本研究提出了一高靈敏度的微波介電材料感測系統，針對系統和感測器進行了優化，最終將其整合成一生醫量測系統。本研究提出一種創新的微波生醫感測系統，結合頻率鎖定迴路（Frequency-Locked Loop, FLL）與步階阻抗共振器（Step-Impedance Resonator, SIR）結構，嵌入接地共平面波導（Grounded Coplanar Waveguide, GCPW）中以及使用級聯架構(Cascade)，用於非接觸式手指脈搏偵測。透過Cascade-SIR-GCPW對介電常數變化的高相位靈敏度，能有效偵測手指表面因毛細血管震動產生的微小變化，並轉換為相位偏移訊號。該相位變化經由FLL轉換為頻率調變訊號，再透過正交頻率解調器產出VI與VQ電壓訊號，利用arctangent演算法重建脈波資訊。
設計中採用5.8 GHz操作頻率與低耗損Rogers 4350B基板，並透過SIR結構並結合Cascade架構最佳化特性導納、電阻以提升靈敏度。理論與實測相位靈敏度分別445°與420°，顯示其優於傳統微帶線設計。FLL系統使用VCO、混頻器、低通濾波器與延遲線，維持訊號正交性並提升訊雜比（SNR），理論預估SNR可達70 dB，實驗中實際提升約18.8 dB。最終以BIOPAC系統為比較基準，手指與脈搏量測心跳頻率誤差僅0.3%，顯示本感測器具備高度準確性。
此設計展現微波電路、頻率控制與感測技術的整合應用，為高靈敏、無接觸式生理訊號量測提供具潛力的解決方案。

A novel microwave for measuring the finger pulse in human subjects is developed using a frequency-locked loop (FLL)-based transmission-mode cascade step-impedance resonator in grounded coplanar waveguide (Cascade SIR-GCPW). The principle relies on phase variations in the transmission coefficient at the operating frequency, induced by periodic capillary vibrations, or fingertip skin surface variation [1]. Additionally, by integrating the cascade structure with the GCPW structure, improving the phase variation and sensitivity. Compared to other structures, the sensitivity of this sensor structure is higher than others transmission mode sensor. The phase-shifted signal drives the FLL to produce a frequency-modulated (FM) signal, with frequency deviation corresponded to the periodic capillary vibrations or variation of the skin. A quadrature frequency discriminator converts the FM signal into dc voltages (VI and VQ), and vital signs are extracted using the arctangent of these voltages. The measured peak intervals and frequency responses were in good agreement with the results from the BIOPAC system, achieving an average heart rate error rate of 0.3%. The proposed sensor offers enhanced sensitivity and accuracy, demonstrating significant potential for advanced biomedical sensing applications.

[1] C.-H. Tseng and C.-Z. Wu, "A novel microwave phased-and perturbation-injection-locked sensor with self-oscillating complementary split-ring resonator for finger and wrist pulse detection," IEEE Transactions on Microwave Theory and Techniques, vol. 68, no. 5, pp. 1933-1942, 2020.
[2] C.-H. Tseng, L.-T. Yu, J.-K. Huang, and C.-L. Chang, "A wearable self-injection-locked sensor with active integrated antenna and differentiator-based envelope detector for vital-sign detection from chest wall and wrist," IEEE Transactions on Microwave Theory and Techniques, vol. 66, no. 5, pp. 2511-2521, 2018.
[3] F.-K. Wang, M.-C. Tang, S.-C. Su, and T.-S. Horng, "Wrist pulse rate monitor using self-injection-locked radar technology," Biosensors, vol. 6, no. 4, p. 54, 2016.
[4] K. Nakajima, T. Tamura, and H. Miike, "Monitoring of heart and respiratory rates by photoplethysmography using a digital filtering technique," Medical engineering & physics, vol. 18, no. 5, pp. 365-372, 1996.
[5] C.-H. Tseng and C.-Y. Yang, "Novel microwave frequency-locked-loop-based sensor for complex permittivity measurement of liquid solutions," IEEE Transactions on Microwave Theory and Techniques, vol. 70, no. 10, pp. 4556-4565, 2022.
[6] H. Gheidi and A. Banai, "An ultra-broadband direct demodulator for microwave FM receivers," IEEE transactions on microwave theory and techniques, vol. 59, no. 8, pp. 2131-2139, 2011.
[7] X. Canalias, P. Vélez, P. Casacuberta, L. Su, and F. Martín, "Transmission-mode phase-variation planar microwave sensor based on a step-impedance shunt stub for high sensitivity defect detection, dielectric constant, and proximity measurements," IEEE Transactions on Microwave Theory and Techniques, 2024.
[8] P. Casacuberta, P. Vélez, J. Muñoz-Enano, L. Su, and F. Martín, "Highly sensitive coplanar waveguide (CPW) reflective-mode phase-variation permittivity sensors based on weakly coupled step-impedance resonators (SIRs)," IEEE Transactions on Microwave Theory and Techniques, vol. 72, no. 3, pp. 1739-1753, 2023.
[9] L. Su, J. Munoz-Enano, P. Velez, P. C. Orta, M. Gil, and F. Martin, "Highly sensitive phase variation sensors based on step-impedance coplanar waveguide (CPW) transmission lines," IEEE Sensors Journal, vol. 21, no. 3, pp. 2864-2872, 2020.
[10] X. Canalias, P. Vélez, P. Casacuberta, L. Su, and F. Martín, "A Method to Boost the Sensitivity in Transmission-Mode Phase-Variation Planar Microwave Sensors," in 2024 IEEE SENSORS, 2024: IEEE, pp. 1-4.
[11] O. Siddiqui, R. Ramzan, M. Amin, and O. M. Ramahi, "A non-invasive phase sensor for permittivity and moisture estimation based on anomalous dispersion," Scientific reports, vol. 6, no. 1, p. 28626, 2016.
[12] K.-C. Peng, M.-C. Sung, F.-K. Wang, and T.-S. Horng, "A wireless-frequency-locked-loop-based vital sign sensor with quadrature tracking and phase-noise reduction capability," IEEE Sensors Journal, vol. 21, no. 8, pp. 9706-9715, 2020.
[13] X. Canalias, P. Casacuberta, P. Vélez, L. Su, and F. Martín, "Highly sensitive transmission-mode phase-variation permittivity sensor based on resonance and antiresonance," IEEE Transactions on Microwave Theory and Techniques, 2024.
[14] N. Kurniawati, P. Vélez, P. Casacuberta, L. Su, X. Canalias, and F. Martín, "Highly sensitive phase-variation microwave sensor operating in transmission based on an open split ring resonator (OSRR)," IEEE Sensors Journal, 2024.
[15] H. M. Stauss, "Heart rate variability," American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, vol. 285, no. 5, pp. R927-R931, 2003.
[16] P. Hung, S. Bonnet, R. Guillemaud, E. Castelli, and P. T. N. Yen, "Estimation of respiratory waveform using an accelerometer," in 2008 5th IEEE International symposium on biomedical imaging: from nano to macro, 2008: IEEE, pp. 1493-1496.
[17] F.-K. Wang et al., "Review of self-injection-locked radar systems for noncontact detection of vital signs," IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology, vol. 4, no. 4, pp. 294-307, 2020.
[18] D. Andreuccetti, "An Internet resource for the calculation of the dielectric properties of body tissues in the frequency range 10 Hz-100 GHz," http://niremf. ifac. cnr. it/tissprop/, 2012.
[19] M. S. Boybay and O. M. Ramahi, "Material characterization using complementary split-ring resonators," IEEE Transactions on instrumentation and Measurement, vol. 61, no. 11, pp. 3039-3046, 2012.
[20] H.-C. Chang, C.-T. M. Wu, and C.-H. Tseng, "A 24 GHz frequency-locked loop-based microwave microfluidic sensor for concentration detection," IEEE Journal of Selected Areas in Sensors, 2024.
[21] K.-C. Peng, M.-C. Sung, F.-K. Wang, and T.-S. Horng, "Noncontact vital sign sensing under nonperiodic body movement using a novel frequency-locked-loop radar," IEEE Transactions on Microwave Theory and Techniques, vol. 69, no. 11, pp. 4762-4773, 2021.
[22] W.-J. Wu and W.-S. Zhao, "A microwave sensor based on frequency-locked loop and multiple complementary split-ring resonators for retrieving complex permittivity of liquid samples," IEEE Sensors Journal, vol. 23, no. 24, pp. 30345-30359, 2023.
[23] L. Su, J. Muñoz-Enano, P. Vélez, M. Gil-Barba, P. Casacuberta, and F. Martin, "Highly sensitive reflective-mode phase-variation permittivity sensor based on a coplanar waveguide terminated with an open complementary split ring resonator (OCSRR)," IEEE Access, vol. 9, pp. 27928-27944, 2021.
[24] B.-H. Kim et al., "A proximity coupling RF sensor for wrist pulse detection based on injection-locked PLL," IEEE Transactions on Microwave Theory and Techniques, vol. 64, no. 5, pp. 1667-1676, 2016.
[25] T.-K. Nguyen and C.-H. Tseng, "A new microwave humidity sensor with near-field self-injection-locked technology," IEEE Sensors Journal, vol. 21, no. 19, pp. 21520-21528, 2021.
[26] C.-H. Tseng, C.-H. Pai, and H.-C. Chang, "A new microwave oscillator-based microfluidic dielectric sensor," IEEE Transactions on Microwave Theory and Techniques, vol. 72, no. 1, pp. 628-637, 2023.
[27] F.-K. Wang et al., "A novel vital-sign sensor based on a self-injection-locked oscillator," IEEE Transactions on Microwave Theory and Techniques, vol. 58, no. 12, pp. 4112-4120, 2010.
[28] W.-J. Wu and W.-S. Zhao, "A microwave sensor system based on oscillating technique for characterizing complex permittivity of liquid samples," IEEE Sensors Journal, vol. 23, no. 21, pp. 25958-25970, 2023.
[29] W.-J. Wu, W.-S. Zhao, and W. Wang, "A novel differential microwave sensor based on reflective-mode phase variation of stepped-impedance transmission lines for extracting permittivity of dielectric materials," IEEE Sensors Journal, vol. 24, no. 3, pp. 2746-2757, 2023.
[30] D. M. Pozar, "Microstrip line," Microwave Engineering, pp. 147-153, 2012.
[31] J. Munoz-Enano, P. Velez, M. G. Barba, and F. Martín, "An analytical method to implement high-sensitivity transmission line differential sensors for dielectric constant measurements," IEEE Sensors Journal, vol. 20, no. 1, pp. 178-184, 2019.
[32] A. Ebrahimi et al., "Highly sensitive phase-variation dielectric constant sensor based on a capacitively-loaded slow-wave transmission line," IEEE Transactions on Circuits and Systems I: Regular Papers, vol. 68, no. 7, pp. 2787-2799, 2021.
[33] J. Muñoz-Enano, P. Vélez, L. Su, M. Gil, P. Casacuberta, and F. Martín, "On the sensitivity of reflective-mode phase-variation sensors based on open-ended stepped-impedance transmission lines: Theoretical analysis and experimental validation," IEEE Transactions on Microwave Theory and Techniques, vol. 69, no. 1, pp. 308-324, 2020.
[34] M. Saadat-Safa, V. Nayyeri, M. Khanjarian, M. Soleimani, and O. M. Ramahi, "A CSRR-based sensor for full characterization of magneto-dielectric materials," IEEE Transactions on Microwave Theory and Techniques, vol. 67, no. 2, pp. 806-814, 2019.
[35] C.-L. Yang, C.-S. Lee, K.-W. Chen, and K.-Z. Chen, "Noncontact measurement of complex permittivity and thickness by using planar resonators," IEEE Transactions on Microwave Theory and Techniques, vol. 64, no. 1, pp. 247-257, 2015.
[36] P.-K. Chan, C.-C. Chen, and C.-L. Yang, "Systolic and diastolic blood pressure estimation from pulse transit time using dual split-ring resonators with notch structure," in 2019 IEEE MTT-S International Microwave Symposium (IMS), 2019: IEEE, pp. 361-364.
[37] C.-T. Chang, C.-L. Yang, U. Dey, and J. Hesselbarth, "Measuring Vital Signs on Fingertip Using K-Band Spherical Dielectric Resonator," in 2020 50th European Microwave Conference (EuMC), 2021: IEEE, pp. 933-936.
[38] P. Casacuberta, P. Vélez, L. Su, X. Canalias, and F. Martín, "Sensitive microfluidic sensor with weakly coupled dumbbell defect-ground-structure resonators for volume fraction determination in liquid mixtures," IEEE Microwave and Wireless Technology Letters, 2024.
[39] A. Karami-Horestani et al., "Reflective-mode phase-variation sensors based on a movable step impedance resonator (SIR) and application to micrometer-scale motion sensing," IEEE Transactions on Microwave Theory and Techniques, 2024.
[40] P. Casacuberta, P. Vélez, J. Muñoz-Enano, L. Su, and F. Martín, "Highly sensitive reflective-mode phase-variation permittivity sensors using coupled line sections," IEEE Transactions on Microwave Theory and Techniques, vol. 71, no. 7, pp. 2970-2984, 2023.
[41] J. Muñoz-Enano et al., "Planar phase-variation microwave sensors for material characterization: A review and comparison of various approaches," Sensors, vol. 21, no. 4, p. 1542, 2021.
[42] X. Canalias, P. Vélez, P. Casacuberta, L. Su, N. Kurniawati, and F. Martín, "Transmission-Mode Phase-Variation Microwave Sensor Applied to Highly Sensitive Micrometer-Scale Thickness Measurements," IEEE Sensors Journal, 2025.