Papers by Keyword: Reflection Coefficient

Abstract: The manuscript investigates the leaf-shaped nanostrip-fed graphene plasmonic nanopatch on a silicon dioxide surface for optical near-field applications. The dispersion properties of graphene and silicon dioxide are demonstrated through Drude and Lorentz modeling to examine the suitability of the materials for the plasmonic nano-antenna design. The nano-antenna parameters T_SUB (substrate thickness), W (width of the nanostrip feed line) and R_L (nano-antenna size) are adjusted to modify the plasmonic resonance frequency from 7.9 THz to 40.9 THz. The proposed leaf-shaped nanostrip-fed graphene plasmonic nanopatch exhibits a reflection of -43.27 dB at 36 THz with a gain of 8.19 dB at T_SUB =125 nm, W = 40 nm and R_L = 50 nm.

Abstract: A mathematical model of diffraction of electromagnetic microwaves on explosive materials with different physical and electromagnetic parameters has been developed. The model was constructed by solving Maxwell's equation for two surfaces separating three dielectric materials, in particular air, explosive material, and the substrate on which the explosive material is located. Different types of soil and wood are considered as the substrate material, which meets the conditions for demining large areas of the locality. The results of the numerical calculation showed that 67 % to 92 % of the energy of electromagnetic radiation is concentrated in the explosive material. In this case, trinitrotoluene, which is placed on dry sand, has the highest absorption rates, while wet wood, due to its high coefficient of dielectric permittivity, successfully transmits electromagnetic microwaves through its surface. The obtained models and numerical results are considered as theoretical basis for predicting the effectiveness of remote methods of detection and disposal of explosive materials using electromagnetic microwaves. The obtained results showed that this method will be least effective for explosive materials placed on wet wood. In this case, the lowest reflection coefficient is observed that complicates the search for explosive material and the lowest absorption coefficient that complicates the artificial detonation of explosive material due to its heating under the influence of electromagnetic microwaves.

Abstract: Nano- and microstructured composite materials have opened a new era for multifunctional materials. In particular, barium hexaferrites and carbon nanotubes can be applied in order to improve electromagnetic properties in composites. Magnetic materials with a texture based on barium ferrite and carbon nanotubes were obtained. The electromagnetic properties of Z – hexaferrites / carbon nanotubes composites were measured at microwave frequencies. It was shown, that imaginary permeability of barium hexaferrites/carbon nanotubes multilayer composites with double texture is as much as that of an isotropic samples at regions 3.4 – 8.5 GHz and 7.1 – 11.6 GHz.

Abstract: The study of signals propagation inside porous media is an important field especially in the biomedical research related to compact bones. The purpose of this paper is to determine a mathematical formulation of the global coefficients of transmission and reflection of nondestructive ultrasonic waves in any bi-phase porous medium. Local coefficients of transmission and reflection on the interface of the porous medium will be determined based on a study of boundary conditions. The behavior of different waves inside the porous medium will be developed so that we can derive a new formulation of global coefficients that takes interior phenomena into consideration. Results are found independently of the geometrical and physical characteristics of the medium. Note that this study is based on normal incident ultrasonic wave propagation.

Abstract: Microstrip ring resonator (MRR) sensor was modeled by simple equivalent lumped element circuits in free space based on simulation data obtained from Microwave Office (AWR) simulator and comparison was made with the measurements using the E5071C Network Analyzer. The calculated reflection coefficient, |G| and complex input impedance Z_in using lumped element model were compared with the measurements results. Both results showed well agreement with a little discrepancy, basically due to imperfect soldering. The MRR was designed to have operating frequencies between 0.5 GHz and 4.5 GHz. The maximum surrounding of magnetic field, H_ϕ is within 15 A/m in free space.

Abstract: PZT-based ultrasonic guided wave has played an important role in health monitoring of pipeline structures. By using the PZT-based ultrasonic guided wave energy method and finite element software ABAQUS, the numerical simulation is performed to analyze various corrosion damaged pipeline structures, emphasizing on the damage identification, sensitivity analysis and longitudinal energy attenuation of the guided wave along various corrosion damaged pipelines. The preliminary analysis of the echo signals shows that the grass-like clutter wave belongs to echoes of the corrosion damage of the pipeline, and the wave energy spreads faster here. At the same time, by frequency spectrum analysis of the echo signal, the relationship between the reflection coefficient and the radial depth of defection is made which can be used to approximately evaluate geometrical dimension of the damage.

Abstract: Ultrasonic guided wave quantitative detection technology has not been widely studied; this limits the application and development of guided waves testing technology greatly. For the quantitative detection study of notches in pipes, the theoretical model of guided waves interacted with notches has been built. Through the model, the relation formula between reflection coefficient and defects axial length and depth has been derived. The relation curves have been plotted based on the relation formula. And then, experiment method was used to verify the curves, the two methods can agree with each other. At last, the size of the defect was evaluated through the theoretical relation curves, the evaluation agrees with the practical size relatively. The research results provide necessary guide in theory to the defects quantification of guided wave detection.

Abstract: Long-External Cavity Laser (L-ECL) is a kind of new and promising type laser because of its dynamic single mode performance. In this paper, firstly, the theory model of L-ECL is discussed; Secondly, the influence of coupling coefficient on the threshold gain of L-ECL is studied based on equivalent external cavity theory; Thirdly, utilizing the theory of equivalent cavity length, combined rate equations, the high frequency response characteristic of L-ECL is analyzed; Lastly, optical spectrums of L-ECL on different grating peak reflectivity are obtained by experiment.

Abstract: With the rapid development of China's national economy, oil and gas development and utilization of resources is also increasing, dwindling reserves of conventional oil and gas reservoirs. These inevitably lead to oil and gas exploration direction shifted gradually from shallow depth, by a conventional steering reservoir unconventional oil and gas reservoirs, fractured reservoirs will become the focus of the current oil and gas exploration areas. This paper studied the basic theory of fractured media, from the speed and the amplitude of pre-stack anisotropic characteristics are analyzed theoretically. Researches of these basic theories of EDA media provide a basis for the exploration of the fractured reservoirs.

Abstract: In order to improve the resolution and accuracy of the inversion, this paper proposed a new inversion method. By introducing constraint sparse spike inversion, the new method can fully take the advantages of high vertical resolution of logging data and the preferable transverse continuity of the seismic data to improve the resolution of the profiles and the quality of imaging and inversion in specific areas. Experimental results showed that this solution can deduce more precise and reasonable inversion result than other inversion solution. Constraint sparse spike inversion can generate reflection coefficients with broad frequency band and solve the marking problems preferably, thereby makes the impedance model obtained from the inversion even close to the actual situation underground.