A tactile sensor and its fabrication method

Abstract

This application discloses a tactile sensor and its fabrication method. The tactile sensor includes a tactile membrane, an optical window, a cavity, a deformation structure, and a capacitor structure. The cavity is enclosed by a cavity wall and two opposing openings at both ends. The two openings respectively house the tactile membrane and the optical window. The deformation structure is located within the cavity and is used to absorb energy from an external light source. Under photothermal action, it deforms, thereby displacing the tactile membrane to generate tactile stimulation that can act on a target object. The capacitor structure converts the tactile stimulation into an electrical signal for tactile information acquisition. This application utilizes the deformation structure to deform within a certain temperature range, thereby displacing the tactile membrane and converting light energy into tactile output. This avoids the dependence of traditional light-driven tactile devices on closed air cavities, gas expansion, and suspended light-absorbing sheets, improving the structural stability and driving efficiency of the tactile sensor and increasing its environmental adaptability.

Description

Technical Field

[0001] This application relates to the field of tactile detection technology, and in particular to a tactile sensor and its preparation method. Background Technology

[0002] Tactile perception, as a core capability for humans to exchange information and regulate behavior with the outside world, plays an irreplaceable role in intelligent robots, virtual reality, wearable medical devices, rehabilitation aids, and novel human-computer interaction systems. Currently, most tactile actuation methods employ traditional technologies such as electromagnetic coils, piezoelectric ceramics, thermal gas expansion structures, hydraulic micropumps, or electroactive polymers. While these have driven the development of tactile devices, they are not suitable for flexible electronics, soft robots, and bio-adhesive devices. For example, electromagnetic and piezoelectric devices often rely on rigid materials and complex driving circuits, making them incompatible with high-curvature or stretchable surfaces. Structures based on closed gas expansion, while providing some flexibility, suffer from complex cavity encapsulation processes and are highly sensitive to internal and external pressure differences, making them unstable in vacuum, underwater, or high-humidity environments. Electroactive polymers are limited by response speed, driving voltage, and material durability, making long-term reliable operation difficult. Furthermore, traditional electric drive systems may generate electromagnetic interference or safety hazards in sensitive scenarios, thus limiting their application in medical and skin-friendly devices.

[0003] In recent years, many schemes have also used photothermal effects to heat the gas in the closed cavity, and the gas pressure increases to drive the tactile membrane to move. Most of the research on light-driven tactile sensing revolves around the fixed route of "lighting - heating of light-absorbing sheet - gas expansion - displacement of top membrane". However, this scheme has limitations in practical applications: (1) The driving method is single. All deformations are due to the volume expansion of the gas, which leads to limited output tactile modes and makes it difficult to achieve directional, gradual or nonlinear tactile stimulation. Once the cavity shape is fixed, the tactile output lacks programmability and plasticity. (2) Existing schemes generally rely on extremely thin suspended light-absorbing sheets as the core light-receiving components. After being heated by light, these sheets have problems such as thermal drift, mechanical fatigue and unstable positioning. The manufacturing and packaging processes are complex, which affects the long-term stability of the sensor and the manufacturing yield of mass production. (3) Gas expansion is sensitive to cavity size, gas type and initial pressure. Different environmental conditions under the same light power will cause fluctuations in output tactile intensity, making it difficult to ensure long-term consistency and environmental adaptability. The cavity must remain sealed, meaning that this type of structure cannot operate in vacuum, liquid media, or high humidity environments, significantly limiting its application range. Furthermore, the thermal diffusion rate of the light-absorbing sheet and the heat dissipation effect of the cavity wall result in low light energy utilization, with some energy failing to be effectively converted into usable mechanical displacement, leading to a decrease in energy conversion efficiency. Summary of the Invention

[0004] This application aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, the purpose of this application is to provide a tactile sensor and its fabrication method, which can solve the problems of existing light-driven tactile sensing devices relying on gas volume expansion, resulting in limited output tactile modes, and relying on extremely thin suspended light-absorbing sheets, leading to low device stability.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0006] A tactile sensor, comprising: Tactile membrane; An optical window, which is positioned opposite the tactile membrane, is used to transmit an external light source; The cavity is formed by a cavity wall and two openings at opposite ends, one opening of which is provided with the tactile membrane, and the other opening of which is provided with the optical window; A deformable structure is provided inside the cavity to absorb the energy of the external light source and deform under the action of photothermal effect, thereby pushing the tactile membrane to produce displacement, so as to form a tactile stimulus that can act on the target object; A capacitor structure, disposed within the cavity, is used to convert the tactile stimulation into an electrical signal to facilitate the acquisition of tactile information.

[0007] According to some embodiments of this application, the deformable structure is a honeycomb structure, the honeycomb structure includes a plurality of sidewalls, the sidewalls mutually enclosing each other to form a plurality of polygonal units, and adjacent polygonal units are connected by the sidewalls, wherein: The inclination angle of the sidewall ranges from 60° to 85°; and / or, The thickness of the sidewall ranges from 50 μm to 500 μm; and / or, The height of the polygonal unit ranges from 0.5mm to 3mm; and / or, The inner diameter of the polygonal unit ranges from 0.3 mm to 2 mm.

[0008] According to some embodiments of this application, the deformable structure is a paper-folding structure, which includes a plurality of undulating folded surface units connected sequentially by crease lines. Adjacent folded surface units are located at different heights, and the included angle between adjacent crease lines is 30° to 120°.

[0009] According to some embodiments of this application, the deformable structure is a helical structure, the helical structure comprising a strip-shaped member, the strip-shaped member being helical, wherein... The helical pitch of the spiral structure is 0.5 mm to 5 mm; and / or, The spiral diameter of the spiral structure is 1 mm to 10 mm; and / or, The spiral structure has 1 to 10 spiral turns.

[0010] According to some embodiments of this application, the material of the deformable structure is one of shape memory polymer-based composite materials, liquid crystal elastomers, and shape memory alloys.

[0011] According to some embodiments of this application, the shape memory polymer-based composite material includes a matrix and a photothermal conversion material. The matrix is ​​one of polyurethane shape memory polymer, epoxy shape memory polymer, polymethyl methacrylate, and polycaprolactone. The photothermal conversion material is at least one of carbon black, carbon nanotubes, graphene, and metal nanoparticles.

[0012] According to some embodiments of this application, the capacitor structure includes a first conductive layer and a second conductive layer, and the deformation structure divides the cavity into a first cavity and a second cavity; the first cavity is located on the side of the deformation structure near the tactile membrane, and the first conductive layer is disposed in the first cavity; the second cavity is located on the side of the deformation structure near the optical window, and the second conductive layer is disposed in the second cavity.

[0013] A method for fabricating a tactile sensor, comprising: Cleaning and pretreatment of optical windows; Preparation of deformable structures: Preparation of cavity walls and tactile membranes; The deformable structure is placed inside the cavity, the tactile membrane and the optical window are respectively attached to the cavity wall, a capacitor structure is set in the cavity, and the tactile membrane, the optical window and the cavity are encapsulated using a packaging process to complete the fabrication of the tactile sensor.

[0014] According to some embodiments of this application, the preparation of the deformable structure includes: Select deformable structural materials; The deformable structural material is processed sequentially using dispersion and degassing processes to obtain a uniform composite slurry or prepolymer. The composite slurry or prepolymer is injected into a precast mold, and an initial deformed structure is obtained by a molding process. The initial deformed structure is heated to a preset deformation temperature range, and a preset external force or displacement is applied within this deformation temperature range to cause it to deform. The structure is then cooled to room temperature while maintaining its deformed state to complete the shaping process and obtain a deformed structure that can be photothermally triggered to recover its shape.

[0015] According to some embodiments of this application, the selected deformation structure material is a shape memory polymer-based composite material, which includes a matrix and a photothermal conversion material, wherein the mass fraction of the photothermal conversion material in the matrix is ​​0.5% to 3.0%.

[0016] The beneficial effects of this application are: This application incorporates a deformation structure within the cavity. This deformation structure deforms within a specific temperature range, causing displacement of the tactile membrane and converting light energy into tactile stimulation. This avoids the reliance on enclosed air cavities, gas expansion, and suspended light-absorbing sheets found in traditional light-driven tactile devices, improving the structural stability and driving efficiency of the tactile sensor and enhancing its environmental adaptability. Simultaneously, a capacitor structure is included to convert tactile stimulation into electrical signals, facilitating the acquisition and processing of these signals.

[0017] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0018] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the structure of a tactile sensor according to this application.

[0019] Figure 2 This is a flowchart of a method for fabricating a tactile sensor according to this application.

[0020] Figure 3 yes Figure 2 Detailed flowchart of S200.

[0021] Figure 4 This is a schematic diagram of the honeycomb structure in Embodiment 1 of this application.

[0022] Figure 5 This is a structural diagram of the tactile sensor according to Embodiment 1 of this application.

[0023] Figure 6 This is a schematic diagram of the deformable structure before deformation in Embodiment 1 of this application.

[0024] Figure 7 This is a schematic diagram of the deformable structure after deformation in Embodiment 1 of this application. Figure 1 .

[0025] Figure 8 This is a schematic diagram of the deformable structure after deformation in Embodiment 1 of this application. Figure 2 .

[0026] Figure 9 This is a graph showing the relationship between the axial deformation height and the corresponding equivalent output force value in Embodiment 1 of this application.

[0027] Figure 10 This is a schematic diagram of the origami-like deformable structure in Embodiment 2 of this application.

[0028] Figure 11 This is a schematic diagram of the spiral structure in Embodiment 3 of this application.

[0029] Figure 12 This is a schematic diagram of the tactile sensor array structure in Embodiment 4 of this application.

[0030] Figure 13 This is the electrical schematic diagram of the row and column scanning capacitor matrix readout structure in Embodiment 5 of this application.

[0031] Figure 14 This is a schematic diagram of the working principle of the external readout circuit in Embodiment 5 of this application.

[0032] Figure label: 100. Tactile membrane; 200. Optical window; 300. Deformation structure; 310. Polygonal element; 311. Sidewall; 320. Folded surface element; 321. Fold line; 330. Strip-shaped component; 400, cavity; 410, first cavity; 411, first conductive layer; 420, second cavity; 521, second conductive layer; 500. Cavity wall; 600. Tactile unit. Detailed Implementation

[0033] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0034] In the description of this application, it should be understood that if directional descriptions are involved, such as up, down, front, back, left, right, etc., indicating the directional or positional relationship based on the directional or positional relationship shown in the accompanying drawings, it is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0035] In the description of this application, if words such as several, greater than, less than, exceeding, above, below, or within appear, "several" means one or more, "more than" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the number itself, and "above," "below," "within," etc. are understood to include the number itself.

[0036] In the description of this application, the use of terms such as "first" and "second" is for the purpose of distinguishing technical features only, and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the order of the technical features indicated.

[0037] In the description of this application, unless otherwise expressly defined, terms such as "setup," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this application in conjunction with the specific content of the technical solution.

[0038] Reference Figures 1 to 14 The following are specific embodiments of this application.

[0039] Depend on Figure 1 As shown, this application provides a tactile sensor, including a tactile membrane 100, an optical window 200, a deformation structure 300, a cavity 400, and a capacitive structure. The optical window 200 is disposed opposite to the tactile membrane 100 and is used to transmit an external light source. The cavity 400 is enclosed by a cavity wall 500 and two openings disposed opposite to each other. The tactile membrane 100 is located at one opening, and the optical window 200 is located at the other opening. The cavity wall 500 is located between the optical window 200 and the tactile membrane 100, and the optical window 200 and the tactile membrane 100 are respectively connected to the cavity wall 500. The deformation structure 300 is disposed inside the cavity 400. The deformation structure 300 is used to absorb energy from the external light source and deforms under the action of photothermal radiation, thereby pushing the tactile membrane 100 to generate displacement, so as to form a tactile stimulus that can act on a target object. The target object is human skin or a detection object used for tactile performance testing. The capacitor structure is located inside the cavity 400 and is used to convert tactile stimulation into electrical signals to facilitate the acquisition of tactile information.

[0040] The cavity wall 500 is made of polydimethylsiloxane (PDMS) or thermoplastic polyurethane (TPU), with a thickness ranging from 0.2mm to 2mm, and has reserved lead wire channels or side wall holes for conductive lead wires to be led out.

[0041] Preferably, the deformable structure 300 pushes the tactile membrane 100 to displace in a direction perpendicular to its surface.

[0042] The working process is as follows: an external light source is transmitted into the cavity 400 through the optical window 200, causing the deformation structure 300 to absorb the energy of the external light source and deform under the action of photothermal effect, thereby pushing the tactile membrane 100 to move in a direction perpendicular to its own surface to form tactile stimulation. At the same time, the capacitor structure converts the tactile stimulation into an electrical signal, which is transmitted to the external readout circuit through conductive leads. The external readout circuit is used to collect the electrical signal and further process the electrical signal.

[0043] This application converts light energy into tactile output by enabling light signals to pass through a reversibly deformable deformation structure. This deformation, occurring within a specific temperature range, drives the tactile membrane to displace, thus avoiding the reliance on enclosed air cavities, gas expansion, and suspended light-absorbing sheets found in traditional light-driven tactile devices. This further enhances the structural stability and driving efficiency of the tactile sensor, increasing its environmental adaptability. Simultaneously, a capacitor structure is incorporated to quantify the tactile stimulus, facilitating the acquisition and processing of tactile signals.

[0044] In some embodiments, the capacitor structure includes a first conductive layer 411 and a second conductive layer 421, and the deformation structure 300 divides the cavity 400 into a first cavity 410 and a second cavity 420. The first cavity 410 is located on the side of the deformation structure 300 near the tactile membrane 100, and the first conductive layer 411 is disposed within the first cavity 410. The second cavity 420 is located on the side of the deformation structure 300 near the optical window 200, and the second conductive layer 421 is disposed within the second cavity 420.

[0045] The first conductive layer 411 and the second conductive layer 421 are respectively connected to the external readout circuit through external flexible conductive leads. Under the action of tactile stimulation, the gap between the tactile membrane 100 and the first conductive layer 411 changes, and the corresponding capacitor structure composed of the first conductive layer 411 and the second conductive layer 421 generates a capacitance change, which is converted into an electrical signal and output to the external readout circuit. The external readout circuit collects, reads, displays or stores the electrical signal.

[0046] The connection methods between the first conductive layer 411 and the second conductive layer 421 and the external flexible conductive leads include: fixing with conductive adhesive or silver paste, hot-press bonding of flexible flat cable, and connection through a reserved conductive through-hole pad structure. The external flexible conductive leads are led out through the reserved lead channel or side wall hole in the cavity wall 500 to avoid open circuit due to compression during the packaging process.

[0047] In some embodiments, the tactile membrane 100 is made of a flexible material, which is one of polydimethylsiloxane (PDMS), silicone rubber, Ecoflex (a biodegradable plastic), thermoplastic polyurethane (TPU), thermoplastic elastomer (TPE), polyurethane film (PU), or medical hydrogel film. The flexible material possesses good flexibility, reversible deformation capability, and mechanical stability, and can maintain a stable tactile response during multiple light-driven cycles. The thickness of the tactile membrane 100 ranges from 0.1 mm to 0.3 mm to obtain good mechanical response sensitivity.

[0048] This application does not limit the material of the tactile membrane 100. As long as it can achieve stable displacement transmission under the deformation drive of the deformable structure and has good flexibility and durability, it can be used to realize the tactile membrane 100 structure of this application.

[0049] In some embodiments, the optical window 200 is made of one of the following materials: glass, polycarbonate (PC), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and acrylic. The thickness of the optical window 200 ranges from 5 mm to 3 mm, preferably from 1 mm to 2 mm, so as to ensure both light transmittance and strength of the optical window 200.

[0050] In some embodiments, the material of the first conductive layer 411 is one of silver nanowires, carbon nanotubes, graphene, and transparent conductive oxides, and the thickness of the first conductive layer 411 ranges from 100 nm to 5 μm, preferably from 2 μm to 4 μm.

[0051] In some embodiments, the second conductive layer 421 is a transparent material, specifically one of indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), and indium zinc oxide (IZO). The thickness of the second conductive layer 421 ranges from 100 nm to 5 μm, preferably from 2 μm to 4 μm.

[0052] This application does not limit the material type of the second conductive layer 421, as long as it has good light transmittance in the working band and has sufficiently low surface resistance to meet the needs of tactile signal acquisition.

[0053] In some embodiments, the deformable structure 300 is made of one of the following materials: shape memory polymer-based composite material, liquid crystal elastomer, and shape memory alloy. The height of the deformable structure 300 ranges from 0.5 mm to 5 mm.

[0054] In some embodiments, the shape memory polymer-based composite material includes a matrix and a photothermal conversion material. The matrix is ​​one of polyurethane shape memory polymer, epoxy shape memory polymer, polymethyl methacrylate, and polycaprolactone. The photothermal conversion material is at least one of carbon black, carbon nanotubes, graphene, and metal nanoparticles. The mass fraction of the photothermal conversion material in the matrix is ​​0.5% to 3.0%. When the mass fraction is less than 0.5%, the photothermal conversion efficiency is low, and the response time is greater than 5 seconds. A mass fraction greater than 3% leads to a decrease in polymer crosslinking density, a decrease in elongation at break, and a shallower light transmission depth, resulting in uneven internal heating.

[0055] Therefore, a photothermal conversion material mass fraction of 0.5%–3.0% in the matrix can improve photothermal conversion efficiency, enabling the deformable structure to complete deformation within 5 seconds, meeting the requirements of real-time tactile feedback. This ensures the material has sufficient elongation at break and structural integrity, guaranteeing reliability under multiple cycles. Simultaneously, the uniform light transmission depth within the composite material allows for even heat distribution throughout the deformable structure, preventing localized overheating or uneven deformation, thus achieving stability and consistency in the displacement of different parts of the deformable structure.

[0056] Furthermore, to ensure uniform dispersion of the photothermal conversion material in the matrix, the carbon nanotubes are multi-walled carbon nanotubes with a diameter ranging from 10 nm to 30 nm and a length ranging from 5 μm to 15 μm. The carbon black is conductive carbon black with a particle size ranging from 20 nm to 50 nm. The metal nanoparticles are gold nanorods or silver nanoparticles with a particle size ranging from 50 nm to 100 nm.

[0057] Meanwhile, the glass transition temperature of the shape memory polymer matrix is ​​set within the range of 40℃ to 65℃. This temperature range is higher than room temperature, which can prevent accidental contact, while it is lower than the pain threshold of human skin burns, which can prevent burns and ensure safe use.

[0058] When the matrix is ​​polycaprolactone (PCL), high molecular weight PCL with a number average molecular weight (Mn) of 60,000 to 80,000 is used to ensure that the deformed structure has sufficient mechanical strength and resilience.

[0059] In some embodiments, when the material of the deformable structure 300 is a liquid crystal elastomer (LCE), its nematic phase isotropic phase transition temperature range is set to 40°C to 65°C. Through the programmability of liquid crystal orientation, the deformable structure 300 can achieve an axial shrinkage rate or bending deformation of 20% to 40% under illumination.

[0060] This requires the addition of a photothermal conversion material to the liquid crystal elastomer. The liquid crystal elastomer serves as the matrix, and the photothermal conversion material is at least one of carbon black, carbon nanotubes, graphene, or metal nanoparticles. The mass fraction of the photothermal conversion material in the matrix is ​​0.5% to 3.0%. The addition of the photothermal conversion material is used to optimize the photothermal conversion efficiency.

[0061] In some embodiments, when the material of the deformation structure 300 is a shape memory alloy, the shape memory alloy is a nickel-titanium alloy (NiTi), and the austenite temperature range of the phase transformation is 45℃~55℃, which can ensure that the martensite-austenite phase transformation can be completed within a safe temperature range during the photothermal drive process, and realize reversible deformation output.

[0062] Since shape memory alloys have limited light absorption capacity, it is necessary to coat the surface of the shape memory alloy with a light-absorbing coating or to dop the shape memory alloy with photothermal nanoparticles to increase the light absorption capacity of the shape memory alloy.

[0063] In some embodiments, the deformable structure 300 may also be a composite structure, composed of a shape memory polymer (SMP) or liquid crystal elastomer (LCE) and a metal material. For composite structures containing metal materials, a high-absorption light-absorbing coating or doped photothermal nanoparticles are required to achieve photothermal drive by coating its surface. The light-absorbing coating may be a polydopamine coating or a carbon composite coating, with the value of the light-absorbing coating ranging from 10 μm to 50 μm, to ensure a light absorption rate of over 90% without significantly hindering the transfer of heat to the internal metal material.

[0064] In some embodiments, the deformable structure 300 is made of a flexible structural material. A flexible structural material refers to a material with a certain degree of flexibility that can deform under external stimuli without structural damage. This includes, but is not limited to, polymer materials, elastomers, thin-film metal materials, or their composite materials. Preferably, it is a bistable flexible structural material, meaning a structure exists in two stable equilibrium states and can stably remain in either state without external force. Since the light absorption capacity of bistable flexible structural materials is limited, it is necessary to coat the surface of the bistable flexible structural material with a light-absorbing coating or dopant photothermal nanoparticles in the shape memory alloy to increase the light absorption capacity of the bistable flexible structural material.

[0065] This application does not limit the type of material for the deformable structure 300. As long as it has light absorption capability and can produce reversible or irreversible deformation under photothermal action, it can be used to constitute the deformable structure 300 of this application.

[0066] Depend on Figure 2 As shown, this application also provides a method for fabricating a tactile sensor, which includes: S100 Cleaning and pretreatment of optical window: Select the substrate of optical window 200 and perform cleaning and surface activation treatment on the substrate to improve the bonding strength between optical window 200 and cavity wall 500 and second conductive layer 421.

[0067] S200. Preparation of deformable structure: Select the material of the deformable structure and process it into a deformable structure that can be triggered by photothermal reaction to restore its shape.

[0068] S300, Preparation of cavity wall and tactile membrane: The cavity wall 500 is made by mold casting or 3D printing and then casting; the tactile membrane 100 is made by spin coating, casting, or commercial film cutting. If spin coating or casting is used, the polymer precursor film formed needs to be cured to obtain an elastic tactile membrane with the required mechanical properties and thickness.

[0069] If the material of the tactile membrane 100 is polydimethylsiloxane (PDMS), the curing temperature is 60℃~90℃ and the curing time is 30min~120min.

[0070] S400, Assembly and Packaging: S410. Place the deformable structure 300 inside the cavity 400. The deformable structure 300 is fixed inside the cavity 400 by a limiting groove, a positioning post, or local adhesive application. Align and attach the tactile membrane 100 to the cavity wall 500 to form the first cavity 410. Attach the optical window 200 to the cavity wall 500 to form the second cavity 420.

[0071] S420. A first conductive layer 411 is disposed on the surface of the tactile membrane 100 near the first cavity 410 or inside the first cavity 410; a second conductive layer 421 is disposed on the surface of the optical window 200 near the second cavity 420 or inside the second cavity 420, and the first conductive layer 411 is located inside the first cavity 410 and the second conductive layer 421 is located inside the second cavity 420.

[0072] S430. The tactile membrane 100, optical window 200 and cavity 400 are encapsulated using an encapsulation process: the encapsulation process is plasma-activated bonding, UV-cured transparent adhesive / epoxy adhesive bonding or hot-press encapsulation, to complete the fabrication of the tactile sensor.

[0073] In this process, plasma-activated bonding involves treating the surface of polydimethylsiloxane (PDMS) to be bonded with oxygen plasma to generate silanol groups on its surface. Subsequently, the PDMS is bonded to the surface at room temperature or 60℃~80℃ and left to cure, thereby achieving covalent bonding of the PDMS–PDMS interface and forming a direct seal with high airtightness and no adhesive layer.

[0074] In some embodiments, in S100, the cleaning process is as follows: the substrate of the optical window 200 is ultrasonically cleaned sequentially: (1) ultrasonically cleaned in deionized water for 5 min to 10 min. (2) ultrasonically cleaned in anhydrous ethanol or isopropanol for 5 min to 10 min. (3) ultrasonically cleaned in deionized water for 5 min. After cleaning, it is dried by blowing or drying at 50℃ to 70℃ for 10 min to 20 min.

[0075] Surface activation treatment includes: oxygen plasma treatment for 30s to 120s with a power of 50W to 200W, or ultraviolet ozone cleaning technology (UV-Ozone) treatment for 5min to 15min.

[0076] In some embodiments, by Figure 3 As shown, S200 mainly includes: S210: Select a deformation-structured material, preferably a shape memory polymer (SMP) matrix, such as polyurethane SMP, epoxy SMP, or polycaprolactone (PCL). Add a photothermal conversion material to the matrix, specifically at least one of carbon black, carbon nanotubes (CNTs), graphene, or metal nanoparticles, with the photothermal conversion material comprising 0.5% to 3.0% of the matrix by mass. S220: The deformable material is processed sequentially by dispersion and degassing processes to obtain a uniform composite slurry or prepolymer: The deformable material is dispersed for 10 min to 30 min using a planetary mixer or high-speed shear machine, and ultrasonic dispersion for 5 min to 15 min is used if necessary to reduce material agglomeration.

[0077] The dispersed material is degassed under vacuum for 5 to 20 minutes to remove air bubbles and obtain a uniform composite slurry or prepolymer.

[0078] Dispersion and degassing processes are used to treat deformable structural materials to ensure that the resulting deformable structures can rapidly and locally heat up and produce controllable deformation when exposed to light, providing a process basis for the consistency of subsequent tactile membrane displacement output.

[0079] S230: The composite slurry or prepolymer is injected into a precast mold, and an initial deformed structure is obtained using a molding process. The molding process involves one of the following methods: thermosetting, photocuring, or solvent evaporation. After molding, the initial deformed structure is obtained by demolding. The precast molds can accommodate honeycomb, origami, and spiral structures.

[0080] If heat curing is used, the curing temperature is 60℃~120℃ and the curing time is 0.5h~3h.

[0081] S240: Shape memory programming for deformable structures: Specifically, the initial deformable structure is heated to a preset deformation temperature range, and a preset external force or displacement is applied within this deformation temperature range to cause it to deform. Then, it is cooled to room temperature while maintaining the deformed state to complete the shaping.

[0082] Example 1 Depend on Figure 4 and Figure 5 As shown, in this embodiment, the deformable structure 300 is a honeycomb structure, which includes several sidewalls 311. The sidewalls 311 enclose each other to form several polygonal units 310. Adjacent polygonal units 310 are connected by the sidewalls 311. The inclination angle of the sidewalls 311 ranges from 60° to 85°, and the thickness of the sidewalls 311 ranges from 50μm to 500μm, preferably 200μm. The height of the polygonal unit 310 ranges from 0.5mm to 3mm, and the inner diameter ranges from 0.3mm to 2mm.

[0083] Preferably, the cross-sectional shape of the polygonal unit 310 is hexagonal.

[0084] The honeycomb structure is made of shape memory polymer-based composite material, with shape memory polymer (SMP) matrix and carbon black powder as photothermal conversion material, which increases the absorption rate of light in the working wavelength band to about 85%, thereby enabling rapid photothermal response under illumination.

[0085] The tactile membrane 100 is a soft silicone flexible tactile membrane with a thickness of 200μm. The side of the tactile membrane 100 near the honeycomb structure is tightly attached and fixed to the cavity wall 500.

[0086] The optical window 200 is a 1mm thick polymethyl methacrylate (PMMA) sheet. PMMA has good optical transparency, allowing external light sources to fully enter the honeycomb structure.

[0087] The working process of this embodiment is as follows: the state of the deformable structure 300 before deformation is as follows: Figure 6 As shown, an external light source shines through the optical window 200 of polymethyl methacrylate (PMMA) onto the honeycomb structure. The carbon black powder in the honeycomb structure absorbs the light energy and generates local heating, causing the shape memory polymer (SMP) to enter the deformation temperature range.

[0088] Because of the bendable nodes in the honeycomb structure, it can undergo steady-state upward geometric deformation after being subjected to photothermal excitation, increasing the overall height h by 0.5mm to 1.2mm. Figure 7 As shown. This height change directly pushes the upper tactile membrane 100 to form a bulge, by... Figure 8As shown, this allows users to clearly feel tactile feedback through their skin. The honeycomb structure provides uniform stress and moderate stiffness, producing a soft and smooth vertical tactile output, making it suitable for applications requiring surface-level tactile feedback.

[0089] Figure 9 The horizontal axis represents the axial deformation height of the deformed structure, and the vertical axis represents the corresponding equivalent output force value. It can be seen that the higher the axial deformation height, the greater the corresponding equivalent output force value.

[0090] Example 2 Depend on Figure 10 As shown, in this embodiment, the deformable structure 300 is a paper-folding structure. The paper-folding structure includes several undulating folded surface units 320 connected sequentially by crease lines 321. Adjacent folded surface units 320 are located at different heights, and the included angle between adjacent crease lines 321 is 30° to 120°, thus forming a three-dimensional origami configuration with periodic undulations.

[0091] Preferably, adjacent folded units 320 are hinged to each other at a preset folding angle, the value of which ranges from 30° to 120°.

[0092] The origami-like structure is made of shape memory polymer-based composite material, with shape memory polymer (SMP) matrix as the matrix and at least one of carbon black, carbon nanotubes (CNTs), graphene, and metal nanoparticles as the photothermal conversion material.

[0093] The working process of this embodiment is as follows: The folding unit 320 is initially in a compressed state, and the included angle between each fold line 321 is small. After the light source irradiates the origami-like structure, the shape memory polymer is locally heated to the deformation region, the strain energy at the nodes of the fold line 321 is released, and the origami-like structure unfolds synchronously along the preset direction.

[0094] Because the origami-like structure has a predictable unidirectional unfolding pattern, and its deformation direction is strong, the tactile membrane above it produces directional tactile stimulation.

[0095] Specifically, when the origami-like structure unfolds horizontally (i.e., parallel to the tactile membrane), the deformation of the origami-like structure unfolds sequentially according to a preset unfolding direction, starting from one end and gradually unfolding. This pushes the tactile membrane 100 area corresponding to the unfolded position to produce an upward displacement. Subsequently, adjacent folded units unfold sequentially, causing the displacement position to move from one end to the other, forming a dynamic change similar to "pushing waves," giving the skin in contact with the tactile membrane 100 a tactile sensation similar to sliding or sweeping. This embodiment can achieve directional tactile output that is difficult to achieve with traditional vertical protrusions, and has unique advantages in applications such as virtual swipe prompts, interface navigation, and directional indication.

[0096] Example 3 Depend on Figure 11 As shown, in this embodiment, the deformable structure 300 is a spiral structure, which includes a strip member 330. The strip member 330 is spiral, the spiral pitch of the spiral structure is 0.5mm to 5mm, the spiral diameter is 1mm to 10mm, and the number of spiral turns is 1 to 10 turns.

[0097] Preferably, the strip member 330 is wound in a spiral manner with a preset central axis as the reference, and the central axis is perpendicular to the surface of the tactile membrane 100.

[0098] The spiral structure is made of shape memory polymer-based composite material, with shape memory polymer (SMP) matrix as the matrix, and the photothermal conversion material is selected from at least one of carbon black, carbon nanotubes (CNT), graphene, and metal nanoparticles.

[0099] The shape memory polymer (SMP) matrix is ​​formed by molding or 3D printing.

[0100] The working process of this embodiment is as follows: Under illumination, the photothermal conversion material in the strip member 330 absorbs energy, and after the temperature rises, the shape memory polymer (SMP) enters a deformable state, causing the strip member 330 to elongate along the axial direction, accompanied by a slight rotational tendency. This type of structure has the characteristic of sequential unfolding during shape memory recovery, so that its top output presents a "spiral upward" displacement sequence.

[0101] Driven by the strip member 330, the tactile membrane 100 produces progressively stronger local bulges, allowing the user to experience a tactile pattern similar to "pulsating rise" or "rotating push". This tactile sensation has strong recognizability and is suitable for scenarios that require clear tactile pulses, such as information encoding, rhythm indication, and virtual button feedback.

[0102] Example 4 Depend on Figure 12 As shown, this embodiment provides an arrayed light-driven tactile sensing device, including a plurality of tactile units 600. Each tactile unit 600 is a tactile sensor, including a tactile membrane 100, an optical window 200, a deformation structure 300, a cavity wall 500, and a capacitor structure. The deformation structure 300 is any of the structures described in Embodiment 1, Embodiment 2, and Embodiment 3.

[0103] The tactile sensors are arranged in an N×M array in a matrix manner. N×M can be 4×4, 8×8 or 16×16. In this embodiment, there is no limitation on the number of rows (N) and columns (M), and their values ​​can be flexibly set to any integer according to the specific application scenario.

[0104] The optical window 200 is made of glass or polymethyl methacrylate (PMMA) sheet.

[0105] The illumination area of ​​each tactile unit 600 can be precisely controlled through any of the following methods: spatial light modulator, scanning laser system, or micro-projection system, to achieve selective illumination. By applying different illumination power, illumination time, or illumination patterns to different units, each tactile unit 600 in the array can independently generate tactile displacement, forming a spatial multi-point tactile distribution.

[0106] Meanwhile, a light source transmission interface is provided on the side of the optical window 200 away from the deformable structure 300, which is used to receive and guide external light sources through the optical window 200 to illuminate the deformable structure 300, ensuring efficient transmission of the light source.

[0107] The arrayed light-driven tactile sensing device of this embodiment can be used for Braille encoding, multi-point tactile pattern display, virtual interface interaction, or tactile presentation of VR / AR scenes. Users can simultaneously feel the dynamic changes of multiple tactile pixels at their fingertips, achieving high-resolution mapping from light signals to tactile signals. Furthermore, this embodiment can achieve higher tactile resolution by expanding the array size, exhibiting good scalability and versatility.

[0108] Example 5 Based on Embodiment 4, this embodiment further includes a row-column scanning capacitive matrix readout structure, which includes a switching device and an external readout circuit. Each tactile unit 600 has a local upper electrode formed on the inner side of its tactile membrane, and all tactile units 600 in the array share a common transparent lower electrode, which is located inside the optical window.

[0109] Several switching devices are provided, and each tactile unit 600 is connected in series. Specifically, a switching device is connected in series between the upper electrode of each tactile unit 600 and the external readout circuit.

[0110] The switching device is a thin-film transistor (TFT), CMOS analog switch, or other electronic switch with on / off function. Figure 13 As shown, the switching device is preferably a thin-film transistor, which has three ports: gate (G), source (S) and drain (D).

[0111] The gate (G) receives the row selection signal and is connected to the corresponding row selection signal line (Row 1 to Row N). There are N row selection signal lines, and each row of haptic units 600 shares the same row selection signal. All selection signal lines (Row 1 to Row N) are connected to the row driving circuit. The row driving circuit controls the on / off state of all switching devices in the corresponding row by applying a selection level or a cut-off level to the row selection line. When a row is selected, the switching devices of all haptic units 600 in that row are simultaneously turned on; when the row is not selected, the corresponding switching device is in a high-impedance state.

[0112] One port of the source (S) or drain (D) is electrically connected to the upper electrode in each tactile unit 600, and the other port is connected to the corresponding column readout line (Col 1 to Col M). There are M column readout lines, and each column of tactile units 600 shares the same column readout line. All column readout lines (Col 1 to Col M) are connected to the input terminal of the capacitance detection circuit. The capacitance detection circuit is used to acquire and convert the capacitance changes of each tactile unit in the selected row during row scanning.

[0113] The capacitance detection circuit is a capacitance-to-digital converter, an integrating capacitance measurement circuit, or an oscillating capacitance detection circuit, or a series-by-series multiplexing circuit composed of an analog switch and a single-channel CDC.

[0114] The source (S) and drain (D) are used to connect the capacitor structure to the column readout line when the switching device is on, and to electrically isolate the capacitor structure from the column readout line when the switching device is off, thereby avoiding signal coupling between different tactile units.

[0115] Figure 13 The tactile capacitor C shown represents a variable capacitance structure formed between the upper electrode and the common transparent lower electrode. When the deformation structure 300 deforms under light-driven conditions and pushes the tactile membrane 100 to produce displacement, the distance between the upper electrode and the common transparent lower electrode changes, thereby causing the capacitance value of the tactile capacitor C to change.

[0116] The common transparent lower electrode is connected to the reference terminal of the capacitance detection circuit. By sharing a common transparent lower electrode with all tactile units 600, capacitive readout of multiple tactile units can be achieved without increasing wiring complexity, while ensuring that each tactile unit has a unified reference reference when selected.

[0117] During the readout process, the row selection signal lines are scanned row by row sequentially by the row driving circuit. At any given sampling moment, only the row selection signal of a particular row is set to the on signal level, turning on the switching devices of all tactile units 600 in that row. This connects the upper electrodes of the tactile units 600 in that row to the corresponding column readout lines, while the switches of the other rows remain off, electrically isolating the capacitance of the corresponding tactile units from the column readout lines. During the selection of a row, the capacitance detection circuit collects the capacitance values ​​on each column readout line, thus obtaining the capacitance data of the M tactile units in that row. Subsequently, the row driving circuit closes the current row and opens the next row selection line, repeating the above process until the scanning of N rows is completed, thereby obtaining the capacitance distribution of the entire N×M array within one sampling period.

[0118] Because the switching device on the non-selective row is in a high-impedance state, the capacitance of its corresponding tactile unit will not couple to the column readout line. Therefore, at any given time, only the tactile unit in the currently selected row is involved in the measurement, and its capacitance signals are electrically independent, without generating significant crosstalk. By increasing the row scanning frequency and the sampling speed of the capacitance detection circuit, this embodiment can achieve high spatial resolution and high temporal resolution tactile signal acquisition while maintaining a limited number of leads.

[0119] In addition, in this embodiment, the row driving circuit and column readout circuit can be integrated on the same substrate as the optical window 200 to form a tactile sensor module with integrated readout circuit. In flexible application scenarios, the row and column lines and switching devices can also be arranged on a flexible substrate and used in conjunction with the tactile membrane 100. The row and column scanning capacitive matrix readout structure in this embodiment can be combined with any deformable structure and tactile unit in embodiments one to three to form an arrayed light-driven tactile sensor that can both generate tactile output and achieve pixel-level self-sensing.

[0120] To simplify analog circuit design and improve the signal-to-noise ratio, this embodiment employs a fully digital capacitance reading scheme, primarily implemented by an external readout circuit. Figure 14 As shown, the external readout circuit includes a capacitance detection circuit, a row drive circuit, an analog multiplexer, a capacitance-to-digital converter, a central processing unit, and a host computer.

[0121] The capacitance detection circuit is an analog signal input port for signal acquisition, which includes M signal input terminals corresponding to the number of columns in the tactile unit 600 array. The signal input terminals are electrically connected to the M columns of readout lines (Col 1 to Col M) of the tactile unit 600 array, respectively, for receiving weak capacitance signals from each tactile unit 600 in parallel.

[0122] The output of the row drive circuit is electrically connected to each of the N row selection lines (Row 1 to Row N) of the haptic unit 600 array, and its input is connected to the synchronization signal output of the central processing control module. The row drive circuit operates as follows: in response to the scanning synchronization signal or clock signal sent by the central processing control module, it sequentially outputs high-level pulses to the row selection lines to achieve row-by-row selection scanning of the haptic unit 600 array. At any given scanning moment, only one row selection line is active.

[0123] The signal acquisition circuit is the core processing unit of the external readout circuit, which includes a cascaded analog multiplexer, a capacitor-to-digital converter block, and a central processing controller.

[0124] The analog multiplexer's signal input side is connected to the haptic unit array interface, and its output side is connected to the input of the capacitor-to-digital converter. The operation is as follows: based on the received channel selection command, the M parallel column readout signals are time-division multiplexed and transmitted to a single or a small number of output channels to achieve time-division multiplexing transmission of multi-channel signals.

[0125] The capacitor-to-digital converter (CDC) uses an integrated capacitor-to-digital converter chip (CDC), which integrates an analog front-end (AFE) and an analog-to-digital converter (ADC). The AFE applies excitation to the input capacitance signal and performs charge-to-voltage conversion. The ADC is configured to quantize the converted analog quantity into a digital code. The CDC outputs digitized capacitance data via a digital bus (such as an I2C or SPI protocol).

[0126] The central processing controller uses a microcontroller (MCU) or a field-programmable gate array (FPGA). As the control center of the external readout circuit, the central processing controller mainly performs the following operations: (1) Timing coordination: sends channel switching signals to the analog multiplexing module and sends row scan trigger signals to the row drive circuit to ensure strict synchronization between row gating and column acquisition in timing. (2) Data processing: reads the raw data output by the CDC module through the digital bus and performs baseline calibration and linearization processing. (3) Communication transmission: packages the processed array tactile data and sends it to external devices through the data transmission interface.

[0127] The host computer communicates with the central processing controller via USB, UART, or a wireless communication interface. The host computer is equipped with visual human-computer interaction software, used to receive tactile data and generate real-time pressure distribution heatmaps, or to store the data and perform further intelligent algorithm analysis.

[0128] The fully digital capacitance reading process is as follows: Step 1, multiplexing: The M columns of readout lines of the tactile unit 600 array are connected to an analog multiplexer. Under the control of the channel selection signal of the central processing unit (MCU), the analog multiplexer sequentially connects the capacitance signal of a certain column to the subsequent stage.

[0129] Step 2, Capacitor-to-Digital Conversion: The selected capacitor signal is directly input to the capacitor-to-digital converter (CDC) chip. The CDC chip integrates a high-precision charge-balancing front-end and an analog-to-digital converter, directly converting the minute capacitance change into a high-resolution digital code, which is then transmitted via a digital interface (such as I2C or SPI).

[0130] Step 3, Synchronization and Processing: The central processing unit (MCU) reads the capacitance data output by the capacitance-to-digital converter (CDC) through the bus; on the other hand, it outputs a synchronization signal to coordinate the scanning rhythm of the row drive circuit, ensuring that the timing of row switching, column gating and CDC sampling are strictly aligned. Finally, the tactile signal data is packaged by the MCU and sent to the host computer.

[0131] This application discloses a tactile sensor and its fabrication method. The tactile sensor incorporates a deformation structure within a cavity, positioned between a tactile membrane and an optical window. This deformation structure deforms within a specific temperature range, displacing the tactile membrane and converting light energy into tactile stimulation. This eliminates the reliance on closed air cavities, gas expansion, and suspended light-absorbing sheets found in traditional tactile sensing devices, resulting in more stable and reliable tactile output, unaffected by gas leakage, cavity deformation, or temperature fluctuations. This improves the structural stability and driving efficiency of the tactile sensor, enhancing its environmental adaptability. Furthermore, the deformation structure can be honeycomb, origami-like, or spiral-shaped, allowing for directional, phased, or gradual deformation under light-driven conditions. This enables various tactile modes such as vertical protrusions, sliding touch, and spiral pulses. The programmable geometry allows for designable, adjustable, and scalable tactile output, resulting in richer and more flexible tactile presentation methods suitable for different application scenarios, thus increasing the versatility of the tactile sensor.

[0132] The tactile sensor also incorporates a capacitor structure to convert tactile stimuli into electrical signals, facilitating the acquisition and processing of tactile signals. By setting up an array of light-driven tactile sensing devices and controlling the illumination of each tactile unit individually, each tactile unit can independently generate displacement, achieving high-resolution two-dimensional tactile display or tactile encoding. It is also equipped with a row and column scanning capacitor matrix readout structure, enabling the integration of tactile output and tactile perception.

[0133] The preparation method employs dispersion and degassing processes to treat the deformable structural material, ensuring that the obtained deformable structure can rapidly and locally heat up and generate controllable deformation under light irradiation, thus providing a process basis for the consistency of subsequent tactile membrane displacement output.

[0134] In the description of this specification, the use of terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," and "some examples" indicates that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0135] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A tactile sensor, characterized in that, include: Tactile membrane; An optical window, which is positioned opposite the tactile membrane, is used to transmit an external light source; The cavity is formed by a cavity wall and two openings at opposite ends, one opening of which is provided with the tactile membrane, and the other opening of which is provided with the optical window; A deformable structure is provided inside the cavity to absorb the energy of the external light source and deform under the action of photothermal effect, thereby pushing the tactile membrane to produce displacement, so as to form a tactile stimulus that can act on the target object; A capacitor structure, disposed within the cavity, is used to convert the tactile stimulation into an electrical signal to facilitate the acquisition of tactile information.

2. A tactile sensor according to claim 1, characterized in that, The deformable structure is a honeycomb structure, which includes several sidewalls that enclose each other to form several polygonal units. Adjacent polygonal units are connected by the sidewalls, wherein: The inclination angle of the sidewall ranges from 60° to 85°; and / or, The thickness of the sidewall ranges from 50 μm to 500 μm; and / or, The height of the polygonal unit ranges from 0.5mm to 3mm; and / or, The inner diameter of the polygonal unit ranges from 0.3 mm to 2 mm.

3. A tactile sensor according to claim 1, characterized in that, The deformable structure is a paper-folding structure, which includes several undulating folded surface units connected sequentially by crease lines. Adjacent folded surface units are located at different heights, and the included angle between adjacent crease lines is 30° to 120°.

4. A tactile sensor according to claim 1, characterized in that, The deformable structure is a helical structure, which includes a ribbon-like component that is helical in shape. The helical pitch of the spiral structure is 0.5 mm to 5 mm; and / or, The spiral diameter of the spiral structure is 1 mm to 10 mm; and / or, The spiral structure has 1 to 10 spiral turns.

5. A tactile sensor according to claim 1, characterized in that, The material of the deformation structure is one of shape memory polymer-based composite materials, liquid crystal elastomers, and shape memory alloys.

6. A tactile sensor according to claim 5, characterized in that, The shape memory polymer-based composite material includes a matrix and a photothermal conversion material. The matrix is ​​one of polyurethane shape memory polymer, epoxy shape memory polymer, polymethyl methacrylate, and polycaprolactone. The photothermal conversion material is at least one of carbon black, carbon nanotubes, graphene, and metal nanoparticles.

7. A tactile sensor according to claim 1, characterized in that, The capacitor structure includes a first conductive layer and a second conductive layer. The deformation structure divides the cavity into a first cavity and a second cavity. The first cavity is located on the side of the deformation structure closer to the tactile membrane, and the first conductive layer is disposed in the first cavity. The second cavity is located on the side of the deformation structure closer to the optical window, and the second conductive layer is disposed in the second cavity.

8. A method for fabricating a tactile sensor, characterized in that, For manufacturing the tactile sensor according to any one of claims 1-7, comprising: Cleaning and pretreatment of optical windows; Preparation of deformable structures: Preparation of cavity walls and tactile membranes; The deformable structure is placed inside the cavity, the tactile membrane and the optical window are respectively attached to the cavity wall, a capacitor structure is set in the cavity, and the tactile membrane, the optical window and the cavity are encapsulated using a packaging process to complete the fabrication of the tactile sensor.

9. A method for manufacturing a tactile sensor according to claim 8, characterized in that, The preparation of the deformable structure includes: Select deformable structural materials; The deformable structural material is processed sequentially using dispersion and degassing processes to obtain a uniform composite slurry or prepolymer. The composite slurry or prepolymer is injected into a precast mold, and an initial deformed structure is obtained by a molding process. The initial deformed structure is heated to a preset deformation temperature range, and a preset external force or displacement is applied within this deformation temperature range to cause it to deform. The structure is then cooled to room temperature while maintaining its deformed state to complete the shaping process and obtain a deformed structure that can be photothermally triggered to recover its shape.

10. A method for manufacturing a tactile sensor according to claim 9, characterized in that, The selected deformation structure material is a shape memory polymer-based composite material, which includes a matrix and a photothermal conversion material, wherein the mass fraction of the photothermal conversion material in the matrix is ​​0.5% to 3.0%.

Images