Understanding the Multiple scattering effect

[Amartansh]

What does it mean by induced source in multiple Electromagnetic scattering by large scatterer? While solving volume source integral to model multiple scattering by large scatterers, do we consider each discrete small region as induced dipole or a point source?
Why it is a rule that these small discrete regions should be smaller than one tenth of the wavelength??

 

[Baluncore]

What does it mean by induced source in multiple Electromagnetic scattering by large scatterer?

When an EM wave encounters a conductive surface, the magnetic component induces a perpendicular current in the surface, that current produces another perpendicular magnetic field. A good conductor therefore reverses and totally cancels the magnetic field into the patch. Turning left twice is the equivalent to reflection. The current induced in the patch by the incident field is the “induced source”.

While solving volume source integral to model multiple scattering by large scatterers, do we consider each discrete small region as induced dipole or a point source?

Each discrete region can be modeled as an individual point source or short dipole at the centroid of the area.

Why it is a rule that these small discrete regions should be smaller than one tenth of the wavelength??

Consider two wire dipoles spaced λ/10. They are close enough to be excited by the same incident wavefront, to support similarly phased currents. Since the two induced currents flow in the same direction the two magnetic fields generated by those currents cancel midway between the two parallel dipoles. In effect the gap between the dipoles is blocked by that magnetic cancellation. If the dipole separation is increased, a diffraction pattern begins to develop behind the array of dipoles and they cease to behave like a good mirror and become an open diffraction grating.

 

[Amartansh]

Thanks a lot for the reply. Really, it made my day. Thanksssss a ton!
Can you tell me if I get it right:
So the reason why we want each discrete induced dipole as very small compared to wavelength (in the discrete volume source integral) is to have a continuous alignment of induced dipoles. This helps to see the effect of net re-radiated field at any measurement point without worrying about field emitted due to the diffraction between the dipoles.
Is this right interpretation?
This is certainly new perspective. Thanks a ton!
Also, I read two more reasons for same. Can you also tell me if these reasons are correct and somehow related to your explanation?

1. Each induced dipole should be << wavelength so that this discrete region appears as homogeneous permittivity region to the incident wave (I guess this means we want to avoid diffraction??).
2. The smallest dipole for which we derive EM field response is called Hertz Dipole and we assume that each induced dipole is a Hertz dipole. The derivation of radiation by Hertz dipole is derived under the assumption that current is uniform along its length and for that it length has to be very small than the wavelength.