Center for Safety Measurement

Daejeon, South Korea

Center for Safety Measurement

Daejeon, South Korea
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Jeon M.Y.,Chungnam National University | Kim N.,ETRI | Han S.P.,ETRI | Ko H.,ETRI | And 4 more authors.
2011 Int. Quantum Electron. Conf., IQEC 2011 and Conf. Lasers and Electro-Optics, CLEO Pacific Rim 2011 Incorporating the Australasian Conf. Optics, Lasers and Spectroscopy and the Australian Conf. | Year: 2011

We propose a high-speed frequency-scanning optical beat source using a wavelength swept laser and a tunable laser for continuous THz wave generation. The beat frequency is scanned at 1 kHz over a range with a 2.16 THz width. © 2011 IEEE.


Jeon M.Y.,Chungnam National University | Kim N.,ETRI | Shin J.,ETRI | Jeong J.S.,ETRI | And 6 more authors.
Technical Digest - 15th OptoElectronics and Communications Conference, OECC2010 | Year: 2010

We propose a widely tunable injection-locked dual-wavelength Erbium-doped fiber laser using two microheater-integrated Fabry-Perot laser diodes and two fiber Bragg gratings. The wavelength spacing can be continuously tuned from 2.4 nm to 9.0 nm.


Jeon M.Y.,Chungnam National University | Kim N.,ETRI | Shin J.,ETRI | Jeong J.S.,ETRI | And 6 more authors.
Optics Express | Year: 2010

We propose a widely tunable dual-wavelength Erbium-doped fiber laser that uses two micro-heater-integrated Fabry-Perot laser diodes (FP-LDs) and two fiber Bragg gratings (FBGs) for tunable continuous-wave (CW) terahertz (THz) radiation. Each wavelength can be independently tuned by using an FP-LD and an FBG. The wavelength fine tuning is achieved by simultaneously applying current to the micro-heater on the FPLD and strain to the FBG. The side-mode suppression ratio is more than 35 dB for both wavelengths. The wavelength spacing of the dual wavelength can be continuously tuned from 3.2 nm to 9.6 nm. Continuous frequency tuning of the CW THz radiation is also successfully achieved using an InGaAs-based photomixer with our dual-wavelength fiber laser as the optical beat source. The emitted CW THz radiation is continuously tuned from 0.3 to 0.8 THz. © 2010 Optical Society of America.


Jeon M.Y.,Chungnam National University | Kim N.,z Photonics Creative Research Center | Han S.-P.,z Photonics Creative Research Center | Ko H.,z Photonics Creative Research Center | And 3 more authors.
IRMMW-THz 2011 - 36th International Conference on Infrared, Millimeter, and Terahertz Waves | Year: 2011

We demonstrate a frequency swept optical beat source for high speed continuous wave THz generation. The range of the sweeping bandwidth is about 2.16 THz (17.3 nm). And we observe CW THz waveforms for several static optical beat sources using a fiber coupled CW THz measurement system in order to confirm the feasibility of our frequency swept optical beat source as a CW THz radiation source. © 2011 IEEE.


Jeon M.Y.,Chungnam National University | Kim N.,z Photonics Creative Research Center | Han S.-P.,z Photonics Creative Research Center | Ko H.,z Photonics Creative Research Center | And 3 more authors.
Optics Express | Year: 2011

We propose a rapidly frequency-swept optical beat source for continuous wave (CW) THz generation using a wavelength swept laser and a fixed distributed feedback (DFB) laser. The range of the sweeping bandwidth is about 17.3 nm (2.16 THz), 1541.42-1558.72 nm. The achieved side mode suppression ratio for both wavelengths within the full sweeping range is more than 45 dB. We observe CW THz signals for tunable optical beat sources using a fiber coupled CW THz measurement system to confirm the feasibility of using our frequency swept optical beat source as a CW THz radiation source. The THz output signal falls to the thermal noise level of the low-temperature grown (LTG) InGaAs photomixer beyond 1.0 THz. The rapidly frequency-swept optical beat source will be useful for generating high-speed tunable CW THz radiation. © 2011 Optical Society of America.


Choi W.,Imperial College London | Choi W.,Center for Safety Measurement | Skelton E.A.,Imperial College London | Pettit J.,Rolls-Royce | And 2 more authors.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2016

A three-dimensional (3-D) generic hybrid model is developed for the simulation of elastic waves in applications in nondestructive evaluation (NDE) that efficiently links different solution strategies but, crucially, is independent of the particular schemes employed. This is an important step forward in facilitating rapid and accurate large-scale simulations, and this advances the two-dimensional (2-D) generic hybrid methodology recently developed by the authors. The hybrid model provides an efficient and effective tool for creating highly accurate simulations that model the wave propagation and scattering, enabling the interpretation of inspection data; the new methodology is verified against other numerical simulations. Furthermore, its deployment to simulate wave reflection from side-drilled holes (SDHs), comparing the results with experimental measurements, provides a realistic demonstration as well as further validation. © 2016 IEEE.


Shi F.,Imperial College London | Choi W.,Center for Safety Measurement | Lowe M.J.S.,Imperial College London | Skelton E.A.,Imperial College London | Craster R.V.,Imperial College London
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2015

The Kirchhoff approximation (KA) for elastic wave scattering from two-dimensional (2D) and three-dimensional (3D) rough surfaces is critically examined using finite-element (FE) simulations capable of extracting highly accurate data while retaining a fine-scale rough surface. The FE approach efficiently couples a time domain FE solver with a boundary integration method to compute the scattered signals from specific realizations of rough surfaces. Multiple random rough surfaces whose profiles have Gaussian statistics are studied by both Kirchhoff and FE models and the results are compared; Monte Carlo simulations are used to assess the comparison statistically. The comparison focuses on the averaged peak amplitude of the scattered signals, as it is an important characteristic measured in experiments. Comparisons, in both two dimensions and three dimensions, determine the accuracy of Kirchhoff theory in terms of an empirically estimated parameter σ2/λ0 (σ is the RMS value, and λ0 is the correlation length, of the roughness), being considered accurate when this is less than some upper bound c, (σ2/λ0 deg;, the accuracy of the KA is improved even when σ2/λ0 > c. In addition, the evaluation results are compared using 3D isotropic rough surfaces and 2D surfaces with the same surface parameters. © 2015 The Author(s) Published by the Royal Society. All rights reserved.


Shi F.,Imperial College London | Choi W.,Center for Safety Measurement | Skelton E.A.,Imperial College London | Lowe M.J.S.,Imperial College London | Craster R.V.,Imperial College London
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2014

A 2-D and 3-D numerical modeling approach for calculating the elastic wave scattering signals from complex stress-free defects is evaluated. In this method, efficient boundary integration across the complex boundary of the defect is coupled with a time-domain finite element (FE) solver. The model is designed to simulate time-domain ultrasonic nondestructive evaluation in bulk media. This approach makes use of the hybrid concept of linking a local numerical model to compute the near-field scattering behavior and theoretical mathematical formulas for postprocessing to calculate the received signals. It minimizes the number of monitoring signals from the FE calculation so that the computation effort in postprocessing decreases significantly. In addition, by neglecting the conventional regular monitoring box, the region for FE calculation can be made smaller. In this paper, the boundary integral method is implemented in a commercial FE code, and it is validated by comparing the scattering signals with results from corresponding full FE models. The coupled method is then implemented in real inspection scenarios in both 2-D and 3-D, and the accuracy and the efficiency are demonstrated. The limitations of the proposed model and future works are also discussed. © 2014 IEEE.

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