Wan-Joon Park

For sensors that emulate human tactile perception, we suggest a simple method for fabricating a highly sensitive force sensor using a conductive polyurethane sponge where graphene flakes are self-assembled into the porous structure of the sponge. The complete sensor device shows a sensitive and reliable detection response for a broad range of pressure and dynamic pressure that correspond to human tactile perception. Sensitivity of the sensor to detect vibration is also confirmed with vertical ac

We describe measurements using a technique for determining interfacial resistances and loss of spin-direction memory (spin relaxation) for nonmagnetic metals and nonmagnetic interfaces. The technique involves inserting the metal of interest, or a multilayer, into the middle of a current-perpendicular (CPP) permalloy-based exchange-biased spin-valve and monitoring the resulting increase in CPP resistance and decrease in magnetoresistance. The technique has the advantage over earlier ones of givin

In this paper, we propose a graphene sensor using two separated single-layered graphenes on a flexible substrate for use as a pressure sensor, such as for soft electronics. The working pressure corresponds to the range in which human perception recognizes surface morphologies. A specific design of the sensor structure drives the piezoresistive character due to the contact resistance between two graphene layers and the electromechanical properties of graphene itself. Accordingly, sensitivity in r

We present a high-performance flexible triboelectric nanogenerator (TENG) based on an interlocked array of surface-functionalized indium tin oxide (ITO) nanohelix (NH) structures. The structural properties of ITO NHs, including a high nanoscale roughness and unique spring-like geometry, provide a large surface area for an effective friction, enhanced tolerance to bending strain, and operational reliability. The TENG device with surface-functionalized ITO NHs exhibits a significantly enhanced (ov

Abstract Development of a sensor for recognizing tactile feeling is essential for realizing artificial systems that can perform human tactile functions for various applications. For achieving the capability of human tactile sensation, highly sensitive responses are required not only to static pressures but also to dynamic high‐frequency vibrations. Here, a highly sensitive force sensor based on interlocked arrays of vertically aligned indium tin oxide (ITO) nanospring structures fabricated on a

Tactile sensors capable of texture recognition are essential for artificial skin functions. In this work, we describe a tactile sensor with a single sensor architecture made of single layer graphene that can recognize surface texture based on the roughness of the interacting surface. Resistance changes due to the local deformation of a local area of the single layer graphene are reflected in the resistance of the entire sensor. By introducing microstructures inspired by human finger prints, surf

A stable three-dimensional stellarator equilibrium can be obtained numerically by a time-dependent relaxation method using small values of dissipation. The final state is an Ohmic steady state which approaches an Ohmic equilibrium in the limit of small dissipation coefficients. A method to speed up the relaxation process and a method to implement the B⋅∇p=0 condition are described. These methods are applied to obtain three-dimensional heliac equilibria using the reduced heliac equations.

The emulation of the tactile sense is presented with the encoding of a complex surface texture through an electrical sensor device. To achieve a functional capability comparable to a human mechanoreceptor, a tactile sensor is designed by employing a naturally formed porous structure of a graphene film. The inherent tactile patterns are achievable by means of proper analysis of the electrical signals that the sensor provides during the event of touching the interacting objects. It is confirmed th

Measurements of current perpendicular (CPP) magnetoresistance (MR) on hybrid and exchange-biased spin valves allow determination of the layer anisotropy parameter β for ferromagnetic alloys, thus allowing testing of whether this CPP β is similar to values obtained from direct measurements on, and theoretical estimates for, dilute bulk ferromagnetic alloys. Of special interest are alloys where β is expected to be negative. In this article, we derive a value of β for a Ni97Cr3 alloy using such spi

We present switching characteristics of patterned submicrometer magnetic tunnel junction arrays containing NiFe and CoFe free layers. The resemblance of magnetization and magnetoresistance (MR) curves was studied by micromagnetic calculations and experimental measurements. Upon analyzing the MR transfer curves, the magnetic vortex and domain wall pinning effects on anomalous switching of each magnetic tunnel junction can be distinguished by remanent states. Data indicates that the low saturation