Hyung-rai Oh

Perpendicular Magnetic Recording Process Using Finite-Element Micromagnetic Simulation

The perpendicular magnetic recording process of a shielded-pole-type head was studied using the finite-element micromagnetic simulation. When the return and write pole are sufficiently close to each other, 40 nm in our simulation, the effective recording field is tilting at an angle of around 30deg. The tilted recording field leads to a more efficient writing since the recording media switching field is reduced according to Stoner-Wohlfarth model. This means that the shielded-pole-type head can be used to write higher coercivity recording media and allow for higher recording density and better thermal stability

Modeling long-term human activeness using recurrent neural networks for biometric data

BackgroundWith the invention of fitness trackers, it has been possible to continuously monitor a user’s biometric data such as heart rates, number of footsteps taken, and amount of calories burned. This paper names the time series of these three types of biometric data, the user’s “activeness”, and investigates the feasibility in modeling and predicting the long-term activeness of the user.MethodsThe dataset used in this study consisted of several months of biometric time-series data gathered by seven users independently. Four recurrent neural network (RNN) architectures–as well as a deep neural network and a simple regression model–were proposed to investigate the performance on predicting the activeness of the user under various length-related hyper-parameter settings. In addition, the learned model was tested to predict the time period when the user’s activeness falls below a certain threshold.ResultsA preliminary experimental result shows that each type of activeness data exhibited a short-term autocorrelation; and among the three types of data, the consumed calories and the number of footsteps were positively correlated, while the heart rate data showed almost no correlation with neither of them. It is probably due to this characteristic of the dataset that although the RNN models produced the best results on modeling the user’s activeness, the difference was marginal; and other baseline models, especially the linear regression model, performed quite admirably as well. Further experimental results show that it is feasible to predict a user’s future activeness with precision, for example, a trained RNN model could predict–with the precision of 84%–when the user would be less active within the next hour given the latest 15 min of his activeness data.ConclusionsThis paper defines and investigates the notion of a user’s “activeness”, and shows that forecasting the long-term activeness of the user is indeed possible. Such information can be utilized by a health-related application to proactively recommend suitable events or services to the user.

Thermal and Magnetic Field Effect of Soft Under Layer for Perpendicular Media

The soft under layer (SUL) is used to improve write head filed strength, field gradient and read-back signal in perpendicular magnetic media. In this study, four type SUL structures were fabricated. Samples were post-annealed and cooled to room temperature under magnetic field along radial direction. VSM, MFM and Guzik spin stand were used to analyze the magnetic properties, domain structure and noise level of the samples.

Effects of post-annealing on magnetic properties and microstructure of CoCrPt-SiO2 perpendicular magnetic recording media

In this work, the effects of post-annealing of CoCrPt-SiO2/Ru perpendicular magnetic recording media on magnetic properties and microstructure have been studied. CoCrPt-SiO2/Ru/Ta thin films were deposited on Si substrate by a dc magnetron sputtering method at room temperature and followed by post-annealing for 30 minutes in the range of 100 ~ 240degC. Magnetic properties such as magnetization, coercivity (Hc) and negative nucleation field (Hn) were measured by a vibrating sample magnetometer. Magnetic anisotropic constant (Ku) of the films was measured by a torque magnetometer. Microstructural and chemical changes were studied.

Perpendicular magnetic recording process simulation using finite element micromagnetic

In this paper, finite element modelling is used to simulate the perpendicular magnetic recording process with micromagnetic considerations. The simulation consists of a full-sized shielded-type head with current coil, a voronoi granular media and soft magnetic underlayer.