# Computational and Experimental Approaches for Determining Scattering Parameters of OPEFB/PLA Composites to Calculate the Absorption and Attenuation Values at Microwave Frequencies

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

_{11}) and transmission (S

_{21}) coefficients obtained from the microstrip transmission line were used to determine the attenuation and absorption of oil palm empty fruit bunch/polylactic acid (OPEFB/PLA) composites in a frequency range between 0.20 GHz and 12 GHz at room temperature. The main structure of semi-flexible substrates (OPEFF/PLA) was fabricated using different fiber loading content extracted from oil palm empty fruit bunch (OPEFB) trees hosted in polylactic acid (PLA) using the Brabender blending machine, which ensured mixture homogeneity. The commercial software package, Computer Simulation Technology Microwave Studio (CSTMWS), was used to investigate the microstrip line technique performance by simulating and determine the S

_{11}and S

_{21}for microwave substrate materials. Results showed that the materials’ transmission, reflection, attenuation, and absorption properties could be controlled by changing the percentage of OPEFB filler in the composites. The highest absorption loss was calculated for the highest percentage of filler (70%) OPEFB at 12 GHz to be 0.763 dB, while the lowest absorption loss was calculated for the lowest percentage of filler 30% OPEFB at 12 GHz to be 0.407 dB. Finally, the simulated and measured results were in excellent agreement, but the environmental conditions slightly altered the results. From the results it is observed that the value of the dielectric constant (${\epsilon}_{r}^{\prime})$ and loss factor (${\epsilon}_{r}^{\u2033})$ is higher for the OPEFB/PLA composites with a higher content of OPEFB filler. The dielectric constant increased from 2.746 dB to 3.486 dB, while the loss factor increased from 0.090 dB to 0.5941 dB at the highest percentage of 70% OPEFB filler. The dielectric properties obtained from the open-ended coaxial probe were required as input to FEM to calculate the S

_{11}and S

_{21}of the samples.

## 1. Introduction

_{2}O

_{3}onto dielectric and magnetic properties of a Fe

_{2}O

_{3}OPEFB/PLA composite at a frequency range of 8–12 GHz. The results of the electromagnetic properties indicate that the permittivity and permeability increased by increasing the Fe

_{2}O

_{3}percentage. Furthermore, the power loss and absorption loss increased with both the increase in frequency and the percentage of Fe

_{2}O

_{3}filler in the composite. The findings also showed that the material transmission, reflection, and absorption properties can be controlled by changing the percentage of Fe

_{2}O

_{3}filler in the composites. Most studies on the microstrip line involve measurements of the transmission coefficient of materials in the microwave frequency range of 4 GHz with samples openly placed on the strapline [13].

_{21}, reflection coefficient S

_{11}, reflection loss, and power loss for the epoxy resin (ER) reinforced with different percentages of micro-sized oil palm empty fruit bunch (OPEFB) at a frequency of 8–12 GHz. The reflection and transmission coefficients of the composites were measured using a rectangular waveguide connected to the vector network analyzer. The results showed that the dielectric properties increased, while S

_{11}and S

_{21}decreased with the OPEFB percentage increasing in the composites. Furthermore, the shielding effectiveness, power loss, and reflection loss increased with increasing OPEFB percentage. The simulated and measured results of S

_{11}and S

_{21}were in good agreement. The scope of this study includes the utilization of the microstrip transmission line technique in the measurement of reflection S

_{11}and transmission S

_{21}coefficients in the frequency range between 0.20 GHz and 12 GHz to determine attenuation and absorption values for OPEFB/PLA composites, as well as a systematic comparison between the experimental results and the theoretical (simulation) results obtained through the application of the COMSOL software.

## 2. Experimental Details

#### 2.1. Materials

^{3}(Grade 4060D) was supplied by Nature Work LLC (Minnetonka, MN, USA), and the COMSOL Multiphysics 3.5 software (COMSOL Multyphysics, Burlington, MA, USA) was utilized in the theoretical simulation of the microstrip results by calculating the Scattering (S)-parameters coefficients of the samples. The RT-Duroid 5880 substrate (manufactured in the USA) was used to place the microstrip layout, and the ferric chloride (FeCl

_{3}) solution from Nature Work LLC (Minnetonka, MN, USA) was used for etching purposes (immersing the microstrip board). Figure 1 depicts the chemical structures of PLA and OPEFB.

#### 2.2. Microstrip Transmission Line Fabrication

_{3}) to a liter of water. The etching process time can be shortened by heating the solution to 50 °C. The purpose of etching is to remove the unwanted part of the metal (copper), leaving only the designed circuit. Next, the substrate was placed on an aluminum slab, giving it a strong and firm grip, as shown in Figure 2b. SMA (Sub-miniature) is then attached to both ends of the duroid. The attachment was done by fixating screws after drilling holes by the side of the duroid. Care is taken to ensure that the inner conductor of the SMA is placed in contact with the line of the microstrip. The measurement of scattering parameter using the fabricated microstrip was achieved by placing the sample flat on the surface of the microstrip avoiding any air gap between the sample and the microstrip transmission line.

#### 2.3. Preparation of OPEFB/PLA Composites

^{−1}, polylactic acid (PLA) was added to the blender and mixed for 5 min after which the OPEFB powder was introduced into the blender. The prepared dough was used to make the substrates 3 mm thick by pressing inside a rectangular mold of 10 × 8 cm

^{2}, which was heated up to 170 °C for 10 min, as illustrated in Table 1.

#### 2.4. Measurement of Scattering Parameters

_{11}and S

_{21}for each of the air (without sample) and OPEFB/PLA composites at different percentages of OPEFB was performed by a microstrip transmission line, Figure 4a,b, using the Agilent N5230A PNA-L network analyzer system (Agilent Technologies, Inc., CA, USA) with a commercial measurement (Agilent 85701B, CA, USA) software package [20], at a frequency range from 0.20 to 12 GHz. Measurement of scattering parameters using the fabricated microstrip transmission line was achieved by placing the OPEFB/PLA samples flat, as shown in Figure 4a, on the surface of the microstrip. To avoid the influence of an air gap during the measurement, a wooden bracket was used to apply uniform pressure on the sample, as shown in Figure 4b. The vector network analyzer (VNA) was calibrated by implementing Electronic Calibration modules (N4691-60004) and the accuracy of the VNA depends on the quality of the calibration standards.

#### 2.5. Measurement of the Complex Permittivity

#### 2.6. Finite Element Method (FEM)

_{21}and reflection S

_{11}coefficients of the microstrip line system. The formed microstrip line geometry is designed and connected to a coaxial mode for port boundary conditions. The coaxial mode is the only fundamental mode that is available as a predefined model in COMSOL simulation [22]. Therefore, the electric field vector in coaxial cable in a radial direction and the magnetic field lines are perpendicular so that their lines appear as concentric circles around the center conductor [23].The electric field distributions surrounding the microstrip for OPEFB/PLA composites, where the lines indicate the direction of the field vector from the positive charge to the negative charge. Few steps need to be performed before the simulation process, which is described as follows: creating the geometry, defining physical parameters and boundary conditions, meshing the geometry, solving the model geometry, obtaining the solution, and performing parametric studies.

## 3. Experimental Results and Discussion

#### 3.1. Reflection and Transmission Coefficient Measurements

_{11}and S

_{21}on the frequency were studied and clarified, as shown in Figure 6 and Figure 7, respectively, by using a microstrip line technique. The decrease in S

_{11}magnitude as the percentage of OPEFB increases is shown in Figure 6, and the difference in magnitude of S

_{11}is distinguishable from one sample to another. The magnitude of S

_{11}at 1 GHz of OPEFB/PLA composites with different % of OPEFB fillers are 0.0836, 0.0821, 0.081, 0.079, and 0.078 for 30%, 40%, 50%, 60%, and 70% OPEFB, respectively. The magnitude of S

_{11}at 12 GHz are 0.335, 0.301, 0.273, 0.262, and 0.251 for 30%, 40%, 50%, 60%, and 70% OPEFB, respectively. Figure 7 shows the effect of frequency and OPEFB loading on the S

_{21}magnitude. It is observed that the S

_{21}magnitude decreases with an increase in the frequency and decreased with an increase in the percentage of OPEFB filler. Furthermore, if the materials have a higher loss factor, they tend to absorb more energy of the electromagnetic waves that were propagating through the sample resulting in a reduced S

_{21}magnitude. The magnitude of S

_{21}at 1 GHz of OPEFB/PLA composites with different % of OPEFB fillers are 0.985, 0.984, 0.975, 0.974, and 0.973 for 30%, 40%, 50%, 60%, and 70% OPEFB, respectively. The magnitude of S

_{21}at 12 GHz are 0.613, 0.585, 0.501, 0.475, and 0.424 for 30%, 40%, 50%, 60%, and 70% OPEFB, respectively.

#### 3.2. Complex Permittivity of OPEFB/PLA Composites

_{11}and S

_{21}of the samples.

#### 3.3. Electric Field Distribution Surrounding the Microstrip Sensor

_{21}and reflection S

_{11}coefficient parameters of OPEFB/PLA composites using (FEM) simulation by the COMSOL software, the solution time is strongly influenced by mesh properties such as element quality geometry, conformity, and mesh density. Therefore, an appropriate approximation of the problem domain is required for the geometry conformity of the area defined by the mesh elements. In this research, the FEM simulation results of the electric field distribution of the microstrip sensor covered with OPEFB/PLA composites are illustrated in Figure 11a–e in which the arrow and the colorful shape represent the direction, intensity, and shape of the electric field distribution. The sample results show the decrement in the intensity of wave propagation as the OPEFB filler content increases, which is dependent on electric permittivity values that change as the filler ratio changes, thus agreeing with experimental S

_{21}and S

_{11}measurement results. As expected, higher loss material has higher absorption and thus lower transmission of the electromagnetic waves through the OPEFB/PLA composites material. Thus, the higher the dielectric constant and loss factor, the less uniform the distribution of the electric field is observed due to scattering as shown in Figure 11d,e [27,28]. On the other hand, the higher the content of OPFEB filler, the higher the absorption loss, and thus the lower the intensity of the propagating wave as shown in the simulation, which is in complete agreement with the experimental loss factor results obtained for the different percentages of OPEFB filler. The simulation results showed that the electric field radiation pattern distributed over the OPEFB/PLA composites is dependent on complex permittivity values which determines the direction of the electric field [29]. Minimization of the discretization error and achieving accurate solutions can be assured by having the mesh with density and size that are sufficiently high and small, respectively [22]. Shown in Table 2 are the relative errors of measurement and simulation of both of S

_{11}and S

_{21}.

#### 3.4. Calculated Attenuation

_{21}, which is obtained via the vector network analyzer by applying the following Equation [10]:

#### 3.5. Microwave Absorption

#### 3.6. Comparison of Measured and Simulated Scattering Parameters

_{11}and S

_{21}) measurement results of an unloaded microstrip line and FEM simulation in the frequency range from 0 GHz to 12 GHz are shown in Figure 14a,b. As expected for the unloaded microstrip, the value of the transmission coefficient is higher than the reflection coefficient. The accuracy of the S

_{11}and S

_{21}values can be determined by calculating the relative error for the measurement data [32] as follows:

_{21}are calculated by replacing S

_{11}with S

_{21}in Equation (6). The mean relative errors between the measured and FEM values for S

_{11}and S

_{21}were 0.478 and 0.049, as listed in Table 3. The high error in S

_{11}was due to the effect of multiple reflections not considered in the FEM simulation, which usually requires a large number of small meshes at the interface between the microstrip and the coaxial cable.

_{11}and S

_{21}for the OPEFB/PLA composites, respectively. In general, there is a good agreement between the measured and simulated for all the composites. Table 2 shows the mean relative error of S

_{11}and S

_{21}and it can be observed that the lowest mean relative error of the S

_{11}value for OPEFB/PLA composites is at 50 wt% OPEFB, while the highest value is at 30 wt% OPEFB. The lowest mean relative error of S

_{21}value is at 70 wt% OPEFB, while the highest value is at 40 wt% OPEFB. The magnitude of S

_{21}decreased with increasing OPEFB filler content, where the 70 wt% OPEFB percentage filler sample was found to have the lowest S

_{21}. These results are in agreement with the impedance mismatch theory where materials with the highest permittivity show lower transmission coefficient values [33]. Therefore, the magnitudes of S

_{21}at 12 GHz are (0.610, 568, 0.499, 0.463, and 0.415) dB for (30, 40, 50, 60, and 70) wt% OPEFB, respectively.

## 4. Error Analysis

## 5. Conclusions

_{11}and transmission S

_{21}coefficients of the composites using the microstrip transmission line technique. Results obtained for the measurement of reflection coefficients revealed that S

_{11}increases with increase in OPEFB particle filler for all samples used in this study and vice versa for the transmission S

_{21}coefficients. The calculated attenuation for the 30 wt% OPEFB filler showed that attenuation was lowest at 2 GHz and the highest attenuation was recorded at 12 GHz. The absorption of the different OPEFB/PLA composites showed that the magnitude of absorption continues to increase as the filler content increases until it reached the highest value. It is observed from the results that the value of the dielectric constant and loss factor is higher for the OPEFB/PLA composites with a higher content of OPEFB filler. The dielectric constant increased from 2.746 dB to 3.486 dB, while the loss factor increased from 0.090 dB to 0.5941 dB at the highest percentage of 70 wt% OPEFB filler. The dielectric properties obtained from the open-ended coaxial probe were required as inputs to FEM to calculate the S

_{11}and S

_{21}of the samples. The comparison between the S

_{11}and S

_{21}for the measured and simulated (FEM) values for the microstrip transmission line technique (unloaded) was studied and the mean relative error between the measured and FEM for S

_{11}and S

_{21}was found to be 0.478 and 0.049, respectively. The results of S

_{11}and S

_{21}calculated by FEM simulation was found to agree with the magnitudes of the reflection and transmission coefficients, S

_{11}and S

_{21}, measured by the microstrip transmission line technique with little relative error.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

- Ahmad, A.F.; Abbas, Z.; Obaiys, S.J.; Ibrahim, N.A.; Zainuddin, M.F.; Salem, A. Permittivity properties of nickel zinc ferrite-oil palm empty fruit bunch-polycaprolactone. Compos. Procedia. Chem.
**2016**, 19, 603–610. [Google Scholar] [CrossRef] [Green Version] - Saba, N.; Paridah, M.T.; Jawaid, M. Mechanical properties of kenaf fibre reinforced polymer composite: A review. Constr. Build. Mater.
**2015**, 76, 87–96. [Google Scholar] [CrossRef] - Jiang, N.; Yu, T.; Li, Y.; Pirzada, T.J.; Marrow, T.J. Hygrothermal aging and structural damage of a jute/poly (lactic acid) (PLA) composite observed by X-ray tomography. Compos. Sci. Technol.
**2019**, 173, 15–23. [Google Scholar] [CrossRef] - Siakeng, R.; Jawaid, M.; Ariffin, H.; Sapuan, S.M.; Asim, M.; Saba, N. Natural fiber reinforced polylactic acid composites: A review. Polym. Compos.
**2019**, 40, 446–463. [Google Scholar] [CrossRef] - Eichner, E.; Heinrich, S.; Schneider, G.A. Influence of particle shape and size on mechanical properties in copper-polymer composites. Powder Technol.
**2018**, 339, 39–45. [Google Scholar] [CrossRef] - Saba, N.; Jawaid, M.; Alothman, O.Y.; Paridah, M.T. A review on dynamic mechanical properties of natural fibre reinforced polymer composites. Constr. Build. Mater.
**2016**, 106, 149–159. [Google Scholar] [CrossRef] - Ahmad, A.F.; Abbas, Z.; Obaiys, S.J.; Zainuddin, M.F. Effect of untreated fiber loading on the thermal, mechanical, dielectric, and microwave absorption properties of polycaprolactone reinforced with oil palm empty fruit bunch biocomposites. Polym. Compos.
**2018**, 39. [Google Scholar] [CrossRef] - Akil, H.; Omar, M.F.; Mazuki, A.A.M.; Safiee, S.Z.A.M.; Ishak, Z.M.; Bakar, A.A. Kenaf fiber reinforced composites: A review. Mater. Des.
**2011**, 32, 4107–4121. [Google Scholar] [CrossRef] - Ibrahim, N.A.; Ahmad, S.N.A.; Yunus, W.M.Z.W.; Dahlan, K.Z.M. Effect of electron beam irradiation and poly (vinyl pyrrolidone) addition on mechanical properties of polycaprolactone with empty fruit bunch fibre (OPEFB) composite. Express Polym.
**2009**, 3, 226–234. [Google Scholar] [CrossRef] - Fahad, A.A.; Abbas, Z.; Shaari, A.H.; Obaiys, J.S.; Sa’ad Aliyu, U. Synthesis, thermal, dielectric, and microwave reflection loss properties of nickel oxide filler with natural fiber-reinforced polymer composite. J. Appl. Polym.
**2019**, 136. [Google Scholar] [CrossRef] - Li, Y.; Xu, G.; Guo, Y.; Ma, T.; Zhong, X.; Zhang, Q.; Gu, J. Fabrication, proposed model and simulation predictions on thermally conductive hybrid cyanate ester composites with boron nitride fillers. Compos. Part. Appl Sci. Manuf.
**2018**, 107, 570–578. [Google Scholar] [CrossRef] - Idris, F.M.; Hashim, M.; Abbas, Z.; Ismail, I.; Nazlan, R.; Ibrahim, I.R. Recent developments of smart electromagnetic absorbers-based polymer-composites at gigahertz frequencies. J. Magn. Magn. Mater.
**2016**, 405, 197–208. [Google Scholar] [CrossRef] - Yakubu, A.; Abbas, Z.; Esa, F.; Tohidi, P. The effect of ZnO nanoparticle filler on the attenuation of ZnO/PCL nanocomposites using microstrip line at microwave frequency. Int. Polym. Proc.
**2015**, 30, 227–232. [Google Scholar] [CrossRef] - Ahmad, A.F.; Aziz, S.A.; Obaiys, S.J.; Zaid, M.H.M.; Matori, K.A.; Samikannu, K.; Aliyu, U.S. Biodegradable poly (lactic acid)/poly (ethylene glycol) reinforced multi-walled carbon nanotube nanocomposite fabrication, characterization, properties, and applications. Polymers
**2020**, 12, 427. [Google Scholar] [CrossRef] [PubMed] [Green Version] - Oi, T.; Shinyama, K.; Fujita, S. Electrical properties of heat-treated polylactic acid. Electr. Eng. Jpn.
**2012**, 180, 1–8. [Google Scholar] [CrossRef] - Abdalhadi, D.M.; Abbas, Z.; Ahmad, A.F.; Matori, K.A.; Esa, F. Controlling the properties of OPEFB/PLA polymer composite by using Fe
_{2}O_{3}for microwave applications. Fiber Polym.**2018**, 19, 1513–1521. [Google Scholar] [CrossRef] - Khamis, A.M.; Abbas, Z.; Ahmad, A.F.; Abdalhadi, D.M.; Mensah, E.E. Experimental and computational study on epoxy resin reinforced with micro-sized OPEFB using rectangular waveguide and finite element method. IET. Microw. Antenna. P
**2020**, 14, 752–758. [Google Scholar] [CrossRef] - Ahmad, A.F.; Abbas, Z.; Obaiys, S.J.; Jusoh, M.A.; Talib, Z.A. Analysis and optimal design of a microstrip sensor for moisture content in rubber latex measurement. Adv. Stud. Theor. Phys.
**2012**, 6, 49–62. [Google Scholar] - Fahad, A.; Abbas, Z.; Obaiys, S.J.; Ibrahim, N.; Yakubu, A. dielectric behavior of OPEFB reinforced polycaprolactone composites at X-Band frequency. Int. Polym. Process.
**2016**, 31, 18–25. [Google Scholar] [CrossRef] - Shafie, S.; El-Sabagh, M.; Dessouky, M.; Shafee, M.; Hammouda, S.; Hegazy, H. December. A simple model for on-chip microstrip transmission lines in millimeter wave circuits. IEEE (ICM)
**2016**, 121–124. [Google Scholar] [CrossRef] - Micheli, D.; Pastore, R.; Vricella, A.; Morles, R.B.; Marchetti, M.; Delfini, A.; Moglie, F.; Primiani, V.M. Electromagnetic characterization and shielding effectiveness of concrete composite reinforced with carbon nanotubes in the mobile phones frequency band. MAT. SCI. ENG. B-ADV
**2014**, 188, 119–129. [Google Scholar] [CrossRef] - Fouineau, A.; Raulet, M.A.; Lefebvre, B.; Burais, N.; Sixdenier, F. Semi-analytical methods for calculation of leakage inductance and frequency-dependent resistance of windings in transformers. IEEE T MAGN
**2018**, 54, 1–10. [Google Scholar] [CrossRef] [Green Version] - Fesharaki, F.; Djerafi, T.; Chaker, M.; Wu, K. S-parameter deembedding algorithm and its application to substrate integrated waveguide lumped circuit model extraction. IEEE Trans. Microw Theory Tech.
**2017**, 65, 1179–1190. [Google Scholar] [CrossRef] - Jayamani, E.; Hamdan, S.; Rahman, M.R.; Bakri, M.B. Comparative study of dielectric properties of hybrid natural fiber composites. Procedia Eng.
**2014**, 97, 536–544. [Google Scholar] [CrossRef] [Green Version] - Thomas, M.S.; Koshy, R.R.; Mary, S.K.; Thomas, S.; Pothan, L.A. Properties of composites. In Starch, Chitin and Chitosan Based Composites and Nanocomposites; Springer: Cham, Swizerland, 2019; pp. 19–42. [Google Scholar] [CrossRef]
- Al-Oqla, F.M.; Sapuan, S.M.; Anwer, T.; Jawaid, M.; Hoque, M.E. Natural fiber reinforced conductive polymer composites as functional materials. Synth. Met.
**2015**, 206, 42–54. [Google Scholar] [CrossRef] - Ishimaru, A. Electromagnetic Wave Propagation, Radiation and Scattering: From Fundamentals to Applications; John Wiley & Sons: Hoboken, NJ, USA, 2017; ISBN 978-1-118-09881-3. [Google Scholar]
- Quan, B.; Liang, X.; Xu, G.; Cheng, Y.; Zhang, Y.; Liu, W.; Ji, G.; Du, Y. A permittivity regulating strategy to achieve high-performance electromagnetic wave absorbers with compatibility of impedance matching and energy conservation. New J. Chem.
**2017**, 41, 1259–1266. [Google Scholar] [CrossRef] - Plaza-González, P.; Monzó-Cabrera, J.; Catalá-Civera, J.M.; Sánchez-Hernández, D. New approach for the prediction of the electric field distribution in multimode microwave-heating applicators with mode stirrers. IEEE Trans. Magn.
**2004**, 40, 1672–1678. [Google Scholar] [CrossRef] [Green Version] - Munalli, D.; Dimitrakis, G.; Chronopoulos, D.; Greedy, S.; Long, A. Electromagnetic shielding effectiveness of carbon fibre reinforced composites. Compos. Part. B Eng.
**2019**, 10. [Google Scholar] [CrossRef] - Jain, R.C. Understanding electromagnetic wave absorbers. IETE J. Educ.
**2000**, 41, 35–43. [Google Scholar] [CrossRef] - Ahmad, A.F.; Abbas, Z.; Ab Aziz, S.; Obaiys, S.J.; Zainuddin, M.F. Synthesis and characterization of nickel oxide reinforced with polycaprolactone composite for dielectric applications by controlling nickel oxide as a filler. Results Phys.
**2018**, 11, 427–435. [Google Scholar] [CrossRef] - Rudd, M.; Baum, T.C.; Ghorbani, K. Determining high-frequency conductivity based on shielding effectiveness measurement using rectangular waveguides. IEEE Trans. Instrum. Meas.
**2019**, 69, 155–162. [Google Scholar] [CrossRef]

**Figure 1.**Chemical structure of (

**a**) polylactic acid (PLA) and chemical structure of oil palm empty fruit bunch (OPEFB) fiber content include (

**b**) cellulose, (

**c**) hemicelluloses, and (

**d**) lignin.

**Figure 2.**(

**a**) Microstrip transmission line printed on a transparent mask. (

**b**) The complete microstrip straight line.

**Figure 6.**Variation of reflection (S

_{11}) for OPEFB/PLA composite at different percentages of OPEFB.

**Figure 7.**Variation in transmission (S

_{21}) for OPEFB/PLA composites at different percentages of OPEFB filler.

**Figure 8.**Variation in dielectric constant of OPEFB/PLA composites at different percentages of OPEFB filler.

**Figure 9.**Variation in loss factor of OPEFB/PLA composites at different percentages of OPEFB filler.

**Figure 11.**Electric field distribution and intensity plot for the different OPEFB/PLA composites (

**a**) 30 wt%, (

**b**) 40 wt%, (

**c**) 50 wt%, (

**d**) 60 wt%, and (

**e**) 70 wt% of OPEFB.

**Figure 13.**Calculated absorption loss of different compositions of OPEFB/PLA composites at various percentages of OPEFB filler.

**Figure 14.**The magnitudes of (

**a**) S

_{11}and (

**b**) S

_{21}for both the measurement and FEM simulation method of the unloaded microstrip line.

**Figure 15.**Variation in the magnitude of S

_{11}for the different OPEFB/PLA composites (

**a**) 30 wt%, (

**b**) 40 wt%, (

**c**) 50 wt%, (

**d**) 60 wt%, and (

**e**) 70 wt% OPEFB for both the measurement and FEM simulation.

**Figure 16.**Variation in the magnitude of S

_{21}for the different OPEFB/PLA composites (

**a**) 30 wt%, (

**b**) 40 wt%, (

**c**) 50 wt%, (

**d**) 60 wt%, and (

**e**) 70 wt% OPEFB for both the measurement and FEM simulation.

OPEFB | PLA | Total Mass (g) | ||
---|---|---|---|---|

Weight (%) | Mass (g) | Weight (%) | Mass (g) | |

30 | 13.50 | 70 | 31.50 | 45 |

40 | 18.00 | 60 | 27.00 | |

50 | 22.50 | 50 | 22.50 | |

60 | 27.00 | 40 | 18.00 | |

70 | 31.50 | 30 | 13.50 |

OPEFB | Relative Error | |
---|---|---|

S_{11} | S_{21} | |

30% | 0.301 | 0.051 |

40% | 0.280 | 0.068 |

50% | 0.273 | 0.054 |

60% | 0.273 | 0.053 |

70% | 0.298 | 0.046 |

Sample | Relative Error | |
---|---|---|

S_{11} | S_{21} | |

AIR | 0.478 | 0.049 |

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Fahad Ahmad, A.; Aziz, S.H.A.; Abbas, Z.; Mohammad Abdalhadi, D.; Khamis, A.M.; Aliyu, U.S.
Computational and Experimental Approaches for Determining Scattering Parameters of OPEFB/PLA Composites to Calculate the Absorption and Attenuation Values at Microwave Frequencies. *Polymers* **2020**, *12*, 1919.
https://doi.org/10.3390/polym12091919

**AMA Style**

Fahad Ahmad A, Aziz SHA, Abbas Z, Mohammad Abdalhadi D, Khamis AM, Aliyu US.
Computational and Experimental Approaches for Determining Scattering Parameters of OPEFB/PLA Composites to Calculate the Absorption and Attenuation Values at Microwave Frequencies. *Polymers*. 2020; 12(9):1919.
https://doi.org/10.3390/polym12091919

**Chicago/Turabian Style**

Fahad Ahmad, Ahmad, Sidek Hj Ab Aziz, Zulkifly Abbas, Daw Mohammad Abdalhadi, Ahmad Mamoun Khamis, and Umar Sa’ad Aliyu.
2020. "Computational and Experimental Approaches for Determining Scattering Parameters of OPEFB/PLA Composites to Calculate the Absorption and Attenuation Values at Microwave Frequencies" *Polymers* 12, no. 9: 1919.
https://doi.org/10.3390/polym12091919