Sensitive element of multi-gradient interlocking structure, preparation method and flexible pressure sensor

Abstract

The invention relates to the technical field of sensitive elements, in particular to a sensitive element of a multi-gradient interlocking structure, a preparation method and a flexible pressure sensor. The sensitive element comprises a packaging layer and a functional layer, and the packaging layer is used for maintaining the form of the functional layer. The functional layer comprises an upper electrode layer, an ionic medium layer and a lower electrode layer which are sequentially arranged from top to bottom. A plurality of first protrusions are arranged on the side, facing the ionic dielectric layer, of the upper electrode layer, and a plurality of second protrusions are arranged on the side, facing the upper electrode layer, of the ionic dielectric layer. The heights of the first protrusions are gradually increased from left to right, and the heights of the second protrusions are gradually reduced from right to left. The first protrusions and the second protrusions are arranged in a staggered mode so as to form a capacitance change area of a multi-gradient interlocking structure. The flexible pressure sensor made of the sensitive element has high sensitivity on the basis of a wide detection range, and is suitable for application scenes such as human health information monitoring and wearable equipment.

Description

Technical Field

[0001] This invention relates to the field of sensing element technology, specifically to a sensing element with a multi-gradient interlocking structure and its preparation method, and a flexible pressure sensor. Background Technology

[0002] Flexible pressure sensors have attracted unprecedented attention in fields such as wearable medical devices, intelligent robots, and electronic skin. Based on different sensing principles, flexible pressure sensors can be classified into various types, such as piezoresistive sensors, capacitive sensors, triboelectric sensors, and piezoelectric sensors. Among them, capacitive sensors have received considerable attention due to their advantages such as low power consumption, fast dynamic response, small signal drift, and ease of fabrication. However, traditional capacitive sensors suffer from limitations in capacitance change due to the incompressibility or poor compressibility of their soft dielectric, resulting in problems such as low sensitivity, slow response speed, and poor performance characterization.

[0003] The sensing element is one of the key components of a sensor. In existing technologies, a common method to improve the performance of flexible pressure sensors is to introduce ions into the dielectric layer of the sensing element, increasing its capacitance density by several orders of magnitude compared to ordinary capacitive sensors, thus significantly improving sensitivity. However, when these sensors are applied to high-sensitivity applications, such as heartbeat and pulse detection, although their sensitivity is higher than that of traditional capacitive sensors, they still suffer from low sensitivity, slow response, and narrow detection range, making them unsuitable for high-sensitivity scenarios. Furthermore, the fabrication of sensing elements in existing technologies involves complex and expensive processes and long manufacturing cycles. Summary of the Invention

[0004] To address the technical problems of low sensitivity and slow response of existing sensitive elements, this invention provides a sensitive element with a multi-gradient interlocking structure and its preparation method, as well as a flexible pressure sensor.

[0005] This invention employs the following technical solution: a sensitive element with a multi-gradient interlocking structure, comprising an encapsulation layer and a functional layer, wherein the encapsulation layer maintains the shape of the functional layer. The functional layer comprises, from top to bottom, an upper electrode layer, an ion dielectric layer, and a lower electrode layer. The ion dielectric layer is adhered to the lower electrode layer on one side facing the upper electrode layer and aligned with the upper electrode layer. Multiple protrusions I arranged in a matrix are provided on the upper electrode layer on the side facing the ion dielectric layer. Multiple protrusions II arranged in a matrix are provided on the upper electrode layer on the side facing the upper electrode layer. Both protrusions I and II are elastic structures; the height of protrusions I gradually increases from left to right, while the height of protrusions II gradually decreases from left to right. Furthermore, protrusions I and II are staggered in the horizontal direction of the upper electrode layer to form a capacitance variation region of the multi-gradient interlocking structure.

[0006] As a further improvement of the present invention, a conductive film is coated on the side of the upper electrode layer facing the ion medium layer, and the conductive film covers the side of the upper electrode layer where the protrusion is located.

[0007] In a typical technical solution of the present invention, a plurality of protrusions form a rectangular array, with adjacent protrusions being equally spaced; a plurality of protrusions form a rectangular array of the same size as the rectangular array, with adjacent protrusions being equally spaced, and the distance between adjacent protrusions and adjacent protrusions is equal.

[0008] As a further improvement of the present invention, both the first protrusion and the second protrusion are conical structures; the distance from the central axis of each first protrusion to the central axis of the two adjacent second protrusions is equal.

[0009] As a further improvement of the present invention, in the horizontal direction of the upper electrode layer, the leftmost protrusion 2 has the same height as the rightmost protrusion 1; among the multiple protrusions 1 in the same row on the rectangular array 1, the height difference between each two adjacent protrusions 1 is Δh1; among the multiple protrusions 2 in the same row on the rectangular array 2, the height difference between each two adjacent protrusions 2 is Δh2, and Δh1=Δh2.

[0010] As a further improvement of the present invention, the conductive film is formed by coating the AgNWs / MXene mixture onto the surface of the upper electrode layer facing the ion medium layer; the shape of the conductive film is the same as the shape of the upper electrode layer facing the ion medium layer and can completely cover the upper electrode layer facing the ion medium layer.

[0011] This invention also provides a method for fabricating a sensitive element with a multi-gradient interlocking structure as described above, comprising the following steps: pouring silicone rubber into an upper electrode layer mold, and sequentially drying and curing it; after curing, demolding to obtain the upper electrode layer. Dropping an AgNWs / MXene mixture onto the side of the upper electrode layer where the first protrusion is located, thereby forming the conductive film on the surface of the upper electrode layer facing the ion dielectric layer. Pouring an ion dielectric layer solution into an ion dielectric layer mold and curing it; after curing, demolding to obtain the ion dielectric layer. Adhering the ion dielectric layer to one side of the lower electrode layer; then arranging the first and second protrusions opposite each other and staggering them to form a sandwich-structured functional layer. Encapsulating the functional layer by printing an encapsulation layer on the surface of the functional layer using 3D printing, thereby obtaining the sensitive element.

[0012] As a further improvement of the present invention, the preparation steps of the AgNWs / MXene mixture are as follows: The AgNWs dispersion and the MXene dispersion are diluted in water to obtain mixture one. The volume ratio of the AgNWs dispersion, the MXene dispersion, and the water is 2:1:20. A certain amount of HPMC is added to mixture one, and after heating and stirring, an AgNWs / MXene mixed solution is obtained, wherein the mass concentration of HPMC in the AgNWs / MXene mixed solution is 1 wt%.

[0013] As a further improvement of the present invention, the ion-dielectric layer solution is prepared by mixing a polyvinyl alcohol solution with a 1-ethyl-3-methylimidazolium tetrafluoroborate solution. The preparation method of the ion-dielectric layer solution is as follows: Polyvinyl alcohol is slowly added to deionized water under stirring at a mass ratio of 1:7, and then heated in a water bath at 90°C while stirring until homogeneous, thus obtaining a polyvinyl alcohol solution. The polyvinyl alcohol solution is cooled to 50°C, and then a 1-ethyl-3-methylimidazolium tetrafluoroborate solution with a solid-liquid ratio of 1 g:3.5 mL to polyvinyl alcohol is added, and the mixture is heated in a water bath at 50°C while stirring until homogeneous, thus obtaining the ion-dielectric layer solution.

[0014] The present invention also includes a flexible pressure sensor comprising a sensing element with the aforementioned multi-gradient interlocking structure and a data processing module. The sensing element is used to sense external pressure and convert the sensed pressure into a changing capacitance value in the capacitance change region, and output the changing capacitance value to the data processing module. The data processing module is used to convert the changing capacitance value into an electrical signal and process the input electrical signal according to the internally constructed relationship between the pressure value and the electrical signal, thereby realizing the conversion of the electrical signal into a pressure value and outputting it.

[0015] The technical solution provided by this invention has the following beneficial effects:

[0016] (1) The sensitive element provided by this invention forms a capacitance change region with a multi-gradient interlocking structure through multiple protrusions (first and second). This allows the sensitive element to more effectively reduce internal air gaps and increase dielectric constant when subjected to pressure, while simultaneously increasing the contact area between the upper electrode layer and the ion-dielectric layer. The synergistic effect of reducing internal air gaps to increase dielectric constant and increasing the contact area between the upper electrode layer and the ion-dielectric layer enhances the sensitivity of the sensitive element, enabling it to meet the requirements of high-sensitivity scenarios (such as detecting heartbeats and pulses). Specifically, the multi-gradient structure allows the functional layer to have a smaller initial contact area and a larger contact area change, thereby improving the sensitivity of the sensitive element. The multi-gradient structure also helps to increase the minimum detection limit and expand the detection range of the sensitive element. The interlocking structure simultaneously reduces the air gap between protrusions (first and second) while increasing the contact area between them, and the synergistic effect enhances the sensitivity of the sensitive element. The multi-gradient structure and interlocking structure can also work together to further increase the contact area of ​​protrusion one and protrusion two during compression, thereby further improving the sensitivity of the sensitive element based on the single interlocking structure.

[0017] (2) The method for preparing the sensitive element provided by the present invention involves providing a conductive film on the upper electrode layer. The conductive film is formed by coating the surface of the upper electrode layer facing the ion-dielectric layer with a mixture of AgNWs / MXene. The silver nanowires (AgNWs) possess excellent overlap, flexibility, and conductivity, allowing the conductive film to not only adhere completely and tightly to the surface of the upper electrode layer with the irregular structure of the protrusion, but also ensuring that the shape of the conductive film is consistent with the shape of the upper electrode layer facing the ion-dielectric layer, thereby improving the conductivity of the upper electrode layer. Furthermore, the layered composition of the two-dimensional material (MXene) can also promote the interconnection of nodes within the AgNWs, thereby reducing the resistance of the prepared conductive film and enhancing its strength. This further improves the conductivity of the conductive film, extends its service life, and protects the upper electrode layer.

[0018] (3) The flexible pressure sensor provided by the present invention has a small structure, high sensitivity on the basis of a wide detection range, good stability and fast response recovery time, making the flexible pressure sensor of this solution applicable to human health information monitoring and wearable devices and other application scenarios. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the sensitive element provided in Embodiment 1 of the present invention.

[0020] Figure 2This is a flowchart illustrating the fabrication process of the sensitive element in Embodiment 2 of the present invention.

[0021] Figure 3 This is a schematic diagram of the two-dimensional stress distribution of the flexible pressure sensor provided in Embodiment 3 of the present invention when subjected to pressure. Figure 1 .

[0022] Figure 4 This is a schematic diagram of the two-dimensional stress distribution of the flexible pressure sensor provided in Embodiment 3 of the present invention when subjected to pressure. Figure 2 .

[0023] Figure 5 This is a schematic diagram of the two-dimensional stress distribution of the flexible pressure sensor provided in Embodiment 3 of the present invention when subjected to pressure. Figure 3 .

[0024] Figure 6 This is a graph showing the relationship between the change in contact area between the upper electrode layer and the ion medium layer of five sets of flexible pressure sensors in the comparative experiment of this invention and the pressure value.

[0025] Figure 7 This is a graph showing the relationship between the relative capacitance change and the pressure value in the capacitance change region of four sets of flexible pressure sensors in the optimization experiment of this invention, under a wide sensing range (0-203 kPa).

[0026] Figure 8 The sensitivity curve of the flexible pressure sensor provided in Embodiment 3 of the present invention is shown.

[0027] Figure 9 The graph shows the response time and recovery time of the flexible pressure sensor provided in Embodiment 3 of the present invention under different pressures.

[0028] Figure 10 The diagram shows the hysteresis test curve of the flexible pressure sensor provided in Embodiment 3 of the present invention.

[0029] Figure 11 The graph shows the change in capacitance over time during a stability test of the flexible pressure sensor provided in Embodiment 3 of the present invention.

[0030] Figure 12 The graph shows the change in capacitance over time for the flexible pressure sensor provided in Embodiment 3 of the present invention under constant loading pressure and five repeated loading / unloading cycles at different rates.

[0031] Figure 13 The graph shows the change in capacitance over time for the flexible pressure sensor provided in Embodiment 3 of the present invention under constant loading rate and five repeated loading / unloading cycles with different applied forces.

[0032] The markings in the diagram are: 1. Upper encapsulation layer; 2. Upper electrode layer; 21. Protrusion 1; 22. Conductive film; 3. Ion dielectric layer; 31. Protrusion 2; 4. Lower electrode layer; 5. Lower encapsulation layer. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Example 1

[0035] This embodiment provides a sensing element with a multi-gradient interlocking structure, which includes an encapsulation layer and a functional layer. The encapsulation layer is used to maintain the shape of the functional layer. Please refer to... Figure 1 As shown, the functional layer includes an upper electrode layer 2, an ion dielectric layer 3, and a lower electrode layer 4 arranged sequentially from top to bottom. The ion dielectric layer 3 is attached to the lower electrode layer 4 on one side facing the upper electrode layer 2 and aligned with the upper electrode layer 2. Multiple protrusions 21 arranged in a matrix are provided on the side of the upper electrode layer 2 facing the ion dielectric layer, and multiple protrusions 31 arranged in a matrix are provided on the side of the ion dielectric layer 3 facing the upper electrode layer 2. Both protrusions 21 and 31 are elastic structures. The elastic structure allows protrusions 21 and 31 to change shape when the functional layer is subjected to pressure and to return to their original shape when the pressure is removed. The height of the multiple protrusions 21 gradually increases from left to right, while the height of the multiple protrusions 31 gradually decreases from right to left. Furthermore, the multiple protrusions 21 and 31 in the horizontal direction of the upper electrode layer 2 are arranged in an alternating pattern to form a capacitance variation region with a multi-gradient interlocking structure. In this embodiment, the shape of the functional layer is maintained by an encapsulation layer, so that a multi-gradient interlocked capacitance change region can be formed between the first protrusion 21 and the second protrusion 31 of the functional layer in this solution. By setting the first protrusion 21 and the second protrusion 31 as elastic structures, they can deform when subjected to pressure and return to their original shape when the pressure is removed. Thus, the capacitance of the capacitance change region can change with the change of the contact area between the first protrusion 21 and the second protrusion 31. The upper electrode layer 2 and the lower electrode layer 4 can convert the pressure they receive into an electrical signal and output it through the capacitance change of the capacitance change region.

[0036] In this embodiment, by setting protrusion 21 and protrusion 31 in a multi-gradient structure, the resulting functional layer has better compressibility. The height of protrusion 21 gradually increases from left to right, while the height of protrusion 31 gradually decreases from left to right. This results in a smaller initial contact area and a larger variation in contact area, thereby improving the sensitivity of the sensing element. The multi-gradient structure also helps to increase the lower detection limit and expand the detection range of the sensing element. Furthermore, by interleaving multiple protrusions 21 and 31, they fill the gaps in the array, forming a structure similar to the conical teeth arrangement of a crocodile's jaws, achieving a very small initial contact area and a larger variation in contact area. Furthermore, the capacitance change region with an interlocking structure can be formed between protrusion 21 and protrusion 31. This allows the sensing element to more effectively reduce the internal air gap and increase the dielectric constant when subjected to pressure, while simultaneously increasing the contact area between the upper electrode layer 2 and the ion-dielectric layer 3. The synergistic effect of reducing the internal air gap to increase the dielectric constant and increasing the contact area between the upper electrode layer 2 and the ion-dielectric layer 3 enhances the sensitivity of the sensing element, enabling it to meet the requirements of high-sensitivity scenarios (such as detecting heartbeats and pulses). Therefore, in this solution, the capacitance change region with a multi-gradient interlocking structure formed by protrusions 21 and 31 allows the functional layer to have a smaller initial contact area and a larger contact area change, thereby improving the sensitivity of the sensing element. Simultaneously, the multi-gradient structure also helps to improve the minimum detection limit and increase the detection range of the sensing element. Simultaneously, the interlocking structure formed between protrusion 21 and protrusion 31 fills the air gap in the multi-gradient structure, allowing the sensitive element to reduce the air gap between protrusion 21 and protrusion 31 more quickly and effectively during compression, thereby increasing the dielectric constant. This interlocking structure also ensures that the sidewalls of protrusion 21 and its adjacent two protrusions 31 contact each other when the sensitive element is under pressure, further increasing the contact area between protrusion 21 and protrusion 31. Therefore, in this invention, the interlocking structure between protrusion 21 and protrusion 31 simultaneously reduces the air gap and increases the contact area, with both working synergistically to enhance the sensitivity of the sensitive element. Furthermore, the multi-gradient structure and the interlocking structure also work together to further increase the contact area of ​​protrusion 21 and protrusion 31 during compression, thereby further improving the sensitivity of the sensitive element based on the interlocking structure alone.

[0037] The encapsulation layer can be a flexible structure, which can be fabricated from rubber using 3D printing. In this embodiment, the encapsulation layer can be a hollow structure, and the functional layer can be installed inside the encapsulation layer. By fixing the functional layer with the encapsulation layer, the protrusions 21 and 31 on the functional layer can form a capacitance change region with a multi-gradient interlocking structure. This allows the functional layer to change capacitance in the capacitance change region when subjected to pressure due to the change in the contact area between protrusions 21 and 31. The capacitance change is then output through the upper electrode layer 2 and the lower electrode layer 4, enabling the functional layer to convert pressure into an electrical signal and output it. Furthermore, the encapsulation layer can be a monolithic structure or a detachable structure. When the encapsulation layer is a single integral structure, the side of the upper electrode layer 2 opposite to the protrusion can be attached to the top of the encapsulation layer, and the side of the lower electrode layer 4 opposite to the ion dielectric layer 3 can be attached to the bottom of the encapsulation layer. When attaching the lower electrode layer 4, the protrusion 21 needs to be staggered into multiple protrusions 21 so that the protrusions 21 and 31 can form a multi-gradient interlocked capacitance change region. When the encapsulation layer is a single integral structure, the functional layer can be assembled first, and then the encapsulation layer can be 3D printed on the outer surface of the functional layer, thus encapsulating the functional layer. This encapsulation design allows the encapsulation layer to not only maintain the shape of the functional layer but also isolate the functional layer from the outside world, preventing external environmental influences on the functional layer and thus improving the sensing sensitivity of the functional layer. When the encapsulation layer is a detachable structure, it can include an upper encapsulation layer 1 and a lower encapsulation layer 5, with the upper encapsulation layer 1 detachably mounted on the lower encapsulation layer 5. The side of the upper electrode layer 2 opposite to protrusion 21 can be attached to the side of the upper encapsulation layer 5 facing downwards. The side of the lower electrode layer 4 opposite to the ion medium layer 3 can be attached to the side of the lower encapsulation layer 5 facing upwards towards the encapsulation layer 1. When the upper encapsulation layer 1 is mounted on the lower encapsulation layer 5, the multiple protrusions 21 can be inserted between the multiple protrusions 31, so that the protrusions 21 and 31 are staggered in the horizontal direction of the upper electrode layer 2.

[0038] A conductive film 22 is also coated on the side of the upper electrode layer 2 facing the ion-dielectric layer 3, covering the side of the upper electrode layer 2 where the protrusion 21 is located. In this embodiment, the shape of the conductive film 22 is the same as the shape of the side of the upper electrode layer 2 facing the ion-dielectric layer 3, and the conductive film 22 completely covers the side of the upper electrode layer 2 facing the dielectric layer. This ensures that when the sensitive element is subjected to pressure, the protrusion 31 on the ion-dielectric layer 3 contacts the portion of the conductive film 22 covering the outer surface of the protrusion 21, and the top of the protrusion 31 facing the upper electrode layer 2 also contacts the portion of the conductive film 22 covering the surface of the upper electrode layer 2 facing the ion-dielectric layer 3. The conductive film 22 is formed by coating the AgNWs / MXene mixture onto the surface of the upper electrode layer 2 facing the ion-dielectric layer 3. Silver nanowires (AgNWs) possess excellent overlap, flexibility, and conductivity, enabling the conductive film 22 to adhere completely and tightly to the surface of the upper electrode layer 2 with the irregular structure of the protrusion 21. This ensures that the shape of the conductive film 22 is consistent with the shape of the upper electrode layer 2 facing the ion-dielectric layer 3, while also improving the conductivity of the upper electrode layer 2. Furthermore, the layered composition of the two-dimensional material (MXene) can promote the interconnection of nodes within the AgNWs, thereby reducing the resistance of the fabricated conductive film 22 and enhancing its strength. This further improves the conductivity and lifespan of the conductive film 22, while also protecting the upper electrode layer 2.

[0039] Multiple protrusions 21 on the upper electrode layer 2 can form a rectangular array 1, and multiple protrusions 31 on the lower electrode layer 4 can form a rectangular array 2. Rectangular array 1 and rectangular array 2 are the same size. In rectangular array 1, adjacent protrusions 21 are evenly spaced. In rectangular array 2, adjacent protrusions 31 are also evenly spaced. In the horizontal direction of the upper electrode layer 2, the leftmost protrusion 31 and the rightmost protrusion 21 have the same height, and the height difference between any two adjacent protrusions 21 in the same row of the rectangular array is the same (Δh1). In rectangular array 2, the height difference between any two adjacent protrusions 31 in the same row is Δh2, and Δh1 = Δh2. This arrangement creates a centrally symmetric structure between the multiple protrusions 21 on the upper electrode layer 2 and the multiple protrusions 21 on the ion-dielectric layer 3, with the midpoint of the vertical cross-section of the capacitance change region as the center of symmetry. This centrosymmetric structure can effectively improve the overall stability of the sensitive element.

[0040] Both protrusion 21 and protrusion 31 can be conical structures. In the horizontal direction of the upper electrode layer 2, the horizontal distance from the central axis of each protrusion 21 to the central axes of its two adjacent protrusions 31 is equal. This design ensures that when the sensing element is subjected to external pressure, both sides of protrusion 21 can contact the sidewalls of protrusions 31 located on either side, thereby increasing the contact area between protrusions 21 and 31 and improving the sensitivity of the sensing element.

[0041] The matrix array can be a 4-column × 3-row matrix array. For each row of protrusions 21, their heights from left to right can be 1mm, 1.3mm, and 1.6mm respectively, the base radius of their cones can be 1mm, and the distance between the centers of two adjacent protrusions 21 can be 4mm. For each row of protrusions 31, their heights from left to right can be 1.6mm, 1.3mm, and 1mm respectively, the base radius of their cones can be 1mm, and the distance between the centers of two adjacent protrusions 31 can be 4mm. When the functional layer is not under pressure, the tip of the highest protrusion 21 on the upper electrode layer 2 will contact the surface of the ion-dielectric layer 3, and simultaneously, the tip of the highest protrusion 31 on the ion-dielectric layer 3 will contact the surface of the upper electrode layer 2. In this embodiment, the length and width of the upper electrode layer 2, the ion-dielectric layer 3, and the lower electrode layer 4 can all be 15.3mm and 11.8mm respectively. The sensing element formed by encapsulating the functional layer through an encapsulation layer can be 16.8 mm long, 12.3 mm wide, and 5.2 mm high. Sensing elements of this size can be applied to applications of small-sized flexible pressure sensors, such as embedding them in gloves to detect and wirelessly upload the state information of various joints in the hand, thus allowing other platforms to perform hand posture recognition applications based on this state information.

[0042] In this embodiment, the upper electrode layer 2 and the lower electrode layer 4 can each be connected to a wire, which is used to output the electrical signals generated by the functional layer. The wire can be a copper wire.

[0043] Example 2

[0044] This embodiment provides a method for fabricating a sensitive element with a multi-gradient interlocking structure as shown in Embodiment 1, based on Embodiment 1. Please refer to... Figure 2 As shown, the preparation method includes the following steps:

[0045] (a) First, use SolidWorks 2021 to build the mold model of the upper electrode layer 2 and the mold model of the ion medium layer 3, and then print the actual molds using a 3D printer.

[0046] (II) Preparation of the upper electrode layer 2

[0047] Silicone rubber is poured into the mold of the upper electrode layer 2, and then the mold of the upper electrode layer 2 is placed in a 45°C drying oven for 4 hours to cure. After curing, the upper electrode layer 2 is obtained by demolding.

[0048] (III) Preparation of conductive film 22

[0049] The AgNWs dispersion and MXene dispersion were diluted in water to obtain mixture one. The volume ratio of AgNWs dispersion, MXene dispersion and water was 2:1:20. A certain amount of hydroxypropyl methylcellulose (HPMC) was added to mixture one, and the amount of HPMC added was required to achieve a concentration of 1% wt% in mixture one. The mixture one containing HPMC was then heated in a water bath at 30°C and magnetically stirred for 1 hour to obtain an AgNWs / MXene mixed solution, which is the conductive film 22 solution. Using a dropper, the AgNWs / MXene solution was dripped onto the side of the upper electrode layer 2 with protrusion 21. After the AgNWs / MXene mixed solution dried, it was repeatedly dripped 4-5 times at various points on the side of the upper electrode layer 2 with protrusion 21 until the entire side of the upper electrode layer 2 with protrusion 21 was covered by the conductive film 22 formed by the AgNWs / MXene mixed solution.

[0050] (iv) Preparation of ion-dielectric layer 3

[0051] PVA was slowly added to deionized water while stirring, with a PVA to deionized water mass ratio of 1 g:7 g. The mixture was then magnetically stirred for 1 hour in a 90°C water bath to obtain a PVA gel solution. The obtained PVA gel solution was cooled to 50°C, and then 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4) was added at a solid-liquid ratio of 1 g:3.5 mL to PVA. The mixture was then magnetically stirred for another 1 hour in a 50°C water bath to obtain ion-dielectric layer 3 solution. This ion-dielectric layer 3 solution was then poured into an ion-dielectric layer 3 mold and cured at room temperature for 20 hours before demolding to obtain ion-dielectric layer 3.

[0052] (V) Assembling Sensitive Components

[0053] The upper encapsulation layer 1 and the lower encapsulation layer 5 are prepared using silicone rubber. The side of the upper electrode layer 2 opposite to protrusion 21 is then bonded to the upper encapsulation layer 1. Conductive silver paste is applied to the side of the lower encapsulation layer 5 facing the upper encapsulation layer 1 to form the lower electrode layer 4. The side of the ion-dielectric layer 3 opposite to protrusion 31 is then attached to the lower electrode layer 4. Protrusions 21 and 31 are then interlocked, and the entire sensitive element is assembled by bonding the upper encapsulation layer 1 and the lower encapsulation layer 5 together.

[0054] It is understandable that, in this solution, before encapsulating the upper encapsulation layer 1 and the lower encapsulation layer 5, a wire can be connected to the upper electrode layer 2 and the lower electrode layer 4 respectively, and the other end of these two wires can be led out of the encapsulated sensitive element.

[0055] A sensitive element with a length of 16.8 mm, a width of 12.3 mm, and a height of 5.2 mm can be fabricated using the above method. The upper electrode layer 2, the ion-dielectric layer 3, and the lower electrode layer 4 can all have lengths and widths of 15.3 mm and 11.8 mm, respectively. The protrusions 21 on the upper electrode layer 2 can be a 4×3 rectangular array. Both protrusions 21 and 31 are conical structures with a base radius of 1 mm. The heights of protrusions 21 from left to right are 1 mm, 1.3 mm, and 1.6 mm, respectively; the heights of protrusions 31 from left to right are 1.6 mm, 1.3 mm, and 1 mm, respectively.

[0056] Example 3

[0057] This embodiment provides a flexible pressure sensor, which includes the sensitive element and data processing module of Embodiment 1. The sensitive element is used to sense external pressure and convert the sensed pressure into a changing capacitance value in the capacitance change region, and output the changing capacitance value to the data processing module. The data processing module is used to convert the changing capacitance value into an electrical signal and process the input electrical signal according to the internally constructed relationship between the pressure value and the electrical signal, thereby realizing the conversion of the electrical signal into a pressure value and outputting it.

[0058] In practical applications, the sensitive element fabricated in Example 2 is typically connected to the data processing module to form a complete flexible pressure sensor. When subjected to pressure, the sensitive element causes a change in capacitance in the capacitance change region due to the change in the contact area between protrusion 21 and protrusion 31. The upper electrode layer 2 and the lower electrode layer 4 can transmit this changing capacitance value to the data processing module via wired or wireless means. The data processing module converts the changing capacitance value into an electrical signal and processes the input electrical signal according to the relationship between the pressure value of its internal components and the electrical signal, thereby converting the electrical signal into a pressure value and outputting it. This enables pressure detection using the aforementioned flexible pressure sensor.

[0059] The flexible pressure sensor provided in this solution can be an ion-capacitive flexible pressure sensor.

[0060] Performance testing

[0061] To verify the performance of the flexible pressure sensor provided in this embodiment, the applicant conducted the following experiments.

[0062] (I) Simulation Experiment

[0063] The sensitive element prepared in Example 2 was assembled with the data processing module into a flexible pressure sensor. The assembled flexible pressure sensor was then simulated using the two-dimensional finite element method in ABAQUS, yielding the following results: Figures 3 to 5 . Figures 3 to 5 This diagram illustrates the two-dimensional stress distribution of protrusions 21 and 31 on the sensing element as the applied pressure to the flexible pressure sensor gradually increases. Figure 3 A schematic diagram of the two-dimensional stress distribution on the flexible pressure sensor when pressure is first applied. Figure 1 As can be seen from the figure, the pressure on the sensitive element is relatively small at this time, and the deformation of protrusion 21 and protrusion 31 is also relatively small.

[0064] Figure 4 For is Figure 3 Schematic diagram of two-dimensional stress distribution on a flexible pressure sensor when pressure is increased. Figure 2 . Figure 5 Is Figure 4 Schematic diagram of two-dimensional stress distribution on a flexible pressure sensor when pressure is increased. Figure 3 .pass Figures 3 to 5 It can be seen that as the pressure increases, the contact area of ​​protrusion 21 and protrusion 31 on the sensitive element also gradually increases.

[0065] (II) Comparative Experiment

[0066] Four different sets of sensitive elements were prepared as comparative examples. The following description only focuses on the differences between the sensitive elements in these four comparative examples and the sensitive elements prepared in this scheme; any undescribed parts can be considered identical to the sensitive elements in this scheme. Control group one: Each protrusion 21 and each protrusion 31 has a height of 1.6 mm, and multiple protrusions 21 and 31 are interlocked to form a gradient interlocked structure. Control group two: Each protrusion 21 and each protrusion 31 has a height of 1.3 mm, and multiple protrusions 21 and 31 are interlocked to form a gradient interlocked structure. Control group three: Each protrusion 21 and each protrusion 31 has a height of 1 mm, and multiple protrusions 21 and 31 are interlocked to form a gradient interlocked structure. Control group four: The protrusions 21 on the upper electrode layer 2 are a multi-gradient rectangular array, and the ion dielectric layer 3 is a planar structure to form a gradient non-interlocked structure.

[0067] Four sets of flexible pressure sensors are formed by connecting the four sets of comparative sensitive elements to the data processing module. These four sets of flexible pressure sensors serve as the control group, while the flexible pressure sensors in this scheme serve as the experimental group. The data processing modules connected to both the control and experimental groups are identical. Simulation experiments are conducted on the five sets of flexible pressure sensors to obtain… Figure 6 . Figure 6 This is a graph showing the relationship between the change in contact area between the upper electrode layer 2 and the ion-dielectric layer 3 of five sets of flexible pressure sensors and the pressure value over a wide sensing range (0-203 kPa). Figure 6 The horizontal axis represents the pressure applied to the flexible pressure sensor, and the vertical axis represents the normalized change in the contact area between the upper electrode layer 2 and the ion-dielectric layer 3. The normalized change in contact area is ΔA / A0, where ΔA = A - A0; A is the real-time contact area between the upper electrode layer 2 and the ion-dielectric layer 3; and A0 is the initial contact area between the upper electrode layer 2 and the ion-dielectric layer 3. Figure 6 It can be seen that, under the same pressure, the contact area between the upper electrode layer 2 and the ion medium layer 3 of the flexible pressure sensor in this scheme has a large normalized change, which indicates that the flexible pressure sensor in this scheme has high sensitivity compared with the other four sets of comparative flexible pressure sensors.

[0068] (III) Optimization Experiment

[0069] This optimization experiment investigates the effect of ion-dielectric layer 3 prepared with different volumes of 1-ethyl-3-methylimidazolium tetrafluoroborate solution on flexible pressure sensors. In this experiment, four different ion-dielectric layers 3 were prepared. Each ion-dielectric layer 3 contained 1g of PVA and 7g of deionized water. The preparation method of the ion-dielectric layer 3 can be found in Example 2. The differences are: the volume of 1-ethyl-3-methylimidazolium tetrafluoroborate solution in the first ion-dielectric layer 3 was 2.5mL; the volume of 1-ethyl-3-methylimidazolium tetrafluoroborate solution added to the second ion-dielectric layer 3 was 3mL; the volume of 1-ethyl-3-methylimidazolium tetrafluoroborate solution added to the third ion-dielectric layer 3 was 3.5mL; and the volume of 1-ethyl-3-methylimidazolium tetrafluoroborate solution added to the fourth ion-dielectric layer 3 was 4mL. By keeping other factors constant, four flexible pressure sensors were constructed using the above four ion-dielectric layers 3. Simulation experiments were conducted on the four flexible pressure sensors to obtain… Figure 7 . Figure 7 This is a graph showing the relationship between the relative capacitance change and the pressure value in the capacitance variation region of four sets of flexible pressure sensors within a wide sensing range (0-203 kPa). The relative capacitance change is ΔC / C0, where ΔC = C - C0; and C is the real-time capacitance value in the capacitance variation region, and C0 is the initial capacitance value in the capacitance variation region. Through analysis of... Figure 7Analysis revealed that as the volume of the 1-ethyl-3-methylimidazolium tetrafluoroborate solution in the ion-dielectric layer 3 increased from 2.5 mL to 3.5 mL, the higher the proportion of the 1-ethyl-3-methylimidazolium tetrafluoroborate solution, the more electron pairs per unit contact area between the upper electrode layer 2 and the ion-dielectric layer 3. This resulted in a higher relative capacitance of the flexible pressure sensor and thus higher sensitivity. However, when the volume of the 1-ethyl-3-methylimidazolium tetrafluoroborate solution in the ion-dielectric layer 3 increased from 3.5 mL to 4 mL, the number of electron pairs per unit contact area between the upper electrode layer 2 and the ion-dielectric layer 3 actually decreased. This is likely because the increased volume of 1-ethyl-3-methylimidazolium tetrafluoroborate leads to increased viscosity and the formation of ion clusters, resulting in a decrease in free ions and ion mobility in the ion-dielectric layer 3 solution. This, in turn, limits the performance of the constructed flexible pressure sensor. Furthermore, excessively high concentrations of 1-ethyl-3-methylimidazolium tetrafluoroborate solution are detrimental to the mechanical properties of the prepared ion-dielectric layer 3 solution. Therefore, in this embodiment, through the above optimization experiments, it can be concluded that the solid-liquid ratio of PVA, deionized water, and 1-ethyl-3-methylimidazolium tetrafluoroborate solution can be 1g:7g:3.5mL when preparing the ion-dielectric layer 3 solution.

[0070] (iv) Sensitivity Test

[0071] In the sensitivity experiment, the dynamic testing method can be used to test the sensitivity of the flexible pressure sensor fabricated in this scheme, and the results are as follows. Figure 8 As shown. Figure 8 This is a sensitivity curve of the flexible pressure sensor fabricated in this scheme. Through analysis of... Figure 8 Analysis shows that the sensitivity of the flexible pressure sensor proposed in this design is approximately 73.04 kPa⁻¹ (R²≈0.98) in the 0 kPa to 31 kPa range, approximately 26.14 kPa⁻¹ (R²≈0.97) in the 31 kPa to 115 kPa range, and approximately 8.64 kPa⁻¹ (R²≈0.99) in the 115 kPa to 203 kPa range. These sensitivity measurement results demonstrate that the flexible pressure sensor proposed in this design exhibits high sensitivity and excellent linearity over a wide pressure detection range. This proves that the flexible pressure sensor proposed in this design can be applied to some high-sensitivity scenarios.

[0072] (V) Response Performance Testing

[0073] Under different pressures, a square wave signal was applied to the flexible pressure sensor, and the response time and recovery time of the flexible pressure sensor output were observed. The results are as follows. Figure 9 As shown. By analyzing... Figure 9Analysis shows that the flexible pressure sensor in this design has a response time of about 65ms and a recovery time of about 70ms at pressures of 5.2kPa, 42kPa, and 115kPa. This demonstrates that the flexible pressure sensor in this design has good response and recovery performance to electrical signals.

[0074] (vi) Hysteresis Test

[0075] Hysteresis testing can be performed as follows: Under a specified temperature environment, the pressure of the flexible pressure sensor is increased to 120 kPa. After the pressure stabilizes, it is reduced and returned to zero. During this operation, the capacitance change and pressure value of the flexible pressure sensor are collected in real time, and the hysteresis test curve of the flexible pressure sensor in this scheme is obtained, as shown below. Figure 10 As shown. By analyzing... Figure 10 Analysis shows that the flexible pressure sensor in this scheme exhibits the maximum hysteresis error at around 10 kPa, with a maximum hysteresis error of approximately 25.4%.

[0076] (vii) Stability Testing

[0077] The flexible pressure sensor in this design was subjected to 2500 cycles of dynamic loading and unloading at a pressure of 15 kPa to test its durability and repeatability. The results are as follows: Figure 11 As shown. Among them Figure 11 Parts a and b demonstrate the good repeatability of the flexible pressure sensor in this design. Figure 11 As shown in section c, the signal of the flexible pressure sensor remained basically stable throughout the entire test, with no significant drift. In summary, the flexible pressure sensor proposed in this solution exhibits excellent stability and durability.

[0078] (viii) Dynamic Response Capability Test

[0079] The flexible pressure sensor in this scheme was tested for its dynamic response capability under the same pressure but different frequencies, and the results are as follows: Figure 12 As shown. By analyzing... Figure 12 Analysis shows that, Figure 12 The results showed that the flexible pressure sensor in this design could maintain a stable capacitance signal at different rates after five repeated loading / unloading cycles under constant loading pressure.

[0080] The dynamic response capability of the flexible pressure sensor in this scheme was tested at the same frequency but different pressures, and the results are as follows: Figure 13 As shown. By analyzing... Figure 13 Analysis shows that, Figure 13Five repeated loading / unloading cycles were performed at a constant loading rate using different applied forces. The results show that the sensor's capacitance change remains stable under continuous compression and release at different pressure values. Figure 12 and 13 It can be seen that the flexible pressure sensor in this solution has good dynamic response capability and stability.

[0081] In summary, through the aforementioned performance tests on the flexible pressure sensor of this solution, the inventors have demonstrated that the flexible pressure sensor of this solution possesses high sensitivity over a wide detection range, while also exhibiting good stability and fast response recovery time. This makes the flexible pressure sensor of this solution suitable for applications such as human health information monitoring and wearable devices.

[0082] The basic principles, main features, and advantages of this invention have been described above. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made without departing from the spirit and scope of the invention, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection claimed by this invention is defined by the appended claims and their equivalents.

Claims

1. A sensing element with a multi-gradient interlocking structure, characterized in that, It includes an encapsulation layer and a functional layer, with the encapsulation layer used to maintain the shape of the functional layer; The functional layer includes an upper electrode layer (2), an ion medium layer (3), and a lower electrode layer (4) arranged sequentially from top to bottom; the ion medium layer (3) is attached to the lower electrode layer (4) on one side of the upper electrode layer (2) and aligned with the upper electrode layer (2); On the side of the upper electrode layer (2) facing the ion medium layer (3), there are multiple protrusions 1 (21) arranged in a matrix; on the side of the upper electrode layer (2) facing the ion medium layer (3), there are multiple protrusions 2 (31) arranged in a matrix; both protrusions 1 (21) and protrusions 2 (31) are elastic structures. The height of multiple protrusions 1 (21) gradually increases from left to right, and the height of multiple protrusions 2 (31) gradually decreases from left to right. In addition, multiple protrusions 1 (21) and multiple protrusions 2 (31) are arranged in a staggered manner in the horizontal direction of the upper electrode layer (2) to form a capacitance change region of a multi-gradient interlocking structure.

2. The sensitive element of the multi-gradient interlocking structure as described in claim 1, characterized in that, A conductive film (22) is also coated on the side of the upper electrode layer (2) facing the ion medium layer (3), and the conductive film (22) covers the side of the upper electrode layer (2) where the protrusion (21) is located.

3. The sensitive element of the multi-gradient interlocking structure as described in claim 1, characterized in that, Multiple protrusions (21) form a rectangular array, with adjacent protrusions (21) being equally spaced; multiple protrusions (31) form a rectangular array (2) of the same size as the rectangular array, with adjacent protrusions (31) being equally spaced, and the distance between adjacent protrusions (21) and adjacent protrusions (31) is equal.

4. The sensitive element of the multi-gradient interlocking structure as described in claim 1, characterized in that, Both the first protrusion (21) and the second protrusion (31) are conical structures; the distance from the central axis of each first protrusion (21) to the central axis of the two adjacent second protrusions (31) is equal.

5. The sensitive element of the multi-gradient interlocking structure as described in claim 1, characterized in that, In the horizontal direction of the upper electrode layer (2), the leftmost protrusion 2 (31) has the same height as the rightmost protrusion 1 (21); among the multiple protrusions 1 (21) in the same row on the rectangular array 1, the height difference between each two adjacent protrusions 1 (21) is Δh1; among the multiple protrusions 2 (31) in the same row on the rectangular array 2, the height difference between each two adjacent protrusions 2 (31) is Δh2, and Δh1=Δh2.

6. The sensitive element of the multi-gradient interlocking structure as described in claim 2, characterized in that, The conductive film (22) is formed by coating the AgNWs / MXene mixture onto the surface of the upper electrode layer (2) facing the ion medium layer (3); the shape of the conductive film (22) is the same as the shape of the upper electrode layer (2) facing the ion medium layer (3) and can completely cover the upper electrode layer (2) facing the ion medium layer (3).

7. A method for preparing a sensitive element with a multi-gradient interlocking structure as described in any one of claims 1-6, characterized in that, It includes the following steps: Silicone rubber is poured into the mold of the upper electrode layer (2) and dried and cured in sequence. After curing, the upper electrode layer (2) is obtained by demolding. The AgNWs / MXene mixture is drop-coated onto the side of the upper electrode layer (2) where the protrusion (21) is located, thereby forming the conductive film (22) on the surface of the upper electrode layer (2) facing the ion medium layer (3). After the ion dielectric layer (3) solution is poured into the ion dielectric layer (3) mold, it is cured. After curing, the ion dielectric layer (3) is obtained by demolding. The ion medium layer (3) is bonded to one side of the lower electrode layer (4); then the protrusion one (21) and the protrusion two (31) are arranged opposite to each other and the protrusion one (21) and the protrusion two (31) are staggered to form a sandwich structure of functional layer; The functional layer is encapsulated by printing an encapsulation layer on its surface using 3D printing, thereby producing the sensitive element.

8. The method for preparing the sensitive element of the multi-gradient interlocking structure as described in claim 7, characterized in that, The preparation steps of the AgNWs / MXene mixture are as follows: The AgNWs dispersion and MXene dispersion were diluted in water to obtain mixture one; the volume ratio of the AgNWs dispersion, the MXene dispersion and the water was 2:1:

20. A certain amount of HPMC was added to the mixture, and the mixture was heated and stirred to obtain an AgNWs / MXene mixed solution with a mass concentration of 1 wt% of HPMC.

9. The method for preparing the sensitive element of the multi-gradient interlocking structure as described in claim 7, characterized in that, The ion-dielectric layer (3) solution is prepared by mixing a polyvinyl alcohol solution with a 1-ethyl-3-methylimidazolium tetrafluoroborate solution; the preparation method of the ion-dielectric layer (3) solution is as follows: Polyvinyl alcohol is slowly added to deionized water at a mass ratio of 1:7 while it is being stirred. Then, the mixture is heated in a water bath at 90°C and stirred until homogeneous to obtain a polyvinyl alcohol solution. The polyvinyl alcohol solution was cooled to 50°C, and then a 1-ethyl-3-methylimidazolium tetrafluoroborate solution with a solid-liquid ratio of 1g:3.5mL to polyvinyl alcohol was added. The solution was heated in a water bath at 50°C and stirred until homogeneous to obtain the ion medium layer (3) solution.

10. A flexible pressure sensor, characterized in that, It includes a sensitive element and a data processing module with a multi-gradient interlocking structure as described in any one of claims 1-6. The sensitive element is used to sense external pressure and convert the sensed pressure into a changing capacitance value in the capacitance change zone, and output the changing capacitance value to the data processing module. The data processing module is used to convert the changing capacitance value into an electrical signal and process the input electrical signal according to the internally constructed relationship between the pressure value and the electrical signal, thereby realizing the conversion of the electrical signal into a pressure value and outputting it.

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