CN114642448A

CN114642448A - Photoinduced ultrasonic transmitter and manufacturing method thereof

Info

Publication number: CN114642448A
Application number: CN202210287845.8A
Authority: CN
Inventors: 胡二涛; 林一波; 韦玮; 余柯涵; 王静; 王博永; 丁建永
Original assignee: Nanjing University of Posts and Telecommunications
Current assignee: Nanjing University of Posts and Telecommunications
Priority date: 2022-03-23
Filing date: 2022-03-23
Publication date: 2022-06-21

Abstract

The invention discloses a photoinduced ultrasonic transmitter and a manufacturing method thereof, wherein the photoinduced ultrasonic transmitter comprises a metal nanoparticle-porous alumina array composite layer for absorbing incident light and converting the incident light into heat, and polydimethylsiloxane serving as a thermal expansion material is filled in nano holes of an alumina array for absorbing the heat and emitting ultrasonic waves through a thermoelastic effect. The substrate is a glass substrate, and the device generates an ultrasonic signal under the action of pulse laser by utilizing a photoinduced ultrasonic principle. The method has simple process, and the generated ultrasound has the characteristics of high intensity, high frequency and wide frequency band.

Description

Photoinduced ultrasonic transmitter and manufacturing method thereof

Technical Field

The invention relates to the technical field of ultrasound, in particular to a photoinduced ultrasonic transmitter and a manufacturing method thereof.

Background

Ultrasound transmitters have wide application in the fields of ultrasound diagnosis and medical imaging. The traditional ultrasonic sound source is a piezoelectric ultrasonic transducer, and has the defects of large volume, low frequency, high driving voltage, easy electromagnetic interference, large volume of a sound wave focusing point and the like. With the continuous development of science and technology, researchers put forward the concept of photoinduced ultrasound, and the generated ultrasonic waves have the characteristics of high intensity, high frequency, wide frequency band and the like, are not interfered by electromagnetism, and have the advantage of miniaturization. The ultrasonic transmitter prepared by utilizing the photoinduced ultrasonic effect can be used in the medical fields of ultrasonic minimally invasive surgery, thrombolysis, directional administration, microinjection and the like.

The photo-induced ultrasound transmitter is generally composed of a light absorbing material and a thermally expansive material. Commonly used absorbing materials include carbon-based materials such as carbon black, carbon nanotubes, candle soot particles, etc., and the thermally expandable material is Polydimethylsiloxane (PDMS). Incident light is absorbed by the absorbing material, and the generated heat is conducted to the PDMS to generate ultrasound by using the thermoelastic effect. However, in most of the photoinduced ultrasonic emission devices, the light absorption material and the thermoelastic material are mixed in a disordered manner, so that heat is conducted randomly in a disordered manner, and the ultrasonic direction is dispersed and the intensity is reduced. Therefore, it is an urgent technical problem to prepare an ultrasonic transmitter with a novel structure to improve the ultrasonic intensity, bandwidth and photothermal conversion efficiency.

Disclosure of Invention

In order to solve the above problems, the present invention provides a photoinduced ultrasonic transmitter and a manufacturing method thereof, wherein the photoinduced ultrasonic transmitter is an ultrasonic transmitter based on self-assembled metal nanoparticles-porous anodic alumina array-PDMS.

In a first aspect, the present invention provides a photoinduced ultrasonic transmitter comprising a transparent glass substrate, a light absorbing portion and a thermal expansion material, the light absorbing portion comprising: porous alumina arrays, metal films and metal nanoparticles; the light absorption part is referred to as a metal nanoparticle-porous alumina array for short, the porous alumina array is a symmetrical bi-pass AAO (anodic Aluminum oxide) nano template, and the porous alumina array is provided with uniformly distributed nano holes;

the metal film is a film layer deposited on the surface of the porous alumina array, and the thickness of the metal film is 50-120 nm; the metal nano particles are adsorbed on the nano hole walls of the porous alumina array, and the size range of the grain diameter is 10-25 nm; the thermal expansion material is Polydimethylsiloxane (PDMS), and is filled in the nano holes.

Preferably, the material of the metal thin film and the metal nanoparticles is selected from aluminum or silver.

Preferably, the center distance of the pores of the porous alumina array is 450nm, and the pore size is 250-350 nm; further preferably, the anodized aluminum oxide has a thickness of 60 μm.

The incident laser pulse is absorbed by the metal nanoparticle-porous alumina array-PDMS composite layer of the photoinduced ultrasonic transmitter and then converted into heat, and then the thermoelastic effect is utilized to generate ultrasound.

Belonging to a second aspect of the same inventive concept, the invention provides a method for manufacturing a photoinduced ultrasonic transmitter, comprising the following steps:

step S1, growing a metal film on the surface of the bi-pass porous anodic aluminum oxide by using a physical vapor deposition method, and depositing metal nano particles in the holes;

step S2, mixing PDMS and a curing agent in a preset mass ratio in a beaker, soaking the prepared metal nanoparticle-porous alumina array composite layer in Polydimethylsiloxane (PDMS) solution, and magnetically stirring for a preset time; standing the beaker, wherein air remained in the holes can form bubbles in the solution, and taking out the beaker after the bubbles in the polydimethylsiloxane mixed solution are completely dissipated;

step S3, soaking the prepared metal nanoparticle-porous alumina array composite layer in PDMS mixed solution to ensure that the PDMS mixed solution is fully soaked in the nanopores of the porous alumina array; taking out the metal nanoparticle-porous alumina array-PDMS composite layer, and placing the metal nanoparticle-porous alumina array-PDMS composite layer on a transparent glass substrate;

and step S4, putting the glass sheet and the metal nanoparticle-porous alumina array-PDMS composite layer into a vacuum drying oven, vacuumizing, heating and curing, and curing PDMS in the nanopores of the metal nanoparticle-porous alumina array to obtain the ultrasonic emitter.

Preferably, in step S1, the thickness of the metal film is 50-120nm, excessive thickness or thickness of the metal film may cause hole blocking and light absorption reduction, and when the metal film is an aluminum film, the deposition rate of the aluminum film is optimally 0.05nm/S, and the deposition time is controlled to be 1000S-2400S, wherein the deposition time is optimally 2000S.

Preferably, in step S2, the stirring time is 1-30 min.

Preferably, in step S4, the vacuum heating time is 5-100min, and the heating temperature is 60-120 ℃.

The invention has the beneficial effects that: 1. in the invention, the thickness of the metal film and the deposition depth, quantity and diameter of the metal nanoparticles in the pores can be controlled by controlling the growth rate and time of physical vapor deposition, so that the prepared metal nanoparticle-porous alumina array has high light absorption coefficient, and the pore blockage and light absorption reduction can be caused by over-thick or over-thin metal film; 2. the light absorption of the device is mainly concentrated on metal nanoparticles in the alumina nano-pores, and the metal nanoparticles are adsorbed on the walls of the nano-pores, so that the heat conduction capability of the metal is greater than that of the alumina, and the heat conduction is mainly along the direction of the walls of the nano-pores, so that the device has the anisotropic heat conduction characteristic. The orderly conduction of heat enables the thermo-elastic material to expand and contract only along the axial direction, so that the photoacoustic conversion efficiency of the ultrasonic emitter can be effectively improved; 3. the prepared ultrasonic transmitter has the metal nanoparticle-porous alumina array with the thickness of 50-70 μm, and the cross section of the array can be cut into the size similar to the diameter of a multimode optical fiber by laser, so that the array can be used for the optical fiber-based ultrasonic transmitter, and has the potential of further miniaturization.

Drawings

FIG. 1a is a schematic structural diagram of a metal nanoparticle-porous alumina array according to the present invention;

FIG. 1b is a schematic cross-sectional view of a photoinduced ultrasonic transmitter according to the present invention;

FIG. 2 is a spectrum absorption diagram of an aluminum nanoparticle-porous alumina array in an embodiment of the present invention.

FIG. 3 is a graph of ultrasonic signals obtained from testing of an embodiment of the present invention;

FIG. 4 is a graph of the frequency spectrum of an ultrasonic signal obtained from testing of an embodiment of the present invention;

wherein, 1 is a metal film, 2 is a porous alumina array, 3 is a metal nanoparticle, 4 is polydimethylsiloxane, 5 is a metal nanoparticle-porous alumina array, and 6 is a transparent glass substrate.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further 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.

Example 1

The device has small volume, simple structure, large generated ultrasonic sound pressure, high frequency, wide frequency band and small divergence angle. The device is divided into a light absorbing part and a thermal expansion part.

Light absorbing portion composition and fabrication process

As shown in FIG. 1a, the light absorbing part of the device, namely the metal nanoparticle-porous alumina array 5, comprises a metal film 1, a symmetric bi-pass AAO nano template 2 of model DP450-300S-50000 and metal nanoparticles 3, wherein the porous alumina array is produced by a Shenzhen topological fine film.

The preparation method comprises the following steps: an aluminum film grows on the surface of the porous anodic aluminum oxide by a physical vapor deposition method, and aluminum nano particles are deposited in the pores, wherein the thickness of the anodic aluminum oxide is 60 micrometers, the pore diameter is 300nm, the pore center distance is 450nm, the deposition rate of the aluminum film is 0.05nm/s, and the thickness of the aluminum film reaches 100nm after 2000s of deposition.

The spectral absorption range of the aluminum nanoparticle-alumina array 5 tested using an integrating sphere is shown in fig. 2.

Partial deployment of thermal expansion material

The thermal expansion material is prepared by mixing polydimethylsiloxane and a curing agent, and the preparation steps are as follows:

mixing 5g of polydimethylsiloxane and 0.5g of curing agent Dow Corning 184 into a small beaker; stirring for 3min by magnetic force to mix thoroughly; the beaker was left to stand until its bubbles dissipated.

Ultrasonic transmitter device fabrication process

The schematic cross-sectional structure of the prepared ultrasonic transmitter device is shown in fig. 1b, and comprises polydimethylsiloxane (4), an aluminum nanoparticle-porous alumina array 5 and a transparent glass substrate 6, in the specific embodiment, a K9 glass sheet is used, and the preparation steps are as follows:

1) soaking the aluminum nano-particle-porous alumina array in a polydimethylsiloxane mixed solution;

2) after the bubbles in the mixed solution are completely dissipated, taking out the aluminum nanoparticle-porous alumina array-PDMS composite layer;

3) and placing the soaked aluminum nanoparticle-porous alumina array-PDMS composite layer on K9 glass, and heating at 90 ℃ for 30 min.

Ultrasonic transmitter apparatus ultrasonic test procedure and results

The prepared photoinduced ultrasonic transmitter is placed in a quartz water tank filled with water, nanosecond pulse laser is used for irradiation, the specific nanosecond pulse laser wavelength is set to be 532nm, the pulse width is 10 nanoseconds, the repetition frequency is 100Hz, and a hydrophone is used for recording ultrasonic signals at a position 3 mm away from a sample.

As shown in FIGS. 3 and 4, at 1.13mj/cm²Under the irradiation of laser with energy density, the sound intensity of 23.7MPa and the frequency bandwidth of-6 dB of 24MHz are obtained.

The invention provides a photoinduced ultrasonic transmitter and a manufacturing method thereof, and the manufacturing process is simple; by utilizing the photoinduced ultrasonic effect, a novel structure is provided, and the structure has anisotropic heat conduction characteristics. When the pulse laser acts on the ultrasonic transmitter, a high-intensity ultrasonic signal is generated.

Claims

1. A photoinduced ultrasonic transmitter comprising a transparent glass substrate, a light absorbing part and a thermal expansion material, characterized in that the light absorbing part comprises: porous alumina arrays, metal films and metal nanoparticles; the metal film is a film layer deposited on the surface of the porous alumina array, and the thickness of the metal film is 50-120 nm; the metal nano particles are adsorbed on the nano hole walls of the porous alumina array, and the size range of the grain diameter is 10-25 nm; the thermal expansion material is Polydimethylsiloxane (PDMS), and the thermal expansion material is filled in the nano holes.

2. The photoinduced ultrasonic transmitter according to claim 1, wherein the material of the metal thin film and the metal nanoparticles is aluminum or silver.

3. The photo-induced ultrasonic transmitter of claim 1, wherein the porous alumina array has a hole center-to-center spacing of 450nm and a hole size of 250-350 nm.

4. The photo-induced ultrasound transducer of claim 1, wherein the anodized aluminum oxide is 60 μm thick.

5. A method for manufacturing a photoinduced ultrasonic transmitter is characterized by comprising the following steps: depositing a metal film on the bi-pass porous anodic aluminum oxide array by using a magnetron sputtering instrument, and depositing metal nano particles in the nano holes in a self-assembly manner, thereby forming a metal nano particle-porous aluminum oxide array composite layer; soaking the prepared metal nanoparticle-porous alumina array composite layer in a PDMS solution, stirring, standing, taking out after the solution is fully soaked in the nanopores of the porous alumina, and placing on a glass substrate; and (3) putting the glass-based metal nanoparticle-porous alumina array-PDMS composite layer into a vacuum drying oven, and curing to obtain the photoinduced ultrasonic transmitter.

6. The method of claim 5, wherein the metal film is an aluminum film, and the deposition rate of the aluminum film is 0.05nm/s and the deposition time is 1000s to 2400 s.

7. The method of claim 6, wherein the metal film is deposited for 2000 s.

8. The method of claim 5, wherein the stirring time is 1-30 min.

9. The method for manufacturing a photoinduced ultrasonic transmitter, according to claim 5, wherein the vacuum drying time is 5-100min, and the drying temperature is 60-120 ℃.