• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.5 s.236
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• pp.770-776
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• 2005

The gains fur NC controller parameter are fixed when the controller is combined with a machine. However, the characteristics of controller could be changed as it has being used by the machine or other environmental conditions. Those result in that the tool positioning accuracy is influenced. The loading torque in servo motor influences on the tool positioning accuracy and it is controlled by the parameter gains. It is required to analyze the torque variation with angular positioning accuracy of the servo motor. This study focus on a measuring method and device for verifying angular positioning accuracy of NC servo motor. We used a high resolution An converter for acquiring analogue signal of rotary encoder in servo motor. The positional accuracy for a nominal tool path, which is generated by the combination of axial movements (X,Y,Z), is analyzed with the servo motor torque. The current variation signal is acquired at the power line using a hall sensor and converted to the loading torque of servo motor. The method of measurement and analysis proposed in this study will be used for determining the gains of parameter in NC controller. This gain tuning is also necessary when the controller is set up at a machine.

• Journal of Biomedical Engineering Research
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• v.7 no.1
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• pp.59-66
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• 1986

A prototype ultrasound sector B-scanner has been developed where the front-end hardware refers to all the necessary circuits for transmitting the ultrasound pulses into the human body and receiving the reflected echo signals from it. The front-end hardware can generally be divided into three parts, i.e., a pulse generator for insonification, a receiver which is responsible for processing of low-level analog signals, and a steering controller for driving the mechanical sector probe whose functions and design concepts are described in this paper. The front-end hardware is implemented which incorporates the following features: improvement of the axial resolution using a circuit which reduces the ring-down time, flexibility of generating time-gain compensation curve, and adoption of a one-chip microcomputer for generating the rate pulses based on the sensor output waveforms.

• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.37-44
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• 1994

The characteristics of stimulated Brillouin scattering wave for applications to high power laser was experimentally investigated. The peak power reflectivity and the phase conjugation fidelity of Stokes wave with respect to the focal length of lens were measured, and the phase conjugation fidelity for a compressed part of the Stokes wave was also investigated. For the long focal length of lens.(f=100 cm), the peak power of the Stokes wave amounts to about twice as high as that of incident wave. The phase conjugation fidelity for the compressed leading pulse is up to 90%, better than that for other temporal parts of the Stokes pulse. In spatial distribution, the Stokes pulse from the axial region has the largest SBS gain, and it has been ascertained as a best candidate to the application due to excellent pulse compression, peak power reflectivity, and good phase conjugation fidelity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.7
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• pp.1363-1368
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• 2015

Aperture-coupled circular polarization microstrip array antenna is proposed in this paper. The proposed antenna is useful for 2.4GHz ISM band and its aperture shape is a modified H-slot. The optimal design parameters for the antenna structure is found by using electromagnetic analysis tool HFSS repeatedly. The HFSS simulation results, such as return loss, axial ratio, radiation pattern and gain of the proposed array antenna are compared with results of the single antenna. It is able to verify that the proposed array antenna is valuable enough to be used in various applications as well as 2.4GHz ISM band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.12
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• pp.1233-1238
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• 2003

In this paper, radially corrugated circular-type microstrip patch antenna was devised and manufactured for GPS (center frequency: 1.575 GHz). Radially corrugated circular-type microstrip patch antenna having radiational corrugation-patch contributed to add size reduction ratio by lowering the resonant frequency because the edge current also has the extended and perpendicular path. As a result, radially corrugated circular-type microstrip patch antenna has 28 % area reduction than planer circular-type patch antenna for linear polarization and 27.7 % area reduction than planer circular-type patch antenna for circular polarization. Radially corrugated circular-type microstrip patch antenna is suitable for miniaturized receive antenna for GPS which has the characteristic of gain 2.1 dBd, axiai ratio 1.3 dB, 2 dB axial bandwidth 15 MHz(0.9 %).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.05a
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• pp.77-81
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• 2006

We report the performance of a four-element, 11.67 GHz, high-Tc superconducting (HTS) microstrip antenna array with corporate feed network and circular polarization for direct broadcasting satellite (DBS) system. Our array antennas were designed and built on a 0.5 mm thick MgO substrate. To compare the superconducting antennas with normal conducting counterpart, One antenna pattern was fabricated from gold thin film, and a second pattern was fabricated from $YBa_2Cu_3O_{7-x}$ (YBCO) superconducting thin film. To improve the axial ratio of circularly polarized arrays, sequential rotation technique were used. Efficiency, radiation pattern, return loss and bandwidth were measured for both antennas at room temperature and at cryogenic temperature. The array produced good circular polarization, and the gain of the array at 77 K, relative to a copper array at room temperature was approximately 1.54 dB. The measured return loss of our HTS antenna array was 35.79 dB at the resonant frequency of 11.67 GHz and The total effective bandwidth was about 3.4 %. The results showed that high-temperature superconductors, when used in microstrip arrays, improved the efficiency of the HTS antenna array for circularly polarization.

• Journal of electromagnetic engineering and science
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• v.17 no.1
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• pp.1-8
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• 2017

This paper introduces a technique to obtain the broadband characteristics of circularly polarized antennas using an L-shaped probe. A waveguide antenna is suitable for obtaining high gain and handling convenience in some applications; however, the asymmetrical structure of the L-shaped probe results in cross-polarization and frequency dependence on the field distribution of higher-order modes (HOM). In addition to the basic characteristics of a waveguide antenna with an L-shaped probe, the author discusses some techniques to reduce the HOM and cross-polarization. As a result, the 3-dB axial ratio (AR) is obtained with the fundamental mode even when the frequency is expanded to the region for HOM of TM. This reduction is mainly due to the cutoff structure to the TM mode around the short wall of the waveguide. Furthermore, some aperture modification techniques can reduce the cross-polarization in a wide range of angles in the radiation pattern. Such techniques and their mechanisms are discussed in this paper. The obtained performance shows that the proposed antennas have a wide range of angles of 3-dB AR in the radiation pattern, broadband characteristics in impedance and AR, and low variation in group velocity.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.1
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• pp.50-57
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• 2001

This paper describes a design for the circularly polarized microstrip EMC cross dipole array antenna with the wide bandwidth. To realize the characteristics of wide bandwidth and circular polarization, the electromagnetic-coupled cross dipole element is proposed. The optimum design parameters of a circularly polarized EMC cross dipole element are calculated by the FDTD and the Ensemble. To obtain the uniform aperture illumination of electric field in an array, offset technique that the cross dipole elements are alternatively arranged on center of the microstrip feed line is adopted. In 20-element array design, the calculated axial ratio and gain are about 0.1dB and 9.9 dBi at 12 GHz, respectively, The frequency characteristics of a fabricated 20-element array antenna are measured. The calculated results agree well with the measured ones.

• Journal of electromagnetic engineering and science
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• v.6 no.1
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• pp.36-46
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• 2006

In this paper, we present a two-element circularly-polarized antenna array for UHF-band RFID reader applications. The antenna element in the array is a comer-truncated rectangular patch placed on a thick plastic-foam dielectric. The patch is fed on one of its edges by a microstrip line printed on a separate thin substrate. The array antenna is fed by a microstrip power divider. Parametric studies on the patch are carried out, from which an optimum design of a single antenna element is derived. The element spacing and the feed network of the array are investigated. A commercial electromagnetic software is employed in the analysis and design of the antenna. The designed array is fabricated and tested. Measurements show good performance characteristics of the fabricated antenna: a 11.2-dBi gain, a reflection coefficient of - 14 dB, an axial ratio less than 3 dB over 3-dB beamwidths of 40 and 60 degrees on two principal planes.

• Journal of electromagnetic engineering and science
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• v.14 no.3
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• pp.299-305
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• 2014

A wideband circularly polarized (CP) antenna with a single feed is proposed for use in global navigation satellite systems. Its primary radiation elements are composed of two orthogonal bowtie dipoles, which are equipped with double-printed vacant-quarter rings to allow direct matching of the antenna to a single $50-{\Omega}$ coaxial line and to produce CP radiation. The crossed bowtie dipole is appropriately incorporated with a planar metallic reflector to produce the desired unidirectional radiation pattern as well as to achieve a wideband characteristic in terms of impedance matching and axial ratio (AR) bandwidths. The designed antenna was fabricated and measured. The prototype antenna with an overall 1.2-GHz frequency size of $0.48{\lambda}_o{\times}0.48{\lambda}_o{\times}0.25{\lambda}_o$ produced a measured ${\mid}S_{11}{\mid}$<-10 dB bandwidth of 1.05-1.79 GHz and a measured 3-dB AR bandwidth of 1.12-1.64 GHz. It also showed right-hand CP radiation with a small gain variation (${\pm}0.3dB$) and high radiation efficiency (>93%) over the operational bandwidth.