植入式電刺激器效能改善之研究

Efficiency Improvement of an Implantable Electrical Stimulator

吳旻鴻(Ming-Hong Wu)

指導教授 ： 婁世亮

中原大學/工學院/醫學工程研究所/碩士(2005年)

https://doi.org/10.6840/cycu200500813

摘要

植入式電刺激器已漸為臨床醫學所接受採用。然而，由於它的體型小，應用環境特殊，不免在設計製作上限制了它的功能或效能。例如，低效率之無線電源傳輸（<3%）即是接收天線大小受限之故。本研究課題針對無線射頻接收功率和刺激電流之提升予以探討。射頻接收功率的探討分為（1）如何增加Class E功率放大器的輸出功率和（2）如何改良接收天線的方位纏繞。刺激電流的探討則側重在電容式電極的製作。
多數植入式電刺激器系統是以Class E約2瓦、2MHz的功率放大器做為射頻功率輸出之工具，因植入子系統體型小之特質，能量耦合效率低，不適於深層應用。本研究改良Class E無線功率傳輸器，將輸出功率由2瓦提升至5瓦。實驗結果顯示，植入子系統所接獲之功率相對提升2倍有餘，這將助益電刺激器植入生物體之深層部位。
本研究研製銥鋁電容式電極用以提高植入子系統（電刺激器）的刺激電流。它的運作是依據電容電極儲存電荷與瞬間放電的原理，瞬間電流與電極面積成正比。吾人據此將鋁粉末燒結成正電極，更又將銥予以氧化，使其導電度提高。經掃描式電子顯微鏡下觀察粉末燒結之鋁電極表面，其電極表面確實有孔洞結構的存在，此孔洞結構可增加電極之表面積。將粉末燒結後之鋁電極與非燒結之鋁片電極置於磷酸緩衝溶液中進行電流測試，結果顯示經粉末燒結後之鋁電極所能儲存之電荷量為鋁電極的2倍。在銥電極部分，由於氧化後之銥電極有助於電極導電度的提升。經驗證，3莫耳濃度之硫酸所氧化之銥電極，其導電度提升約1.45倍最為顯著。
ㄧ般而言，電刺激器之單向天線植入方位與發射天線形成45°時，耦合效能最低，所耦合之電能無法提供電刺激器充足之功率。本研究製做單向、雙向與三向三種接收天線。分別於0~360°範圍內偏轉，探討所接獲之電能。實驗結果顯示，同感值之單向與雙向接收天線於偏轉範圍內，雙向接收天線於YX平面偏轉45°的位置，可獲得最佳的電能耦合效果，意味著雙向接收天線在這植入方位能接獲充分之電源。若先將接收天線在YZ平面朝Z軸方向傾角45°，於該平面上，再向X軸旋轉0~90°於這區間，發現雙向接收天線耦合電能效率較佳。這個實驗結論是，雙向接收天線可容忍較大的偏轉範圍。三向接收天線由於是三個線圈並聯，並聯後之電感值下降，致使耦合電能效率大幅下降。因此，雙向接收天線於0~90°範圍內偏轉所接收的電能優於三向接收天線的表現。

關鍵字

無線電源傳輸 ； 植入式功能器 ； Class E功率放大器

並列摘要

Implantable stimulators based on techniques of wireless power transmitter have been gradually accepted and applied in clinical cases. However, the stimulators are restricted in few applications due to some technical issues remained to be overcome. In this course, the issues of increasing coupled power and stimulus current of implantable stimulators were studied.
Class-E power amplifier is commonly used in developing implanted devices for wireless power and signal transmission. It is a technique featuring in its high conversion efficiency, but its output power is limited. From an implanted device point of view, this limitation directly hinders the power to be received. Potentially, many clinical applications that require stimulations deep into body are thus excluded. This study improves the output power from the Class-E wireless power transmitter from 2W to 5W. An experiment was studied to compare how much power an implanted unit can receive in various thickness of a medium. The study results conclude that the 5W transmitter enables the implant to function two times deeper than the 2W transmitter does.
The approach to increasing stimulus current in this study is by enlarging area and enhancing conductivity of capacitor electrodes. One of the capacitor electrodes was designed in using aluminum. More importantly, the aluminum electrode was made of sintered powder rather than a bulk plate. By doing so, a study result indicates the powder made aluminum electrode can hold electric charges two times more. It must be noted that the material of aluminum should be replaced by a noble metal such as tantalum when biocompatible issues are taken into account. Another capacitor electrode was developed by using iridium. To increase the electrical conductivity, a chemistry reaction was applied on the electrode by oxidizing iridium with sulfuric acid. The conductivity of the oxidized iridium electrode varies when the concentration of the sulfuric acid is used. Our study results show 45% increase of conductivity is the best achievement which is the accomplishment of a resultant electrode oxidized by 3-mole sulfuric acid.
Generally speaking, when the receiving antenna and the transmission antenna are in 45∘, the coupled RF power is the minimum. Consequently, the stimulator cannot power up. A well designed implant device must be able to accommodate any implanted position in the body. In this study, three types of receiving antenna were coiled: single axes, double axes, and triple axes. A series of studies were carried out to compare the performance of the receiving antennas. The study results indicate that the antenna made from the double axes coils is superior to others in most of angles to the transmission antenna.

並列關鍵字

Wireless power transmitter ； Class E power amplifier ； Implantable device

參考文獻

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