CN114449431B - Method and system for carrying out nondestructive testing on loudspeaker diaphragm by using terahertz waves - Google Patents
Method and system for carrying out nondestructive testing on loudspeaker diaphragm by using terahertz waves Download PDFInfo
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Abstract
The invention relates to a method and a system for carrying out nondestructive testing on a loudspeaker diaphragm by using terahertz waves. The method comprises the following steps: the terahertz transceiver integrated equipment comprises terahertz transceiver integrated equipment, a gain antenna and a control computer. The terahertz wave is emitted by the emission source, and is converged by the gain antenna and directly irradiated to the surface of the loudspeaker. And the terahertz detector measures the intensity of the reflected terahertz waves and performs time-frequency analysis. The frequency of each point on the surface of the speaker having the maximum energy is obtained, imaging is performed, and the position of the damage or abnormal shape of the speaker is detected from the frequency abnormal point on the image. The present invention does not require expensive ultrasound detection equipment and highly radioactive radiographic equipment. The vibration frequency of each point on the surface of the terahertz wave is obtained by transmitting terahertz waves to a loudspeaker, collecting echo data, analyzing and carrying out time-frequency analysis on phase information. And determining the position of the loudspeaker surface with damage or abnormal shape according to the abnormal frequency occurrence position in the frequency image.
Description
Technical Field
The invention relates to the field of nondestructive testing of a vibrating diaphragm of a loudspeaker by using terahertz waves. In particular to a method and a system for realizing nondestructive detection by using terahertz waves.
Background
With the development of industry and the continuous improvement of technical level in China, the requirements of the product line on the organization state and the structure of the finished product are gradually improved. In this context, non-destructive testing techniques have entered the field of view of a wide range of researchers. The nondestructive testing technology is to utilize the change of the reaction of heat, sound, light, electricity, magnetism and the like caused by the abnormal structure or defect of the material on the premise of not influencing the service performance and the organizational structure of a tested object when the object is tested, and combine the advanced processing method and the special instrument and equipment to carry out the testing. The main non-destructive inspection methods today are inspection using ultrasound or X-rays. However, in recent decades, with intensive research in the fields of photonics and electronics by researchers, the technology of radiation and detection of terahertz waves has also been developed rapidly. Its wavelength is in the range of 0.03mm to 3 mm. Compared with ultrasonic nondestructive detection, terahertz waves have higher frequency and the frequency domain coverage of terahertz wave equipment is wider. More detailed object conditions can be obtained through analysis of terahertz echoes. In addition, the wavelength of terahertz waves is longer and safer than that of X-ray nondestructive testing. This property enables terahertz wave to detect subtle structural changes of the loudspeaker through the surface material. The advantages enable the terahertz waves to have wide application prospects in the field of nondestructive testing.
The existing nondestructive testing method mainly comprises the steps of injecting ultrasonic waves into a loudspeaker for testing or irradiating the loudspeaker with X rays. Ultrasonic testing has high requirements on the shape of the object to be tested and the grain size of the defect position. The disadvantage of the X-ray detection method is that the radiation is too strong to be handled and used.
Disclosure of Invention
In view of the technical deficiencies, the invention provides a method and a system for nondestructive testing by using terahertz waves. After the terahertz waves are reflected on the surface of the loudspeaker, the phase information in the echo can accurately represent the fine distance change between the loudspeaker and the wave source. And analyzing the phase information through Hilbert-Huang transformation to obtain the instantaneous frequency and instantaneous amplitude of each point on the surface of the loudspeaker, and calculating the amplitude to obtain the frequency and corresponding energy of each point of the loudspeaker at the moment. Further, the image is rendered by combining the vibration frequency of each point having the maximum energy and the position information of each point. The abnormal defect point of the loudspeaker can be determined in position by finding out the position of the abnormal vibration frequency from the image.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a method for carrying out nondestructive testing on a loudspeaker diaphragm by using terahertz waves comprises the following steps:
the method comprises the steps that terahertz waves with preset frequency are transmitted by terahertz transmitting-receiving integrated equipment, the terahertz waves irradiate a loudspeaker to be tested along a set propagation direction after passing through a gain antenna, and the terahertz waves interfere with vibration signals of a loudspeaker diaphragm to generate interference echo signals;
the position of a loudspeaker fixed on the displacement table is adjusted in real time through the movement of the displacement table, so that the loudspeaker moves in a plane where a vibrating diaphragm of the loudspeaker is located according to a preset step length and a track, and the terahertz wave scanning irradiation range can cover the whole vibrating diaphragm;
setting sampling times, and controlling the terahertz transceiving integrated equipment to acquire and store echo intensity sequences of a series of terahertz waves corresponding to each sampling point of the diaphragm after the vibration interference of the diaphragm of the loudspeaker;
analyzing the value of the echo intensity sequence, acquiring echo phase information, and analyzing the maximum energy and frequency of each sampling point on the surface of the loudspeaker diaphragm according to Hilbert-Huang transform;
and visualizing the frequency-coordinate atlas of the maximum energy of each sampling point of the loudspeaker diaphragm to judge whether the loudspeaker diaphragm to be tested has defects and the positions of the defects.
The preset frequency meets the Shannon sampling theorem, and multiple times of setting is carried out according to the overtone frequency of the signal to be detected.
The displacement table moves in two dimensions in the horizontal direction and the vertical direction in the plane of the loudspeaker diaphragm.
The preset track moves row by row, so that the terahertz waves scan each sampling point on the surface of the loudspeaker diaphragm row by row.
The analyzing the maximum energy frequency of each sampling point on the surface of the loudspeaker diaphragm according to Hilbert-Huang transform comprises the following steps:
1) decomposing the terahertz echo signal by using an Empirical Mode Decomposition (EMD) method, and decomposing the terahertz echo signal into a form of combining a plurality of empirical mode functions (IMFs) and residual errors, wherein the Empirical Mode Decomposition (EMD) method is specifically expressed as follows:
where ε (t) is the terahertz echo signal, i is the number of empirical mode components, IMF i Is a natural empirical mode component, r K The residual term is obtained by subtracting each empirical mode component from the original signal;
2) performing Hilbert transform on each empirical mode component IMF, setting the IMF component as x (t), then performing Hilbert transform on the IMF component into H [ x (t) ], and converting local estimation into global estimation:
wherein, tau refers to the whole time interval of the signal where x (t) is located;
3) obtaining an analytic signal of a real-valued function of the echo signal, wherein the specific complex number expression form is as follows:
wherein u (t) is a real-valued function,
is the analytic signal of x (t),
is the function H [ x (t) after Hilbert transform of u (t)]Analyzing the signal
The mode and the argument of (a) represent the amplitude and the phase of the two-dimensional signal, i.e. the instantaneous frequency and the instantaneous amplitude of the echo signal;
4) and acquiring the frequency of the maximum energy of the signal at the moment by taking the maximum instantaneous amplitude as the maximum energy, and taking the frequency as the vibration frequency of the point on the surface of the loudspeaker diaphragm to make a frequency-coordinate graph of the maximum energy.
And judging whether the loudspeaker diaphragm to be detected is damaged or abnormal in shape according to the energy frequency difference value of any point and surrounding points on the maximum energy frequency spectrogram of each sampling point of the loudspeaker diaphragm.
A system for nondestructive testing of a loudspeaker diaphragm using terahertz waves, comprising: the terahertz receiving and transmitting integrated device comprises terahertz receiving and transmitting integrated equipment, a gain antenna, a displacement platform, a control computer and a loudspeaker to be tested;
the terahertz transceiver integrated equipment comprises a vector network analyzer, a spread spectrum module and a frequency expander which are sequentially connected; the waveguide output port of the frequency expander is connected with a gain antenna; the gain antenna is horn-shaped, and the opening of the gain antenna faces the loudspeaker to be tested; the vector network analyzer is connected with a control computer; the terahertz wave is emitted by the vector network analyzer, is received by the gain antenna and directly irradiates the surface of the loudspeaker, and is used as a vector network analyzer of the terahertz detector to collect a reflected terahertz echo intensity sequence signal;
the displacement platform is a two-dimensional platform and comprises a servo motor, a driver, a transverse linear motion module and a longitudinal linear motion module, the loudspeaker is fixed on the transverse motion module, and the transverse linear motion module and the longitudinal linear motion module are driven to move through the servo motor, so that the position of the loudspeaker is adjusted; the driver is connected with the control computer through a communication interface;
the control computer comprises a storage part and a processing part, the storage part stores programs, and the processing part loads the programs to execute the method steps to realize the detection of the defect or abnormal form position of the surface of the loudspeaker diaphragm.
And the surface of the loudspeaker is covered with tin foil paper for improving the transmissivity of echo signals.
The invention has the following beneficial effects and advantages:
1. the invention provides a novel nondestructive testing method, which can realize fine measurement of a loudspeaker and defect judgment of the surface of the loudspeaker by utilizing higher spatial resolution of terahertz waves.
2. The invention adopts a phase recovery method, can accurately measure the slight distance change between the loudspeaker and the detection device, and further determines the position of the surface defect of the loudspeaker and the frequency change condition with maximum energy around the position.
3. The invention uses a displacement translation stage to move the loudspeaker. Due to the fact that the emission source of the terahertz waves is fixed, the terahertz waves can be covered on various positions of the surface of the loudspeaker by the translation stage.
4. The terahertz wave detector can detect without contacting with a loudspeaker, and is low in radiation energy of terahertz waves, safe and reliable.
Drawings
Fig. 1 is a schematic view of nondestructive testing of a speaker using terahertz waves.
FIG. 2 is a flow chart of the present invention.
FIG. 3 shows the detection result of the present invention when a speaker is playing pure 150Hz sound; (a) a vibration amplitude image of a loudspeaker diaphragm; (b) a phase image of the vibration of the loudspeaker diaphragm; (c) the frequency image with the maximum energy at each point of the loudspeaker.
FIG. 4 is a diagram of the test results of the present invention when a speaker is playing a pure 400Hz tone; (a) an image of the amplitude of the vibration of the loudspeaker diaphragm, (b) an image of the phase of the vibration of the loudspeaker diaphragm, (c) an image of the frequency of the points of the loudspeaker having the greatest energy.
The terahertz transmission and receiving integrated equipment comprises a terahertz transmission source, a terahertz detector, a gain antenna, a loudspeaker, a displacement translation table and an electronic computer, wherein 1 is terahertz transmission and receiving integrated equipment, 2 is the terahertz transmission source, the terahertz detector is also the terahertz emission source, 3 is the gain antenna, 4 is the displacement translation table, and 5 is the electronic computer.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather should be construed as modified in the spirit and scope of the present invention as set forth in the appended claims.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
Fig. 1 is a schematic diagram of the system of the present invention. The invention uses terahertz waves to carry out nondestructive testing on the loudspeaker diaphragm. The system comprises: the terahertz transceiver integrated equipment comprises terahertz transceiver integrated equipment 1, a gain antenna 2, a sound source loudspeaker 3, a displacement translation stage 4 and an electronic computer 5. The terahertz transceiver integrated equipment 1 comprises a vector network analyzer, a spread spectrum module and a frequency expander which are sequentially connected; the waveguide output port of the frequency expander is connected with the gain antenna; the booster antenna 2 has a horn shape, and is opened toward the speaker 3. The vector network analyzer is connected with a control computer 5. The terahertz waves are emitted by the vector network analyzer, and are converged by the gain antenna and directly irradiated to the surface of the loudspeaker 3. Meanwhile, a vector network analyzer serving as a terahertz detector measures the intensity of the reflected terahertz waves, and the control computer 5 detects the defect position of the surface of the loudspeaker through a time-frequency analysis principle. The position of the loudspeaker fixed on the displacement table is adjusted in real time through the movement of the displacement table, so that the loudspeaker moves in a plane where the vibrating diaphragm is located according to a preset step length and a track, and the terahertz wave scanning irradiation range can cover the whole vibrating diaphragm.
Referring to fig. 2, which is a flow chart of the present invention, terahertz waves are emitted to a speaker whose surface is covered with tinfoil, so that the terahertz waves are reflected on the surface of the speaker. In order to ensure that the information on the surface of the loudspeaker is collected, the loudspeaker is moved by using a displacement translation stage. After analyzing and imaging the collected terahertz echo signals, extracting the vibration frequency with maximum energy of each point on the surface of the loudspeaker, and determining the defect part on the surface of the loudspeaker, wherein the method comprises the following steps:
1. a method for carrying out nondestructive testing on a loudspeaker diaphragm by using terahertz waves is characterized by comprising the following steps
And 2, adding a gain antenna corresponding to the frequency range at the front end of the frequency expander to enable terahertz waves emitted by a Vector Network Analyzer (VNA) to be intensively irradiated onto the surface of the loudspeaker.
And 3, setting parameters in the vector network analyzer to enable the sampling frequency of the parameters to be not lower than 6 times of the maximum frequency of the sound played by the tested loudspeaker.
And 4, starting a loudspeaker to play sound and simultaneously starting a data acquisition program and a displacement translation stage control program to acquire the terahertz echo.
The detailed steps are as follows:
And 2, adding a gain antenna corresponding to the frequency range at the front end of the frequency expander to enable terahertz waves emitted by a Vector Network Analyzer (VNA) to be intensively irradiated onto the loudspeaker.
And 3, setting parameters in the vector network analyzer so that the sampling frequency of the parameters is not lower than 6 times of the maximum frequency of the sound played by the tested loudspeaker.
3.1, the setting of the sampling frequency of the vector network analyzer comprises the following steps:
a. setting parameters including the number n of sampling points and the medium frequency bandwidth m in a vector network analyzer;
b. calculating the sampling frequency:
wherein, the scanning time t is obtained by the vector network analyzer according to the number n of sampling points and the medium frequency bandwidth m;
c. if the calculated sampling frequency f s If the Shannon sampling theorem is satisfied, stopping setting the parameters, otherwise, returning to the step a to reset the parameters.
The Shannon sampling theorem formula is as follows:
wherein f is s,min Is f s B is the bandwidth of the sound signal to be measured, M is
Fractional part of the result, N is the integer part, f max The maximum frequency of the sound played by the loudspeaker in the echo signal to be tested is obtained. This enables the maximum frequency in the sound played by the loudspeaker to be measured. However, overtones of the played sound often occur during speaker operation. The wavelength of an overtone is typically an integer fraction of the fundamental, i.e., the frequency of an overtone will be an integer multiple of the frequency of the sound played by the speaker. The second overtones and the third overtones are the most common. Therefore, in this embodiment, in order to measure the region where the main third harmonic occurs in the speaker, the sampling frequency of the vector network analyzer needs to be set to 6 times or more of the maximum frequency of the sound played by the speaker.
4.1, when data acquisition is carried out on each point on the surface of the loudspeaker, the loudspeaker is fixed on the displacement translation table, so that the loudspeaker can move horizontally and vertically in two dimensions on the plane where the vibrating diaphragm is located according to a preset track. The translation stage control program sets the distance to 1mm for 1s movement, and the whole movement range covers the area of the loudspeaker diaphragm. The preset track is moved row by row and column by column, so that the laser scans each sampling point on the loudspeaker diaphragm row by column.
And 5, analyzing the terahertz echo signal, acquiring phase information, and analyzing the frequency with the maximum energy of each point on the surface of the loudspeaker through Hilbert-Huang transform.
5.1, the analyzing the frequency with maximum energy of each point on the surface of the loudspeaker through the Hilbert-Huang transform comprises the following steps:
the echo signal of terahertz is decomposed using the proposed Empirical Mode Decomposition (EMD) algorithm in the hilbert-yellow transform into a form of a combination of a plurality of empirical mode functions (IMFs) and a residual. The specific expression form is shown in the following formula.
In formula (3), ε (t) is an echo signal of the terahertz wave, IMF i Are K natural empirical mode components, r K Is the residual remainder left after the original signal has subtracted the IMF. When empirical mode decomposition is carried out, the upper envelope line and the lower envelope line of the original terahertz echo signal are determined firstly. After the upper envelope line and the lower envelope line are determined, the mean value of the ordinate is taken from two points with the same abscissa and different ordinate on the two lines, and then the mean value line of the two envelope lines is obtained. An intermediate signal obtained by subtracting the mean line from the original signal of the terahertz wave needs to be subjected to IMF (intrinsic mode function) determination. If the intermediate signal is within the entire data section, the number of extreme points and the number of zero-crossing points must be equal or differ by at most not more than one. In addition, the average value of the upper envelope formed by the local maximum point and the lower envelope formed by the local minimum point is zero at any time, that is, the upper and lower envelopes are locally symmetrical with respect to the time axis. If the intermediate signal satisfies the above condition, the intermediate signal is an IMF component of the original signal of the terahertz wave. When next IMF decomposition is carried out, the obtained IMF component is subtracted from the original echo signal, and the operation is repeated to decompose the original echo signal.
After obtaining the IMF components of the original signal, a hilbert transform is performed on each IMF component. The IMF component is defined as x (t), and Hilbert transform is performed on the IMF component to H [ x (t) ]
The significance of the hilbert transform implemented by equation (4) is to convert a local estimate into a global estimate, where τ is the overall time interval of the signal where x (t) is located.
It can be seen from equation (4) that the result of the hilbert transform is the output of a linear time invariant system of the input x (t). The impulse response of the system is
In other words, hilbert passes the original signal through a filter or a redirector. In a physical sense, the analytic signal of a real-valued function can be represented as the sum of the real-valued function itself and its hilbert transform. The concrete expression is as follows.
In equation (5), u (t) is a real-valued function,
is the analytic signal of u (t).
Is a function of u (t) after the Hilbert transform. In this process, the real and imaginary parts of the analytic signal have the same power spectrum and the same autocorrelation function. The practical significance of the hilbert transform is to convert the received real signal into an analytic signal. During this transformation, the one-dimensional signal becomes a signal on the two-dimensional complex plane. The modulus and argument of the complex number represent the amplitude and phase of the two-dimensional signal, resulting in the instantaneous frequency and instantaneous amplitude of the signal. After the instantaneous frequency and the instantaneous amplitude of the echo signal are obtained, the frequency with the maximum energy contained in the signal at the moment can be obtained. The present invention considers this frequency as the dominant frequency of vibration at that point on the loudspeaker diaphragm surface and stores it.
When the frequency with the maximum energy of each point on the diaphragm is acquired, frequency data is combined with the position of the point and imaged by the data. If the vibrating diaphragm of the loudspeaker is damaged or is not complete in form, the generated image can judge the quality condition or the damage condition of the vibrating diaphragm at the actual position through the abnormal frequency in a certain area. Typically, the frequency of the vibration with the greatest energy at the location of the breakage will suddenly change, and this will lead to a situation where the frequency suddenly changes in the area around it. It can be said that the morphology of the loudspeaker at this location has changed if an abrupt change in the vibration frequency occurs in the image.
FIG. 3 is a diagram showing the detection result of the present invention when a speaker is playing pure 150Hz sound; wherein, (a) is a vibration amplitude image of the loudspeaker diaphragm; (b) phase images of the vibration of the loudspeaker diaphragm; (c) the center frequency of vibration at each point of the loudspeaker is shown. FIG. 4 shows the detection result of the present invention when a speaker is playing a pure 400Hz sound; (a) the image (b) is a vibration amplitude image of the diaphragm of the loudspeaker, and the image (c) is a vibration center frequency image of each point of the loudspeaker, and as can be seen from the graph (c) in fig. 3 and the graph (c) in fig. 4, the distribution of the yellow points has abnormal frequency when the loudspeaker works, and it can be determined that the position is an abnormal position.
The foregoing is directed to the primary features of the present invention and it is believed that those skilled in the art will recognize that many changes and modifications may be made thereto without departing from the principles of the invention as set forth in the following claims.
Claims (8)
1. A method for carrying out nondestructive testing on a loudspeaker diaphragm by using terahertz waves is characterized by comprising the following steps:
the method comprises the steps that terahertz waves with preset frequency are transmitted by terahertz transmitting-receiving integrated equipment, the terahertz waves irradiate a loudspeaker to be tested along a set propagation direction after passing through a gain antenna, and the terahertz waves interfere with vibration signals of a loudspeaker diaphragm to generate interference echo signals;
the position of a loudspeaker fixed on the displacement table is adjusted in real time through the movement of the displacement table, so that the loudspeaker moves in a plane where a vibrating diaphragm of the loudspeaker is located according to a preset step length and a track, and the terahertz wave scanning irradiation range can cover the whole vibrating diaphragm;
setting sampling times, and controlling the terahertz transceiving integrated equipment to acquire and store echo intensity sequences of a series of terahertz waves corresponding to each sampling point of the diaphragm after vibration interference of the diaphragm of the loudspeaker;
analyzing the value of the echo intensity sequence, acquiring echo phase information, and analyzing the maximum energy and frequency of each sampling point on the surface of the loudspeaker diaphragm according to Hilbert-Huang transform;
and visualizing the frequency-coordinate atlas of the maximum energy of each sampling point of the loudspeaker diaphragm to judge whether the loudspeaker diaphragm to be tested has defects and the positions of the defects.
2. The method for nondestructive testing of a diaphragm of a loudspeaker by using terahertz waves as claimed in claim 1, wherein the preset frequency satisfies shannon's sampling theorem and is set in multiples according to harmonic overtone frequencies of signals to be tested.
3. The method for nondestructive testing of a loudspeaker diaphragm using terahertz waves as claimed in claim 1, wherein said stage movement is a two-dimensional movement in both horizontal and vertical directions in a plane in which the loudspeaker diaphragm is located.
4. The method for nondestructive testing of a loudspeaker diaphragm by using terahertz waves as claimed in claim 1 or 3, wherein the predetermined trajectory is a line-by-line movement, so that the terahertz waves scan each sampling point on the surface of the loudspeaker diaphragm line-by-line.
5. The method of claim 1, wherein the analyzing the maximum energy frequency of each sampling point on the surface of the loudspeaker diaphragm according to the hilbert-yellow transform comprises:
1) decomposing the terahertz echo signal by using an Empirical Mode Decomposition (EMD) method, and decomposing the terahertz echo signal into a form of combining a plurality of empirical mode functions (IMFs) and residual errors, wherein the Empirical Mode Decomposition (EMD) method is specifically expressed as follows:
where ε (t) is the terahertz echo signal, i is the number of empirical mode components, IMF i Is a natural empirical mode component, r K The residual error is obtained by subtracting each empirical mode component from the original signal;
2) performing Hilbert transform on each empirical mode component IMF, setting the IMF component as x (t), then performing Hilbert transform on the IMF component into H [ x (t) ], and converting local estimation into global estimation:
wherein, tau refers to the whole time interval of the signal where x (t) is located;
3) obtaining an analytic signal of a real-valued function of the echo signal, wherein the specific complex number expression form is as follows:
wherein u (t) is a real-valued function,
is the analytic signal of x (t),
is the function H [ x (t) after Hilbert transform of u (t)]Analyzing the signal
The mode and the argument of (a) represent the amplitude and the phase of the two-dimensional signal, i.e. the instantaneous frequency and the instantaneous amplitude of the echo signal;
4) and acquiring the frequency of the maximum energy of the signal at the moment by taking the maximum instantaneous amplitude as the maximum energy, and taking the frequency as the vibration frequency of the point on the surface of the loudspeaker diaphragm to make a frequency-coordinate graph of the maximum energy.
6. The method for nondestructive testing of a loudspeaker diaphragm by using terahertz waves as claimed in claim 1, wherein on the maximum energy frequency spectrogram of each sampling point of the loudspeaker diaphragm, whether the loudspeaker diaphragm to be tested is damaged or morphologically abnormal is determined according to the energy frequency difference between any point and surrounding points.
7. A system for nondestructive testing of a loudspeaker diaphragm using terahertz waves, comprising: the terahertz transmitting and receiving integrated device comprises terahertz transmitting and receiving integrated equipment (1), a gain antenna (2), a displacement platform (4), a control computer (5) and a loudspeaker to be tested (3);
the terahertz receiving and transmitting integrated equipment (1) comprises a vector network analyzer, a spread spectrum module and a frequency expander which are sequentially connected; the waveguide output port of the frequency expander is connected with a gain antenna (2); the gain antenna (2) is horn-shaped, and the opening of the gain antenna faces the loudspeaker (3) to be tested; the vector network analyzer is connected with a control computer (5); the terahertz wave is emitted by the vector network analyzer, is received by the gain antenna (2) and directly irradiates the surface of the loudspeaker (3), and meanwhile, the vector network analyzer serving as the terahertz detector collects reflected terahertz echo intensity sequence signals;
the displacement platform (4) is a two-dimensional platform and comprises a servo motor, a driver, a transverse linear motion module and a longitudinal linear motion module, the loudspeaker (3) is fixed on the transverse motion module, and the transverse linear motion module and the longitudinal linear motion module are driven to move through the servo motor, so that the position of the loudspeaker (3) is adjusted; the driver is connected with a control computer (5) through a communication interface;
the control computer (5) internally comprises a storage part and a processing part, wherein the storage part stores programs, and the processing part loads the programs to execute the method steps of any one of claims 1 to 6 so as to realize the detection of the defect or abnormal form position of the surface of the loudspeaker diaphragm.
8. The system for nondestructive testing of a loudspeaker diaphragm using terahertz waves as set forth in claim 7, wherein the surface of the loudspeaker (3) is covered with tinfoil paper for improving the echo signal transmittance.
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