INTRODUCTION 



The advent of deep- running nuclear submarines has 

 brought about an urgent need for greater detection ranges 

 and, consequently, a requirement for new and improved 

 raeans of generating sound underwater, at increasingly 

 lower frequencies. This requirement has increased the 

 size and cost of sonar equipment, and sonar advances to date 

 have been considerably dependent upon transducer construc- 

 tion. As the number of transducer engineers is somewhat 

 limited, it has been necessary to concentrate most of their 

 efforts on established techniques. However, it has been 

 recognized that some investigation should be directed 

 toward unconventional methods of generating sound, 

 particularly in the low-frequency region. Accordingly, 

 the Bureau of Ships established a problem to investigate 

 novel sound sources. The personnel at NEL assigned to 

 this problem were all experienced in the field of generating 

 high-power signals, and had previously conducted inter- 

 mittent studies of the underwater spark as a sound source. 

 Thus it was logical to use this technique as a point of 

 departure in undertaking the new assignment. Although 

 other government laboratories no longer were exploring 

 this approach, a study was made of previous work by 

 others before the study was resumed at NEL. 



Work with the underwater spark at this laboratory 

 prior to May 1956 has already been reported. ■'• The early 

 work had clearly indicated that much of the success of the 

 spark source was directly related to the electrodes and 

 the geometry of the gap. It was therefore decided that this 

 particular phase would be studied thoroughly, leaving major 

 power increases to later. 



A number of other techniques, such as exciting metals 

 into vibration by contact with solid carbon dioxide, or vibra- 

 ting wires, reeds, plates, etc., have been given limited 

 trials, but have not been explored sufficiently to warrant 

 reporting at this time. The work on novel sound sources is 

 continuing. 



"Underwater- Spark Sound Source, " by L. R. Padberg, Jr. 

 (Article 32 in NEL Report 698, Lorad Summary Report , 

 CONFIDENTIAL, 22 June 1956) 



