20 Lab 5 – Principles of Ultrasound

Acknowledgment

This project is made possible with funding by the Government of Ontario and through eCampusOntario’s support of the Virtual Learning Strategy. To learn more about the Virtual Learning Strategy visit: https://vls.ecampusontario.ca.

PHY255 Stay-At-home Experiment 5

Principles of Ultrasonic Imaging

Theoretical Background

In this experiment, we will use the phone to generate sound “chirps”, send them through the speaker of the phone, and detect the echoes of the chirps from nearby surfaces. A correlation computation is then completed in the background of the app to find the timing at which the echoes return to the phone. The timing can then be multiplied by the speed of sound (then divided by 2) to retrieve the distance at which the echoes happened.

Due to the fact that sound usually travels in every direction, when you do your measurements, you not only get reflections from your target object, but also from the floor, the ceiling, all walls nearby, and other obstacles with hard surfaces nearby. It is then up to you to interpret the result and decide which reflection corresponds to the target object. You may try to use some foam or soft material to screen as many other directions of the phone as possible. (For example, you may wrap your phone loosely in a blanket – just make sure not to muffle the microphone.)

It is also possible that your phone has multiple speakers and multiple microphones. You can search online for the location of speakers and microphones for your phone to find out. If your phone has more than one speakers, you should muffle all the speakers that you do not wish to use.

What you will need:

• A smart phone installed with the Phyphox app
• Another device that is capable browsing internet through WiFi (such as a laptop, a tablet, or another smart phone)
• 2~4 meters of empty and quiet space (if you do not have enough space at home, you can come to UTM.)
• Two objects with different sizes and flat-and-solid surface (such as a hard cover book, a cardboard box, or a wood/metal box).
• A tool to measure distance. If you do not have a ruler or a tape measure, you can use an object with a known length (for example, a piece of letter size paper has a length of 279mm, a piece of A4 paper has a length of 297mm).

Procedures:

1. In the Phyphox app, click on the “Sonar” sensor.
2. On the other device, use the web browser to remotely access (watch this video about how to start remote access) your Phyphox app, and then select the “Echo Location” tab
3. Search online and find the location(s) of the speaker(s) of your phone.
4. Place the phone on the floor (or some other flat surface) with the speaker facing forward and with a few meters of empty space in front of your phone.
5. Turn up the volume of the speaker of the phone to about half of the maximum.
6. Use your other device to remotely control your phone from at least 2 meters away (if possible, you can go to a different room) so that your body is not interfering with the measurement.
7. Make sure the speaker of the phone is facing a mostly empty space. Start a measurement of sonar. As the measurement is running, you can use your mouse to read the data from the graph. Note down the locations and amplitudes of all the peaks that are showing on the “Echo Locations” plot. Also measure the amplitude at a location where there is not apparent peak. The peaks and the base level will be your detection background noise.
8. Place the larger object at 7 or more different distances to the phone where there are no background peaks. For each placement, measure the actual distance, and note down the locations and amplitudes of the peak that is corresponding to your object on the “Echo Locations” graph.
9. Place the smaller object at 7 or more different distances to the phone where there are no background peaks. For each placement, measure the actual distance, and note down the locations and amplitudes of the peak that is corresponding to your object on the “Echo Locations” graph. If you do not see a significant peak, you should move the object closer until you see a peak.
10. For each object, compare the actual distances versus measured locations. Is the sonar more accurate for the larger object?
11. For each object, plot the amplitude (clarify the definition of amplitude) of the peak versus the echo location. If you notice outliers in your data, redo a measurement at that location. Does the general shape and trend of the plot match your expectations? Briefly explain.
12. From your amplitude-location data, figure out the empirical power-law relation (i.e., in the form of ) between the amplitude of the peak and the echo location. Propose an explanation of the exponent (i.e., the parameter ) in your power law.
13. Using the amplitude-location plot and the background noise to estimate the limiting distances at which your phone will not be able to detect each object with sonar.
14. *If you have enough space*, place the object at the calculated limiting distance, and run the sonar again to verify your calculations.
15. Divide the size of the object by the corresponding limiting distance to get the angular resolution of the sonar (in radians). Does the angular resolution values calculated from your two objects match each other?
16. If you increase the volume of the phone, will the angular resolution improve? Verify your prediction with a simple measurement.
17. Suppose you can increase the volume indefinitely. Do you think you can achieve an arbitrarily precise angular resolution? Why or why not?
18. Switch to the “Chirp” tab in the “Sonar” sensor, and you will see the waveform of the chirps. This chirp is not a simple harmonic function. Do you think we can replace this chirp waveform by a short segment of sine wave to detect objects? Why or why not?

Requirements of the experimental report:

• Font size: 12
• Line spacing: 1.5
• Only write these sections: Results, Discussions, and Suggestions of improvement.
• Total marks: 20/20
• Results (15/20):
  • Complete all the calculations that are required in the procedures above.
  • Answer all the questions and briefly explain your reasoning.
  • Show sample calculations.
  • Attach graphs or tables when necessary.
  • If you write a program for calculations, attach the code in the appendix.
• Discussions (5/20):
  • Identify the sources of error in your measurements.
  • Feel free to do more tests to verify your claims if possible.
  • Make a reasonable conclusion based on your results.
  • Compare your results with other sources (and add citations).
• Suggestions of improvement (+2 bonus; total marks capped at 20/20):
  • What other quantities can be determined with the same experimental design?
  • What can be done to reduce the uncertainties at no cost while staying at home?
  • Did you enjoy this experiment? What are the aspects that you dislike the most about this experiment?
• No page limit. But please try to be straightforward and concise!
• Join the classmates on the course discussion board!
  • Ask specific questions related to experimental procedures or calculations. (Remember to thank the student who helped you the most!)
  • If you understand the issue, try to answer the questions from other students without directly instructing them what to do.
  • The student who helped others the most (judging by the number of “thanks”) will be awarded with +1 bonus! (total marks capped at 20/20)