Electromagnetic pulsed‐wave radiation in spherical models of dispersive biological substances

Abstract

In analytical studies, we investigated induced-field patterns and SAR distributions in a lossy, dispersive, homogeneous, dielectric sphere typical of muscle tissue as irradiated by a plane-wave pulse train consisting of a pulse-modulated sinusoidal carrier wave. Calculations were made for carrier frequencies of 1, 3, and 15 GHz, pulse widths of 0.333, 2.0 and 4 ns, and pulse repetition rates of 1.11 x 10(6), 100 x 10(6), and 181.18 x 10(6) pps. The classical Mie solution was modified for a train of incident pulses that was represented by a Fourier series, and the fast-Fourier transform was used to sum the series. Computationally, the technique proved to be feasible and less expensive than we expected. The calculated field patterns show that the sphere's physical dimensions and the internal wavelength of the carrier greatly influence the nature of pulse-train propagation in the sphere. Harmonics having internal wavelengths nearly equal to the radius of the sphere produce most of the absorption; other harmonics produce little absorption. An intense hot spot is observed in spheres with radii that match the carriers' wavelengths.

Thermal and nonthermal mechanisms of interaction of radio-frequency energy with biological systems

“…Consider a uniform sphere of radius in air, subject to an incident plane wave of amplitude . The field inside the sphere can be obtained analytically using Mie scattering theory [8]- [10]. The solution depends greatly on the wavelength of the radiation in the sphere as compared to the radius .…”

“…The response of this system is characterized by four time constants. Two are of the form ns (10) These represents "Maxwell-Wagner" dispersions, associated with the transition of the inner and outer media from principally conductive to principally capacitive in nature [6]. (At radian frequencies the media are principally dielectric; at lower frequencies they are principally conductive and hence exclude fields.)…”

Time Domain Dosimetry in Layered Media

“…5 the electric field along the z diameter of a lossy dielectric sphere resulting from the incidence of a linear polarized wave has been represented, showing the frequently found, and well known, result that the field in the emerging side is of same order than the one in the entering side [5]. For arbitrary time variation the Fourier expansion allows to calculate the time domain fields [6]. Thus the diffraction by layered spherical obstacles is formally solved in a similar way as in the plane case.…”

Analyses of Transient Energy Deposition in Biological Bodies Exposed to Electromagnetic Pulses Using Parameter Extraction Method

“…The main problem in deriving the pulse waveform inside biological bodies is due to the difficulty in incorporating the frequency dependence of the dielectric properties of the biological tissues, which is represented by the four-term ColeCole model [20]. Some studies adopted the fast Fourier transform or fast inverse Laplace transform (FILT) [21] in the calculation of the exact time-domain waveforms but a new calculation is required at every observation point inside biological bodies [22,23]. As a result, large computational resources are needed in obtaining solutions across the whole analysis region.…”