D類功率放大器應用於射頻能量傳輸對生物組織之熱效應探討

Tissue Thermal Effect Studies of Class D RF Transmission

許明政(Ming-Jeng Hsu)

指導教授 ： 婁世亮

中原大學/工學院/醫學工程研究所/碩士(2006年)

https://doi.org/10.6840/cycu200600836

摘要

植入式生醫功能器需要電源才能正常工作。雖然科學家企圖研發人體自身的生物燃料電池以供應植入式功能器所需之電源。植入式功能器仍以電池和射頻無線傳輸提供電源較為常見。其中，射頻的方式是以電磁波耦合的原理，使用二個（體外之發射與體內之接收）線圈既耦合電能又傳輸訊號。由於它具有這一舉兩得的優點，因此獲得相當的重視。文獻顯示，多數以射頻傳輸電源的植入式功能器，其效率在相距3公分處只能接收到約50 mW的電能。這樣的效率限制了植入式功能器的應用層面，也就是只能將生醫功能器植於皮下。為此吾人研發半橋式D類放大器提高輸出功率，企求達成深層植入的目標。
由於無線射頻電源發送器(power transmitter)的輸出功率大為提高，組織熱效應因之而生。本研究課題的目的即在於探討高功率無線電源傳輸在生物組織中之熱效應現象，其中將以特定吸收率 (Specific Absorption Rate, SAR) 之分佈表現之。
在本課題中，吾人已完成高功率D類放大器之射頻電源傳輸系統，有效提升功率接收效率。傳輸效能尤以1.1 MHz的頻率為最佳。傳輸/接收線圈間距為5公分，並以400 kHz至1.2 MHz傳輸電源，能夠接收到176至490 mW，明顯優於文獻所提之接收功率(50 mW)。
在特定吸收率分佈的繪製部分，以頻率1.1 MHz、功率10 W之電磁波，對厚度為4公分之豬肉組織進行照射，發射線圈與組織相距3.5公分，結果顯示(1)瘦豬肉部分：SAR之最大值發生在座標(6,1)，值約為5.58，表示如此的射頻能量，在5分鐘內將造成瘦豬肉0.4787 ℃的溫度上升。理想的情況下，照射的時間必須限制為52.22分鐘。(2) 豬油部分：SAR之最大值發生在座標(10,1)，值約為2.95，表示如此的射頻能量，在5分鐘內將造成豬油0.4027 ℃的溫度上升。理想的情況下，照射的時間必須限制為62.08分鐘。
在特定吸收率分佈的升溫驗證部份，以頻率1.1 MHz、功率10 W之電磁波，對厚度為4公分之豬肉組織照射5分鐘，發射線圈與組織相距3.5公分，在SAR之最大值的區域，(1) 瘦豬肉部分：吾人以SAR值所預測之升溫為0.4787±0.0705 ℃，而實際量測之升溫為0.3171±0.0723 ℃。(2) 豬油部分：吾人以SAR值所預測之升溫為0.4027±0.0151 ℃，而實際量測之升溫為0.5028±0.0360 ℃。

關鍵字

熱效應 ； 特定吸收率 ； D類功率放大器 ； 射頻電源傳輸

並列摘要

In general, implantable biomedical devices require electrical power to perform its functionality. In this course, a class-D based radio frequency (RF) power amplifier was developed for transmitting electrical energy from an external device to an implanted unit. The output power of the transmitter can be as high as several hundred watts (W) which is significantly higher than those emitted from class-E based transmitters.
As the high output power can potentially damage tissues caused by thermal effects, safety issues must be taken into account. Specific Absorption Rate (SAR) in watts per kilogram (W/kg) is a measure at which RF energy is exposed to an element or mass of a biological body. In other words, the SAR is a measurement of the heat absorbed by tissues. Thus understanding the distribution of the SAR in tissues is important in studying potential tissue damage when RF power is applied.
In conducting the SAR distribution studies, the RF electromagnetic frequency and energy of 1.1 MHz/10 W were exposed on a stack of pork for 5 minutes. The pork was either lean meat or fat with densities 969.7 kg/m3 and 729.3 kg/m3, respectively. Both lean meat and fat were examined on a set of pre-defined locations. For those locations, the amplitudes of the electrical field and the temperatures before and after the RF exposures were recorded. The SAR values can be derived from the recorded electric fields.
The study results show that the maximum SAR values are 5.58 and 2.95 in lean and fat tissues, respectively. Based on these values, it means that the heat produced by the RF power can be used to predict the lean and fat tissues raise 0.4787±0.0705 ℃ and 0.4027±0.0151 ℃, respectively. As to the recorded temperature changes, the lean meat and the fat tissue increased 0.3171±0.0723 ℃ and 0.5028±0.0360 ℃, respectively.

並列關鍵字

Thermal effect ； SAR ； Class D power amplifier ； Radio frequency

參考文獻

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