Susumu J. Yakura

Study of High-Power Wideband Terahertz-Pulse Generation Using Integrated High-Speed Photoconductive Semiconductor Switches

A 3-D finite-difference time-domain analysis of a photoconductive-semiconductor-switch-based terahertz (THz) source, integrated with a standard dipole and a large-aperture radiator, is presented. The simulation analysis is based on the coupling of semiconductor equations for charge transport with Maxwell electromagnetic equations. The simulation provides the transient field redistribution, carrier generation characteristics, and the field acceleration as a result of the bias voltage on the device, contributing to the nonlinear behavior of THz-pulse generation. A comparison of the radiation characteristics of the two antenna types shows that the large-aperture antenna produces approximately three times higher radiation amplitude and broader power spectrum than those produced by the dipole antenna.

An FDTD Interaction Scheme of a High-Intensity Nanosecond-Pulsed Electric-Field System for In Vitro Cell Apoptosis Applications

A finite-difference time-domain analysis of a high-intensity nanosecond-pulsed electric-field (nsPEF) system, composed of a pulse-forming line (PFL) and a universal electroporation cuvette, is described. The simulation scheme is based on interactions of 1-D transmission-line equations for the PFL and 3-D Maxwells curl equations for the cuvette volume. Simulations incorporate system adjustment to facilitate maximum transfer of electrical energy from the PFL to the cuvette medium. Experimental validation of the voltage across the cuvette electrodes through the laboratory-constructed nsPEF system with an energy density of ~1 J/cm3 reveals an overall agreement with some discrepancies. The distribution profiles of the transient field inside the cell suspension area during the excitation of 5-kV 10-ns pulses would adequately account for the feasibility of using an integrated model as a design benchmark for the interaction physics of the generated nanosecond pulses and culture vessel. The observed nsPEF effects on cells include increased transmembrane potentials across organelle membranes without permanently damaging the cell membrane, increasing the probability of electric field interactions with intracellular structures.

AN ELECTROMAGNETIC TOPOLOGY APPROACH: CROSSTALK CHARACTERIZATIONS OF THE UNSHIELDED TWISTED-PAIR CABLE

Abstract—The inductive effect of near-end crosstalk for a category five unshielded, twisted-pair cable has been verified using the electromagnetic topology simulation method. Crosstalk reduction and its dependency on such parameters as driving signals, circuit configuration and impedance, are studied. The simulation results are consistent with analytical analysis. Results show that the straightthrough, differential-generator, twisted-pair receptor model is the most effective configuration to control the near-end crosstalk level. This is due to the influences from both the neutralizing mutual inductance and the single current generator. The simulation results also show that electromagnetic topology-based predictions are valid only for cables that are electrically short. Simulations are carried out using a compaction scheme with a single equivalent circuit. As a result, the unshielded, twisted-pair cable portion of the circuit can be combined with a larger network for analyzing the overall response of the entire network system.

MINIMIZING CROSSTALKS IN UNSHIELDED TWISTED-PAIR CABLES BY USING ELECTROMAGNETIC TOPOLOGY TECHNIQUES

Crosstalk reduction is analyzed for a reconfigured category-five cable network using electromagnetic topology-based simulation. The reconfigured network results in a marked reduction in inductive near-end crosstalk for the unshielded twisted-pair cable network. Analyses show that half-loop shifting of the generator-pair wires placed next to the receptor is the most effective way to control the near-end crosstalk level. This is primarily due to additional coupling sources induced on receptor wires that effectively deactivate the original cross coupling effect. The analysis also reveals the usefulness of electromagnetic topology-based simulations. The technique applied in this paper is applicable for any large network systems. A sub-network compaction scheme is critical in creating the equivalent junctions that provide a significant reduction in total computational time and total computer memory requirement for analyzing large network systems. For a 5.28-m long cable we have considered in this paper, the results are valid up to 10 MHz.

Electromagnetic topology quasisolutions for aperture interactions using transmission line matrix

A hybrid simulation technique that integrates transmission line matrix method with electromagnetic topology solutions has been employed to link a field scattering problem at an aperture in order to analyze the frequency and temporal characteristics of electromagnetic pulses. Using this same unified multiconductor transmission line network formulation any subsequent coupling with cables at the other side of the aperture can be integrated into the solution. The hybrid circuit can also be integrated to any existing topological simulation circuit for analyzing very large electrical systems. Incorporation of the compaction technique in the topological simulation reduces the number of simulation grids significantly, resulting in efficient computation without sacrificing accuracy. The simulation results for scattering fields at the aperture compare well with the finite-difference time domain method.

Modeling timing variations in digital logic circuits due to electrical fast transients

Integrated circuits (ICs) sometimes fail when their power supply is disrupted by external noise, like an electrical fast transient (EFT). Soft failures in these cases are often caused by timing errors in the IC, for example when delays through logic become too large to meet internal timing constraints. Methods are needed to predict when these failures will occur. A closed-form expression is proposed in this paper to predict the change in propagation delay through logic as a result of an EFT on the IC power supply. The expression uses process parameters that can be found from SPICE models of FETs within the IC or through external measurements of the IC when SPICE models are unavailable. The model is used to predict the frequency of a CMOS ring oscillator manufactured in 0.5 um technology. Predicted results closely match those found through measurements with a maximum relative error of approximately 1%.

A generic topological simulation scheme for studying aperture electromagnetic field interactions and cable couplings

A modified electromagnetic topology (EMT) simulation scheme for the interactions of an electromagnetic wave with an aperture and with cables of an electrical system beyond the aperture is described. The modified EMT simulation scheme addresses a concept in dealing with an aperture node of the topological circuitry without having to specify the details of the entire electrical circuitry. The results of the modified EMT simulation scheme have been validated through experiments for aperture∕wave interactions and the induced currents on the cable near the aperture. The aperture transfer functions, obtained for both the simulation and experimental cases, have shown the characteristic response similar to that of the high-pass filter with a cutoff frequency. The simulated and measured currents on a cable, placed behind the aperture, resulted in good agreement with each other, providing the good validation of the modified EMT simulation scheme. Under this scheme, any change in topological circuitry can be handled...

Electromagnetic Topology: a Modular Junction Approach for a System Level Interaction Problem

A new approach to perform electromagnetic topology based simulation is proposed by incorporating modular scattering junction concept. This method substitutes the multi- step computation technique and is convenient to implement. The method also allows for incorporating substructural modifications and does not require repeating solutions to the entire system. The overall simulation utilizes transmission line matrix compaction, finite-difference time-domain method, and reciprocity theorem to simulate the system interaction. Results are compared with experiments conducted in the laboratory. A good agreement is shown for the simulated and experimental data.

A Modular Junction Topological Approach to Aperture - System Interaction Problem

A new approach to perform electromagnetic topology based simulation is proposed by incorporating a modular scattering junction concept. This method substitutes the multistep computation technique presented earlier and is convenient to implement. The method also allows for incorporating substructural modifications without repeating solutions to the entire system. The simulation of the overall interaction utilizes transmission-line matrix compaction, finite-difference time-domain method, and reciprocity theorem to create different junctions. Results are compared with experiments conducted in the laboratory. A good agreement is shown for the simulated and experimental data.

An Electromagnetic Topology Method for Cable Interactions Using a Radiating Dipole at Apertures

Simulations, based on electromagnetic topology, have been carried out to characterize external field penetration through apertures and their interactions with a cable linking two personal computers. Experimentally determined scattering parameters for the cable linking the two computers have been used in the study. The simulation involves coupling of the generated aperture fields with the cable by treating aperture fields as distributed source elements. The transfer function for the topological network is generated by assuming a short circuited radiating dipole antenna at the aperture with finite-difference time-domain (FDTD)-created driving sources. Results show that the effects on cables depend on the nature of the external pulse, the scattering parameter, the aperture, and the cable response. The simulation has been performed using an electromagnetic topology-based code, CRIPTE, which allowed us to analyze coupling of the field with multiconductor transmission lines.