Lee S.-S.,Korea Aerospace Research Institute
IEEE Transactions on Industrial Electronics | Year: 2014
A new step-down converter is presented. It is composed of an auxiliary switch, a diode, and a coupled winding to the buck inductor in the conventional buck converter. By transferring the buck-inductor current to the coupled winding in a very short period, the negatively built-up leakage inductor current of the buck winding guarantees the zero-voltage switching (ZVS) operation of the buck switch in all load conditions. Furthermore, since the negatively built-up leakage inductor current is minimized after the zero voltage of the buck switch is achieved, the unnecessary current build-up and the conduction loss are minimized. Therefore, efficient ZVS operation with load variation is achieved. The operation principle, ZVS analysis, design, and experimental results of the proposed converter are presented. © 1982-2012 IEEE.
Park S.-H.,Korea Aerospace Research Institute
Journal of Sound and Vibration | Year: 2013
A design method of micro-perforated panel absorbers is proposed for the enhancement of acoustic absorption inside the payload fairings of launch vehicles. An empirical acoustic resistance model of a micro-perforated panel absorber in a high sound pressure environment is suggested to this end. The resistance model is especially appropriate for the launcher fairing application, so that the incident pressure to the surface of bare fairings is considered as a main variable. Other design variables, e.g., the minute hole diameter, the perforation ratio and the thickness of the panel, are also considered in the proposed model. The estimated acoustic resistances and corresponding absorption coefficients are verified by comparing them with the measured results for several micro-perforated panel absorbers having a practical range of parameters. The estimated and measured results show good agreement when the perforation ratio is in the range of 1.4 to 5.3. The effects of design parameters on the absorption coefficient are discussed. It is demonstrated that the micro-perforated panel absorber with a large hole diameter (about 1.0 mm), which shows a poor sound absorption at low pressure levels, can be a good sound absorber at high incident pressure levels. A set of design charts is provided and this enables one to readily design a micro-perforated panel absorber for the mitigation of acoustic loads in launcher fairings. © 2012 Elsevier Ltd.
Yoon W.-J.,Korea Aerospace Research Institute |
Chung S.-H.,Pusan National University
IEEE Transactions on Industrial Electronics | Year: 2012
The standard tag collection algorithm (TCA) in ISO/IEC 18000-7 has difficulty in collecting data from a massive number of active radio frequency identification (RFID) tags in a timely manner, so it should be improved to allow successful application of active RFID systems to a wide variety of industrial fields. We propose a novel TCA, which is an identified slot scan-based TCA (ISS-TCA), to improve the performance of tag collection (TC) in active RFID systems. In the proposed ISS-TCA, an active RFID reader differentiates identified slots from collided and empty slots via an ISS phase, in which active RFID tags send minimal responses. The reader then avoids collided and empty slots in the following TC phase, in which it collects the actual data from the tags. This reduces the cost of collided and empty slots during TC, resulting in improved TC performance. We carried out simulations to evaluate and compare the performances of the standard TCA and the proposed ISS-TCA in TC. The simulation results with up to 500 tags showed that the proposed ISS-TCA reduced the average time required for TC by 33.2% or 27.3% when the reader collected 50 or 100 bytes of additional data from the tags, respectively. We also experimentally evaluated the performance improvement of TC by the proposed ISS-TCA using an active RFID reader and 60 tags that were implemented for this paper. The experimental results confirmed that the proposed ISS-TCA could improve the TC performance in practice, confirming the simulation results, and showed that it could also decrease the average battery consumption of the tags by 39.3%. © 2011 IEEE.
Korea Aerospace Research Institute | Date: 2014-11-24
Provided are a surface inspection apparatus and a surface inspection method. More particularly, disclosed are a surface inspection apparatus and a surface inspection method to allow for inspection of a foreign material on non-uniformly colored diffusive surfaces containing a metal or polymer material or the like.
Korea Aerospace Research Institute | Date: 2014-06-03
Disclosed is a method for four-path tree structured vector quantization, comprising: (a) placing codebook vectors where magnitudes of vectors are arranged in order at lowermost nodes; (b) configuring upper nodes by averaging vector values of the lowermost adjacent four nodes; (c) calculating mean square errors to paths of the upper nodes (A, B, C, and D) corresponding to four paths from an input vector X; (d) presetting a threshold between 0 and 1 after the (c); (e) calculating thresholds between the input vector X and four paths A, B, C, and D, based on the mean square errors; and (f) comparing the thresholds calculated in the (d) with the preset threshold to select a path having a threshold greater than the preset threshold, in which dynamic four-path tree structured vector quantization is used instead of conventional dynamic two-path tree structured vector quantization, thereby more efficiently and quickly searching a codebook.