上海交通大学：《物理实验》精品课程教学资源（讲义）8 Interference of Ultrasonic Sound Waves

Experiment8.Interference of Ultrasonic Sound Waves OBJECTIVES 1.To observe the interference and diffraction phenomena with ultrasonic sound waves,and uncoverthe law of wave intensity distribution. 2.To observe and study on the ultrasonic beat. 3.To master the principle and the method of Gassy Leb computer measurement and data analysis system. PRINCIPLE The interference and diffraction of coherent(same phase)ultrasonic sound waves,and the principle of ultrasonic sound wave beat are similar to the related phenomena of light. Beats of Ultrasonic Sound Waves Two ultrasonic sound waves of different frequencies interfere with each other and produce the beats of ultrasonic sound waves.Consider two sound waves of same amplitudes and different frequencies, YA=AoSin(2mfat)and YB=AoSin(2ft).Their synthesis wave is exactly Y=2 AoCos〔π(E-fa)t)Sin〔2πt(f+fa)/2) The frequency ofthe synthesis wave is f=f+) The period T of the synthesis wave is called beat period,and corresponding frequency f is called beat frequency. f=1/T Interference of Ultrasonic Sound Waves In this lab,you will use one signal generator to drive two identical ultrasonic transducers to produce two beams of coherent ultrasonic sound waves.The two waves interfere with each other.The result for the angle of maximum intensity ofinterference is sima=n后，n0+12 where n=0,1,2,is referred to as the order of the particular maximum,A is the length of ultrasonic sound wave,and d is the distance between the two ultrasonic transducers. Observation of Ultrasonic Diffraction Place the ultrasonic transducers on the focus of the convex reflector to produce ultrasonic plane wave. Use Gassy Leb computer measurement and data analysis system to observe the phenomena ofsingle, double or multiple silt diffraction(Figure 1)

Experiment 8. Interference of Ultrasonic Sound Waves OBJECTIVES 1. To observe the interference and diffraction phenomena with ultrasonic sound waves, and uncover the law of wave intensity distribution. 2. To observe and study on the ultrasonic beat. 3. To master the principle and the method of Gassy Leb computer measurement and data analysissystem. PRINCIPLE The interference and diffraction of coherent (same phase) ultrasonic sound waves, and the principle of ultrasonic sound wave beat are similar to the related phenomena of light. Beats of Ultrasonic Sound Waves Two ultrasonic sound waves of different frequencies interfere with each other and produce the beats of ultrasonic sound waves. Consider two sound waves of same amplitudes and different frequencies, YA=A0Sin(2πfat) and YB=A0Sin(2πfbt). Their synthesis wave is exactly Y = 2A0Cos〔π(fb-fa)t〕Sin〔2πt(fb+fa)/2〕 The frequency of the synthesis wave is f = 1 2 (fa+ fb) The period T of the synthesis wave is called beat period, and corresponding frequency f is called beat frequency. f = 1/T Interference of Ultrasonic Sound Waves In this lab, you will use one signal generator to drive two identical ultrasonic transducers to produce two beams of coherent ultrasonic sound waves. The two waves interfere with each other. The result for the angle of maximum intensity of interference is 𝑠𝑖𝑛 𝛼 = 𝑛 𝛌 𝑑 , n=0,±1,±2… where n = 0, 1, 2, is referred to as the order of the particular maximum, λ is the length of ultrasonic sound wave, and d is the distance between the two ultrasonic transducers. Observation of Ultrasonic Diffraction Place the ultrasonic transducers on the focus of the convex reflector to produce ultrasonic plane wave. Use Gassy Leb computer measurement and data analysis system to observe the phenomena of single， double or multiple silt diffraction(Figure 1)

Figure 1.Experiment set-up (1)Apparatus ofUltrasonic Interference Experiment ALTERNATIVE RESEARCHPROJECT 1.Observe the beat of ultrasonic sound wave and measure the beat frequency.2 2.Observe ultrasonic sound wave interference and measure the wavelength of it by using oscilloscope and optic bench. 3.Observe ultrasonic sound wave interference and measure the wavelength of it by using rotating platform. 4.Observe single,double and multiple silt diffraction by using rotating platform,computer measurement and data analysis system. APPARATUS Ultrasonic transducer,No.416000; Signal generator,No.416012; AL amplifier,No.416010; Rotating platform,No.311902; Motor driver,No.311902; DC power supply,No.52154; DC source box,No.524031; Oscilloscope,optic bench; Multimeter,wires EXPERIMENT TIPS 1.Read experimental introduction booklet carefully or refer to experimental reports with the goal of being familiar with basic requirements and experimental procedure. 2.Read the manual ofrelated experimental apparatus. 3.Read the manual of Gassy Leb computer measurement and data analysis system.Refer to online document for a more detailed usage of Gassy Leb

Figure 1. Experiment set-up (1)Apparatus of Ultrasonic Interference Experiment ALTERNATIVE RESEARCH PROJECT 1. Observe the beat of ultrasonic sound wave and measure the beat frequency.2 2. Observe ultrasonic sound wave interference and measure the wavelength of it by using oscilloscope and optic bench. 3. Observe ultrasonic sound wave interference and measure the wavelength of it by using rotating platform. 4. Observe single, double and multiple silt diffraction by using rotating platform, computer measurement and data analysis system. APPARATUS Ultrasonic transducer, No. 416000; Signal generator, No. 416012; AL amplifier, No. 416010; Rotating platform, No. 311902; Motor driver, No. 311902; DC power supply, No. 52154; DC source box, No. 524031; Oscilloscope, optic bench; Multimeter, wires EXPERIMENT TIPS 1. Read experimental introduction booklet carefully or refer to experimental reports with the goal of being familiar with basic requirements and experimental procedure. 2. Read the manual of related experimental apparatus. 3. Read the manual of Gassy Leb computer measurement and data analysis system. Refer to online document for a more detailed usage of Gassy Leb

4.Turn on the computer,and open experimental document in file C:\Data to learn how to set the experiment parameters and how the experiment data displays. 5 Create a private file named after your student number for your group in C:\StuData.Order all related experimental documents and save them in the file of your group,and create a text named after your name to record related experimental information. 6.Click 'Gassy Leb'icon to open the program,and click 'set'to open the window of experiment setting.Select 'imput A',and choose the range of signal.Click 'display'to observe the distribution of waves intensity,and select the bottom'y2'(Figure 2). Figure 2.The schematic diagram of Gassy Leb 0S路凸⊙回仓)届11刚su Stndad UAI/V 0g0 00 08 00 00的0 a 003g 8 0029 00 8 CASSYP FomFTDplCom 0030 043 ao Quartty VoRage LiAT 00 Heat Range3V.3V 00% 00 010 00 L CAvsed Vaet ZomPort C 46

4. Turn on the computer, and open experimental document in file C:\Data to learn how to set the experiment parameters and how the experiment data displays. 5. Create a private file named after your student number for your group in C:\StuData. Order all related experimental documents and save them in the file of your group, and create a text named after your name to record related experimental information. 6. Click ‘Gassy Leb’ icon to open the program, and click ‘set’ to open the window of experiment setting. Select ‘imput A’, and choose the range of signal. Click ‘display’ to observe the distribution of waves intensity, and select the bottom ‘y 2 ’(Figure 2). Figure 2.The schematic diagram of Gassy Leb