臺灣博碩士論文加值系統

電阻抗影像系統是一種生物阻抗儀器，具高度發展潛力於組織及人體量測；且有下列優點：非侵入式、無輻射危害，及成本低，但最重要的特點是，它提供與其他醫療儀器不同的資訊：阻抗電特性。為了量測物體在不同頻率下、電阻抗的改變，及阻抗分布的成像，便需要多頻率及多通道功能。電阻抗影像系統主要分為六模組：(1)數位震盪器，(2)電流產生器，(3)電壓量測，(4) 輸出入介面板，(5)輸出入介面，(6)使用者圖形控制介面。數位震盪器以28位元、DDS (Direct Digital Synthesis) AD9833產生20kHz到100kHz、振幅1Vrms、0V準位的正弦波；電流產生器使用12位元乘法數位轉類比器AD5447，做成32個通道，並控制振幅在-1Vrms至+1Vrms，且每個通道皆能各自被使用者更改以建構成任意電流型態，32個改良型Howland電壓控制型電流源憑藉高輸出阻抗輸出±1 mArms振幅之穩定電流；電壓量測器含類比解多工器，其負責切換32個通道電壓給類比轉數位器，和震盪器訊號至另一個類比轉數位器；輸出入介面板有編碼模組和公用匯流排將各模組視為定址裝置來存取，並提供2個空置的接頭作未來擴充用；輸出入介面以並列輸出經排針讓使用者自行定義傳輸協定；使用者圖控介面提供頻率、電流型態，及電壓量測控制功能。本研究另一個重要目標：穩定電流源、改良型Howland電流源；由6種常用運算放大器，透過OrCAD Pspcie做模擬與實際電路測試；經模擬條件：增加量1 kHz和負載電阻1 kΩ，結果指出OPA37有最好的頻率響應，從100 Hz到截止12.115 MHz，並評估出實際電路該選用之電阻大小；在100 kHz實際電路測試中，OPA37最差只有0.0105的標準誤差。

Electrical impedance tomography (EIT) system is a kind of biomedical instrument that has great potential in tissue or body measurement. It has some advantages: non-invasive, no radiation hazard, low cost. The most important characteristic is that it can show electrical property in terms of impedance different from the other medical instrument. In order to measure the variance at different frequency and image the distribution of the impedance in object, it needs a multi-frequency and multi-channel function respectively. The EIT system has six major modules: (1) digital oscillator, (2) current generator, (3) voltage measurement, (4) I/O interface board, (5) I/O interface, (6) graphic user interface. The digital oscillator takes 28-bit DDS (Direct Digital Synthesis) AD9833 as oscillator to generate a sinusoidal signal sweeping from 20 kHz to 100 kHz at 1 Vrms with zero offset. The current generator uses 12-bit multiplying DAC AD5447 to control voltage amplitude from -1 Vrms to +1 Vrms and each of 32-channel can be programmed individually by user to construct arbitrary current pattern. 32-channel enhanced Howland voltage controlled current source output current at stable ±1 mArms by high output impedance. The voltage measurement includes analog demultiplexer to switch 32-channel voltage to an ADC and the oscillator signal to an ADC. The I/O interface board has codec module and public address and data bus to control and access EIT system module as address device. It also provides two reserved connector for extended module. The I/O interface is in parallel way via head pins for user-definition protocol. The GUI provides frequency, current pattern and voltage measurement function. Another major approach in this study is the stable current source: enhanced Howland VCCS. The 6 commonly used OP (Operating Amplifier) experiment by OrCAD Pspice simulation and actual circuit testing. The simulation results indicates the OPA37 has the best frequency response from 100 Hz to 2.3 MHz cutoff frequency and estimates the resistor value that should be at 10 kΩ level in actual circuit, with simulation condition 1 kHz increment and output load resistor 1 kΩ. The OPA37 only has about 0.07% standard derivation at 100 kHz in actual circuit.

CONTENTS
摘要..................................................I
ABSTRACT..................................................II
ACKNOWLEDGMENT..................................................III
LIST of TABLES..................................................VI
LIST of FIGURES ..................................................VII
Chapter 1 Introduction ..................................................1
1.1 Tissue electrical characteristics..................................................1
1.2 Electrical impedance tomography..................................................7
1.3 Literature review..................................................9
1.3.1 Rensselaer Polytechnic Institute: Adaptive Current Tomography 4..................................................10
1.3.2 Sheffield University: Mk3.5..................................................11
1.3.2 Dartmouth University: H-F EIT..................................................12
1.4 Motivations and purposes..................................................14
Chapter 2 Materials and Methods..................................................16
2.1 Research framework..................................................16
2.2 Hardware design..................................................17
2.2.1 I/O interface card of EIT..................................................17
2.2.2 Digital control module..................................................19
2.2.3 Current source module..................................................23
2.2.4 Data acquisition module..................................................32
2.3 Software design..................................................36
2.3.1 Demodulation algorithm..................................................36
2.3.2 User interface on PC..................................................37
2.4 NCKU BINIL EIT system specification..................................................37
Chapter 3 Results and Discussion ..................................................39
3.1 Digital oscillator module card..................................................39
3.2 Current source module card..................................................40
3.3 Data acquisition module card..................................................58
3.4 Graphic user interface..................................................59
Chapter 4 Conclusions and Prospects ..................................................60
4.1 Conclusions ..................................................60
4.2 Prospects..................................................62
References..................................................63
Appendix A..................................................67

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