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Electric and Magnetic Properties of Biological Materials
Published in Ben Greenebaum, Frank Barnes, Bioengineering and Biophysical Aspects of Electromagnetic Fields, 2018
Camelia Gabriel, Azadeh Peyman
A model that combines features from Debye-type and universal dielectric response behavior was proposed by Raicu (1999). In the course of modeling broad dielectric dispersions, as is often observed in the dielectric spectrum of biological materials, Raicu (1999) found that neither approach was good enough over a wide frequency range. He proposed the following very general function
Dielectric properties of calcium-substituted lanthanum ferrite
Published in Journal of Asian Ceramic Societies, 2020
Refka Andoulsi-Fezei, Nasr Sdiri, Karima Horchani-Naifer, Mokhtar Férid
The present work is a contribution to the study of the dielectric properties of La0.8Ca0.2FeO3-δ. As concerns the electric properties, complex impedance spectroscopy analyses were carried out. The dielectric data were analyzed based on the universal dielectric response model. The present study reveals interesting features. In fact, a gigantic dielectric constant is obtained at different temperatures. At low frequencies, both ε’ and tan(δ) show a dispersive trend. This behavior was explained based on the Maxwell Wagner polarization model. On the other hand, we proposed the most likely mechanism for explaining the observed dielectric behavior. The variations in ε” with frequency obey Giuntini’s law. From the dielectric data, we estimated the binding energy (Wm). It increases from 0.22 to 0.34 eV when the temperature rises from 350 to 800°C. However, the minimum hopping distance (Rmin) shows a decreasing trend from 2.16 to 0.12 pm. As concerns the modulus analyses, the results show that the short-range movement of charge carriers dominates the relaxation process at 350°C, whereas at 400 and 500°C, the long-range movement becomes predominant.
Dielectric characterisation of rock aggregates with different grain size distributions
Published in Road Materials and Pavement Design, 2023
Benhui Fan, Frédéric Bosc, Benjamin Smaniotto, Zhong-Sen Li, Jinbo Bai, Cyrille Fauchard
The real and imaginary parts of dielectric permittivity can be derived from the Kramers–Kronig relationships (Alvarez et al., 1991): Several models have been developed based on this relationship, for example, Debye model and its derivatives such as Cole–Cole and Cole-Davidson models that have large applications in electrochemistry. In the case of construction materials, Jonscher universal dielectric response has been widely used to fit the dielectric properties by the electric susceptibility (Bourdi et al., 2008; Ihamouten et al., 2018; Jonscher, 1999). To do the fitting by Jonscher model, the Origin non-linear curve fitting programme has been used to optimise the parameters by multiple iterations. where ε0 = 8.854 × 10−12 F/m is the permittivity of free space; ε∞ (F/m) is the limiting high-frequency value of the real part of the effective permittivity. n is an empirical parameter without dimension that characterises the charge in the amplitude as a function of frequency. Its value is usually between 0 and 1. χr is the real part of the electric susceptibility to the frequency. ωr is a reference radial frequency for the fitting. The parameters used in the model are listed in Table 4. It can be found that the Jonscher model can be well fitted for all 10 samples with the correlation coefficient R2 approaching 1. This allows us to use the fitting parameters to derive the dielectric constant at higher frequencies that are not reached by the analyzer impedance. As mentioned before, the resonant frequency in the cavity is 540 MHz, then the dielectric constants at 540 MHz for the 10 LA discs are calculated, and the results are as listed in Table 4. The average dielectric constant of the 10 LA discs is about 5.47 ± 1.04. The result indicates a scatter of the dielectric constant for the 10 pieces of aggregates. Some empirical equations based on the relationship between the dielectric constant and density may help us estimate the dielectric constant of the aggregates [4, 18, 19] though they can hardly give an exact value. The calculated values based on three empirical equations have been listed in Table 5. Compared with the values deduced by Shutke, the average value of 5.5 fitted by the Jonscher model can be viewed as a reasonable reference for the LA samples. Although a simple average may be arbitrary and less representative of the whole aggregates, we must mention again that our primary interest in this part is to obtain the dielectric constant of the aggregates at high frequency that can be compared with the values calculated by mixing laws based on method 2 and method 3.