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Development of pyramidal microwave absorber using sugar cane bagasse (SCB).

1. INTRODUCTION

Agricultural waste is made up of organic compounds from plants. SCB is the byproduct from the production and processing of sugar cane (Saccarhum officinarum) to produce sugar. This residue is obtained after the extraction of the juice that is used to produce sugar. The worldwide production of SCB in 2005 was 54 million dry tons [1]. 1000 kg of raw sugar cane produces 280 kg of baggage. Perlis state in northern Malaysia has the potential to produce large quantities of SCB, especially in the Chuping area.

Carbon is one of the main elements in most agricultural wastes. The parameters for this carbon material are its pore structure and surface area. The volumes of the pores limit the sizes of the molecules that can be adsorbed. The surface area limits the amount of material that can be absorbed, assuming a suitable molecular size. Carbon is important because it is very suitable for transforming microwave energy to thermal energy [2]. An electric field is produced when microwaves pass through the absorber, and the electrical energy is transformed into thermal energy.

This waste material can be used in many industries and for various applications. Suhardy et al. produced an alternative paper product using this material [3,4], and his experimental results showed that the carbon and silica contents of the SCB were approximately 90% and 10% respectively, whereas these contents in rice straw were approximately 64% and 36% respectively.

In 2009, Azevedo and Galiana developed a process for extracting ethanol from sugar cane for the power industry sector, especially in Brazil. The implication was the process provided clean and renewable source of energy that could be used as a biofuel and for generating bioelectricity [5]. Similarly other countries have produced ethanol from biological products, including corn in the U.S., sugar beets in Germany and wheat in Europe.

The interior surfaces of the RF anechoic chamber are sometimes similar to those of an acoustic anechoic chamber, but there is a difference between the two chambers. The function of a microwave absorber is to absorb waves that are reflected by the walls and the ceiling of the anechoic chamber [6-16].

Different absorber materials are used for the microwave range frequency (1 GHz to 40GHz). Polyurethane and polystyrene are the two example materials that are used extensively in laboratory studies. The two most popular microwave absorbers that are currently on the market are Eccosorb's VHP-8-NRL absorber [17] and TDK ICT-030 absorber [18]. The following are references to others who have conducted research on microwave absorbers: Hasnain et al. [19], Salleh et al. [20], Yusof et al. [21], Farhany et al. [22], Noordin et al. [23], Nornikman et al. [24], Malek et al. [25], and Ibrahim et al. [26].

Other than the material used in the absorber, its shape is its main parameter. Many shapes have been used in the design of the absorbers, including pyramidal [27], wedge shapes [28]; oblique, hexagonal shapes [29]; twisted, convoluted, flat shapes [30]; and multi-layer flat shapes [31].

2. MATERIALS AND METHODS

Figure 1 shows a flowchart of the steps followed in an SCB pyramidal microwave absorber. The work begins with collecting raw SCB from the flea market in Kangar, Perlis. The SCB is dried in the sun for a week, cut into small pieces, and ground to make small particles.

The dielectric properties, i.e., dielectric constant and loss tangent, of the material are two important parameters that must be considered when modeling a pyramidal microwave absorber. The measurements to define the values of these dielectric properties involve the transmission line, resonant cavity, free space, and the dielectric probe technique. The type of measurement used depends on the physical condition of the material, i.e., whether it is liquid, semi-solid, or solid.

In this work, the dielectric probe method was used to determine the dielectric constant (real part, [[epsilon]'.sub.r], and imaginary part, [[epsilon]".sub.r]) of the SCB. This measurement is an important factor in defining the physical and chemical properties that are related to the storage and loss of energy with respect to different kinds of materials. Figure 2 shows the measurement of the dielectric properties of the SCB using a dielectric probe.

The equipment used in this measurement is an Agilent dielectric probe with software, a network analyzer, two coaxial cables, and the material to be tested [26]. Coaxial cables were used to connect the dielectric probe to ports 1 and 2 of the network analyzer. The dielectric probe had glass-to-metal contact point that was hermetically sealed.

Figure 3 represents an SCB pyramidal microwave absorber in CST's Microwave Studio simulation software. The two main parts of the microwave absorber the pyramid-shaped body and the pyramidal base (square-shaped particle board). The dimensions of the base were 15 x 15 x 2 cm. The dimensions of the pyramidal body were 5 x 15 x 13 cm for width, length, and height, respectively. This design was based on four references [27-30]. The dielectric constant, [[epsilon].sub.r], for this design of the SCB pyramidal absorber was 1.44, which was consistent with the value of the dielectric constant measured previously in [31].

Figure 4 shows the simulation setup in CST's Microwave Studio. The source signal is the starting point of the signal before transmission occurs. The distance between the pyramidal microwave absorber and the source of the signal source (port), [Z.sub.pos], was 50 cm [32-37].

The distance also affects the reflection loss of the pyramidal microwave absorber. The source signal dimension is 15 cm width x 15 cm length, same dimension of pyramidal base part. The source signal is located as a normal incident (0[degrees]) signal from the pyramidal base part.

The next stage is to fabricate the SCB pyramidal microwave absorber, as shown in Figure 5. The ground SCB was mixed with polyester resin, and methyl ethyl ketone peroxide (MEKP) was used as the hardening agent. Then, the mixture was placed in a pyramidal-shaped mold and pressed with a hand press machine to produce its solid, pyramidal shape.

The next stage is the measurement of reflection loss using the radar cross section (RCS) method [38-41]. The equipment used in this measurement was a signal generator, a spectrum analyzer, a pair of coaxial cables, seven pairs of horn antennas, the reference metal and a tripod to hold the horn antennas and the reference metal [42,43]. The angle between the pyramidal microwave absorber and the horn antenna was 60[degrees]. Figure 6(a) shows the different effective frequency ranges of horn antennas, i.e., 1.80-2.60 GHz, 2.80-3.80 GHz, 4.0-5.8 GHz, 6.0-8.2 GHz, 8.4-12.4 GHz, and 12.6-18.0 GHz. Figure 6(b) shows the spectrum analyzer and signal generator that were used in this measurement.

3. RESULTS AND DISCUSSION

The best reflection loss at a certain point cannot be used to determine the overall performance of the pyramidal microwave absorber because it only represents a very limited range of frequencies. The overall performance of pyramidal microwave absorber must be represented by using the average of the reflection losses.

Table 1 shows a comparison of the average values of dielectric constant and loss tangent for rice husks and SCB using the dielectric probe measurement technique. The average dielectric constant of the SCB was 1.44, while that of the rice husk was 2.03. The average loss tangents for rice husk and SCB were 0.132 and 0.161, respectively.

Figure 7 shows the dielectric constant of SCB using the dielectric probe measurement technique. The measurement was taken in the frequency range of 0.02 to 10 GHz. The figure shows that the dielectric constant of SCB varies, depending on the frequency. For example, the dielectric constant at a frequency of 0.4 GHz was 2.26, while the dielectric constant was only 0.75 when the frequency was 4.9 GHz. The average dielectric constant for SCB was 1.44.

Figure 8 shows the loss tangent of SCB using the dielectric probe measurement technique. The loss tangent value of the SCB ranged from 0.1 to 1.0. The graph shows that the loss tangent values were 0.38 and 0.28 at 0.4 and 4.9 GHz, respectively.

Figure 9 shows the reflection losses for SCB and rice husks in the frequency range of 0.01 to 20.0 GHz. The figure shows that SCB pyramidal microwave absorber had a better reflection-loss performance than the rice husk pyramidal microwave absorber.

Table 2 shows the comparison of the different pyramidal microwave absorbers using different types of materials. The SCB pyramidal microwave absorber had better reflection loss values than the rice husk pyramidal microwave absorber. Their average reflection losses were -44.388 dB and -38.237 dB, respectively.[right arrow]

For the frequency range of 0.01 GHz to 1.0 GHz, SCB absorber show better performance with -29.657 dB compared to rice husk absorber with only -16.031 dB.

Figure 10 and Table 3 represent the reflection loss performance of the SCB pyramidal microwave absorber using different thicknesses of the base of the absorber. Four different thicknesses of the base of the pyramidal microwave absorbers, i.e., 1, 2, 3, and 4cm, were tested, and their reflection losses versus frequency graphs were compared. The results showed that the base thickness of 1 cm had the best average reflection loss result, i.e., -45.798 dB. The best reflection loss with the 1-cm base thickness was -85.498 dB at a frequency of 11.58 GHz, while the best loss with the 2-cm thickness was only -75.676 dB at 16.66 GHz. For the low frequency range (0.01 to 1.00GHz), the 1-cm base thickness also had the best average reflection loss, i.e., -33.446 dB.

The results of using three different heights of the pyramidal shapes, i.e., 9, 13, and 17 cm, are shown in Figure 11 and Table 4. The results of the parametric study showed that the pyramidal microwave absorber that was 17 cm high had the best average reflection loss. The pyramid with this height achieved an average reflection loss of -51.094, whereas the 13 and 9 cm pyramids achieved -44.435 dB and -39.756 dB, respectively. The best single results occurred for the 13-cm pyramid at a frequency of 16.66 GHz.

Figure 12 and Table 5 show the effect on the distance between the waveguide port and the pyramidal microwave absorber. The initial distance was 50 cm, while the other distance was 35 cm. The graph shows that the distance = 50 cm had better average reflection loss than the distance = 35 cm. The average reflection loss between 0.01 and 20.0 GHz for 50 cm and 35 cm were -44.435 dB and -43.207 dB, respectively.

Figure 13 and Table 6 compare the average reflection losses with different angles between the waveguide port and the absorber. The three angle values used in the parametric study value were the normal incident angle of 0[degrees] and oblique incident angles of 30[degrees] and 45[degrees]. The results of the simulation indicated that the normal incident angle achieved the best average return loss for frequencies between 0.01 and 20.0 GHz, i.e., -44.435 dB, than the 30[degrees] and 45[degrees] oblique incident angles, i.e., -61.650 dB and -62.331 dB, respectively.

Figure 14 compares the simulation results with the results achieved by the fabricated SCB pyramidal microwave absorber. The created region was done because of the limitation of the frequency range of the horn antennas. The seven regions (Regions A to G) were created from 1.80 to 18.0GHz.

Table 7 compares the results achieved via simulation and actual operation of a fabricated pyramidal microwave absorber using SCB. The simulated results had a better average reflection loss (range between 1.80 and 18.0 GHz), i.e., -52.380 dB than the fabricated absorber, i.e., -45.900 dB.

4. CONCLUSIONS AND FUTURE WORK

The cost of the pyramidal microwave absorber can be reduced by using SCB as the main material. This SCB-polyester-MEKP absorber was less expensive than microwave absorbers on the commercial market, and the main materials of the latter absorbers are not environmentally friendly. This is due to their usage of nearly 100% of non-environmentally chemical materials. Both polystyrene and polyurethane can increase the pollution that enters the environment. The SCB-polyester-MEKP absorbers can reduce the use of chemical-based material by almost 90%. The results of this study proved that agricultural waste, such as SCB, has huge potential for being used as an alternative material in fabricating microwave absorbers. In the future, this work could be extended to compare the performance of the proposed SCB microwave absorbers with commercially available microwave absorbers.

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Liyana Zahid (1), *, Fareq Malek (1), Hassan Nornikman (2), Nur A. Mohd Affendi (1), Azuwa Ali (1), Nuriziani Hussin (1), Badrul H. Ahmad (2), and Mohamad Z.A. Abd Aziz (2)

(1) School of Electrical System Engineering, Universiti Malaysia Perlis (UniMAP), Pauh Putra, Arau, Perlis 02600, Malaysia

(2) Center for Telecommunication Research and Innovation (CeTRI), Faculty of Electronic and Computer Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, Durian Tunggal, Melaka 76100, Malaysia

Received 26 January 2013, Accepted 4 March 2013, Scheduled 12 March 2013

* Corresponding author: Liyana Zahid (liyanazahid@yahoo.com).

Table 1. Average dielectric constants and average loss tangents
for SCB and rice husks.

Material             Average dielectric       Average loss
                         constant,        tangent, tan [delta]
                     [[epsilon].sub.r]

Rice husks                  2.03                 0.132
Sugar cane bagasse          1.44                 0.161

Table 2. Average reflection loss performance of pyramidal
microwave absorbers using different materials.

Frequency     Simulated average reflection loss (dB)
range (GHz)
              Sugarcane bagasse   Rice husks [24]

0.01-1             -29.657            -16.031
1-5                -41.295            -35.911
5-10               -48.001            -46.173
10-15              -47.751            -40.749
15-20              -43.055            -34.175
0.01-20            -44.435            -38.237

Table 3. Average reflection loss performance of pyramidal
microwave absorber using different base thicknesses ([B.sub.t]).

Frequency     Average reflection loss (dB) with
range (GHz)   different base thickness

              [B.sub.t] = 1 cm   [B.sub.t] = 2 cm (normal)

0.01 to 1         -33.446                 -29.657
1 to 5            -43.819                 -41.295
5 to 10           -50.468                 -48.001
10 to 15          -49.218                 -47.751
15 to 20          -41.758                 -43.055
0.01 to 20        -45.798                 -44.435
Best point        -85.498                 -75.676

Frequency     Average reflection loss (dB) with
range (GHz)   different base thickness

              [B.sub.t] = 3 cm   [B.sub.t] = 5 cm

0.01 to 1         -27.826            -23.461
1 to 5            -39.902            -36.479
5 to 10           -46.497            -42.945
10 to 15          -45.392            -42.698
15 to 20          -42.205            -38.071
0.01 to 20        -42.890            -39.392
Best point        -57.179             -48.35

Table 4. Average reflection loss performance of pyramidal
microwave absorber using different pyramid heights ([P.sub.h]).

Frequency           Average reflection loss (dB) with different
range (GHz)                   pyramid heights

              [P.sub.h] = 9 cm    [P.sub.h] =     [P.sub.h] = 17 cm
                                 13 cm (normal)

0.01 to 1         -20.338           -29.657            -48.244
1 to 5            -33.169           -41.295            -53.693
5 to 10           -42.955           -48.001            -57.331
10 to 15          -44.714           -47.751            -49.359
15 to 20          -40.766           -43.055            -45.099
0.01 to 20        -39.756           -44.435            -51.094
Best point        -54.919           -75.676            -67.658

Table 5. Average reflection loss performance of pyramidal
microwave absorber using different distances between the
waveguide port and the absorber, [Z.sub.pos].

Frequency     Average reflection loss (dB) with
range (GHz)   different distances between the waveguide
              port and the absorber, [Z.sub.pos]

              [Z.sub.pos] = 35 cm   [Z.sub.pos] = 50
                                      cm (normal)

0.01 to 1           -28.044             -29.657
1 to 5              -40.608             -41.295
5 to 10             -46.936             -48.001
10 to 15            -46.969             -47.751
15 to 20            -40.847             -43.055
0.01 to 20          -43.207             -44.435
Best point          -60.170             -75.676

Table 6. Average reflection loss performance of pyramidal
microwave absorber using different angles between the
waveguide port and the absorber.

Frequency     Average reflection loss (dB) with
range (GHz)   different angles between the
              waveguide port and the absorber

              Angle = 0[degrees]     Angle =       Angle =
                   (normal)        30[degrees]   45[degrees]

0.01 to 1          -29.657           -27.966       -27.269
1 to 5             -41.295           -26.011       -42.222
5 to 10            -48.001           -31.042       -48.665
10 to 15           -47.751           -37.686       -41.823
15 to 20           -43.055           -35.398       -39.242
0.01 to 20         -44.435           -32.636       -42.244
Best point         -75.676           -61.650       -62.331

Table 7. Average reflection loss performance of
fabricated pyramidal microwave absorber using sugar
cane bagasse and rice husks.

Region, based   Frequency   Average reflection
on different      range     loss (dB)
horn antenna      (GHz)
                            Simulated   Fabricated
                            microwave   microwave
                            absorber     absorber

A               1.80-2.60    -30.890     -40.250
B               2.60-3.80    -38.360     -42.820
C               3.80-5.80    -55.880     -45.920
D               5.80-8.20    -52.270     -48.210
E               8.20-12.4    -56.410     -48.380
F               12.4-18.0    -54.410     -44.820
G               1.80-18.0    -52.380     -45.900
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Author:Zahid, Liyana; Malek, Fareq; Nornikman, Hassan; Affendi, Nur A. Mohd; Ali, Azuwa; Hussin, Nuriziani;
Publication:Progress In Electromagnetics Research
Article Type:Report
Geographic Code:9MALA
Date:May 1, 2013
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