Jo Mar 25, 2023
Sodium hypochlorite antiseptic solution (NaOCl) has been widely used all over the world to prevent the spread of epidemic diseases. However, due to its low sterilizing power, it needs high concentration of activated chlorine, which is harmful to the human body and environment and results in the corrosion of metal products.
Scientists found that disinfection is caused by hypochloric acid(HOCl), not sodium hypochlorite (NaOCl) and recommended using hypochloric acid with pH 6~7.2, ORP≧900mV for disinfection. Accordingly, hypochloric acid is being produced by electrolysing admixed solution of NaCl, HCl and H2O in electrolytic baths without diaphragms, but this method is restricted in its output.
A research team led by Choe Hyon Ho, a section head at the Faculty of Electronics, has succeeded in preparing neutral electrolytic water with hypochloric acid by mixing sodium hypochlorite (NaOCl), chlorhydric acid (HCl) and water (H2O) sodium hypochlorite antiseptic solution at the sodium hypochlorite antiseptic solution production sites existing in the DPRK.
They determined the ratio of additional amount of chlorhydric acid to the mixing amount of water for preparing neutral electrolytic water through some basic experiments.
The preparation method can satisfy the demand for neutral electrolytic water with hypochloric acid for several uses with less consumption of salt, electrolytic plates and electric power than before.
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Jo Mar 23, 2023
When silicon is anisotropically etched, the etch rate of individual crystal planes of silicon is different from one another. Therefore, corner undercutting in KOH solution is critical and it is difficult to form full convex corners without compensation. Consequently, an abnormal square structure can be generated, which affects the operation characteristics of elements.
In the fabrication of diaphragms for a pressure sensing unit with square-shaped convex corners, compensation patterns should be arranged in each corner so that the beam part, where resistances are set up, is not changed by etching.
Several compensation methods have been used to solve this problem. Triangular, square and banded compensation patterns have been widely used to protect rectangular edges and these are now recognized to be classic compensation methods.
However, general principles to design individual compensation structures and compensation patterns, especially formulae to determine the dimension of compensation patterns do not seem to be introduced in detail.
Jon Chung Hyok, a researcher at the Faculty of Semiconductor Institute, has proposed a method to determine the shape and dimension of reasonable compensation patterns to make very thin diaphragms from 10~15㎛ to 250~300㎛ in thickness with square mass.
First, for fabrication of V-grooves structures with mass by corner compensation, he showed the compensation mechanism by several compensation patterns. The experiments on different types of compensation patterns showed that a diagonal-type compensation pattern is the best in performance. However, when etching depth should be ranged from 150㎛ to 200㎛, this compensation pattern is not suitable for compensation because the dimension of the mass and diaphragm should be restricted along their edges.
Next, on the analysis of the experimental results, he determined conditions for V-grooves structure from the given compensation pattern.
He concluded that when two types of compensation patterns are combined, the dimension of a square compensation pattern should be calculated before compensated corners with band compensation patterns are used to satisfy the insufficient etching depth, in order to increase the compensation effect.
Subsequently, he has made a diaphragm with the mass where a/h is less than 3.72 and b/h is less than 3.33 by applying corner compensation patterns.
More information about this is found in his paper “V-grooves Structures of Semiconductor Pressure Sensors with mass by Convex Corner Compensation” published in “Journal of Analog and Digital Devices” (EI).
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Jo Mar 22, 2023
Choe Myong Guk, a section head at the Faculty of Mechanical Science and Technology, has developed a system to find errors in mechanical drawings designed on SolidWorks software.
The system helps to promptly detect and correct errors in the dimension, surface finish symbols and geometrical tolerance in drawings.
The system consists of 3 modules: structurized module, analyzing module and post-processing module.
The structurized module serves as a preprocessing module which imports necessary data from SolidWorks models and converts it into a more convenient form for analyzing errors. It can be seen as a communication module because it manages data transfer between SolidWorks software and the check system.
The analyzing module is the most important kernel in the system because it detects errors from structured data. AI technology is introduced to the module to find dimensional errors such as over-dimension, lack-dimension and wrong dimension in drawings. It can also find errors in surface finish and geometrical tolerance symbols that do not satisfy technological and economic conditions. It can find 90% of errors that might occur in mechanical part drawings, assembly drawings and sheet metal drawings.
The post-processing module is a terminal module of the system. It highlights errors detected by the analyzing module in different colors and symbols. In addition, it exports checked drawing files to other file formats such as PDF.
The system will prove to be useful in the machine building industry or design examination institutes by detecting and correcting errors in mechanical drawings before production.
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Jo Mar 20, 2023
Obstacles in self-mixing (SM) based displacement sensing are time-consuming estimation of parameters such as an optical feedback factor and a linewidth enhancement factor, and the complex algorithm of displacement retrieval.
There have been presented fringe counting (FM) method and consecutive samples based unwrapping (CSU) method to avoid such complexities.
However, the FC method has very low resolution and the CSU method requires normalization of SM signals (SMSs), which is very complicated and even impossible when SMSs are affected by a speckle noise.
Kim Chol Hyon, a researcher at the Faculty of Physical Engineering, has proposed a new method of displacement reconstruction with high resolution, which does not need any complex processes such as parameter estimation or normalization. In addition, the method can be applied to all feedback regimes and work well even when SMSs are subject to a speckle noise.
He has presented a direct simple method of reconstructing the displacement of the target from self-mixing signals based on the velocity of the target for a weak feedback regime. Also, he has reported a simple method of displacement retrieval for moderate and strong regimes.
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Jo Mar 19, 2023
A research team led by Kim Myong Il, a section head at the Faculty of Mechanical Science and Technology, has designed a CNC hobbing machine for dry and wet cutting by high-speed tools or carbide cutting tools, in consideration of future development in the field of cutting tools.
This machine consists of a machine body, a control panel, a control cabinet, a cooling and chip removal device, an oil pump, etc. It is designed for handsome appearance, in conformity with human-machine engineering demand, and for convinience of machining, maintenance and material conveying.
With 6 control axes and 4 simultanous axes, it can cut spur gears, bevel gears, worm wheels and non-circular gears such as elliptic gears.
The technical characteristics of the machine are as follows.
Maximum work piece diameter: 500mm
Modulus range of gear machining: 1.5~6
This machine has remarkably upgraded machining accuracy and productivity and is good for environmental protection.
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Jo Mar 17, 2023
Measurement of low concentration oxygen gas is very important in chemical processes where several kinds of material gas and fuel gas are used. If the concentration of combustible oxygen gas gets high, it might cause explosion, which will have vicious influence upon the whole process. So, real-time measurement of oxygen at low concentration is essential for taking proper measures.
Two common techniques for sensing oxygen at low concentration are luminescent optical sensing and electrochemical sensing. Both demonstrate high sensitivity to low concentration oxygen. Fluorescent oxygen sensing has seen widespread adoption thanks to its inherent stability. However, application of this technique is limited due to complicated fabrication and short life time. On the other hand, electrochemical sensors are widely used and available in different forms according to the demands of users.
A research team led by Choe Chol Man, an institute head at the Faculty of Electronics, made an amperometric oxygen sensor based on the electrochemical method to manufacture an oxygen concentration measuring instrument, and introduced a refrigerator and a gas cleaning instrument for removing the effect of interference elements, thus completing a system of measuring low concentration oxygen gas.
The left picture shows the construction of the oxygen sensor incorporating a cathode, an anode, an electrolyte solution and a gas permeable membrane, all of which affect the characteristics of the sensor. They used silver with good oxygen reduction characteristics as a cathode, and silver/silver chloride electrode as an anode. KCl saturation solution and PTFE thin film were selected as an electrolyte and a gas permeable membrane, respectively.
They introduced digital signal processing technology to remove atmospheric noises so that the instrument could work properly in any operation environment, thus ensuring the stability and reliability of the instrument. The right picture shows the installation of the system.
The specification of the system is as follows.
Measurable band: 0~10%
Response time: 30s
Accuracy: 0.1%
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