Experiment was done by using an oscilloscope and a piezoelectric transducer to generate ultrasonic sound waves. We had to move the transmitter whilst receiver remains constant on a angled 1 meter track or vice versa.

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As you change the separation between the transmitter and the receiver, one signal changes in size and the other remains the same. Which one of these signals changes? What causes this change in amplitude? Why does one signal remain the same?

And that is the question I don't understand.

I believe signal generated with a piezoelectric transducer was fed to the oscilloscope with the signal collected by the sensor (receiver). And the one collected with the sensor was the one that changed. (I don't know why. Maybe because of energy lost?)

Also I have used this formula A = D/f to calculated the amplitude. 5.0X10^-6 m (5.0X10^-6 = 0.18 / 35950) Does this sound reasonable? With this amplitude I believe its enough for the signal to bounce off the receiver and transmitter and cause constructive and destructive interference. (Approx. receiver radius of 1.5 cm, transmitter 1.5 cm+)

  • $\begingroup$ Can you draw a diagram of the experiment. I'd guess you're measuring constructive and destructive interference, but exactly how this is happened depends on the geometry you're using. $\endgroup$ – John Rennie May 10 '14 at 7:41
  • $\begingroup$ @JohnRennie I have added a diagram as requested. $\endgroup$ – user45699 May 10 '14 at 7:49
  • $\begingroup$ I'd be surprised if you could generate a standing wave with that geometry. Still, if the receiver amplitude oscillates up and down as you move the transmitter that is probably the reason. If the signal falls monotonically with distance it's just the inverse square law decay of amplitude with distance. $\endgroup$ – John Rennie May 10 '14 at 8:03
  • $\begingroup$ @JohnRennie Have I calculated the amplitude correctly? If so it is most likely that the signal is reflecting off the transmitter and the receiver right? $\endgroup$ – user45699 May 11 '14 at 9:56

Channel 2 changes in size, Channel 1 does not.

The former follows from of the inverse square law, and the latter follows because Channel 1 is a direct line to the signal generator output.

  • $\begingroup$ Could you please explain why it follows the inverse square law? $\endgroup$ – user45699 May 10 '14 at 12:08
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    $\begingroup$ @user45699: Can you hear me talking to you if I'm 5 miles away? If not, then why not? That's all you need to know to answer this question, no formulas needed. $\endgroup$ – DumpsterDoofus May 10 '14 at 12:12
  • $\begingroup$ The sound waves are propagating omnidirectional way. The definition reduces in a inverse square law. Thank you. Haha how did I not thought of this. $\endgroup$ – user45699 May 10 '14 at 12:15
  • $\begingroup$ for second question, ultrasonic waves are bouncing off the transmitter and the receiver, resulting constructive and destructive interference right? $\endgroup$ – user45699 May 11 '14 at 9:54

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