CN112710740B - Time reversal multi-bolt damage ultrasonic detection method and system based on PN code - Google Patents
Time reversal multi-bolt damage ultrasonic detection method and system based on PN code Download PDFInfo
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Abstract
The invention provides a time reversal multi-bolt damage ultrasonic detection method based on PN codes, which comprises the steps of respectively modulating linear sweep sine waves by utilizing a plurality of different PN codes at a transmitting end to obtain a plurality of different detection signals, respectively transmitting different detection signals through each input port, and capturing signals modulated by different PN codes (the detection signals transmitted by different input ports) at each output port; and at a receiving end, modulating the sweep frequency signal captured by the output port when the bolt is in a perfect state by using the PN code to obtain a modulation signal, performing time reversal on the modulation signal to obtain a reference signal of the bolt, and obtaining a value of a convolution result of the output signal and the reference signal in focusing time so as to judge the damage degree of each bolt. The invention can realize the simultaneous detection of a plurality of bolts and greatly improve the detection efficiency of the detection system. Correspondingly, the invention also discloses a bolt damage ultrasonic detection system based on the PN code.
Description
Technical Field
The invention relates to the technical field of bolt damage detection, in particular to a time reversal multi-bolt damage ultrasonic detection method and system based on PN codes.
Background
Bolts are a key component of a large number of structures and devices. Environmental factors such as corrosion can cause the bolt strength to weaken, thereby causing the bolt to loosen and even break. In order to reduce accidents caused by bolt damage and the like, in recent years, a series of bolt damage detection methods have been proposed by domestic and foreign scholars. For example, yang et al determined the state of the bolts in the composite insulation panel by predicting the torque level. Wangdansheng et al use the root mean square values of the real and imaginary parts of the piezoelectric admittance to identify the bolt state in the frame node. Wang et al characterize the bolt pretension by measuring the impedance change of the piezoelectric spacer.
Ultrasonic detection based on piezoelectric sensors is a common method for bolt state detection. Since ultrasonic energy can be propagated through the bolt, the states of bolt connection, loosening and the like can be monitored by using a response signal energy method. Wang et al thus propose a time reversal method using time reversal techniques to monitor the axial load of a bolted connection between two steel plates. Yang and Chang study the attenuation characteristics of ultrasonic guided waves through complex bolted structures and based on this, propose a method for detecting the integrity of bolted structures using the mathematical relationship between the energy attenuation introduced by the guided wave propagation in the bolted structure and the system-specific damping. The time domain focusing can be carried out on the signals by a time inversion method, and in the reasonable and elegant way, the screw connection state of the composite material is monitored by adopting a time inversion technology. Huo et al calculated the wavelet energy ratio of the time-reversal signals to characterize the bolt torque. Wang et al describe bolt pretension in terms of the time domain energy of the guided wave signal. Na and Lee propose electromechanical impedance techniques to improve the damage detection performance of surface area composite plates. Gulizz et al use both ultrasound and electromechanical impedance to monitor the state of damage to a structure.
Although the above detection scheme can realize effective detection of the bolt state, in the existing bolt damage detection scheme, a single detection mode is adopted for the bolt, only one bolt can be detected at a time, and synchronous detection of a plurality of bolts cannot be realized. And may have hundreds of bolts among the large-scale structure, when needs detect a large amount of bolts, then need spend a large amount of check-out time, detection efficiency is low, can't realize carrying out real-time detection to the state of all bolts.
Therefore, it is desirable to provide a PN code based time reversal multi-bolt damage ultrasonic detection method and system capable of synchronously detecting states of a plurality of bolts and having high detection efficiency to solve the above problems.
Disclosure of Invention
The invention aims to provide a PN code-based time reversal multi-bolt damage ultrasonic detection method and system which can synchronously detect states of a plurality of bolts and have high detection efficiency.
In order to achieve the above object, an embodiment of the present invention provides a time reversal multi-bolt damage ultrasonic detection method based on PN codes, which is suitable for an ultrasonic detection system having a plurality of input ports and a plurality of output ports, wherein each input port corresponds to a plurality of bolts, and the plurality of bolts respectively correspond to different output ports. The detection method comprises the following steps: at a transmitting end, selecting the same number of PN codes according to the number of input ports, wherein the PN codes are different; respectively utilizing each PN code to carry out time delay modulation on the linear sweep sine wave so as to obtain detection signals with the same number as the input ports; and the input ports synchronously transmit the detection signals to the bolts corresponding to the input ports through the piezoelectric sensors, and each input port corresponds to one detection signal. At a receiving end, receiving an output signal of the detection signal after passing through a bolt corresponding to the output port through the output port; when the bolt is in a good state, the input port respectively transmits sweep frequency signals captured by the output port when the linear sweep frequency sine waves are transmitted to the bolt, and the sweep frequency signals are subjected to time delay modulation by adopting the same PN code and modulation mode as the input port corresponding to the output port to obtain modulation signals corresponding to the bolt; time reversal is carried out on the modulation signal to obtain a reference signal of the bolt; and carrying out convolution operation on the output signal and the reference signal, taking the value of the convolution result in the focusing time, and judging the damage degree of the bolt according to the value.
Specifically, the detection method further comprises: and under the condition that the bolt is in a perfect state, the linear sweep sine waves are transmitted to the corresponding bolt through the input port in advance, and are captured and stored by the output port corresponding to the bolt after passing through the bolt.
Preferably, the detection signal is obtained by performing time-delay modulation on the linear swept sine wave based on the following formula:
wherein x is n (t) represents the detection signal transmitted by the nth input port, t represents time, M represents the chip number, M represents the code length of a single PN code, sw (t) represents a linear swept sine wave,
m chip, t, representing the nth PN code 0 Represents the signal length of sw (t);
performing time delay modulation on the frequency sweep signal based on the following formula to obtain the modulation signal:
wherein, 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, v n,q (t) represents the swept frequency signal corresponding to the bolt (n, q), t represents time, M represents a chip number, M represents a code length of a single PN code,
m chip, t, representing the nth PN code 0 Represents the signal length of sw (t);
time-inverting the modulated signal based on the following equation to obtain the reference signal:
wherein tro n,q (t) said reference signal, v, corresponding to the bolt (n, q) n,q (t) represents the swept frequency signal for the bolt (n, q), t represents time, M represents the chip number, M represents the code length of a single PN code,
m chip, t, representing the n PN code 0 Signal representing sw (t)Length.
In particular, the output signal y captured by the qth output port q (t) is:
wherein x is n (t) represents a detection signal emitted from the nth of the input ports, N represents an input port number, N represents the number of input ports,
represents the convolution of h nq (t) represents an ultrasonic channel response function between the nth input port to the qth output port;
the convolution result at the focusing time t = M × t is obtained based on the following formula 0 Value of beta n,q ：
Wherein tro n,q (t) represents said reference signal, y, for the bolt (n, q) q (t) represents the output signal(s),
representing convolution, t representing time, M representing code length of a single PN code, t 0 Represents the signal length of sw (t), and "|" represents taking the absolute value.
Preferably, the detection method further comprises: dividing all bolts to be detected into N groups in advance, wherein each group comprises a plurality of bolts; the bolts in different groups are configured to correspond to different input ports, all the bolts in the same group respectively correspond to the same input port, and each bolt in the group respectively corresponds to different output ports.
Specifically, the input port transmits the detection signal to the bolt through the piezoelectric sensor, and the output port receives an output signal of the detection signal passing through the corresponding bolt through the piezoelectric sensor.
In order to achieve the above object, the present invention further provides a PN code based time reversal multi-bolt damage ultrasonic detection system, which includes a piezoelectric sensor, multiple input ports, multiple output ports, a PN code generator, a modulator, a processor, and a signal generator for providing a linear frequency sweep sine wave, where each input port corresponds to multiple bolts, and the multiple bolts correspond to different output ports respectively; at a transmitting end, the PN code generator generates PN codes with the same number as the input ports, the PN codes are different, the modulator respectively utilizes the PN codes to perform time delay modulation on linear sweep frequency sine waves so as to obtain detection signals with the same number as the input ports, a plurality of the input ports synchronously transmit the detection signals to bolts corresponding to the input ports through piezoelectric sensors, and each input port corresponds to one detection signal; and at a receiving end, receiving an output signal of the detection signal after passing through a bolt corresponding to the output port through the output port, respectively transmitting sweep frequency signals captured by the output port to the bolt through the input port when the modulator calls the bolt in an intact state, performing time delay modulation on the sweep frequency signals by adopting a PN code and a modulation mode which are the same as those of the input port corresponding to the output port to obtain modulation signals corresponding to the bolt, performing time reversal on the modulation signals by using the processor to obtain reference signals of the bolt, performing convolution operation on the output signal and the reference signals, and taking a value of a convolution result in focusing time 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 to obtain the detection signal based on the following formula:
wherein x is n (t) represents the detection signal transmitted by the nth input port, t represents time, M represents the chip number, M represents the code length of a single PN code, and sw (t) represents the linear sweep sineThe wave is generated by a wave generator,
m chip, t, representing the nth PN code 0 Represents the signal length of sw (t);
the modulator modulates the sweep frequency signal to obtain the modulation signal based on the following formula:
wherein, 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, v n,q (t) represents the swept frequency signal corresponding to the bolt (n, q), t represents time, M represents a chip number, M represents a code length of a single PN code,
m chip, t, representing the nth PN code 0 Represents the signal length of sw (t);
the processor performs time reversal on the modulation signal based on the following formula to obtain the reference signal:
wherein tro n,q (t) said reference signal, v, corresponding to the bolt (n, q) n,q (t) represents the swept frequency signal for the bolt (n, q), t represents time, M represents the chip number, M represents the code length of a single PN code,
m chip, t, representing the n PN code 0 Indicates the signal length of sw (t).
In particular, the output signal y captured by the qth output port q (t) is:
wherein x is n (t) represents a detection signal emitted from the nth of the input ports, N represents an input port number, N represents the number of input ports,
represents the convolution of h nq (t) represents an ultrasonic channel response function between an nth input port to a qth output port;
the processor finds the convolution result at the focus time t = M × t based on 0 Value of beta n,q ：
Wherein tro n,q (t) represents said reference signal, y, for the bolt (n, q) q (t) represents the output signal(s),
representing convolution, t representing time, M representing code length of a single PN code, t 0 Represents the signal length of sw (t), and "| |" represents taking the absolute value.
Specifically, the input port transmits the detection signal to the bolt through the piezoelectric sensor, and the output port receives an output signal of the detection signal after passing through the corresponding bolt through the piezoelectric sensor.
Compared with the prior art, the invention utilizes a plurality of different PN codes to respectively modulate the linear sweep sine wave to obtain a plurality of different detection signals, each input port of the transmitting end respectively transmits different detection signals, and signals modulated by different PN codes (detection signals transmitted by different input ports) are captured by each output port; and at a receiving end, modulating the sweep frequency signal captured by the output port when the bolt is in a perfect state by using the PN code to obtain a modulation signal, performing time reversal on the modulation signal to obtain a reference signal of the bolt, and obtaining a value of a convolution result of the output signal and the reference signal in focusing time so as to judge the damage degree of each bolt. The invention utilizes the correlation of PN codes to realize the analysis and identification of signals from different bolts, can realize the simultaneous detection of a plurality of bolts and greatly improves the detection efficiency of a detection system.
Drawings
Fig. 1 is a schematic diagram of a PN code-based time-reversal multi-bolt damage ultrasonic detection system according to an embodiment of the present invention.
Fig. 2a is a block diagram of a transmitting end according to an embodiment of the present invention.
Fig. 2b is a 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 adopted in the bolt damage ultrasonic detection test of the present invention.
Detailed Description
The technical solutions of the present invention are further described below by way of specific embodiments, but the present invention is not limited thereto.
The invention discloses a PN code-based time reversal multi-bolt damage ultrasonic detection method and a PN code-based time reversal multi-bolt damage ultrasonic detection system, which are suitable for ultrasonic detection of damage states of a plurality of bolts simultaneously so as to improve bolt detection efficiency, and are further suitable for detection of structures with a large number of bolts.
The embodiment provides a time reversal multi-bolt damage ultrasonic detection method based on a PN code, which is suitable for a detection system (shown in figure 1) with a plurality of input ports and a plurality of output ports, wherein each input port corresponds to a plurality of bolts, and the plurality of bolts correspond to different output ports respectively. Specifically, the PN code-based time reversal multi-bolt damage ultrasonic detection method comprises the following steps:
at the transmitting end, the same number of PN codes are selected according to the number of the input ports, and the PN codes are different. Respectively utilizing each PN code to carry out time delay modulation on the linear sweep sine wave so as to obtain detection signals with the same number as the input ports; respectively carrying out time delay modulation on a linear sweep sine wave by utilizing a PN code to obtain a detection signal, for example, carrying out time delay modulation on the linear sweep sine wave by utilizing the PN code 1 to obtain the detection signal transmitted by an input port 1, carrying out time delay modulation on the linear sweep sine wave by utilizing the PN code N to obtain the detection signal transmitted by the input port N, and carrying out time delay modulation on the linear sweep sine wave by utilizing the PN code N to obtain the detection signal transmitted by the input port N; finally, the same number of detection signals as the number of input ports (PN codes) are obtained. Then, a plurality of input ports transmit detection signals to the corresponding bolts synchronously through the piezoelectric sensors, each input port corresponds to one detection signal, and the detection signals are captured by the output ports corresponding to the bolts after passing through the bolts. In the embodiment shown in fig. 1, the number of input ports is N, correspondingly, the number of PN codes is N, the number of detection signals is also N, and the number of output ports is Q.
At the receiving end, the output signal of the detection signal passing through the bolt corresponding to the output port is received through the output port (all signals passing through the N bolts corresponding to the output port are superposed). When the bolt is in a good state, the input port respectively transmits a sweep frequency signal captured by the output port to the bolt when a linear sweep frequency sine wave (the same as the linear sweep frequency sine wave adopted by the input port corresponding to the bolt) is obtained, and the sweep frequency signal is subjected to time delay modulation by adopting a PN code and a modulation mode which are the same as those of the input port corresponding to the output port to obtain a modulation signal of each bolt; for example, the input port 1 transmits a detection signal to pass through the bolts (1, 1) and then is captured by the output port 1, and if the detection signal is obtained by adopting PN code 1 modulation, the output port 1 also obtains the modulation signal of the bolts (1, 1) by adopting PN code 1 modulation; for another example, the input port n transmits a detection signal, and the detection signal passes through the bolt (n, 1) and is captured by the output port 1, and if the detection signal is obtained by using PN code n modulation, the output port 1 also obtains the modulation signal of the bolt (n, 1) by using PN code n modulation. Then, the modulation signal is subjected to time reversal to obtain a reference signal of the bolt. And finally, carrying out convolution operation on the output signal and the reference signal, taking the value of the convolution result in the focusing time, and judging the damage degree of the bolt according to the value.
The description of "output port corresponding to input port" refers to an output port for receiving the detection signal transmitted by the input port, the description of "bolt corresponding to input port" refers to a bolt through which the detection signal transmitted by the input port passes, and the description of "bolt corresponding to output port" refers to a bolt through which the signal is captured by the output port.
In this embodiment, the detection method further includes: when the bolt is in a perfect state (just assembled and corrosion is not generated), linear sweep sine waves are transmitted to the bolt corresponding to the bolt through the input port in advance, and the linear sweep sine waves are captured and stored by the output port corresponding to the bolt after passing through the bolt. Namely, the output port captures and stores the sweep frequency signal for being called when the bolt is detected subsequently. For example, a linear sweep sine wave is transmitted to the bolts (1, 1) through the input port 1 in advance, and the linear sweep sine wave passes through the bolts (1, 1) and is captured by the output port 1, and at this time, the output port 1 obtains a sweep signal corresponding to the bolts (1, 1).
In this embodiment, the detection method further includes: dividing all bolts to be detected into N groups in advance, wherein each group comprises Q bolts; the bolts in different groups are configured to correspond to different input ports, all the bolts in the same group respectively correspond to the same input port, and all the bolts in the group respectively correspond to different output ports. For example, group 1 bolts (1, 1), \ 8230, (1, Q) correspond to input port 1, and group 1 bolts (1, 1), \ 8230, (1, Q) correspond to output ports 1-Q, respectively; the nth group of bolts (n, 1), (8230), (n, Q) correspond to the input port n, and the nth group of bolts (n, 1), (8230), (n, Q) correspond to the output ports 1-Q respectively; the Nth group of bolts (N, 1), (8230), (N, Q) correspond to the input port N, and the Nth group of bolts (N, 1), (8230), (N, Q) correspond to the output ports 1-Q respectively. Each output port corresponds to at most one bolt corresponding to the same input port, the output port 1 captures signals of N bolts (1, 1), \8230and (N, 1) corresponding to different input ports 1-N, the output port Q captures signals of N bolts (1, Q), \8230and (N, Q) corresponding to different input ports 1-N, and the output port Q also captures signals of N bolts from the bolts (1, Q) corresponding to different input ports 1-N to the bolts (N, Q). In this embodiment, each input port transmits a detection signal to the corresponding bolt through the piezoelectric sensor, and each output port captures an output signal 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.
Wherein x is n (t) represents the detection signal transmitted by the nth input port, t represents time, M represents a chip number, M represents a code length of a single PN code, sw (t) represents a linear swept sine wave,
m chip, t, representing the n PN code 0 Indicates the signal length of sw (t).
Correspondingly, the swept frequency signal is modulated by using the same modulation mode and PN code as the input port to obtain a modulation 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 represented as:
wherein, smo n,q (t) represents the modulated signal of the bolt (n, q) corresponding to the input port n and the output port q at the output port, v n,q (t) represents the sweep frequency signal corresponding to the bolt (n, q), t represents time, M represents the chip number, M represents the code length of a single PN code,
m chip, t, representing the n PN code 0 Indicates the signal length of sw (t).
Time reversal is carried out on the modulation signal of the bolt (n, q) at the output port q based on the following formula, and a reference signal of the bolt (n, q) is obtained:
wherein tro n,q (t) represents a reference signal corresponding to the bolt (n, q), v n,q (t) represents the sweep frequency signal corresponding to the bolt (n, q), t represents time, M represents the chip number, M represents the code length of a single PN code,
m chip, t, representing the n PN code 0 Indicates the signal length of sw (t).
Output signal y captured at the q-th output port q (t) is expressed as:
wherein x is n (t) denotes a detection signal emitted from the nth input port, N denotes an input port number, N denotes the number of input ports,
represents the convolution of h nq (t) represents an ultrasonic channel response function between the nth input port to the qth output port.
Obtaining a convolution result of a reference signal and an output signal of a bolt (n, q) corresponding to the input port n and the output port q at the focusing time t = M × t based on the following formula 0 Value of beta n,q ：
Wherein tro n,q (t) denotes a reference signal, y, corresponding to the bolt (n, q) q (t) represents the output signal(s),
representing convolution, t representing time, M representing code length of a single PN code, t 0 Represents the signal length of sw (t), and "| |" represents taking the absolute value. According to the value of beta n,q The degree of damage of the bolt (n, q) can be judged.
Accordingly, another embodiment provides a PN code based time-reversal multi-bolt damage ultrasonic detection system, which includes a piezoelectric sensor (not shown), a plurality of input ports 1-N, 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, wherein each input port corresponds to a plurality of bolts, and the plurality of bolts respectively correspond to different output ports. At the transmitting end, a PN code generator generates the same number of PN codes as the number of input ports, each PN code being different. The modulator respectively utilizes each PN code to carry out time delay modulation on the linear sweep frequency sine wave so as to obtain detection signals with the same number as the input ports; that is, a linear sweep sine wave is time-delayed by a PN code to obtain a detection signal, and finally, the same number of detection signals as the number of input ports (PN codes) are obtained. A plurality of input ports transmit detection signals to the bolts corresponding to the input ports synchronously through the piezoelectric sensors, and each input port corresponds to one detection signal. At the receiving end, the output signal of the detection signal passing through the bolt corresponding to the output port is received through the output port (all signals passing through the N bolts corresponding to the output port are superposed). When the modulator calls the bolt in a good state, the input port respectively transmits a sweep frequency signal captured by the output port to the bolt when the linear sweep frequency sine wave (which is the same as the linear sweep frequency sine wave adopted by the input port corresponding to the bolt) is transmitted, and the sweep frequency signal is subjected to time delay modulation by adopting a PN code and a modulation mode which are the same as those of the input port corresponding to the output port to obtain a modulation signal. The processor 40 performs time reversal on the modulation signal to obtain a reference signal of the bolt, performs convolution operation on the output signal and the reference signal, and obtains a value of a convolution result at a focusing time so as to judge the damage degree of the bolt according to the value.
The configuration of the input port and the output port, how the modulator modulates the linear frequency sweep sine wave to obtain the detection signal, how the modulator modulates the frequency sweep signal to obtain the modulation signal, how the processor 40 performs time reversal on the modulation signal to obtain the reference signal, and how the convolution operation is performed on the reference signal and the output signal to find the value of the convolution result at the focusing time may refer to the corresponding description in the detection method, which is not described herein again. The modulator may be any conventional modulator, and the processor 40 may 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 modulator also includes a first modulator 31 and a second modulator 32. As shown in fig. 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, the first PN code generator 11 generates N PN codes (PN codes 1 to N), the first signal generator 21 provides N linear frequency sweep sine waves, and the first modulator 31 modulates the linear frequency sweep sine waves by using the PN codes 1 to 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), the second signal generator provides N linear sweep frequency sine waves, and the second modulator 32 utilizes the PN codes 1-N to respectively modulate sweep frequency signals obtained when the linear sweep frequency sine waves pass through the bolts in an intact state so as to obtain modulation signals of the bolts.
Referring to fig. 3, fig. 3 shows a 2-input 2-output detection system, which is used to simultaneously detect 4 bolts Status1-4 with different damage states, where the four bolts Status1-4 are corroded for 0.5 hour, 1 hour, 1.5 hours, and 2 hours (the corrosion of the bolts Status1-4 is gradually deepened). The signal width of the linear sweep sine wave adopted in this embodiment is 1s, the frequency range is from 1kHz to 200kHz, and 2 PN codes each containing 7 chips are used to modulate the linear sweep sine wave, respectively, to generate 2 sets of detection signals. The reception and transmission of signals is achieved by connecting the piezoelectric sensor with NI-6361,the sampling frequency was 2MS/s. Finally, the signal captured by the output port is processed through matlab, so as to obtain an output result (the value beta is obtained n,q ) As shown in table 1 below.
TABLE 1
As can be seen from Table 1, for bolts Status1-4, as the degree of corrosion of the bolts deepens, the value β output by the detection system increases n,q And gradually decreases. Therefore, the damage state of the bolt can be judged through the energy value output by the detection system.
In order to further verify the feasibility of the invention, the bolts Status1-4 in the 4 states are separately detected, and the results of the separate detection are processed by wavelet analysis. The corresponding wavelet analysis results are shown in table 2 below.
TABLE 2
As can be seen from table 2, when each bolt was tested individually, the results of the wavelet analysis also decreased as the corrosion of the bolt increased. Thereby further verifying the feasibility of the invention.
In summary, the present invention utilizes a plurality of different PN codes to respectively modulate a linear swept sine wave to obtain a plurality of different detection signals, each input port of the transmitting end respectively transmits a different detection signal, and each output port captures a signal modulated by a different PN code (the detection signal transmitted by a different input port); and at a receiving end, modulating the sweep frequency signal captured by the output port when the bolt is in a perfect state by using the PN code to obtain a modulation signal, performing time reversal on the modulation signal to obtain a reference signal of the bolt, and obtaining a value of a convolution result of the output signal and the reference signal in focusing time so as to judge the damage degree of each bolt. The invention utilizes the correlation of PN codes to realize the analysis and identification of signals from different bolts, can realize the simultaneous detection of a plurality of bolts and greatly improves the detection efficiency of a detection system.
The above disclosure is only a preferred embodiment of the present invention, and certainly should not be taken as limiting the scope of the present invention, which is therefore intended to cover all equivalent changes and modifications within the scope of the present invention.
Claims (6)
1. A time reversal multi-bolt damage ultrasonic detection method based on PN codes is applicable to an ultrasonic detection system with a plurality of input ports and a plurality of output ports, each input port corresponds to a plurality of bolts, and the plurality of bolts respectively correspond to different output ports, and the detection method is characterized by comprising the following steps:
at a transmitting end, selecting the same number of PN codes according to the number of input ports, wherein the PN codes are different; respectively carrying out time delay modulation on the linear sweep sine waves by utilizing the PN codes so as to obtain detection signals with the same number as the input ports; the input ports transmit the detection signals to the corresponding bolts synchronously through piezoelectric sensors, and each input port corresponds to one detection signal;
at a receiving end, receiving an output signal of the detection signal passing through a bolt corresponding to the output port through the output port; when the bolt is in a good state, the input port respectively transmits sweep frequency signals captured by the output port when the linear sweep frequency sine waves are transmitted to the bolt, and the sweep frequency signals are subjected to time delay modulation by adopting the same PN code and modulation mode as the input port corresponding to the output port to obtain modulation signals corresponding to the bolt; time reversal is carried out on the modulation signal to obtain a reference signal of the bolt; carrying out convolution operation on the output signal and the reference signal, taking the value of the convolution result in focusing time, and judging the damage degree of the bolt according to the value;
performing time delay modulation on the linear sweep sine wave based on the following formula to obtain the detection signal:
wherein x is n (t) represents the detection signal transmitted by the nth input port, t represents time, M represents the chip number, M represents the code length of a single PN code, sw (t) represents a linear swept sine wave,
m chip, t, representing the nth PN code 0 Represents the signal length of sw (t);
performing time delay modulation on the frequency sweep signal based on the following formula to obtain the modulation signal:
wherein, smo n,q (t) represents the modulated 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 frequency signal corresponding to the bolt corresponding to the input port n and the output port q, t represents time, M represents a chip serial number, M represents a code length of a single PN code,
m chip, t, representing the n PN code 0 Represents the signal length of sw (t);
time-inverting the modulated signal based on the following equation to obtain the reference signal:
wherein tro n,q (t) represents the reference signal corresponding to the bolt corresponding to the input port n and the output port q, v n,q (t) represents the sweep frequency signal corresponding to the bolt corresponding to the input port n and the output port q, t represents time, M represents a chip serial number, and M represents a single PN codeThe length of the code is long, and the code length is short,
m chip, t, representing the nth PN code 0 Represents the signal length of sw (t);
output signal y captured at the q-th output port q (t) is:
wherein x is n (t) represents a detection signal emitted from the nth of the input ports, N represents an input port number, N represents the number of input ports,
represents the convolution of h nq (t) represents an ultrasonic channel response function between the nth input port to the qth output port;
obtaining the convolution result at the focusing time M x t based on the following formula 0 Value of beta n,q ：
Wherein tro n,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(s),
representing convolution, t representing time, M representing code length of a single PN code, t 0 Represents the signal length of sw (t), and "|" represents taking the absolute value.
2. The detection method according to claim 1, further comprising: and under the condition that the bolt is in a good state, the linear frequency sweeping sine waves are transmitted to the corresponding bolt through the input port in advance, and are captured and stored by the output port corresponding to the bolt after passing through the bolt.
3. The detection method according to claim 1 or 2, further comprising:
dividing all bolts to be detected into N groups in advance, wherein each group comprises a plurality of bolts;
the bolts in different groups are configured to correspond to different input ports, all the bolts in the same group respectively correspond to the same input port, and each bolt in the group respectively corresponds to different output ports.
4. The detection method according to claim 1 or 2, wherein the output port receives an output signal of the detection signal after passing through a bolt corresponding thereto by a piezoelectric sensor.
5. A time reversal multi-bolt damage ultrasonic detection system based on PN codes is characterized by comprising a piezoelectric sensor, a plurality of input ports, a plurality of output ports, a PN code generator, a modulator, a processor and a signal generator for providing linear sweep sine waves, wherein each input port corresponds to a plurality of bolts which respectively correspond to different output ports; at a transmitting end, the PN code generator generates PN codes with the same number as the input ports, the PN codes are different, the modulator respectively utilizes the PN codes to perform time delay modulation on linear sweep frequency sine waves so as to obtain detection signals with the same number as the input ports, a plurality of the input ports synchronously transmit the detection signals to bolts corresponding to the input ports through piezoelectric sensors, and each input port corresponds to one detection signal; at a receiving end, receiving an output signal of the detection signal after passing through a bolt corresponding to the output port through the output port, when the modulator calls the bolt in a perfect state, respectively transmitting a sweep frequency signal captured by the output port to the bolt through the input port, performing time delay modulation on the sweep frequency signal by adopting a PN code and a modulation mode which are the same as those of the input port corresponding to the output port to obtain a modulation signal corresponding to the bolt, performing time reversal on the modulation signal by the processor to obtain a reference signal of the bolt, performing convolution operation on the output signal and the reference signal, and taking a value of a convolution result in focusing time to judge the damage degree of the bolt according to the value;
the modulator performs time delay modulation on the linear swept sine wave based on the following formula to obtain the detection signal:
wherein x is n (t) represents the detection signal transmitted by the nth input port, t represents time, M represents the chip number, M represents the code length of a single PN code, sw (t) represents a linear swept sine wave,
m chip, t, representing the n PN code 0 Represents the signal length of sw (t);
the modulator modulates the sweep frequency signal to obtain the modulation signal based on the following formula:
wherein, smo n,q (t) represents the modulated 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 frequency signal corresponding to the bolt corresponding to the input port n and the output port q, t represents time, M represents a chip number, M represents a code length of a single PN code,
m chip, t, representing the n PN code 0 Represents the signal length of sw (t);
the processor performs time reversal on the modulation signal based on the following formula to obtain the reference signal:
wherein tro n,q (t) represents the reference signal corresponding to the bolt corresponding to the input port n and the output port q, v n,q (t) represents the sweep frequency signal corresponding to the bolt corresponding to the input port n and the output port q, t represents time, M represents a chip serial number, M represents a code length of a single PN code,
m chip, t, representing the n PN code 0 Represents the signal length of sw (t);
output signal y captured at the q-th output port q (t) is:
wherein x is n (t) represents a detection signal emitted from the nth input port, N represents an input port number, N represents the number of input ports,
represents the convolution of h nq (t) represents an ultrasonic channel response function between an nth input port to a qth output port;
the processor finds the convolution result at the time of focus M x t based on 0 Value of beta n,q ：
Wherein tro n,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，
Representing convolution, t representing time, M representing code length of a single PN code, t 0 Represents the signal length of sw (t), and "| |" represents taking the absolute value.
6. The detection system according to claim 5, wherein the output port receives an output signal of the detection signal through a corresponding bolt via a piezoelectric sensor.
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