김정훈 교수

Antennas implanted in a human body are largely applicable to hyperthermia and biotelemetry. To make practical use of antennas inside a human body, resonance characteristics of the implanted antennas and their radiation signature outside the body must be evaluated through numerical analysis and measurement setup. Most importantly, the antenna must be designed with an in-depth consideration given to its surrounding environment. In this paper, the spherical dyadic Green's function (DGF) expansions

This paper provides a state-of-the-art report on the up-to-date research on the emerging 3D concrete printing technology from the concrete materials perspective. It reviews the recent research focused on understanding and characterizing the rheological necessities of the concrete printing process and discusses how the researchers are tailoring compatible mix proportions for the 3D concrete printing process by using eco-friendly binders, waste aggregates, chemical admixtures, and nano-additives.

Since conventional above-knee prostheses are passive type devices with constant mechanical properties, the knee joint motions are not similar to that of normal persons. On the other hand, active type prostheses can improve the swing phase gait but these are expensive, heavy and consume large energy. Thus we propose a semi-active prosthesis using the rotary magnetorheological (MR) damper. The torque dissipation in the knee joint can be controlled by the magnetic field induced by the solenoid. A 3

This study presents the development of a modular knee exoskeleton system that supports the knee joints of hemiplegic patients. The device is designed to realize the polycentric motion of real human knees using a four-bar linkage and to minimize its total weight. In order to determine the user's intention, force-sensitive resistors (FSRs) in the user's insole, a torque sensor on the robot knee joint, and an encoder in the motor are used. The control algorithm is based on a finite state machine (F

This work presents three online controllers for maintaining dynamic stability of a humanoid robot using force/torque sensor. Those are damping controller, landing orientation controller and landing position controller. The legs of a humanoid robot are relatively long and serially connected with compliant force/torque sensor at the ankle. This architecture has the inherent characteristics of a lightly damped system. Most research on balance control overlook the deterministic vibration caused by s

Recent advances in mobility, manipulation, and intelligence of robots have promoted the usability of humanoid robots to support humans in their daily lives in the future. The multi-axis force-torque sensor is an essential sensor for the biped humanoid robot to maintain balance during walking and running since it is used to calculate the zero-moment point, the criterion of dynamic stability. Forcetorque sensors will be widely used in the future because they are essential for service robots to int

Abstract This paper presents three online controllers for maintaining dynamic stability of a humanoid robot and describes simplified walking patterns for easy tuning in real experiments. The legs of a humanoid robot are relatively long and serially connected with compliant force/torque sensor at the ankle. This architecture has the inherent characteristics of a lightly damped system. Most research on balance control overlook the deterministic vibration caused by structural compliance. In additio

We investigate the time-frequency characteristics of high-order harmonics generated in atomic gases by intense femtosecond laser pulses, using the Wigner distribution function. The dynamically induced chirp of high harmonics is calculated both quantum mechanically and semiclassically, and a good agreement between them is reached as long as the tunneling effect is properly taken into account. Using the time-frequency analysis, we demonstrate that the large harmonic blueshift observed experimental

We investigate the self-phase modulation of intense femtosecond laser pulses propagating in an ionizing gas and its effects on collective properties of high-order harmonics generated in the medium. Plasmas produced in the medium are shown to induce a positive frequency chirp on the leading edge of the propagating laser pulse, which subsequently drives high harmonics to become positively chirped. In certain parameter regimes, the plasma-induced positive chirp can help to generate sharply peaked h

Graphene, owing to its inherent chemical inertness, biocompatibility, and mechanical flexibility, has great potential in guiding cell behaviors such as adhesion and differentiation. However, due to the two-dimensional (2D) nature of graphene, the microfabrication of graphene into micro/nanoscale patterns has been widely adopted for guiding cellular assembly. In this study, we report crumpled graphene, i.e., monolithically defined graphene with a nanoscale wavy surface texture, as a tissue engine

Workability is regarded as one of the important parameters of high-performance concrete and monitoring it is essential in concrete quality management at construction sites. The conventional workability test methods are basically based on length and time measured by a ruler and a stopwatch and, as such, inevitably involves human error. In this paper, we propose a 4D slump test method based on digital measurement and data processing as a novel concrete workability test. After acquiring the dynamic