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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.

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.

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.

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.

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.

A composite right/left-handed (CRLH) leaky-wave antenna (LWA) using a stepped impedance resonator (SIR) is presented. By applying the SIR technique to a conventional CRLH structure, a balanced condition is achieved through the adjustment of the SIR parameters. Therefore, the structure requires no interdigital or multilayered capacitor to achieve the balanced condition. A differential microstrip configuration is also used for the utilization of a virtual ground to eliminate the need for ground vias. The simplicity of the structure allows for applications at high frequencies. An LWA consisting of 14 unit cells of the proposed structure is designed and measured. Continuous beam scanning from the backward direction to the forward direction is demonstrated.

Reconstruction of electromagnetic (EM)fields inside dielectric objects is studied. Such reconstruction methods have been developed mainly for noninvasive specific absorption rate (SAR)measurement. The methods enable us to measure the field inside the dielectric phantom illuminated by the device under test (DUT), without invasive insertion of the probe inside the phantom. In the proposed reconstruction method, EM currents on the surface of the dielectric object are reconstructed from field observed on the surface enclosing both the phantom and DUT. The fields inside the phantom are evaluated by the reconstructed currents. The validity and usefulness of the proposed method are demonstrated numerically and experimentally using a dielectric object located near a dipole antenna.

This paper presents artificial magnetic conductor (AMC) structure employed for low-profile antenna operates in Wi-Fi 5 GHz band for wearable internet of things (IoT) devices. A proposed AMC structure comprises of a combination of ring slots. This structure can improve the impedance bandwidth of a planar dipole antenna when the size of AMC surface is approximately half wavelength. The simulation results demonstrate that a dipole antenna on the proposed AMC surface is low profile and has less effect when operating on human body.

This paper investigates an FDTD modeling method for precisely calculating the characteristics of a single, that is, a nonperiodic antenna located above a metasurface that consists of an infinite periodic conducting element on a flat dielectric substrate. The original FDTD method requires enormous computational resources to analyze such structures because an appropriate periodic boundary condition (PBC) is not supported, and a brute force approach has to be used for this reason. Another option is to use the array scanning method in which a single source is synthesized from a superposition of infinite phased array of point sources. In this method, some problems such as a mutual coupling between the single antenna and the metasurface, a computational error contained in a numerical integration over the Brillouin zone and so on have not been resolved yet. In order to resolve these difficulties and to reduce computational resources, a surface impedance boundary condition (SIBC) is incorporated into the FDTD method in this paper. The validity of the method is numerically confirmed by calculating an input impedance and a radiation pattern of a horizontal dipole antenna located above the metasurface.

We developed a new exposure system to irradiate microwaves locally on a rabbit eye using a small coaxial-to-waveguide adapter filled with low-loss dielectric material as an antenna. A numerical rabbit model was also developed using X-ray computer tomography images, and the specific absorption rates (SARs) in the rabbit, especially in the eye, were analyzed with the finite-difference time-domain method. The temperature elevation in the exposed eye was also evaluated by solving a bioheat equation. Our exposure system can generate incident power density of 15 mW/cm2 at the surface of a rabbit eye with input power of 1 W. When the incident power density on the rabbit eye is 300 mW/cm2 , average SAR over the exposed eye and the whole body were approximately 108 and 1.8 W/kg, respectively. The exposure system can realize localized exposure to the eye with the ratio of exposed-eye averaged SAR to the whole-body averaged SAR was 60. The developed exposure system can achieve high-intensity exposure such as the threshold of cataracts, i.e., the eye-averaged SAR over 100 W/kg or the lens temperature over 41 degC with the incident power density of 300mW/cm2 without significant whole-body thermal stresses

MHz frequency range is widely used as Induction Heating (IH) heater, wireless power transfer (WPT) system and so on. On the other hands, the FDTD method is powerful tools for complicated models. However, long calculation time is required in MHz range analysis by FDTD method, because, time period of MHz range becomes long, and the time step size of the FDTD method should be small with cell size reducing. In this paper, in order to accelerate of FDTD MHz range analysis, we utilize an Autoregressive moving average model (ARMA) for MHz range FDTD analysis. In this paper, we calculate input impedance of dipole antenna. In the ARMA model, linear transfer function H(z) as indicated below is used to estimate calculation result such as input impedance of the antenna.

In this paper, quite wide band negative permittivity structure is developed. The proposed structure is based on the split ring resonators. The proposed structure has 45% band width at 1.3 GHz, therefore the structure has 544 MHz negative permeability range at 1.3 GHz.

In the past few years, there has been a focus on clean energy and the installation of solar cell modules on the walls of high-rise structures such as buildings. Solar cell modules embedded in window glass, which occupies a large portion of the walls of high-rise buildings, are being studied. However, solar cell modules easily reflect electromagnetic waves and the effect of electromagnetic wave interference cannot be ignored. Therefore, in this paper, we study a method for suppressing electromagnetic wave interference in the frequency bandwidth of terrestrial digital broadcasts when using solar cell modules embedded in window glass. By appropriately selecting the structure of the solar cell module and the shapes of the wires connecting solar cell pairs, at least 10-dB reflections can be suppressed in the frequency range from 470 MHz to 770 MHz of terrestrial digital broadcasts while preserving the lighting function of the window glass. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(10): 28–34, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20206

Finite difference time domain (FDTD) methods have been applied to complex models mixing dielectrics and conductors because model development is simple and a practical level of accuracy is easily obtained. However, to correctly determine the impedance of a linear antenna, the cell size must be extremely small regardless of the structure's simplicity. The reason is believed to be the inability to model the rapidly fluctuating electromagnetic field near the antenna conductor electrode. In this paper, we explain the causes of several errors of FDTD methods, and propose a method that reduces the errors in the FDTD calculation by incorporating the spatial distribution of the quasi-static approximation of the electromagnetic field into the FDTD cells and improves the accuracy without using an extremely small cell size. In addition, we compare the proposed method to the results of the Galerkin moment method and demonstrate its effectiveness. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(8): 32–40, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20106

In this paper, the authors investigated the reflection and absorption characteristics of a general photovoltaic (PV) module. As a result, the electromagnetic waves could be attenuated only 6 dB in typical PV module. However, if the PV module is installed in the outer wall of buildings, electromagnetic interference is caused by the surroundings. To reduce this electromagnetic interference, the authors suggested a method to absorb electromagnetic wave using multiple PV modules that have deference impedance, and simulation was performed. As a result, it was confirmed that using a typical PV module and the PV module including electronic device, the reflection waves of those PV modules could be attenuated up to 12 dB.

The characteristics of metal cavity-attached resistor-loaded bow-tie antennas, which are widely employed as antennas for subsurface detection radars using broadband pulses, are investigated theoretically and experimentally in this paper. Two kinds of antennas are considered: isolated antennas having a structure which separates electrically the bow-tie antenna and the metal cavity, and connected-type antennas which connect the bow-tie antenna and the metal cavity via a resistor. The inner cavity surfaces of both types are coated with ferrite. In this paper, the characteristics of both types of antennas are discussed from the point of view of the effects of the ferrite absorber on the above-ground and subsurface underground radiation power, the coupling between the transmitter and the receiver, and the effects on the transient reception characteristics. The reasonableness of the analysis of the ferrite absorber is verified experimentally. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(8): 66–73, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1119

This paper presents a full-wave analysis of a ground penetrating radar (GPR) using the finite-difference time-domain (FDTD) method. The antenna treated here consists of a resistor-loaded bow-tie antenna, which is covered with a rectangular conducting cavity of which inner walls are coated partially or fully with ferrite absorber. Some techniques are introduced into the FDTD analysis to obtain the accurate results and to save the computer resources. The validity of the FDTD analysis is confirmed experimentally. Furthermore, the effects of the ferrite absorber on the GPR characteristics are theoretically investigated in detail. The FDTD results indicate that the remarkable improvement of the antenna characteristics for the GPR system cannot be attained by the ferrite absorber.

The bi-static radars consist of transmitting antenna and receiving antenna. The antennas are placed side by side. However transmitted pulse from transmitting antenna is directly received by the receiving antenna. Therefore, if the radar and the target are close, transmitted pulse and wave which reflected from the target are observed to overlap each other and artificial image occurs. On the other hand, EBG (Electromagnetic Band-Gap) structure that is one of metamaterial reduces the electromagnetic coupling in specific frequency. This study proposed novel bi-static radar antenna that inserting EBG structures between the transmitting antennas.

In this paper a new measurement technique for whole body SAR of small phantom is proposed. The method is based on Wheeler cap method. Wheeler cap method is originally used for antenna efficiency measurement. In recent years, mobile phones are widely used. It is considered that a part of the radiated electromagnetic wave by mobile phones is absorbed into the human body. A lot of studies are accomplished about the interaction of the human body and the electromagnetic wave from such a background. The thermal effects are dominant in the microwave frequency region. And the quantity of energy absorption is evaluated by using SAR (Specific Absorption Rate). In order to measure the SAR from electric fields, electric field sensors are used. Optical fiber thermometer or Thermo camera are used to measure the SARs from a temperature rise. However, these methods are needed a huge measurement time to measure whole body SAR. On the other hand, it is necessary to measure the whole body SARs. However, it is not easy to measure the whole body SARs by the conventional technique. In this study, we will use wheeler cap method to measure the whole body SAR. The effectiveness of the method is confirmed by experimentally and numerically.

The bistatic radars consist of transmitting antenna and receiving antenna. There antennas are placed side by side. However transmitted pulse from transmiting antenna is directly received by the receiving antenna. Therefore, if the radar and the target are close, transmitted pulse and wave which reflected from the target overlap each other and artificial image occurs. On the other hand, EBG (Electromagnetic Band-Gap) structure that is one of metamaterial reduces the electromagnetic coupling in specific frequency. This study shows that inserting EBG structures between the transmitting antenna and the receiving antenna reduce the artificial image.

Recently, body-centric wireless communication using a device including a radio terminal placed in/on body has received a lot of attention [1]. In order to investigate the transmission mechanism of the wearable device for on-body wireless communications analytically, we derive the exact solution represented by the eigenfunction solution for the scattered electric field and discuss them. We then consider the propagation characteristic by the wearable device attached to a human arm by approximating the arm as a dielectric circular cylinder. First, the frequency-domain integral representations of the eigenfunction solutions for the scattered electric fields are derived. From this, the transmission coefficient between the transmitting and the receiving antennas in the vicinity of the dielectric cylinder is obtained analytically. Then, we evaluate the influence of the infinite dielectric circular cylinder on the bit error rate (BER) performance for the digital communication using the ISM band of 915MHz and the UWB band.

EBG structures have been developed widely for reducing electromagnetic coupling. On the other hand, Bistatic radar is a system which comprises a transmitter antenna and receiver antenna. In recent years, the bistatic subsurface radar is applied to detect relatively shallow structure such as tumor detection, steel reinforced detection in concrete and etc… On the other hand, the electromagnetic coupling between transmitter antenna and receiver antenna becomes problem, because, the bistatic radar detects a reflection wave from the target by the receiver antenna, therefore artifact caused by the coupling. To reduce this coupling a cavity is used, however, the cavity is not enough to reduce the electromagnetic coupling between transmitter antenna and receiver antenna. We have proposed bistatic radar system using EBG structure. In this paper, the bistatic radar system using EBG structures will be introduced briefly. And, the target detection result by using proposed bistatic radar system will be indicated.

Bistatic radar is system which comprises a transmitter antenna and receiver antenna which are separated by a distance that is comparable to the expected target distance. In recent years, the bistatic subsurface radar is applied to detect relatively shallow structure such as tumor detection, steel reinforced detection in concrete and etc… On the other hand, the electromagnetic coupling between transmitter antenna and receiver antenna is problem, because, the bistatic radar detects a reflection wave from the target by the receiver antenna, therefore artifact caused by the coupling. To reduce this coupling a cavity is used, however, the cavity is not enough to reduce the electromagnetic coupling between transmitter antenna and receiver antenna. On the other hand, the EBG structure is used as electromagnetic insulator. In this research, in order to reduce the electromagnetic coupling the EBG structure is applied.

For full-fledged applications of radar imaging of buried objects by using electromagnetic waves, it is important to analyze theoretically and experimentally the fundamental problems such as the scattering of the electromagnetic wave by various objects and the electromagnetic wave propagation from the antenna above the ground into the ground. As the first step toward such a goal, this paper studies the transient electromagnetic fields scattered by an infinite perfectly conducting circular cylinder placed near a dipole antenna in free space. First, the transient electromagnetic fields are calculated rigorously for the case where one dipole antenna is placed in parallel to a conducting cylinder. Furthermore, geometrical optics approximation also is derived. From the computed results, it is shown that the transient scattered field can be interpreted as the total sum of the scattered fields corresponding to optical paths. It is shown also that the geometrical optics approximation is extremely accurate in the backscattering region important for the analysis of inverse scattering problems such as the detection of a buried object. Next, the transient transmission and reception responses are analyzed theoretically in the case where two dipole antennas are placed in parallel to the circular cylinder and its validity is confirmed by experiments.

Berenger's perfectly matched layer (PML) absorbing boundary condition (ABC) has been found very effective for truncating the unbounded spatial domain in the finite-difference time-domain (FDTD) computation. The PML ABC was originally introduced for a free-space spatial domain and later extended to a lossy medium using the stretched coordinates. In this paper, we propose a novel PML ABC for a dispersive medium in an ordinary Cartesian coordinate. It is also shown that the PML for the lossy medium can be easily derived from our formulation.

This paper proposes a technique for improving the accuracy of the finite difference time domain (FDTD) method to analyze a short dipole antenna. The improvement is achieved by incorporating a quasi-static field behavior into the FDTD update equations. A closed form of the quasi-static field is obtained from a low frequency limit of a sinusoidal current distribution. The effectiveness of the modified algorithm is tested by comparing with the method of moments (MoM).

This work proposes a technique for improving the accuracy of the finite difference time domain (FDTD) method for a dipole and a square loop antenna analysis. The improvement is achieved by incorporating a quasi-static field behavior into the FDTD update equations. In the case of a dipole antenna, a closed form of the quasi-static field is obtained from a low frequency limit of a sinusoidal current distribution. The effectiveness of the proposed algorithm is confirmed for both dipole and square loop antennas by comparing with the method of moment (MoM).

The properties of transient electromagnetic fields transmitted from an antenna and scattered from buried objects are investigated in connection with the radar imaging of an invisible target (e.g., underground imaging). The early-time scattering fields are calculated exactly when a short horizontal dipole is located over the interface separating air and the lossy medium, and a perfectly conducting infinite cylinder is buried in the lossy medium. The approximate transient scattering fields are also derived and compared with the exact transient field. It is shown that the present approximation is good when the antenna deviates from directly over the buried cylinder, but invalid when the antenna is located over the buried cylinder. It is also found that the geometrical-optics approximation is effective only when the propagation path is nearly normal to the ground surface. >

Most of earlier investigations concerning radomes have been restricted to the cases that the radome is two dimensional, or the radome and the primary antenna are not too large compared to a wave-length, although there are increasing necessity in analysis and design of practical three dimensional large radomes. Recently, it has become possible to respond to this requirements by the appearance of high speed large computers. The purpose of this report is to analyze the radiation characteristics of an aperture antenna covered by an arbitrarily curved three dimensional large radome. In this analysis, the aperture antenna is also arbitrarily shaped, illuminated and located. Moreover, it is permitted that the radome is multilayered or even inhomogeneous. The analysis is essentially based on the method of local slab model approximation. The radiation patterns for various parameters of radomes are shown.

The dependence of the radiation patterns and antenna gains on the measurement distance when both transmitting antenna and receiving antenna have the same order of large dimensions is discussed. The antenna under test is the transmitting antenna. The near-zone radiation patterns (Fresnel pattern) and the antenna gains of various kinds of circular aperture distributions vs the measurement distances are calculated for an arbitrary size of the receiving probe antenna. It is found both theoretically and experimentally that the near-zone measurement error of the radiation patterns introduced when the receiving antenna is of comparable or the same dimension as the transmitting antenna is smaller than the error introduced when the receiving antenna is very small. Thus, it is concluded that as a range criterion 2D/sup 2//sub a// lambda is more appropriate than 2(D/sub a/+D/sub b/)/sup 2// lambda for pattern measurements (D/sub a/ and D/sub b/ are linear dimensions of the transmitting and receiving antennas, and D/sub a/>or=D/sub b/ is assumed). It is shown that the gain error for any aperture distribution obtained by using a large receiving probe antenna is greater at any range distance than the error obtained by using a small antenna such as a dipole. >

This paper proposes a technique for improving the accuracy of the finite difference time domain (FDTD) method for analyzing planar structures printed on a dielectric substrate. The improvement is achieved by incorporating a quasi-static field behavior to the FDTD update equations. The modified FDTD algorithm is applied to printed antennas. The validity of the method is confirmed numerically and experimentally.