Effect of beneficiation of Harin-Hamza Futuk bentonite for drilling fluid formulation

This research focused on beneficiation and characterization of raw Garin Hamza Futuk (GHF) Bentonite for oil and gas drilling fluid formulation. The FTIR results confirmed that GHF bentonitic clay is rich in montmorillonite mineral noticed at approximately 3620-3630cm-1 stretching band in the higher frequency level. In the lower frequency region, montmorillonite had a strong band at 1024.24 and 1028.09 cm-1 for Sivibration of layered silicates.The X-ray fluorescence (XRF) results showed slight reduction in free silica (Quartz) by about 1%. The SEM images of the beneficiated samples were more dispersed than the raw sample with some large flocs structure confirming their montmorillonitic nature. The optimum amount of poly anionic cellulose (PAC)used for instant drilling fluid formulation was found to be at 2.0 g, while the aged formulation was achieved at 0.8g PAC when compared with the API grade. Hence, GHF bentonite can be used for drilling fluid formulation.

Binomial stub loaded compact Vivaldi antenna for superwideband applications

A compact antipodal Vivaldi antenna with superwideband characteristics is presented in this paper. For improved matching of input impedance at lower frequency region, techniques like binomial tapering of outer edges, binomial slit loaded outer edge, and protruded binomial tapered stub loading have been adopted. The antenna operates in a wide frequency range from 2 to 20 GHz. Experimental results show, stable radiation pattern with peak realized gain of more than 8 dBi, group delay within 1 ns, 164% fractional bandwidth, radiation efficiency of more than 90%, which are in good agreement with the simulated results. The compact size of the proposed antenna (1.14λ0 × 1.21λ0) with wide frequency bandwidth and directional radiation characteristics make it suitable for through-wall radar and medical imaging applications.

Influence of Microstructure-Evolution Changes on the Dielectric Properties of Strontium Titanate Prepared via Mechanical Alloying

SrTiO3 is a dielectric material of considerable interest. However, the relationships between microstructure and dielectric properties have not been studied in detail. Hence, we have undertaken an extensive experimental work to study the evolution of the dielectric properties against morphological changes of SrTiO3. SrTiO3 was prepared using the mechanical alloying method and samples with nano-sized starting powder were obtained. The milled powder was pressed into pellets and sintered at various temperatures ranging from 500 °C to 1400 °C. XRD studies showed that these ceramics completely formed a perovskite phase at 900 °C. FeSEM studies show the presence of small grain sizes ranging from 120 to 600 nm. Dielectric constant (εr’) and dielectric loss tangent (tan δ) were measured as a function of frequency and correlated with the microstructure. εr’ and tan δ against frequency show a falling trend at the lower frequency region due to the changing interfacial effect. For sintering temperatures 1000 °C to 1100 °C, grain size and XRD peak data show a significant increase with the corresponding increase in εr’, suggesting a sudden increase in the polarizability due to significant increase in crystallinity. With increasing sintering temperature, εr’ increased proportionally with XRD peak and grain size increases, further confirming polarizability and crystallinity relationship. tan δ correlation with microstructure does not have a common trend.

Synthesis and Characterization of PANI/PVDF Composites for Dielectric and AC Conductivity

The polymer composites of polyaniline (PANI) with PVDF have been synthesized by polymerization method. The different composites of PANI with PVDF are obtained by adding 0.5, 1, 1.5, 2 and 2.5 N solutions of PVDF during the polymerization to get the PANI/PVDF composites. The synthesized samples of PANI and composite of PANI with PVDF polymer were characterized by using X-Ray diffraction (XRD). The dielectric properties such as dielectric constant, dielectric loss and AC conductivity for the composites of PANI/PVDF at different weight percentages are studied as a function of frequency in the range 5 Hz–35 MHz at ambient temperature. It is found that the dielectric permittivity decreased exponentially at lower frequency region up to 300 Hz and then the dielectric permittivity remains constant at higher frequency region as the frequency increased. It is also observed that the dielectric permittivity increased as the concentration of PVDF in the polymer composite increased as compared to PANI. Further, it is observed that the dielectric loss increased as a weight percentage of PVDF increased in the composite of PANI. In case of AC conductivity as the frequency increased the AC conductivity remains constant up to 6.75 MHz and afterwards it increases as frequency increased. This is due to the increase in charge carriers through the hopping mechanism in the polymer composites. It is also observed that as a weight percentage of PVDF increased the AC conductivity is also increased

Microwave Absorbing Property of Thin Coating in the Broadband Low-Frequency Range

Coatings with flake carbonyl-iron powder as absorber and polyurethane resin as matrix were prepared. The complex permittivity, complex permeability and microwave-absorbing properties were investigated in the frequency range of 2–18 GHz. Both the complex permittivity and permeability of the flaky carbonyl-iron were increased compared to the spherical powders. The minimum reflection loss decreased and the matching frequency shifted to the lower frequency region with increase in the coating thickness. The band width can reach nearly 16GHz as the RL was below than-4 dB with thickness only 1.4 mm. The minimum reflection loss value of-14.5 dB was obtained at 3.56 GHz for the 1.6mm coatings with 89 wt% carbonyl-iron powders. These results showed that the coatings were favorable for the broadband low-frequency microwave absorption with a small thickness.

Effect of Ti Content on Microwave Absorbing Properties of Nd-Fe Alloys

The Nd7.69Fe92.31-xTix (x = 0, 4, 8, 12) alloy were prepared by arc smelting and high energy ball milling method. The morphology and phase structure of the powders were analyzed by Scanning Electron Microscope (SEM), X-ray diffraction (XRD) and the effect of the Ti content on microwave absorbing properties of the powders were measured by a vector network analyzer (VNA). The results reveal that the samples mainly consisted of Nd2Fe17 and α-Fe crystal structure. The minimum absorption peak frequency shifts to lower frequency region firstly and then shifts to higher frequency region with the increasing amount of Ti content. The minimum reflection loss of Nd7.69Fe84.31Ti8 powder is-31.35 dB and the bandwidth of R < -5 dB reach 3.6 GHz when the coating thickness is 2.0 mm. With the increasing of the coating thickness, the minimum reflectivity peak value of the Nd7.69Fe84.31Ti8 moves to lower frequency region and the minimum reflection loss increase firstly and then decrease. And the minimum reflection value of Nd7.69Fe84.31Ti8 alloy can reach to-38.74 dB (microwave absorption rate 99.99%) at 5.68 GHz, and the bandwidth of R < -10 dB reach 1.12 GHz with the best matching thickness of 2.2 mm.

Extraction of Cochlear Non-linearities with the Bispectral Analysis

SummaryObjectives: Transient Otoacoustic Emission (TEOAEs) are low intensity sounds generated by active mechanisms in the cochlea and elicited by broadband and short acoustic stimuli. TEOAEs are a quick, non-invasive, and very reliable measure to objectively assess the peripheral auditory system. In the current study, we present a recent technique to extract and evaluate non-linearities in TEOAEs, and apply it for the preliminary analysis of TEOAE recordings of a group of worker of a fiberglass manufacturing facility exposed to styrene solvent.Methods: Bispectral analysis was applied to TEOAEs to extract the quadratic frequency couplings (QFCs) in TEOAEs. Amplitude of QFCs was calculated in a group of 7 styrene-exposed workers (14 ears) and compared with normative results obtained on normal hearing young adults.Results: Difference in amplitude of QFCs were found between workers and controls. In workers, TEOAE non-linear components were found in the 1.5 – 4 kHz frequency range, whereas in control subjects they were found in a lower frequency region, ranging from 1 to 3 kHz.Conclusion: The amplitude of QFCs highlighted differences in TEOAEs recorded among workers and controls.

Structure and Diffused Ferroelectric Properties in Ba(Ti0.8Sn0.2)O3 Ceramics

Temperature-dependent Raman scattering, dielectric properties, and Impedance spectra have been carried out on Ba(Ti0.8Sn0.2)O3 ceramic sample. The number of modes observed for the compositions of cubic symmetry is more than that predicted by group theory, and the A1(TO1) and E(TO2) modes become Raman active below the critical temperature (around 300K) in the lower frequency region. This gives evidence that there are some deviations of the local structure from the average global symmetry. Moreover, The characteristic of A1(TO3) mode is confirmed be associated with the diffused dielectric properties. Impedance/modulus analyses indicate that a third resistance-capacitance (RC) response is present in the sample, in addition to the grain and grain-boundary RC elements above 573K. Thus, it probably inferred that the existence of inter- and/or intra-granular surface layers associate with the abnormal dielectric properties, which is different from the normal ferroelectrics. Variation of bulk ac conductivity as a function of temperature shows that Ba(Ti0.8Sn0.2)O3 follows the classical Arrhenius relation.The results show that the activation energy of grains and grain boundaries are 0.61 and ~1.08 eV, respectively.

Hexagonal Monopole Strip Antenna with Rectangular Slot for 100–1000 MHz SFCW GPR Applications

A printed ultra wideband (UWB) monopole antenna is proposed for applications on stepped frequency continuous wave (SFCW) ground penetrating radar (GPR) within a frequency range of 100–1000 MHz. The proposed antenna consists of a hexagonal strip line with resistive loading and a rectangular slot that is added to the ground plane side of the printed antenna implemented on FR4 epoxy materials. The resistive loading at the hexagonal monopole is effective to increase bandwidth in the higher frequency region, while the rectangular slot is used to improve bandwidth characteristic in the lower frequency region. This paper investigates the characteristic improvement in the lower frequency region by applying a parametric study on the rectangular slot that is added at the ground plane side of the UWB monopole antenna. Computer simulation was conducted and measurements were carried out to validate the result.