Papers by Keyword: Electromagnetic Wave

Abstract: ZnFe₂O₄ nanomaterials were prepared using a solid-state reaction method using high energy milling (750 rpm) for 30 hours and calcined at 1000°C for 5 hours. The characterizations used include XRD, SEM, VSM, and VNA. The measurement results show that the sample has a single phase with a cubic structure. The surface morphology of heterogeneous samples with a particle size of 250-400 nm shows magnetic performance with Ms 2.38 emu/g and Hc 11.29 kOe. The sample also can absorb electromagnetic waves in the frequency range of 2-18 GHz with a minimum RL value of ~-18.79 dB at a frequency of 3.66 GHz, while RL ~-13.32 dB has a bandwidth of 0.9 GHz.

Abstract: Conductivity tensor is an important concept in materials, this work studies conductivity tensors in cylindrical quantum wires with parabolic potential in the presence of two external fields, a linearly polarized electromagnetic wave, and a laser field. This work is also only considered for the case of electron-acoustic phonon scattering. Research results are obtained by using quantum kinetic equations for the carrier system in a quantum wire. The conductivity tensor is calculated by solving the quantum kinetic equation of the system, which is a function of the external field frequency, the external field amplitude, the temperature of the helium, and parameters specific to the quantum wire. Results will also be examined and plotted for quantum wire GaAs / GaAsAl.

Abstract: The heating mechanism of electric and magnetic loss materials under microwave irradiation is expounded. The heating rate, material composition and road performance of four kinds of microwave ice and snow roads including carbon fiber, magnetite ore, steel fiber and ferrite are reviewed. And analyze their respective characteristics and applicable conditions. The problems existing in microwave melting ice and snow technology are discussed, and the application prospects of electromagnetic wave absorbing materials in microwave melting ice and snow road are prospected.

Abstract: In this paper, a novel microwave absorber of thin, light weight, flexible, green and low cost magnetic nanocomposite sheet that can work in high frequency range is fabricated. The vast and increasing numbers in electronic and telecommunication devices has create electromagnetic interference (EMI) in which may lead to application disturbance. Therefore, electromagnetic (EM) wave absorber with the ability of high absorption rate is strongly demanded. Here, durian shell (Durio zibethinus Murray) embedded magnetite (Fe₃O₄) nanocomposite sheets were prepared via pulping and lumen loading technique. The nanocomposite sheets were fabricated by varying the weight percentage of the filler content (2-10 wt% of Fe₃O₄) at constant thickness and varying the thickness of the sheets (0.1-1.0 mm) at constant filler content. FESEM micrograph shows that the Fe₃O₄ nanoparticles are in cubical and spherical shape with the 20–50 nm of size range. The microwave absorption properties of the sheets were tested by a vector network analyze (VNA) in the frequency range of 4-18 GHz. The samples were also tested using vibrating sample magnetometer (VSM) in order to study the magnetic properties. The absorption or maximum reflection loss (R_L) of the samples increases continually and the increase of both filler content and sample thickness has led to the shift of dip to lower frequency region.

Abstract: A nondestructive method is designed and employed to monitoring the early hydration of concrete mixes. The concrete mixes are prepared with Portland cement content and water to cement ratio 0.45. Retarder (citric acid) and accelerator (triethanolamine) are used to investigate the effects on the hydration process. The variations of dielectric constant and the intensity of reflected EM wave (amplitude) are measured within the frequency of 1.5GHz using Ground Penetrating Radar (GPR) at 25 °C for each sample from 10min to 3 days after mixing with water. The electric resistivity of Portland cement paste samples is measured using a non-contacting electric resistivity device at 25 °C.The amplitude tested changes sharply corresponding to the changes of microstructure and hydration products in the concrete mix during early hydration. The relative dielectric constant decreases with increasing hydrating time. The electrical resistivity changes in agreement with the dielectric properties. The dielectric properties mainly depend on the electrical properties and water content. The test results of samples in presence of retarder and accelerator shows that the relative dielectric constant decrease slower and faster respectively compared to the plain sample. The effect of these two admixtures can be reflected on the amplitude-time curve. The results demonstrate that the dielectric properties of concrete mix can be used as an effective ways of studying the hydration progress of concrete during hydration.

Abstract: In order to clarify the relationship between the mechanical properties of synthetic quartz and the electromagnetic phenomena during its fracture, a series of uniaxial compression tests were carried out at quasi-static and dynamic rates. Not only the stress-strain curves but also the output of ferrite-core antenna located close to the specimens were measured in a shield box made of permalloy plates. Since the synthetic quartz has three characteristic axes, i.e. optical axis, electric axis and machine axis, the effect of loading direction on the mechanical properties and electromagnetic phenomena of quarts was also examined. The dynamic compressive strength was greater than those in static tests and there is strain-rate dependence in their strength of synthetic quartz. It was also found that there are not any remarkable differences due to the loading direction with respect to the intensity of electromagnetic waves measured in the dynamic compression tests, i.e. the electromagnetic phenomenon does not depend on the loading direction.

Abstract: The importance of knowing dielectric value on a medium is to perceive the capability of conducting electromagnetic wave. Most of failure on electromagnetic instruments, were due to an inaccuracy of selecting material. Improper usage of materials may cause the attenuation of electromagnetic energy. So, it is important to measure the attenuation value. In this study, we compared the attenuation value on three media such as clay, silicon and wood. The problem mentioned above, could resolved by applying the electromagnetic propagation formula using skylab program. In this study we compared the effect constitutive parameters to the attenuation value and frequency in three media. The result shows, among three materials, at the same frequency we obtain that electromagnetic energy much easily attenuated on clay compared to other materials followed by silicon and wood. The reason is due to the conductivity value. In this study, we obtain that clay is the most sensitive on attenuation value on frequency followed by silicon and wood.

Abstract: Monodisperse CoFe₂O₄ and Co_0.4Zn_0.6Fe₂O₄ hollow nanospheres were synthesized in large scale by solvothermal method in ethylene glycol solution. The structure, shape and size of the samples were investigated by Fourier Transform infrared, X-ray powder diffraction and scanning electron microscopy. The results indicate that the products are spherical with an average diameter less than 200 nm. Magnetic studies revealed that the saturation magnetization of Co_0.4Zn_0.6Fe₂O₄ is 78.6 emu/g, higher than the CoFe₂O₄, which is 69 emu/g, while the coercivity of the Co_0.4Zn_0.6Fe₂O₄ is 184 Oe , obviously lower than that of CoFe₂O₄ which is 832 Oe. The electromagnetic parameters were measured at 2-18 GHz using HP8722ES vector network analyzer and then the microwave absorption properties were calculated through the transmission line theory. As to the Co_0.4Zn_0.6Fe₂O₄, the absorption bandwidth with reflection loss below-10 dB is up to 3GHz, from 10GHz to 13GHz with a thickness of 2 mm. A maximum reflection loss-45.6 dB was found at 12.9 GHz for the CoFe₂O₄ with a thickness of 1.8 mm. As a result, the as-prepared hollow nanospheres show good prospects of being applied in EM wave absorption materials.