Can somebody tell me exactly what is 'S' in frequency domain? I know that s=σ+jw where σ is neper frequency and jw is complex frequency but i want the precise information on s you can suggest me a book in which it is clearly explained. Thank you.
This is the way I think of it, but I may be completely wrong. Think of s as having a magnitude and phase (when expressed exponentially). If you express that rectangularly it can be seen as the sum of two orthogonal components. Call them what you will. One is the cosine component and the other is the sine component. I view complex numbers this way since the rectangular components are often difficult to visualize. Writing a polynomial with s and t allows you to express sine and cosine components that vary in time. Or, said another way, frequency and phase varying in time. If I said this incorrectly, we will soon find out :)