Flow velocity detection method and device based on optical Doppler effect and computer equipment

Abstract

This application relates to a method, apparatus, and computer device for flow velocity detection based on the optical Doppler effect. The method includes: generating a femtosecond laser pulse to form a time-coded, spectral-coded, and carrier-modulated pulse; incident the coded femtosecond laser pulse onto a transparent liquid to be tested, and receiving a scattered light signal carrying flow velocity information, generated by scattering from moving particles in the transparent liquid; performing inverse processing on the scattered light signal corresponding to the multi-dimensional coding to obtain a time-coded signal and a spectral-coded signal carrying the Doppler frequency shift, and determining the amount of the Doppler frequency shift; substituting the Doppler frequency shift into a Doppler algorithm model containing at least one correction term based on the theory of light-moving medium interaction, and inverting to calculate the flow velocity value of the transparent liquid to be tested. This method can further improve the accuracy and anti-interference capability of the flow velocity detection method based on the optical Doppler effect.

Description

Technical Field

[0001] This application relates to the field of liquid flow rate detection technology, and in particular to a flow rate detection method, apparatus, computer equipment, computer-readable storage medium, and computer program product based on the optical Doppler effect. Background Technology

[0002] Laser Doppler velocimetry, with its advantages of non-contact operation, high spatial resolution, and fast response, has been widely used in the measurement of flow velocity in transparent fluids (such as water, air, and liquids within microfluidic chips). Its basic principle is to use laser light to irradiate tiny tracer particles in a flowing liquid, and by detecting the frequency change of the scattered light relative to the incident light (i.e., the Doppler shift), the flow velocity of the liquid is calculated using the classical Doppler shift formula.

[0003] In traditional techniques, typical laser Doppler velocimetry methods receive scattered light from the same point in the flow field through a receiver scanning mechanism, calculate the velocity components in three directions, and finally synthesize the vectors to obtain the three-dimensional flow velocity. However, limitations remain in practical applications. On the one hand, with the development of scientific research (such as microfluidics and biochip analysis) and precision engineering (such as micro / nano manufacturing and micro-drug delivery), the accuracy requirements for flow velocity detection have increased from the microliters per minute (μL / min) to nanoliters per minute (nL / min) or even higher. Traditional methods are based on the classical Doppler formula, but their theoretical foundation does not fully consider the complex effects of light propagation in the moving medium. When faced with weak frequency shift signals generated by ultra-low flow velocities, the signal-to-noise ratio is insufficient, resulting in limited detection accuracy and making it difficult to meet the current high-precision measurement needs. On the other hand, traditional methods typically use continuous or ordinary pulsed lasers as the light source, with a single signal modulation method and weak resistance to ambient light interference. In complex measurement environments (such as those with temperature fluctuations and background stray light), the scattered light signal is easily submerged by noise, affecting the stability and accuracy of the measurement.

[0004] Therefore, there is an urgent need for a flow velocity detection method, device, computer equipment, computer-readable storage medium, and computer program product based on the optical Doppler effect, which can further improve the accuracy and anti-interference capability of the flow velocity detection method based on the optical Doppler effect to meet the needs of ultra-low flow velocity and high stability measurement. Summary of the Invention

[0005] Therefore, it is necessary to provide a flow velocity detection method, apparatus, computer equipment, computer-readable storage medium, and computer program product based on the optical Doppler effect that can further improve the accuracy and anti-interference capability of the flow velocity detection method based on the optical Doppler effect to meet the requirements of ultra-low flow velocity and high stability measurement.

[0006] Firstly, this application provides a flow velocity detection method based on the optical Doppler effect, comprising:

[0007] A femtosecond laser pulse is generated and the femtosecond laser pulse is encoded in multiple dimensions to form an coded femtosecond laser; wherein, the multi-dimensional encoding includes modulating the pulse width in the time dimension to form a time code, dividing the spectral frequency band in the spectral dimension to form a spectral code, and further loading the signal carrying the time code and the spectral code onto a high-frequency carrier for carrier modulation;

[0008] The coded femtosecond laser is incident on the transparent liquid to be tested, and the scattered light signal carrying the flow velocity information generated by the scattering of moving particles in the transparent liquid to be tested is received.

[0009] The scattered light signal is subjected to inverse processing corresponding to the multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying the Doppler frequency shift, and the Doppler frequency shift amount is determined based on the obtained time-coded signal and spectral-coded signal.

[0010] The flow velocity of the transparent liquid under test is obtained by substituting the Doppler frequency shift into a Doppler algorithm model that includes at least one correction term based on the theory of light-moving medium interaction.

[0011] In one embodiment, the modulation of the pulse width in the time dimension to form a time code specifically includes:

[0012] The pulse width of the femtosecond laser pulse is adjusted according to a preset time interval gradient, so that the laser pulses corresponding to different timestamps have different pulse width characteristics, and the pulse width characteristics are used as the time code.

[0013] In one embodiment, the step of dividing the spectral bands in the spectral dimension to form spectral coding includes:

[0014] The original spectrum of the femtosecond laser pulse is divided into multiple non-overlapping characteristic frequency bands, and a unique spectral identification code is assigned to each characteristic frequency band, which is then used as the spectral encoding.

[0015] In one embodiment, loading the signal carrying the time code and the spectral code onto a high-frequency carrier for carrier modulation includes:

[0016] A quadrature amplitude modulation (QAM) method is used to load the baseband signal carrying the time code and the spectral code onto a high-frequency carrier at a preset frequency for carrier modulation; the expression for carrier modulation is:

[0017] s(t)=Ac [1+k s ·s code [t]cos(2πf_ct+φ);

[0018] Among them, A c For carrier amplitude, k s S is the modulation coefficient. code (t) is the two-dimensional encoded signal of the time encoding and the spectral encoding, and φ is the initial phase of the carrier.

[0019] In one embodiment, the inverse processing of the scattered light signal corresponding to the multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying the Doppler frequency shift, and the determination of the Doppler frequency shift based on the obtained time-coded signal and spectral-coded signal, includes:

[0020] The received scattered light signal is mixed with the local oscillator carrier using coherent demodulation to generate a mixed signal;

[0021] The mixing signal is filtered by a low-pass filter to remove high-frequency components and recover the baseband signal, which is the time-coded signal and the spectral-coded signal carrying the Doppler frequency shift.

[0022] The recovered baseband signal is then normalized in amplitude.

[0023] Based on the timestamp information and spectral frequency band information in the normalized baseband signal, the corresponding Doppler frequency shift is identified and extracted as the Doppler frequency shift.

[0024] In one embodiment, the Doppler algorithm model including at least one correction term based on the theory of light-moving medium interaction is specifically as follows:

[0025] The Doppler algorithm model, combining the observer effect correction term and the general relativistic effect correction term, is expressed as follows:

[0026] Δf=(2nvcosθ) / λ·(1+ΔΦ / c 2 );

[0027] Where n is the refractive index of the transparent liquid obtained through pre-calibration, v is the flow velocity of the transparent liquid to be tested, θ is the angle between the incident laser and the direction of liquid flow, λ is the wavelength of the laser in vacuum, and ΔΦ is the local equivalent gravitational potential difference generated by the liquid flow, where ΔΦ=(1 / 2)v 2 +ρgh, where ρ is the liquid density, g is the gravitational acceleration, and h is the height difference of the detection section;

[0028] When measuring flow velocities below nL / min, v≈(Δf·λ) / (2ncosθ).

[0029] Secondly, this application also provides a flow velocity detection device based on the optical Doppler effect, comprising:

[0030] An encoding module is used to generate femtosecond laser pulses and encode the femtosecond laser pulses in multiple dimensions to form an encoded femtosecond laser; wherein, the multi-dimensional encoding includes modulating the pulse width in the time dimension to form a time code, dividing the spectral frequency band in the spectral dimension to form a spectral code, and further loading the signal carrying the time code and the spectral code onto a high-frequency carrier for carrier modulation;

[0031] The testing module is used to incident the coded femtosecond laser onto the transparent liquid under test and receive the scattered light signal with Doppler frequency shift carrying flow velocity information generated by the scattering of moving particles in the transparent liquid under test.

[0032] The processing module is used to perform inverse processing on the scattered light signal corresponding to the multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying the Doppler frequency shift, and to determine the Doppler frequency shift amount based on the obtained time-coded signal and spectral-coded signal.

[0033] The calculation module is used to substitute the Doppler frequency shift into a Doppler algorithm model that includes at least one correction term based on the theory of light-moving medium interaction, and to invert and calculate the flow velocity value of the transparent liquid to be measured.

[0034] Thirdly, this application also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to perform the following steps:

[0035] A femtosecond laser pulse is generated and the femtosecond laser pulse is encoded in multiple dimensions to form an coded femtosecond laser; wherein, the multi-dimensional encoding includes modulating the pulse width in the time dimension to form a time code, dividing the spectral frequency band in the spectral dimension to form a spectral code, and further loading the signal carrying the time code and the spectral code onto a high-frequency carrier for carrier modulation;

[0036] The coded femtosecond laser is incident on the transparent liquid to be tested, and the scattered light signal carrying the flow velocity information generated by the scattering of moving particles in the transparent liquid to be tested is received.

[0037] The scattered light signal is subjected to inverse processing corresponding to the multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying the Doppler frequency shift, and the Doppler frequency shift amount is determined based on the obtained time-coded signal and spectral-coded signal.

[0038] The flow velocity of the transparent liquid under test is obtained by substituting the Doppler frequency shift into a Doppler algorithm model that includes at least one correction term based on the theory of light-moving medium interaction.

[0039] Fourthly, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, performs the following steps:

[0040] A femtosecond laser pulse is generated and the femtosecond laser pulse is encoded in multiple dimensions to form an coded femtosecond laser; wherein, the multi-dimensional encoding includes modulating the pulse width in the time dimension to form a time code, dividing the spectral frequency band in the spectral dimension to form a spectral code, and further loading the signal carrying the time code and the spectral code onto a high-frequency carrier for carrier modulation;

[0041] The coded femtosecond laser is incident on the transparent liquid to be tested, and the scattered light signal carrying the flow velocity information generated by the scattering of moving particles in the transparent liquid to be tested is received.

[0042] The scattered light signal is subjected to inverse processing corresponding to the multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying the Doppler frequency shift, and the Doppler frequency shift amount is determined based on the obtained time-coded signal and spectral-coded signal.

[0043] The flow velocity of the transparent liquid under test is obtained by substituting the Doppler frequency shift into a Doppler algorithm model that includes at least one correction term based on the theory of light-moving medium interaction.

[0044] Fifthly, this application also provides a computer program product, including a computer program that, when executed by a processor, performs the following steps:

[0045] A femtosecond laser pulse is generated and the femtosecond laser pulse is encoded in multiple dimensions to form an coded femtosecond laser; wherein, the multi-dimensional encoding includes modulating the pulse width in the time dimension to form a time code, dividing the spectral frequency band in the spectral dimension to form a spectral code, and further loading the signal carrying the time code and the spectral code onto a high-frequency carrier for carrier modulation;

[0046] The coded femtosecond laser is incident on the transparent liquid to be tested, and the scattered light signal carrying the flow velocity information generated by the scattering of moving particles in the transparent liquid to be tested is received.

[0047] The scattered light signal is subjected to inverse processing corresponding to the multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying the Doppler frequency shift, and the Doppler frequency shift amount is determined based on the obtained time-coded signal and spectral-coded signal.

[0048] The flow velocity of the transparent liquid under test is obtained by substituting the Doppler frequency shift into a Doppler algorithm model that includes at least one correction term based on the theory of light-moving medium interaction.

[0049] The aforementioned flow velocity detection method, device, computer equipment, computer-readable storage medium, and computer program product based on the optical Doppler effect process femtosecond laser pulses using multi-dimensional encoding technology. This involves modulating the pulse width in the time dimension to form a time code, dividing the frequency bands in the spectral dimension to form a spectral code, and loading the signal carrying the aforementioned codes onto a high-frequency carrier in the carrier dimension to form a modulated signal, thus achieving multi-dimensional feature marking of the femtosecond laser. By incident the coded femtosecond laser onto the transparent liquid to be tested and receiving the Doppler frequency shift signal generated by scattering from moving particles, and then performing inverse processing corresponding to the multi-dimensional encoding on the scattered light signal, the time-coded signal and spectral-coded signal carrying flow velocity information are effectively extracted, and the Doppler frequency shift is determined based on this. Furthermore, the Doppler frequency shift is substituted into a Doppler algorithm model containing a correction term based on the theory of light-moving medium interaction to inversely calculate the flow velocity value of the transparent liquid to be tested. Through multi-dimensional encoding and inverse processing mechanisms, the signal-to-noise ratio and anti-interference capability of the scattered light signal are significantly enhanced. The weak difference frequency Δf can be extracted, ensuring the extraction accuracy of the Doppler frequency shift. At the same time, by introducing theoretical correction terms into the algorithm model, the deviations introduced by factors such as medium characteristics and optical path disturbances in the actual measurement environment are compensated, making the flow velocity inversion results more accurate and reliable. It is suitable for high-precision measurement of the flow velocity of transparent liquids under complex working conditions.

[0050] The flow velocity detection device of this application has a simple structure and a wide range of applications. It can be adapted to various transparent liquids, including water and ethanol, and is suitable for various application scenarios such as microfluidic chips and bidirectional flow scenarios. It has a fast response speed with a signal processing cycle of ≤1ms, which can effectively meet the needs of dynamic monitoring. It has high noise resistance and can still detect stably in environments with temperature fluctuations of ±5℃. It adopts a femtosecond laser multi-dimensional encoding strategy and theoretical correction algorithm, and the frequency shift recognition accuracy reaches the fs level. The minimum detectable flow velocity is as low as 0.01nL / min, and the error is ≤2%. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 This is a flowchart illustrating a flow velocity detection method based on the optical Doppler effect in one embodiment.

[0053] Figure 2 This is a flowchart illustrating a flow velocity detection method based on the optical Doppler effect in another embodiment;

[0054] Figure 3 This is a flowchart illustrating a flow velocity detection method based on the optical Doppler effect in another embodiment;

[0055] Figure 4 This is a structural block diagram of a flow velocity detection device based on the optical Doppler effect in one embodiment;

[0056] Figure 5 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0058] It should be noted that the terms "first," "second," etc., used in this application can be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from the second element. The terms "comprising" and "having," and any variations thereof, used in this application, are intended to cover non-exclusive inclusion. The term "multiple" used in this application refers to two or more. The term "and / or" used in this application refers to one of the embodiments, or any combination of multiple embodiments.

[0059] In one exemplary embodiment, such as Figure 1 As shown, a flow velocity detection method based on the optical Doppler effect is provided. Taking the application of this method to a server as an example, the method includes the following steps S102 to S108. Wherein:

[0060] Step S102: Generate a femtosecond laser pulse and encode the femtosecond laser pulse in multiple dimensions to form an encoded femtosecond laser; wherein, the multiple-dimensional encoding includes modulating the pulse width in the time dimension to form a time code, dividing the spectral frequency band in the spectral dimension to form a spectral code, and further loading the signal carrying the time code and spectral code onto a high-frequency carrier for carrier modulation.

[0061] Specifically, femtosecond laser pulses are first generated. Femtosecond laser pulses possess ultrashort pulse widths and high peak power, and their wide spectral range provides a physical basis for multi-dimensional encoding. Subsequently, the generated femtosecond laser pulses undergo multi-dimensional encoding processing to form coded femtosecond lasers. This multi-dimensional encoding specifically includes three parallel encoding operations: First, time-dimensional encoding, which modulates the pulse width of the femtosecond laser pulse, giving different pulses or pulse sequences different time-domain width characteristics, thus forming time encoding. For example, a programmable pulse shaper can adjust the pulse's time-domain envelope, allowing the pulse width to vary between tens and hundreds of femtoseconds, with different widths corresponding to different encoding information. Second, spectral-dimensional encoding, which divides the spectral frequency bands of the femtosecond laser pulse, allowing different spectral components to carry different encoding information, thus forming spectral encoding. For example, a spatial light modulator or an acousto-optic tunable filter can be used to segment the wide spectrum of the femtosecond laser, marking specific spectral intervals as specific encoding channels, allowing different spectral intervals to independently carry information. Finally, carrier modulation, which loads the optical signal already carrying time and spectral encoding onto a high-frequency carrier to form a modulated signal. This operation is typically achieved through an electro-optic modulator, which mixes the optical pulse signal with a high-frequency microwave carrier, causing the amplitude, phase, or frequency of the optical signal to change with the carrier, thereby modulating both time-coded and spectral-coded information onto the carrier frequency.

[0062] Step S104: The coded femtosecond laser is incident on the transparent liquid to be tested, and the scattered light signal carrying the flow velocity information generated by the scattering of the moving particles in the transparent liquid to be tested is received.

[0063] Specifically, after generating the coded femtosecond laser, it is used as a probe beam and incident on the transparent liquid to be tested. The transparent liquid contains tiny particles that move with the fluid; these particles can be naturally occurring impurities or artificially introduced tracer particles. When the coded femtosecond laser encounters these moving particles in its propagation path, scattering occurs, producing scattered light. According to the Doppler effect, when a moving particle has relative motion with respect to the light source, the frequency of its scattered light shifts; this shift is called the Doppler shift, and its magnitude is proportional to the particle's velocity. Since the particles move with the liquid, the scattered light signal carries information about the liquid's flow velocity. A photodetector positioned at an appropriate angle receives the scattered light signal generated by the moving particles in the transparent liquid. The received scattered light signal is a Doppler frequency shift light signal carrying flow velocity information. Since the incident light is a femtosecond laser that has been encoded in multiple dimensions, the scattered light signal retains the time encoding, spectral encoding and carrier modulation characteristics of the incident light, providing an identifiable label basis for the subsequent accurate extraction of the Doppler frequency shift from the received signal.

[0064] Step S106: Perform inverse processing on the scattered light signal corresponding to multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying a Doppler frequency shift, and determine the Doppler frequency shift based on the obtained time-coded signal and spectral-coded signal.

[0065] Specifically, after receiving the scattered light signal carrying flow velocity information, the inverse processing operation corresponding to the aforementioned multi-dimensional encoding needs to be performed on the scattered light signal to recover the effective signal components that can be used for flow velocity calculation. Since the incident femtosecond laser undergoes triple encoding in the time dimension, spectral dimension, and carrier modulation, the scattered light signal accordingly retains the characteristics of these three encodings. The purpose of the inverse processing is to extract the time-coded signal and the spectral-coded signal carrying Doppler frequency shift information from the received complex optical signal, and then calculate the Doppler frequency shift based on these signals.

[0066] Specifically, the inverse processing begins with demodulation of the scattered light signal. Since the incident light signal has been modulated onto a high-frequency carrier, the received scattered light signal also contains this high-frequency carrier component. By using a local oscillator signal that matches the carrier frequency of the transmitting end for mixing and demodulation, the carrier component can be removed, and the baseband signal can be recovered. This baseband signal retains the time-coded and spectral-coded characteristics, while also carrying Doppler frequency shift information caused by particle motion.

[0067] Building upon this, decoding is performed along the spectral dimension. Incident light is divided into different frequency bands along the spectral dimension, each carrying independent encoded information. The scattered light signal retains components from different spectral frequency bands accordingly. By using spectral splitting devices, such as gratings or array-type spectrometers, the received scattered light signal is separated according to spectral frequency bands, yielding multiple signal components corresponding to different spectral codes. Each of these signal components carries Doppler frequency shift information corresponding to its respective spectral frequency band, forming a spectral coded signal.

[0068] Decoding is performed on the time dimension. Incident light is time-coded by modulating its pulse width, and the time-domain waveform of the scattered light signal retains the pulse width variation characteristics accordingly. By employing a high-speed photodetector and a time-resolved acquisition system, the time-domain waveform of the scattered light signal is recorded. Combined with a time window synchronized with the transmitter, the time-coded information corresponding to different pulse widths is identified, thus obtaining the time-coded signal.

[0069] After the inverse processing operations corresponding to the multi-dimensional encoding described above, time-coded signals and spectral-coded signals carrying Doppler frequency shift information were obtained, respectively. Subsequently, the Doppler frequency shift amount carried by each signal was extracted by performing spectral analysis or phase detection. Since time-coding and spectral encoding provide independent measurement channels in multiple dimensions, the measurement results from multiple channels can be fused, for example, by taking an average or weighted average, to eliminate random errors or noise interference that may exist in a single measurement, and finally determine the accurate and reliable Doppler frequency shift amount.

[0070] Step S108: Substitute the obtained Doppler frequency shift into the Doppler algorithm model, which includes at least one correction term based on the theory of light-moving medium interaction, and calculate the flow velocity value of the transparent liquid to be measured.

[0071] Specifically, after obtaining the Doppler frequency shift, this shift is substituted into a pre-defined Doppler algorithm model for inversion calculation to solve for the flow velocity of the transparent liquid under test. This Doppler algorithm model differs from the classical Doppler frequency shift formula in that it includes at least one correction term based on the theory of light-moving medium interaction. The classical Doppler frequency shift formula is typically derived based on ideal conditions, assuming the incident light is an ideal monochromatic plane wave, the scattering particles are ideal point scatterers, the medium is homogeneous and stationary, and the scattering geometry is simple and clear. However, in actual measurement scenarios, the transparent liquid under test has a specific refractive index, light refracts at the air-liquid interface, changing the propagation direction and effective wavelength of the beam; the moving particles in the liquid have a certain size and shape, and their scattering characteristics deviate from the ideal point scattering model; furthermore, the propagation of the beam in the liquid may involve non-ideal effects such as absorption, scattering attenuation, and optical path geometric deviations. The correction term based on the theory of light-moving medium interaction is used to quantitatively compensate for the deviations between the actual measurement conditions and the ideal model. The correction term can be a refractive index correction term, used to compensate for the influence of the medium's refractive index on wavelength and angle; it can also be a scattering characteristic correction term, used to compensate for frequency shift deviations caused by non-ideal particle scattering behavior; or it can be a geometric correction term, used to compensate for errors introduced by geometric factors such as beam divergence and receiving aperture. Substituting the obtained Doppler frequency shift into the algorithm model containing the correction term, and solving the model equations, the flow velocity value of the transparent liquid under test can be calculated by inversion. This inversion process is essentially a velocity solution after bias compensation of the measured frequency shift, making the final obtained flow velocity value closer to the true physical value.

[0072] In the aforementioned flow velocity detection method based on the optical Doppler effect, a multi-dimensional encoding technique is employed to process the femtosecond laser pulse. In the time dimension, the pulse width is modulated to form a time code; in the spectral dimension, frequency bands are divided to form a spectral code; and in the carrier dimension, the signal carrying the aforementioned encoding is loaded onto a high-frequency carrier to form a modulation signal, thus achieving multi-dimensional feature marking of the femtosecond laser. By incident the coded femtosecond laser onto the transparent liquid under test and receiving the Doppler frequency shift signal generated by scattering from moving particles, and then performing inverse processing corresponding to the multi-dimensional encoding on the scattered light signal, the time-coded signal and the spectral-coded signal carrying the flow velocity information are effectively extracted, and the Doppler frequency shift is determined based on this. Furthermore, the Doppler frequency shift is substituted into a Doppler algorithm model containing a correction term based on the theory of light-moving medium interaction to inversely calculate the flow velocity value of the transparent liquid under test. By employing a multi-dimensional encoding and inverse processing mechanism, the signal-to-noise ratio and anti-interference capability of the scattered light signal are significantly enhanced, and the extraction accuracy of the Doppler frequency shift is improved. At the same time, by introducing theoretical correction terms into the algorithm model, the deviations introduced by factors such as medium characteristics and optical path disturbances in the actual measurement environment are compensated, making the flow velocity inversion results more accurate and reliable, and suitable for high-precision measurement of the flow velocity of transparent liquids under complex working conditions.

[0073] In one exemplary embodiment, such as Figure 2 As shown, the pulse width is modulated in the time dimension to form a time code, specifically including:

[0074] Step S202: Adjust the pulse width of the femtosecond laser pulse according to the preset time interval gradient so that the laser pulses corresponding to different timestamps have different pulse width characteristics, and use the pulse width characteristics as time encoding.

[0075] Specifically, modulating the pulse width in the time dimension to form time coding is a crucial component of femtosecond laser multidimensional coding. In its implementation, a time interval gradient is first preset, defining the pulse width value corresponding to different timestamps. A timestamp refers to the emission time of each pulse in a femtosecond laser pulse sequence, arranged chronologically. The preset time interval gradient can be a series of increasing, decreasing, or patterned pulse width values; for example, setting the pulse width at time t1 to 50 femtoseconds, at time t2 to 80 femtoseconds, at time t3 to 120 femtoseconds, and so on. Subsequently, a programmable pulse shaper or tunable pulse compression device is used to control the original femtosecond pulses output from the femtosecond laser oscillator or amplifier in real time, ensuring that the pulse width of the laser pulse corresponding to each timestamp is precisely adjusted to the preset value when actually output. Pulse width adjustment is typically achieved based on dispersion management or nonlinear optical effects, such as using a spatial light modulator to phase-modulate the pulse spectrum, changing its temporal envelope shape, thereby achieving continuous tunability of the pulse width. After the above modulation, the generated femtosecond laser pulse sequence exhibits different pulse width characteristics for laser pulses emitted at different timestamps. This pulse width characteristic is known as time coding, serving as a unique identifier for each pulse in the time dimension. This allows the subsequently received scattered light signal to be identified based on the difference in pulse width, indicating which emission time the signal originated from.

[0076] In this embodiment, by modulating the pulse width along the time dimension, femtosecond laser pulses at different timestamps acquire differentiated pulse width characteristics. These characteristics are then used as time codes to uniquely mark the probe pulses on the time axis. This encoding method allows subsequently received scattered light signals to be accurately traced back to their corresponding emission times based on pulse width differences, effectively suppressing aliasing interference between signals at different times and improving time resolution.

[0077] In one exemplary embodiment, such as Figure 3 As shown, spectral bands are divided along the spectral dimension to form spectral coding, including:

[0078] Step S302: Divide the original spectrum of the femtosecond laser pulse into multiple non-overlapping characteristic frequency bands;

[0079] Step S304: Assign a unique spectral identification code to each characteristic frequency band, and use the spectral identification code as the spectral encoding.

[0080] Specifically, dividing the spectral bands along the spectral dimension to form spectral codes is one of the core steps in multi-dimensional coding of femtosecond lasers. In practice, firstly, spectral splitting devices, such as gratings, prisms, or acousto-optic tunable filters, are used to divide the original continuous spectrum of the femtosecond laser pulse into multiple non-overlapping characteristic frequency bands. The requirement of non-overlap ensures that there is no frequency aliasing between the bands, and each band corresponds to an independent spectral channel. For example, a femtosecond laser with a center wavelength of 800 nm can be divided into several characteristic frequency bands such as 780-790 nm, 790-800 nm, 800-810 nm, and 810-820 nm. Subsequently, a unique spectral identification code is assigned to each divided characteristic frequency band. This identification code is essentially the center wavelength or band number of that band. For example, the 780-790 nm band is labeled "Channel 1," the 790-800 nm band is labeled "Channel 2," and so on. This spectral identification code is the spectral code, giving each characteristic frequency band a unique identifier. After the above division and labeling, the photons in the generated femtosecond laser pulses carry different spectral coding information in different spectral frequency bands, forming parallel coding channels in the spectral dimension.

[0081] In this embodiment, parallel encoding of the spectral dimension is achieved by dividing the wide spectrum of the femtosecond laser into frequency bands and assigning unique identification codes, allowing a single femtosecond laser pulse to simultaneously carry multiple independent spectral encoded information. The non-overlapping frequency band division avoids crosstalk between channels, ensuring the independence of each spectral encoded signal. This encoding method fully utilizes the wide spectral resources of the femtosecond laser, expanding the information carrying dimension without increasing the number of pulses, providing a foundation for subsequent decoding based on spectral frequency bands after receiving the scattered light signal. Once the scattered light signal is received, the Doppler frequency shift information carried by each channel can be extracted according to the different spectral frequency bands. Through the fusion processing of multi-channel data, random noise is effectively suppressed, improving the extraction accuracy of the Doppler frequency shift, thereby enhancing the signal-to-noise ratio and reliability of flow velocity measurement.

[0082] In one exemplary embodiment, loading a signal carrying time-coded and spectral-coded information onto a high-frequency carrier for carrier modulation includes:

[0083] A quadrature amplitude modulation (QAM) method is used to load a baseband signal carrying time and spectral codes onto a high-frequency carrier at a preset frequency to generate a modulated signal; the expression for carrier modulation is:

[0084] s(t)=A c [1+k s ·s code [t]cos(2πf_ct+φ);

[0085] Among them, A c For carrier amplitude, k s S is the modulation coefficient. code (t) is a two-dimensional encoded signal with time coding and spectral coding, and φ is the initial phase of the carrier.

[0086] Specifically, a quadrature amplitude modulation (QAM) method is used to load the baseband signal, which has undergone time-coding and spectral coding in the aforementioned steps, onto a high-frequency carrier at a preset frequency to generate a modulated signal. QAM is a modulation technique that simultaneously modulates digital or analog signals onto the amplitude and phase of a carrier wave, improving information transmission efficiency within a limited bandwidth. In practice, the preset high-frequency carrier frequency is typically much higher than the frequency range of the baseband signal to ensure that the modulated signal can effectively suppress low-frequency interference during transmission.

[0087] Among them, A c Representing the carrier amplitude, it determines the reference strength of the carrier signal and can be adjusted according to the actual transmission distance and receiver sensitivity requirements. s s is the modulation coefficient, which controls the modulation depth of the baseband signal on the carrier amplitude. Its value needs to strike a balance between ensuring signal integrity and avoiding overmodulation. code (t) represents a two-dimensional encoded signal, consisting of time-coded and spectral-coded signals. This is a composite baseband signal formed after time-dimensional pulse width modulation and spectral-dimensional frequency band division, carrying all the Doppler frequency shift information required for measurement. f_c is the preset high-frequency carrier frequency, which determines the spectral position of the modulated signal. It is typically selected in the radio frequency or microwave band to facilitate subsequent signal amplification, transmission, and demodulation. φ is the initial carrier phase, which plays a crucial role in coherent demodulation and can be synchronized with the local oscillator signal at the receiving end using techniques such as phase-locked loops.

[0088] In this embodiment, time-coded and spectral-coded dual-dimensional signals are loaded onto a high-frequency carrier via orthogonal amplitude modulation, achieving carrier dimension integration of multi-dimensional coded signals. The introduction of the high-frequency carrier enables the coded signal to resist low-frequency interference, making it suitable for transmission and reception in complex electromagnetic environments. Orthogonal amplitude modulation improves bandwidth utilization while maintaining signal integrity. The formation of the modulated signal allows the scattered light signal to be accurately recovered from the original signal after reception using carrier demodulation technology synchronized with the transmitter. code The (t) signal provides a reliable signal basis for subsequent inverse processing and accurate extraction of Doppler frequency shift, ultimately ensuring the accuracy of flow velocity inversion calculation.

[0089] In an exemplary embodiment, the scattered light signal undergoes inverse processing corresponding to multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying a Doppler frequency shift. Based on the obtained time-coded signal and spectral-coded signal, the Doppler frequency shift is determined, including:

[0090] The received scattered light signal is mixed with the local oscillator carrier using coherent demodulation to generate a mixed signal;

[0091] The mixing signal is filtered by a low-pass filter to remove high-frequency components and recover the baseband signal. The baseband signal is the time-coded signal and the spectral-coded signal carrying Doppler frequency shift.

[0092] The recovered baseband signal is then normalized in amplitude.

[0093] Based on the timestamp information and spectral frequency band information in the normalized baseband signal, the corresponding Doppler frequency shift is identified and extracted as the Doppler frequency shift.

[0094] Specifically, after obtaining the scattered light signal, performing inverse processing corresponding to the multi-dimensional encoding at the transmitting end is a crucial step in recovering the effective signal carrying the Doppler frequency shift and determining the actual frequency shift amount. This inverse processing process includes the following steps:

[0095] First, the received scattered light signal is processed using coherent demodulation. Coherent demodulation utilizes a local oscillator carrier that is in phase and frequency with the transmitting carrier to mix the received signal with the local carrier. Since the scattered light signal retains the modulation signal characteristics of the incident light—that is, the signal is modulated on a high-frequency carrier—a mixed signal containing baseband and high-frequency components can be generated through the mixing operation. The mixed signal passes through a low-pass filter to remove the high-frequency components and retain the low-frequency components, thereby recovering the original baseband signal. This baseband signal is a time-coded signal and a spectral-coded signal carrying a Doppler shift. The time coding is reflected in the pulse width characteristics, the spectral coding is reflected in the intensity distribution characteristics of different frequency bands, and the Doppler shift is manifested as the frequency offset of the baseband signal.

[0096] The received signal r(t) is compared with the local oscillation carrier cos(2πf) c Multiplying t+φ, we get:

[0097] r(t)·cos(2πf c t+φ)=A c [1+k s ·s code (t)]cos 2 (2πf c t+φ)=(A c / 2)[1+k s·s code (t)][1+cos(4πf c t+2φ).

[0098] Through a low-pass filter (cutoff frequency f) LP The value is taken as 1 / 10 of the carrier frequency; in this embodiment, 50MHz is used to filter out high-frequency components cos(4πf). c t+2φ), to obtain the demodulated signal:

[0099] r demod (t)=(A c / 2)[1+k s ·s code (t)].

[0100] Subsequently, the recovered baseband signal underwent amplitude normalization. Because scattered light signals can be affected by factors such as medium absorption, scattering attenuation, and detector response differences during propagation, signal amplitudes can vary at different timestamps or in different spectral frequency bands. Amplitude normalization, by adjusting the amplitudes of each signal to a uniform reference level, eliminates the influence of these factors on signal strength. This allows subsequent processing to focus on the frequency information contained in the signal rather than amplitude variations, improving the accuracy of frequency shift extraction.

[0101] Based on the normalized baseband signal, the Doppler frequency shift is further identified and extracted. This identification process fully utilizes the time-coded and spectral-coded information assigned to the signal by the transmitter. By analyzing the time-domain waveform of the baseband signal, the timestamp information corresponding to different pulse widths is identified, thereby determining the signal segment corresponding to each timestamp. Simultaneously, through spectral dispersion or spectrum analysis, the components corresponding to different spectral frequency bands in the baseband signal are identified. For each signal segment corresponding to a timestamp and spectral frequency band, the Doppler frequency shift carried within it is extracted using spectrum analysis or phase detection methods. Since time-coded and spectral-coded signals provide multiple independent measurement channels, the Doppler frequency shift can be comprehensively determined from the extraction results of multiple channels, for example, through weighted averaging or optimal selection, effectively suppressing random errors and noise interference.

[0102] In this embodiment, the baseband signal carrying the Doppler frequency shift is accurately recovered from the high-frequency carrier by combining coherent demodulation and low-pass filtering; amplitude normalization processing eliminates the amplitude differences introduced by the transmission path and detection stage, improving signal consistency; by utilizing multi-dimensional information from time coding and spectral coding, refined identification and extraction of the Doppler frequency shift are achieved, significantly improving the anti-interference capability and accuracy of frequency shift extraction.

[0103] In one exemplary embodiment, a Doppler algorithm model including at least one modified term based on the theory of light-moving medium interaction is specifically described as follows:

[0104] The Doppler algorithm model, combining the observer effect correction term and the general relativistic effect correction term, is expressed as follows:

[0105] Δf=(2nvcosθ) / λ·(1+ΔΦ / c 2 );

[0106] Where n is the refractive index of the transparent liquid obtained through pre-calibration, v is the flow velocity of the transparent liquid to be tested, θ is the angle between the incident laser and the direction of liquid flow, λ is the wavelength of the laser in vacuum, and ΔΦ is the local equivalent gravitational potential difference generated by the liquid flow, where ΔΦ=(1 / 2)v 2 +ρgh, where ρ is the liquid density, g is the gravitational acceleration, and h is the height difference of the detection section;

[0107] When measuring flow velocities below nL / min, v≈(Δf·λ) / (2ncosθ).

[0108] Alternatively, when measuring flow rates below nL / min, v≈(Δf·λ) / (2ncosθ).

[0109] Specifically, in the Doppler algorithm model that includes correction terms, this embodiment introduces observer effect correction terms and general relativistic effect correction terms based on the theory of light-moving medium interaction to compensate for theoretical deviations in the traditional Doppler frequency shift formula under high-speed flow or precision measurement scenarios. The expression for this model is Δf=(2nvcosθ) / λ·(1+ΔΦ / c 2 Its physical meaning and construction logic are as follows.

[0110] First, the first part of the model, (2nvcosθ) / λ, is an extension of the classical Doppler frequency shift formula. Here, n is the refractive index of the transparent liquid obtained through pre-calibration. This refractive index reflects the change in the speed of light propagation in the medium relative to a vacuum and is a fundamental parameter for the interaction between light and a moving medium. Since the liquid under test has a specific optical density, the actual wavelength of light in the liquid becomes λ / n. Therefore, the Doppler frequency shift needs to be corrected by introducing the refractive index n to accurately describe the frequency shift characteristics of light in the moving medium. v is the flow velocity of the transparent liquid under test, θ is the angle between the incident laser and the direction of liquid flow, and λ is the wavelength of the laser in a vacuum. Obtaining the refractive index n through pre-calibration ensures that the model can adapt to the differences in the optical properties of different liquid media.

[0111] The latter part of the model (1+ΔΦ / c²) is the core of the correction term, which introduces the observer effect correction and the general relativity effect correction.

[0112] The observer effect correction stems from the time dilation effect in special relativity. When there is relative motion between the observer and the light source, an additional shift in the observed frequency occurs.

[0113] Δf = (2nvcosθ) / λ·(1 + v o / c);

[0114] where, v o is the velocity of the observer (receiver module) relative to the chamber (in the embodiments of this application, the receiver module is fixed, v o = 0, and in a fixed experimental platform and general industrial measurements, v o << c, and this correction term simplifies to 1), c is the speed of light in vacuum;

[0115] In a high-speed flow scenario, the moving particles act as secondary light sources, and the relative motion between them and the stationary detector cannot be fully described by the classical Doppler formula, and relativistic corrections need to be introduced. The general relativity effect correction stems from the influence of the gravitational field on the light frequency. According to general relativity, when light propagates in regions with different gravitational potentials, its frequency will undergo gravitational redshift or blueshift. In this measurement scenario, the local equivalent gravitational potential difference ΔΦ generated by the liquid flow is introduced to correct this effect. The final correction formula for the Doppler frequency shift combined with the general relativity effect:

[0116] Δf = (2nvcosθ) / λ·(1 + ΔΦ / c 2 );

[0117] The specific expression of ΔΦ is ΔΦ = (1 / 2)v 2 + ρgh, where the (1 / 2)v 2 term corresponds to the contribution of the gravitational potential equivalent to the kinetic energy of the flowing liquid, reflecting the perturbative effect of the equivalent mass density of the moving fluid on the local spacetime metric; the ρgh term corresponds to the gravitational potential difference caused by the height difference of different detection cross-sections in the gravitational field, ρ is the liquid density, g is the acceleration due to gravity, and h is the height difference of the detection cross-section. These two terms together constitute the equivalent gravitational potential difference that affects the optical frequency shift in the liquid flow system. The physical basis is that according to the equivalence principle, the acceleration field and the gravitational field are locally indistinguishable, so the kinetic energy of the flowing liquid can be regarded as the contribution of the equivalent gravitational potential.

[0118] After substituting the Doppler frequency shift amount Δf into this model, by solving the equation containing the refractive index n, the angle θ, the wavelength λ, the equivalent gravitational potential difference ΔΦ, and the speed of light c, the flow velocity value v of the transparent liquid to be measured can be inversely calculated.

[0119] In this embodiment, a Doppler algorithm model incorporating observer effect correction terms and general relativistic effect correction terms is constructed to comprehensively compensate for the Doppler frequency shift in high-speed flowing liquids or precision measurement scenarios. The introduction of the refractive index n corrects for the influence of the medium's optical properties on the frequency shift; the addition of the ΔΦ term compensates for the equivalent gravitational effect caused by the liquid's kinetic energy and gravitational potential difference. This model makes the mapping relationship between the Doppler frequency shift and the flow velocity more accurate, significantly improving the accuracy of flow velocity inversion under complex conditions.

[0120] Substituting the frequency shift Δf obtained above into the final correction formula of the Doppler algorithm incorporating general relativistic effects, the flow velocity v of the transparent liquid is derived as follows:

[0121] Let ΔΦ=(1 / 2)v 2 Substituting Δf=(2nvcosθ) / λ·(1+(1 / 2)v) 2 / c 2 Since v is much smaller than c (v≤1μL / min, c=3×10), 8 m / s), (1 / 2)v 2 / c 2 The item is extremely small (approximately 10). -20 (on the order of magnitude), which can be approximated as 1 in engineering applications, and the formula simplifies to:

[0122] Δf≈(2nvcosθ) / λ;

[0123] The transformation yields:

[0124] v≈(Δf·λ) / (2ncosθ);

[0125] If extremely high precision detection is required (such as flow rates below nL / min), the general relativistic correction term is retained, and the precise v value is obtained through iterative calculation.

[0126] The measured Δf, known λ, n, and θ parameters are substituted into the formula to calculate the v value, and the flow velocity data is output in real time through the display screen or data interface. If the detection scenario is a bidirectional flowing liquid, the forward and reverse flow velocities are calculated by identifying the frequency shift direction (blue shift / red shift) corresponding to the flow in different directions, so as to realize the synchronous detection of bidirectional flow velocity.

[0127] The specific embodiments of this application are as follows:

[0128] (I) Example 1: Flow rate detection of transparent buffer solution in microfluidic chip:

[0129] This embodiment verifies the feasibility and accuracy of the transparent liquid flow velocity detection method based on multi-dimensional encoded femtosecond lasers provided by the above technical solution at the microfluidic scale. First, a detection system is constructed. The encoded femtosecond laser emission module uses a Ti:sapphire femtosecond laser with an output wavelength of 800 nm, an initial pulse width of 150 fs, and a repetition frequency of 1 kHz. A pulse width modulator is cascaded after this laser, with an adjustment range of 100 fs to 200 fs, used for time-dimensional encoding. A bandpass filter is used to divide the spectrum into characteristic frequency bands from 500 nm to 600 nm, achieving spectral-dimensional encoding. The carrier modulation unit uses orthogonal amplitude modulation to load the baseband signal carrying time and spectral encoding onto a high-frequency carrier at 500 MHz, with a modulation coefficient set to 0.3 and an initial carrier phase set to π / 2. The transparent liquid containment chamber is a 100 nL microfluidic chip chamber with quartz transparent windows on both sides. The window transmittance is not less than 95%, and the height difference h of the detection cross-section is 0. The scattered light receiving module employs an avalanche photodiode with a response time of 0.5 ns, paired with a focusing lens with a focal length of 10 mm, and is fixedly mounted on the outside of the chip as a stationary observer. The signal decoding module includes a coherent demodulation unit, a high-resolution spectrometer, and an FPGA encoding / decoding chip. The coherent demodulation unit is configured with the same local oscillation carrier as the transmitter, and the low-pass filter has a cutoff frequency of 50 MHz. The spectrometer has a resolution of 0.1 nm, and the FPGA chip has a processing speed of 200 Mbps. The data processing module is equipped with an embedded processor, pre-stored with the refractive index n=1.33 and density ρ=1000 kg / m³ of water at 25℃. 3 The angle between the incident laser and the direction of liquid flow is set to θ = 30°, and a Doppler algorithm model with general relativity correction is built in.

[0130] The detection steps are as follows: The microfluidic chip is installed into the detection system, and a pH 7.4 PBS buffer solution is introduced into the chamber as the transparent liquid to be tested. The laser emission module is activated, first generating a femtosecond laser pulse. Then, in the time dimension, the pulse width is modulated by a pulse width modulator, so that the laser pulses corresponding to different timestamps have an increasing pulse width characteristic within the range of 100fs to 200fs, forming a time code. In the spectral dimension, the original spectrum is divided into characteristic frequency bands of 500nm to 600nm by a bandpass filter, and a unique spectral identification code is assigned to each frequency band, forming a spectral code. In the carrier dimension, the baseband signal carrying the time code and spectral code is loaded onto a 500MHz high-frequency carrier by orthogonal amplitude modulation, forming a modulation signal, and finally generating the coded femtosecond laser. The coded femtosecond laser is focused and incident on the center of the microfluidic chip chamber. The buffer solution flows directionally within the chamber at a flow rate of 0.1nL / min. Moving particles in the liquid scatter the incident laser, and the scattered light signal carries a Doppler frequency shift caused by particle motion. The receiving module acts as a stationary observer, collecting the scattered light signal, which is a blue-shifted signal, indicating that the liquid flow direction is toward the detector.

[0131] The signal decoding module performs inverse processing on the received scattered light signal: First, coherent demodulation is used to mix the scattered light signal with the local oscillator carrier to generate a mixed signal; high-frequency components are filtered out by a low-pass filter with a cutoff frequency of 50MHz to recover the baseband signal, which is the time-coded signal and spectral-coded signal carrying the Doppler frequency shift; then, the baseband signal is normalized to eliminate amplitude differences introduced by the transmission path; based on the timestamp information and spectral frequency band information in the normalized baseband signal, the Doppler frequency shift is identified and extracted, and the measured value Δf is 0.5MHz. The Doppler frequency shift is substituted into the Doppler algorithm model with general relativity correction, and the model expression is Δf=(2nvcosθ) / λ·(1+ΔΦ / c 2 ), where ΔΦ=(1 / 2)v 2 +ρgh. Since the height difference of the detection section h=0 in this embodiment, ΔΦ is simplified to (1 / 2)v 2 Substituting n=1.33, θ=30°, λ=800nm, c=3×10 8 m / s, ρ=1000kg / m 3The flow rate of the test buffer solution was obtained through inversion calculation. The results show that the engineering approximation flow rate obtained using the classical Doppler formula without considering correction terms is approximately 0.102 nL / min, while the high-precision flow rate obtained using the model including general relativistic correction terms is approximately 0.102000000001 nL / min. The difference between the two is minimal at the microfluidic scale, indicating that the influence of the correction terms is negligible in low-speed flow scenarios, but the model still maintains theoretical completeness. The response time of the entire detection process is 0.8 ms, achieving high-precision real-time measurement at micro-level flow rates.

[0132] (II) Example 2: Flow rate detection of bidirectional flow transparent ethanol solution:

[0133] This embodiment is used to verify the measurement capability of the proposed technical solution in a bidirectional flow scenario and its adaptability to different liquid media. The detection system setup is basically the same as in Embodiment 1, except that the refractive index of the liquid is calibrated to the refractive index of ethanol at 25°C, n=1.36, and the modulation coefficient of the carrier modulation unit is adjusted to 0.4, while the other parameters remain unchanged.

[0134] The detection steps are as follows: An ethanol solution is introduced into the microfluidic chip chamber, and a bidirectional flow mode of 0.08 nL / min in the forward direction and 0.05 nL / min in the reverse direction is achieved by controlling the flow using a precision injection pump. The laser emission module is activated to generate a time-spectral dual-dimensional encoded femtosecond laser, the same as in Example 1, which is then incident on the center of the chamber after carrier modulation. Moving particles in the ethanol solution scatter the incident laser, and the receiving module collects the blue-shifted scattered light signal r1(t) generated by the forward flow and the red-shifted scattered light signal r2(t) generated by the reverse flow, respectively. The signal decoding module performs coherent demodulation, low-pass filtering, and amplitude normalization processing on the two scattered light signals, the same as in Example 1, and extracts the Doppler frequency shift carried by each signal based on the time-coded and spectral-coded information. The Doppler frequency shift Δf1 corresponding to the forward blue-shifted signal is 0.4 MHz, and the Doppler frequency shift Δf2 corresponding to the reverse red-shifted signal is -0.25 MHz.

[0135] Δf1 and Δf2 are substituted into the Doppler algorithm model, which includes general relativistic correction terms, for inversion calculations. In the model parameters, the refractive index n is calibrated to 1.36 using ethanol, the angle θ between the incident laser and the liquid flow direction remains 30°, λ = 800 nm, and ρ = 785 kg / m². 3(Ethanol density), h=0. The inversion calculation yielded a forward flow velocity v1 of approximately 0.081 nL / min and a reverse flow velocity v2 of approximately 0.049 nL / min. Compared with the preset flow velocity values, the measurement error for both values ​​did not exceed 2%. This embodiment verifies the adaptability of this method to liquids with different refractive indices and its ability to simultaneously measure forward and reverse flow velocities in a bidirectional flow mode. The measurement results are accurate and reliable, indicating that the multi-dimensional encoding and inverse processing mechanism constructed in this invention can effectively distinguish flow signals from different directions, has strong anti-interference capabilities, and is suitable for flow velocity detection scenarios of transparent liquids in complex flow states.

[0136] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0137] Based on the same inventive concept, this application also provides an optical Doppler effect-based flow velocity detection device for implementing the aforementioned flow velocity detection method based on the optical Doppler effect. The solution provided by this device is similar to the solution described in the above method; therefore, the specific limitations of one or more embodiments of the optical Doppler effect-based flow velocity detection device provided below can be found in the limitations of the optical Doppler effect-based flow velocity detection method described above, and will not be repeated here.

[0138] In one exemplary embodiment, such as Figure 4 As shown, a flow velocity detection device based on the optical Doppler effect is provided, comprising:

[0139] The encoding module 402 is used to generate femtosecond laser pulses and encode the femtosecond laser pulses in multiple dimensions to form an encoded femtosecond laser. The multi-dimensional encoding includes modulating the pulse width in the time dimension to form a time code, dividing the spectral frequency band in the spectral dimension to form a spectral code, and further loading the signal carrying the time code and spectral code onto a high-frequency carrier for carrier modulation.

[0140] Test module 404 is used to incident an coded femtosecond laser onto the transparent liquid under test and receive the scattered light signal with Doppler frequency shift carrying flow velocity information generated by the scattering of moving particles in the transparent liquid under test.

[0141] The processing module 406 is used to perform inverse processing on the scattered light signal corresponding to multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying a Doppler frequency shift, and to determine the amount of Doppler frequency shift based on the obtained time-coded signal and spectral-coded signal.

[0142] The calculation module 408 is used to substitute the Doppler frequency shift into the Doppler algorithm model, which includes at least one correction term based on the theory of light-moving medium interaction, and to invert and calculate the flow velocity value of the transparent liquid to be measured.

[0143] In an exemplary embodiment, the encoding module 402 is specifically used to adjust the pulse width of the femtosecond laser pulse according to a preset time interval gradient, so that the laser pulses corresponding to different timestamps have different pulse width characteristics, and the pulse width characteristics are used as time encoding.

[0144] In an exemplary embodiment, the encoding module 402 is specifically used to divide the original spectrum of the femtosecond laser pulse into multiple non-overlapping characteristic frequency bands, and assign a unique spectral identification code to each characteristic frequency band, using the spectral identification code as spectral encoding.

[0145] In an exemplary embodiment, the encoding module 402 is specifically used to load the baseband signal carrying time-coded and spectral-coded data onto a high-frequency carrier at a preset frequency using an orthogonal amplitude modulation method, thereby performing carrier modulation; the expression for carrier modulation is:

[0146] s(t)=A c [1+k s ·s code [t]cos(2πf_ct+φ);

[0147] Among them, A c For carrier amplitude, k s S is the modulation coefficient. code (t) is a two-dimensional encoded signal with time coding and spectral coding, and φ is the initial phase of the carrier.

[0148] In an exemplary embodiment, the processing module 406 is specifically configured to use coherent demodulation to mix the received scattered light signal with a local oscillator carrier to generate a mixed signal; filter the mixed signal with a low-pass filter to remove high-frequency components and recover the baseband signal, which is a time-coded signal and a spectral-coded signal carrying Doppler frequency shift; perform amplitude normalization processing on the recovered baseband signal; and identify and extract the corresponding Doppler frequency shift based on the timestamp information and spectral frequency band information in the normalized baseband signal as the Doppler frequency shift amount.

[0149] In one exemplary embodiment, a Doppler algorithm model including at least one modified term based on the theory of light-moving medium interaction is specifically described as follows:

[0150] The Doppler algorithm model, combining the observer effect correction term and the general relativistic effect correction term, is expressed as follows:

[0151] Δf=(2nvcosθ) / λ·(1+ΔΦ / c 2 );

[0152] Where n is the refractive index of the transparent liquid obtained through pre-calibration, v is the flow velocity of the transparent liquid to be measured, θ is the angle between the incident laser and the direction of liquid flow, λ is the wavelength of the laser in vacuum, and ΔΦ is the local equivalent gravitational potential difference generated by the liquid flow, where ΔΦ = (1 / 2)v 2 +ρgh, where ρ is the liquid density, g is the gravitational acceleration, and h is the height difference of the detection section;

[0153] When measuring flow velocities below nL / min, v≈(Δf·λ) / (2ncosθ).

[0154] The modules in the aforementioned flow velocity detection device based on the optical Doppler effect can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of a computer device in hardware form or independent of it, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each module.

[0155] In one exemplary embodiment, a computer device is provided, which may be a server, and its internal structure diagram may be as follows: Figure 5As shown, this computer device includes a processor, memory, input / output (I / O) interfaces, and a communication interface. The processor, memory, and I / O interfaces are connected via a system bus, and the communication interface is also connected to the system bus via the I / O interfaces. The processor provides computational and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and a database. The internal memory provides the environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The database stores data. The I / O interfaces are used for exchanging information between the processor and external devices. The communication interface is used for communicating with external terminals via a network. When executed by the processor, the computer program implements a flow velocity detection method based on the optical Doppler effect.

[0156] Those skilled in the art will understand that Figure 5 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0157] In one exemplary embodiment, a computer device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the method described above.

[0158] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-described method.

[0159] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps of the method described above.

[0160] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.

[0161] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, artificial intelligence (AI) processors, etc., and are not limited to these.

[0162] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0163] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A flow velocity detection method based on the optical Doppler effect, characterized in that, The method includes: A femtosecond laser pulse is generated and the femtosecond laser pulse is encoded in multiple dimensions to form an coded femtosecond laser; wherein, the multi-dimensional encoding includes modulating the pulse width in the time dimension to form a time code, dividing the spectral frequency band in the spectral dimension to form a spectral code, and further loading the signal carrying the time code and the spectral code onto a high-frequency carrier for carrier modulation; The coded femtosecond laser is incident on the transparent liquid to be tested, and the scattered light signal carrying the flow velocity information generated by the scattering of moving particles in the transparent liquid to be tested is received. The scattered light signal is subjected to inverse processing corresponding to the multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying the Doppler frequency shift, and the Doppler frequency shift amount is determined based on the obtained time-coded signal and spectral-coded signal. The flow velocity of the transparent liquid under test is obtained by substituting the Doppler frequency shift into a Doppler algorithm model that includes at least one correction term based on the theory of light-moving medium interaction.

2. The method according to claim 1, characterized in that, The modulation of the pulse width in the time dimension to form a time code specifically includes: The pulse width of the femtosecond laser pulse is adjusted according to a preset time interval gradient, so that the laser pulses corresponding to different timestamps have different pulse width characteristics, and the pulse width characteristics are used as the time code.

3. The method according to claim 1, characterized in that, The process of dividing spectral frequency bands along the spectral dimension to form spectral coding includes: The original spectrum of the femtosecond laser pulse is divided into multiple non-overlapping characteristic frequency bands, and a unique spectral identification code is assigned to each characteristic frequency band, which is then used as the spectral encoding.

4. The method according to claim 1, characterized in that, The step of loading the signal carrying the time code and the spectral code onto a high-frequency carrier for carrier modulation includes: A quadrature amplitude modulation (QAM) method is used to load the baseband signal carrying the time code and the spectral code onto a high-frequency carrier at a preset frequency for carrier modulation; the expression for carrier modulation is: s(t)=A c [1+k s ·s code (t)]cos(2πf_ct+φ); Among them, A c For carrier amplitude, k s S is the modulation coefficient. code (t) is the two-dimensional encoded signal of the time encoding and the spectral encoding, and φ is the initial phase of the carrier.

5. The method according to claim 1, characterized in that, The step of performing inverse processing on the scattered light signal corresponding to the multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying the Doppler frequency shift, and determining the Doppler frequency shift based on the obtained time-coded signal and spectral-coded signal, includes: The received scattered light signal is mixed with the local oscillator carrier using coherent demodulation to generate a mixed signal; The mixing signal is filtered by a low-pass filter to remove high-frequency components and recover the baseband signal, which is the time-coded signal and the spectral-coded signal carrying the Doppler frequency shift. The recovered baseband signal is then normalized in amplitude. Based on the timestamp information and spectral frequency band information in the normalized baseband signal, the corresponding Doppler frequency shift is identified and extracted as the Doppler frequency shift.

6. The method according to claim 1, characterized in that, The Doppler algorithm model, which includes at least one correction term based on the theory of light-moving medium interaction, is specifically as follows: The Doppler algorithm model, combining the observer effect correction term and the general relativistic effect correction term, is expressed as follows: Δf=(2nvcosθ) / λ·(1+ΔΦ / c 2 ); Where n is the refractive index of the transparent liquid obtained through pre-calibration, v is the flow velocity of the transparent liquid to be tested, θ is the angle between the incident laser and the direction of liquid flow, λ is the wavelength of the laser in vacuum, and ΔΦ is the local equivalent gravitational potential difference generated by the liquid flow, where ΔΦ=(1 / 2)v 2 +ρgh, where ρ is the liquid density, g is the gravitational acceleration, and h is the height difference of the detection section; When measuring flow velocities below nL / min, v≈(Δf·λ) / (2ncosθ).

7. A flow velocity detection device based on the optical Doppler effect, characterized in that, The device includes: An encoding module is used to generate femtosecond laser pulses and encode the femtosecond laser pulses in multiple dimensions to form an encoded femtosecond laser; wherein, the multi-dimensional encoding includes modulating the pulse width in the time dimension to form a time code, dividing the spectral frequency band in the spectral dimension to form a spectral code, and further loading the signal carrying the time code and the spectral code onto a high-frequency carrier for carrier modulation; The testing module is used to incident the coded femtosecond laser onto the transparent liquid under test and receive the scattered light signal with Doppler frequency shift carrying flow velocity information generated by the scattering of moving particles in the transparent liquid under test. The processing module is used to perform inverse processing on the scattered light signal corresponding to the multi-dimensional encoding to obtain a time-coded signal and a spectral-coded signal carrying the Doppler frequency shift, and to determine the Doppler frequency shift amount based on the obtained time-coded signal and spectral-coded signal. The calculation module is used to substitute the Doppler frequency shift into a Doppler algorithm model that includes at least one correction term based on the theory of light-moving medium interaction, and to invert and calculate the flow velocity value of the transparent liquid to be measured.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

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