A device for measuring particle velocity under strong background interference using modulated laser

Abstract

The present invention proposes a device for measuring particle velocity under strong background interference using modulated laser light. The device comprises a laser light intensity modulation system for modulating the laser light into a laser with varying intensity according to a modulation frequency; a data acquisition and processing system for collecting the scattered light signal from the particles when the laser light of varying intensity irradiates the particles, performing a bandpass filter on the scattered light signal centered on the modulation frequency, and obtaining the particle velocity based on the bandpass filtered scattered light signal. The device proposed by the present invention is suitable for measuring particle velocity under strong background interference and can solve the problem of particle velocity measurement failure caused by strong background noise during the measurement process.

Description

Technical Field

[0001] The present invention relates to the field of particle velocity measurement, in particular to a device for measuring particle velocity using laser. Background Art

[0002] With the increasing demand for fluid velocity measurement in scientific research and industrial applications, a variety of velocity measurement methods have been developed to meet different measurement conditions. These include Pitot tubes, which measure flow field velocity based on pressure; hot wire anemometers, which have been widely used for fluid velocity measurement for many years; and Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology, which uses Doppler shift. However, in some cases, these measurement methods cannot meet measurement requirements. For example, Pitot tube velocity measurement cannot meet the requirement of non-contact measurement, and TDLAS cannot measure the entire flow field. The above measurement methods directly measure the flow field. However, when the flow field contains tiny particles or when tiny particles are artificially introduced, the equation of motion for small circular particles in the fluid medium is the Basset–Boussinesq–Oseen (BBO) equation under the small Reynolds number approximation. To a certain extent, the particle velocity can be approximated to the velocity of the fluid in which the small particle resides. Currently, most commonly used particle-based velocity measurement technologies have developed in response to the demand for fluid velocity measurement. Common particle velocity measurement methods include laser Doppler velocimetry (LDA) and particle image velocimetry (PIV). Currently, commercial LDVs all use a dual-beam interference fringe mode. The drawback of this mode is that when the density of the measured flow field varies greatly and is irregular and non-uniform, it is difficult to ensure that the two laser beams intersect to form interference fringes. Furthermore, when the particle number density in the measured flow field is high, multiple particles may be present in the measured area. In this case, the scattering signal intensity no longer alternates between strong and weak, but tends to be white noise, making the LDV inoperative. PIV measurement technology requires a moderate number density of tracer particles in the measured area. Both excessively high and low particle number densities in the measured area have an adverse effect on the PIV measurement results. In addition, PIV measurement is relatively complex and requires the use of a lens group to convert a volume light source into a surface light source. The resulting surface light source is a divergent light source. As the distance from the measurement area to the light source point increases, the light source area increases and the laser power density decreases. In order to ensure that the camera can capture the tracer particles, a high-power laser is required. When measuring high-speed moving particles at long distances, existing lasers are difficult to meet the measurement requirements. In summary, with the demand for flow field velocity measurement, a variety of particle-based velocity measurement methods suitable for different conditions have been developed.

[0003] In 1968, Thompson proposed the Laser Transit Velocimetry (LTV) method for measuring particle velocity in his paper "A tracer-particle fluid velocity meter incorporating a laser." The method involves placing two separate, highly focused, parallel laser beams in a flow field. Two photoelectric detectors are set up to receive the laser scattering signals from particles passing through the beams. When a particle passes through the measurement area, the two detectors detect a pulse signal with a predetermined time interval. Using digital signal processing techniques, the time interval between the two pulse signals can be identified after data processing. Given the known spacing between the two parallel laser beams, the average particle velocity over the measurement period is the laser beam spacing divided by the time interval. Compared to LDV and PIV, this particle velocity measurement method boasts simpler optical setup and data processing, and can detect even small tracer particles without requiring high laser power. However, this measurement method also has some disadvantages. It is difficult to apply to measurement conditions with high background noise, and background noise is often difficult to eliminate during actual measurements. First, during the measurement process, the laser used as the light source will be reflected by the boundaries of the measured area, and this reflected light will become strong background noise during the measurement. Second, in actual measurements, particle concentration is generally uncontrollable. Multiple particles passing through the measurement area will scatter the laser light, and this multiple scattering of the laser light by multiple particles will become background signal during the measurement. Furthermore, in some measurement environments, the object being measured has its own luminous light sources. For example, when measuring the velocity of particles in the exhaust plume of a solid rocket engine, the exhaust plume itself emits light, which contributes to the measurement as background light. This background light is generally correlated. In addition to the aforementioned types of background noise, the instrumentation during the measurement process can also generate correlated noise signals, and the noise generated by the equipment also contributes to the background noise during the measurement. In summary, the measurement method described in the paper "A tracer-particle fluid velocity meter incorporating a laser" is difficult to apply to such measurement environments.

[0004] In the paper "Velocity Measurement of Particles Ejected from a Small-Size Solid Rocket Motor," Pagliaroli et al. used a particle velocity measurement method similar to Thompson's. Slightly different from Thompson's measurement method, Pagliaroli et al. did not use a laser as a light source but instead directly measured the high-temperature particle radiation signal. They then cross-correlated the two detected signals to obtain the signal time delay. This measurement method is suitable for situations where the particles themselves are luminous. Furthermore, this measurement method has high requirements for the luminescence properties of the particles and is only suitable for measuring the velocity of large, bright particles. This method cannot be applied to particle velocity measurements under high background noise interference. Summary of the Invention

[0005] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0006] Therefore, the purpose of the present invention is to provide a device for measuring particle velocity under strong background interference using modulated laser, so as to solve the problem that strong background noise causes particle velocity measurement failure during particle velocity measurement.

[0007] To achieve the above objectives, an embodiment of the present invention provides a device for measuring particle velocity under strong background interference using modulated laser light, comprising:

[0008] A laser light intensity modulation system for modulating the laser light into a laser light with varying intensity according to a modulation frequency;

[0009] The data acquisition and processing system is used to collect the scattering signal of the laser by the particle when the laser with varying intensity irradiates the particle, and to perform bandpass filtering on the scattering signal centered on the modulation frequency, and to obtain the velocity of the particle based on the scattering signal after bandpass filtering.

[0010] In addition, the device for measuring particle velocity under strong background interference using modulated laser according to the above embodiment of the present invention may also have the following additional technical features:

[0011] Furthermore, in one embodiment of the present invention, the data acquisition and processing system is further configured to:

[0012] The signal delay time of the particle passing through the two photoelectric probe measurement areas is obtained, and the velocity of the particle is obtained according to the signal delay time and the distance between the two photoelectric probe measurement areas.

[0013] Furthermore, in one embodiment of the present invention, the modulation frequency is the laser intensity variation frequency.

[0014] Furthermore, in one embodiment of the present invention, the laser light intensity modulation system includes: a laser, a lens group, an amplitude modulator, and an analyzer, wherein:

[0015] The laser is used to emit laser light;

[0016] The amplitude modulator is used to receive the laser light entering after passing through the lens group and perform amplitude modulation on the laser light;

[0017] The polarizer is used to receive amplitude-modulated laser light, wherein the light intensity of the laser light changes with time after passing through the polarizer.

[0018] Furthermore, in one embodiment of the present invention, the laser light intensity modulation system further comprises: a signal generator, a power amplifier and a DC power supply, wherein:

[0019] The signal generator is used to generate a low voltage signal;

[0020] The power amplifier is used to amplify the low voltage signal into a high voltage signal and provide an AC voltage component for the amplitude modulator;

[0021] The DC power supply is used to provide a DC voltage component for the amplitude modulator.

[0022] Furthermore, in one embodiment of the present invention, the laser light intensity modulation system further comprises: a three-dimensional translation stage and a five-axis translation stage, wherein:

[0023] The lens group is arranged on the three-dimensional translation stage, and the three-dimensional translation stage is used to adjust the position of the lens group to control the diameter and incident direction of the laser beam;

[0024] The amplitude modulator is arranged on the five-axis translation stage, and the five-axis translation stage is used to adjust the spatial position and deflection angle of the amplitude modulator.

[0025] Furthermore, in one embodiment of the present invention, the data acquisition and processing system includes: a lens, two photoelectric probes, a bandpass filter, and a pinhole, wherein:

[0026] The lens is used to focus the laser signal with varying intensity;

[0027] The bandpass filter is used to filter out stray light with a wavelength not within the bandpass range;

[0028] The pinhole is used to perform spatial filtering on the light signal focused by the lens to remove light outside the measurement range;

[0029] The two photoelectric probes are used to receive the scattered signals of the particles to the laser.

[0030] Furthermore, in one embodiment of the present invention, the data acquisition and processing system further includes:

[0031] A light-shielding cylinder is fixed to the photoelectric probe and is used to prevent stray light from entering the photoelectric probe.

[0032] Furthermore, in one embodiment of the present invention, the data acquisition and processing system further comprises: a data acquisition card and a terminal, wherein:

[0033] The data acquisition card is connected to the photoelectric probe and is used to record the data received by the two photoelectric probes;

[0034] The terminal is connected to the data acquisition card and is used to control the data acquisition card and process the data.

[0035] Furthermore, in one embodiment of the present invention, the two photoelectric probes are also included, the first photoelectric probe is placed on the pitch displacement platform to adjust the measurement angle, and the second photoelectric probe is placed on the pitch and translation combined displacement platform to adjust the measurement angle and measurement position.

[0036] The device for measuring particle velocity under strong background interference using modulated laser proposed in an embodiment of the present invention can achieve the measurement of particle velocity in high-temperature and highly complex environments compared with the existing technology. For example, it can measure the velocity of dense small particles in the flame of a real solid rocket engine, providing measurement technology support for the research and development of solid rocket engines and providing measurement data for the establishment of a solid rocket engine database. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0038] Figure 1 A schematic structural diagram of a device for measuring particle velocity under strong background interference using modulated laser provided by an embodiment of the present invention.

[0039] Figure 2 This is a schematic diagram comparing the photoelectric probe signal before and after bandpass filtering provided by an embodiment of the present invention.

[0040] Figure 3 This is a schematic diagram of the cross-correlation results of the two photoelectric probe signals after bandpass filtering provided by an embodiment of the present invention.

[0041] Figure 4 This is a schematic diagram of the direct cross-correlation calculation results of two photoelectric probes provided by an embodiment of the present invention.

[0042] Figure 5This is a schematic diagram of the overall structure of a device for measuring particle velocity under strong background interference using modulated laser provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0044] The following describes an apparatus for measuring particle velocity under strong background interference using modulated laser light according to an embodiment of the present invention with reference to the accompanying drawings.

[0045] Example 1

[0046] Figure 1 A schematic structural diagram of a device for measuring particle velocity under strong background interference using modulated laser provided by an embodiment of the present invention.

[0047] like Figure 1 As shown, the device for measuring particle velocity under strong background interference using modulated laser comprises:

[0048] The laser light intensity modulation system 100 is used to modulate the laser light into a laser light with varying intensity according to a modulation frequency;

[0049] The data acquisition and processing system 200 is used to collect the scattered signal of the laser by the particle when the laser with varying intensity irradiates the particle, and to perform bandpass filtering on the scattered signal centered on the modulation frequency, and to obtain the particle velocity based on the scattered signal after bandpass filtering.

[0050] The purpose of the present invention is to propose a device for measuring particle velocity using modulated laser. The laser is modulated into a laser with varying intensity by a laser light intensity modulation system. The laser light intensity variation frequency is the modulation frequency. The laser with varying intensity is irradiated on the particles. Two photoelectric probes are used to sequentially receive and record the scattered signals of the particles to the laser. The scattered signals are bandpass filtered with the modulation frequency as the center. The filtered signals of the two probes are cross-correlated. The signal delay time Δt is obtained through the maximum correlation point of the signal. This delay time is the time taken for the particle to pass through the measurement area of ​​the two photoelectric probes. By calibrating the distance L between the measurement areas of the two photoelectric probes, the particle velocity can be obtained.

[0051] Figure 5 This is a schematic diagram of the overall structure of a device for measuring particle velocity under strong background interference using modulated laser provided by an embodiment of the present invention.

[0052] Furthermore, in one embodiment of the present invention, the data acquisition and processing system is further configured to:

[0053] The signal delay time of the particle passing through the two photoelectric probe measurement areas is obtained, and the particle speed is obtained based on the signal delay time and the distance between the two photoelectric probe measurement areas.

[0054] Furthermore, in one embodiment of the present invention, the modulation frequency is the laser intensity variation frequency.

[0055] Furthermore, in one embodiment of the present invention, the laser light intensity modulation system includes: a laser, a lens group, an amplitude modulator, and an analyzer, wherein:

[0056] Laser is used to emit laser light;

[0057] The amplitude modulator is used to receive the laser light entering through the lens group and perform amplitude modulation on the laser light;

[0058] The polarizer is used to receive amplitude-modulated laser light, wherein the intensity of the laser light changes with time after passing through the polarizer.

[0059] Furthermore, in one embodiment of the present invention, the laser light intensity modulation system further comprises: a signal generator, a power amplifier and a DC power supply, wherein:

[0060] The signal generator is used to generate a low voltage signal;

[0061] The power amplifier is used to amplify the low voltage signal into a high voltage signal and provide an AC voltage component for the amplitude modulator;

[0062] The DC power supply is used to provide a DC voltage component for the amplitude modulator.

[0063] Furthermore, in one embodiment of the present invention, the laser light intensity modulation system further comprises: a three-dimensional translation stage and a five-axis translation stage, wherein:

[0064] The lens group is set on a three-dimensional translation stage, which is used to adjust the position of the lens group to control the diameter and incident direction of the laser beam;

[0065] The amplitude modulator is arranged on a five-axis translation stage, which is used to adjust the spatial position and deflection angle of the amplitude modulator.

[0066] Furthermore, in one embodiment of the present invention, the data acquisition and processing system includes: a lens, two photoelectric probes, a bandpass filter, and a pinhole, wherein:

[0067] The lens is used to focus the laser signal with varying intensity;

[0068] Bandpass filters are used to filter out stray light whose wavelength is not within the bandpass range;

[0069] The pinhole is used to perform spatial filtering on the light signal focused by the lens, removing light outside the measurement range;

[0070] Two photoelectric probes are used to receive the scattered signals of the particles to the laser.

[0071] Furthermore, in one embodiment of the present invention, the data acquisition and processing system further includes:

[0072] The light-shielding tube is fixed to the photoelectric probe to prevent stray light from entering the photoelectric probe.

[0073] Furthermore, in one embodiment of the present invention, the data acquisition and processing system further comprises: a data acquisition card and a terminal, wherein:

[0074] The data acquisition card is connected to the photoelectric probe and is used to record the data received by the two photoelectric probes;

[0075] The terminal is connected to the data acquisition card and is used to control the data acquisition card and process data.

[0076] Specifically, the lens is placed inside the light-shielding tube, which has threads. The lens is fixed inside the light-shielding tube by a fixing ring. By adjusting the position of the fixing ring, the position of the lens can be adjusted to measure different areas; the band-pass filter is placed behind the lens, and the band-pass filter is placed inside the lens through a fixing ring. The function of the band-pass filter is to filter out stray light whose wavelength is not within the band-pass range; the pinhole is placed behind the band-pass filter, and the pinhole is fixed inside the light-shielding tube by a fixing ring. The function of the pinhole is to perform spatial filtering on the light signal focused by the lens and remove light outside the measurement range; the light-shielding tube is fixed to the photoelectric probe by threads, and the light-shielding tube serves as a fixed connection and prevents stray light from entering the probe; the photoelectric probe is connected to a data acquisition card, and the data acquisition card is used to record data from the photoelectric probe; the data acquisition card is connected to a computer, and the computer is used to control the data acquisition card and perform data processing.

[0077] Furthermore, in one embodiment of the present invention, it also includes two photoelectric probes (photomultiplier tubes are selected as photoelectric probes in the experiment), the first photoelectric probe is placed on the pitch displacement platform to adjust the measurement angle, and the second photoelectric probe is placed on the pitch and translation combined displacement platform to adjust the measurement angle and measurement position.

[0078] Example 2

[0079] The measuring device is used to measure the velocity of particles ejected from the nozzle along with the air flow, and the laser modulation frequency is selected to be 2.1MHz and the filter bandwidth is 0.05MHz. Figure 2 This is the comparison of the first photoelectric probe signal before and after filtering. After bandpass filtering of the signal, the signal noise is reduced.

[0080] Perform cross-correlation calculation on the signal after bandpass filtering of the probe, and perform outer envelope calculation on the cross-correlation result to remove the modulation frequency in the cross-correlation result. The result is as follows: Figure 3 shown. Figure 3 It clearly shows that the maximum correlation value appears at -5.09×10 -5 seconds, which means that the time it takes to pass through the two detection areas is Δt = -5.09×10 -5 Second.

[0081] In the same measurement environment, if the laser is not modulated, the cross-correlation calculation is performed directly on the signals of the two photoelectric probes. The calculation results are as follows: Figure 4 As shown, from Figure 4 The maximum correlation value point of the signal cannot be found in the , which means that the speed measurement fails.

[0082] from Figure 3 It can be clearly found that the maximum correlation value of the signal is at -5.09×10 -5 s, the distance L between the two detection intervals is 6.425 mm through calibration, so the average speed of the particles in the measurement area is This measurement case illustrates that bandpass filtering of the signal received by the photoelectric probe after the laser is amplitude modulated can eliminate the background noise of the measurement signal, thereby obtaining particle velocity measurement results under high background noise interference.

[0083] The device proposed in this invention utilizes modulated lasers to measure particle velocity. Advantages include: After amplitude modulation of the laser, the intensity variation frequency of the scattered light from the particles is the same as the modulation frequency. Bandpass filtering of the signal received by the detector significantly reduces the impact of background noise on the measurement results. The amplitude modulator response frequency is adjustable, allowing different modulation frequencies to be selected based on the performance of the data acquisition card and computer, increasing the velocity measurement range and reducing the performance requirements for the data acquisition card and computer. Compared to the device proposed in the paper "A tracer-particle fluid velocity meter incorporating a laser," only a single laser beam is located within the measurement area, simplifying the optical path layout and increasing the degree of integration. The position of the lens at the receiving end is adjustable, and this lens, in conjunction with the pinhole behind it, facilitates adjustment of the detection range and depth of field. A filter is included in the receiving end to reduce the impact of background and ambient stray light on the measurement results. Compared to the measurement device proposed in the paper "Velocity Measurement of Particles Ejected from a Small-Size Solid Rocket Motor," this device, in addition to the aforementioned advantages, can measure the velocity of both luminous and non-luminous particles.

[0084] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0085] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0086] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limiting the present invention. A person skilled in the art may change, modify, replace, and modify the above embodiments within the scope of the present invention.

Claims

1. A device for measuring particle velocity under strong background interference using modulated laser, characterized in that: include: A laser light intensity modulation system for modulating the laser light into a laser light with varying intensity according to a modulation frequency; a data acquisition and processing system for collecting a scattering signal of the laser light produced by the particle when the laser light of varying intensity is irradiated on the particle, performing a bandpass filter on the scattering signal centered on the modulation frequency, and obtaining a velocity of the particle based on the scattering signal after the bandpass filtering; The data acquisition and processing system is further used for: The signal delay time of the particle passing through the two photoelectric probe measurement areas is obtained, and the velocity of the particle is obtained according to the signal delay time and the distance between the two photoelectric probe measurement areas.

2. The device according to claim 1, characterized in that The modulation frequency is the frequency at which the laser light intensity changes.

3. The device according to any one of claims 1 to 2, characterized in that The laser light intensity modulation system includes: a laser, a lens group, an amplitude modulator, and a polarizer, wherein: The laser is used to emit laser light; The amplitude modulator is used to receive the laser light entering after passing through the lens group and perform amplitude modulation on the laser light; The polarizer is used to receive amplitude-modulated laser light, wherein the light intensity of the laser light changes with time after passing through the polarizer.

4. The device according to claim 3, characterized in that The laser light intensity modulation system further includes: a signal generator, a power amplifier and a DC power supply, wherein: The signal generator is used to generate a low voltage signal; The power amplifier is used to amplify the low voltage signal into a high voltage signal and provide an AC voltage component for the amplitude modulator; The DC power supply is used to provide a DC voltage component for the amplitude modulator.

5. The device according to claim 3, characterized in that The laser light intensity modulation system further includes: a three-dimensional translation stage and a five-axis translation stage, wherein: The lens group is arranged on the three-dimensional translation stage, and the three-dimensional translation stage is used to adjust the position of the lens group to control the diameter and incident direction of the laser beam; The amplitude modulator is arranged on the five-axis translation stage, and the five-axis translation stage is used to adjust the spatial position and deflection angle of the amplitude modulator.

6. The device according to any one of claims 1-2, characterized in that The data acquisition and processing system includes: a lens, two photoelectric probes, a bandpass filter, and a pinhole, wherein: The lens is used to focus the laser signal with varying intensity; The bandpass filter is used to filter out stray light with a wavelength not within the bandpass range; The pinhole is used to perform spatial filtering on the light signal focused by the lens to remove light outside the measurement range; The two photoelectric probes are used to receive the scattered signals of the particles to the laser.

7. The device according to claim 6, characterized in that The data acquisition and processing system also includes: A light-shielding cylinder is fixed to the photoelectric probe and is used to prevent stray light from entering the photoelectric probe.

8. The device according to claim 6, characterized in that The data acquisition and processing system also includes: a data acquisition card and a terminal, wherein: The data acquisition card is connected to the photoelectric probe and is used to record the data received by the two photoelectric probes; The terminal is connected to the data acquisition card and is used to control the data acquisition card and process the data.

9. The device according to claim 6, characterized in that Also includes: The two photoelectric probes are arranged such that the first photoelectric probe is placed on a pitch displacement platform to adjust the measuring angle, and the second photoelectric probe is placed on a pitch and translation combined displacement platform to adjust the measuring angle and the measuring position.

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