Yukio Yamanaka

Development of realistic high-resolution whole-body voxel models of Japanese adult males and females of average height and weight, and application of models to radio-frequency electromagnetic-field dosimetry

With advances in computer performance, the use of high-resolution voxel models of the entire human body has become more frequent in numerical dosimetries of electromagnetic waves. Using magnetic resonance imaging, we have developed realistic high-resolution whole-body voxel models for Japanese adult males and females of average height and weight. The developed models consist of cubic voxels of 2 mm on each side; the models are segmented into 51 anatomic regions. The adult female model is the first of its kind in the world and both are the first Asian voxel models (representing average Japanese) that enable numerical evaluation of electromagnetic dosimetry at high frequencies of up to 3 GHz. In this paper, we will also describe the basic SAR characteristics of the developed models for the VHF/UHF bands, calculated using the finite-difference time-domain method.

New applications of millimeter-wave incoherent imaging

A compact wideband millimeter wave detection element for the 35 GHz band has been developed mainly for passive imaging technologies. Using this element, fruit, timber, and foods in cardboard boxes have been observed nondestructively. The thermal radiation emitted from fruit changes as it is ripening, timber with knots and/or damages by white ants, and food temperature in cardboard box can be detected through incoherent passive imaging.

Computation with a parallel FDTD system of human-body effect on electromagnetic absorption for portable telephones

Using our recently implemented parallel finite-difference time-domain computation system on Linux-based personal computers, we investigated the human-body effect on the peak specific absorption rate (SAR) in the human head for portable telephones. Taking into account the whole human body, we found that there was a difference within 5.3% for the 1- and 10-g averaged spatial peak SARs and a difference within 19% for the SAR in the brain and eyes compared to the isolated head model. Moreover, in most realistic-use positions, we found that the SAR was slightly decreased due to the body effect. These results further support the rationale of using an isolated human-head model in the SAR evaluation for portable telephones.

Dielectric properties of tissue-equivalent liquids and their effects on specific absorption rate

The radio frequency safety of mobile phones has been evaluated in terms of specific absorption rate (SAR). Standard methods for measurement of the SAR, including recipes for tissue-equivalent dielectric liquids, have recently been the subject of discussion among international standards organizations. Standards currently recommend glycol-type liquids as tissue-equivalent liquids for frequencies above 1 GHz. Although the ingredients are specified in the recipes provided, some fundamental information, such as the stability of dielectric properties, remains unclear. We measured the change of dielectric properties with time and with temperature of tissue-equivalent liquids recommended in the standard documents, and evaluated their effects on SAR. The conductivity decreased with increasing temperature in all glycol-type specimens. The permittivity, on the other hand, was almost constant. With the evaporation of water, the permittivity decreased, although the conductivities remained constant. Experimental results proved that dielectric properties are affected by environmental conditions, and that it is inevitably necessary to adjust the dielectric properties regularly, through the addition of ingredients, in order to follow the standards. The SAR values, however, were not affected significantly by the change in dielectric properties; thus, a larger tolerance of the dielectric properties may be acceptable in practical SAR measurements.

A circuit approach to simulate discharge current injected in contact with an ESD-gun

An equivalent circuit modeling was proposed for simulating the discharge current injected in contact with an ESD-gun, which is being prescribed in the IEC 61000-4-2. Based on the structure and dimension of the ESD-gun, all the circuit parameters were determined from both calculation and measurement. The equivalent circuit derived here was validated by comparing the calculated waveform of the discharge current with the measured result.

Performance analysis of interference problems involving DS-SS WLAN systems and microwave ovens

Theoretical and experimental investigations are carried out on the degradation in the performance of DS-SS wireless LAN systems (WLANs) (IEEE802.11b) systems caused by electromagnetic noise radiating from microwave ovens in the 2.4-GHz frequency band. Based on the time-domain oven-noise model, theoretical expressions for short-duration bit-error rates (BERs) and packet-error rate (PERs) are derived. Measurements were done using commercially available microwave ovens and a noise simulator that consisted of a function generator and an RF synthesizer. The PERs measured with actual oven noise were found to correlate well with those derived by simulated noise, and they were in reasonable agreement with the theoretical estimates given by the derived approximate formulae. It is concluded that the noise simulator and the derived approximate expressions were very useful in evaluating the BER and PER of WLAN systems that have incurred interference from microwave ovens.

A time-domain microwave oven noise model for the 2.4 GHz band

A time-domain noise model is developed for analyzing the performance degradation of wireless communication systems in the 2.4 GHz band caused by microwave ovens, taking into account the noise generation mechanism and its characteristics. The proposed noise model consists of a series of frequency-modulated tone bursts, which can be realized with a set of FM/AM modulators. It yields a simple and general expression of the noise waveform in terms of six parameters that can be determined from measurements. Band-limited noise waveforms can also be derived from the model via simple approximations. Comparisons of both the waveform and the frequency spectrum are made between actual noise and the proposed model, which clearly demonstrate the validity and usefulness of the model.

Method for Determining Whether or Not Information is Contained in Electromagnetic Disturbance Radiated From a PC Display

To evaluate the possibility of information leakage by observing the electromagnetic disturbance radiated from a PC display, we propose an evaluation method by using a spectrum analyzer that is commonly used for electromagnetic interference measurement without reconstructing the displayed image. In this method, we measured the spectrum when the white and time-varying stripe patterns are displayed, and determined whether or not the disturbance contains the frequency component of the display pattern from the level difference. By using the patterns, we can easily evaluate the possibility of information leakage in radiated disturbance from a PC display in a wide frequency range.

Millimeter-Wave Imaging Technologies and Their Applications

A compact wideband millimeter wave detection element for the 35 GHz band has been developed mainly for passive imaging technologies. Applications of this element include security areas as well as food industry areas. Human bodies can be detected through fire flame, the thermal radiation emitted from fruit changes as it is ripening. Timber with knots and/or damages by white ants, and food temperature in cardboard box can be detected through passive mm-wave imaging.

APD Measurement for Evaluating Disturbances Related to the Performance of Digital Communication Systems

The measured values of electromagnetic disturbances should strongly correlate with degradation in the communication quality of digital wireless communication systems. The Amplitude Probability Distribution (APD) of a disturbance represents statistical information as applicable measurement readings that meet the above requirement. In this paper, correlations between APD measurements of disturbances and the bit error rate (BER) as a quality degradation index for victim systems are quantitatively investigated. Disturbance regulation by APD measurements is discussed from the viewpoint of protecting systems from disturbances. This investigation specifically considers the situation in which a repetition pulse disturbance impacts PHS and W-CDMA systems assumed as victims. The results confirm high correlations between the APD and BER not only experimentally but also theoretically under some conditions. A disturbance regulation criterion based on APD measurements is thus proposed for compliance testing of electronic appliances with the potential to act as disturbance noise sources.