Back-scatter by dielectric spheres (Refractive index approx 1.6

Two independent sets of experimental results are presented on the back-scatter from plexiglass spheres. These are compared with theoretical computations for refractive indices m = 1.60, 1.61 and 1.61-0.0025i. For (ratio of perimeter to wavelength) , the upper limit of the experimental data, the theoretical values are practically identical to one another and agreement with experiment is excellent. For , the theoretical values diverge from one another. The small absorption coefficient has an increasingly important effect as the spheres grow larger, but even at , the cross section remains above its asymptotic value. Except for the interval , plexiglass spheres have larger cross sections than metal ones between . This is due to the focusing action of the dielectric sphere and the back surface reflection.