Abstract-A rigorous analytical procedure is developed that allows the exact evaluation of the complete integral representations for the time-harmonic electromagnetic (EM) field components generated by a vertical magnetic dipole (VMD) lying on the surface of a flat and homogeneous lossy half-space. Closed-form expressions for the radial distributions of the EM field components induced on the surface of the half-space are provided in terms of exponential functions and modified Bessel functions. Such expressions make it possible to overcome the limitations implied by the previously published quasi-static solutions, which are valid only in the low-frequency range. Numerical results are presented to show where the quasi-static approximations deviate from the exact solutions for a given homogeneous medium as frequency is changed. The computed amplitude and phase frequency spectra of the EM field components demonstrate that the quasi-static approach produces inaccurate results at frequencies higher than 1 MHz, and that, in particular, it leads to underestimating the EM field strength. Finally, it is also shown that at a frequency equal to or greater than 10 MHz excellent results in terms of accuracy may be obtained by using the high-frequency asymptotic forms of the exact solutions.
Abstract-A high-order closed-form solution for the specific absorption rate (SAR) distribution induced inside a plane geometry fatmuscle tissue by a shortwave diathermy induction coil is presented. The solution is derived starting from the complete integral expressions for the electromagnetic field components generated by a currentcarrying circular loop located horizontally above a stratified earth. It is valid in a wide frequency range, and is flexible to any multi-turn coil configuration. The spatial distribution of the SAR induced in the muscle tissue by a flat round coil is computed by using the proposed formulation, the zero-order quasi-static one, and the finite difference time domain (FDTD) method. Excellent agreement is demonstrated to exist between the results provided by the new approach and those achieved through FDTD simulations. On the contrary, the performed computations show that the zero-order solution leads to over-estimate the SAR. The performances of the round and figure-eight coil geometries are compared. Despite of what has been argued in previously published papers, it turns out that the figure-eight coil is less energetically efficient than the round one. The work in the present paper is an extension of a previous work.
Plane-geometry single-and multileaf coil antennas fed by radio-frequency (RF) generators are frequently used to produce electric currents and therapeutic ohmic heating in subcutaneous fat and muscle tissues by electromagnetic induction. In particular, the butterfly (two-leaf) configuration has been regarded as a high-efficiency geometry for diathermy purposes. The aim of this letter is to prove by numerical simulation that any multileaf coil is significantly less efficient than the round one and that, in general, efficiency worsens with increasing the number of leaves. Simulation results show that for a given power density to be deposited in the tissue, replacing a single leaf with a multileaf structure causes an increase of energy consumption by at least 20%.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.