阅读说明：本技术 一种低温低气压环境的声衰减系数测量装置及测量方法 (Sound attenuation coefficient measuring device and method in low-temperature and low-pressure environment ) 是由 沈茹珊 李超 崔寒茵 林伟军 于 2020-04-29 设计创作，主要内容包括：本发明属于声波测量设备技术领域,具体地说,涉及一种用于低温低气压环境的声衰减系数测量装置及测量方法,包括：设置在完全封闭的低温低压的环境模拟容器(6)内的发射换能器(1)、接收换能器(2)、第一固定支架(3)、第二固定支架(4)和第三固定支架(5)；设置在封闭的低温低压的环境模拟容器(6)外的信号发生器、放大电路和示波器,信号发生器和放大电路均与示波器连接；以及设置在上位机的数据处理模块；所述第三固定支架(5)呈水平放置,第三固定支架(5)的两端分别设有第一固定支架(3)和第二固定支架(4),第一固定支架(3)上安装发射换能器(1),第二固定支架(4)上安装接收换能器(2)。(The invention belongs to the technical field of sound wave measuring equipment, and particularly relates to a sound attenuation coefficient measuring device and a sound attenuation coefficient measuring method for a low-temperature and low-pressure environment, wherein the sound attenuation coefficient measuring device comprises the following steps: the transmitting transducer (1), the receiving transducer (2), the first fixed bracket (3), the second fixed bracket (4) and the third fixed bracket (5) are arranged in a completely closed low-temperature and low-pressure environment simulation container (6); the signal generator, the amplifying circuit and the oscilloscope are arranged outside the closed low-temperature and low-pressure environment simulation container (6), and the signal generator and the amplifying circuit are connected with the oscilloscope; the data processing module is arranged on the upper computer; the third fixed bolster (5) are the level and place, and the both ends of third fixed bolster (5) are equipped with first fixed bolster (3) and second fixed bolster (4) respectively, and installation transmitting transducer (1) is gone up in first fixed bolster (3), and installation receiving transducer (2) are gone up in second fixed bolster (4).)

1. An acoustic attenuation coefficient measuring apparatus for use in a low temperature, low pressure environment, the apparatus comprising: the transmitting transducer (1), the receiving transducer (2), the first fixed bracket (3), the second fixed bracket (4) and the third fixed bracket (5) are arranged in a completely closed low-temperature and low-pressure environment simulation container (6); the signal generator, the amplifying circuit and the oscilloscope are arranged outside the closed low-temperature and low-pressure environment simulation container (6), and the signal generator and the amplifying circuit are connected with the oscilloscope; the data processing module is arranged on the upper computer;

the third fixing support (5) is horizontally arranged, a first fixing support (3) and a second fixing support (4) are respectively arranged at two ends of the third fixing support (5), the transmitting transducer (1) is installed on the first fixing support (3), and the receiving transducer (2) is installed on the second fixing support (4);

the signal generator transmits a trigger signal and transmits the trigger signal to the transmitting transducer (1); converting the trigger signal into an acoustic wave signal;

the sound wave signal is transmitted in the gas of the low-temperature and low-pressure environment pre-simulated by the environment simulation container (6), and the generated direct wave signal and the secondary reflection echo signal are transmitted to the receiving transducer (2); the receiving transducer (2) receives the direct wave signal and the secondary reflection echo signal and transmits the direct wave signal and the secondary reflection echo signal to an amplifying circuit for amplification;

and the data processing module calculates the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal is transmitted in a certain to-be-detected gas in a low-temperature and low-pressure environment according to the distance between the transmitting transducer and the receiving transducer, the acoustic reflectivity, the voltage amplitude of the amplified direct wave signal and the voltage amplitude of the amplified secondary reflection echo signal.

2. The acoustic attenuation coefficient measurement device for low temperature and low pressure environment of claim 1, wherein the data processing module specifically comprises:

the acquisition unit is used for acquiring the direct wave signal and the secondary echo signal which are amplified by the amplifying circuit;

the processing unit is used for acquiring the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal propagates in a certain gas in a low-temperature and low-pressure environment according to the acquired direct wave signal and the secondary echo signal after amplification processing and by using a formula (1):

wherein a is the sound attenuation coefficient; d is the propagation distance of the sound wave signal between the transmitting transducer (1) and the receiving transducer (2); r is the reflectivity of the sound wave on the gas contact surface of the receiving transducer (2) and a certain gas to be measured in a low-temperature low-pressure environment; u shape_RThe voltage amplitude of the amplified direct wave signal is obtained; u shape_R2The voltage amplitude of the secondary reflection echo signal after amplification processing is obtained.

3. The acoustic attenuation coefficient measurement device for low-temperature and low-pressure environment according to claim 1, wherein the environment simulation container (6) is used for providing low-temperature and low-pressure atmosphere environment; wherein the low temperature is-80-20 ℃; the low air pressure is 600Pa-1 atm.

4. The acoustic attenuation coefficient measurement device for low temperature and low pressure environment according to claim 1, wherein the transmitting transducer (1) and the receiving transducer (2) are horizontally placed relatively, and the distance between the two is 0.15-0.25 m.

5. The acoustic attenuation coefficient measurement device for low temperature and low pressure environments of claim 1, wherein the frequency of the acoustic signal is 20-40 kHz.

6. A method for measuring acoustic attenuation coefficient for low temperature and low pressure environments, the method comprising:

the signal transmitter generates a trigger signal and transmits the trigger signal to the transmitting transducer (1);

the transmitting transducer (1) converts the trigger signal into an acoustic signal;

the sound wave signal is transmitted in the gas of the low-temperature and low-pressure environment pre-simulated by the environment simulation container (6), and the generated direct wave signal and the secondary reflection echo signal are transmitted to the receiving transducer (2); the receiving transducer (2) receives the direct wave signal and the secondary reflection echo signal and transmits the direct wave signal and the secondary reflection echo signal to an amplifying circuit for amplification;

and the data processing module calculates the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal is transmitted in a certain to-be-detected gas in a low-temperature and low-pressure environment according to the distance between the transmitting transducer and the receiving transducer, the acoustic reflectivity, the voltage amplitude of the amplified direct wave signal and the voltage amplitude of the amplified secondary reflection echo signal.

7. The method according to claim 6, wherein the data processing module calculates the acoustic attenuation coefficient of the acoustic wave signal when propagating in a certain gas to be measured in the low-temperature and low-pressure environment according to the distance between the transmitting transducer and the receiving transducer, the acoustic reflectivity, the voltage amplitude of the amplified direct wave signal and the voltage amplitude of the amplified secondary reflection echo signal; the method specifically comprises the following steps:

according to the obtained amplified direct wave signal and secondary echo signal, and by using a formula (1), obtaining the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal is transmitted in a certain gas to be measured in a low-temperature low-pressure environment as follows:

wherein a is the sound attenuation coefficient; d is the propagation distance of the sound wave signal between the transmitting transducer (1) and the receiving transducer (2); r is the reflectivity of the sound wave on the gas contact surface of the receiving transducer (2) and a certain gas to be measured in a low-temperature low-pressure environment; u shape_RThe voltage amplitude of the amplified direct wave signal is obtained; u shape_R2The voltage amplitude of the secondary reflection echo signal after amplification processing is obtained.

Technical Field

The invention belongs to the technical field of acoustic measurement equipment for the atmosphere of the high layers of the earth and the surface of a mars, and particularly relates to an acoustic attenuation coefficient measurement device and an acoustic attenuation coefficient measurement method for a low-temperature and low-pressure environment.

Background

Low temperature and low pressure is a special atmospheric environment which exists both in the immediate space above the earth at an altitude of 20-100km and on the surface of a mars over hundred million km from the earth. The environment changes and the propagation properties of the acoustic waves also change. Therefore, the sound attenuation coefficient also changes in the gas environment at low temperature and low pressure. The research on the sound attenuation of the special atmospheric environment is helpful for improving the knowledge of the physical characteristics of the acoustic aspect of the unknown environment, and provides a foundation for solving the problems by using acoustic means in the subsequent environment.

The atmosphere of the high earth (near space) and the atmosphere of the surface of the mars are both low-temperature and extremely low-pressure environments. The sound attenuation coefficient in the atmosphere with extremely low pressure and low temperature is the basis for comprehensively recognizing the earth and planet acoustic environment and is also a necessary parameter for planet sound detection application. The acoustic attenuation coefficient, an important acoustic parameter of a gaseous medium, is composed mainly of the classical and relaxation attenuations in a gas. The classical attenuation is the consumption of energy of a sound wave due to gas viscosity, heat conduction effect, etc., and is proportional to the square of the frequency of the sound wave and also related to the temperature and pressure of the gas. Relaxation attenuation is caused by the vibration relaxation effect of gas molecules, and is not only related to the gas environment (temperature, humidity and air pressure), but also has a complex change relation with the frequency of sound waves. The measurement of the acoustic wave attenuation coefficient is started relatively late, and the amplitude of the received acoustic wave is easily influenced by the external environment, so that the measurement accuracy of the acoustic wave attenuation coefficient by many existing measurement methods is low at present. Common methods for measuring the acoustic attenuation coefficient mainly include: resonance, variable-range pulse, radiation force, and back-scattered spectroscopy. However, since the process of measuring the attenuation needs to be performed in a closed low-temperature and low-pressure environment, these methods that require changing the distance over which the sound wave is received by moving the acoustic transducer cannot be realized. If the experimental container is opened or closed to change the distance of sound wave propagation in the measuring process, the consistency of the experimental environment can be damaged, the consistency of environmental parameters such as temperature, air pressure and the like among experimental results at different distances cannot be ensured, and the measuring result of the sound attenuation coefficient has larger error. Therefore, no acoustic attenuation measurement experiment in gas at low temperature and low pressure has been realized domestically.

Disclosure of Invention

In order to solve the defects of the existing measuring method, the invention provides a device and a method for measuring the acoustic attenuation coefficient in a low-temperature and low-pressure environment, wherein an environment simulation container is used for simulating the gas environment condition of low temperature and low pressure, the temperature is set to be a low-temperature range of-80 ℃ to 20 ℃, and the gas pressure is set to be a low-pressure range of 600Pa to 1atm, so that the purpose of measuring the acoustic attenuation coefficient is realized.

The invention provides a sound attenuation coefficient measuring device for a low-temperature and low-pressure environment, which comprises: the transmitting transducer, the receiving transducer, the first fixing support, the second fixing support and the third fixing support are arranged in the completely closed low-temperature and low-pressure environment simulation container; the signal generator, the amplifying circuit and the oscilloscope are arranged outside the closed low-temperature and low-pressure environment simulation container, and the signal generator and the amplifying circuit are connected with the oscilloscope; the data processing module is arranged on the upper computer;

the third fixing support is horizontally arranged, a first fixing support and a second fixing support are respectively arranged at two ends of the third fixing support, a transmitting transducer is arranged on the first fixing support, and a receiving transducer is arranged on the second fixing support;

the signal generator transmits a trigger signal and transmits the trigger signal to the transmitting transducer; converting the trigger signal into an acoustic wave signal;

the sound wave signal is transmitted in the gas of the low-temperature low-pressure environment pre-simulated by the environment simulation container, and the generated direct wave signal and the secondary reflection echo signal are transmitted to the receiving transducer; the receiving transducer receives the direct wave signal and the secondary reflection echo signal and transmits the direct wave signal and the secondary reflection echo signal to the amplifying circuit for amplification;

and the data processing module calculates the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal is transmitted in a certain to-be-detected gas in a low-temperature and low-pressure environment according to the distance between the transmitting transducer and the receiving transducer, the acoustic reflectivity, the voltage amplitude of the amplified direct wave signal and the voltage amplitude of the amplified secondary reflection echo signal.

As an improvement of the above technical solution, the data processing module specifically includes:

the acquisition unit is used for acquiring the direct wave signal and the secondary echo signal which are amplified by the amplifying circuit;

the processing unit is used for acquiring the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal propagates in a certain gas in a low-temperature and low-pressure environment according to the acquired direct wave signal and the secondary echo signal after amplification processing and by using a formula (1):

wherein a is the sound attenuation coefficient; d is the propagation distance of the sound wave signal between the transmitting transducer and the receiving transducer; r is the reflectivity of the sound wave on the gas contact surface of the receiving transducer and a certain gas to be measured in the low-temperature and low-pressure environment; u shape_RThe voltage amplitude of the amplified direct wave signal is obtained; u shape_R2The voltage amplitude of the secondary reflection echo signal after amplification processing is obtained.

As one improvement of the technical scheme, the environment simulation container is used for providing an atmospheric environment with low temperature and low pressure; wherein the low temperature is-80-20 ℃; the low air pressure is 600Pa-1 atm.

As one improvement of the technical scheme, the transmitting transducer and the receiving transducer are horizontally arranged relatively, and the distance between the transmitting transducer and the receiving transducer is 0.15-0.25 m.

As one improvement of the technical scheme, the frequency of the sound wave signal is 20-40 kHz.

The invention also provides a sound attenuation coefficient measuring method for a low-temperature and low-pressure environment, which comprises the following steps:

the signal transmitter generates a trigger signal and transmits the trigger signal to the transmitting transducer;

the transmitting transducer converts the trigger signal into a sound wave signal;

the sound wave signal is transmitted in the gas of the low-temperature low-pressure environment pre-simulated by the environment simulation container, and the generated direct wave signal and the secondary reflection echo signal are transmitted to the receiving transducer; the receiving transducer receives the direct wave signal and the secondary reflection echo signal and transmits the direct wave signal and the secondary reflection echo signal to the amplifying circuit for amplification;

and the data processing module calculates the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal is transmitted in a certain to-be-detected gas in a low-temperature and low-pressure environment according to the distance between the transmitting transducer and the receiving transducer, the acoustic reflectivity, the voltage amplitude of the amplified direct wave signal and the voltage amplitude of the amplified secondary reflection echo signal.

As one improvement of the above technical solution, the data processing module calculates an acoustic attenuation coefficient of an acoustic wave signal when the acoustic wave signal propagates in a certain gas to be measured in a low-temperature and low-pressure environment according to a distance between the transmitting transducer and the receiving transducer, an acoustic reflectivity, a voltage amplitude of the amplified direct wave signal, and a voltage amplitude of the amplified secondary reflection echo signal; the method specifically comprises the following steps:

according to the obtained amplified direct wave signal and secondary echo signal, and by using a formula (1), obtaining the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal is transmitted in a certain gas to be measured in a low-temperature low-pressure environment as follows:

wherein a is the sound attenuation coefficient; d is the propagation distance of the sound wave signal between the transmitting transducer and the receiving transducer; r is the reflectivity of the sound wave on the gas contact surface of the receiving transducer and a certain gas to be measured in the low-temperature and low-pressure environment; u shape_RFor straightening after amplification treatmentThe voltage amplitude of the arrival signal; u shape_R2The voltage amplitude of the secondary reflection echo signal after amplification processing is obtained.

Compared with the prior art, the invention has the beneficial effects that:

the measuring device has a simple structure, an environment simulator does not need to be started repeatedly, the consistency of environment parameters such as temperature, air pressure and the like among experimental results of different distances is ensured, and the error of the measuring result of the sound attenuation coefficient is reduced; in addition, the measuring method provided by the invention realizes quantitative measurement of more accurate sound attenuation coefficient in low-temperature and low-pressure environment aiming at measuring the sound attenuation coefficient in the atmospheric environment of low-temperature environment at-80-20 ℃ and low-pressure environment with the air pressure of 600Pa-1atm, and obtains the conclusion that the sound attenuation coefficient is increased along with the reduction of the air pressure.

Drawings

FIG. 1 is a schematic structural diagram of an acoustic attenuation coefficient measuring apparatus for a low-temperature and low-pressure environment according to the present invention;

FIG. 2 is a schematic diagram of direct wave and secondary reflection echo in an acoustic attenuation coefficient measuring apparatus for low temperature and low pressure environment according to the present invention;

FIG. 3 is a schematic diagram of time domain waveforms of a direct wave and a secondary reflection echo of an embodiment of the acoustic attenuation coefficient measuring apparatus for a low-temperature and low-pressure environment of the present invention.

Detailed Description

The invention will now be further described with reference to the accompanying drawings.

The invention provides a sound attenuation coefficient measuring device for low-temperature and low-pressure environment, as shown in fig. 1, the device comprises: the transmitting transducer 1, the receiving transducer 2, the first fixed bracket 3, the second fixed bracket 4 and the third fixed bracket 5 are arranged in a completely closed low-temperature and low-pressure environment simulation container 6; the signal generator, the amplifying circuit and the oscilloscope are arranged outside the closed low-temperature and low-pressure environment simulation container 6, and the signal generator and the amplifying circuit are connected with the oscilloscope; the data processing module is arranged on the upper computer;

the third fixed support 5 is horizontally arranged, a first fixed support 3 and a second fixed support 4 are respectively arranged at two ends of the third fixed support 5, the transmitting transducer 1 is installed on the first fixed support 3, and the receiving transducer 2 is installed on the second fixed support 4;

the signal generator transmits a trigger signal and transmits the trigger signal to the transmitting transducer 1; converting the trigger signal into an acoustic wave signal, and displaying the acoustic wave signal through an oscilloscope;

the sound wave signal is transmitted in the gas of the low-temperature and low-pressure environment pre-simulated by the environment simulation container 6, and the generated direct wave signal and the secondary reflection echo signal are transmitted to the receiving transducer 2; the receiving transducer 2 receives the direct wave signal and the secondary reflection echo signal, and transmits the direct wave signal and the secondary reflection echo signal to an amplifying circuit for amplification;

and the data processing module calculates the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal is transmitted in a certain to-be-detected gas in a low-temperature and low-pressure environment according to the distance between the transmitting transducer and the receiving transducer, the acoustic reflectivity, the voltage amplitude of the amplified direct wave signal and the voltage amplitude of the amplified secondary reflection echo signal.

As shown in fig. 2, the direct wave signal reaches the receiving transducer 2 after propagating through the propagation distance d of the acoustic wave signal between the transmitting transducer 1 and the receiving transducer 2; the secondary reflection echo signal reaches the receiving transducer 2 after being reflected twice between the transmitting transducer 1 and the receiving transducer 2 and being transmitted by the transmission distance 3d of the sound wave signal between the transmitting transducer 1 and the receiving transducer 2; the frequency of the sound wave signal is 20-40 kHz.

The signal emitter is; HP33120A model signal generator.

The oscilloscope is; a tek DPO3032 oscilloscope.

Wherein, the data processing module is a computer.

The environment simulation container 6 is used for providing an atmospheric environment with low temperature and low pressure; wherein the low temperature is-80-20 ℃; the low air pressure is 600Pa-1 atm. The atmospheric environment includes gas composition, temperature and pressure parameters. Wherein, the environment simulation container 6 is filled with air or nitrogen; the temperature value is preset in the environment simulation container 6, and the air pressure is continuously adjusted to obtain different atmospheric environments.

The transmitting transducer 1 and the receiving transducer 2 are horizontally arranged relatively, and the distance between the transmitting transducer 1 and the receiving transducer 2 is 0.2 m.

The data processing module specifically comprises:

the acquisition unit is used for acquiring the direct wave signal and the secondary echo signal which are amplified by the amplifying circuit;

the processing unit is used for acquiring the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal propagates in a certain gas to be measured in a low-temperature and low-pressure environment according to the acquired direct wave signal and the secondary echo signal after amplification processing and by using a formula (1):

wherein a is the sound attenuation coefficient; d is the propagation distance of the acoustic signal between the transmitting transducer 1 and the receiving transducer 2; r is the reflectivity of the sound wave on the gas contact surface of the receiving transducer 2 and a certain gas to be measured in the low-temperature and low-pressure environment; u shape_RThe voltage amplitude of the amplified direct wave signal is obtained; u shape_R2The voltage amplitude of the secondary reflection echo signal after amplification processing is obtained.

The derivation process of formula (1) for calculating the acoustic attenuation coefficient of the acoustic wave signal when propagating in a certain gas in a low-temperature and low-pressure environment is as follows:

performing attenuation analysis on the voltage amplitudes of the received amplified direct wave signal and the secondary reflection echo signal:

because the amplified direct wave signal and the secondary reflection echo signal are emitted by the sound wave signal with the same voltage amplitude, and are amplified by the same times through the amplifying circuit in the receiving process, the voltage amplitude of the emitted sound wave and the influence of the amplifying circuit on the attenuation result can be not considered; the sound pressure changes according to an exponential decay law, i.e. when a sound wave signal propagates in a gaseous medium

U_d＝U₀e^-αd,

Wherein, U_dIs the sound pressure value at the propagation distance d of the acoustic signal between the transmitting transducer 1 and the receiving transducer 2; u shape₀Is the sound pressure value at the starting point; a is the sound attenuation coefficient of the sound wave signal when the sound wave signal is transmitted in a certain gas in a low-temperature and low-pressure environment; d is the propagation distance of the acoustic signal between the transmitting transducer 1 and the receiving transducer 2, in meters (m).

Since the twice-reflected echo signal is an acoustic wave signal obtained by two reflections, when calculating the amplitude, the reflectivity and transmittance of the acoustic wave at the receiving transducer 2 and the gas contact surface are used:

wherein, R is the reflectivity of the sound wave on the gas contact surface of the receiving transducer 2 and a certain gas to be measured in the low-temperature and low-pressure environment; t is the transmissivity of the sound wave on the gas contact surface of the receiving transducer 2 and a certain gas to be measured in the low-temperature low-pressure environment; z₁Acoustic impedance of a certain gas to be measured in a low-temperature and low-pressure environment of a sound wave signal; z₂To receive the acoustic impedance of the transducer;

wherein the content of the first and second substances,

Z₁＝ρc

wherein Z is₁The acoustic impedance of the gas to be measured; rho is the density of the gas to be measured; c is the sound velocity of the gas to be measured;

receivingAcoustic impedance Z of transducer₂Is a known value;

when the same sound wave signal is transmitted in a certain gas to be measured in a low-temperature low-pressure environment, the voltage amplitude of the direct wave signal after amplification treatment is as follows:

U_R＝U_T×e^-αd×T²×A_T ²,

the voltage amplitude of the secondary emission echo signal after amplification processing is as follows:

U_R2＝U_T×e^-α3d×T²×R²×A_T ²,

wherein, U_RThe voltage amplitude of the amplified direct wave signal is obtained; u shape_R2The voltage amplitude of the secondary reflection echo signal after amplification processing is obtained; u shape_TA voltage amplitude for acoustic signal transmission; a. the_TThe electro-acoustic conversion efficiency;

compared with the two formulas, the obtained sound attenuation coefficient of the sound wave signal when the sound wave signal is transmitted in a certain gas to be measured in a low-temperature and low-pressure environment is as follows:

the invention also provides a sound attenuation coefficient measuring method for a low-temperature and low-pressure environment, which comprises the following steps:

the signal transmitter generates a trigger signal and transmits the trigger signal to the transmitting transducer 1;

the transmitting transducer 1 converts the trigger signal into an acoustic wave signal and displays the acoustic wave signal through an oscilloscope;

the sound wave signal is transmitted in the gas of the low-temperature and low-pressure environment pre-simulated by the environment simulation container 6, and the generated direct wave signal and the secondary reflection echo signal are transmitted to the receiving transducer 2; the receiving transducer 2 receives the direct wave signal and the secondary reflection echo signal, and transmits the direct wave signal and the secondary reflection echo signal to an amplifying circuit for amplification;

and the data processing module calculates the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal is transmitted in a certain to-be-detected gas in a low-temperature and low-pressure environment according to the distance between the transmitting transducer and the receiving transducer, the acoustic reflectivity, the voltage amplitude of the amplified direct wave signal and the voltage amplitude of the amplified secondary reflection echo signal.

According to the obtained amplified direct wave signal and secondary echo signal, and by using a formula (1), obtaining the acoustic attenuation coefficient of the acoustic wave signal when the acoustic wave signal propagates in a certain gas to be measured in a low-temperature and low-pressure environment as follows:

wherein a is the sound attenuation coefficient; d is the propagation distance of the acoustic signal between the transmitting transducer 1 and the receiving transducer 2; r is the reflectivity of the sound wave on the gas contact surface of the receiving transducer 2 and a certain gas to be measured in the low-temperature and low-pressure environment; u shape_RThe voltage amplitude of the amplified direct wave signal is obtained; u shape_R2The voltage amplitude of the secondary reflection echo signal after amplification processing is obtained.