A fiber-optic acoustic sensor based on biomimetic flexible cilia and a preparation method thereof

Abstract

The application belongs to the field of optical fiber sensing and micro-nano manufacturing technology, and particularly relates to a kind of optical fiber acoustic sensor based on bionic flexible cilium and its preparation method, including flexible sensing substrate: material is elastic polymer, array type optical fiber bragg grating is encapsulated in its inside, the FBG array contains at least two grating sensing units distributed along the optical fiber axial direction;Bionic cilium array: polymer microcolumn structure is arranged on the surface of the flexible sensing substrate;The bionic cilium array is formed by in-situ solidification on the surface of the flexible sensing substrate coated with photosensitive material using two-photon polymerization technology;The bionic cilium array contains at least two groups of different height cilium groups, and different height cilium groups correspond to different grating sensing units in the flexible sensing substrate in position respectively.The application can solve the problem of low sensitivity and lack of frequency selectivity of the existing flexible optical fiber acoustic sensor.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing and micro / nano manufacturing technology, specifically relating to a fiber optic acoustic sensor based on biomimetic flexible cilia and its fabrication method. Background Technology

[0002] With the rapid development of soft robots, wearable medical monitoring devices, and underwater biomimetic sensing technologies, endowing intelligent systems with biological skin-like sensing capabilities has become a current research hotspot. Among numerous sensing modalities, acoustic and vibration sensing are crucial for voice interaction, cardiopulmonary sound monitoring, and fluid environment analysis. Traditional acoustic sensors mainly rely on capacitive, piezoelectric, or resistive principles. Although the technology is relatively mature, it faces many challenges in practical applications. First, these electronic sensors are usually made of rigid metals or semiconductor materials, lacking flexibility and making it difficult to fit tightly against human skin or complex robotic surfaces, resulting in low acoustic coupling efficiency and poor wearing comfort. Second, electronic sensors are highly susceptible to electromagnetic interference, unable to operate normally in strong electromagnetic environments such as nuclear magnetic resonance chambers and high-voltage substations, and are prone to short circuits or performance degradation in humid or corrosive environments.

[0003] Fiber optic sensors, with their inherent safety, resistance to electromagnetic interference, corrosion resistance, small size, and ease of constructing distributed sensor networks, have become an ideal alternative to traditional electronic sensors. Fiber Bragg grating (FBG) sensors, in particular, are highly favored due to their wavelength-encoded characteristics. However, standard communication single-mode optical fibers are made of silicon dioxide, which has a high Young's modulus. When directly encapsulated in flexible materials for detecting airborne sound waves or weak vibrations, the sound waves cannot directly drive the fiber to produce sufficient axial deformation, resulting in low sensor sensitivity and difficulty in capturing low-decibel sound signals. To address this issue, researchers, inspired by the lateral lines of fish or the auditory hairs of insects, have proposed constructing micro / nano-fiber arrays on the surface of optical fibers. Utilizing the fibers as mechanical levers to capture weak fluid flows or sound pressure and amplify and transmit them to the fiber root can significantly improve detection sensitivity.

[0004] Despite the immense potential of biomimetic cilia structures, existing fiber optic cilia sensors still face significant limitations in structural design and manufacturing processes. In terms of structural function, most current biomimetic sensors employ arrays of cilia with uniform height and thickness. According to mechanical vibration theory, microstructures of a single size often possess only a single inherent resonant frequency. This means that the sensor can only exhibit high sensitivity to sound within a specific frequency band, lacking a frequency division mechanism similar to the human cochlea. In other words, it cannot directly distinguish sound signals of different frequencies at the physical level, often requiring complex circuit filtering or algorithmic demodulation. Regarding manufacturing processes, existing micro-nano fabrication technologies such as traditional photolithography and electron beam lithography, while highly precise, are primarily suitable for rigid planar substrates such as silicon wafers. They are illegible for constructing high aspect ratio three-dimensional microstructures on flexible curved substrates such as polydimethylsiloxane (PDMS). While mold replication can fabricate flexible cilia, the demolding process easily leads to breakage or collapse of high aspect ratio structures, and it is difficult to achieve precise customized layouts of cilia of different heights.

[0005] Therefore, overcoming the limitations of existing micro / nano manufacturing processes on flexible substrates to construct a fiber optic acoustic sensor that possesses both high sensitivity and frequency selectivity similar to that of the biological cochlea, and can be perfectly integrated with flexible skin, is a pressing technical challenge. Two-photon polymerization technology, as a true three-dimensional direct-writing technology, boasts nanometer-level processing precision and resolution exceeding the diffraction limit, enabling the direct printing of arbitrarily complex three-dimensional microstructures on various substrate surfaces. This provides a novel technical approach to solving the aforementioned problems. Summary of the Invention

[0006] The purpose of this invention is to provide a fiber optic acoustic sensor based on biomimetic flexible cilia and its fabrication method, thereby solving the problems of low sensitivity and lack of frequency selectivity in existing flexible fiber optic acoustic sensors.

[0007] The specific technical solution adopted by this invention is as follows: A fiber optic acoustic sensor based on biomimetic flexible cilia and its fabrication method, comprising: Flexible sensing substrate: The material is an elastic polymer, and an array of fiber Bragg gratings is encapsulated inside it. The FBG array includes at least two grating sensing units distributed along the fiber axis. Bionic cilia array: a polymer micropillar structure disposed on the surface of the flexible sensing substrate; the bionic cilia array is formed by in-situ curing on the surface of the flexible sensing substrate coated with photosensitive material using two-photon polymerization technology; the bionic cilia array includes at least two groups of cilia of different heights, and the cilia of different heights correspond to different grating sensing units inside the flexible sensing substrate.

[0008] Preferably, the flexible sensing substrate is made of polydimethylsiloxane, and a photosensitive interface coupling layer formed by curing photosensitive resin is provided between the PDMS surface and the biomimetic cilia array.

[0009] Preferably, the height distribution of the biomimetic cilia array exhibits gradient or partitioned step changes. The grating sensing unit corresponding to the longer cilia is used to detect low-frequency sound waves, while the grating sensing unit corresponding to the shorter cilia is used to detect high-frequency sound waves. The passive selection of sound wave frequency is achieved by utilizing the mechanical resonance characteristics of the cilia.

[0010] A method for fabricating a fiber optic acoustic sensor based on biomimetic flexible cilia includes the following steps: Step 1: Encapsulate the array-type FBG in a liquid flexible polymer precursor and solidify it to form a flexible sensing substrate; Step 2: Spin-coat liquid photosensitive material onto the surface of the flexible sensing substrate; Step 3: Using two-photon polymerization laser direct writing technology, a focused laser beam passes through the photosensitive material layer, and latent image structures with different height parameters are exposed and printed above the areas corresponding to different FBG sensing units. Step 4: Develop the exposed sample to remove the unpolymerized photosensitive material and obtain a flexible sensor with an array of cilia of varying lengths.

[0011] The technical effects achieved by this invention are as follows: This invention utilizes the inherent frequency differences caused by the varying lengths of cilia; long cilia resonate with low-frequency sound waves, while short cilia resonate with high-frequency sound waves. Combined with the spatial distribution of the FBG array, the frequency components of sound can be directly distinguished by the drift of grating signals of different wavelengths, thus simulating the function of the human cochlea.

[0012] This invention employs two-photon polymerization technology, which breaks through the limitations of traditional photolithography on flexible substrates, and can manufacture fine fibrous structures with micron-sized diameters and high aspect ratios, greatly improving the ability to capture weak airflow and sound pressure.

[0013] In this invention, the cilia act as a lever structure, converting weak acoustic vibrations into torque at the root, which significantly amplifies the local deformation acting on the flexible PDMS substrate, thereby greatly improving the strain sensitivity of the embedded FBG.

[0014] The sensor in this invention has good overall flexibility and can be attached to complex curved surfaces. Through surface modification and photosensitive interface layer design, the problem of poor adhesion and easy detachment of hard photosensitive resin fibers on soft PDMS is solved. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of the fiber optic acoustic sensor based on biomimetic flexible cilia of the present invention. Figure 2 This is a schematic diagram illustrating an embodiment of the present invention. Detailed Implementation

[0016] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0017] like Figures 1-2 As shown, a fiber optic acoustic sensor based on biomimetic flexible cilia and its fabrication method include: Flexible sensing substrate: The material is an elastic polymer, which encapsulates an array of fiber Bragg gratings inside. The FBG array contains at least two grating sensing units distributed along the fiber axis. Bionic cilia array: a polymer micropillar structure disposed on the surface of a flexible sensing substrate; the bionic cilia array is formed by in-situ curing on the surface of a flexible sensing substrate coated with photosensitive material using two-photon polymerization technology; the bionic cilia array contains at least two groups of cilia of different heights, and the cilia of different heights correspond to different grating sensing units inside the flexible sensing substrate.

[0018] Preferably, the flexible sensing substrate is made of polydimethylsiloxane, and a photosensitive interface coupling layer formed by curing photosensitive resin is provided between the PDMS surface and the biomimetic cilia array.

[0019] Preferably, the height distribution of the biomimetic cilia array exhibits a gradient change or a step change in partitions. The grating sensing unit corresponding to the longer cilia is used to detect low-frequency sound waves, while the grating sensing unit corresponding to the shorter cilia is used to detect high-frequency sound waves. The passive selection of sound wave frequency is achieved by utilizing the mechanical resonance characteristics of the cilia.

[0020] like Figures 1-2 As shown, a method for fabricating a fiber optic acoustic sensor based on biomimetic flexible cilia includes the following steps: Step 1: Encapsulate the array-type FBG in a liquid flexible polymer precursor and solidify it to form a flexible sensing substrate; Step 2: Spin-coat liquid photosensitive material onto the surface of the flexible sensing substrate; Step 3: Using two-photon polymerization laser direct writing technology, a focused laser beam passes through the photosensitive material layer, and latent image structures with different height parameters are exposed and printed above the areas corresponding to different FBG sensing units. Step 4: Develop the exposed sample to remove the unpolymerized photosensitive material and obtain a flexible sensor with an array of cilia of varying lengths.

[0021] like Figures 1-2As shown, in an actual implementation example of the present invention, for instance: a method for fabricating a fiber optic acoustic sensor based on biomimetic flexible cilia includes the following steps: First: Select an optical fiber with two FBG measurement points (center wavelengths of 1550nm and 1555nm, with a spacing of 5mm) inscribed on it. Straighten and fix it in the center of the mold, pour in PDMS (Sylgard 184) with a ratio of 10:1, heat at 80℃ for 2 hours to cure, and after demolding, cut it into flexible base strips with dimensions of 20mm×5mm×1mm.

[0022] Then: the surface of the PDMS substrate was treated with oxygen plasma (30W power, 30s). Subsequently, IP-L780 photosensitive resin was spin-coated onto its surface at a speed of 2000rpm for 30s, and then baked on a hot plate at 100℃ for 5 minutes.

[0023] Next: Place the sample into the two-photon laser direct writing system. Design and print a cilia array with a height of 300 μm and a diameter of 10 μm in the region directly above FBG1. Design and print a cilia array with a height of 100 μm and a diameter of 10 μm in the region directly above FBG2 (1555 nm).

[0024] Finally: Immerse the sample in PGMEA developer for 20 minutes to wash away the unexposed resin, then clean with isopropanol and dry with nitrogen.

[0025] This invention utilizes the inherent frequency differences caused by the varying lengths of cilia; long cilia resonate with low-frequency sound waves, while short cilia resonate with high-frequency sound waves. Combined with the spatial distribution of the FBG array, the frequency components of sound can be directly distinguished by the drift of grating signals of different wavelengths, thus simulating the function of the human cochlea.

[0026] This invention employs two-photon polymerization technology, which breaks through the limitations of traditional photolithography on flexible substrates, and can manufacture fine fibrous structures with micron-sized diameters and high aspect ratios, greatly improving the ability to capture weak airflow and sound pressure.

[0027] In this invention, the cilia act as a lever structure, converting weak acoustic vibrations into torque at the root, which significantly amplifies the local deformation acting on the flexible PDMS substrate, thereby greatly improving the strain sensitivity of the embedded FBG.

[0028] The sensor in this invention has good overall flexibility and can be attached to complex curved surfaces. Through surface modification and photosensitive interface layer design, the problem of poor adhesion and easy detachment of hard photosensitive resin fibers on soft PDMS is solved.

[0029] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A fiber optic acoustic sensor based on biomimetic flexible cilia, characterized in that: include: Flexible sensing substrate: The material is an elastic polymer, and an array of fiber Bragg gratings is encapsulated inside it. The FBG array includes at least two grating sensing units distributed along the fiber axis. Bionic cilia array: a polymer micropillar structure disposed on the surface of the flexible sensing substrate; the bionic cilia array is formed by in-situ curing on the surface of the flexible sensing substrate coated with photosensitive material using two-photon polymerization technology; the bionic cilia array includes at least two groups of cilia of different heights, and the cilia of different heights correspond to different grating sensing units inside the flexible sensing substrate.

2. The fiber optic acoustic sensor based on biomimetic flexible cilia according to claim 1, characterized in that: The flexible sensing substrate is made of polydimethylsiloxane, and a photosensitive interface coupling layer formed by photosensitive resin curing is provided between the PDMS surface and the biomimetic cilia array.

3. The fiber optic acoustic sensor based on biomimetic flexible cilia according to claim 2, characterized in that: The height distribution of the biomimetic cilia array exhibits gradient or partitioned step changes. The grating sensing unit corresponding to the longer cilia is used to detect low-frequency sound waves, while the grating sensing unit corresponding to the shorter cilia is used to detect high-frequency sound waves. The passive selection of sound wave frequency is achieved by utilizing the mechanical resonance characteristics of the cilia.

4. A method for fabricating a fiber optic acoustic sensor based on biomimetic flexible cilia, used to fabricate the fiber optic acoustic sensor according to any one of claims 1-3, characterized in that: Includes the following steps: Step 1: Encapsulate the array-type FBG in a liquid flexible polymer precursor and solidify it to form a flexible sensing substrate; Step 2: Spin-coat liquid photosensitive material onto the surface of the flexible sensing substrate; Step 3: Using two-photon polymerization laser direct writing technology, a focused laser beam passes through the photosensitive material layer, and latent image structures with different height parameters are exposed and printed above the areas corresponding to different FBG sensing units. Step 4: Develop the exposed sample to remove the unpolymerized photosensitive material and obtain a flexible sensor with an array of cilia of varying lengths.

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