Microwave Engineering Europe - July/August 2008 - (Page 12)

12 COVER FEATURE — EM SIMULATION region to determine the new incident ﬁeld distribution on the Huygens box region of subdimension 2 considering the effect of the backscattering ﬁelds, i.e., secondary reﬂections and effects on the source. v) and so on. This scheme is applied iteratively until the effect of backscattering becomes negligible. It can also be additionally subdivided in nested subdimensions (D1i, Dnj). The Python script enables these iterations to run automatically with determination a criterion. This approach signiﬁcantly reduces the computational time and the need for large memory resources, allowing the simulation of problems that could not be solved before. III. Examples Examples from different applications, such as optical devices and exposure assessments and the analysis of spatial diversity antennas, are illustrated in Figures 2 and 3 respectively. Another example is currently one of the most challenging problems in medical device simulation, namely, the research and design of safe and compatible medical implants for use in MRI machines. In addition to EMC issues, excessive heating at the tips of long leads is a major issue. The simulation of a complex implant or device (requiring micro resolutions) embedded in an inhomogeneous body and surrounded by a large electrical resonator, however, exceeds the applicability of traditional tools. In the example shown in Figure 5, the lead is represented by a previously determined lumped-element representation, but the energy deposition at the tip of the lead and the resulting temperature distribution were solved with the full-wave solver SEMCAD FW and the temperature solver SEMCAD T º. The appropriate modeling of step gradients at the tips requires a spatial resolution of better than 0.025 mm, resulting in an extremely small FDTD time step. This problem can only be reasonably resolved with the newly developed Huygens Box method as demonstrated in Table 1. Table 1: Computational requirements (All simulations run on a SEMCAD X CIB1500 hardware acceleration system. If only software solvers were used, the simulation would take more than 213 days!). Figure 5: (a) model with the Huygens box, b) Induced surface currents on the implant and leads; (c) SAR distribution in the body passing through the tips of the leads. As Table 1 shows, the Huygens Box approach reduces the simulation time by almost a factor of 8 while using ﬁve times less RAM. For smaller devices such as stents, the computational beneﬁts are much greater. The limitation of representing the lead with a lumped element model will be overcome in the next release of SEMCAD Huygens. IV. Conclusions The novel general Huygens Box technique and its implementation have proven to be a user-friendly and open interface to bridge multiple spatial dimensions, a major breakthrough for application engineers to analyze the EM issues of current and future devices and applications. The SEMCAD Huygens is easy to use and can be interfaced with any commercial or inhouse code or even measurement results. SPEAG is developing new algorithms to enhance the effectiveness of this new technique while collaborating with different software houses to provide user-friendly interfaces with different EM packages and the SEMCAD X solver family. V. References [1] www.acceleware.com [2] www.semcad.com [3] A. Taﬂove, S. Hagness; “Computational Electrodynamics: The Finite Difference Time Domain Method “, 3rd edition, pg 186-212. [4] N. Kuster, L. H. Bomholt; “A block iterative technique to expand MMP`s applicability to EM problems of higher complexity”, IEEE Trans MTT, vol. 42, no. 5, pp. 875–883, 1994. [5] http://www.zurichmedtech.com [6] http://www.itis.ethz.ch/index/index_ humanmodels.htm European Print Edition www.mwee.com/subscribe Outside Europe: a Digital Edition is available Microwave Engineering Europe ● July/August 2008 ● www.mwee.com http://www.acceleware.com http://www.semcad.com http://www.zurichmedtech.com http://www.itis.ethz.ch/index/index_humanmodels.html http://www.mwee.com/subscribe http://www.mwee.com

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Microwave Engineering Europe - July/August 2008 Contents News Comment Cover Feature: Effective EM Simulations with Micro−λ Resolution in Macro-λ Objects — General Huygens Box Implementation RF CMOS: Programmable Transceiver IC Minimises OEM Inventory for Femtocells CAD/EDA: Software-Defined Radio Platforms CAD/EDA: Cadence Enhances RF Verification While AWR Delivers an Improved Microwave Office How to Meet the Design Challenges of WiMAX Power Amplifiers Products Calendar

Microwave Engineering Europe - July/August 2008

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