本論文中，我們搭建並設計了一個基於真實汽車座椅的生理信號檢測系統。測量信號的原理是由於心臟的收縮與舒張所引起之身體振動，被稱為心衝擊描記圖(Ballistocardiography，BCG)。此外在座椅的測量中，由呼吸引起之胸腔體積變化也會由於身體位移而混合於BCG信號中。在我們的系統中，透過將氣袋嵌入座椅並連接到壓阻式傳感器，以測量身體相關的生理振動並轉換為電信號。然後將接收的電信號由運算放大器放大。再通過類比數位轉換器將放大的信號轉換成數位信號。最後微控制器透過通用非同步收發傳輸器(Universal Asynchronous Receiver and Transmitter，UART)將轉換後的數位信號輸出到桌上型電腦或筆記型電腦以進行後續信號處理。該系統的取樣頻率為240赫茲，解析度為24位元。
當系統將信號傳送至桌上型電腦或筆記型電腦後，我們將輸入的BCG信號處理分成呼吸以及心跳兩個不同流程做處理。在各自流程中，通過信號的前處理和峰值偵測方法提取出呼吸和心跳之正確位置。最後將計算出的心率和呼吸率分別與心電圖（Electrocardiography，ECG）和阻抗呼吸描記法（Impedance Pneumography，IPG）進行比較。
接下來，為了找到最合適的氣袋以及放置位置，我們對於不同材質和形狀的氣袋，不同測量方式和不同外部影響設計了一連串的實驗流程。對於不同材質和形狀的氣袋，考慮了四種材質和三種形狀。對於不同的測量方式，考慮了五種放置位置和三種椅背角度。對於不同的外部影響，考慮了兩種坐姿和三種衣服厚度。在上述流程之後，透過體重指數（Body Mass Index，BMI）分類不同受試者來進行驗證。結果證實，心跳和呼吸的準確率最高皆可以達到97％以上，另外對於心跳與呼吸，其均方根誤差（Root Mean Square Error，RMSE）分別可達到低於2 BPM (Beats per Minute)及0.5 RPM (Respiration per Minute)以下。此外亦透過推車考慮移動狀態對於信號之影響。最後，在成本考量的情況下對於數據做不同的取樣率和解析度之比較。並提出了適合的取樣頻率可以降低至 80 赫茲以及解析度可以降低至 16 位元。

In this thesis, we build and design a physiological signal detection system based on real car seat. The principle of the measured signal is the body vibration caused by the contraction and relaxation of the heart, which is called ballistocardiography (BCG). In addition, in the seat measurement, the volume change of the chest caused by the respiration is also mixed in the BCG signal due to the body displacement. In our system, the air bag is embedded into the seat and connected to a piezoresistive sensor to measure body-related physiological vibrations and converted to the electrical signal. Then the received electrical signal is amplified by the operational amplifier (OP). The amplified signal is then converted to a digital signal by an analog to digital converter (ADC). Finally, the microcontroller unit (MCU) outputs the converted digital signal to the personal computer (PC) or notebook through the universal asynchronous receiver and transmitter (UART) for subsequent signal processing. This system has a sampling frequency of 240 Hz and a resolution of 24 bits.

When the system sends the signal to PC or notebook, we process the incoming BCG signal into two different flow including respiration and heart. In their respective process, the correct peak position of respiration and heartbeat is extracted by the preprocessing of the signal and the peak detection method. Finally, the calculated heart rate and respiratory rate will be compared with the electrocardiography (ECG) and impedance pneumography (IPG) respectively.

Next, in order to find the most suitable air bag and placement, we design a series of experimental procedures for air bags of different materials and shapes, different measurement ways and different external influences. For air bags of different materials and shapes, four materials and three shapes are considered. For different measurement ways, five placement positions and three angles of backrest are considered. For different external influences, two sitting postures and three cloth thicknesses are considered. After the above procedures, experimental verification is performed by different subjects through body mass index (BMI) classification. The results confirm that the highest accuracy rate of respiration and heartbeat can reach more than 97\%, and the root mean square error (RMSE) of heartbeat and respiration can be lower than 2 beats per minute (BPM) and 0.5 respiration per minute (RPM) respectively. In addition, the effect of the signal on the moving state is also considered by the cart. Finally, under the consideration of cost, the data is also analyzed and compared with different sampling rates and resolutions. It is proposed that the suitable sampling frequency can be reduced to 80 Hz and the resolution can be reduced to 16 bits.

1 Introduction 1
1.1 Backgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Main Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Thesis Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Related Works and Physiological knowledge 7
2.1 Different Methodologies in Automotive Environment . . . . . . . . . . . . . 7
2.1.1 Bioelectrical Effects . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.2 Mechanical Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.1.3 Comparsion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 Pressure Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2.1 Capacitive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2.2 Piezoelectric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2.3 Piezoresistive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3 Ballistocardiograph (BCG) . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.1 BCG Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.2 BCG Measurement Ways . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3.3 Relationship between ECG and BCG . . . . . . . . . . . . . . . . . 26
2.3.4 BCG Related Work . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3 Proposed Seat Sensing System and Signal Processing Methodologies 31
3.1 System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2 Sensing Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2.1 Types of Air Bags . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2.2 Piezoresistive Sensor (MPX2010) . . . . . . . . . . . . . . . . . . . 34
3.2.3 Operational Amplifier (LM833) . . . . . . . . . . . . . . . . . . . . 35
3.2.4 A/D Converter (LTC2445) . . . . . . . . . . . . . . . . . . . . . . . 37
3.2.5 Microchip MCU (dsPIC33EP256MC506) . . . . . . . . . . . . . . . 39
3.3 Experiment Setup and Proposed Signal Processing Flow . . . . . . . . . . . 41
3.3.1 Experiment Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.3.2 Signal Preprocessing . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.3.3 Peak Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4 Implementation and Evaluation Results 57
4.1 Comparison of Different Material and Measurement Ways . . . . . . . . . . 58
4.1.1 Different Air Bag Materials . . . . . . . . . . . . . . . . . . . . . . 59
4.1.2 Different Positions of Air Bag under Different Angle of Backrest . . 60
4.2 Consider Different External Effect . . . . . . . . . . . . . . . . . . . . . . . 64
4.2.1 Different Posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.2.2 Different Clothes Thickness . . . . . . . . . . . . . . . . . . . . . . 65
4.2.3 Different Subjects . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.2.4 Comparison with Literature . . . . . . . . . . . . . . . . . . . . . . 67
4.3 Moving State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.4 Optimal Sampling Rate and Resolution Bits . . . . . . . . . . . . . . . . . . 72
4.4.1 Sampling Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.4.2 Resolution Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5 Conclusion and Future Works 75
5.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.2 Future Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
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