Tunable ultrasound sensor based on polymer bubbles and method of making and use thereof

Abstract

The application belongs to the technical field of controllable ultrasonic sensors, and particularly relates to a controllable ultrasonic sensor based on polymer bubbles, a preparation method and application thereof. The application provides a controllable ultrasonic sensor based on polymer bubbles. Compared with a traditional quartz optical fiber ultrasonic sensor, the controllable ultrasonic sensor can realize ultrahigh-sensitivity ultrasonic detection, and the controllable characteristics of the bubble size and morphology make the controllable ultrasonic sensor more practical and capable of being applied to more ultrasonic fields, and the controllable ultrasonic sensor can realize detection of ultrahigh-sensitivity ultrasonic waves with tunable resonant wavelengths.

Description

Technical Field

[0001] This invention belongs to the field of adjustable ultrasonic sensor technology, specifically relating to an adjustable ultrasonic sensor based on polymer bubbles, its preparation method, and its application. Background Technology

[0002] Ultrasound refers to sound waves with frequencies above 20kHz, exceeding the upper limit of human hearing. The advantages of ultrasound lie in its strong directivity, easy energy concentration, and ability to transmit over long distances in various media (such as gases, liquids, solids, and solid solutions). Ultrasound is essentially a mechanical vibration that can detect relevant physical information of a carrier. Furthermore, the high energy transmitted by ultrasound can alter or affect the properties of the carrier. Therefore, ultrasound is widely used in practical life and work, mainly including: ultrasonic detection (such as thickness measurement, flaw detection, and imaging), ultrasonic processing (such as dust removal, cleaning, welding, drilling, and solid pulverization), humidification, and pharmaceutical manufacturing.

[0003] Traditional ultrasonic electronic sensors convert sensed ultrasonic signals into electrical signals. Currently, piezoelectric ultrasonic sensors are mainly used in ultrasonic applications. Piezoelectric ultrasonic sensors detect ultrasonic signals based on the piezoelectric properties of materials. Traditional electronic ultrasonic sensors use electrical signals as the transmission and conversion medium, making them susceptible to extreme environments such as high humidity, high temperature, flammable and explosive factors, and electromagnetic interference. In contrast, fiber optic ultrasonic sensors use light waves as the carrier and optical fibers as the medium to achieve the sensing and transmission of ultrasound. Due to their significant advantages such as small size, light weight, resistance to electromagnetic interference, corrosion resistance, and high sensitivity, fiber optic ultrasonic sensors can perform tasks that are difficult or even impossible for traditional electronic sensors in many extreme situations, thus gaining widespread attention.

[0004] In the prior art, Gang et al. (Sensors 2018, 10.3390 / s18072315) proposed a sensitivity-enhanced air microbubble-type FPI fiber ultrasonic sensor, which is fabricated by fusion splicing single-mode fiber (SMF) and hollow-core fiber (HCF) and continuously discharging at the hydrogen-loaded (HCF) pre-treated area. During the discharge process, the hydrogen in the air microbubble is continuously heated, which not only increases the diameter of the air microbubble but also smooths its surface.

[0005] Yin et al. (IEEE Sensors Journal 2019, 10.1109 / JSEN.2019.2924646) proposed an open-cavity FPI bubble displacement sensor. Using focused femtosecond laser technology, a portion of the wall of an HCF (hydrocarbon fluoride) bubble is removed to form an open cavity. The remaining bubble wall portion acts as a support beam, easily deformable under external pressure. When the bubble is subjected to external displacement or pressure, highly sensitive displacement measurement is achieved through changes in the optical signal.

[0006] Yin et al. (Journal of Lightwave Technology 2022, 10.1109 / JLT.2022.3169919) proposed an FPI ultrasonic sensor based on fiber optic bubble. The FPI sensor is formed by constructing a bubble at the end face of the fiber optic cable through multiple discharges of HCF and then inserting SMF into the bubble.

[0007] While the bubble-type FPI ultrasonic sensor mentioned above improves its sensitivity through techniques such as gas pressure-assisted arc discharge, the material constituting the bubble is silica fiber itself. Since silica fiber has a large Young's modulus (approximately 70 GPa), further improvements in the sensitivity of the bubble-type FPI sensor are hindered. Furthermore, the thickness of the fabricated bubble and the length of the FPI cavity are not adjustable, requiring the mass production of multiple sensors with different sensitivities and resonant frequency characteristics to adapt to complex measurement environments. This necessitates high repeatability in sensor fabrication, and its signal demodulation relies on a high-end, wide-wavelength tuned laser. Therefore, a tunable ultrasonic sensor is needed to overcome these technical shortcomings. Summary of the Invention

[0008] To address the shortcomings of the existing technologies, the present invention aims to provide a tunable ultrasonic sensor based on polymer bubbles, its preparation method, and its application. Addressing the technical deficiencies of insufficient sensitivity and tunability in existing fiber optic ultrasonic sensors, this invention proposes a tunable ultrasonic sensor based on polymer bubbles. Compared to traditional quartz fiber optic ultrasonic sensors, it can achieve ultra-high sensitivity ultrasonic detection. Furthermore, its tunable bubble size and morphology make it more practical and applicable to a wider range of ultrasonic fields, enabling the detection of ultra-high sensitivity ultrasonic waves with tunable resonant wavelengths.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] The tunable ultrasonic sensor based on polymer bubbles consists of a single-mode optical fiber, a dual-hole optical fiber, and a photothermal organic polymer bubble, wherein the photothermal organic polymer bubble is composed of a polymer colloid and a photothermal material.

[0011] The single-mode optical fiber is fused to the dual-hole optical fiber, and the photothermal organic polymer bubble is bonded to the dual-hole optical fiber.

[0012] Preferably, the polymer colloid includes a transparent photocurable adhesive and a transparent thermocurable adhesive, and the photothermal material includes metal nanoparticles and colored dyes. The mass ratio of the polymer colloid to the photothermal material is 10-70:1, and both the polymer colloid and the photothermal material have waterproof properties.

[0013] Preferably, the transparent photocurable adhesive is selected from photosensitive polymers, the transparent thermocurable adhesive is selected from epoxy resins, siloxane polyurethanes, and acrylates, and the photothermal material is selected from metal nanoparticles, organic dyes, carbon-based materials, and transition metal oxides.

[0014] Preferably, the photosensitive polymer is selected from methyl methacrylate and methyl acrylate.

[0015] Preferably, the photothermal organic polymer bubble is capable of deformation under irradiation with visible light of a specific wavelength at different power levels;

[0016] The wavelength range of the specific wavelength visible light is 400-760nm, and the power is 10-100mW.

[0017] Preferably, the cavity length between the free end face of the dual-hole optical fiber and the expansion apex of the photothermal organic polymer bubble, as well as the thickness of the photothermal organic polymer bubble, can change after being irradiated with visible light of a specific wavelength.

[0018] The wavelength of the visible light at the specific wavelength is 400-760nm.

[0019] This invention also protects a method for fabricating a tunable ultrasonic sensor based on polymer bubbles, comprising the following steps:

[0020] S1. Attach one end of the dual-hole optical fiber to the syringe outlet with adhesive, and then cut the free end face of the dual-hole optical fiber flat.

[0021] S2. Mix the polymer colloid and the photothermal material to obtain a photothermal organic polymer hybrid material;

[0022] S3. After applying the photothermal organic polymer mixture from step S2 to the flattened end face of the dual-hole optical fiber in step S1, push the syringe piston and pressurize the dual-hole optical fiber, then blow out the photothermal organic polymer bubbles, and maintain the syringe pressure until the photothermal organic polymer bubbles solidify.

[0023] S4. Separate the dual-hole fiber from the syringe, and then fuse the single-mode fiber with the dual-hole fiber to obtain a tunable ultrasonic sensor based on polymer bubbles.

[0024] This invention also protects the application of a polymer bubble-based tunable ultrasonic sensor in the fabrication of a fiber optic ultrasonic sensor, characterized in that the application is based on a test sensing system, the test sensing system comprising:

[0025] An ultrasonic generator is used to drive a piezoelectric ultrasonic transducer and generate ultrasonic waves.

[0026] A tunable ultrasonic sensor based on polymer bubbles is used to detect ultrasonic waves. The ultrasonic waves act on the photothermal organic polymer bubbles, causing the reflected light to drift. The modulated reflected light is then demodulated to extract the ultrasonic wave information.

[0027] A fixed-wavelength laser I is used as a sensing laser source to generate a sensing laser. The sensing laser acts on a photothermal organic polymer bubble and is reflected to obtain the reflected sensing laser.

[0028] Fixed wavelength laser II, which serves as a heating laser source to generate heating laser, is absorbed by photothermal organic polymer bubbles, and the heating laser is used to tune the organic polymer bubbles to cause deformation;

[0029] The spectrometer is used to detect the spectral information of the tunable ultrasonic sensor based on polymer bubbles. The spectrometer can acquire the spectral information of the photothermal organic polymer bubble after deformation in real time, and by controlling the deformation of the photothermal organic polymer bubble, the sensing laser output wavelength of the fixed wavelength laser I is located at the maximum slope of the reflection spectrum of the tunable ultrasonic sensor based on polymer bubbles.

[0030] A wavelength division multiplexer is used to combine sensing laser and heating laser into a single beam for transmission, as well as to transmit modulated reflected light.

[0031] Fiber optic circulators are used to transmit sensing laser light and modulated reflected light.

[0032] A photodetector is used to convert modulated reflected light signals into electrical signals. The modulated reflected light is sequentially guided into the photodetector through a two-hole fiber, a single-mode fiber, a wavelength division multiplexer, and a fiber optic circulator, and then converted into electrical information.

[0033] An oscilloscope is used to acquire electrical signals from a photodetector and display the ultrasonic signal response.

[0034] Preferably, the application method is as follows:

[0035] A fixed-wavelength laser I generates a sensing laser, which is then guided into a single-mode fiber via a fiber circulator and a wavelength division multiplexer. The laser is then transmitted through the single-mode fiber to a dual-hole fiber, where it is reflected back and forth into an air cavity formed by the end face of the dual-hole fiber and a photothermal organic polymer bubble.

[0036] A fixed-wavelength laser II generates a heating laser, which is then guided into a single-mode fiber along with a sensing laser through a wavelength division multiplexer. The heating laser is then transmitted through the single-mode fiber to a dual-hole fiber, and then enters an air cavity formed by the end face of the dual-hole fiber and a photothermal organic polymer bubble.

[0037] In this process, heating lasers of different powers are used to irradiate the photothermal organic polymer bubble, causing the photothermal organic polymer bubble to undergo thermal expansion deformation to different degrees. The sensing laser acts on the photothermal organic polymer bubble and is reflected, and the reflected sensing laser is obtained. A spectrometer is used to detect the spectral information of the adjustable ultrasonic sensor based on the polymer bubble. The spectrometer can acquire the spectral information of the photothermal organic polymer bubble after deformation in real time. By tuning the reflected spectrum with the heating laser, the sensing laser output wavelength of the fixed wavelength laser I is located at the maximum slope of the reflected spectrum of the adjustable ultrasonic sensor based on the polymer bubble, so as to obtain the optimal ultrasonic response effect, that is, to obtain the photothermal organic polymer bubble under the optimal ultrasonic response condition.

[0038] An ultrasonic generator drives a piezoelectric ultrasonic transducer to generate ultrasonic waves. The ultrasonic waves act on a photothermal organic polymer bubble via the piezoelectric ultrasonic transducer, modulating the reflected light to obtain modulated reflected light. The modulated reflected light inside the photothermal organic polymer bubble is sequentially guided to a photodetector through a dual-hole optical fiber, a single-mode optical fiber, a wavelength division multiplexer, and an optical fiber circulator. The photodetector converts the modulated reflected light optical signal into an electrical signal. Finally, an oscilloscope is used to acquire the electrical signal of the photodetector and obtain the ultrasonic signal response. For detecting different ultrasonic signal responses, the laser power of a fixed-wavelength laser II can be adjusted to achieve real-time adjustable detection.

[0039] Preferably, a fixed-wavelength laser I, a photodetector, and a wavelength division multiplexer are connected to the fiber optic circulator via optical fibers. An oscilloscope is electrically connected to the photodetector via wires. The fixed-wavelength laser II is connected to the wavelength division multiplexer via optical fibers, and the wavelength division multiplexer is connected to a polymer bubble-based tunable ultrasonic sensor via optical fibers. An ultrasonic generator is electrically connected to a piezoelectric transducer via wires, and the piezoelectric transducer emits ultrasonic waves that affect the polymer bubble-based tunable ultrasonic sensor. The polymer bubble-based tunable ultrasonic sensor is detachably connected to a spectrometer via a single-mode optical fiber.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] 1. The sensing material of this invention is a polymer colloid with low Young's modulus, which has a significantly better response to ultrasonic strain than traditional quartz optical fiber, and therefore has higher detection sensitivity.

[0042] 2. The sensing technology of this invention can adjust the size and morphology of photothermal organic polymer bubbles by using the photothermal effect provided by the heating laser, thereby achieving real-time control of the sensor's resonant wavelength, sensitivity, and frequency response, and further improving its adaptability.

[0043] 3. The purpose of this invention is to provide an adjustable ultrasonic sensor based on polymer bubbles, which has the advantages of high sensitivity, wide bandwidth, high resolution, compact structure and flexible adjustable features, and can be applied to a variety of practical measurement scenarios, thus improving the shortcomings of traditional fiber optic ultrasonic sensors. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of the adjustable ultrasonic sensor based on polymer bubbles according to the present invention;

[0045] Figure 2 This is a schematic diagram of the structure of the test sensing system of the present invention;

[0046] Figure 3 This is a schematic diagram of the spectrum of the adjustable ultrasonic sensor based on polymer bubbles according to the present invention;

[0047] Figure 4 The sinusoidal and pulsed ultrasonic signal responses of the adjustable ultrasonic sensor based on polymer bubbles of the present invention are shown in (a) and (b) respectively.

[0048] Figure 5 This is a diagram showing the trajectory of the sensor laser and the reflected sensor laser during the tuning of the spectrometer of this invention.

[0049] Figure 6 This is a diagram showing the trajectory of the modulated reflected light during ultrasonic detection according to the present invention.

[0050] Explanation of reference numerals in the attached figures:

[0051] 1. Single-mode optical fiber; 2. Dual-hole optical fiber; 3. Photothermal organic polymer bubbles. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Parameters not specifically specified can be performed using conventional techniques. These all fall within the scope of protection of this invention, but are not limited to it.

[0053] Example 1

[0054] The method for fabricating a tunable ultrasonic sensor based on polymer bubbles includes the following steps:

[0055] S1. First, attach one end of the dual-hole optical fiber to the outlet of a 60mL syringe with strong adhesive, and use an optical fiber cutter to cut the end face of the dual-hole optical fiber flat.

[0056] S2. Place the beaker on a precision electronic weighing instrument, pour 1g of polymer colloidal polydimethylsiloxane into the beaker and weigh it, and add photothermal organic material metal cesium propylene dye into the beaker at a mass ratio of 60:1, stir evenly, and mix into a photothermal organic polymer material that can absorb 650nm laser.

[0057] S3. Fix the flattened end of the double-hole fiber onto the optical microscopy platform, apply photothermal organic polymer material to the end face, push the syringe to pressurize the double-hole fiber and blow out a polymer bubble with a diameter of 300μm, and maintain the syringe pressure until the bubble solidifies.

[0058] S4. Remove the syringe and fusion splice the single-mode fiber with the dual-hole fiber. Introduce a heating laser with an incident wavelength of 650nm and an incident power of 30mW into the dual-hole fiber and irradiate the bubble. Due to the photothermal material doped in the bubble, the photothermal effect causes the bubble to expand under heat, and the length and shape of the bubble cavity can be controlled in real time.

[0059] Example 2

[0060] The method for fabricating a tunable ultrasonic sensor based on polymer bubbles includes the following steps:

[0061] S1. First, attach one end of the dual-hole optical fiber to the outlet of a 60mL syringe with strong adhesive, and use an optical fiber cutter to cut the end face of the dual-hole optical fiber flat.

[0062] S2. Place the beaker on a precision electronic weighing instrument, pour 1g of polymer colloidal thermoplastic polyurethane rubber into the beaker and weigh it, and add photothermal organic material gold nanoparticles into the beaker at a mass ratio of 50:1, stir evenly, and mix into a photothermal organic polymer material that can absorb 532nm laser.

[0063] S3. Fix the flat-cut end of the double-hole fiber onto the optical microscopy platform, apply photothermal organic polymer material to the end face, push the syringe to pressurize the double-hole fiber and blow out a polymer bubble with a diameter of 260μm, and maintain the syringe pressure until the bubble solidifies.

[0064] S4. Remove the syringe and fusion splice the single-mode fiber with the dual-hole fiber. Introduce a heating laser with an incident wavelength of 532nm and an incident power of 10mW into the dual-hole fiber and irradiate the bubble. Due to the photothermal material doped in the bubble, the photothermal effect causes the bubble to expand under heat, and the length and shape of the bubble cavity can be controlled in real time.

[0065] Example 3

[0066] The method for fabricating a tunable ultrasonic sensor based on polymer bubbles includes the following steps:

[0067] S1. First, attach one end of the dual-hole optical fiber to the outlet of a 60mL syringe with strong adhesive, and use an optical fiber cutter to cut the end face of the dual-hole optical fiber flat.

[0068] S2. Place the beaker on a precision electronic weighing instrument, pour 1g of polymer colloidal polyurethane acrylate UV glue into the beaker and weigh it, and add carbon fiber powder, a photothermal organic material, into the beaker at a mass ratio of 70:1. Stir evenly to form a photothermal organic polymer material that can absorb 760nm laser.

[0069] S3. Fix the flat-cut end of the double-hole fiber onto the optical microscopy platform, apply an appropriate amount of photothermal organic polymer material to the end face, push the syringe to pressurize the double-hole fiber and blow out a polymer bubble with a diameter of 350μm, and maintain the syringe pressure until the bubble solidifies.

[0070] S4. Remove the syringe and fusion splice the single-mode fiber with the dual-hole fiber. Introduce a laser with an incident wavelength of 760nm and an incident power of 50mW into the dual-hole fiber and irradiate the bubble. Due to the photothermal material doped in the bubble, the photothermal effect causes the bubble to expand due to heat. The length and shape of the bubble cavity can be controlled in real time.

[0071] Example 4

[0072] The method for fabricating a tunable ultrasonic sensor based on polymer bubbles includes the following steps:

[0073] S1. First, attach one end of the dual-hole optical fiber to the outlet of a 60mL syringe with strong adhesive, and use an optical fiber cutter to cut the end face of the dual-hole optical fiber flat.

[0074] S2. Place the beaker on a precision electronic weighing instrument, pour 1g of polymer colloidal epoxy resin UV glue into the beaker and weigh it, and add photothermal organic material TiO2 into the beaker at a mass ratio of 10:1, stir evenly, and mix into a photothermal organic polymer material that can absorb 400nm laser.

[0075] S3. Fix the flat-cut end of the double-hole fiber onto the optical microscopy platform, apply an appropriate amount of photothermal organic polymer material to the end face, push the syringe to pressurize the double-hole fiber and blow out a polymer bubble with a diameter of 350μm, and maintain the syringe pressure until the bubble solidifies.

[0076] S4. Remove the syringe and fusion splice the single-mode fiber with the dual-hole fiber. Introduce a laser with an incident wavelength of 400nm and an incident power of 70mW into the dual-hole fiber and irradiate the bubble. Due to the photothermal material doped in the bubble, the photothermal effect causes the bubble to expand due to heat. The length and shape of the bubble cavity can be controlled in real time.

[0077] The structure of a tunable ultrasonic sensor based on polymer bubbles is as follows: Figure 1 As shown, to verify the beneficial effects of the present invention, the tunable ultrasonic sensor based on polymer bubbles prepared in Example 1 of the present invention was used for experimental testing:

[0078] The principle of ultrasonic bubble detection is as follows: A sensing laser beam emitted by a fixed-wavelength laser I enters a double-hole fiber 2 through a single-mode fiber 1. After being transmitted through the double-hole fiber 2, the sensing laser beam is reflected back and forth in the air cavity formed by the end face of the double-hole fiber 2 and the photothermal organic polymer bubble 3, forming a Fabry-Perot interferometer. Ultrasonic waves act on the photothermal organic polymer bubble 3, causing the bubble to undergo periodic axial stretching or compression, resulting in a change in the length of the cavity. The ultrasonic signal can be demodulated by detecting the change in the modulated reflected light.

[0079] The changes in the reflection spectrum are detected using a demodulator, so that the sensing laser output wavelength of the fixed wavelength laser I is located at the maximum slope of the reflection spectrum of the tunable ultrasonic sensor based on polymer bubbles. Under this condition, the ultrasonic wave is detected to obtain the best ultrasonic response effect.

[0080] Simultaneously, a heating laser of another characteristic wavelength is coupled into the dual-hole optical fiber 2. Since the bubble is doped with photothermal material, the characteristic wavelength laser irradiates the photothermal organic polymer bubble 3, causing it to expand due to the photothermal effect. This allows for real-time control of the bubble cavity length and morphology. Therefore, because the bubble sensor of this invention has tunable resonant wavelength, the real-time control of the bubble cavity length and morphology via the heating laser allows for matching the sensing light source with the sensor's operating point. The sensing light source only needs to use a relatively inexpensive fixed-wavelength laser I, eliminating the need for a high-end wide-wavelength tunable laser.

[0081] like Figure 2 As shown, a fixed wavelength laser is used as the sensing laser source I. The sensing laser is introduced into the single-mode fiber 1 through the fiber circulator and wavelength division multiplexer. The sensing laser is transmitted to the photothermal organic polymer bubble 3 through the dual-hole fiber 2 and reflected by the photothermal organic polymer bubble 3. The reflected laser is coupled back to the dual-hole fiber 2 and output through the single-mode fiber 1.

[0082] A fixed-wavelength laser II is used as the heating source to generate heating laser light. This heating laser light, along with the sensing laser light, is guided into a single-mode fiber 1 via a wavelength division multiplexer. After transmission through a dual-hole fiber 2, heating laser light of different powers irradiates the photothermal organic polymer bubble 3, causing the bubble to undergo varying degrees of thermal expansion. A spectrometer is used to detect the changes in the reflection spectrum. The reflection spectrum tuning diagram is shown below. Figure 3 As shown;

[0083] The reflection spectrum is tuned by adjusting the power of the heating laser, so that the sensing laser output wavelength of the fixed wavelength laser I is located at the maximum slope of the sensor's reflection spectrum. Ultrasonic waves act on the photothermal organic polymer bubble 3, and the sensing laser acts on the photothermal organic polymer bubble 3 and is reflected, obtaining the reflected sensing laser. A spectrometer is used to detect the spectral information of the adjustable ultrasonic sensor based on the polymer bubble. The spectrometer can acquire the spectral information of the photothermal organic polymer bubble 3 after deformation in real time. By tuning the reflection spectrum with the heating laser, the output wavelength of the reflected sensing laser is located at the maximum slope of the reflection spectrum of the adjustable ultrasonic sensor based on the polymer bubble, so as to obtain the optimal ultrasonic response.

[0084] An ultrasonic generator drives a piezoelectric ultrasonic transducer to produce ultrasonic waves. These waves cause a shift in the reflection spectrum. The spectral change information modulated by the ultrasonic waves is then fed back into a photodetector via an optical fiber circulator, converting the optical signal into an electrical signal. Finally, an oscilloscope is used to acquire the electrical signal. The experimental results are as follows: Figure 4 As shown.

[0085] like Figure 4 As shown, a tunable ultrasonic sensor based on polymer bubbles detected a 1MHz ultrasonic signal. Figure 4 (a) The sinusoidal signal is neat and without distortion. Figure 4 (b) The pulse signal exhibits a high signal-to-noise ratio and low resonance characteristics. Experimental results show that this invention improves sensor sensitivity through low Young's modulus polymer bubbles and achieves tunable sensing through photothermal materials. Due to its advantages such as high sensitivity, tunability, and compact structure, the tunable ultrasonic sensor based on polymer bubbles has broad application prospects in defect detection, medical imaging technology, marine exploration, and oil exploration.

[0086] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims and their equivalents, this invention also intends to include these modifications and variations. The above-described embodiments are merely preferred embodiments for fully illustrating the invention, and their scope of protection is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on this invention are all within the scope of protection of this invention, which is defined by the claims.

Claims

1. A tunable ultrasonic sensor based on polymer bubbles, characterized in that, It is composed of a single-mode optical fiber (1), a dual-hole optical fiber (2), and a photothermal organic polymer bubble (3), wherein the photothermal organic polymer bubble (3) is composed of a polymer colloid and a photothermal material; The single-mode optical fiber (1) is fused to the dual-hole optical fiber (2), and the photothermal organic polymer bubble (3) is bonded to the dual-hole optical fiber (2); The photothermal organic polymer bubble (3) deforms under different power irradiation with visible light of a specific wavelength; The wavelength range of the specific wavelength visible light is 400~760nm, and the power is 10~100mW; The polymer colloid includes transparent photocurable adhesive and transparent thermocurable adhesive, and the photothermal material includes metal nanoparticles and colored dyes. The mass ratio of the polymer colloid to the photothermal material is 10~70:1, and both the polymer colloid and the photothermal material have waterproof properties. The cavity length between the free end face of the dual-hole optical fiber (2) and the expansion vertex of the photothermal organic polymer bubble (3), as well as the thickness of the photothermal organic polymer bubble (3), change after being irradiated with visible light of a specific wavelength. By real-time control of the cavity length and morphology of the photothermal organic polymer bubble (3), the sensing light source can be matched with the working point of the ultrasonic sensor; the sensing light source uses a fixed wavelength laser. The method for fabricating the polymer bubble-based tunable ultrasonic sensor includes the following steps: S1. Adhere one end of the double-hole fiber (2) to the syringe outlet with adhesive, and then cut the free end face of the double-hole fiber (2) flat. S2. Mix the polymer colloid and the photothermal material to obtain a photothermal organic polymer hybrid material; S3. After applying the photothermal organic polymer mixture from step S2 to the flattened end face of the dual-hole optical fiber (2) in step S1, push the syringe piston and pressurize the dual-hole optical fiber (2), then blow out the photothermal organic polymer bubble (3), and maintain the syringe pressure until the photothermal organic polymer bubble (3) solidifies. S4. Separate the dual-hole fiber (2) from the syringe, and then fuse the single-mode fiber (1) with the dual-hole fiber (2) to obtain a tunable ultrasonic sensor based on polymer bubbles.

2. The adjustable ultrasonic sensor based on polymer bubbles as described in claim 1, characterized in that, The transparent photocurable adhesive is selected from photosensitive polymers, the transparent thermocurable adhesive is selected from epoxy resin, siloxane polyurethane or acrylate, and the photothermal material is selected from metal nanoparticles, organic dyes, carbon-based materials or transition metal oxides.

3. The adjustable ultrasonic sensor based on polymer bubbles as described in claim 2, characterized in that, The photosensitive polymer is selected from methyl methacrylate or methyl acrylate.

4. The application of the polymer bubble-based tunable ultrasonic sensor as described in claim 1 in the fabrication of fiber optic ultrasonic sensors, characterized in that, The application is based on a test sensing system, which includes: An ultrasonic generator is used to drive a piezoelectric ultrasonic transducer and generate ultrasonic waves. A tunable ultrasonic sensor based on polymer bubbles is used to detect ultrasonic waves. The ultrasonic waves act on the photothermal organic polymer bubbles (3), causing the reflected light to be modulated. The modulated reflected light demodulates the ultrasonic information. A fixed wavelength laser I is used as a sensor laser source to generate a sensor laser. The sensor laser acts on the photothermal organic polymer bubble (3) and is reflected to obtain the reflected sensor laser. A fixed wavelength laser II is used as a heating laser source to generate heating laser. The heating laser is absorbed by the photothermal organic polymer bubble (3), and the organic polymer bubble (3) is tuned by the heating laser to cause deformation. The spectrometer is used to detect the spectral information of the tunable ultrasonic sensor based on polymer bubbles. The spectrometer can acquire the spectral information of the photothermal organic polymer bubble (3) after deformation in real time. A wavelength division multiplexer is used to combine sensing laser and heating laser into a single beam for transmission, as well as to transmit modulated reflected light. Fiber optic circulators are used to transmit sensing laser light and modulated reflected light. The photodetector is used to convert the modulated reflected light signal into an electrical signal. The modulated reflected light is sequentially guided into the photodetector through a dual-hole fiber (2), a single-mode fiber (1), a wavelength division multiplexer, and a fiber optic circulator, and then converted into electrical information. An oscilloscope is used to acquire electrical signals from a photodetector and display the ultrasonic signal response.

5. The application according to claim 4, characterized in that, The application method is as follows: A fixed-wavelength laser I generates a sensing laser, which is then guided into a single-mode fiber (1) via a fiber circulator and a wavelength division multiplexer. The laser is then transmitted through the single-mode fiber (1) to a double-hole fiber (2), and then reflected back and forth in an air cavity formed by the end face of the double-hole fiber (2) and a photothermal organic polymer bubble (3). A fixed-wavelength laser II generates a heating laser, which is then guided into a single-mode fiber (1) together with a sensing laser via a wavelength division multiplexer. The heating laser is then transmitted through the single-mode fiber (1) to a double-hole fiber (2), and then enters an air cavity formed by the end face of the double-hole fiber (2) and a photothermal organic polymer bubble (3). In this process, heating lasers of different powers are used to irradiate the photothermal organic polymer bubble (3), causing the photothermal organic polymer bubble (3) to undergo thermal expansion deformation to different degrees. The sensing laser acts on the photothermal organic polymer bubble (3) and is reflected to obtain the reflected sensing laser. The spectrometer is used to detect the spectral information of the tunable ultrasonic sensor based on the polymer bubble. An ultrasonic generator is used to drive a piezoelectric ultrasonic transducer to generate ultrasonic waves. The ultrasonic waves are applied to the photothermal organic polymer bubble (3) via the piezoelectric ultrasonic transducer to modulate the reflected light and obtain modulated reflected light. The modulated reflected light in the photothermal organic polymer bubble (3) is sequentially introduced to the photodetector through a dual-hole optical fiber (2), a single-mode optical fiber (1), a wavelength division multiplexer, and an optical fiber circulator. The photodetector converts the modulated reflected light optical signal into an electrical signal. Finally, an oscilloscope is used to collect the electrical signal of the photodetector and obtain the ultrasonic signal response. To detect different ultrasonic signal responses, real-time adjustable detection can be achieved by adjusting the laser power of the fixed-wavelength laser II.

6. The application according to claim 5, characterized in that, A fixed-wavelength laser I, a photodetector, and a wavelength division multiplexer are connected to the fiber optic circulator via optical fibers. An oscilloscope is electrically connected to the photodetector via wires. The fixed-wavelength laser II is connected to the wavelength division multiplexer via optical fibers. The wavelength division multiplexer is connected to a polymer bubble-based tunable ultrasonic sensor via optical fibers. An ultrasonic generator is electrically connected to a piezoelectric transducer via wires. The piezoelectric transducer emits ultrasonic waves that affect the polymer bubble-based tunable ultrasonic sensor. The polymer bubble-based tunable ultrasonic sensor is detachably connected to a spectrometer via a single-mode optical fiber (1).

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