A flexible force-electric coupling sensor and a preparation method thereof

Abstract

This invention discloses a flexible force-electric coupling sensor and its fabrication method. It includes a first electret layer, a first insulating layer, a core electrode, a second insulating layer, and a second electret layer stacked sequentially; and a sensing electrode is provided. The first and second electret layers store permanent charges and are symmetrically arranged with the core electrode as the plane of symmetry. When deformation occurs, a potential difference or current can be formed between the sensing electrode and the core electrode. The interfaces between the first and second electret layers and the core electrode are provided with concave-convex structures. The flexible force-electric coupling sensor and its fabrication method provided by this invention, by providing concave-convex structures on the opposite surfaces of the two electret layers in a symmetrical sensor structure, effectively increases the field plate area and concentrates the charge at the protrusions, thereby enhancing the amplitude of potential or electric field changes during deformation, and thus increasing the open-circuit voltage or short-circuit charge, significantly improving the sensitivity of the flexible force-electric coupling sensor.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a flexible force-electric coupling sensor and its fabrication method. Background Technology

[0002] The description in this section provides only background information related to the disclosure of this invention and does not constitute prior art.

[0003] The deep integration of 5G, artificial intelligence (AI), and the Internet of Things (IoT) to form the intelligent network of things (AIoT) will connect human society and physical systems into an organic whole, impacting all aspects of daily life in the future. According to predictions from the Qianzhan Industry Research Institute, the total number of IoT-connected devices worldwide will reach 75 billion by 2025, a fivefold increase within ten years. The future demand for various sensors in smart healthcare, smart homes, smart transportation, and other areas will be enormous.

[0004] Electret piezoelectric films are a crucial type of electro-mechanical coupling sensor. Traditional PVDF piezoelectric film sensors suffer from low sensitivity, requiring high gain in practical applications. This not only increases manufacturing costs but also significantly limits their application in acoustic fields with high sensitivity requirements, such as smart healthcare, smart homes, and intelligent transportation. In contrast, piezoelectric electret film sensors offer higher sensitivity and can be effectively used in these applications.

[0005] Some existing technologies utilize bilayer series or parallel electret films to improve the sensitivity of electret film sensors. For example, Chinese invention patent CN 102522495 A provides a method to improve the signal-to-noise ratio of piezoelectric electret film sensors. It uses a lamination method to stack piezoelectric electret films in series or parallel, thereby multiplying the charge and voltage output of the piezoelectric electret film sensor to improve its sensitivity.

[0006] However, the sensitivity of the electret thin film sensors in the above-mentioned existing technologies is still insufficient to meet the high-sensitivity application requirements of smart healthcare, smart homes, and smart transportation.

[0007] It should be noted that the above description of the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of the present invention and facilitating understanding by those skilled in the art. It should not be assumed that the above technical solutions are known to those skilled in the art simply because they have been described in the background section of this invention. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a flexible force-electric coupling sensor and its preparation method, so as to further improve the sensitivity of electret thin film force-electric sensors.

[0009] To address the aforementioned technical problems, in a first aspect, the present invention provides a flexible force-electric coupling sensor, comprising a first electret layer, a first insulating layer, a core electrode, a second insulating layer, and a second electret layer stacked sequentially; and a sensing electrode is disposed on the side of the first electret layer facing away from the core electrode; permanent charges are stored in the first electret layer and the second electret layer, and the polarity direction and shape of the first electret layer and the second electret layer are symmetrically arranged with the core electrode as the plane of symmetry; when the flexible force-electric coupling sensor is deformed by an external force, a potential difference or current can be formed between the sensing electrode and the core electrode; both the first interface of the first electret layer contacting the first insulating layer and the second interface of the second electret layer contacting the second insulating layer are provided with concave-convex structures.

[0010] The above technical solution utilizes electret layers symmetrically arranged on both sides of the core electrode to enhance the electric field strength at the core electrode. When the flexible force-electric coupling sensor deforms due to pressure, both the open-circuit voltage and the short-circuit charge between the core electrode and the sensing electrode will be increased. Furthermore, the present invention also deliberately sets a concave-convex structure at the interface between the two electret layers. The formation of the concave-convex structure increases the effective area of ​​the field plate on the one hand, and has a certain tip charge concentration effect on the other hand. This makes the change in potential more obvious when deformation occurs, thereby significantly improving the sensitivity of the flexible force-electric coupling sensor.

[0011] Furthermore, the concave-convex structure is symmetrically distributed with the core electrode as the plane of symmetry. The perfectly symmetrical concave-convex structure helps to enhance the concentration of charge at the tip. Compared with the case where the concave-convex structure in the two electret layers is not perfectly symmetrical or completely offset, its electric field concentration effect is more obvious, thus bringing about a better sensitivity improvement effect.

[0012] Regarding the specific dimensions of the concave-convex structure, the structure further includes periodically repeating protrusions and recesses, with the edges of the protrusions being prismatic. The width of the protrusions is 0.001-2 mm, more preferably 0.5-2 mm. The width of the recesses is also 0.001-2 mm, more preferably 0.5-2 mm. The height difference between the protrusions and recesses is 1 / 10-1 / 2 of the thickness of the first or second electret layer, more preferably 1 / 3-1 / 2. A concave-convex structure with a smaller size can also achieve charge concentration, but considering the ease of fabrication and the difficulty of aligning the upper and lower electret layers, the preferred size range is in the millimeter range, for example, 0.5-2 mm.

[0013] Furthermore, the permanent charge tends to concentrate towards the edge of the protrusion. Typically, electret fabrication relies on corona polarization. In this method, applying a non-perpendicular deflection electric field at a suitable angle allows the formed charge to shift towards one side of the protrusion. This charge shifting and concentration further enhances the tip electric field concentration effect, thereby further improving sensitivity.

[0014] Furthermore, the thickness of the first electret layer and the second electret layer is 1-300 μm. Also considering the ease of film preparation, films that are too thin are not easy to process into uneven structures. Therefore, a more preferred range is 100-300 μm.

[0015] Furthermore, the first electret layer and the second electret layer are made of high resistivity dielectric materials, specifically including any one or a combination of two or more materials such as HDPE, PP, and PVDF. The specific material selection can refer to example materials in the prior art or seek various novel materials with resistivity and other electrical properties that are close to or superior, as long as they can achieve the corresponding electret function.

[0016] Furthermore, the flexible force-electric coupling sensor also includes a first waterproof layer covering the side of the first electret layer facing away from the core electrode and a second waterproof layer covering the side of the second electret layer facing away from the core electrode; the sensing electrode is disposed within the first waterproof layer or is in electrical contact with the first waterproof layer.

[0017] Furthermore, the flexible force-electric coupling sensor also includes a first shielding layer covering the first waterproof layer, a second shielding layer covering the second waterproof layer, and a shielding electrode; the shielding electrode is electrically connected to the second shielding layer.

[0018] Secondly, the present invention also provides a method for fabricating the above-mentioned flexible force-electric coupling sensor, which includes the following steps:

[0019] A polarized film is obtained by polarizing a polymer film, and the polarized film is then baked and aged to obtain a first electret layer and a second electret layer. The polarization treatment can be carried out by referring to various polarization methods in existing preparation processes, such as corona polarization treatment, which is a preferred method.

[0020] A first electret layer, a first insulating layer, a core electrode, a second insulating layer, and a second electret layer are sequentially bonded together to form a stacked structure, and sensing electrodes are correspondingly disposed thereon to obtain the flexible force-electric coupling sensor.

[0021] Furthermore, the voltage of the corona polarization treatment is ±5-15kV, and the temperature is 15-35℃;

[0022] The baking and aging treatment is performed at a temperature of 80-100℃ for 20-40 minutes.

[0023] Furthermore, the preparation method specifically includes:

[0024] A continuous polymer film is provided, and an uneven structure is formed on the surface of the polymer film by etching.

[0025] Furthermore, during the corona polarization treatment, the electric field direction forms a non-perpendicular angle with the surface of the polymer film having the uneven structure, the angle being in the range of 60-80°, so that the charge formed by the corona polarization treatment tends to concentrate towards the edge of the protrusion of the uneven structure.

[0026] Through the above preparation process, a flexible force-electric coupling sensor with a double electret layer having an uneven structure can be obtained. The charge is concentrated at the edge of the convex structure, which has a better electric field concentration effect. Therefore, its sensitivity is further improved compared with the existing flexible force-electric coupling sensor with a double electret layer.

[0027] By employing the above technical solutions, the beneficial effects of the present invention include at least the following:

[0028] The flexible force-electric coupling sensor and its fabrication method provided by this invention, by setting concave and convex structures on the opposite surfaces of the double electret layers in the symmetrical sensor structure, achieves the effect of increasing the field plate area and concentrating the charge at the protrusions, thereby enhancing the amplitude of potential or electric field change during deformation, and thus increasing the open circuit voltage or short circuit charge, thereby significantly improving the sensitivity of the flexible force-electric coupling sensor.

[0029] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of a flexible force-electro-coupled sensor provided in a typical embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the fabrication process of a flexible force-electric coupling sensor provided in a typical embodiment of the present invention;

[0032] Figure 3 This is an output charge-pressure test diagram of a flexible force-electric coupling sensor provided in a typical embodiment of the present invention;

[0033] Figure 4This is an output voltage-pressure test diagram of a flexible force-electric coupling sensor provided in a typical embodiment of the present invention;

[0034] Figure 5 This is a low-pressure cyclic test diagram of a flexible force-electric coupling sensor provided in a typical embodiment of the present invention;

[0035] Figure 6 This is a high-pressure cyclic test diagram of a flexible force-electric coupling sensor provided in a typical embodiment of the present invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that in the description of this invention, the terms "first," "second," etc., are used only for descriptive purposes and to distinguish similar objects; there is no order between them, nor should they be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0038] See appendix Figure 1-2 This description discloses a flexible force-electric coupling sensor according to a preferred embodiment, comprising a first electret layer, a first insulating layer, a core electrode, a second insulating layer, and a second electret layer stacked sequentially. A sensing electrode is disposed on the side of the first electret layer facing away from the core electrode. The first and second electret layers store permanent charges, and their shapes are symmetrically arranged with respect to the core electrode. When the flexible force-electric coupling sensor is deformed by an external force, a potential difference is formed between the sensing electrode and the core electrode. Both the first interface between the first electret layer and the first insulating layer, and the second interface between the second electret layer and the second insulating layer, have uneven structures. Furthermore, these uneven structures are symmetrically distributed with respect to the core electrode.

[0039] This invention also provides a method for fabricating the above-mentioned flexible force-electric coupling sensor, see below. Figure 2 As shown, the main processes include:

[0040] A corona-polarized polymer film is obtained by corona polarization treatment, and the corona-polarized film is then subjected to baking and aging treatment to obtain a first electret layer and a second electret layer.

[0041] A first electret layer, a first insulating layer, a core electrode, a second insulating layer, and a second electret layer are sequentially bonded together to form a stacked structure, and sensing electrodes are correspondingly disposed thereon to obtain the flexible force-electric coupling sensor.

[0042] The specific process can be divided into electrode / insulating layer module fabrication, electret / waterproof layer module fabrication, and outer layer module fabrication processes, for example... Figure 2 As shown, an insulating layer is first applied to both sides of the electrode. Figure 2 In the example, only one side of the fabrication is shown; the other side is fabricated in the same way (the illustration of the other side is omitted for brevity), thus forming an electrode / insulating layer module.

[0043] Before, after, or simultaneously, a polymer film, such as any one or more combinations of HDPE, PP, and PVDF, is applied to the waterproof layer. The thickness of the film can be 100-300μm. Then, the film is placed in a corona polarization device for corona polarization treatment. The voltage can be negative or positive. The voltage is controlled at ±5-15kV at room temperature. It is best to apply a deflection electrode to form a tilted electric field. The tilt angle is best set to 60-80° to form a raised structure with concentrated edge charge. Finally, an electret / waterproof layer module is formed.

[0044] Finally, the electrode / insulation layer module and the electret / waterproof layer module are bonded together, and a shielding layer is formed by bonding, brushing or other methods on the outer layer. During or after the fabrication process, the corresponding external electrodes of each layer are connected to form a flexible force-electric coupling sensor that can be applied.

[0045] Of course, after the corresponding structural device is finally formed, it would be best if it could also be like... Figure 2 As shown, secondary aging is carried out under high temperature drying to enhance the bonding of each layer. The optimal aging temperature is 80-100℃ and the time is 12-36h.

[0046] In this process, the aforementioned uneven structure should be formed on the corresponding surface of the polymer film before corona polarization. For example, a product with an uneven structure of the same size can be directly purchased, or the uneven structure can be formed on the surface of the polymer film by mechanical cutting, laser etching, or plasma etching. There are no restrictions on the relevant structure formation method, as long as it can form the above structure.

[0047] Example 1

[0048] This embodiment illustrates the fabrication process and final device structure of a flexible force-electric coupling sensor, as shown below:

[0049] Using the above preparation method, the first insulating layer, the core electrode, and the second insulating layer are bonded together to form a core electrode / insulating layer module;

[0050] HDPE film with a thickness of 200μm is laminated onto the surface of the waterproof layer. The surface of the film has a strip-shaped uneven structure with a raised width of 0.5mm and a recessed width of 0.5mm, and an uneven depth of 100μm. Then, it is placed in a corona polarization device, a deflection electric field is applied, the tilt direction is perpendicular to the edge of the uneven structure, the tilt angle is 75°, a -10kV electric field is applied for polarization for 10min, and then it is dried and aged at 100℃ for 20min to obtain two electret / waterproof layer modules.

[0051] By bonding the two modules together, applying silicone to both sides, and then attaching conductive cloth as a shielding layer, and leading out the corresponding external electrodes, a flexible force-electric coupling sensor can be obtained.

[0052] Figures 3-6 The test results for this flexible force-electric coupling sensor are shown. As can be seen from the figure, the flexible force-electric coupling sensor exhibits excellent sensitivity in both short-circuit charge and open-circuit voltage as the pressure changes, and the pressure-voltage or pressure-charge correlation has good linearity within the test range, showing excellent application potential.

[0053] Furthermore, under repeated cyclic testing conditions, regardless of whether the pressure is high or low, its cyclic performance remains excellent.

[0054] Comparative Example 1

[0055] This comparative example is largely the same as Example 1, with the main difference being:

[0056] The polymer film adhered to the waterproof layer does not form an uneven structure on the surface, but is a flat film of the same thickness.

[0057] This comparative example has a structure similar to existing dual-layer parallel or series devices. When the flexible force-electric coupling sensor obtained from this comparative example was subjected to pressure-charge or pressure-voltage tests under the same conditions, it was found that both the charge curve and voltage curve of this comparative example were lower than those in Example 1. Statistical results show that, within the pressure range of 1-10N, the charge amount of Comparative Example 1 is approximately 70% of that of Example 1, and the voltage is approximately 60% of that of Example 1.

[0058] Comparative Example 2

[0059] This comparative example is largely the same as Example 1, with the main difference being:

[0060] During corona polarization, no deflection electrode was applied; instead, corona polarization was performed using a vertical electric field of the same strength.

[0061] When the flexible force-electric coupling sensor obtained by the comparative example was subjected to pressure-charge or pressure-voltage tests under the same conditions, it was found that the charge curve basically overlapped with that of Example 1, but the voltage curve was slightly lower than that of Example 1. Statistical results showed that in the range of pressure value of 1-10N, the charge amount of Comparative Example 1 was comparable to that of Example 1, but the voltage was about 90% of that of Example 1.

[0062] This indicates that the implementation of the tilted electric field provided by this invention does not significantly affect the charge change induced by pressure, but it does significantly affect the induced voltage generated by deformation during circuit breaking. This is likely related to the charge concentration on the edges of the protruding structure.

[0063] Example 2

[0064] This embodiment is largely the same as Embodiment 1, with the main difference being the preparation process of the electret / waterproof layer module:

[0065] The polymer film was replaced with a PVDF film with a thickness of 100 μm. The surface of the film has a strip-shaped uneven structure with a raised width of 1 mm and a recessed width of 1 mm, and an uneven depth of 35 μm. Then, the film was placed in a corona polarization device, a deflection electric field was applied, the tilt direction was perpendicular to the edge of the uneven structure, the tilt angle was 60°, a -15 kV electric field was applied for polarization for 10 min, and then the film was dried and aged at 80 °C for 30 min to obtain two electret / waterproof layer modules.

[0066] The flexible force-electric coupling sensor prepared in this embodiment still exhibits better sensitivity than the implementation method without concave-convex structure setting and without tilted electric field setting under the same conditions.

[0067] Example 3

[0068] This embodiment is largely the same as Embodiment 1, with the main difference being the preparation process of the electret / waterproof layer module:

[0069] The polymer film was replaced with a PP film with a thickness of 300 μm. The surface of the film has a strip-shaped uneven structure with a raised width of 2 mm and a recessed width of 2 mm, and an uneven depth of 150 μm. Then, it was placed in a corona polarization device, a deflection electric field was applied, the tilt direction was perpendicular to the edge of the uneven structure, the tilt angle was 80°, a -5 kV electric field was applied for polarization for 10 min, and then dried and aged at 90°C for 40 min to obtain two electret / waterproof layer modules.

[0070] The flexible force-electric coupling sensor prepared in this embodiment still exhibits better sensitivity than the implementation method without concave-convex structure setting and without tilted electric field setting under the same conditions.

[0071] Through the above implementation examples, it can be clearly seen that the flexible force-electric coupling sensor and its preparation method provided by the embodiments of the present invention, by setting concave and convex structures on the opposite surfaces of the double electret layers in the symmetrical sensor structure, achieves the effect of increasing the field plate area and concentrating the charge at the protrusions, thereby enhancing the potential change amplitude during deformation, and thus increasing the open circuit voltage or short circuit charge, thereby significantly improving the sensitivity of the flexible force-electric coupling sensor.

[0072] Based on the improved sensitivity, the flexible force-electrocoupled sensor provided in this embodiment of the invention is very suitable for applications in high-end smart healthcare, smart home, intelligent transportation and other fields where high sensitivity is required.

[0073] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A flexible force-electro-coupled sensor, characterized in that, It includes a first electret layer, a first insulating layer, a core electrode, a second insulating layer, and a second electret layer stacked in sequence; and a sensing electrode is provided on at least one side of the first electret layer facing away from the core electrode; The first electret layer and the second electret layer store permanent charges, and the polarity direction and shape of the first electret layer and the second electret layer are symmetrically arranged with the core electrode as the plane of symmetry. When the flexible force-electric coupling sensor is deformed by an external force, a potential difference or current can be formed between the sensing electrode and the core electrode. Both the first interface where the first electret layer contacts the first insulating layer and the second interface where the second electret layer contacts the second insulating layer are provided with an uneven structure. The method for fabricating the flexible force-electric coupling sensor is as follows: A polymer film is subjected to corona polarization treatment to obtain a polarized film, and the polarized film is then subjected to baking and aging treatment to obtain a first electret layer and a second electret layer. Specifically, this includes: providing a continuous polymer film and etching an uneven structure on the surface of the polymer film; Furthermore, during the corona polarization treatment, the electric field direction forms a non-perpendicular angle with the surface of the polymer film having the uneven structure, so that the charge generated by the corona polarization treatment tends to concentrate towards the edge of the protrusion of the uneven structure.

2. The flexible force-electrocoupled sensor according to claim 1, characterized in that, The concave-convex structure is symmetrically distributed with the core electrode as the plane of symmetry.

3. The flexible force-electrocoupled sensor according to claim 2, characterized in that, The concave-convex structure includes periodically repeating protrusions and concave portions, and the edges of the protrusions are prismatic. The width of the protrusions is 0.001-2 mm, the width of the concave portions is 0.001-2 mm, and the height difference between the protrusions and concave portions is 1 / 10-1 / 2 of the thickness of the first electret layer or the second electret layer.

4. The flexible force-electrocoupled sensor according to claim 3, characterized in that, The permanent charge tends to concentrate towards the edge of the protrusion.

5. The flexible force-electrocoupled sensor according to claim 3, characterized in that, The thickness of the first electret layer and the second electret layer is 1-300 μm; The first electret layer and the second electret layer are made of high resistivity dielectric materials, including any one or a combination of two or more of HDPE, PP, and PVDF.

6. The flexible force-electrocoupled sensor according to claim 1, characterized in that, It also includes a first waterproof layer covering the side of the first electret layer facing away from the core electrode and a second waterproof layer covering the side of the second electret layer facing away from the core electrode; The sensing electrode is disposed within the first waterproof layer or is in electrical contact with the first waterproof layer.

7. The flexible force-electrocoupled sensor according to claim 6, characterized in that, It also includes a first shielding layer covering the first waterproof layer, a second shielding layer covering the second waterproof layer, and shielding electrodes; The shielding electrode is electrically connected to the second shielding layer.

8. A method for fabricating the flexible force-electric coupling sensor according to any one of claims 1-7, characterized in that, include: A first electret layer, a first insulating layer, a core electrode, a second insulating layer, and a second electret layer are sequentially bonded together to form a stacked structure, and sensing electrodes are correspondingly disposed thereon to obtain the flexible force-electric coupling sensor.

9. The preparation method according to claim 8, characterized in that, The voltage for the corona polarization treatment is ±5-15kV, and the temperature is 15-35℃. The baking and aging treatment is performed at a temperature of 80-100℃ for 20-40 minutes.

10. The preparation method according to claim 8, characterized in that, The non-perpendicular angle formed between the direction of the electric field and the surface of the polymer film having the aforementioned uneven structure ranges from 60° to 80°.

Images