Flexible dual-mode capacitance touch sensor based on three-gradient micro-dome porous structure

Abstract

The invention relates to a flexible dual-mode capacitive touch sensor based on a three-gradient micro-dome porous structure. The sensor adopts a sandwich structure and comprises an upper electrode layer, a TGP dielectric layer and a lower electrode layer, wherein the upper electrode layer and the lower electrode layer respectively cover the upper surface and the lower surface of the TGP dielectric layer; the TGP dielectric layer comprises a gradient part and a porous part, the porous part is located on the upper surface of the lower electrode layer, and the gradient part is distributed on the porous part; the gradient part comprises three kinds of micro-dome structures and flat-top protrusions. Different pressure working characteristics of the two structures are fully utilized, so that the porous structure works in a low-pressure area, the gradient structure works in a medium-high pressure area, the performance of the porous structure and the gradient structure is synergistically enhanced, the linear range of the sensor is widened, and the sensitivity is further improved.

Description

Technical Field

[0001] This invention relates to the field of flexible tactile sensor technology, specifically to a flexible dual-mode capacitive tactile sensor based on a three-gradient micro-dome porous structure and its fabrication method, which can be used in multiple fields such as medical detection, electronic skin, and human-computer interaction. Background Technology

[0002] In the field of human-computer interaction, flexible sensors have attracted widespread attention as an indispensable component. Unlike traditional sensors made of metal or semiconductor materials, flexible sensors offer a reliable option for human-computer interaction due to their inherent flexibility. This has sparked extensive interest and research into flexible sensors, which have potential applications in various fields such as electronic skin, health monitoring, and human-computer interaction technologies.

[0003] Traditional capacitive sensors are primarily composed of rigid silicon semiconductors, measuring external pressure by utilizing changes in capacitance caused by variations in substrate spacing. Capacitive sensors possess high sensitivity, stability, and reliability, making them indispensable devices in critical industries such as aerospace, medical devices, and nuclear power. However, despite their excellent performance, the rigidity of traditional rigid capacitive sensors makes them prone to failure under deformation conditions or in complex structural environments. Researchers have begun exploring how to leverage the superior properties of flexible materials to replace traditional semiconductor substrates, thereby transforming sensor design.

[0004] To improve sensor sensitivity, researchers mainly construct hemispherical or pyramidal microstructures on the surface of dielectric layers or electrodes, or introduce porous microstructures. Bao et al. [Nie, Baoqing, et al. "Iontronic microdroplet array for flexible ultrasensitive tactile sensing." Lab on a Chip 14.6(2014):1107-1116.] designed a capacitive pressure sensor with a pyramidal microstructure using an inverted pyramidal template. The pressure sensitivity of this microstructured film far exceeds that of unstructured elastic films of similar thickness, and can be adjusted by using different microstructures.

[0005] In recent years, there have been some research achievements in double-layer capacitive sensors. Baoqing Nie et al. [Bai N, Wang L, Wang Q, et al. Graded intrafillable architecture-based iontronic pressure sensor with ultra-broad-range high sensitivity [J]. Nature Communications, 2020, 11(1): 209. Bai N, Wang L, Xue Y, et al. Graded Interlocks for Iontronic Pressure Sensors with High Sensitivity and High Linearity over a Broad Range [J]. ACS Nano, 2022, 16(3): 4338-4347.] proposed an ion droplet array, in which nanodroplets are sandwiched between polymer films of two patterned transparent electrodes to form a double layer with a unit area capacitance. Under the action of external force, the deformation of the film leads to circumferential expansion at the contact point of the highly elastic vertical electrodes, achieving high mechanical sensitivity and high pressure resolution. However, this method requires the fabrication of a series of completely identical ion droplets, which requires high processing precision and is difficult to fabricate.

[0006] Recent studies have shown that gradient structures offer a new option for solving sensor problems. Ji B et al. [Ji B, Zhou Q, Lei M, et al. Gradient architecture‐enabled capacitive tactile sensor with high sensitivity and ultrabroad linearity range[J]. Small, 2021, 17(43):2103312.] proposed a gradient structure dielectric based on microdots. This type of structure enables progressive contact between the dielectric layer and the electrode, thereby improving the compressibility of the structure and avoiding signal saturation, significantly expanding the detection range. Although gradient structures have high sensitivity in the low to medium pressure range, due to the limited size of the sensor itself, it cannot support gradients of more than three levels and more microdot pixels. The linearity performance is not good in a wider pressure range, especially the sensitivity performance is poor under high pressure.

[0007] Meanwhile, research shows that porous structures exhibit good sensitivity and linearity in the low-pressure range, while the capacitance change is small in the high-pressure range. The different pressure operating characteristics of porous structures and other structures make it possible for the two structures to work together. Shixue He et al. [Shixue He, Jian Wu, Benlong Su, Shouyao Liu, Youshan Wang, et al. Design of PDMS / CNT flexible pressure sensor based on double structure with the regulation of electrical properties [J].Composites Science and Technology, Volume 242, 2023, 110166, ISSN 0266-3538.] proposed a dielectric structure coupling porous structure and surface microstructure, which significantly improved the linear operating range of the sensor. However, this sensor can only sense pressure changes and is not suitable for applications requiring coordinated sensing of pressure, curvature, etc. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing a flexible dual-mode capacitive tactile sensor based on a three-gradient micro-dot porous structure and its fabrication method. This sensor employs a three-gradient porous structure (TGP) dielectric, where the gradient structure is embodied in an array of micro-dots of three different heights, with all dome pixels distributed on a flexible substrate of the porous structure. By coupling these two structures, the different pressure operating characteristics of the two structures are fully utilized, allowing the porous structure to operate in the low-pressure region and the gradient structure in the medium-to-high-pressure region, achieving synergistic enhancement of their performance, widening the sensor's linear range, and further improving sensitivity.

[0009] The technical solution of the present invention to solve the aforementioned technical problem is, A flexible dual-mode capacitive tactile sensor based on a three-gradient micro-dome porous structure, the sensor adopts a sandwich configuration including an upper electrode layer, a TGP dielectric layer, and a lower electrode layer; The upper electrode layer and the lower electrode layer cover the upper and lower surfaces of the TGP dielectric layer, respectively. The upper electrode layer is made of foamed copper-nickel alloy with a thickness of 0.8-1.2 mm; The lower electrode layer is made of carbon nanofiber cloth with a thickness of 0.08-0.12 mm; The TGP dielectric layer is made of sodium bicarbonate / carbon nanotube (CNT) / polydimethylsiloxane (PDMS) composite material with a thickness of 3.6-4.4 mm; wherein the mass ratio of sodium bicarbonate to PDMS is 1:15, and the carbon nanotubes are 2.0 wt% of PDMS.

[0010] The TGP dielectric layer includes a gradient portion and a porous portion. The porous portion is located on the upper surface of the lower electrode layer, and the gradient portion is distributed on the porous portion. The gradient portion includes three micro-dome structures and a flat-top protrusion. The three micro-dome structures are a first micro-dome protrusion, a second micro-dome protrusion, and a third micro-dome protrusion. The flat-top protrusion has a height of 2500 μm, the first micro-dome protrusion has a height of 2100 μm, the second micro-dome protrusion has a height of 1400 μm, and the third micro-dome protrusion has a height of 700 μm. The projections of the flat-top protrusion and the three micro-dome protrusions are circles with the same diameter and a radius of 700 μm. That is, the third micro-dome protrusion is hemispherical. The first and second micro-dome protrusions are both structures with a hemispherical top and a cylindrical bottom, and the diameters of the sphere and the cylinder are the same. The flat-top protrusion is cylindrical. All the protrusions of the gradient structure are distributed in a 7x7 square array. Among them, there are 5 flat-top protrusions, located at the center of the array and at the four corners of the 5*5 array centered on this center; The number of the first micro-dot protrusions is 4, located at the four corners of the 3*3 array at the center of the matrix; The number of second micro-dome protrusions is 12, located in the 5*5 array at the center of the matrix, and symmetrically distributed in a "grid" shape, excluding the flat-top protrusions and the first micro-dome protrusions. The number of the third micro-dot protrusions is 28, occupying the remaining empty spaces in the 7*7 array; The spacing between adjacent protrusions is 1100 μm, and all protrusions are distributed in a 23 × 23 mm area. 2 On a porous structure 2 (1400 μm thick) serving as a flexible substrate.

[0011] Both the gradient and porous sections are made of a mixture of NaHCO3-doped CNTs and PDMS, with a sodium bicarbonate to PDMS mass ratio of 1:15 and carbon nanotubes comprising 2.0 wt% of PDMS.

[0012] The essential features of this invention are: This invention optimizes the traditional dielectric structure by employing a TGP (Transient Gradient Geometric Surface) dielectric, and the gradient and porous structures improve the sensor's sensitivity. Secondly, the synergistic effect of these two structures expands the sensor's linear operating range. Thirdly, compared to other single-function sensors, it adds a bending measurement function, which can be used to measure the curvature of an object.

[0013] Compared with the prior art, the beneficial effects of the present invention are: 1. High pressure detection accuracy. Traditional dielectric structures suffer from low detection accuracy due to the small change in electrode spacing. The TGP structure alters the capacitance by changing the dielectric constant and electrode contact area, resulting in a significantly higher change compared to that achieved by compressing the electrode spacing. Therefore, the TGP dielectric inherits the high sensitivity characteristics of both gradient and porous structures, further improving sensitivity. Figure 4 It can be seen that the average sensitivity of this sensor can reach 0.181 kPa within its operating range. -1 Its sensitivity performance is quite good.

[0014] 2. Wide linear operating range. Traditional single-structure dielectrics have extremely limited linear operating ranges. The TGP structure combines gradient and porous structures, allowing the porous structure to operate in the low-pressure range and the gradient structure in the medium-to-high-pressure range. The synergistic effect of these two structures significantly expands the sensor's linear operating range. Figure 4 It can be seen that the linearity R of this sensor is good within a wide pressure range of 0-1800 kPa. 2 =0.99, demonstrating excellent linearity.

[0015] 3. Dual Sensing of Tactile Pressure and Bending. Traditional capacitive sensors detect objects through pressure, which limits their large-scale application in fields such as electronic skin, health monitoring, and human-computer interaction. This sensor features bending measurement capabilities, enabling better perception of relevant object parameters through dual sensing of tactile pressure and bending degree. Figure 5 It can be seen that this sensor still exhibits reliable sensitivity and linearity when performing the bending measurement function.

[0016] 4. High resistance to damage. Both PDMS and the electrode materials used have high resistance to damage. Since the robotic arm may collide with hard objects during the grasping process, this invention uses materials with high resistance to damage.

[0017] 5. Strong anti-interference capability. This sensor is less affected by external factors such as noise, has a high signal-to-noise ratio, and strong anti-interference capability, effectively improving the sensor's sensitivity and maximizing the conversion of pressure into capacitance, resulting in more accurate capacitance measurement.

[0018] 6. Good temperature stability. The materials used in this sensor have good heat resistance. Figure 6 As can be seen from the experimental data, this sensor can still maintain good working condition at 45℃. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the sensor of the present invention; Figure 2 This is a schematic diagram of the gradient structure of the TGP structure dielectric of the sensor of the present invention; Figure 3 This is a schematic diagram of the principle of the sensor tactile sensing module of the present invention; Figure 4 This describes the pressure-capacitance relationship of the sensor of this invention within this pressure range (0 kPa - 1800 kPa).

[0020] Figure 5 This describes the pressure-capacitance relationship of the sensor in this invention within this bending range (0°-60°).

[0021] Figure 6 This is the pressure-capacitance relationship of the sensor of the present invention under temperature (25℃-45℃) testing.

[0022] Wherein, 1-lower electrode layer; 2-porous portion; 3-gradient portion; 4-upper electrode layer; 31- First micro-dot protrusion; 32- Second micro-dot protrusion; 33- Third micro-dot protrusion; 34- Flat-top protrusion. Detailed Implementation

[0023] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention and do not limit the scope of protection of this application.

[0024] Example 1: This invention discloses a flexible dual-mode capacitive tactile sensor based on a three-gradient micro-dome porous structure, such as... Figure 1 As shown, the sensor adopts a sandwich configuration, including an upper electrode layer 4, a TGP dielectric layer, and a lower electrode layer 1; Among them, the upper electrode layer 4 and the lower electrode layer 1 cover the upper and lower surfaces of the TGP dielectric layer, respectively. The upper electrode layer is made of foamed copper-nickel alloy (provided by Suzhou Kunshan Guangjiayuan New Material Co., Ltd.), with a thickness of 1mm; The material of the lower electrode layer is carbon nanofiber cloth (purchased from Suzhou Chint Rong Scientific Research New Materials Co., Ltd.), with a thickness of 0.1 mm; the above two materials are not limited to this.

[0025] The TGP dielectric layer is made of sodium bicarbonate / carbon nanotube (CNT) / polydimethylsiloxane (PDMS) composite material with a thickness of 3.9 mm; The TGP dielectric layer includes a gradient portion 3 and a porous portion 2. The porous portion 2 is located on the upper surface of the lower electrode layer 1, and the gradient portion 3 is distributed on the porous portion 2. The gradient portion 3 includes three micro-dome structures and a flat-top protrusion 34. The three micro-dome structures are a first micro-dome protrusion 31, a second micro-dome protrusion 32, and a third micro-dome protrusion 33. Among them, the height of the flat-top protrusion 34 is 2500μm, the height of the first micro-dome protrusion is 2100μm, the height of the second micro-dome protrusion is 1400μm, and the height of the third micro-dome protrusion is 700μm; the projections of the flat-top protrusion 34 and the three micro-dome protrusions are circles with the same diameter and a radius of 700μm, that is, the third micro-dome protrusion 33 is hemispherical, the first micro-dome protrusion 31 and the second micro-dome protrusion 32 are both structures with a hemispherical top and a cylindrical bottom, and the diameters of the sphere and the cylinder are the same; while the flat-top protrusion 34 is a cylinder; Specifically, such as Figure 2 As shown, all the protrusions of the gradient structure are distributed in a 7*7 square array (a total of 49 protrusion units). Among them, there are 5 flat-top protrusions 34, located at the center of the array and at the four corners of the 5*5 array centered on this center; There are four first micro-dot protrusions 31, located at the four corners of the 3*3 array at the center of the matrix; There are 12 second micro-dome protrusions 32, located in the 5*5 array at the center of the matrix, and are symmetrically distributed in a "grid" shape, except for the remaining positions after removing the flat-top protrusions 34 and the first micro-dome protrusions 31. The number of the third micro-dome protrusions 33 is 28, occupying the remaining empty spaces in the 7*7 array; The spacing between adjacent protrusions is 1100 μm, and all protrusions are distributed in a 23 × 23 mm area. 2 On a porous structure 2 (1400 μm thick) serving as a flexible substrate.

[0026] Both the gradient portion 3 and the porous portion 2 are made of a mixture of NaHCO3-doped CNTs and PDMS, wherein the mass ratio of sodium bicarbonate to PDMS is 1:15, and the carbon nanotubes account for 2.0 wt% of the PDMS mass fraction.

[0027] The basic working principle of this sensor: When the porous structure is in operation, the electrode spacing and the equivalent dielectric constant of the dielectric material jointly determine the capacitive response characteristics of the sensor. During compression, the air inside the pores is gradually filled by the PDMS composite material with a higher dielectric constant, causing a dynamic change in the equivalent dielectric constant of the porous PDMS composite material. This change can be expressed by the following equation: (1) In dielectric property analysis, The dielectric constant of air. The dielectric constant of the PDMS composite material is represented by... The proportion of air in the volume. This represents the volume percentage of the PDMS composite material. Based on the above parameters, the capacitance value of the porous dielectric structure ( This can be represented by the following relation: (2) For ease of representation in the formula, the flat-top protrusion 34 in the gradient structure is used to compress the flat-top protrusion 34 of the porous structure. The three micro-dome structures, namely the first micro-dome protrusion 31, the second micro-dome protrusion 32, and the third micro-dome protrusion 33, are represented by the first micro-dome protrusion 31, the second micro-dome protrusion 32, and the third micro-dome protrusion 33, respectively.

[0028] Under low pressure, the flat-topped protrusions of the 34 pixels in the gradient structure deform, causing the pores in the porous structure to be compressed under external force. The PDMS composite material gradually replaces the space originally occupied by air. This mechanism significantly improves the capacitive response characteristics of the sensor in the low-pressure region by simultaneously changing the electrode spacing and the equivalent dielectric constant.

[0029] For the gradient structure design, based on the above equivalent circuit model analysis, it is shown that the total capacitance of the three-gradient structure can be approximately expressed as the sum of the capacitances of each micro-dome: (3) in, C x crown The superscript 1 represents the total capacitance of a single micro-dome unit (including the contribution of the air layer above the dome). The superscripts 1, 2, and 3 correspond to micro-domes of different sizes with radii of 2100 μm, 1400 μm, and 700 μm, respectively, while the superscript 0 represents a flat-topped protrusion. In the low-pressure range, the capacitance characteristics of smaller micro-dome units, due to the gap between them and the upper electrode, are mainly manifested as the series effect between the air dielectric and the PDMS. Therefore, C x crown The expression is as follows: (4) At this point, the capacitance characteristic of a single micro-dome unit can be expressed by the following equation: (5) In capacitance characteristic analysis, C p This represents the total capacitance of the micro-dome unit after it is fully compressed. The superscripts 1, 2, and 3 correspond to three different heights of micro-dome structures: 2100μm, 1400μm, and 700μm, respectively. The superscript 0 represents a flat-top protrusion. C air This indicates the capacitance formed by the air gap above the dome; the superscript has the same meaning as above. Because... C air far below C p Furthermore, since the micro-dots and air are connected in series, the capacitive contributions of the second micro-dot protrusion 32 and the third micro-dot protrusion 33 are negligible. At this point, the total capacitance of the micro-dot unit is... C gradient It can be simplified to: (6) It can be seen that in the low-pressure range, the response characteristics of the TGP dielectric layer are mainly determined by the first micro-dot protrusion 31, which has the largest height. As the pressure gradually increases, after the first micro-dot protrusion 31 is compressed, the second micro-dot protrusion 32 and the third micro-dot protrusion 33 successively contact the upper electrode, and their capacitance characteristics change from the original air series mode to a parallel mode with the pixel of the first micro-dot protrusion 31. This stage... C gradient They can be simplified as follows: (7) (8) In the medium to high pressure range, the capacitive response characteristics of the TGP dielectric layer are successively dominated by the second micro-dot protrusion 32 and the third micro-dot protrusion 33. In actual experiments, by adjusting the height and distribution of the gradient micro-dot units, a gradient design of the contact area can be achieved, thereby enabling customized control of the dielectric response in different pressure ranges.

[0030] Based on the above mechanism analysis, the overall capacitance characteristics of the TGP structure can be described by the following expression: (9) In summary, the TGP structure dielectric allows for operation within a small pressure range. First increase the pressure, then increase the pressure. C gradient Furthermore, the two structures work together to achieve sensitive and linear changes in capacitance over a wide pressure range.

[0031] In summary, this study established an equivalent circuit model for the TGP dielectric structure. The TGP dielectric structure optimizes the capacitive response characteristics in both low-pressure and high-pressure regions through the synergistic effect of the porous network and gradient micro-dots. In the initial pressure stage, the porous structure deforms first, transmitting pressure to the porous region through five planar pixels with flat-topped protrusions (34 pixels). As the pressure increases beyond the linear response range of the porous structure (0-150 kPa), the gradient micro-dots (first micro-dot protrusion 31, second micro-dot protrusion 32, and third micro-dot protrusion 33) are sequentially and completely compressed. This working mechanism... Figure 3 This is illustrated quite vividly in the text. This hybrid working mechanism not only significantly extends the linear detection range of the sensor, but also further enhances the sensor's sensitivity in high-pressure regions through the incompletely compressed pores.

[0032] If the height difference between the micro-dots is large, a noticeable non-linear transition may occur. This is because the excessive height difference between the dome radius and the dome causes the second micro-dome protrusion 32 to fail to respond promptly after the first micro-dome protrusion 31 is fully compressed. If the height difference between the micro-dots is small, the linear range of pressure detection will be significantly reduced. This may be because a small height difference (less than the dome radius) causes the lower pixel dome to begin responding before the higher pixel dome is fully compressed, thus shortening the working range of the first micro-dome protrusion 31. Choosing a height difference equal to the dome radius will exhibit good linearity and a good pressure detection range.

[0033] The fabrication process of this embodiment based on a flexible dual-mode capacitive tactile sensor with a three-gradient micro-dome porous structure is as follows: 1. Fabrication of the TGP dielectric layer. This study used a NaHCO3 / CNT-doped PDMS composite system to prepare a dielectric layer with a gradient and porous structure. In the preparation process, sodium bicarbonate powder was first ground for 10 minutes to enhance its reactivity. Then, a specific ratio of carbon nanotubes, ground sodium bicarbonate, and PDMS prepolymer (the mass fraction of carbon nanotubes to PDMS prepolymer was 2.0 wt%; the mass ratio of sodium bicarbonate to PDMS prepolymer was 1:15) was dispersed in n-hexane solvent and uniformly mixed by ultrasonic treatment at 150W for 30 minutes. After removing the solvent by heating the mixture at 90℃ for 1 hour, a curing agent was added at a mass ratio of 10:1 and stirred until homogeneous. The mixture was injected into a 3D printing mold, allowed to stand for 30 seconds, and then cured at 130℃ for 3 hours. During this process, sodium bicarbonate completely decomposed to form a porous structure. Demolding was then performed to complete the fabrication of the TGP dielectric layer. 2. Mounting of the upper and lower electrode layers. Then, ethylene oxide is used to bond the upper and lower electrodes to the upper and lower surfaces of the TGP dielectric, respectively, completing the encapsulation. 3. Sensor wiring. Lead the upper and lower electrode layers out to the electrode terminals, and fix the copper wires to the electrode terminals to begin measurement.

[0034] Sensor capacitance measurements were performed using a Keysight 4990A impedance analyzer at a 10kHz test frequency and a 1V AC signal. The sensor capacitance value was acquired through a scanning method, and the value reflects changes in the applied pressure.

[0035] To verify the pressure-capacitance characteristics of a tactile sensor, a pressure tester and impedance analyzer can be used to measure the relationship between the sensor's capacitance and pressure. For example... Figure 4 As shown, the pressure-capacitance relationship of the sensor can be measured over a wide pressure range (0 kPa-1800 kPa), allowing for the derivation of the relationship between applied pressure and ΔC / C0 through data analysis. The sensor maintains high responsiveness across the ultra-wide 0-1800 kPa range, with an average sensitivity of 0.181 kPa. -1 Compared to the current technology's 0-1700kPa and 0.065kPa... -1 The sensitivity has been improved. (By...) Figure 5 It can be seen that the sensor of the present invention has excellent sensitivity and linearity, and the accuracy of pressure measurement is improved compared with other similar sensors.

[0036] To verify the bending-capacitance characteristics of the sensor, a press, protractor, and impedance analyzer can be used to measure the relationship between the sensor's capacitance and pressure. For example... Figure 5 As shown, the bending angle-capacitance relationship of the sensor can be measured over a wide pressure range (0 kPa-1800 kPa), and the relationship between bending degree and ΔC / C0 can be derived through data analysis. Figure 5 It is known that when the angle exceeds 45°, the sensor output changes slowly and there is a risk of structural deformation. Therefore, the effective measurement range is limited to 0-45°. Under the extreme bending state of 45°, ΔC / C0 reaches a maximum of 182. The sensor of this invention exhibits excellent sensitivity and linearity in measuring bending, demonstrating its good pressure and bending dual-modal measurement performance.

[0037] In the temperature experiment, the variable temperature test of the high-temperature mica heating box showed that the sensor has good environmental adaptability. Figure 6 Its wide linear range and high sensitivity characteristics enable it to perform reliably under complex conditions such as high temperatures. Within the temperature range of 25~45℃, the sensor's performance fluctuation is less than 3.5%, demonstrating good temperature stability.

[0038] Sensors, as multifunctional monitors, can be used in fields such as human-computer interaction, tactile perception, and medical testing.

[0039] Matters not covered in this invention are common knowledge.

Claims

1. A flexible dual-mode capacitive tactile sensor based on a three-gradient micro-dome porous structure, characterized in that, The sensor adopts a sandwich configuration, including an upper electrode layer, a TGP dielectric layer, and a lower electrode layer; The upper electrode layer and the lower electrode layer cover the upper and lower surfaces of the TGP dielectric layer, respectively. The TGP dielectric layer includes a gradient portion and a porous portion. The porous portion is located on the upper surface of the lower electrode layer, and the gradient portion is distributed on the porous portion. The gradient portion includes three micro-dome structures and a flat-top protrusion. The three micro-dome structures are a first micro-dome protrusion, a second micro-dome protrusion, and a third micro-dome protrusion. All the protrusions of the gradient structure are distributed in a 7x7 square array. Among them, there are 5 flat-top protrusions, located at the center of the array and at the four corners of the 5*5 array centered on this center; The number of the first micro-dot protrusions is 4, located at the four corners of the 3*3 array at the center of the matrix; The number of second micro-dome protrusions is 12, located in the 5*5 array at the center of the matrix, and symmetrically distributed in a "grid" shape, excluding the flat-top protrusions and the first micro-dome protrusions. The number of the third micro-dome protrusions is 28, occupying the remaining empty spaces in the 7*7 array.

2. The flexible dual-mode capacitive tactile sensor based on a three-gradient micro-dome porous structure as described in claim 1, characterized in that, The height of the flat-topped protrusion is 2500 μm, the height of the first micro-dot protrusion is 2100 μm, the height of the second micro-dot protrusion is 1400 μm, and the height of the third micro-dot protrusion is 700 μm. The projections of the flat-topped protrusion and the three types of micro-dot protrusions are circles with the same diameter and a radius of 700 μm. That is, the third micro-dot protrusion is hemispherical. The first and second micro-dot protrusions are both structures with a hemispherical top and a cylindrical bottom, and the diameters of the sphere and the cylinder are the same. The flat-topped protrusion is cylindrical. The distance between adjacent protrusions is 1100μm.

3. The flexible dual-mode capacitive tactile sensor based on a three-gradient micro-dome porous structure as described in claim 1, characterized in that, The upper electrode layer is made of foamed copper-nickel alloy and has a thickness of 1 mm; The lower electrode layer is made of carbon nanofiber cloth with a thickness of 0.1 mm.

4. The flexible dual-mode capacitive tactile sensor based on a three-gradient micro-dome porous structure as described in claim 1, characterized in that, The porous structure has dimensions of 23mm × 23mm.

5. The flexible dual-mode capacitive tactile sensor based on a three-gradient micro-dome porous structure as described in claim 1, characterized in that the gradient... Both the partial and porous parts are made of sodium bicarbonate / carbon nanotube (CNT) / polydimethylsiloxane (PDMS) composite material, with a sodium bicarbonate to PDMS mass ratio of 1:15, carbon nanotubes accounting for 2.0 wt% of PDMS mass, a dielectric layer thickness of 3.9 mm, and an overall sensor thickness of 5 mm.

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