Mid‐Field Forward Scattering
作者:
C. I. Beard,
T. H. Kays,
V. Twersky,
期刊:
Journal of Applied Physics
(AIP Available online 1962)
卷期:
Volume 33,
issue 9
页码: 2851-2867
ISSN:0021-8979
年代: 1962
DOI:10.1063/1.1702565
出版商: AIP
数据来源: AIP
摘要:
Experimental and theoretical results are given for forward scattering by spheres with radius large compared to wavelength, and with index of refraction &eegr; near unity. Both the intensity and phase of the scattered field (relative to that incident) are measured and computed for several spheres as functions of the separations of transmitter and receiver from the scatterer (sayTandR). The scattering function of primary interest is that which reduces to the usual scattering amplitude in the limit of transmitter and receiver essentially at infinity—say, the functionFsuch thatF→f0asTandR→∞. Differences betweenFandf0arise from ``quadratic phase error'' terms involving not only the apertures of the horns, but also the size and dielectric properties of the scatterer. In the ``mid‐field region,'' where the sphericity of the wavefronts is significant, the magnitude of the corrections introduced inFis of the order of Imf0, and Imf0itself is an order of magnitude smaller than Ref0; consequently, although the ``finite geometry'' has only a second‐order effect on the forward intensity |F|2, it has a first‐order effect on the forward scattered phase arc tan[ImF/ReF]. In addition, since Imf0is proportional to the total scattering cross section, the sphericity of the wavefronts has a first‐order effect on the intensity integrated over all angles. Differences of a hundred percent in the phases ofFandf0may be encountered even in measurements for whichTandRfulfill the usual ``far‐field criterion.'' However, approximations for the far‐field phase may be obtained by extrapolating measurements for several values ofTandRin the usual laboratory geometry.
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