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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 1:55 |
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Conference: Bucharest University Faculty of Physics 2001 Meeting
Section: Biophysics; Medical Physics
Title:
Peculiarities of Pulsed Microwave Absorption in Water and Consequences upon Biological Effects of Tissue Exposure to Microwave Fields
Authors:
Simona Miclaus, Paul Bechet
Affiliation:
Academia Fortelor Terestre, Str. Revolutiei 3-5, 2400 Sibiu
E-mail
Keywords:
Abstract:
Present paper’s aim is the comparative theoretical study of very high frequency (300MHz-300GHz) electromagnetic continuous/pulsed fields propagation in water. The water is considered as a plane layer, and the waves are incident on it, from air. We looked for differences between transmission and absorbtion of electromagnetic energy when the signal contained only the carrier, or it was pulse modulated, with different pulse parameters. Choosing water as a dispersive dielectric was due to the fact that most tissues contain water, and water is the one that is significant for microwave frequencies absorption in tissues.
We used MATHCAD software in our study. First we calculated the FFT transform (time domain to frequency domain transformation) of the microwave signal – incident E component of the field. Known dielectric characteristics for pure water were used in order to calculate the transmission coefficient for the spectral components of the signal. Then we calculated the transfer fuction and we represented the transmitted signal at different depths in the water layer, and the temporal evolution of transmission too. Finnaly, we were able to calculate the specific absorption rate (in W/kg) for the whole train pulses, for the first harmonic and/or for the carrier only.
The results show that absorption of energy is different for a continuous wave, comparative to a pulsed one. For the pulsed wave, the absorption is influenced by the carrier frequency of the signal and pulse repetition frequency. Duty factor of the pulse is less important. As the ratio between the carrier frequency and the pulse repetition frequency increases, the role of the carrier becomes dominant for the absorption. When one looks for the biological effects of microwave exposure, it is important to foreknow both the field source parameters of emission and the dielectric characteristics of the exposed target/tissue for the interest frequency region, so as to first make a theoretical assesement on what may specifficaly happen.
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