Flexible embroidery conductive sensing unit of multi-layer stress decoupling isolation structure and preparation method of flexible embroidery conductive sensing unit

Abstract

The invention provides a flexible embroidery conductive sensing unit with a multilayer stress decoupling isolation structure and a preparation method thereof. The flexible embroidery conductive sensing unit comprises a substrate fabric layer, a stress decoupling isolation layer and a sensing function embroidery layer which are sequentially stacked from bottom to top, the base fabric layer is used as a wearing carrier; the stress decoupling isolation layer comprises an anchoring area and a suspension area; the stress decoupling isolation layer is attached to the substrate fabric layer in a non-full-surface connection mode so as to form a low-strain area at the corresponding position of a sensing area, and strain of the substrate fabric layer is inhibited from being transmitted upwards through a shear hysteresis effect; and the sensing function embroidery layer is constructed by conductive yarns on the stress decoupling isolation layer through an embroidery process. According to the sensing unit, the stress decoupling isolation layer with a specific connection mode is arranged between the substrate fabric layer and the sensing function layer, and the transmission of deformation of the substrate fabric layer to a sensing area is inhibited by using a shear hysteresis effect, so that signal interference is reduced, and the sensing stability is improved.

Description

Technical Field

[0001] This invention relates to the field of smart wearable electronics technology, and in particular to a flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure and its preparation method. Background Technology

[0002] With the development of wearable electronics technology, flexible sensors based on embroidery techniques have attracted attention due to their high degree of design freedom, mature technology, and ease of mass production. By selecting conductive yarns and combining them with different needlework structures, sensing units for sensing physical quantities such as tension, pressure, or contact can be formed on the surface of fabrics.

[0003] Computer embroidery typically involves embroidery software generating stitch paths, which are then executed by an embroidery machine. By selecting the type of stitch (such as satin stitch, dadami stitch, etc.), stitch density, and threading method, linear or planar conductive structures with specific geometric shapes and electrical continuity can be formed on fabric or film substrates.

[0004] Conductive yarns (such as silver-plated nylon yarns and stainless steel composite yarns) are widely used in the fabrication of conductive interconnects and fabric sensors. Their resistance changes with the stretching, bending, or contact state of the yarn; or they can be used together with electrode structures to form flexible sensing units such as resistive / capacitive types. To improve device reliability, conductive lead areas, pads, or interface areas are usually provided in practical applications, and encapsulation layers (such as silicone rubber or thin films) are used to achieve waterproof, oxidation-proof, and wear-resistant protection.

[0005] Elastic knitted or woven fabrics undergo in-plane stretching, bending, and torsion deformations during wear. In multilayer composite structures, hot pressing and hot melting (e.g., using thermoplastic films, hot melt adhesive films, or adhesive meshes) or adhesive bonding (e.g., pressure-sensitive adhesives) are common connection methods. Different connection area ratios and interfacial force transmission paths significantly affect the strain level experienced by the upper structure.

[0006] In the prior art, the closest solution to the present invention usually revolves around forming embroidered conductive patterns on elastic fabrics and outputting electrical signals, but there are different implementation forms in terms of interlayer connection methods and strain transmission paths. Typical solutions can be summarized as follows.

[0007] Option A: Direct embroidery of conductive yarn onto an elastic fabric substrate. This approach typically uses an elastic fabric (such as spandex-containing knitted fabric) as a substrate, directly embroidering conductive yarns onto the substrate surface to form electrodes, conductive networks, or sensing patterns. Conductive leads are then placed on the same substrate to connect to external circuits. To improve durability, an encapsulation layer can be further applied to the surface of the sensing area. The sensing mechanism can be resistive (resistance changes due to deformation of the conductive path) or capacitive (capacitance changes due to changes in electrode spacing or equivalent dielectric environment).

[0008] Because the embroidery stitches typically form a relatively continuous mechanical coupling with the substrate within the sensing area, when the substrate undergoes in-plane stretching or bending, the substrate strain is easily transmitted directly to the sensing pattern area. This causes the sensing output to be simultaneously affected by both the target stimulus and the substrate deformation. Under cyclic loading or multi-degree-of-freedom deformation conditions, this coupling effect can easily cause nonlinearity, hysteresis, or baseline drift in the output, and affect the zero-point consistency and sensitivity stability under different wearing conditions.

[0009] Option B: A flexible interlayer is used for full-area bonding / hot-pressing lamination. This approach typically involves first laminating a flexible film or intermediate layer (such as TPU film or adhesive film) onto the surface of an elastic fabric substrate using hot pressing or adhesive bonding, often forming a large-area or even full-surface continuous bond within the target area. Subsequently, conductive patterns are embroidered onto the surface of this film or intermediate layer to form a sensing layer, which can then be further encapsulated. The aim is usually to provide a smoother embroidery base, improve yarn fixation and abrasion resistance, or reduce the impact of localized wrinkles on the signal.

[0010] However, when the intermediate layer and the substrate are bonded over a continuous large area, the relative slip space at the interface is limited. When the substrate is stretched in-plane, the intermediate layer is easily deformed synchronously through the bonding interface, which may still transmit significant strain to the embroidery sensing layer. This type of structure has limited improvement on the parasitic coupling between substrate strain and sensing output, and the large-area bonding may also lead to an increase in overall stiffness, a decrease in local comfort, and the risk of in-plane fatigue and delamination under cyclic washing or stretching conditions.

[0011] Option C: A solution using rigid / semi-rigid island patches or localized reinforcing sheets to support the sensing pattern. This approach typically involves fixing a relatively non-stretchable patch (e.g., a thicker film, a cured coating area, or locally reinforced fabric) at a specific location on an elastic fabric. Sensing electrodes or conductive patterns are primarily arranged on this patch. Connections to external circuits can utilize wavy or serpentine wiring, or elastic conductors to accommodate overall stretching. A robust connection between the patch and the substrate is usually achieved through stitching, gluing, or thermoforming.

[0012] This type of solution achieves low-deformation regions through localized stiffening. However, when the patch is firmly connected to the substrate, stress concentration can easily occur at the patch boundary during large substrate deformation, affecting signal stability and adversely impacting fabric softness and fit. Under repeated bending and stretching conditions, the boundary area may also experience warping, delamination, or signal fluctuations caused by stress concentration.

[0013] Based on the above typical solutions, existing embroidered flexible sensors generally suffer from the problem of coupling between the sensing area and the substrate deformation under wearable deformation conditions: when the fabric is stretched, bent, or twisted, the in-plane strain of the substrate is easily transmitted to the conductive yarn network, causing non-targeted changes in the sensing signal. For devices that primarily detect pressure or contact, the strain changes induced by the substrate may superimpose on or even dominate the target stimulus, thereby reducing measurement accuracy and distinguishability.

[0014] The viscoelastic characteristics of textile materials make embroidered structures prone to exhibiting hysteresis and nonlinear response under cyclic loading. Friction and relative slippage between conductive yarns and fabric fibers may also exacerbate this phenomenon, affecting signal repeatability and predictability.

[0015] Existing improvement solutions, such as serpentine conductive path designs, have limited applicability to the geometry of sensing structures; rigid island structures can reduce local elongation, but usually at the cost of fabric softness and comfort; and flexible interlayers with full-area bonding may still be insufficient in terms of stress isolation for the textile substrate.

[0016] Therefore, there is an urgent need for an embroidered flexible sensing structure and its fabrication method that can effectively control the interlayer force transmission path, reduce the coupling of substrate strain to the sensing area, reduce hysteresis and drift, and take into account the softness of the fabric and the comfort of wearing. Summary of the Invention

[0017] In view of this, the purpose of the present invention is to provide a flexible embroidered conductive sensing unit with a multilayer stress decoupling isolation structure and its preparation method. The sensing unit provides a stress decoupling isolation layer with a specific connection method between the substrate fabric layer and the sensing functional layer, and uses the shear hysteresis effect to suppress the transmission of deformation of the substrate fabric layer to the sensing area, thereby reducing signal interference and improving sensing stability.

[0018] To achieve the above objectives, the present invention adopts the following technical solution: a flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure, comprising a base fabric layer, a stress decoupling and isolation layer, and a sensing embroidery layer stacked sequentially from bottom to top; The base fabric layer serves as the wearable carrier; the stress decoupling isolation layer includes an anchoring area and a suspension area; the stress decoupling isolation layer is attached to the base fabric layer through a non-full surface connection method to form a low strain zone at the corresponding position of the sensing area, and to suppress the upward transmission of strain in the base fabric layer through the shear hysteresis effect; the sensing function embroidery layer is constructed by embroidering conductive yarns on the stress decoupling isolation layer.

[0019] In a preferred embodiment, the non-full surface connection method is that the stress decoupling isolation layer and the base fabric layer are connected in a floating island manner within a plane. That is, the stress decoupling isolation layer is fixedly connected to the base fabric layer only in one or more predetermined anchoring areas by hot pressing or adhesive, forming the suspended area at the corresponding position of the sensing area; the total area of ​​the anchoring area accounts for no more than 30% of the total planar projection area of ​​the stress decoupling isolation layer.

[0020] In a preferred embodiment, the total area of ​​the anchoring zone is calculated with the planar projected area of ​​the stress decoupling isolation layer outline as the denominator; and the sum of the projected area of ​​the fixed connection area of ​​the stress decoupling isolation layer and the base fabric layer on the plane and the projected area of ​​the point-like locking on the plane as the numerator, wherein the projected area of ​​the point-like locking is calculated based on the area of ​​the circumcircle of the locking point.

[0021] In a preferred embodiment, if the embroidery stitch forms a dotted knot in the non-anchored area, the connection area corresponding to the dotted knot is also included in the total area of ​​the anchored area.

[0022] In a preferred embodiment, stress decoupling is achieved by utilizing the shear hysteresis effect; when the base fabric layer is stretched, since the stress decoupling isolation layer is only fixedly connected to the base fabric layer in the anchoring area, the stress decoupling isolation layer in the suspended area does not need to be stretched synchronously with the base fabric layer, but can adapt to the deformation of the base fabric layer through interface shear deformation and relative slip. When the base fabric layer is stretched in the plane, the anchoring zone provides a fixed constraint, and the base fabric layer in the suspended zone undergoes relative slippage below the stress decoupling isolation layer. Within the suspended zone, the tensile strain of the base fabric layer tends to be absorbed in the form of interfacial shear deformation, and is not easily transmitted to the top surface of the stress decoupling isolation layer and the sensing embroidery layer thereon.

[0023] In a preferred embodiment, the anchoring area accounts for 10% to 25%.

[0024] In a preferred embodiment, the elastic modulus of the stress decoupling isolation layer is 1.2 to 25 times that of the elastic modulus of the base fabric layer.

[0025] 8. The flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure according to claim 1, characterized in that it further includes an elastic interconnect layer and an encapsulation protective layer; the elastic interconnect layer is formed by embroidering conductive yarn on a base fabric layer, and adopts a wavy routing to adapt to the large deformation of the base fabric layer, one end of which is connected to the sensing function embroidered layer, and the other end is connected to an external circuit; the encapsulation protective layer covers the surface of the sensing function embroidered layer.

[0026] This invention also provides a method for fabricating a flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure. The method for fabricating the flexible embroidered conductive sensing unit with the multi-layer stress decoupling and isolation structure includes the following steps: Step S1: Select a two-way elastic fabric as the base fabric layer. The preferred material is a nylon or spandex blended knitted fabric. Perform a pre-shrinking treatment on the base fabric layer: soak the fabric in warm water at 40℃ to 60℃ for 30 to 60 minutes, take it out and let it air dry naturally. Mark the preset position of the sensing unit and the interconnection wire path on the base fabric layer. Step S2: When the stress decoupling isolation layer is a thermoplastic film, a floating island-style local thermoplastic composite is adopted: the film is cut into a predetermined shape using a laser cutter, the film is placed at a predetermined position on the base fabric layer, and hot pressure is applied to the anchoring area to melt the film in the anchoring area and penetrate into the fabric fibers to achieve a fixed connection; no pressure or only low pressure is applied to the corresponding positions of the edge area and the sensing area to form a suspended area and maintain a relative sliding space; When the stress decoupling isolation layer is a non-thermal melt film, local bonding is used to form the anchoring area: hot melt adhesive film, hot melt adhesive mesh or pressure-sensitive adhesive is coated or attached to the predetermined anchoring area, and it is fixed to the base fabric layer by hot pressing or cold pressing; no adhesive or pressure is applied to the suspended area to maintain relative slippage; Step S3: The fabric with the stress decoupling isolation layer is clamped in a computer embroidery machine. The embroidery software is used to design the sensing pattern and generate the embroidery code. The sensing pattern is formed by embroidering on the surface of the stress decoupling isolation layer with conductive yarn. During embroidery, the stitches preferably penetrate the stress decoupling isolation layer within the anchoring area and form a stitch lock or mechanical connection with the base fabric layer. In the suspended area, by controlling the needle depth, using backing, or adjusting the bottom thread tension, the stitches are made to avoid forming a lock with the base fabric layer as much as possible, so as to maintain the relative slippage characteristics between the stress decoupling isolation layer and the base fabric layer. Step S4: Perform a pre-stretching cycle on the embroidered sensing layer to reduce the irreversible deformation effect of the first stretch; perform 10 to 20 stretching cycles using a universal testing machine; Step S5: After the sensing pattern is embroidered, the embroidery machine does not cut the thread and continues to embroider until the base fabric layer area forms an elastic interconnect layer; the embroidery path smoothly transitions from a tightly packed electrode pattern to a wavy line. Step S6: Mix the polydimethylsiloxane (PDMS) pre-engineer and curing agent at a mass ratio of 10:1 to 20:1 and degas under vacuum; cover the surface of the sensing functional embroidery layer and interconnect layer using screen printing, dispensing, or spraying processes, control the encapsulation layer thickness to 30 μm to 100 μm, and cure at room temperature.

[0027] In a preferred embodiment, a high-density dadami stitch or satin stitch is used, with a stitch density of 5 to 10 stitches / mm to form a continuous, low-resistance conductive structure; the sensing embroidery layer uses a multi-layered serrated pattern to expand the working range: first, the first serrated layer is embroidered, and then the second serrated layer is superimposed, with the embroidery directions of the two layers deflected by 15° to 30° to increase the contact points.

[0028] Compared with the prior art, the present invention has the following beneficial effects: 1. By introducing a stress decoupling isolation layer and employing a non-full-surface connection method, a low-strain zone can be formed in the sensing area, thereby reducing parasitic changes caused by the stretching of the substrate fabric layer. Under experimental conditions, when the substrate fabric layer is subjected to a 30% tensile strain, the parasitic capacitance change rate of the sensing unit in this invention is reduced, which helps to improve the repeatability and reliability of long-term use.

[0029] 2. Due to the buffering effect of the stress decoupling isolation layer on the interface force transmission, fatigue peeling is not likely to occur between the encapsulation layer and the base fabric layer during washing and cyclic stretching.

[0030] 3. The preparation process of this invention is based on mature textile embroidery and hot pressing technology, which does not require photolithography, vacuum deposition or cleanroom environment. The embroidery process is compatible with existing textile industrial equipment. The conductive yarn and elastomer material can be commercially available. The thickness of each layer and pattern parameters can be controlled by software, which makes it feasible for mass production. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the flexible embroidery conductive sensing unit of the multi-layer stress decoupling isolation structure of the present invention; Figure 2 This is a schematic diagram of the floating island-type non-full surface connection structure between the stress decoupling isolation layer (2) and the base fabric layer (1) of the present invention, wherein (a) is a schematic diagram of the central anchored floating island connection, and (b) is a schematic diagram of the multi-point anchored floating island connection. Figure 3 A schematic diagram of the multi-layer superimposed serrated pattern of the embroidery layer (3) for sensing function, showing the superposition method and relative orientation relationship of the first serrated layer (3a) and the second serrated layer (3b); Figure 4 This is a schematic diagram comparing the stress / strain distribution of the structure of the present invention and the control structure under tensile load on the base fabric layer, wherein (a) is the control structure without stress decoupling isolation layer, and (b) is the floating island decoupling structure of the present invention. Figure 5 The output characteristic curve and hysteresis loop comparison diagram of the pressure sensing unit in Example 1 are shown, where (a) is the control structure and (b) is the structure of the present invention. Figure 6The graph shows the trend of the rate of change of electrical performance parameters with the number of washing cycles, which is the result of the water resistance test. Figure 7 This is a flowchart illustrating the preparation method of the flexible embroidery conductive sensing unit of the present invention.

[0032] Explanation of reference numerals in the attached figures: 1—Base fabric layer; 2—Stress decoupling isolation layer; 2a—Anchoring area; 2b—Suspension area; 3—Sensing embroidery layer; 3a—First serrated layer; 3b—Second serrated layer; 4—Elastic interconnect layer; 5—Encapsulation and protection layer. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0034] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0035] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0036] A flexible embroidered conductive sensing unit with a multilayer stress decoupling and isolation structure and its fabrication method, referenced Figure 1-7 It includes a base fabric layer, a stress decoupling isolation layer, and a sensing embroidery layer, which are stacked sequentially from bottom to top.

[0037] The base fabric layer, serving as the wearable carrier, is made of elastic knitted or woven fabric with a thickness of 50 μm to 500 μm, preferably 150 μm to 300 μm. The base fabric layer material is preferably a bi-directional elastic nylon / spandex blend or a polyester / spandex blend, with a spandex content of 10 wt% to 15 wt%. The elastic modulus of the base fabric layer is typically 2 MPa to 10 MPa.

[0038] The stress decoupling isolation layer is located between the base fabric layer and the sensing functional embroidered layer, with a thickness of 100 μm to 500 μm, preferably 150 μm to 300 μm. The elastic modulus of the stress decoupling isolation layer is 12 MPa to 50 MPa, significantly greater than that of the base fabric layer, and its elastic modulus ratio (stress decoupling isolation layer / base fabric layer) is typically 1.2 to 25. The stress decoupling isolation layer is attached to the base fabric layer via a non-full-surface bonding method to form a low-strain zone at the corresponding location in the sensing area and to suppress the upward transmission of strain from the base fabric layer through shear hysteresis. The preferred material for the stress decoupling isolation layer is a thermoplastic polyurethane (TPU) film, a polyester (PET) film, or a polyimide (PI) film.

[0039] The sensing functional embroidered layer is constructed from conductive yarns on a stress decoupling isolation layer using an embroidery process, with a thickness of 200μm to 800μm. Because the sensing functional embroidered layer is attached to the stress decoupling isolation layer, and the stress decoupling isolation layer and the base fabric layer are connected via a non-full-surface bonding method, the influence of the synchronous stretching of the base fabric layer on the geometry and relative position of the sensing functional embroidered layer can be reduced when the base fabric layer is stretched. The conductive yarn is preferably silver-plated nylon yarn or stainless steel composite yarn with a linear resistance of less than 200Ω / m.

[0040] I. Definition of a structure with non-full surface bonding: The stress decoupling isolation layer is bonded to the base fabric layer using a non-full-surface connection method. Non-full-surface connection means that the stress decoupling isolation layer and the base fabric layer are not continuously and fully fixed within a plane, but rather connected in a floating island manner. Specifically, the stress decoupling isolation layer is fixed to the base fabric layer only in one or more predetermined anchoring areas by heat pressing or adhesive, forming a suspended area at the corresponding position in the sensing area. The total area of ​​the anchoring area accounts for no more than 30% of the total planar projected area of ​​the stress decoupling isolation layer, preferably 5% to 25%, more preferably 10% to 25%.

[0041] The total area of ​​the anchoring zone is the actual fixed connection area between the stress decoupling isolation layer and the base fabric layer. The anchoring zone can be set as a central area (central anchoring type) or several discrete anchoring points (multi-point anchoring type). The suspended area refers to the area outside the anchoring zone where there is no continuous surface bonding between the stress decoupling isolation layer and the base fabric layer, and relative slippage between the two layers is allowed. The sensing embroidery layer is preferably arranged at the corresponding position of the suspended area. The total area of ​​the anchoring zone is calculated with the planar projected area of ​​the outer contour of the isolation layer as the denominator; and the sum of the projected area of ​​the fixed connection area formed by hot pressing / adhesion on the plane and the projected area of ​​the point-like locking on the plane as the numerator, wherein the projected area of ​​the point-like locking can be calculated based on the area of ​​the circumscribed circle of the locking point.

[0042] If the embroidery stitches form dotted knots in the non-anchored area, the area corresponding to the dotted knots is also included in the total area of ​​the anchored area. As an example, the hot pressing parameters can be selected as a temperature of 130℃ to 150℃, a pressure of 0.3MPa to 0.5MPa, and a time of 8s to 15s.

[0043] II. Physical Mechanism of Shear Hysteresis Effect This invention utilizes the shear hysteresis effect to achieve stress decoupling. When the base fabric layer is stretched, since the stress decoupling isolation layer is only fixedly connected to the base fabric layer in the anchoring area, the stress decoupling isolation layer in the suspended area does not need to be stretched synchronously with the base fabric layer. Instead, it can adapt to the deformation of the base fabric layer through interfacial shear deformation and relative slippage.

[0044] Specifically, when the base fabric layer is subjected to in-plane tension, the anchoring zone provides a fixed constraint, and the base fabric layer in the suspended zone can slip relative to the stress decoupling isolation layer. Because the stress decoupling isolation layer has a high elastic modulus (12 MPa to 50 MPa) and its in-plane stiffness is greater than that of the base fabric layer (2 MPa to 10 MPa), the in-plane strain of the stress decoupling isolation layer can be significantly reduced within the suspended zone. The tensile strain of the base fabric layer tends to be absorbed in the form of interfacial shear deformation and is less likely to be transferred to the top surface of the stress decoupling isolation layer and the sensing embroidery layer thereon.

[0045] This shear hysteresis mechanism is typically influenced by the following factors: First, the anchoring area accounts for no more than 30% (preferably 5% to 25%, more preferably 10% to 25%), to ensure that the suspended area has sufficient area, allowing the base fabric layer to have relative sliding space below the isolation layer; second, the stress decoupling isolation layer has sufficient in-plane stiffness (elastic modulus is 1.2 to 25 times that of the base fabric layer), making it less susceptible to being dragged by the base fabric layer in the suspended area and thus less likely to experience significant synchronous stretching. Under the conditions of the embodiment, when the anchoring area accounts for 5% to 25% and the base fabric layer is subjected to a 30% uniaxial tensile strain, the strain on the top surface of the stress decoupling isolation layer corresponding to the sensing area can be reduced to below 3%, and the corresponding strain attenuation rate can be greater than 90%.

[0046] III. Basis for Determining the Range of Key Parameters An anchoring area ratio of no more than 30% can be used as one of the upper limits for non-full surface bonding. To obtain a higher strain attenuation effect, the anchoring area ratio is preferably 5% to 25%, more preferably 10% to 25%. Under the conditions of the embodiment, when the anchoring area ratio is close to 30%, the strain attenuation rate may decrease to about 73% to 83%; when the anchoring area ratio is in the range of 5% to 25%, the strain attenuation rate can reach more than 90%. The lower limit of 5% for the anchoring area ratio can be determined based on structural stability. When the anchoring area is too small (e.g., less than 5%), the fixed connection strength between the stress decoupling isolation layer and the base fabric layer may be insufficient, and there is a risk of delamination or detachment during repeated stretching or washing. Under the conditions of the embodiment, when the anchoring area ratio is greater than 5%, the structure still remains intact after 50 washes and 5000 stretching cycles.

[0047] The considerations for selecting an elastic modulus ratio (stress decoupling isolation layer / base fabric layer) of 1.2 to 25 are as follows: When the ratio is less than 1.2, the internal stiffness of the stress decoupling isolation layer is insufficient, making it easily dragged by the base fabric layer and causing synchronous stretching, thus reducing the stress decoupling effect; when the ratio is greater than 25, although the decoupling effect may be further improved, an overly stiff isolation layer may affect the softness of the fabric and wearing comfort. Under the conditions of the embodiment, when the elastic modulus ratio is in the range of 1.2 to 25, a high strain attenuation effect and acceptable softness can be balanced.

[0048] The sensing unit also includes a flexible interconnect layer and an encapsulation protective layer. The flexible interconnect layer is formed by embroidering conductive yarns onto a base fabric layer, using wavy routing to accommodate large deformations of the base fabric layer. One end of the flexible interconnect layer connects to the sensing functional embroidered layer, and the other end connects to an external circuit. The encapsulation protective layer covers the surface of the sensing functional embroidered layer, with a thickness of 20μm to 100μm, and serves for waterproofing, oxidation prevention, and mechanical protection.

[0049] The present invention also provides a method for preparing the above-mentioned flexible embroidered conductive sensing unit, comprising the following steps.

[0050] Step S1: Pretreatment of the base fabric layer; Select a two-way elastic fabric as the base fabric layer, preferably a nylon / spandex blend knitted fabric (spandex content 10wt% to 15wt%). Perform pre-shrinkage treatment on the base fabric layer: Immerse the fabric in warm water at 40℃ to 60℃ for 30min to 60min, remove and air dry naturally to eliminate internal stress in the fabric; Mark the preset positions of the sensing units and the interconnection wire paths on the base fabric layer.

[0051] Step S2: Preparation and lamination of the stress decoupling isolation layer; When the stress decoupling isolation layer is a thermoplastic film (e.g., TPU film), a floating island-style local thermoplastic lamination can be used: the film is cut into a predetermined shape using a laser cutter, placed at a predetermined position on the substrate fabric layer, and hot-pressed in the anchoring area to melt the film in the anchoring area and penetrate into the fabric fibers to achieve a fixed connection; no pressure or only low pressure (e.g., less than 0.1 MPa) is applied to the corresponding positions of the edge area and sensing area to form a suspended area and maintain relative sliding space. The hot-pressing parameters can be selected as follows: temperature 130℃ to 150℃ (preferably 140℃), pressure 0.3 MPa to 0.5 MPa (preferably 0.4 MPa), and holding time 8s to 15s (preferably 10s). The total area of ​​the anchoring area is controlled to be 5% to 30% of the total area of ​​the planar projection of the stress decoupling isolation layer, preferably 10% to 25%.

[0052] When the stress decoupling isolation layer is a non-thermal-melting film (e.g., PET or PI film), localized bonding can be used to form anchoring areas: hot melt adhesive film, hot melt adhesive mesh, or pressure-sensitive adhesive is coated or attached to the predetermined anchoring area, and then fixed to the substrate fabric layer by hot or cold pressing; the suspended areas are not coated or pressurized to maintain relative slippage. The hot pressing temperature is 110°C to 160°C, the pressure is 0.1 MPa to 0.5 MPa, and the time is 5 s to 20 s. The total area of ​​the anchoring area is still controlled to be 5% to 30% of the total planar projection area of ​​the stress decoupling isolation layer.

[0053] Step S3: Digital Embroidery Sensing Functional Layer; The fabric with the stress decoupling isolation layer is clamped in a computer embroidery machine. The embroidery software is used to design the sensing pattern and generate embroidery codes. Conductive yarn is used to embroider the sensing pattern on the surface of the stress decoupling isolation layer. During embroidery, the stitches preferably penetrate the stress decoupling isolation layer within the anchoring area and form a stitch lock or mechanical connection with the base fabric layer to improve structural integrity. In the suspended area, the stitches can be kept as separate from the base fabric layer as possible by controlling the needle depth, using a backing (soluble backing paper / release film), or adjusting the bobbin tension, to maintain the relative slippage characteristics between the stress decoupling isolation layer and the base fabric layer. The main sensing areas of the sensing pattern are preferably arranged in the corresponding positions of the suspended areas. If a small number of point-like knots appear in the non-anchoring area due to process tolerances, the corresponding actual connection area shall be included in the total area of ​​the anchoring area, and the total area of ​​the anchoring area shall still meet the requirement of accounting for 5% to 30% (preferably 10% to 25%) of the total area of ​​the stress decoupling isolation layer planar projection.

[0054] High-density dadami or satin stitch is used, with a stitch density of 5 to 10 stitches / mm (preferably 8 stitches / mm) to form a continuous, low-resistance conductive structure. Embroidery machine parameters can be set as follows: top thread tension 2.0 to 3.0, bottom thread tension 1.5 to 2.5, and embroidery speed 400 to 600 stitches / min.

[0055] The sensing function embroidery layer can use a multi-layered zigzag pattern to expand the working range: first embroider the first zigzag layer (line spacing 0.3mm to 0.5mm, zigzag height 2mm to 3mm), then embroider the second zigzag layer (line spacing 0.5mm to 0.8mm, zigzag height 3mm to 5mm), with the two layers of embroidery oriented 15° to 30° to increase the contact points.

[0056] Step S4: Pre-stretching treatment; The embroidered sensing layer undergoes a pre-stretching cycle to reduce the irreversible deformation effect of the initial stretch. A universal testing machine can be used to perform 10 to 20 (preferably 15) stretching cycles, with a strain range of 0 to 50%, a stretching rate of 10 mm / min to 50 mm / min (preferably 20 mm / min), and an interval of 5 to 10 seconds between each cycle. Under the conditions of the example, the hysteresis effect can be reduced from over 40% initially to less than 5% after pre-treatment.

[0057] Step S5: Embroidering the elastic interconnect layer; After the sensing pattern is embroidered, the embroidery machine does not cut the thread and continues to embroider until the base fabric layer area is formed to form an elastic interconnect layer. The embroidery path smoothly transitions from a tightly packed electrode pattern to a wavy line, with a wavelength of 3mm to 8mm (preferably 5mm), an amplitude of 1mm to 3mm (preferably 2mm), and a stitch density reduced to 2 stitches / mm to 3 stitches / mm.

[0058] Step S6: Encapsulation treatment; Mix polydimethylsiloxane (PDMS) pre-mover and curing agent at a mass ratio of 10:1 to 20:1 (preferably 15:1) and degas under vacuum. Cover the surface of the sensing functional embroidered layer and interconnect layer using screen printing, dispensing, or spraying processes, controlling the encapsulation layer thickness to 30μm to 100μm (preferably 50μm), and cure at room temperature for 24h or at 60℃ for accelerated curing for 4h.

[0059] Performance testing methods: Hysteresis error test: Perform loading and unloading cycles within a specified input range, and record the correspondence between the output signal and the input quantity. Hysteresis error is calculated as "absolute value of the difference between maximum loaded output and unloaded output / full-scale output × 100%"; during the test, the loading / unloading rate, number of cycles, and pre-cycle conditions are fixed.

[0060] Strain decay rate test: The specimen is clamped on a uniaxial tensile platform with a gauge length of 20 mm to 50 mm (preferably 30 mm) and a tensile rate of 10 mm / min to 50 mm / min (preferably 20 mm / min). The average strain of the substrate fabric layer is measured using digital image correlation (DIC) or by setting markers on the top surface of the substrate fabric layer and the stress decoupling isolation layer and performing image tracking. Average strain on the top surface of the stress decoupling isolation layer corresponding to the sensing area The strain attenuation rate is calculated using the following formula:

[0061] when = 30%, If the value is less than 3%, the attenuation rate is considered to be greater than 90%.

[0062] Baseline drift / parasitic change rate test: Under conditions without external target stimulation, a specified range of stretching cycles is applied only to the base fabric layer, and the change in the baseline value of the output signal is recorded. Baseline drift is calculated as (baseline after cycle − initial baseline) / initial baseline × 100%; the parasitic capacitance or resistance change rate can be calculated using the same caliber, and the trend of change with the number of cycles is reported.

[0063] Wash resistance test: conducted according to ISO 6330 standard, with a single standard washing cycle as the counting unit. Zero point, sensitivity, hysteresis error, and rate of change of resistance or capacitance are compared before and after washing, and the trend of change with the number of washes is reported.

[0064] Example 1: Pressure sensing unit based on thermoplastic polyurethane floating island This embodiment provides a pressure sensing unit for smart insoles, which is required to maintain an effective response to pressure input even under bending deformation conditions. The sensing unit is a capacitive structure; under external pressure, the equivalent spacing / contact state between the embroidered electrodes changes, causing a change in capacitance and outputting a pressure signal.

[0065] Material Selection: The base fabric layer is a polyester / spandex blend knitted fabric (87% polyester, 13% spandex), 300 μm thick, with an elastic modulus of 5 MPa. The conductive yarn is silver-plated polyamide yarn with a linear resistance of less than 100 Ω / m. The stress decoupling isolation layer is a 0.15 mm thick thermoplastic polyurethane (TPU) film with an elastic modulus of 30 MPa (elastic modulus ratio of 6). The encapsulation material is polydimethylsiloxane (PDMS).

[0066] Preparation process: Step 1 (Substrate Pretreatment): Soak the polyester / spandex blended knitted fabric in 50℃ warm water for 45 minutes, then remove and air dry naturally; mark the preset positions of circular sensing units with a diameter of 20mm on the substrate.

[0067] Step 2 (Stress Decoupling Isolation Layer Composite): The TPU film is cut into circular pieces with a diameter of 20mm using a laser cutter. A precision heat press is used for point-by-point hot pressing, applying heat (140℃, 0.4MPa, 10s) only to the central 7mm diameter area of ​​the TPU disc. This allows the TPU to melt in the anchoring area and penetrate the fabric fibers to form a fixed connection. No pressure is applied to the outer annular area (radius 3.5mm to 10mm), creating a suspended area, thus forming a floating island-type non-full-surface connection structure. The anchoring area of ​​this structure accounts for approximately 12.25% of the total projected area of ​​the isolation layer, meeting the requirement of an anchoring area ratio of 5% to 30%.

[0068] Step 3 (Embroidering the Sensing Functional Layer): Embroider concentric interdigitated electrodes (0.4mm spacing, 8 stitches / mm) with a diameter of 18mm on the TPU film surface. The electrodes are mainly arranged at corresponding positions in the floating island suspension area. During embroidery, the stitches only penetrate the isolation layer and the base fabric layer in the central anchoring area to form a lock; in the suspension area, by adjusting the bobbin tension, the stitches are made to avoid forming locks with the base fabric layer as much as possible, so as to maintain the relative sliding characteristics between the isolation layer and the base fabric layer.

[0069] Step 4 (Pre-stretching treatment): Perform 15 tensile cycles (0 to 50% strain, 20 mm / min) using a universal testing machine, with a 5-second interval between each cycle.

[0070] Step 5 (Encapsulation): Mix PDMS pre-driving agent and curing agent at a mass ratio of 15:1, degas under vacuum, and then screen print the mixture onto the surface of the sensing electrode. The encapsulation layer is about 50 μm thick and is cured at room temperature for 24 hours.

[0071] Performance test results: Stress decoupling effect: A uniaxial tension of 0% to 30% was applied to the substrate fabric. The baseline capacitance value of the control group (without stress decoupling isolation layer) drifted by more than 40%; the baseline capacitance value of the structure in this embodiment changed by less than 2%. According to the strain attenuation rate test caliber: when the substrate was stretched by 30%, the strain in the sensing area was about 1.5%, corresponding to a strain attenuation rate of about 95%.

[0072] Pressure response: Sensitivity reaches 0.15 kPa⁻¹ in the range of 0 to 50 kPa, and loading and unloading hysteresis error is less than 4.5%.

[0073] Application verification: After integrating the sensing unit into the smart insole, it can be used to identify gait patterns such as standing, walking, and running, with a pressure detection error of less than 5%.

[0074] Example 2: Strain / Attitude Monitoring Sensing Unit Based on Multi-Point Anchored Floating Island This embodiment provides a strain / posture monitoring sensing unit for joint areas of sports knee braces or compression garments, which is required to maintain stable output under repeated bending and stretching conditions.

[0075] Material selection The base fabric layer is a polyester / spandex blend knitted fabric (85% polyester, 15% spandex), 250 μm thick, with an elastic modulus of approximately 4 MPa. The stress decoupling isolation layer is a 0.20 mm thick TPU film with an elastic modulus of approximately 30 MPa (elastic modulus ratio of 7.5). The conductive yarn is made of stainless steel composite yarn or silver-plated nylon yarn.

[0076] Preparation process: Step 1 (Substrate Pretreatment): Soak the polyester / spandex blended knitted fabric in 50°C warm water for 40 minutes, then remove and air dry naturally; mark the preset positions of elliptical sensing units with a major axis of 30mm and a minor axis of 20mm on the substrate.

[0077] Step 2 (Stress Decoupling Isolation Layer Composite): The TPU film is cut into elliptical pieces with a major axis of 30mm and a minor axis of 20mm, and four discrete anchoring points are set (each anchoring point has a diameter of approximately 3.5mm, and the total anchoring area is approximately 38.5mm²). Local hot pressing is used to achieve a fixed connection at the anchoring points (140℃, 0.4MPa, 10s). The total area of ​​the ellipse is approximately 471mm², corresponding to approximately 8.2% of the total anchoring area, which meets the limitation range of 5% to 30% for the anchoring area; the remaining areas are left unpressurized, forming a suspended area.

[0078] Step 3 (Embroidery Sensing Functional Layer): The sensing functional embroidery layer uses a double-layered zigzag pattern: first, embroider the first zigzag layer (line spacing 0.4mm, zigzag height 2.5mm), then embroider the second zigzag layer (line spacing 0.6mm, zigzag height 4mm). The embroidery direction between the two layers is offset by 20° to increase contact points. The main sensing areas are arranged at the corresponding positions in the suspended area, and the stitches only penetrate the isolation layer and the base at the anchor points to form a lock.

[0079] Step 4 (Pre-stretching treatment): Perform 15 tensile cycles (0 to 50% strain, 20 mm / min) using a universal testing machine, with an 8-second interval between each cycle.

[0080] Step 5 (Embroidering the Elastic Interconnect Layer): After the sensing pattern is embroidered, the embroidery machine does not cut the thread and continues to embroider until the base fabric area forms the elastic interconnect layer; the interconnect layer uses a wavy stitch (wavelength 5mm, amplitude 2mm, stitch density 2.5 stitches / mm).

[0081] Step 6 (Encapsulation): Mix the PDMS pre-driving agent and curing agent at a ratio of 15:1 and degas under vacuum. Then, use a dispensing process to cover the surface of the sensing functional embroidery layer and interconnect layer. The encapsulation layer thickness is about 50μm. Accelerate curing at 60℃ for 4 hours.

[0082] Performance test results: After cyclic loading (1 Hz, 500 cycles) within a strain range of 0% to 40%, the baseline drift was less than 4% and the hysteresis error was less than 5%; after 50 cycles of water washing resistance testing (ISO 6330 standard, 40℃), the resistivity change rate was less than 10%. These results indicate that the multi-point anchored floating island structure can also effectively reduce substrate deformation coupling and improve cyclic stability.

[0083] Comparative Example 1: Traditional Embroidery Sensor without Stress Decoupling Isolation Layer Using the same base fabric and conductive yarn as in Example 1, the interdigitated electrode pattern is directly embroidered on the elastic fabric without setting a stress decoupling isolation layer; the remaining process conditions are the same as in Example 1.

[0084] Comparative test results: When the substrate is stretched by 30%, the capacitance drift is greater than 45% (less than 2% in Example 1); the loading / unloading hysteresis is 38% (less than 5% in Example 1); the sample fails after 50 washes (resistance change rate of Example 1 is less than 10%); the coefficient of variation of the standard deviation of response repeatability is 27% (less than 5% in Example 1). These comparative results demonstrate that the stress decoupling isolation layer structure of this invention is superior to the traditional direct embroidery structure in terms of signal stability, hysteresis suppression, and water resistance.

[0085] Comparative Example 2: Fully Adhesive Stress Decoupling Isolation Layer Using a TPU film of the same size as in Example 1, hot pressing (140°C, 0.4MPa, 10s) was applied uniformly over the entire circular area to bond the TPU to the base fabric over the entire area (anchoring area accounting for 100%). Subsequently, the same interdigitated electrode pattern as in Example 1 was embroidered on the TPU surface.

[0086] Comparative test results: When the substrate is stretched by 30%, the capacitance drift of the fully bonded sample is 18% (less than 2% in Example 1), the hysteresis error is 15% (less than 5% in Example 1), and the strain attenuation rate is only about 40% (greater than 90% in Example 1). This comparative example shows that, in the system of this invention, the use of a non-full surface bonding method (anchor area ratio not greater than 30%) plays a key role in obtaining a higher stress decoupling effect.

Claims

1. A flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure, characterized in that, It includes a base fabric layer, a stress decoupling isolation layer, and a sensing embroidery layer, which are stacked sequentially from bottom to top; The base fabric layer serves as a wearable carrier; The stress decoupling isolation layer includes an anchoring region and a suspended region; The stress decoupling isolation layer is attached to the base fabric layer through a non-full surface connection method to form a low strain zone at the corresponding position of the sensing area, and to suppress the upward transmission of strain in the base fabric layer through the shear hysteresis effect; the sensing function embroidery layer is constructed by embroidering conductive yarn on the stress decoupling isolation layer.

2. The flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure according to claim 1, characterized in that, The non-full-surface connection method is that the stress decoupling isolation layer and the base fabric layer are connected in a floating island manner within the plane. That is, the stress decoupling isolation layer is fixedly connected to the base fabric layer only in one or more predetermined anchoring areas by hot pressing or adhesive, forming the suspended area at the corresponding position of the sensing area; the total area of ​​the anchoring area accounts for no more than 30% of the total area of ​​the plane projection of the stress decoupling isolation layer.

3. The flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure according to claim 1, characterized in that, The total area of ​​the anchoring zone is calculated with the planar projected area of ​​the stress decoupling isolation layer as the denominator; and the sum of the projected area of ​​the fixed connection area of ​​the stress decoupling isolation layer and the base fabric layer on the plane and the projected area of ​​the point-like locking on the plane as the numerator, wherein the projected area of ​​the point-like locking is calculated based on the area of ​​the circumcircle of the locking point.

4. The flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure according to claim 1, characterized in that, If the embroidery stitches form dotted knots in the non-anchored area, the area corresponding to the dotted knots is also included in the total area of ​​the anchored area.

5. The flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure according to claim 1, characterized in that, Stress decoupling is achieved by utilizing the shear hysteresis effect. When the base fabric layer is stretched, since the stress decoupling isolation layer is only fixedly connected to the base fabric layer in the anchoring area, the stress decoupling isolation layer in the suspended area does not need to be stretched synchronously with the base fabric layer. Instead, it can adapt to the deformation of the base fabric layer through interface shear deformation and relative slip. When the base fabric layer is stretched in the plane, the anchoring zone provides a fixed constraint, and the base fabric layer in the suspended zone undergoes relative slippage below the stress decoupling isolation layer; Within the suspended region, the tensile strain of the base fabric layer tends to be absorbed in the form of interfacial shear deformation, rather than being easily transmitted to the top surface of the stress decoupling isolation layer and the sensing embroidery layer thereon.

6. The flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure according to claim 1, characterized in that, The anchorage area accounts for 10% to 25% of the total area.

7. The flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure according to claim 1, characterized in that, The elastic modulus of the stress decoupling isolation layer is 1.2 to 25 times that of the base fabric layer.

8. The flexible embroidered conductive sensing unit with a multi-layer stress decoupling and isolation structure according to claim 1, characterized in that, It also includes a flexible interconnect layer and an encapsulation protection layer; the flexible interconnect layer is formed by embroidering conductive yarns on the base fabric layer, using wavy routing to adapt to large deformations of the base fabric layer, with one end connected to the sensing function embroidery layer and the other end connected to the external circuit; the encapsulation protection layer covers the surface of the sensing function embroidery layer.

9. A method for fabricating a flexible embroidered conductive sensing unit with a multilayer stress decoupling and isolation structure, characterized in that, The preparation of a flexible embroidered conductive sensing unit with a multilayer stress decoupling and isolation structure as described in any one of claims 1-8 includes the following steps: Step S1: Select a two-way elastic fabric as the base fabric layer. The preferred material is a nylon or spandex blended knitted fabric. Perform a pre-shrinking treatment on the base fabric layer: soak the fabric in warm water at 40℃ to 60℃ for 30 to 60 minutes, take it out and let it air dry naturally. Mark the preset position of the sensing unit and the interconnection wire path on the base fabric layer. Step S2: When the stress decoupling isolation layer is a thermoplastic film, a floating island-style local thermoplastic composite is adopted: the film is cut into a predetermined shape using a laser cutter, the film is placed at a predetermined position on the base fabric layer, and hot pressure is applied to the anchoring area to melt the film in the anchoring area and penetrate into the fabric fibers to achieve a fixed connection; no pressure or only low pressure is applied to the corresponding positions of the edge area and the sensing area to form a suspended area and maintain a relative sliding space; When the stress decoupling isolation layer is a non-thermal melt film, local bonding is used to form the anchoring area: hot melt adhesive film, hot melt adhesive mesh or pressure-sensitive adhesive is coated or attached to the predetermined anchoring area, and it is fixed to the base fabric layer by hot pressing or cold pressing; no adhesive or pressure is applied to the suspended area to maintain relative slippage; Step S3: The fabric with the stress decoupling isolation layer is clamped in a computer embroidery machine. The embroidery software is used to design the sensing pattern and generate the embroidery code. The sensing pattern is formed by embroidering on the surface of the stress decoupling isolation layer with conductive yarn. During embroidery, the stitches preferably penetrate the stress decoupling isolation layer within the anchoring area and form a stitch lock or mechanical connection with the base fabric layer. In the suspended area, by controlling the needle depth, using backing, or adjusting the bottom thread tension, the stitches are made to avoid forming a lock with the base fabric layer as much as possible, so as to maintain the relative slippage characteristics between the stress decoupling isolation layer and the base fabric layer. Step S4: Perform a pre-stretching cycle on the embroidered sensing layer to reduce the irreversible deformation effect of the first stretch; perform 10 to 20 stretching cycles using a universal testing machine; Step S5: After the sensing pattern is embroidered, the embroidery machine does not cut the thread and continues to embroider until the base fabric layer area forms an elastic interconnect layer; the embroidery path smoothly transitions from a tightly packed electrode pattern to a wavy line. Step S6: Mix the polydimethylsiloxane (PDMS) pre-engineer and curing agent at a mass ratio of 10:1 to 20:1 and degas under vacuum; cover the surface of the sensing functional embroidery layer and interconnect layer using screen printing, dispensing, or spraying processes, control the encapsulation layer thickness to 30 μm to 100 μm, and cure at room temperature.

10. The method for preparing a flexible embroidered conductive sensing unit with a multilayer stress decoupling and isolation structure according to claim 9, characterized in that, High-density dadami stitch or satin stitch is used, with a stitch density of 5 to 10 stitches / mm to form a continuous, low-resistance conductive structure; the sensing function embroidery layer uses a multi-layer superimposed serrated pattern to expand the working range: first embroider the first serrated layer, then superimpose the second serrated layer, with the two layers of embroidery direction deflected by 15° to 30° to increase contact points.

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