RF and Microwave Noise Suppression In a Transmission Line Using Fe-Si-Al/Ni-Zn Magnetic Composite Films

Transcription

1 Journal of the Korean Physical Society, Vol. 48, No. 6, June 2006, pp RF and Microwave Noise Suppression In a Transmission Line Using Fe-Si-Al/Ni-Zn Magnetic Composite Films J. W. Lee, Y. K. Hong, K. Kim and J. Joo Department of Physics, Korea University, Seoul Y. W. Yoon, S. W. Kim, Y. B. Kim and K. Y. Kim Korea Institute of Science and Technology, Seoul (Received 22 November 2005) Radio-frequency (RF) and microwave noise suppression by using magnetic composite films on a microstrip line (MSL) was studied in the frequency range from 50 MHz to 13.5 GHz. The MSL was composed of a Cu transmission line, dielectric materials, and a Cu substrate. The Fe-Si-Al/Ni-Zn magnetic composite films were placed on the MSL, and the reflection and the transmission characteristics were investigated. We observed that RF and microwave noise suppression caused by the Fe-Si-Al/Ni-Zn magnetic composite films varied with the concentration ratio of the sendust (Fe-Si- Al) and the Ni-Zn ferrite. The frequency dependence of the power loss due to the composite films on the MSL was measured and the power loss increased at higher frequencies with increasing concentration of the sendust in the composites. The electromagnetic interference shielding efficiencies of the magnetic composite films in the far-field region are also discussed. PACS numbers: Ak Keywords: Magnetic composite films, EMI shielding efficiency, Noise suppression, Microstrip line, Power loss I. INTRODUCTION With increasing use of semiconducting electronics and integration of electronic components in the RF and the microwave frequency regions, electromagnetic interference (EMI) in electronic devices and on transmission lines should be reduced to enhance the lifetimes and the efficiencies of the devices [1 5]. Various types of conducting and magnetic materials and their composites have been studied for suppressing electromagnetic noise in the RF and the microwave regions [6 9]. The packing cases of electrical equipment for EMI shielding made from metallic or magnetic materials have been used to reduce electromagnetic radiation [10]. Instead using EMI shielding packing cases, direct reduction of electromagnetic noise from the signal line or the electrical components is possible by installing non-conducting magnetic materials with high permeability near the sources of the electromagnetic noise, i.e., in the near-field region [6]. In this paper, we report the effects of non-conducting Fe-Si-Al/Ni-Zn magnetic composite films on electromagnetic noise suppression by using a microstrip line (MSL) in the frequency range from 50 MHz to 13.5 GHz. We observed an increase in RF and microwave noise suppres- jjoo@korea.ac.kr; Tel: ; Fax: sion with increasing concentration of the Fe-Si-Al in the composite films. II. EXPERIMENT The magnetic composite films to reduce electromagnetic noise consisted of sendust (Fe-Si-Al) and Ni-Zn ferrite. A plate-like Fe-Si-Al alloy, with an average thickness of 2 µm and a large aspect ratio of 20, was produced by mechanical attrition of the alloy granule powders. The average diameter of the spherically shaped Ni-Zn ferrite powders was 1 µm. Attrition of the granule powders was performed by using an attrition mill in a hydrocarbon solvent. The plate-like powders and polymer binder were mixed in an agate mortar. The weight ratio of the plate-like powders and polymer binder was 75 : 25. The magnetic mixtures containing the plate-like powders and polymer binder were tape-casted. In the dried composites films, the soft magnetic flake powders were oriented with their planes parallel to the plane generated by shear stress. Table 1 lists the concentration of each element for the Fe-Si-Al sendust and the Ni-Zn ferrite. Figure 1 shows a cross-sectional SEM image of the various composite films of Fe-Si-Al/Ni-Zn. For the SF

2 RF and Microwave Noise Suppression In a Transmission J. W. Lee et al Table 1. Concentration (wt.%) of elements in the composite of Ni-Zn ferrite and Fe-Si-Al sendust. Ni-Zn Ferrite (Ni-Zn Fe 2 O 3 ) Ni(wt.%) Zn (wt.%) Cu (wt.%) Fe (wt.%) Ni(6.93) Zn (16.6) Cu (2.88) Fe (45.2) Sendust Fe (wt.%) Al (wt.%) Si (wt.%) Fe(variable) Al (9.7) Si (5.4) Fig. 2. Schematic diagram of the RF and microwave noise suppressor on the MSL connected to a VNA. Fig. 1. Cross-sectional SEM images of the composite films with different concentrations of the Fe-Si-Al sendust. sample, which has the concentration ratio of 50 : 50 of Fe-Si-Al : Ni-Zn ferrite, the Ni-Zn ferrite powders were placed between the Fe-Si-Al layers while the F100 or the S100 sample has the form of whole powders or whole plate-like powders, respectively, as shown in Figure 1. It should be noted that the thin flakes were aligned parallel to the film plane, which reduced the eddy current [6]. The magnetic hysteresis curves were measured by using a vibrating sample magnetometer (VSM, Lake-shore 7304). The DC conductivity (σ DC ) of the magnetic composite films was measured by using the 4-probe method or the van der Pauw method in order to eliminate the contact resistance, and a Keithley 237 SMU with PC interface programs at room temperature (RT). Figure 2 shows the schematic diagram of the experimental setup, including the MSL with a characteristic impedance of 50 Ω [11,12]. Teflon (ɛ r = 2.5) or epoxy (ɛ r = 4.5) was used for the dielectric material in the MSL. The MSL was connected to a HP 8719ES vector network analyzer (VNA) with a synthesized sweep oscillation and a scattering (S)-parameter test set. S11 (reflection) and S21 (transmission) were measured from 50 MHz to 13.5 GHz. The transmission power loss was deduced from the equation of P (loss)/p (in) = 1 ( Γ 2 + T 2 ) (db), where S11 = 20log Γ, S21 = 20log T, Γ is the reflec- Fig. 3. Magnetic hysteresis curves for the Fe-Si-Al/Ni-Zn magnetic composite films with different concentration ratios of ferrite and sendust. tion coefficient defined as Γ = (Z Z 0 )/(Z + Z 0 ), and T is the transmission coefficient. The film was cut into the 50 mm by 50 mm pieces with thicknesses of 50 µm and 100 µm and were placed on the center of the MSL while maintaining constant distance between the signal line and sample. We measured the electromagnetic interference (EMI) shielding efficiency (SE) in the far-field region for the magnetic composite films in the frequency range of GHz by using the ASTM D method [13 17]. III. RESULT AND DISCUSSIONS The magnetic hysteresis curves of the composite films were measured by using a VSM in the magnetic field range from 1000 G to 1000 G, as shown in Figure 3. The coercivities (H c ) of the samples, F100, SF37, SF55,

3 Journal of the Korean Physical Society, Vol. 48, No. 6, June 2006 Table 2. Concentration ratio of sendust : ferrite, initial magnetic permeability (µ i), and dc conductivity (σ DC) of the composite samples. Sample Concentration Initial magnetic σ DC(S/cm) ratio (wt. %) of permeability sendust : ferrite (µ i,cgs unit) F100 0 : SF37 3 : SF55 5 : SF73 7 : S : Fig. 5. Frequency dependence of the power loss, P loss /P in, on the MSL when using the Fe-Si-Al/Ni-Zn magnetic composite films (thickness 100 µm). Fig. 4. Comparison of the (a) reflection parameter S11 and the (b) transmission parameter S21 due to the magnetic composite films on the MSL. SF73, and S100, were measured to be 44, 29, 28, 26, and 22 G, respectively. The remanences, B r, of the samples, F100, SF37, SF55, SF73, and S100, were measured to be 15, 35, 39, 47, and 58 emu/cm 3, respectively. We calculated the initial permeability (µ i ) of the magnetic composite films by using the slope of the magnetic hysteresis curves, and the µ i s at RT are listed in Table 2. The initial permeability (µ i ) and the remanence (B r ) of the magnetic composite films increased as the concentration of the sendust increased. The σ DC (RT) of the magnetic composite films also increased as the concen- tration of the sendust increased [18,19]. Figure 4 compares the transmission (S21) and reflection (S11) characteristics of the MSL with and without the Fe-Si-Al/Ni-Zn composite films. The S11 with the magnetic composite samples decreased as the concentration of the sendust increased compared to that without samples. This implies that the reflectance increased with increasing concentration of the sendust. The periodic minima of the reflection characteristics (S11) observed here were caused by impedance mismatching between the sample holder and the connector of VNA. The S21 increased as the concentration of the sendust increased, implying a reduction in the transmittance. The variations of S11 and S21 due to the loading of the samples imply that RF and microwave electromagnetic radiations from the transmission line are partially absorbed or reflected in the near-field region by the Fe-Si-Al/Ni- Zn composite films because of the ferrimagnetic nature of the composite films. This is the origin for the RF and the microwave noise suppression by the systems. It is noted that other non-conducting and magnetic films with reduced eddy currents are also possible for noise reduction. Figure 5 shows the normalized power loss (P loss /P in ) of the magnetic composite films with different concentrations of the sendust and the Ni-Zn ferrite and was obtained from the equation of P loss /P in = 1 ( Γ 2 + T 2 ) by using the measured S11 and S21 parameters. As the frequency was increased up to 6 GHz, the power loss (P loss /P in ) increased while the power loss (P loss /P in ) decreased as the frequency increased from 6 GHz to 9 GHz. The P loss /P in of composite films with the same thickness ( 100 µm) increased as the concentration of the sendust increased. This results agrees with those for σ DC and µ i [6]. Therefore, the RF and the microwave noise suppression of the magnetic composite films studied here is proportional to the intrinsic properties of the

4 RF and Microwave Noise Suppression In a Transmission J. W. Lee et al IV. CONCLUSION RF and microwave noise suppression was studied by using the Fe-Si-Al/Ni-Zn magnetic composite films on the MSL. As the concentration of the sendust increased, the σ DC and the µ i increased. We observed an increase in the power loss of the systems as the concentration of the sendust was increased. The same results were also observed in the far-field EMI SE. RF and microwave noise suppression on the MSL can be controlled by using the intrinsic properties, such as the conductivity and the permeability, of the magnetic composites, as well as the thickness of the sample and the dielectric constant of the background materials. Fig. 6. Comparison of P loss /P in of the systems on the MSL for different thicknesses of the samples and different dielectric materials. ACKNOWLEDGMENTS This work was supported in part by Korea Science and Engineering Foundation funded by the Ministry of Science and Technology and in part by a grant from the Korea Institute of Industrial Technology Evaluation & Planning funded by the Ministry of Commerce, Industry and Energy, Republic of Korea. REFERENCES Fig. 7. EMI SE of the various Fe-Si-Al/Ni-Zn magnetic composite films, as a function of frequency, in the far-field region. systems, such as the conductivity and the magnetic permeability [8]. Figure 6 compares the normalized power losses of the composite films on the MSL for different dielectric materials and thicknesses of the films. With increasing dielectric constant of the dielectric material on the MSL, the power loss decreased in the measured frequency range. The power loss increased with increasing thickness of the composite films [20 22]. Figure 7 shows the EMI SE of the magnetic composite films (thickness 100 µm) in the far-field region. The EMI SE increased with increasing concentration of the sendust, i.e., increasing σ DC and µ i, in the measured frequency region. The EMI SE of the magnetic composite films increased with increasing frequency. The characteristics of the EMI shielding using the Fe-Si-Al/Ni-Zn composites in the far-field region are qualitatively similar with those measured by using the MSL method. [1] R. J. Astalos and R. E. Camley, J. Appl. Phys. 83, 3744 (1998). [2] S. E. Moon, M. H. Kwak, Y. T. Kim, H. C. Ryu, S. J. Lee and K. Y. Kang, J. Korean Phys. Soc. 46, 273 (2005). [3] N. Cramer, D. Lucic, R. E. Camley and Z. Celinski, J. Appl. Phys. 87, 6911 (2000). [4] B. Kuanr, L. Malkinski, R. E. Camley and Z. Celinski, J. Appl. Phys. 93, 8591 (2003). [5] W. S. Sul, S. D. Kim, S. D. Lee, T. S. Kang, D. An, Y. H. Chun, I. S. Hwang and J. K. Rhee, J. Korean Phys. Soc. 43, 1076 (2003). [6] H. Ono, S. Yoshida and S. Ando, J. Appl. Phys. 93, 6662 (2003). [7] S. Yoshida, H. Ono, S. Ando, F. Tsuda, T. Ito, Y. Shimada, M. Yamaguchi, K. I. Arai, S. Ohnuma and T. Masumoto, IEEE Trans. Magn. 37, 2401 (2001). [8] Y. Shimada, M. Yamaguchi, S. Ohnuma, T. Itoh, W. D. Li, S. Ikeda, K. H. Kim and H. Nagura, IEEE Trans. Magn. 39, 3052 (2003). [9] K. H. Kim, M. Yamaguchi and K. I. Arai, J. Appl. Phys. 93, 8002 (2003). [10] C. Y. Lee, D. E. Lee, Y. K. Hong, J. H. Shim, C. K. Jeong and J. Joo, Phys. Rev. E 67, (2003). [11] Guillermo Gonzalez, Microwave Transistor Amplifiers, 2nd ed. (Prentice-Hall, New Delhi, 1997). [12] K. G. Gupta, Ramesh Garg, Inder Bahl and Prakash Bhartia, Microstrip Lines and Slotlines, 2nd ed. (Artech House, Norwood, 1996). [13] H. W. Ott, Noise Reduction Techniques in Electronic Systems, 2nd ed. (John Wiley & Sons, New York, 1988).

5 Journal of the Korean Physical Society, Vol. 48, No. 6, June 2006 [14] Y. K. Hong, C. Y. Lee, C. K. Jeong, D. E. Lee, K. Kim and J. Joo, Rev. Sci. Instrum. 74, 1098 (1997). [15] J. Baker-Jarvis and M. D. Janezic, IEEE Trans. Electromag. Compat. 38, 67 (1996). [16] ASTM D , Standard Test Method for Measuring the Electromagnetic Shielding Effectiveness of Planar Materials (1999). [17] H. Ono, T. Ito, S. Yoshida, Y. Takase, O. Hashimoto and Y. Shimada, IEEE Trans. Magn. 40, 2853 (2004). [18] M. D. Huang, N. N. Lee, B. J. Kim, B. S. Hong and Y. P. Lee, J. Korean Phys. Soc. 46, 150 (2005). [19] F. Tsuda, H. Ono, S. Shinohara and R. Sato, IEEE EMC Symposium Record. 2, 867 (2000). [20] K. H. Kim, S. Ohnuma and M. Yamaguchi, IEEE Trans. Magn. 40, 2838 (2004). [21] K. H. Kim and M. Yamaguchi, IEEE Trans. Magn. 39, 3031 (2003). [22] K. H. Kim, S. Ikeda, M. Yamaguchi and K. I. Arai, J. Appl. Phys. 93, 8588 (2003).