Yoshitsugu Kamimura

Thirty minutes mobile phone use has no short-term adverse effects on central auditory pathways

OBJECTIVE To investigate whether pulsed high-frequency electromagnetic field (pulsed EM field) emitted by a mobile phone for 30 min has short-term adverse effects on the human central auditory system. METHODS We studied the auditory brainstem response (ABR), the ABR recovery function and middle latency response (MLR) before and after using a mobile phone for 30 min in 15 normal hearing volunteers. RESULTS None of the 3 measures were affected by exposure to pulsed EM field emitted by a mobile phone for 30 min. CONCLUSIONS Based on the ABR and MLR methods utilized in the study, we conclude that 30 min mobile phone use has no short-term adverse effects on the human auditory system.

The 1.5 GHz electromagnetic near-field used for cellular phones does not promote rat liver carcinogenesis in a medium-term liver bioassay.

We have recently established that local exposure to a 929.2 MHz electromagnetic near‐field, used for cellular phones, does not promote rat liver carcinogenesis in a medium‐term bioassay system. In the present study, a 1.439 GHz electromagnetic near‐field (EMF), another microwave band employed for cellular phones in Japan, was similarly investigated. Time division multiple access (TDMA) signals for the Personal Digital Cellular (PDC) Japanese cellular telephone standard system were directed to rats through a quarter‐wavelength monopole antenna. Numerical dosimetry showed that the peak SARs within the liver were 1.91–0.937 W/kg, while the whole‐body average specific absorption rates (SARs) were 0.680–0.453 W/kg, when the time‐averaged antenna radiation power was 0.33 W. Exposure was for 90 min a day, 5 days a week, over 6 weeks, to male F344 rats given a single dose of diethylnitrosamine (200 mg/kg, i.p.) 2 weeks previously. At week 3, all rats were subjected to a two‐thirds partial hepatectomy. At week 8, the experiment was terminated and the animals were killed. Carcinogenic potential was scored by comparing the numbers and areas of the induced glutathione S‐transferase placental form (GST‐P)‐positive foci in the livers of exposed (48) and sham‐exposed rats (48). Despite increased serum levels of corticosterone, adrenocorticotropic hormone (ACTH) and melatonin, the numbers and the areas of GST‐P‐positive foci were not significantly altered by the exposure. These findings clearly indicated that local body exposure to a 1.439 GHz EMF, as in the case of a 929.2 MHz field, has no promoting effect on rat liver carcinogenesis in the present model.

Evaluation of SAR in a human body model due to wireless power transmission in the 10 MHz band

This study discusses a computational method for calculating the specific absorption rate (SAR) due to a wireless power transmission system in the 10 MHz frequency band. A two-step quasi-static method comprised of the method of moments and the scalar potential finite-difference method are proposed. The applicability of the quasi-static approximation for localized exposure in this frequency band is discussed by comparing the SAR in a lossy dielectric cylinder computed with a full-wave electromagnetic analysis and the quasi-static approximation. From the computational results, the input impedance of the resonant coils was affected by the existence of the cylinder. On the other hand, the magnetic field distribution in free space and considering the cylinder and an impedance matching circuit were in good agreement; the maximum difference in the amplitude of the magnetic field was 4.8%. For a cylinder-coil distance of 10 mm, the difference between the peak 10 g averaged SAR in the cylinder computed with the full-wave electromagnetic method and our quasi-static method was 7.8%. These results suggest that the quasi-static approach is applicable for conducting the dosimetry of wireless power transmission in the 10 MHz band. With our two-step quasi-static method, the SAR in the anatomically based model was computed for different exposure scenarios. From those computations, the allowable input power satisfying the limit of a peak 10 g averaged SAR of 2.0 W kg(-1) was 830 W in the worst case exposure scenario with a coil positioned at a distance of 30 mm from the chest.

Intercomparison of induced fields in Japanese male model for ELF magnetic field exposures: effect of different computational methods and codes

The present study provides an intercomparison of the induced quantities in a human model for uniform magnetic field exposures at extremely low frequency. A total of six research groups have cooperated in this joint intercomparison study. The computational conditions and numeric human phantom including the conductivity of tissue were set identically to focus on the uncertainty in computed fields. Differences in the maximal and 99th percentile value of the in situ electric field were less than 30 and 10 % except for the results of one group. Differences in the current density averaged over 1 cm(2) of the central nerve tissue are 10 % or less except for the results of one group. This comparison suggests that the computational uncertainty of the in situ electric field/current density due to different methods and coding is smaller than that caused by different human phantoms and the conductivitys of tissue, which was reported in a previous study.

Acute Ocular Injuries Caused By 60-ghz Millimeter-wave Exposure

The goal of this study was to examine the clinical course of 60-GHz millimeter-wave induced damages to the rabbit eye and to report experimental conditions that allow reproducible induction of these injuries. The eyes of pigmented rabbits (total number was 40) were irradiated with 60-GHz millimeter-waves using either a horn antenna or one of two lens antennas (6 and 9 mm diameter; ϕ6, ϕ9) Morphological changes were assessed by slit-lamp microscopy. Additional assessments included corneal fluorescein staining, iris fluorescein angiography, and lens epithelium light microscopy. Under the standardized eye-antenna positioning, the three antennas caused varying damages to the eyelids or eyeglobes. The most reproducible injuries without concurrent eyelid edema and corneal desiccation were achieved using the ϕ6 lens antenna: irradiation for 6 min led to an elevation of the corneal surface temperature (reaching 54.2 ± 0.9°C) plus corneal edema and epithelial cell loss. Furthermore, mitotic cells appeared in the pupillary area of the lens epithelium. Anterior uveitis also occurred resulting in acute miosis (from 6.6 ± 1.4 to 2.2 ± 1.4 mm), an increase in flares (from 6.7 ± 0.9 to 334.3 ± 130.8 photons per second), and iris vasodilation or vessel leakage. These findings indicate that the three types of millimeter-wave antennas can cause thermal injuries of varying types and levels. The thermal effects induced by millimeter-waves can apparently penetrate below the surface of the eye.

Effect of the averaging volume and algorithm on the in situ electric field for uniform electric- and magnetic-field exposures

The present study quantified the volume-averaged in situ electric field in nerve tissues of anatomically based numeric Japanese male and female models for exposure to extremely low-frequency electric and magnetic fields. A quasi-static finite-difference time-domain method was applied to analyze this problem. The motivation of our investigation is that the dependence of the electric field induced in nerve tissue on the averaging volume/distance is not clear, while a cubical volume of 5 x 5 x 5 mm(3) or a straight-line segment of 5 mm is suggested in some documents. The influence of non-nerve tissue surrounding nerve tissue is also discussed by considering three algorithms for calculating the averaged in situ electric field in nerve tissue. The computational results obtained herein reveal that the volume-averaged electric field in the nerve tissue decreases with the averaging volume. In addition, the 99th percentile value of the volume-averaged in situ electric field in nerve tissue is more stable than that of the maximal value for different averaging volume. When including non-nerve tissue surrounding nerve tissue in the averaging volume, the resultant in situ electric fields were not so dependent on the averaging volume as compared to the case excluding non-nerve tissue. In situ electric fields averaged over a distance of 5 mm were comparable or larger than that for a 5 x 5 x 5 mm(3) cube depending on the algorithm, nerve tissue considered and exposure scenarios.

Development of a 2.45-GHz Local Exposure System for In Vivo Study on Ocular Effects

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

Quality assurance: Recommended guidelines for safe heating by capacitive-type heating technique to treat patients with metallic implants

Abstract This article is a redissemination of the previous Japanese Quality Assurance Guide guidelines. Specific absorption rate and temperature distribution were investigated with respect to various aspects including metallic implant size and shape, insertion site, insertion direction, blood flow and heating power, and simulated results were compared with adverse reactions of patients treated by radio frequency capacitive-type heating. Recommended guidelines for safe heating methods for patients with metallic implants are presented based on our findings.

Dosimetry Using a Localized Exposure System in the Millimeter-Wave Band for in vivo Studies on Ocular Effects

We developed a millimeter-wave (MMW) exposure system for in vivo experiments for operating frequencies ranging from 24.5 to 95 GHz. The MMWs are localized to the rabbit ocular tissue with a spot-focus lens antenna. The MMW energy absorption and consequent temperature elevation are evaluated by numerical simulation using measured antenna distribution and precisely modeled rabbit ocular data. Results suggest that corneal damage occurs at an incident power density of 300 mW/cm2 with our exposure system at frequencies from 26.5 to 95 GHz.

Human Body Impedance for Contact Current Measurement in Japan

The radio-frequency protection guideline of Japan recommend the limits of contact current for contact hazard due to an ungrounded metallic object under an electromagnetic field in the frequency range from 10 kHz to 15 MHz. To arrange the standard measurement methods of contact current in Japan, the contact body impedance for the Japanese in the frequency range from 75kHz to 15MHz is obtained, and the simplified equivalent circuit is determined using nonlinear least squares method. In addition, the human body impedance is obtained from numerical simulation using the impedance method and voxel human model, and compared it with measured one.