Biomedical subjects

John H Booske

Publications and source records attributed to John H Booske.

4 recordsLinked to original sources

PubMed2006

Ultrawideband temperature-dependent dielectric properties of animal liver tissue in the microwave frequency range.

The development of ultrawideband (UWB) microwave diagnostic and therapeutic technologies, such as UWB microwave breast cancer detection and hyperthermia treatment, is facilitated by accurate knowledge of the temperature- and frequency-dependent dielectric properties of biological tissues. To this end, we characterize the temperature-dependent dielectric properties of a representative tissue type-animal liver-from 0.5 to 20 GHz. Since discrete-frequency linear temperature coefficients are impractical and inappropriate for applications spanning wide frequency and temperature ranges, we propose a novel and compact data representation technique. A single-pole Cole-Cole model is used to fit the dielectric properties data as a function of frequency, and a second-order polynomial is used to fit the Cole-Cole parameters as a function of temperature. This approach permits rapid estimation of tissue dielectric properties at any temperature and frequency.

Animals↗

PubMed2006

FDTD analysis of a gigahertz TEM cell for ultra-wideband pulse exposure studies of biological specimens.

Gigahertz transverse electromagnetic (GTEM) transmission cells have been previously used to experimentally study exposure of biological cells to ultra-wideband (UWB), monopolar, electromagnetic pulses. Using finite-difference time-domain (FDTD) simulations we examine the time-dependent electric field waveforms and energy dose spatial distributions within a finite volume of biological cell culture medium during these experiments. The simulations show that when one or more flasks containing cell culture media are placed inside the GTEM cell, the uniform fields of the empty GTEM cell are significantly perturbed. The fields inside the cell culture medium, representing the fields to which the biological cells are exposed, are no longer monopolar and are spatially highly nonuniform. These effects result from a combination of refraction and distortion of the incident wave, combined with excitation of resonant eigenmodes within the cell culture medium volume. The simulations show that these distortions of the incident waveform may be mitigated by supporting the sample on a high permittivity pedestal and modifying the incident waveform to more closely approximate a Gaussian pulse. Under all simulated conditions, the estimated maximum temperature rises are completely negligible, ensuring that any experimentally observed unusual cell function or histopathology can be associated with nonthermal effects.

Cell Culture Techniques↗

PubMed2004

Eulerian method for computing multivalued solutions of the Euler-Poisson equations and applications to wave breaking in klystrons.

We provide methods of computing multivalued solutions to the Euler-Poisson system and test them in the context of a klystron amplifier. An Eulerian formulation capable of computing multivalued solutions is derived from a kinetic description of the Euler-Poisson system and a moment closure. The system of the moment equations may be closed due to the special structure of the solution in phase space. The Eulerian moment equations are computed for a velocity modulated electron beam, which has been shown by prior Lagrangian theories to break in a finite time and form multivalued solutions. The results of the Eulerian moment equations are compared to direct computation of the kinetic equations and a Lagrangian method also developed in the paper. We use the Lagrangian formulation for the explicit computation of wave breaking time and location for typical velocity modulation boundary conditions.

Journal Article↗

PubMed2004

Mechanisms for phase distortion in a traveling wave tube.

We present a view of the physics of phase distortion in a traveling wave tube (TWT) based on unique insights afforded by the MUSE models of a TWT [IEEE Trans. Plasma Sci. 30, 1063 (2002)]]. The conclusion, supported by analytic theory and simulations, is that prior to gain compression phase distortion is due to harmonic frequencies in the electron beam and the resulting "intermodulation" frequency at the fundamental, and not the often cited "slowing down of electrons in the electron beam." We draw these conclusions based on MUSE simulations that allow explicit control of electron beam frequency content, an analytic solution to the S-MUSE model [IEEE Trans. Plasma Sci. 30, 1063 (2002)]] that reveals that phase distortion is due to the fact that the fundamental frequency is an intermodulation product of itself, and large signal LATTE [IEEE Trans. Plasma Sci. 30, 1063 (2002)]] simulations that are modified to remove the effect of the slowing down of electrons in the electron beam. As applications of the theory we compare S-MUSE simulations to an amplitude phase model using the analytic phase transfer curve, we study dependence of phase distortion on circuit dispersion and electron beam parameters at the second harmonic with large signal LATTE simulations for narrow and wide band TWT designs, and we consider the phase distortion theory in the context of TWT linearization.

Journal Article↗