Verification of the electromagnetic deep-penetration effect in the real world

Abstract

The deep penetration of electromagnetic waves into lossy media can be obtained by properly generating inhomogeneous waves. In this work, for the very first time, we demonstrate the physical implementation and the practical relevance of this phenomenon. A thorough numerical investigation of the deep-penetration effects has been performed by designing and comparing three distinct practical radiators, emitting either homogeneous or inhomogeneous waves. As concerns the latter kind, a typical Menzel microstrip antenna is first used to radiate improper leaky waves. Then, a completely new approach based on an optimized 3-D horn TEM antenna applied to a lossy prism is described, which may find applications even at optical frequencies. The effectiveness of the proposed radiators is measured using different algorithms to consider distinct aspects of the propagation in lossy media. We finally demonstrate that the deep penetration is possible, by extending the ideal and theoretical evidence to practical relevance, and discuss both achievements and limits obtained through numerical simulations on the designed antennas.

Complex Refraction Metasurfaces for Locally Enhanced Propagation Through Opaque Media

“…Indeed, in refs. [3,4] it was found theoretically and recently confirmed experimentally, [5] that propagation inside an opaque medium exhibits deeply penetrating waves, by tuning the imaginary wave-vector component k ′′ to be orientated parallel to the incident interface, obtaining only a purely real component of k ⋅ û in the direction û that penetrates the opaque material. This was proposed by illuminating the opaque media from lossless free space with inhomogeneous waves, such as those coming from a leaky waveguide, at carefully engineered angles.…”

“…Propagation through a medium that would normally block, absorb, interfere or distort the passage of incident electromagnetic waves is a sought-after phenomenon, with the intriguing promise of enabling "seeing through walls". Recent research works have reported such phenomena in different contexts by using several alternative methods, such as propagation through scattering media using speckle correlations, [1] scattering-invariant modes, [2] propagation through lossy materials by complex wave-vector engineering, [3][4][5] propagation through layered Bragg media within forbidden bands using spatial shaping, [6] non-Hermitian exceptional points, [7] or exploiting parity-time-symmetry in evanescent waves, [8] among others.…”

Optimized Leaky-Wave Antenna for Hyperthermia in Biological Tissue Theoretical Model

“…It has been demonstrated in the literature that the incidence of an inhomogeneous wave incoming from a non-dissipative medium on a lossy medium may produce a transmitted wave that can penetrate deeper than the one produced by the incidence of a more conventional homogeneous wave, both numerically [2] and analytically [3][4][5][6]. In order to obtain a deep-penetration effect, the incoming wave must fulfill some conditions that bind the minimum attenuation vector to the electromagnetic characteristics of the medium and the incidence angle [5].…”

“…Moreover, in [6], an alternative and equivalent description, more suitable for ray tracing techniques, has been developed, and, among the results, it is demonstrated that the deep-penetration effect can be achieved at the interface between two lossy media. The deep-penetration phenomenon requires an incidence angle different from 0 • , and in any case, the presence of an attenuation vector in the incidence wave constitutes a sufficient condition for a possible enhancement of the penetration in a lossy medium, i.e., even in case of normal incidence, an inhomogeneous wave may allow deeper penetration [2]. It has to be noted, by the way, that a less attenuated field does not necessarily correspond to a stronger field inside the medium, or at its surface.…”

“…This happens due to asymmetries in general, periodically placed along the LWA, that disturb the normal flow of the energy producing radiation out of a guided mode [12][13][14]. The LWA design proposed here is based on the Menzel antenna, already considered in [2], and opportunely modified for the hyperthermia application requirements. The antenna in [2] has been designed to operate at 12 GHz.…”