Wearable
electronic medical devices measuring continuous biological
signals for early disease diagnosis should be small and lightweight
for consecutive usability. As a result, there has been an increasing
need for new energy supply systems that provide continuous power without
any interruption to the operation of the medical devices associated
with the use of conventional batteries. In this work, we developed
a patch-type self-charging supercapacitor that can measure biological
signals with a continuous energy supply without batteries. The glucose
oxidase coated on the surface of the microneedle-type glucose sensor
encounters glucose in the interstitial fluids of the human body. Electrons
created by glucose oxidation operate the self-powered system in which
charging begins with the generation of potential differences in supercapacitor
electrodes. In an 11 mM glucose solution, the self-powered solid-state
supercapacitors (SPSCs) showed a power density of 0.62 mW/cm2, which resulted in self-charging of the supercapacitor. The power
density produced by each SPSC with a drop of 11 mM glucose solution
was higher than that produced by glucose-based biofuel cells. Consequently,
the all-in-one self-powered glucose sensor, with the aid of an Arduino
Uno board and appropriate programming, effectively distinguished normal,
prediabetic, and diabetic levels from 0.5 mL of solutions absorbed
in a laboratory skin model.
We present a low temperature and solution-based fabrication process for reduced graphene oxide (rGO) electrodes for electric double layer capacitors (EDLCs).
With the evolution of semiconducting industries, thermomechanical
failure induced in a multilayered structure with a high aspect ratio
during manufacturing and operation has become one of the critical
reliability issues. In this work, the effect of thermomechanical stress
on the failure of multilayered thin films on Si substrates was studied
using analytical calculations and various thermomechanical tests.
The residual stress induced during material processing was calculated
based on plate bending theory. The calculations enabled the prediction
of the weakest region of failure in the thin films. To verify our
prediction, additional thermomechanical stress was applied to induce
cracking and interfacial delamination by various tests. We assumed
that, when accumulated thermomechanical-residual and externally applied
mechanical stress becomes larger than a critical value the thin-film
cracking or interfacial delamination will occur. The test results
agreed well with the prediction based on the analytical calculation
in that the film with maximum tensile residual stress is the most
vulnerable to failure. These results will provide useful analytical
and experimental prediction tools for the failure of multilayered
thin films in the device design stage.
For multifunctional wearable sensing systems, problems related to wireless and continuous communication and soft, noninvasive, and disposable functionality issues should be solved for precise physiological signal detection. To measure the critical transitions of pressure, temperature, and skin impedance when continuous pressure is applied on skin and tissue, we developed a sensor for decubitus ulcers using conventional analog circuitry for wireless and continuous communication in a disposable, breathable fabric-based multifunctional sensing system capable of conformal contact. By integrating the designed wireless communication module into a multifunctional sensor, we obtained sensing data that were sent sequentially and continuously to a customized mobile phone app. With a small-sized and lightweight module, our sensing system operated over 24 h with a coin-cell battery consuming minimum energy for intermittent sensing and transmission. We conducted a pilot test on healthy subjects to evaluate the adequate wireless operation of the multifunctional sensing system when applied to the body. By solving the aforementioned practical problems, including those related to wireless and continuous communication and soft, noninvasive, and disposable functionality issues, our fabric-based multifunctional decubitus ulcer sensor successfully measured applied pressure, skin temperature, and electrical skin impedance.
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