A method for extracting the vibration characteristics of ultra-high frequency targets

Abstract

A method for extracting the vibration characteristics of ultra-high frequency targets relates to the field of laser coherent vibration measurement technology, and solves the problem that the accuracy of extracting the vibration information of the target in a laser ultra-high frequency vibration measurement system still needs to be improved. The method is as follows: according to the amplitude deviation between the in-phase carrier signal I of the baseband signal and the quadrature carrier signal Q of the baseband signal, the deviation between I and the frequency of the ideal carrier signal, and the deviation between Q and the frequency of the ideal carrier signal, a phase error gain factor is calculated; the target vibration information is obtained by using a target vibration information compensation algorithm model containing the phase error gain factor. The present invention quantifies and compensates the phase error caused by amplitude and frequency deviation, reduces the influence of uneven two-way carrier modulation on the demodulation accuracy, and realizes high-precision demodulation of ultra-high frequency micro-vibration signals.

Description

Technical Field

[0001] The present invention relates to the technical field of laser coherent vibration measurement, and specifically relates to a method for extracting ultra-high frequency target vibration characteristics. Background Art

[0002] In the field of laser Doppler ultra-high frequency micro-vibration measurement, the target vibration demodulation algorithms mainly include the differential cross-multiplication algorithm and the arctangent phase discrimination algorithm. Among them, the arctangent has become the mainstream demodulation method because of its simple implementation method and ability to suppress amplitude noise. The traditional arctangent demodulation method only needs to restore the phase generated by target modulation according to simple trigonometric function relations, and then extract the target vibration information.

[0003] The traditional arctangent micro-vibration signal demodulation algorithm depends on the orthogonality of the photocurrent signal output by the detector, and uses the orthogonal baseband signal to demodulate the micro-vibration signal with high precision. Due to the deviation between the actual measured values of the amplitude and phase of the baseband signal and the theoretical values, if the traditional arctangent algorithm demodulates the micro-vibration signal in an ideal orthogonal manner, it will lead to a decrease in demodulation accuracy and cannot accurately extract the characteristics of the micro-vibration signal.

[0004] Therefore, it is necessary to design a new demodulation algorithm research to achieve high-precision demodulation of ultra-high frequency micro-vibration signals. Summary of the Invention

[0005] In order to solve the problem that the accuracy of extracting the target vibration information of the laser ultra-high frequency vibration measurement system still needs to be improved, the present invention provides a method for extracting ultra-high frequency target vibration characteristics.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0007] A method for extracting ultra-high frequency target vibration characteristics includes:

[0008] Step 1: Calculate the phase error gain factor δ according to the amplitude deviation ΔU between the in-phase carrier signal I of the baseband signal and the quadrature carrier signal Q of the baseband signal, the deviation f ei between I and the ideal carrier signal frequency, and the deviation f eq between Q and the ideal carrier signal frequency;

[0009] Step 2: Obtain the target vibration information by using the target vibration information compensation algorithm model containing δ.

[0010] The beneficial effects of the present invention are:

[0011] A method for extracting ultra-high frequency target vibration characteristics of the present invention quantifies and compensates for the phase error caused by amplitude and frequency deviation, reducing the influence of uneven two-way carrier modulation on the demodulation accuracy. The phase caused by target vibration is accurately compensated by using the target vibration information compensation algorithm model. Therefore, the target vibration information can be accurately extracted, and high-precision demodulation of ultra-high frequency micro-vibration signals can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a flowchart of a method for extracting ultra-high frequency target vibration characteristics of the present invention.

[0013] Figure 2 It is a diagram of the quadrature demodulation process of a method for extracting ultra-high frequency target vibration characteristics of the present invention.

[0014] Figure 3 It is a diagram of the arctangent demodulation process of a method for extracting ultra-high frequency target vibration characteristics of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be further described in detail below with reference to the drawings and embodiments.

[0016] A method for extracting ultra-high frequency target vibration characteristics, as Figure 1 , the method is specifically as follows:

[0017] Let the photocurrent signal be mixed with two carrier signals respectively and pass through a low-pass filter, retaining the difference frequency component containing the target vibration information and removing the sum frequency component containing high-frequency noise, obtaining two orthogonal I&Q baseband signals.

[0018] Due to the influence of noise, there will always be a certain deviation in the amplitude and frequency of the two I&Q baseband signals (I refers to the in-phase carrier signal of the baseband signal and Q refers to the quadrature carrier signal of the baseband signal), resulting in a deviation in the target vibration information demodulated by the arctangent. Therefore, phase compensation is required to accurately demodulate the target vibration information. Assume that the amplitude deviation of the two carrier signals is ΔU, and the deviations between the two carrier signals and the ideal carrier signal frequency are f ei and f eq . Therefore, the two baseband signals can be expressed as

[0019]

[0020] Among them, u i (t) represents the amplitude of the in-phase carrier signal of the baseband signal, u q (t) represents the amplitude of the quadrature carrier signal of the baseband signal, U represents the amplitude of the ideal carrier signal, ΔU represents the amplitude deviation between the in-phase carrier signal and the quadrature carrier signal, f ei represents the deviation between the in-phase carrier signal and the ideal carrier signal frequency, feq represents the deviation between the frequency of the orthogonal carrier signal and the frequency of the ideal carrier signal, t represents time, and f c represents the frequency of the ideal carrier signal.

[0021] In order to obtain the target vibration information, the present invention performs frequency mixing of the photocurrent signal with two carrier signals respectively, and after frequency mixing, passes through a low-pass filter to retain the difference-frequency component containing the target vibration information and remove the sum-frequency component containing high-frequency noise, thereby obtaining two orthogonal I&Q baseband signals. As Figure 2 shows the quadrature demodulation process: The photocurrent signal and the sine carrier signal sin(2πf AOM t) perform coherent frequency mixing in the first mixer 1, and then the difference-frequency component generated after frequency mixing is filtered out by the first low-pass filter 2. The photocurrent signal and the cosine carrier signal cos(2πf AOM t) perform coherent frequency mixing in the second mixer 3 respectively, and then the difference-frequency component generated after frequency mixing is filtered out by the second low-pass filter 4. The difference-frequency component containing the target vibration information is retained to obtain mutually orthogonal baseband signals, and the orthogonal baseband signals are an important prerequisite for subsequent signal processing. Figure 2 The sin(2πf AOM t) in represents the in-phase carrier signal, and cos(2πf AOM t) represents the orthogonal carrier signal, and f AOM represents the carrier frequency of the acousto-optic modulator.

[0022]

[0023] Among them, I(t) represents the in-phase carrier signal of the baseband signal, Q(t) represents the orthogonal carrier signal of the baseband signal, Δi(t) represents the photocurrent signal, and h LPF represents the transfer function of the low-pass filter, K represents the optoelectronic conversion parameter, P m and P r represent the powers of the measurement light and the local oscillator light respectively, represents the phase information containing the target displacement information s(t), is the delay phase, and λ represents the wavelength of the measurement light.

[0024] From the expression formulas (2) of the two baseband signals, the calculated phase value containing the target displacement information s(t), amplitude deviation ΔU, and frequency deviation f ei and f eq can be derived.

[0025]

[0026] On this basis, we define the phase error gain factor containing phase information and deviation information,

[0027]

[0028] The phase deviation caused by the instability of the carrier signal can be expressed as an expression of the phase error gain factor.

[0029]

[0030] Wherein, represents the phase deviation caused by the instability of the in-phase carrier signal and the quadrature carrier signal, that is, the above

[0031] The amplitude deviation ΔU is an extremely small quantity, and the frequency deviations f ei and f eq are approximately equal to each other. Therefore, the phase error gain factor δ is an extremely small quantity. The present invention can perform Taylor expansion on f(δ) using the Taylor series expansion formula, and then obtain

[0032]

[0033] where o(·) represents a higher-order infinitesimal.

[0034] So far, the target vibration information compensation algorithm model including the phase error gain factor δ has been obtained. First, the phase error gain factor is obtained based on the amplitude deviation ΔU and the frequency deviation of the two carrier signals, and then the true value of the target vibration information is obtained using the target vibration information compensation algorithm model.

[0035] The target vibration information includes target displacement information, target velocity information, and target acceleration information. As Figure 3 , the arctangent demodulation process is shown: The I&Q two-channel baseband signals pass through the corresponding low-pass filters to obtain I(t) and Q(t) in formula (2). I(t) and Q(t) both perform division operations in the divider 5 (formula (3)), and then the tangent function containing the target vibration information is demodulated in the arctangent operator 6 (corresponding to f(δ)) to obtain the phase information containing the target vibration characteristics. This phase information is then made continuous using the phase unwrapping module 7 (i.e., using the phase unwrapping algorithm). The continuous phase information enters the band-pass filter 8 to obtain the target displacement information, and the target displacement information undergoes a first-order differentiation operation in the differentiator 9 to obtain the target velocity information, and undergoes a second-order differentiation operation to obtain the target acceleration information.

[0036] The laser Doppler ultra-high frequency micro-vibration measurement technology uses the coherent superposition of the local oscillator light and the signal light to convert the high-frequency optical wave signal into an intermediate-frequency signal, and then converts the intermediate-frequency signal into a baseband signal through the modulation and demodulation technology of the carrier signal, so as to realize the measurement of the Doppler frequency shift caused by the micro-vibration target and restore the vibration characteristics of the detection target. Among them, the stability of the carrier signal is an important factor determining the characteristics of the micro-vibration target, and the stability of the carrier signal includes amplitude stability and frequency stability. The technical solution in the present invention quantifies the amplitude and frequency deviations caused by the carrier instability, and quantitatively compensates the phase error caused by the amplitude and frequency deviations, reducing the influence of uneven two-way carrier modulation on the demodulation accuracy.

[0037] Due to the instability of the carrier frequency in the laser ultra-high frequency vibration measurement system, it is often necessary to improve the demodulation accuracy of vibration information through phase compensation. The present invention establishes an arctangent phase compensation algorithm, introduces a phase error compensation factor, and quantitatively compensates the demodulation output phase containing the target vibration information, accurately compensating for the decrease in demodulation accuracy caused by the amplitude and phase deviations of the baseband signal. This compensation algorithm can improve the demodulation accuracy of the target vibration information. The present invention directly calculates the value of the phase error compensation factor through the amplitude and frequency deviations of the carrier signal, and accurately compensates the phase caused by the target vibration. This phase is obtained by demodulating the Doppler frequency shift caused by the target vibration, so the target vibration information can be accurately extracted.

[0038] In addition, in the present invention, descriptions such as "first" and "second" are only for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of these features. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0039] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for extracting the vibration characteristics of ultra-high frequency targets, characterized in that, Including: Step 1. Calculate the phase error gain factor δ based on the amplitude deviation ΔU between the in-phase carrier signal I of the baseband signal and the quadrature carrier signal Q of the baseband signal, the deviation f between I and the ideal carrier signal frequency, ei and the deviation f between Q and the ideal carrier signal frequency. eq ​ Step 2: Obtain the target vibration information by using a target vibration information compensation algorithm model including δ; The target vibration information compensation algorithm model is: Among them, represents the phase value, represents the phase information including the target displacement information s(t), is the delayed phase, λ represents the wavelength of the measurement light, and o(·) represents a higher-order infinitesimal; The I and Q are expressed as: where, u i (t) represents the amplitude of the in-phase carrier signal of the baseband signal, u q (t) represents the amplitude of the quadrature carrier signal of the baseband signal, U represents the amplitude of the ideal carrier signal, ΔU represents the amplitude deviation between the in-phase carrier signal and the quadrature carrier signal, f ei represents the deviation between the frequency of the in-phase carrier signal and the frequency of the ideal carrier signal, f eq represents the deviation between the frequency of the quadrature carrier signal and the frequency of the ideal carrier signal, t represents time, f c represents the frequency of the ideal carrier signal; The method for obtaining the target vibration information compensation algorithm model is: Let the photocurrent signal be mixed with I and Q respectively, and after mixing, pass through a low-pass filter to retain the difference frequency component containing the target vibration information and remove the sum frequency component containing high-frequency noise, obtaining where, I(t) represents the in-phase carrier signal of the baseband signal, Q(t) represents the quadrature carrier signal of the baseband signal, Δi(t) represents the photocurrent signal, h LPF represents the transfer function of the low-pass filter of the low-pass filter, K represents the optoelectronic conversion parameter, P m and P r respectively represent the powers of the measurement light and the local oscillator light; Derivation according to formula (2) Define the phase error gain factor δ including phase information and deviation information as The phase deviation caused by the instability of the in-phase carrier signal and the quadrature carrier signal is expressed as an expression of δ, Use the Taylor series expansion to perform Taylor expansion on f(δ), and then obtain the target vibration information compensation algorithm model.

2. The ultra-high frequency target vibration feature extraction method according to claim 1, characterized in that, The target vibration information includes target displacement information, target velocity information, and target acceleration information.

3. The ultra-high frequency target vibration feature extraction method according to claim 2, characterized in that The target displacement information is obtained by filtering the continuous phase information through a band-pass filter, the target velocity information is obtained by performing a first-order differentiation operation on the target displacement information in a differentiator, and the target acceleration information is obtained by performing a second-order differentiation operation on the target displacement information in a differentiator.

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