Incomplete-Leaf Multilevel Fast Multipole Algorithm for Multiscale Penetrable Objects Formulated With Volume Integral Equations

Recently introduced incomplete-leaf (IL) tree structures for multilevel fast multipole algorithm (referred to as IL-MLFMA) is proposed for the analysis of multiscale inhomogeneous penetrable objects, in which there are multiple orders of magnitude differences among the mesh sizes. Considering a maximum Schaubert-Wilton-Glisson function population threshold per box, only overcrowded boxes are recursively divided into proper smaller boxes, leading to IL tree structures consisting of variable box sizes. Such an approach: 1) significantly reduces the CPU time for near-field calculations regarding overcrowded boxes, resulting a superior efficiency in comparison with the conventional MLFMA where fixed-size boxes are used and 2) effectively reduces the computational error of the conventional MLFMA for multiscale problems, where the protrusion of the basis/testing functions from their respective boxes dramatically impairs the validity of the addition theorem. Moreover, because IL-MLFMA is able to use deep levels safely and without compromising the accuracy, the memory consumption is significantly reduced compared with that of the conventional MLFMA. Several examples are provided to assess the accuracy and the efficiency of IL-MLFMA for multiscale penetrable objects

Error Control of MLFMA within a Multiple-Precision Arithmetic Framework

We present a new error control scheme that provides the truncation numbers as well as the required digits of machine precision for the multilevel fast multipole algorithm (MLFMA). The proposed method is valid for all frequencies, whereas the previous studies on error control are valid only for high-frequency problems. When combined with a multiple-precision arithmetic framework, the proposed method can be used to solve low-frequency problems that would otherwise experience overflow issues. Numerical results in the form of optimal truncation numbers and machine precisions for a variety of box sizes and desired relative error thresholds are presented and compared with the results available in the literature

Extension of forward-backward method with DFT-based acceleration algorithm for the efficient analysis of large periodic arrays with arbitrary boundaries

An extension of the discrete Fourier transform (DFT)-based forward-backward algorithm is developed using the virtual-element approach to provide a fast and accurate analysis of electromagnetic radiation/scattering front electrically large, planar, periodic, finite (phased) arrays with arbitrary boundaries. Both the computational complexity and storage requirements of this approach are O(N-tot) (N-tot is the total number of unknowns). The numerical results for both printed and freestanding dipole array's with circular and/or elliptical boundaries are presented to validate the efficiency, and accuracy of this approach. (c) 2005 Wiley Periodicals, Inc

Solution of Potential Integral Equations with NSPWMLFMA

In this contribution, we present a numerical implementation of recently developed potential integral equations (PIEs) by using nondirective stable plane wave multilevel fast multipole algorithm (NSPWMLFMA). The proposed method is efficient and accurate to solve large scattering problems involving perfectly conducting bodies with geometrical details, which require dense discretizations with respect to the operating wavelength. Numerical results in the form of scattered field from various objects are provided to assess the accuracy and efficiency of PIEs solved using NSPWMLFMA

Applications of hybrid discrete Fourier transform-moment method to the fast analysis of large rectangular dipole arrays printed on a thin grounded dielectric substrate

Recently a discrete Fourier transform-method of moments (DFT-MoM) scheme was developed for fast analysis of electrically large rectangular planar dipole arrays, which has been shown to be very efficient in terms of number reduction of unknown variables and computational complexity. The applications of this DFT-MoM to treat dipole arrays printed on a grounded dielectric substrate are examined in this Letter. Numerical results are presented to validate its efficiency and accuracy. (C) 2002 Wiley Periodicals, Inc

Wireless Sensing in Complex Electromagnetic Media: Construction Materials and Structural Monitoring

In this paper, wireless sensing in the presence of complex electromagnetic media created by combinations of reinforcing bars and concrete is investigated. The wireless displacement sensing system, primarily designed for use in structural health monitoring (SHM), is composed of a comb-like nested split-ring resonator (NSRR) probe and a transceiver antenna. Although each complex medium scenario is predicted to have a detrimental effect on sensing in principle, it is demonstrated that the proposed sensor geometry is able to operate fairly well in all scenarios except one. In these scenarios that mimic real-life SHM, it is shown that this sensor exhibits a high displacement resolution of 1 mu m, a good sensitivity of 7 MHz/mm in average, and a high dynamic range extending over 20 mm. For the most disruptive scenario of placing concrete immediately behind NSRR, a solution based on employing a separator behind the probe is proposed to overcome the handicaps introduced by the medium. In order to obtain a one-to-one mapping from the measured frequency shift to the displacement, a numerical fit is proposed and used. The effects of several complex medium scenarios on this fit are discussed. These results indicate that the proposed sensing scheme works well in real-life SHM applications

An Electromagnetic Sensing System Incorporating Multiple Probes and Single Antenna for Wireless Structural Health Monitoring

In this study, a wireless and passive displacement/strain sensing system is proposed for structural health monitoring (SHM). The wireless and passive interrogation of the sensing unit [a variant of a nested split-ring resonator (NSRR)] is achieved through the near-field interaction and electromagnetic coupling between the single antenna in the system and the multiple sensors called the NSRR probes. It is demonstrated that the system can acquire data from more than one NSRR probe simultaneously in a real-life scenario, where the probes are confined within concrete inside a beam, while the antenna monitors them from outside

Multi-Point Single-Antenna Sensing Enabled by Wireless Nested Split-Ring Resonator Sensors

In this paper, simultaneous multi-point wireless sensing is proposed and demonstrated via multiple sensors in nested split-ring resonator (NSRR) geometry coupled to a single illuminator antenna. In this passive multi-point sensing system, each probe in the sensor array is assigned a non-overlapping spectral interval for frequency shift in response to local mechanical loading around a unique operating resonance frequency in the band of the antenna. Here, it is shown that the antenna is capable of capturing the responses from all probes in a single frequency sweep. Furthermore, the inter-coupling between the array elements and the effect of antenna illumination on the coupling are experimentally investigated in a systematic way. In addition, as a proof-of-concept real-life application in structural health monitoring, two NSRR sensors are located inside a concrete beam to monitor the strain forming on reinforcing bars, and this dual-probe system is demonstrated to record strain simultaneously via both of the embedded probes