• Korean Journal of Optics and Photonics
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• v.20 no.3
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• pp.156-165
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• 2009

We theoretically derive the set of general paraxial zoom locus equations for all zoom lens systems with finite object distance, including the infinite object distance case, by using the Gaussian bracket method and matrix representation of paraxial ray tracing. We make the zoom locus program by means of a numerical calculation method according to these equations in Visual Basic Language. Consequently, the solutions of this method can be consistently and flexibly used in all types of zoom lens in the step of initial design about zoom loci. Finally, in order to verify the justification and usefulness of this method, we show that two examples, such as $M_{4a}$ and $M_{4h}$ types of 4 groups, and one example, $M_{5n}$ type of 5 groups, which are very complicated zoom lens systems, can be rapidly and diversely traced through various interpolations by using this program.

• Korean Journal of Optics and Photonics
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• v.20 no.3
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• pp.166-174
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• 2009

When the object distance of a zoom lens with finite object distances is varied, we can fix the image at a fixed image plane by moving only one zoom lens group (autofocus group) without moving all zoom lens groups for the autofocus. We theoretically formulated and numerically calculated the moving distances of the autofocus group by using Gaussian brackets and a paraxial ray tracing method. The solutions of this method can be consistently and flexibly used in the initial design for the moving distance of autofocus group within these zoom loci in all types of zoom lens. Finally, in order to verify the usefulness of this method, we show that the moving distance of an autofocus group can be rapidly and diversely obtained in one example of $M_{5n}$ zoom lens type.

• Geophysics and Geophysical Exploration
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• v.14 no.2
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• pp.140-145
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• 2011

In order to analyze the influence of the noise on a cross-well traveltime tomography to detect a small scale low velocity body in a homogeneous medium, the first arrival travel times were computed one a tunnel model by a finite-difference ray tracing scheme. Three different types and four different intensity levels of white noises were added to the computed first arrival travel times, and velocity tomograms were constructed using an iterative inversion method (SIRT). Tomograms with the noise intensity up to 10% of the maximum traveltime delay in the tunnel model, showed the exact location of the tunnel. However, the velocity shown at the tunnel location was not close to air velocity but only slightly less than the velocity of the background medium. The additive random noise showed significantly less degree of influence on the resulting tomogram than the source- and receiver consistent noise.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.12
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• pp.982-992
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• 2017

In this paper, we introduce a method of selection for the optimal transmission polarization of a W-band seeker through the extraction of the one-dimensional scattering center of a ground tank target. We calculated the surface scattering and edge scattering using the shooting and bouncing ray tracing method of the CST A-solver. Based on 4-channel RCS data, using the one-dimensional RELAX algorithm, which is a kind of spectral estimation technique, scattering centers of ground targets were extracted. According to the changes in the polarization state and look angle, we compared and analyzed the scattering center results. Through simulation, we verified that the scattering center results can be applied when feature vectors are used for target recognition.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.3
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• pp.397-404
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• 2020

In this paper, the propagating-wave attenuation characteristics at 1, 3, and 6 GHz in the open environment roadway where the ground-reflected wave dominates are analyzed through a propagation model simulation using a ray-tracing method and propagation measurements. Simulations has been performed by varying the ground material, the transmitting antenna height, and the receiving antenna height. The measurements were conducted using a directional transmission antenna installed at 10 m mast and a omnidirectional receiving antenna installed at 1.5 m mast in an open environment. Comparison of simulation and measurement results confirms that the null points having the weak signal strength depend on those parameters. Although this research has been investigated for the wide road, the derived result could be useful for installing the transmitter and receiver in the roadway open environment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.1 s.104
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• pp.39-44
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• 2006

This paper proposes a method of moments(MoM)/Monte-Carlo simulation and Physical Optics(PO) model to determine Bistatic Coherent Reflectivity of sea surfaces at various wind speeds. For the MoM simulation, a Gaussian random rough sea surface was generated based on the data of Tae-An ocean at various wind speeds and sea surface heights. The numerical results of the MoM/Monte Carlo simulations were used to verify the validity region of the PO model. It was found that the numerical result for a flat surface agrees quite well with the Fresnel reflection coefficient. The validity of the PO model on the rough sea surface is shown by using ray tracing method.

• Journal of the Optical Society of Korea
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• v.20 no.4
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• pp.488-499
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• 2016

We present a design and optical simulation of a cost-effective hybrid daylighting/LED system composed of mixing sunlight and light-emitting diode (LED) illumination powered by renewable solar energy for indoor lighting. In this approach, the sunlight collected by the concentrator is split into visible and non-visible rays by a beam splitter. The proposed sunlight collector consists of a Fresnel lens array. The non-visible rays are absorbed by the solar photovoltaic devices to provide electrical power for the LEDs. The visible rays passing through the beam splitters are coupled to a stepped thickness waveguide (STW) by tilted mirrors and confined by total internal reflection (TIR). LEDs are integrated at the end of the STW to improve the lighting quality. LEDs’ light and sunlight are mixed in the waveguide and they are coupled into an optical fiber bundle for indoor illumination. An optical sensor and lighting control system are used to control the LED light flow to ensure that the total output flux for indoor lighting is a fixed value when the sunlight is inadequate. The daylighting capacity was modeled and simulated with a commercial ray tracing software (Lighttools^TM). Results show that the system can achieve 63.8% optical efficiency at geometrical concentration ratio of 630. A required accuracy of sun tracking system achieved more than ±0.5^o . Therefore, our results provide an important breakthrough for the commercialization of large scale optical fiber daylighting systems that are faced with challenges related to high costs.

• Journal of the Optical Society of Korea
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• v.20 no.4
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• pp.500-509
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• 2016

Integrating spheres play a central role in the radiometric calibration of remote sensors. With the development of the wide field of view (FOV) remote sensors, aperture diameters of remote sensors are becoming larger and larger. To satisfy the radiometric calibration requirements of full FOV and full aperture, an 8000mm diameter large aperture integrating sphere uniform source with a variable exit port was designed and manufactured. This integrating sphere will be used for pre-launch test and radiometric calibration of remote satellites. In this paper, optical theories were used to design the output spectral radiance. The LightTools software based on ray-tracing simulation method was used to determine the best combination and distribution of inner light sources. A spectral experiment was made to verify the spectral radiance design. To reduce the influence of longtime power-on, a new characteristic measurement method was developed to obtain the radiation characteristic of the integrating sphere, which could greatly improve the measuring efficiency. This method could also be applied to measure other large aperture uniform sources. The obtained results indicate that the spatial uniformity is 98.35%, and the angular uniformity at center position is 98.78%.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.43.1-43.1
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• 2018

Star formation in galaxies predominantly takes place in giant molecular clouds (GMCs). While it is widely believed that UV radiation feedback from young massive stars can destroy natal GMCs by exciting HII regions and driving their expansion, our understanding on how this actually occurs remains incomplete. To quantitatively assess the effect of UV radiation feedback on cloud disruption, we conduct a series of theoretical studies on the dynamics of HII regions and its role in controlling the star formation efficiency (SFE) and lifetime of GMCs in a wide range of star-forming environments. We first develop a semi-analytic model for the expansion of spherical dusty HII regions driven by the combination of gas and radiation pressures, finding that GMCs in normal disk galaxies are destroyed by gas-pressure driven expansion with SFE < 10%, while more dense and massive clouds with higher SFE are disrupted primarily by radiation pressure. Next, we turn to radiation hydrodynamic simulations of GMC dispersal to allow for self-consistent star formation as well as inhomogeneous density and velocity structures arising from supersonic turbulence. For this, we develop an efficient parallel algorithm for ray tracing method, which enables us to probe a range of cloud masses and sizes. Our parameter study shows that the net SFE, lifetime (measured in units of free-fall time), and the importance of radiation pressure (relative to photoionization) increase primarily with the initial surface density of the cloud. Unlike in the idealized spherical model, we find that the dominant mass loss mechanism is photoevaporation rather than dynamical ejection and that a significant fraction of radiation escapes through low optical-depth channels. We will discuss the astronomical.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.772-772
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• 2001

In this paper, we proposed the image-based 3D ray-tracing indoor propagation model using patch scattering model which can calculate the scattering phenomenon of the indoor structures. A patch scattering model for modeling indoor structures defines a scattering phenomenon by using RCS(Radar Cross Section) about rectangular patch without complex calculation, for example generating image antennas about each indoor structures. RCS is simply defined as a ratio of scattering power to incident power, and we use bistatic PCS which is simplified numerically by Physical Optics. Also, a simple indoor compensation factor is defined as empirical constant from measured data instead of complex numerical expression because basic patch scattering model cannot include important multipath components, so we san use patch scattering model in indoor environment using indoor compensation factor.