Measuring+the+Velocity+of+Acoustic+Wave+by+Using+the+Ultrasonic+Wave

Measuring the Velocity of Acoustic Wave by Using the

Ultrasonic Wave

AN Panlong, XU Liping, LIU Zheng Guang,

Department of Physics, North University of China, Taiyuan, 030051, Phone :+86 351 3925287 E-Mail: anpanlong2005795278@http://wendang.chazidian.com

Abstract: In this text propagation velocity of the and have nothing to do with frequency. In addition,

ultrasonic wave in the air is obtained. We use the according to the wave theory ,we have : piezoelectric transducer between which a sanding

ν=λ×f

wave is created to operate the experiment. By calculation, we can know the function of piezoelectric f is frequency ,λis wave length . transducer, and by using the standing wave testing, We use three different ways to measure the velocity Llissajous’s figures, and comparing the graphs of the of sound wave and according to the method of double phase , we get the exact magnitude of the subtraction in groups which to be used to analyze velocity of sound wave.. The accordance between the datums .at last , We prove the different experimental value of the velocity is environment influence of the temperature upon the tested .Furthermore, the influence of temperature on velocity of sound. the velocity is discussed.. Key words: ultrasonic wave; piezoelectric transducer;

II. Working principle and velocity; standing wave

measurement device

1. Working principle

I. Introduction

Ultrasonic wave is a mechanical wave and its wave frequency is greater than or equal to 2×10Hz. Its velocity is related with the medium, and is determined

by the states of the medium. Ultrasonic wave has shorter wave length and better energy convergence than general acoustic wave. Besides, the directivity of the ultrasonic wave is good, so it can be used to measure the sound

velocity and acquire the alteration of the characters and other states of the medium. This is very important in industrial process, for instance, measuring the concentration of chlorine, table sugar, and sulfuric acid. And it can measure the boundary surface of all sorts of oil in the petroleum pipe line.

The velocity formula of sound propagation in the air is[2] :

νT=4

Fig. 1 The structure of the piezoelectric transducer

The speed is decided on the character of Medium

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As shown in Fig.1, The head makes into the trumpet form with the light metals, the tail part makes into the taper or column with the heavy metals, central part is the piezoelectric ceramic ring, This kind of structure enlarged the radiation area, strengthened the coupling effect between the oscillator and medium. Because the longitudinal extension of the oscillator directly influence the head of the light metals, the metals stretch and shrink in the same lengthways , but engender little influence on the heavy

metals .Thus, shoot of wave is directly strong, and has a good character of flat surface .

2. Lissajous’s figures [3], [4](Li/cm) (42000Hz)

2. Measurement principle and device

The device work based on the principle: When the piezoelectric ceramic subject to the concordant stress in the direction of polarization, a direct proportional voltage with the stress at the direction of polarization will be produced; and applied the electric field at the direction of polarization, then a direct proportional telescopic shape change will be produced. Meanwhile, the position of the telescopic shape change with the maximum can be determined, by detecting the maximal air pressure, while moving the piezoelectric transducer. Thus, the maximal air pressure of the standing wave is transformed into the electric signal by the piezoelectric transducer, and can be observed in the oscilloscope. Then, length and frequency of the standing wave are given through

the oscilloscope.

L1 L7

L2 L8

L3

L9

L4

L5

L6

L10 L11 L12

3. comparing the double phase graph (Li/cm)

(42000Hz)

L1 L7

L2 L8

L3 L9

L4 L5

L6

L10 L11 L12

12.9295

Fig. 2 The setting drawing of the sound velocimeter

2. t=35.0°C

1.standing wave test (Li/cm) (39000Hz) L1

3.1587

L2

3.6090

L3

4.0621

L4 L5 L6

III. Experimental methods and data

1. t=21..6°C

1. standing wave testing[1]

(Li/cm) (39000Hz)

L7 L8 L9 L10 L11 L12

2.Lissajous’s figures way (Li/cm) (42000Hz) L1 L7

L2 L8

L3 L9

10.6762

L4 L5 L6

L10 L11 L12

11.9655

L1 L7

L2 L8

L3

L9

L4 L10

L5

L6

3.compare double phase curve (Li/cm) (42000Hz) L1 L7

L2 L8

L3 L9

10.9842

L4 L5 L6

L11 L12 L10 L11 L12

13.5055

725

IV. Data analysis and processing

(called mole ‘s constant )has the value R=8.31J/mol .K

T is thermodynamic temperature, and T =273+t , M is the mole mass of air, M=29×10Kg/mol.

Then we can calculate the theoretic value of γ(adiabatic coefficient) accurately. The result of test enunciate that the results of experiment are consistent with the value of theory.

?3

V. Conclusion

The mechanical and electrical signal can be converted by the piezoelectric transducer, and ultrasonic wave can be produced by this machine. Three methods of measuring the velocity of acoustic wave in the air are discussed in this paper,and the value of the velocity of the ultrasonic wave is gotten. We can draw three points: ①This measurement clarified the error between the speed of the acoustic wave and frequency. The velocity of acoustic wave in the air has no relations with frequency, and it is decided by the character of environment. ②By means of this test ,we are familiar with the work principle of piezoelectric transducer ,and we can design the other such kind of instrument and apply them in vast field of measurement.③ By analyzing the data of velocity of acoustic wave in different temperature, we proved the speed of acoustic wave will rise with the increase of temperature.

Data processing result[5] (1):

t=21.6 0C

T＝344.36m/s

0.018

λ(cm)

(m/s) e(m/s)

t=35.00C

Sd (%)

Data processing result[5] (2):

T＝352.10m/s

λ(cm)

(m/s) e(m/s)

Sd (%)

REFERENCES

[1] Lu peijiao,To Determine t he Wave Speed of Ultrasonic

by Standing Wave Method, PHYSICAL EXPERIMENT OF COLLEGE, Vol19 No. 2 Jun .2006, P.27-29

[2] Zhang xufeng,Wang zhibin,Wang bingren, Physical

experiment of college,The China Machine Press, From Beijing:P.76-79.

[3] Deng fajin, Physics of College ,The Science Press ,From

Beijing:P.283-287.

[4] Richard P .Olenick ,Tom M .Apostol & David

L .Goodstein ,The Mechanical Universe Introduction to Mechanics and Heat, The Peking university Press ,P.310-315.

[5] Ai baoqin ,Ma xiaochun , A Discussion of Error in

Measuring the Velocity of Sound in the Atmosphere, Journal of Xianyang Normal University, Vol.21 No. 4 Aug.2006,P.81-83

As it is shown in the two charts ,the velocity of acoustic wave are uniform in different frequency ,and the speed will change accompany with the variation of temperature ,and the temperature is the important factor that affect the speed .We also know, the speed can be stated mathematically as ν=

whereγ is the ratio of heat capacity, γ=

CpCV

=1.4,

R is the air constant, the constant universally adopted

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Measuring the Velocity of Acoustic Wave by Using the UltrasonicWave

作者：

作者单位：AN Panlong， XU Liping， LIU Zheng GuangDepartment of Physics, North University of China, Taiyuan, 030051

[会议论文] 2007 引用本文格式：AN Panlong.XU Liping.LIU Zheng Guang Measuring the Velocity of Acoustic Wave by Using the Ultrasonic Wave