Numerical coupling models for complex systems and results

The paper gives a status of present electromagnetic (EM) coupling modeling capabilities. Starting from topologically designed systems, it shows how formal rules of the EM topology approach can provide guidance for EM coupling analysis or the development of protection against intentional electromagnetic interference (EMI)- related threats, even in the case of a poorly shielded system. After a review of currently available mature numerical techniques, a strategy allowing one to chain different numerical tools (including three-dimensional analysis tools, cable-networks tools, and circuit analysis procedures) is proposed in order to achieve EM coupling assessments on real complex systems. The paper also gives a status on several scientific trends likely to enhance modeling capabilities in the future.     

Development of modular electrical systems

Modular systems provide the ability to achieve product variety through the combination and standardization of components. A methodology that combines system modeling, integration analysis, and optimization techniques for development of modular systems is presented. The approach optimizes integration and interactions of system elements and creates functional and physical modules for the electrical system. The Hatley/Pirbhai methodology (1987) is used for modeling functional requirements of a system. The model defines system interfaces (interactions) to support its functions. Once the interactions among functions are identified, an incidence matrix of the interfaces is developed. A clustering algorithm is developed to identify clusters in the incidence matrix, group the functions, and create modules. A Hatley/Pirbhai architecture model is developed to represent modular system design. A detailed discussion on the importance of system modeling in design of modular systems and on the constraints that limit development of modular vehicle systems is also presented. The approach presented is systematic and can be used to support product development and decision-making in engineering design     

ARIADNE: A constraint-based approach to computer-aided synthesis and modeling of Analog integrated circuits

The ARIADNE approach to computer-aided synthesis and modeling of analog circuits is presented. It is a mathematical approach based on the use of equations. Equations are regarded as constraints on a circuit's design space and analog circuit design is modeled as a constraint satisfaction problem. To generate and efficiently satisfy constraints, advanced computational techniques such as constraint propagation, interval propagation, symbolic simulation, and qualitative simulation are applied. These techniques cover design problems such as topology construction, modeling, nominal analysis, tolerance analysis, sizing and optimization of analog circuits. The advantage of this approach is the clear separation of design knowledge from design procedures. Design knowledge is modeled in declarative equation-based models (DEBMs). Design procedures are implemented into general applicable CAD tools. The ARIADNE approach closely matches the reasoning style applied by experienced designers. The integration of synthesis and modeling into one frame and the clear separation of design knowledge from design procedures eases the process of extending the synthesis system with new circuit topologies, turning it into an open design system. This system can be used by both inexperienced and experienced designers in either interactive or automated mode.     

Investigation of the Electromagnetic Interference Threat Posed by a Wireless Network Inside a Passenger Aircraft

Recent years have witnessed an incisive push to allow the use of wireless networks inside passenger aircraft. Research was recently conducted to investigate the internal electromagnetic (EM) environment excited by a wireless network inside a passenger aircraft to provide quantification of the ensuing EM interference threat. An airbus A319 EM model was developed and validated using experimental data and analytical techniques. The validated model was applied to the investigation of an 800 MHz cellular network. The peak electric field strength inside each of the A319 EM models examined was much less than the most severe RTCA/DO-160D radiated susceptibility test levels. The current coupled to a cable running along the length of the fuselage was much less than the minimum operating parameters of an extremely sensitive avionic system (e.g., strain sensor). The results obtained help to quantify and reinforce the conclusion of the major research efforts that the likelihood of interference with flight critical systems is low. The model presented herein can be easily adapted to study EM propagation for various types of wireless network and aircraft configurations, and the modeling approach employed could be of potential use in modeling other large, complex structures.     

Generalized Kirchoff's current and Voltage law formulation for coupled circuit-electromagnetic Simulation with surface Integral equations

In this paper, a new formulation for coupled circuit-electromagnetic (EM) simulation is presented. The formulation employs full-wave integral equations to model the EM behavior of two- or three-dimensional structures while using modified nodal analysis to model circuit interactions. A coupling scheme based on charge and current continuity and potential matching, realized as a generalization of Kirchoff's voltage and current laws, ensures that the EM and circuit interactions can be formulated as a seamless system. While rigorous port models for EM structures can be obtained using the approach discussed herein, it is shown that the coupling paradigm can reveal additional details of the EM-circuit interactions and can provide a path to analysis-based design iteration.     

Integrated model parameter extraction using large-scaleoptimization concepts

A robust approach to modelling parameter extraction in microwave circuit design is presented. The approach not only attempts to match DC and AC measurements under different bias conditions simultaneously, but also employs the DC characteristics of the device as constraints on Bias-dependent parameters, this improving the uniqueness and reliability of the solution. The approach is an expansion of the hierarchical modeling techniques recently proposed J.W. Bandler and S.H. Chen (1988). Based on J.W. Bandler and Q.J. Zhang's (1987) automatic decomposition concepts for large-scale optimization, a sequential model building method is proposed which can be combined with powerful l₁ optimization techniques to establish a model with simple topology and sufficient accuracy. Practical FET models are used to illustrate the formulation. A detailed numerical example is presented to show the effectiveness of the approach     

Hybrid approach for modeling transient EM fields generated by large earthing systems

A new hybrid approach is adopted in this paper for modeling the transient electromagnetic fields radiated by grounding systems under lightning strokes. This approach is based on electrical dipole theory for determining EM fields’ radiation in infinite conductive medium, modified images theory, taking into account the interface in the half space and transmission line approach for determining the longitudinal and leakage currents. This model can be used to predict the transient characteristic of grounding systems because it can calculate electromagnetic field in any point of interest; it is sufficiently accurate, time efficient, and easy to apply.     

Copper interconnect electromigration behaviors in various structures and lifetime improvement by cap/dielectric interface treatment

Copper interconnect electromigration performance was examined in various structures and three low-k materials (k = 2.65–3.6) using advanced BEOL technology. Strong current dependence effect on electromigration lifetime in three levels via terminated metal lines structure was shown. Moreover, different process approach will lead to different EM behavior and related failure mode. Multi-modality electromigration behavior of Cu dual damascene interconnects were studied. Both Superposition and Weak-Link models were used for statistical determination of lifetimes of each failure models (Statistical method). Results were correlated to the lifetimes of respective failure models physically identified according to resistance time evolution behaviors (Physical method). Good agreement was achieved. Various testing structures are designed to identify the EM failure modes. Extensive failure analysis was carried out to understand the failure phenomena of various test structures. The activation energies of failure modes were calculated. The weak links of interconnect system were also identified. A significant improvement of electromigration (EM) lifetime is achieved by modification of the pre-clean step before cap-layer deposition and by changing Cu cap/dielectric materials. A possible mechanism for EM lifetime enhancement was proposed. Cu-silicide formation before cap-layer deposition and adhesion of Cu/cap interface were found to be critical factors in controlling Cu electromigration reliability. The adhesion of the Cu/cap interface can be directly correlated to electromigration MTF and activation energy. Results of present study suggest that interface of Cu interconnects is the key factor for EM performance for advanced BEOL technology design rules.     

Quantifying and cancelation memory effects in high power amplifier for OFDM systems

A modeling approach to power amplifier design for implementation in OFDM radio units is presented. The power amplifier model assesses the impact of linear memory effects within the system using a Wiener representation, and employs a linear novel parametric estimation technique using Hilbert space. In addition, in order to model the nonlinear memory effects the previous topology is generalized by inserting the truncated Volterra filter before the static nonlinearity. Predistortion based on the Hammerstein model is introduced to deal with the nonlinear response. The new general algorithm is proposed to evaluate the Hammerstein model parameters for an OFDM system. A representative test bed was designed and implemented. The assessment of the new methods for PA and PD modeling are confirmed by experimental measurements. The measurement results reveal the preference of the new techniques over the existing approaches.     

An efficient electromagnetic-physics-based numerical technique for modeling and optimization of high-frequency multifinger transistors

We present a fast wavelet-based time-domain modeling technique to study the effect of electromagnetic (EM)-wave propagation on the performance of high-power and high-frequency multifinger transistors. The proposed approach solves the active device model that combines the transport physics, and Maxwell's equations on nonuniform self-adaptive grids, obtained by applying wavelet transforms followed by hard thresholding. This allows forming fine and coarse grids in the locations where variable solutions change rapidly and slowly, respectively. A CPU time reduction of 75% is achieved compared to a uniform-grid case, while maintaining the same degree of accuracy. After validation, the potential of the developed technique is demonstrated by EM-physical modeling of multifinger transistors. Different numerical examples are presented, showing that accurate modeling of high-frequency devices should incorporate the effect of EM-wave propagation and electron-wave interactions within and around the device. Moreover, high-frequency advantages of multifinger transistors over single-finger transistors are underlined through numerical examples. To our knowledge, this is the first time in the literature a fully numerical EM-physics-based simulator for accurate modeling of high-frequency multifinger transistors is introduced and implemented.     

Initial results for automated computational modeling ofpatient-specific electromagnetic hyperthermia

Developments in finite-difference time-domain (FD-TD) computational modeling of Maxwell's equations, super-computer technology, and computed tomography (CT) imagery open the possibility of accurate numerical simulation of electromagnetic (EM) wave interactions with specific, complex, biological tissue structures. One application of this technology is in the area of treatment planning for EM hyperthermia. In this paper, we report the first highly automated CT image segmentation and interpolation scheme applied to model patient-specific EM hyperthermia. This novel system is based on sophisticated tools from the artificial intelligence, computer vision, and computer graphics disciplines. It permits CT-based patient-specific hyperthermia models to be constructed without tedious manual contouring on digitizing pads or CRT screens. The system permits in principle near real-time assistance in hyperthermia treatment planning. We apply this system to interpret actual patient CT data, reconstructing a 3-D model of the human thigh from a collection of 29 serial CT images at 10 mm intervals. Then, using FD-TD, we obtain 2-D and 3-D models of EM hyperthermia of this thigh due to a waveguide applicator. We find that different results are obtained from the 2-D and 3-D models, and conclude that full 3-D tissue models are required for future clinical usage.     

A New Approach to Volumes Irradiated by Unknown Sources

We suggest an approach to the characterization of electromagnetic (EM) environments irradiated by unknown sources. The approach is based on the numerical solution of Maxwell's equations subject to the constraints imposed by the measured values of the field at a small number of measurement points and by boundary conditions. A thorough examination of a method for the numerical solution is presented. The examples attempted demonstrate the approach but reveal deficiencies in the numerical method. Possible future directions are suggested.     

Fast computer-aided simulation of switching power regulators basedon progressive analysis of the switches' state

A new method for time-domain analysis of power electronics circuits is developed based on the following principles: (a) at each instant, the switching topology is a linear time-invariant circuit; (b) at each instant, the voltage across a capacitor and the current through an inductor have a certain value, like an independent voltage- or current source, respectively; (c) generally, no switching relationship between the externally and internally controlled switches may be assumed; (d) prior knowledge of the internally controlled switches' operation is not available; and (e) the switching action may change the response of the circuit immediately after the switching moment, implying that some constraints may be in violation of the presumed switches' states. The algorithm is based on solving a system of algebraical modified nodal equations at each integration step. The number of systems to be solved equals the number of topologies the converter goes through in a cycle. This feature, and the fact that no solutions of time-differential equations or Laplace transform inverses are required, cause the algorithm to be a fast one. At each step, the presumed state of all the switches is checked, and if some constraints are violated, the program looks for another valid topology. An example, with parasitic effects taken into account, is presented; the experimental results, as well as the simulation results obtained by using other available algorithms, confirmed the accuracy of the results achieved with the presented approach     

Lifetime Prediction and Design-for-Reliability of IC Interconnections with Electromigration Induced Degradation in the Presence of Manufacturing Defects

The degradation of IC interconnects due to electromigration (EM) is strongly influenced by physical defects and imperfections on interconnect traces that significantly accelerate EM damage through increased current density and elevated temperature. In this work, an IC reliability simulator is developed to incorporate the effect of these physical defects on circuit interconnect reliability. Based on a statistical defect modeling approach, circuit-level reliability with defective interconnects under EM degradation is evaluated. This has also been successfully integrated into a tool called ARET. Additionally, an approach for identifying circuit reliability hotspots has also been developed. Based on this hotspot identification, the concept of local design-for-reliability (LDFR) is proposed for improved circuit-level reliability under electromigration.     

An EM Algorithm for Ion-Channel Current Estimation

Parameter estimation of a continuous-time Markov chain observed through a discrete-time memoryless channel is studied. An expectation-maximization (EM) algorithm for maximum likelihood estimation of the parameter of this hidden Markov process is developed and applied to a simple example of modeling ion-channel currents in living cell membranes. The approach follows that of Asmussen, Nerman and Olsson, and Ryden, for EM estimation of an underlying continuous-time Markov chain.     

The mean field theory in EM procedures for blind Markov randomfield image restoration

A Markov random field (MRF) model-based EM (expectation-maximization) procedure for simultaneously estimating the degradation model and restoring the image is described. The MRF is a coupled one which provides continuity (inside regions of smooth gray tones) and discontinuity (at region boundaries) constraints for the restoration problem which is, in general, ill posed. The computational difficulty associated with the EM procedure for MRFs is resolved by using the mean field theory from statistical mechanics. An orthonormal blur decomposition is used to reduce the chances of undesirable locally optimal estimates. Experimental results on synthetic and real-world images show that this approach provides good blur estimates and restored images. The restored images are comparable to those obtained by a Wiener filter in mean-square error, but are most visually pleasing.     

Electromagnetic 3-D model for active linear devices: application to pHEMTs in the linear regime

In this paper, we describe a three-dimensional (3D) electromagnetic (EM) approach to the modeling of active devices in their linear regime. The technique basically relies on the self-consistent introduction of distributed controlled current sources in the 3D EM simulation of passive components. The approach is validated by comparing measured and calculated results for a pseudomorphic high electron-mobility transistor in the millimeter-wave range. However, it may also be applied to a larger class of field-effect transistors, including MESFETs.     

Metasurface Patch for Wireless Power Transfer in Implantable Devices

Wireless power transfer (WPT) systems enable the long-term operation and miniaturization of implantable devices by eliminating the need for battery replacement and wired power supplies. Although wireless power transfer systems for implantable devices are extensively studied, their practical application is still challenging owing to the constraints and requirements of the human body, such as reflection loss owing to differences in the tissue dielectric properties, mm-sized devices, and electromagnetic (EM) wave attenuation of the tissue. Here, a phase-gradient metasurface patch is presented to achieve 5.8 GHz EM power focusing at a focal point of depth 10 mm in the tissue via EM wavefront modulation at the skin–air interface. The proposed metasurface patch is fabricated by arranging subwavelength-thickness (<λ/10) unit cell structures composed of four metallic layers separated by dielectric substrates that exhibit high-Q resonance properties and a sufficient phase modulation range with enhanced transmission. By applying the fabricated metasurface patch to a wireless power transfer system for implantable devices, it is experimentally confirmed that the transmission coefficient (S₂₁) is improved by 6.37 dB compared with that of a wireless power transfer system without the metasurface patch. Furthermore, it is confirmed that the transmission coefficient can be maintained for an incident angle variation up to 30° from the transmitter to the metasurface patch, resulting in a stable power delivery of the proposed wireless power transfer system.     

Parallelization of the EM algorithm for 3-D PET image reconstruction

The EM algorithm for PET image reconstruction has two major drawbacks that have impeded the routine use of the EM algorithm: the long computation time due to slow convergence and a large memory required for the image, projection, and probability matrix. An attempt is made to solve these two problems by parallelizing the EM algorithm on multiprocessor systems. An efficient data and task partitioning scheme, called partition-by-box, based on the message passing model is proposed. The partition-by-box scheme and its modified version have been implemented on a message passing system, Intel iPSC/2, and a shared memory system, BBN Butterfly GP1000. The implementation results show that, for the partition-by-box scheme, a message passing system of complete binary tree interconnection with fixed connectivity of three at each node can have similar performance to that with the hypercube topology, which has a connectivity of log(2) N for N PEs. It is shown that the EM algorithm can be efficiently parallelized using the (modified) partition-by-box scheme with the message passing model.     

Accurate analysis and modeling of laminated multilayered 3-D optical waveguides

The theoretical investigation of waveguides having nonuniform cross-sections is an attractive and challenging problem which deserves serious interest. In this paper, we present a novel analysis of laminated multilayered three-dimensional waveguide, based on two modes: 1) a new coupled transmission line approach that considers the sloping of the layers along the longitudinal direction and 2) a transmission line matrix integral equation (TLMIE) modeling that complete and extends the investigation of the field propagation. In method 1), we neglect radiation modes and their EM coupling. All physical effects instead are accounted for by the full-wave TLMIE method. By using TLMIE, we validate the EM analysis and calculate TE/TM losses, arising from radiation modes.