Grass-shaped alumina-based photoinduced ultrasonic transducer and preparation method thereof
By developing a method for fabricating a grass-like alumina-based photo-induced ultrasonic transducer, the problems of insufficient light absorption in thin layers and severe sound attenuation in thick layers of photo-induced ultrasonic transducers have been solved. This method enables efficient high-frequency and wide-bandwidth ultrasonic signal output, making it suitable for harsh electromagnetic environments and personalized medical devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-16
- Publication Date
- 2026-03-24
AI Technical Summary
Existing photo-induced ultrasonic transducers suffer from insufficient light absorption in thin layers and severe sound attenuation in thick layers. Furthermore, the alumina pore walls restrict PDMS oscillation, resulting in low ultrasonic sound pressure levels and making it difficult to achieve efficient ultrasonic output at high frequencies and wide bandwidths.
A grass-like alumina-based photo-ultrasonic transducer was used. Alumina films were prepared by atomic layer deposition and then treated with a water bath to form grass-like alumina films. By combining metal films and PDMS thermal expansion materials, porosity and thickness were controlled to achieve efficient light absorption and thermal expansion conversion.
It improves the ultrasonic sound pressure level, realizes high-frequency and wide-bandwidth ultrasonic signal output, is suitable for harsh electromagnetic environments and personalized medical devices, and has the potential for miniaturization.
Smart Images
Figure CN121715313A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of ultrasonic transducers, and particularly relates to a grass-shaped alumina-based photo-induced ultrasonic transducer and a preparation method thereof. BACKGROUND
[0002] Traditional ultrasonic transducers are electrically driven devices, which realize electric-acoustic conversion by using the piezoelectric effect of materials. However, the limited bandwidth and poor anti-electromagnetic interference capability of the traditional ultrasonic transducers limit their application in high-standard environments. As a new type of technology, photo-induced ultrasonic technology uses laser instead of electricity as an excitation source to obtain ultrasonic waves, and has characteristics that traditional piezoelectric technology cannot have, such as high frequency and large bandwidth, which are required for imaging and sensing. At the same time, the photo-induced ultrasonic technology has a relatively simple transducer structure, avoiding the complexity of electronic component assembly, and making it possible to develop ultrasonic transducers of various shapes.
[0003] With the continuous research on photo-induced ultrasonic transducers, the photo-induced ultrasonic transducer technology has developed rapidly. Compared with traditional piezoelectric ultrasonic transducers, photo-induced ultrasonic transducers have the following advantages:
[0004] (1) The preparation method is simple, and with the continuous miniaturization of the transducer, a small area of photoacoustic composite material can output ultrasonic signals with high amplitude, high frequency and wide bandwidth. The high amplitude feature can be used in ultrasonic treatment, such as crushing stones or killing cancer cells, and the high frequency feature can provide a compact focus for ultrasonic treatment. At the same time, the repetition frequency of the laser pulse is 10-20 Hz, and the extremely low duty cycle can reduce the damage of ultrasonic heat effect to human tissues.
[0005] (2) Since the photo-induced ultrasonic transducer is a passive device that uses optical signals as an excitation source, it can be used in harsh electromagnetic environments such as inside a magnetic resonance imaging scanner or a radio frequency ablation device without being affected by interference.
[0006] (3) The photo-induced ultrasonic transducer is a flexible device that can mechanically deform due to its flexibility. This feature can be used to precisely control ultrasonic waves in clinical practice. Combined with the easy-to-produce feature, personalized medical devices can be realized.
[0007] Photo-induced ultrasonic transducers are usually composed of light-absorbing materials and thermal expansion materials. Commonly used absorbing materials include carbon-based materials such as carbon black, carbon nanotubes, and candle soot particles, and the thermal expansion material is polydimethylsiloxane (PDMS). The incident light is absorbed by the absorbing material, and the generated heat is conducted to the PDMS, which produces ultrasonic waves using the thermal elastic effect. To solve the dilemma of insufficient light absorption of photoacoustic materials in thin layers and severe acoustic attenuation in thick layers, it is urgent to develop ultrasonic emitters with new structures and precise thickness control to achieve higher ultrasonic output intensity.
[0008] In Lin Yibo's master's thesis, "Research on Photoinduced Ultrasonic Transducer Based on Porous Anodic Alumina Array [D], Nanjing University of Posts and Telecommunications, 2023," a photoinduced ultrasonic transducer was fabricated using an anodic alumina array template. However, under 8 MJ laser energy irradiation, the generated ultrasonic sound pressure was only 1.6 MPa. This is mainly because in the anodic alumina array template, the air holes are distributed perpendicularly in-plane, and the holes are surrounded by alumina. The excessively thick alumina pore walls limit the incorporation of the elastomer PDMS. Furthermore, the alumina pore walls restrict the oscillation of PDMS, preventing the elastomers from resonating synergistically. Summary of the Invention
[0009] To address the aforementioned issues, based on the thesis "Lin Yibo, Research on Photo-induced Ultrasonic Transducers Based on Porous Anodic Alumina Arrays [D]. Master's Thesis, Nanjing University of Posts and Telecommunications, 2023", this invention provides a grass-like alumina-based photo-induced ultrasonic transducer and its preparation method.
[0010] This invention first prepares an alumina thin film using atomic layer deposition, and then obtains a grass-like alumina thin film through water bath treatment. The ultrasonic transducer finally prepared by this method has an acoustic pressure of 2.52 MPa under 8 MJ laser energy irradiation, which is 0.92 MPa higher than the original.
[0011] The technical solution of this invention to solve the technical problem is as follows:
[0012] In a first aspect of the invention, a grass-like alumina-based photo-ultrasonic transducer is provided, comprising: a light-absorbing portion and a thermally expanding material;
[0013] The device consists of a polydimethylsiloxane (PDMS)-metal film-grass-alumina (GLA) composite layer cured on a transparent glass substrate.
[0014] The light-absorbing portion is a metal thin film-GLA composite layer; it can efficiently absorb incident light and convert it into heat energy; the grass-like alumina thin film is a graded refractive index film, which is first prepared by atomic layer deposition and then subjected to water bath treatment to obtain the grass-like alumina thin film; the thickness of the grass-like alumina thin film is mainly controlled by water bath time and temperature, while the porosity is mainly affected by the thickness of the alumina; the metal thin film is deposited in the pores of the grass-like alumina thin film;
[0015] The thermally expanding material is polydimethylsiloxane (PDMS), which absorbs heat energy and generates ultrasound through the thermoelastic effect. The thermally expanding material fills the nanopores of the grass-like alumina.
[0016] Furthermore, the thickness of the alumina film is 20-80 nm.
[0017] Furthermore, the thickness of the grass-like alumina film is 200-500 nm.
[0018] Furthermore, the metal film is gold or silver.
[0019] Furthermore, the thickness of the metal thin film is 100-190 nm.
[0020] The working principle of the grass-like alumina-based photo-ultrasonic transducer of the present invention is as follows: after the incident pulsed laser is absorbed by the PDMS-metal thin film-grass-like alumina composite layer, it is converted into heat, and then ultrasound is generated by utilizing the thermoelastic effect.
[0021] In a second aspect of the invention, a method for preparing a grass-like alumina-based photo-ultrasonic transducer as described in the first aspect is provided.
[0022] The preparation method includes the following steps:
[0023] S1, first prepare an alumina thin film using atomic layer deposition;
[0024] S2, Alumina film is subjected to water bath treatment to obtain GLA film;
[0025] S3, then a metal film is deposited on the prepared GLA film by physical vapor deposition to form a metal film-GLA composite layer;
[0026] S4, then spin-coat a PDMS film onto the obtained metal film-GLA composite layer; to obtain a PDMS composite layer-metal film-grassy alumina;
[0027] S5. The obtained PDMS composite layer-metal film-grass-alumina is placed in a vacuum drying oven and cured to obtain a photo-ultrasonic transducer.
[0028] Furthermore, in step S1, the reaction chamber temperature for atomic layer deposition is 150-300℃, the trimethylaluminum TMA pulse time is 0.1-0.2s in one cycle, the N2 purge is 3-5s, the O3 purge is 3-5s, and the thickness of the prepared alumina film is 20-80nm.
[0029] Further, in step S2, the water bath treatment involves placing the alumina film prepared in step 1 in deionized water at 80-95°C for 10-40 minutes. During the water bath, a clamp is used to fix the sample to prevent it from moving due to water flow fluctuations and causing damage to the microstructure. After boiling, the film sample is taken out and immersed in ethanol to remove residual water stains on the surface.
[0030] Furthermore, in step S3, the deposition rate is 0.125-0.158 nm / s.
[0031] Further, in step S4, the specific process is as follows: PDMS and curing agent are mixed in a pre-defined mass ratio in a beaker and magnetically stirred. Residual air will form bubbles in the solution; the solution is placed in a vacuum drying oven and the air is vented; the PDMS mixture is removed after the bubbles in the PDMS mixture have completely dissipated; the PDMS mixture is spin-coated onto the metal film-grass-like alumina film composite layer at a speed of 1000-1500 r / min, so that it is fully immersed in the nanopores of the grass-like alumina; the mass ratio of PDMS to curing agent is 10:1.
[0032] Further, in step S5, the specific process is as follows: the PDMS composite layer-metal film-grass-alumina is placed in a vacuum drying oven, and vacuum heating is performed to cure the PDMS in the nanopores of the metal film-grass-alumina to obtain an ultrasonic transducer; the temperature is 70-90℃ and the heating time is 20-180min.
[0033] The present invention has the following beneficial effects:
[0034] 1. In this invention, the thickness of the grass-like alumina film can be controlled by the water bath time and temperature, and the porosity of the grass-like alumina film can be controlled by the thickness of the alumina film.
[0035] 2. In this invention, the thickness of the metal film deposited in the pore can be controlled by controlling the growth rate and time of physical vapor deposition, so that the prepared metal film - grass-like alumina has a high light absorption coefficient. If the metal film is too thick or too thin, it will cause pore blockage and reduced light absorption.
[0036] 3. The grass-like alumina film in this invention has an open pore structure, which can increase the amount of PDMS incorporated, allowing it to fully contact the absorbent material and increase the synergistic resonance effect of PDMS.
[0037] 4. The thickness of the metal thin film - grass-like alumina can be controlled and it can be directly prepared on the end face of the optical fiber, so it can be used in fiber-based ultrasonic transmitters, thus having the potential for further miniaturization. Attached Figure Description
[0038] Figure 1 This is a schematic diagram of a grass-like alumina thin film-based ultrasonic transducer.
[0039] Figure 2 This is a SEM microstructure image of a grass-like alumina film.
[0040] Figure 3 This is the spectral reflectance diagram obtained from the test in Example 1.
[0041] Figure 4 The image shows the ultrasonic pressure signal of 210nm GLA-110nmAu obtained from Example 1.
[0042] Figure 5 The image shows the ultrasonic pressure signal of 400nm GLA-180nm Au obtained from Example 1.
[0043] Figure 6 The image shows the spectrum of the ultrasonic signal obtained in Example 1.
[0044] Figure 1 In the diagram, 1 is a grass-like alumina film, 2 is a metal film, 3 is PDMS, and 4 is a glass substrate. Detailed Implementation
[0045] 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. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments.
[0046] Example 1
[0047] This invention discloses the structure and preparation method of a grass-like alumina-based photo-ultrasonic transducer. The structure is simple, and it generates high ultrasonic sound pressure, high frequency, and wide bandwidth.
[0048] This device is divided into a light absorption section and a thermal expansion section, such as Figure 1 As shown, the device consists of a polydimethylsiloxane (PDMS)-metal film-grass-like alumina (GLA) composite layer cured on a transparent glass substrate.
[0049] The light-absorbing portion is a metal thin film-GLA composite layer; the grass-like alumina thin film is a graded refractive index thin film, which is first prepared by atomic layer deposition and then subjected to water bath treatment to obtain the grass-like alumina thin film; the thickness and porosity of the grass-like alumina thin film are controlled by water bath time and temperature; the metal thin film is deposited in the pores of the grass-like alumina thin film;
[0050] The thermal expansion material is polydimethylsiloxane (PDMS), which fills the nanopores of the grass-like alumina.
[0051] The preparation methods for each part are as follows:
[0052] 1. Composition and fabrication process of the light-absorbing component
[0053] This section includes Figure 1 The grass-like alumina film (1) and the metal film (2) are shown in the figure.
[0054] S1. Alumina thin films were prepared using atomic layer deposition (ALD). The reaction chamber temperature for ALD was 300°C. In one cycle, the trimethylaluminum (TMA) pulse duration was 0.2 s, followed by N2 purging for 3 s and O3 purging for 3 s. 600 cycles were prepared. The resulting alumina thin film had a thickness of 72 nm.
[0055] S2, using a constant-temperature water bath, the alumina film prepared in step 1 is treated with water. Specifically, the alumina film on the prepared glass slide is placed in a constant-temperature water bath containing deionized water. The water bath temperature is approximately 90 degrees Celsius, and the bath time is 30 minutes. During the water bath, the sample is fixed with clamps to prevent movement due to water flow fluctuations, which could damage the microstructure. After boiling, the film sample is removed and immersed in ethanol to remove any residual water. The surface structure of the grass-like alumina film is as follows... Figure 2 As shown, the grass-like alumina film has a thickness of 400 nm.
[0056] S3, a gold film was grown on a grass-like alumina film obtained after a water bath by physical vapor deposition. The gold film deposition rate was 0.14 nm / s and the thickness of the deposited gold film was 180 nm.
[0057] 2. Preparation process of thermal expansion material
[0058] The thermal expansion material is prepared by mixing polydimethylsiloxane (PDMS) and a curing agent, and the preparation steps are as follows:
[0059] 1) Take 5g of Corning 184 polydimethylsiloxane and 0.5g of curing agent and add them to a small beaker; stir magnetically for 10 minutes to mix thoroughly; residual air will form bubbles in the solution; place the solution in a vacuum drying oven to remove air; remove it after the bubbles in the PDMS mixture have completely dissipated; spin-coat the PDMS mixture onto the metal film-grass-alumina film composite layer at a speed of 1000r / min; allow it to fully penetrate into the nanopores of the grass-alumina; thus obtaining the PDMS composite layer-metal film-grass-alumina.
[0060] 2) Place the PDMS composite layer-metal film-grass-alumina into an oven and heat it at 90℃ for 30 minutes. Then, vacuum heat curing is performed to solidify the PDMS within the nanopores of the metal film-grass-alumina, thus obtaining an ultrasonic transducer.
[0061] The cross-sectional structure of the fabricated ultrasonic transmitter device is as follows: Figure 1 As shown, it includes a grass-like alumina film (1), a metal film (2), polydimethylsiloxane (3), and a K9 glass substrate (4).
[0062] Performance testing:
[0063] The prepared photo-induced ultrasonic emitter was placed in a quartz water bath and irradiated with a nanosecond pulsed laser. The nanosecond pulsed laser had a wavelength of 532 nm, a pulse width of 10 ns, a repetition frequency of 100 Hz, and an incident spot diameter of approximately 10 mm. The ultrasonic signal was recorded using a hydrophone at a distance of 3 mm from the sample.
[0064] like Figure 3 As shown, the transducer has a light reflectance of about 20% in the wavelength range of 400-600nm, and its absorptivity is about 80% because the sample is opaque.
[0065] like Figure 4 As shown, for 210nm GLA-110nm Au, the transducer produces the maximum ultrasonic pressure signal of 1.02MPa under irradiation with 15MJ laser energy.
[0066] like Figure 5 and 6 As shown, for a 400nm GLA-180nm Au, under irradiation with 8MJ laser energy, the transducer obtains a sound pressure signal of 2.52MPa and a bandwidth of -6dB of 16MHz.
[0067] In summary, this invention provides a photoinduced ultrasonic transmitter and its fabrication method, which has a simple preparation process; it also provides a novel structure that generates a high-intensity ultrasonic signal when a pulsed laser is applied to the ultrasonic transmitter.
[0068] The above are merely embodiments of the present invention and do not limit the scope of the patent. Any equivalent modifications made based on the content of this specification, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.
Claims
1. A grass-like alumina-based photo-ultrasonic transducer, comprising: The device comprises a light-absorbing portion and a thermally expanding material; characterized in that the device consists of a polydimethylsiloxane (PDMS)-metal film-grass-alumina (GLA) composite layer cured on a transparent glass substrate; The light-absorbing portion is a metal thin film-GLA composite layer; the grass-like alumina thin film is a graded refractive index thin film, which is first prepared by atomic layer deposition and then treated with water bath to obtain the grass-like alumina thin film; the metal thin film is deposited in the pores of the grass-like alumina thin film; The thermal expansion material is polydimethylsiloxane (PDMS), which fills the nanopores of the grass-like alumina.
2. The grass-like alumina-based photo-ultrasonic transducer according to claim 1, characterized in that, The thickness of the alumina film is 20-80 nm.
3. The grass-like alumina-based photo-ultrasonic transducer according to claim 1, characterized in that, The thickness of the grass-like alumina film is 200-500 nm.
4. The grass-like alumina-based photo-ultrasonic transducer according to claim 1, characterized in that, The metal film is gold or silver; the thickness of the metal film is 100-190 nm.
5. The method for preparing the grass-like alumina-based photo-ultrasonic transducer according to any one of claims 1-4, characterized in that, The preparation method described above, Includes the following steps: S1, first prepare an alumina thin film using atomic layer deposition; S2, Alumina film is subjected to water bath treatment to obtain GLA film; S3, then a metal film is deposited on the prepared GLA film by physical vapor deposition to form a metal film-GLA composite layer; S4, then spin-coat a PDMS film onto the obtained metal film-GLA composite layer; to obtain a PDMS composite layer-metal film-grassy alumina; S5. The obtained PDMS composite layer-metal film-grass-alumina is placed in a vacuum drying oven and cured to obtain a photo-ultrasonic transducer.
6. The method for preparing the grass-like alumina-based photo-ultrasonic transducer according to claim 5, characterized in that, In step S1, the reaction chamber temperature for atomic layer deposition is 150-300℃, the trimethylaluminum TMA pulse time is 0.1-0.2s in one cycle, the N2 purge is 3-5s, the O3 purge is 3-5s, and the thickness of the prepared alumina film is 20-80nm.
7. The method for preparing the grass-like alumina-based photo-ultrasonic transducer according to claim 5, characterized in that, In step S2, the water bath treatment involves placing the alumina film prepared in step 1 in deionized water at 80-95°C for 10-40 minutes.
8. The method for preparing the grass-like alumina-based photo-ultrasonic transducer according to claim 5, characterized in that, In step S3, the deposition rate is 0.125-0.158 nm / s.
9. The method for preparing the grass-like alumina-based photo-ultrasonic transducer according to claim 5, characterized in that, In step S4, the specific process is as follows: PDMS and curing agent are mixed in a pre-defined mass ratio in a beaker and magnetically stirred. Residual air will form bubbles in the solution. The solution is placed in a vacuum drying oven and the air is vented. The solution is removed after the bubbles in the PDMS mixture have completely dissipated. The PDMS mixture is spin-coated onto the metal film-grass-like alumina film composite layer at a speed of 1000-1500 r / min, allowing it to fully penetrate into the nanopores of the grass-like alumina. The mass ratio of PDMS to curing agent is 10:
1.
10. The method for preparing the grass-like alumina-based photo-ultrasonic transducer according to claim 5, characterized in that, In step S5, the specific process is as follows: the PDMS composite layer-metal film-grass-alumina is placed in a vacuum drying oven, and then vacuum-heated to cure. The PDMS is cured in the nanopores of the metal film-grass-alumina to obtain an ultrasonic transducer; the transducer is heated in a vacuum drying environment at 70-90℃ for 20-180 minutes.