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

Abstract

Abstract 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.