Flexible piezoelectric sensor array applied to aircraft and preparation method thereof

Abstract

The invention discloses a flexible piezoelectric sensor array applied to an aircraft and a preparation method of the flexible piezoelectric sensor array. The flexible piezoelectric sensor array comprises a lower substrate layer, a lower electrode layer, a piezoelectric sensitive layer, an upper electrode layer, an upper substrate layer and a packaging layer, the lower electrode layer is arranged on the lower substrate layer, and the upper surface of the lower electrode layer is attached to the lower surface of the piezoelectric sensitive layer element; the upper electrode layer is arranged on the upper substrate layer, and the lower surface of the upper electrode layer is attached to the upper surface of the piezoelectric sensitive layer element; the upper electrode layer and the lower electrode layer are both used for being communicated with external test equipment so as to monitor the change of voltage or charge of the sensor in real time; and the packaging layer is embedded into the flexible piezoelectric sensor array and is used for sealing and protecting the device. The device can be conformally attached to the surface of a complex structure of an aircraft, the structure of an aircraft body cannot be damaged, real-time monitoring of aerodynamic parameters and structural health conditions of the aircraft is achieved, and then intelligent control over the aircraft is achieved.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of aircraft structure health status monitoring, and in particular to a flexible piezoelectric sensor array used in an aircraft and a preparation method thereof. Background Art

[0002] Structural health monitoring is an important part of aircraft safety operation and maintenance. Therefore, the research on the monitoring of aerodynamic parameters and structural health status of aircraft structural surfaces is of great significance. Traditional structural monitoring technology requires the installation of antennas and sensors, and requires drilling holes to destroy the body structure, resulting in a series of losses such as aerodynamic force and cost. At present, the monitoring research on aircraft aerodynamic parameters and structural conditions mainly focuses on the detection of gas flow rate and pressure near the surface of the structure. Usually, based on micro-nano processing technology, a number of pressure sensors or flow rate sensors are prepared to form a large-area sensor array, which is embedded in the aircraft composite material or installed on the surface of the structure to achieve real-time monitoring of aircraft structural surface parameters. HUANG YongAn wrote an article in Article 63, 2073–2081 (2020) titled "Conformable, programmable and step-linear sensor array for large-range wind pressure measurement on curved surface". In this article, a capacitive sensor is proposed, in which the same volume of gas is passed into the cavity of each sensor unit as a reference pressure. Changes in the flow field pressure outside the sensor unit will cause changes in capacitance, and the pressure value can be obtained by measuring the capacitance value. However, this sensor array has shortcomings: it requires external equipment to provide reference air pressure, which is not conducive to large-scale expansion and independent use of the sensor array, and will increase the additional weight of the aircraft.

[0003] The existing aerodynamic and structural health monitoring technology for the surface of aircraft structures is invasive monitoring. The embedding and fixation of sensors on the body, as well as their own rigidity and thickness, to a certain extent destroy the main structure of the aircraft and also cause aerodynamic loss. Summary of the invention

[0004] In view of the technical problems existing in the prior art, the present invention provides a flexible piezoelectric sensor array for use in aircraft and a preparation method thereof, which can be conformally attached to the complex structural surface of an aircraft without damaging the main structure of the aircraft.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is: A flexible piezoelectric sensor array used in an aircraft, comprising a lower substrate layer, a lower electrode layer, a piezoelectric sensitive layer, an upper electrode layer, an upper substrate layer and a packaging layer; The lower electrode layer is arranged on the lower substrate layer, and the upper surface of the lower electrode layer is in contact with the lower surface of the piezoelectric sensitive layer element; The upper electrode layer is arranged on the upper substrate layer, and the lower surface of the upper electrode layer is in contact with the upper surface of the piezoelectric sensitive layer element; the upper electrode layer and the lower electrode layer are both used for communicating with external testing equipment to monitor the change of sensor voltage or charge in real time; The packaging layer is embedded in the flexible piezoelectric sensor array to seal and protect the device.

[0006] Preferably, the upper substrate layer and the lower substrate layer are both made of polyimide film, and the thickness is 50um-80um.

[0007] Preferably, the upper electrode layer and the lower electrode layer are both made of aluminum.

[0008] Preferably, the piezoelectric sensitive layer is made of lead zirconate titanate piezoelectric ceramic material.

[0009] Preferably, the piezoelectric sensitive layer has a diameter of 0.8 mm, a thickness of 0.2 mm, and a cylindrical shape.

[0010] Preferably, the packaging layer is made of polydimethylsiloxane with a thickness of 0.46 mm.

[0011] Preferably, the lower substrate layer, the lower electrode layer, the upper electrode layer and the upper substrate layer are all in the shape of a serpentine island bridge structure.

[0012] The present invention also discloses a method for preparing the flexible piezoelectric sensor array applied to an aircraft as described above, comprising the steps of: S1. Prepare a glass substrate; sputter a conductive layer on the base layer; prepare a plurality of piezoelectric sensitive elements; S2, cutting the polyimide film to form a plurality of patterned base electrode layers; S3, transferring one of the patterned base electrode layers onto a glass substrate; S4, bonding the piezoelectric sensor to the base electrode layer on the glass substrate; S5, bonding another patterned substrate electrode layer onto the piezoelectric sensor; S6, spin coating a packaging layer flush with the top substrate on the glass substrate, and curing and forming; S7. Release from the glass substrate to obtain the prepared flexible piezoelectric sensor array.

[0013] Preferably, in step S1, a magnetron sputtering process is used to sputter the conductive layer onto the base layer.

[0014] Preferably, in step S4 and step S5, the piezoelectric sensor is bonded to the electrode layer by conductive epoxy resin.

[0015] Compared with the prior art, the advantages of the present invention are: The flexible piezoelectric sensor array of the present invention can be deformed and can be conformally attached to the complex structural surface of the aircraft without damaging the aircraft's main structure, thereby realizing real-time monitoring of the aircraft's aerodynamic parameters and structural health status, and further realizing intelligent control of the aircraft; the flexible piezoelectric array adopts micro-nano processing technology and flexible electronic technology, so the thickness can be made very thin, thereby reducing damage to the flow field on the structural surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall structure of the flexible piezoelectric sensor array in an embodiment of the present invention.

[0017] Figure 2 It is a schematic diagram of the layered structure of the flexible piezoelectric sensor array in an embodiment of the present invention.

[0018] Figure 3 The present invention is a flow chart of an embodiment of the method for preparing a flexible piezoelectric sensor array.

[0019] Figure 4 It is a schematic diagram of the structure of the serpentine island bridge in the present invention.

[0020] Figure 5 It is a schematic diagram of the charge distribution generated by the piezoelectric element of the present invention when it is subjected to a load.

[0021] Figure 6 It is a schematic diagram of the multi-channel multiplexing structure of the present invention.

[0022] Legend: 1. Lower substrate layer; 2. Lower electrode layer; 3. Piezoelectric sensitive layer; 4. Upper electrode layer; 5. Upper substrate layer; 6. Packaging layer. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0024] like Figure 1-Figure 2 As shown, the flexible piezoelectric sensor array for aircraft aerodynamic and structural parameter monitoring provided by the embodiment of the present invention is attached to the surface of the aircraft wing, and the specific structure includes a lower substrate layer 1, a lower electrode layer 2, a piezoelectric sensitive layer 3, an upper electrode layer 4, an upper substrate layer 5, and a packaging layer 6; The lower electrode layer 2 is disposed on the lower substrate layer 1, and the upper surface of the lower electrode layer 2 is bonded to the lower surface of the piezoelectric sensitive layer 3; The upper electrode layer 4 is disposed on the upper substrate layer 5, and the lower surface of the upper electrode layer 4 is in contact with the upper surface of the piezoelectric sensitive layer 3; the upper electrode layer 4 and the lower electrode layer 2 are used to communicate with external testing equipment to monitor the changes in sensor voltage or charge in real time; The packaging layer 6 is embedded in the entire flexible piezoelectric sensor array to seal and protect each device.

[0025] Specifically, Figure 2 As shown, the lower electrode layer 2 is used to conduct the electrical signals of the column sensors in the flexible piezoelectric sensor array, and is connected to the external testing equipment to realize the collection and processing of the sensor electrical signals; the upper electrode layer 4 is used to conduct the electrical signals of the lateral sensors in the flexible piezoelectric sensor array, and is connected to the external testing equipment to realize the collection and processing of the sensor electrical signals.

[0026] The above-mentioned substrate layers and electrode layers are all serpentine island-bridge structures, which can realize large-area expansion of the flexible piezoelectric sensor array. Figure 4 The figure shows the specific structure of the island bridge structure. The circular structures at both ends are islands (piezoelectric elements), and the snake-like winding structure in the middle is the connecting bridge, which constitutes a serpentine island bridge structure. The serpentine folded part in the middle of the serpentine island bridge structure can be released and unfolded when stretched. The narrower the serpentine line, the more folded parts, and the greater the overall expansion; this island bridge structure is made into a large rectangular array, and displacement loads are applied in two horizontal directions, and the array can be expanded to several times the original area.

[0027] The intersection of the column position where the strobe signal in the lower electrode layer 2 is located and the row position where the strobe signal in the upper electrode layer 4 is located can determine the coordinates of a single sensor. Figure 6 As shown, when the second column of the lower electrode layer 2 is scanned and selected by the acquisition system (at this time, the column is used as the negative electrode), when scanning the signals of each row of the upper electrode layer 4, it is scanned that there is an electrical signal in the second row of the upper electrode layer 4. Then the position of the sensor is the second row and the second column, that is, the coordinates in the sensor array are (2, 2).

[0028] By sequentially selecting and scanning the column and row signals, the electrical signals of all sensors in the array can be quickly collected. Figure 5 As shown, when the piezoelectric element is subjected to a load, positive and negative charges are accumulated on the two surfaces of the piezoelectric element; when collecting sensor signals, electrical signals are obtained through the upper and lower electrode layers (one layer is used as a negative electrode layer, and the other layer is used as a positive electrode layer).

[0029] The device of the present invention adopts a multi-channel multiplexing design method for the electrodes, which can improve the acquisition rate of the output signal of the flexible piezoelectric sensor array and effectively reduce the number of wires, thereby reducing the additional weight of the aircraft. Specifically, Figure 2As shown, the lower electrode layer 2 is composed of 3 column acquisition channels (1 column is 1 acquisition channel), and the upper electrode layer 4 is composed of 3 row acquisition channels (1 row is 1 acquisition channel). Figure 6 The figure shows the signal acquisition process of each sensor in the first column. When acquiring the sensor signal in the first column, column channel 1 is selected, and the acquisition system scans the rows in turn to acquire the electrical signals of each sensor. In this process, column channel 1 is equivalent to being reused. Therefore, when acquiring the sensor signal in a certain column, the column channel will be reused. Through the above-mentioned multiplexing design, the signal acquisition efficiency is improved.

[0030] like Figure 2 As shown in the figure, if the electrical signal of each sensor is output independently, 2X9=18 wires are required. In this way, if sensors are arranged on the large surface of the aircraft, the signal lead wires will be numerous, which will increase the weight of the aircraft. Figure 2 The sensor shown uses a shared electrode method, and only 3+3=6 signal lead wires are needed. When hundreds of sensors are arranged in an array on the surface of the aircraft structure, Figure 2 This design method will greatly reduce the number of wires, thereby reducing the weight of the aircraft.

[0031] Specifically, the upper substrate layer 5 and the lower substrate layer 1 are both made of polyimide (PI) film, and the thickness is 50um-80um. Of course, in other embodiments, the thickness may also be 0-100um.

[0032] The materials of the upper electrode layer 4 and the lower electrode layer 2 are both aluminum (Al), with a thickness ranging from 0 to 50 um. Of course, in other embodiments, aluminum, copper, gold and other conductive materials may also be used to replace aluminum.

[0033] The material of the piezoelectric sensitive layer 3 is lead zirconate titanate piezoelectric ceramic (PZT) or PVDF. Lead zirconate titanate piezoelectric ceramic has a high piezoelectric coefficient and electromechanical coupling coefficient, so as to obtain a self-powered, wide-bandwidth, high-sensitivity, and simple-structured array-type flexible piezoelectric sensor.

[0034] The piezoelectric sensitive layer 3 element has a diameter of 0.8 mm, a thickness of 0.2 mm, and a cylindrical shape; The material of the encapsulation layer 6 is polydimethylsiloxane (PDMS) with a thickness of 0.46 mm. It is spin-coated on the entire flexible piezoelectric sensor array structure and cured to seal and protect the device.

[0035] Working principle: Reference Figure 1As shown, the sensor array is bonded to the wing surface. When the piezoelectric sensitive layer 3 is subjected to the pressure of the airflow on the wing surface, polarization occurs inside the piezoelectric sensitive element, converting the pressure change into charge or voltage change. The upper electrode layer 4 and the lower electrode layer 2 are connected to the external test equipment. According to the linear relationship between pressure and charge or voltage, the magnitude of the measured pressure can be obtained.

[0036] Among them, flexible pressure sensors are generally divided into three types according to their working mechanism, including capacitive, piezoresistive and piezoelectric. Compared with the other two sensors, piezoelectric sensors can achieve self-power supply and have the advantages of wide bandwidth, high sensitivity, high signal-to-noise ratio and simple structure. Piezoelectric pressure sensors use the piezoelectric effect of piezoelectric elements to convert the measured pressure into an electrical signal. The piezoelectric effect refers to the phenomenon that when a piezoelectric material is subjected to an external force, an electric polarization phenomenon is generated inside, so that the same number of positive and negative charges are generated on the upper and lower surfaces of the piezoelectric material. The amount of charge or the voltage on both sides is in a certain proportional relationship with the force, which can be amplified by a charge amplifier or a voltage amplifier and converted into a voltage or current output. According to the output voltage or current signal finally collected, the corresponding measured pressure value can be obtained.

[0037] like Figure 3 As shown, the method for preparing a flexible piezoelectric sensor array for aircraft aerodynamic and structural parameter monitoring provided by an embodiment of the present invention is performed according to the following steps: S1. See Figure 3 As shown in (a), a glass substrate is prepared; a conductive layer (such as an aluminum layer) with a thickness of 20 μm is sputtered on the PI film (as a base layer) by a magnetron sputtering process; and a number of piezoelectric sensitive elements with a thickness of 0.2 mm are prepared; S2. See Figure 3 As shown in (b), the PI film is cut with a micro-cutting machine to form two patterned flexible PI substrates and electrodes; S3. See Figure 3 As shown in (c), one of the patterned PI substrates is transferred to a glass substrate; S4. See Figure 3 As shown in (d), the piezoelectric sensor is bonded to the electrode of the flexible substrate using conductive epoxy resin; S5. See Figure 3 As shown in (e), the electrode side of another flexible substrate is bonded to the piezoelectric sensor with conductive epoxy resin; S6. See Figure 3 As shown in (f), a certain area of ​​PDMS flush with the top PI substrate is spin-coated on the glass substrate and cured; S7, see Figure 3 As shown in (g), the prepared flexible piezoelectric sensor array is released from the glass substrate.

[0038] In summary, the present invention has simple structural design and processing technology, and has the characteristics of ultra-thin device thickness, wide-band response, high scalability, high sensitivity, high resolution, high sampling rate and little impact on the flow field. It can measure the pressure distribution on the wing surface over a large area, which is of great significance for the prevention of aircraft flow separation and stall.

[0039] The flexible piezoelectric sensor array of the present invention can be deformed and can be conformally attached to the complex structural surface of the aircraft without damaging the aircraft's main structure, thereby realizing real-time monitoring of the aircraft's aerodynamic parameters and structural health status, and further realizing intelligent control of the aircraft; the flexible piezoelectric array adopts micro-nano processing technology and flexible electronic technology, so the thickness can be made very thin, thereby reducing damage to the flow field on the structural surface.

[0040] Glossary: Flexible electronics technology: Flexible electronics technology refers to the technology of manufacturing electronic devices with materials that can be bent, folded or stretched. This technology enables electronic products to adapt to surfaces of various shapes, thus opening up application areas that cannot be achieved with traditional rigid circuit boards; Micro-nano processing technology: Micro-nano processing technology refers to the technology of precise processing of materials at the micron and nanometer scales, including magnetron sputtering, photolithography, electron beam direct writing, etc. PVDF: polyvinylidene fluoride.

[0041] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0042] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0043] In the present invention, unless otherwise clearly specified and limited, the terms "assemble", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0044] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A flexible piezoelectric sensor array used in an aircraft, characterized in that: It comprises a lower substrate layer (1), a lower electrode layer (2), a piezoelectric sensitive layer (3), an upper electrode layer (4), an upper substrate layer (5) and a packaging layer (6); The lower electrode layer (2) is arranged on the lower substrate layer (1), and the upper surface of the lower electrode layer (2) is bonded to the lower surface of the piezoelectric sensitive layer (3) element; The upper electrode layer (4) is arranged on the upper substrate layer (5), and the lower surface of the upper electrode layer (4) is in contact with the upper surface of the piezoelectric sensitive layer (3) element; the upper electrode layer (4) and the lower electrode layer (2) are both used for connecting with external testing equipment to monitor the change of sensor voltage or charge in real time; The packaging layer (6) is embedded in the flexible piezoelectric sensor array and is used to seal and protect the device.

2. The flexible piezoelectric sensor array used in an aircraft according to claim 1, characterized in that: The upper substrate layer (5) and the lower substrate layer (1) are both made of polyimide film, and the thickness is 50 um to 80 um.

3. The flexible piezoelectric sensor array used in an aircraft according to claim 1, characterized in that: The materials of the upper electrode layer (4) and the lower electrode layer (2) are both aluminum.

4. The flexible piezoelectric sensor array used in an aircraft according to claim 1, 2 or 3, characterized in that: The piezoelectric sensitive layer (3) is made of lead zirconate titanate piezoelectric ceramic material.

5. The flexible piezoelectric sensor array used in an aircraft according to claim 4, characterized in that: The piezoelectric sensitive layer (3) has a diameter of 0.8 mm, a thickness of 0.2 mm, and a cylindrical shape.

6. The flexible piezoelectric sensor array used in an aircraft according to claim 1, 2 or 3, characterized in that: The material of the packaging layer (6) is polydimethylsiloxane, and the thickness is 0.46 mm.

7. The flexible piezoelectric sensor array used in an aircraft according to claim 1, 2 or 3, characterized in that: The lower substrate layer (1), the lower electrode layer (2), the upper electrode layer (4) and the upper substrate layer (5) are all in the shape of a serpentine island bridge structure.

8. A method for preparing a flexible piezoelectric sensor array for use on an aircraft based on any one of claims 1 to 7, characterized in that: Includes steps: S1. Prepare a glass substrate; sputter a conductive layer on the base layer; prepare a plurality of piezoelectric sensitive elements; S2, cutting the polyimide film to form a plurality of patterned base electrode layers; S3, transferring one of the patterned base electrode layers onto a glass substrate; S4, bonding the piezoelectric sensor to the base electrode layer on the glass substrate; S5, bonding another patterned substrate electrode layer onto the piezoelectric sensor; S6, spin coating a packaging layer (6) flush with the top substrate on the glass substrate, and curing to form; S7. Release from the glass substrate to obtain the prepared flexible piezoelectric sensor array.

9. The preparation method according to claim 8, characterized in that: In step S1 , a conductive layer is sputtered onto the base layer using a magnetron sputtering process.

10. The preparation method according to claim 8 or 9, characterized in that: In step S4 and step S5, the piezoelectric sensor is bonded to the electrode layer by means of conductive epoxy resin.

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