中間周波数帯接触電流に対する電磁ドシメトリにおける数値誤差評価

摘要

Contact currents occur when a person touches conductive surfaces at a different electric potentials. In the low frequency to intermediate frequency, the flow of electric current from an object in the field to the body of the individual may result in the stimulation of peripheral nerves. Therefore, basic restriction is regulated in terms of in-situ electric field in the ICNIRP guidelines. Contact current which does not produce induced quantities exceeding the basic restriction is used as a reference level. There has been increasing concern on evaluating induced quantities in the body due to contact current, since IH cookers have been utilized in addition that wireless power transmission systems have been emerging. Some recent studies have conducted dosimetry for contact current. Note that a quasi-static finite-difference time-domain (FDTD) method is one of the well-known computational methods for human dosimetry, due to its capability for handling realistic structures and source. In the present study, we investigated the effectiveness of quasi-static FDTD method for a cylinder composed of biological tissue. As a result, computational error evaluated by comparing induced electric fields in homogeneous cylinder computed by quasi-static FDTD method with values obtained from analytical solutions was 2-3% up to 50MHz.%電磁界ばく露により異なる電位ポテンシャルを持つ導電性物体と人体が接触するとき，接触電流が生じる．極低周波から中間周波数の接触電流が人体の末梢神経系を流れる場合には刺激を与える可能性がある．こうした電磁界の生体影響を防護するため，ICNIRPガイドラインでは接触電流の参考レベルと体内電界の基本制限の二つの指標を設けている．近年では，IH調理器の普及や無線電力伝送の実用化に向け，接触電流による体内誘導量の評価に関心が高まっている．また，計算機の発達に伴い，数値解析を用いて接触電流による体内誘導量の評価が行われている．特に．準静的FDTD（Finite-Difference Time-Donain）法は複雑な渡瀬に適用できることから，今後，より現実的な問題への適用が期待される．本稿では，準静的FDTD法による数値解析の有効性の検討を目的とし，損失性誘電体からなる円柱を対象として評価した．その結果，準静的FDTD法の誤差は，50MHz以下の周波数帯において解像度2.5mmの均質な円柱モデルでおおよそ2-3％であった．