Voiceprint sensor based on fiber aerogel structure and preparation method and application thereof

Abstract

The invention discloses a voiceprint sensor based on a fiber aerogel structure and a preparation method and application thereof, and the voiceprint sensor comprises a nanofiber aerogel sensing layer which is of a sandwich structure and comprises a first conductive polyurethane nanofiber membrane, a conductive polyvinyl alcohol nanofiber membrane and a second conductive polyurethane nanofiber membrane from top to bottom in sequence; the first conductive polyurethane nanofiber membrane and the second conductive polyurethane nanofiber membrane are respectively prepared by compounding polyethylene glycol-polyurethane, poly trimethylene ether glycol-polyurethane, N, N-dimethylformamide and ZnCl2 ionic liquid, and are respectively used as an upper electrode and a lower electrode; the conductive polyvinyl alcohol nanofiber membrane is prepared by compounding polyvinyl alcohol and hydroxylated multi-walled carbon nanotubes, and is clamped between the two conductive polyurethane nanofiber membranes; the two copper foils are respectively adhered to one end of the surface of the upper electrode and one end of the surface of the lower electrode, and one end of each copper foil extends outwards and is connected with a wire. The preparation method is simple, the sensing performance is excellent, and the performance is stable.

Description

An acoustic fingerprint sensor based on a fiber aerogel structure, its preparation method and application Technical Field

[0001] This invention relates to an acoustic fingerprint sensor based on a fiber aerogel structure, its preparation method, and its application, belonging to the field of dynamic pressure sensing technology. Background Technology

[0002] In the rapid iteration of flexible electronics and high-precision sensing technologies, voiceprint sensors, as core devices for capturing and converting acoustic vibration signals, have been widely applied in key areas such as health monitoring, wearable devices, and voiceprint recognition. However, traditional rigid sensing materials (such as silicon-based and metal-based materials) are limited by the rigidity of their mechanical properties, making it difficult to achieve flexible conformal bonding with complex curved surfaces such as human skin and joints. Furthermore, they have a high response threshold for low-frequency (20-200 Hz) acoustic vibration signals, resulting in insufficient sensitivity and failing to meet the requirements for accurate detection of weak acoustic vibration signals.

[0003] While existing flexible conductive composite materials (such as carbon nanotube / polymer composite films and graphene-based flexible films) have overcome the deformation limitations of rigid materials and possess a certain degree of flexible adaptability, they still face multiple technical bottlenecks in practical applications: First, a high proportion of conductive fillers needs to be added to construct a continuous conductive network, which significantly increases the brittleness of the material and reduces its mechanical flexibility and durability; second, conductive fillers are prone to agglomeration in the polymer matrix, resulting in poor uniformity and insufficient stability of the conductive network, leading to large fluctuations in the sensing signal; third, unreasonable microstructure design can easily cause irreversible collapse under repeated sound pressure impacts, resulting in rapid decay of sensing performance and shortened service life.

[0004] In recent years, three-dimensional nanofiber aerogels, prepared by electrospinning and freeze-drying, have provided a new technical approach to solving the aforementioned problems due to their high specific surface area, hierarchical porous structure, and excellent structural flexibility. Their unique three-dimensional network can transform weak acoustic vibrations into significant fiber network deformation, thereby amplifying the piezoresistive response signal and potentially overcoming the sensitivity limitations of traditional flexible materials. However, these materials still have technical challenges: the interfacial interactions between nanofibers are weak, and conductive fillers easily detach from the fiber matrix, making it difficult to form a stable and continuous conductive pathway. Furthermore, while the porous structure of aerogels is beneficial for acoustic vibration capture, their structural elastic recovery is insufficient, making them prone to permanent deformation under cyclic loading, affecting sensing stability and repeatability. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides an acoustic fingerprint sensor based on a fiber aerogel structure, its preparation method, and its application. The preparation method is simple, and the sensor exhibits excellent and stable performance.

[0006] To achieve the above objectives, the present invention employs an acoustic signature sensor based on a fiber aerogel structure, comprising:

[0007] The nanofiber aerogel sensing layer has a sandwich structure, consisting of a first conductive polyurethane nanofiber membrane, a conductive polyvinyl alcohol nanofiber membrane, and a second conductive polyurethane nanofiber membrane, arranged from top to bottom. The first and second conductive polyurethane nanofiber membranes are both made of polyethylene glycol-polyurethane, polytrimethylene ether glycol-polyurethane, N,N-dimethylformamide, and ZnCl2 ionic liquid, and serve as the upper and lower electrodes of the sensor, respectively. The conductive polyvinyl alcohol nanofiber membrane is made of polyvinyl alcohol and hydroxylated multi-walled carbon nanotubes, and is sandwiched between the first and second conductive polyurethane nanofiber membranes.

[0008] Two copper foils are provided, which are respectively adhered to one end of the upper surface of the upper electrode and one end of the lower surface of the lower electrode, and one end of each copper foil extends outward and is connected to a wire.

[0009] As an improvement, the nanofiber aerogel sensing layer is prepared by sequential electrospinning combined with freeze-drying process to form a nanofiber aerogel with a three-dimensional porous network structure.

[0010] The conductivity of the three-dimensional porous network structure is jointly regulated by the proportion of hydroxylated multi-walled carbon nanotubes added to the conductive polyvinyl alcohol nanofiber membrane, and the sandwich structure composed of the first conductive polyurethane nanofiber membrane, the conductive polyvinyl alcohol nanofiber membrane, and the second conductive polyurethane nanofiber membrane.

[0011] A second aspect of the present invention also provides a method for fabricating the aforementioned acoustic signature sensor based on a fiber aerogel structure, comprising the following steps:

[0012] (1) Preparation of sandwich-structured nanofiber aerogel sensing layer

[0013] a) Weigh out polyethylene glycol-polyurethane and polytrimethylene ether glycol-polyurethane, dissolve them in N,N-dimethylformamide solution, and add ZnCl2 ionic liquid to prepare conductive polyurethane spinning solution;

[0014] b) Weigh out polyvinyl alcohol, dissolve it in water, and add hydroxylated multi-walled carbon nanotubes to prepare a conductive polyvinyl alcohol spinning solution;

[0015] c) Electrospinning the conductive polyurethane spinning solution to obtain a second conductive polyurethane nanofiber membrane;

[0016] d) Electrospinning of conductive polyvinyl alcohol spinning solution on the upper surface of the second conductive polyurethane nanofiber membrane to obtain a conductive polyvinyl alcohol nanofiber membrane.

[0017] e) Continue electrospinning the conductive polyurethane spinning solution on the upper surface of the conductive polyvinyl alcohol nanofiber membrane to obtain the first conductive polyurethane nanofiber membrane and form a three-layer composite membrane.

[0018] f) The three-layer composite membrane was freeze-dried to obtain a sandwich-structured nanofiber aerogel sensing layer.

[0019] (2) Sensor packaging

[0020] The first conductive polyurethane nanofiber membrane is used as the upper electrode and the second conductive polyurethane nanofiber membrane is used as the lower electrode. Copper foil is attached to one end of the upper surface of the upper electrode and one end of the lower surface of the lower electrode, and one end of the copper foil extends outward and is connected to a wire to complete the encapsulation.

[0021] As an improvement, in step a), the mass ratio of polyethylene glycol-polyurethane and polytrimethylene ether glycol-polyurethane is 1:(1-5), and the mass concentration of ZnCl2 ionic liquid is 5%-15%.

[0022] As an improvement, in step b), the mass concentration of hydroxylated multi-walled carbon nanotubes in the conductive polyvinyl alcohol spinning solution is 0.1%-5%.

[0023] As an improvement, in steps c), d), and e), the electrospinning time is 5-10 hours, respectively.

[0024] As an improvement, in step f), the freeze-drying temperature is -70°C and the time is 10-15 hours.

[0025] A third aspect of the present invention also provides an application of a voiceprint sensor based on a fiber aerogel structure prepared by the aforementioned method in flexible wearable devices, health monitoring devices, or high-precision voiceprint recognition devices.

[0026] The principle of this invention is:

[0027] This invention designs an innovative "sandwich structure" three-dimensional nanofiber aerogel sensing layer. This structure, through the synergy of materials and processes, efficiently captures acoustic vibration energy and converts it into electrical signals. The porous elastic structure and conductive pathways of the sensing layer are fundamental to its two core functions. Firstly, the structure employs a unique "polyurethane (containing ZnCl2 ionic liquid) / PVA-MWCNT-OH / polyurethane (containing ZnCl2 ionic liquid)" sandwich structure design. Through freeze-drying, a three-dimensional network with both high porosity and ultralight properties is constructed. When sound waves propagate, the resulting pressure changes rapidly penetrate and drive significant elastic deformation throughout the aerogel network (especially the middle layer rich in MWCNT-OH PVA fiber network). This efficiently converts the weak acoustic mechanical energy into structural deformation energy, solving the problem of insufficient response to low-frequency weak acoustic vibrations. On the other hand, the conductivity of the sensing layer is constructed and synergistically amplifies the signal through a dual mechanism: firstly, hydroxylated multi-walled carbon nanotubes in the intermediate layer are uniformly dispersed through hydrogen bonding with PVA molecular chains, forming a stable electronic conduction pathway that runs through the network; secondly, the ZnCl2 ionic liquid in the upper and lower polyurethane nanofiber membranes not only serves as a flexible electrode current collector but also provides a high-mobility ion conduction pathway. When acoustic waves induce network deformation, it simultaneously causes changes in the resistance of the intermediate layer's electronic conduction network (piezoresistive effect) and alters the ion migration path and distribution (change in ion conductivity). This electron-ion coupling conduction mechanism further amplifies the structural deformation energy and converts it into a highly sensitive, high signal-to-noise ratio electrical signal output, thereby achieving efficient and stable sensing from acoustic waves to deformation to electrical signals.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] (1) A novel "sandwich structure" three-dimensional nanofiber aerogel sensing layer was constructed by electrospinning and freeze-drying processes. This structure innovatively combines a polyurethane solution containing ZnCl2 ionic liquid, which has both hydrophilicity (PEG-PU) and mechanical strength (PO3G-PU), and a polyvinyl alcohol (PVA) solution containing hydroxylated multi-walled carbon nanotubes (MWCNT-OH). Through sequential electrospinning and integrated freeze-drying, a "polyurethane / PVA-MWCNT-OH / polyurethane" sandwich configuration is formed. This design solves the problem of unstable conductive pathways caused by weak interfacial interactions in traditional nanofiber aerogels: the two dense polyurethane fiber membranes are physically encapsulated and bonded to ZnCl2. 2+ The coordination and cross-linking effect effectively anchors MWCNT-OH in the intermediate PVA fiber, constructing a stable electron-ion coupled continuous conductive network, which significantly improves the reliability of the conductive path and the signal stability.

[0030] (2) The sensing layer is prepared using a simple and scalable process of solution blending, sequential electrospinning, and freeze-drying. Its unique sandwich structure not only provides excellent overall flexibility and surface fit, but also provides strong mechanical support and constraint for the middle porous PVA-MWCNT-OH layer with the upper and lower polyurethane layers, effectively suppressing the permanent deformation and collapse of the pure aerogel structure under cyclic sound pressure, thereby ensuring the structural resilience and sensing repeatability of the sensor in long-term use and extending its service life.

[0031] (3) The core raw materials are readily available and the cost is controllable. The process parameters are clear and controllable. The sensor has the advantages of being lightweight and having stable signal output. It can be flexibly adapted to various application scenarios such as flexible wearable devices, health monitoring, and high-precision voiceprint recognition. Its practical value and industrialization potential are outstanding. Attached Figure Description

[0032] Figure 1 is a schematic diagram of the sandwich structure of the acoustic signature sensor of the present invention;

[0033] Figure 2 shows the sensitivity test results of the voiceprint sensor in Embodiment 2 of the present invention;

[0034] Figure 3 shows the response / recovery time test results of the acoustic signature sensor in Embodiment 2 of the present invention;

[0035] Figure 4 is a response diagram of the resistance change of the acoustic fingerprint sensor under different tensile strains in Embodiment 2 of the present invention;

[0036] Figure 5 is a response diagram of the resistance change of the acoustic fingerprint sensor at different frequencies in Embodiment 2 of the present invention;

[0037] Figure 6 shows the repeatability test results of the acoustic signature sensor in Embodiment 2 of the present invention. Detailed Implementation

[0038] The following embodiments are further illustrations of the present invention and serve as explanations of the technical content of the present invention. However, the essence of the present invention is not limited to the embodiments described below. Those skilled in the art can and should know that any simple changes or substitutions based on the spirit of the present invention should fall within the protection scope claimed by the present invention.

[0039] Example 1

[0040] This embodiment provides an acoustic fingerprint sensor based on a fiber aerogel structure, and the specific preparation method is as follows:

[0041] 1. Preparation of sandwich-structured nanofiber aerogel sensing layer

[0042] (1) Weigh 5g of polyethylene glycol-polyurethane (PEG-PU) and 5g of polytrimethylene ether glycol-polyurethane (PO3G-PU) and dissolve them in N,N-dimethylformamide (DMF) solution to prepare a 10% polyurethane solution. Add 10g of ZnCl2 ionic liquid to prepare a 10% conductive polyurethane spinning solution.

[0043] (2) Weigh 12g of polyvinyl alcohol (PVA) and place it in a single-necked round-bottom flask. Add water to dissolve it and prepare a 15% polyvinyl alcohol solution. Add 0.06g of hydroxylated multi-walled carbon nanotubes (MWCNT-OH) to prepare a 0.5% conductive polyvinyl alcohol spinning solution.

[0044] (3) Electrospinning treatment of conductive polyurethane spinning solution was carried out for 5 hours to obtain a second conductive polyurethane nanofiber membrane.

[0045] (4) Electrospinning of conductive polyvinyl alcohol spinning solution on the upper surface of the second conductive polyurethane nanofiber membrane for 10 hours to obtain conductive polyvinyl alcohol nanofiber membrane.

[0046] (5) On the upper surface of the conductive polyvinyl alcohol nanofiber membrane, the conductive polyurethane spinning solution is electrospun again for 5 hours to obtain the first conductive polyurethane nanofiber membrane, thus forming a three-layer composite membrane.

[0047] (6) The three-layer composite membrane was freeze-dried at -70℃ for 12 hours to obtain the sandwich-structured nanofiber aerogel sensing layer.

[0048] 2. Sensor Packaging

[0049] The first conductive polyurethane nanofiber membrane is used as the upper electrode and the second conductive polyurethane nanofiber membrane is used as the lower electrode. Copper foils are attached to one end of the upper surface of the upper electrode and one end of the lower surface of the lower electrode, and one end of each copper foil extends outward and is connected to a wire to complete the encapsulation.

[0050] 3. Performance test connection

[0051] One end of the wire is connected to external experimental equipment to measure the performance of the sensor.

[0052] Example 2

[0053] This embodiment provides a sandwich-structured nanofiber aerogel acoustic sensor, the preparation method of which is basically the same as that in Example 1, the only difference being:

[0054] In the preparation stage of the sandwich structure nanofiber aerogel sensing layer, 0.12g of hydroxylated multi-walled carbon nanotubes were weighed and added to a 15% polyvinyl alcohol solution. The mixture was mixed evenly to prepare a conductive polyvinyl alcohol spinning solution with a mass ratio of 1%. The subsequent electrospinning and freeze-drying steps were the same as in Example 1.

[0055] The remaining preparation steps (sensor packaging, performance testing connection) are the same as in Example 1.

[0056] The sensing performance of the voiceprint sensor prepared in this embodiment was tested, and the results are as follows:

[0057] Sensitivity Testing: This invention fabricates a sandwich-structured nanofiber aerogel acoustic sensor using a combined electrospinning and freeze-drying process. It exhibits high sensitivity with segmented response over a wide tensile strain range (sensitivity of 1.08 in the 0-50% strain range and 2.43 in the 50-120% strain range), as shown in Figure 2. This is due to its unique sandwich structure design: First, a polyurethane (PEG-PU / PO3G-PU mixture) solution containing ZnCl2 ionic liquid is used as conductive solution A, and a polyvinyl alcohol (PVA) solution loaded with 1% hydroxylated multi-walled carbon nanotubes (MWCNT-OH) is used as conductive solution B. A three-layer precursor of "polyurethane / PVA-MWCNT-OH / polyurethane" is constructed through sequential electrospinning, followed by freeze-drying to form an integrated aerogel sensing layer. The upper and lower dense polyurethane nanofiber membranes serve as both flexible electrodes and mechanical support. This structure achieves dual optimization in sensing mechanism: under initial strain (0-50%), the porous fiber network of the intermediate PVA-MWCNT-OH undergoes reversible bending and contact, causing initial reconstruction of the conductive pathway and generating a stable sensitivity response; when the strain further increases (50-120%), the upper and lower polyurethane layers and the intermediate layer deform synergistically, producing a stronger compression and densification effect on the porous network. At the same time, the ionic conductive path provided by the ZnCl2 ionic liquid and the electronic conductive path of MWCNT-OH are coupled and enhanced, leading to a rapid reconstruction of the conductive pathway, thereby achieving a significant leap in sensitivity. Compared to conventional single-structure or physically blended nanofiber sensors, traditional methods often suffer from low sensitivity, narrow response range, significant signal hysteresis, and poor cycle stability due to weak fiber interfaces, easy aggregation of conductive fillers, or lack of elastic recovery. In contrast, this invention combines ionic and electronic conductivity through a sandwich configuration and utilizes the mechanical constraint of the dense layer on the porous layer to achieve high sensitivity, good response linearity, and excellent structural reliability over a wide strain range. This demonstrates the effectiveness and advantages of this strategy in constructing high-performance flexible sensors suitable for health monitoring, wearable devices, and voiceprint recognition.

[0058] Response / Recovery Time Test: The sandwich-structured nanofiber aerogel acoustic sensor prepared in this invention achieves rapid response and recovery times (370 ms / 296 ms, as shown in Figure 3), which is directly related to its precisely controlled multi-level structure and conductive network design. This sensor constructs a three-layer composite aerogel structure of "polyurethane (containing ZnCl2 ionic liquid) / PVA-MWCNT-OH / polyurethane (containing ZnCl2 ionic liquid)" through electrospinning and freeze-drying processes. The highly elastic, low-density three-dimensional nanofiber network formed by freeze-drying endows the overall structure with excellent deformation recovery capability, ensuring rapid and reversible deformation under sound pressure. Simultaneously, the uniformly dispersed hydroxylated multi-walled carbon nanotubes (MWCNT-OH) in the middle layer are bonded to the PVA matrix through hydrogen bonds and work synergistically with the ionic conductive pathways provided by the ZnCl2 ionic liquid in the upper and lower polyurethane films to jointly construct a stable and efficient electron-ion coupling conductive pathway, ensuring efficient synchronization between mechanical deformation and electrical signal conversion. Compared to traditional sensors employing dense composite membranes, disordered macroporous aerogels, or fillers prone to aggregation, which often result in slow dynamic response (typically > 500 ms) due to high structural viscoelasticity, pore blockage, or unstable interfacial conductivity, this invention strengthens interfacial bonding, optimizes porous elasticity, and achieves synergistic dual conductivity mechanisms through a sandwich configuration. This significantly improves dynamic response speed while maintaining high sensitivity, achieving millisecond-level signal tracking capability. This is crucial for health monitoring, wearable devices, and voiceprint recognition applications that require real-time and accurate capture of dynamic, weak sound wave vibrations such as voice and heart sounds, demonstrating its core performance advantage in rapid response.

[0059] Strain response test: The sandwich-structured nanofiber aerogel acoustic sensor prepared in this invention exhibits a reliable and repeatable strain response under tensile strain stimulation (as shown in Figure 4). This performance is attributed to its unique multi-level structural design: a three-layer composite aerogel network of "polyurethane (containing ZnCl2 ionic liquid) / PVA-MWCNT-OH / polyurethane (containing ZnCl2 ionic liquid)" constructed by electrospinning and freeze-drying processes, combined with a continuous conductive pathway constructed by hydroxylated multi-walled carbon nanotubes uniformly dispersed in PVA fibers. The structure has the following core advantages: (1) The two dense polyurethane nanofiber membranes serve as flexible electrodes and mechanical constraint layers, ensuring that strain is uniformly transmitted within the sensing layer and avoiding stress concentration, thereby generating stable and predictable interlayer synergistic deformation at different strain levels; (2) The three-dimensional porous nanofiber network formed by the intermediate PVA-MWCNT-OH layer can track the dynamic changes in the contact and slip state between fibers in real time, and accurately convert macroscopic tensile deformation into a high signal-to-noise ratio resistance signal through the electron (MWCNT-OH)-ion (ZnCl2) coupling conductivity mechanism; (3) The high elasticity of the polyurethane matrix, the hydrogen bonding between PVA fibers, and the overall support provided by the sandwich structure enable the sensor to quickly return to the initial structural state after loading / unloading cycles, exhibiting low hysteresis and high repeatability response characteristics. Compared with traditional flexible sensors that often suffer from signal nonlinearity, baseline drift, and poor cyclic stability due to their reliance on single materials, uneven packing, or lack of structural support, the structure of this invention achieves a highly stable and repeatable correspondence between electrical signal output and strain amplitude over a wide strain range. This provides a crucial material basis for fields requiring precise quantification of dynamic deformation, such as health monitoring (e.g., joint movement, muscle vibration), wearable devices, and voiceprint recognition, demonstrating its significant performance advantages in measurement consistency and long-term reliability.

[0060] Dynamic stability test: The excellent dynamic stability exhibited by the sandwich-structured nanofiber aerogel acoustic sensor prepared in this invention (as shown in Figure 5) is fundamentally due to its integrated structure and robust interface design. Through a combined process of electrospinning and freeze-drying, hydroxylated multi-walled carbon nanotubes are uniformly dispersed and firmly anchored in a three-dimensional polyvinyl alcohol nanofiber network. At the same time, two layers of polyurethane nanofiber membranes containing ZnCl2 ionic liquid serve as electrodes and mechanical reinforcement layers, tightly wrapping the conductive network to form an integrated "sandwich" structure. The design exhibits the following core advantages in dynamic cycling: (1) The sandwich structure provides external constraint and overall support for the porous fiber network in the middle layer, significantly improving the fatigue resistance and resistance to permanent deformation of the aerogel, and enabling the fiber network to maintain structural integrity during repeated stretching and rebound; (2) MWCNT-OH is tightly bound to the PVA molecular chain through hydrogen bonding and is physically anchored by the upper and lower polyurethane layers, effectively preventing its migration or detachment under dynamic strain, and ensuring the long-term reliability of the electron-ion coupling conductive pathway; (3) The uniform and interconnected multi-level nanofiber network promotes uniform strain distribution and avoids fiber breakage or interface failure caused by local stress concentration. Compared with the common traditional nanofiber sensors based on physical blending, easy agglomeration of fillers or loose structure, which are prone to signal attenuation and baseline drift in dynamic cycling, this invention achieves a high degree of consistency between the output waveform and peak value of the electrical signal of the sensor at different stretching rates through the strategies of "structural integration constraint" and "multi-level interface reinforcement". This is of key significance for the flexible acoustic sensor to maintain stable and reliable sensing performance in application scenarios such as health monitoring and wearable devices that need to cope with complex dynamic deformation.

[0061] Cyclic stability test: The sandwich-structured nanofiber aerogel acoustic sensor prepared in this invention can still maintain excellent electrical signal stability after 3000 tensile cycles (as shown in Figure 6). This key performance is directly due to the highly integrated, tough and self-healing three-dimensional network structure constructed by the synergistic process of electrospinning and freeze-drying. Specifically, the upper and lower polyurethane nanofiber membranes containing ZnCl2 ionic liquid serve as flexible electrodes and mechanical reinforcement layers. Together with the middle layer of polyvinyl alcohol / hydroxylated multi-walled carbon nanotube composite fiber network, they form a stable "sandwich" structure through physical entanglement and interfacial interactions. This structure provides the entire sensing layer with excellent overall fatigue resistance and deformation recovery capabilities, effectively resisting structural relaxation or fiber breakage that may be caused by long-term cyclic strain. At the same time, the hydroxylated multi-walled carbon nanotubes are uniformly dispersed and firmly anchored to the PVA fiber skeleton through hydrogen bonding. Combined with the ionic conductivity pathway provided by the ZnCl2 ionic liquid, they jointly construct an "electron-ion" coupled conductive network with extremely high mechanical and electrical stability. This avoids the migration or interfacial failure of conductive fillers under cyclic stress, ensuring long-term reliable electrical signal transmission. In addition, the uniform, interconnected, and multi-level porous nanofiber network formed by freeze-drying can effectively disperse cyclic loads and prevent microstructural damage caused by local stress concentration. Compared to existing flexible sensors based on physical blending, weak interface bonding, or loose structure, which often exhibit signal attenuation or baseline drift after hundreds of cycles, this invention achieves a high degree of consistency between the electrical signal output waveform and peak value after multiple cycles through the synergistic design of sandwich structure constraint, multi-level interface reinforcement, and dual-path conductive network. This provides a key material basis for maintaining stable and reliable sensing performance of the acoustic fingerprint sensor under long-term, dynamic working conditions (such as continuous health monitoring and wearable device applications), fully demonstrating its significant advantages in cycle durability.

[0062] Example 3

[0063] This embodiment provides a sandwich-structured nanofiber aerogel acoustic sensor, the preparation method of which is basically the same as that in Example 1, the only difference being:

[0064] In the preparation stage of the sandwich structure nanofiber aerogel sensing layer, 0.24g of hydroxylated multi-walled carbon nanotubes were weighed and added to a 15% polyvinyl alcohol solution. The mixture was mixed evenly to prepare a conductive polyvinyl alcohol spinning solution with a mass ratio of 2%. The subsequent electrospinning and freeze-drying steps were the same as in Example 1.

[0065] The remaining preparation steps (sensor packaging, performance testing connection) are the same as in Example 1.

[0066] This invention presents an innovative method for fabricating a "sandwich structure" nanofiber aerogel acoustic sensor, aiming to address the core challenges of traditional flexible sensors in terms of conductive path stability and structural durability. Specifically, a three-layer composite structure of "polyurethane (containing ZnCl2 ionic liquid) / PVA-MWCNT-OH / polyurethane (containing ZnCl2 ionic liquid)" is constructed through electrospinning and freeze-drying. The dense upper and lower polyurethane layers act as flexible electrodes and provide mechanical support, effectively strengthening interfacial bonding and inhibiting the detachment of the conductive filler in the middle layer. This results in a stable and continuous conductive path and significantly improves the elastic recovery of the aerogel under cyclic loading. Examples 1 to 3 of this invention, by systematically varying the amount of hydroxylated multi-walled carbon nanotubes (MWCNT-OH) added to the middle layer (0.06g, 0.12g, and 0.24g, corresponding to contents of 0.5%, 1%, and 2%), play a crucial role in precisely investigating and comparing the gradient effect of conductive filler concentration on the final sensor performance. This comparison visually reveals how the MWCNT-OH content regulates the density of the conductive network in the sensing layer, the uniformity of the porous morphology, and the overall electromechanical response characteristics. This allows for the determination of the optimal formulation that achieves the best balance between sensitivity, stability, and durability, providing clear experimental evidence and data support for the optimization and customization of sensor performance. This design not only directly addresses the issues of easy failure and structural collapse in traditional conductive networks but also, through controlled comparative experiments, lays a solid technological foundation for the fabrication of voiceprint sensors with high sensitivity, excellent flexibility, and long-term stability. This strongly promotes the practical application of this technology in flexible wearable devices, health monitoring, and high-precision voiceprint recognition.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An acoustic signature sensor based on a fiber aerogel structure, characterized in that, include: The nanofiber aerogel sensing layer has a sandwich structure, consisting of a first conductive polyurethane nanofiber membrane, a conductive polyvinyl alcohol nanofiber membrane, and a second conductive polyurethane nanofiber membrane, arranged from top to bottom. The first and second conductive polyurethane nanofiber membranes are both made of polyethylene glycol-polyurethane, polytrimethylene ether glycol-polyurethane, N,N-dimethylformamide, and ZnCl2 ionic liquid composites, and serve as the upper and lower electrodes of the sensor, respectively. The conductive polyvinyl alcohol nanofiber membrane is made of polyvinyl alcohol and hydroxylated multi-walled carbon nanotubes, and is sandwiched between the first and second conductive polyurethane nanofiber membranes. Two copper foils are attached to one end of the upper surface of the upper electrode and one end of the lower surface of the lower electrode, respectively, with one end of each copper foil extending outwards and connected to a wire.

2. The acoustic signature sensor based on a fiber aerogel structure according to claim 1, characterized in that, The nanofiber aerogel sensing layer is prepared by sequential electrospinning combined with freeze-drying to form a nanofiber aerogel with a three-dimensional porous network structure. The conductivity of the three-dimensional porous network structure is jointly regulated by the proportion of hydroxylated multi-walled carbon nanotubes added to the conductive polyvinyl alcohol nanofiber membrane, and the sandwich structure composed of the first conductive polyurethane nanofiber membrane, the conductive polyvinyl alcohol nanofiber membrane, and the second conductive polyurethane nanofiber membrane.

3. A method for fabricating an acoustic signature sensor based on a fiber aerogel structure as described in any one of claims 1-2, characterized in that, The process includes the following steps: (1) Preparing a sandwich-structured nanofiber aerogel sensing layer: a) Weigh polyethylene glycol-polyurethane and polytrimethylene ether glycol-polyurethane, dissolve them in N,N-dimethylformamide solution, and add ZnCl2 ionic liquid to prepare a conductive polyurethane spinning solution; b) Weigh polyvinyl alcohol, dissolve it in water, and add hydroxylated multi-walled carbon nanotubes to prepare a conductive polyvinyl alcohol spinning solution; c) Electrospin the conductive polyurethane spinning solution to obtain a second conductive polyurethane nanofiber membrane; d) Electrospin the conductive polyvinyl alcohol spinning solution on the upper surface of the second conductive polyurethane nanofiber membrane to obtain... e) Continue electrospinning the conductive polyurethane spinning solution on the upper surface of the conductive polyurethane nanofiber membrane to obtain the first conductive polyurethane nanofiber membrane and form a three-layer composite membrane; f) Perform freeze-drying treatment on the three-layer composite membrane to obtain a sandwich-structured nanofiber aerogel sensing layer; (2) Packaging of the sensor: The first conductive polyurethane nanofiber membrane is used as the upper electrode and the second conductive polyurethane nanofiber membrane is used as the lower electrode; Copper foil is attached to one end of the upper surface of the upper electrode and the lower surface of the lower electrode, and one end of the copper foil extends outward and is connected to the wire to complete the packaging.

4. The method for fabricating an acoustic signature sensor based on a fiber aerogel structure according to claim 3, characterized in that, In step a), the mass ratio of polyethylene glycol-polyurethane and polytrimethylene ether glycol-polyurethane is 1:(1-5), and the mass concentration of ZnCl2 ionic liquid is 5%-15%.

5. The method for fabricating an acoustic signature sensor based on a fiber aerogel structure according to claim 3, characterized in that, In step b), the mass concentration of hydroxylated multi-walled carbon nanotubes in the conductive polyvinyl alcohol spinning solution is 0.1%-5%.

6. The method for fabricating an acoustic signature sensor based on a fiber aerogel structure according to claim 3, characterized in that, In steps c), d), and e), the electrospinning time is 5-10 hours, respectively.

7. The method for fabricating an acoustic signature sensor based on a fiber aerogel structure according to claim 3, characterized in that, In step f), the freeze-drying temperature is -70℃ and the time is 10-15h.

8. An acoustic fingerprint sensor based on a fiber aerogel structure, prepared by the method described in any one of claims 1-2 or any one of claims 3-7, is used in flexible wearable devices, health monitoring devices, or high-precision acoustic fingerprint recognition devices.

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