A piezoelectric tactile sensor and a tactile sensing system based on negative poisson's ratio

Abstract

The utility model relates to the field of bionic touch technology, concretely is piezoelectric tactile sensor and tactile response system based on negative poisson's ratio. This piezoelectric tactile sensor based on negative poisson's ratio includes flexible base layer, the negative poisson's ratio structure fibre assembly by multiple fibre silk and is arranged on it, the piezoelectric layer that is arranged on the fibre assembly top, and the electrode layer that is arranged on the piezoelectric layer top and is connected with negative poisson's ratio structure electricity. Negative poisson's ratio structure produces lateral expansion when being pressed, amplifies local strain and enhances piezoelectric response, thereby still can keep high sensitivity and good linearity in the actual environment containing noise, effectively promotes the decoupling perception ability to normal force, tangential force and bending and so on multi -axis load.

Description

Technical Field

[0001] This utility model relates to the field of biomimetic tactile technology, specifically to a piezoelectric tactile sensor and mechanical gripper based on negative Poisson's ratio. Background Technology

[0002] Tactile sensors are core sensing components for robot dexterity, human-computer interaction, and wearable health monitoring. Traditional piezoelectric tactile sensors generally adopt a structure in which a planar piezoelectric thin film (such as PVDF) is directly attached to a flexible substrate. Their working principle relies on the compressive strain in the thickness direction caused by external force, and the output signal mainly reflects the magnitude of normal pressure. This type of structure is macroscopically isotropic and lacks response mechanisms and resolution capabilities for multidimensional mechanical loads such as tangential shear force and in-plane bending deformation.

[0003] In the process of realizing this invention, the inventors discovered that the above structure faces significant limitations in practical applications: due to the low intrinsic sensitivity caused by relying solely on the slight compression in the thickness direction of the thin film to generate charge; at the same time, circuit noise, mechanical assembly errors and environmental disturbances will further amplify the random fluctuations of the signal, causing the output voltage-pressure relationship to deviate from the ideal linear model, making it difficult to achieve stable and high-resolution multi-axis tactile perception in noisy real environments. Summary of the Invention

[0004] One of the objectives of this invention is to provide a piezoelectric tactile sensor based on negative Poisson's ratio and its fabrication method, so as to solve the problem that the existing flexible tactile sensors have insufficient local strain amplification capability, resulting in the inability to effectively ensure a low signal-to-noise ratio in scenarios with small contact force or light touch.

[0005] To solve the above-mentioned technical problems, the embodiments of this utility model are implemented as follows: Firstly, a piezoelectric tactile sensor based on negative Poisson's ratio is provided, comprising: Flexible base layer; A fiber assembly is disposed on the flexible substrate, the fiber assembly comprising a three-dimensional negative Poisson's ratio structure composed of multiple fiber filaments; A piezoelectric layer is disposed on the side of the fiber assembly away from the flexible base layer; An electrode layer is disposed on the side of the fiber assembly away from the piezoelectric layer, and the electrode layer is electrically connected to the negative Poisson's ratio structure.

[0006] Furthermore, the electrode layer comprises a plurality of uniformly distributed electrode points, which are spaced apart, and each electrode point is electrically connected to at least one node of the negative Poisson's ratio structure.

[0007] Furthermore, the nodes of the negative Poisson's ratio structure are the vertices of the connecting rods or the intersections of the connecting rods in the negative Poisson's ratio structure.

[0008] Furthermore, the negative Poisson's ratio structure includes any one of a star-shaped reentrant cell, a tetrahedral reentrant cell, or a reentrant cellular cell.

[0009] Furthermore, the fiber filament is any one of aramid fiber filament, carbon fiber filament, and high-strength polyimide fiber filament.

[0010] Furthermore, the polarization direction of the piezoelectric layer is set to be polarized along the axial direction of the fiber rod, or locally oriented polarized at the node position corresponding to the negative Poisson's ratio structure.

[0011] Furthermore, the piezoelectric layer is a polyvinylidene fluoride layer or a polyvinylidene fluoride-trifluoroethylene copolymer layer.

[0012] Furthermore, the flexible base layer may be any one of a silicone rubber layer, a polyurethane layer, or a polyimide film layer.

[0013] Furthermore, the piezoelectric tactile sensor also includes an encapsulation layer disposed on the electrode layer.

[0014] The second aspect also discloses a tactile sensing system, including any one of the piezoelectric tactile sensors based on negative Poisson's ratio.

[0015] The beneficial effects of the above-mentioned technical solutions provided by the embodiments of this utility model include at least the following: This utility model discloses a piezoelectric tactile sensor based on negative Poisson's ratio. It involves setting a negative Poisson's ratio structure fiber assembly composed of multiple fibers on a flexible substrate, and then sequentially arranging a piezoelectric layer and an electrode layer on it, with the electrode layer electrically connected to the negative Poisson's ratio structure. Because the negative Poisson's ratio structure expands laterally under pressure, it amplifies local strain and efficiently transmits it to the piezoelectric layer, overcoming the problems of low sensitivity and poor multiaxial response caused by traditional planar piezoelectric structures that rely solely on thickness compressive strain. Simultaneously, the mechanical nonlinearity compensation characteristics of this structure can suppress signal drift under noise interference, solving the technical problems of unstable output and poor linearity in noisy real-world environments. Therefore, it significantly improves the sensor's multiaxial decoupling detection capability, sensitivity, and measurement stability for normal force, tangential force, and bending deformation.

[0016] Other features and advantages of this invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0017] The technical solution of this utility model will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 A schematic diagram of a piezoelectric tactile sensor based on negative Poisson's ratio provided for the first embodiment of this utility model; Figure 2 A schematic diagram of a piezoelectric tactile sensor based on negative Poisson's ratio provided for the second embodiment of this utility model; Figure 3 This is an embodiment of the present utility model. Figure 1 A magnified diagram of A; Figure 4 The strain curves are a comparison between a conventional positive Poisson's ratio structure and a three-dimensional negative Poisson's ratio structure. Figure 5 This is a comparison curve of the measured output voltage and pressure characteristics of this sensor and conventional piezoelectric thin film sensors.

[0019] The image shows: 10. Flexible substrate; 20. Fiber assembly; 30. Piezoelectric layer; 40. Encapsulation layer; 50. Electrode layer; 501. Metal nanowire. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] In this application, the term "exemplary" is used to mean "used as an example, illustration, or description." Any implementation described as "exemplary" in this application is not necessarily to be construed as being more preferred or advantageous than other implementations. The following description is provided to enable any person skilled in the art to implement and use this application. Details are set forth in the following description for illustrative purposes. It should be understood that those skilled in the art will recognize that this application can be implemented without using these specific details. In other instances, well-known structures and processes are not described in detail to avoid obscuring the description of this application with unnecessary detail. Therefore, this application is not intended to be limited to the embodiments shown, but rather to be consistent with the broadest scope of the principles and features disclosed in this application. In traditional piezoelectric tactile sensors, piezoelectric materials are typically attached to a flexible substrate as planar thin films. Their charge output primarily relies on compressive strain in the thickness direction, lacking an effective response mechanism to tangential shear forces, in-plane bending deformation, and multi-directional coupled loads. Furthermore, limited by the uniformity of structural stiffness distribution and strain transfer efficiency, the piezoelectric response amplitude caused by small external forces is low. With the superposition of instrument background noise and environmental mechanical disturbances, the signal-to-noise ratio significantly decreases, leading to poor measurement repeatability and degraded linearity, making it difficult to support high-precision multi-axis tactile sensing requirements. For example, when a robot's finger grasps a soft object, normal pressure feedback alone cannot determine slippage trends or local deformation states; similarly, when wearable devices conform to the curved surface of the human body, non-uniform strain caused by bending is easily misinterpreted as pressure changes. These problems essentially stem from the lack of active strain control capabilities in traditional structures, which cannot apply directional and amplified local mechanical excitation to the piezoelectric layer during stress application.

[0022] Based on the same utility model concept, please refer to the appendix for the first aspect. Figure 1 The diagram also discloses a piezoelectric tactile sensor based on negative Poisson's ratio, comprising: Flexible base layer; The fiber assembly, located on a flexible substrate, comprises a three-dimensional negative Poisson's ratio structure composed of multiple fiber filaments. A piezoelectric layer is disposed on the side of the fiber assembly away from the flexible substrate; An electrode layer is disposed on the side of the piezoelectric layer away from the piezoelectric layer, and the electrode layer is electrically connected to the negative Poisson's ratio structure.

[0023] This embodiment provides a multi-axis responsive piezoelectric tactile sensor structure with macroscopically negative Poisson's ratio characteristics. A flexible substrate provides overall support and deformation compatibility, while fiber components construct a three-dimensional negative Poisson's ratio structure with mechanical amplification capabilities. The piezoelectric layer efficiently converts structural strain into charge signals, and the electrode layer enables spatial acquisition and extraction of electrical signals. Interface adaptation design is employed between each layer. The inventive concept of this embodiment lies in transforming the negative Poisson's ratio structure from a passive load-bearing unit into an active strain amplification medium. When an external force is applied to the piezoelectric tactile sensor, the negative Poisson's ratio result undergoes lateral expansion. Furthermore, the electrode layer is electrically connected to the negative Poisson's ratio structure, amplifying the local strain of the piezoelectric layer. This achieves multi-axis decoupled detection of normal force, tangential force, and bending, thereby overcoming the sensitivity bottleneck of traditional planar piezoelectric devices and maintaining stable output characteristics in noisy testing environments.

[0024] The flexible substrate, serving as the foundational support layer for the entire sensor, must possess low modulus, high ductility, and excellent interfacial bonding capabilities. Its material can be selected from any one of polydimethylsiloxane (PDMS), thermoplastic polyurethane (TPU), or polyimide (PI) film. Furthermore, the surface of the flexible substrate is treated with oxygen plasma or a chemical coupling agent to enhance its adhesion to the fiber components. The flexible substrate not only provides mechanical support but also acts as a stress buffer and distribution regulator during complex deformations such as bending and stretching, preventing localized stress concentration that could lead to piezoelectric layer rupture.

[0025] The fiber assembly, situated on a flexible substrate, is constructed from multiple continuous fiber filaments using three-dimensional weaving, laser micro-nano assembly, or template-assisted directional deposition processes to form a macroscopic negative Poisson's ratio structure. This structure is not a simple geometric arrangement but rather a periodic array of units with reentrant topological characteristics. Typical units include star-shaped reentrant units, tetrahedral reentrant units, or reentrant honeycomb units. The fiber material can be any of aramid fiber, carbon fiber, or high-strength polyimide fiber. The fiber filaments are connected via micro-melting spot welding, nano-silver paste bridging, or UV-cured adhesive dots, forming a mechanical system where rigid nodes and flexible linkages work together. When subjected to pressure perpendicular to the substrate, the assembly undergoes lateral expansion deformation induced by the reentry angle, resulting in significant tensile and shear strain at its internal linkages and junctions. This is the physical source of the strain amplification effect, which is independent of external preload and exhibits adaptability and repeatability.

[0026] The piezoelectric layer covers the surface of the fiber assembly away from the flexible substrate, forming a continuous thin film that coats the periphery of the fiber filaments or is selectively deposited in the node region. The piezoelectric layer is made of either polyvinylidene fluoride (PVDF) or poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)). The polarization direction of the piezoelectric layer can be uniformly set along the axial direction of the fiber rod, or it can be locally oriented polarized at the node position corresponding to the negative Poisson's ratio structure to match the principal strain direction at that location. The piezoelectric layer is not an independent suspended film, but forms a mechanical coupling interface with the fiber assembly. When the fiber assembly undergoes negative Poisson's ratio deformation, its connecting rod elongation and node displacement directly pull or shear the piezoelectric layer, causing it to generate a charge density much higher than that under conventional planar compression mode.

[0027] The electrode layer is located on the side of the piezoelectric layer away from the fiber assembly and is electrically connected to the negative Poisson's ratio structure. This electrical connection means that the electrode layer forms an ohmic contact with at least one mechanical node of the negative Poisson's ratio structure through a conductive path. Please refer to the appendix. Figure 3 As shown, this contact can be achieved through methods such as embedded metal plating, filling node gaps with conductive adhesive, or in-situ growth of metal nanowires 501 at the node; the electrode layer material is any one of gold (Au), silver (Ag), copper (Cu), or conductive polymer (such as PEDOT:PSS), and the electrode layer consists of multiple independent electrode lattice electrodes. This electrode layer serves as a piezoelectric charge collection surface on one hand, and forms an electrical anchor point with the rigid node of the negative Poisson's ratio structure on the other hand, further enhancing the strain gradient of the piezoelectric layer at the node and improving the local electromechanical conversion efficiency.

[0028] The aforementioned components are arranged spatially as a flexible base layer, fiber assembly, piezoelectric layer, and electrode layer, forming a closed-loop chain for mechanical input, structural amplification, charge conversion, and signal extraction. The negative Poisson's ratio deformation of the fiber assembly is the source of strain amplification, directly determining the equivalent tensile strain amplitude of the piezoelectric layer. The polarization orientation of the piezoelectric layer is matched with the fiber orientation to ensure that the maximum piezoelectric coefficient participates in the response. The electrical connection between the electrode layer and the negative Poisson's ratio node ensures the effective extraction of high-impedance piezoelectric signals and suppresses charge leakage and crosstalk. Together, these four components constitute a strongly coupled mechanical and electrical system, rather than a simple stacking of layers.

[0029] The above technical solution achieves the following: when an external force is applied to the sensor surface, the force is transmitted to the fiber assembly; the fiber assembly undergoes lateral expansion due to its negative Poisson's ratio characteristics, thereby inducing significant tensile and shear strain within the piezoelectric layer. This strain drives the piezoelectric layer to generate high-density charge, which is efficiently discharged through the electrical connection path between the electrode layer and the negative Poisson's ratio structural nodes. Due to the strain amplification effect, the output voltage amplitude of the piezoelectric layer under the same normal load is more than twice that of the traditional planar structure. This effect is entirely derived from the above four basic structural units and their specific spatial configuration, without introducing additional sensing elements or external compensation circuits. Therefore, it has the advantages of simple structure, easy mass production, and suitability for large-area flexible integration.

[0030] Appendix Figure 4 This is a comparison of strain curves between a conventional positive Poisson's ratio structure and a three-dimensional negative Poisson's ratio structure. (Attached) Figure 4 The equivalent tensile strain of a conventional positive Poisson's ratio support structure and a three-dimensional negative Poisson's ratio structure under normal pressure was calculated by finite element simulation. The theoretical comparison curves shown are obtained. According to the attached figure, the strain amplification capability of the three-dimensional negative Poisson's ratio structure relative to the conventional positive Poisson's ratio structure can be effectively obtained.

[0031] Appendix Figure 5 This is a comparison of the measured output voltage and pressure characteristics of this sensor with those of a conventional piezoelectric film. Specifically, in an actual experiment, a loading platform was used to progressively load the sensor in increments of 0.5 N within the range of 0 to 5 N, recording the peak output voltage curves of both the conventional piezoelectric film and this negative Poisson's ratio-based piezoelectric tactile sensor. As can be seen from the curves, due to the noise in the test circuit and environmental disturbances, each data point exhibits some random fluctuation. Therefore, a "dot + dashed line" approach was used to directly connect each measurement point, without superimposing a smoothed fitting line, to more accurately reflect the measurement results.

[0032] Table 1. Measured output voltage data of the two sensors under different normal pressures.

[0033]

[0034] According to Table 1 and Figure 5 It can be seen that although there are slight fluctuations at each measurement point, the overall output level of the sensor in this embodiment is higher than that of the conventional structure across the entire measurement range. Especially in the medium-to-high load range, V_new / V_normal is basically maintained at more than twice, indicating that even under real test conditions with noise, this structure still has a significant sensitivity advantage.

[0035] In this embodiment, the electrode layer consists of a plurality of uniformly distributed electrode points, which are spaced apart, and each electrode point is electrically connected to at least one node with a negative Poisson's ratio structure.

[0036] Understandably, by configuring the electrode layer into a discrete, spatially ordered, and electrically isolated array of electrode points, and directionally coupling each electrode point to a key mechanical response location of the negative Poisson's ratio structure, this design allows each electrode point to form an independent electrical signal path, enabling the extraction of the piezoelectric response of its corresponding local region. The uniform distribution and spacing of the electrode points ensure a balance between spatial sampling density and channel isolation. In this embodiment, connecting each electrode point to at least one node ensures that each sensing unit is anchored at the location where the structural strain amplification effect is most significant, improving micro-force sensing capability and signal-to-noise ratio.

[0037] In this embodiment, the electrode points are spaced out, meaning that there is an insulating gap between any two adjacent electrode points without conductive material covering them. Its core function is to physically block the ohmic path and capacitive coupling path between adjacent electrode points, ensuring that the signals of each channel are electrically isolated at the hardware acquisition level, thus avoiding the computational overhead and error accumulation caused by subsequent software decoupling.

[0038] The synergistic effects of the various technical features are as follows: the uniform distribution of the electrode points determines the spatial sampling topology; the spacing ensures the independence of the channels; and the connection of at least one node establishes a precise mapping relationship between electrical output and mechanical input. The node, as the mechanical hub of the negative Poisson's ratio structure, has its displacement / rotation changes amplified by the fiber assembly, which directly drives the local area of ​​the piezoelectric layer connected to it to generate enhanced polarization charge. This charge is assigned to the sensing channel defined by the corresponding electrode point, thereby completing the physical encoding of multi-point pressure distribution at the hardware layer.

[0039] Through the above technical solution, the following is achieved: when an external force is applied to any area of ​​the sensor surface, the negative Poisson's ratio structure below that area undergoes non-uniform deformation, and the corresponding node generates a displacement response; after the displacement is amplified by the negative Poisson's ratio effect of the fiber component, it causes a local strain enhancement in the adjacent piezoelectric layer; the piezoelectric charge excited by the strain is captured to the electrode point electrically connected to the node and output to the external acquisition circuit through an independent lead; since each electrode point is spaced apart from each other and each is bound to a specific node, the mechanical excitation at different positions is converted into multiple voltage signals that do not interfere with each other, so that even under actual working conditions containing environmental disturbances and circuit noise, the spatial distribution map of pressure can still be stably resolved, solving the technical problems of signal aliasing, insufficient spatial resolution and low signal-to-noise ratio of weak force response caused by continuous electrode coverage in traditional planar piezoelectric sensors, and achieving the technical effect of improving the accuracy and robustness of multi-point tactile imaging.

[0040] In this embodiment, the nodes of the negative Poisson's ratio structure are the links of the negative Poisson's ratio structure or the vertices where the links intersect.

[0041] In this embodiment, the specific unit form is not limited, and the physical entity of the node is defined. When the structure is subjected to normal compression, it undergoes lateral expansion deformation, causing significant axial tensile and bending coupled strain in the internal fiber linkages.

[0042] The connecting rod refers to the basic linear load-bearing unit that constitutes the negative Poisson's ratio structure. Its cross-section is circular, elliptical, or polygonal, and the material can be aramid fiber, carbon fiber, or high-strength polyimide fiber. The connecting rod can be a straight rod, an arc rod, or a segmented broken line rod.

[0043] The vertex where the connecting rods meet refers to the rigid intersection point formed by the physical connection of at least two connecting rods. This location exhibits a high degree of stress / strain concentration when the structure is under stress. Therefore, directly connecting the electrode point to this vertex can maximize the capture of the piezoelectric response signal caused by structural deformation.

[0044] The above technical solution achieves the following: Under the premise that each of the defined, uniformly distributed electrode points is electrically connected to at least one node with a negative Poisson's ratio structure, the node is strictly anchored to a measurable, locatable, and manufacturable physical entity, namely, an actual existing connecting rod body or its rigid apex formed by their intersection. Because the node is defined as a connecting rod or its intersection apex, the electrode connection has a clear mechanical basis and process traceability.

[0045] In a further embodiment, the negative Poisson's ratio structure includes any one of a star-shaped reentrant cell, a tetrahedral reentrant cell, or a reentrant cellular cell.

[0046] The technical solution involved in this embodiment, by adopting a three-dimensional periodic unit structure with clear geometric reentrant topological characteristics in the fiber assembly, endows the overall fiber skeleton with macroscopic negative Poisson's ratio characteristics, thereby generating a lateral size expansion effect under the action of external force, realizing strain amplification of the piezoelectric layer; the structural design takes into account mechanical adjustability, manufacturing feasibility and multi-axis response consistency, and is a key physical carrier to support the sensor to achieve high sensitivity and multi-directional decoupled tactile perception.

[0047] The above technical solution achieves the following: when an external tactile load, including normal pressure, in-plane tangential force, or bending moment, is applied, the negative Poisson's ratio structure undergoes cooperative deformation. Any configuration of the star-shaped re-entry unit, tetrahedral re-entry unit, or re-entry cellular unit can, through its inherent re-entry geometry, convert local compressive strain into an effective tensile / shear strain increment borne by the piezoelectric layer. This strain increment directly improves the charge separation efficiency in the polarization direction of the piezoelectric layer, thereby obtaining a higher amplitude output voltage signal under the same external force input. Therefore, this embodiment, without changing the intrinsic properties of the piezoelectric material, effectively solves the problems of weak response, low sensitivity, and susceptibility to noise interference of traditional planar piezoelectric sensors by simply limiting the specific topology of the negative Poisson's ratio structure, significantly improving the signal-to-noise ratio and measurement stability of the sensor under conditions containing instrument noise and environmental disturbances.

[0048] In this embodiment, the fiber filament is any one of aramid fiber filament, carbon fiber filament, or high-strength polyimide fiber filament.

[0049] The fiber filaments refer to the basic linear load-bearing units that constitute the negative Poisson's ratio structure. They extend continuously along the direction of the structural links and are hinged or fixed to each other to form a three-dimensional woven skeleton with macroscopic negative Poisson's ratio response characteristics.

[0050] Through the above technical solution, the following is achieved: In the negative Poisson's ratio-based piezoelectric tactile sensor architecture, by limiting the fiber filaments to any one of aramid fiber filaments, carbon fiber filaments, or high-strength polyimide fiber filaments, the fiber assembly can maintain the geometric deformability of the negative Poisson's ratio structure under the constraint of a flexible base layer, and provide stable and repeatable lateral expansion driving capability under normal / tangential composite loads, thereby continuously amplifying the local tensile strain of the piezoelectric layer; Due to the high strength and high modulus characteristics of the fiber filament material, fatigue damage and permanent deformation of the structure under repeated loading are effectively suppressed, avoiding the attenuation of the strain amplification coefficient caused by buckling instability of the connecting rod; As a result, under actual measurement conditions containing instrument noise and environmental disturbances, the slope of the sensor output voltage response to pressure changes can maintain a high and stable numerical level throughout the entire range, improving the weak force resolution capability and long-term working reliability. This effect is entirely due to the mechanical and interface characteristics of the fiber filament material itself, and does not depend on other technical features such as electrode arrangement, polarization mode, or packaging structure.

[0051] In a further embodiment, the polarization direction of the piezoelectric layer is set to be polarized along the axial direction of the fiber rod, or locally directional polarized at the corresponding negative Poisson's ratio structural node position.

[0052] This technical solution focuses on the polarization orientation design of the piezoelectric functional layer, aiming to match the charge response direction of the piezoelectric material with the dominant strain direction excited by the negative Poisson's ratio structure under external force, thereby improving the charge output efficiency per unit stress input. The core principle is that the strength of the positive piezoelectric effect of a piezoelectric material is highly dependent on the angle between the direction of the applied mechanical strain and the direction of the internal polarization vector of the material; when the two are aligned, the charge output reaches its maximum value; when they are perpendicular or deviate by a large angle, the effective piezoelectric coefficient significantly decreases. Therefore, the polarization direction is not solely determined by process convenience but must be specifically configured based on the mechanical response characteristics of the negative Poisson's ratio structure.

[0053] Through the above technical solution, the polarization direction of the piezoelectric layer is actively adapted to the physical path where strain energy is most concentrated during the deformation process of the negative Poisson's ratio structure under external force. When axial polarization is used, the fiber rods generate significant axial tension under the negative Poisson's ratio mechanism. This tensile strain is in the same direction as the polarization direction, directly exciting a strong longitudinal piezoelectric voltage. When node-local directional polarization is used, the complex multiaxial strain at the node, especially the shear and tensile-compressive coupling components, is transformed into a polarization response consistent with its principal direction, avoiding the strain and polarization mismatch loss caused by traditional uniform polarization of the entire sheet. Because the polarization direction of the piezoelectric layer achieves spatial matching with the inherent strain field of the negative Poisson's ratio structure, under the same external load, the charge separation efficiency is higher, the output signal amplitude is larger, and the influence of random noise is relatively reduced. Thus, under actual measurement conditions containing instrument noise and environmental disturbances, it can still maintain a higher output voltage and pressure slope and better linearity, solving the problems of weak response to complex loads, insufficient sensitivity in noisy environments, and low signal-to-noise ratio of traditional planar piezoelectric thin film sensors.

[0054] In a further embodiment, the piezoelectric layer is a polyvinylidene fluoride (PVDF) layer or a polyvinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)) layer.

[0055] In this embodiment, the piezoelectric layer, as the core functional layer, undertakes the crucial task of converting mechanical strain into electrical signals. Its material selection directly determines the sensor's piezoelectric response intensity, signal-to-noise ratio performance, and process adaptability in flexible configurations. PVDF (Polyvinylidene fluoride) and P(VDF-TrFE) (Poly(vinylidene fluoride-trifluoroethylene) copolymer) are both flexible piezoelectric polymers with a β-phase dominant structure, possessing excellent film-forming properties, mechanical flexibility, and environmental stability. They can be uniformly covered on the surface of a three-dimensional curved fiber skeleton using various processes such as solution coating, doctor blade deposition, hot calendering, or electrospinning. They are particularly suitable for surfaces with negative Poisson's ratio structures composed of multiple fibers, and these structures exhibit discontinuous, multi-protrusion, and anisotropic topological characteristics, placing high demands on the material's rheological behavior and interfacial wettability.

[0056] Through the above technical solution, the following is achieved: In the negative Poisson's ratio-based piezoelectric tactile sensor architecture, by selecting PVDF or P(VDF-TrFE) as the piezoelectric layer material, the piezoelectric functional layer can both conform to the complex geometry of the three-dimensional woven fiber negative Poisson's ratio skeleton to complete conformal coverage, and output high-amplitude, low-drift electrical signals under small strain excitation; because PVDF and its copolymers themselves have a Young's modulus of 0.2–2 GPa and a dielectric constant... With a modulus of 10–13, the modulus gradient between the sensor and the flexible substrate and fiber components is gradual, effectively suppressing interface debonding and stress shielding effects. Furthermore, under actual measurement conditions including instrument noise and environmental disturbances, the sensor's ability to resolve multiaxial loads such as normal and tangential forces, as well as its output signal-to-noise ratio, are substantially improved.

[0057] In a further embodiment, the flexible base layer may be any one of a silicone rubber layer, a polyurethane layer, or a polyimide film layer.

[0058] The flexible substrate serves as the mechanical support base and deformation coordination interface for the entire piezoelectric tactile sensor. Its core function is to provide structural support while fully adapting to multimodal mechanical deformations such as bending, stretching, and torsion. It also forms a stable and reliable interlayer coupling with the upper fiber components, piezoelectric layer, and electrode layer, avoiding interface debonding, stress concentration, or signal distortion caused by modulus mismatch. The flexible substrate does not participate in the piezoelectric energy conversion process, but its mechanical properties directly affect the overall extensibility, conformability, and long-term service stability of the sensor, especially in curved surface attachments, such as robot knuckles and human joints, or dynamic deformation scenarios, such as wearable respiratory monitoring, where it plays a decisive role.

[0059] Through the above technical solution, it is achieved that: the piezoelectric tactile sensor based on negative Poisson's ratio can flexibly configure the underlying support structure according to the differentiated requirements of end applications for flexibility, strength, thermal stability and environmental adaptability.

[0060] Please refer to the attached document. Figure 2 and 3 As shown in this embodiment, the piezoelectric tactile sensor further includes an encapsulation layer disposed on the electrode layer.

[0061] In this embodiment, by adding an encapsulation layer outside the electrode layer, a physical omnidirectional protective barrier is formed over the internal functional structure. This effectively blocks external interference factors such as ambient moisture, dust particles, sweat ions, and mechanical scratches while maintaining overall flexibility, thereby improving the long-term operational reliability and environmental adaptability of the device under complex operating conditions. This encapsulation layer does not participate in the generation or conduction of electrical signals; it exists only as a passive protective structure. Its introduction does not change the original sensing mechanism or signal output path of the sensor, but it significantly delays the failure process such as electrode oxidation, piezoelectric layer hydrolysis aging, and interlayer short circuits.

[0062] The encapsulation layer is a continuous and dense thin film structure covering the surface of the electrode layer. The encapsulation layer uses an elastomer material that combines biocompatibility and light transmittance, such as polydimethylsiloxane (PDMS), thermoplastic polyurethane (TPU), or medical-grade silicone rubber; it can also use an acrylic photosensitive resin with UV curing properties to adapt to roll-to-roll flexible electronics manufacturing processes.

[0063] The encapsulation layer and the electrode layer are directly bonded together without an intermediate adhesive layer. The encapsulation layer can be formed by spin coating, scraping, inkjet printing, vacuum evaporation or molding.

[0064] The various technical features form a hierarchical protection system: the flexible base layer provides macroscopic support and initial deformation tolerance, the fiber component constructs a negative Poisson's ratio mechanical amplification framework, the piezoelectric layer and the electrode layer jointly complete the force-to-electric conversion and signal extraction, and the encapsulation layer added in this embodiment is located on the outermost layer, undertaking the role of terminal environment isolation.

[0065] The above technical solution achieves the following: while maintaining the original multi-axis response capability and flexibility of the sensor, a physical barrier with chemical inertness, mechanical flexibility and interface conformality is constructed by setting an encapsulation layer on the electrode layer; because it directly covers the signal output terminal, it can block water vapor penetration, ion migration and particle embedding path in the first time, thereby inhibiting the electrochemical corrosion and bridging short circuit of the electrode metal layer.

[0066] Based on the same inventive concept, a second aspect also discloses a tactile sensing system, including the aforementioned piezoelectric tactile sensor based on negative Poisson's ratio.

[0067] This embodiment integrates the negative Poisson's ratio-based piezoelectric tactile sensor as a functional unit into a complete signal chain, forming a closed-loop sensing system with data acquisition, conditioning, transmission, and decision feedback capabilities. This system is not limited to improving the performance of a single sensor device, but focuses on the adaptability design between the device and peripheral circuits, control logic, and application scenarios. Therefore, even under actual working conditions with instrument noise, environmental disturbances, and mechanical installation deviations, it can still stably output high signal-to-noise ratio, multi-axis resolvable tactile response signals. For example, during the process of a robot's dexterous hand grasping fragile objects, the system needs to simultaneously identify whether the normal contact force exceeds a threshold, whether tangential slippage occurs, and the trend of local bending deformation of the fingertip. Traditional methods relying solely on single-point voltage amplitude judgment are prone to false triggering due to noise interference; while this system, through the inherent multi-axis coupling response characteristics of its structure and the collaboration of a back-end decoupling algorithm, significantly improves the robustness and real-time performance of state discrimination.

[0068] The tactile sensing system refers to a complete functional system consisting of at least one negative Poisson's ratio piezoelectric tactile sensor, a signal conditioning circuit, an analog-to-digital conversion module, a main control unit, and an optional human-machine interface. This system can operate in open-loop monitoring mode (such as wearable health parameter recording) or be embedded in a closed-loop control loop (such as force feedback adjustment at the end effector of a surgical robot). Its physical implementation is not limited to rigid circuit board integration; it can also utilize flexible printed circuits (FPCs) or stretchable interconnect structures to achieve conformal connection with curved surface sensor arrays. The main control unit can be a microcontroller (MCU), digital signal processor (DSP), or system-on-chip (SoC), and its built-in program supports preprocessing operations such as baseline drift correction, bandpass filtering, peak detection, and multi-channel timing alignment of the raw piezoelectric signal. As an optional implementation, the system can also be configured with a wireless communication module (such as Bluetooth BLE, Zigbee or low-power Wi-Fi) to realize remote aggregation and cloud analysis of sensor array data; in another optional implementation, the main control unit is directly connected to the actuator (such as a micro servo motor or shape memory alloy driver) to form an integrated tactile closed-loop subsystem of "perception-decision-execution".

[0069] In one embodiment, a star-shaped reentry unit skeleton is combined with aramid fiber filaments. Alternatively, a PVDF piezoelectric layer polarized along the fiber rod axis can be combined with a flexible silicone rubber base layer. Furthermore, an encapsulation layer can be included to enhance environmental resistance.

[0070] The piezoelectric tactile sensor based on negative Poisson's ratio plays the role of a mechanical-to-electrical signal conversion unit in the system: its flexible base layer provides macroscopic adhesion and interface stress buffering; the negative Poisson's ratio structure composed of fiber components undergoes lateral expansion deformation under external force, amplifying the local strain borne by the piezoelectric layer; the piezoelectric layer converts this strain into a charge / voltage signal; the electrode layer completes charge collection and leads it to the external circuit; the encapsulation layer provides dustproof, moisture-proof, and mechanical wear protection. Reliable bonding is achieved between components through interface compatibility design, avoiding signal attenuation or hysteresis caused by interlayer debonding. The electrical connection between the sensor and the signal conditioning circuit can be achieved using various methods such as anisotropic conductive film (ACF), micro-spring probes, or laser-welded flexible gold wires, ensuring a low-impedance path is maintained even under non-planar mounting conditions such as bending and torsion.

[0071] The above technical solution achieves deep integration of high-performance piezoelectric tactile sensing units with engineering-ready signal processing and system integration architecture. Because the integrated sensor itself possesses the strain amplification effect brought by its negative Poisson's ratio structure, a node-oriented electrical connection mechanism, multiple selectable negative Poisson's ratio configurations, and broad compatibility with piezoelectric materials / polarization methods / substrate materials, the entire tactile sensing system can continuously output high-amplitude, low-fluctuation response signals with statistically significant differences even under real measurement conditions containing instrument noise and environmental disturbances. For example, in minimally invasive surgical robot applications, this system is deployed on the inner side of the instrument's end-effector gripper arm. When gripping tissue, the lateral expansion of the sensor skeleton causes enhanced tensile strain in the PVDF layer, resulting in a higher peak output voltage compared to conventional planar PVDF films under the same load. Furthermore, the standard deviation decreases within the 0.1–0.5 N micro-force range, thus supporting the system's accurate identification of differences in tissue elastic modulus and potential tear risks. In intelligent prosthetic applications, multiple sensor units are distributed across the palm and fingertips. Combined with the spatial electrode array and the multi-channel synchronous sampling capability of the main control unit, contact pressure cloud maps can be reconstructed, and grip stability can be determined in real time, significantly improving user confidence and safety. Therefore, this embodiment not only expands the application dimensions of a single sensor but also constructs a complete technology chain from microscopic material structure to macroscopic human-computer interaction systems, providing a reusable, scalable, and verifiable system-level paradigm for the industrialization of flexible tactile sensing technology.

[0072] Based on the same utility model concept, the third aspect also discloses an application method of a piezoelectric tactile sensor based on negative Poisson's ratio, which is applied in wearable health monitoring, robot tactile sensing and human-computer interaction and other application scenarios.

[0073] Obviously, those skilled in the art can make various modifications and variations to this utility model without departing from its spirit and scope. This disclosure is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims. Thus, if these modifications and variations of this utility model fall within the scope of the claims of this utility model and their equivalents, this utility model is also intended to include these modifications and variations.

Claims

1. A piezoelectric tactile sensor based on negative Poisson's ratio, characterized in that, include: Flexible base layer; A fiber assembly is disposed on the flexible substrate, the fiber assembly comprising a three-dimensional negative Poisson's ratio structure composed of multiple fiber filaments; A piezoelectric layer is disposed on the side of the fiber assembly away from the flexible base layer; An electrode layer is disposed on the side of the fiber assembly away from the piezoelectric layer, and the electrode layer is electrically connected to the negative Poisson's ratio structure.

2. The piezoelectric tactile sensor based on negative Poisson's ratio according to claim 1, characterized in that, The electrode layer consists of multiple uniformly distributed electrode points, which are spaced apart, and each electrode point is electrically connected to at least one node of the negative Poisson's ratio structure.

3. The piezoelectric tactile sensor based on negative Poisson's ratio according to claim 2, characterized in that, The nodes of the negative Poisson's ratio structure are the vertices of the connecting rods or the intersections of the connecting rods in the negative Poisson's ratio structure.

4. The piezoelectric tactile sensor based on negative Poisson's ratio according to claim 1, characterized in that, The negative Poisson's ratio structure includes any one of star-shaped reentrant cells, tetrahedral reentrant cells, or reentrant cellular cells.

5. The piezoelectric tactile sensor based on negative Poisson's ratio according to claim 1, characterized in that, The fiber filament is any one of aramid fiber filament, carbon fiber filament, and high-strength polyimide fiber filament.

6. The piezoelectric tactile sensor based on negative Poisson's ratio according to claim 1, characterized in that, The polarization direction of the piezoelectric layer is set to be polarized along the axial direction of the fiber rod, or to be locally directionally polarized at the node position corresponding to the negative Poisson's ratio structure.

7. The piezoelectric tactile sensor based on negative Poisson's ratio according to claim 1 or 6, characterized in that, The piezoelectric layer is a polyvinylidene fluoride layer or a polyvinylidene fluoride-trifluoroethylene copolymer layer.

8. The piezoelectric tactile sensor based on negative Poisson's ratio according to claim 1, characterized in that, The flexible base layer can be any one of a silicone rubber layer, a polyurethane layer, or a polyimide film layer.

9. The piezoelectric tactile sensor based on negative Poisson's ratio according to any one of claims 1-6, characterized in that, The piezoelectric tactile sensor also includes an encapsulation layer disposed on the electrode layer.

10. A tactile sensing system, characterized in that, Including the piezoelectric tactile sensor based on negative Poisson's ratio as described in any one of claims 1-9.

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