Hakjun Lee

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Supercapacitor is an electrical energy storage device which offers remarkably high energy density when compared to conventional capacitors and high power density when compared to batteries. While using the supercapacitors for energy storage, the main disadvantage is their limited voltage due to contemporary technology restrictions. Therefore, for higher(More)
The number of mobile commerce users is rapidly increasing because mobile commerce provides us with usability that can be able to pay for goods or services anytime, anywhere using mobile devices. To provide the secure mobile commerce, a number of security protocols have been proposed. Recently, An unlinkable anonymous payment scheme (UAPS) based on near(More)
In this paper, we propose a new in-plane XYθz nano-positioning stage that utilizes piezoelectric actuators and flexure mechanisms. The proposed stage has an aperture and is compact, which facilitates its application in measurement equipment, especially those used for biological specimens. The stage has four piezoelectric actuators and four bridge-type(More)
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