GLOSSARY 



ACOUSTIC AXIS. Reference line adopted in transducer cali- 

 bration, usually the direction of maximum response. 



ADP. Ammonium dihydrogen phosphate crystal having marked 

 piezoelectric properties. 



A/S. Antisubmarine. 



BAFFLE. A shield used to modif) an acoustic path. 



BATHYTHERMOGRAPH. An instrument which records the 

 temperature of sea water as a function of depth. 



BDI. Bearing deviation indicator. 



BTL. Bell Telephone Laboratories. 



CAVITATION. The formation of vapor or gas cavities in water, 

 caused by sharp reductions in local pressure. 



CREST FACTOR. In this volume, V2 times the ratio of peak- 

 to-rms pressure of an acoustic wave. 



CRYSTAL TRANSDUCER. A transducer which utilizes piezo- 

 electric crystals, usually Rochelle salt. ADP. quartz, or tour- 

 maline. 



DDL Depth deviation indicator. 



DIRECTIVITY INDEX. A measure of the directional prop- 

 erties of a transducer. It is the ratio, in db, of the average 

 intensity, or response, over the whole sphere surrounding the 

 projector, or hydrophone, to the intensity, or response, on 

 the acoustic axis. 



DOME. A transducer enclosure, usual!) streamlined, used with 

 echo-ranging or listening devices to minimize turbulence and 

 cavitation noises arising from the passage of the transducer 

 through the water. 



ECHO REPEATER. Artificial target, used in sonar calibration 

 and training, which returns a synthetic echo by receiving, 

 amplifying, and retransmitting an incident ping. 



ERSB. Expendable radio sono buoy. 



HUSL. Harvard Underwater Sound Laboratory. 



HYDROPHON E. An underwater microphone. 



HYDROPHONE, VELOCITY TYPE. A pressure-gradient hy- 

 drophone. 



MAGNETOSTRICTION EFFECT. Phenomenon exhibited b\ 

 certain metals, particularly nickel and its alloys, which change 

 in length when magnetized, or, (Villari ellect) when mag- 

 netized and then mechanically distorted, undergo a corre- 

 sponding change in magnetization. 



MIT- USE. The Massachusetts Institute of Technology Under- 

 water Sound Laboratory. 



NDRC. National Defense Research Committee. 



OSRI). Office ol Scientific Research and Development. 



PIEZOELECTRIC EFFECT. Phenomenon, exhibited by cer- 

 tain crystals, in which mechanical compression produces a 

 potential difference between opposite crystal faces, or, an 

 applied electric field produces corresponding changes in di- 

 mensions. 



PING. Acoustic pulse signal projected b) echo-ranging trans- 

 ducer. 



PPI. Plan position indicator. 



PRESSURE-GRADIENT TRANSDUCER. Transducer, such 

 as a moving-ribbon hydrophone, in which the moving ele- 

 ment responds to pressure difference rather than to pressure. 



PROJECTOR. An underwatei acoustic transmitter. 



RADIO SONO BUOY. A buoy listening device that contains a 

 hydrophone lor receiving target signals and a radio trans- 

 mitter for relaxing the signals to patrolling air or surface 

 craft. 



RANGE RALE. Rate of change of range between own ship 

 and target. 



REAR RESPONSE. The maximum pressure within ±60 <le 

 grees from the rear of the transduce! in db relative to the 

 pressure on the acoustic axis. 



ROCHELLE SALT. Potassium sodium tartrate (KNaC 4 H 4 () |; • 

 IH..O) piezoelectric crystal used in sonar transducers. 



SCANNING SONAR. Echo-ranging s\stem in which the ping 

 is transmitted simultaneously throughout the entire angle to 

 be searched, and a rapidly rotating narrow beam scans for the 

 returning echoes. 



SEARCHLIGHT-TYPE SONAR. Echo-ranging s\stem in 

 which the same narrow beam pattern is used for transmission 

 and reception. 



SONAR. Generic term applied to methods or apparatus that 

 use SOund for NAvigation and Ranging. 



SPTLI. Split projector test unit. 



TRANSDUCER. An) device for converting energy from one 

 lorm to another (electrical, mechanical, or acoustical). In 

 sonar, usually combines the functions of a hydrophone and a 

 projector. 



LTSRL. Underwater Sound Reference Laboratories. 



X-CUT. A cut in which the electrode faces of a piezoelectric 

 crystal are perpendicular to an X or electrical axis. 



\-CUT. A cut in which the electrode faces of a piezoelectric 

 crystal are perpendicular to a Y or mechanical axis. 



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