PATH LENGTH 7.6 

 LEAD ZIRCONATE 

 LEAD METANIOBATE 



Fig. 5. Multiple reflections. 



FACES PARALLEL 



2° ANGULAR DISPLACEMENT 



4° ANGULAR DISPLACEMENT 



Fig. 6. Pulse shape with nonparallel transducers. 



receiver at "35 inches." In other words, a 

 reflected signal passing through the system 3 

 times arrives at the receiver 2 electronic time 

 delays before the third succeeding transmission. 

 This reflection must be minimized and the thresh- 

 old adjusted well up on the pulse front to avoid 

 errors due to this reflection. 



Photographs of these reflected signals are 

 shown in Fig. 5- The top line shows the attenu- 

 ation with the path length reduced to one-third 

 the normal length for purposes of illustration. 

 It can be seen that the reflections are only 

 about 6 or "? db less than the desired signal. 

 In the bottom line the normal path length is used 

 and it is seen that the signal is roughly 18 db 

 below the desired signal. With the conventional 

 pulse shape the reflections from the large center 

 portion of the pulse are a serious source of 

 interference to the smaller "signal" cycle which 

 came earlier in the pulse. With either of the 

 improved pulses shown, reflections should not be 

 a serious problem. 



The preceding illustrations have been pre- 

 pared with the transmitting and receiving trans- 

 ducers accurately aligned. If angular misalign- 

 ment is introduced, a change in the pulse shape 

 will result as shown in Fig. 6. The effect of 

 even a very small displacement is seen to produce 



SYSTEM 27°C 



I4°C 



Fig. 7- Effect of temperature. 



PATH LENGTH 7.6 

 LEAD ZIRCONATE 

 LEAD METANIOBATE 



SYSTEM PSIG 



TEMPERATURE 85°C 1000 PSIG 

 2000 PSIG 

 3000 PSIG 

 4000 PSIG 



Fig. 8. Pressure effect. 



a considerable lengthening of the pulse rise time 

 as well as causing a serious reduction in signal 

 amplitude . 



Considerable stress has been given to the fact 

 that the attenuation in the acoustic path 

 increases as the temperature is lowered. This 

 problem is illustrated in Fig. 7- We see, how- 

 ever, that the pulse amplitude was reduced by 

 about 3 db as the temperature was reduced from 

 27°C to 3°C. It should also be noted that no sig- 

 nificant change in the rise time occurred. 



Similar tests were made to determine the effect 

 of hydrostatic pressure. Photographs taken of 

 the waveforms observed during this test are shown 

 in Fig. 8. Unfortunately these tests were made 

 in paraffin oil, about which our knowledge as to 

 the acoustic attenuation as a function of pres- 

 sure is even more nebulous than for sea water. 

 There is, however, no indication of any change 

 whatsoever in the pulse shape or amplitude. This - 

 test was carried to 10,000 psig with no change 

 noted. 



THE WIDE BAUD AMPLIFIER 



With these facts in hand it appears that we 

 now have the basic knowledge required to effect 



160 



