The real part of the relative permittivity, �š�r, is called the dielectric constant, but one must note that it is not constant in frequency. The ratio of the imaginary part to real part selleck bio is called the loss tangent, exactly tan�� = �š�r/ �š�r.Some researchers have studied and reviewed the dielectric properties of textiles [19�C21]. As textile materials are anisotropic materials, their characterization also depends on the electric field orientation. This anisotropy is fully described with a permittivity tensor, although in most practical applications like the ones surveyed in this paper, a specific component of this tensor is enough to characterize the behaviour of the textile material Inhibitors,Modulators,Libraries Inhibitors,Modulators,Libraries for a specific application.
Thus, the relative permittivity describes the behaviour of the material tested under a specific electric field orientation and frequency.
The dielectric behaviour of Inhibitors,Modulators,Libraries textile materials depends on the properties of the constituent fibres and polymers [19], and on the fibre packing density in the fibrous material [18,20]. However, textile fabrics are rough, porous and heterogeneous, having air in between the fibres, making their characterization difficult [23]. In addition, Inhibitors,Modulators,Libraries the ability of the fibres to Inhibitors,Modulators,Libraries absorb moisture must also be considered in the characterization of the dielectric Inhibitors,Modulators,Libraries behaviour of textiles, as will be explained further in Section 2.4.
Thus, the accurate measurement of dielectric characteristics of textiles is challenging and different experimental Inhibitors,Modulators,Libraries techniques have been used, such as the Cavity Perturbation Method [4,10], MoM-segment method [9], Resonance Method [21], Free Space Method [24] and Transmission Line Method [25�C27].
Among these techniques, the simplest ones and thus very promising ones are the techniques based on the measurement of the behaviour of transmission lines [25�C27].In general, Inhibitors,Modulators,Libraries textiles present a very low dielectric constant as they are very porous materials and the presence of air approaches the relative permittivity to one. As an example, Table 1 shows the dielectric properties of normal textile fabrics, possible dielectric substrates, that were Batimastat obtained with a waveguide cavity method, under 2.6 GHz [10].Table 1.Dielectric Properties of normal fabrics tested in [10].
The low dielectric constant reduces the surface AV-951 wave losses which are tied to guided wave propagation within the substrates.
Therefore, lowering neverless the dielectric constant increases spatial waves and hence increases the impedance bandwidth of the antenna, allowing the development of antennas with acceptable efficiency and high gain [3,28�C30]. Again, one should note that the relative permittivity value changes with the moisture content of the substrate affecting thenthereby the bandwidth of the antenna [2,29].2.2. Thickness of the Dielectric FabricsThe bandwidth and efficiency performance of a planar microstrip ant
Performing accurate and reliable experimental observations is a major challenge in modern hydrology [1,2].