Jianyang Zhou

Enhanced spatial near-infrared modulation of graphene-loaded perfect absorbers using plasmonic nanoslits.

Modulating spatial near-infrared light for ultra-compact electro-optic devices is a critical issue in optical communication and imaging applications. To date, spatial near-infrared modulators based on graphene have been reported, but they showed limited modulation effects due to the relatively weak light-graphene interaction. In combination with graphene and metallic nanoslits, we design a kind of ultrathin near-infrared perfect absorber with enhanced spatial modulation effects and independence on a wide range of incident angles. The modulated spectral shift of central wavelength is up to 258.2 nm in the near-infrared range, which is more promising in applications than state-of-the-art devices. The modulation enhancement is attributed to the plasmonic nanoslit mode, in which the optical electric field is highly concentrated in the deep subwavelength scale and the light-graphene interaction is significantly strengthened. The physical insight is deeply revealed by a combination of equivalent circuit and electromagnetic field analysis. The design principles are not only crucial for spatial near-infrared modulators, but also provide a key guide for developing active near-infrared patch nanoantennas based on graphene.

Through-Casing Hydraulic Fracture Evaluation by Induction Logging II: The Inversion Algorithm and Experimental Validations

Evaluation of hydraulic fractures has been under intensive study since the last decade. Among published works, only a few have included casing effects. This paper focuses on the through-casing electromagnetic (EM) induction imaging method that evaluates hydraulic fractures with enhanced contrasts. An experimental system and an inverse scattering algorithm are presented. The laboratory scaled experimental system is built for the feasibility study of the EM induction imaging method for the through-casing hydraulic fracture evaluation. To develop the inverse scattering algorithm, fractures outside boreholes with metallic casing are modeled by a novel hybrid approximation method. This method combines the distorted Born approximation and the mixed order stabilized bi-conjugate gradient fast Fourier transform method to solve the forward scattering problem. The variational Born iterative method is applied to solve the nonlinear inverse problem iteratively. Experimental results show that the inverse scattering algorithm is effective for EM contrast enhanced through-casing hydraulic fracture evaluation.

Through-Casing Hydraulic Fracture Evaluation by Induction Logging I: An Efficient EM Solver for Fracture Detection

Hydraulic fracturing is an essential way to improve the production of unconventional shale oil and gas. It is important to characterize the produced fractures using either acoustic or electromagnetic (EM) methods. Conventional EM solvers in the low-frequency range face significant challenges by such multiscale problems where the fracture width is orders of magnitude smaller than its diameters. Furthermore, the cased borehole environment is extremely difficult to simulate with conventional EM solvers due to meshing difficulties and the multiscale nature of the problem. In this paper, we develop a hybrid distorted Born approximation and 3-D mixed ordered stabilized biconjugate gradient fast Fourier transform (DBA-BCGS-FFT) method to simulate the very challenging 2-D, 2-D-axisymmetric, and 3-D hydraulic fracture models under both open and cased borehole environments. Numerical examples show that this method has orders of magnitude higher efficiency than the finite element method. The capabilities of the DBA-BCGS-FFT method for the induction tool fracture mapping are demonstrated by comparing with laboratory experimental results and other reference results.

Application of mixed order BCGS-FFT on contrast enhanced oil reservoir imaging

Summary form only given. With the rapid advancements in material science and manufacturing technology, applications of materials with special properties have been widely expanded. Some specially made nanoparticles can be used as contrast agents to change the contrast modalities (ε, μ, and σ) of the unknown objects in electromagnetic imaging problem to improve the imaging quality. Due to the potentials of the enhanced contrast imaging, many attempts have recently been made to apply this technique to various fields, for example oil reservoir imaging. In the application of the contrast enhanced oil reservoir imaging, nanoparticles with large permittivity, magnetic permeability and/or electrical conductivity are injected to the reservoir through the injection well. As the nanoparticles propagate into the reservoir, the three contrast modalities of the oil can be significantly changed depending on the fluid saturation rate. The enhanced contrasts of the oil can result in a stronger scattered signal which will lead to an enhancement in imaging result. However, the low operating frequency and large contrast modalities of the nanoparticles can be challenging for currently available electromagnetic field solvers for scattering problems.

Large-Scale Uniform Silver Nanocave Array for Visible Light Refractive Index Sensing Using Soft UV Nanoimprint

In this paper, a wafer-scale uniform silver nanocave array is fabricated by soft ultraviolet nanoimprint lithography. We investigate its plasmonic effects using far-field and near-field experimental approaches and illuminate the physics inside by theoretical analysis and computational simulation. The array shows robust multispectral features for various surrounding media and possesses the sensitivity up to 514.7 nm/RIU in the visible range, which is promising for the mass production of high-performance plasmonic refractive index sensors.

Application of BCGS-FFT and distorted born approximation for hydraulic fracturing detection and imaging

With the ever increasing number of research on hydraulic fracture aiming at improved oil production, forward and inverse solvers based on electromagnetic method to detect and reveal properties of hydraulic fracture have become an important subject of research. Most of existing forward and inverse methods are developed to simulate the well logging model, such as Method of Moments (MoM) and Born Approximation. Those methods have the advantages to reconstruct the geometrical and electromagnetic information of formation. However, they are not fast enough and the memory cost are large. Moreover, when those methods are used to simulate hydraulic fractures, they are not able to obtain the accurate result.

Spectral element method for band-structure calculations of 3D phononic crystals

The spectral element method (SEM) is a special kind of high-order finite element method (FEM) which combines the flexibility of a finite element method with the accuracy of a spectral method. In contrast to the traditional FEM, the SEM exhibits advantages in the high-order accuracy as the error decreases exponentially with the increase of interpolation degree by employing the Gauss–Lobatto–Legendre (GLL) polynomials as basis functions. In this study, the spectral element method is developed for the first time for the determination of band structures of 3D isotropic/anisotropic phononic crystals (PCs). Based on the Bloch theorem, we present a novel, intuitive discretization formulation for Navier equation in the SEM scheme for periodic media. By virtue of using the orthogonal Legendre polynomials, the generalized eigenvalue problem is converted to a regular one in our SEM implementation to improve the efficiency. Besides, according to the specific geometry structure, 8-node and 27-node hexahedral elements as well as an analytic mesh have been used to accurately capture curved PC models in our SEM scheme. To verify its accuracy and efficiency, this study analyses the phononic-crystal plates with square and triangular lattice arrangements, and the 3D cubic phononic crystals consisting of simple cubic (SC), bulk central cubic (BCC) and faced central cubic (FCC) lattices with isotropic or anisotropic scatters. All the numerical results considered demonstrate that SEM is superior to the conventional FEM and can be an efficient alternative method for accurate determination of band structures of 3D phononic crystals.

The rotated cartesian coordinate method to remove the axial singularity of cylindrical coordinates in finite-difference schemes

SUMMARY When modelling the propagation of 3-D non-axisymmetric viscoelastic waves in cylindrical coordinates using the finite-difference time-domain (FDTD) method, one encounters a mathematical singularity due to the presence of 1/r terms in the viscoelastic wave equations. For many years this issue has been impeding the accurate numerical solution near the axis. In this paper, we propose a simple but effective method for the treatment of this numerical singularity problem. By rotating the Cartesian coordinate (RCC) system around the z-axis in cylindrical coordinates, the numerical singularity problems in both 2-D and 3-D cylindrical coordinates can be removed. This algorithm has three advantages over the conventional treatment techniques: 1) the excitation source can be directly loaded at r = 0; 2) the central difference scheme with second-order accuracy is maintained; 3) the stability condition at the axis is consistent with the FDTD in Cartesian coordinates. This method is verified by several 3-D numerical examples. Results show that the method is accurate and stable at the singularity point. The improved FDTD algorithm is also applied to sonic logging simulations in non-axisymmetric formations and sources. This article is protected by copyright. All rights reserved

Simultaneous Fabrication of Two Kinds of Plasmonic Crystals by One Nanoimprint Mold

Plasmonic crystals (e.g., metallic nanohole arrays and metallic nanoparticle arrays) are widely used in the field of nanophotonics due to their effects on light confinement. Soft nanoimprint lithography is a promising technology for large-scale production of high-quality plasmonic crystals in industry. However, this technology suffers from a high cost of the solid mold with a limited pattern for lithography. In order to reduce the cost, we develop an approach to simultaneous fabrication of both a plasmonic nanohole array and a plasmonic nanoparticle array by only using one solid mold. They show good morphological uniformity, and demonstrate high efficiencies of light trapping in the visible range and the infrared range, respectively. In combination with electromagnetic simulation, we can preliminarily design the expensive mold and guide the production of plasmonic crystals more efficiently.

Contrast enhanced through casing hydraulic fractures mapping

Hydraulic fracturing is being performed in more than 60 years in more than a million wells and counting. Despite the long history in hydraulic fracturing, the growth of fractures over time is not well understood. The creation of hydraulic fractures can be monitored in real time via micro-seismic method. However, this method is only effective during fracturing process. After hydraulic fractures are created, the growth of fractures remains unknown. There is a lack of methods to effectively characterize fractures in the post fracturing period.