E.S. Siah

Coupling studies and shielding techniques for electromagnetic penetration through apertures on complex cavities and vehicular platforms

The multilevel fast multipole moment method is employed to compute the electromagnetic coupling and shielding of various aperture-coupled metallic enclosures. A phenomenological study of electromagnetic coupling, due to various slot shapes and sizes, with or without the presence of wire penetration is conducted. These slots are situated on over-moded cavities and two methods are proposed to mitigate slot coupling into the cavitys interior. As part of this work, we also investigate the coupling through similar slots and apertures within a complex platform such as an automobile. The proposed methods have shown to increase shielding by as much as 5-35 dB within the frequency range of interest.

Fast parameter optimization of large-scale electromagnetic objects using DIRECT with Kriging metamodeling

With the advent of fast methods to significantly speed up numerical computation of large-scale realistic electromagnetic (EM) structures, EM design and optimization is becoming increasingly attractive. In recent years, genetic algorithms, neural network and evolutionary optimization methods have become increasingly popular for EM optimization. However, these methods are usually associated with a slow convergence bound and, furthermore, may not yield a deterministic optimal solution. In this paper, a new hybrid method using Kriging metamodeling in conjunction with the divided rectangles (DIRECT) global-optimization algorithm is used to yield a globally optimal solution efficiently. The latter yields a deterministic answer with fast convergence bounds and inherits both local and global-optimization properties. Three examples are given to illustrate the applicability of the method, Le., shape optimization for a slot-array frequency-selective surface, antenna location optimization to minimize EM coupling from the antenna to RF devices in automobile structures, and multisensor optimization to satisfy RF coupling constraints on a vehicular chassis in the presence of a wire harness. In the first example, DIRECT with Kriging surrogate modeling was employed. In the latter two examples, the adaptive hybrid optimizer, superEGO, was used. In all three examples, emphasis is placed on the speed of convergence, as well as on the flexibility of the optimization algorithms.

Fast parameter optimization using Kriging metamodeling [antenna EM modeling/simulation]

In this paper, we propose a hybrid optimizer, which combines the Kriging macro-modeling and the divided rectangles method (DIRECT) to perform global optimization. The latter yields a deterministic answer with fast convergence rate and possesses local as well as global optimization properties. Two examples are presented, where DIRECT optimizer is combined with Kriging metamodeling. The first example involves optimization of the shape of a slot array Frequency Selective Surface (FSS). In the second example, the electromagnetic coupling between the harness and the FM antenna on a Deville model automobile is minimized. Both examples demonstrate the exceptional rate of convergence and the flexibility of the proposed optimizer.

A thin broadband cavity-backed slot spiral antenna for automotive applications

A second mode slot spiral antenna having maximum radiation between the broadside and horizontal directions is proposed for automotive applications. The antenna is situated in a shallow cavity and can be conformally mounted at various locations on a car. Finite element and fast multipole moment method simulations of the isolated and mounted antennas are provided and compared with measurements. It is shown that a 5.5 diameter aperture with 0.5 inch deep cavity can provide coverage for DAB, PCS and SDARS systems.

Electromagnetic analysis and shielding of slots on resonant and non-resonant realistic structures with MLFMM

Coupling and interference in electronic devices is of increasing concern due to the presence of either intentional or unintentional internal or external electromagnetic sources. Such sources can cause sufficient disruption to the circuit or chip logic to the point where the functionality and logic state of the electronic device can be altered due to such extraneous sources. Coupling into these devices can occur either from ventilation slots or though power/signal lines which penetrate into the enclosure of the cavity structure. The latter can introduce conduction noise and ground fluctuations into the signal ports. Plane wave illumination, of unity field strength, onto a microwave filter is calculated to give an induced voltage of 4 mV at the 50 /spl Omega/ output port. The actual excitation was a pulse train with a period of 300 ns with the same center frequency as the filter (2.150 GHz). These calculations were carried out using a well-validated method of moments simulator. Thus, a large amplitude pulse signal of 300 V/m may induce a noise signal of 0.12 V. This could potentially cause failures in logic states for digital circuits and spurious waveforms for analog amplifier circuits. Furthermore, cavity enclosures can amplify the external signals by as much as 10 dB to 20 dB, especially in the overmoded region. This can be seen where the EFS fluctuations due to cavity and slot resonances pose a problem for a circuit configuration. Moreover, the presence of wires through the slot enhance coupling into the cavity. This is demonstrated where we show the electric field shielding factor measured in the middle of the cavity due to a plane wave incidence, for wires penetrating through aperture and into the cavity. The penetration is through a circular slot of area 60 cm/sup 2/. Both the straight and bent (longer) wires deteriorate the EFS quite significantly at lower frequencies and even at higher frequencies for the bent wire. We particularly note that the bent wire causes low EFS even away from the cavity resonances due to greater re-radiation of energy from external illumination into the cavity enclosure. This is computed with the well-validated multilevel fast multipole method (MLFMM).

Fast frequency domain tools for system analysis of EMI/EMC topologies

With the increased use of wireless devices and applications, coupling and interference in electronic devices due to either intentional or un-intentional electromagnetic sources is of increased concern. Such sources can cause sufficient disruption to the circuit or chip logic to the point where the functionality and logic state of the electronic device can be altered due to such extraneous sources. In this paper, we employ fast EM algorithms such as the multilevel fast multipole moment method (MLFMM) and the hybrid finite-element boundary-integral (FE-BI) method for the analysis of coupling from external sources into realistic geometries. Specifically, the MLFMM is employed to analyze large-scale problems such as vehicular structures whereas the FE-BI method is used to analyze volumetric structures with dielectric media such as printed circuit boards. In this paper, the method of moments (MoM) accelerated by MLFMM is employed to analyze for the fields within an automobile chassis in the presence or absence of a wire harness and for different aperture sizes. The employed FE-BI method focuses on the analysis of plane wave illumination onto passive circuit geometries such as the microstrip interdigital filter and active circuit topologies like an active microstrip low noise amplifier.

Optimization for RF coupling and interference reduction of devices in complex systems

In recent years, evolutionary optimization methods such as genetic algorithms have become increasingly popular in EM optimization problems. However, these methods tend to have slow convergence bounds and further, they do not yield a deterministic optimal solution. In this paper, we propose a new method of using Kriging meta-modeling in conjunction with the divided rectangles (DIRECT) global optimizer to yield a global optimum solution. DIRECT yields a deterministic answer with a fast convergence bound and inherits both local and global optimization properties. This proposed hybrid optimization routine is applied here to two examples dealing with electromagnetic coupling reduction. One of them deals with minimizing coupling to sensors from antenna radiation on automobiles. The other example focuses on multi-sensor optimization subject to RF coupling constraints.