OLVINA - Activity 1 (Sonar) [PDF]

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EXPERIMENT NO

.5

SONAR OBJECTIVES  To demonstrate sound propagation with the use of sonar.  To interpret data with the use of statistical methods on dealing with errors. BACKGROUND Sonar (sound navigation and ranging) is a technique that uses sound propagation for navigation, object detection and mapping. There are two types of sonar, passive sonar: listening for incoming sound, and active sonar: transmitting sound pulses and receiving echoes. Active sonar is what will be used in this activity with the use of your mobile phone (speaker and microphone) as illustrated in Fig. 1.

Fig. 1. Illustration of sound propagation (transmission and reflection).

To measure the distance of an object using sonar, the time from pulse transmission to reception is measured and converted into a range using the known speed of sound (343 m/s), and it is given in this relation: . Last Modified: Oct. 2020 by P.M. Ong. For DLSU use only. NOT FOR CITATION, SALE, NOR REDISTRIBUTION.

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Where as the speed of sound in air (343 m/s), t as the time of pulse transmission to reception, and as distance of an object. The total distance traveled by the sound wave is 2 , i.e., from transmission to reception. More background information about this experiment can be found in your Phyphox App in the “Experiment info” of the “Sonar” experiment under the “Acoustics” section. And you may visit this wiki page: https://phyphox.org/wiki/index.php/Experiment:_Sonar to know more on the possible problems that you will encounter and recommended resolutions. MATERIALS / TOOLS  Mobile phone with Phyphox mobile application  PC / Laptop (control/monitor and plotting: https://phyphox.org/remote-control/)  Box / echo shield for the mobile phone (e.g. foam, box container that can fit your mobile phone, which shields all directions from phone except the speaker and microphone location). NOTE: Try different materials with different sizes, which will show minimal noise (unwanted ripples or peaks) in your graph.  Sound reflector material (i.e. hard and flat material; e.g. tray)  Measuring tape  Support for the reflector that will hold it in a vertical position (optional) PROCEDURE Preliminary: •

Watch the video on how to use your smartphone as a sonar for this experiment in this link https://www.youtube.com/watch?v=Ebj3v701HE0&feature=youtu.be.

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Since you are going to use your mobile phone as sensor in this experiment, you need a second device (such as a laptop or tablet with internet browser) as control and monitor screen. Instructions can be found in this link https://phyphox.org/remotecontrol/ and connection instructions in this link https://www.youtube.com/watch?v=mPUHCW ypn9M.

Do this experiment on a flat surface (e.g. floor). 1. Under the Phypox app, connect your mobile phone with your laptop or tablet (instructions can be found on the second and third links under the Preliminary section). This second device would serve as your monitor and control during the duration of this experiment. If you do not have a second device, you would need a support stand for the target so you can do this experiment. 2. Place your mobile phone inside the box. Making sure that the microphone (receiver) is placed facing the box opening. Last Modified: Oct. 2020 by P.M. Ong. For DLSU use only. NOT FOR CITATION, SALE, NOR REDISTRIBUTION.

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Fig. 2. Sample setup [3].

3. Spread the measuring tape in such a way that it will be convenient for you to manually measure the distance from your mobile phone to the flat object (to echolocate). The mobile phone microphone (receiver) is assumed to be the reference point. Take note of the predefined distances in your data sheet. Sample setup configuration is shown in Fig. 2. 4. Take a photo of your setup including the flat object as target. You may use some marker in place of your mobile phone so you can use your mobile phone’s camera. 5. Under the “Echo Location” tab, make sure that the correct speed of sound (343 m/s in air) is entered. 6. You will refer to the “Normalized to spherical surface” plot to check the distance of your target. Once measuring, the highest peak on the graph should correspond approximately to the actual distance of the target. Some small ripples (unwanted peaks) may be present as noise depending on how good your setup is and on your environment noise level. TIPS: •

Check if your setup is good enough by pressing the “start” button to start acquiring data and placing the target object near your phone. Gradually increase the distance of your target object from your phone and check if you are getting the correct distance peak with smaller noise (unwanted ripples).

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You may want to change your box or do the experiment with lesser environmental noise if the data is still too noisy (meaning, many unwanted ripples or peaks are still present that it makes it too hard to distinguish the main peak, i.e., the supposed target’s location). Remember that the sound is moving in 360˚ direction, and the type of material and size of the material used as barrier are important. Also, since

Last Modified: Oct. 2020 by P.M. Ong. For DLSU use only. NOT FOR CITATION, SALE, NOR REDISTRIBUTION.

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you are measuring reflected sound waves, noisy environment could affect your measurement. 7. Once you have achieved a setup with minimal noise, press the “Timed Run” option to set the desired “Start delay(s)” time and “Experiment duration(s)”. TIP: •

The delay should be enough time before you expect the measurement to begin, and the experiment duration should be enough time so you will get a good approximate peak at the target’s location (reference: actual distance). Configure several times to optimize your setup. As an example – delay: 3 s, experiment duration: 10 s.

8. Place your object at the initial distance (50 cm) and start your data collection. 9. After your measurement, tap the “Normalized to spherical surface” plot. Select the “Pick data” and pinpoint the main peak to know the measurement value of the object’s distance. 10. Record your result and print-screen your plots from the Phyphox App both from “Echo Location” and “Timing” tabs. Do this for every remaining distance mentioned: 100-250 cm at 50 cm interval. REFERENCES 1. R.W.T.H.A. University. Phyphox [Online]. Available: https://phyphox.org/download/. 2. R.W.T.H.A. University. Phyphox [Online]. Available: https://www.youtube.com/watch?v=Ebj3v701HE0&feature=youtu.be. 3. J. Lopez, Sonar experiment. DLSU, 2020.

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OLVINA, Timothy Fenol __________________________________________________ __________________________________________________ __________________________________________________ October 31, 2021 Date Performed: __________________________________________________ General Physics Laboratory 2 T-STEM 12-G2 Course Code & Section: __________________________________________________

Names:

DATA SHEET 50

100

150

Distance* obtained from Phyphox (cm)

70.74

70.39

234.17

324.06

364.08

% Error

41.48

29.61

56.11

62.03

45.63

Distance (cm)

200

250

*Distance of the target object, which is ideally the main peak or highest peak from the graph. A. Insert the image of your setup. Experimental Set Up [Procedure]

Materials Experimental Set Up [Contents of the Box]

B. Insert the print-screened plots of your result from Phyphox (echo location and Timing). NOTE: For the complete set of screenshots, please open the files uploaded in the GDrive for better quality. Thank you ! [Results] 100cm

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GDrive for Results:

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https://drive.google.com/drive/folders/1DvBVNhElnH C2PyS01bBjrgQQ8Rd9q8ZB?usp=sharing

QUESTIONS 1. Is the measured distance (Phyphox) differs from the actual value? Elaborate your answer and include the discussion of errors (if necessary). In the researcher's rendition of the Physics experiment, the measured distance by Phyphox differs from the actual value. The most probable cause would involve the environmental error. Though the researcher chose to conduct the experiment in the night to prevent the occurence of noise from passing mechanisms, the researcher encountered unprecedented hindrances during the 5 trials. Furthermore, instrumental error may have played a role of inaccurate readings from the experiment. During the experimentation, there was no procedure dedicated to the calibration of the phone to adapt to the researcher's environment. By "adapt," the device was not able to mute the background noise and only trigger upon hearing the "chirp" noise. Lastly, though may not be as significant as the other two, human error was part of the reason of accumulating high percentage errors for all trials. The measurement of the distance between the reflector and the sound systemmay have been off slightly.

2. From the relationship between (sound) velocity ( ), distance ( ) and time ( ) in Eq. 1, solve for the total time it takes for the sound waves (chirp) to travel from your phone to your target at 100 cm and back to your phone. Use both your measured data and actual data and get their % difference. Be mindful of the unit of measurement(s) used. Provide your analysis by comparing this result with the “Timing” result of the 100 cm data. General Formula for Total Time: Total Time = [ 2 * (d / 100) ] / v (a) The laboratory teacher defined the speed of sound v to be 343m/s. Distance d has the value of 100cm or 1m; hence, the total distance is 2m. In essence, the total time for this situation would be 0.005831s (b) On the other hand, the experimental value for total time for the researcher's attempt at the experiment with a distance of 100cm is 0.004104s. Hence, the percentage error is 29.62%. (c) From the screenshot provided, the total time that the experiment had occured was approximately 0.004s, which is a close approximation from the value obtained from letter (b). The researcher deduced this since the peak of the line graph entitled "Normalized to Spherical Surface" was located at, if not near, that point

3. An ocean vessel using sonar sends a sound wave to the bottom of the sea and receives an echo after 0.3 sec. Assume a speed of sound in water to be 1480 m/s. Calculate the depth of the sea.

The resulting solution would be " d = [(0.3 * 1480) * (100 / 2)], " and the aforementioned equation resulted with 22,200m. Hence, the depth of the sea is 22,200m after receiving an echo after 0.3s, assuming that the speed of sound in water is 1480m/s.

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4. A ship sends an ultrasound to the bottom of the ocean floor at 2,618 m from the surface. The ultrasound speed in water is about 1531 m/s. Calculate the time taken by the sound waves to get reflected to the surface. Given the situation, the researcher evaluated the solution to be " t = [(2 * 2618) / 1531]." Consequently, the research evaluated the equation and concluded that it would take 3.42s for the sound waves to get reflected to the surface.

5. Whenever a wave is used as a probe (e.g. ultrasound), it is difficult to detect target details that is smaller than the wave’s wavelength, . Higher frequency ultrasound would allow greater detail, but it lessen the penetration depth compared to lower frequencies. The acceptable effective scan depth is about 500 into a tissue. (A) Calculate the minimum frequency of ultrasound that will allow you to see details as small as 0.250 mm in human tissue given the speed of sound in tissue is about 1540 m/s. (B) What is the effective depth to which this sound is effective as a diagnostic probe? Review:

where : speed of sound in a medium, f : frequency.

(a) Given the relationship triangle of speed, frequency and wavelength, the researcher came up with the equation " f = (1540 / 0.250)." Hence, the researcher concluded that the minimum frequency of ultrasound to see details as small as 0.250m is 6,160,000 Hz. (b) There is a rule stating that one can effectively scan into a tissue at depth of "500 times the wavelength" (LumenLearning, n.d.). Therefore, the researcher deduced that for this scenario, the effective depth would be 12.5cm. Reference: LumenLearning (n.d.). Ultrasound. https://courses.lumenlearning.com/physics/chapter/17-7-ultrasound/

FEEDBACK (nongraded): If you observe high level of unwanted ripples (noise) in your measurement, what do you think is/are causing them? Do the barrier’s properties (i.e. type and size) affect your data? Or is it more of the background noise level? Elaborate your analysis. The main contributor to high level of unwanted noise is the experimental site and set-up. While doing his rendition of the experiment, the researcher noticed that at an elevated platform, the Phyphox software rendered a closer experimental value when compared to when the device was flat on the floor. Furthermore, under the advice of the researcher's instructor, the researcher noticed fairly better results when the reflector was repaced from a carton box into a sturdy picture frame. However, despite the researcher's efforts to improve the results, it proved to be futile as the percentage error throughtout the 5 distances were significantly high... Last Modified: Oct. 2020 by P.M. Ong. For DLSU use only. NOT FOR CITATION, SALE, NOR REDISTRIBUTION.

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