經皮式無線射頻傳輸充電系統製作與電磁波之生物效應探討

Development of a Transcutaneous Radio Frequency Battery Charging System and Bio-effect Studies of Electromagnetic Wave

林家慶(Chia-Ching Lin)

指導教授 ： 婁世亮

中原大學/工學院/生物醫學工程學系/碩士(2008年)

https://doi.org/10.6840/cycu200900354

摘要

以一次式電池做為植入式生醫功能器電源之應用曾經喧騰一時，心臟節律器所使用之鋰電池就是眾所皆知的例子；將無線射頻傳輸電能的技術應用在植入式生醫功能器者也不乏其人。為萬全計，射頻傳輸與二次式電池之合併運用，則是這領域目前之趨勢。問題是，無線射頻傳輸所衍生之電磁波（或電磁輻射）對生物組織產生的效應為何是必須關切的。
本研究之目的，首在研究發展一套植入式生醫功能器用的無線充電裝置，該整合裝置包含射頻無線傳輸電能模組、充電模組以及微型充電電池；研究目的之二，則是在探討該無線充電裝置傳輸能量之時所產生之中頻非游離輻射對活體動物是否造成負面生物效應。
本研究課題已完成一套植入式生醫無線充電雛型系統，其中電磁波功率發射子系統是依據 E 類功率放大器所製備，可操作於 0.4 至 2 MHz 之間，至少具有中頻射頻功率 180 W。當充電之時，參數設在射頻功率 120 W，頻率操作於 0.4 MHz，可在縱向位移 1.5 cm 和側向位移 2.5 cm 的範圍內 ，於 2 小時快速充電完成 120 mAh 之微型二次電池。研究中，我們使用三軸式全向性電磁場強度計量測這電磁波發射子系統之電場和磁場強度 。於零位移所量測得的電場與磁場強度分別為 281 V/m 和 23.1 A/m，這樣的場強已超過 CNS 14959 限制範圍。唯有當量測位置距離發射線圈高於 15 cm，電場和磁場強度方可符合 CNS 14959 的公眾曝曬規範。
在中頻射頻之生物組織效應研究裡，我們分有單次輻射探討和多次（間隔）輻射探討。單次輻射的研究結果顯示，以上述無線充電參數（120 W 和 0.4 MHz）輻射大鼠之組織 120 分鐘，大鼠皮膚與天線接觸面有 2.42 ± 0.98 ℃ 之溫升。然而，當操作頻率為 2 MHz 之時，大鼠皮膚溫升 5.26 ± 0.78 ℃ 。對此輻射實驗，三天後，我們在大鼠組織病理切片的探討上，發現少數炎症細胞或出現於血管血液中，或著邊於血管內壁上；除此之外，末梢血液白血球數量亦有顯著增加，因而組織顯現輕微發炎。但是隨日數增加，此炎症現象皆能自行恢復正常。
本研究課題的間隔輻射實驗是由D類高功率放大器製備的電磁波功率發射器所完成。該實驗以三天為一個週期，輻射大鼠之組織 120 分鐘，使用高功率 1200 W輻射，操作頻率範圍在1.1 MHz，為期兩週進行四次輻射。在實驗過程中，盡可能排除天線熱源，以達射頻輻射對組織的作用探討。病理切片結果顯示，大鼠的皮膚以及肌肉組織並無形態異常或有發炎反應產生，白血球數量與輻射前亦無顯著改變。
多次間隔性實驗在輻射功率與次數上，皆明顯比單次輻射實驗嚴苛，從實驗結果發現，單次輻射實驗產生輕微炎症影響，而多次間隔輻射實驗卻與未輻射前無顯著影響。據此，吾人結論這等發炎現象主因於天線發熱傷及大鼠皮膚與皮下組織所致。

關鍵字

射頻 ； 二次電池 ； 電磁波 ； 生物效應 ； 血液學 ； 病理切片

並列摘要

Primary battery cells are commonly used for implantable biomedical devices as a power supply. A well-known example is lithium iodine batteries for pacemakers. Nowadays, radio frequency technology emerges as a substitution for the battery cells. Specifically speaking, the RF technology is more like a supplement to the battery cells because it can be used to re-charge secondary batteries. A major concern of the RF utilization for power transmission in this application is biological effects to tissues.
In this course, a prototype of implantable wireless battery charging system was first developed. It consists of an RF power transmission subsystem and an implant subsystem. This subsystem is equipped with a receiving coil, a voltage regulation circuit, a battery charger circuit, and an assembly of micro-secondary battery cell （120 mAh）. The power transmission subsystem radiates electro- magnetic waves via a transmission coil, which was driven by a class-E power amplifier. Based on this prototype system, the course aims on biological effects resulted from the RF exposures during power transmission.
The transmission subsystem can be operated at 0.4, 1.2 and 2 MHz with output power up to 180 W. When the transmission and receiving coils were distanced within vertical and lateral displacements of 1.5 and 2.5 cm, respectively, a well discharged battery can be fully charged in two hours by a radiation setting of 0.4 MHz and 120 W. A radiation meter was used to measure electric field and magnetic field at this setting. The measurements of the electric and magnetic fields were 281 V/m and 23.1 A/m, respectively when the transmission coil was zero distance to the measured spot. It must be noted that these measured exceed the public radiation exposure limit regulated by CNS 14959.
Wistar rats were used in the biological effect studies. In this course, single and intermittent（or multiple）radiation exposures were applied. All exposures were set up so that the transmission coil centered at the back near the thigh of a rat. In the single exposure study, a rat was exposed by the radiation for 120 minutes from the transmission subsystem whose exposure setting was set at 0.4 MHz and 120 W. The skin temperature of the rat increased 2.42 ± 0.98 ℃. When the frequency setting was adjusted to 2 MHz, the skin temperature increases were 5.26 ± 0.78 ℃. Biopsy and hematology studies followed this radiation exposure three days after were performed. Some inflammatory cells in blood vessels and on vessel wall were observed. Yet, leukocyte counts in peripheral blood vessels increased significantly. These findings imply that the skin and the subcutaneous tissues of the rat were mild inflammation. However, the aforementioned inflammation was diminished a few days later.
Instead of using the class-E based RF transmission subsystem, the intermittent radiation study was performed by a transmission subsystem based on a class-D power amplifier. Each intermittent radiation study session was carried out in a period of three days for consecutive four periods. The radiation delivering to a rat took place only in the beginning of each study period for 120 minutes by an exposure setting of 1.1 MHz and 1200 W. During the radiation exposure, effort was made so that there was no contact between the transmission coil and the skin of the rat. The biopsy findings showed no significant morphology changes and inflammation. In addition, the leukocyte counts that were examined during the intermittent study remained steady.
Except for the coil-skin contact in the single exposure study setup, the exposure settings designed in this course were harder on the intermittent exposure study than the single exposure study. However, the single exposure study induced the inflammation, which surprisingly was not found the intermittent exposure study. A reasonable conclusion is that the inflammation cause is due to the thermal effect by the surface heat of the transmission coil that directly contacted the skin of the rat.

並列關鍵字

biological effect ； radio frequency ； rechargeable battery ； electromagnetic wave ； biopsy ； hematology

參考文獻

[52] M. Matsuo, “Design of a high-efficiency class E tuned power oscillator,” Transactions on Circuits and Systems - I: Fundamental Theory and Applications, vol. 47, no. 11, 2000, pp. 1645-1649.

[1] M. Guanying, Y. Guozheng and H. Xiu, “Power transmission for gastrointestinal microsystems using inductive coupling,” Physiological Measurement, vol. 28, 2007, pp. N9-N18.

[3] C. Niu, H. Hao, L. Li, B. Ma and M. Wu, “The transcutaneous charger for implanted nerve stimulation device,” IEEE EMBS Annual International Conference, 2006, pp. 4941-4944.

[4] P. Huang, J. Guo, C. A. Megerian, D. J. Young, W. H. Ko, “A laboratory study on a capacitive displacement sensor as an implant microphone in totally implant cochlear hearing aid systems,” IEEE EMBS Annual International Conference, 2007, pp. 5691-5694.

[5] R. S. Clement and D. R. Kipke, “Characteristics of stapedius muscle electromyograms elicited by cochlear implant stimulation in the rat,” IEEE EMBS Annual International Conference, 2004, pp.4221-4224.