Lightning strike piezoelectric guided wave online sensing method and device

Abstract

The application discloses a lightning stroke piezoelectric wave online sensing method and device, comprising the following steps: arranging a piezoelectric sheet on the back of a composite material structure to be monitored; the front of the composite material structure to be monitored is subjected to a lightning stroke; the piezoelectric sheet converts a mechanical quantity of a lightning stroke wave response into a lightning stroke piezoelectric wave response signal, and transmits the lightning stroke piezoelectric wave response signal to an optical transmitter through a wire for short-distance transmission; the optical transmitter converts the lightning stroke piezoelectric wave response signal into a lightning stroke piezoelectric wave response optical signal, and transmits the lightning stroke piezoelectric wave response optical signal through an optical fiber for long-distance transmission; and an optical receiver receives the lightning stroke piezoelectric wave response optical signal, and converts the lightning stroke piezoelectric wave response optical signal into a lightning stroke piezoelectric wave response signal which is output to a data acquisition device. The lightning stroke piezoelectric wave online sensing method and device are adopted, the cathode of the piezoelectric sheet is short-circuited to the structure to be monitored, the resistive voltage generated in the conduction of the lightning current is avoided to cause damage of the sensor, and meanwhile, the quality of the lightning stroke piezoelectric wave response signal is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a lightning piezoelectric guided wave online sensing technology, and in particular to a lightning piezoelectric guided wave online sensing method and device. BACKGROUND

[0002] Composite materials are widely used in modern advanced aircraft. Since composite materials have low electrical conductivity, lightning is one of the important factors affecting the safety of aircraft in flight, thereby affecting the application of composite materials in aircraft.

[0003] To solve the above problems, the existing technology mostly uses lightning online monitoring technology in the aviation composite material structure. However, due to the short duration and large energy of lightning, accompanied by strong electromagnetic field interference, and it is also difficult for laboratory special equipment to effectively monitor lightning events online, which brings challenges to the high-reliability real-time online monitoring of lightning damage effects of composite material structures.

[0004] The piezoelectric guided wave structural health monitoring method uses the piezoelectric sheet integrated in the structure to collect the structure guided wave response signal under the lightning impact force effect in real time, which provides a new technical means for large-area online monitoring of composite material lightning events. Therefore, how to effectively realize the online sensing of lightning piezoelectric guided wave in the strong electromagnetic environment of lightning is the key to improving the reliability of lightning guided wave online monitoring technology and putting the technology into practical application.

[0005] Generally speaking, the lightning piezoelectric guided wave online sensing of composite materials needs to face two problems: first, the passive piezoelectric sensing part of the composite material lightning piezoelectric guided wave online monitoring system, when performing online sensing of lightning guided wave response signal, the strong electromagnetic field of lightning current makes the lightning energy coupled to the signal transmission line to produce induced voltage; second, the lightning current is conducted through the structure or the lead to produce resistive voltage, which seriously affects the quality of the lightning piezoelectric guided wave response signal, and even causes the sensor to fail and damage. SUMMARY

[0006] The present application considers the problems of lightning strong electromagnetic field coupling interference and lightning strong current resistance coupling interference, and proposes a lightning piezoelectric guided wave online sensing method which comprehensively uses electromagnetic shielding, piezoelectric sheet short circuit protection and piezoelectric guided wave signal photoelectric conversion transmission, not only solves the problem of damage of piezoelectric sheet integrated in composite material structure in severe lightning environment, but also solves the problem of too large crosstalk amplitude, too low signal-to-noise ratio and inaccurate wave arrival time extraction caused by lightning indirect effect, which directly affects the signal quality.

[0007] To achieve the above purpose, the present application provides a lightning piezoelectric guided wave online sensing method, comprising the following steps:

[0008] S1, arranging a piezoelectric sheet on the back of a composite material structure to be monitored;

[0009] S2, the front of the composite material structure to be monitored is struck by lightning, and a lightning impact wave response is generated in the structure;

[0010] S3, the piezoelectric sheet converts the mechanical quantity of the lightning wave response into a lightning piezoelectric wave response signal, and transmits the signal to an optical transmitter through a wire for short distance transmission;

[0011] S4, the optical transmitter converts the lightning piezoelectric wave response signal into a lightning piezoelectric wave response optical signal, and transmits the lightning piezoelectric wave response optical signal through an optical fiber for long distance transmission;

[0012] S5, the optical receiver receives the lightning piezoelectric wave response optical signal and converts it into a lightning piezoelectric wave response signal output to a data acquisition device.

[0013] A lightning piezoelectric wave online sensing device, comprising a piezoelectric sheet arranged on the back of a composite material to be monitored, an optical transmitter electrically connected to the positive electrode of the piezoelectric sheet through a wire, an optical receiver in communication with the optical transmitter through an optical fiber, and a data acquisition device connected to the optical receiver;

[0014] The negative electrode of the piezoelectric sheet is electrically connected to the piezoelectric sheet at the arrangement position and the composite material to be monitored, and the negative electrode of the piezoelectric sheet is electrically connected to the shorting point of the composite material to be monitored. The shorting point is arranged on the back of the composite material to be monitored near the position of the piezoelectric sheet, for reducing the influence of the resistive voltage generated by the lightning current conducting in the composite material to be monitored, and avoiding damage to the piezoelectric sheet due to the resistive voltage.

[0015] Preferably, the back of the composite material to be monitored and around the position of the piezoelectric sheet is covered with a metal foil for enhancing the electromagnetic shielding capability.

[0016] Preferably, the negative electrode of the piezoelectric sheet and the shorting point of the composite material to be monitored are connected through a conductor, conductive adhesive, metal foil or wire;

[0017] The positive electrode of the piezoelectric sheet is connected to the optical transmitter through an electromagnetic shielding joint and a wire in sequence.

[0018] Preferably, the distance between the shorting point and the arrangement position of the piezoelectric sheet is greater than 0 mm and less than or equal to 100 mm.

[0019] Preferably, the wire is a single wire, a twisted pair wire, a coaxial wire or a multi-core shielded wire, and the wire is wrapped with an electromagnetic shielding layer, and the electromagnetic shielding layer is electrically connected to the shorting point for reducing the interference of the strong electromagnetic field of the lightning current on the line.

[0020] Preferably, the electromagnetic shielding layer is a metal foil made of copper or aluminum.

[0021] Preferably, the optical transmitter is arranged inside an electromagnetic shielding shell, which is short-circuited with the composite material to be monitored to weaken the influence of the lightning current strong electromagnetic field.

[0022] The electromagnetic shielding shell is made of one of steel, copper, aluminum or iron, or any combination thereof.

[0023] Preferably, the optical receiver and the data acquisition device are arranged inside an electromagnetic shielding cabinet.

[0024] Preferably, the optical fiber is a 50 / 125 μm multimode optical fiber, a 62.5 / 125 μm multimode optical fiber, a 100 / 140 μm multimode optical fiber or a 200 μm quartz optical fiber.

[0025] The present application has the following advantages:

[0026] (1) By short-circuiting the piezoelectric sheet cathode with the structure to be monitored, the resistive voltage generated by the conduction of lightning current in the structure is avoided to cause damage to the sensor.

[0027] (2) By arranging the electromagnetic shielding layer and the electromagnetic shielding shell with electromagnetic shielding function, the induced voltage generated by the coupling of the lightning current strong electromagnetic field to the wire and the circuit is reduced.

[0028] (3) The lightning piezoelectric guided wave response signal processing is converted into an optical signal, which is transmitted through an optical fiber, avoiding the conduction of lightning current through a wire, weakening the influence of the indirect effect of lightning, improving the transmission reliability in a strong electromagnetic field environment, and improving the quality of the lightning piezoelectric guided wave response signal.

[0029] The technical solutions of the present application will be further described in detail below with reference to the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A flowchart of a lightning piezoelectric guided wave online sensing method of the present application;

[0031] Figure 2 A structure principle diagram of a lightning piezoelectric guided wave online sensing device of the present application;

[0032] Figure 3 A partial view of the piezoelectric sheet short-circuited with the surface of the composite material structure to be monitored according to the experimental example of the present application;

[0033] Figure 4 A coordinate position diagram of the piezoelectric sheet and the simulated lightning current attachment point according to the experimental example of the present application;

[0034] Figure 5The lightning piezoelectric guided wave response signal I obtained by the piezoelectric sheet described in the experimental example of the present application i (t) waveform diagram.

[0035] Figure 6 The lightning piezoelectric guided wave response signal I obtained by the piezoelectric sheet described in the experimental example of the present application i (t) spectrum analysis diagram.

[0036] Wherein: 1, the composite material to be monitored; 2, the piezoelectric sheet; 3, the short circuit point; 4, the electromagnetic shielding joint; 5, the wire; 6, the optical transmitter; 7, the optical fiber; 8, the optical receiver; 9, the data acquisition device; 10, the electromagnetic shielding cabinet; 11, the metal foil. DETAILED DESCRIPTION

[0037] The present application will be further described below in conjunction with the drawings. It should be noted that the present embodiment is based on the technical solution, and gives a detailed implementation and specific operation process, but the protection scope of the present application is not limited to the present embodiment.

[0038] Figure 1 The flow chart of the lightning piezoelectric guided wave online sensing method of the present application is shown in FIG. 1, which is a lightning piezoelectric guided wave online sensing method, comprising the following steps: Figure 1

[0039] S1, arranging a piezoelectric sheet 2 on the back of the composite material structure 1 to be monitored;

[0040] S2, the front of the composite material structure 1 to be monitored is subjected to lightning strike, and a lightning impact force guided wave response is generated in the structure;

[0041] S3, the piezoelectric sheet 2 converts the mechanical quantity of the lightning guided wave response into a lightning piezoelectric guided wave response signal, and transmits it to the optical transmitter 6 through the wire 5 for short distance transmission;

[0042] When the lightning strikes the composite material structure plate to be monitored 1, a guided wave can be excited from the attachment point due to the impact force of the lightning. The excited guided wave propagates along the composite material structure plate to be monitored 1, and then is coupled and transmitted to the piezoelectric sheet 2 adhered to the surface, which can convert the mechanical guided wave response into an electrical response signal under the direct piezoelectric effect.

[0043] S4, the optical transmitter 6 converts the lightning piezoelectric guided wave response signal into a lightning piezoelectric guided wave response optical signal, and transmits the lightning piezoelectric guided wave response optical signal through the optical fiber 7 for long distance transmission;

[0044] S5, the optical receiver 8 receives the lightning piezoelectric guided wave response optical signal and converts it into a lightning piezoelectric guided wave response signal output to the data acquisition device 9.

[0045] Figure 2 ​As shown in a structural schematic diagram of a lightning piezoelectric guided wave online sensing device of the present application, Figure 2 The lightning piezoelectric guided wave online sensing device comprises a piezoelectric sheet 2 arranged on the back of a composite material 1 to be monitored, an optical transmitter 6 electrically connected to the positive electrode of the piezoelectric sheet 2 through a wire 5, an optical receiver 8 in communication with the optical transmitter 6 through an optical fiber 7, and a data acquisition device 9 connected to the optical receiver 8. The optical receiver 8 is located at the rear end away from the lightning current attachment point, and the effective electromagnetic protection of overall shielding ensures the high reliability of the output of the lightning piezoelectric guided wave response signal.

[0046] The negative electrode of the piezoelectric sheet 2 is electrically connected to the arrangement position of the piezoelectric sheet 2 and the composite material 1 to be monitored, and the negative electrode of the piezoelectric sheet 2 is electrically connected to the shorting point 3 of the composite material 1 to be monitored. The shorting point 3 is arranged on the back of the composite material 1 to be monitored near the position of the piezoelectric sheet 2, which is used to reduce the influence of the resistive voltage generated by the conduction of lightning current in the composite material 1 to be monitored, and to avoid damage to the piezoelectric sheet 2 due to the resistive voltage.

[0047] Preferably, the back of the composite material 1 to be monitored and the position around the piezoelectric sheet 2 are covered with a metal foil 11 to enhance the electromagnetic shielding capability.

[0048] Preferably, the lightning guided wave response mechanical quantity is converted into a lightning piezoelectric guided wave response signal by conductive glue coupling. The negative electrode of the piezoelectric sheet 2 and the shorting point 3 of the composite material 1 to be monitored are connected through a conductor plug, conductive glue bonding, metal foil 11 bonding or wire 5.

[0049] The positive electrode of the piezoelectric sheet 2 is connected to the optical transmitter 6 in sequence through the electromagnetic shielding joint 4 and the wire 5.

[0050] Preferably, the distance between the shorting point 3 and the arrangement position of the piezoelectric sheet 2 is greater than 0 mm and less than or equal to 100 mm. This reduces the influence of the resistive voltage generated by the conduction of lightning current in the structure, avoids damage to the piezoelectric sheet 2 due to the resistive voltage, and the size of the resistive voltage is related to the distance between the piezoelectric sheet 2 and the shorting point 3. The smaller the distance, the smaller the resistive voltage, and the easier the piezoelectric sheet 2 to survive.

[0051] Preferably, the wire 5 is a single wire, a twisted pair, a coaxial cable or a multi-core shielded wire. The wire 5 is wrapped with an electromagnetic shielding layer, and the electromagnetic shielding layer is electrically connected to the shorting point 3 to reduce the interference of the strong electromagnetic field of lightning current on the line. It should be noted that the degree of interference depends on the length and field strength of the line affected by the strong electromagnetic field of lightning current. Using the wire 5 for short-distance signal transmission helps to reduce the size of the induced voltage; using the electromagnetic shielding layer for protection helps to reduce the field strength of the strong electromagnetic field. The shielding effectiveness is related to the material properties and thickness. The higher the conductivity of the material, the greater the thickness, the higher the shielding effectiveness, and the smaller the induced voltage of the strong electromagnetic field of lightning current coupled to the wire 5 and the circuit.

[0052] Preferably, the electromagnetic shielding layer is a metal foil 11 made of copper or aluminum.

[0053] Preferably, the optical transmitter 6 is disposed inside the electromagnetic shielding shell, which is short-circuited to the composite material 1 to be monitored, in order to weaken the influence of the strong electromagnetic field of the lightning current; the electromagnetic shielding shell is made of steel, copper, aluminum, or iron, or any combination thereof. In this embodiment, the optical transmitter 6 is encapsulated in a 1.5mm thick hollow aluminum shielding shell, adapted for online piezoelectric guided wave sensing, and includes a filtering circuit and an optical transmission circuit, enabling highly reliable conversion of the lightning piezoelectric guided wave response signal into a lightning piezoelectric guided wave response optical signal under severe lightning strike conditions.

[0054] Preferably, both the optical receiver 8 and the data acquisition device 9 are housed inside the electromagnetic shielding cabinet 10. The optical receiver 8 includes an optical receiving circuit and a filtering circuit, which convert the lightning strike piezoelectric guided wave response optical signal into a lightning strike piezoelectric guided wave response signal and improve the signal-to-noise ratio.

[0055] Preferably, the optical fiber 7 is a 50 / 125μm multimode fiber, a 62.5 / 125μm multimode fiber, a 100 / 140μm multimode fiber, or a 200μm silica fiber. Since the optical fiber 7 is an insulating material, lightning current will not be conducted through the optical fiber 7. Therefore, it can effectively prevent the lightning current from being conducted through the conductor 5 and generating interference voltage. At the same time, the optical signal transmission in the optical fiber 7 has anti-electromagnetic interference characteristics, which can ensure high-reliability transmission of the lightning piezoelectric guided wave response optical signal in harsh lightning environments.

[0056] Experimental example:

[0057] For ease of verification, this embodiment will use a layup direction of [45° / 0° / -45° / 90°] 2s The carbon fiber reinforced composite material to be monitored has dimensions of 600mm × 600mm × 2mm. The center of the carbon fiber reinforced composite material is set as the origin of the coordinate system, the piezoelectric element placement point is P1, and the lightning current attachment point is E1. The following system is established: Figure 4 The rectangular coordinate system shown.

[0058] Table 1 shows the coordinates of the piezoelectric element and the lightning current attachment point.

[0059] Coordinates (mm, mm) Coordinates (mm, mm) [P1] (-180，-180) E1 (-32，131)

[0060] This experimental example includes the following steps:

[0061] (1) Piezoelectric elements are arranged on the surface of carbon fiber reinforced composite material. The piezoelectric elements convert the mechanical quantities of the lightning guided wave response into the lightning piezoelectric guided wave response signal:

[0062] The piezoelectric element 2 is bonded to the inner surface of the carbon fiber reinforced composite material. A copper foil with a thickness of 0.2 mm to 0.4 mm is used to cover the inner surface of the carbon fiber reinforced composite material around the piezoelectric element. A short-circuit point is selected at a distance of 80 mm from the piezoelectric element. The negative electrode of the piezoelectric element is connected to the optical transmitter through the electromagnetic shielding connector 4 and the wire 3. The electromagnetic shielding layer of the wire is connected to the short-circuit point of the carbon fiber reinforced composite material through the 0.2 mm thick copper foil.

[0063] (2) The front of the composite material structure to be monitored is subjected to a lightning strike signal.

[0064] (3) The piezoelectric element converts the mechanical quantity of the lightning guided wave response into the lightning piezoelectric guided wave response signal, and transmits it to the optical transmitter over a short distance through the wire;

[0065] (4) The optical transmitter converts the lightning piezoelectric guided wave response signal into a lightning piezoelectric guided wave response optical signal, and transmits the lightning piezoelectric guided wave response optical signal over a long distance through an optical fiber.

[0066] Lightning piezoelectric guided wave response optical signals are transmitted over long distances via 62.5 / 125μm multimode optical fiber. Meanwhile, ST connectors are used for the fiber optic connectors to ensure a tight connection, and the outer shell of the fiber optic connectors is made of aluminum to enhance the resistance to electromagnetic interference.

[0067] (5) Use optical receiver 8 to receive the lightning strike piezoelectric guided wave response optical signal, process and convert it into a lightning strike piezoelectric guided wave response signal and output it to data acquisition device 9.

[0068] Using this experimental example, we obtained the following: Figure 5 The lightning strike piezoelectric guided wave response signal I is shown. i (t) indicates that there is a crosstalk signal caused by the indirect effect of lightning current at time 300μs, but its amplitude is smaller than that of the lightning piezoelectric guided wave response signal I. i (t) is relatively low. In the range of 300 to 600 μs, wave packets exhibiting the propagation characteristics of the first antisymmetric mode (A0 mode) of Lamb waves can be identified as direct wave packets of the A0 mode based on their arrival time.

[0069] like Figure 6 As shown, the guided wave response signal I to a lightning strike... i (t) Spectral analysis shows that the signal energy is mainly concentrated in the 0–30 kHz range. Noise signals with frequencies above 50 kHz are filtered out by the filtering circuits of optical transmitter 6 and optical receiver 8. This demonstrates that this experimental example can reliably perform online sensing of the dynamic response propagating in the form of guided waves in composite material structures under the effect of lightning strikes.

[0070] Therefore, the application adopts the lightning piezoelectric guided wave on-line sensing method and device, comprehensively solves the piezoelectric sheet short-circuit protection, electromagnetic shielding and guided wave signal photoelectric conversion transmission, solves the damage problem of the piezoelectric sheet in the lightning harsh environment, solves the problem that the amplitude of the interference signal caused by the indirect effect of lightning is too large, and the effective information of the lightning piezoelectric guided wave response signal is lost, and realizes the high-reliability on-line sensing of the lightning piezoelectric guided wave response signal.

[0071] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that: the technical solutions of the present application can still be modified or replaced by the equivalent, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for online sensing of lightning-induced piezoelectric guided waves, wherein the method employs an online sensing device for lightning-induced piezoelectric guided waves, characterized in that: The device includes a piezoelectric sheet disposed on the back of the composite material to be monitored, an optical transmitter electrically connected to the positive electrode of the piezoelectric sheet via a wire, an optical receiver communicating with the optical transmitter via an optical fiber, and a data acquisition device connected to the optical receiver. The negative electrode of the piezoelectric element is electrically connected to the composite material to be monitored at the arrangement position of the piezoelectric element, and the negative electrode of the piezoelectric element is electrically connected to the short-circuit point of the composite material to be monitored. The short-circuit point is arranged on the back side of the composite material to be monitored near the piezoelectric element, in order to reduce the influence of the resistive voltage generated by the conduction of lightning current in the composite material to be monitored, and to avoid damage to the piezoelectric element due to resistive voltage. The negative electrode of the piezoelectric element is connected to the short-circuit point of the composite material to be monitored via a conductor plug, a conductive adhesive, a metal foil adhesive, or a wire. The positive electrode of the piezoelectric element is connected to the optical transmitter in sequence via an electromagnetic shielding connector and a wire; The method includes the following steps: S1. Arrange a piezoelectric sheet on the back side of the composite material structure to be monitored; S2. The front of the composite material structure to be monitored is struck by lightning, and a lightning impact force guided wave response is generated in the structure. S3. The piezoelectric element converts the mechanical quantity of the lightning guided wave response into a lightning piezoelectric guided wave response signal, which is then transmitted to the optical transmitter over a short distance via a wire. When lightning strikes the composite material structure plate to be monitored, the impact force of the lightning can generate guided waves from the attachment point. The generated guided waves propagate along the composite material structure plate to be monitored and are then coupled to the piezoelectric sheet bonded to the surface. Under the direct piezoelectric effect, the piezoelectric sheet can convert the mechanical guided wave response into an electrical response signal. S4. The optical transmitter converts the lightning piezoelectric guided wave response signal into a lightning piezoelectric guided wave response optical signal, and transmits the lightning piezoelectric guided wave response optical signal over long distances through optical fiber. S5. The optical receiver receives the lightning strike piezoelectric guided wave response optical signal and converts it into a lightning strike piezoelectric guided wave response signal, which is then output to the data acquisition equipment.

2. The online sensing method for lightning strike piezoelectric guided waves according to claim 1, characterized in that: The back of the composite material to be monitored and around the piezoelectric element are covered with a metal foil to enhance electromagnetic shielding capabilities.

3. The online sensing method for lightning strike piezoelectric guided waves according to claim 1, characterized in that: The distance between the shorting point and the arrangement position of the piezoelectric element is greater than 0 mm and less than or equal to 100 mm.

4. The online sensing method for lightning strike piezoelectric guided waves according to claim 1, characterized in that: The conductor is a single wire, twisted pair, coaxial cable, or multi-core shielded wire. The conductor is wrapped with an electromagnetic shielding layer, which is electrically connected to the short-circuit point to reduce the interference of the strong electromagnetic field of lightning current on the line.

5. The online sensing method for lightning strike piezoelectric guided waves according to claim 4, characterized in that: The electromagnetic shielding layer is a metal foil made of copper or aluminum.

6. The online sensing method for lightning strike piezoelectric guided waves according to claim 1, characterized in that: The optical transmitter is located inside the electromagnetic shielding shell, and the electromagnetic shielding shell is short-circuited with the composite material to be monitored in order to weaken the influence of the strong electromagnetic field of the lightning current. The electromagnetic shielding shell is made of steel, copper, aluminum, or iron, or any combination thereof.

7. The online sensing method for lightning strike piezoelectric guided waves according to claim 1, characterized in that: Both the optical receiver and the data acquisition device are housed inside an electromagnetic shielding cabinet.

8. The online sensing method for lightning strike piezoelectric guided waves according to claim 1, characterized in that: The optical fiber is a 50 / 125μm multimode fiber, a 62.5 / 125μm multimode fiber, a 100 / 140μm multimode fiber, or a 200μm silica fiber.

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