Microbubble high temporal-spatial resolution visualization platform and method in megasonic field

Abstract

The invention discloses a microbubble high temporal-spatial resolution visualization platform and method in a megasonic field. The present invention comprises: a container for containing a liquid; the megasonic standing wave generating device is used for forming a megasonic standing wave field so as to position a single microbubble at an antinode; the bubble generation device is used for locally generating the microbubbles in an antinode area of a megasonic standing wave field; the lighting device is used for lighting the microbubbles with nanosecond stroboscopic light; and the imaging device is used for acquiring an image of the illuminated microbubble by microsecond exposure. The microbubbles are fixed by applying sound standing waves, the situation that the microbubbles are moved out of a view field and cannot be observed for a long time is avoided, and the high spatial resolution of the platform is achieved. A nanosecond stroboscopic LED light source is also combined, so that inaccurate shot images caused by overlong exposure time of a high-speed camera are avoided, and high time resolution of the platform is realized.

Description

Technical Field

[0001] This invention relates to the field of mega-sound microbubble dynamics technology, specifically a platform and method for stabilizing a single microbubble in a mega-sound field using acoustic standing waves and achieving high spatiotemporal resolution observation of its oscillation behavior. It is suitable for the visualization study of microbubble oscillation behavior in a mega-sound field. Background Technology

[0002] The dynamic behavior of microbubbles in an ultrasonic field is a core issue in acoustic cavitation research. When sound waves act on a liquid, the microbubbles within it oscillate, grow, and collapse, a phenomenon with significant applications in numerous fields. In biomedicine, microbubbles can serve as ultrasound contrast agents, enhancing tissue imaging contrast; in targeted drug therapy, the collapse of microbubbles under ultrasound can promote drug release and cellular uptake; in tumor treatment, cavitation effects can induce cell membrane perforation or generate localized high temperatures for ablation of tumor tissue; in industry, the microjets and shock waves generated by cavitation microbubbles are crucial for ultrasonic cleaning, emulsification, and enhanced chemical reactions. However, accurately studying the tiny size and high-frequency dynamic behavior of mega-sonic microbubbles currently faces significant challenges.

[0003] Current technologies for observing microbubble cavitation behavior face two major challenges: First, microbubbles are extremely small, typically ranging from tens to hundreds of micrometers. To resolve the morphological details of micrometer-sized bubbles, a high-magnification microscopic optical system is required, which leads to a drastic reduction in the field of view. Microbubbles moving actively in a megahertz field can easily move out of this narrow field of view in a short time, making it difficult to acquire continuous and complete dynamic data. Second, the oscillation frequency of microbubbles in a megahertz field can reach the megahertz level. Currently, high-speed cameras used to observe ultrasonic cavitation phenomena cannot capture the complete single-cycle oscillation behavior of microbubbles in a megahertz field.

[0004] For microbubble generation and manipulation technology, laser-induced cavitation is a commonly used technique. It generates cavitation bubbles in liquids using pulsed lasers. However, the location of the microbubbles generated by this method is random, making it difficult to control and observe them precisely. Moreover, existing technologies mostly focus on the statistical behavior of microbubble swarms or the overall transient collapse event, lacking an effective means to observe individual microbubbles under stable conditions with high magnification and complete oscillation cycles.

[0005] Given the aforementioned limitations, it is necessary to develop a novel high spatiotemporal resolution visualization platform for microbubbles in mega-sound fields to improve the stability and accuracy of the observation process. Summary of the Invention

[0006] To address the problem of unstable position and extremely short cavitation period of single microbubbles under mega-sound conditions in existing experimental setups, this invention proposes a single microbubble cavitation observation platform and method based on acoustic standing waves. Since microbubbles experience primary radiative forces that cause them to migrate towards antinodes in an acoustic standing wave field with a frequency lower than the microbubble's resonant frequency, the microbubble can be fixed at the antinode. Combined with high-frequency light pulse illumination and high-speed imaging, high-resolution visualization of single microbubble cavitation phenomena in a mega-sound field can be achieved.

[0007] A high spatiotemporal resolution visualization platform for microbubbles in a megasonite field according to the present invention includes:

[0008] A container used to hold liquids;

[0009] A megasonic standing wave generator is used to form a megasonic standing wave field with a frequency of 1–5 MHz in the liquid to position a single microbubble at the antinode.

[0010] A bubble generating device for locally generating the microbubbles in the antinode region of the megason standing wave field;

[0011] An illumination device for illuminating the microbubbles with nanosecond-level stroboscopic light;

[0012] An imaging device for acquiring images of the illuminated microbubbles at microsecond-level exposures;

[0013] A synchronous triggering device is used to synchronously control the bubble generating device, the lighting device, and the imaging device to achieve high spatiotemporal resolution observation of the microbubbles in a megasonite field.

[0014] The present invention discloses a high spatiotemporal resolution visualization method for microbubbles in a megasonite field, employing the aforementioned platform. The method includes the following steps:

[0015] Step a) Establish a megason standing wave field with a frequency of 1–5 MHz in the container liquid, so that individual microbubbles are captured by acoustic radiation force and located at the antinodes of the standing wave.

[0016] Step b) Inducing the generation of the microbubbles at the antinodes using a pulsed laser;

[0017] Step c) Illuminate the microbubble with nanosecond-level stroboscopic light and continuously image the microbubble with microsecond-level exposure and a frame rate of ≥300,000 fps;

[0018] Step d) Synchronously trigger the pulsed laser, pulsed light, and imaging to obtain a high spatiotemporal resolution oscillation image of microbubbles in a megaacoustic field.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) The present invention fixes the microbubbles by applying acoustic standing waves, preventing them from moving out of the field of view and thus making it impossible to observe them for a long time, thereby achieving high spatial resolution of the platform.

[0021] (2) The present invention combines a nanosecond-level strobe LED light source to avoid inaccurate images caused by excessive exposure time of high-speed cameras, thereby achieving high temporal resolution of the platform.

[0022] (3) The present invention utilizes highly repeatable experimental data to superimpose images within multiple acoustic cycles and reconstruct the dynamic behavior of bubbles within a single cycle by using a periodic reconstruction method, thus solving the problem that high-speed cameras with low frame rates cannot observe the single-cycle oscillation behavior of microbubbles in mega-sound fields. Attached Figure Description

[0023] Figure 1 Schematic diagram of a high spatiotemporal resolution visualization platform for microbubbles in a mega-sound field;

[0024] Figure 2 Schematic diagram of microbubbles in a megason standing wave field;

[0025] Figure 3 Schematic diagram of the radius curve of microbubble oscillation period reconstruction;

[0026] Figure 4 Schematic diagram of microbubble oscillation timing;

[0027] Figure 5 Schematic diagram of PIV results superimposed on the flow field around the microbubble. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and examples.

[0029] like Figure 1 As shown in the figure, this application provides a high spatiotemporal resolution visualization platform for microbubbles in a megahertz field, including an experimental water tank, a signal generator, a high voltage amplifier, a piezoelectric transducer, an oscilloscope, a pulsed laser, a sheet laser, an LED light source, a high-speed camera, and a trigger.

[0030] The experimental water tank is used to contain experimental liquids and provide a stable environment in which megasonic waves propagate and generate microbubbles.

[0031] A signal generator is used to generate sinusoidal electrical signals of a specific frequency, with a frequency range of 1–5 MHz and a sound pressure amplitude of 10–100 kPa.

[0032] A high-voltage amplifier is used to amplify the weak electrical signal from the signal generator, thereby driving the piezoelectric transducer to generate a megasonic wave of sufficient intensity, while ensuring that the signal intensity reaches the range that the oscilloscope can accurately measure and display, and then transmitting the amplified electrical signal to the oscilloscope.

[0033] Piezoelectric transducers are used to convert electrical signals from high-voltage amplifiers into mechanical vibrations, thereby generating megasonic waves in experimental media to drive and manipulate microbubbles.

[0034] An oscilloscope is used to monitor the waveform of the electrical signal transmitted by a high-voltage amplifier.

[0035] Pulsed lasers are used to precisely generate microbubbles. High-energy laser pulses are focused onto a tiny point in a liquid through a lens, instantly ionizing the liquid to form plasma and generating micron-sized cavitation bubbles.

[0036] A sheet laser is used to illuminate tracer particles incorporated into an experimental liquid medium.

[0037] An LED light source is used to provide a 10-nanosecond stroboscopic flash for bright-field shadow imaging of bubbles, so that the temporal resolution of the experiment is determined by the light pulse rather than the camera exposure time, resulting in clearer and higher-contrast bubble shadow images.

[0038] A high-speed camera is used to capture images of microbubbles inside a water tank from the outside, with a frame rate of 300,000 frames per second and an exposure time of 1 microsecond.

[0039] The trigger is used to precisely trigger the pulsed laser, high-speed camera and LED light source separately, control the pulsed laser to emit laser light to create microbubbles in the megasonic standing wave field, and trigger the high-speed camera and LED light source to capture images of the microbubbles.

[0040] The pulsed laser is located on one side of the experimental water tank, the high-speed camera is located on one side of the experimental water tank, the LED light source is located on one side of the experimental water tank, the sheet laser is located on one side of the experimental water tank, and the piezoelectric transducer is located at the bottom of the experimental water tank.

[0041] The trigger is connected to the pulsed laser, the high-speed camera, and the LED light source respectively; the signal generator is connected to the high-voltage amplifier and the oscilloscope; and the high-voltage amplifier is connected to the piezoelectric transducer.

[0042] Example 1: A method for observing and analyzing the oscillation radius and modes of microbubbles using the above platform:

[0043] A piezoelectric transducer was fixed to the bottom of the experimental water tank. The electrical signal output from the signal generator was amplified by a high-voltage amplifier to drive the piezoelectric transducer to generate an upward megasonic wave with a frequency of 1MHz and an amplitude of 50kPa. When the upward megasonic wave propagated to the surface of the liquid in the experimental water tank, due to the large difference in acoustic impedance between the gas and the liquid, the megasonic wave was almost completely reflected, forming a downward reflected wave. The two interfered with each other to form a stable megasonic standing wave field in the liquid medium, producing periodically arranged antinodes and nodes. At the same time, an oscilloscope was used to monitor the electrical signal input to the piezoelectric transducer to ensure the accuracy and stability of the input megasonic signal.

[0044] The hydrophone was moved inside the experimental water tank to obtain data and determine the sound pressure distribution of the megason standing wave field. Let λ be the wavelength of the sound wave. It was confirmed that the antinodes were located approximately λ / 4 below the liquid surface. The positions and sound pressure distribution of the microbubbles in the megason standing wave field are as follows: Figure 2 As shown.

[0045] A pulsed laser is triggered by a trigger to emit a pulsed laser near the antinode of a megason standing wave field. The pulsed laser is focused into the experimental water tank through an optical path system. The residual gas generated by laser-induced cavitation migrates and converges in the megason standing wave field due to the action of acoustic radiation force, generating a stable microbubble with a radius of about 5 μm.

[0046] A trigger is used to activate an LED light source to emit a stroboscopic flash with an exposure time of 10 ns, simultaneously triggering a high-speed camera to... ( ) frame rate shooting continuous shooting The total acquisition time was approximately 3.344 ms, covering approximately 3344 oscillation cycles. The high-speed camera was gradually increased from an initial magnification of 1.4x to 20x to display complete and clear microbubble images. However, since the camera sampling frequency was much lower than the microbubble oscillation frequency, direct sampling could not distinguish the details within a single cycle, which was a serious undersampling problem. Therefore, the acquired microbubble images were reconstructed periodically over time.

[0047] Furthermore, the core of the reconstruction lies in utilizing the high repeatability of bubble oscillations to piece together a high-resolution curve for a single cycle from low-resolution data points collected over multiple cycles through phase calculation and alignment. The key point is the camera sampling interval. With bubble cycle The ratio should be non-integer to ensure the bubble is in a different phase for each frame. The phase calculation formula is:

[0048]

[0049] in It is a frame index. It is the first The phase corresponding to the frame.

[0050] target period Divided into Each phase box represents a phase box. The time resolution is used to divide all frames according to their phase. Assign the data to the corresponding bins, and average the bubble radius data within each bin:

[0051]

[0052] The final result is a single-cycle bubble oscillation curve consisting of 125 data points with a time resolution of 8 ns, as shown below. Figure 3 As shown in the figure, the collected microbubble oscillation time sequence diagram is as follows. Figure 4 As shown.

[0053] Example 2: Method for observing and analyzing the flow field around microbubbles using a platform:

[0054] Fluorescent tracer particles with a concentration of 0.01%–0.02% and a diameter of approximately 1 μm were added to the liquid in the experimental tank. The procedure in Example 1 was repeated, and the sheet laser was turned on. The optical path was adjusted to ensure that the light precisely cut through the center of the microbubble stabilized by the acoustic standing wave, illuminating the fluorescent tracer particles. A bandpass filter matching the light excited by the fluorescent particles was installed in front of a high-speed camera to effectively block stray light and receive only the fluorescence signal from the particles, thus obtaining a high signal-to-noise ratio image. The motion of the particles surrounding the microbubble was recorded using the high-speed camera, and the velocity distribution of the flow field around the microbubble was calculated using software analysis.

[0055] Furthermore, all timing sequences are uniformly triggered by a trigger to ensure that the sheet laser emits high-frequency laser pulses, while simultaneously and strictly synchronizing the high-speed camera to perform exposure at each laser pulse moment.

[0056] Furthermore, the acquired particle images are imported into software for processing. The laser pulse time interval is known. The instantaneous velocity vector of each region is calculated, and finally generated as follows: Figure 5 The PIV flow field calculation results shown are an instantaneous velocity vector diagram covering the space around the bubble.

[0057] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0058] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments, including components, without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A high spatiotemporal resolution visualization platform for microbubbles in a megasonite acoustic field, characterized in that, include: A container used to hold liquids; A megasonic standing wave generator is used to form a megasonic standing wave field with a frequency of 1–5 MHz in the liquid to position a single microbubble at the antinode. A bubble generating device for locally generating the microbubbles in the antinode region of the megason standing wave field; An illumination device for illuminating the microbubbles with nanosecond-level stroboscopic light; An imaging device for acquiring images of the illuminated microbubbles at microsecond-level exposures; A synchronous triggering device is used to synchronously control the bubble generating device, the lighting device, and the imaging device to achieve high spatiotemporal resolution observation of the microbubbles in a megasonite field.

2. The high spatiotemporal resolution visualization platform for microbubbles in a megasonographic field according to claim 1, characterized in that, The megasonic standing wave generator includes a piezoelectric transducer fixed to the bottom of the container and a signal generator and a high-voltage amplifier connected thereto, used to generate a megasonic standing wave field with a frequency of 1–5 MHz and a sound pressure of 10–100 kPa.

3. A high spatiotemporal resolution visualization platform for microbubbles in a megasonographic field according to claim 1 or 2, characterized in that, The illumination device is an LED light source that can emit 10 ns-level stroboscopic flashes, and its flash timing is controlled by a synchronous triggering device. The imaging device is a high-speed camera with a frame rate of ≥300,000 fps and an exposure time of ≤1 µs, and is equipped with a microscope objective that can be enlarged to 20×.

4. The high spatiotemporal resolution visualization platform for microbubbles in a megasonographic field according to claim 3, characterized in that, It also includes a sheet laser device and fluorescent tracer particles, used to illuminate the surrounding flow field after the microbubble is positioned, and to acquire particle images through an imaging device to calculate the velocity vector field.

5. A method for high spatiotemporal resolution visualization of microbubbles in a megasonite field, using the platform described in any one of claims 1-4, characterized in that, The method includes the following steps: Step a) Establish a megason standing wave field with a frequency of 1–5 MHz in the container liquid, so that individual microbubbles are captured by acoustic radiation force and located at the antinodes of the standing wave. Step b) Inducing the generation of the microbubbles at the antinodes using a pulsed laser; Step c) Illuminate the microbubble with nanosecond-level stroboscopic light and continuously image the microbubble with microsecond-level exposure and a frame rate of ≥300,000 fps; Step d) Synchronously trigger the pulsed laser, pulsed light, and imaging to obtain a high spatiotemporal resolution oscillation image of microbubbles in a megaacoustic field.

6. The method for high spatiotemporal resolution visualization of microbubbles in a megasonite field according to claim 5, characterized in that, Step a) Generates an upward megasonic wave by using a piezoelectric transducer fixed to the bottom of the container, and uses the reflection from the liquid surface to form a standing wave field.

7. The method for high spatiotemporal resolution visualization of microbubbles in a megasonite field according to claim 5, characterized in that, Step d) First, a laser is generated by triggering a trigger, and then the LED strobe light and high-speed camera are triggered synchronously to capture bubble images within a single trigger cycle.

8. A method for high spatiotemporal resolution visualization of microbubbles in a megasonite field according to any one of claims 5 to 7, characterized in that, It also includes: step e) reconstructing the acquired multi-frame low-sampling images by phase and stitching them together to form a bubble oscillation curve with 125 phase points and an equivalent time resolution of 8 ns within a single period.

9. The method for high spatiotemporal resolution visualization of microbubbles in a megasonite field according to claim 8, characterized in that, Step e) Reconstruct the single-cycle oscillation curve as follows: Calculate the phase of the M frames of images acquired by the high-speed camera within the total sampling time M·Δt, according to the frame number m: in The camera sampling interval, This is the bubble oscillation period; The bubble oscillation period is divided into N = 125 phase boxes, each with a width of 8 ns; The bubble radius measured in each frame is arranged according to The corresponding phase boxes were inserted and averaged to obtain 125 data points, which were then stitched together to form a single-cycle radius-time curve with a time resolution of 8 ns.

10. A method for high spatiotemporal resolution visualization of microbubbles in a megasonite field according to any one of claims 5 to 7, characterized in that, It also includes: step f) adding fluorescent tracer particles to the liquid, illuminating the particles with a sheet laser and imaging them simultaneously, and obtaining the velocity distribution of the flow field around the microbubble using the PIV algorithm.

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