Electromagnetic properties and microwave absorption properties of BaTiO3-carbonyl iron composite in S and C bands

Article abstract of DOI:10.1016/j.jmmm.2011.02.013

BaTiO₃ powders are prepared by solgel method. The carbonyl iron powder is prepared via thermal decomposition of iron pentacarbonyl. Then BaTiO₃carbonyl iron composite with different mixture ratios was prepared using the as-prepared material. The structure, morphology, and properties of the composites are characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, scanning electron microscopy (SEM), and a network analyzer. The complex permittivity and reflection loss of the composites have been measured at different microwave frequencies in S- and C-bands employing vector network analyzer model PNA 3629D vector. The effect of the mass ratio of BaTiO₃/carbonyl iron on the microwave loss properties of the composites is investigated. A possible microwave absorbing mechanism of BaTiO₃carbonyl iron composite has been proposed. The BaTiO₃carbonyl iron composite can find applications in suppression of electromagnetic interference, and reduction of radar signature.

Full text of DOI:10.1016/j.jmmm.2011.02.013

Journal of Magnetism and Magnetic Materials 323 (2011) 1805–1810
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials
journal homepage: www.elsevier.com/locate/jmmm
Electromagnetic properties and microwave absorption properties
of BaTiO –carbonyl iron composite in S and C bands
3
n
Yang Rui-gang
a
School of Machinery and Electronics Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China
b
Institute of Applied Mechanics and Biomedical Engineering, Taiyuan University of Technology, Taiyuan 030024, China
a r t i c l e i n f o
a b s t r a c t
Article history:
BaTiO3 powders are prepared by sol–gel method. The carbonyl iron powder is prepared via thermal
Received 6 October 2010
Received in revised form
decomposition of iron pentacarbonyl. Then BaTiO –carbonyl iron composite with different mixture ratios
3
was prepared using the as-prepared material. The structure, morphology, and properties of the composites
6
February 2011
are characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, scanning electron
microscopy (SEM), and a network analyzer. The complex permittivity and reflection loss of the composites
have been measured at different microwave frequencies in S- and C-bands employing vector network
Available online 15 February 2011
Keywords:
BaTiO
3
analyzer model PNA 3629D vector. The effect of the mass ratio of BaTiO
loss properties of the composites is investigated. A possible microwave absorbing mechanism of BaTiO
carbonyl iron composite has been proposed. The BaTiO –carbonyl iron composite can find applications in
suppression of electromagnetic interference, and reduction of radar signature.
2011 Elsevier B.V. All rights reserved.
3
/carbonyl iron on the microwave
Carbonyl iron
3
–
Electromagnetic property
Microwave absorbing
3
&
1
. Introduction
dielectric materials, permeability remains constant throughout the
frequency range, and their larger propagation constant enables wave
absorber to be made thinner[12]. These absorbers being purely
dielectric, polarization and conductive losses are the main mechan-
ism for the absorption of microwave, and the complex permittivity
In recent years, electromagnetic wave in GHz range is being
increasingly used in wireless communication tools, local area net-
works, personal digital assistant, and other communication equip-
ments. However, many problems occurred along with it, which are a
misoperation of precise electronic equipment and leak of secret
information due to leakage of electromagnetic wave. Thus, electro-
magnetic compatibility (EMC) and electromagnetic interference
0
00
) is an important parameter to be measured. Only a few
r
(e
ꢀj
e
r
studies concerning absorbers using ferroelectric materials have been
reported [13,14]. In this article, we report the complex permittivity
and reflection loss of composite absorber in S- and C-band
(EMI) are becoming serious problems, and much attention has been
3
(30–6000 MHz), based on different ratios of BaTiO and carbonyl
paid towards finding suitable microwave absorber to solve this
problem [1,2]. The microwave absorber can be used to minimize the
electromagnetic reflection from the metal plate such as aircrafts,
ships, tanks, and the walls of anechoic chambers and electronic
equipment [3–5]. For the purpose of preparing a low-reflecting
absorber in the desired frequency range, two fundamental condi-
tions must be satisfied [6]: the first is that the incident wave can
enter the absorber to a greatest extent (impedance matching
characteristic), and the second is that the electromagnetic wave
entering into the materials can be almost entirely attenuated and
absorbed within the finite thickness of the absorber (attenuation
characteristic). Ferromagnetic fillers such as different kinds of
ferrites and carbonyl iron are generally used in composite absorbers,
but their permeabilities drastically reduce at frequencies in the GHz
range [7–11]. However, if the fillers are made of ferroelectric and
iron. Absorption spectra for different absorber thicknesses have been
theoretically predicted based on the model of a single layer absorber
backed by a perfect conductor [15]. Measured and calculated
absorption spectra have been compared. Matching frequencies for
minimum reflection and corresponding matching thicknesses have
been estimated and compared with values obtained experimentally.
3
BaTiO exhibits various electrical and magnetic properties of
which the complex permeability and the complex permittivity, in
particular, are important in determining their high-frequency char-
acteristics. Carbonyl iron particle, with the inside structure looking
like that of an onion and the component including 0.8–1.1 at% carbon,
0.8–1.2 at% nitrogen, and 0.4–0.7 at% oxygen possesses relatively
lower electrical conductivity in comparison with other metallic
particles [16]. Carbonyl iron is predicted to possess high-frequency
relaxation loss and a very wide bandwidth [17]. Carbonyl iron/rubber
composites are reported to have the good electromagnetic wave
absorption properties [18]. Good properties of the disaggregated
flake-shaped carbonyl-iron particle composites are reported [16].
Also, carbonyl iron has attracted much attention because of its
several unique properties. It is highly stable in air, soluble
n
Correspondence address: School of Machinery and Electronics Engineering,
Taiyuan University of Science and Technology, Taiyuan 030024, China.
E-mail address: yangruigang12316@163.com
0304-8853/$ - see front matter & 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2011.02.013

1
806
Y. Rui-gang / Journal of Magnetism and Magnetic Materials 323 (2011) 1805–1810
in various solvents, and exhibits dramatic changes in its electronic
structure and physical properties in the protonated state. It
also shows magnetic behavior because of its high spin density [19].
It has been found that, in magnetic materials, the relaxation of
magnetic oscillations is strongly affected by structural disorder, both
crystallographic and geometrical, such as pores, cracks, defects, and
surface roughness. Composite materials, in which magnetic particles
are embedded in insulating binders, introduce an additional disorder
in the form of filler–matrix interfaces. This makes the magnetic
relaxation behavior still more complex. This additional disorder
brings about changes in the internal magnetic fields by reducing
exchange and dipole interactions through demagnetization fields. As
a result of dipole interactions various effects have been observed,
e.g., the anomalous broadening of the resonance band, the shift of
resonance to higher frequencies, a considerable decrease in complex
permeability, etc. [20].
A
B
C
4
000
3500
3000
2500
2000
1500
1000
500
2
. Experimental work
Wave number (cm-1)
Fig. 1. FTIR spectra of BaTiO
3
/carbonyl iron composites obtained with different
2
.1. Synthesis of BaTiO powder
3
mass ratios of BaTiO /carbonyl iron: (A) N, (B) 6, and (C) 0.
3
BaTiO
absorbent cotton as template. Some amount of tetrabutyl titanate
the mol ratio of Ti/Ba was 1:1) was dissolved in a mixture of
3
powders are prepared by sol–gel method using the
(
anhydrous ethanol and acetic acid. The entire mixture was stirred
at 30 1C for half an hour. Then the mixture was dropped on the
dried absorbent cotton and dried at 30 1C for 5 h. Then the above
dried absorbent cotton was heated in an oven in the air at 950 1C
for 2 h to obtain BaTiO
3
samples.
2
.2. Synthesis of BaTiO
3
–carbonyl iron composite
The carbonyl iron powder was prepared via thermal decom-
position of iron pentacarbonyl (Fe(CO) ) obtained from Jiangsu
5
Xuyi Tianyi Ultrafine Powder Co. Ltd. in our laboratory. Carbonyl
iron and barium titanate powder were thoroughly mixed sepa-
rately in the mass ratios of 3:1, 6:1, 8:1, 10:1, and 12:1 using a
20
30
40
50
θ (°)
60
70
80
ball mill for 6 h to obtain BaTiO
.3. Characterization
Fourier transform infrared spectroscopy (FTIR) spectra of the
3
–carbonyl iron composite.
2
3
Fig. 2. XRD patterns of BaTiO obtained by sol–gel method.
2
bending, respectively (shown in Fig. 1C). The characteristic absorp-
tion bands of BaTiO can all be found in the curves of Fig. 1B, and the
peaks of carbonyl iron are weak. It may be because the carbonyl iron
was enwrapped by the BaTiO particles after the ball mill process.
3
samples were taken in dried KBr powder on a Nexus 670 spectro-
meter (Nicolet, USA). The morphology of as-prepared samples
was investigated using scanning electron microscope (SEM). The
samples for measuring electromagnetic properties were prepared
3
3.2. XRD and SEM characterization
by dispersing the carbonyl iron/BaTiO
3
composite powder in
paraffin wax. The volume fraction of the powder is 60%. The
powder/wax composites were die-pressed to form cylindrical
toroidal specimens with 7.0 mm outer diameter, 3.0 mm inner
diameter, and 3 mm thickness. The measurements of electromag-
netic wave loss property for the specimens were carried out using
a PNA 3629D vector network analyzer in the 30–6000 MHz range.
Typical XRD pattern of the BaTiO
As shown in Fig. 2, the crystalline peaks appeared at 2
32.2, 38.9, 45.2, 51.3, and 55.9 correspond to (1 0 0), (1 1 0),
(1 1 1), (2 0 0), (2 1 0), and (2 1 1) reflections, which correspond
to the peaks of pure tetragonal perovskite structure [21].
SEM was used to determine the morphology and distribution
3
particles is shown in Fig. 2.
¼22.6,
y
3
of BaTiO and carbonyl iron. As shown in Fig. 3, it could be found
3
. Results and discussion
that the carbonyl iron is of spherical shape, and the BaTiO of belt
3
shape. The particle size of the carbonyl iron powder ranges from
3.1. FTIR spectral analysis
10 to 100
mm and most of the particles are in the range of 50
mm.
The slenderness ratio of the BaTiO
3
belt is about 20:1.
The FTIR spectra of the samples are shown in Fig. 1. The
characteristic absorption bands of BaTiO
4
vibrations (shown in Fig. 1A). The peaks at 1750 cm are attributed
3
are at 600 and
60 cm , which are identified as the metal–oxygen stretching
3.3. Analysis of electromagnetic parameters and wave absorbing
property
ꢀ
1
ꢀ
1
to the characteristic normal dimeric carboxylic C¼O stretching; the
The frequency dependences of the complex permittivity and
permeability of the carbonyl iron and BaTiO microwave absorber
ꢀ
1
peaks at 1250 and 1000 cm correspond to C–CO–C stretching and
3

Y. Rui-gang / Journal of Magnetism and Magnetic Materials 323 (2011) 1805–1810
1807
3
Fig. 3. SEM images of the samples: (A) carbonyl iron and (B) BaTiO .
are shown in Figs. 4 and 5, respectively. From Fig. 4, it can be
found that the consistency of the real component of the dielectric
permittivity, as the frequency is first increased and then
decreased, is simply due to the fact that the polarization of the
dielectric dipoles in the RAM are in-phase with the oscillation of
the electric field vector of the electromagnetic wave. On the other
hand, the imaginary component, as the frequency, shows an
increase. This could be due to the loss process during the
oscillation of the dipoles, under the influence of the electromag-
netic wave, which dominates in the high-frequency regime.
Ref. [22] reported that the dielectric loss presents different loss
mechanisms as the frequency increases. When the frequency is
relatively low, the loss is determined by the leak conductance and
the loss is independent of the frequency. As the frequency
increases to microwave frequency band, the mechanisms are
relaxation polarization loss and electric conductance loss. The
increase in the imaginary component of the permittivity, as the
frequency increases, may be the consequence of the increase of
the relaxation polarization loss and the electric conductance loss.
The variation dielectric parameter of the composite is the com-
frequency shifts to the lower frequency range with the increase of
the carbonyl iron content. The increase of the carbonyl iron
content brings about changes in the internal magnetic fields by
increasing exchange and dipole interactions through demagneti-
zation fields. As a result of dipole interactions, the resonance
frequency shifts to lower frequencies [24]. From Fig. 5, it can be
found that the loss tangent of the composite increases with the
increase of the carbonyl iron content in the 3–5 GHz range.
0
00
0
00
Electromagnetic parameters(
tures of absorbing materials. The normalized input impedance (Z)
m
,
m
,
e
, ) are the intrinsic fea-
e
with respect to the impedance in free space, and reflection loss
(R
L
) are given by
qffiffiffiffiffiffiffiffiffiffiffi
pffiffiffiffiffiffiffiffiffi
Z ¼
m
=
e
r
tanh½ꢀjð2
p
=cÞð m e
r
Þfdꢁ
r
r
R
L
ðdBÞ ¼ ꢀ20log½9ðZꢀ1Þ=ðZþ1Þ9ꢁ
where mr and
r
e are the relative complex permeability and
permittivity of the absorber medium; f and c are the frequency
of microwave in free space and the velocity of light, respectively;
and d is the sample thickness.
Fig. 6 shows the calculated reflection loss as a function of
frequency for samples. The microwave absorbance of the samples
00
prehensive effect of carbonyl iron and BaTiO
samples gradually increases with the increase of the mass ratio
of BaTiO /carbonyl iron (especially in the 4–6 GHz). In the
frequency ranges,
3
. The
e
of the
R
3
L L
can be predicted from R , the larger the negative value of R , the
0
0
0
. This could be due to the
r
e
is larger than
e
greater will be the microwave absorption properties of materials.
The most important and interesting observation is that the
reflection loss is found to depend sensitively on the mass ratio
r
loss process during the oscillation of the dipoles, under the
influence of the TEM wave, which dominates in the high-
0
0
frequency regime. The
increase of the BaTiO content. BaTiO
exhibiting high resistivity. The characteristic feature of BaTiO
e
of the samples increase with the
of the carbonyl iron/BaTiO
wave absorbance of the sample in the frequency bands is very
low. With an increase of the mass ratio of carbonyl iron/BaTiO
the microwave absorbance peaks of the sample also increases. For
the sample obtained with the mass ratio of carbonyl iron/BaTiO
3
composite. For sample A, the micro-
r
3
3
is a ferroelectric material
is
ions
fitting octahedral interstices. At room temperature, there are
3
3
,
2
+
2ꢀ
4+
that the Ba
and O
ions form an fcc lattice with Ti
3
4
+
possibly minimum energy positions for the Ti ions, which are
off-centered and therefore give rise to permanent electric dipoles.
Fig. 5 shows that the real part mr of the complex permeability
of 8:1, there exist two absorbance peaks, the value of reflection
loss peaks is up to ꢀ24 dB. The bandwidth of the reflectivity
below ꢀ5 dB is up to 3.1 GHz when the carbonyl iron/BaTiO
3
for the BaTiO
3
–carbonyl iron composite absorbing materials is
mass ratio of the sample is larger than 10:1. The comprehensive
microwave absorption properties of the sample decrease. For
sample C, the microwave absorbing peaks value is up to ꢀ37 dB
at 5.22 GHz. It could be because of the larger magnetic loss
tangent of the composite. The variation of reflection loss results
of the samples is coherent with the variations of the complex
permittivity and permeability (Figs. 4 and 5) of the sample as in
the formulas above. The variation of reflection loss indicated that
there are close relationship between the material composition
and material properties.
nearly independent of the mass ratio of BaTiO
3
/carbonyl iron. It
0
can be found that the
m
gradually decreases for the domain-wall
r
motion and relaxes as the frequency increases [23]. A peak can be
0
0
00
first increases to the maximum at
r
seen on the
m
plots, and the
m
r
about 2–3 GHz and then decreases with the increase of the
frequency because of the domain-wall resonance and relaxation
0
0
of BaTiO
of carbonyl iron. The peak of the
m
3
–carbonyl iron
r
composite shifts to lower frequent ranges with the increase of the
carbonyl iron content. The resonance peak and the resonance

1
808
Y. Rui-gang / Journal of Magnetism and Magnetic Materials 323 (2011) 1805–1810
3
3
3
3
2
2
2
2
2
1
1
1
1
1
6
4
2
0
8
6
4
2
0
8
6
4
2
0
8
6
4
2
0
2
30
ε'
ε"
ε'
ε"
2
2
1
1
5
0
5
0
5
0
-
0
1000 2000 3000 4000 5000 6000
f (MHz)
0
1000 2000 3000 4000 5000 6000
f (MHz)
2
2
2
2
1
1
1
1
1
6
4
2
0
8
6
4
2
0
8
6
4
2
0
2
3
3
2
5
0
5
ε'
ε"
ε'
ε"
20
1
1
5
0
5
0
-
0
1000 2000 3000 4000 5000 6000
f (MHz)
0
1000 2000 3000 4000 5000 6000
f (MHz)
30
25
20
15
10
5
0
ε'
ε"
0
1000 2000 3000 4000 5000 6000
f (MHz)
3
Fig. 4. Frequency dependences of the complex permittivity of samples obtained with different mass ratios of BaTiO /carbonyl iron: (A) 3, (B) 6, (C) 8, (D) 10, and (E) 12.
4
. Conclusions
pentacarbonyl (Fe(CO)
different mixture ratios has been prepared using the as-prepared
material. The effect of the mol ratio of BaTiO –carbonyl iron on the
microwave loss properties of the composites is investigated. A
5 3
). Then BaTiO –carbonyl iron composite with
BaTiO
3
powders are prepared by sol–gel method. The carbonyl
3
iron powder was prepared via thermal decomposition of iron

Y. Rui-gang / Journal of Magnetism and Magnetic Materials 323 (2011) 1805–1810
1809
8
7
6
5
4
3
2
1
0
12
μ'
1
0
8
6
4
2
0
μ"
μ'
μ"
0
1000
2000
3000
4000
5000
6000
0
1000
2000
3000
4000
5000
6000
f (MHz)
f (MHz)
2
2
2
1
1
1
1
1
4
2
0
8
6
4
2
0
8
6
4
2
0
2
24
22
20
18
16
14
12
10
8
μ'
μ"
μ'
μ"
6
4
2
0
-
-2
0
1000
2000
3000
4000
5000
6000
0
1000
2000
3000
4000
5000
6000
f (MHz)
f (MHz)
1
1
1
4
2
0
8
6
4
2
0
μ'
μ"
0
1000
2000
3000
f (MHz)
4000
5000
6000
3
Fig. 5. Frequency dependences of the complex permeability of samples obtained with different mass ratios of BaTiO /carbonyl iron: (A) 3, (B) 6, (C) 8, (D) 10, and (E) 12.
possible microwave absorbing mechanism of BaTiO
composite has been proposed. The BaTiO –carbonyl iron composite
can find applications in suppression of electromagnetic interference
EMI) and reduction of radar signature. For the sample obtained
3
–carbonyl iron
3
with the mass ratio of BaTiO /carbonyl iron of 10:1, there exist two
3
absorbance peaks, and the value of reflection loss peaks is up to
ꢀ24 dB. The bandwidth less than ꢀ5 dB is up to 3.1 GHz in the
whole frequency range.
(

1
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Y. Rui-gang / Journal of Magnetism and Magnetic Materials 323 (2011) 1805–1810
0
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