Electromagnetic Characterization of a Composite (RE-CB-MT) by Time Domain Spectroscopy

The aim of this article is to study the dielectric behavior (ε, σ) in microwaves domain of composites made with Epoxy Resin (RE), Carbon Black (CB), and Magnesium Titanate (MT) on a large band of frequency. This kind of composites is very solicited for applications and miniaturization of the components circuits (cavities, antennas, substrates, etc.) in hyperfrequency electronics. In this study we have also highlighted the effect of the fillers nature and their concentrations on the behavior of these composites. The results obtained by time domain spectroscopy (TDS) have revealed the strong dependence of complex permittivity of the composite materials on both the nature and the concentration of conductive environment. Low frequency analysis (500 MHz) has been investigated to determine the conductivity of composites which is related to the percolation phenomenon. Moreover, the comparison between experimental results and theoretical models shows that the modeling Lichtenecker law is applicable to the ternary mixture in this frequency range and is in accordance with the approach postulated by Bottreau.

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Polarizability of Aspirin at Terahertz Frequencies Using Terahertz Time Domain Spectroscopy (THz-TDS)

Applied Spectroscopy ◽

10.1177/0003702818815177 ◽

2018 ◽

Vol 73 (3) ◽

pp. 253-260 ◽

Cited By ~ 2

Author(s):

Tianyao Zhang ◽

Zhaohui Zhang ◽

Mark A. Arnold

Keyword(s):

Time Domain ◽

Low Frequency ◽

Field Vector ◽

Organic Crystals ◽

Frequency Range ◽

Terahertz Time Domain Spectroscopy ◽

Time Domain Spectroscopy ◽

Time Domain Signal ◽

Pulse Experiment ◽

Measured Time

A novel application of terahertz time-domain spectroscopy (THz-TDS) is described for the determination of permittivity and polarizability of organic crystals, as exemplified by measurements with the polymorph I form of crystalline aspirin (acetylsalicylic acid). The coherent nature of the THz pulse experiment, coupled with gated-detection, permits direct measure of differences in the phase angle of the electric field vector after passing through a pellet composed of the aspirin crystals embedded within an inert polymer matrix. An effective media model is used to extract dielectric information for the crystals from the measured time-domain signal that is representative of the entire pellet composition. Polarizability is then obtained for these organic crystals by using the Clausius–Mossotti relationship. Dielectric spectra and polarizability spectra are presented over the 0.3–3 THz frequency range (10–100 cm−1). The average polarizability values measured over the low frequency range (10–20 cm−1) are 22.4 ± 0.3 and 22.4 ± 0.5 Å3 for aspirin crystals embedded within matrixes of polytetrafluoroethylene (PTFE) and polyethylene (PE), respectively.

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Synthesis and Characterization of Magnetoelectric Nanocomposites

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.155.173 ◽

2009 ◽

Vol 155 ◽

pp. 173-188

Author(s):

Kanhaiya Lal Yadav

Keyword(s):

Annealing Temperature ◽

Strong Dependence ◽

Low Frequency ◽

Magnetic Characteristics ◽

Frequency Range ◽

Field Frequency ◽

Maximum Value ◽

Citrate Gel Process ◽

Small Crystallite

A simple citrate gel process was used to prepare nanocomposites of xCuFe2O4–(1−x)BiFeO3 (henceforth, CFBF) and xNi0.75Co0.25Fe2O4-(1-x)BiFeO3 (henceforth, NCFBF) with x=0.1, 0.2, 0.3 and 0.4. The phase was found to be formed at 500 °C and 700 °C for CFBF and NCFBF respectively. TEM observation showed that the average particles size is around 40 nm. The variation of the dielectric constant and the dielectric loss with frequency showed dispersion in the low frequency range. All the samples exhibit strong magnetic characteristics. The coercivity and squareness increased with the increase in annealing temperature and were maximum for samples annealed at 500°C and 700°C for CFBF and NCFBF nanocomposites, respectively, and further decrease in coercivity is attributed to decrease in aspect ratio and pinning effects in the nanocrysatllites. The ME coefficient αE showed strong dependence on HBias and maximum value of ME coefficients were 303 and 309 mV/cm Oe at magnetic field frequency of 50 kHz for CFBF and NCFBF nanocomposites respectively. The large values of ME coefficients are attributed to low coercivity, large magnetization and small crystallite size of constituent phases.

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