RSM2013 Proc. 2013, Langkawi, Malaysia Determination of Pulverized Material Permittivity for Microwave Absorber Application E. Baharudin 1* , A. Ismail 1** , A. R. H. Alhawari 1 , E. S. Zainudin 2 , D. L. Abang Abdul Majid 3 , F. Che Seman 4 , N. H. Khamis 5 1 Department of Computer and Communication Systems Engineering, Faculty of Engineering, UPM 2 Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, UPM 3 Department of Aerospace Engineering, Faculty of Engineering, UPM 4* Department of Communication Engineering, Faculty of Electrical and Electronic Engineering, UTHM 5 Department of Communication Engineering, Faculty of Electrical Engineering, UTM ** Institute of Advanced Technology, UPM Abstract— This paper presents the material characterization of agricultural waste by determining its dielectric properties for microwave absorber application. Three proposed materials, which are empty fruit bunch, oil palm frond and rice husk were investigated for the frequency ranging from 10 GHz to 20 GHz. The methodology was developed using the combination of three techniques involving coaxial probe technique, material density measurement and dielectric mixture model. It is found that the material density and air-particle permittivity have the impact on the wave absorption of the material. The result shows that all three agricultural wastes are capable to absorb electromagnetic signal. The average dielectric constant for solid pulverized agricultural waste are 3.49, 4.06 and 3.31 for empty fruit bunch, oil palm frond and rice husk respectively. Furthermore, at of 15.0 GHz, the solid pulverized empty fruit bunch, oil palm frond and rice husk indicate the highest loss tangent with value of 0.2201, 0.2579 and 0.2218 respectively which contributed from the loss factor of the material complex permittivity. Keywords—permittivity, agricultural waste, coaxial probe technique, material density, dielectric mixture model, microwave absorber. I. INTRODUCTION Material characterization for microwave absorber has continue to attract much attention due the vast development of radio frequency (RF) sources and rapid growth of communication and electronic devices which leads to the increment of serious electromagnetic interference (EMI) issues [1][2]. Microwave absorber plays the role by eliminating unwanted radiation that could interfere with system’s operation or it can help to reduce the signal reflections externally. Therefore, the need for high performance microwave absorbing material with the advantage of tiny thickness, low density, wide bandwidth and flexibility simultaneously has become a great challenge [3]. In the development of microwave absorber, it is important to identify a suitable material to meet the above requirement. Many studies have shown that the use of dielectric and magnetic material such as ferrite and carbon fibers, as microwave absorber and currently the development has been focused into agricultural waste materials [4], where they are environmentally friendly, fully biodegradable, abundantly available, renewable, cheap and have low density [5]. This research focuses on identifying potential agricultural waste that suits the properties of microwave absorber. Furthermore, the determinations of the dielectric properties using coaxial probe technique and density measurement with the dielectric mixture model are also highlighted. II. MATERIAL AND METHOD A. Permittivity and Coaxial Probe Technique When electric filed is applied towards a dielectric material, part of the energy is reflected and part is transmitted through the surface and part of energy is absorbed. These three conditions signify the electrical property in terms of complex relative permittivity of the material. It is a measure of material’s effect on the electric field [6]. The mathematical expression of the complex permittivity is: ߝ כ ൌ ߝ ᇱ െ  ߝ " (1) where ε’ is the dielectric constant or stored component and ε” is loss factor or dissipative component. Another important property that justifies the wave absorption of materials is the loss tangent and it is given by: ݐ ߜൌ ఌ " ఌ ᇲ (2) which is also known as the dissipation factor, D. The higher the loss tangent, then the more effective the absorber will be [7]. Several methods can be used to determine dielectric properties [8] depending on the structure of the material. The coaxial probe technique is known for its broadband measurement and suitable for liquid and powdered materials [9][10] was used. In addition, when measuring agricultural materials, they are frequency, temperature and density dependence. 89