Won Keun Kim

Fabrication of Graphene Embedded LiFePO4 Using a Catalyst Assisted Self Assembly Method as a Cathode Material for High Power Lithium-Ion Batteries

We have designed a unique microstructure of graphene embedded LiFePO4 by a catalyst assisted self assembly method as a cathode material for high power lithium-ion batteries. The stable amide bonds between LiFePO4 and graphene were formed by the catalyst assisted self assembly. High conductive graphene provides a fast electron transfer path, and many pores inside the structure facilitate the lithium-ion diffusion. The graphene embedded LiFePO4 fabricated by the novel method shows enhanced cycling performance and rate-capability compared with that of carbon coated LiFePO4 as a cathode material for high power lithium-ion batteries.

Signal-to-noise ratio and bandwidth for pseudo-random codes in an ultrasonic imaging system

Signal-to-noise ratio and image resolution in an ultrasonic imaging system are compared for four kinds of excitation signals, namely, a single pulse, an unmodulated pseudo-random code, a modulated pseudo-random code and a deconvolved pseudo-random code, all for a given length and amplitude. It was predicted and found from measurements that the best S/N and resolution are obtainable with the deconvolved pseudo-random code.

Fabric Active Transducer Stimulated by Water Motion for Self-Powered Wearable Device

The recent trend of energy-harvesting devices is an adoption of fabric materials with flexible and stretchable according to the increase of wearable electronics. But it is a difficult process to form a core structure of dielectric layer or electrode on fabric materials. In particular, a fabric-based energy-harvesting device in contact with water has not been studied, though there are many challenging issues including insulation and water absorption in a harsh environment. So we propose an effective method to obtain an electrical energy from the water contact using our new fabric energy harvesting device. Our water motion active transducer (WMAT) is designed to obtain electrical energy from the variable capacitance through the movement and contact of water droplet. In this paper, we succeeded in generating an electrical energy with peak to peak power of 280 μW using a 30 μL of water droplet with the fabric WMAT device of 70 mm × 50 mm dimension. Furthermore, we specially carried out spray-coating and transfer processes instead of the conventional spin-coating process on fabric materials to overcome the limitation of its uneven morphology and porous and deformable assembly.