Takuji Arima

Local exposure of the rat cortex to radiofrequency electromagnetic fields increases local cerebral blood flow along with temperature

Few studies have shown that local exposure to radiofrequency electromagnetic fields (RF) induces intensity-dependent physiological changes, especially in the brain. The aim of the present study was to detect reproducible responses to local RF exposure in the parietal cortex of anesthetized rats and to determine their dependence on RF intensity. The target cortex tissue was locally exposed to 2-GHz RF using a figure-eight loop antenna within a range of averaged specific absorption rates (10.5, 40.3, 130, and 263 W/kg averaged over 4.04 mg) in the target area. Local cerebral blood flow (CBF) and temperatures in three regions (target area, rectum, and calf hypodermis) were measured using optical fiber blood flow meters and thermometers during RF exposure. All parameters except for the calf hypodermis temperature increased significantly in exposed animals compared with sham-exposed ones during 18-min exposures. Dependence of parameter values on exposure intensity was analyzed using linear regression models. The elevation of local CBF was correlated with temperature rise in both target and rectum at the end of RF exposure. However, the local CBF elevation seemed to be elevated by the rise in target temperature, but not by that of the rectal temperature, in the early part of RF exposure or at low-intensity RF exposure. These findings suggest that local RF exposure of the rat cortex drives a regulation of CBF accompanied by a local temperature rise, and our findings may be helpful for discussing physiological changes in the local cortex region, which is locally exposed to RF.

Finite-Difference Frequency-Domain Algorithm for Band-Diagram Calculation of 2-D Photonic Crystals Composed of Debye-Type Dispersive Materials

Wave propagation characteristics in metamaterials including photonic crystals have been widely investigated due to their inherent capabilities for developing a novel devices in the fields of optics, microwave, and antenna engineering. This letter propose a novel finite-difference frequency-domain (FDFD) algorithm for calculating band diagrams of photonic crystals composed of Debye-type dispersive materials. It will be shown that this method is highly accurate and stable in band-diagram calculation by comparison to the finite-difference time-domain (FDTD) method.

Local Exposure System for Rats Head Using a Figure-8 Loop Antenna in 1500-MHz Band

Cellular phones are used in the vicinity of the human head, resulting in localized exposure to this part of the body. To simulate exposure during cellular phone use, microwave energy absorption should be focused within the head region of laboratory animals. In this paper, we developed an exposure system using a figure-8 loop antenna to permit localized exposure of a rat head to 1500-MHz microwave fields, simulating human head exposure to cellular phones. We have numerically estimated the specific absorption rate (SAR) in a rat exposed to microwave fields via our new exposure system. The high ratio of SAR averaged over the target tissue (i.e., the brain) to that averaged over the whole body suggests that the figure-8 antenna can realize greater localized exposure than the previously used exposure system. We have also confirmed the effectiveness of our proposed system experimentally.

Recall accuracy of mobile phone calls among Japanese young people

This study aimed to elucidate the recall accuracy of mobile phone calls among young people using new software-modified phone (SMP) technology. A total of 198 Japanese students aged between 10 and 24 years were instructed to use a SMP for 1 month to record their actual call statuses. Ten to 12 months after this period, face-to-face interviews were conducted to obtain the self-reported call statuses during the monitoring period. Using the SMP record as the gold standard of validation, the recall accuracy of phone calls was evaluated. A total of 19% of the participants (34/177) misclassified their laterality (i.e., the dominant side of ear used while making calls), with the level of agreement being moderate (κ-statistics, 0.449). The level of agreement between the self-reports and SMP records was relatively good for the duration of calls (Pearson’s r, 0.620), as compared with the number of calls (Pearson’s r, 0.561). The recall was prone to small systematic and large random errors for both the number and duration of calls. Such a large random recall error for the amount of calls and misclassification of laterality suggest that the results of epidemiological studies of mobile phone use based on self-assessment should be interpreted cautiously.

Experimental verification of spoof surface plasmons in wire metamaterials.

In this paper, we experimentally demonstrate the excitation of spoof surface plasmon polaritons (SPPs) on a wire-medium metamaterial slab in the microwave region. The spoof SPPs are excited on the opposite side of the slab from the source, which is desirable for applications such as sensing devices. Using the prism coupling method, we verify the excitation of spoof SPPs by measuring the reflection spectrum and near-field enhancement. The excitation of spoof SPPs is also verified by using the grating coupling method, where we demonstrate transmission enhancement through the metamaterial slab by placing diffraction gratings on both sides of the slab. Numerical investigation shows that the enhanced transmission can be attributed to the dispersion relations of the spoof SPPs and the periodicity of the diffraction grating. These properties can be used to realize extraordinary transmission and directional beaming.

Improvement of FDTD accuracy for analyzing printed antennas by using quasi-static approximation

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.

Differential-Type CRLH Leaky-Wave Antenna Using Stepped Impedance Resonators

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.

FDFD and FDTD analysis of 2-Dimensional lossy photonic crystals

In this paper, a new FDFD algorithm for calculating a band gap diagram of 2-Dimensional (2D) lossy photonic crystals (PC) is developed. It is also shown that the FDTD method can not be successfully applied to the lossy PCs.

Development of a liquid-type human-body equivalent antenna using NaCl solution

Radio-frequency (RF) safety guidelines requires to estimate the ankle induced current in the human body standing on the ground in Very High Frequency (VHF) band because of the whole-body resonance. In this presentation we have investigated the human-body equivalent antenna for estimation of the induced ankle current. First, we verified that the numerical calculation is valid for designing the specification of the antenna, i.e., the electrical properties of the tissue-equivalent liquid. Next, we determined the optimized electrical properties of the tissue-equivalent liquid for simulating the actual induced ankle current. Consequently, we demonstrated the human-body equivalent antenna using of 2.6-% NaCl solution for the tissue-equivalent liquid at 21-degree C can estimate ankle induced current within 20-% error.

FDTD analysis of printed antenna on thin dielectric sheet including quasi-static approximation

In this paper, a new modeling method for thin dielectric films is proposed. In this method, how the physically correct field distribution is introduced to the FDTD cell is important. A quasi-static field distribution is utilized because this field is dominant in the region near the conductor edge. In this method, it is possible to analyze a printed antenna on thin dielectric film with high accuracy even when a fine cell is not used. The validity and effectiveness of the method are confirmed experimentally.