70 IEEE TRANSACTIONS ONELECTROMAGNETIC COMPATIBILITY, VOL. 54, NO. 1, FEBRUARY2012 Microwave Frequency Characteristics of Magnetically Functionalized Carbon Nanotube Arrays Vladimir A. Labunov, Vadim A. Bogush, Alena L. Prudnikava, Boris G. Shulitski, Ivan V. Komissarov, Alexander S. Basaev, Beng Kang Tay, Member, IEEE, and Maziar Shakersadeh Abstract—This paper reports the results of a comprehensive study of the interaction of electromagnetic radiation (EMR) of the wide frequency range (8–12, 26–37, and 78–118 GHz) with ar- rays of vertically aligned and disordered carbon nanotubes (CNTs) which have been obtained by the floating catalyst chemical va- por deposition method. The obtained nanotubes represent a com- posite of multiwall CNTs with encapsulated magnetic nanopar- ticles of iron phases, i.e., magnetically functionalized nanotubes (MFCNTs). MFCNTs were formed on silicon substrates, and dis- ordered arrays in the form of powder were obtained by separating the MFCNT arrays mechanically from the walls of the quartz reac- tor. The frequency dependences of the reflection and transmission coefficients of EMR of MFCNTs of two types were investigated. The high electromagnetic shielding efficiency (40 dB) of MFCNTs as- sociated with the reflection of electromagnetic waves was detected. Possible mechanisms of attenuation of electromagnetic signals by aligned and disordered MFCNTs were discussed. Index Terms—Carbon nanotubes (CNTs), electromagnetic radi- ation (EMR), microwave frequency, shielding. I. INTRODUCTION T HE increasing use of active electromagnetic resource, in- crement of power and the number of emitters of electro- magnetic waves, and expanding the range of electromagnetic signals with the transition to the high-frequency region require the establishment and improvement of the high-performance broadband electromagnetic radiation (EMR) screens and radio absorbing coatings [1], [2]. EMR screens are designed to protect radio equipment and wildlife [3], to shield radiation sources and high-sensitivity sensors, to protect various objects from detec- tion [4]. Manuscript received December 20, 2011; accepted December 26, 2011. Date of current version February 17, 2012. This work was supported in part by the Scientific Technical Program of the Union State “Nanotechnologiya-SG” under Grant 1.3.1/09-1034. V. A. Labunov, V. A. Bogush, A. L. Prudnikava, B. G. Shulitski, and I. V. Komissarov are with the Department of Micro- and Nanoelectronics, Laboratory of Integrated Micro- and Nanosystems, Belarusian State Univer- sity of Informatics and Radioelectronics, Minsk 220013, Belarus (e-mail: labunov@bsuir.by; v.a.bogush@tut.by; prudnikova@bsuir.by; shulitski@bsuir. by; komissarov@yahoo.com). A. S. Basaev is with Technological Center, Scientific and Manufacturing Complex, Moscow Institute of Electronic Technology, Zelenograd 124498, Moscow, Russia (e-mail: as@tcen.ru). B. K. Tay and M. Shakersadeh are with the School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 Singapore (e-mail: ebktay@ntu.edu.sg; MAZIAR@ntu.edu.sg). Digital Object Identifier 10.1109/TEMC.2012.2182772 The EMR shielding efficiency (SE) in a given frequency range is defined by the specific properties of materials, i.e., the com- plex magnetic and dielectric permeabilities, specific conductiv- ity, dimensions, and mutual influence of structural elements in composite media [5], [6]. Development of technologies for the creation and study of materials and composites for the microwave frequency range applications is of current importance because they could po- tentially be used to create devices for the microwave signals processing, such as filters, moderating systems, phase changers, and directional couplers [7]. In addition, they can be used to form the elements of hybrid systems, such as heteromagnetic micro- and nanosystems [8], [9]. II. ELECTROMAGNETIC SHIELDING AND SHIELDING MATERIALS Electromagnetic shielding phenomenon is associated with a decrease of the electromagnetic field strength in a shielded re- gion of space, which is achieved by the reflection of electromag- netic waves from the surface of the screen and/or absorption of EMR energy by the screen material. At the same time SE of the screen, defined as the ratio of the field strength in a protected area before mounting the screen to the field strength at the same point in space after installing it, is a dimensionless quantity (≥1), and can be characterized by the attenuation of the EMR screen [1], [10]. Thus, the attenuation is generally determined by the physical processes of reflection and absorption of EMR. In order to obtain a high reflection coefficient of the screen, most often metal thin films, meshes, particles, etc., are used as the screen coatings. The drawbacks of such screens are low cor- rosion resistance and thermal stability, high weight and cost, proneness to abrasion, and the appearance of scratches and cracks, which can be secondary sources of radiation and, thus, reduce the SE as the frequency of EMR increases. In addition, a high value of the reflection coefficient of the screen for many practical applications is undesirable because the reflected EMR may have negative effects on the objects in the shielded area. Another mechanism of electromagnetic shielding is the ab- sorption of EMR which is observed in the materials having electric and/or magnetic dipoles interacting with an alternating electromagnetic field. Electric dipoles can be found in the mate- rials with high dielectric permittivity, such as BaTiO 3 . Magnetic dipoles are contained in materials having a high value of mag- netic permeability, such as Fe 3 O 4 , etc. [11], [12]. Absorbing 0018-9375/$31.00 © 2012 IEEE