Vincent A. Thomas

The use of SPICE lumped circuits as sub-grid models for FDTD analysis

A general approach for including lumped circuit elements in a finite difference time domain (FDTD) solution of Maxwells equations is presented. The methodology allows the direct access to SPICE to model the lumped circuits, while the full 3-dimensional solution to Maxwells equations provides the crosstalk and dispersive properties of the microstrips and striplines in the circuit.<<ETX>>

FDTD analysis of an active antenna

Coupled FDTD-SPICE simulations are performed for an active antenna problem. The results are comparable to previously published results using FDTD in conjunction with special integration techniques for the nonlinear elements. Some differences occur, and better agreement with experiment is observed for our newer approach. The main advantages are that all of the SPICE device models are directly available for FDTD modeling and the efficient SPICE integration schemes can be used directly. No user intervention is required for either the device models or the integration schemes.<<ETX>>

Small signal analysis of active circuits using FDTD algorithm

The FDTD method is extended to analyze a microwave amplifier. This amplifier includes matching circuits, DC bias circuits, and an active device. Equivalent current sources are used to model the active element. With the small signal model of the active element, the FDTD full-wave simulations show good agreement with measured results. >

Performance improvements with advanced design foils in high-current electron beam diodes

A design for the vacuum/pressure barrier of an electron-beam diode ready to be fielded on a large krypton-fluoride excimer laser is described. The barrier is a composite foil, fabricated from carbon fibers, Kapton-membrane, epoxy, and copper foil. This composite foil has advantages over more traditional metal foils, exhibiting particularly high tensile strength and a high modulus of elasticity. Other important properties of these composites for use in KrF excimer laser applications include: high electron transmission with low loss to scattering, chemical compatibility with fluorine, low porosity, and low reflectivity in the ultraviolet. The mechanical properties of the composite foil allow the design of support structures (hibachis) which incorporate larger openings than are possible with metal foils with similar electron transmission characteristics. >

Modeling combined collisional/collisionless plasma interpenetration

This paper describes one technique by which multifluid modeling capability can be achieved within the context of a Lagrangean single-fluid model. This technique is applied to the interpenetration of laser-produced, substantially collisionless plasmas. A single-fluid model by itself cannot simulate the interpenetration of a collisionless plasma correctly, but must be augmented with some other tool. One tool that can calculate collisionless plasma interpenetration correctly is ISIS, a particle code for plasma simulations which includes appropriate collision models. However, ISIS does not have the necessary physics to do the laser deposition, the atomic physics, the radiation transport, and does not possess a realistic electron temperature model. With appropriate integration of the single-fluid code and ISIS, a new capability is achieved which allows simulation of the colliding plasma problem, a problem that neither code can properly simulate individually.

Inclusion Of Lumped Elements In Finite Difference Time Domain Electromagnetic Calculations

A general approach for including lumped circuit elements in a finite difference, time domain (FD-TD) solution of Maxwell`s equations is presented. The methodology allows the direct access to SPICE to model the lumped circuits, while the full 3-Dimensional solution to Maxwell`s equations provides the electromagnetic field evolution. This type of approach could be used to mode a pulsed power machine by using a SPICE model for the driver and using an electromagnetic PIC code for the plasma/electromagnetics calculation. The evolution of the driver can be made self consistent with the behavior of the plasma load. Other applications are also possible, including modeling of nonlinear microwave circuits (as long as the non-linearities may be expressed in terms of a lumped element) and self-consistent calculation of very high speed computer interconnections and digital circuits.

Coupling Of The Pisces Semiconductor Device Modeler To A 3D Maxwell FD-TD Solver

A code non-invasive approach for the coupling of the 3D Maxwell equations in their FD-TD difference form to the PISCES device simulator has been developed. The algorithms are coupled through the standard PISCES input setup, which is reset every time step. The method requires the specification of a time dependent current drive to the device, in parallel with an effective capacitance that represents external displacement current effects. To do this, an effective parallel capacitance is simulated in the PISCES setup, by first setting the serial capacitance C, and then by changing the drive voltage impulsively each time step so that the time derivatives of the applied voltage V{sub app} are ignored. The V{sub app} is made very large relative to the potential at the device terminals, and R is continually adjusted to set the effective current V{sub app}/R to the desired drive value each cycle. The success of this procedure is demonstrated through calculations for a diode at the end of a microstrip transmission line. Comparison is made with simple analytic solutions at low frequency to avoid capacitive effects in the non-ideal PISCES diode.