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The knife-edge effect or knife-edge diffraction is a truncation of a portion of the incident radiation that strikes a sharp well-defined obstacle, such as a mountain range or the wall of a building. The knife-edge effect is explained by the Huygens–Fresnel principle , which states that a well-defined obstruction to an electromagnetic wave ...
The uniform theory of diffraction approximates near field electromagnetic fields as quasi optical and uses knife-edge diffraction to determine diffraction coefficients for each diffracting object-source combination.
In applied mathematics, the Biot–Tolstoy–Medwin (BTM) diffraction model describes edge diffraction. Unlike the uniform theory of diffraction (UTD), BTM does not make the high frequency assumption (in which edge lengths and distances from source and receiver are much larger than the wavelength). BTM sees use in acoustic simulations.
Knife-edge diffraction is the propagation mode where radio waves are bent around sharp edges. For example, this mode is used to send radio signals over a mountain range when a line-of-sight path is not available. However, the angle cannot be too sharp or the signal will not diffract.
[3]: 375 Very few rigorous solutions to diffraction problems are known however, and most problems in optics are adequately treated using the Huygens-Fresnel principle. [ 3 ] : 370 In 1939 Edward Copson , extended the Huygens' original principle to consider the polarization of light, which requires a vector potential, in contrast to the scalar ...
The two-dimensional Fourier transform of an edge is also only non-zero on a single line, orthogonal to the edge. This function is sometimes referred to as the edge spread function (ESF). [9] [10] However, the values on this line are inversely proportional to the distance from the origin. Although the measurement images obtained with this ...
The most common scanning aperture techniques are the knife-edge technique and the scanning-slit profiler. The former chops the beam with a knife and measures the transmitted power as the blade cuts through the beam. The measured intensity versus knife position yields a curve that is the integrated beam intensity in one direction.
The diffraction pattern of a beam of x-rays passing through a stationary crystal. The dots are areas of constructive interference; the crystal's atomic structure can be worked out from the pattern. In ptychography, a sample (which does not need to be crystalline) is moved sequentially through the beam, creating a range of diffraction patterns.