- Email: [email protected]
A novel thermo-tunable band-stop filter employing a conductive rubber split-ring resonator
Accepted Manuscript A novel thermo-tunable band-stop filter employing a conductive rubber split-ring resonator
Kepeng Qiu, Jianqiang Jin, Zijun Liu, Fuli Zhang, Weihong Zhang PII: DOI: Reference:
S0264-1275(16)31555-6 doi: 10.1016/j.matdes.2016.12.038 JMADE 2583
To appear in:
Materials & Design
Received date: Revised date: Accepted date:
15 July 2016 12 December 2016 13 December 2016
Please cite this article as: Kepeng Qiu, Jianqiang Jin, Zijun Liu, Fuli Zhang, Weihong Zhang , A novel thermo-tunable band-stop filter employing a conductive rubber splitring resonator. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Jmade(2016), doi: 10.1016/j.matdes.2016.12.038
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 A Novel Thermo-Tunable Band-Stop Filter Employing a Conductive Rubber Split-Ring Resonator
Kepeng Qiu*, Jianqiang Jin, Zijun Liu, Fuli Zhang, Weihong Zhang Northwestern Polytechnical University, Xi’an, People’s Republic of China
RI
PT
*[email protected]
Abstract
SC
This paper presents the design and related applications of a thermally tunable band-stop filter employing conductive rubber that incorporates electrically conductive particles. The relationship
NU
between the environmental temperature and the volume resistivity of conductive rubber materials was experimentally established. The experimental results demonstrated that the conductive rubber
MA
has a temperature-sensitive resistance property. The conductive rubber material was employed in the design of a C-shaped split-ring resonator (SRR) structure. The influence of environmental
D
temperature on the electromagnetic properties of the SRR structure was analysed using a
PT E
numerical simulation and experimental testing. The results demonstrated that the design of thermally tunable metamaterials was possible. As such, an H-shaped conductive rubber SRR was employed in the design of a novel thermally tunable band-stop filter. The results of a numerical
CE
simulation and experimental testing verified its band-stop characteristic, and demonstrated that the filtering performance of the H-shaped conductive rubber SRR can be controlled by the
AC
environmental temperature. Lastly, by comparison of the effective dielectric properties of the two types of SRRs, it demonstrates the effectiveness of conductive rubber and their temperature-controllable band-stop characteristics. Keywords: Conductive Rubber, Temperature Control, Split-Ring Resonator, Band-Stop Filter.
1. Introduction The split-ring resonator (SRR) is an essential component of microwave metamaterials and has its theoretical basis in Veselago’s work about left-handed metamaterial in the late 1960s [1].
ACCEPTED MANUSCRIPT SRRs and wires can be appropriately arranged to form composite media that exhibit double-negative electromagnetic properties in the vicinity of the resonant frequency [2−3]. In addition, a wide range of equivalent electromagnetic properties can be achieved by varying the parameters of the metamaterial structures. Normally, the novel electromagnetic properties of a specific metamaterial structure only
PT
appear within a specific resonance frequency range. The structure of the metamaterial must be redesigned to ensure an equivalent response at different excitation frequencies, which greatly
RI
reduces the service efficiency. As a consequence, dynamic control of the resonance frequency of an electromagnetic metamaterial structure has been a subject of intense interest. This task involves
SC
the control of the equivalent capacitance and equivalent inductance of the structure, which co-determine the resonance frequency. The most direct approach is to change the parameters of the
incorporation of microwave switches [7−10].
NU
metamaterial structures by mechanical control [4−6]. Another effective method is the
MA
In customizing the metamaterial properties, other tuning methods have appeared. By introducing yttrium iron garnet rods into SRRs and wire arrays, the left-handed passband of the
D
metamaterial was continuously and reversibly adjusted by externally applied DC magnetic fields
PT E
[11]. By integrating a digital potentiometer into each SRR of an array as a variable voltage divider, the magnetic metamaterial was tuned by using digitally addressable SRRs [12]. Tunable materials based on liquid-crystal materials were also designed to realize the continuous control of
CE
electromagnetic properties by modulating the collective orientation of the liquid-crystal molecules using applied electric and magnetic fields [13−16]. The metamaterials comprising semiconductor
AC
SRRs were thermally tunable in the terahertz regime [17]. At present, the tunable electromagnetic spectrum has been covered nearly from the microwave frequency band to the terahertz and infrared bands [18].
An SRR, similar to a resonance circuit, resonates when excited by an incident electromagnetic field at a specific frequency. This induces a ring current where the resulting magnetic moment either strengthens or weakens the incident electromagnetic field, thus displaying band-pass or band-stop characteristics in response to an incident electromagnetic field. When properly coupled to coplanar-waveguides (CPWs) or microstrip transmission lines, SRRs and complementary SRRs (CSRRs) can efficiently inhibit signal propagation in the vicinity of their
ACCEPTED MANUSCRIPT quasi-static resonant frequencies [19]. A low-pass filter was obtained using cascaded multi-CSRR cells [20], and a high-pass filter was designed with two CSRR sections having additional microstrip patches [21]. Currently, significant advances have been made regarding the miniaturization of band-pass filters and ultra-wideband filters [22−26]. According to the tunable characteristics of artificial electromagnetic materials, the resonant frequency for an SRR band-stop
PT
filter was tuned by using MEMS switches [27] or by varying the inductor values [28]. Tunable band-stop filters can also be designed using RF-MEMS switches and microelectromechanical
RI
deflectable cantilever-type rings [29−30]. Pradhanet et al. [31] presented a tunable filter on a silicon substrate using complementary split-ring resonators (CSRRs) and an RF-MEMS variable
SC
capacitor. However, this fabrication process is quite complex and expensive.
In the present work, flexible SRR-structured band-stop filters, which are controlled through
NU
the environmental temperature, were developed by combining the tunable characteristics of artificial electromagnetic materials based on conductive rubber that incorporates conductive
MA
particles.
D
2. Temperature Effects of Conductive Rubber
PT E
Conductive rubber is a type of highly polymeric material that is formed by uniformly mixing flexible polymeric substrate materials with conductive particles. This imparts electrical conductivity while preserving the flexibility of the substrate material. The unique nature of the
CE
composite presents a conductive mechanism and resistance characteristics that differ from those of metallic conductors, particularly at low conductive particle concentrations where the conductivity
AC
occurs predominantly via electron tunnelling across numerous small barriers and includes a strong temperature dependency. These characteristics offer potential benefits for creating tunable electromagnetic structures. According to quantum tunneling theory [32−33], and assuming that conductivity occurs between two conductive particles with a statistical average separation of ω (i.e. the barrier width assuming a plane parallel junction between particles), the relationship between the macroscopic current density J(ε) and an electric field ε applied to the junction is
ACCEPTED MANUSCRIPT 2 J J 0 exp 1 ， 0 . 2 0
(1)
Here, J0 is the current density in the absence of effects owing to ε and containing all nonexponential temperature effects. 2mV0 h2 is the tunnelling constant, where m is the electron mass, h is a reduced Planckʼs constant, and V0 is the barrier height; and 0 4V0 e ,
PT
where e is the electron charge. The value of ε derives from two sources applied at both ends of a conductive particle junction, namely, an externally applied electric field A and an electric field
RI
induced by thermal disturbance T:
SC
A T .
(2)
When A < T, the component of J(ε) lying in the direction of A is (3)
NU
1 J J A T J A T . 2
The partial conductivity as a result of T is defined in terms of J as
A 0
J
A
dJ T . dT
MA
T lim
(4)
P T T d T
P T 0
. dJ T dT dT
PT E
0
D
Thus, the tunnel conductance induced by T is given as follows:
(5)
CE
A T 2 Here, P T exp represents the probability of a given T at temperature T, 8 T
AC
where A is the area of a plane parallel junction, and is the Boltzmann constant. Substituting Eqs. (1) and (4) into Eq. (5), and applying saddle point integration yields the conductivity T1 , T T0
0 exp
(6)
where 0 represents the conductivity in the absence of temperature effects, T1 A 02 8 , and T0 A 02 4 2 .
From the forgoing discussion, it is known that σ is co-influenced by the environmental temperature T and the average distance between conductive particles ω. As T increases, the rubber matrix undergoes thermal expansion, resulting in an enlarged interparticle spacing, which leads to
ACCEPTED MANUSCRIPT a decreased value of σ, and also enhances the probability of electron transition between particles. Therefore, thermal disturbance plays a positive role, and the value of σ increases. A YAOS BD400H resistivity tester for semiconductor materials was utilized to explore the temperature characteristics of the electrical resistance for samples of the conductive rubber adopted in the present study. According to the testing standards for the apparatus, the dimensions
PT
of the tested samples were 11 mm × 120 mm. As an example, for a conductive rubber material filled with nickel-plated carbon particles with a thickness d = 0.81 mm, the volume resistivity of
RI
the material was tested in a test chamber over a temperature range of −20ºC to 120ºC, at intervals of 10ºC. Each temperature was held for 40 min to ensure that the temperature of the chamber was
SC
consistent with the actual temperature of the material. The experimental results are shown in Fig. 1(a). As the temperature increased, the value of ω clearly played a major role. The volume
NU
resistivity was positively correlated with T. Fig. 1(b) shows the test results for a conductive rubber material filled with copper-plated silver particles. As observed in Fig. 1(b), the volume resistivity
MA
500
C+Ni
300 200
D
400
PT E
Volume resistivity (mOhm-cm)
of the rubber material increases as T increases.
100
0
Volume resistivity (mOhm-cm)
AC
CE
-40
-20
0
20
40
60
80
100 120 140
Temperature (°C)
(a) 14
Al+Ag
12 10 8 6 4
(a)
2 -40 -20
0
20
40
60
80
100 120 140
Temperature (°C)
(b) Fig. 1. Temperature effects of conductive rubber filled with (a) nickel-plated carbon particles and
ACCEPTED MANUSCRIPT (b) copper-plated silver particles. From experimental observation, the volume resistivity of the conductive rubber materials increased gradually. This was more significant above 80ºC, indicating that conductive rubber materials rapidly expand when heated to a high temperature. The theoretical discussion above indicates that the resulting increased separation between conductive particles serves as the leading
PT
cause of increased resistivity. Because the resistivity of the conductive rubber material varies with respect to temperature,
RI
SRRs based on this material should also exhibit a dynamically changing resistivity with respect to environmental temperature, which will further influence the behaviour of the structure in response
SC
to incident electromagnetic waves. A C-shaped SRR structure is designed, as shown in Fig. 2, where d is the thickness of the rubber plate, w represents the width of the split ring, l is the
NU
electrical dimension of the split ring, v is the inner side length of the split ring, and g is the width of the split-ring gap. The conductive rubber selected for the structure was silicone rubber filled
MA
with copper-plated silver particles, where σ = 4 × 104 S/m at room temperature. The dimensions were d = 0.81 mm, w = 1 mm, l = 5 mm, and g = 1.5 mm. The conductive rubber SRR was
D
positioned in a waveguide that was oriented with respect to the varying electric and magnetic
PT E
fields shown in Fig. 2. The waveguide-SRR assembly was placed in a temperature test chamber held at different stabilized temperatures from −20ºC to 100ºC at 20ºC intervals, where each
AC
CE
temperature was held for 40 min.
Conductive Rubber
l
g d
v
H y
w
x z
K
E
l
Fig. 2. Dimensions of C-shaped SRR. The test results are shown in Fig. 3, where, with increasing temperature, the resonance intensity of the SRR gradually decreases, as does the resonance frequency. At an environmental temperature of 80ºC, the maximum attenuation owing to the structural resonance decreases to −8 dB, losing the band-stop characteristic, and the resonance peak of the transmission curve becomes
ACCEPTED MANUSCRIPT very weak at a temperature of 100ºC. 0 -2 -4
10
11
(a)
SC
0 -2
NU
-4 -6
Simulation Conductivity (S/m) 4329 3968 2666 1418 1086 791 433
-8
-10 -12 -14
MA
S21 (dB)
12
RI
Frequency (GHz)
PT
S21 (dB)
Experiment -6 Teamperature (°C) -20 -8 0 20 -10 40 -12 60 80 -14 100 -16 8 9
9
10
11
12
Frequency (GHz)
(b)
PT E
D
8
Fig. 3. Scattering parameter S21 of C-shaped SRR obtained by (a) experimental test and (b) numerical simulation based on measured conductivities.
CE
To validate the experimental results, computer simulation technology (CST) Microwave Studio was applied to perform simulation analyses regarding the influence of temperature on the
AC
electromagnetic resonance properties of the examined C-shaped SRR. The direction and orientation of the incident electromagnetic wave was fixed according to the experimental conditions shown in Fig. 2, and the waveguide boundary conditions were selected as the simulation boundary conditions. The experimental values of σ for the conductive rubber material obtained at each specific temperature from −20ºC to 100ºC were applied to the simulation model of the SRR. The results of the simulation analyses are shown in Fig. 4, which are consistent with the experimental results given in Fig. 3, further verifying that the changing electrical resistivity of the material is responsible for the observed electromagnetic properties of the SRR. This makes the design of thermally tunable metamaterials possible, further demonstrating the feasibility of the
ACCEPTED MANUSCRIPT proposed design method.
3. Thermally Tunable Band-Stop Filters 3.1 H-Shaped Conductive Rubber SRR As alternatives to the conventional C-shaped SRR, a corresponding H-shaped SRR structure
PT
based on silicone rubber filled with copper-plated silver particles, which exhibits a negative refractive index [34], was designed as shown in Fig. 4. The unique electromagnetic performance
RI
of the H-shaped conductive rubber SRR was analysed and verified by means of a numerical simulation and experimental testing. An H-shaped conductive rubber SRR electromagnetic
SC
simulation model with waveguide boundary conditions was established using CST Microwave Studio. The direction and orientation of the incident electromagnetic wave was fixed according to
NU
the conditions illustrated in Fig. 4. A simulation frequency range of 8–14 GHz was selected. In addition, an H-shaped conductive rubber SRR test sample was fabricated, as shown in Fig. 5(a).
MA
The structural dimensions of the sample were d = 0.51 mm, h = 5.5 mm, v = 5 mm, and w = 1 mm. Polyethylene foam was selected as the supporting structure of the test sample, and the
PT E
D
substrate-SRR assembly was positioned in a BJ100 waveguide tube, as shown in Fig. 5(b).
AC
CE
v
x
w
y
E
H
z K
d
Fig. 4. Dimensions of H-shaped conductive rubber SRR.
Fig. 5. Experimental sample of H-shaped conductive rubber SRR.
ACCEPTED MANUSCRIPT As shown in Fig. 6, the experimental and simulation results were essentially consistent, and a resonance frequency of 11 GHz was obtained in both cases, indicative of a band-stop characteristic where the maximum attenuation is −22 dB, and the phase of S21 exhibited a marked change at the resonance frequency. However, the values for the attenuation owing to resonance differed to some extent because of inevitable measurement errors and the addition of polyethylene foam.
PT
0
-12 -16
SC
Experiment S11 S12 Simulation S11 S21
-20 -24 8
9
NU
S (dB)
-8
RI
-4
10
11
12
MA
Frequency (GHz)
(a)
200
D
150
50
PT E
Phase (degree)
100
0
-50
-100
Experiment S11 S21
CE
-150
AC
-200 8
9
10
Simulation S11 S21 11
12
Frequency (GHz)
(b)
Fig. 6. Comparisons between experimental and simulation results of (a) scattering parameters and (b) phases.
Fig. 7 presents the surface current and electric field distribution of the H-shaped conductive rubber SRR at the resonance frequency. Excited by incident electromagnetic waves in the plane of the SRR, a relatively strong induced electric field is generated at the ends owing to the accumulation of electric charges, forming an equivalent capacitance. Meanwhile, currents are induced within the centre arm of the H-shaped structure. These currents generate a magnetic flux
ACCEPTED MANUSCRIPT that resists the magnetic flux of the incident wave and forms an equivalent inductance. The equivalent inductance and capacitance together form a resonant circuit appearing at the resonance
PT
frequency, which induces the band-stop characteristics.
RI
Fig. 7. Distributions of (a) surface current and (b) electric field at resonance frequency.
SC
3.2 Thermally Tunable Characteristics
Research [35] has shown that SRRs based on conductive rubber materials exhibit band-stop
NU
characteristics near the resonance frequency, and that the resonant properties of conductive rubber SSRs vary with respect to the environmental temperature owing to the temperature-sensitive
MA
resistance property of the conductive rubber material. Based on the above characteristics, an H-shaped thermally tunable band-stop filter employing a conductive rubber SRR was designed.
D
As previously conducted for the C-shaped SRR, the experimental values of σ for the
PT E
conductive rubber material obtained at each specific temperature from −20ºC to 100ºC were applied to a simulation model of the H-shaped conductive rubber SRR structure. The simulation results are presented in Fig. 8, which clearly illustrates the changing electromagnetic
CE
characteristics of the H-shaped SRR with respect to temperature. As the temperature increases, the resonance frequency of the H-shaped SRR gradually decreases, and the attenuation at resonance
AC
also weakens, thus weakening its band-stop characteristics. When the environmental temperature is −20ºC, the resonance frequency is 11.5 GHz and the maximum attenuation is −22 dB. However, as the environmental temperature increases, the band-stop characteristics slowly weaken, and the resonance frequency shifts to a lower value. In the temperature range of 80–100ºC, the changes in the band-stop characteristics of the structure are the most significant. The figure indicates that the filtering performance of the H-shaped structure can be controlled according to the environmental temperature.
ACCEPTED MANUSCRIPT
11.5 11.4
-16 Transmission Resonance
-18
11.3 11.2
-20
-22
PT
11.1
Frequency (GHz)
11.0
-20
0
20
40
60
Temperature (°C)
80
100
RI
Transmission minimum (dB)
-14
SC
Fig. 8. Transmission minimum and resonance frequency with respect to temperature obtained by
NU
numerical simulation based on experimentally determined conductivities.
3.3 Comparisons of the two conductive rubber SRRs
MA
The above results demonstrate that both the C-shaped and H-shaped conductive rubber SRRs have band-stop characteristics and their resonant properties vary with respect to the environmental
D
temperature owing to the temperature-sensitive resistance property of conductive rubber materials.
PT E
However, there exists the difference of band-stop characteristics because of the difference of electromagnetic properties. Their effective dielectric properties were computed to further analyze the temperature-controllable band-stop characteristics for different conductive rubber SRRs. The
CE
effective parameters were retrieved from scattering parameters via a well-established algorithm specifically designed for waveguide system.
AC
The effective electromagnetic parameters of C-shaped and H-shaped SRRs are respectively given in Figs. 9 and 10. It can be seen that the effective permittivity exhibits a Lorentz-like spectra profile with abrupt change around 9.5 GHz, followed by negative value from 9.6 to 11 GHz for the C-shaped SRR. The effective permittivity of H-shape SRR changes abruptly around 8.5 GPz, followed by negative value from 8.6 to 13 GHz. The H-shaped SRR has the lower resonant frequency and the wider negative value range than the C-shaped one. This clearly demonstrates the effectiveness of conductive rubber SRRs which exhibit unique properties of metamaterial. The required temperature-controllable band-stop characteristics can be obtained from the novel conductive rubber SRRs.
PT
ACCEPTED MANUSCRIPT
RI
Fig. 9. Effective electromagnetic parameters of C-shaped SRR with geometrical dimensions:
PT E
D
MA
NU
SC
l=5 mm, v=3.4 mm, g=1 mm, w=0.9 mm, d=0.8 mm.
Fig. 10. Effective electromagnetic parameters of H-shaped SRR with geometrical dimensions:
4. Conclusions
CE
h=5.4 mm, v=3 mm, w=1 mm, d=0.8 mm.
AC
Based on their unique conductive mechanism, the volume resistivity of conductive rubber materials was shown theoretically and experimentally to increase with increasing environmental temperature. Conversely, the conductivity demonstrated a decreasing trend. The temperature dependence of the resistivity was particularly striking when the environmental temperature ranged from 80ºC to 100ºC, which caused a dramatic expansion of the conductive rubber material, resulting in a substantially increased separation between conductive particles. Combined with this unique temperature-dependent resistance, a flexible C-shaped SRR was designed. Both experimental and simulation results demonstrated that its resonance frequency and the attenuation of incident electromagnetic waves owing to resonance decreased as the temperature increased.
ACCEPTED MANUSCRIPT This phenomenon verified that thermally tunable electromagnetic metamaterials can be designed based on conductive rubber materials. Owing to the band-stop characteristics of the SRR structure near the resonance frequency, a novel thermally tunable band-stop filter employing an H-shaped conductive rubber SRR was designed, and simulations demonstrated a band-stop characteristic with respect to incident electromagnetic waves near the resonance frequency. According to the
PT
changing volume resistivity of the conductive rubber material with respect to temperature, the H-shaped conductive rubber SRR exhibited a resonance frequency and an attenuation owing to
RI
resonance that decreased as the temperature increased. The results of a simulation demonstrated that the H-shaped artificial electromagnetic structure designed using a conductive rubber material
SC
exhibited the function of temperature control. The difference of the effective dielectric properties between the C-shaped and H-shaped SRRs demonstrates the effectiveness of conductive rubber
NU
SRRs which exhibit unique properties of metamaterial and the temperature-controllable band-stop characteristics. Considering high requirements on the temperature environment, such as EMI,
MA
radar and absorber, this work is expected to be useful for the advance of metamaterial application.
D
Acknowledgments
PT E
This work is supported by the National Natural Science Foundation of China (11372250,
References
CE
11372248) and the Aeronautical Science Foundation of China (2015ZA53001).
[1] V.G. Veselago. The electrodynamics of substances with simultaneously negative values of
AC
and . Soviet Phys Uspekhi, 1968, 10: 509-514. [2] J. B. Pendry, A. J. Holden, D. J. Robbins, W. J. Stewart. Magnetism from conductors and enhanced nonlinear phenomena. Microwave Theory & Techniques IEEE Transactions on, 47(11) (1999) 2075-2084. [3] D. R. Smith, W. J. Padilla, D. C. Vier, S. C. Nemat-Nasser, S. Schultz. Composite medium with simultaneously negative permeability and permittivity. Physical Review Letters, 84(18) (2000) 4184-4187. [4] J. F. Wang, S. B. Qu, J. Q. Zhang, H. Ma, Y. M. Yang, C. Gu, X. Wu, Z. Xu. A tunable left-handed metamaterial based on modified broadside-coupled split-ring resonators. Progress
ACCEPTED MANUSCRIPT in Electromagnetics Research Letters, 6 (2009) 35-45. [5] Y. H. Fu, A. Q. Liu, W. M. Zhu, X. M. Zhang, D. P. Tsai, J. B. Zhang. A micromachined reconfigurable metamaterial via reconfiguration of asymmetric split-ring resonators. Advanced Functional Materials, 21(18) (2011) 3589-3594. [6] F. L. Zhang, S. Q. Feng, K. P. Qiu, Z. J. Liu, Y. C. Fan, W. H. Zhang. Mechanically
PT
stretchable and tunable metamaterial absorber. Applied Physics Letters, 106(9) (2015) 207402.
RI
[7] T. K. Chang, R. J. Langley, E. A. Parker. An active square loop frequency selective surface. IEEE Microwave & Guided Wave Letters, 3(10) (1993) 387-388.
SC
[8] L. Liu, S. Matitsine, P. K. Tan. Electromagnetic smart screen for tunable transmission applications. Microwave & Optical Technology Letters, 50(6) (2008) 1510-1514.
NU
[9] T. Hand, S. Cummer. Characterization of tunable metamaterial elements using mems switches. IEEE Antennas & Wireless Propagation Letters, 6(1) (2007) 401 - 404.
MA
[10] E. Ekmekci, K. Topalli, T. Akin, G.Turhan. A tunable multi-band metamaterial design using micro-split SRR structures. Optics Express, 17(18) (2009) 16046-58.
D
[11] L. Kang, Q. Zhao, H. Zhao, J. Zhou. Ferrite-based magnetically tunable left-handed
PT E
metamaterial composed of SRRs and wires. Optics Express, 16(22) (2008) 17269-75. [12] T. H. Hand, S. A. Cummer. Tunable magnetic metamaterial using digitally addressable split-ring resonators. IEEE Antennas & Wireless Propagation Letters, 8(4) (2009) 262-265.
CE
[13] X. Wang, D. H. Kwon, D. H. Werner, I. C. Khoo, A. V. Kildishev, V. M. Shalaev. Tunable optical negative-index metamaterials employing anisotropic liquid crystals. Applied Physics
AC
Letters, 91(14) (2008)143122. [14] S. Xiao, U. K. Chettiar, A. V. Kildishev, V. Drachev, I. C. Khoo, V. M. Shalaev. Tunable magnetic response of metamaterials. Applied Physics Letters, 95(3) (2009) 033115. [15] F. Zhang, L. Kang, Q. Zhao, J. Zhou, X. Zhao, D. Lippens. Magnetically tunable left handed metamaterials by liquid crystal orientation. Optics Express, 17(6) (2009) 4360-6. [16] F. Zhang, W. Zhang, Q. Zhao, J. Sun, K. Qiu, J. Zhou. Electrically tunable fishnet metamaterial based on nematic liquid crystal. Optics Express, 19(2) (2011) 1563-8. [17] J. Han, A. Lakhtakia. Semiconductor split-ring resonators for thermally tunable terahertz metamaterials. Journal of Modern Optics, 56(4) (2009) 554-557.
ACCEPTED MANUSCRIPT [18] A. D. Boardman, V. V. Grimalsky, Y. S. Kivshar, S.V. Koshevaya, M. Lapine, N.M. Litchinitser. Active and tunable metamaterials. Laser & Photonics Review, 5(5) (2011) 287-307． [19] J. García-García, F. Martín, F. Falcone, J. Bonache, J. D. Baena, I. Gil. Microwave filters with improved stopband based on sub-wavelength resonators. IEEE Transactions on
PT
Microwave Theory & Techniques, 53(6) (2005) 1997-2006. [20] J. Zhang, B. Cui, S. Lin, X. W. Sun. Sharp-rejection low-pass filter with tunable transmission
RI
zero using complementary split-ring resonators (CSRRS). Progress in Electromagnetics Research, 69 (2007) 219-226.
SC
[21] C. Li, K. Y. Liu, F. Li. Design of microstrip highpass filters with complementary split-ring resonators. Electronics Letters, 43(1) (2007) 35-36.
NU
[22] S. Khalid, W. P. Wen, L. Y. Cheong. A novel synthesis procedure for ultra wideband (UWB) bandpass filters. Progress in Electromagnetics Research, 141(141) (2013) 249-266.
MA
[23] S. Sun, L. Zhu. Multiple-resonator-based bandpass filters. IEEE Microwave Magazine, 10(2) (2009) 88-98.
D
[24] C. P. Chen, Z. Ma, T. Anada. Synthesis of ultra-wideband bandpass filter employing parallel
PT E
coupled stepped-impedance resonators. Iet Microwave Antennas & Propagation, 2(8) (2008) 766-772.
[25] H. H. Hu, Z. Y. Xiao, W. Q. He, S. Gao. Novel compact ultra-wideband filter with wide
CE
stop-band. Microwave & Optical Technology Letters, 51(1) (2009) 53–55. [26] C. Kim, X. Cheng, D. E. Senior, Y. K. Yoon. Compact frequency and bandwidth tunable
AC
stopband filters using split-ring resonators and varactors coupled transmission line. International Journal of Electronics and Communications, 66(11) (2012) 865–870. [27] K. N. Jose, M. R. Baiju. A Tunable Bandstop Filter using Defected Ground Structures and MEMS Switches on CPW. Perspectives in Science, 2016. [28] T. K. Ramya, C. J. Bindu, A. Pradeep, Bi. Paul, S. Mridula. Compact Tunable Filters for Broadband Applications. Procedia Computer Science, 46(2015) 957-964. [29] D. Bouyge, A. Crunteanu, A. Pothier, P. Martin, P. Blondy, A. Velez, J. Bonache, J. Orlianges, F. Martin. Reconfigurable 4 pole bandstop filter based on RF-MEMS-loaded split-ring resonators. In: Proceeding of international microwave symposium digest, (2010) 588–591.
ACCEPTED MANUSCRIPT [30] D. Bouyge，D. Mardivirin，J. Bonache，A. Crunteanu. Split-ring resonators (SRRs) based on micro-electro-mechanical deflectable cantilever-type rings: application to tunable stopband filter. IEEE Microwave & Wireless Components Letters, 5(2011) 243–245. [31] B. Pradhan, B. Gupta. Realization and characterization of surface micromachined tunable band-stop CSRR filter using MEMS bridges on silicon substrate. Microelectronic
PT
Engineering, 133(2015) 66-72. [32] P. Sheng, E. K. Sichel, J. I. Gittleman. Fluctuation-induced tunneling conduction in
RI
carbon-polyvinylchloride composites. Physical Review Letters, 40(18) (1978) 1197-1200. [33] P. Sheng. Fluctuation-induced tunneling conduction in disordered materials. Physical Review
SC
B, 21(6) (1980) 347-349.
[34] J. Zhou, T. Koschny, L. Zhang, G. Tuttle, C. M. Soukoulis. Experimental demonstration of
NU
negative index of refraction. Applied Physics Letters, 88(22) (2006) 221103. [35] F. Zhang, Z. Liu, K. Qiu, W. Zhang, C. Wu, S. Feng. Conductive rubber based flexible
AC
CE
PT E
D
MA
metamaterial. Applied Physics Letters, 106(6) (2015) 77.
ACCEPTED MANUSCRIPT
AC
CE
PT E
D
MA
NU
SC
RI
PT
Graphical abstract
ACCEPTED MANUSCRIPT Highlights
The conductive rubber has the obvious temperature effects and the relationship between environmental temperature and volume resistivity is obtained by the experimental testing.
The electromagnetic characteristics of the C-shaped conductive rubber SRR are temperature-dependent.
PT
The new temperature-controllable band-stop filter is designed according to the band-stop
CE
PT E
D
MA
NU
SC
RI
characteristics of the H-shaped conductive rubber SRR.
AC
Kepeng Qiu, Jianqiang Jin, Zijun Liu, Fuli Zhang, Weihong Zhang PII: DOI: Reference:
S0264-1275(16)31555-6 doi: 10.1016/j.matdes.2016.12.038 JMADE 2583
To appear in:
Materials & Design
Received date: Revised date: Accepted date:
15 July 2016 12 December 2016 13 December 2016
Please cite this article as: Kepeng Qiu, Jianqiang Jin, Zijun Liu, Fuli Zhang, Weihong Zhang , A novel thermo-tunable band-stop filter employing a conductive rubber splitring resonator. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Jmade(2016), doi: 10.1016/j.matdes.2016.12.038
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 A Novel Thermo-Tunable Band-Stop Filter Employing a Conductive Rubber Split-Ring Resonator
Kepeng Qiu*, Jianqiang Jin, Zijun Liu, Fuli Zhang, Weihong Zhang Northwestern Polytechnical University, Xi’an, People’s Republic of China
RI
PT
*[email protected]
Abstract
SC
This paper presents the design and related applications of a thermally tunable band-stop filter employing conductive rubber that incorporates electrically conductive particles. The relationship
NU
between the environmental temperature and the volume resistivity of conductive rubber materials was experimentally established. The experimental results demonstrated that the conductive rubber
MA
has a temperature-sensitive resistance property. The conductive rubber material was employed in the design of a C-shaped split-ring resonator (SRR) structure. The influence of environmental
D
temperature on the electromagnetic properties of the SRR structure was analysed using a
PT E
numerical simulation and experimental testing. The results demonstrated that the design of thermally tunable metamaterials was possible. As such, an H-shaped conductive rubber SRR was employed in the design of a novel thermally tunable band-stop filter. The results of a numerical
CE
simulation and experimental testing verified its band-stop characteristic, and demonstrated that the filtering performance of the H-shaped conductive rubber SRR can be controlled by the
AC
environmental temperature. Lastly, by comparison of the effective dielectric properties of the two types of SRRs, it demonstrates the effectiveness of conductive rubber and their temperature-controllable band-stop characteristics. Keywords: Conductive Rubber, Temperature Control, Split-Ring Resonator, Band-Stop Filter.
1. Introduction The split-ring resonator (SRR) is an essential component of microwave metamaterials and has its theoretical basis in Veselago’s work about left-handed metamaterial in the late 1960s [1].
ACCEPTED MANUSCRIPT SRRs and wires can be appropriately arranged to form composite media that exhibit double-negative electromagnetic properties in the vicinity of the resonant frequency [2−3]. In addition, a wide range of equivalent electromagnetic properties can be achieved by varying the parameters of the metamaterial structures. Normally, the novel electromagnetic properties of a specific metamaterial structure only
PT
appear within a specific resonance frequency range. The structure of the metamaterial must be redesigned to ensure an equivalent response at different excitation frequencies, which greatly
RI
reduces the service efficiency. As a consequence, dynamic control of the resonance frequency of an electromagnetic metamaterial structure has been a subject of intense interest. This task involves
SC
the control of the equivalent capacitance and equivalent inductance of the structure, which co-determine the resonance frequency. The most direct approach is to change the parameters of the
incorporation of microwave switches [7−10].
NU
metamaterial structures by mechanical control [4−6]. Another effective method is the
MA
In customizing the metamaterial properties, other tuning methods have appeared. By introducing yttrium iron garnet rods into SRRs and wire arrays, the left-handed passband of the
D
metamaterial was continuously and reversibly adjusted by externally applied DC magnetic fields
PT E
[11]. By integrating a digital potentiometer into each SRR of an array as a variable voltage divider, the magnetic metamaterial was tuned by using digitally addressable SRRs [12]. Tunable materials based on liquid-crystal materials were also designed to realize the continuous control of
CE
electromagnetic properties by modulating the collective orientation of the liquid-crystal molecules using applied electric and magnetic fields [13−16]. The metamaterials comprising semiconductor
AC
SRRs were thermally tunable in the terahertz regime [17]. At present, the tunable electromagnetic spectrum has been covered nearly from the microwave frequency band to the terahertz and infrared bands [18].
An SRR, similar to a resonance circuit, resonates when excited by an incident electromagnetic field at a specific frequency. This induces a ring current where the resulting magnetic moment either strengthens or weakens the incident electromagnetic field, thus displaying band-pass or band-stop characteristics in response to an incident electromagnetic field. When properly coupled to coplanar-waveguides (CPWs) or microstrip transmission lines, SRRs and complementary SRRs (CSRRs) can efficiently inhibit signal propagation in the vicinity of their
ACCEPTED MANUSCRIPT quasi-static resonant frequencies [19]. A low-pass filter was obtained using cascaded multi-CSRR cells [20], and a high-pass filter was designed with two CSRR sections having additional microstrip patches [21]. Currently, significant advances have been made regarding the miniaturization of band-pass filters and ultra-wideband filters [22−26]. According to the tunable characteristics of artificial electromagnetic materials, the resonant frequency for an SRR band-stop
PT
filter was tuned by using MEMS switches [27] or by varying the inductor values [28]. Tunable band-stop filters can also be designed using RF-MEMS switches and microelectromechanical
RI
deflectable cantilever-type rings [29−30]. Pradhanet et al. [31] presented a tunable filter on a silicon substrate using complementary split-ring resonators (CSRRs) and an RF-MEMS variable
SC
capacitor. However, this fabrication process is quite complex and expensive.
In the present work, flexible SRR-structured band-stop filters, which are controlled through
NU
the environmental temperature, were developed by combining the tunable characteristics of artificial electromagnetic materials based on conductive rubber that incorporates conductive
MA
particles.
D
2. Temperature Effects of Conductive Rubber
PT E
Conductive rubber is a type of highly polymeric material that is formed by uniformly mixing flexible polymeric substrate materials with conductive particles. This imparts electrical conductivity while preserving the flexibility of the substrate material. The unique nature of the
CE
composite presents a conductive mechanism and resistance characteristics that differ from those of metallic conductors, particularly at low conductive particle concentrations where the conductivity
AC
occurs predominantly via electron tunnelling across numerous small barriers and includes a strong temperature dependency. These characteristics offer potential benefits for creating tunable electromagnetic structures. According to quantum tunneling theory [32−33], and assuming that conductivity occurs between two conductive particles with a statistical average separation of ω (i.e. the barrier width assuming a plane parallel junction between particles), the relationship between the macroscopic current density J(ε) and an electric field ε applied to the junction is
ACCEPTED MANUSCRIPT 2 J J 0 exp 1 ， 0 . 2 0
(1)
Here, J0 is the current density in the absence of effects owing to ε and containing all nonexponential temperature effects. 2mV0 h2 is the tunnelling constant, where m is the electron mass, h is a reduced Planckʼs constant, and V0 is the barrier height; and 0 4V0 e ,
PT
where e is the electron charge. The value of ε derives from two sources applied at both ends of a conductive particle junction, namely, an externally applied electric field A and an electric field
RI
induced by thermal disturbance T:
SC
A T .
(2)
When A < T, the component of J(ε) lying in the direction of A is (3)
NU
1 J J A T J A T . 2
The partial conductivity as a result of T is defined in terms of J as
A 0
J
A
dJ T . dT
MA
T lim
(4)
P T T d T
P T 0
. dJ T dT dT
PT E
0
D
Thus, the tunnel conductance induced by T is given as follows:
(5)
CE
A T 2 Here, P T exp represents the probability of a given T at temperature T, 8 T
AC
where A is the area of a plane parallel junction, and is the Boltzmann constant. Substituting Eqs. (1) and (4) into Eq. (5), and applying saddle point integration yields the conductivity T1 , T T0
0 exp
(6)
where 0 represents the conductivity in the absence of temperature effects, T1 A 02 8 , and T0 A 02 4 2 .
From the forgoing discussion, it is known that σ is co-influenced by the environmental temperature T and the average distance between conductive particles ω. As T increases, the rubber matrix undergoes thermal expansion, resulting in an enlarged interparticle spacing, which leads to
ACCEPTED MANUSCRIPT a decreased value of σ, and also enhances the probability of electron transition between particles. Therefore, thermal disturbance plays a positive role, and the value of σ increases. A YAOS BD400H resistivity tester for semiconductor materials was utilized to explore the temperature characteristics of the electrical resistance for samples of the conductive rubber adopted in the present study. According to the testing standards for the apparatus, the dimensions
PT
of the tested samples were 11 mm × 120 mm. As an example, for a conductive rubber material filled with nickel-plated carbon particles with a thickness d = 0.81 mm, the volume resistivity of
RI
the material was tested in a test chamber over a temperature range of −20ºC to 120ºC, at intervals of 10ºC. Each temperature was held for 40 min to ensure that the temperature of the chamber was
SC
consistent with the actual temperature of the material. The experimental results are shown in Fig. 1(a). As the temperature increased, the value of ω clearly played a major role. The volume
NU
resistivity was positively correlated with T. Fig. 1(b) shows the test results for a conductive rubber material filled with copper-plated silver particles. As observed in Fig. 1(b), the volume resistivity
MA
500
C+Ni
300 200
D
400
PT E
Volume resistivity (mOhm-cm)
of the rubber material increases as T increases.
100
0
Volume resistivity (mOhm-cm)
AC
CE
-40
-20
0
20
40
60
80
100 120 140
Temperature (°C)
(a) 14
Al+Ag
12 10 8 6 4
(a)
2 -40 -20
0
20
40
60
80
100 120 140
Temperature (°C)
(b) Fig. 1. Temperature effects of conductive rubber filled with (a) nickel-plated carbon particles and
ACCEPTED MANUSCRIPT (b) copper-plated silver particles. From experimental observation, the volume resistivity of the conductive rubber materials increased gradually. This was more significant above 80ºC, indicating that conductive rubber materials rapidly expand when heated to a high temperature. The theoretical discussion above indicates that the resulting increased separation between conductive particles serves as the leading
PT
cause of increased resistivity. Because the resistivity of the conductive rubber material varies with respect to temperature,
RI
SRRs based on this material should also exhibit a dynamically changing resistivity with respect to environmental temperature, which will further influence the behaviour of the structure in response
SC
to incident electromagnetic waves. A C-shaped SRR structure is designed, as shown in Fig. 2, where d is the thickness of the rubber plate, w represents the width of the split ring, l is the
NU
electrical dimension of the split ring, v is the inner side length of the split ring, and g is the width of the split-ring gap. The conductive rubber selected for the structure was silicone rubber filled
MA
with copper-plated silver particles, where σ = 4 × 104 S/m at room temperature. The dimensions were d = 0.81 mm, w = 1 mm, l = 5 mm, and g = 1.5 mm. The conductive rubber SRR was
D
positioned in a waveguide that was oriented with respect to the varying electric and magnetic
PT E
fields shown in Fig. 2. The waveguide-SRR assembly was placed in a temperature test chamber held at different stabilized temperatures from −20ºC to 100ºC at 20ºC intervals, where each
AC
CE
temperature was held for 40 min.
Conductive Rubber
l
g d
v
H y
w
x z
K
E
l
Fig. 2. Dimensions of C-shaped SRR. The test results are shown in Fig. 3, where, with increasing temperature, the resonance intensity of the SRR gradually decreases, as does the resonance frequency. At an environmental temperature of 80ºC, the maximum attenuation owing to the structural resonance decreases to −8 dB, losing the band-stop characteristic, and the resonance peak of the transmission curve becomes
ACCEPTED MANUSCRIPT very weak at a temperature of 100ºC. 0 -2 -4
10
11
(a)
SC
0 -2
NU
-4 -6
Simulation Conductivity (S/m) 4329 3968 2666 1418 1086 791 433
-8
-10 -12 -14
MA
S21 (dB)
12
RI
Frequency (GHz)
PT
S21 (dB)
Experiment -6 Teamperature (°C) -20 -8 0 20 -10 40 -12 60 80 -14 100 -16 8 9
9
10
11
12
Frequency (GHz)
(b)
PT E
D
8
Fig. 3. Scattering parameter S21 of C-shaped SRR obtained by (a) experimental test and (b) numerical simulation based on measured conductivities.
CE
To validate the experimental results, computer simulation technology (CST) Microwave Studio was applied to perform simulation analyses regarding the influence of temperature on the
AC
electromagnetic resonance properties of the examined C-shaped SRR. The direction and orientation of the incident electromagnetic wave was fixed according to the experimental conditions shown in Fig. 2, and the waveguide boundary conditions were selected as the simulation boundary conditions. The experimental values of σ for the conductive rubber material obtained at each specific temperature from −20ºC to 100ºC were applied to the simulation model of the SRR. The results of the simulation analyses are shown in Fig. 4, which are consistent with the experimental results given in Fig. 3, further verifying that the changing electrical resistivity of the material is responsible for the observed electromagnetic properties of the SRR. This makes the design of thermally tunable metamaterials possible, further demonstrating the feasibility of the
ACCEPTED MANUSCRIPT proposed design method.
3. Thermally Tunable Band-Stop Filters 3.1 H-Shaped Conductive Rubber SRR As alternatives to the conventional C-shaped SRR, a corresponding H-shaped SRR structure
PT
based on silicone rubber filled with copper-plated silver particles, which exhibits a negative refractive index [34], was designed as shown in Fig. 4. The unique electromagnetic performance
RI
of the H-shaped conductive rubber SRR was analysed and verified by means of a numerical simulation and experimental testing. An H-shaped conductive rubber SRR electromagnetic
SC
simulation model with waveguide boundary conditions was established using CST Microwave Studio. The direction and orientation of the incident electromagnetic wave was fixed according to
NU
the conditions illustrated in Fig. 4. A simulation frequency range of 8–14 GHz was selected. In addition, an H-shaped conductive rubber SRR test sample was fabricated, as shown in Fig. 5(a).
MA
The structural dimensions of the sample were d = 0.51 mm, h = 5.5 mm, v = 5 mm, and w = 1 mm. Polyethylene foam was selected as the supporting structure of the test sample, and the
PT E
D
substrate-SRR assembly was positioned in a BJ100 waveguide tube, as shown in Fig. 5(b).
AC
CE
v
x
w
y
E
H
z K
d
Fig. 4. Dimensions of H-shaped conductive rubber SRR.
Fig. 5. Experimental sample of H-shaped conductive rubber SRR.
ACCEPTED MANUSCRIPT As shown in Fig. 6, the experimental and simulation results were essentially consistent, and a resonance frequency of 11 GHz was obtained in both cases, indicative of a band-stop characteristic where the maximum attenuation is −22 dB, and the phase of S21 exhibited a marked change at the resonance frequency. However, the values for the attenuation owing to resonance differed to some extent because of inevitable measurement errors and the addition of polyethylene foam.
PT
0
-12 -16
SC
Experiment S11 S12 Simulation S11 S21
-20 -24 8
9
NU
S (dB)
-8
RI
-4
10
11
12
MA
Frequency (GHz)
(a)
200
D
150
50
PT E
Phase (degree)
100
0
-50
-100
Experiment S11 S21
CE
-150
AC
-200 8
9
10
Simulation S11 S21 11
12
Frequency (GHz)
(b)
Fig. 6. Comparisons between experimental and simulation results of (a) scattering parameters and (b) phases.
Fig. 7 presents the surface current and electric field distribution of the H-shaped conductive rubber SRR at the resonance frequency. Excited by incident electromagnetic waves in the plane of the SRR, a relatively strong induced electric field is generated at the ends owing to the accumulation of electric charges, forming an equivalent capacitance. Meanwhile, currents are induced within the centre arm of the H-shaped structure. These currents generate a magnetic flux
ACCEPTED MANUSCRIPT that resists the magnetic flux of the incident wave and forms an equivalent inductance. The equivalent inductance and capacitance together form a resonant circuit appearing at the resonance
PT
frequency, which induces the band-stop characteristics.
RI
Fig. 7. Distributions of (a) surface current and (b) electric field at resonance frequency.
SC
3.2 Thermally Tunable Characteristics
Research [35] has shown that SRRs based on conductive rubber materials exhibit band-stop
NU
characteristics near the resonance frequency, and that the resonant properties of conductive rubber SSRs vary with respect to the environmental temperature owing to the temperature-sensitive
MA
resistance property of the conductive rubber material. Based on the above characteristics, an H-shaped thermally tunable band-stop filter employing a conductive rubber SRR was designed.
D
As previously conducted for the C-shaped SRR, the experimental values of σ for the
PT E
conductive rubber material obtained at each specific temperature from −20ºC to 100ºC were applied to a simulation model of the H-shaped conductive rubber SRR structure. The simulation results are presented in Fig. 8, which clearly illustrates the changing electromagnetic
CE
characteristics of the H-shaped SRR with respect to temperature. As the temperature increases, the resonance frequency of the H-shaped SRR gradually decreases, and the attenuation at resonance
AC
also weakens, thus weakening its band-stop characteristics. When the environmental temperature is −20ºC, the resonance frequency is 11.5 GHz and the maximum attenuation is −22 dB. However, as the environmental temperature increases, the band-stop characteristics slowly weaken, and the resonance frequency shifts to a lower value. In the temperature range of 80–100ºC, the changes in the band-stop characteristics of the structure are the most significant. The figure indicates that the filtering performance of the H-shaped structure can be controlled according to the environmental temperature.
ACCEPTED MANUSCRIPT
11.5 11.4
-16 Transmission Resonance
-18
11.3 11.2
-20
-22
PT
11.1
Frequency (GHz)
11.0
-20
0
20
40
60
Temperature (°C)
80
100
RI
Transmission minimum (dB)
-14
SC
Fig. 8. Transmission minimum and resonance frequency with respect to temperature obtained by
NU
numerical simulation based on experimentally determined conductivities.
3.3 Comparisons of the two conductive rubber SRRs
MA
The above results demonstrate that both the C-shaped and H-shaped conductive rubber SRRs have band-stop characteristics and their resonant properties vary with respect to the environmental
D
temperature owing to the temperature-sensitive resistance property of conductive rubber materials.
PT E
However, there exists the difference of band-stop characteristics because of the difference of electromagnetic properties. Their effective dielectric properties were computed to further analyze the temperature-controllable band-stop characteristics for different conductive rubber SRRs. The
CE
effective parameters were retrieved from scattering parameters via a well-established algorithm specifically designed for waveguide system.
AC
The effective electromagnetic parameters of C-shaped and H-shaped SRRs are respectively given in Figs. 9 and 10. It can be seen that the effective permittivity exhibits a Lorentz-like spectra profile with abrupt change around 9.5 GHz, followed by negative value from 9.6 to 11 GHz for the C-shaped SRR. The effective permittivity of H-shape SRR changes abruptly around 8.5 GPz, followed by negative value from 8.6 to 13 GHz. The H-shaped SRR has the lower resonant frequency and the wider negative value range than the C-shaped one. This clearly demonstrates the effectiveness of conductive rubber SRRs which exhibit unique properties of metamaterial. The required temperature-controllable band-stop characteristics can be obtained from the novel conductive rubber SRRs.
PT
ACCEPTED MANUSCRIPT
RI
Fig. 9. Effective electromagnetic parameters of C-shaped SRR with geometrical dimensions:
PT E
D
MA
NU
SC
l=5 mm, v=3.4 mm, g=1 mm, w=0.9 mm, d=0.8 mm.
Fig. 10. Effective electromagnetic parameters of H-shaped SRR with geometrical dimensions:
4. Conclusions
CE
h=5.4 mm, v=3 mm, w=1 mm, d=0.8 mm.
AC
Based on their unique conductive mechanism, the volume resistivity of conductive rubber materials was shown theoretically and experimentally to increase with increasing environmental temperature. Conversely, the conductivity demonstrated a decreasing trend. The temperature dependence of the resistivity was particularly striking when the environmental temperature ranged from 80ºC to 100ºC, which caused a dramatic expansion of the conductive rubber material, resulting in a substantially increased separation between conductive particles. Combined with this unique temperature-dependent resistance, a flexible C-shaped SRR was designed. Both experimental and simulation results demonstrated that its resonance frequency and the attenuation of incident electromagnetic waves owing to resonance decreased as the temperature increased.
ACCEPTED MANUSCRIPT This phenomenon verified that thermally tunable electromagnetic metamaterials can be designed based on conductive rubber materials. Owing to the band-stop characteristics of the SRR structure near the resonance frequency, a novel thermally tunable band-stop filter employing an H-shaped conductive rubber SRR was designed, and simulations demonstrated a band-stop characteristic with respect to incident electromagnetic waves near the resonance frequency. According to the
PT
changing volume resistivity of the conductive rubber material with respect to temperature, the H-shaped conductive rubber SRR exhibited a resonance frequency and an attenuation owing to
RI
resonance that decreased as the temperature increased. The results of a simulation demonstrated that the H-shaped artificial electromagnetic structure designed using a conductive rubber material
SC
exhibited the function of temperature control. The difference of the effective dielectric properties between the C-shaped and H-shaped SRRs demonstrates the effectiveness of conductive rubber
NU
SRRs which exhibit unique properties of metamaterial and the temperature-controllable band-stop characteristics. Considering high requirements on the temperature environment, such as EMI,
MA
radar and absorber, this work is expected to be useful for the advance of metamaterial application.
D
Acknowledgments
PT E
This work is supported by the National Natural Science Foundation of China (11372250,
References
CE
11372248) and the Aeronautical Science Foundation of China (2015ZA53001).
[1] V.G. Veselago. The electrodynamics of substances with simultaneously negative values of
AC
and . Soviet Phys Uspekhi, 1968, 10: 509-514. [2] J. B. Pendry, A. J. Holden, D. J. Robbins, W. J. Stewart. Magnetism from conductors and enhanced nonlinear phenomena. Microwave Theory & Techniques IEEE Transactions on, 47(11) (1999) 2075-2084. [3] D. R. Smith, W. J. Padilla, D. C. Vier, S. C. Nemat-Nasser, S. Schultz. Composite medium with simultaneously negative permeability and permittivity. Physical Review Letters, 84(18) (2000) 4184-4187. [4] J. F. Wang, S. B. Qu, J. Q. Zhang, H. Ma, Y. M. Yang, C. Gu, X. Wu, Z. Xu. A tunable left-handed metamaterial based on modified broadside-coupled split-ring resonators. Progress
ACCEPTED MANUSCRIPT in Electromagnetics Research Letters, 6 (2009) 35-45. [5] Y. H. Fu, A. Q. Liu, W. M. Zhu, X. M. Zhang, D. P. Tsai, J. B. Zhang. A micromachined reconfigurable metamaterial via reconfiguration of asymmetric split-ring resonators. Advanced Functional Materials, 21(18) (2011) 3589-3594. [6] F. L. Zhang, S. Q. Feng, K. P. Qiu, Z. J. Liu, Y. C. Fan, W. H. Zhang. Mechanically
PT
stretchable and tunable metamaterial absorber. Applied Physics Letters, 106(9) (2015) 207402.
RI
[7] T. K. Chang, R. J. Langley, E. A. Parker. An active square loop frequency selective surface. IEEE Microwave & Guided Wave Letters, 3(10) (1993) 387-388.
SC
[8] L. Liu, S. Matitsine, P. K. Tan. Electromagnetic smart screen for tunable transmission applications. Microwave & Optical Technology Letters, 50(6) (2008) 1510-1514.
NU
[9] T. Hand, S. Cummer. Characterization of tunable metamaterial elements using mems switches. IEEE Antennas & Wireless Propagation Letters, 6(1) (2007) 401 - 404.
MA
[10] E. Ekmekci, K. Topalli, T. Akin, G.Turhan. A tunable multi-band metamaterial design using micro-split SRR structures. Optics Express, 17(18) (2009) 16046-58.
D
[11] L. Kang, Q. Zhao, H. Zhao, J. Zhou. Ferrite-based magnetically tunable left-handed
PT E
metamaterial composed of SRRs and wires. Optics Express, 16(22) (2008) 17269-75. [12] T. H. Hand, S. A. Cummer. Tunable magnetic metamaterial using digitally addressable split-ring resonators. IEEE Antennas & Wireless Propagation Letters, 8(4) (2009) 262-265.
CE
[13] X. Wang, D. H. Kwon, D. H. Werner, I. C. Khoo, A. V. Kildishev, V. M. Shalaev. Tunable optical negative-index metamaterials employing anisotropic liquid crystals. Applied Physics
AC
Letters, 91(14) (2008)143122. [14] S. Xiao, U. K. Chettiar, A. V. Kildishev, V. Drachev, I. C. Khoo, V. M. Shalaev. Tunable magnetic response of metamaterials. Applied Physics Letters, 95(3) (2009) 033115. [15] F. Zhang, L. Kang, Q. Zhao, J. Zhou, X. Zhao, D. Lippens. Magnetically tunable left handed metamaterials by liquid crystal orientation. Optics Express, 17(6) (2009) 4360-6. [16] F. Zhang, W. Zhang, Q. Zhao, J. Sun, K. Qiu, J. Zhou. Electrically tunable fishnet metamaterial based on nematic liquid crystal. Optics Express, 19(2) (2011) 1563-8. [17] J. Han, A. Lakhtakia. Semiconductor split-ring resonators for thermally tunable terahertz metamaterials. Journal of Modern Optics, 56(4) (2009) 554-557.
ACCEPTED MANUSCRIPT [18] A. D. Boardman, V. V. Grimalsky, Y. S. Kivshar, S.V. Koshevaya, M. Lapine, N.M. Litchinitser. Active and tunable metamaterials. Laser & Photonics Review, 5(5) (2011) 287-307． [19] J. García-García, F. Martín, F. Falcone, J. Bonache, J. D. Baena, I. Gil. Microwave filters with improved stopband based on sub-wavelength resonators. IEEE Transactions on
PT
Microwave Theory & Techniques, 53(6) (2005) 1997-2006. [20] J. Zhang, B. Cui, S. Lin, X. W. Sun. Sharp-rejection low-pass filter with tunable transmission
RI
zero using complementary split-ring resonators (CSRRS). Progress in Electromagnetics Research, 69 (2007) 219-226.
SC
[21] C. Li, K. Y. Liu, F. Li. Design of microstrip highpass filters with complementary split-ring resonators. Electronics Letters, 43(1) (2007) 35-36.
NU
[22] S. Khalid, W. P. Wen, L. Y. Cheong. A novel synthesis procedure for ultra wideband (UWB) bandpass filters. Progress in Electromagnetics Research, 141(141) (2013) 249-266.
MA
[23] S. Sun, L. Zhu. Multiple-resonator-based bandpass filters. IEEE Microwave Magazine, 10(2) (2009) 88-98.
D
[24] C. P. Chen, Z. Ma, T. Anada. Synthesis of ultra-wideband bandpass filter employing parallel
PT E
coupled stepped-impedance resonators. Iet Microwave Antennas & Propagation, 2(8) (2008) 766-772.
[25] H. H. Hu, Z. Y. Xiao, W. Q. He, S. Gao. Novel compact ultra-wideband filter with wide
CE
stop-band. Microwave & Optical Technology Letters, 51(1) (2009) 53–55. [26] C. Kim, X. Cheng, D. E. Senior, Y. K. Yoon. Compact frequency and bandwidth tunable
AC
stopband filters using split-ring resonators and varactors coupled transmission line. International Journal of Electronics and Communications, 66(11) (2012) 865–870. [27] K. N. Jose, M. R. Baiju. A Tunable Bandstop Filter using Defected Ground Structures and MEMS Switches on CPW. Perspectives in Science, 2016. [28] T. K. Ramya, C. J. Bindu, A. Pradeep, Bi. Paul, S. Mridula. Compact Tunable Filters for Broadband Applications. Procedia Computer Science, 46(2015) 957-964. [29] D. Bouyge, A. Crunteanu, A. Pothier, P. Martin, P. Blondy, A. Velez, J. Bonache, J. Orlianges, F. Martin. Reconfigurable 4 pole bandstop filter based on RF-MEMS-loaded split-ring resonators. In: Proceeding of international microwave symposium digest, (2010) 588–591.
ACCEPTED MANUSCRIPT [30] D. Bouyge，D. Mardivirin，J. Bonache，A. Crunteanu. Split-ring resonators (SRRs) based on micro-electro-mechanical deflectable cantilever-type rings: application to tunable stopband filter. IEEE Microwave & Wireless Components Letters, 5(2011) 243–245. [31] B. Pradhan, B. Gupta. Realization and characterization of surface micromachined tunable band-stop CSRR filter using MEMS bridges on silicon substrate. Microelectronic
PT
Engineering, 133(2015) 66-72. [32] P. Sheng, E. K. Sichel, J. I. Gittleman. Fluctuation-induced tunneling conduction in
RI
carbon-polyvinylchloride composites. Physical Review Letters, 40(18) (1978) 1197-1200. [33] P. Sheng. Fluctuation-induced tunneling conduction in disordered materials. Physical Review
SC
B, 21(6) (1980) 347-349.
[34] J. Zhou, T. Koschny, L. Zhang, G. Tuttle, C. M. Soukoulis. Experimental demonstration of
NU
negative index of refraction. Applied Physics Letters, 88(22) (2006) 221103. [35] F. Zhang, Z. Liu, K. Qiu, W. Zhang, C. Wu, S. Feng. Conductive rubber based flexible
AC
CE
PT E
D
MA
metamaterial. Applied Physics Letters, 106(6) (2015) 77.
ACCEPTED MANUSCRIPT
AC
CE
PT E
D
MA
NU
SC
RI
PT
Graphical abstract
ACCEPTED MANUSCRIPT Highlights
The conductive rubber has the obvious temperature effects and the relationship between environmental temperature and volume resistivity is obtained by the experimental testing.
The electromagnetic characteristics of the C-shaped conductive rubber SRR are temperature-dependent.
PT
The new temperature-controllable band-stop filter is designed according to the band-stop
CE
PT E
D
MA
NU
SC
RI
characteristics of the H-shaped conductive rubber SRR.
AC