Beamforming Optimization in Internet of Things Applications Using Robust Swarm Algorithm in Conjunction with Connectable and Collaborative Sensors.

The integration of the Internet of Things (IoT) with Wireless Sensor Networks (WSNs) typically involves multihop relaying combined with sophisticated signal processing to serve as an information provider for several applications such as smart grids, industrial, and search-and-rescue operations. These applications entail deploying many sensors in environments that are often random which motivated the study of beamforming using random geometric topologies. This paper introduces a new algorithm for the synthesis of several geometries of Collaborative Beamforming (CB) of virtual sensor antenna arrays with maximum mainlobe and minimum sidelobe levels (SLL) as well as null control using Canonical Swarm Optimization (CPSO) algorithm. The optimal beampattern is achieved by optimizing the current excitation weights for uniform and non-uniform interelement spacings based on the network connectivity of the virtual antenna arrays using a node selection scheme. As compared to conventional beamforming, convex optimization, Genetic Algorithm (GA), and Particle Swarm Optimization (PSO), the proposed CPSO achieves significant reduction in SLL, control of nulls, and increased gain in mainlobe directed towards the desired base station when the node selection technique is implemented with CB.

Multi-walled carbon nanotube-based RF antennas.

A novel application that utilizes conductive patches composed of purified multi-walled carbon nanotubes (MWCNTs) embedded in a sodium cholate composite thin film to create microstrip antennas operating in the microwave frequency regime is proposed. The MWCNTs are suspended in an adhesive solvent to form a conductive ink that is printed on flexible polymer substrates. The DC conductivity of the printed patches was measured by the four probe technique and the complex relative permittivity was measured by an Agilent E5071B probe. The commercial software package, CST Microwave Studio (MWS), was used to simulate the proposed antennas based on the measured constitutive parameters. An excellent agreement of less than 0.2% difference in resonant frequency is shown. Simulated and measured results were also compared against identical microstrip antennas that utilize copper conducting patches. The proposed MWCNT-based antennas demonstrate a 5.6% to 2.2% increase in bandwidth, with respect to their corresponding copper-based prototypes, without significant degradation in gain and/or far-field radiation patterns.

A finite difference thermal model of a cylindrical microwave heating applicator using locally conformal overlapping grids: part II--numerical results and experimental evaluation.

In this paper, we present numerical results obtained from a robust, locally conformal 3-D Orthogonal Grid Finite Difference (OGFD) thermal algorithm introduced in Part I of our current investigation [Al-Rizzo et al., 2006] integrated with an Orthogonal Grid Finite-Difference Time Domain (OGFDTD) scheme [Al-Rizzo et al., 2000], which accurately models the volumetric electromagnetic (EM) power deposition pattern. A unified meshing scheme, which utilizes identical overlapping grids in Cartesian and cylindrical coordinates, is employed within the load zone in the OGFDTD and OGFD models. Local temperature profiles excited by the absorbed microwave energy were measured at seven locations within the sample as a function of heating time. In order to benchmark, or validate our model, an alternative analysis of the coupled EM and thermal simulations was performed using state-of-the-art, Finite Element Method-based Ansoft's High Frequency Structure Simulator (HFSS) and the coupled thermal/stress analysis tool ePHYSICS (http://www.ansoft.com). Additionally, we compare our numerical simulations against measured dynamic temperature profiles induced within a mineral ore sample maintained for exposure period of 28.5 minutes inside a cylindrical multimode heating furnace energized at 915 MHz with a microwave source power of 12.5 kW and accompanied with significant temperature elevation. A combination of convective and radiation thermal boundary conditions are considered at the interfaces between the cavity walls, air, and sample. There is a general agreement between simulated and measured spatial and temporal temperature profiles, which validates the proposed model. Results indicate that inevitable fluctuations in the frequency spectrum and output power of the magnetron, non-uniformity of sample packing, and heat released by uncontrolled exothermic chemical reactions have a significant effect on the comparisons between measured and computed temperature patterns.

A finite difference thermal model of a cylindrical microwave heating applicator using locally conformal overlapping grids: part I--theoretical formulation.

In this paper, we present a versatile mathematical formulation of a newly developed 3-D locally conformal Finite Difference (FD) thermal algorithm developed specificallyfor coupled electromagnetic (EM) and heat diffusion simulations utilizing Overlapping Grids (OGFD) in the Cartesian and cylindrical coordinate systems. The motivation for this research arises from an attempt to characterize the dominant thermal transport phenomena typically encountered during the process cycle of a high-power, microwave-assisted material processing system employing a geometrically composite cylindrical multimode heating furnace. The cylindrical FD scheme is only applied to the outer shell of the housing cavity whereas the Cartesian FD scheme is used to advance the temperature elsewhere including top and bottom walls, and most of the inner region of the cavity volume. The temperature dependency of the EM constitutive and thermo-physical parameters of the material being processed is readily accommodated into the OGFD update equations. The time increment, which satisfies the stability constraint of the explicit OGFD time-marching scheme, is derived. In a departure from prior work, the salient features of the proposed algorithm are first, the locally conformal discretization scheme accurately describes the diffusion of heat and second, significant heat-loss mechanisms usually encountered in microwave heating problems at the interfacial boundary temperature nodes have been considered. These include convection and radiation between the surface of the workload and air inside the cavity, heat convection and radiation between the inner cavity walls and interior cavity volume, and free cooling of the outermost cavity walls.

FDTD analysis of dielectric-loaded longitudinally slotted rectangular waveguides.

A versatile electromagnetic (EM) computational algorithm, based on the Finite-Difference Time-Domain (FDTD) technique, is developed to analyze longitudinally oriented, square-ended, single slot fixtures and slot-pair configurations cut in the broad wall of a WR-975 guide operating at a frequency of 915 MHz. The finite conductivity of the waveguide walls is accounted for by employing a time-domain Surface-Impedance Boundary Conditions (SIBC) formulation. The proposed FDTD algorithm has been validated against measurements performed on a probe-excited slot cut along the center line of the broad wall of a WR-284 guide and available experimental data for energy coupled from a longitudinal slot pair in the broad wall of a WR-340 guide. Numerical results are-presented to exploit the influence of the constitutive parameters of the processed material as well as protective insulating window slabs mounted on the exterior surface of the slots. Particular attention is given to the resonant length, scattering parameters, and the electric field distribution within lossy objects placed in the near-field region over a range of slot offsets and workloads with extensive results being reported for the first time. It is shown that the FDTD technique can accurately predict the coupling and power absorption characteristics in loads located in the near field zone of the slotted waveguide structures and, therefore, should prove to be a powerful design tool applicable to a wide class of slotted waveguide applicators that may be difficult to analyze using other available techniques.