A device for demonstrating ultrasonic interference and measuring sound velocity

Abstract

The present invention discloses an ultrasonic interference phenomenon demonstration and sound velocity measurement device, comprising: a platform, a linear translation stage, a mobile transmitting transducer assembly, a fixed transmitting transducer assembly, a receiving transducer assembly, a signal generator, a signal amplifier, and a dual-trace oscilloscope. The three transducer assemblies each include a transducer, a mounting seat, and a vertical pole, the vertical pole is fixedly connected to the lower part of the mounting seat, the mounting seat is provided with a slit, and the transducer is placed directly opposite the slit. The signal generator excites the transducers in the mobile transmitting transducer assembly and the fixed transmitting transducer assembly to generate ultrasonic waves, which are emitted through the slit to form two independent ultrasonic emission sources. The two waves emitted will be superimposed when they propagate to the slit of the receiving transducer assembly. The device has a simple structure and is easy to operate. It can demonstrate the ultrasonic interference phenomenon very intuitively and accurately measure its wavelength and sound velocity. It can also be used to demonstrate and observe the beat frequency phenomenon.

Description

Technical Field

[0001] The invention relates to a university physics teaching experimental instrument, in particular to a device for measuring wavelength and wave speed by utilizing an ultrasonic interference method, and belongs to the technical field of physical experiment measurement. Background Art

[0002] The propagation of sound waves is closely related to the characteristics and state of the medium. By measuring the speed of sound in the medium, the physical characteristics and state changes of the medium can be detected. The measurement of the speed of sound is an important part of university physics experimental teaching. At present, the main methods for measuring the speed of sound are: standing wave method (resonance interference method), phase comparison method, Doppler effect method and time difference method; among them, the standing wave method and phase comparison method are the most typical. The core of these two methods is to first measure the wavelength of the sound wave and then calculate the speed of sound.

[0003] The standing wave method generates a standing wave between the sound wave generator and the receiver, and determines the half-wavelength by measuring the distance between two adjacent nodes of the standing wave. The key point is to determine the conditions for the formation of standing waves, that is, the position of the nodes. The judgment method is to observe the intensity of the received wave through an oscilloscope. When it reaches the maximum, the position of the transducer is the node. However, near the maximum value of the wave intensity, the signal amplitude on the oscilloscope does not change significantly, which can easily cause human error when determining the node position based on this.

[0004] The phase comparison method is to change the distance between the sound wave generator and the receiver, thereby changing the phase difference between the received wave and the transmitted wave. The phase difference can be determined by observing the Lissajous figure of the vertical vibration synthesis of the transmitted wave and the received signal on the oscilloscope, and then the wavelength can be determined based on the periodic changes of the Lissajous figure; because the scanning display line on the oscilloscope screen has a certain width, it is difficult to accurately distinguish between straight line segments and extremely flat ellipses, so it is easy to make large human errors when judging whether the phases of two vibrations are the same (or opposite) based on the Lissajous figure. Summary of the invention

[0005] In order to overcome the shortcomings of the above two wavelength measurement methods, the present invention provides an ultrasonic interference phenomenon demonstration and sound velocity measurement device. The device uses the complete destructive coherence condition to determine the wavelength, which can significantly reduce the human error in wavelength measurement and can also demonstrate the beat frequency phenomenon.

[0006] The technical solution adopted by the present invention is as follows:

[0007] An ultrasonic interference phenomenon demonstration and sound velocity measurement device includes: a platform, a linear translation stage, a mobile transmitting transducer assembly, a fixed transmitting transducer assembly, a receiving transducer assembly, a signal generator, a signal amplifier, and a dual-trace oscilloscope; wherein,

[0008] The mobile transmitting transducer assembly, the fixed transmitting transducer assembly and the receiving transducer assembly all include: a mounting seat, a vertical pole and a transducer; the transducer is placed in the mounting seat, the vertical pole is fixedly connected to the lower part of the mounting seat, a front cover is provided at the end of the mounting seat, the front cover is provided with a vertical slit, and the transducer is installed facing the slit; the transducers of the mobile transmitting transducer assembly and the fixed transmitting transducer assembly are used to transmit ultrasonic waves, and the transducer of the receiving transducer assembly is used to receive ultrasonic waves; the vertical pole of the mobile transmitting transducer assembly is installed on the slider of the linear translation stage, the vertical poles of the fixed transmitting transducer assembly and the receiving transducer assembly are fixedly connected to the platform, the slit of the mobile transmitting transducer assembly faces the slit of the receiving transducer assembly, and the centers of the two slits are at the same height.

[0009] The linear translation stage can be purchased on the market or customized by the manufacturer. The specific structure includes: a frame, a lead screw, a slider, and a micrometer drum. There is a scale ruler on the frame. The frame of the linear translation stage is fixed on the platform, the lead screw is rotatably connected to the frame, the end of the lead screw is connected to the micrometer drum, and the slider is rotatably connected to the lead screw by a thread. By rotating the micrometer drum, the lead screw rotates, which is further converted into linear movement of the slider on it, thereby driving the mobile transmitting transducer assembly connected to the slider to move along the two center connecting lines of the slit of the mobile transmitting transducer assembly and the slit of the fixed transmitting transducer assembly. The moving distance can be read from the scale ruler and the drum.

[0010] One output terminal CHA of the signal generator is connected to the transducer input terminal of the mobile transmitting transducer assembly and the input terminal CH2 of the dual-trace oscilloscope at the same time, and the other output terminal CHB of the signal generator is connected to the transducer input terminal of the fixed transmitting transducer assembly; the input terminal of the signal amplifier is connected to the transducer output terminal of the receiving transducer assembly, and the output terminal of the signal amplifier is connected to the input terminal CH1 of the dual-trace oscilloscope.

[0011] The measurement principle is as follows Figure 5 As shown, L is the distance between the centers of the slits of the mobile transmitting transducer assembly and the receiving transducer assembly; D is the distance between the centers of the slits of the fixed transmitting transducer assembly and the receiving transducer assembly.

[0012] Ultrasonic waves are generated by the signal generator to excite the transducers of the mobile transmitting transducer assembly and the fixed transmitting transducer assembly, and are emitted through the slit. The slit can be regarded as the emission source of the ultrasonic wave. The mobile transmitting transducer assembly is installed on the slider of the linear translation stage and can move parallel to it. Its ultrasonic emission source is called the mobile wave source; the fixed transmitting transducer assembly is fixed on the platform and does not move, and its ultrasonic emission source is called the fixed wave source; the two ultrasonic emission sources are close to each other, and they are far away from the transducer of the receiving transducer assembly. Generally, the fixed wave source and the mobile wave source emit sinusoidal ultrasonic waves of the same frequency, and their wavelength is denoted as λ. When they propagate in front of the receiving transducer assembly, the two waves can be coherently superimposed at the slit position. Assume that the phases of the ultrasonic waves emitted from the fixed wave source and the mobile wave source are respectively It is obvious that the phase difference between the ultrasonic waves they emit and the slits of the receiving transducer assembly is:

[0013]

[0014] Then their amplitude after coherent superposition is: Among them A D ,A L are the amplitudes of the waves emitted by the fixed wave source and the moving wave source when they reach the slit of the receiving transducer assembly. Obviously, when When, A=A D +A L , interference is extremely large; when When, A=|A D -A L |, the interference is minimized, where k is an integer. When the distance L changes by one or several wavelengths, the interference remains the same at maximum or minimum.

[0015] If the frequencies of the two wave sources are different, denoted as f1 and f2 respectively, but the frequency difference is very small, that is, |f2-f1|<<f1,f2, then the beat frequency phenomenon produced when the two waves are superimposed can be observed on a dual-trace oscilloscope, and the frequency is: Δf=|f1-f2|.

[0016] This device can achieve the following three experimental purposes:

[0017] (I) Demonstrate and observe the interference phenomenon when waves of the same frequency are superimposed: (a) Move the mobile wave source, that is, change the distance L between the centers of the two slits of the mobile transmitting transducer assembly and the receiving transducer assembly, and you can see the change in interference intensity. (b) Keep the mobile wave source stationary and adjust the phase difference between the CHB output and CHA output of the signal generator, that is, change Changes in the interference intensity can also be observed.

[0018] (II) Measure the wavelength and speed of sound of ultrasonic waves: Let the moving wave source follow the linear translation stage to move slowly and continuously in the direction of the line connecting the slit center of the mobile transmitting transducer assembly and the slit center of the receiving transducer assembly. You can see the signal strength fluctuating on the dual-trace oscilloscope. Every time the interference is extremely large (or extremely small), that is, the moment when the signal on the dual-trace oscilloscope reaches the maximum (or minimum), record the scale of the linear translation stage and the reading of the micrometer drum wheel. The sum of the two is recorded as L. i , then the wavelength of this sound wave is: λ=|L i+1 -L i |. Then use v=λf to calculate the speed of sound v.

[0019] When using two adjacent interference maxima to determine the wavelength, a problem similar to the standing wave method will be encountered, that is, near the interference maximum, the signal amplitude on the dual-trace oscilloscope does not change significantly, and determining the position of the moving wave source when constructively coherent is easy to cause human error. This problem can be avoided when using two adjacent interference minima to determine the wavelength. At this time, by adjusting the gear of the vertical attenuation sensitivity of the dual-trace oscilloscope and amplifying the waveform of the signal on the dual-trace oscilloscope, the position of the moving wave source when the interference is minimal can be determined relatively easily. The weaker the destructively coherent signal, the more accurate the position determination, so when measuring, the two waves should be as close to completely destructively coherent as possible, which requires that the amplitude A of the waves emitted by the fixed wave source and the moving wave source when they reach the slit of the receiving transducer assembly D and A L This can be achieved by adjusting the output signal amplitude of one channel CHB or CHA of the signal generator, thereby changing the relative strength of the ultrasonic wave source.

[0020] (III) Demonstrate and observe the beat frequency phenomenon when two waves are superimposed: Keep the mobile transmitting transducer assembly still, and fine-tune the CHA or CHB output frequency of the signal generator so that they are no longer equal, but the frequency difference must be small enough (for naked eye observation). At this time, you can intuitively see the signal waveform fluctuating on the dual-trace oscilloscope. This change is the beat frequency, and its frequency is equal to the difference between the frequencies of the two channel signals.

[0021] The above is an analysis of the principle that the device can be used to more accurately measure wavelength and wave speed. In order to optimize the device itself, the following improvements can be made to the technical solution:

[0022] In order to make adjustment more convenient and accurate during data measurement, the distance between the mobile transmitting transducer assembly and the receiving transducer assembly should be at least five times the distance between the mobile transmitting transducer assembly and the fixed transmitting transducer assembly. At this time, the fixed transmitting transducer assembly needs to be fixed to a platform adjacent to one side of the mobile transmitting transducer assembly, and the receiving transducer assembly needs to be fixed to a platform away from the side of the mobile transmitting transducer assembly.

[0023] In order to avoid systematic errors in measurement as much as possible, the slit centers of the mobile transmitting transducer assembly, the fixed transmitting transducer assembly, and the receiving transducer assembly are on the same horizontal plane; if the distance between the horizontal plane and the platform is H, then it is required Where L max is the maximum value of the distance between the slit of the mobile transmitting transducer assembly and the center of the slit of the receiving transducer assembly, and θ is the directional angle of the transducer in the mobile transmitting transducer assembly. This can avoid the interference of the sound waves reflected by the platform on the two columns of coherent waves.

[0024] Furthermore, choosing a transducer with a diameter greater than 15 mm and a pointing angle no greater than 45 degrees can minimize system errors.

[0025] In order to ensure that the moving direction of the linear translation stage is in the direction of the line connecting the slit center of the mobile transmitting transducer assembly and the slit center of the receiving transducer assembly, and also to facilitate the installation alignment and height adjustment of each transducer assembly, the platform preferably adopts an optical flat plate.

[0026] In order to facilitate installation and adjustment, the mounting base is made into a hollow cavity that can accommodate the transducer, including: a body, a front cover, a rear cover, a fastening screw and a socket; a front cover is arranged at one end of the body, and the front cover is provided with a vertical slit, and a rear cover is arranged at the other end, which is provided with a through hole, and the socket is installed in the through hole, and the fastening screw is installed on the body, and the body, the front cover and the rear cover form a hollow cavity, the transducer is placed facing the slit, and the transducer is tightened in the hollow cavity with the fastening screw, and the transducer is connected to the socket through a wire, and then connected to the outside through the socket; these structures make wiring more convenient, and the fastening screws can also prevent the transducer from moving relative to the slit due to movement and collision, so that the device is easier to adjust and the measurement accuracy is enhanced.

[0027] A further improvement to the vertical pole is to set a height adjustment device on the vertical pole. By adjusting the height of the vertical pole, the position of the slit of the mounting seat is adjusted so that the center of each slit is located in the same horizontal plane. The height adjustment device can be set only on the vertical pole of the mobile transmitting transducer assembly and the vertical pole of the receiving transducer assembly, or the height adjustment device can be set on all three vertical poles.

[0028] In order to make the measurement result more accurate, the width of the slit of the mounting seat cannot be too wide and the length cannot be too small. Preferably, the width of the slit is between 0.5-1.5 mm and the length of the slit is not less than the diameter of the transducer.

[0029] Furthermore, the front cover of the mounting seat is made of metal material, especially copper alloy, steel and other metals with high density.

[0030] In order to make the measurement result more accurate, it is necessary to measure multiple sets of data for statistical averaging, so the translation stroke of the linear translation stage is required to be large enough. Preferably, the maximum stroke of the linear translation stage is not less than 5 cm.

[0031] Furthermore, in order to observe interference and beat frequency phenomena more stably and clearly and to accurately measure wavelength and sound velocity, the signal generator adopts a signal generator based on direct digital synthesis technology.

[0032] Furthermore, by selecting a transducer with a lower operating frequency, the wavelength of the ultrasonic wave is longer, thereby making the measurement error smaller, so the operating frequency of the transducer is selected to be no greater than 45kHz.

[0033] In summary, the present invention has a simple structure and is easy to operate. It can accurately determine the position of the moving wave source during destructive coherence, has a small human error, can very intuitively demonstrate the interference phenomenon of ultrasonic waves, accurately measure its wavelength and sound speed, and can also demonstrate and observe the beat frequency phenomenon. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of an embodiment of an ultrasonic interference phenomenon demonstration and sound velocity measurement device of the present invention.

[0035] Figure 2 The invention discloses a linear translation stage for demonstrating ultrasonic interference phenomenon and measuring sound velocity.

[0036] Figure 3 It is a cross-sectional view of an embodiment of a mounting base and a vertical pole height adjustment device of an ultrasonic interference phenomenon demonstration and sound velocity measurement device of the present invention.

[0037] Figure 4 The present invention Figure 3 A view of the front cover of the mounting base.

[0038] Figure 5 It is a schematic diagram of the measurement principle of an ultrasonic interference phenomenon demonstration and sound velocity measurement device of the present invention. DETAILED DESCRIPTION

[0039] In order to facilitate the viewing of the various reference numerals in the drawings of the specification, the reference numerals appearing in the drawings of the specification are uniformly described as follows:

[0040] Figure 1 and Figure 5 In the middle: 1 is a platform; 2 is a linear translation stage; 3 is a mobile transmitting transducer assembly; 4 is a fixed transmitting transducer assembly; 5 is a receiving transducer assembly; 6 is a signal generator; 7 is a signal amplifier; 8 is a dual-trace oscilloscope.

[0041] Figure 2In the middle: 2-1 is a frame; 2-2 is a screw rod; 2-3 is a slider; 2-4 is a micrometer drum wheel; 2-5 is a scale ruler.

[0042] Figure 3 to Figure 4 In the middle: 9 is the transducer; 9-1 is the body; 9-2 is the front cover; 9-3 is the slit; 9-4 is the back cover; 9-5 is the fastening screw; 9-6 is the socket; 10 is the vertical pole; 10-1 is the sleeve; 10-2 is the sleeve fixing screw; 10-3 is the vertical pole locking knob.

[0043] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0044] like Figures 1 to 4 The present invention is a specific embodiment of an ultrasonic interference phenomenon demonstration and sound velocity measurement device, comprising: a platform 1, a linear translation stage 2, a mobile transmitting transducer assembly 3, a fixed transmitting transducer assembly 4, a receiving transducer assembly 5, a signal generator 6, a signal amplifier 7, and a dual-trace oscilloscope 8; wherein:

[0045] The specific structure of the linear translation stage 2 is as follows Figure 2 , including: a frame 2-1, a screw rod 2-2, a slider 2-3, a micrometer drum wheel 2-4, and a scale ruler 2-5 on the frame; the frame 2-1 of the linear translation stage is fixed on the platform 1; the screw rod 2-2 is rotatably connected to the frame 2-1, and the end of the screw rod 2-2 is connected to the micrometer drum wheel 2-4, and the slider 2-3 is rotatably connected to the screw rod 2-2 through a thread. When the micrometer drum wheel 2-4 is rotated, the screw rod 2-2 rotates together, and then further converted into a linear movement of the slider 2-3 thereon.

[0046] The mobile transmitting transducer assembly 3, the fixed transmitting transducer assembly 4, and the receiving transducer assembly 5 all include: a mounting base, a vertical pole 10, and a transducer 9; the transducer 9 is placed in the mounting base, the vertical pole 10 is fixedly connected to the lower part of the mounting base, and a front cover 9-2 is provided at the end of the mounting base, and the front cover is provided with a vertical slit 9-3, and the transducer 9 faces the slit.

[0047] The vertical rod 10 of the mobile transmitting transducer assembly 3 is installed on the slider 2-3 of the linear translation stage 2, and the vertical rod 10 of the fixed transmitting transducer assembly 4 and the receiving transducer assembly 5 is fixed on the platform 1. The slit of the mobile transmitting transducer assembly 3 faces the slit of the receiving transducer assembly 5, and the centers of the two slits are at the same height.

[0048] When the micrometer drum 2-4 is rotated, it is converted into a linear translation of the slider 2-3 on it through the screw rod 2-2, thereby driving the mobile transmitting transducer assembly 3 on the slider 2-3 to move along the line connecting the slit center of the mobile transmitting transducer assembly 3 and the slit center of the fixed transmitting transducer assembly 5. The moving distance can be read from the scale ruler 2-5 and the micrometer drum 2-4.

[0049] The transducers 9 of the mobile transmitting transducer assembly 3 and the fixed transmitting transducer assembly 4 are used to transmit ultrasonic waves, and the transducer 9 of the receiving transducer assembly 5 is used to receive ultrasonic waves.

[0050] One output terminal CHA of the signal generator 6 is connected to the input terminal of the transducer of the mobile transmitting transducer assembly 3 and the input terminal CH2 of the dual-trace oscilloscope 8 at the same time, and another output terminal CHB of the signal generator 6 is connected to the input terminal of the transducer of the fixed transmitting transducer assembly 4; the input terminal of the signal amplifier 7 is connected to the output terminal of the transducer of the receiving transducer assembly 5, and the output terminal of the signal amplifier 7 is connected to the input terminal CH1 of the dual-trace oscilloscope 8.

[0051] For further optimization, the fixed transmitting transducer assembly 4 is fixedly connected to a side adjacent to the mobile transmitting transducer assembly 3, and the receiving transducer assembly 5 is fixedly connected to a side away from the mobile transmitting transducer assembly 3, so that the distance between the receiving transducer assembly 5 and the mobile transmitting transducer assembly 3 is greater than the distance between the fixed transmitting transducer assembly 4 and the mobile transmitting transducer assembly 3, and this ratio can be 5-10 times.

[0052] In addition, the slit centers of the mobile transmitting transducer assembly 3, the fixed transmitting transducer assembly 4, and the receiving transducer assembly 5 are in the same horizontal plane. If the distance between the horizontal plane and the platform 1 is H, then , where L max is the maximum value of the distance between the slit of the mobile transmitting transducer assembly 3 and the slit center of the receiving transducer assembly 5, and θ is the directional angle of the transducer in the mobile transmitting transducer assembly 3, so as to avoid the interference of the sound waves reflected by the platform 1 on the two columns of coherent waves.

[0053] Furthermore, the diameter of the transducer 9 is greater than 15 mm, and the pointing angle is not greater than 45 degrees, which can avoid system errors as much as possible. For example, the specifications of the transducer are: diameter 16 mm, pointing angle 45 degrees.

[0054] Figure 3 A specific embodiment of the mounting base is shown. Figure 4The A-direction view of the front cover 9-2 of the mounting seat shows the shape of the slit: the mounting seat has a closed hollow cavity, such as a hollow rectangular block as shown in the figure, specifically including: a main body 9-1, a front cover 9-2, a rear cover 9-4, a fastening screw 9-5, and a socket 9-6; a front cover 9-2 and a rear cover 9-4 are respectively provided at both ends of the main body 9-1; a slit 9-3 is provided on the front cover 9-2, and a through hole is opened on the rear cover 9-4, and a socket 9-6 is installed in the through hole; the main body 9-1, the front cover 9-2 and the rear cover 9-4 form a hollow cavity, and the transducer 9 is placed in the hollow cavity, facing the slit 9-3, and then the fastening screw 9-5 is used to support the transducer 9, and the transducer 9 is connected to the socket 9-6 through a wire, and then connected to an external device such as a signal generator 6 or a signal amplifier 7 through the socket.

[0055] Figure 3 An embodiment of the improvement of the vertical pole 10 is also shown in the figure, in which a height adjustment device is arranged at the lower part of the vertical pole 10, and the height adjustment device includes a sleeve 10-1, a sleeve fixing screw 10-2, and a vertical pole locking knob 10-3; the bottom of the sleeve 10-1 is fixed to the slider 2-3 of the platform 1 or the linear translation stage 2 by the sleeve fixing screw 10-2, and the sleeve 10-1 is sleeved on the outside of the vertical pole 10, and the two can slide relative to each other to change the length of the vertical pole 10 extending out of the sleeve 10-1, and the vertical pole 10 can be locked by the vertical pole locking knob 10-3 after the length is adjusted. By changing the length of the vertical pole 10 extending out of the sleeve 10-1, the height of the slit 9-3 is finally adjusted; wherein the vertical poles of the mobile transmitting transducer assembly 3 and the receiving transducer assembly 5 should be provided with a height adjustment device to ensure that the slit centers of the mobile transmitting transducer assembly 3 and the receiving transducer assembly 5 are at the same height. In order to obtain a better effect, height adjustment devices can also be provided on the three vertical poles at the same time, so that the centers of the three slits can be adjusted to the same height relatively conveniently.

[0056] The size of the slit 9 - 3 is required to be neither too wide nor too short. The width of the slit 9 - 3 is preferably between 0.5 and 1.5 mm, for example, 1 mm. The length of the slit 9 - 3 is not less than the diameter of the transducer 9 .

[0057] For the front cover 9-2 of the mounting seat, it is better to use metal material, preferably copper alloy, steel and other metals with high density.

[0058] The linear translation stage 2 is required to have a maximum stroke that cannot be too small. Preferably, the maximum stroke of the linear translation stage is not less than 5 cm.

[0059] For the transducer 9, a relatively low operating frequency should be selected, and preferably the operating frequency of the transducer is not greater than 45 kHz.

[0060] The working process of demonstration and measurement using this device is as follows:

[0061] First, it is necessary to determine the resonant frequency of the transducer in the receiving transducer assembly 5. The specific method is: only turn on the CHA output of the signal generator, select the output waveform as a sine wave, and adjust it to a suitable amplitude, such as 8 to 12 volts peak-to-peak; select the CH1 input signal of the dual-trace oscilloscope as the trigger source of the dual-trace oscilloscope, and fine-tune the CHA output signal frequency of the signal generator near the transducer operating frequency so that the signal amplitude displayed on the dual-trace oscilloscope reaches the maximum. At this moment, this frequency is the resonant frequency of the transducer in the receiving transducer assembly 5.

[0062] (1) Observe the interference phenomenon. Turn on the CHB output of the signal generator again, select the output waveform as sine, and adjust its frequency to make it the same as the CHA output frequency of the signal generator. Turn off the CHA output of the signal generator, and adjust the CHB output voltage amplitude so that the signal amplitude displayed by the dual-trace oscilloscope is equal to that when the CHA of the signal generator is turned on alone. Then turn on the CHA output of the signal generator again, and select the input signal of CH2 of the dual-trace oscilloscope as the trigger source of the dual-trace oscilloscope. (a) Observe the effect of the initial phase change on the interference. Keep the mobile transmitting transducer assembly 3 stationary, adjust the phase difference between the CHB output and CHA output signals of the signal generator, and you will find the change in the intensity of the interference superposition signal. It can be found that when the phase difference is 180°, if the interference is originally maximum, it will become minimum interference at this time; when the phase difference is 360°, the interference situation will be restored. (b) Observe the effect of the phase delay caused by the spatial propagation distance on the interference. Keeping the phase difference between the outputs of signal generators CHB and CHA unchanged, rotating the micrometer drum of the linear translation stage 2 to move the transmitting transducer assembly 3 closer to or farther away from the receiving transducer assembly 5, it will be found that the intensity of the interference superposition signal changes periodically.

[0063] (2) Measure the sound velocity. Select the input signal of CH2 of the dual-trace oscilloscope 8 as the trigger source of the dual-trace oscilloscope. Turn the micrometer drum of the linear translation stage 2 to make the mobile transmitting transducer assembly 3 move slowly in one direction all the time. During the movement, in order to accurately determine the relative position of the mobile transmitting transducer assembly 3 when the interference minimum occurs, the ultrasonic waves emitted by the mobile transmitting transducer assembly 3 and the fixed transmitting transducer assembly 4 should be as equal in intensity as possible when they propagate to the slit of the receiving transducer assembly 5. This can be achieved by gradually comparing the amplitude of the CHA or CHB signal of the fine-tuning signal generator. Using this method, the relative position L of the mobile transmitting transducer assembly 3 each time the interference minimum occurs can be determined more accurately. i Each time the interference minimum is found, the readings of the scale of the linear translation stage 2 and the micrometer drum are recorded. After that, the wavelength and the speed of sound can be calculated.

[0064] The following is a measurement example to illustrate the actual measurement effect of the device.

[0065] Here we use a transducer with an operating frequency of 40kHz. First, we determine the resonant frequency of the transducer in the receiving transducer assembly 5, and the result is: f = 40.016kHz. Then we measure. The following table shows a set of 14 measurement results. Here we can use the difference method to analyze the data and divide the data into two groups. The wavelength of the ultrasonic wave is: λ i =|L i+7 -L i | / 7,(i=1,2,…,7).

[0066] <![CDATA[L i (mm)]]> 16.24 25.10 34.08 42.78 51.39 60.02 68.80 <![CDATA[L i+7 (mm)]]> 77.44 85.75 94.77 103.42 111.91 120.90 129.47 <![CDATA[|L i+7 -L i |(mm)]]> 61.20 60.65 60.69 60.64 60.52 60.88 60.67 <![CDATA[λ i (mm)]]> 8.743 8.664 8.670 8.663 8.646 8.697 8.667

[0067] The minimum graduation of the micrometer drum 2-4 used in the measurement is 0.1mm, and its error limit is 0.05mm. The wavelength measurement results and their standard uncertainties are: ,and

[0068]

[0069] The relative uncertainty of the signal generator output frequency is: u(f) / f=0.10%. Comprehensively, we can get:

[0070]

[0071] That is, the measurement result is: v = (347.3 ± 1.3) m / s, (confidence level P = 68%). Under the experimental measurement conditions, considering the air temperature t and relative humidity H, the theoretical value of the speed of sound in the air under this state can be obtained by looking up the table: v T =348.2m / s, (t=26.0℃, H=70%). The relative error of the measurement is:

[0072] (3) Observe the beat frequency phenomenon. Move the transmitting transducer assembly 3 and keep it still, and fine-tune the output frequency of the signal generator CHB so that it is no longer equal to the frequency of CHA. Select the input signal of CH2 of the dual-trace oscilloscope as the trigger source of the dual-trace oscilloscope. At this time, you can intuitively see the high and low changes of the signal waveform on the dual-trace oscilloscope. When observing the beat frequency phenomenon directly on the dual-trace oscilloscope with your eyes, the frequency difference between the CHA and CHB of the signal generator should not be too large, about 1Hz is appropriate. If the frequency difference is relatively large, you can add a half-wave rectifier circuit after the signal amplifier, and then input the rectified signal into a low-pass filter. Directly observe the output signal of the low-pass filter on the dual-trace oscilloscope, which is the beat frequency signal. At this time, you need to select the input signal of CH1 as the trigger source of the dual-trace oscilloscope.

[0073] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited by the above embodiments. Any technical solutions that are non-substantially improved on the basis of the above embodiments shall be deemed to be included in the patent protection scope of the present invention.

Claims

1. An ultrasonic interference phenomenon demonstration and sound velocity measurement device, characterized in that: include: Platform, linear translation stage, mobile transmitting transducer assembly, fixed transmitting transducer assembly, receiving transducer assembly, signal generator, signal amplifier, dual-trace oscilloscope; The mobile transmitting transducer assembly, the fixed transmitting transducer assembly, and the receiving transducer assembly all include: a mounting seat, a vertical pole, and a transducer; the transducer is placed in the mounting seat, the vertical pole is fixedly connected to the lower part of the mounting seat, a front cover is provided at the end of the mounting seat, the front cover is provided with a vertical slit, and the transducer faces the slit; the transducers of the mobile transmitting transducer assembly and the fixed transmitting transducer assembly are used to transmit ultrasonic waves, and the transducer of the receiving transducer assembly is used to receive ultrasonic waves; the vertical pole of the mobile transmitting transducer assembly is installed on the slider of the linear translation stage, and the vertical poles of the fixed transmitting transducer assembly and the receiving transducer assembly are fixed on the platform, the slit of the mobile transmitting transducer assembly faces the slit of the receiving transducer assembly, and the centers of the two slits are at the same height; The linear translation stage is installed on the platform, and the micrometer drum wheel of the linear translation stage is rotated, so that the mobile transmitting transducer assembly moves along the direction of the two center connecting lines of the mobile transmitting transducer assembly slit and the fixed transmitting transducer assembly slit; One output terminal CHA of the signal generator is connected to the input terminal of the transducer of the mobile transmitting transducer assembly and the input terminal CH2 of the dual-trace oscilloscope at the same time, and another output terminal CHB of the signal generator is connected to the input terminal of the transducer of the fixed transmitting transducer assembly; the input terminal of the signal amplifier is connected to the output terminal of the transducer of the receiving transducer assembly, and the output terminal of the signal amplifier is connected to the input terminal CH1 of the dual-trace oscilloscope.

2. The ultrasonic interference phenomenon demonstration and sound velocity measurement device according to claim 1, characterized in that: The distance between the mobile transmitting transducer assembly and the receiving transducer assembly is more than five times the distance between the mobile transmitting transducer assembly and the fixed transmitting transducer assembly.

3. An ultrasonic interference phenomenon demonstration and sound velocity measurement device according to any one of claims 1 or 2, characterized in that: The slit centers of the mobile transmitting transducer assembly, the fixed transmitting transducer assembly, and the receiving transducer assembly are in the same horizontal plane; let the distance between the horizontal plane and the platform be H, and the maximum distance between the slit center of the mobile transmitting transducer assembly and the slit center of the receiving transducer assembly be L max , the pointing angle of the transducer in the mobile transmitting transducer assembly is θ, and 4. The ultrasonic interference phenomenon demonstration and sound velocity measurement device according to claim 3, characterized in that: The platform is an optical flat plate.

5. The ultrasonic interference phenomenon demonstration and sound velocity measurement device according to any one of claims 1, 2 or 4, characterized in that: The mounting base has a closed hollow cavity, and the mounting base includes a body, a front cover, a rear cover, a fastening screw, and a socket; the body, the front cover and the rear cover form a hollow cavity, the transducer is placed in the hollow cavity, the fastening screw is installed on the body and presses against the transducer, the front cover is provided with a slit, the rear cover is provided with a through hole, a socket is installed on the through hole, and the transducer is connected to the socket through a wire.

6. The ultrasonic interference phenomenon demonstration and sound velocity measurement device according to claim 5, characterized in that: The vertical pole is provided with a height adjustment device.

7. An ultrasonic interference phenomenon demonstration and sound velocity measurement device according to any one of claims 1, 2, 4, and 6, characterized in that: The width of the slit is between 0.5-1.5 mm, and the length of the slit is not less than the diameter of the transducer.

8. The ultrasonic interference phenomenon demonstration and sound velocity measurement device according to claim 7, characterized in that: The front cover of the mounting seat is made of metal material.

9. An ultrasonic interference phenomenon demonstration and sound velocity measurement device according to any one of claims 1, 2, 4, 6, and 8, characterized in that: The signal generator is a signal generator based on direct digital synthesis technology.

10. The ultrasonic interference phenomenon demonstration and sound velocity measurement device according to claim 9, characterized in that: The operating frequency of the transducer is no greater than 45 kHz.

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