Flexible conformal piezoelectric strain sensor

Abstract

The invention discloses a flexible conformal piezoelectric strain sensor which comprises a flexible piezoelectric film strain sensing unit (1) and a flexible signal processing circuit (2). The flexible piezoelectric film strain sensing unit (1) and the flexible signal processing circuit (2) are integrated in a near-in-situ flexible connection mode; the flexible piezoelectric film strain sensing unit (1) comprises a piezoelectric film (1-1), an upper electrode layer (1-2), a lower electrode layer (1-3), an insulating layer (1-4) and a shielding layer (1-5); the upper electrode layer (1-2) and the lower electrode layer (1-3) respectively cover the upper surface and the lower surface of the piezoelectric film (1-1) to form a capacitor structure; the insulating layer (1-4) covers the upper electrode layer (1-2) and the lower electrode layer (1-3) respectively; and the shielding layer (1-5) covers the insulating layer (1-4). The invention provides a flexible strain sensor, which adopts a high-sensitivity adaptive design method, takes a piezoelectric polymer film as a strain sensing unit, and is in near-in-situ flexible connection with a flexible signal processing circuit, so that the flexible conformality of the sensor is realized, and the sensitivity is considered.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible strain sensor, in particular to a flexible conformal piezoelectric strain sensor. BACKGROUND

[0002] The strain of physical structure surface is very important in manufacturing processing, structure engineering and other fields. A variety of strain gauges with different characteristics can be respectively applied to most strain detection environments, but they still cannot meet the requirements of flexibility, conformality, high performance and low cost at the same time, and they also perform poorly in high-frequency strain detection. The thin film strain sensor made of piezoelectric polymer material (such as polyvinylidene fluoride (PVDF) and its copolymer) has the advantages of flexibility, high-frequency response, simple structure and process, low cost, and can conform to the measured structure to realize strain measurement without weakening the rigidity of the measured structure.

[0003] However, in order to realize high spatial resolution strain sensing and flexibility, a small area (such as a few square millimeters) of a piezoelectric thin film with a relatively thin thickness (such as 10-100 microns) is usually used to generate an electric signal. In order to maintain good flexibility, the thickness of the device needs to be reduced, and the sensitive element can only use a single layer of piezoelectric film, and in order to improve the spatial resolution, the sensitive element needs to use a smaller area. Under this design requirement, the electric signal generated by the sensitive element is very weak and is easily affected by parasitic capacitance, thereby reducing the sensitivity of the sensor. And it is more susceptible to external noise interference, which further affects the reading accuracy of the signal. In particular, when the sensor is applied to the surface of a metal structure, the electrode layer is easy to form a capacitor structure with the surface of the metal structure, which may significantly reduce the sensitivity of the sensor. SUMMARY

[0004] The purpose of the present application is to provide a flexible conformal piezoelectric strain sensor, which includes a flexible piezoelectric thin film strain sensing unit and a flexible signal processing circuit.

[0005] The flexible piezoelectric thin film strain sensing unit and the flexible signal processing circuit are integrated by near-in-situ flexible connection.

[0006] The flexible piezoelectric thin film strain sensing unit includes a piezoelectric thin film, an upper electrode layer, a lower electrode layer, an insulating layer, and a shielding layer.

[0007] The upper electrode layer and the lower electrode layer are respectively covered on the upper and lower surfaces of the piezoelectric thin film to form a capacitor structure.

[0008] The insulating layer is respectively covered on the upper electrode layer and the lower electrode layer.

[0009] The shielding layer is covered on the insulating layer.

[0010] Further, the circuit topology of the flexible signal processing circuit is as follows:

[0011] The circuit signal input interface group CONN1 is used for flexible connection with the flexible piezoelectric film strain sensing unit.

[0012] The 1st terminal and the 4th terminal of the circuit signal input interface group CONN1 are grounded.

[0013] The 2nd terminal of the circuit signal input interface group CONN1 is connected with the gate of the junction field effect transistor Q11.

[0014] The 2nd terminal of the circuit signal input interface group CONN1 is grounded after being connected with the resistance R12 in series.

[0015] The source of the junction field effect transistor Q11 is grounded after being connected with the source resistance R11 in series.

[0016] One end of the drain resistance R13 is connected with an external power supply, and the other end is connected with the drain of the junction field effect transistor Q11.

[0017] The source of the junction field effect transistor Q11 is connected with the 3rd terminal of the circuit signal output interface group CONN2.

[0018] The 3rd terminal of the circuit signal input interface group CONN1 is connected with the gate of the junction field effect transistor Q21.

[0019] The 3rd terminal of the circuit signal input interface group CONN1 is grounded after being connected with the resistance R22.

[0020] The source of the junction field effect transistor Q21 is grounded after being connected with the source resistance R21 in series.

[0021] One end of the drain resistance R23 is connected with an external power supply, and the other end is connected with the drain of the junction field effect transistor Q21.

[0022] The source of the junction field effect transistor Q21 is connected with the 2nd terminal of the circuit signal output interface group CONN2.

[0023] The 1st terminal of the circuit signal output interface group CONN2 is grounded, and the 4th terminal is connected with an external power supply.

[0024] Further, the leakage current of the gate to the source of the junction field effect transistor should be ≤1pA, and the gate input capacitance should be ≤1pF.

[0025] The resistance value of the gate parallel resistance should be ≥50G ohms.

[0026] Further, the flexible piezoelectric film strain sensing unit and the flexible signal processing circuit are realized near in-situ flexible integration through the flexible connection interface and conductive glue.

[0027] Further, the piezoelectric thin film includes but is not limited to a piezoelectric polymer thin film, a piezoelectric ceramic thin film, and an inorganic non-ceramic piezoelectric thin film.

[0028] The piezoelectric polymer thin film includes but is not limited to a polyvinylidene fluoride thin film and a polyvinylidene fluoride copolymer thin film.

[0029] The piezoelectric ceramic thin film includes a lead zirconate titanate thin film.

[0030] The inorganic non-ceramic piezoelectric thin film includes a zinc oxide thin film.

[0031] The material of the upper electrode layer, the lower electrode layer, and the shielding layer includes but is not limited to one or more of Al, Cu, Ag, Ti / Au, and Cr / Au.

[0032] The preparation method of the upper electrode layer and the lower electrode layer includes but is not limited to vacuum evaporation plating, sputtering plating process, and electrode pasting method.

[0033] The preparation method of the shielding layer includes but is not limited to vacuum evaporation plating and sputtering plating process.

[0034] Further, the upper electrode layer or the lower electrode layer is a patterned electrode layer located on the same plane.

[0035] Further, the upper electrode layer and the lower electrode layer are patterned or arrayed electrode layers, each having a plurality of strain sensing sensitive surface units.

[0036] Further, the upper electrode layer is provided with a signal output interface, and the lower electrode layer is provided with a grounding interface.

[0037] The upper electrode layer is not conductive between the strain sensing sensitive surface units.

[0038] The lower electrode layer is conductive between the strain sensing sensitive surface units.

[0039] Further, the upper electrode layer is provided with a grounding interface, and the lower electrode layer is provided with a signal output interface.

[0040] The upper electrode layer is conductive between the strain sensing sensitive surface units.

[0041] The lower electrode layer is not conductive between the strain sensing sensitive surface units.

[0042] Further, a protective layer is further included.

[0043] The protective layer covers the surface of the shielding layer and protects the device as a whole.

[0044] The technical effect of the present application is self-evident, and the present application provides a flexible strain sensor, which adopts a high-sensitivity adaptive design method, uses a piezoelectric polymer film as a strain sensing sensitive unit, and is flexibly connected with a flexible signal processing circuit in situ to realize flexible conformal of the sensor and take into account the sensitivity.

[0045] The present application can greatly reduce the parasitic capacitance between the sensitive surface unit and the signal processing circuit, and also reduce the interference of external noise, thereby realizing the consideration of the flexible conformal ability and high sensitivity of the sensor.

[0046] The strain sensing sensitive surface unit can be designed in combination with the measured physical structure features, and the present application can realize high spatial resolution, high sensitivity, and in-situ conformal accurate measurement of the strain of any physical structure surface. Compared with the design of the resistance strain gauge, the present application is simpler and easier, does not need complex signal conditioning, and has lower cost and workload, and is more widely applicable to structures. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 It is a structure diagram and a top view of a flexible piezoelectric film strain sensing unit of the flexible conformal piezoelectric strain sensor.

[0048] Figure 2 It is a structure diagram of a flexible piezoelectric film strain sensing unit adopting a full-face lower electrode.

[0049] Figure 3 It is a conformal diagram of the flexible piezoelectric film strain sensing unit and the curved measured physical structure.

[0050] Figure 4 It is a schematic diagram of a double-channel flexible signal processing circuit.

[0051] Figure 5 It is a physical diagram of a double-channel flexible signal processing circuit.

[0052] Figure 6 It is a flexible connection interface structure diagram.

[0053] Figure 7 It is a schematic diagram of application of the flexible conformal piezoelectric strain sensor to milling cutter strain test.

[0054] Figure 8 It is a schematic diagram of application of the flexible conformal piezoelectric strain sensor to bearing strain test.

[0055] In the figure: flexible piezoelectric film strain sensing unit 1, piezoelectric film 1-1, upper electrode layer 1-2, lower electrode layer 1-3, insulating layer 1-4, shielding layer 1-5, protective layer 1-6, signal output interface 1-2-1, signal output interface 1-2-2, ground interface 1-3-1, measured physical structure 4, flexible signal processing circuit 2, circuit signal input interface group CONN1, circuit signal output interface group CONN2, junction field effect transistor Q11, junction field effect transistor Q21, source resistance R11, source resistance R21, drain resistance R13, drain resistance R23, gate parallel resistance R12, gate parallel resistance R22, circuit flexible substrate 2-1, circuit conductor 2-2, flexible connection interface and conductive silver paste 3, flat plate electrode interface C-1, circular through-hole electrode interface C-2, circular through-hole electrode interface C-3, flat plate electrode interface C-4, milling cutter 5, bearing 6. DETAILED DESCRIPTION

[0056] The application will be further described below in conjunction with examples, but should not be understood as limiting the above-mentioned subject matter of the application to the following examples. Various substitutions and modifications can be made according to ordinary technical knowledge and conventional means in the art without departing from the above-mentioned technical idea of the application, and all should be included in the protection scope of the application.

[0057] Example 1

[0058] Reference Figures 1 to 6 , the flexible piezoelectric film strain sensing unit 1 and the flexible signal processing circuit 2.

[0059] The flexible piezoelectric film strain sensing unit 1 and the flexible signal processing circuit 2 are integrated by near-in-situ flexible connection.

[0060] The flexible piezoelectric film strain sensing unit 1 includes a piezoelectric film 1-1, an upper electrode layer 1-2, a lower electrode layer 1-3, an insulating layer 1-4, and a shielding layer 1-5.

[0061] The upper electrode layer 1-2 and the lower electrode layer 1-3 are respectively covered on the upper and lower surfaces of the piezoelectric film 1-1 to form a capacitor structure.

[0062] The insulating layer 1-4 is respectively covered on the upper electrode layer 1-2 and the lower electrode layer 1-3.

[0063] The shielding layer 1-5 is covered on the insulating layer 1-4.

[0064] The circuit topology of the flexible signal processing circuit 2 is as follows:

[0065] The circuit signal input interface group CONN1 is used for flexible connection with the flexible piezoelectric film strain sensing unit 1;

[0066] The No. 1 terminal and the No. 4 terminal of the circuit signal input interface group CONN1 are grounded.

[0067] The No. 2 terminal of the circuit signal input interface group CONN1 is connected to the gate of the junction field effect transistor Q11.

[0068] The No. 2 terminal of the circuit signal input interface group CONN1 is connected to the gate of the junction field effect transistor Q11.

[0069] The source of the junction field effect transistor Q11 is connected to the No. 3 terminal of the circuit signal output interface group CONN2.

[0070] One end of the drain resistor R13 is connected to an external power supply, and the other end is connected to the drain of the junction field effect transistor Q11.

[0071] The source of the junction field effect transistor Q11 is connected to the No. 3 terminal of the circuit signal output interface group CONN2.

[0072] The No. 3 terminal of the circuit signal input interface group CONN1 is connected to the gate of the junction field effect transistor Q21.

[0073] The No. 3 terminal of the circuit signal input interface group CONN1 is connected to the gate of the junction field effect transistor Q21.

[0074] The source of the junction field effect transistor Q21 is connected to the No. 2 terminal of the circuit signal output interface group CONN2.

[0075] One end of the drain resistor R23 is connected to an external power supply, and the other end is connected to the drain of the junction field effect transistor Q21.

[0076] The source of the junction field effect transistor Q21 is connected to the No. 3 terminal of the circuit signal output interface group CONN2.

[0077] The No. 1 terminal of the circuit signal output interface group CONN2 is grounded, and the No. 4 terminal is connected to an external power supply.

[0078] The gate-to-source leakage current of the junction field effect transistor should be ≤1 pA, and the gate input capacitance should be ≤1 pF.

[0079] The gate parallel resistor has a resistance value ≥50 G ohms.

[0080] The flexible piezoelectric thin film strain sensing unit 1 and the flexible signal processing circuit 2 are realized by near-in-situ flexible integration through a flexible connection interface and conductive glue.

[0081] The piezoelectric thin film 1-1 includes but is not limited to a piezoelectric polymer thin film, a piezoelectric ceramic thin film, and an inorganic non-ceramic piezoelectric thin film 1-1.

[0082] The piezoelectric polymer thin film includes but is not limited to a polyvinylidene fluoride thin film and a polyvinylidene fluoride copolymer thin film.

[0083] The piezoelectric ceramic film comprises a lead zirconate titanate film.

[0084] The inorganic non-ceramic piezoelectric film 1-1 comprises a zinc oxide film.

[0085] The material of the upper electrode layer 1-2, the lower electrode layer 1-3 and the shielding layer 1-5 comprises one or more of Al, Cu, Ag, Ti / Au, Cr / Au, but is not limited thereto.

[0086] The preparation method of the upper electrode layer 1-2 and the lower electrode layer 1-3 comprises vacuum evaporation plating, sputtering plating process, and electrode pasting method, but is not limited thereto.

[0087] The preparation method of the shielding layer 1-5 comprises vacuum evaporation plating and sputtering plating process, but is not limited thereto.

[0088] The upper electrode layer 1-2 or the lower electrode layer 1-3 is a patterned electrode layer located in the same plane; the sensitive surface element electrodes for collecting electrical signals, the interfaces and the electrode traces therebetween in the upper electrode layer 1-2 or the lower electrode layer 1-3 are located in the same plane.

[0089] The upper electrode layer 1-2 and the lower electrode layer 1-3 are patterned or arrayed electrode layers, each having a plurality of strain sensing sensitive surface elements.

[0090] The upper electrode layer 1-2 is provided with a signal output interface 1-2-1, and the lower electrode layer 1-3 is provided with a grounding interface 1-3-1.

[0091] The upper electrode layer 1-2 is provided with a signal output interface 1-2-1, and the lower electrode layer 1-3 is provided with a grounding interface 1-3-1.

[0092] The lower electrode layer 1-3 is provided with a signal output interface 1-2-1, and the upper electrode layer 1-2 is provided with a grounding interface 1-3-1.

[0093] The upper electrode layer 1-2 is provided with a signal output interface 1-2-1, and the lower electrode layer 1-3 is provided with a grounding interface 1-3-1.

[0094] The upper electrode layer 1-2 is provided with a signal output interface 1-2-1, and the lower electrode layer 1-3 is provided with a grounding interface 1-3-1.

[0095] The lower electrode layer 1-3 is provided with a signal output interface 1-2-1, and the upper electrode layer 1-2 is provided with a grounding interface 1-3-1.

[0096] A protective layer 1-6 is further included.

[0097] The protective layer 1-6 covers the surface of the shielding layer 1-5 and protects the device as a whole.

[0098] Embodiment 2:

[0099] A flexible conformal piezoelectric strain sensor comprises a flexible piezoelectric film strain sensing unit 1 and a flexible signal processing circuit 2.

[0100] The flexible piezoelectric film strain sensing unit 1 and the flexible signal processing circuit 2 are integrated through a near-in-situ flexible connection method.

[0101] The flexible piezoelectric film strain sensing unit 1 includes a piezoelectric film 1-1, an upper electrode layer 1-2, a lower electrode layer 1-3, an insulating layer 1-4, and a shielding layer 1-5.

[0102] The upper electrode layer 1-2 and the lower electrode layer 1-3 respectively cover the upper and lower surfaces of the piezoelectric film 1-1 to form a capacitor structure.

[0103] The insulating layers 1-4 cover the upper electrode layer 1-2 and the lower electrode layer 1-3 respectively.

[0104] The shielding layer 1-5 covers the insulating layer 1-4.

[0105] Example 3:

[0106] The flexible conformal piezoelectric strain sensor has the same technical content as Example 2. Furthermore, the circuit topology of the flexible signal processing circuit 2 is as follows:

[0107] The circuit signal input interface group CONN1 is used for flexible connection with the flexible piezoelectric film strain sensing unit 1;

[0108] Terminals 1 and 4 of the circuit signal input interface group CONN1 are grounded;

[0109] Terminal 2 of the circuit signal input interface group CONN1 is connected to the gate of the junction field effect transistor Q11;

[0110] Connect the No. 2 terminal of the circuit signal input interface group CONN1 in series with resistor R12 and then to ground;

[0111] The source of the junction field effect transistor Q11 is connected in series with the source resistor R11 and then grounded;

[0112] One end of the drain resistor R13 is connected to the external power supply, and the other end is connected to the drain of the junction field effect transistor Q11;

[0113] The source of the junction field effect transistor Q11 is connected to terminal 3 of the circuit signal output interface group CONN2;

[0114] Terminal 3 of the circuit signal input interface group CONN1 is connected to the gate of the junction field effect transistor Q21;

[0115] Connect the No. 3 terminal of the circuit signal input interface group CONN1 to the resistor R22 and then to the ground;

[0116] The source of the junction field effect transistor Q21 is connected in series with the source resistor R21 and grounded;

[0117] One end of the drain resistor R23 is connected to an external power supply, and the other end is connected to the drain of the junction field effect transistor Q21;

[0118] The source of the junction field effect transistor Q21 is connected to the 2nd terminal of the circuit signal output interface group CONN2;

[0119] The 1st terminal of the circuit signal output interface group CONN2 is grounded, and the 4th terminal is connected to an external power supply.

[0120] Embodiment 4:

[0121] The flexible conformal piezoelectric strain sensor, the technical content is the same as any one of embodiments 2-3, further, the leakage current from the gate to the source of the junction field effect transistor should be ≤1pA, and the gate input capacitance should be ≤1pF.

[0122] The resistance value of the gate parallel resistor is ≥50G ohms.

[0123] Embodiment 5:

[0124] The flexible conformal piezoelectric strain sensor, the technical content is the same as any one of embodiments 2-4, further, the flexible piezoelectric film strain sensing unit 1 and the flexible signal processing circuit 2 are realized by a flexible connection interface and conductive glue to achieve near in-situ flexible integration.

[0125] Embodiment 6:

[0126] The flexible conformal piezoelectric strain sensor, the technical content is the same as any one of embodiments 2-5, further, the piezoelectric film 1-1 includes but is not limited to a piezoelectric polymer film, a piezoelectric ceramic film, and an inorganic non-ceramic piezoelectric film 1-1.

[0127] The piezoelectric polymer film includes but is not limited to a polyvinylidene fluoride film and a polyvinylidene fluoride copolymer film.

[0128] The piezoelectric ceramic film includes a lead zirconate titanate film.

[0129] The inorganic non-ceramic piezoelectric film 1-1 includes a zinc oxide film.

[0130] Embodiment 7:

[0131] The flexible conformal piezoelectric strain sensor, the technical content is the same as any one of embodiments 2-6, further, the materials of the upper electrode layer 1-2, the lower electrode layer 1-3, and the shielding layer 1-5 include but are not limited to one or more of Al, Cu, Ag, Ti / Au, and Cr / Au.

[0132] The preparation method of the upper electrode layer 1-2 and the lower electrode layer 1-3 includes but is not limited to vacuum evaporation plating, sputtering plating process, and electrode pasting method.

[0133] The preparation method of the shielding layer 1-5 includes but is not limited to vacuum evaporation plating and sputtering plating process.

[0134] Embodiment 8:

[0135] The flexible conformal piezoelectric strain sensor has the technical content of any one of Embodiments 2-7, and further, the upper electrode layer 1-2 or the lower electrode layer 1-3 is a patterned electrode located on the same plane; in the upper electrode layer 1-2 or the lower electrode layer 1-3, the sensitive surface element electrodes for collecting electrical signals, the interfaces, and the electrode traces therebetween are located on the same plane.

[0136] Embodiment 9:

[0137] The flexible conformal piezoelectric strain sensor has the technical content of any one of Embodiments 2-8, and further, the upper electrode layer 1-2 and the lower electrode layer 1-3 are patterned or arrayed electrode layers, each having a plurality of strain sensing sensitive surface elements.

[0138] Embodiment 10:

[0139] The flexible conformal piezoelectric strain sensor has the technical content of any one of Embodiments 2-8, and further, the upper electrode layer 1-2 is provided with a signal output interface 1-2-1, and the lower electrode layer 1-3 is provided with a grounding interface 1-3-1.

[0140] The strain sensing sensitive surface element electrodes of the upper electrode layer 1-2 are not conductive to each other.

[0141] The strain sensing sensitive surface element electrodes of the lower electrode layer 1-3 are conductive to each other.

[0142] Embodiment 11:

[0143] The flexible conformal piezoelectric strain sensor has the technical content of any one of Embodiments 2-10, and further, the upper electrode layer 1-2 is provided with a grounding interface 1-3-1, and the lower electrode layer 1-3 is provided with a signal output interface 1-2-1.

[0144] The strain sensing sensitive surface element electrodes of the upper electrode layer 1-2 are conductive to each other.

[0145] The strain sensing sensitive surface element electrodes of the lower electrode layer 1-3 are not conductive to each other.

[0146] Embodiment 12:

[0147] The flexible conformal piezoelectric strain sensor has the technical content of any one of Embodiments 2-11, and further, the flexible conformal piezoelectric strain sensor further comprises a protective layer 1-6.

[0148] The protective layer 1-6 covers the surface of the shielding layer 1-5, and the device is integrally encapsulated and protected.

[0149] Embodiment 13:

[0150] The flexible conformal piezoelectric strain sensor comprises a flexible piezoelectric film strain sensing unit and a flexible signal processing circuit.

[0151] The high-sensitivity adaptive design method is characterized in that the design for improving the sensitivity of the sensor needs to adapt to the requirements of structural flexibility, conformality and high spatial resolution strain sensing.

[0152] The flexible piezoelectric film strain sensing unit and the flexible signal processing circuit are realized by near-in-situ flexible integration through a flexible connection interface and conductive glue.

[0153] The flexible piezoelectric film strain sensing unit is composed of a piezoelectric film, upper and lower electrode layers, an insulating layer, a shielding layer and a protective layer.

[0154] The piezoelectric film should have good mechanical flexibility, including but not limited to: piezoelectric polymer film (such as polyvinylidene fluoride (PVDF) film and its copolymer film, etc.), piezoelectric ceramic film (such as lead zirconate titanate (PZT) film, etc.), inorganic non-ceramic piezoelectric film (such as zinc oxide (ZnO) film, etc.), etc.

[0155] The piezoelectric film can be cut to any size as needed, and the upper and lower electrode layers are prepared on the upper and lower surfaces of the piezoelectric film by patterning or arraying, respectively, to form individual strain sensing sensitive surface elements. The shape and number of surface elements are designed according to application requirements.

[0156] The upper and lower electrode layers cover the upper and lower surfaces of the piezoelectric film to form a capacitor structure, and the insulating layer and the shielding layer are sequentially covered on the upper and lower electrode layers. The shielding layer is further encapsulated and protected by the protective layer.

[0157] The upper and lower electrode layers and the shielding layer can be made of metals including but not limited to Al, Cu, Ag, Ti / Au, Cr / Au or metal combinations, which require good electrical conductivity and physical and chemical stability.

[0158] The upper and lower electrode layers and the shielding layer require good combination with the material of the previous layer, sufficient thickness and flexibility, and do not fail after repeated bending.

[0159] The failure means that the electrical performance does not decrease significantly, which affects signal reading and shielding effect.

[0160] The upper and lower electrode layers and the shielding layer can be prepared by vacuum evaporation plating, sputtering plating process and electrode pasting method, and the type and thickness of the metal can be selected.

[0161] The upper electrode layer or the lower electrode layer is the same face patterned electrode, including sensitive face element electrodes for collecting electrical signals, interfaces and electrode traces therebetween.

[0162] If the signal output interface is arranged on the upper electrode layer, a grounding interface is arranged on the lower electrode layer, both of which are interchangeable, and all interfaces are connected with the flexible signal processing circuit through flexible connection interfaces to realize high-sensitivity reading of electrical signals.

[0163] The length of the interface connected with the upper and lower electrode layers can be adjusted, and should be as short as possible under the premise of meeting the connection requirements and not interfering with the sensitive elements.

[0164] The electrode traces and interfaces should be as small as possible in width under the premise of meeting the conduction and connection requirements.

[0165] The upper electrode layer on which the signal output interface is arranged is not conductive between the sensitive face element electrodes, while the lower electrode layer on which the grounding interface is arranged can be designed to be conductive between the sensitive face element electrodes to simplify the number of interfaces.

[0166] The insulation layer insulates and isolates the upper and lower electrode layers from the shielding layer, and is required to have good insulation and flexibility under the premise of being as thin as possible. It can be prepared by soaking, spraying, spin coating, adhesive, heat sealing and other processes.

[0167] The protection layer has the same requirements and preparation process as the insulation layer, in addition, it is also required to have sufficient mechanical properties, corrosion resistance, wear resistance and other properties to be able to play a sufficient protection role.

[0168] According to the working environment and requirements, if the shielding layer is stable and meets the requirements of protecting the sensor, the protection layer can no longer be prepared.

[0169] The protection layer is used to protect the overall sensor device, including protecting the overall sensitive face element, or protecting part or the entire flexible signal processing circuit.

[0170] The flexible signal processing circuit is composed of a flexible circuit board and electronic elements.

[0171] (1) In terms of circuit design, the signal processing circuit design is simplified, a voltage reading method is adopted to convert the charge signal generated by the strain sensitive face element into a voltage signal for reading, and impedance matching is realized at the same time.

[0172] (2) In terms of circuit preparation, a combination of flexible printed circuit board and electronic elements with as small size as possible is adopted, and the layout of electronic elements is optimized according to the conformal requirements of application scenarios.

[0173] (3) In the interface design: design the through-hole electrode and the flat electrode on the flexible circuit to realize the flexible connection between the electrodes on the two surfaces of the piezoelectric film and the circuit.

[0174] The simplified signal processing circuit design can reduce the number of electronic components, thereby reducing the influence of the electronic components on the flexibility of the circuit.

[0175] The impedance matching refers to the input impedance of the rear-stage circuit being much larger than the output impedance of the front-stage.

[0176] The impedance matching is realized by adopting an emitter follower circuit composed of a junction field effect transistor (JFET), a source resistor and a drain resistor.

[0177] The leakage current from the gate to the source of the JFET should be ≤1 pA, and the gate input capacitance should be ≤1 pF.

[0178] The working point of the JFET is selected by adjusting the resistance values of the source resistor and the drain resistor, so as to realize the level matching between the signal reading circuit and the rear-stage circuit. The resistance value of the source-drain resistor is selected in the range of tens of K ohms to hundreds of K ohms.

[0179] In particular, the gate parallel resistor is used to avoid the floating of the gate potential, so as to realize the stable working point of the JFET. The resistance value of the gate parallel resistor is selected in the range of ≥50 G ohms.

[0180] In summary, the piezoelectric polymer film with light weight, high mechanical flexibility, good processability and chemical stability is adopted, and the strain sensing sensitive surface element is designed according to the characteristics of the measured physical structure surface, so as to improve the spatial resolution of strain detection. In order to suppress the influence of the parasitic capacitance, the sensor is designed according to the principle of minimum parasitic capacitance: first, the strain sensing part is combined with the flexible signal processing circuit in a near-in-situ flexible connection mode, so as to maximize the length of the signal output to the signal input; second, the electrode layout of the sensitive surface element electrode to its respective interface is optimized according to the surface element structure, so as to reduce the introduction of parasitic capacitance, that is, the shortest and least crossing of the upper and lower electrode traces. At the same time, since the length of the connecting line is shortened, the sensitive element is less susceptible to external noise interference, which also improves the accuracy of the device. The present application can significantly reduce the parasitic capacitance and external noise interference, improve the sensitivity, and realize the conformal sensing of the sensor and the structure surface with high spatial resolution and high sensitivity.

[0181] Example 14:

[0182] The flexible conformal piezoelectric strain sensor comprises a flexible piezoelectric film strain sensing unit and a flexible signal processing circuit.

[0183] Figure 11 shows a structural diagram of the flexible piezoelectric film strain sensing unit 1, 2 shows a top view of its upper and lower electrode layers, and 3 shows a decomposition diagram of the upper and lower electrode layers in 2.

[0184] like Figure 1 As shown in Figure 1, the flexible piezoelectric film strain sensing unit 1 consists of a piezoelectric film 1-1, upper and lower electrode layers 1-2 and 1-3, an insulating layer 1-4, a shielding layer 1-5, and a protective layer 1-6. Two sensitive elements are shown in this example, but this is not limited to two. PVDF is used as the piezoelectric film 1-1. 20nm Ti / 50nm Au is deposited on its upper and lower surfaces using a mask and sputtering process as electrode layers 1-2 and 1-3. Then, an insulating layer 1-4 is formed using a plastic encapsulation process. 20nm Ti / 50nm Au is deposited on both sides of the insulating layer using a sputtering process as shielding layer 1-5. Finally, the protective layer 1-6 is plastic encapsulated.

[0185] like Figure 1 As shown in Figure II, the electrode layer is divided into an upper electrode layer 1-2 and a lower electrode layer 1-3. Each electrode layer includes sensitive surface element electrodes for collecting electrical signals, interfaces, and electrode traces therebetween. In this embodiment, the signal output interfaces 1-2-1 and 1-2-2 are provided in the upper electrode layer 1-2, and the grounding interface 1-3-1 is provided in the lower electrode layer 1-3. The sensitive surface element electrodes in the upper and lower electrode layers 1-2 and 1-3 are squares with a side length of 2 mm, an electrode trace width of 0.2 mm, an interface width of 0.5 mm, and the interface portion has a relatively long redundant length so that it can be cut as needed. The axes of the upper and lower electrodes are staggered as much as possible, the distance between them is as short as possible, and arc transitions are adopted. A 0.1 mm chamfer is adopted at each connection point.

[0186] like Figure 1 As shown in III, the two sensitive surface elements of the upper electrode layer 1-2 are separated from each other, and the two sensitive surface elements of the lower electrode layer 1-3 are connected through an electrode line.

[0187] like Figure 2 As shown, when the sensor is applied to a non-metallic structure to be measured, in order to simplify the electrode preparation process, a 20nm Ti / 50nm Au layer is directly prepared as the entire lower electrode 1-3 by sputtering without using a mask.

[0188] like Figure 3 As shown, the prepared flexible piezoelectric film strain sensing unit 1 can be conformally attached to the surface of the physical structure 4 to be measured.

[0189] Example 15:

[0190] Flexible conformal piezoelectric strain sensor, the technical content is the same as any one of embodiments 1-14, further, the principle diagram of the dual-channel flexible signal processing circuit 2 is as follows Figure 4As shown, the circuit adopts a voltage readout method, the circuit signal input interface group is CONN1, which is used to flexibly connect with the strain sensing unit 1, and the circuit signal output interface group is CONN2, which is used to connect with the subsequent circuit.

[0191] This embodiment takes two signal processing channels as an example. Each channel consists of a junction field effect transistor (JFET) (Q11 and Q21), a source resistor (R11 and R21), a drain resistor (R13 and R23), and a gate parallel resistor (R12 and R22). The actual diagram of the flexible signal processing circuit is shown in the figure below. Figure 5 As shown, the circuit conductor 2-2 is prepared in the circuit flexible substrate 2-1.

[0192] In this embodiment, interfaces 2 and 3 of CONN1 are signal input interfaces, interfaces 1 and 4 of CONN1 are shield ground and signal ground interfaces, respectively; interfaces 2 and 3 of CONN2 are signal output interfaces, interfaces 1 and 4 of CONN1 are power ground and power interfaces, respectively. Specifically, interfaces 1 and 4 of CONN1 share a common ground with interface 1 of CONN2. This embodiment is designed for an operating point of 0.6V. Accordingly, the junction field effect transistors (JFETs) Q11 and Q21 are TF414 models; source resistors R11 and R21 are 30K ohm 0402 chip resistors; drain resistors R13 and R23 are 110K ohm 0402 chip resistors; gate parallel resistors R12 and R22 are 50G ohm 0805 chip resistors; and the power supply for interface 4 of CONN1 is 3.3V.

[0193] Example 16:

[0194] A flexible conformal piezoelectric strain sensor, having the same technical content as any one of embodiments 1-15, further comprising: Figure 6 The left figure shows a top view of the flexible connection between the strain sensing part 1 and the flexible signal processing circuit 2, and the right figure is a partial cross-sectional structural diagram of positions I, II, and III in the flexible connection interface 3 in the left figure. The flexible connection between the electrode interface of the strain sensing part 1 in Example 1 and the interface CONN1 of the flexible signal processing circuit 2 in Example 2 is achieved through the flexible connection interface 3. Since there are electrode interfaces on both the front and back sides of the strain sensing part 1, and there is also a shielding layer that needs to be grounded, circular through-hole electrode interfaces C-2 and C-3 and flat electrode interfaces C-1 and C-4 are respectively prepared on the flexible circuit 2. Conductive silver glue is used as a flexible connection medium, and circular through-hole electrodes are used to achieve flexible connection between the flexible circuit and the signal output interface, and flat electrodes are used to achieve flexible connection between the flexible circuit and the grounding interface and the shielding layer. The specific connection method is as follows: Figure 6As shown in FIG. 1 , the signal output interfaces 1-2-1 and 1-2-2 located on the upper electrode layer 1-2 are connected to interfaces No. 2 (C-2) and No. 3 (C-3) of the flexible circuit interface CONN1; Figure 6 As shown in II, the ground interface 1-3-1 located at the lower electrode layer 1-3 is connected to the No. 4 (C-4) interface of the flexible circuit interface CONN1; Figure 6 As shown in Figure III, the shielding electrodes 1-5 are connected to the No. 1 (C-1) interface of the flexible circuit interface CONN1. Figure 6 As shown, metal filaments 4 (such as molybdenum wires, silver wires, etc.) can also be embedded in the conductive silver paste to enhance the reliability of the connection.

[0195] Example 17:

[0196] An application of the flexible conformal piezoelectric strain sensor according to any one of embodiments 1-16, comprising:

[0197] like Figure 7 As shown, a flexible conformal piezoelectric strain sensor having two sensitive elements and two signal processing channels is conformally mounted on the surface of the milling cutter 5 to detect its strain.

[0198] Example 18:

[0199] An application of the flexible conformal piezoelectric strain sensor according to any one of embodiments 1-16, comprising:

[0200] like Figure 8 As shown, a flexible conformal piezoelectric strain sensor having two sensitive surface elements and two signal processing channels is conformally mounted on the side of the bearing 6 to detect its strain.

Claims

1. A flexible, conformal piezoelectric strain sensor, characterized by: The flexible piezoelectric film strain sensing unit (1) and the flexible signal processing circuit (2) are integrated by a near-in-situ flexible connection mode. The flexible piezoelectric film strain sensing unit (1) and the flexible signal processing circuit (2) are integrated by a near-in-situ flexible connection mode. The flexible piezoelectric film strain sensing unit (1) includes a piezoelectric film (1-1), an upper electrode layer (1-2), a lower electrode layer (1-3), an insulating layer (1-4), and a shielding layer (1-5). The upper electrode layer (1-2) and the lower electrode layer (1-3) are respectively covered on the upper and lower surfaces of the piezoelectric film (1-1), forming a capacitor structure. The insulating layer (1-4) is respectively covered on the upper electrode layer (1-2) and the lower electrode layer (1-3). The shielding layer (1-5) is covered on the insulating layer (1-4).

2. The flexible, conformal piezoelectric strain sensor of claim 1, wherein: The circuit topology of the flexible signal processing circuit (2) is as follows: The circuit signal input interface group CONN1 is used for flexible connection with the flexible piezoelectric film strain sensing unit (1); The 1st and 4th terminals of the circuit signal input interface group CONN1 are grounded. The 2nd terminal of the circuit signal input interface group CONN1 is connected to the gate of the junction field effect transistor Q11. The 2nd terminal of the circuit signal input interface group CONN1 is connected to the ground after being connected in series with the resistance R12. The source of the junction field effect transistor Q11 is connected to the ground after being connected in series with the source resistance R11. One end of the drain resistance R13 is connected to an external power supply, and the other end is connected to the drain of the junction field effect transistor Q11. The source of the junction field effect transistor Q11 is connected to the 3rd terminal of the circuit signal output interface group CONN2. The 3rd terminal of the circuit signal input interface group CONN1 is connected to the gate of the junction field effect transistor Q21. The 3rd terminal of the circuit signal input interface group CONN1 is connected to the ground after being connected to the resistance R22. The source of the junction field effect transistor Q21 is connected to the ground after being connected in series with the source resistance R21. One end of the drain resistance R23 is connected to an external power supply, and the other end is connected to the drain of the junction field effect transistor Q21. The source of the junction field effect transistor Q21 is connected to the 2nd terminal of the circuit signal output interface group CONN2. The 1st terminal of the circuit signal output interface group CONN2 is grounded, and the 4th terminal is connected to an external power supply.

3. The flexible, conformal piezoelectric strain sensor of claim 2, wherein: The leakage current from the gate to the source of the junction field effect transistor is ≤1pA, and the gate input capacitance should be ≤1pF. The resistance value of the gate parallel resistance is ≥50G ohms.

4. The flexible, conformal piezoelectric strain sensor of claim 1, wherein: The flexible piezoelectric film strain sensing unit (1) and the flexible signal processing circuit (2) are integrated by a near-in-situ flexible connection mode.

5. The flexible, conformal piezoelectric strain sensor of claim 1, wherein: The piezoelectric film (1-1) includes but is not limited to piezoelectric polymer film, piezoelectric ceramic film, and inorganic non-ceramic piezoelectric film (1-1). The piezoelectric polymer film includes but is not limited to polyvinylidene fluoride film and polyvinylidene fluoride copolymer film. The piezoelectric ceramic film includes lead zirconate titanate film. The inorganic non-ceramic piezoelectric film (1-1) includes zinc oxide film. The materials of the upper electrode layer (1-2), the lower electrode layer (1-3), and the shielding layer (1-5) include but are not limited to one or more of Al, Cu, Ag, Ti / Au, and Cr / Au. The preparation method of the upper electrode layer (1-2) and the lower electrode layer (1-3) includes but is not limited to vacuum evaporation plating, sputtering plating process, and electrode pasting method. The preparation method of the shielding layer (1-5) includes but is not limited to vacuum evaporation plating and sputtering plating process.

6. The flexible, conformal piezoelectric strain sensor of claim 1, wherein: The upper electrode layer (1-2) or the lower electrode layer (1-3) is a patterned electrode located on the same plane.

7. The flexible, conformal piezoelectric strain sensor of claim 1, wherein: The upper electrode layer (1-2) or the lower electrode layer (1-3) is a patterned or arrayed electrode layer, and each strain sensing sensitive surface unit is provided.

8. The flexible, conformal piezoelectric strain sensor of claim 7, wherein: The upper electrode layer (1-2) is provided with a signal output interface (1-2-1), and the lower electrode layer (1-3) is provided with a grounding interface (1-3-1). The upper electrode layer (1-2) is provided with a signal output interface (1-2-1), and the lower electrode layer (1-3) is provided with a grounding interface (1-3-1). The upper electrode layer (1-2) is provided with a signal output interface (1-2-1), and the lower electrode layer (1-3) is provided with a grounding interface (1-3-1).

9. The flexible, conformal piezoelectric strain sensor of claim 7, wherein: The upper electrode layer (1-2) is provided with a signal output interface (1-2-1), and the lower electrode layer (1-3) is provided with a grounding interface (1-3-1). The upper electrode layer (1-2) is provided with a signal output interface (1-2-1), and the lower electrode layer (1-3) is provided with a grounding interface (1-3-1). The upper electrode layer (1-2) is provided with a signal output interface (1-2-1), and the lower electrode layer (1-3) is provided with a grounding interface (1-3-1).

10. The flexible, conformal piezoelectric strain sensor of claim 1, wherein: The upper electrode layer (1-2) is provided with a signal output interface (1-2-1), and the lower electrode layer (1-3) is provided with a grounding interface (1-3-1). The protection layer (1-6) covers the surface of the shielding layer (1-5) and protects the device as a whole.

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