Ting-Wei Wang

Smart clothing has emerged as a promising Internet of Things (IoT)-based healthcare platform by enabling distributed physiological sensing through body sensor networks (BSNs). However, most systems rely on embedded chips and batteries, increasing complexity, weight, and cost that limit practicality. We present a battery-free chipless smart clothing that integrates thermoplastic polyurethane (TPU)-encapsulated passive LC relay networks to establish magnetic coupling between an external sensor reader and underlying arteries. Arterial pulsations induce resonant frequency shifts in the coupled system, enabling real-time pulse signal detection. Each sensing coil of passive LC relay networks is positioned at the carotid, heart, radial, and femoral arteries, and four pickup coils are routed to a centralized hub on the upper left arm. A lightweight wireless reader with four channels simultaneously acquires multisite physiological signals. Importantly, passive LC relay networks serve as magnetic field repeaters, enhancing magnetic coupling across extended distances. By matching resonant frequencies of passive LC relay networks and sensor reader at 7.3 MHz, the system achieved a power transfer efficiency (PTE) of 46.56%, clearly outperforming the capacitor-free configuration, which yielded only 6%. Notably, a minimum PTE threshold of 0.24% was established for distinguishable pulse detection. The system showed robustness after water-spray exposure and supported signal acquisition through outer garments up to 21.22 mm thick between the sensor reader and centralized hub, confirming resilience to sweat and compatibility with layered clothing. Overall, our battery-free chipless BSN offers lightweight, low-cost, and disposable smart clothing solutions for simultaneous multisite hemodynamic monitoring, potentially calculating pulse wave velocity for peripheral vascular stiffness assessment.

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.

Recent advancements in flexible patches offer stretchability and adaptability to body contours. However, most of them require skin contact, causing potential discomfort for long-term health monitoring. We present a noncontact electromagnetic induction-based patch sensor that integrates a passive inductance-capacitance (LC) tank, inductance-to-digital converter application-specific integrated circuit (ASIC), and wireless module into a flexible substrate, characterizing compact of 9× 5 cm and lightweight of 6 g. The proposed patch sensor employs biomedical eddy current sensing to establish magnetic coupling between the sensor coil's magnetic field and the counteracting magnetic fields generated by the biomedical target's eddy currents. This enables the measurement of resonance frequency variations in response to pulsatile signals across multiple physiological sites, including the heart, lungs, carotid, radial, and femoral arteries, without direct skin contact. The sensor demonstrates high applicability across various fabric materials and thicknesses, effectively detecting heart rate (HR) through fabric layers up to 5.35 mm thick when positioned at the chest. The accuracy of HR and respiratory rate (RR) measurements across all tested physiological sites achieved mean absolute errors (MAEs) within ±5 beats per minute (bpm) and ±3 respirations per minute (rpm), respectively. Furthermore, the sensor can effectively respond to real-time physiological state changes, as demonstrated by cold pressor test (CPT)-induced HR variations and different breathing modes, highlighting its practicality in real-life scenarios. In conclusion, the proposed patch sensor provides an all-in-one flexible, noncontact solution capable of multisite physiological monitoring, offering high accuracy, comfort, and adaptability for wearable health monitoring.

Noncontact electrocardiogram (ECG) sensors have been widely explored as unobtrusive, long-term solutions for detecting atrial fibrillation (AF). Recent clinical studies have demonstrated that abnormal activation of the autonomic nervous system plays a crucial role in the pathogenesis of AF, highlighting the importance of coordination between autonomic activity and cardiac electrophysiology, which shifts most standalone ECG-based AF detection toward AF prediction. In this study, we present a flexible electronic sensor with a bandwidth of 0.05-1000 Hz, utilizing capacitive coupling to enable noncontact simultaneous measurement of capacitive SKNA (cSKNA) and capacitive ECG (cECG) signals. The flexible design ensures effective signal capture by conforming to body curvature, enhancing capacitive coupling. Human measurements involving cold pressor tests (CPTs) were conducted to validate the cSKNA and cECG functionality and applicability of the proposed sensor under various fabric conditions, including different humidity levels, thicknesses, and materials. Moreover, human trials demonstrated the sensor's capability to simultaneously capture cSKNA and cECG signals, effectively revealing neuro-cardiac interactions in real-time. Notably, during CPT-induced sympathetic nerve activation interventions, increases in measured cSKNA that exceeded the sympathetic burst threshold were associated with heart rate (HR) acceleration derived from the measured cECG signals, effectively demonstrating the sensor's capability in capturing neuro-cardiac responses. In conclusion, the proposed sensor offers a noncontact unobtrusive sensing solution for monitoring neuro-cardiac interactions, providing new insights for establishing predictive AF models through a more convenient and comfortable sensing system without electrode preparation. Its ease of use and versatility make the sensor suitable for potential applications in wearable chest bands and smart beds in the future.

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.

Repetitive transcranial magnetic stimulation (rTMS) system is an important therapeutic tool used in non-invasive brain stimulation. The electric field induced by the time-varying magnetic field in a stimulating coil could activate nerve fibers in the brain, resulting in depolarization or hyperpolarization of the neurons. However, the potential adverse effects of rTMS on heart rhythm have not been extensively investigated. This study aims to develop an optimized design of rTMS system to evaluate the potential adverse effects of rTMS on mouse heart rhythm via vagus nerve modulation for pre-clinical application. The rTMS-induced electric field in the vagus nerve of brain produced by the strong rate of current change of 1.04 × 108 A/s in a stimulating coil, which was directly determined by circuit design in charging voltage of the capacitor bank and inductance value of a stimulating coil. A finite element method (FEM) mathematical simulation indicated that the maximum eddy current was 25.4 μA/mm2, which was greatly exceeded the vagus nerve activation threshold of 5.6 μA/mm2. The animal experiment results also verify that the induced electric field activates the RR-interval prolonging effect might be attributed to vagus nerve stimulation (VNS) from rTMS, and the most pronounced heart rhythm prolonging effect at 20 Hz magnetic field treatment, causing the average heart rate decreased to 58.65% of that before rTMS in 10 mice. In conclusion, above-threshold rTMS at 20 Hz could produce maximum adverse effect on heart rhythm through direct vagus nerve activation for pre-clinical applications such as safety screening.