Curvilinear arrays

FIGURE 25.9 Steering by element selection for a curvilinear array. The beam will shift to a new location as the center of the active aperture is shifted over the entire airay. 

As the process of steering and focusing is repeated for a sequence of look angles, a sector-shaped image data set is acquired. The line density available from phased-array scanners is not as restricted as with curvilinear arrays, but some limitations exist in certain systems, due to the relatively large size of delay increments available in tapped delay lines. Heterodyned systems and digital beam-formers have less limitations in this area. 

The dislocation method of stress analysis is also useful for determining craze stress fields in anisotropic (e.g., oriented) polymers . All one needs here is the stress field of a single dislocation in a single crystal with the same symmetry as the oriented polymer (the text by Hirth and Lothe provides a number of simple cases plus copious references to more complete treatments in the literature) the craze stress field can be generated by superposition of the stress fields of an array of these dislocations of density a(x). Dislocations may also be used to represent the self-stress fields of curvilinear crazes (produced by craze growth in a non-homogeneous stress field for example). Such a method has been developed by Mills... 

The following example utilizing a ray-tradng program illustrates how an array of fixed lamps can produce relatively uniform irradiation of a curvilinear surface. 

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