Figure 1. Global Mortality Rates by Cause of Death. Cardiovascular diseases claim the highest number of lives, accounting for 31.8%. 17

Figure 2. Graph depicting awareness and treatment rates of hypertension among individuals categorized by gender. Females exhibit higher rates of awareness and treatment compared to males, with awareness rates for males... 18

Figure 3. Non-invasive blood flow measurement methods. (a) Measurement of vessel thickness using ultrasound [24]. Ultrasound probe generates ultrasound from the skin surface, analyzing the signals reflected from the vessel... 20

Figure 4. Various Debye models. Usually the two-component circuit is too simple to mimic with sufficient precision the frequency dependence of the variables measured. The three-component model combines features of... 22

Figure 5. Electrical resistance model of the artery with its own electrical properties. The artery has a time-varying cross-sectional area and a constant length. Bio-impedance (Z) of the artery is equivalent to the resistance (R) as... 24

Figure 6. Graph illustrating the time-varient representation of vascular information using bio-impedance. The graph shows fluctuations representing vascular information, but there are challenges regarding direct conversion... 24

Figure 7. Schematic diagram of blood pressure calibration using the law of conservation of energy. The left-hand side of the energy conservation equation represents the energy exerted by the heart to propel blood, while the... 26

Figure 8. Illustration explaining PTT, which is inversely proportional to the velocity of blood flow. While the changes in blood flow cannot be directly converted into blood pressure, they manifest as pulse waves in the form... 26

Figure 9. Neckband for continuous blood pressure measurement [58]. (a), (b). The neckband is composed of an IPG and an ECG, designed for utilizing the energy conservation law method. The IPG measures the pulse wave... 27

Figure 10. the method for calibrating blood pressure using the Moens-Korteweg formula. The Moens-Korteweg formula is an equation that relates the characteristics of the blood vessels (thickness, elasticity, internal radius)... 28

Figure 11. Wristband for continuous blood pressure measurement consisting of two IPGs [60]. A wristband composed of two IPGs is used to measure blood pressure using the vascular information of the radial artery in the... 29

Figure 12. The measurement of blood pressure waveform using the Bramwell-Hill equation. The Bramwell-Hill equation expresses the relationship between pulse wave velocity, blood density, blood pressure and the cross-... 30

Figure 13. Continuous blood pressure measurement using information obtained from PPG and IPG sensors and the Bramwell-Hill equation. Real-time changes in the cross-sectional area of the blood vessel provide the... 30

Figure 14. Method of obtaining information close to cross-sectional area using IPG. As IPG typically consists of four electrodes, it has a wide measurement range. Although it can contain volumetric information of the blood... 32

Figure 15. Adopting the working principle of the antenna to narrow the measurement range. The size of the antenna can be adjusted according to the operating frequency, allowing the antenna size to be reduced as desired.... 33

Figure 16. Working principle of a half-wavelength dipole antenna. The size of a half-wavelength dipole antenna is half the wavelength, allowing the electric energy from the source to distribute to the ends of the dipole antenna,... 34

Figure 17. Basic structure of the microstrip antenna (patch antenna) which consists of transmission line, antenna path, ground layer, and dielectric substrate. (a) Top view. (b) Side view. 35

Figure 18. Consideration of the size of the bipolar IPG sensor for application. The proposed sensor will be applied to a wristband to measure changes in the radial artery. Therefore, the lateral dimension of the sensor should be... 37

Figure 19. Utilizing a low-profile antenna type for the bipolar IPG sensor. A low-profile antenna is suitable for wristbands. An outer insulator is added to prevent direct contact between the skin and the metal (patch). 38

Figure 20. (a) Fabrication photo of the bipolar IPG sensor. Copper was used for the metal layer, and FR-4 was applied to the insulator layer. (b) Simulation and experimental results of the bipolar IPG sensor for the operating... 39

Figure 21. Finite element analysis simulation environment to determine the linearity between cross-sectional area and bio-impedance. The cross-sectional area of the blood vessel varies with the cardiac cycle. The simulation... 40

Figure 22. Configuration changes of the cross-sectional area of blood vessels with respect to the cardiac cycle. The blood vessel can be divided into the internal radius and cross-sectional area. In the vasodilatory phase, the... 40

Figure 23. Relationship between the total thickness of the blood vessel and the reciprocal of impedance. As the total thickness of the blood vessel increases, the impedance decreases, resulting in an increase in the reciprocal of... 41

Figure 24. Blood flow reflecting at a branching point. Blood within the radial artery flows distally but reflects at a branching point and returns. 42

Figure 25. Pulse waveforms generated by blood reflecting at a branching point. The blood reflecting and returning creates a second peak. The PPT can be easily obtained by differentiating the waveform. 43

Figure 26. Long-term maintenance with a single calibration using a reference device. Systolic and diastolic pressure can be obtained from the reference device to determine 𝛼 and PPT. 44

Figure 27. Blood pressure sensing performance results with a PPG sensor and a cuff device (n＝20). (a) the pictures of the hand wearing wrist cuff device, PPG sensor on the fingertip and the proposed sensor on the wrist. The... 46

Figure 28. Optimal frequency distribution. 47

Figure 29. Experimental process diagram. The effectiveness of the algorithm is tested on 20 patients. After one calibration, no further calibration is required. Pre-exercise experiments are conducted to verify the accuracy of... 48

Figure 30. Blood pressure waveforms obtained before and after exercise. Both blood pressure and heart rate (HR) increased. 48

Figure 31. Filtering for blood pressure calibration. Signal filtering is included to match the obtained bio-impedance values with blood pressure values. Figure shows three cycles of the bio-impedance and a representative... 49

Figure 32. Bland-Altman plots for pre-exercise measurements. The accuracy of the proposed sensor during rest is found to be very high. 50

Figure 33. Bland-Altman plots for post-exercise measurements. The black and red data represent measurements with and without the correction technique, respectively. 51

Figure 34. Bland-Altman plot comparing pre-exercise (black) and post-exercise measurements (red) with the correction technique applied. Both systolic and diastolic blood pressure show high correlation and low errors. 52

Figure 35. Blood pressure measurements for long-term without calibration. Blood pressure waveforms at a time and after 24 hours. The estimated systolic and diastolic blood pressures are compared with the reference blood... 54

Figure 36. Experiment results for the robustness of the proposed sensor. (a) the picture of the sensor with water. (b) signal to noise comparison of the sensor with and without moisture. (c), (d) sensed bio-impedance signals at... 55

Figure 37. Safety comparison with the guidelines of the International Commission of IEEE [69] and ICNIRP. 56

Figure 38. The sensed signal using the powers: (a) 250, (b) 100, and (c) 50 μW, respectively. (d) SNR graphs of the sensor for various power consumptions. 56