A. Vander Vorst

Applications of RF/microwaves in medicine

Medical applications of RF/microwaves are highlighted in this paper. The emphasis is placed on newer emerging diagnostic and therapeutic applications, such as microwave breast cancer detection, and treatment with localized high power used in ablation of the heart, and liver, benign prostate hypertrophy, angioplasty, and others. A very brief outline of biological effects of RF/microwaves and associated issues is given as background to the applications.

Fully-Depleted SOI CMOS Technology for Low-Voltage Low-Power Mixed Digital/Analog/Microwave Circuits

This paper demonstrates that fully-depleted (FD) silicon-on-insulator (SOI) technology offers unique opportunities in the field of low-voltage, low-power CMOS circuits. Beside the well-known reduction of parasitic capacitances due to dielectric isolation, FD SOI MOSFETs indeed exhibit near-ideal body factor, subthreshold slope and current drive. These assets are both theoretically and experimentally investigated. Original circuit studies then show how a basic FD SOI CMOS process allows for the mixed fabrication and operation under low supply voltage of analog, digital and microwave components with properties significantly superior to those obtained on bulk CMOS. Experimental circuit realizations support the analysis.

Spectral domain form of new variational expression for very fast calculation of multilayered lossy planar line parameters

A new spectral domain formulation of the propagation characteristics for planar and coplanar lines is presented. It is based on a newly established variational principle, valid for a spatial as well as for a spectral formulation. In combination with conformal mapping, it drastically reduces the complexity of the numerical computation and leads to rapidly convergent results even when higher order modes are considered. Mathieu functions are shown to be very efficient expressions for trial fields of the dominant and the higher order modes in slots. Calculation is fast: it is made on-line on a regular PC. Results obtained on open and shielded lines have been successfully checked with new experimental data and with previously published data. The method is general enough to accommodate gyrotropic substrates. The paper however is limited to isotropic media. >

A novel nanostructured microstrip device for tunable stopband filtering applications at microwaves

The authors present a novel microstrip structure using a nanoscale porous substrate filled by a ferromagnetic material, forming an array of nanowires perpendicular to the ground plane. When compared with photonic bandgap structures, the stopband behavior is created here by a gyromagnetic resonance phenomenon in the metallic nanowires. This resonance is tuned by means of a DC magnetic field parallel to the nanowires, in a very good agreement with the gyromagnetic theory. Also, tuning can be achieved over more than one octave, because the nanoscale geometry ensures that fields penetrate into the whole wire area up to 40 GHz. Other advantages are detailed in this work.

Measurements of complex permittivity of biological and organic liquids up to 110 GHz

A new procedure for measuring the complex permittivity of liquids has been set up. It is based on measuring the scattering parameters of waveguide two-ports, up to 110 GHz, and on an original calibration method previously developed by the authors. Measurements describe the complex permittivity of biological and organic liquids at frequencies above 20 GHz, up to 110 GHz. The liquids are methanol, dioxane, and blood. Comparisons with the well established Debye equations have been made and some parameters have been recalculated when necessary.

1990-1995 advances in investigating the interaction of microwave fields with the nervous system

After a short review of the nervous system and its constituents, recent data on microwave bioeffects are reviewed and evaluated, in particular, the effects on the brain and the spinal cord and under low-level irradiation. Special attention is paid to new results on the effects of modulated and pulsed waves with respect to both continuous wave (CW) irradiation, and, in particular, to the frequency of the modulation. The last section is devoted to modeling and simulation of the nervous system and nervous fibers, where significant progress has been made during the last years. Except for some tutorial aspects, the reviewed literature essentially covers the 1990-1995 period.

A Computer Optimization of the Rayleigh-Ritz Method

A method has been developed to improve the use of the RayIeigh-Ritz procedure. A criterion is established, which is a measure of the cumulative improvement due to the addition of more and more terms in the series expansion. Without calculating the exact roots of determinantal equations, the convergence is accelerated by skipping unnecessary intermediate steps. The computation time is drastically reduced because the final result is obtained after only a few (not more than 5 to 7) values of determinants of increasing order. Inhomogeneneously loaded waveguides are chosen as an application because the exact solution is available to check the validity of the method. The results obtained with the method described in this paper are compared with other approximate procedures. The comparison shows a definite advantage for the suggested technique.

A new variational formulation, applicable to shielded and open multilayered transmission lines with gyrotropic non-Hermitian lossy media and lossless conductors

A new variational expression is derived for the propagation constant of inhomogeneous shielded and open planar lines with gyrotropic lossy substrates. It yields rapidly convergent results even when higher order modes are considered. Results obtained on open and shielded lines and structures agree very well with experimental results. The efficiency of the formulation is such that calculations are made on-line on a regular PC. >

Application of a Variation-Iteration Method to Inhomogeneously Loaded Waveguides

An approximate technique for eigenvalue equations, the variation-iteration method, is commonly used in theoretical physics. Through an adequate numerical treatment it reduces to the inverse iteration method. It is shown here that this technique is most promising. Starting from an initial trial function, iterates are calculated, in which the components relative to the unwanted true eigenfunctions are eliminated. Both an upper and a lower bound of the unknown eigenvalues are calculated. This leads to an approbate eigenvalue within a specified accuracy with respect to the exact (unknown) eigenvalue. An extrapolation technique further accelerates the convergence. The computation time is shorter than when using the Rayleigh-Ritz procedure. The method is applied here to the dielectric-slab loaded waveguide, because the exact solution is available to check the validity of the method. The influence of the geometry, the dielectric constant, and the frequency is evaluated.

Microwave bioelectromagnetics in Europe

Results of a survey in the area of microwave bioelectromagnetics made among about 40 European research teams are presented. The research fields covered are behavioral effects; biophysics; cells, membranes, and microorganisms; clinical investigations; development and genetics; dosimetry and radar effects; the heart; hyperthermia; imaging; the immune system and immunology; and nerves and the nervous system.<<ETX>>Results of a survey in the area of microwave bioelectromagnetics made among about 40 European research teams are presented. The research fields covered are behavioral effects; biophysics; cells, membranes, and microorganisms; clinical investigations; development and genetics; dosimetry and radar effects; the heart; hyperthermia; imaging; the immune system and immunology; and nerves and the nervous system. >