A piezoelectric thin film sensor

Abstract

This utility model discloses a piezoelectric thin film sensor, including a piezoelectric thin film layer and electrode layers disposed on the upper and lower sides of the piezoelectric thin film layer; a variable stiffness buffer layer is disposed on the side of one electrode layer away from the piezoelectric thin film layer, and a base layer is disposed on the side of the other electrode layer away from the piezoelectric thin film layer. The variable stiffness buffer layer is made of a flexible material, and an air bladder is disposed inside the variable stiffness buffer layer. In this piezoelectric thin film sensor, the air bladder inside the variable stiffness buffer layer is connected to an air source device through a micro-channel. In the inflated state, it can locally support the buffer layer to form a protrusion to increase the pressure. In the contracted state, it does not affect the surface flatness of the buffer layer. The clamping force is transmitted only through the silicone substrate. Combined with the real-time monitoring of the pressure signal and the inflation and deflation control of the air bladder by the external control device, the pressure can be dynamically adjusted to ensure safe and reliable clamping and adapt to different screen sizes and shapes.

Description

Technical Field

[0001] This utility model relates to the field of sensor technology, and in particular to a piezoelectric thin film sensor. Background Technology

[0002] Piezoelectric thin film sensors are flexible electronic devices that work based on the piezoelectric effect. They can convert mechanical stress (such as pressure, vibration, bending, etc.) into electrical signals, or vice versa, convert electrical signals into mechanical deformation. They are widely used in sensing, energy harvesting, medical monitoring, industrial production and other fields.

[0003] In the clamping process of display screen manufacturing, piezoelectric thin film sensors are used to assist in clamping the display screen. Because the surface of the display screen (especially flexible screens and ultra-thin screens) has weak resistance to local pressure, when the clamping force is unevenly distributed, local pressure concentration is very likely to occur (such as the contact area between the edge of the clamping claw and the screen body), which can lead to indentations, cracks or even damage to the internal circuitry of the screen body. Although existing piezoelectric thin film sensors can detect overall pressure, they lack an active relief mechanism for local pressure concentration and can only passively feed back pressure signals, which cannot fundamentally reduce the damage caused by local overpressure.

[0004] Therefore, a piezoelectric thin film sensor is proposed to solve the above problems. Utility Model Content

[0005] The purpose of this invention is to provide a piezoelectric thin film sensor to solve the above-mentioned problems.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] A piezoelectric thin film sensor includes a piezoelectric thin film layer and electrode layers disposed on the upper and lower sides of the piezoelectric thin film layer; a variable stiffness buffer layer is disposed on the side of one electrode layer away from the piezoelectric thin film layer, and a base layer is disposed on the side of the other electrode layer away from the piezoelectric thin film layer. The variable stiffness buffer layer is made of a flexible material, and an air bladder is disposed inside the variable stiffness buffer layer. A microchannel is disposed on the air bladder extending to the outside of the variable stiffness buffer layer. The air bladder has an inflated state and a contracted state. In the inflated state, the air bladder supports the side of the variable stiffness buffer layer away from the electrode layer.

[0008] Optionally, the base layer is made of a flexible material, and a telescopic member is provided on the side of the base layer away from the electrode layer. A base is provided on the side of the telescopic member away from the base layer. A support member is provided between the base layer and the base, and the support member is located in the middle of the base layer. There are multiple telescopic members distributed in an array.

[0009] Optionally, the telescopic component includes a threaded shaft, an internal threaded sleeve, and a flexible part. The flexible part is fixedly disposed on the side of the base away from the electrode layer, the threaded shaft is fixedly disposed on the end of the flexible part away from the base, one end of the internal threaded sleeve is rotatably connected to the side of the base close to the base, and the threaded shaft is threadedly connected to the internal threaded sleeve.

[0010] Optionally, the base has a box structure with an open side facing the base layer. Adjustment ports are provided on both sides of the base, and the adjustment ports correspond to the telescopic components. A strip is provided on the side of the box, and a through hole is provided on the side of the strip facing the base layer.

[0011] Optionally, the number of airbags is 4-16, arranged in a matrix or a surrounding pattern.

[0012] Optionally, the base is provided with a miniature air pump, the number of which matches the number of airbags, and the air outlets of the multiple miniature air pumps are respectively connected to the miniature pipes on the multiple airbags.

[0013] Optionally, the electrode layer includes an electrode sheet and an lead-out structure disposed on the side of the electrode sheet.

[0014] Optionally, the piezoelectric thin film layer is made of PVDF material.

[0015] Optionally, the variable stiffness buffer layer and the base layer are both made of silicone, and the airbag body is made of polyurethane film.

[0016] Optionally, the variable stiffness buffer layer has anti-slip texture on the side away from the electrode layer.

[0017] Compared with the prior art, the beneficial effects of this utility model are:

[0018] 1. The variable stiffness buffer layer and the base layer are made of flexible silicone material, which not only meets the surface contact requirements of the display screen but also provides basic support. Furthermore, the airbags distributed in a ring or matrix pattern inside the variable stiffness buffer layer are connected to the air source equipment through micro-channels. In the inflated state, the buffer layer can be locally supported to form a bulge to increase the pressure. Moreover, the pressure can be adjusted by controlling the amount of air inflation. In the contracted state, the flatness of the buffer layer surface is not affected. The clamping force is transmitted only through the silicone base. Combined with the real-time monitoring of the pressure signal and the control of airbag inflation and deflation by external control equipment, dynamic pressure adjustment can be achieved to ensure safe and reliable clamping and adapt to different screen sizes and shapes.

[0019] 2. For curved screens, by adjusting the length of the telescopic components distributed in an array below the base layer, and using the cooperation between the threaded shaft and the internal threaded sleeve to change the length of the telescopic components, combined with the deformation of the flexible part and the flexible base layer, the base layer bends with the middle support as the fulcrum. Simultaneously, the piezoelectric film layer, electrode layer and variable stiffness buffer layer adapt to the curvature of the curved screen. The airbag can still work normally and protect vulnerable parts as the buffer layer bends, which comprehensively improves the practicality, adaptability, fit and safety of the sensor in different screen contact applications. Attached Figure Description

[0020] The accompanying drawings further illustrate the present invention, but the content of the drawings does not constitute any limitation on the present invention.

[0021] Figure 1 This is a schematic diagram of the structure of this utility model;

[0022] Figure 2 This is a partial sectional view of the present invention (only the base is cut open);

[0023] Figure 3 This is a cross-sectional view of the variable stiffness buffer layer and airbag of this utility model;

[0024] Figure 4 This is a schematic diagram of the telescopic component structure of this utility model.

[0025] In the attached diagram: 1. Piezoelectric thin film layer; 2. Electrode layer; 21. Electrode sheet; 22. Lead-out structure; 3. Variable stiffness buffer layer; 31. Airbag; 32. Micro-channel; 33. Micro-air pump; 34. Anti-slip texture; 4. Base layer; 5. Telescopic component; 51. Flexible part; 52. Internal threaded sleeve; 53. Threaded shaft; 61. Base; 611. Strip; 612. Through hole; 613. Adjustment port; 62. Support component. Detailed Implementation

[0026] The embodiments of this utility model are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model. In the description of this utility model, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this utility model. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this utility model, "multiple" means two or more, and "several" means one or more, unless otherwise explicitly specified.

[0027] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for mutual communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0028] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0029] The following disclosure provides many different embodiments or examples for implementing various structures of this invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the scope of the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0030] In this embodiment, reference Figure 2 As shown, a piezoelectric thin-film sensor includes a piezoelectric thin-film layer 1 and electrode layers 2 disposed on the upper and lower sides of the piezoelectric thin-film layer 1. The piezoelectric thin-film layer 1 is preferably made of PVDF (polyvinylidene fluoride) material. PVDF material has high sensitivity and can detect local pressures of 0.1-5N. The electrode layer 2 includes electrode sheets 21 and lead-out structures 22 disposed on the sides of the electrode sheets 21. The electrode sheets 21 are preferably vapor-deposited aluminum electrodes, which can efficiently conduct electrical signals, ensuring accurate pressure signal output. The lead-out structures 22 are preferably copper wires, facilitating stable transmission of electrical signals to external control devices.

[0031] One of the electrode layers 2 has a variable stiffness buffer layer 3 on the side away from the piezoelectric thin film layer 1. This variable stiffness buffer layer 3 is the part that directly contacts the screen, and the side of the variable stiffness buffer layer 3 that contacts the screen has anti-slip texture 34. The anti-slip texture 34 is a cross stripe pattern, which can increase the friction when in contact with the display screen and prevent relative sliding. The other electrode layer 2 has a base layer 4 on the side away from the piezoelectric thin film layer 1. This base layer 4 mainly serves as a basic support. Both the variable stiffness buffer layer 3 and the base layer 4 are made of flexible materials, preferably silicone. Silicone has good flexibility and elasticity and can well adapt to the contact requirements of the display screen surface.

[0032] refer to Figure 3As shown, to increase the contact area between a certain position and the display screen, thereby dispersing local pressure, an airbag 31 is provided inside the variable stiffness buffer layer 3. Specifically, the airbag 31 is positioned between the side of the variable stiffness buffer layer 3 closest to the electrode layer 2 and the side furthest from the electrode layer 2, completely contained within the variable stiffness buffer layer 3. Preferably, there are multiple airbags 31, arranged in a ring-like or matrix-like distribution. Therefore, depending on the size and shape of the screen to be clamped, the number of airbags 31 corresponds to the screen being clamped. The number of airbags 31 is preferably between 4 and 16, and the distribution can be either ring-like or matrix-like. The material of the airbag 31 is preferably a polyurethane film, which has good airtightness and elasticity. The shape of the airbag 31 is preferably elongated, considering that the screen is a planar structure, and an elongated structure can adapt well to the screen; however, in other embodiments, if the screen is relatively small, a shape with a shorter length, such as a sphere or rectangle, can also be used. The airbag 31 is provided with a micro-channel 32 extending to the outside of the variable stiffness buffer layer 3. The micro-channel 32 is preferably made of polyimide tubing, which is a flexible tube that can be bent to change shape. The end of the micro-channel 32 away from the airbag 31 can be connected to the air outlet of the air source device, and the airbag 31 has two states: an inflated state and a contracted state.

[0033] The contracted state is the initial state of the airbag 31. In this state, there is no additional gas inside the airbag (or only a small amount of basic air pressure is retained). The airbag is naturally curled up or flattened, completely placed inside the variable stiffness buffer layer 3, and does not protrude from the surface of the buffer layer. In this state, the side of the variable stiffness buffer layer 3 away from the electrode layer 2 maintains a flat and flexible surface. When in contact with the display screen, the clamping force is transmitted only through the natural elasticity of the silicone material. The contact area is determined by the base size of the corresponding area of ​​the airbag.

[0034] The inflated state refers to the working state when the airbag 31 is inflated by an air source device, such as an air pump. The air source injects gas into the airbag 31 through a micro-channel 32. The polyurethane film bladder bulges due to the increased internal air pressure, expanding from a flat shape to a hemispherical or protruding shape. This, in turn, partially supports the side of the variable stiffness buffer layer 3 away from the electrode layer 2, creating a protrusion on the surface of the variable stiffness buffer layer 3 in that area. This protrusion formed by the airbag 31 shortens the distance between the airbag and the screen, increasing the pressure on the display screen while maintaining a constant bearing force. Therefore, by controlling the inflation amount, the degree of protrusion on the surface of the variable stiffness buffer layer 3 can be controlled, thereby controlling the pressure on the display screen.

[0035] The external control device is mainly used to receive pressure signals from the sensors and determine whether they exceed a preset threshold (e.g., the preset threshold for the flexible screen is 1N). If the threshold is exceeded, the corresponding micro air pump 33 is controlled to deflate the airbag 31 to reduce the pressure on the screen; conversely, the airbag 31 is inflated when the pressure is below the threshold. Once the pressure is normal, the air pump is controlled to maintain its original state, keeping the airbag 31 in the same state. At the same time, it can coordinate the linkage of various components to ensure clamping safety.

[0036] Since there are multiple airbags 31, in order to control the inflation of each airbag 31 individually, a miniature air pump 33 is provided on the base 61, which is the air source device mentioned above. The number of miniature air pumps 33 matches the number of airbags 31. The air outlets of multiple miniature air pumps 33 are connected to the miniature pipes 32 on multiple airbags 31 respectively, so that each miniature air pump 33 can control the inflation of one airbag 31.

[0037] In summary, based on the aforementioned structure, by setting a variable stiffness buffer layer 3 and using silicone material, it utilizes its excellent flexibility and elasticity to adapt to the contact requirements of the display screen surface. Furthermore, the internally distributed airbags 31, arranged in a ring or matrix pattern, can locally support the surface of the variable stiffness buffer layer 3 to form protrusions when inflated, effectively increasing the pressure on the corresponding display screen. This pressure can be controlled by adjusting the amount of inflation. In the contracted state, the airbags do not affect the flatness of the variable stiffness buffer layer 3 surface; the clamping force is transmitted only through the natural elasticity of the silicone base. Moreover, the anti-slip texture 34 on the contact side between the variable stiffness buffer layer 3 and the screen increases friction and prevents relative slippage. In addition, the flexible base layer 4 provides stable support. The overall structural design is ingenious, and the external control device can control the inflation and deflation of the airbags 31 in real time based on the pressure signal, achieving dynamic pressure adjustment. This ensures both safety and reliability when clamping the screen and adaptability to screens of different sizes and shapes, comprehensively improving the practicality and adaptability of the sensor in screen contact applications.

[0038] refer to Figure 2 and Figure 4As shown, in other embodiments, considering that the screen being clamped is a curved screen, in order to better adapt to the shape of the curved screen, specifically for the clamping requirements of the curved screen, the side of the base layer 4 away from the electrode layer 2 is connected to the base 61 through a telescopic member 5, and there are multiple telescopic members 5 arranged in an array. A support member 62 is provided between the base layer 4 and the base 61, and the support member 62 is directly opposite the middle position of the base layer 4, providing the base layer 4 with the most basic support. The telescopic member 5 is composed of a flexible part 51, an internal threaded sleeve 52 and a threaded shaft 53. The flexible part 51 is fixedly set on the side of the base layer 4 away from the electrode layer 2, the threaded shaft 53 is fixedly set on the end of the flexible part 51 away from the base layer 4, and the internal threaded sleeve 52 is threadedly fitted onto the threaded shaft 53. The end of the internal threaded sleeve 52 away from the base layer 4 is rotatably connected to the base 61, and a handle for hand gripping is also installed on the internal threaded sleeve 52. Therefore, when the object being clamped is a curved screen, the operator can adjust the overall length of the telescopic component 5 by rotating the internal threaded sleeve 52 at different positions using the threaded engagement: if it is necessary to adapt to the large arc area on the left side of the curved screen, hold the handle on the telescopic component 5 of the left array and rotate the internal threaded sleeve 52 clockwise, so that the threaded shaft 53 retracts along the internal threaded sleeve 52 towards the base 61, shortening the length of the left telescopic component 5 (e.g., shortening by 2mm); for the gently curved area on the right side, hold the handle on the telescopic component 5 of the right array and rotate the internal threaded sleeve 52 counterclockwise, so that the threaded shaft 53 extends outward, extending the length of the right telescopic component 5 (e.g., extending by 1mm).

[0039] Furthermore, refer to Figure 3 As shown, since the base layer 4 is made of flexible silicone and is integrally connected with the flexible part 51 of the telescopic component 5, when the lengths of the telescopic components 5 at different positions differ, the base layer 4 will bend adaptively with the middle support 62 as the fulcrum. On the left side, the telescopic component 5 shortens and generates an inward pulling force, which, together with the slight deformation of the flexible part 51, forms a bend that matches the large arc on the left side of the curved screen; on the right side, the telescopic component 5 extends and generates an outward pushing force, and the flexible part 51 naturally stretches with the base layer 4, forming an arc that fits the gentle arc surface on the right side. This bending is simultaneously transmitted to the piezoelectric film layer 1, electrode layer 2, and variable stiffness buffer layer 3 covering the base layer 4: the silicone substrate of the variable stiffness buffer layer 3 undergoes flexible deformation with the curvature of the base layer 4, and its side away from the electrode layer 2 will naturally conform to the curved surface of the curved screen; at the same time, the silicone material of the flexible part 51 has good extensibility and will not generate rigid tension when the base layer 4 bends, ensuring that the overall shape of the variable stiffness buffer layer 3 is completely adapted to the curved screen and avoiding local suspension or excessive compression.

[0040] During this process, because the airbag 31 inside the variable stiffness buffer layer 3 is elastic, the airbag 31 will naturally adapt to the curvature of the curved screen as the buffer layer bends. The position of the airbag 31 that bends and deforms always corresponds to the stress area of ​​the curved screen. When the pressure in a certain area exceeds the limit during clamping, the airbag 31 can still expand by inflating to generate a bulge, ensuring that parts of the curved screen such as the curved edge that are susceptible to local pressure damage are effectively protected.

[0041] refer to Figure 2 and Figure 4 As shown above, by adjusting the length of the telescopic components 5 distributed in the array and combining the deformation adaptability of the flexible part 51, the variable stiffness buffer layer 3 can accurately match the shape of curved screens with different curvatures without affecting the pressure detection and local pressure adjustment functions of the sensor, thus significantly improving the adaptability and safety of the curved screen clamping.

[0042] refer to Figure 1 As shown, when adapting to a curved screen, the box structure of the base 61 provides stable support for the entire adjustment process. Its opening structure facing the base 4 provides sufficient space for the bending deformation of the base 4 and other components, avoiding interference between the base 4 and the base 61 when bending.

[0043] refer to Figure 1 As shown, adjustment ports 613 are provided on both sides of the base 61, and the adjustment ports 613 correspond to the telescopic components 5. The size of the adjustment ports 613 is slightly larger than the handle, allowing the operator to reach into the adjustment ports 613 to grip the handle, facilitating operation of the telescopic components 5 at different positions. For example, when it is necessary to adjust the telescopic component 5 corresponding to the edge of the curved screen, the inner threaded sleeve 52 can be precisely rotated through the adjustment port 613, thereby adjusting the extension length of the threaded shaft 53.

[0044] Furthermore, referring to Figure 1, a strip 611 is provided on the side of the housing, and a through hole 612 is opened on the side of the strip 611 facing the base 4. The strip 611 and the through hole 612 on the side of the housing are used to fix the base 61 to the clamping device. After determining the bending shape of the base 4 and the variable stiffness buffer layer 3, bolts are used to pass through the through hole 612 to fix the strip 611 to the clamping device, thereby ensuring the stability of the entire sensor during the clamping process of the curved screen.

[0045] In the description of this specification, the references to terms such as "embodiment," "one implementation," "some implementations," "illustrative implementation," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with the described implementation or example is included in at least one implementation or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same implementation or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more implementations or examples.

[0046] The technical principles of this utility model have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of this utility model and should not be construed as limiting the scope of protection of this utility model in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of this utility model without inventive effort, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A piezoelectric thin film sensor, characterized by: It includes a piezoelectric thin film layer (1) and electrode layers (2) laid on the upper and lower sides of the piezoelectric thin film layer (1); one of the electrode layers (2) is provided with a variable stiffness buffer layer (3) on the side away from the piezoelectric thin film layer (1), and the other electrode layer (2) is provided with a base layer (4) on the side away from the piezoelectric thin film layer (1). The variable stiffness buffer layer (3) is made of a flexible material. An air bladder (31) is provided inside the variable stiffness buffer layer (3). A micro-channel (32) extending to the outside of the variable stiffness buffer layer (3) is provided on the air bladder (31). The air bladder (31) has an inflated state and a contracted state. When in the inflated state, the air bladder (31) will support the side of the variable stiffness buffer layer (3) away from the electrode layer (2).

2. A piezoelectric thin film sensor according to claim 1, wherein The base layer (4) is made of flexible material. A telescopic member (5) is provided on the side of the base layer (4) away from the electrode layer (2). A base (61) is provided on the side of the telescopic member (5) away from the base layer (4). A support member (62) is provided between the base layer (4) and the base (61). The support member (62) is located in the middle of the base layer (4). There are multiple telescopic members (5) and they are arranged in an array.

3. A piezoelectric thin film sensor according to claim 2, wherein The telescopic component (5) includes a flexible part (51), an internal threaded sleeve (52), and a threaded shaft (53). The flexible part (51) is fixedly disposed on the side of the base layer (4) away from the electrode layer (2). The threaded shaft (53) is fixedly disposed on the end of the flexible part (51) away from the base layer (4). One end of the internal threaded sleeve (52) is rotatably connected to the side of the base (61) close to the base layer (4). The threaded shaft (53) is threadedly connected to the internal threaded sleeve (52).

4. A piezoelectric thin film sensor according to claim 2, wherein The base (61) has a box structure and an open structure on the side facing the base (4). Adjustment ports (613) are provided on both sides of the base (61), and the adjustment ports (613) correspond to the telescopic member (5). A strip plate (611) is provided on the side of the box, and a through hole (612) is opened on the side of the strip plate (611) facing the base (4).

5. A piezoelectric thin film sensor according to claim 2, wherein The number of airbags (31) is 4-16, arranged in a matrix or around the perimeter.

6. A piezoelectric thin film sensor according to claim 5, wherein The base (61) is provided with a miniature air pump (33), the number of which matches the number of airbags (31), and the air outlets of the multiple miniature air pumps (33) are respectively connected to the miniature pipes (32) on the multiple airbags (31).

7. A piezoelectric thin film sensor according to claim 1, wherein The electrode layer (2) includes an electrode sheet (21) and an lead-out structure (22) disposed on the side of the electrode sheet (21).

8. The piezoelectric thin film sensor according to claim 1, wherein The piezoelectric thin film layer (1) is made of PVDF material.

9. The piezoelectric thin film sensor according to claim 1, wherein The variable stiffness buffer layer (3) and the base layer (4) are both made of silicone, and the airbag (31) is made of polyurethane film.

10. The piezoelectric thin film sensor according to claim 1, wherein The variable stiffness buffer layer (3) has anti-slip texture (34) on the side away from the electrode layer (2).

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