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A surface-impedance boundary condition (SIBC) is presented for an unconditionally stable alternating-direction implicit (ADI) finite-difference time-domain (FDTD) method. The conformal SIBC formulation based on locally conformal grids is capable of modeling the conductor loss of arbitrarily-shaped lossy metal structures. The work is described in the framework of the finite-integration technique (FIT) formulation of the ADI-FDTD. The paper focuses on the proposed ADI-FDTD SIBC formulation and its extensive validation. For this purpose, cylindrical and spherical cavity resonators are used for numerical tests. The quality factor Q is directly proportional to wall loss and is particularly sensitive to the accuracy of loss calculation. The resonator structure consists only of a vacuum-filled metal cavity and is thus free of additional sources of error that are caused by other extensions to the basic ADI-FDTD algorithm. The formulation is validated by comparison with analytic results and numerical data calculated using CST Microwave Studio (MWS). The convergence rate of the results is of second order, i.e. the error reduces to one quarter as the mesh resolution is doubled. Index Terms--Finite-difference time-domain (FDTD) methods, losses, resonators.

A conformal first-order or Leontovic surface-impedance boundary condition (SIBC) for the modeling of lossy curved surfaces in a Cartesian grid is presented for the finite-integration technique (FIT). Equivalently, the model can be derived using the contour-path formulation of the finite-difference time domain (FDTD) method. The SIBC is based on a lumped-element representation of the impedance combined with a conformal modeling scheme. The validity of the proposed model is evaluated by investigating the quality factors of rectangular, cylindrical and spherical cavity resonators. The convergence rate of the conformal SIBC model is shown to be of second order. Index Terms--Finite-difference time-domain (FDTD) methods, losses, resonators.

The von Neumann analysis is applied to investigate the stability of a source connected on a wire described by a thin-wire model. Both a soft source and a resistive voltage source (RVS) are shown to limit the stable range of values for wire radius or time step. Using the yon Neumann analysis, a stable RVS model for thin wires is developed. The proposed model is verified by comparison with a hard source, an original RVS and NEC-generated reference data. The stabilized RVS introduces no additional stability constraints on those of the wire model while maintaining fast decay of incident fields of the original RVS model. Index Terms--Finite-difference time-domain (FDTD) methods, stability.

An improved thin-wire model for the finite-difference time-domain method is proposed. The new model can be used to accurately model straight wire sections connected to other metal structures. In addition, the model includes the effect of charge accumulation at wire end caps. The end-cap model is based on conservation of charge and Coulomb's law. Using the end-cap model, unconnected wires such as wire antennas are also accurately modeled. The results indicate a significant improvement in predicting the resonance frequency of a dipole antenna. Index Terms--FDTD, sub-cell model, thin-wire model.

The development of small integrated antennas plays a significant role in the progress of rapidly expanding wireless communication applications. This paper describes a novel dual-band planar inverted-F antenna (PIFA) for wireless local area network applications. The proposed PIFA uses single feed only. A novel top-plate geometry, a U-shaped slot, is discussed. An example is given for this novel slot shape for frequency bands of 2.4 and 5.2 GHz. Simulation based upon method of moments (MoM) is used to model the performance of the antenna. Comparisons with results measured on fabricated antenna structures are provided for simulations validation. Index Terms--Antennas, dual-band antennas, handset antennas, printed antennas, slot antennas, wireless communications.

Radio frequency identification (RFID) systems for the paper industry is an emerging research topic due to the need for an automated identification system for the paper industry which would carry on the identification codes of paper and board reels throughout their life cycle. This paper discusses the application of passive ultra-high frequency (UHF) RFID systems to the paper industry. Challenges, benefits, and the application environment of using passive UHF RFID systems in the paper industry are presented and discussed. The major challenges are development of globally operable tag antenna designs and integration of reader units and reader antennas to paper handling machinery. To confront and solve these challenges, this paper presents novel tag antenna designs for paper and board reel identification and proposes solutions for reader and reader antenna integration to paper handling machinery. In addition, the identification locations within the paper reel supply chain and the effects of RFID systems to supply chain visibility are presented and discussed. In addition, test results of using passive UHF RFID systems in the paper industry environment are presented. Note to Practitioners--An automated identification system, which would carry on the identification code of a specified paper or board reel throughout its life cycle, is needed in the paper industry. Nowadays when barcode identification systems are used the identity of the reels disappear when the wrapping of the reel and at the same time the barcode are removed. The RFID tag, however, would be attached to the paper reel core and thereby the identification code of the reel is restored throughout its life cycle. RFID systems would benefit the paper industry by enhancing the supply chain visibility and providing a more automated identification system than barcode identification. In the future, paper reels will be identified with clamp truck-integrated reader units which, on the other hand, enables adding more real-time information about the locations of the paper reels to information databases but also sets challenges for paper reel tag performance and integration of RFID reader units and reader antennas to paper handling machinery. This paper concentrates on passive UHF RFID systems and their application to the paper industry. Challenges and benefits of RFID systems in the specific application environment of the paper industry are presented and discussed. [ABSTRACT FROM AUTHOR]