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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



Fig. 10 — The pattern of the slant plate lens of Fig. 9 when enclosed in a horn (vertical 



plane)./ = 9 KC. 



Fig. 11— The horizontal plane pattern of the horn and lens of Fig. 10. / = 9 KC. 



In some acoustic investigations it is desirable to have a source of plane 

 waves of extended area. Figures 10 and 11 show that a shielded acoustic lens 

 provides a simple way of achieving this result. The broad band nature of 



