Then you drop one element off from one end, put another element on at the other end, infront of the group, and advance the active group along the array in this way. When i was doing this i was totally unaware that it would work. I hope it would work, but i was worried that there would be cross-coupling from the end elements of the group into what should have been passive elements, so that you might not be able to get a well-defined active aperture. But it did work, and that proved to be the way forward, because you could make finer and finer elements and get more lines into the array........ "  -- tony whittingham, describing his work in real-time imaging in the mid 1970s. ^ images of the earlier models were nevertheless hampered by the problems of small crystal size, lobe artifacts, unwanted specular reflections, low dynamic range, unsatisfactory lateral resolution and image noise from electronic processing. There was an overwhelming need for the refinement of beam characteristics. Fredrick (fritz) thurstone , olaf von ramm and h melton jr at the duke university published some of the earliest and most important work on electronic focusing using annular arrays ('71-'74), both on transmit and receive. Similar techniques were subsequently employed in the design of linear arrays transducers. Basing on these designs, a number of centers and private laboratories were starting to embark on making machines geared to examination of the abdomen. Albert macovski at the standford university filed a patent in 1974 for a circular array where the elements generate dynamically focused beams that could also be swept through space by adjusting the delays to the array. This was one of the more advanced designs in dynamic focusing techniques. Another important design - "signal processor for ultrasonic imaging" was described by the william beaver group of the varian associates® in palo alto in california in 1975 where selection of scan angles and focusing distances were effected. George kossoff in australia also filed a patent in 1973 on a linear array system incoporating phased-focusing electronics. viagra for sale buy viagra buy generic viagra viagra without a doctor prescription buy viagra online viagra without a doctor prescription viagra online cheap generic viagra generic viagra online cheap viagra online A summary of the advances in design can be found with m maginness's article (at stanford) "state-of-the-art in two-dimensional ultrasonic transducer array technology" in 1976. It was martin h wilcox , founder and engineer at the advanced diagnostic research corporation (adr®, a company founded in 1972 in tempe, arizona), who designed and produced one of the earliest commercially available models of a linear-array real-time scanner in 1973 and very much set the standard for subsequent designs to follow. The array contained 64 crystals in a row (3 times the number in the earlier cardiac counterparts and 3 times as long and wide), fabricated with the best material available and in the best accoustic configur.

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