Tunable Metamaterial Bandstop Filter Based on Ferromagnetic Resonance Qingmin Wang, Lingyu Zeng, Ming Lei, and Ke Bi

Tunable metamaterial bandstop filter based on ferromagnetic resonance Qingmin Wang, Lingyu Zeng, Ming Lei, and Ke Bi

Citation: AIP Advances 5, 077145 (2015); doi: 10.1063/1.4927399 View online: http://dx.doi.org/10.1063/1.4927399 View Table of Contents: http://scitation.aip.org/content/aip/journal/adva/5/7?ver=pdfcov Published by the AIP Publishing

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Tunable metamaterial bandstop filter based on ferromagnetic resonance Qingmin Wang, Lingyu Zeng, Ming Lei, and Ke Bia State Key Laboratory of Information Photonics and Optical Communications & School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China (Received 30 May 2015; accepted 13 July 2015; published online 21 July 2015)

Tunable wideband microwave bandstop filters have been investigated by experiments and simulations. The negative permeability is realized around the ferromagnetic resonance frequency which can be influenced by the demagnetization factor ofthe ferrite rods. For the filter composed of two ferrite rods withff di erent size, it exhibits a -3 db stop bandwidth as large as 500 MHz, peak absorption of -40 db and an out-of-stopband insertion loss of -1.5 db. This work provides a new way to fabricate the microwave bandstop filters. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4927399]

I. INTRODUCTION Tunable filters, with high attenuation and wide attenuation band, play critical roles inmodern communication and radar systems.1,2 Because of low loss, tunable resonance frequency, wide oper- ating frequency range and high stability, ferromagnetic resonance (FMR)–based bandstop filters, such as yttrium iron garnet (YIG) based filters, have been investigated and realized.3–9 Moreover, FMR–based microwave filters contributes to development of monolithic microwave integrated cir- cuits due to low cost and small size.10 However, most of those filters are composed of microstrip and ferrite structures, which increases the complexity. Metamaterials provide a way to solve the problem. Since the property of metamaterials is derive from the subwavelength structures instead of the employed materials, the metamaterials can be controlled by lattice arrangement and unit cell geometry.11,12 It is desirable to design FMR–based filters using ferrite metamaterials in place of single ferrite.13–15 Recently, ferrite metamaterials of various materials and shapes are investigated in theory and experiments, which are suitable for mul- tiple operated wavebands.16,17 FMR–based bandstop filters rely on resonance to absorb microwave power at the FMR frequency.18 By interacting with an incoming microwave, FMR can arise in ferrite under an applied magnetic field.19–21 The FMR frequency can be influenced by the applied magnetic field, the property of used ferrite and the composite structure of the metamaterial. In previous work, our group investigated the effect of the saturation magnetization on FMR and designed a magnetically tunable wideband microwave filter using ferrite-based metamaterials. The bandwidth can be tuned by adjusting the saturation magnetization of the ferrite rods.22 Here, we use the size effect of the FMR to design a tunable metamaterial bandstop filter. Since the frequency of FMR can be tuned by the size of the ferrite rods, the stopband of the filter can be influenced by the size of the ferrite metamaterials, which provides a new way to design tunable filters.

II. EXPERIMENT In order to simplify fabrication and apply to the frequency of 8-12 GHz that is most widely used in microwave devices, ferrite rods are employed to design the metamaterial. The unit cell of

aCorrespondence author. E-mail address:[email protected]

2158-3226/2015/5(7)/077145/5 5, 077145-1 © Author(s) 2015

FIG. 1. Schematic diagram of the tunable microwave bandstop filter using ferrite-based metamaterial structure.

the metamaterial structure is composed of two ferrite rods. One rod was sliced with dimension of 1 × 1 × 10 mm3. The other one was sliced with dimensions of 1 × 1 × 10 mm3, 2 × 1 × 10 mm3 and 2.5 × 1 × 10 mm3, respectively. The distance d between the two ferrite rods is 0.6 mm. The ferrite material chosen for this work was yttrium iron garnet (YIG) ferrite. The saturation magnetization 4πMs, linewidth ∆H, and relative permittivity εr of the YIG rods were 1950 Gs, 10 Oe, and 14.5, respectively. As shown in Figure1, the tunable metamaterial bandstop filter was fabricated by inserting the ferrite rods into a Teflon substrate. The transmission spectra for the tunable microwave bandstop filter were measured by a microwave measurement system. The microwave measurement system is composed of a vector network analyzer (N5230C, Agilent Technologies, USA) and an electromagnet.23 The sample was placed in two X-band rectangular waveguides put in the middle of two magnets. By adjusted by input current, a bias magnetic field provided by the electromagnets was applied inthe z direction. The propagation of the incident electromagnetic wave was along the y axis, and the electric field and magnetic field were along the z and x axes, respectively. Numerical predictions of the transmission spectra were calculated using the commercial time-domain package CST Microwave Studio TM. All the parameters for the simulation are chosen to be consistent with the experimental ones.

III. RESULTS AND DISCUSSION FMR can take place in ferrite by interacting with an electromagnetic wave. FMR frequency can be expressed by  ω = γ H0 + Nx − Nz 4πMs H0 + Ny − Nz 4πMs (1) [ ( ) ] where H0 is the applied magnetic field,π 4 Ms is the saturation magnetization,Nx, Ny, and Nz are the demagnetization factor for x, y, and z directions, respectively. From Eq.(1), it can be predicted that the FMR frequency is influenced by the demagnetization factor. When the sizes of the ferrite rodin x and z directions remain unchanged, the Ny will decrease as the size of ferrite rod in the y direction increases. Hence, the FMR frequency decrease as the size of ferrite rod in the y direction increases. In this work, we use size of ferrite on behalf of demagnetization factor of to investigate. In order to understand the electromagnetic properties of the tunable bandstop filter, the transmission spectra of the one ferrite rod unit cell was simulated first. The schematic diagram of one ferrite rod unit cell is shown in Figure 2(a). All the parameters of the ferrite rod are the same as those in the experiments. An incoming electromagnetic wave incident along y axis, the electric field direction along the z axis and to the magnetic field direction along the x axis, respectively. A magnetic field H0 = 2600 Oe is applied. The dependence of the effective calculated permeability on

FIG. 2. (a) Schematic diagram of one ferrite rod unit cell for the bandstop filter; (b) Real part of theeffective permeability retrieved from the simulated scattering parameters for the unit cell with a series of rod length l.

frequency with a series of l is shown in Fig. 2(b). Because of the appearance of FMR, the unit cell exhibits a Lorentz type dispersion for the permeability with negative values around the FMR frequency.24,25 On account of the stopband will appear in transmission spectrum when the permeability is negative, the ferrite rod can be used to fabricate filters. In addition, the FMR frequency decreases as l increases from 1 mm to 2.5 mm, which is consistent with that predicted by Eq.(1). Therefore, the stopband of the filters based on FMR can be tuned by the sizes of the ferrite rods. Figure3 shows the measured transmission spectra for the tunable bandstop filter composed of one rod unit cells with a series of l under H0 = 2600 Oe. It can be seen that the stopband center frequency ranges from 10.05 GHz to 10.50 GHz as l increases from 1 mm to 2.5 mm, tuning at the rate of 0.3 GHz/mm and the width of the stopband changes as the transformation of l, which behaves excellent size dependence. Besides that, we can see that the stopband appears on the frequency region where the permeability shows negative values, which is in good agree with the above experimental data and discussion about Figure2. Figure 4(a) shows the schematic diagram of two ferrite rods unit cell with different rods sizes for the bandstop filter. The dimension of one ferrite rodis1 × 1 × 10 mm3, and that of the other ferrite rod is 1 × 1 × 10 mm3, 2 × 1 × 10 mm3 and 2.5 × 1 × 10 mm3, respectively. As is shown in Figure 4(b), when l = 1 mm, the two kinds of rods with the same size, there is only a Lorentz type dispersion on the dependence of calculated effective permeability on frequency corresponded to one FMR. When the l = 2 mm or 2.5 mm corresponded to the different size of the two kinds ferrite rods, two Lorentz type dispersions appear at the frequency of 8 – 12 GHz, which indicates two FMRs take place in the two ferrite rods unit cell. Furthermore, based on the FMR theory discussed above

FIG. 3. Measured transmission spectra for the magnetically tunable microwave bandstop filter composed of one rod unit cells with a series of rod length l.

FIG. 4. (a) Schematic diagram of two ferrite rods unit cell for the bandstop filter; (b) Real part offf thee ective permeability retrieved from the simulated scattering parameters for the second ferrite rods with different length l.

FIG. 5. Measured transmission spectra for the magnetically tunable microwave bandpass filter with (a)ff di erent l and (b) a series of H0.

and the simulated data shown in Figure 4(b), the dispersion moves to lower frequency region as the l increases from 2 to 2.5 mm, indicating the FMR frequencies coming along with the negative permeability frequency regions moves to lower frequency. Hence, by changing the l of ferrite rods, we can get a material with remarkable stopband, indicating the tunable bandstop filter depending on size factors can be realized. Figure 5(a) shows the measured transmission spectra for the tunable metamaterial bandstop filter withff di erent l under an applied magnetic field H0 = 2600 Oe. When l of the second ferrite rods has the different sizes of 1 mm, 2 mm and 2.5 mm, as the l increases, the stopband center frequency moves to lower frequency and the width of the stopband broadens, which indicates the frequency and width of the tunable metamaterial bandstop filters can be tuned by the size factor. When l = 2.5 mm, the experimental transmission spectrum exhibits a -3 db stop bandwidth as large as 500 MHz, peak absorption of -40 db and an out-of-stopband insertion loss of -1.5 db. It can be seen the filtering property is superior when l = 2.5 mm. Figure 5(b) shows the measured transmission spectra for the magnetically tunable microwave bandstop filter under a series of applied magnetic field H0. The employed l = 2.5 mm of the second ferrite rods is optimal. The stopband center frequency increases as the H0 increases, which realizes the magnetically tunable property.

IV. CONCLUSIONS The tunable metamaterial bandstop filters have been prepared by using ferrite-based metamaterial structure. Based on the dependence of the FMR frequency on the size of the ferrite rod, the

broad bandwidth can be obtained. The experimental results are in good agreement with the simulation ones. The stopband frequency of this filter can be tuned by the size of the ferrite metamaterials, which is suitable for practical applications in tunable microwave devices.

ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China under Grant Nos. 51402163, 61376018, 51032003, 11274198, 51102148 and 51221291; the China Postdoc- toral Science Foundation under Grant Nos. 2013M530042 and 2014T70075; and the Fundamental Research Funds for the Central Universities under Grant No. 2015RC18. 1 G. L. Matthaei, IEEE Trans. Microw. Theory Tech. 13, 203 (1965). 2 I. C. Hunter, L. Billonet, B. Jarry, and P. Guillon, IEEE Trans. Microw. Theory Tech. 50, 794 (2002). 3 X. Yang, J. Wu, S. Beguhn, T. Nan, Y. Gao, Z. Zhou, and N. X. Sun, IEEE Microwave Wireless Compon. Lett. 23, 184 (2013). 4 A. Cismaru and R. Marcelli, IEEE Trans. Magn. 42, 10 (2006). 5 G. Qiu, C. S. Tsai, B. S. T. Wang, and Y. Zhu, IEEE Trans. Magn. 44, 3123 (2008). 6 X. Yang, Y. Gao, J. Wu, S. Beguhn, T. X. Nan, Z. Y. Zhou, M. Liu, and N. X. Sun, IEEE Trans. Magn. 49, 5485 (2013). 7 B. K. Kuanr, D. L. Marvin, T. M. Christensen, R. E. Camley, and Z. Celinski, J. Appl. Phys. Lett. 87, 222506 (2005). 8 I. Harward, R. E. Camley, and Z. Celinski, Appl. Phys. Lett. 105, 173503 (2014). 9 Y. Guo, F. R. Shen, and X. Y. Chen, Appl. Phys. Lett. 101, 012410 (2012). 10 J. D. Adam, S. V. Krishnaswamy, S. H. Talisa, and K. C. Yoo, J. Magn. Magn. Mater. 83, 15235 (1990). 11 R. A. Shelby, Science 292, 77 (2001). 12 K. Bi, J. Zhou, H. Zhao, X. Liu, and C. Lan, Opt. Express 21, 10746 (2013). 13 Y. He, P. He, V. G. Harris, and C. Vittoria, IEEE Trans. Magn. 42, 2852 (2006). 14 G. Dewar, New J. Phys. 7, 161 (2005). 15 H. Zhao, J. Zhou, L. Kang, and Q. Zhao, Opt. Express 17, 13373 (2009). 16 U. Ebels, J. L. Duvail, P. E. Wigen, L. Piraux, L. D. Buda, and K. Ounadjela, Phys. Rev. B 64, 144421 (2001). 17 L. P. Carignan, A. Yelon, D. Menard, and C. Caloz, IEEE Trans. Magn. 59, 10 (2011). 18 N. Cramer, D. Lucic, R. E. Camley, and Z. Celinski, J. Appl. Phys. 87, 911 (2000). 19 P. He, J. Gao, Y. Chen, P. V. Parimi, C. Vittoria, and V. G. Harris, J. Phys. D: Appl. Phys. 42, 155005 (2009). 20 F. Xu, Y. Bai, F. Ai, L. Qiao, H. Zhao, and J. Zhou, J. Phys. D: Appl. Phys. 42, 065416 (2009). 21 J. N. Gollub, J. Y. Chin, T. J. Cui, and D. R. Smith, Opt. Express 17, 2122 (2009). 22 K. Bi, W. Zhu, M. Lei, and J. Zhou, Appl. Phys. Lett. 106, 173507 (2015). 23 D. R. Smith, S. Schultz, P. Markoš, and C. M. Soukoulis, Phys. Rev. B 65, 195104 (2002). 24 X. Chen, T. M. Grzegorczyk, B. Wu, J. Pacheco, and J. A. Kong, Phys. Rev. E 70, 016608 (2004). 25 C. Croënne, B. Fabre, D. Gaillot, O. Vanbésien, and D. Lippens, Phys. Rev. B 77, 125333 (2008).