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This paper investigates the correlation between maximum temperature increases and peak spatial-average specific absorption rates (SARs), calculated by different average schemes and masses. For evaluating the effect of mass on the correlation properly, a three-dimensional Green's function is presented. From our computational investigation, no best average mass for peak spatial-average SAR exist from the aspect of the correlation with maximum temperature increase. This is attributed to the frequency dependent penetration depth of EM waves. Maximum temperature increase in the head including the pinna is reasonably correlated with peak spatial-average SARs for most average schemes and masses considered in this paper. Maximum temperature increase in the head only (excluding the pinna) is reasonably correlated with peak 10-g SARs for the average schemes considered in this paper. The rationale for this result is explained using the Green's function. The point to be stressed here is that the slope correlating them is largely dependent on the average scheme and mass. Additionally, good agreement is observed in the slopes obtained by using two head models, which have been developed at Osaka University and Nagoya Institute of Technology. However, weak correlation is observed for the brain, which is caused by the difference of the positions where peak SAR and maximum temperature increase appear. The 95th percentile values of the slope correlating maximum temperature increases in the head or brain and peak spatial-average SAR are quantified for different average schemes and masses. Index Terms--Bio-heat transfer equation, human exposures, specific absorption rate (SAR), temperature increase.

This paper discusses the correlation between peak spatial-average specific absorption rate (SAR) and maximum temperature increase for antennas attached to the human trunk. Frequency bands considered are 150, 400, and 900 MHz, which are assigned for occupational communications. This problem is throughly investigated with the aid of Green's function. In particular, the effect of variation of thermal constants on the temperature increase is revealed by using one-dimensional model. Computational results suggests that one of the most dominant factors which affect the correlation between peak SAR and maximum temperature increase is blood flow in tissues. This is confirmed by considering a three-dimensional realistic human body model. Uncertainties caused by the calculation of peak SAR and the difference in the body model shape are also quantified. Index Terms--Blood flow, Green's function, specific absorption rate (SAR), temperature increase.

The frequency-tunability for a Smith-Purcell free-electron laser oscillator in the millimeter wave region is enhanced with the aid of a quasi-periodic distributed Bragg reflector (DBR) made of metallic waveguide gratings with rectangular grooves. For a quasi-periodic DBR, the grating parameters are adjusted by means of genetic algorithms to get the desired reflection coefficient, thus compensating for the frequency dependence of the overall output characteristics. For a typical numerical example, flat output characteristics have been obtained over 10% bandwidth around the center frequency 121 GHz. Index Terms--Metallic Bragg reflector, millimeter waves, Smith-Purcell free-electron laser (FEL), tunability.

This paper investigates the correlation between the peak specific absorption rate (SAR) and the maximum temperature increase in head models of adults and children due to a dipole antenna. Much attention is paid to the effect of variation of electrical and thermal constants on the correlation for the child models, since these constants of child tissues are different from those of adult tissues. For investigating these correlations thoroughly, a total of 1400 situations are considered for the following six models: 3-year-old child, 7-year-old child, and adult models developed at the Nagoya Institute of Technology and the Osaka the University. The numerical results are analyzed on the basis of statistics. We find that the maximum temperature increases in the head can be estimated linearly in terms of peak SAR averaged over 1- or 10-g of tissue. In particular, no clear difference is observed between the adult and child models in terms of the slopes correlating the maximum temperature increase with the peak SAR. Also, the effect of electrical and thermal constants of tissue on these correlation is found to be marginal. Further, we discuss possible maximum temperature increases in the head and brain for SAR limits prescribed in safety guidelines. For the adult model developed at the Osaka Univ., these are found to be 0.26 [degrees]C and 0.10 [degrees]C at the SAR value of 1.6 W/kg for 1-g cubic tissue and 0.59 [degrees]C and 0.21 [degrees]C at the SAR value of 2.0 W/kg for 10-g cubic tissue. Similarly, for the 3-year-old child model at Osaka Univ., these are 0.23 [degrees]C and 0.11 [degrees]C for the value of 1-g SAR and 0.53 [degrees]C and 0.20 [degrees]C for the value of 10-g SAR. Index Terms--Bioheat equation, dipole antenna, dosimetry, specific absorption rate (SAR), temperature increase.

With the use of a generalized transfer-matrix method based on the mode-matching approach for waveguide step discontinuities, reflection properties of metallic waveguide gratings with rectangular grooves are investigated. A proper design for a compact and wide-band reflector grating which can support single-mode operation is also discussed. A waveguide grating with symmetrical and similar cross sections is shown to be of great significance for single-mode support and for constructing a compact reflector. In addition, it is found possible to obtain metallic waveguide gratings which satisfy all the specified requirements by properly adjusting only basic grating parameters. Index Terms--Compact reflector, metallic grating, single-mode operation, wide-band characteristics.

Reflection characteristics of metallic waveguide gratings with rectangular grooves are investigated with the effect of the Joule loss taken into account. For this purpose, the scattering matrix for each step discontinuity is first found by using the mode-matching method with an impedance boundary condition at the surface of the conductor. Then, the scattering matrix for the overall waveguide grating is obtained by generalized transfer matrix methods. Numerical results show that Joule loss occurs mainly at horizontal wall sections. In order to suppress the loss of a reflector grating, it is shown that it should have a deep grating depth with a small number of periods. This configuration coincides with that for a compact and wideband reflector grating, which can well support single-mode operation, as was pointed out in our previous work. Index Terms--Compact reflector, metallic grating, single-mode operation, wideband characteristics.

This paper attempts to correlate the maximum temperature increase in the head and brain with the peak specific absorption rate (SAR) value due to handset antennas. The rationale for this study is that physiological effects and damage to humans through electromagnetic-wave exposure are induced by temperature increases, while the safety standards are regulated in terms of the local peak SAR. For investigating these correlations thoroughly, the total of 660 situations is considered. The numerical results are analyzed on the basis of statistics. We find that the maximum temperature increases in the head and brain can be estimated in terms of peak SARs averaged over 1 and 10 g of tissue in these regions. These correlations are less affected by the positions, polarizations, and frequencies of a dipole antenna. Also, they are reasonably valid for different antennas and head models. Further, we discuss possible maximum temperature increases in the head and brain for the SAR values prescribed in the safety standards. They are found to be 0.31 [degrees]C and 0.13 [degrees]C for the Federal Communications Commission Standard (1.6 W/kg for 1 g of tissue), while 0.60 [degrees]C and 0.25 [degrees]C for the International Commission on Non-Ionizing Radiation Protection Standard (2.0 W/kg for 10 g of tissue). Index Terms--Dosimetry, finite-difference time-domain (FDTD) method, specific absorption rate (SAR), temperature increase.

The temperature increases in a human head due to electromagnetic (EM) wave exposure from a dipole antenna are investigated in the frequency range of 900 MHz to 2.45 GHz. The maximum temperature increases in the head and brain are compared with the values of 10 [degrees]C and 3.5 [degrees]C (found in literature pertaining to microwave-induced physiological damage). In particular, the estimation scheme for maximum temperature increases of the head and brain tissues is discussed in terms of a peak average specific absorption rate (SAR) as prescribed in safety standards. The rationale for this attempt is that maximum temperature increases and peak average SARs have not been well correlated yet. For this purpose, the SAR in the head model is initially calculated by the finite-difference time-domain method. The temperature increase in the model is then calculated by substituting the SAR into the bioheat equation. Numerical results demonstrate that the temperature increase distribution in the head is largely dependent on the frequency of EM waves. This is mainly because of the frequency dependency of the SAR distribution. Similarly, maximum temperature increases in the head and brain are significantly affected by the frequency and polarization of the EM wave. The maximum temperature increases in the head (excluding auricles) and brain are determined through linear extrapolation of the peak average SAR in these regions. According to this scheme, it is found that the peak SAR averaged over 1 g of tissue in the head should be approximately 65 W/kg to achieve the maximum temperature increase of 10 [degrees]C induced in the head excluding auricles. This corresponds to a factor of about 40 compared to the FCC standard. On the other hand, the peak SAR for 10 g of tissue should be around 40 W/kg, which implies a factor of about 20 compared to the ICNIRP standard. Index Terms--Dipole antenna, dosimetry, finite-difference time-domain (FDTD) method, RF safety standards, specific absorption rate (SAR).

With the use of a generalized transfer matrix method based on the mode-matching approach for waveguide step discontinuities, reflection properties of metallic waveguide gratings with rectangular grooves are investigated. A proper design procedure for a compact and wide-band reflector grating which can well support single-mode operation is also discussed. Symmetrical waveguide configuration is shown to be of great significance for single-mode support. From the provided design process, it is found possible to obtain metallic waveguide gratings which satisfy all the specified requirements by properly adjusting only basic grating parameters. Index Terms--Compact reflector, metallic grating, single-mode operation, wide-band characteristics.

The effectiveness and limitation of the periodic boundary condition (PBC) in the analysis of single-pass electron beam devices are discussed. A Cherenkov traveling-wave amplifier consisting of a dielectric-loaded parallel plate waveguide and a planar relativistic electron beam is picked up as an example of electron beam devices. The numerical results obtained without the PBC are compared with those obtained with the PBC. Then, errors caused by the approximation are found to be mainly attributed to two factors. One is caused by the initial condition, which is inherent to the analysis with the PBC. The other factor is the magnitude of the growth rate. The upper bound for the growth rate is given for which the analysis with the PBC is valid. The analysis with the PBC could be effective for estimating energy transfer efficiency because of its relatively small error and significantly low computational cost. Index Terms--Cherenkov traveling-wave amplifiers, electron beam devices, FDTD methods, high-power microwave generation, particle simulation, periodic boundary approximation.

The full-wave analysis based on the singular integral equation method is developed to correctly investigate dispersion properties and field distributions inside a rectangular waveguide grating used in low-voltage traveling wave amplifiers. Simplified treatments of periodic structures with rectangular grating are widely used in the analysis of microwave electron beam devices, providing an actually good accuracy for the calculation of dispersion curves of natural modes in a wide range of grating parameters. However, they do not guarantee the correct field distributions in a close proximity to the grating just where an electron beam is usually passed to get more effective beam-wave coupling. The amplitude of the minus-first spatial harmonic, which is mostly responsible for the resonant beam-wave interaction, can be substantially larger than that predicted by the simplified analysis. In addition, the contribution of the higher spatial harmonics to the total field is shown to be significantly larger than that evaluated from the simplified treatment. Consequences of the enhanced influence of higher harmonics on beam-wave interaction are discussed. Index Terms--Cherenkov microwave sources, periodic structures, singular integral equation method, spectral problems.

The Cherenkov laser is a powerful and tunable source of short millimeter or submillimeter waves. A Cherenkov laser with a Bragg cavity is proposed as a model of a compact free-electron laser. It comprises a planar relativistic electron beam and a parallel plate waveguide. The Bragg cavity is formed by dieletric gratings. It is shown that a compact Cherenkov laser can be realised with the use of a Bragg cavity consisting of dielectric gratings.

Particle simulation of nonlinear saturation and efficiency enhancement in a dielectric grating-based single-pass Cherenkov laser shows that variation of the groove depth in a constant permittivity environment has an effect similar to variation of permittivity in a constant thickness dielectric. The dielectric grating provides significant efficiency enhancement in energy transfer, and the results may be improved further by adiabatically changing the groove depths in consonance with the decrease in the average velocity of the electron beam. A two-dimensional model of the laser is examined.

A two-dimensional model helps understand the efficiency enhancement in energy conversion for a Cherenkov laser loaded with a Kerr-like medium. Numerical simulations show that proper choice of the non-linear parameter for a Kerr-like medium increases the efficiency of electron transfer from the electron beam to the electromagnetic wave. The finite-difference time-domain method helps analyze the interactions of a group of electrons and the electromagnetic wave.

An increase in the permittivity of loaded dielectrics or a decrease in the period of wiggler magnetic field along wave propagation direction improves the efficiency of a dielectric-loaded Raman-type free-electron laser. The two methods help synchronize the electromagnetic wave with the electron beam. Tapering of the loaded dielectric permittivity improves the efficiency.

Specific absorption rates (SARs) and temperature increases in the human eye are calculated for exposure to obliquely incident plane waves in the frequency range of 600 MHz and 6.0 GHz. The average SARs and the temperature increases in lens are found to take maximum values only in the hot-spot frequency range for oblique incidence (30[degrees]-50[degrees]). Index Terms--Finite difference time domain (FDTD) method, human eye, oblique incidence of electromagnetic wave, specific absorption rate (SAR), temperature increases.

For the study of electromagnetic fields generated by precursory effects of earthquakes, the problem of transmission to the atmosphere is investigated for a subhertz plane electromagnetic wave obliquely incident from a homogeneous earth's crust of semi-infinite extent through an inhomogeneous earth's crust of finite thickness. To analyze the problem, the inhomogeneous earth's crust is subdivided into a number of thin homogeneous layers. Then, an easier problem of propagation through a composite multilayered medium replacing the homogeneous and inhomogeneous earth's crusts and the atmosphere is treated. To confirm the validity of the above formulation, an exponential inhomogeneity for the conductivity of the earth's crust is considered for a specific example. First, for the case of the inhomogeneous earth's crust, the overall power transmission coefficient on the earth-atmosphere interface at normal incidence is found to show a broader frequency characteristic and to take a maximum value at a definite subhertz frequency, shifting to a lower frequency. For the general case of oblique incidence as well, these features of the overall power transmission coefficient are retained except in the vicinity of the critical angle of incidence for the H-wave. At the critical angle of incidence, the power flow density carried by a surface wave along the earth-atmosphere interface becomes anomalously large for the H-wave. [ABSTRACT FROM AUTHOR]

For the purpose of providing for a theoretical background for the study of electromagnetic fields generated by precursory effects of earthquakes, the problem of transmission and total reflection at the earth-atmosphere interface is investigated in detail for a subhertz plane electromagnetic wave incident from the earth's crust. The term 'subhertz' means 'below 1 Hz.' First, for the special case of normal incidence, the overall power transmission coefficient at the earth-atmosphere interface is found to take a maximum value at a definite frequency f0 which is inversely proportional to the square of the depth of a virtual hypocenter. A typical value of f0 falls around 0.01 Hz. For oblique incidence as well, this feature of the overall power transmission coefficient is retained except in the vicinity of the critical angle of incidence for the H-wave. At the critical angle of incidence, the power flow carried by a surface wave along the interface becomes anomalously large for the H-wave. However, over a wide range of angles of incidence greater than the critical angle, the power flow carried by the E-wave exceeds that carried by the H-wave by orders of magnitude. Finally, the energy conservation relations for the incident, reflected, and transmitted waves at the earth-atmosphere interface are discussed. For an incident wave coming from the earth's crust, the interactive power between the incident and reflected waves plays a crucial role for the conservation of energy at the interface. [ABSTRACT FROM AUTHOR]

The temperature rises in the human eye for plane wave exposures are investigated in the frequency range between 600 MHz and 6 GHz, which covers the hot spot frequency range. As a first step, the specific absorption rates (SARs) are calculated with the use of the finite-difference time-domain (FDTD) method and the mechanism of hot-spot formation is discussed. Then the temperature rises in the human eye are calculated by using Pennes' bioheat equation. In addition, the dependence of SARs and temperature rises on the electromagnetic (EM) wave polarization and the eye dimension is discussed. Furthermore, the temperature rises calculated are compared with the values found in the literature pertaining to microwave-induced cataract formation. Numerical results show that hot spots appear in a certain frequency range and that the location and number of hot spots depend on the frequencies of the incident wave. In particular, the averaged SARs and the temperature rise are found to depend obviously on the polarization of the EM wave. Additionally, the deviations in the SAR and the temperature rise caused by the eye size are found to be within 10%. Furthermore, the maximum temperature rise due to the incident EM power density of 5.0 mW/[cm.sup.2], which is the maximum permissible exposure limit for controlled environments, is found to be 0.30 [degrees] C at 6.0 GHz. This value is small but not negligible, as compared with the threshold temperature rise 3.0 [degrees] C for cataract formation. Index Terms--Electromagnetic (EM) wave polarization, finite-difference time-domain (FDTD) method, hot spots, human eye, specific absorption rate (SAR).

Dispersion characteristics of the rectangular waveguide grating for microwave amplifier applications are studied for the first time in the rigorous mathematical manner on the basis of singular integral equation (SIE) method. In particular, the validity of the simplified approach is discussed by comparing the results obtained by both methods. Numerical results show that the dispersion curves obtained by the SIE method are in surprisingly good agreement with those obtained before. Additionally, it has been pointed out that there exists some regime where the differences between the SIE and simplified treatments become notable. Index Terms--Cherenkov microwave sources, periodic structures, singular integral equation method, spectral problems.