Numerical simulation and dimension reduction analysis of electromagnetic logging while drilling of horizontal wells in complex structures

Electromagnetic logging while drilling(LWD)is one of the key technologies of the geosteering and formation evaluation for high-angle and horizontal wells.In this paper,we solve the dipole source-generated magnetic/electric fields in 2D formations efficiently by the 2.5D finite diff erence method.Particularly,by leveraging the field’s rapid attenuation in spectral domain,we propose truncated Gauss–Hermite quadrature,which is several tens of times faster than traditional inverse fast Fourier transform.By applying the algorithm to the LWD modeling under complex formations,e.g.,folds,fault and sandstone pinch-outs,we analyze the feasibility of the dimension reduction from 2D to 1D.For the formations with smooth lateral changes,like folds,the simplified 1D model’s results agree well with the true responses,which indicate that the 1D simplification with sliding window is feasible.However,for the formation structures with drastic rock properties changes and sharp boundaries,for instance,faults and sandstone pinch-outs,the simplified 1D model will lead to large errors and,therefore,2.5D algorithms should be applied to ensure the accuracy.

Optical colorimetric LiTaO_(3)wafers for highprecision lithography on frequency control of SAW devices

Surface acoustic wave(SAW)resonators based on lithium tantalate(LT,LiTaO_(3))wafers are crucial elements of mobile communication filters.The use of intrinsic LT wafers typically brings about low fabrication accuracy of SAW resonators due to strong UV reflection in the lithography process.This hinders their resonance frequency control seriously in industrial manufacture.LT doping and chemical reduction could be applied to decrease the UV reflection of LT wafers for high lithographic precision.However,conventional methods fail to provide a fast and nondestructive approach to identify the UV performance of standard single-side polished LT wafers for highprecision frequency control.Here,we propose a convenient on-line sensing scheme based on the colorimetry of reduced Fe-doped LT wafers and build up an automatic testing system for industrial applications.The levels of Fe doping and chemical reduction are evaluated by the lightness and color difference of LT-based wafers.The correlation between the wafer visible colorimetry and UV reflection is established to refine the lithography process and specifically manipulate the frequency performance of SAW resonators.Our study provides a powerful tool for the fabrication control of SAW resonators and will inspire more applications on sophisticated devices of mobile communication.

The Spectral Integral Method(SIM)for the Scattering from an Arbitrary Number of Circular PEC Cylinders

We present an accurate spectral integral method(SIM)for the analyses of scattering from multiple circular perfect electric conductor(PEC)cylinders.It solves the coupled surface integral equations by using the Fourier series and addition theorem to decouple the system.The SIM has exponential convergence so that the error decreases exponentially with the sample density on the surfaces,and requires only about 2–3 points per wavelength(PPW)to reach engineering accuracy defined as higher than 99%accuracy(or with an error smaller than 1%).Numerical results demonstrate that the SIM is much more accurate and efficient than the method of moments(MoM),and thus can be potentially used as the exact radiation boundary condition in the finite element and spectral element methods.

Multiple resonant excitations of surface plasmons in a graphene stratified slab by Otto configuration and their independent tuning

Multiple resonant excitations of surface plasmons in a graphene stratified slab are realized by Otto configuration at terahertz frequencies. The proposed graphene stratified slab consists of alternating dielectric layers and graphene sheets, and is sandwiched between a prism and another semi-infinite medium. Optical response and field distribution are determined by the transfer matrix method with the surface current density boundary condition.Multiple resonant excitations appear on the angular reflection spectrum, and are analyzed theoretically via the phase-matching condition. Furthermore, the effects of the system parameters are investigated. Among them, the Fermi levels can tune the corresponding resonances independently. The proposed concept can be engineered for promising applications, including angular selective or multiplex filters, multiple channel sensors, and directional delivery of energy.

A Hybrid FETD-FDTD Method with Nonconforming Meshes

A quasi non-overlapping hybrid scheme that combines the finite-difference time-domain(FDTD)method and the finite-element time-domain(FETD)method with nonconforming meshes is developed for time-domain solutions of Maxwell’s equations.The FETD method uses mixed-order basis functions for electric and magnetic fields,while the FDTD method uses the traditional Yee’s grid;the two methods are joined by a buffer zone with the FETD method and the discontinuous Galerkin method is used for the domain decomposition in the FETD subdomains.The main features of this technique is that it allows non-conforming meshes and an arbitrary numbers of FETD and FDTD subdomains.The hybrid method is completely stable for the time steps up to the stability limit for the FDTD method and FETD method.Numerical results demonstrate the validity of this technique.

Wideband high-efficient linear polarization rotators

We demonstrate a wideband polarization rotator with characteristics of high efficiency and large-range incidence angle by using a very simple anisotropic reflective metasurface. The calculated results show that reflection coefficient of cross polarization is larger than 71% over an octave frequency bandwidth from -4.9 GHz to -10.4 GHz. The proposed metasurface can still work very well even at incidence angle of 60°. The experiment at microwave frequencies is carried out and its results agree well with the simulated ones.

Fast Inhomogeneous Plane Wave Algorithm for Homogeneous Dielectric Body of Revolution

To solve the electromagnetic scattering problem for homogeneous dielectric bodies of revolution(BOR),a fast inhomogeneous plane wave algorithm is developed.By using the Weyl identity and designing a proper integration path,the aggregation and disaggregation factors can be derived analytically.Compared with the traditional method of moments(MoM),both the memory and CPU time requirements are reduced for large-scale homogeneous dielectric BOR problems.Numerical results are given to demonstrate the validity and the efficiency of the proposed method.