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
\alpha
(ratio of perimeter to wavelength)
\leq 7.5
, the upper limit of the experimental data, the theoretical values are practically identical to one another and agreement with experiment is excellent. For
\alpha >7.5
, the theoretical values diverge from one another. The small absorption coefficient has an increasingly important effect as the spheres grow larger, but even at
\alpha \simeq 100
, the cross section remains above its asymptotic value. Except for the interval
30< \alpha <40
, plexiglass spheres have larger cross sections than metal ones between
6 < \alpha < 60
. This is due to the focusing action of the dielectric sphere and the back surface reflection.