A photo-induced ultrasonic transducer based on transition metal sulfide and its preparation method

Abstract

The present invention provides a transition metal sulfide-based photoacoustic transducer and a method for preparing the same, belonging to the field of optical fiber sensing technology. The present invention combines transition metal sulfides with multi-walled carbon nanotubes as a light-absorbing layer. The transition metal sulfides, with their narrow band gap and high specific surface area, are capable of photocatalysis, which enhances the light absorption capacity of the multi-walled carbon nanotubes. The combination of the two materials forms a heterojunction with a high-quality interface, increasing the specific surface area of ​​the light-absorbing layer. This not only reduces thermal resistance but also increases the surface area of ​​the material on the same optical fiber end face, thereby increasing the heat capacity of the light-absorbing layer and rapidly transferring heat energy to the thermoelastic expansion layer, thereby improving the photoacoustic conversion efficiency. A maximum sound pressure intensity of 0.75 MPa at 2 mm was achieved, effectively enhancing the photoacoustic conversion efficiency of the photoacoustic transducer.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a transition metal sulfide-based photo-induced ultrasonic transducer and a preparation method thereof. Background Art

[0002] Photoacoustic transducers are optical ultrasound sources designed based on the photoacoustic effect, and are generally composed of a light-absorbing coating and an elastic matrix. Under the excitation of incident pulsed light, the absorbing coating converts light energy into a local temperature rise and generates acoustic waves along the laser profile. It has the advantages of wide bandwidth, large imaging depth, high peak pressure, and high spatial resolution. Optical ultrasound transducers can be made into highly miniaturized components at the end face of the optical fiber, making them easy to integrate into medical devices such as catheters and needles to provide real-time image guidance, especially for guiding minimally invasive surgical procedures. Because traditional piezoelectric transducers are large in size, their application in fields such as intravascular imaging or minimally invasive surgical guidance is limited. In contrast, photoacoustic detection technology has the advantages of wide bandwidth and high amplitude. Its combination with optical ultrasound sensors can realize all-optical ultrasound imaging. At the same time, all-optical ultrasound detection equipment is not subject to electromagnetic interference, allowing it to be used in clinical scenarios such as magnetic resonance imaging or radiofrequency ablation. Photoacoustic conversion efficiency is a key performance metric for photoacoustic transducers. The peak ultrasonic pressure of a fiber-optic ultrasonic transducer is constrained by its bandwidth, and is also dependent on the material of the light-absorbing particles, the composite coating fabrication method, and the coating's thickness and uniformity. Imperfect fabrication methods not only result in low photoacoustic conversion efficiency but also inefficiently utilize expensive nanomaterials, increasing device costs.

[0003] Patents both domestically and internationally have proposed photoacoustic transducers with various structures, each with its own advantages and disadvantages. In the prior art, "PDMS composites with photostable NIR dyes for multi-modal ultrasound imaging," Noimark et al. at University College London used a solution-based method to fabricate carbon-based composite films on micron-thick optical fibers. They dip-coated the fibers with Epolight 9837 dye-polydimethylsiloxane and multi-walled carbon nanotube-polydimethylsiloxane composite solutions, respectively, resulting in hemispherical coatings less than 20 μm thick at their thickest point. Ultrasonic transmitters coated with the dye-polydimethylsiloxane composite achieved a peak ultrasonic pressure of 1 MPa, corresponding to a bandwidth of 20 MHz. However, the dye-based composites can compromise photostability under long-term exposure to laser or ultrasound, ultimately leading to reduced photoacoustic conversion efficiency. In the existing technology "CuInS2 Quantum Dot and Polydimethylsiloxane Nanocomposites for All-Optical Ultrasound and Photoacoustic Imaging," Bodian et al. at University College London coated the end face of an optical fiber with a composite material made from a mixture of CuInS2 quantum dots (CIS-QDs) and polydimethylsiloxane. Due to the wavelength-selective absorption properties of CIS-QDs, the fiber optic transmitter can simultaneously excite ultrasound waves while allowing another wavelength of excitation laser light to pass through, achieving photoacoustic-ultrasound dual-modal imaging based on a single fiber optic transmitter. Under pulsed laser irradiation, the CIS-PDMS film of the fiber optic ultrasound transmitter generates ultrasound waves with a pressure exceeding 3.5 MPa. However, the synthesis of quantum dots is relatively complex, greatly increasing the difficulty and cost of device production. Chinese patent application number CN109433571B proposes a flexible photoacoustic thin film transducer and its fabrication method. The transducer consists, from bottom to top, of a flexible substrate (transparent polydimethylsiloxane polymer); a light-absorbing layer (carbon nanotubes); and a thermoelastic layer (polydimethylsiloxane polymer). The flexible transducer maintains close contact with the surface of the probe, significantly increasing coupling efficiency for probes with irregular surfaces. However, this transducer, which only uses carbon nanotubes as the light-absorbing layer, suffers from low photoacoustic conversion efficiency. Chinese patent application number CN110339992A proposes a photoacoustic transducer and its fabrication method. The transducer uses chemical vapor deposition to grow a carbon nanotube array film on a silicon wafer. Polydimethylsiloxane is solidified onto the carbon nanotube array film, which is then thinned using inductively coupled plasma etching. Applying a pulsed laser to the thinned carbon nanotube array film generates a high-frequency ultrasonic signal.However, this chemical vapor deposition reaction is often limited by the equilibrium constant, resulting in low material utilization efficiency and waste. In addition, inductively coupled plasma etching also makes the production cost of the transducer too expensive. Chinese patent application number CN112604928B proposes a photoacoustic transducer based on halogen perovskite materials. The basic principle of this transducer is to use the halogen perovskite material as a light-absorbing layer to convert light energy into heat energy, and polydimethylsiloxane as a thermal expansion layer, which undergoes thermal expansion after absorbing heat to generate ultrasonic waves. The transducer produced by this method has high photoacoustic conversion efficiency and a wide spectral bandwidth. However, the halogen perovskite material contains some chemical impurities, which not only affect its stability but also may contain toxic substances such as lead, making the device potentially toxic and limiting its scope of use.

[0004] Therefore, the problems of low photoacoustic conversion efficiency, complex production and high cost in existing technologies are technical difficulties that need to be solved urgently. Summary of the Invention

[0005] The object of the present invention is to provide a transition metal sulfide-based photoacoustic transducer and a preparation method thereof, wherein the photoacoustic transducer has high photoacoustic conversion efficiency, low cost and simple manufacturing process.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a transition metal sulfide-based photoacoustic transducer, comprising an optical fiber and a photoacoustic conversion composite layer attached to the end face of the optical fiber; the photoacoustic conversion composite layer comprises a light absorption layer and a thermoelastic expansion layer arranged in sequence from bottom to top;

[0008] The light absorption layer comprises multi-walled carbon nanotubes and transition metal sulfide composite particles; and the thermoelastic expansion layer is a polydimethylsiloxane film layer.

[0009] Preferably, the transition metal sulfide includes one or more of molybdenum disulfide, tungsten disulfide, niobium disulfide, iron trisulfide, copper trisulfide, iron disulfide and nickel disulfide.

[0010] Preferably, the light absorbing layer has a thickness of 10 to 15 μm.

[0011] Preferably, the thickness of the thermoelastic expansion layer is 15 to 20 μm.

[0012] Preferably, the photoacoustic conversion composite layer has a thickness of 25 to 35 μm.

[0013] The present invention provides a method for preparing a transition metal sulfide-based photoacoustic transducer according to the above technical solution, comprising the following steps:

[0014] Etching the end face of the optical fiber to obtain an optical fiber end face;

[0015] Dispersing and mixing multi-walled carbon nanotubes, transition metal sulfides, and an alcohol solvent, applying the resulting mixed dispersion to the end face of the optical fiber, and volatilizing the solvent to form a light absorption layer on the end face of the optical fiber;

[0016] A polydimethylsiloxane prepolymer and a curing agent are mixed, and the obtained polydimethylsiloxane solution is dip-coated on the light absorption layer to form a polydimethylsiloxane film layer. After curing, a transition metal sulfide-based photoacoustic transducer is obtained.

[0017] Preferably, the usage ratio of the multi-walled carbon nanotubes, transition metal sulfide and alcohol solvent is 2 mg: (2-2.5) mg: (1-2) mL.

[0018] Preferably, the dispersing and mixing comprises ultrasonic treatment and standing in sequence; the ultrasonic treatment time is 30 to 40 minutes, and the standing time is 2.5 to 3 hours.

[0019] Preferably, the mass ratio of the polydimethylsiloxane prepolymer to the curing agent is 10:1.

[0020] Preferably, the curing comprises: curing at room temperature for 24 hours and then curing at a constant temperature of 60-65° C. for more than 3 hours.

[0021] The present invention provides a transition metal sulfide-based photoacoustic transducer, comprising an optical fiber and a photoacoustic conversion composite layer attached to the end face of the optical fiber; the photoacoustic conversion composite layer comprises a light absorption layer and a thermoelastic expansion layer arranged in sequence from bottom to top; the light absorption layer comprises multi-walled carbon nanotubes and transition metal sulfide composite particles; and the thermoelastic expansion layer is a polydimethylsiloxane film layer. The present invention combines transition metal sulfides with multi-walled carbon nanotubes as a light absorption layer. The transition metal sulfides with a narrow band gap and a high specific surface area can perform photocatalysis, and the photocatalytic effect can improve the light absorption capacity of the multi-walled carbon nanotubes. There is a significant charge transfer effect between the materials of the light absorption layer, and carriers can be quickly transmitted at the interface, reducing non-radiative recombination of carriers at the interface, reducing thermal resistance and heat loss, and thus improving thermal conductivity. The transition metal sulfide and the inner and outer tubes of the multi-walled carbon nanotubes have different tubular structural characteristics. The combination of the two materials can form a heterojunction with high interface quality, thereby increasing the specific surface area of ​​the light absorption layer, reducing thermal resistance, and increasing the surface area of ​​the material on the same optical fiber end face, so that the heat capacity of the light absorption layer is increased and heat energy is quickly transferred to the thermoelastic expansion layer, thereby improving the photoacoustic conversion efficiency. Therefore, the photoacoustic transducer proposed in the present invention is not only non-toxic and non-sensitizing, but also reduces the thermal resistivity of the light absorption layer, improves the light absorption capacity and stability, and thus also improves the sound pressure intensity of the photoacoustic transducer, achieving a maximum sound pressure intensity of 0.75 MPa at 2 mm. The photoacoustic transmitter achieves a sound pressure intensity performance similar to that of a large-diameter optical fiber (≥125 μm) with a smaller optical fiber diameter (105 / 125 μm), effectively improving the photoacoustic conversion efficiency of the photoacoustic transducer.

[0022] The present invention adopts a bottom-up method to prepare a photoultrasonic transducer. This method can reduce the thickness of the ultrasonic coating, thereby improving the ultrasonic bandwidth and pressure. The production process is simple and there is no need to directly add expensive nanomaterials to the polymer, which reduces the waste of nanomaterials and lowers costs. It solves the problem of relatively complex and high cost in the production of existing photoultrasonic transducers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the cross-sectional structure of the photoacoustic transducer of the present invention;

[0024] Figure 2 This is a flowchart of the production of the photoacoustic transducer of the present invention;

[0025] Figure 3 This is a comparison diagram of ultrasonic time domain signals of the multi-walled carbon nanotube-polydimethylsiloxane film photoacoustic transducer in Comparative Example 1 and the multi-walled carbon nanotube-molybdenum disulfide-polydimethylsiloxane composite film photoacoustic transducer in Example 1. DETAILED DESCRIPTION

[0026] like Figure 1 As shown, the present invention provides a transition metal sulfide-based photoacoustic transducer, comprising an optical fiber and a photoacoustic conversion composite layer attached to the end face of the optical fiber; the photoacoustic conversion composite layer comprises a light absorption layer and a thermoelastic expansion layer arranged in sequence from bottom to top;

[0027] The light absorption layer comprises multi-walled carbon nanotubes and transition metal sulfide composite particles; and the thermoelastic expansion layer is a polydimethylsiloxane film layer.

[0028] The photoacoustic transducer provided by the present invention includes an optical fiber; the present invention has no special limitation on the optical fiber, and any optical fiber used for the photoacoustic transducer known in the art can be used; in an embodiment of the present invention, the optical fiber is preferably a multimode optical fiber, and the diameter of the optical fiber is specifically 105 / 125μm multimode optical fiber.

[0029] The photoacoustic transducer provided by the present invention includes a photoacoustic conversion composite layer attached to the end face of the optical fiber; the photoacoustic conversion composite layer includes a light absorption layer and a thermoelastic expansion layer arranged in sequence from bottom to top; the light absorption layer includes multi-walled carbon nanotubes and transition metal sulfide composite particles; and the thermoelastic expansion layer is a polydimethylsiloxane film layer (PDMS film).

[0030] In the present invention, the transition metal sulfide preferably includes one or more of molybdenum disulfide, tungsten disulfide, niobium disulfide, iron trisulfide, copper trisulfide, iron disulfide, and nickel disulfide. When two or more of the aforementioned transition metal sulfides are present, the present invention does not specifically limit the ratio of the different types of transition metal sulfides and can be adjusted according to actual needs. The present invention utilizes transition metal sulfides to enhance the thermal conductivity of the composite film layer, effectively improving the sound pressure intensity and photoacoustic conversion efficiency of the fiber optic ultrasonic transducer.

[0031] In the present invention, the mass ratio of the multi-walled carbon nanotubes to the transition metal sulfide in the multi-walled carbon nanotube and transition metal sulfide composite particles is preferably 2: (2 to 2.5), more preferably 1: 1. In the multi-walled carbon nanotube and transition metal sulfide composite particles, functional groups (such as hydroxyl groups) on the surface of the carbon nanotubes react with reactive groups (such as sulfate ions) in the transition metal sulfide to form chemical bonds.

[0032] In the present invention, the thickness of the light absorption layer is preferably 10 to 15 μm, which is used to absorb light energy and convert it into heat energy; the thickness of the thermoelastic expansion layer is preferably 15 to 20 μm, which generates ultrasonic waves through thermal expansion; the thickness of the photoacoustic conversion composite layer is preferably 25 to 35 μm, more preferably 30 μm.

[0033] like Figure 2As shown, the present invention provides a method for preparing a transition metal sulfide-based photoacoustic transducer as described in the above technical solution, comprising the following steps:

[0034] Etching the end face of the optical fiber to obtain an optical fiber end face;

[0035] Dispersing and mixing multi-walled carbon nanotubes, transition metal sulfides, and an alcohol solvent, applying the resulting mixed dispersion to the end face of the optical fiber, and volatilizing the solvent to form a light absorption layer on the end face of the optical fiber;

[0036] A polydimethylsiloxane prepolymer and a curing agent are mixed, and the obtained polydimethylsiloxane solution is dip-coated on the light absorption layer to form a polydimethylsiloxane film layer. After curing, a transition metal sulfide-based photoacoustic transducer is obtained.

[0037] The present invention etches the end face of the optical fiber to obtain the optical fiber end face.

[0038] In the present invention, the reagent used for the etching treatment is preferably hydrofluoric acid, and the mass fraction of the hydrofluoric acid is preferably 40.0%; the time of the etching treatment is preferably 5 minutes, and the present invention preferably uses a surface profiler to measure the etching depth every half minute until the etching depth reaches 100±10nm.

[0039] The present invention preferably utilizes an optical fiber etching system to perform etching on the optical fiber end face. The experimental translation stage controls the optical fiber end face to be immersed in hydrofluoric acid. Since the core doping concentration is generally higher than the cladding, the optical fiber produces a concave end face under the action of hydrofluoric acid, which is conducive to the subsequent attachment of light-absorbing particles.

[0040] After the etching is completed, the present invention preferably places the optical fiber vertically with the etched end face downward, and allows it to dry naturally or in the air.

[0041] After obtaining the optical fiber end face, the present invention disperses and mixes multi-walled carbon nanotubes, transition metal sulfides and alcohol solvent, dip-coats the obtained mixed dispersion on the optical fiber end face, and volatilizes the solvent to form a light absorption layer on the optical fiber end face.

[0042] In the present invention, the alcohol solvent is preferably anhydrous ethanol; the usage ratio of the multi-walled carbon nanotubes, transition metal sulfide and alcohol solvent is preferably 2 mg: (2-2.5) mg: (1-2) mL, more preferably 2 mg: 2 mg: 1-1.5 mL.

[0043] In the present invention, the dispersing and mixing preferably includes ultrasonic treatment and standing in sequence; the ultrasonic treatment time is preferably 30 to 40 minutes, more preferably 35 minutes, and the standing time is preferably 2.5 to 3 hours. In the present invention, the mixed solution is thoroughly mixed by ultrasound, fine bubbles generated during the solution mixing are removed, and the solution is thoroughly mixed and dissolved, thereby obtaining a stable mixed dispersion.

[0044] In the present invention, a three-dimensional optical profiler is preferably used for the dip coating, and the thickness is tested during the dip coating process until the desired thickness of the light absorbing layer is reached.

[0045] In the present invention, the solvent volatilization is preferably carried out at natural room temperature until there is no liquid on the surface; after the alcohol solvent evaporates, the multi-walled carbon nanotube-transition metal sulfide adheres to the end face of the optical fiber. Since the multi-walled carbon nanotubes are fully dispersed in the mixed dispersion, when the alcohol solvent completely evaporates, the multi-walled carbon nanotube-transition metal sulfide mixed particles fully cover the core part.

[0046] After the solvent evaporates, a light absorption layer is formed on the end face of the optical fiber, and the light absorption layer contains uniform multi-walled carbon nanotube-transition metal sulfide mixed particles.

[0047] After forming a light absorption layer on the end face of the optical fiber, the present invention mixes a polydimethylsiloxane prepolymer and a curing agent, and dip-coats the obtained polydimethylsiloxane solution on the light absorption layer to form a polydimethylsiloxane film layer. After curing, a transition metal sulfide-based photoacoustic transducer is obtained.

[0048] In the present invention, the mass ratio of the polydimethylsiloxane prepolymer and the curing agent is preferably 10:1; the present invention has no particular limitation on the specific models and types of the polydimethylsiloxane prepolymer and the curing agent, and any commercially available product known in the art can be used, such as Dow Corning PMX-200 or Gadler 107-51-7.

[0049] After the polydimethylsiloxane prepolymer and the curing agent are mixed, a large number of bubbles are present in the obtained polydimethylsiloxane solution. In the present invention, it is preferred to stir the mixture with ultrasonic waves at 40 kHz for 10 minutes, and then place the mixture in a sealed negative pressure tank and let it stand for 45 minutes to expel the bubbles (air pressure ≤ -0.05 MPa). In view of the low density of polydimethylsiloxane (the density of the polydimethylsiloxane solution obtained when the mass ratio of the polydimethylsiloxane prepolymer to the curing agent is 10:1 is 970 kg / m 3 ), and has good hydrophobicity, which can better adapt to applications in liquid environments; the polydimethylsiloxane solution obtained by mixing the polydimethylsiloxane prepolymer and the curing agent is a viscous liquid with a large surface tension, and the thermal expansion layer will have a large expansion amplitude. Due to the continuous expansion and contraction of the expansion layer, ultrasound can be better generated.

[0050] The present invention preferably uses a three-dimensional optical profilometer for the dip coating, and the thickness is measured during the dip coating process until the desired thickness of the polydimethylsiloxane film layer is reached. The present invention employs a "dip coating method" to form the polydimethylsiloxane film layer, thereby avoiding film concavity caused by capillary action, ensuring a smooth composite coating, and greatly simplifying the manufacturing process.

[0051] In the present invention, the curing preferably includes: curing at room temperature for 24 hours, followed by constant temperature curing at 60-65°C for more than 3 hours, more preferably curing at 62-63°C for 3-5 hours. In the present invention, the optical fiber dipped in polydimethylsiloxane is preferably placed vertically to ensure that the composite film layer and the optical fiber are on the same vertical plane, and to avoid deformation of the composite film layer due to gravity when placed horizontally.

[0052] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0053] Example 1

[0054] Fiber end face etching was performed using a fiber etching system. First, a multimode fiber end face with a core diameter of 105 / 125 μm was immersed in hydrofluoric acid (40.0 wt%) using a test stage. The etching depth was measured every half minute using a surface profilometer until the etching depth reached 100 ± 10 nm. The fiber was then placed vertically with the etched end face facing downward and allowed to dry naturally to obtain the fiber end face.

[0055] 10 mg of multi-walled carbon nanotubes, 10 mg of molybdenum disulfide, and 5 mL of anhydrous ethanol were mixed (the mixing ratio was 2:2:1), ultrasonicated for 40 min, and then allowed to stand for 3 h to obtain a stable mixed solution;

[0056] S3: Dip-coat the mixed solution onto the end face of the optical fiber, and after the anhydrous ethanol evaporates, form a light absorption layer on the end face of the optical fiber;

[0057] S4: The polydimethylsiloxane prepolymer and curing agent in the commercially available Dow Corning PMX-200 product were mixed at a mass ratio of 10:1, and the mixture was thoroughly stirred under 40 kHz ultrasonic stirring for 10 minutes. The mixture was then placed in a sealed negative pressure tank and allowed to stand for 45 minutes at an air pressure of ≤-0.05 MPa to expel bubbles, thereby obtaining a polydimethylsiloxane solution.

[0058] S5: Dip-coat the polydimethylsiloxane solution on the light absorbing layer, place it vertically at room temperature for curing for 24 hours, and then place it in a constant temperature box at 65°C for 3 hours until the film layer is completely cured to form a polydimethylsiloxane film layer, thereby obtaining a photoacoustic transducer; the thickness of the light absorbing layer is 15 μm, the thickness of the polydimethylsiloxane film layer is 15 μm, and the thickness of the photoacoustic conversion composite layer is 30 μm.

[0059] A fiber-coupled pulsed laser with a central wavelength of 1064nm is used as the incident pulse light. The incident pulse light passes through the optical fiber and acts on the absorption coating formed by multi-walled carbon nanotube-molybdenum disulfide mixed particles. Under the excitation of the incident pulse light, the absorption coating converts light energy into heat energy and quickly transfers it to the polydimethylsiloxane elastic expansion layer. The polydimethylsiloxane film layer expands due to heat. When there is no light, the polydimethylsiloxane film layer begins to contract after the heat energy is no longer affected, thereby converting heat energy into ultrasonic mechanical energy.

[0060] Example 2

[0061] The only difference from Example 1 is that the mixing ratio of multi-walled carbon nanotubes, molybdenum disulfide and anhydrous ethanol is 2:2:1.5.

[0062] Example 3

[0063] The only difference from Example 1 is that the mixing ratio of multi-walled carbon nanotubes, molybdenum disulfide and anhydrous ethanol is 2:2:2.

[0064] Example 4

[0065] The only difference from Example 1 is that 10 mg of multi-walled carbon nanotubes, 10 mg of tungsten disulfide and 10 mL of anhydrous ethanol are mixed (the mixing ratio is 2:2:2). Others are the same as in Example 1.

[0066] A fiber-coupled pulsed laser with a central wavelength of 1064nm is used as the incident pulse light. The incident pulse light passes through the optical fiber and acts on the absorption coating formed by multi-walled carbon nanotube-tungsten disulfide mixed particles. Under the excitation of the incident pulse light, the absorption coating converts light energy into heat energy and quickly transfers it to the polydimethylsiloxane elastic expansion layer. The polydimethylsiloxane film layer expands due to heat. When there is no light, the polydimethylsiloxane film layer begins to contract after the heat energy is no longer affected, thereby converting heat energy into ultrasonic mechanical energy.

[0067] Example 5

[0068] The only difference from Example 4 is that the mixing ratio of multi-walled carbon nanotubes, tungsten disulfide and anhydrous ethanol is 2:2:1.5.

[0069] Example 6

[0070] The only difference from Example 4 is that the mixing ratio of multi-walled carbon nanotubes, tungsten disulfide and anhydrous ethanol is 2:2:1.

[0071] Example 7

[0072] The only difference from Example 1 is that 10 mg of multi-walled carbon nanotubes, 10 mg of niobium disulfide and 5 mL of anhydrous ethanol are mixed (the mixing ratio is 2:2:1).

[0073] A fiber-coupled pulsed laser with a central wavelength of 1064nm is used as the incident pulse light. The incident pulse light passes through the optical fiber and acts on the absorption coating formed by multi-walled carbon nanotube-niobium disulfide mixed particles. Under the excitation of the incident pulse light, the absorption coating converts light energy into heat energy and quickly transfers it to the polydimethylsiloxane elastic expansion layer. The polydimethylsiloxane film layer expands due to heat. When there is no light, the polydimethylsiloxane film layer begins to contract after the heat energy is no longer affected, thereby converting the heat energy into ultrasonic mechanical energy.

[0074] Example 8

[0075] The only difference from Example 7 is that the mixing ratio of multi-walled carbon nanotubes, niobium disulfide and anhydrous ethanol is 2:2:1.5.

[0076] Example 9

[0077] The only difference from Example 7 is that the mixing ratio of multi-walled carbon nanotubes, niobium disulfide and anhydrous ethanol is 2:2:2.

[0078] Comparative Example 1

[0079] The only difference from Example 1 is that molybdenum disulfide is not added, and the rest is the same as Example 1.

[0080] Performance Testing

[0081] 1) In order to verify the performance of the photoacoustic transducer, a fiber optic ultrasonic transducer signal bandwidth test system was built. The fiber optic ultrasonic transducer signal bandwidth test system includes a high-frequency underwater acoustic transducer, a digital oscilloscope, a water tank filled with deionized water, a pulse laser, and the prepared fiber optic ultrasonic transducer. The distance between the high-frequency underwater acoustic transducer and the fiber optic ultrasonic transducer is 2 mm. The excitation current of the pulse laser is set to I = 300 mA, the pulse width Δt = 5 ns, and the repetition frequency f p =10Hz, the sampling interval of the digital oscilloscope is 20ns and the bandwidth is 10MHz.

[0082] In order to verify the role of molybdenum disulfide in the composite film layer, the composite film layer of Example 1 and Comparative Example 1 was compared and tested to test the ultrasonic amplitude and spectrum energy concentration. The results are shown in FIG. Figure 3 .

[0083] Depend on Figure 3It can be seen that the optical fiber ultrasonic transducer based on multi-walled carbon nanotube-molybdenum disulfide-polydimethylsiloxane composite film (MWCNT-MoS2-PDMS) has a higher ultrasonic amplitude and more concentrated spectral energy than the optical fiber ultrasonic transducer based on multi-walled carbon nanotube-polydimethylsiloxane composite film (MWCNT-PDMS). This is because the addition of transition metal sulfide-molybdenum disulfide in the light absorption layer composite film enables the composite film to make more full use of photothermal energy, improves the photoacoustic conversion efficiency, and also makes it have the potential to be used in the field of high-energy ultrasound focused therapy.

[0084] 2) The above-mentioned fiber optic ultrasonic transducer signal bandwidth test system was used to test the sound pressure intensity of the photoacoustic transducers prepared in Examples 1 to 9. After obtaining the original voltage signal of the ultrasonic pulse wave using a digital oscilloscope, the spectrum distribution of the pulse wave was obtained by Fourier transform. The detection distance was set to 2 mm, 4 mm, and 6 mm. The specific data are shown in Tables 1 to 3. The unit of sound pressure intensity is MPa.

[0085] Table 1 Sound pressure intensity of photoacoustic transducers of Examples 1 to 3

[0086]

[0087] Table 2 Sound pressure intensity of photoacoustic transducers of Examples 4 to 6

[0088]

[0089]

[0090] Table 3 Sound pressure intensity of photoacoustic transducers of Examples 7 to 9

[0091]

[0092] As can be seen from Tables 1 to 3, the photoacoustic transducer prepared by the present invention has a high sound pressure intensity, achieving a maximum sound pressure intensity of 0.75 MPa at 2 mm. With a smaller fiber diameter (105 / 125 μm), it achieves a sound pressure intensity performance similar to that of a large-diameter fiber (≥125 μm) (fiber diameter 140 μm, sound pressure intensity detected at 2 mm is 0.75 MPa), indicating that the present invention effectively improves the photoacoustic conversion efficiency of the photoacoustic transducer.

[0093] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A photoacoustic transducer based on transition metal sulfide, characterized in that: It includes an optical fiber and a photoacoustic conversion composite layer attached to the end face of the optical fiber; the photoacoustic conversion composite layer includes a light absorption layer and a thermoelastic expansion layer arranged in sequence from bottom to top; The light absorption layer includes multi-walled carbon nanotubes and transition metal sulfide composite particles; the thermoelastic expansion layer is a polydimethylsiloxane film layer; The transition metal sulfide includes one or more of molybdenum disulfide, tungsten disulfide, niobium disulfide, iron trisulfide, copper trisulfide, iron disulfide and nickel disulfide.

2. The photoacoustic transducer according to claim 1, characterized in that: The thickness of the light absorbing layer is 10 to 15 μm.

3. The photoacoustic transducer according to claim 1, wherein: The thickness of the thermoelastic expansion layer is 15 to 20 μm.

4. The photoacoustic transducer according to claim 1, 2 or 3, characterized in that: The thickness of the photoacoustic conversion composite layer is 25 to 35 μm.

5. The method for preparing a transition metal sulfide-based photoacoustic transducer according to any one of claims 1 to 4, characterized in that: The following steps are involved: Etching the end face of the optical fiber to obtain an optical fiber end face; Dispersing and mixing multi-walled carbon nanotubes, transition metal sulfides, and an alcohol solvent, dip-coating the resulting mixed dispersion on the end face of the optical fiber, and volatilizing the solvent to form a light absorption layer on the end face of the optical fiber; A polydimethylsiloxane prepolymer and a curing agent are mixed, and the obtained polydimethylsiloxane solution is dip-coated on the light absorption layer to form a polydimethylsiloxane film layer. After curing, a transition metal sulfide-based photoacoustic transducer is obtained.

6. The preparation method according to claim 5, characterized in that The usage ratio of the multi-walled carbon nanotubes, transition metal sulfide and alcohol solvent is 2 mg: (2-2.5) mg: (1-2) mL.

7. The preparation method according to claim 5, characterized in that The dispersion mixing includes ultrasonic treatment and standing in sequence; the ultrasonic treatment time is 30 to 40 minutes, and the standing time is 2.5 to 3 hours.

8. The preparation method according to claim 5, characterized in that The mass ratio of the polydimethylsiloxane prepolymer to the curing agent is 10:

1.

9. The preparation method according to claim 5, characterized in that The curing comprises: curing at room temperature for 24 hours, and then curing at a constant temperature of 60-65° C. for more than 3 hours.

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