For doing this, time shifted Gaussian wave is to be constructed so that the value of the waveform is zero at zero instant of time. Therefore the source should also be zero at t = 0. One thing to be noted here is that for FDTD simulation, field values are initialized as zero. Once г corresponding to the maximum frequency is known, it is possible to construct the Gaussian wave for the FDTD simulation. A Gaussian wave as a function of time can be expressed asįlere г determines the width of the Gaussian pulse and related with maximum frequency component as One may set the highest wavelength larger than 20 cell size to obtain a reasonably accurate result (to be discussed later in numerical dispersion section). For simulation, the cell size of the problem space and the highest wavelength of the source waveform plays an important role. Gaussian WaveįDTD simulations should provide the numerical results for all the wavelengths present in the spectrum. The field in the time domain is captured and frequency-domain response can be obtained by the Fourier transform of the captured field. In this chapter, either modulated Gaussian or Gaussian pulses are used for simulations to investigate the scattering characteristics of periodic structures.
The wavelength spectrum of the source waveform must include all the wavelengths of interest for the simulation. In general, waveform is selected depending on the problems under consideration. It is the source that excites electric and magnetic fields as a function of time. For FDTD simulation, sources are one of the necessary and important parameters which demand special attention.
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