CN116147754A - A Method for Extracting Vibration Feature of UHF Target - Google Patents

Abstract

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

Description

A method for extracting ultra-high frequency target vibration features

Technical Field

The invention relates to the technical field of laser coherent vibration measurement, and in particular to a method for extracting ultra-high frequency target vibration characteristics.

Background Art

In the field of laser Doppler ultra-high frequency micro-vibration measurement, the target vibration demodulation algorithm mainly includes the differential cross-multiplication algorithm and the inverse tangent phase detection algorithm. Among them, the inverse tangent has become the mainstream demodulation method because of its simple implementation and ability to suppress amplitude noise. The traditional inverse tangent demodulation method only needs to recover the phase generated by the target modulation based on a simple trigonometric function relationship, and then extract the target vibration information.

The traditional inverse tangent micro-vibration signal demodulation algorithm relies on the orthogonality of the detector output photocurrent signal and uses the orthogonal baseband signal to demodulate the micro-vibration signal with high precision. Since there is a deviation between the actual measured value and the theoretical value of the amplitude and phase of the baseband signal, if the traditional inverse tangent algorithm demodulates the micro-vibration signal in an ideal orthogonal manner, the demodulation accuracy will decrease and the micro-vibration signal characteristics cannot be accurately extracted.

Therefore, it is necessary to design a new demodulation algorithm to achieve high-precision demodulation of ultra-high frequency micro-vibration signals.

Summary of the invention

In order to solve the problem that the accuracy of extracting target vibration information of a laser ultra-high frequency vibrometer system still needs to be improved, the present invention provides an ultra-high frequency target vibration feature extraction method.

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

A method for extracting ultra-high frequency target vibration features, comprising:

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 orthogonal carrier signal Q of the baseband signal, the deviation fei between I and the ideal carrier signal frequency, and the deviation _feq between Q and the ideal carrier signal frequency;

Step 2: Utilize the target vibration information compensation algorithm model including δ to obtain the target vibration information.

The beneficial effects of the present invention are:

The ultra-high frequency target vibration feature extraction method of the present invention quantizes and compensates for the phase error caused by the amplitude and frequency deviation, and reduces the influence of the uneven modulation of the two carriers on the demodulation accuracy. The target vibration information compensation algorithm model is used to accurately compensate for the phase caused by the target vibration, so that the target vibration information can be accurately extracted to achieve high-precision demodulation of the ultra-high frequency micro-vibration signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of an ultra-high frequency target vibration feature extraction method of the present invention.

FIG. 2 is a diagram of an orthogonal demodulation process of an ultra-high frequency target vibration feature extraction method of the present invention.

FIG. 3 is a diagram of an inverse tangent demodulation process of an ultra-high frequency target vibration feature extraction method of the present invention.

DETAILED DESCRIPTION

The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

A method for extracting ultra-high frequency target vibration features is shown in Figure 1. The specific method is as follows:

The photocurrent signal is mixed with two carrier signals respectively and passed 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 to obtain two orthogonal I&Q baseband signals.

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 orthogonal carrier signal of the baseband signal) will always have a certain deviation due to the influence of noise, resulting in deviation of the target vibration information demodulated by the inverse tangent. 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 _fei and _feq respectively. Therefore, the two baseband signals can be expressed as

Among them, _ui (t) represents the amplitude of the in-phase carrier signal of the baseband signal, _uq (t) represents the amplitude of the orthogonal 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 orthogonal carrier signal, _fei represents the deviation between the in-phase carrier signal and the ideal carrier signal frequency, _feq represents the deviation between the orthogonal carrier signal and the ideal carrier signal frequency, t represents time, and _fc represents the ideal carrier signal frequency.

In order to obtain the target vibration information, the present invention allows the photocurrent signal to be mixed with two carrier signals respectively and then pass through a low-pass filter after mixing, retaining the difference frequency component containing the target vibration information, removing the sum frequency component containing high-frequency noise, and obtaining two orthogonal I&Q baseband signals. As shown in Figure 2, the orthogonal demodulation process: the photocurrent signal and the sine carrier signal sin (2πf _AOM t) are coherently mixed in the first mixer 1, and then the difference frequency component generated after mixing is filtered out by the first low-pass filter 2, the photocurrent signal and the cosine carrier signal cos (2πf _AOM t) are coherently mixed in the second mixer 3, and then the difference frequency component generated after mixing is filtered out by the second low-pass filter 4, retaining the difference frequency component containing the target vibration information, and obtaining mutually orthogonal baseband signals. The orthogonal baseband signal is an important prerequisite for subsequent signal processing. In Figure 2, sin (2πf _AOM t) represents the in-phase carrier signal, cos (2πf _AOM t) represents the orthogonal carrier signal, and f _AOM represents the carrier frequency of the acousto-optic modulator.

表示包含目标位移信息s(t)的相位信息，

为延迟相位，λ表示测量光的波长。Where, 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, h _LPF represents the transfer function of the low-pass filter, K represents the photoelectric conversion parameter, P _m and P _r represent the power of the measurement light and the local oscillator light, respectively.

represents the phase information containing the target displacement information s(t),

is the delayed phase, and λ is the wavelength of the measured light.

From the expression formula (2) of the two baseband signals, the calculated phase values including the target displacement information s(t), the amplitude deviation ΔU, and the frequency deviations _fei and _feq can be derived:

On this basis, we define the phase error gain factor that contains phase information and deviation information,

The phase deviation caused by the instability of the carrier signal can be expressed as the expression of the phase error gain factor,

表示同相载波信号和正交载波信号的不稳定引起的相位偏差，

即上述

in,

Indicates the phase deviation caused by the instability of the in-phase carrier signal and the orthogonal carrier signal.

That is,

The amplitude deviation ΔU is a very small quantity, and the frequency deviations _fei and _feq are approximately equal, so the phase error gain factor δ is a very small quantity. The present invention can use the Taylor series expansion to perform Taylor expansion on f(δ), and then obtain

Here, o(·) represents a higher-order infinitesimal.

So far, the target vibration information compensation algorithm model including the phase error gain factor δ is obtained. First, the phase error gain factor is obtained according to the amplitude deviation ΔU and frequency deviation of the two carrier signals, and then the target vibration information compensation algorithm model is used to obtain the true value of the target vibration information.

The target vibration information includes target displacement information, target velocity information and target acceleration information. As shown in FIG3 , the inverse tangent demodulation process is shown: the I&Q two-way baseband signal is passed through the corresponding low-pass filter to obtain I(t) and Q(t) of formula (2), I(t) and Q(t) are divided in the divider 5 (formula (3)), and then the tangent function containing the target vibration information is demodulated in the inverse tangent operator 6 (corresponding to f(δ)) to obtain the phase information containing the target vibration characteristics, and the phase information is then made continuous by the phase unwrapping module 7 (i.e., by the phase unwrapping algorithm), and the continuous phase information enters the bandpass filter 8 to obtain the target displacement information, and the target displacement information is subjected to a first differential operation in the differentiator 9 to obtain the target velocity information, and the target acceleration information is obtained after a second differential operation.

Laser Doppler ultra-high frequency micro-vibration measurement technology utilizes the coherent superposition of local oscillator light and signal light to convert high-frequency light wave signals into intermediate frequency signals, and then converts the intermediate frequency signals into baseband signals through the modulation and demodulation technology of the carrier signal, thereby realizing the measurement of the Doppler frequency shift caused by the micro-vibration target and restoring the vibration characteristics of the detection target. Among them, the stability of the carrier signal is an important factor in 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 carrier instability, and quantizes and compensates for the phase errors caused by amplitude and frequency deviations, thereby reducing the influence of uneven modulation of the two carriers on the demodulation accuracy.

Due to the instability of the carrier frequency in the laser ultra-high frequency vibrometer system, phase compensation is often required to improve the demodulation accuracy of the vibration information. The present invention establishes an inverse tangent phase compensation algorithm, introduces a phase error compensation factor, and quantitatively compensates for the demodulation output phase containing the target vibration information, and accurately compensates for the decrease in demodulation accuracy caused by the baseband signal amplitude and phase deviation. The 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 deviation of the carrier signal, and accurately compensates for the phase caused by the target vibration. The phase is obtained by demodulating the Doppler shift frequency caused by the target vibration, so the target vibration information can be accurately extracted.

In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (6)

1. A method for extracting ultra-high frequency target vibration features, comprising: 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 orthogonal carrier signal Q of the baseband signal, the deviation fei between I and the ideal carrier signal frequency, and the deviation _feq between Q and the ideal carrier signal frequency; Step 2: Utilize the target vibration information compensation algorithm model including δ to obtain the target vibration information. 2. A method for extracting ultra-high frequency target vibration features according to claim 1, characterized in that the target vibration information compensation algorithm model is:

in,

represents the phase value,

represents the phase information containing the target displacement information s(t),

is the delayed phase, λ is the wavelength of the measured light, and o(·) represents a high-order infinitesimal. 3. A method for extracting ultra-high frequency target vibration characteristics as claimed in claim 2, characterized in that the I and Q are expressed as:

Among them, _ui (t) represents the amplitude of the in-phase carrier signal of the baseband signal, _uq (t) represents the amplitude of the orthogonal 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 orthogonal carrier signal, _fei represents the deviation between the in-phase carrier signal and the ideal carrier signal frequency, _feq represents the deviation between the orthogonal carrier signal and the ideal carrier signal frequency, t represents time, and _fc represents the ideal carrier signal frequency. 4. The method for extracting ultra-high frequency target vibration features according to claim 3, wherein the target vibration information compensation algorithm model is obtained by: The photocurrent signal is mixed with I and Q respectively, and after mixing, it 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 to obtain

Wherein, 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, h _LPF represents the transfer function of the low-pass filter, K represents the photoelectric conversion parameter, P _m and P _r represent the power of the measurement light and the local oscillator light respectively; According to formula (2),

The phase error gain factor δ, which includes phase information and deviation information, is defined as

The phase deviation caused by the instability of the in-phase carrier signal and the orthogonal carrier signal

Expressed as an expression for δ,

The Taylor series expansion is used to perform Taylor expansion on f(δ), thereby obtaining the target vibration information compensation algorithm model. 5. A method for extracting ultra-high frequency target vibration features as described in claim 1, characterized in that the target vibration information includes target displacement information, target velocity information and target acceleration information. 6. A method for extracting ultra-high frequency target vibration features as described in claim 1, characterized in that the target displacement information is continuous phase information obtained by filtering with a bandpass filter, the target velocity information is target displacement information obtained by a first differential operation in a differentiator, and the target acceleration information is target displacement information obtained by a second differential operation in a differentiator.

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