Dependence of specific absorption rate and its distribution inside a homogeneous fruit model on frequency, angle of incidence, and wave polarization

Electromagnetic regulatory guidelines prescribed by the international and national organizations are in effect worldwide to protect humans from immediate health effects. For restricting human exposure to electromagnetic radiation in near field, a quantitative term ‘specific absorption rate (SAR) limit’ has been coined and well established in literature. In addition, reference power density limit has also been prescribed in far field for human safety. At the same time, plants and fruits also absorb reasonable amount of electromagnetic energy due to high permittivity and electrical conductivity. Unfortunately, there is not much concern regarding electromagnetic energy absorption in plants and fruits, and no prescribed SAR limit in spite of recent reports in literature. Unlike humans, plants and fruits are of asymmetric shapes and sizes; therefore even at a particular frequency and fixed reference power density, electromagnetic energy absorption rate i.e., SAR in plants and fruits is expected to differ depending upon angle of incidence and wave polarization. To address these issues in detail, a typical bunch of three single layered water apples has been prototyped and exposed to plane wave irradiation at five different frequency bands as per the existing Indian electromagnetic regulatory guidelines. Broadband dielectric properties of water apples have been measured using open ended coaxial probe technique; thereafter, measured dielectric properties have been fed into the designed model. At a particular frequency, reasonable variations in magnitude and position of maximum local point (MLP) SAR, 1 g averaged SAR, and 10 g averaged SAR data have been noted for six different combinations of angle of incidence and wave polarization. This whole course of action is repeated over five different frequency bands. Moreover, variations in observed SAR data are also compared with previously reported variations in SAR data for a multilayer fruit structure. Observations indicate different order of changes in SAR for different fruit structures due to similar combinations of frequency, power density, angle of incidence, and wave polarization. Hence, direct definition of SAR limits for plant and fruit structures should be adopted even in far field in conjunction with reference power density.

Enhancement of Radar Detection Accuracy Using H-Beam Wave Polarization in Random Media

This work addresses the range in which the accuracy of object identification is enhanced regardless of radar parameters. We compute the radar cross-section (RCS) of conducting objects in free space and random media. We use beam wave incidence and postulate its coherency with a finite width around an object located in the far field. Accordingly, we examine the impact of radar parameters on the RCS, where these parameters include the incident angle, target size and complexity, medium fluctuation intensity and the beam size of the incident waves. H-wave polarization is assumed for the waves’ incidence.

Trace of evanescent wave polarization by atomic vapor spectroscopy

Various efforts have been made to determine the polarization state of evanescent waves in different structures. The present study shows the reliability of magneto-optical spectroscopy of D1 and D2 lines of rubidium metal and polarization-dependent transitions to investigate and trace the changes in the polarization state of evanescent fields during total internal reflection over different angles. For this purpose, we design and fabricate atomic- evanescent Rb vapor cells and examine the effect of polarization changes of evanescent waves, depending on the propagation direction of evanescent waves in anisotropic rubidium vapor media under 88 mT external magnetic field by different configurations theoretically and experimentally. The results confirm the dependency of allowed $$\sigma^{ \pm } { }\;{\text{and}}\;\pi$$ σ ± and π transitions on the magneto optical configuration as a tool to determine changes in the polarization of evanescent waves in more complicated wave states in anisotropic media.

Active Control of the THz Wave Polarization State by an Electronically Controlled Graphene Composite Metasurface

Active control of terahertz (THz) wave polarization state is of great significance for sensitive detection, imaging and communication. Here, a tunable THz quarter wave plate is designed by electronically controlling a composite metasurface consisting of the gold cross antennas and a monolayer graphene. The graphene composite metasurface acts as a quarter-wave plate when the chemical potential of graphene is 0 eV, by which the polarization state of the incident THz wave is converted from linear polarization to circular polarization. After the chemical potential of graphene is increased gradually, and to 0.5 eV, the transmitted polarization state of the THz wave is changed from right circular polarization to right elliptical polarization, and to linear polarization. Furthermore, the polarization state of the THz wave is able to be changed from left circular polarization to left elliptical polarization, and to linear polarization if the device is clockwise rotated by 90°. Therefore, the polarization state of THz wave could be actively controlled by the proposed tunable THz quarter wave plate. Our work will offer a new avenue for tunable THz polarization modulation devices.

Trace of evanescent wave polarization by atomic vapor spectroscopy

Various efforts have been made to determine the polarization state of evanescent waves in different structures. The present study shows the reliability of magneto-optical spectroscopy of D1 and D2 lines of rubidium metal and polarization-dependent transitions to investigate and trace the changes in the polarization state of evanescent fields during total internal reflection over different angles. For this purpose, we design and fabricate atomic evanescent Rb vapor cells and examine the effect of polarization changes of evanescent waves, depending on the propagation direction of evanescent waves in anisotropic rubidium vapor media under different external magnetic field configurations theoretically and experimentally. The results confirm the dependency of allowed transitions on the magneto optical configuration as a tool to determine changes in the polarization of evanescent waves in more complicated wave states in anisotropic media.