Ting-Wei Wang

Body sensor network (BSN) is rapidly evolving in mobile health (m-health), enabling the monitoring of multiple physiological sites through interconnected wireless wearable devices for efficient health management. However, the extensive use of devices on the body often requires substantial batteries and IC chips, increasing system complexity, weight, and cost, thus limiting practical applications. We present a battery-free, chipless physiological sensor employing an on-body passive LC repeater to enhance magnetic coupling between a sensor reader and the biomedical target. The passive LC repeater, encapsulated in flexible thermoplastic polyurethane (TPU), integrates seamlessly with skin or clothing to capture contact and noncontact physiological signals, including heart, lung, carotid, radial, and even femoral signals using an external coil connected to a compact 2.1×2.3 cm, lightweight 7.8 g sensor reader, simplifying signal acquisition, and reducing the complexity of readout techniques compared to cumbersome vector network analyzers (VNAs). To demonstrate its robust performance, the skin-attached passive LC repeater was sprayed with water and fully immersed, yet the sensor reader, positioned 2 cm away, continued to successfully capture physiological signals. In conclusion, this study presents a battery-free, chipless BSN solution utilizing on-body passive LC circuitry characterized by a simple structure, lightweight design, and low cost, ideal for disposable skin electronics and smart clothing, offering superior wearable, unobtrusive, and long-term health monitoring solutions.

Smartwatches commonly employ photoplethysmography (PPG) sensors for pulse measurement and health index computation, including heart rate (HR), blood pressure (BP), etc. However, PPG’s susceptibility to skin tone variations presents challenges to accuracy. This study presents a biomedical eddy current sensor (BECS)-based wristwatch that integrates a passive LC tank, inductance-to-digital converter ASIC, and wireless module fully embedded into the case back of the wristwatch. The BECS technology relies on magnetic coupling between the magnetic fields generated by the LC coil and the counteracting magnetic fields induced by wrist artery, enabling the measurement of resonant frequency variations in response to arterial pulse signals. To enhance pulse measurement sensitivity, the optimal operating resonant frequency was determined by implementing a capacitor array and measuring pulse signals by human measurement to derive personalized design parameters. The proposed BECS-based wristwatch demonstrates pulse signal measurement insensitivity to skin tone compared to PPG-based modalities, as validated among subjects with different Fitzpatrick skin types. Importantly, the personalized BP algorithm was implemented based on HR and modified normalized pulse volume (mNPV), both derived from the measured pulse signals. The BP performance demonstrates low mean absolute errors (MAE) of 3.18 ± 2.61 mmHg for systolic BP (SBP) and 3.64 ± 2.57 mmHg for diastolic BP (DBP) among ten subjects, meeting the Association for the Advancement of Medical Instrumentation (AAMI) standard below 5 ± 8 mmHg. The generalization of each personalized BP model was further verified through train-test split validation, with all results remaining within AAMI criteria. In conclusion, this study introduces a novel BECS-based wristwatch, highlighting its skin-tone friendliness and accurate BP monitoring, offering a promising alternative to optical modalities, thereby driving future smartwatch innovations.

Continuous cuffless blood pressure (BP) sensors are evolving for long-term cardiovascular monitoring, especially in diagnostic and prognostic stages. The existing techniques rely on photoplethysmography (PPG) and bio-impedance that have limitations, such as sensitivity to skin tone and high skin-electrode contact impedance that would degrade physiological signals measurement. To this end, this study presents a novel wearable coil-based ring-type sensor utilizing the novel biomedical eddy current technique for continuous BP measurement. The LC-based ring sensor generates the AC magnetic fields along with the finger in parallel with the digital arteries, detecting the resonant frequency variations in response to real-time vessel pulsations. The proposed ring-type sensor is characterized by its compact form with a diameter of 2.42 cm and supporting wireless data transmission. To optimize personalized sensing, the various resonant frequencies on vessel pulse measurements were investigated by human trials. The novel ring sensor is employed for the estimation of BP, demonstrating high Pearson’s correlations (systolic BP (SBP): 0.88, diastolic BP (DBP): 0.80) and low mean absolute error (MAE) within 10 subjects (SBP: 3.64 ± 2.71 mmHg, DBP: 3.20 ± 2.66 mmHg), revealing the significant potential use of biomedical eddy current-based ring sensor for continuous, accurate, and comprehensive cardiovascular monitoring.

Continuous monitoring of heart rate (HR) and respiratory rate (RR) plays a pivotal role in evaluating cardiopulmonary coordination. Wearable technologies have empowered long-term monitoring of cardiopulmonary parameters across a spectrum of activities, including physical exercise, mental states, dietary habits, and the effects of pharmaceutical interventions. This study presents a wearable pocket-sized cardiopulmonary sensor based on biomedical eddy current sensing technology. The novel sensor utilizes the magnetic coupling between ac coil-produced magnetic fields and cardiopulmonary eddy current-induced counteracting magnetic fields to measure resonant frequency variation in response to synchronized cardiac and lung activities without skin contact. The proposed pocket-sized sensor is characterized by its compact form with a diameter of 4.53 cm and supporting wireless data transmission. Importantly, the influence of resonant frequencies on cardiopulmonary signals was investigated through capacitor adjustments, resulting in personalized optimization of measurement conditions. In practical applications, the effect of wide fabric thicknesses on measurement performance was assessed, demonstrating identifiable signals for allowing the determination of HR and RR. In real-life scenarios, HR and RR were measured during both resting and physical exercise conditions, effectively showcasing the potential of a single compact sensor to capture essential cardiorespiratory coordination (CRC) indicators. These findings provide strong validation for the novel sensor’s promising potential in the realm of wearable, long-term, all-in-one cardiopulmonary healthcare.