Time-domain analysis of a CRLH coupled-line coupler using the CN-FDTD method

2018 ◽  
Vol 11 (1) ◽  
pp. 94-103 ◽  
Author(s):  
Mahdieh Gholami Mayani ◽  
Shahrooz Asadi ◽  
Shokrollah Karimian
Keyword(s):  
Time Domain ◽  
Finite Difference Time Domain ◽  
Fdtd Method ◽  
Time Domain Analysis ◽  
Step Size ◽  
Dramatic Decrease ◽  
Coupled Line ◽  
Left Handed ◽  
Difference Time ◽  
Good Agreement

In this study, the implicit Crank–Nicolson finite-difference time-domain (CN-FDTD) method is applied to discretize the governing telegrapher's equations of a composite right-/left-handed (CRLH) coupled-line coupler. The unconditionally stable CN-FDTD is compared with the conventional leap-frog (LF) FDTD method. The results obtained from the CN-FDTD scheme show up to 10 times increase in the temporal step size, reflecting in a dramatic decrease in processing time; in addition to having a good agreement with the LF method and the measurements.

Two-dimensional finite difference-time domain analysis of focus boom noise with velocity disturbance in the atmosphere

2021 ◽  
Vol 263 (6) ◽  
pp. 589-597
Author(s):  
Takao Tsuchiya ◽  
Masashi Kanamori
Keyword(s):  
Finite Difference ◽  
Sound Wave ◽  
Time Domain ◽  
Finite Difference Time Domain ◽  
Fdtd Method ◽  
Time Domain Analysis ◽  
Two Dimensional ◽  
Supersonic Transport ◽  
Explicit Finite Difference ◽  
Difference Time

In this paper, two-dimensional linear sound wave analysis in the stratified atmosphere with temperature gradient and velocity disturbance is numerically applied to the analysis and prediction of focus boom noise. Focus boom occurs when a supersonic transport accelerates or ascent or descent maneuvers at supersonic speed. Its overpressure is typically more than three times greater than that of a cruise sonic boom. As a result, supersonic transports in future commercial operation are likely to face restrictions on their flight conditions. The compact-explicit finite difference-time domain method is applied to the analysis of two-dimensional linear sound wave propagation. Some numerical experiments are carried out for the case of acceleration. As a result, it is shown that the complex wavefront is accurately analyzed by the FDTD method compared with the ray tracing method. It is also shown that a noise disturbed by velocity disturbance in the atmosphere reaches the ground over a wider area than the focus boom in the no disturbance case.

Focusing Technique for Holographic Subsurface Radar Based on Image Entropy

2021 ◽  
Vol 36 (4) ◽  
pp. 373-378
Author(s):  
Haewon Jung ◽  
Dal-Jae Yun ◽  
Hoon Kang
Keyword(s):  
Numerical Simulation ◽  
Time Domain ◽  
Finite Difference Time Domain ◽  
Software Package ◽  
Reconstruction Algorithm ◽  
Simulation Software ◽  
Material Information ◽  
Difference Time ◽  
Actual Depth ◽  
Good Agreement

An image focusing method for holographic subsurface radar (HSR) is proposed herein. HSR is increasingly being utilized to survey objects buried at shallow depths and the acquired signals are converted into an image by a reconstruction algorithm. However, that algorithm requires actual depth and material information or depends on human decisions. In this paper, an entropy-based image focusing technique is proposed and validated by numerical simulation software package based on finite-difference time-domain method and experiment. The resulting images show good agreement with the actual positions and shapes of the targets.

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