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In this article, we reconstruct the internal electric field due to a dipole antenna embedded in a dielectric phantom for developing a noninvasive specific absorption rate (SAR) measurement system. The reconstruction method is based on the surface equivalent theorem and boundary conditions, which relate the external field radiated from the embedded antenna to equivalent electromagnetic surface currents on the human body. The electric field data sampled at spatial points on a surface enclosing the phantom are used in the inverse calculation. All field integrals are discretized and numerically solved to obtain the electromagnetic currents on the phantom's surface. The internal electric field distribution and SAR value in a phantom can be calculated from the reconstructed surface currents if the electric properties of the phantom are known. The validity of the method was demonstrated numerically and experimentally using a dipole antenna embedded in the lossy rectangular phantom, which has a dielectric constant close to human skin tissue at 2.5 GHz. Comparison with forward numerical simulations has shown that the surface current and electric field distribution can be predicted with great precision. Carefully performing the experiments using a self-made phantom validated our numerical demonstration and provided satisfactory reconstruction results.

It has been demonstrated that inoculation of Welsh onions (Allium fistulosum) with arbuscular mycorrhizal (AM) fungi during the nursery period followed by transplantation was effective in improving growth and reducing phosphorus fertilizer application. However, what range of soil phosphorus fertility is suitable for AM fungal inoculation remains unclear. To elucidate the optimal level of soil phosphorus fertility in a non-allophanic Andosol, we conducted a series of Welsh onion inoculation experiments under field conditions. Experiments were conducted in 2009–2010 and 2015–2016 in experimental plots at Tohoku University, northern Japan. Soil phosphorus fertility levels varied as follows: very high, high, medium, and low at 750–1,000, 150–250, 70–150, and 30–70 mg P2O5 kg soil−1, respectively (Truog method). Welsh onions were inoculated with a commercial Rhizophagus sp. R10 inoculum and grown for 7–9 weeks in a greenhouse nursery bed. The seedlings were transplanted into plots under the application of one, two or three levels of phosphorus fertilization. In the medium and high plots, inoculation increased marketable yields of Welsh onions irrespective of phosphorus fertilization, while no effect was found in the very high plot. In the low plot, inoculation did not clearly improve the yield, which was low irrespective of the treatments. These results indicate that AM fungal inoculation of Welsh onions in this soil was effective when available phosphorus ranged from 70 to 200 mg P2O5 kg soil−1.

Winter flooding of paddy rice production is characterized by flooding of paddy fields during the winter fallow season. It has attracted attention in terms of its ecological function, supporting the biodiversity of paddy field ecosystems. Therefore, recent winter flooding in Japan has been conducted by organic farming. However, it is not well documented how organic farming with winter flooding affect the productivity of rice. We conducted field experiments to examine changes in rice yield in organic farming with winter flooding compared with those in conventional and organic farming over the period of 5 and 9 years. The yields in organic farming with winter flooding were lower than those in conventional farming but were almost the same as those in organic farming. We found a trend that shows the relative yield of organic farming with winter flooding compared to that of conventional farming increased during the first several years after the conversion from conventional farming to organic farming with winter flooding, but that it decreased after several years. This trend may be caused by the flourishing of weeds during continuous organic farming with winter flooding. Therefore, we tested four weed control methods: rice bran application, mechanical weeding, repeated puddling, and side-row fertilizer application. Although each method suppressed weeds to certain extents, some combinations of different weeding methods more effectively suppressed weed growth, thereby resulting in enhanced rice yields. We found a trend in rice yield and a possibility of combining several weed control methods in organic farming with winter flooding.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2021-07-27, 資料番号: PA2210014000

Reconstruction of the electromagnetic (EM) fields inside a dielectric object is investigated in order to develop a noninvasive specific absorption rate measurement. The proposed reconstruction method is based on the boundary integral equation (BIE) derived from the surface equivalence theorem that relates the equivalent EM currents on the surface enclosing the primary source to the radiated external fields. The EM currents are reconstructed by solving the discretized BIE using the field data sampled on the surface surrounding all of the target objects that consist of the dielectric phantom and radiating antenna. The field distribution inside the dielectric object is obtained from the reconstructed currents. A probe correction technique is also proposed to enable the application of this method to practical probe measurements. As the first step to the practical applications, the validity and usefulness of the proposed method are demonstrated numerically and experimentally using lossless and lossy homogeneous dielectric objects located near a dipole antenna, respectively. It is shown that the accuracy tends to deteriorate in the case of the lossy phantom, but this can easily be improved without significant modification of the proposed method.

To ensure human safety against electromagnetic exposures from wireless power transfer (WPT) systems operating at MHz-band frequencies, a compliance test must be conducted using either numerical simulations or measurements. In practice, measurements of the specific absorption rate (SAR) inside a human-equivalent liquid phantom are required for exposure evaluation. However, accurate measurements of SAR are difficult, especially at a location close to the phantom boundary, owing to the boundary effect, caused by the field disturbance due to the SAR probe itself. Hence, it is necessary to use an extrapolation method to determine the internal electric field or SAR. In this study, we propose a new extrapolation expression based on the characteristic of electromagnetic fields inside the phantom in order to estimate internal electric field strength or SAR. The validity of the proposed expression was demonstrated both numerically and experimentally. From the results, we confirmed that the difference in the internal electric field strength inside a liquid phantom was less than 3% between our proposed extrapolation expression and the method of moments (MoM). For SAR measurements using two types of actual WPT systems, i.e., solenoid and flat-spiral types, we found that the proposed expression can be used to evaluate the spatial peak 10-g average SAR with a difference of less than 30% compared with those numerically obtained by MoM.

The FDTD method, which is one of the electromagnetic field analysis methods, has a problem that the time step width becomes small and the analysis cost increases due to the CFL condition when an attempt is made to accurately discretize and analyze a structure that is thinner than the wavelength. There is a subcell method as an analysis method for avoiding this problem, but few examples have been analyzed for a thin multilayer medium. Therefore, the purpose of this research is to reduce the cost of the analysis of multi-layer media that is thinner than the wavelength. In this paper, we analyze the effectiveness of this method by analyzing the antenna on a multilayer dielectric slab using the subcell method.

This paper studies electric field reconstruction for antenna inside phantom. The application is aimed for non-invasive SAR measurement of in-body antenna. The method relates electromagnetic currents on the surface enclosing the test subject (antenna and phantom combination) to the scattered external field received by probe. From the surface currents, we were able to reconstruct the internal electric field of phantom with known permittivity, e r = 45. It is shown that we can obtain good result in lossless sphere case.

The finite-difference time-domain (FDTD) method has been widely employed for analyzing various electromagnetic problems, including low-frequency problems. It provides accurate results in most cases, however, relatively long calculation time is required for slow convergence problems, such as array antennas. For this reason, the autoregressive moving average (ARMA) model has been applied to FDTD radiation pattern analysis because the radiation patterns calculation requires multi-dimensional (time and space) data. In this paper, we applied two-dimensional ARMA to FDTD radiation pattern analysis to reduce the calculation time. We confirm effectiveness of the method by calculating the radiation pattern of Yagi-Uda antenna.

In this research, reconstruction method for current distribution of dipole antenna is proposed. The reconstruction method for current distribution of antenna is useful, because the radiated electromagnetic field can be estimate by using dipole antenna current. The proposed reconstruct method utilize boundary integral method. The effectiveness of the proposed method is confirmed by comparing with simulation result based on MoM.

A single-cut near-field (NF) far-field transformation technique is proposed for antenna measurements, which utilizes a two-dimensional (2-D) plane-wave expansion. This technique enables the prediction of single-cut far-field from the NF sampled on the same plane, having the flexibility of the NF data acquisition. The proposed method involves an approximation of 3-D Green's function under the assumption that the heights of the antenna under test and probe is small enough in comparison to the measurement distance. The proposed technique is validated numerically and experimentally.

In this paper, we propose an experimental approach for determining the internal electric field for exposure evaluation of wireless power transfer (WPT) systems by using measured magnetic near-field data. Two WPT systems are fabricated and used in the measurements: one without ferrite tiles, and the other with ferrite tiles and a metal plate. The amplitude and phase of the magnetic near field in the vicinity of the WPT systems are then measured by using in-house magnetic-field probes and a near-field measurement system. Numerical dosimetry of human exposure is performed using the measured near field as an incident field in the impedance method to derive the internal electric field strength inside numerical human models. Validation of the proposed approach has been demonstrated by comparing measurement results with those obtained from numerical simulations. Additionally, the coupling factor, which represents the relationship between the incident magnetic field and the induced electric field in the human body, at different distances is derived for realistic exposure scenarios.

The accuracy of a single-cut near-field far-field transformation technique is studied. The technique is based on the two-dimensional (2D) plane-wave expansion and the approximation that the antenna under test (AUT) is low enough along the direction vertical to the cut-plane under observation. We employ an AUT high enough to break condition for the approximation and observe accuracy of the transformation technique.

In this paper, a FDTD modeling method for calculating characteristics of an antenna above a metasurface is presented. A surface impedance boundary condition (SIBC) is introduced into the FDTD method to reduce computational time and resources. The validity of the proposed method is numerically confirmed by calculating an input impedance and a radiation pattern of a horizontal dipole antenna located above the metasurface.