Читать книгу Electromagnetic Metasurfaces - Christophe Caloz - Страница 14

Temporal dispersion is the property according to which the response of a medium, at a given instant of time, depends on the excitation at previous times. This can be mathematically expressed by the time-domain counterparts³ of (2.3), as

(2.5a)

(2.5b)

where only the time dependence of the fields is explicitly mentioned and the spatial dependence is omitted for conciseness. These expressions indicate that the material responses, and , are the temporal convolution of the susceptibilities and excitation functions. They may be alternatively written as

(2.6a)

(2.6b)

Since the convolution in the time domain corresponds to the multiplication in the frequency domain, the time-domain Fourier transform of (2.6) corresponds to (2.3).