Modeling plant canopy through numerical simulation of cylindrical array

The design, modeling and initial measurement results of a mid-size cylindrical polarimetric phased array radar (CPPAR) antenna for weather sensing applications are presented. Elevation scanning is obtained using the frequency scanning concept while azimuth scanning is achieved through commutation. The cylindrical array consists of 950 patch elements mounted on the surface of a cylinder with diameter and height of 2 meters. The simulation and measurement results of the cylindrical antenna array are presented.

The purpose of the present paper is development of mathematical model, numerical simulation and matching characteristics measurements of microstrip antenna arrays with a longitudinal arrangement of printed dipoles.

The dynamics of the quasi-optical two-dimensional Josephson junction arrays for oscillators is investigated. Numerical time-domain simulations of small-scale parallel arrays were performed. It is found that the DC biasing circuit determines the states of these arrays. It is also found that other states exist in which parts of the array operate in phase. The authors investigate the sensitivity of in-phase states to variations in junction critical currents and to nonvanishing fluctuations. It is found that the DC self-field effects do not provide a stable phase-locking mechanism and that RF interactions are necessary for locking the array in phase. >

Wave-optics and ray-field tracing methods for the simulation of micro-lens arrays (MLAs) taking into account the coherence and polarization effects of light source, randomization of microlens array parameters are implemented. The influence of the parameters of radiation source (wavelength, wavefront curvature, beam radius, coherence radius, etc.) and micro-lens array (periodic or random, aspect ratio, pitch size, refractive index, array surface shape and profile (convex, concave), etc.) on the output parameters (intensity distribution, radiation pattern, optical efficiency) of a diffracted beam is investigated. Numerical simulations of the intensity distributions and spreading angle of a diffracted beam have been carried out. The new ray-field approach based on the coherent states representation is developed for calculation of the optical efficiency of the microlens arrays. Such wave beams can be tracked simply through the arbitrary curved surfaces. User Friendly Interface is developed for introducing initial parameters of light source and MLA array and for graphical and data outputs of simulated results.

Combining the advantages of vacuum tubes and modern photocathode based photoemission technology, we propose a photoconductive vacuum diode array device, which allows for fast modulation of electron emission. A series of conceptual vacuum diode arrays are modeled and simulated CST. Limited by space charge effect, the electric fields, electron trajectories and electron transition time are calculated and analyzed. The numerical simulations show that the 10 × 10 square array, consisted of 100 volumes of 5 μm × 5 μm × 5 μm diode with a φ2μm vacuum channel in it, could transport electron with current density no less than 795 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> when the bias voltage is bigger than 20 V. And the emission density will arise when the number of volumes declines, which means that diode array can generate and transport a relatively high terahertz current signal when beat frequency is in terahertz range (0.1-2THz). Also, the time of electron flight drops to near 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup> s at a 60 V bias when the number of volumes increases to 100, which allows operating at terahertz frequencies. These results demonstrate that photoconductive vacuum diode array device can open the area to a wide field of applications in terahertz signal generation and fundamental fast logic device technologies.

We extend the multilevel Green's function interpolation method (MLGFIM) developed for quasi-electrostatic problems to full-wave simulations. The difficulty in applying the interpolation approach lies in the additional rapidly changing phase term associated with the full-wave Green's functions. To enhance the efficiency and accuracy of the full-wave Green's function interpolation, a scattered point set consisting of two staggered Tartan grids in conjunction with radial basis function interpolation is employed. To further reduce the computational complexity, the QR factorization technique is applied to compress the low rank Green's function matrices. For electromagnetic scattering from PEC spheres up to a diameter of eight wavelengths, the proposed method compares well with Mie's scattering in accuracy and shows the O(NlogN) efficiency. As the method is "kernel independent", its extension to structures in layered medium is straightforward. In the numerical simulations of finite microstrip patch arrays up to 11 by 11 elements, the proposed method demonstrates very favorable dependencies of CPU time and memory storage requirement versus the number of unknowns

The microwave network theory of antenna arrays improves on the classical array factor modeling approach by including in the analysis the effects of mutual coupling between array elements. Network theory allows numerical simulations of antenna arrays to be combined with network models for transmitter and receiver electronics to provide a full model for the signal and noise response of the system. The network theory framework provides definitions for active array figures of merit, such as aperture efficiency, receiving efficiency, and noise‐matching efficiency, and can be used to link the array system model with the analytical tools of array signal processing and statistically optimal beamformer design. An application is given to high‐sensitivity array feed receivers used for radio astronomy.

Theoretical treatment and computer simulation of microelectrode arrays

In this work, we study optical properties of all-dielectric metasurfaces on the top of high-index substrate. We perform numerical simulations of spherical nanoparticle arrays for different permittivities of the substrate, and propose a simple model with separate contributions from nanoparticle arrays and bare substrate into the total reflection, which fully agrees with numerical results. For the single nanoparticle in homogeneous environment, zero backscattering, or Kerker effect, is observed when electric and magnetic moments are in-phase. In contrast, the reflection suppression from nanoparticle-coated substrate occurs when the out-of-phase condition is satisfied, i.e. for the wavelength between the resonances of electric and magnetic dipole moments. The influence of high-index substrate is crucial for designing optical metasurfaces and photovoltaic elements with nanoparticle-enhanced light trapping.

Chamber-IV of the Collaborative High Altitude Flow Facility was designed to obtain high fidelity spacecraft-thruster interaction data. CHAFF-IV uses a total chamber pumping concept by lining the entire chamber with an array of cryogenically cooled, radial fins. Details of Monte Carlo numerical simulation and experimental investigation of the radial fin target array pumping efficiency are presented.

The results of numerical simulations of phase-locked 1D and 2D Josephson-junction arrays are reported. It is shown that the multi-junction structures with non-local junction interaction provide phase-locked oscillation state within wide critical current margins /spl Delta/I/sub c/ up to 40...50%. The effective non-local interaction in 2D structure based on 4-junction interferometer cell can be provided by the regular single flux quantum array flow across it. The wide tolerable spread in /spl Delta/I/sub c/ allows one to realize both (i) phase-locked 2D high-T/sub c/ Josephson-junction array with the oscillation frequency F close to characteristic value F/sub c/ and (ii) based on Nb tunnel Josephson-junction technology 1D array with the voltage-controlled phase-locked oscillation frequency within wide frequency band from 0.4 F/sub c/ to 1.2 F/sub c/.

International audience

The development of THz multielement uncooled imagers based on focal plane arrays (FPAs) requires an optimization of the system parameters to achieve a homogeneous sensitivity of the array elements. Results of numerical simulation of the eight-element linear array of planar antennas with detecting elements, on a substrate of finite dimensions are presented. We establish how the substrate thickness h and the relative permittivity epsilon influence antenna pattern and antenna-detector matching for each element. We show that the antenna pattern depends on the detector position more than the antenna-detector impedance matching. The gain of array elements, the antenna-detector matching, and the homogeneity of the detector sensitivity can be simultaneously optimized by the proper choice of the substrate thickness h and the relative permittivity epsilon. We show that multielement systems with large substrate thickness and high relative permittivity are not suitable for the imaging system implementation. To achieve uniform multielement system sensitivity, substrates with low permittivity (epsilon < 5) and/or low thickness (h < 60 mkm for the Si substrate) should be used. Finally, we investigate the operation of the detector array with optimally chosen substrate parameters together with the focusing lens, and show that the system is able to work as FPA without significant image corruption.

We present a high-performance program for parallel simulation of multi-physics problems. This program is intended to perform large-scale numerical simulation of antenna array, integrated circuit (IC) and system in package (SIP) using Finite Element Method (FEM) and its advanced acceleration techniques. In this paper, we demonstrate the architecture and main features of the program. The Domain Decomposition Method (DDM), p-adaptive, fast frequency sweep and multi-physics coupling strategy are discussed as well. Several numerical examples are presented to demonstrate its capability in multi-physics simulations.

Millimeter-wave (MMW) imaging has a wide prospect in personnel security inspection since it can provide high-resolution imaging results without health hazards. A novel multiple-plane sparse multiple-input multiple-output (MIMO) array topology is proposed in this paper. Compared with the planar array, the proposed array can detect more details of target from multiple views with better focusing performance. Additionally, the multi-plane arrays are easier to fabricate than the cylindrical arrays since it consists of subarrays with the same planar structure. Moreover, the antenna elements are distributed sparsely in the proposed multiple-plane array, which significantly reduces the overall system cost. Numerical simulations are provided to demonstrate the superiority of the proposed array topology.