Discussion on the field and power definition in finite-size object scattering problem

In some applications, such as the emissivity calculation of finite object, incident power, scattering power and absorbing power must be known. However, when calculating these powers from the corresponding fields defined conventionally, we may get incorrect result of the emissivity. The reason is that the powers calculated from the conventional defined incident and scattering fields are not coincide to physical regularity, although the field definition itself is theoretically correct. The property of existing everywhere and with uniform amplitude of the conventionally defined incident field leads to a very strong forward scattering field of finite object. This actually is not reasonable considering from the physical angle. In order to solve this problem, a new definition system for incident and scattering fields regarding the finite-size object scattering is proposed. By the new definitions, both the fields and powers have clear physical meaning, and the problem existing in the conventional definition system can be solved.