Seungki Hong

Wearable fall detector using integrated sensors and energy devices

Wearable devices have attracted great attentions as next-generation electronic devices. For the comfortable, portable, and easy-to-use system platform in wearable electronics, a key requirement is to replace conventional bulky and rigid energy devices into thin and deformable ones accompanying the capability of long-term energy supply. Here, we demonstrate a wearable fall detection system composed of a wristband-type deformable triboelectric generator and lithium ion battery in conjunction with integrated sensors, controllers, and wireless units. A stretchable conductive nylon is used as electrodes of the triboelectric generator and the interconnection between battery cells. Ethoxylated polyethylenimine, coated on the surface of the conductive nylon electrode, tunes the work function of a triboelectric generator and maximizes its performance. The electrical energy harvested from the triboelectric generator through human body motions continuously recharges the stretchable battery and prolongs hours of its use. The integrated energy supply system runs the 3-axis accelerometer and related electronics that record human body motions and send the data wirelessly. Upon the unexpected fall occurring, a custom-made software discriminates the fall signal and an emergency alert is immediately sent to an external mobile device. This wearable fall detection system would provide new opportunities in the mobile electronics and wearable healthcare.

Optimal Design of a Novel Permanent Magnetic Actuator using Evolutionary Strategy Algorithm and Kriging Meta-model

The novel permanent magnetic actuator (PMA) and its optimal design method were proposed in this paper. The proposed PMA is referred to as the separated permanent magnetic actuator (SPMA) and significantly superior in terms of its cost and performance level over a conventional PMA. The proposed optimal design method uses the evolutionary strategy algorithm (ESA), the kriging meta-model (KMM), and the multi-step optimization. The KMM can compensate the slow convergence of the ESA. The proposed multi-step optimization process, which separates the independent variables, can decrease time and increase the reliability for the optimal design result. Briefly, the optimization time and the poor reliability of the optimum are mitigated by the proposed optimization method.

Ultra-high responsivity, silicon nanowire photodetectors for retinal prosthesis

In this paper, a novel silicon nanowire photodetector on a flexible substrate is presented for replacing the function of photoreceptors in the retina to restore vision for the blind. An extremely high surface-to-volume-ratio characteristic of nanowire is capable of developing highly-sensitive photonic sensors. Therefore, a nanowire photodetector can be used as a stand-alone visual perception device without an external camera. The nanowire photodetector is first fabricated on a rigid substrate, and then transferred to a flexible substrate to fit the curvature of an eyeball. Experimental results using the fabricated silicon nanowire photodetector show very high photosensitivity and photoresponsivity for a wide range of light intensities and wavelengths. Mechanical bending tests are performed, and the results show that the optical performance of the flexible photodetector is well-preserved after repeated bending of 200 times. The presented performance evaluation results indicate the first viable alternative to using a camera for image acquisition.

Design of electromagnetic force driving actuator for Automatic Transfer Breaker based on three-link structure

In the circuit breaker, the actuator which generates the driving force, mainly effects on the successful operation. The existing Automatic Transfer Breaker (ATB) had applied motor spring actuator, but it had technical and economic limitations, such as need for continuous components exchanges and maintenance costs. In this paper, the spring actuator is replaced with Electromagnetic Force driving Actuator (EMFA), to overcome limits. Linkage system following EMFA is designed as three-link structure to gain the benefits in operational and designing respect. In order to obtain the dynamic characteristics of the EMFA, transient analysis is performed by combining the finite element method (FEM) and the time difference method (TDM). By comparing experimental data with simulated data, it is confirmed that the analysis of dynamic characteristics is appropriate.