Interference phenomena transmissivity

UVA S/NIR Spectroscopy. In previous work witii ZnS c-s particles, we observed oscillations in tire UV/WS spectrum caused by interference patterns between the shell and core materials. (11) The phenomenon is a result of the difference in refi active index between the two layers. Such behavior is predicted by Mie light-scattering theory ch can be used to calculate shell thickness and refiactive index from UVA S data. (22) Oscillations increase in anplitude and the transmission window undergoes a red shift as these properties increase in magnitude. 

This phenomenon is termed free diffusion. Statistical considerations indicate the possibility of calculating the concentration of the diffusing particles with a given initial situation as a function of space and time. Assume that no force effects exist between the suspended particles and the molecules of the solvent, but only that occasional transmissions of collision momentum occur, and further, that the particles do not interfere with each other s movements and are very small in comparison with the dimensions of the vessel in a unidimensional diffusion process, we obtain, for the probability dW that at a time t a particle will be encountered in the plane between x and x + dx, the relation... 

Multipath transmission The propagation phenomenon that results in signals reaching the receiving antenna by two or more paths. When two or more signals arrive simultaneously, wave interference results. The received signal fades if the wave interference is time varying or if one of the terminals is in motion. 

Disturbance current The unwanted current of any irregular phenomenon associated with transmission that tends to limit or interfere with the interchange of information. 

A material absorbs ultrasonic energy at a different rate for different frequencies. A constructive use of this phenomenon is ultrasonic spectroscopy, covered in the next section. Another consequence is that a single spike pulsed into the sample for time-of-flight measurements is distorted during transmission. This makes it difficult to time the interval between echoes precisely. A continuous sine wave is a single frequency, but it interferes with itself upon reflection. A compromise is found in a tone burst, a sine wave applied for a short time. 

Color, however, is a very complex phenomenon. Objects can modify light not only by reflectance and selective absorption, as we have seen, but also by transmission, scattering, dispersion, interference, etc.—sometimes all at once. It is the combination of all these possible interactions which ultimately determine the appearance of an object. 

Another interesting feature of the Q-hmctions in Fig. 3.8.3 is a small-amplitude ripple superimposed on each of the main curves. This ripple appears to be the result of interference between the Fraunhofer diffraction peak and a surface wave that takes occasional short-cuts through the particle just under the outer boundary. Because this phenomenon depends on unattenuated transmission to maximize the amplitude of the ripple, the strongly absorbing medium in Fig. 3.8.4 fails to show a corresponding effect. 

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