V.V. Liepa

Full wave analysis of infinitely periodic lossy wedges

The volume-surface integral equation (VSIE) is modified to solve the scattering problem of a wedge absorber not only for side incidence but also for forward incidence. The model is assumed to consist of infinitely periodic lossy wedges backed by a perfect conductor. By taking advantage of periodicity in the x-direction and homogeneity in the z-direction of the wedge absorber geometry, the infinite limits on volume and surface integrals are reduced to surface and line integrals, respectively, over only one period. To solve the modified VSIE numerically, a point matching technique is applied. The computer code was checked by calculating the reflection coefficient of a lossy slab backed by a perfect conductor.<<ETX>>

Electromagnetic analysis of plane wave illumination effects onto passive and active circuit topologies

The finite element-boundary integral method, incorporating the multilevel fast multipole method to reduce the storage cost of the boundary integral matrix, is applied to the analysis of two microstrip filter circuits illuminated by a plane wave. Simulated results indicate that significant voltages are induced across the output ports close to the filters resonances. The study is further extended to a microstrip low-noise amplifier circuit. It is shown that, at certain field strengths, the plane wave illuminating the microstrip amplifier circuit can introduce considerable gain deviation and nonlinearity to its operation.

Electromagnetic Interference in an Implantable Loop Recorder Caused by a Portable Digital Media Player

The implantable loop recorder has been shown to be a cost‐effective tool for diagnosis of intermittent cardiovascular symptoms such as syncope and palpitations. Electromagnetic interference in these recorders may be caused by commonly encountered electronic devices such as antitheft electronic surveillance systems and magnetic resonance imaging cameras. In this report, we describe interference in two patients with implantable loop recorders from a portable digital media player.

EM coupling and suppression through slots into lossless overmoded cavities using the multilevel fast multipole algorithm

With increased use of wireless communication devices and integrated wireless sensors, the problem of electromagnetic coupling and interference from radiating devices into electronic components or tissues cells becomes more crucial. Previous works in this area have concentrated on the use of the Finite Difference Time Domain or approximate models for EMC analysis. In this paper, we employ the multilevel fast multipole algorithm for EMC analysis on complicated platforms. To being with, we will investigate the effect of various aperture shapes on coupling into an overmoded lossless rectangular cavity. Further, the effect on EM coupling due to penetration of wire traces through apertures into the cavity interior will be investigated. Finally, a method of improving shielding via the use of a sequence of an array of wire strips and slot shadowing will be investigated and presented.

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.

An engineer's approach for terminating finite element meshes in scattering analysis

When solving open-region scattering problems via the finite-element method, the infinite region exterior to the scatterer must be truncated with an artificial boundary in order to limit the number of unknowns. An approach that can be used to truncate the infinite region in a finite-element analysis is proposed which involves an artificial conducting boundary (either electric or magnetic). As can be expected, this boundary will cause nonphysical reflections of the scattered field; however, these can be minimized by coating the inner face of the boundary with a layer or several layers of fictitious dielectric whose thickness and constitutive parameters can be so chosen that it absorbs the field over a wide range of incidence angles. Based on the formulation presented, a simple finite-element program was written using a banded matrix algorithm with a variable bandwidth storage scheme. Numerical results are presented.<<ETX>>

Measured back scattering cross section of thin wires

Prof. Ralph E. Hiatt was instrumental in designing the first anechoic chamber at the Radiation Laboratory Willow Run Facility of the University of Michigan. During the nineteen sixties it was one of the largest such facilities in the world. It is therefore appropriate to describe some of the basic RCS measurements, such as these wires, carried out in this chamber. A set of back scattering patterns was measured for a thin (metallic) wire (a//spl lambda/=6.27/spl times/10-3) for l//spl lambda/=0.3(0.25)0.5(0.5)1.60(0.10)5.42, where a is the radius of the wire, l is the wire length, and /spl lambda/ is the wavelength. From the set of patterns a number of curves were extracted showing the amplitude and phase of each back scattering lobe as a function of the wire length. These curves provide a convenient means of cross section estimation and may be used to reconstruct with reasonable accuracy the back scattering pattern for any value of l//spl lambda/, l//spl lambda//spl les/5.42. These data have been found useful in studies dealing with scattering form composite geometrical shapes where it is often found useful to compare the back scattering patterns with those of a thin wire, especially in the resonance region. A block diagram of a CW system used for the measurement is shown.

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).

A quadruple-gap loop antenna for low frequency radiated emission measurements

This paper discusses the detailed design and optimization of a four-quadrant loop antenna with interchangeable feed. This antenna is designed to minimize electric field sensitivity while maintaining superior magnetic field response in both the transmitting and receiving modes. Direct tradeoffs between magnetic and electric field sensitivity, field uniformity, antenna dimension, feed design, and operational bandwidth are discussed. Finally, the antenna factor of the quadruple-gap loop antenna is directly compared with theoretical formulations. The discussions put forth are directly applicable when considering loop antennas in low frequency radiated emission testing.

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.