Enlargement of Measurement Range of Self-mixing Dis...

Jo Jul 26, 2024

Increasing the measurable distance and the displacement measurement limit of a self-mixing displacement sensor poses one of the most important problems to improve the sensor’s performance.

In order to solve the problem, there has to be found an estimation method of the optical feedback factor for a strong feedback regime.

The hardship of the estimation in this regime is brought about by a strong speckle noise and the restriction of normalization methods presented hitherto.

Kim Chol Hyon, a section head at the Faculty of Physical Engineering, has found an approach to improving the accuracy of the self-mixing sensor, which can work even for long range and large displacement, by deciding the region of the optical feedback factor based on the ratio of fringe height and by using it and the fringe counting method.

The experiments showed that the SM displacement sensor based on the new approach will be a great help to the enlargement of the measurement range of the sensor.

If further information is needed, please refer to his paper “Amelioration of accuracy of displacement measurement in strong feedback regime based on region decision: enlargement of measurement range of self-mixing displacement sensor” in “Optics Communications” (SCI).

Betterment of Displacement Retrieval Method Based o...

Jo Jul 25, 2024

To raise the speed and accuracy of displacement retrieval by overcoming the weakness of time-consuming parameter estimation and complex displacement retrieval algorithm is very important in improving the real-time quality of measurement.

Kim Il Hyok, a student at the Faculty of Physical Engineering, has proposed a new method for parameter estimation and displacement retrieval which does not require complex normalization and is of high precision of displacement retrieval and incomparably less time-consuming than existing data fitting based methods.

It is a high-speed and high-precision method of displacement reconstruction based on data-fitting method in the near-half-fringe zone collaborating with the fringe-counting method. The method proposed is applicable to any optical feedback level and to any motion. The method provides the fastest estimation and the highest precision of displacement retrieval. Its displacement reconstruction error is less than 16nm and its estimation speed is over 30 times as fast as conventional methods.

You can find the details in his paper “Betterment of displacement retrieval method based on data fitting in near-half-fringe zone” in “Applied optics” (SCI).

Lattice Boltzmann Simulation of Dielectric Barrier ...

Jo Jul 23, 2024

Dielectric Barrier Discharge (DBD) has been applied in many fields such as ozone synthesis, degradation of VOCs, plasma etching, surface modification, actuators, sterilization of medical devices, etc., and it has been attracting a great deal of attention of researchers in recent years. In order to find and control the features of DBDs, a lot of efforts have been devoted to their theoretical, numerical and experimental investigation. The advance in numerical simulation encouraged the development of DBD technology.

DBD is generally produced between two electrodes, which have several shapes such as parallel plate, concentric cylinder, and so on. Parallel plate electrodes are preferred as it not only makes it easy to produce large area plasma, but is also flexible and convenient for treating film-like materials or gases.

So far, finite element method (FEM) has been dominant in simulating DBD plasma. Despite the fact that FEM is well-defined and powerful for unstructured grid, it is essentially non-conservative and complicated. In order to avoid checkboard instability due to unstructured grids, special care is needed with its integrals.

In recent years, the LB method has been successfully applied to some hydrodynamic problems such as Navier–Stokes and advection–diffusion equations. It is based on the well-known Boltzmann equation rather than hydrodynamic equations. Unlike other methods, the LB method chases distribution of particles within each discretized node, which ensures that non-linearity is local and non-locality is linear. Although the LB method is more memory-sensitive and requires weak compressibility, it is preferred for simulating multicomponent flow in complex geometries such as porous media. Parallel computation is available in this method, which means it is faster than others. LB method is not only simple, but also relatively stable to implement. Its stability depends mainly on lattice velocity and advection velocity, which allows us to adjust only two parameters for stability.

Choe Yong Son, a researcher at the Faculty of Physical Engineering, applied a lattice Boltzmann (LB) D1Q3 scheme to the numerical simulation of multi-component plasma by dielectric barrier discharge (DBD).

DBD in atmospheric argon is generated in a small gap of 0.5mm between two parallel plate electrodes, and is driven by high voltage AC of about 20kHz.

In order to find the characteristics of the DBD plasma, he coupled the LB numerical model with continuity and Poisson equations. The simulation results showed that LB method can be used for simulation of DBD plasma.

For more information, please refer to his paper “One-dimensional lattice Boltzmann simulation of parallel plate dielectric barrier discharge plasma in atmospheric argon” in “Mathematics and Computers in Simulation” (SCI).