CN112710740B - Time reversal multi-bolt damage ultrasonic detection method and system based on PN code - Google Patents

Abstract

The invention provides a PN code-based time-reversed multi-bolt damage ultrasonic detection method, which uses a plurality of different PN codes at the transmitting end to modulate the linear sweep sine wave respectively to obtain a plurality of different detection signals, and pass through each input port. Each transmits different detection signals, and each output port captures signals modulated with different PN codes (detection signals sent by different input ports). The captured frequency sweep signal is modulated to obtain the modulated signal, and the time inversion of the modulated signal is performed to obtain the reference signal of the bolt, and the value of the convolution result of the output signal and the reference signal at the focusing time is obtained, so as to judge the damage of each bolt degree. The invention can realize the simultaneous detection of multiple bolts, and greatly improves the detection efficiency of the detection system. Correspondingly, the present invention also discloses a bolt damage ultrasonic detection system based on PN code.

Description

A time-reversed multi-bolt damage ultrasonic detection method and system based on PN code

technical field

The invention relates to the technical field of bolt damage detection, in particular to a time-reversed multi-bolt damage ultrasonic detection method and system based on a PN code.

Background technique

Bolts are critical components of a large number of structures and equipment. Environmental factors such as corrosion can reduce the strength of bolts, which can lead to bolts loosening or even breaking. In order to reduce the occurrence of accidents caused by bolt damage, in recent years, scholars at home and abroad have proposed a series of bolt damage detection methods. For example, Yang et al. determined the state of bolts in composite heat shields by predicting torque levels. Wang Dansheng et al. used the root mean square value of the real and imaginary parts of piezoelectric admittance to identify bolt states in frame nodes. Wang et al. characterized the bolt preload by measuring the impedance change of the piezoelectric gasket.

Ultrasonic detection based on piezoelectric sensors is a common method for bolt condition detection. Since ultrasonic energy can propagate through the bolt, the response signal energy method can be used to monitor bolt connection and looseness. From this, Wang et al. proposed a time-reversal method to monitor the axial load of the bolted connection between two steel plates using the time-reversal technique. Yang and Chang studied the attenuation characteristics of ultrasonic guided waves through complex bolted structures, and based on this, they proposed a method to detect the integrity of bolted structures by using the mathematical relationship between the energy attenuation and system-specific damping introduced by guided waves propagating in the bolted structure. method. Since the time inversion method can focus the signal in the time domain, Yuan Shenfang et al. proposed to use the time inversion technology to monitor the screw connection state of the composite material. Through the bolt loosening, the change of the peak value of the focused signal overcomes the frequency dispersion and modal mixing in the monitoring process. The disadvantage of reducing the signal-to-noise ratio caused by factors such as stacking, environmental noise, boundary reflection and signal scattering. Huo et al. calculated the wavelet energy ratio of the time-reversed signal to characterize the bolt torque. Wang et al. described the bolt preload in terms of the time-domain energy of the guided wave signal. Na and Lee proposed electromechanical impedance technology to improve damage detection performance of surface area composite sheets. Gulizz et al. used both supersonic and electromechanical impedance to monitor the damage status of structures.

Although the above detection schemes can effectively detect the state of bolts, the existing bolt damage detection schemes all use a single detection method for bolts, which can only detect one bolt at a time, and cannot realize the simultaneous detection of multiple bolts. There may be hundreds or thousands of bolts in large structures. When a large number of bolts need to be inspected, it takes a lot of inspection time, and the inspection efficiency is low, and it is impossible to detect the status of all bolts in real time.

Therefore, there is an urgent need to provide a PN code-based time-reversal multi-bolt damage ultrasonic detection method and system capable of synchronously detecting the states of multiple bolts and having high detection efficiency to solve the above problems.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a PN code-based time-reversal multi-bolt damage ultrasonic detection method and system capable of synchronously detecting the states of a plurality of bolts and having high detection efficiency.

In order to achieve the above object, an embodiment of the present invention provides a time-reversed ultrasonic detection method for multi-bolt damage based on a PN code, which is suitable for an ultrasonic detection system with multiple input ports and multiple output ports. The input port corresponds to a plurality of bolts, and the plurality of bolts respectively correspond to different output ports. The detection method includes: at the transmitting end, selecting the same number of PN codes according to the number of input ports, and each of the PN codes is different; and using each of the PN codes to perform time delay modulation on a linear sweep sine wave to obtain a The input ports have the same number of detection signals; a plurality of the input ports transmit the detection signals to the bolts corresponding thereto synchronously through piezoelectric sensors, and each of the input ports corresponds to one of the detection signals. At the receiving end, the output signal after the detection signal passes through the bolt corresponding to the output port is received through the output port; when the bolt is in good condition, the input port transmits the linear sweep sine wave to the bolt and outputs the output The frequency sweep signal captured by the port, and the same PN code and modulation method as the input port corresponding to the output port are used to delay the modulation of the frequency sweep signal to obtain the modulation signal corresponding to the bolt; time inversion is performed on the modulation signal. , obtain the reference signal of the bolt; perform convolution operation on the output signal and the reference signal, and take the value of the convolution result at the focusing time, and judge the damage degree of the bolt according to the value.

Specifically, the detection method further includes: when the bolt is in good condition, transmitting the linear frequency sweep sine wave to the corresponding bolt through the input port in advance, and the linear frequency sweep sine wave passes through the bolt and is mixed with the bolt. The output port corresponding to the bolt is captured and stored.

Preferably, the detection signal is obtained by performing time delay modulation on the linear swept sine wave based on the following formula:

表示第n个PN码的第m个码片，t₀表示sw(t)的信号长度；Among them, x _n (t) represents the detection signal transmitted by the nth input port, t represents the time, m represents the chip serial number, M represents the code length of a single PN code, sw(t) represents the linear sweep sine wave,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t);

The modulated signal is obtained by performing time delay modulation on the frequency sweep signal based on the following formula:

表示第n个PN码的第m个码片，t₀表示sw(t)的信号长度；Among them, smo _n,q (t) represents the modulated signal at the output port of the bolt (n, q) corresponding to the input port n and the output port q, and v _{n, q} (t) represents the said bolt (n, q) corresponding to the Frequency sweep signal, t represents time, m represents chip serial number, M represents the code length of a single PN code,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t);

Time inversion is performed on the modulated signal based on the following formula to obtain the reference signal:

表示第n个PN码的第m个码片，t₀表示sw(t)的信号长度。Among them, tron _,q (t) represents the reference signal corresponding to bolt (n, q), v _{n, q} (t) represents the frequency sweep signal corresponding to bolt (n, q), t represents time, m represents the chip serial number, M represents the code length of a single PN code,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t).

Specifically, the output signal y _q (t) captured by the qth output port is:

表示卷积，h_nq(t)表示第n个输入端口到第q个输出端口之间的超声波信道响应函数；Wherein, x _n (t) represents the detection signal transmitted by the nth input port, n represents the serial number of the input port, N represents the number of input ports,

represents convolution, h _nq (t) represents the ultrasonic channel response function between the nth input port and the qth output port;

Calculate the value β _n,q of the convolution result at the focusing time t=M×t ₀ based on the following formula:

表示卷积，t表示时间，M表示单个PN码的码长，t₀表示sw(t)的信号长度，“||”表示取绝对值。Wherein, tron _,q (t) represents the reference signal corresponding to the bolt (n,q), y _q (t) represents the output signal,

Represents convolution, t represents time, M represents the code length of a single PN code, t ₀ represents the signal length of sw(t), and "||" represents the absolute value.

Preferably, the detection method further includes: dividing all the bolts to be detected into N groups in advance, each group including several bolts; configuring bolts of different groups to correspond to different input ports, and all bolts in the same group. They correspond to the same input port, and each bolt in this group corresponds to a different output port.

Specifically, the input port transmits the detection signal to the bolt through the piezoelectric sensor, and the output port receives the output signal after the detection signal passes through the corresponding bolt through the piezoelectric sensor.

In order to achieve the above purpose, the present invention also provides a PN code-based time-reversed multi-bolt damage ultrasonic detection system, comprising a piezoelectric sensor, multiple input ports, multiple output ports, a PN code generator, a modulator, a processing and a signal generator for providing a linear sweep sine wave, each of the input ports corresponds to multiple bolts, and the multiple bolts correspond to different output ports respectively; at the transmitting end, the PN code generator generates There are the same number of PN codes as the number of the input ports, and each of the PN codes is different. The modulator uses each of the PN codes to perform time delay modulation on the linear sweep sine wave to obtain the same value as the input port. A number of detection signals, a plurality of the input ports transmit the detection signals to the corresponding bolts synchronously through piezoelectric sensors, and each of the input ports corresponds to one of the detection signals; at the receiving end, received through the output ports The detection signal passes through the output signal after the bolt corresponding to the output port, and the modulator retrieves the frequency sweep signal captured by the output port when the input port transmits the linear sweep sine wave to the bolt when the bolt is in good condition. , and use the same PN code and modulation method as the input port corresponding to the output port to perform time delay modulation on the frequency sweep signal to obtain the modulation signal corresponding to the bolt, and the processor performs time inversion on the modulated signal to obtain the bolt The reference signal is the reference signal, the output signal and the reference signal are convolved, and the value of the convolution result at the focusing time is obtained, so as to judge the damage degree of the bolt according to the value.

Preferably, the modulator performs time delay modulation on the linear swept sine wave based on the following formula to obtain the detection signal:

表示第n个PN码的第m个码片，t₀表示sw(t)的信号长度；Among them, x _n (t) represents the detection signal transmitted by the nth input port, t represents the time, m represents the chip serial number, M represents the code length of a single PN code, sw(t) represents the linear sweep sine wave,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t);

The modulator modulates the frequency sweep signal based on the following formula to obtain the modulated signal:

表示第n个PN码的第m个码片，t₀表示sw(t)的信号长度；Among them, smo _n,q (t) represents the modulated signal at the output port of the bolt (n, q) corresponding to the input port n and the output port q, and v _{n, q} (t) represents the said bolt (n, q) corresponding to the Frequency sweep signal, t represents time, m represents chip serial number, M represents the code length of a single PN code,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t);

The processor performs time inversion on the modulated signal based on the following formula to obtain the reference signal:

表示第n个PN码的第m个码片，t₀表示sw(t)的信号长度。Among them, tron _,q (t) represents the reference signal corresponding to bolt (n, q), v _{n, q} (t) represents the frequency sweep signal corresponding to bolt (n, q), t represents time, m represents the chip serial number, M represents the code length of a single PN code,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t).

Specifically, the output signal y _q (t) captured by the qth output port is:

表示卷积，h_nq(t)表示第n个输入端口到第q个输出端口之间的超声波信道响应函数；Wherein, x _n (t) represents the detection signal transmitted by the nth input port, n represents the serial number of the input port, N represents the number of input ports,

represents convolution, h _nq (t) represents the ultrasonic channel response function between the nth input port and the qth output port;

The processor calculates the value β _n,q of the convolution result at the focusing time t=M×t ₀ based on the following formula:

表示卷积，t表示时间，M表示单个PN码的码长，t₀表示sw(t)的信号长度，“||”表示取绝对值。Wherein, tron _,q (t) represents the reference signal corresponding to the bolt (n,q), y _q (t) represents the output signal,

Represents convolution, t represents time, M represents the code length of a single PN code, t ₀ represents the signal length of sw(t), and "||" represents the absolute value.

Specifically, the input port transmits the detection signal to the bolt through the piezoelectric sensor, and the output port receives the output signal after the detection signal passes through the corresponding bolt through the piezoelectric sensor.

Compared with the prior art, the present invention uses a plurality of different PN codes to modulate the linear sweep sine wave respectively to obtain a plurality of different detection signals, each input port of the transmitting end transmits different detection signals respectively, and the All are signals modulated by different PN codes (detection signals sent by different input ports); at the receiving end, the PN code is also used to modulate the frequency sweep signal captured by the output port when the bolt is in good condition to obtain a modulated signal, and the modulation The signal is time-reversed to obtain the reference signal of the bolt, and the value of the convolution result of the output signal and the reference signal at the focusing time is obtained, so as to judge the damage degree of each bolt. The invention utilizes the correlation of the PN code to realize the analysis and identification of the signals from different bolts, to realize the simultaneous detection of multiple bolts, and to greatly improve the detection efficiency of the detection system.

Description of drawings

FIG. 1 is a schematic diagram of a time-reversed ultrasonic detection system for multi-bolt damage based on a PN code according to an embodiment of the present invention.

FIG. 2a is a structural block diagram of a transmitter according to an embodiment of the present invention.

FIG. 2b is a structural block diagram of a receiving end according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of a 2-input 2-output detection system used in the bolt damage ultrasonic detection test of the present invention.

Detailed ways

The technical solutions of the present invention are further described below through specific embodiments, which do not constitute any limitation to the present invention.

The invention discloses a time-reversed multi-bolt damage ultrasonic detection method based on PN code and a PN code-based time-reversed multi-bolt damage ultrasonic detection system, which are suitable for ultrasonic detection of the damage state of multiple bolts at the same time, so as to detect the damage of multiple bolts simultaneously. Improve the bolt detection efficiency, so that it can be better applied to the detection of structures with a large number of bolts.

This embodiment provides a time-reversed multi-bolt damage ultrasonic detection method based on PN code, which is suitable for a detection system with multiple input ports and multiple output ports (as shown in FIG. 1 ), each input port corresponds to A plurality of bolts, which in turn correspond to different output ports. Specifically, the time-reversed multi-bolt damage ultrasonic detection method based on PN code includes:

At the transmitting end, according to the number of input ports, the same number of PN codes are selected, and each PN code is different. The linear sweep sine wave is time-delay modulated by each PN code to obtain the same number of detection signals as the input ports; that is, a PN code is used to perform delay modulation on a linear sweep sine wave to obtain a detection signal. Signal, for example, use PN code 1 to perform time delay modulation on the linear sweep sine wave to obtain the detection signal transmitted by input port 1, and use PN code n to perform delay modulation on the linear sweep frequency sine wave to obtain the detection signal transmitted by input port n, The PN code N is used to perform time delay modulation on the linear swept sine wave to obtain the detection signal transmitted by the input port N; finally, the same number of detection signals as the input port (PN code) are obtained. Then, a plurality of input ports transmit detection signals to corresponding bolts synchronously through piezoelectric sensors, each input port corresponds to a detection signal, and the detection signals are captured by the output port corresponding to the bolt after passing through the bolt. In the embodiment shown in FIG. 1, the number of input ports is N, correspondingly, the number of PN codes is also N, the number of detection signals is also N, and the number of output ports is Q. Q bolts are tested.

At the receiving end, the output signal after the detection signal passes through the bolt corresponding to the output port is received through the output port (all the signals after passing through the N bolts corresponding to the output port are superimposed). When the bolt is in good condition, the input port transmits a linear sweep frequency sine wave to the bolt respectively (the same as the linear sweep frequency sine wave used by the input port corresponding to the bolt). The corresponding input port is the same PN code and modulation method to delay modulation of the frequency sweep signal to obtain the modulation signal of each bolt; The detection signal is obtained by modulating the PN code 1, then the modulation signal of the output port 1 for the bolt (1, 1) is also obtained by modulating the PN code 1; for another example, the input port n transmits the detection signal through the bolt (n, 1) Then it is captured by output port 1. If the detection signal is obtained by modulating with PN code n, the modulated signal of bolt (n, 1) by output port 1 is also obtained by modulating with PN code n. Then, the modulated signal is time-reversed to obtain the reference signal of the bolt. Finally, perform convolution operation on the output signal and the reference signal, and take the value of the convolution result at the focusing time, and judge the damage degree of the bolt according to the value.

Among them, the description of "output port corresponding to the input port" in the text refers to the output port that receives the detection signal emitted by the input port, and the description of "bolt corresponding to the input port" refers to the bolt through which the detection signal emitted by the input port passes. , the description "bolt corresponding to output port" refers to the bolt to which the output port captures the signal.

In this embodiment, the detection method further includes: when the bolts are in good condition (just assembled, when no corrosion occurs), transmitting linearly swept sine waves to the corresponding bolts through the input port in advance, and the linearly swept sine waves respectively. After passing through the bolt, it is captured and stored by the output port corresponding to the bolt. That is, the output port captures and stores the aforesaid frequency sweep signal, which can be retrieved for subsequent bolt detection. For example, a linear sweep sine wave is transmitted to bolt (1,1) through input port 1 in advance, and the linear sweep sine wave is captured by output port 1 after passing through the bolt (1,1). (1,1) corresponds to the frequency sweep signal.

In this embodiment, the detection method further includes: dividing all bolts to be detected into N groups in advance, each group including Q bolts; configuring bolts of different groups to correspond to different input ports, and all bolts in the same group The bolts correspond to the same input port, and each bolt in the group corresponds to a different output port. For example, the first group of bolts (1,1),...,(1,Q) all correspond to input port 1, and the first group of bolts (1,1),...,(1,Q) correspond to output port 1- Q; the nth group of bolts (n, 1), ..., (n, Q) all correspond to the input port n, and the nth group of bolts (n, 1), ..., (n, Q) correspond to the output ports 1- Q; the Nth group of bolts (N,1),...,(N,Q) all correspond to the input port N, and the Nth group of bolts (N,1),...,(N,Q) correspond to the output port 1- Q. Each output port corresponds to at most one of the bolts corresponding to the same input port, and output port 1 captures N bolts (1,1), ..., (N,1) corresponding to different input ports 1-N respectively. The signal of the bolt, the output port q captures the signals of N bolts (1,q),...,(N,q) corresponding to different input ports 1-N respectively. Signals of N bolts from bolts (1,Q) to (N,Q) corresponding to different input ports 1-N. In this embodiment, each input port transmits a detection signal to the corresponding bolt through the piezoelectric sensor, and each output port captures the output signal after passing through the corresponding bolt through the piezoelectric sensor.

Specifically, in this embodiment, the detection signal is obtained by performing time-delay modulation on the linear swept sine wave based on the following formula, and the modulation method is simple and easy to implement.

表示第n个PN码的第m个码片，t₀表示sw(t)的信号长度。Among them, x _n (t) represents the detection signal transmitted by the nth input port, t represents the time, m represents the chip serial number, M represents the code length of a single PN code, sw(t) represents the linear sweep sine wave,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t).

Correspondingly, the same modulation method and PN code as the input port are used to modulate the frequency sweep signal to obtain the modulated signal. For example, the modulation signal of the bolt (n, q) corresponding to the input port n and the output port q at the output port q can be expressed as for:

表示第n个PN码的第m个码片，t₀表示sw(t)的信号长度。Among them, smo _n,q (t) represents the modulation signal of the bolt (n, q) corresponding to the input port n and the output port q at the output port, and v _{n, q} (t) represents the frequency sweep corresponding to the bolt (n, q) signal, t represents time, m represents the chip serial number, M represents the code length of a single PN code,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t).

Based on the following formula, perform time inversion on the modulation signal of bolt (n, q) at output port q to obtain the reference signal of bolt (n, q):

表示第n个PN码的第m个码片，t₀表示sw(t)的信号长度。Among them, tron _,q (t) represents the reference signal corresponding to the bolt (n, q), v _{n, q} (t) represents the frequency sweep signal corresponding to the bolt (n, q), t represents the time, and m represents the chip serial number , M represents the code length of a single PN code,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t).

The output signal y _q (t) captured by the qth output port is expressed as:

表示卷积，h_nq(t)表示第n个输入端口到第q个输出端口之间的超声波信道响应函数。Among them, x _n (t) represents the detection signal transmitted by the nth input port, n represents the serial number of the input port, N represents the number of input ports,

represents the convolution, and h _nq (t) represents the ultrasonic channel response function between the nth input port and the qth output port.

Calculate the value β _n,q of the convolution result of the reference signal of the bolt (n,q) corresponding to the input port n and the output port q and the output signal at the focusing time t=M×t ₀ based on the following formula:

表示卷积，t表示时间，M表示单个PN码的码长，t₀表示sw(t)的信号长度，“||”表示取绝对值。根据该值β_n,q的大小可以判断螺栓(n,q)的损伤程度。Among them, tron _{, q} (t) represents the reference signal corresponding to the bolt (n, q), y _q (t) represents the output signal,

Represents convolution, t represents time, M represents the code length of a single PN code, t ₀ represents the signal length of sw(t), and "||" represents the absolute value. According to the value of β _{n, q} , the damage degree of the bolt (n, q) can be judged.

Correspondingly, another embodiment provides a PN code-based time-reversed multi-bolt damage ultrasonic detection system, the detection system includes a piezoelectric sensor (not shown), a plurality of input ports 1-N, and a plurality of output ports. 1-Q, a PN code generator, a modulator, a processor 40 and a signal generator for providing a linear swept sine wave, each input port corresponds to a plurality of bolts, and the plurality of bolts correspond to different output ports respectively. At the transmitting end, the PN code generator generates the same number of PN codes as the number of input ports, and each PN code is different. The modulator uses each PN code to perform delay modulation on the linear sweep sine wave to obtain the same number of detection signals as the input ports; One detection signal, and finally, the same number of detection signals as the input port (PN code) is obtained. A plurality of input ports transmit detection signals to the bolts corresponding to them synchronously through piezoelectric sensors, and each input port corresponds to a detection signal. At the receiving end, the output signal after the detection signal passes through the bolt corresponding to the output port is received through the output port (all the signals after passing through the N bolts corresponding to the output port are superimposed). The modulator selects the sweep frequency signal captured by the output port when the input port transmits a linear sweep frequency sine wave (same as the linear sweep frequency sine wave used by the input port corresponding to the bolt) to the bolt when the bolt is in good condition, and uses the same frequency sweep signal as the bolt. The same PN code and modulation method as the input port corresponding to the output port perform time delay modulation on the frequency sweep signal to obtain a modulated signal. The processor 40 performs time inversion on the modulated signal to obtain the reference signal of the bolt, performs convolution operation on the output signal and the reference signal, and obtains the value of the convolution result at the focusing time to judge the damage degree of the bolt according to the value.

Among them, the configuration of the input port and the output port, how the modulator modulates the linear sweep sine wave to obtain the detection signal, how to modulate the sweep signal to obtain the modulated signal, and how the processor 40 performs time inversion on the modulated signal to obtain the reference signal And to perform a convolution operation on the reference signal and the output signal and obtain the value of the convolution result at the focus time, reference may be made to the corresponding description in the foregoing detection method, which will not be repeated here. The modulator can be an existing modulator, and the processor 40 can be any electronic device with corresponding data processing capability, such as a notebook computer. In this embodiment, the PN code generator includes a first PN code generator 11 and a second PN code generator 12, the signal generator includes a first signal generator 21 and a second signal generator (not shown), and the modulation The modulator also includes a first modulator 31 and a second modulator 32 . As shown in Figures 2a and 2b, the transmitting end is provided with a first PN code generator 11, a first signal generator 21 and a first modulator 31, and the first PN code generator 11 generates N PN codes (PN code 1-N), the first signal generator 21 provides N linearly swept frequency sine waves, and the first modulator 31 modulates the linearly swept frequency sine waves with PN codes 1-N to obtain N detection signals. The receiving end is provided with a second PN code generator 12, a second signal generator and a second modulator 32, the second PN code generator 12 generates N PN codes (PN codes 1-N), and the second signal generates The second modulator 32 uses PN codes 1-N to modulate the swept frequency signals obtained when the linear sweep sine waves pass through the bolts in the intact state to obtain the modulated signals of each bolt.

Please refer to Fig. 3. Fig. 3 shows a 2-input 2-output detection system. Through the 2-input 2-output detection system, 4 bolts Status1-4 with different damage states are detected at the same time, and the four bolts Status1-4 correspond to corrosion respectively. 0.5 hours, 1 hour, 1.5 hours, 2 hours (the corrosion of bolt Status1-4 gradually deepens). The signal width of the linear swept sine wave used in this embodiment is 1s, and the frequency range is from 1kHz to 200KHz. The linear swept sine wave is modulated by two PN codes containing 7 chips respectively, so as to generate two sets of detection Signal. The NI-6361 is used to connect piezoelectric sensors to realize signal reception and transmission, and the sampling frequency is 2MS/s. Finally, the signal captured by the output port is processed by matlab, so as to obtain the output result (the aforementioned value β _n,q ) as shown in Table 1 below.

Table 1

It can be seen from Table 1 that for bolt Status1-4, with the deepening of the corrosion degree of the bolt, the value β _n,q output by the detection system gradually decreases. It can be seen that the damage state of the bolt can be judged by the energy value output by the detection system.

In order to further verify the feasibility of the present invention, the bolt Status 1-4 in the above four states are also independently detected, and the independent detection results are processed by using wavelet analysis. The corresponding wavelet analysis results are shown in Table 2 below.

Table 2

It can be seen from Table 2 that when each bolt is tested individually, the result of wavelet analysis also decreases with the deepening of bolt corrosion. Thus, the feasibility of the present invention can be further verified.

In summary, the present invention uses a plurality of different PN codes to modulate the linear sweep sine wave respectively to obtain a plurality of different detection signals, each input port of the transmitting end transmits a different detection signal, and each output port captures a different detection signal. The PN code modulated signal (detection signal sent by different input ports); at the receiving end, the PN code is also used to modulate the frequency sweep signal captured by the output port when the bolt is in good condition to obtain the modulated signal, and the modulated signal is time-reversed. Obtain the reference signal of the bolt, and obtain the value of the convolution result of the output signal and the reference signal at the focusing time, so as to judge the damage degree of each bolt. The invention utilizes the correlation of the PN code to realize the analysis and identification of the signals from different bolts, to realize the simultaneous detection of multiple bolts, and to greatly improve the detection efficiency of the detection system.

The above disclosures are only preferred examples of the present invention, and of course, the scope of the rights of the present invention cannot be limited by this. Therefore, equivalent changes made according to the scope of the patent application of the present invention still belong to the scope covered by the present invention.

Claims (6)

1. A time-reversed multi-bolt damage ultrasonic detection method based on PN code, suitable for an ultrasonic detection system with a plurality of input ports and a plurality of output ports, each of the input ports corresponds to a plurality of bolts, the plurality of bolts corresponding to different output ports respectively, and it is characterized in that, the detection method includes: At the transmitting end, according to the number of input ports, the same number of PN codes are selected, and each PN code is different; the linear sweep sine wave is time-delay modulated by each of the PN codes, so as to obtain the same number as the input port. A number of detection signals; a plurality of the input ports transmit the detection signals to the bolts corresponding thereto synchronously through piezoelectric sensors, and each of the input ports corresponds to one of the detection signals; At the receiving end, the output signal after the detection signal passes through the bolt corresponding to the output port is received through the output port; when the bolt is in good condition, the input port transmits the linear sweep sine wave to the bolt and outputs the output The frequency sweep signal captured by the port, and the same PN code and modulation method as the input port corresponding to the output port are used to delay the modulation of the frequency sweep signal to obtain the modulation signal corresponding to the bolt; time inversion is performed on the modulation signal. , obtain the reference signal of the bolt; perform convolution operation on the output signal and the reference signal, and take the value of the convolution result at the focusing time, and judge the damage degree of the bolt according to the value; The detection signal is obtained by performing time delay modulation on the linear swept sine wave based on the following formula:

Among them, x _n (t) represents the detection signal transmitted by the nth input port, t represents the time, m represents the chip serial number, M represents the code length of a single PN code, sw(t) represents the linear sweep sine wave,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t); The modulated signal is obtained by performing time delay modulation on the frequency sweep signal based on the following formula:

Among them, smo _n,q (t) represents the modulation signal of the bolt corresponding to the input port n and the output port q at the output port, v _n,q (t) represents the sweep corresponding to the bolt corresponding to the input port n and the output port q frequency signal, t represents time, m represents the chip serial number, M represents the code length of a single PN code,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t); Time inversion is performed on the modulated signal based on the following formula to obtain the reference signal:

Wherein, tron _,q (t) represents the reference signal corresponding to the bolts corresponding to the input port n and the output port q, _vn,q (t) represents the sweep corresponding to the bolts corresponding to the input port n and the output port q frequency signal, t represents time, m represents the chip serial number, M represents the code length of a single PN code,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t); The output signal y _q (t) captured by the qth output port is:

Wherein, x _n (t) represents the detection signal transmitted by the nth input port, n represents the serial number of the input port, N represents the number of input ports,

represents convolution, h _nq (t) represents the ultrasonic channel response function between the nth input port and the qth output port; Calculate the value β _n,q of the convolution result at the focusing time M×t ₀ based on the following formula:

Wherein, tron _,q (t) represents the reference signal corresponding to the bolt corresponding to the input port n and the output port q, y _q (t) represents the output signal,

Represents convolution, t represents time, M represents the code length of a single PN code, t ₀ represents the signal length of sw(t), and "||" represents the absolute value. 2 . The detection method according to claim 1 , further comprising: transmitting the linear sweep sine wave to the corresponding bolt through the input port in advance when the bolt is in good condition. After passing through the bolt, the frequency sine wave is captured and stored by the output port corresponding to the bolt. 3. detection method according to claim 1 and 2, is characterized in that, also comprises: All the bolts to be tested are divided into N groups in advance, and each group includes several bolts; Bolts of different groups are configured to correspond to different input ports, all bolts in the same group correspond to the same input port, and each bolt in the group corresponds to different output ports. 4 . The detection method according to claim 1 or 2 , wherein the output port receives the output signal after the detection signal passes through the corresponding bolt through a piezoelectric sensor. 5 . 5. A time-reversed multi-bolt damage ultrasonic detection system based on PN code, is characterized in that, comprises piezoelectric sensor, multiple input ports, multiple output ports, PN code generator, modulator, processor and for A signal generator providing a linear sweep frequency sine wave, each input port corresponds to a plurality of bolts, and the plurality of bolts correspond to different output ports respectively; at the transmitting end, the PN code generator generates a The number of ports has the same number of PN codes, and each of the PN codes is different. The modulator uses each of the PN codes to delay-modulate the linear sweep sine wave to obtain the same number of detection signals as the input ports. , a plurality of the input ports transmit the detection signal synchronously to the corresponding bolt through the piezoelectric sensor, and each input port corresponds to a detection signal; at the receiving end, the detection signal is received through the output port Through the output signal after the bolt corresponding to the output port, the modulator retrieves the swept-frequency signal captured by the output port when the input port transmits the linear swept-frequency sine wave to the bolt when the bolt is in good condition, and uses the same The same PN code and modulation method as the input port corresponding to the output port perform time delay modulation on the frequency sweep signal to obtain the modulated signal corresponding to the bolt, and the processor performs time inversion on the modulated signal to obtain the reference signal of the bolt, Perform convolution operation on the output signal and the reference signal, and obtain the value of the convolution result at the focusing time, so as to judge the damage degree of the bolt according to the value; The modulator obtains the detection signal by performing time delay modulation on the linear swept sine wave based on the following formula:

Among them, x _n (t) represents the detection signal transmitted by the nth input port, t represents the time, m represents the chip serial number, M represents the code length of a single PN code, sw(t) represents the linear sweep sine wave,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t); The modulator modulates the frequency sweep signal based on the following formula to obtain the modulated signal:

Among them, smo _n,q (t) represents the modulation signal of the bolt corresponding to the input port n and the output port q at the output port, v _n,q (t) represents the sweep corresponding to the bolt corresponding to the input port n and the output port q frequency signal, t represents time, m represents the chip serial number, M represents the code length of a single PN code,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t); The processor performs time inversion on the modulated signal based on the following formula to obtain the reference signal:

Wherein, tron _,q (t) represents the reference signal corresponding to the bolts corresponding to the input port n and the output port q, _vn,q (t) represents the sweep corresponding to the bolts corresponding to the input port n and the output port q frequency signal, t represents time, m represents the chip serial number, M represents the code length of a single PN code,

represents the mth chip of the nth PN code, and t ₀ represents the signal length of sw(t); The output signal y _q (t) captured by the qth output port is:

Wherein, x _n (t) represents the detection signal transmitted by the nth input port, n represents the serial number of the input port, N represents the number of input ports,

represents convolution, h _nq (t) represents the ultrasonic channel response function between the nth input port and the qth output port; The processor calculates the value β _n,q of the convolution result at the focus time M×t ₀ based on the following formula:

Wherein, tron _,q (t) represents the reference signal corresponding to the bolt corresponding to the input port n and the output port q, y _q (t) represents the output signal,

Represents convolution, t represents time, M represents the code length of a single PN code, t ₀ represents the signal length of sw(t), and "||" represents the absolute value. 6 . The detection system according to claim 5 , wherein the output port receives the output signal after the detection signal passes through the corresponding bolt through a piezoelectric sensor. 7 .

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