A shallow buried non-metallic object detection system

Abstract

The present invention discloses a shallow buried non-metallic object detection system, the system comprising: an acoustic wave transmitting component, an acoustic wave receiving component and a spectrum analyzer; the acoustic wave transmitting component is used to transmit two sound source / vibration source signals of different frequencies; the acoustic wave receiving component is used to receive the signal, amplify and filter it, and then send it to the spectrum analyzer; the spectrum analyzer is used to perform fast Fourier transform on the collected signal, draw a spectrum diagram of the signal, and detect whether there is a sum frequency or difference frequency signal in addition to the frequencies of the two sound sources / vibration sources in the signal spectrum diagram. If there is, the buried object is a non-metallic object, thereby realizing the detection of the buried non-metallic object. The system of the present invention identifies non-metallic objects by the difference in the acoustic properties of the material, and has the advantages of simple operation, low cost, easy implementation, and not being affected by weather and soil moisture.

Description

Technical Field

[0001] The invention relates to the field of geophysical exploration technology, and in particular to a shallow buried non-metallic object detection system. Background Art

[0002] Shallow buried non-metallic objects refer to non-metallic objects buried within 1 meter underground. Since their flexibility is much greater than that of rigid objects such as metals and rocks, they are also called flexible objects. With the advancement of science and technology, the physical and chemical properties of many non-metallic materials have made a qualitative leap, and because these non-metallic materials have the advantages of low cost, light weight, non-toxicity, corrosion resistance, easy processing, manufacturing and maintenance, they can gradually replace metal materials in some fields, such as non-metallic water supply and gas supply pipelines in municipal construction, non-metallic pressure vessels in the petrochemical and pharmaceutical industries, and non-metallic mines and bombs in the military.

[0003] In the field of traditional geophysical exploration, since the target objects to be detected are mainly metal products, researchers have developed many detection methods based on electrical and magnetic principles. However, due to the characteristics of non-metallic materials that they are not (weakly) conductive or magnetic, these traditional methods are not ideal when detecting non-metallic objects. Summary of the invention

[0004] The purpose of the present invention is to overcome the above technical defects and propose an acoustic detection system and method based on nonlinear resonance effect for shallow buried non-metallic objects. Since the acoustic characteristics (characteristic impedance) of non-metallic objects are quite different from those of soil, metal objects and rocks, the influence of interfering objects in the soil can be effectively avoided, making the detection accuracy of non-metallic objects higher.

[0005] In order to achieve the above-mentioned object, the present invention proposes a shallow buried non-metallic object detection system, the system comprising: an acoustic wave transmitting component, an acoustic wave receiving component and a spectrum analyzer;

[0006] The sound wave transmitting component is used to transmit two sound source / vibration source signals of different frequencies;

[0007] The sound wave receiving component is used to receive signals, amplify and filter them, and then send them to the spectrum analyzer;

[0008] The spectrum analyzer is used to perform fast Fourier transform on the collected signal, draw a spectrum diagram of the signal, and detect whether there is a sum frequency or difference frequency signal in the signal spectrum diagram in addition to the frequencies of the two sound sources / vibration sources. If so, the buried object is a non-metallic object, thereby realizing the detection of buried non-metallic objects.

[0009] As an improvement of the above system, the sound wave transmitting component includes two sound sources, and the sound wave signals emitted by each sound source have different frequencies; the sound source includes: a signal generator, a power amplifier and a speaker;

[0010] The signal generator generates an excitation signal required for detection, wherein the excitation signal is a single-frequency excitation, a random excitation or a swept-frequency excitation with a frequency range lower than 2000 Hz;

[0011] The power amplifier uses a power amplifier with adjustable amplification factor to amplify the power of the excitation signal generated by the signal generator;

[0012] The loudspeaker converts the electrical signal output by the power amplifier into a ground excitation signal and radiates the excitation energy into the soil.

[0013] As an improvement of the above system, the acoustic wave emission component includes two vibration sources, and the vibration signal emitted by each vibration source has a different frequency; the vibration source includes: a signal generator, a power amplifier and an exciter;

[0014] The signal generator generates an excitation signal required for detection, wherein the excitation signal is a single-frequency excitation, a random excitation or a swept-frequency excitation with a frequency range lower than 2000 Hz;

[0015] The power amplifier uses a power amplifier with adjustable amplification factor to amplify the power of the excitation signal generated by the signal generator;

[0016] The exciter converts the electrical signal output by the power amplifier into a ground excitation signal and radiates the excitation energy into the soil.

[0017] As an improvement of the above system, the sound wave receiving component includes: a sensor array, a preamplifier, a filter and a signal acquisition card;

[0018] The sensor array is an array composed of multiple sensors, which is used to convert sound wave signals / vibration signals into electrical signals;

[0019] The preamplifier is used to amplify the electrical signal;

[0020] The analog filter is used to filter the amplified electrical signal;

[0021] The signal acquisition card is used to convert the filtered analog electrical signal into a digital electrical signal and output it to the spectrum analyzer.

[0022] As an improvement to the above system, the sensor is a seismic detector, an accelerometer or a vibrometer.

[0023] As an improvement to the above system, the number of channels of the signal acquisition card is not less than the number of sensors in the sensor array.

[0024] As an improvement to the above system, the signal sampling frequency of the signal acquisition card is 3-5 times the sensor frequency.

[0025] The advantages of the present invention are:

[0026] 1. The system of the present invention identifies non-metallic objects by differences in the acoustic properties of materials, and has the advantages of being simple to operate, low cost, easy to implement, and not affected by weather and soil moisture;

[0027] 2. The nonlinear resonance effect adopted by the system of the present invention can effectively avoid the influence of interference objects such as metals and rocks on the detection results, has strong pertinence, and can greatly improve the detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of shallow buried non-metallic object detection;

[0029] Figure 2(a) is a diagram of the soil-buried object stable state;

[0030] Figure 2(b) is a diagram of the soil-buried object compression state;

[0031] Figure 2(c) shows the tensile state of the soil-buried object;

[0032] Figure 3 It is a nonlinear equivalent model of soil-buried non-metallic object;

[0033] FIG4( a ) is a schematic diagram of the spectrum of the detection signal without an object;

[0034] Figure 4(b) is a schematic diagram of the spectrum of the detection signal of a rigid body;

[0035] FIG4( c ) is a schematic diagram of the detection signal spectrum of a non-metallic object;

[0036] Figure 5 It is a schematic diagram of the buried non-metallic object detection system of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the accompanying drawings.

[0038] The principle of the present invention is as follows: The schematic diagram of shallow buried non-metallic object detection based on nonlinear resonance effect is as follows Figure 1As shown. When a dual sound source or vibration source (or a single sound source or vibration source that can emit two excitation signals at the same time) is used to excite the ground, when there is no buried object under the surface, the sound wave will gradually attenuate in the process of propagating deep into the soil, and only the excitation source signal and the interference noise signal can be detected on the surface. Therefore, the frequency components of the received signal and the excitation source signal are very similar, but there is a certain degree of attenuation in the amplitude. When there is a buried object under the surface, the soil-buried object can be regarded as a forced vibration system. When the sound wave coupled into the soil propagates to the surface of the object, firstly, due to the large difference in acoustic impedance between the buried object and the soil, strong reflection or scattering will occur at the soil-buried object interface; secondly, under the action of sound pressure, the system composed of the soil-buried object will resonate, thereby increasing the intensity of the reflected echo of the target object; thirdly, due to the large flexibility of non-metallic objects, nonlinear effects will occur under the action of sound pressure, which will change the frequency component of the sound wave, and actually modulate the sum frequency (or difference frequency) of the two sound wave signals. The signal modulated by the buried object is reflected and propagates back to the surface. The echo signal is picked up by the sensor array installed on the surface, and then the collected signal is subjected to fast Fourier transform (FFT) to draw a spectrum diagram of the signal. By comparing the signal components in the spectrum diagram with the frequency components of the excitation source signal, it can be determined whether there are buried non-metallic objects in the detection area.

[0039] The nonlinear effect of soil-buried object forced vibration means that when the system is not subjected to external force, the system is in a stable state, as shown in Figure 2(a); when the soil is subjected to external force, there will be two processes of compression and tension. Due to the greater flexibility of non-metallic objects, during the compression process, the soil squeezes the non-metallic object to cause deformation, and the interface between the two is tightly combined, as shown in Figure 2(b); during the tension process, the different flexibility of the soil and non-metallic objects leads to a certain degree of separation at the interface between the two, as shown in Figure 2(c). The equivalent mechanical model of the compression and tension stages is shown in Figure 3 As shown, k1 and k2 represent the stiffness of soil and buried objects respectively.

[0040] The nonlinear effect modulates the acoustic wave signal at the soil-buried non-metallic object interface and generates new sum frequency or difference frequency signals, as shown in formula (1):

[0041] f=mf1±nf2(m,n are natural numbers)(1)

[0042] Figure 4(a), Figure 4(b) and Figure 4(c) respectively show the schematic diagrams of the detection signal spectrum when there is no buried object, the buried object is a rigid body (such as metal or rock), and the buried object is non-metal. The detection of buried non-metallic objects can be achieved by analyzing the frequency components in the spectrum diagram.

[0043] like Figure 5 As shown, the present invention proposes a shallow buried non-metallic object detection system, the detection system mainly includes three parts: a sound wave transmitting part, a sound wave receiving part and a signal processing part, wherein the signal transmitting part adopts two sound sources / vibration sources to respectively transmit signals of different frequency components (or adopts a single sound source / vibration source that can simultaneously transmit two excitation signals), specifically including: signal generators 1 and 2, power amplifiers 1 and 2, speakers (exciters) 1 and 2; the signal receiving part includes: a sensor array (the sensor adopts a vibration measuring instrument such as a seismic detector, an accelerometer or a vibrometer), a preamplifier, a filter, and a signal acquisition card; the signal analysis part includes: a spectrum analyzer.

[0044] (1) Signal generator

[0045] An arbitrary waveform signal generator is used to generate the excitation signal required for detection. Generally, single-frequency excitation, random excitation or swept frequency excitation with a frequency range below 2000Hz is used. The signals of signal generators 1 and 2 need to have a certain frequency component difference.

[0046] (2) Power amplifier

[0047] A power amplifier with adjustable amplification factor is used to amplify the modulated signal generated by the signal generator, thereby increasing the penetration depth of the sound wave in the soil. The specific amplification factor in practical applications should be determined based on soil parameters (such as looseness, humidity, etc.).

[0048] (4) Speaker (exciter)

[0049] The function of the loudspeaker (exciter) is to convert the electrical signal into a ground excitation signal and radiate the excitation energy into the soil. The loudspeaker is non-contact with the ground surface, which has the advantage of not damaging the surface vegetation and infrastructure, but the acoustic wave coupling efficiency is relatively low, so the detection depth is limited. If the object is buried deep, a contact exciter can be used, so that the exciter and the soil are directly mechanically connected, which can transmit the acoustic energy to the soil to a greater extent.

[0050] (5) Sensor array

[0051] Sensors use instruments such as seismometers, accelerometers or vibrometers to measure vibrations and convert vibration signals into electrical signals. In theory, only a single sensor can be used for measurement, but in order to improve the reliability of the detection system, multiple sensors are generally used in an array.

[0052] (6) Preamplifier and filter

[0053] The sound wave signal reflected back to the surface by the buried object is relatively weak after attenuation by the soil, and is mixed with noise signals. In order to improve the signal-to-noise ratio, it is necessary to first use a preamplifier to amplify the signal, and then use an analog filter to filter it, which is conducive to subsequent signal processing and analysis.

[0054] (7) Signal acquisition card

[0055] The signal acquisition card converts analog electrical signals into digital electrical signals. The number of channels of the acquisition card should not be less than the number of sensors in the sensor array, and the signal sampling frequency is generally 3-5 times the sensor frequency.

[0056] (8) Spectrum Analyzer

[0057] The function of the spectrum analyzer is to perform fast Fourier transform on the collected signal to obtain the signal's spectrum diagram, and analyze the signal's frequency components to find out whether there are sum frequency or difference frequency signals in the signal spectrum diagram in addition to the excitation source frequencies f1 and f2, thereby realizing the detection of buried non-metallic objects.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A shallow buried non-metallic object detection system, characterized in that: The system comprises: an acoustic wave transmitting component, an acoustic wave receiving component and a spectrum analyzer; The sound wave transmitting component is used to transmit two sound source / vibration source signals of different frequencies; The sound wave receiving component is used to receive signals, amplify and filter them, and then send them to the spectrum analyzer; The spectrum analyzer is used to perform fast Fourier transform on the collected signal, draw a spectrum diagram of the signal, and detect whether there is a sum frequency or difference frequency signal in addition to the frequencies of the two sound sources / vibration sources in the signal spectrum diagram. If so, the buried object is a non-metallic object, thereby realizing the detection of the buried non-metallic object; The acoustic wave emission component includes two sound sources, and the acoustic wave signals emitted by each sound source have different frequencies; the sound source includes: a signal generator, a power amplifier and a speaker; the signal generator generates an excitation signal required for detection, and the excitation signal is a single-frequency excitation, a random excitation or a swept frequency excitation with a frequency range lower than 2000 Hz; the power amplifier uses a power amplifier with adjustable amplification factor to amplify the excitation signal generated by the signal generator; the speaker converts the electrical signal output by the power amplifier into a ground excitation signal, and radiates the excitation energy into the soil; or The acoustic wave emission component includes two vibration sources, and the vibration signal emitted by each vibration source has a different frequency; the vibration source includes: a signal generator, a power amplifier and an exciter; the signal generator generates an excitation signal required for detection, and the excitation signal is a single-frequency excitation, a random excitation or a swept frequency excitation with a frequency range lower than 2000 Hz; the power amplifier uses a power amplifier with adjustable amplification factor to amplify the power of the excitation signal generated by the signal generator; the exciter converts the electrical signal output by the power amplifier into a ground excitation signal, and radiates the excitation energy into the soil; The sound wave receiving component includes: a sensor array, a preamplifier, a filter and a signal acquisition card; The sensor array is an array composed of multiple sensors, which is used to convert sound wave signals / vibration signals into electrical signals; The preamplifier is used to amplify the electrical signal; The filter is used to filter the amplified electrical signal; The signal acquisition card is used to convert the filtered analog electrical signal into a digital electrical signal and output it to the spectrum analyzer; The sensor is a seismometer, an accelerometer or a vibrometer; The number of channels of the signal acquisition card is not less than the number of sensors in the sensor array.

2. The shallow buried non-metallic object detection system according to claim 1 is characterized in that: The signal sampling frequency of the signal acquisition card is 3-5 times the sensor frequency.

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