2015 IEEE 2015 International Conference on Computer, Communication, and Control Technology (I4CT 2015), April 21 - 23 in Imperial Kuching Hotel, Kuching, Sarawak, Malaysia
Microwave Absorbing Material Based on Rice Husk Ash/ CNTs Composites Y.S. Lee1, F. Malek2, E.M. Cheng3, W.W. Liu4, F.H. Wee1, Z. Liyana1, M.N.A Karim1 1
School of Computer and Communication Engineering, 2 School of Electrical System Engineering, 3 School of Mechatronic Engineering, Univerisiti Malaysia Perlis (UniMAP), Pauh Putra Campus, Arau, Perlis 02600, Malaysia 4 Institute of Nano Electronic Engineering (INEE), Universiti Malaysia Perlis (UniMAP), 01000 Kangar, Perlis, Malaysia
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[3]. This work is to increase the RHA dielectric properties and microwave absorption by composites with carbon nanotube (CNTs) nanomaterial. This paper presents an analysis of the measuring methods and a comparison of different materials in terms of their specific MAMs effects. The electromagnetic reflectivity is also one of the most important parameter for designing perfect MAMs. The reflectivity simulation was performed with different microwave absorbers and thicknesses over frequency range 8.2- 12.4 GHz.
Abstract— This paper presents the different type of microwave absorbing materials based on rice husk ash and carbon nanotubes (RHACNTs) composites. The microwave absorption and complex relative permittivity of RHACNTs composites were investigated in microwave frequency region X-band (8.2-12.4 GHz). A rectangular waveguide (WR-90) transmission line method was used to measure scattering parameter and Nicolson-Ross-Weir algorithm to calculate the complex relative permittivity ( - j ) of RHACNTs samples. The microwave absorption properties of rice husk ash with carbon nanotubes (0-5 wt %) was measured the modes of waveguides with perfectly conducting enclosures with metal backed plate. It was observed that the increase of carbon nanotubes (CNTs) influenced the and values. However, the different MAMs of RHACNTs composite have difference microwave absorption more than -10 dB at specify frequency. The complex relative permittivity and thickness of materials are important parameters for the microwave absorbing properties.
II.
The experiment data evolves in the dielectric properties in X-band was measured. The MAMs were prepared in different ratio of RHA: CNTs (RHA =70:0, RCNT-2= 70:2, and RCNT-5= 70:5 weight ratios) with dimension 22.860 mm x 10.160 mm x 5 mm. The preparation process of the dielectric properties of RHACNTs was mixed with PE resin and stir for 1 hour. Next, put the harden agent MEKP into the RHACNTs composites to make the MAMs harden. After the stirring, the composites of the MAMs was poured into the rectangular standard steel mold flange and the rectangular sample of the mixture formed after cured in room temperature 25 oC for 24 hours shown in Figure 1.
Keywords—composites; complex permittivity; microwave absorbing material; waveguide
I.
PREPARATION MATERIALS
INTRODUCTION
The rapid growth of technological advances are increasingly necessary require new materials which can reduce/absorb electromagnetic radiations. Microwave absorbing materials (MAMs) are materials which reduce/absorb microwave radiation in microwave frequency. MAMs were used to reduce the electromagnetic interference and protect commercial electronic equipment [1, 2]. Rice husk ash (RHA) is agriculture waste that invaluable source which can collect from rice mills or farmers. RHA has their unique materials properties such as dielectric properties. Lee, et al. has reported RHA and rice husk are lossy material which can used to absorb microwave energy
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Figure 1: Sample fabricated inside sample holder.
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III.
MEASUREMENT AND CALCULATION
The rectangular waveguide transmission line method is used to measure the material properties of the MAMs, shown in Figure 2. The two coaxial cables are connected between Agilent network analyzer E8362B and a pair of rectangular waveguide adaptors (WR-90). The MAMs were place into the sample holder as shown in Figure 1. The incident signal from port 1 passes through the target MAMs and detected at port 2. Then, the S11 and S21 of the scattering parameter can directly obtain from the PNA [4]. The calibration of the measurement is to eliminate the testing error induced by the gap between sample and flange.
where λ0 is free space wavelength, and λc is the cutoff wavelength. The complex permittivity ) consist of real part and imaginary part ( of the complex permittivity. The as known as dielectric constant which has ability to store energy, while loss factor ( represents how well the material convert the energy to heat and dissipate [8]. In this works, the MAMs are non-magnetic material. Therefore, we assume the complex permeability is . IV.
SIMULATION PART
In simulation, the sample holder was designed using perfect electric conductor (PEC), and the sample was fitted inside the sample holder. MAMs were simulated with 5 mm thickness of metal backed plate as Figure 3 (a). Figure 3(a) shows the single layer MAMs simulation setup with metal baked plate and Figure 3 (b) shows the cutting plane (half plane) for the setup. The dimension of the sample holder is 22.860 mm x 10.160 mm x 5 mm.
Figure 2: Illustration of transmission line.
The Nicolson-Ross-Weir conversion method was used to calculate permittivity and permeability from the results of the S-parameters (S11 and S21) [5, 6]. For many years, the NRW method has been the most common method for performing such conversion [7]. Measurement of the reflection coefficient and the transmission coefficient is required for the material under test to be measured. The S11 and S21 can be obtained from the measurement. In the NRW algorithm, the reflection coefficient (Γ) and transmission coefficient (Τ) are expressed by S-parameters (S11, S21). The Γ and Τ can be written as:
Reflection coefficient: Figure 3 (a): Single layer MAMs simulation setup with metal baked plate and (b) half cutting plane for the setup.
Transmission coefficient: V.
RESULTS AND DISCUSSION
These complex relative permittivity ( ) of RHACNTs composites have been calculated from experimental scattering parameters using the calculations given in NRW algorithms. Material with low dielectric loss only can store energy, but does not able to dissipate most of the energy stored. The calculated complex permittivity was shown in Figure 4(a) and 4(b). It is observed that in RHA the dielectric constant and loss factor increases with
The relative permittivity (εr) and permeability (μr) calculations are given as:
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increase of CNTs content. The dielectric constant of RHA is increases from 4.45 to 7.2 with 2 wt% CNTs composites and 10.8 when composites with 5 wt% CNTs. RCNT-5 sample has very high loss factor 4.75, while RCNT-2 and RHA samples los factor are 2 and 0.39.
microwave absorption of RHACNTs samples with different thickness.
(a)
Figure 5: Reflectivity of samples. Table 1: The microwave absorption of samples with different thickness.
Samples RHA RHA RCNT-2 RCNT-2 RCNT-5 RCNT-5
(b)
Thickness, mm 5 2 5 3 5 2
VI.
Absorption, % < 34 < 34 < 44 < 90 < 32 < 90
Frequency, GHz 8.2-10.2 10.2-12.4 8.2-12.4 9 – 11 8.2-12.4 10.5- 12.4
CONCLUSIONS
In this study, the complex permittivity and microwave absorbing properties of RHACNTs were investigated in 8.212.4 frequency range. The RHACNTs samples were successful fabricated and measured the scattering parameter for calculated the complex permittivity of RHACNTs samples. The experimental results indicate that the CNTs in rice husk ash affect the microwave absorbing behavior. The simulation shows that the dielectric properties and thickness of samples were important for microwave absorption. Hence, the RCNT-2 and RCNT-5 composites are potential use as microwave absorber materials with certain thickness in 8.2-12.4 GHz frequency range.
Figure 4: (a) Real part and (b) imaginary part complex permittivity of the MAMs.
From Figure 5, RCNT-5 with 2 mm thickness shows microwave absorption more than 90 % (< -10 dB) microwave energy from 10.5- 12.4 GHz. For sample RCNT2, it has 3 GHz bandwidth for absorb 90 % of microwave energy between 9 – 11 GHz with 3 mm thickness. Samples with 5 mm thickness obviously shows lower absorption compare with RCNT-2 and RCNT-5 with certain thickness in frequecny range 8.2-12.4 GHz. RHA samples with 5mm thickness only have 25 % microwave absorption when attach with metal backed plate. Table 1 shows the
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