Laser Doppler space sound field reconstruction system and method

Abstract

The invention relates to a laser Doppler space sound field reconstruction system and method, and belongs to the field of laser application. The laser Doppler space sound field reconstruction system comprises an optical fiber laser, a 1 * 2 optical fiber coupler, an optical fiber acousto-optic modulator, an acousto-optic driving power supply, an optical fiber attenuator, a 2 * 1 optical fiber coupler, an optical fiber loop device, a photoelectric detector, a signal acquisition card, an industrial personal computer, a transceiving integrated lens, a piezoelectric deflecting mirror, a target sound field driving device and a hard reflecting plate. According to the laser Doppler space sound field reconstruction system, the problems of non-contact high-precision measurement and reconstruction of the space sound field are solved, laser Doppler vibration measurement and the space sound field measurement technology are combined, and the advantages of non-contact, high precision and high signal-to-noise ratio of an optical measurement method are utilized; the influence of measurement equipment on the target space sound field in a conventional measurement method is effectively avoided, the space sound field is reconstructed through a filtered back projection algorithm, and visual dynamic distribution of the intensity parameters of the target sound field is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of laser applications, and particularly relates to a laser Doppler spatial sound field reconstruction system and method. Background Art

[0002] In recent years, the technology of laser ultrasonic non-destructive testing has developed rapidly and is widely used in the fields of life science, optical fiber communication, radio frequency identification, gas detection, etc. The design and manufacturing processes of high-frequency ultrasonic devices such as MEMS ultrasonic sensors, micro-nano resonators, micro-nano ultrasonic transducers, and surface acoustic wave devices are very complex. The dynamic visualization distribution of their spatial sound fields is crucial for device performance detection and stable operation. Non-destructively and real-time monitoring the working states of these devices can improve the product quality during the device design and manufacturing processes.

[0003] The laser Doppler spatial sound field measurement method hardly interferes with the sound field and the sound source, and the laser Doppler ultrasonic detection technology has the advantages of fast detection speed, high spatial resolution, and wide frequency band range. Therefore, the combination of laser Doppler detection and spatial ultrasonic measurement technology is applicable to various complex detection processes.

[0004] The laser Doppler detection system emits a beam of measurement laser. The incident light passes through the target area of the spatial sound field and returns to the laser Doppler detection system after passing through a hard reflector. The reflected light carries the information of the spatial sound field. The reflected light is mixed with the local oscillator light to obtain the information of the target sound field. The slice measurement of the target sound field is realized by parallel beam scanning, and the target sound field is reconstructed by using the filtered back-projection algorithm, and finally the high-precision inversion of the laser Doppler spatial sound field is realized.

[0005] Existing conventional spatial sound field measurement devices include sound level meters, microphones (microphones, microphones, microphone heads, microphones), etc. When measuring the spatial sound field, the measurement devices need to be placed in the target sound field area. However, no matter how small the measurement device is, as long as it is placed in the target sound field, it will affect the measurement result, thereby reducing the measurement accuracy of the spatial sound field. Summary of the Invention

[0006] The present invention aims to solve the technical problems in the prior art that the spatial sound field measurement device has low measurement accuracy and does not have the ability of non-contact measurement, and provides a laser Doppler spatial sound field reconstruction system and method. The present invention adopts the laser Doppler ultra-high frequency spatial sound field reconstruction technology, which has the advantages of non-contact, high precision, anti-interference, etc. By using the optical non-contact measurement technology, the visualization distribution of the spatial sound field intensity is realized by extracting the information of the target sound field carried by the reflected light.

[0007] To solve the above technical problems, the technical solution of the present invention is specifically as follows:

[0008] A laser Doppler spatial sound field reconstruction system, comprising: a fiber laser, a 1×2 fiber coupler, a fiber acousto-optic modulator, a fiber attenuator, a 2×1 fiber coupler, a photodetector, a signal acquisition card, and an industrial control computer, which are sequentially arranged in the optical path direction; wherein the fiber acousto-optic modulator is further connected to an acousto-optic drive power supply, the 2×1 fiber coupler is further sequentially connected to a fiber loop mirror, a transceiver integrated lens, a piezoelectric deflecting mirror, and a hard reflector, the fiber loop mirror is further connected to the 1×2 fiber coupler, and a target sound field driving device is further arranged between the piezoelectric deflecting mirror and the hard reflector;

[0009] The laser beam emitted by the fiber laser is divided into two parts after passing through the 1×2 fiber coupler. One part of the laser serves as the local oscillator light and enters the fiber acousto-optic modulator, and then enters the 2×1 fiber coupler after passing through the fiber attenuator. The acousto-optic drive power supply is the signal drive source of the fiber acousto-optic modulator; the other part of the laser serves as the signal light and enters the fiber loop mirror. Then, the signal light is reflected on the surface of the piezoelectric deflecting mirror through the transceiver integrated lens, passes through the target sound field area of the target sound field driving device, returns to the transceiver integrated lens after passing through the hard reflector and then through the piezoelectric deflecting mirror. The signal light carrying the target spatial sound field information enters the 2×1 fiber coupler together with the local oscillator light after passing through the fiber loop mirror, and undergoes frequency mixing on the photosensitive surface of the photodetector, enters the industrial control computer through the signal acquisition card, and uses the arctangent phase extraction algorithm to accurately invert the target sound field parameters, and finally reconstruct the spatial sound field intensity distribution.

[0010] In the above technical solution, the wavelength of the fiber laser can be within the theoretically allowed range, preferably 1550 nm.

[0011] In the above technical solution, the laser beam emitted by the fiber laser is divided into two parts, a high-power beam and a low-power beam, after passing through the 1×2 fiber coupler. The high-power beam serves as the signal light, and the low-power beam serves as the local oscillator light.

[0012] In the above technical solution, the signal acquisition card is an AD analog-to-digital converter.

[0013] In the above technical solution, the piezoelectric deflecting mirror adopts a one-dimensional motion structure or a two-dimensional motion structure.

[0014] A laser Doppler spatial sound field reconstruction method applicable to the above laser Doppler spatial sound field reconstruction system, comprising the following steps:

[0015] First, the laser Doppler spatial sound field reconstruction system needs to perform system initialization operations, measure the local oscillator light and signal light powers, check whether the powers of the local oscillator light and the signal light match. If they do not match, the optical power of the local oscillator optical path needs to be adjusted through the fiber attenuator until the powers of the local oscillator light and the signal light are in a matching state;

[0016] Secondly, the photoelectric detector is used to detect the photocurrent signal of the signal light, and the signal acquisition card collects the photocurrent signal to realize the conversion from analog signal to digital signal;

[0017] Then, the photocurrent signal is accurately demodulated by the inverse tangent phase demodulation algorithm, and the filtered back-projection algorithm realizes the inversion of the target space sound field parameters.

[0018] Finally, the visual measurement and reconstruction of the target spatial sound field intensity is achieved through the inversion of spatial sound field parameters.

[0019] In the above technical solution, the system initialization operation includes optical path alignment and power-on debugging.

[0020] In the above technical solution, an optical fiber power meter is used to measure the optical power of the local oscillator light and the signal light.

[0021] The beneficial effects of the present invention are:

[0022] The laser Doppler spatial sound field reconstruction system of the present invention combines laser Doppler vibration measurement technology with spatial sound field inversion, and uses a filtered back-projection algorithm to achieve visual measurement and reconstruction of spatial sound field intensity parameters. By establishing an all-fiber laser Doppler vibration measurement optical path, the incident light penetrates the target sound field area and is reflected on the surface of a hard reflector. The echo light carries the target sound field information and enters the photodetector together with the local oscillation light and is mixed. The photocurrent signal is subjected to orthogonal mixing low-pass filtering to form two orthogonal baseband signals. The inverse tangent phase demodulation algorithm is used to achieve accurate measurement of the target sound field parameters, and then the filtered back-projection algorithm is used to invert the spatial sound field intensity information. The reconstruction system of the present invention adopts an all-fiber optical path structure, the optical path structure is simple, and the optical path transmission is all completed in the optical fiber. There are no optical components for free light transmission, which can effectively avoid stray light interference.

[0023] The laser Doppler spatial sound field reconstruction system of the present invention solves the problem of non-contact high-precision measurement and reconstruction of the spatial sound field. By combining laser Doppler vibrometer with spatial sound field measurement technology and utilizing the advantages of non-contact, high precision and high signal-to-noise ratio of optical measurement methods, the influence of measurement equipment on the target spatial sound field in conventional measurement methods is effectively avoided. The spatial sound field is then reconstructed through a filtered back-projection algorithm to achieve a visualized dynamic distribution of the target sound field intensity parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0025] Figure 1 It is a schematic diagram of the laser Doppler spatial sound field reconstruction system of the present invention.

[0026] Figure 2Flow chart of the laser Doppler spatial sound field reconstruction method of the present invention.

[0027] The reference signs in the figure are represented as:

[0028] 1 - Fiber laser, 2 - 1×2 fiber coupler, 3 - Fiber acousto-optic modulator, 4 - Acousto-optic drive power supply, 5 - Fiber attenuator, 6 - 2×1 fiber coupler, 7 - Fiber circulator, 8 - Photoelectric detector, 9 - Signal acquisition card, 10 - Industrial control computer, 11 - Transceiver integrated lens, 12 - Piezoelectric deflecting mirror, 13 - Target sound field drive device, 14 - Hard reflector. Detailed implementation manners

[0029] The inventive concept of the present invention is as follows: Existing spatial sound field measurement devices do not have the ability of non-contact measurement. The object of the present invention is to solve the problems of non-contact high-precision measurement and reconstruction of the spatial sound field. By combining the laser Doppler vibration measurement technology with the spatial sound field measurement technology, a laser Doppler spatial sound field reconstruction method and system are proposed, which have the advantages of optical non-contact, strong anti-interference ability and high measurement accuracy. The present invention utilizes the advantages of non-contact, high-precision and high signal-to-noise ratio of the optical measurement method, effectively avoids the influence of the measurement device on the target spatial sound field in the conventional measurement method, and then reconstructs the spatial sound field through the filtered back-projection algorithm to realize the visual dynamic distribution of the target sound field intensity parameter.

[0030] The present invention combines laser Doppler vibrometry technology with spatial sound field inversion, and uses the filtered back-projection algorithm to realize the visualization measurement and reconstruction of spatial sound field intensity parameters. A full-fiber laser Doppler vibrometry optical path is established. The incident light penetrates the target sound field region, reflects on the surface of the hard reflector, and the reflected light carries the target sound field information and enters the photodetector together with the local oscillator light for mixing. The photocurrent signal undergoes quadrature mixing low-pass filtering to form two orthogonal baseband signals. The arctangent phase demodulation algorithm is used to accurately measure the target sound field parameters, and then the filtered back-projection algorithm is used to invert the spatial sound field intensity information. The main structure of the present invention includes a fiber laser, a 1×2 fiber coupler, a fiber acousto-optic modulator, an acousto-optic drive power supply, a fiber attenuator, a 2×1 fiber coupler, a fiber circulator, a photodetector, a signal acquisition card, an industrial control computer, a transceiver integrated lens, a piezoelectric deflecting mirror, a target sound field driving device, and a hard reflector. The laser beam emitted by the fiber laser is divided into two parts after passing through the 1×2 fiber coupler. One part of the laser serves as the local oscillator light and enters the fiber acousto-optic modulator, and then enters the 2×1 fiber coupler after passing through the fiber attenuator. The acousto-optic drive power supply is the signal drive source of the fiber acousto-optic modulator. The other part of the laser serves as the signal light and enters the fiber circulator. The signal light is reflected on the surface of the piezoelectric deflecting mirror through the transceiver integrated lens, passes through the target sound field region, then passes through the hard reflector and the piezoelectric deflecting mirror again, and returns to the transceiver integrated lens. The signal light carrying the target spatial sound field information enters the 2×1 fiber coupler together with the local oscillator light after passing through the fiber circulator, and undergoes mixing on the photosensitive surface of the photodetector, and enters the industrial control computer through the signal acquisition card. The arctangent phase extraction algorithm is used to accurately invert the target sound field parameters, and finally the spatial sound field intensity distribution is reconstructed.

[0031] The present invention will be described in detail below with reference to the accompanying drawings.

[0032] Combined with Figure 1Specifically describe the laser Doppler spatial sound field reconstruction system of the present invention, including: fiber laser 1, 1×2 fiber coupler 2, fiber acousto-optic modulator 3, acousto-optic drive power supply 4, fiber attenuator 5, 2×1 fiber coupler 6, fiber loop coupler 7, photodetector 8, signal acquisition card 9, industrial control computer 10, transceiver integrated lens 11, piezoelectric deflecting mirror 12, target sound field drive device 13 and hard reflector 14. The fiber laser 1, 1×2 fiber coupler 2, fiber acousto-optic modulator 3, fiber attenuator 5, 2×1 fiber coupler 6, photodetector 8, signal acquisition card 9 and industrial control computer 10 are arranged in sequence in the optical path direction; the fiber acousto-optic modulator 3 is also connected to the acousto-optic drive power supply 4, the 2×1 fiber coupler 6 is also sequentially connected to the fiber loop coupler 7, transceiver integrated lens 11, piezoelectric deflecting mirror 12 and hard reflector 14, the fiber loop coupler 7 is also connected to the 1×2 fiber coupler 2, and the target sound field drive device 13 is arranged between the piezoelectric deflecting mirror 12 and the hard reflector 14.

[0033] The laser Doppler spatial sound field reconstruction system of the present invention adopts an all-fiber optical path structure. The optical path structure is simple, and the optical path transmission is completed in the fiber. There are no optical components for free light transmission, which can effectively avoid stray light interference. The wavelength of the fiber laser 1 is selected as 1550 nm (but not limited to 1550 nm). The fiber laser 1 emits a beam of laser, which is divided into a high-power part and a low-power part by the 1×2 fiber coupler 2. The specific power distribution ratio is determined by the detection distance and the smoothness of the surface of the hard reflector 14. In principle, the high-power beam is used as the signal light, and the low-power beam is used as the local oscillator light. After passing through the fiber acousto-optic modulator 3 and the fiber attenuator 5, the local oscillator light enters the 2×1 fiber coupler 6. The acousto-optic drive power supply 4 is the signal drive source of the fiber acousto-optic modulator 3. The signal light passes through the fiber loop coupler 7, transceiver integrated lens 11 and piezoelectric deflecting mirror 12, is reflected on the surface of the piezoelectric deflecting mirror 12, passes through the target sound field area of the target sound field drive device 13, and is reflected on the surface of the hard reflector 14. After passing through the target sound field area, it passes through the hard reflector 14 and then passes through the piezoelectric deflecting mirror 12 and returns to the transceiver integrated lens 11. That is, the signal light carrying the target spatial sound field information returns to the fiber loop coupler 7 along the original path, passes through the output port of the fiber loop coupler 7, and enters the 2×1 fiber coupler 6 together with the local oscillator light, and mixing occurs on the photosensitive surface of the photodetector 8. The photocurrent signal generated by the photodetector 8 is subjected to analog-to-digital conversion through the AD module of the signal acquisition card 9. The data processing software of the industrial control computer 10 deeply processes the experimental data, including signal processing processes such as quadrature mixing low-pass filtering, arctangent demodulation, phase unwrapping, phase compensation, and spatial sound field inversion, to realize the visual measurement and accurate inversion of the spatial sound field intensity distribution.

[0034] The piezoelectric deflecting mirror 12 can adopt a one-dimensional motion structure or a two-dimensional motion structure. The one-dimensional motion structure can enable the incident light to perform a line scan in the spatial sound field region, and the laser Doppler spatial sound field reconstruction system can obtain two-dimensional spatial sound field data; the two-dimensional motion structure can enable the incident light to perform a plane scan in the spatial sound field region, and the laser Doppler spatial sound field reconstruction system can obtain three-dimensional spatial sound field data. The routes of the line scan and the plane scan are not fixed. The conventional scan routes are one-dimensional linear scan and two-dimensional circular scan, and the specific routes can be determined according to the target sound field range and the positional relationship between the piezoelectric deflecting mirror 12 and the hard reflector 14. The scanning frequency of the piezoelectric deflecting mirror 12 determines the accuracy of the spatial sound field reconstruction.

[0035] The working principle of the laser Doppler spatial sound field reconstruction system of the present invention is as follows:

[0036] The laser beam emitted by the fiber laser 1 is divided into two parts after passing through the 1×2 fiber coupler 2. One part of the laser serves as the local oscillator light and enters the fiber acousto-optic modulator 3, and then enters the 2×1 fiber coupler 6 after passing through the fiber attenuator 5. The acousto-optic drive power supply 4 is the signal drive source of the fiber acousto-optic modulator 3. The other part of the laser serves as the signal light and enters the fiber loop mirror 7. The signal light is reflected on the surface of the piezoelectric deflecting mirror 12 through the transceiver integrated lens 11, passes through the target sound field region, passes through the hard reflector 14 and then passes through the piezoelectric deflecting mirror 12 and returns to the transceiver integrated lens 11. The signal light carrying the target spatial sound field information enters the 2×1 fiber coupler 6 together with the local oscillator light after passing through the fiber loop mirror 7, and undergoes mixing on the photosensitive surface of the photodetector 8, and enters the industrial control computer 11 through the signal acquisition card 9. The arctangent phase extraction algorithm is used to accurately invert the target sound field parameters, and finally the spatial sound field intensity distribution is reconstructed.

[0037] Combined with Figure 2 Specifically describe the laser Doppler spatial sound field reconstruction method applicable to the above laser Doppler spatial sound field reconstruction system of the present invention. The reconstruction method process mainly includes system initialization, measuring the power of the local oscillator light and the signal light, whether the power is matched, adjusting the fiber attenuator 5, optical current signal acquisition, AD analog-to-digital conversion, arctangent phase demodulation, filtered back projection algorithm, and spatial sound field reconstruction. Specifically, it includes the following steps:

[0038] First of all, the laser Doppler spatial sound field reconstruction system needs to go through initialization operations such as optical path alignment and power-on debugging, measure the optical power of the local oscillator light and the signal light using a fiber optic power meter, and check whether the power of the local oscillator light and the signal light is matched. If not, the optical power of the local oscillator optical path needs to be adjusted through the fiber attenuator 5 until the power of the local oscillator light and the signal light is in the best matching state.

[0039] Secondly, a photodetector 8 is used to detect the photocurrent signal of the signal light, and a signal acquisition card 9 (AD analog-to-digital converter) acquires the signal with high precision to achieve the conversion from analog signal to digital signal.

[0040] Then, the photocurrent signal is accurately demodulated by the arctangent phase demodulation algorithm, and the filtered back-projection algorithm is used to invert the target spatial sound field parameters.

[0041] Finally, through the inversion of the spatial sound field parameters, the visualization measurement and reconstruction of the target spatial sound field intensity are achieved.

[0042] The principle of the laser Doppler spatial sound field reconstruction process of the present invention is as follows:

[0043] First, the laser Doppler spatial sound field reconstruction system needs to go through initialization operations such as optical path alignment and power-on debugging. The optical power of the local oscillator light and the signal light is measured by a fiber optic power meter, and it is checked whether the optical powers of the local oscillator light and the signal light match. If they do not match, the optical power of the local oscillator optical path needs to be adjusted by a fiber optic attenuator 5 until the optical powers of the local oscillator light and the signal light are in the best matching state. Secondly, a photodetector 8 is used to detect the photoelectric signal of the signal light, and a signal acquisition card 9 (AD analog-to-digital converter) acquires the signal with high precision to achieve the conversion from analog signal to digital signal. Then, the photocurrent signal is accurately demodulated by the arctangent phase demodulation algorithm, and the filtered back-projection algorithm is used to invert the target spatial sound field parameters. Finally, through the inversion of the spatial sound field parameters, the visualization measurement and reconstruction of the target spatial sound field intensity are achieved.

[0044] The laser Doppler spatial sound field reconstruction method of the present invention has been shown to be practical and effective through simulations and experiments.

[0045] Obviously, the above embodiments are merely examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A laser Doppler spatial sound field reconstruction system, characterized in that: include: An optical fiber laser (1), a 1×2 optical fiber coupler (2), an optical fiber acousto-optic modulator (3), an optical fiber attenuator (5), a 2×1 optical fiber coupler (6), a photodetector (8), a signal acquisition card (9) and an industrial computer (10) are sequentially arranged in the direction of the optical path; wherein the optical fiber acousto-optic modulator (3) is also connected to an acousto-optic driving power supply (4); the 2×1 optical fiber coupler (6) is also sequentially connected to an optical fiber circulator (7), a transceiver integrated lens (11), a piezoelectric deflection mirror (12) and a hard reflector (14); the optical fiber circulator (7) is also connected to the 1×2 optical fiber coupler (2); and a target sound field driving device (13) is also arranged between the piezoelectric deflection mirror (12) and the hard reflector (14); A fiber laser (1) emits a laser beam which passes through a 1×2 fiber coupler (2) and is divided into two parts. One part of the laser light enters a fiber acousto-optic modulator (3) as a local oscillator light, and then enters a 2×1 fiber coupler (6) after passing through a fiber attenuator (5). An acousto-optic driving power supply (4) is a signal driving source for the fiber acousto-optic modulator (3); the other part of the laser light enters a fiber circulator (7) as a signal light, and then the signal light passes through a transceiver integrated lens (11) and is reflected on the surface of a piezoelectric deflection mirror (12), and passes through a target sound field driving device. After reaching the target sound field area of ​​(13), the signal light passes through the hard reflector (14) and then the piezoelectric deflection mirror (12) and then returns to the transceiver integrated lens (11). The signal light carrying the target spatial sound field information passes through the optical fiber circulator (7) and enters the 2×1 optical fiber coupler (6) together with the local oscillator light, and is mixed on the photosensitive surface of the photodetector (8). It passes through the signal acquisition card (9) and enters the industrial control computer (10). The target sound field parameters are accurately inverted using the inverse tangent phase extraction algorithm, and finally the spatial sound field intensity distribution is reconstructed.

2. The laser Doppler spatial sound field reconstruction system according to claim 1, characterized in that: The wavelength of the optical fiber laser (1) is 1550 nm.

3. The laser Doppler spatial sound field reconstruction system according to claim 1, characterized in that: The optical fiber laser (1) emits a laser beam which passes through a 1×2 optical fiber coupler (2) and is divided into a high-power beam and a low-power beam. The high-power beam is used as signal light, and the low-power beam is used as local oscillator light.

4. The laser Doppler spatial sound field reconstruction system according to claim 1, characterized in that: The signal acquisition card (9) is an AD analog-to-digital converter.

5. The laser Doppler spatial sound field reconstruction system according to claim 1, characterized in that: The piezoelectric deflection mirror (12) adopts a one-dimensional motion structure or a two-dimensional motion structure.

6. A laser Doppler spatial sound field reconstruction method applicable to the laser Doppler spatial sound field reconstruction system according to any one of claims 1 to 5, characterized in that: The following steps are involved: First, the laser Doppler spatial sound field reconstruction system needs to perform system initialization operations, measure the power of the local oscillator light and the signal light, and check whether the power of the local oscillator light and the signal light match. If they do not match, it is necessary to adjust the optical power of the local oscillator light path through the optical fiber attenuator (5) to adjust the power of the local oscillator light and the signal light to a power matching state; Secondly, a photoelectric detector (8) is used to detect the photocurrent signal of the signal light, and a signal acquisition card (9) collects the photocurrent signal to realize the conversion from analog signal to digital signal; Then, the photocurrent signal is accurately demodulated by the inverse tangent phase demodulation algorithm, and the filtered back-projection algorithm realizes the inversion of the target space sound field parameters. Finally, the visual measurement and reconstruction of the target spatial sound field intensity is achieved through the inversion of spatial sound field parameters.

7. The laser Doppler spatial sound field reconstruction method according to claim 6, characterized in that: System initialization operations include optical path alignment and power-on debugging.

8. The laser Doppler spatial sound field reconstruction method according to claim 6, characterized in that: Use a fiber optic power meter to measure the optical power of the local oscillator light and the signal light.

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