大腦/腦幹與小腦的電場強度分布之模擬結果

在一些研究中，顯示了暴露在低頻射頻電磁場的生物實驗樣本，其癌症發病 率高於正常樣本 [43]。對吾人所關心的人體組織器官而言，SAR 值的分布將受到 電場強度大小的直接影響。圖7.19中顯示針對腦組織部分，包括大腦含腦幹，以 及小腦的電場強度分布的模擬結果，吾人得以觀察出，在靠近輻射源的一側，大 腦的側葉、腦幹、以及小腦的後葉，分別具有明顯的電場吸收累積情形。其中腦 幹負責維持生命，大腦側葉負責聽覺，小腦的後葉負責人體的內分泌系統。因此，

為了防止與避免輻射的危害，吾人應避免手機使用者在使用手機通話的時候把手 機緊貼在耳朵上，或建議使用免持聽筒，這樣的方式，可以避免當人體組織或頭 部組織直接曝曬在手機的近場低頻電磁輻射場下。

Fig 7.18: 大腦及腦幹組織於各單位格點於計算時間為 5000∆t，比較有無顱骨時的 電場強度 |E| 之分布結果。

Fig 7.19: 小腦組織於各單位格點於計算時間為 5000∆t，比較有無顱骨時的電場強 度 |E| 之分布結果。

第 八 章 結論

8.1 本文之貢獻

在經過實解驗證吾人所開發之數值方法的準確性後，進行了人體特定比吸收 率 SAR 的模擬。首先，本論文求得了人體頭部各組織的最大 SAR 值。可以清楚 的看到，使用手機通話時，比較靠近手機的組織器官 (皮膚與肌肉) 較內部器官 (腦部組織與顱骨)，具有較高的 SAR 值。此外，本文的模擬結果與實際產品測量 值相比 (7.1 節) 相比，可以發現，兩者相當的接近，這驗證了吾人所開發之數值 方法進行模擬的可行性與可信度。

其次，在研究中，由頭部各器官組織之電場強度分布情形可以得之，SAR 在 腦部組織依舊具有吸收的情形，如果長時間使用手機進行通話時，更加必須注意 的是，手機輻射將會直接對頭部造成熱損害 [44]，根據本文之模擬結果，吾人參 考了低頻射頻電磁場曝曬下的生物研究 [43]，我們接著討論了腦部各個組織中的 電場強度的分布情形，並且觀察顱骨的存在，是否會影響腦部的電磁場強度分布 情形，結果是肯定的，由於顱骨的材料係數 (導電率與介電常數) 與相鄰組織之材 料係數的明顯差異，進而增加穿透頭骨時所發生的電磁散射，導致入射至腦部的 電場強度，可以發現，與無顱骨的模擬情況比較，電場強度吸收情形明顯降低許 多。最後，我們給出了手機的使用方式建議，在手機收發訊號時，當手機緊貼耳 朵，低頻射頻電磁場直接曝曬頭部或人體時，靠近手機的一側，會直接受到低頻 射頻電磁場的影響。使用者可選擇避免將手機與人體直接接觸；然而，業界在手 機設計時，通過天線設計、手機材質、輻射功率以及工作頻段的選取，也是至關 重要的考量因素，為了輻射安全，必須遵守手機的 SAR 安全標準。綜合以上所 述，本論文的模擬預測結果表明，在設計手機時，可優先進行數值模擬。手機的 材質、工作頻段、輻射功率，對於預測手機的 SAR 值結果亦至關重要。這樣的結 論，對於降低手機設計成本以及降低實驗測試次數皆有相當的幫助。

Fig 8.1: 在 log 尺度下，頭部組織 SAR 分布之模擬結果。

8.2 未來工作與展望

本論文中，吾人所開發之數值方法，對求解三維馬克斯威爾方城組以模擬實 際的複雜幾何物理問題，已經得到了良好的驗證，並且證實了我們的模擬結果，

與實際物理上之實驗測量結果數值相當接近，這樣的結果，亦證實了吾人所開發 之 PRK-DRP FDTD 具備一定的實用性以及優秀的準確度，並且在計算複雜幾何 散射物體之物理問題中，可針對在計算空間中，吾人所關注之散射物體或區域，

進行求解其電磁場之全場/散射場 (Total-Field / Scattered-Field) 並進行分離，進一 步將問題複雜化。例如求解天線輻射問題，藉由近場外推遠場，求得感興趣的天 線輻射場型，或藉此技術，以分析天線的輻射效率以及其天線指向性。另外，本 文所探討之頭部比吸收率問題為總場問題，在本研究中，複雜幾何散射體以及金 屬等色散介質材料之數值處理方法，亦已通過整合，已經成熟發展，足以解決深 入之電磁物理現象。由於所有的電器和電子設備，在其工作時，都會產生間歇或 連續性的電壓／電流變化，這將導致在不同頻帶內產生電磁能量，在電子電路產 業中，諸如此類需要特別關注之電磁現象，分為電磁相容性 (EMC) 與電磁干擾 (EMI) 兩樣重點，為了降低電路中所產生之 EMI 效應，與產品所選擇之屏蔽材料 與電路佈局息息相關。因此，透過吾人所開發之數值方法，未來可應用在電子電 路設計。吾人所開發之非交錯網格下之時域有限差分程式較適合執行平行計算於 GPUs 上，藉由於實際測試前先行模擬並優化產品，以期降低研究經費與所需時 間。

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