Reduction in human interaction with magnetic resonant coupling WPT systems with grounded loop

Wireless power transfer (WPT) systems have attracted considerable attention in relation to providing a reliable and convenient power supply. Among the challenges in this area are maintaining the performance of the WPT system with the presence of a human body and minimizing the induced physical quantities in the human body. This study proposes a magnetic resonant coupling WPT (MRC-WPT) system that utilizes a resonator with a grounded loop to mitigate its interaction with a human body and achieve a high-efficiency power transfer at a short range. Our proposed system is based on a grounded loop to reduce the leakage of the electric field, resulting in less interaction with the human body. As a result, a transmission efficiency higher than 70% is achieved at a transmission distance of approximately 25 cm. Under the maximum-efficiency conditions of the WPT system, the use of a resonator with a grounded loop reduces the induced electric field, the peak spatial-average specific absorption rate (psSAR), and the whole-body averaged SAR by 43.6%, 69.7%, and 65.6%, respectively. The maximum permissible input power values for the proposed WPT systems are 40 and 33.5 kW, as prescribed in the International Commission of Non-Ionizing Radiation Protection (ICNIRP) guidelines to comply with the limits for local and whole-body average SAR

Calculated Epithelial/Absorbed Power Density for Exposure from Antennas at 10–90 GHz: Intercomparison Study Using a Planar Skin Model

International audienceInternational organizations have collaborated to revise standards and guidelines for human protection from exposure to electromagnetic fields. In the frequency range of 6-300 GHz, the permissible spatially averaged epithelial/absorbed power density, which is primarily derived from thermal modeling, is considered as the basic restriction. However, for the averaging methods of the epithelial/absorbed power density inside human tissues, only a few groups have presented calculated results obtained using different exposure conditions and numerical methods. Because experimental validation is extremely difficult in this frequency range, this paper presents the first intercomparison study of the calculated epithelial/absorbed power density inside a human body model exposed to different frequency sources ranging from 10-90 GHz. This intercomparison aims to clarify the difference in the calculated results caused by different numerical electromagnetic methods in dosimetry analysis from 11 research groups using planar skin models. To reduce the comparison variances caused by various key parameters, computational conditions (e.g., the antenna type, dimensions, and dielectric properties of the skin models) were unified. The results indicate that the maximum relative standard deviation (RSD) of the peak spatially averaged epithelial/absorbed power densities for one- and three-layer skin models are less than 17.49% and 17.39%, respectively, when using a dipole antenna as the exposure source. For the dipole array antenna, the corresponding maximum RSD increases to 32.49% and 42.55%, respectively. Under the considered exposure scenarios, the RSD in the spatially averaged epithelial/absorbed power densities decrease from 42.55% to 16.7% when the frequency is increased from 10-90 GHz. Furthermore, the deviation from the two equations recommended by the exposure guidelines for deriving the spatially averaged epithelial/absorptive power density is mostly within 1 dB. The fair agreement in the intercomparison results demonstrates that the variances of the spatially averaged epithelial/absorbed power densities calculated using planar skin models are marginal

Application of the Finite Difference Parabolic Equation Model in Forestry Remote Telemetry

In this article, the finite difference parabolic equation (FDPE) method is presented to calculate the propagation loss (PL) for electromagnetic waves (EWs) in the forest environment. The FDPE method is more efficient and convenient than the empirical models and has more advantages on compatibility and accuracy for long-range EWs prediction. The Debye–Cole dual dispersion model is used to simulate the effective permittivity of vegetation. The results of the FDPE model are compared with those of the advanced refractive effects prediction system and measurement results, and a good agreement is observed. Research found that PL for EWs varies with the effective permittivity. Also, the effective permittivity is a function of radio frequency, weight moisture content, and volume content of vegetation. Thus, it is necessary to establish a statistical model to determine some relations between the PL and plant biophysical parameters. The polynomial fitting method is adopted to process a large amount of PL data for obtaining a linear function. Then, the volume content and moisture content of vegetation can be determined according to the polynomial fitting function. It provides a novel and efficient method for forestry remote telemetry, which is specifically suitable for large-scale inaccessible region with serious environment

Relationship of external field strength with local and whole-body averaged specific absorption rates in anatomical human models

The International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines and the IEEE C95.1 standard are currently under revision. In the guidelines/standard, the dominant effect for electromagnetic field exposures at frequencies above 100 kHz is the thermal effect. The whole-body-and 10g-averaged specific absorption rates (SARs), which are surrogates for core and local temperature elevations, respectively, are set as metrics for exposure evaluation. The external field strengths or incident power density, corresponding to the limit for SARs, are also used as metrics for practical compliance purposes. Although the limits for the SARs are identical amongst the guidelines/standard, the limits for the external field strengths differ by a factor of 7.4-12.9 in an intermediate frequency range (100 kHz-100 MHz). Due to the fact that the standard/guidelines were published before the computation with anatomical human models was available, it is worth revisiting the relationship between the SARs and external field strengths by computations using the human models. Intercomparison using different numerical codes was also performed to verify the results. For the main finding, as expected, the 10g-averaged SAR was a less restrictive factor for whole-body exposure over the frequencies considered in this paper. It was also found that the relationship between SARs and external field strength was satisfied, but was more conservative in the ICNIRP guidelines, whereas there were slight discrepancies below 30 MHz in the IEEE standard. The computational results would be useful for revising the permissible external field strength based on scientific results.Peer reviewe

Intercomparison of in Situ Electric Fields in Human Models Exposed to Spatially Uniform Magnetic Fields

IEEE C95.1 (radio frequency) and C95.6 (low frequency) standards for human protection from electromagnetic fields are currently under revision. In the next revision, they will be combined into one standard covering the frequency range from 0 Hz to 300 GHz. Although the C95.1 standard considers anatomical human models for deriving the relationship between internal and external field strengths, homogeneous ellipses are used in the C95.6 standard. In the guidelines of the International Commission on Non-Ionizing Radiation Protection, anatomical human models are used together with reduction factors to account for numerical uncertainty. It is worth revisiting their relationship when using different anatomical models. In this paper, five research groups performed a comparative study to update the state-of-the-art knowledge of in situ electric fields in anatomical human models when exposed to uniform low-frequency magnetic fields. The main goals were to clarify both numerical uncertainty and model variability. The computational results suggest a high consistency among in situ field strengths across laboratories; agreement in the 99th percentile with a discrepancy of under 5% was achieved. The in situ electric fields varied as expected given the models' different dimensions. The induction factor, which is the ratio of the in situ electric fields for the temporal derivative of the external magnetic flux density, is derived for body parts and tissues. The classification of body parts into 'the limb' and 'other tissues' is shown to be critical for determining the in situ field strength.Peer reviewe

Effect of Incidence Angle on the Spatial-Average of Incident Power Density Definition to Correlate Skin Temperature Rise for Millimeter Wave Exposures

Publisher Copyright: © 1964-2012 IEEE.This article reports on an intercomparison study on the effect of the incidence angle on the spatial average of incident power density (PD) and resultant temperature rise using computational and thermographic measurement approaches. Two definitions of the spatial average of incident PD - the peak spatial-average normal component of the Poynting vector and peak spatial-average norm of the Poynting vector - were compared. First, an intercomparison of incident PD and temperature rise in a layered skin model was conducted for a 4 × 4 dipole array antenna. The variations caused by antenna type, antenna-body distance, and skin model to these definitions were then discussed. The results revealed that both definitions are in good agreement and correlate with the peak temperature rise for small or moderate incidence angles. The heating factor was enhanced for transverse-magnetic-like polarized waves for peak spatial-average normal component of the Poynting vector for large-angle incidences because of the Brewster effect. The normal incidence scenario was confirmed to be essential for considering the peak skin temperature rise.Peer reviewe