency of the (EB) is similar with that of the TS. The increase in TS and EB may be attributed to the random distribution of FCIP in HNBR matrix, the strong interfacial interaction caused from
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the high specific surface of FCIP[37], and the synergistic effect of macromolecule chain slippage and orientation of FCIP[38]. The TS and EB decrease at higher FCIP loading due to the aggregation tendency of FCIP in rubber matrix[37]. Table I shows that the Young’s modulus increases with the increasing of FCIP in RAC. The increase
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of Young’s modulus, which is likely attributed to the steric hindrance of FCIP itself
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and the strong interaction of filler-matrix[37] reveals that the flexibility of the RAC will reduce. Even so, the RAC-400 is still flexible.
Table I. Tensile properties of the RAC with different mass fraction of FCIP Tensile Strength
Elongation at Break
Young’s Modulus
(MPa)
(%)
(MPa)
HNBR
10.41±1.05
1483
1.23
RAC-100
17.58±1.39
1800
1.16
RAC-200
16.02±0.69
1774
2.50
RAC-300
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Composite type
12.14±0.95
1480
3.06
9.09±0.42
1125
5.02
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RAC-400
3.3 Microwave absorbing properties of the single-layered RAC In order to achieve the electromagnetic characteristic of the RAC with different
mass fraction of FCIP, the specimen RAC-200, RAC-300 and RAC-400 were fabricated. Their electromagnetic parameters including complex permittivity and complex permeability were measured by waveguide transmission line method. The measured electromagnetic parameters would be used to simulate the reflectivity of the 9
ACCEPTED MANUSCRIPT designed MSC and the single-layered RAC with different thickness. Generally, the absorbing properties of magnetic composites are attributed to hysteresis, domain wall resonance, nature ferromagnetic resonance and eddy current
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losses. The domain wall resonance usually does not occur in gigahertz frequency band, while the hysteresis loss can be neglected in weak fields. Contrast to eddy current loss in spherical iron carbonyl particles (SCIP) composite, nature resonance occurs in FCIP composite in gigahertz frequency band[39].
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According to the λ/4 resonance mechanism, the absorbing peak of single-layered
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composite panel exists at the frequency point where standing wave is generated[40]. Base on transmission line theory, the microwave absorption (MA) properties of the prepared composites can be calculated by the reflection loss (RL) as the following formulas[41, 42]:
Zin=(µr/ɛr)1/2tanh[2 fdj(µr/ɛr)1/2]
(1)
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RL=20log10│(Zin-Z0)/(Zin+Z0)│
Zin--- the normalized input impedance of the absorber; Z0---impedance of free space;
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µr---relative complex permittivity of the absorber; ɛr---relative complex permeability of the absorber;
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c---velocity of electromagnetic wave in vacuum; d---thickness of the absorber;
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π
(2)
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Fig.4. 3D plot of the calculated reflectivity of RAC-200 (a), RAC-300 (b), RAC-400 (c) versus frequency and thickness. Frequency dependence of reflectivity of the three
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samples with the thickness of 2mm (d)
The calculated theoretical reflectivity of single-layered RAC with different thickness was presented in the three dimensional (3D) plots in Fig.4. As shown in
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Fig.4(a), (b), (c), all of the single-layered RAC (including RAC-200, RAC-300,
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RAC-400), reveal similar tendency. With the thickness of the RAC increasing, the absorption peaks become stronger, and shift to lower frequency simultaneously till disappear out of the measured frequency band. Generally, when reflectivity -10dB, the materials can be applied for electromagnetic wave absorbing[43]. The frequency region which is below -10dB can be marked “available absorption bandwidth”. Fig.4 (a), (b), (c) suggest that just increasing the thickness of the single-layered RAC cannot extend the “available absorption bandwidth”. Fig.4 (d) shows the frequency dependence of reflectivity of the single-layered 11
ACCEPTED MANUSCRIPT RAC with the thickness of 2mm. In Fig.4 (d), when the thickness of the single-layered RAC is 2mm, the available bandwidth of RAC-200, RAC-300, RAC-400 are 3.8GHz, 2.2GHz, 1.1GHz, while the corresponding peak value are
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-17dB, -16dB, -14dB respectively. With the mass ratio of FCIP increasing, the absorbing properties of the single-layered RAC are weakening in 2GHz-18GHz frequency band. Obviously, when the thickness of the single-layered RAC is fixed, it is difficult to improve their absorbing properties just improving the mass ratio of
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fillers.
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In order to improve the radar absorbing properties of RAC, a modified step-configuration (MSC) will be developed in this research.
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3.4 Microwave absorbing properties of the novel MSC
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Fig.5. The diagram of NTSS (I), and the reflectivity of NTSS with different side length of the top layer (II) Before the MSC is proposed, several normal three layers periodic stepped
structures (NTSS) are investigated with the electromagnetic parameter of RAC-400. As showed in Fig.5 (I), the geometric parameters of the NTSS are marked as “a, b, c and h1, h2, h3”. And a=15mm, b=12mm, c= (0, 4, 8, 10, 12mm respectively), h1=1mm, h2=1mm, h3=3mm. When c is 0 mm, the corresponding NTSS is marked as NTSS-C0, and the reflectivity of NTSS-C0 is depicted in Fig.5 (II). Meanwhile, the 12
ACCEPTED MANUSCRIPT NTSS-C4, NTSS-C8, NTSS-C10, NTSS-C12 represent the NTSS with c= (4, 8, 10, 12mm) respectively, and the corresponding reflectivity of NTSS are depicted in the same graph Fig.5 (II). As shown in Fig.5 (II), with c increases from 0 mm to 12 mm,
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the volume fraction of the NTSS unit increases from 32.8% (NTSS-C0) to 71.2% (NTSS-C12). The absorption properties of the NTSS strengthen first, and weaken subsequently. It reveals that the absorption properties of the NTSS probably reach to a top with the increase of volume fraction of the NTSS unit, and the top might exist
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between NTSS-C8 and NTSS-C10.
Fig.6 The schematic of designed MSC (I), the fabricated MSC (II), the simulated reflectivity of the MSC with different D (III), L, H (IV). The inset is the detail of 2~4GHz in (III). The outline of the proposed MSC is shown in Fig.6 (I). The bottom layer and middle layer are slabs with the side length 15mm (L1=15mm) and 12mm (L2=12mm), 13
ACCEPTED MANUSCRIPT the height 1mm (H1=1mm) and 1mm (H2=1mm). The top layer of the designed MSC is a cube with four cubes surrounded. The geometric parameters of the cubes are marked as D, H and L, W, H. On the premise of retaining the basic outline, the
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influences of size of the top layer cubes on the absorption performance are investigated. As shown in Fig.6 (III), when L, W, H are 8mm, 2mm, 3mm respectively, from 2GHz-2.75GHz, the absorption of MSC improve with the increasing of D, and from 18GHz to 30GHz, the absorption decrease. In order to
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balance the absorption in low frequency band (2~4GHz) and the broadband
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absorption, edge length of the center cube of the top layer is designed as 4mm. The influence of edge length of the four surrounding cubes on the absorption is also studied, and shown in Fig.6 (IV). When D, W, H are 4mm, 2mm, 3mm respectively, with L increasing from 4mm to 8mm, the effective absorbing bandwidth ( -10dB)
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increase gradually in the whole 2GHz-30GHz frequency range. When D, W, L are 4mm, 2mm, 8mm respectively, with H increasing from 1mm to 3mm, the total thickness of MSC increase from 3mm to 5mm. Obviously, the effective absorbing
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bandwidth extends with the increasing of thickness. Integrating the absorption in low frequency stage and effective absorbing
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bandwidth in 2GHz-30GHz frequency range, the best geometrical parameter for MSC is confirmed as D=4mm, L=8mm, W=2mm, H=3mm. Namely the assembly (D=4mm, L=8mm, W=2mm, H=3mm, H1=H2=1mm, L1=15mm, L2=12mm) is selected for fabrication of MSC whose total thickness is 5mm, and the volume fraction of this MSC is 54.13%, falling in between 49.87% (NTSS-C8) and 59.47% (NTSS-10). As an important factor for designed artificial absorbing structure, impedance matching of the designed structure is investigated. The effective input impedance (Zeff) of the designed structure can be obtained from the formula[27, 44]: 14
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Zeff = [
=(
1/2 )
(3)
εeff, µeff are the effective permittivity and permeability respectively. In this paper, the structures are backed by a metallic plane, │S21│= 0. The real
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and imaginary part of complex S11 can be gained from the simulation of the structures by CST Microwave Studio software. The real and imaginary part of Zeff can be calculated according to formula (3). The real part and imaginary part of Zeff are
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marked as Zeff(real) and Zeff(imag) . Generally, if the Zeff(real) is closer to unity and Zeff(imag) is closer to zero, the Zeff of the structure is matched to that of free space
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better, and the reflection is weaker[27]. In order to illustrate the degree of the Zeff(real) close to unity and Zeff(imag) close to zero, the formula “Ʃ[Zeff(real)-1]2/n” and “Ʃ [Zeff(imag)-0]2/n” (“n” is the amount of frequency points in the test frequency range), which are similar with variance in statistics, are introduced in this research, and
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marked as α and β for short. The statistical results are summarized in table II. Table II. The matching degree of Zeff(real) to 1 and Zeff(imag.) to 0 for different
Structure NTSS-C8
β=Ʃ [Zeff(imag.)-0]2/n
49.87%
0.2245
0.2709
54.13%
0.1762
0.2061
59.47%
0.2794
0.3179
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MSC
α=Ʃ [Zeff(real)-1]2/n
Volume Fraction
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structures
NTSS-C10
As shown in table II, “α” and “β” of the MSC are 0.1762 and 0.2061
respectively, which are less than that of NTSS-C8 (0.2245 and 0.2709) and NTSS-C10 (0.2794 and 0.3179). It means that, compared with that of the NTSS-C8 and NTSS-C10, Zeff(real) of the MSC is closer to unity, and Zeff(imag.) of the MSC is closer to zero. It suggests that the impedance of the MSC matches better with the 15
ACCEPTED MANUSCRIPT impedance of free space than that of NTSS-C8 and NTSS-C10 over the test frequency range[27, 44]. The radar absorption property of the designed MSC with different content of
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FCIP is simulated, and the simulated reflectivity of the designed MSC is presented in Fig.7 (I). To aid comparisons with the simulated reflectivity, the measured experimental reflectivity of the fabricated MSC-300 and MSC-400 are also depicted
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in the same graph, as showed in Fig.7 (II).
Fig.7. The comparison of simulated and experimental reflectivity of MSC with different content of FCIP (I, II).
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The simulated reflectivity of MSC-200, MSC-300, and MSC-400 are shown in Fig.7 (I). The former possesses effective bandwidth (
-10dB in general) from
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3.71GHz to 30GHz, the middle one from 2.72GHz-30GHz, while the latter covers 2.38GHz-29.28GHz.
The experimental reflectivity curves in Fig.7 (II) show that the effective
bandwidth of the fabricated MSC-300 is from 2.72GHz to 30GHz, and that of the MSC-400 covers the total frequency range of 2-30GHz. In addition, for the different MSC, the tendency of experimental reflectivity and simulated reflectivity are similar in the frequency range of 2-30GHz. It means that the experiment and the simulation 16
ACCEPTED MANUSCRIPT match well. Therefore, the simulation about the MSC by CST software is credible. 3.5 Absorption mechanism As marked at the simulated reflectivity curve (Fig.7 II), there are four absorption
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peaks corresponding with frequency points 3.24GHz, 7.18GHz, 15.09GHz, 24.85GHz, respectively. The distributions of the electric field, magnetic field, and power loss (PL) of MSC-400 at the four absorption peaks are simulated. As shown in Fig.8, the 3D diagrams and cross sections of the distributions are mapped. At the first frequency
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point 3.24GHz, as shown in Fig.8 (a), the electric field concentrates on the gap of the
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top layer of MSC-400 in the x-z plane and the gap between the top layers of adjacent units in the x-z plane. As for the magnetic field, in the y-z plane, concentration not only takes place on the gap of top layer of MSC-400 and two side edges of the MSC-400 bottom, it also distributes in the gap between the middle layers of adjacent
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units. The PL concentrates on the two side edges of the bottom of MSC-400, overlapping the magnetic field distribution. The result indicates that the power loss of electromagnetic wave on MSC-400 is attributed to magnetic loss. More precisely, the
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field concentration derives from nature resonance[39]. In addition, the power loss distributes in the inner of the MSC-400 bottom layer. Therefore, the power loss at
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3.24GHz may be attributed to the standing wave which is generated in the bottom layer of MSC-400 according to λ/4 resonance[40]. Fig.8 (b) shows that the electric field distribution on the MSC-400 at 7.18GHz shifts to the top gap of the top layer in the x-z plane. The magnetic field distribution concentrates on the inner of the gap of the top layer and the surface of top layer in the y-z plane. The PL at 7.18GHz concentrates on the surface of top layer in the y-z plane. The PL distribution and the magnetic field distribution overlap on the surface of top layer at 7.18GHz indicating that the PL at 7.18GHz is mainly attributed to strong edge diffractions of magnetic 17
ACCEPTED MANUSCRIPT field. Fig.8 (c) gives the electric field, magnetic field, PL distribution at 15.09GHz. The electric field distribution concentrates on the gap of top layers between adjacent units in the x-z plane. The magnetic field distributes on the top of MSC-400 in the y-z
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plane and concentrates on the gap of the adjacent units in the x-z plane. The PL distribution which is similar to that of magnetic field, concentrates on the top of MSC-400 in the y-z plane, and the two sides of MSC-400 in the x-z plane. Strong resonance between adjacent units and strong edge diffraction are two major
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mechanisms for field distortion.
Fig.8. The distributions of electric field, magnetic field, and power loss of the MSC-400 at the different absorption peaks. The corresponding frequency points are (a) 3.24GHz, (b) 7.18GHz, (c) 15.09GHz, (d) 24.85GHz respectively As shown in Fig.8 (d), at 24.85GHz, the electric field distribution is similar with the distribution at 15.09GHz. The difference is that the electric field distributes 18
ACCEPTED MANUSCRIPT in the gap of MSC-400 in the x-z plane at 24.85GHz while is weakened at 15.09GHz. The distribution of magnetic field and PL are nearly identical in the y-z plane. In the x-z plane, the magnetic field concentrates on the bottom of MSC-400 gap and the gap
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between middle layers of adjacent units while the PL concentrates on the two side edges of the bottom layer and the middle layer. This PL distribution suggests that when the electromagnetic wave concentrates on the designed MSC-400, the power loss results from the magnetic loss in the way of edge diffraction and resonance
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between the adjacent units. In a word, the power loss of the electromagnetic wave on
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the designed MSC-400 is mainly attributed to the magnetic loss induced by λ/4 resonance of magnetic field in the bottom layer, the edge diffraction of magnetic field at the edge of top layer, and the resonance of magnetic field between adjacent units. Fig.9 summarizes the bandwidth and corresponding thickness of the typical radar
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absorbing materials and structures. Except that of compressed graphene foam[3], the bandwidth of radar absorbers without structural design are relatively narrow[2, 5, 6, 17]. It is clear that the fabricated MSC with small thickness in this work possesses absorbing
property.
Its
absorbing
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excellent
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2GHz~18GHz, and extends to 30GHz.
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bandwidth
covers
the
whole
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Fig.9. Bandwidth and corresponding thickness for the typical radar absorbing materials and structures Conclusion
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4.
In summary, a broadband flexible MSC with more than 90% absorption ( -10dB) in 2-30GHz is designed and fabricated. The components of the MSC are
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highly resilient HNBR and magnetic FCIP. The total thickness of the MSC is 5mm.
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The incident energy is concentrated at the special designed structure, and dissipated subsequently. At low frequency, the great reflection loss of this MSC is mainly caused by the λ/4 resonance, while the incident energy disspation at high frequency is contributed by the edge diffraction and resonance between the adjacent units. The similar normal stepped stuctures with different volume fraction are investigated. It demonstrates that the excellent absorption property of the MSC also relys on the matching degree of effective impedance. It is shown that the fabricated flexible MSC is a potential practical composite structure in radiation protection and radar stealth. 20
ACCEPTED MANUSCRIPT Acknowledgement This work is supported by the National Natural Science Foundation of China (11872113) and the Project of State Key Laboratory of Explosion Science and
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Technology. References
[1] C.X. Wang, M.J. Chen, H.S. Lei, K. Yao, H.M. Li, W.B. Wen, D.N. Fang, Radar stealth and
mechanical properties of a broadband radar absorbing structure, Compos Part B-Eng 123 (2017) 19-27. [2] Y.C. Qing, D.D. Min, Y.Y. Zhou, F. Luo, W.C. Zhou, Graphene nanosheet- and flake carbonyl iron
SC
particle-filled epoxy-silicone composites as thin-thickness and wide-bandwidth microwave absorber, Carbon 86 (2015) 98-107.
[3] Y. Zhang, Y. Huang, T.F. Zhang, H.C. Chang, P.S. Xiao, H.H. Chen, Z.Y. Huang, Y.S. Chen,
M AN U
Broadband and Tunable High-Performance Microwave Absorption of an Ultralight and Highly Compressible Graphene Foam, Adv Mater 27(12) (2015) 2049-2053.
[4] T. Wang, P. Wang, Y. Wang, L. Qiao, A broadband far-field microwave absorber with a sandwich structure, Mater. Des. 95 (2016) 486-489.
[5] C.Q. Song, X.W. Yin, M.K. Han, X.L. Li, Z.X. Hou, L.T. Zhang, L.F. Cheng, Three-dimensional reduced graphene oxide foam modified with ZnO nanowires for enhanced microwave absorption properties, Carbon 116 (2017) 50-58.
[6] Y.C. Qing, W.C. Zhou, F. Luo, D.M. Zhu, Epoxy-silicone filled with multi-walled carbon nanotubes
TE D
and carbonyl iron particles as a microwave absorber, Carbon 48(14) (2010) 4074-4080. [7] L. Yang, H.L. Fan, J. Liu, Y. Ma, Q. Zheng, Hybrid lattice-core sandwich composites designed for microwave absorption, Mater. Des. 50 (2013) 863-871. [8] Y.C. Qing, X. Wang, Y.Y. Zhou, Z.B. Huang, F. Luo, W.C. Zhou, Enhanced microwave absorption of multi-walled carbon nanotubes/epoxy composites incorporated with ceramic particles, Compos Sci
EP
Technol 102 (2014) 161-168.
[9] M.S. Cao, W.L. Song, Z.L. Hou, B. Wen, J. Yuan, The effects of temperature and frequency on the dielectric properties, electromagnetic interference shielding and microwave-absorption of short carbon
AC C
fiber/silica composites, Carbon 48(3) (2010) 788-796. [10] B. Wu, H.M. Tuncer, A. Katsounaros, W.P. Wu, T.C. Matthew, K. Ying, L.H. Zhang, W.I. Milne, Y. Hao, Microwave absorption and radiation from large-area multilayer CVD graphene, Carbon 77 (2014) 814-822.
[11] X.J. Zhang, G.S. Wang, W.Q. Cao, Y.Z. Wei, M.S. Cao, L. Guo, Fabrication of multi-functional PVDF/RGO composites via a simple thermal reduction process and their enhanced electromagnetic wave absorption and dielectric properties, Rsc Adv 4(38) (2014) 19594-19601. [12] Y.J. Chen, M.S. Cao, T.H. Wang, Q. Wan, Microwave absorption properties of the ZnO nanowire-polyester composites, Appl Phys Lett 84(17) (2004) 3367-3369. [13] Y. Wang, H.T. Guan, S.F. Du, Y.D. Wang, A facile hydrothermal synthesis of MnO2 nanorod-reduced graphene oxide nanocomposites possessing excellent microwave absorption properties, Rsc Adv 5(108) (2015) 88979-88988. [14] J.L. Xu, X.S. Qi, C.Z. Luo, J. Qiao, R. Xie, Y. Sun, W. Zhong, Q. Fu, C.X. Pan, Synthesis and
21
ACCEPTED MANUSCRIPT enhanced microwave absorption properties: a strongly hydrogenated TiO2 nanomaterial, Nanotechnology 28(42) (2017). [15] J. Zhang, J.W. Liu, C.Y. Liang, F. Zhang, R.C. Che, Highly crystalline manganese selenide nanorods: Synthesis, characterization, and microwave absorption properties, J Alloy Compd 548 (2013) 13-17. [16] J.S. Li, H. Huang, Y.J. Zhou, C.Y. Zhang, Z.T. Li, Research progress of graphene-based microwave absorbing materials in the last decade, J Mater Res 32(7) (2017) 1213-1230.
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[17] Q.H. Liu, Q. Cao, H. Bi, C.Y. Liang, K.P. Yuan, W. She, Y.J. Yang, R.C. Che, CoNi@SiO2@TiO2 and CoNi@Air@TiO2 Microspheres with Strong Wideband Microwave Absorption, Adv Mater 28(3) (2016) 486-+.
[18] Y.X. Huang, W.L. Song, C.X. Wang, Y.N. Xu, W.Y. Wei, M.J. Chen, L.Q. Tang, D.N. Fang, Compos Sci Technol 162 (2018) 206-214.
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Multi-scale design of electromagnetic composite metamaterials for broadband microwave absorption, [19] X.F. Liu, Y.X. Chen, X.R. Cui, M. Zeng, R.H. Yu, G.S. Wang, Flexible nanocomposites with enhanced microwave absorption properties based on Fe3O4/SiO2 nanorods and polyvinylidene fluoride, J Mater Chem A 3(23) (2015) 12197-12204.
M AN U
[20] Y.Y. Zhou, W.C. Zhou, Y.C. Qing, F. Luo, D.M. Zhu, Temperature dependence of the electromagnetic properties and microwave absorption of carbonyl iron particles/silicone resin composites, J Magn Magn Mater 374 (2015) 345-349.
[21] B.S. Zhang, Y. Feng, H. Xiong, Y. Yang, H.X. Lu, Microwave-absorbing properties of De-aggregated flake-shaped carbonyl-iron particle composites at 2-18 GHz, Ieee T Magn 42(7) (2006) 1778-1781.
[22] Y.Y. Zhou, W.C. Zhou, R. Li, Y. Mu, Y.C. Qing, Enhanced antioxidation and electromagnetic 637 (2015) 10-15.
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properties of Co-coated flaky carbonyl iron particles prepared by electroless plating, J Alloy Compd [23] Y. Cheng, Y.G. Xu, J. Cai, L.M. Yuan, D.Y. Zhang, Effect of the bio-absorbent on the microwave absorption property of the flaky CIPs/rubber absorbers, J Magn Magn Mater 389 (2015) 106-112. [24] M.J. Park, J.H. Choi, S.S. Kim, Wide bandwidth pyramidal absorbers of granular ferrite and
EP
carbonyl iron powders, Ieee T Magn 36(5) (2000) 3272-3274. [25] W.H. Choi, C.G. Kim, Broadband microwave-absorbing honeycomb structure with novel design concept, Compos Part B-Eng 83 (2015) 14-20.
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[26] M. Olszewska-Placha, B. Salski, D. Janczak, P.R. Bajurko, W. Gwarek, M. Jakubowska, A Broadband Absorber With a Resistive Pattern Made of Ink With Graphene Nano-Platelets, Ieee T Antenn Propag 63(2) (2015) 565-572. [27] Q. Zhou, X.W. Yin, F. Ye, X.F. Liu, L.F. Cheng, L.T. Zhang, A novel two-layer periodic stepped structure for effective broadband radar electromagnetic absorption, Mater. Des. 123 (2017) 46-53. [28] W.L. Song, Z.L. Zhoup, L.C. Wang, X.D. Cheng, M.J. Chen, R.J. He, H.S. Chen, Y.Z. Yang, D.N. Fang, Constructing Repairable Meta-Structures of Ultra-Broad-Band Electromagnetic Absorption from Three-Dimensional Printed Patterned Shells, Acs Applied Materials & Interfaces 9(49) (2017) 43179-43187. [29] W. Li, T.L. Wu, W. Wang, P.C. Zhai, J.G. Guan, Broadband patterned magnetic microwave absorber, J Appl Phys 116(4) (2014). [30] B.C. Wang, J.Q. Wei, L. Qiao, T. Wang, F.S. Li, Influence of the interface reflections on the microwave reflection loss for carbonyl iron/paraffin composite backed by a perfect conduction plate, J
22
ACCEPTED MANUSCRIPT Magn Magn Mater 324(5) (2012) 761-765. [31] B.C. Wang, J.Q. Wei, Y. Yang, T. Wang, F.S. Li, Investigation on peak frequency of the microwave absorption for carbonyl iron/epoxy resin composite, J Magn Magn Mater 323(8) (2011) 1101-1103. [32] P.J. Joseph, A.D. Tyson, W.D. Burnside, An Absorber Tip Diffraction Coefficient, Ieee T Electromagn C 36(4) (1994) 372-379. [33] H. Zou, S.H. Li, L.Q. Zhang, S.N. Yan, H.G. Wu, S.A. Zhang, M. Tian, Determining factors for high performance silicone rubber microwave absorbing materials, J Magn Magn Mater 323(12) (2011)
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1643-1651.
[34] Y.H. Zhai, Y. Zhang, W.T. Ren, Electromagnetic characteristic and microwave absorbing
performance of different carbon-based hydrogenated acrylonitrile-butadiene rubber composites, Mater Chem Phys 133(1) (2012) 176-181.
[35] F. Nanni, P. Travaglia, M. Valentini, Effect of carbon nanofibres dispersion on the microwave
SC
absorbing properties of CNF/epoxy composites, Compos Sci Technol 69(3-4) (2009) 485-490.
[36] Y.G. Xu, D.Y. Zhang, J. Cai, L.M. Yuan, W.Q. Zhang, Microwave absorbing property of silicone rubber composites with added carbonyl iron particles and graphite platelet, J Magn Magn Mater 327 (2013) 82-86.
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[37] B. Pradhan, S. Roy, S.K. Srivastava, A. Saxena, Synergistic effect of carbon nanotubes and clay platelets in reinforcing properties of silicone rubber nanocomposites, J Appl Polym Sci 132(15) (2015). [38] H. Acharya, S.K. Srivastava, A.K. Bhowmick, Synthesis of partially exfoliated EPDM/LDH nanocomposites by solution intercalation: Structural characterization and properties, Compos Sci Technol 67(13) (2007) 2807-2816.
[39] M.A. Abshinova, S.M. Matitsine, L. Liu, C.R. Deng, L.B. Kong, High Microwave Magnetic Permeability of Composites with Submicron Iron Flakes, J Phys Conf Ser 266 (2011).
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[40] Z.J. Li, Z.L. Hou, W.L. Song, X.D. Liu, W.Q. Cao, X.H. Shao, M.S. Cao, Unusual continuous dual absorption peaks in Ca-doped BiFeO3 nanostructures for broadened microwave absorption, Nanoscale 8(19) (2016) 10415-10424.
[41] H.T. Guan, J.B. Xie, G. Chen, Y.D. Wang, Facile synthesis of alpha-MnO2 nanorods at low temperature and their microwave absorption properties, Mater Chem Phys 143(3) (2014) 1061-1068.
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[42] H.L. Yu, T.S. Wang, B. Wen, M.M. Lu, Z. Xu, C.L. Zhu, Y.J. Chen, X.Y. Xue, C.W. Sun, M.S. Cao, Graphene/polyaniline nanorod arrays: synthesis and excellent electromagnetic absorption properties, J Mater Chem 22(40) (2012) 21679-21685.
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[43] J.Z. He, X.X. Wang, Y.L. Zhang, M.S. Cao, Small magnetic nanoparticles decorating reduced graphene oxides to tune the electromagnetic attenuation capacity, J Mater Chem C 4(29) (2016) 7130-7140.
[44] D.R. Smith, D.C. Vier, T. Koschny, C.M. Soukoulis, Electromagnetic parameter retrieval from inhomogeneous metamaterials, Phys Rev E 71(3) (2005).
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