Pinghung Wei

Epidermal electronics with advanced capabilities in near-field communication

Epidermal electronics with advanced capabilities in near field communications (NFC) are presented. The systems include stretchable coils and thinned NFC chips on thin, low modulus stretchable adhesives, to allow seamless, conformal contact with the skin and simultaneous capabilities for wireless interfaces to any standard, NFC-enabled smartphone, even under extreme deformation and after/during normal daily activities.

A stretchable and flexible system for skin-mounted measurement of motion tracking and physiological signals

In this paper, we present a stretchable wearable system capable of i) measuring multiple physiological parameters and ii) transmitting data via radio frequency to a smart phone. The electrical architecture consists of ultra thin sensors (<; 20 μm thick) and a conformal network of associated active and passive electronics in a mesh-like geometry that can mechanically couple with the curvilinear surfaces of the human body. Spring-like metal interconnects between individual chips on board the device allow the system to accommodate strains approaching ~30% A representative example of a smart patch that measures movement and electromyography (EMG) signals highlights the utility of this new class of medical skin-mounted system in monitoring a broad range of neuromuscular and cardiovascular diseases.

Epidermal electronics: Skin sweat patch

An ultrathin, stretchable, and conformal sensor system for skin-mounted sweat measurement is characterized and demonstrated in this paper. As an epidermal device, the sweat sensor is mechanically designed for comfortable wear on the skin by employing interdigitated electrodes connected via stretchable serpentine-shaped conductors. Experimental results show that the sensor is sensitive to measuring frequency, sweat level and stretching deformation. It was found that 20kHz signals provide the most sensitive performance: electrical impedance changes 50% while sweat level increases from 20 to 80. In addition, sensor elongation from 15 up to 50% affected the measurement sensitivity of both electrical impedance and capacitance.

A conformal sensor for wireless sweat level monitoring

A conformal, wearable and wireless system for continuously monitoring the local body sweat loss during exercise is demonstrated in this work. The sensor system includes a sweat absorber, an inter-digitated capacitance sensor, and a communication hub for data processing and transmission. Experimental results show that the sensor has excellent sensitivity and consistent response to sweat rate and level. A 150% variation in the sensor capacitance is observed with 50μL/cm2 of sweat collected in the absorber. During wear tests, the sensor system is placed on the subjects right anterior thigh for measuring the local sweat response during exercise (eg. running), and the measured sweat loss (147μL) was verified by the weight change within the absorbent material (144mg). With a conformal and wireless design, this system is ideal for applications in sport performance, dehydration monitoring, and health assessment.

Archipelago platform for skin-mounted wearable and stretchable electronics

In this investigation, the “archipelago” design is presented as a platform for skin-mounted wearable and stretchable electronics. The electronic components of the design were distributed between islands connected by stretchable serpentine structures. The analytical results show that at 20% overall elongation, the serpentines stretch 60% due to the rigidity of the islands. This 20% elongation is defined as the system stretchability. The 60% elongation on the serpentines is defined as the effective stretchability. At 60% effective stretch, the calculated equivalent plastic strain in a serpentine interconnect is 0.67%, which is well below the fracture limit of copper. Elongation experiments show that the archipelago structure has the system stretchability up to 76% for one-time-stretching, translating to 228% of the effective stretchability on the serpentines. Fatigue-tension experiments show that at 20% system stretch, the archipelago structure can withstand on average 71,950 cycles without electrical or mechanical degradation.

Bio-integrated systems with stretchable designs for skin-mounted wearable health monitoring

We present ultrathin, flexible and stretchable epidermal health monitoring devices that contain physiological sensors, an analog front end processor, a core microprocessor, flash memory module, rechargeable battery, and a wireless communication (Bluetooth low energy) module. The system is mechanically matched to the Youngs modulus of human skin and designed to record heart rate, electromyography signals, activity, respiration and sleep quality to facilitate continuous (electro-)physiological data recording outside of the hospital setting.

Soft bio-integrated systems for continuous health monitoring

Electronically-enabled wearable systems that monitor physiological activity and electrophysiological activity hold the key to truly personalized medical care outside of the hospital setting. However, fundamental technical challenges exist in achieving medical systems that are comfortable, unobtrusive and fully integrated without external connections to bench top instruments. In particular, there is a fundamental mismatch in mechanical coupling between existing classes of rigid electronics and soft biological substrates, like the skin. Here we describe new mechanical and electrical design strategies for wearable devices with mechanical properties that approach that of biological tissue. These systems exploit stretchable networks of conformal sensors (i.e. electrodes, temperature sensors, and accelerometers) and associated circuitry (i.e. microcontroller, memory, voltage regulators, rechargeable battery, wireless communication modules) embedded in ultrathin, elastomeric substrates. Quantitative analyses of sensor performance and mechanics under tensile and torsional stresses illustrate the ability to mechanically couple with soft tissues in a way that is mechanically invisible to the user. Representative examples of these soft biointegrated systems can be applied for continuous sensing of muscle and movement activity in the home and ambulatory settings.