Acoustic metasurface designing and processing method, needle-shaped focusing acoustic beam imaging probe, method and system

Abstract

The invention relates to an acoustic metasurface designing and processing method, a needle-shaped focusing acoustic beam imaging probe, a method and a system, and belongs to the field of ultrasonic medical treatment. Plane ultrasonic waves are focused into needle-shaped focusing sound beams through the metasurface, imaging is carried out in a linear scanning mode, rapid ultrasonic imaging can be achieved while the imaging precision is guaranteed, and therefore the problem that in the prior art, the imaging quality and the imaging speed cannot be considered at the same time in the ultrasonic imaging technology is solved. According to the needle-shaped focusing acoustic beam imaging system of the acoustic metasurface, through real-time data interaction among the mechanical scanning system, the transmitting circuit and the beam forming system, low-cost rapid ultrasonic imaging can be achieved, and the imaging quality is higher.

Description

Technical Field

[0001] This invention relates to the field of ultrasound medical devices, specifically to a method for designing and fabricating an acoustic metasurface, a needle-shaped focused acoustic beam imaging probe, and a method and system thereof. Background Technology

[0002] Currently, ultrasound imaging methods mainly include plane wave imaging and focused imaging. Plane wave imaging involves the entire array transmitting and receiving plane waves, which can quickly obtain large-area ultrasound images. However, the weak echo signal results in a low signal-to-noise ratio, making it difficult to obtain clear images. Focused imaging uses delay control during transmission to focus ultrasound waves at a specific point or along a line, scanning point by point to construct the image. This can obtain strong echo signals and high image quality, but it requires scanning the entire imaging area at each focal point, resulting in a slower imaging speed. Furthermore, both methods require complex signal processing and computation systems, placing high demands on hardware. Therefore, current ultrasound imaging systems face the challenge of simultaneously achieving both high imaging speed and high image quality.

[0003] To improve the speed and quality of ultrasound imaging, Chinese invention patent CN120549536A discloses a method using deep learning to reconstruct ultrasound images from a trained ultrasound localization network, resulting in high-resolution ultrasound images. However, this method is only applicable to specific scenarios and requires retraining for new applications, limiting its widespread use. Chinese invention patent CN119745426A discloses a method for achieving rapid ultrasound imaging through the design of a torsional ultrasound transducer unit and parallel data interaction, improving imaging speed at the hardware level. However, achieving the torsion of the transducer unit requires a sophisticated mechanical structure, increasing equipment cost and limiting its application scope. US patent US6551246 discloses a method using transmitted plane waves at different angles to receive the phase of reflected signals, then recombining different images into a final image. This method, which improves image quality by reducing the frame rate, does not fundamentally resolve the inherent contradiction between imaging speed and image quality in current ultrasound imaging systems. Summary of the Invention

[0004] The problem to be solved by this invention is to overcome the difficulty of balancing imaging quality and imaging speed in existing ultrasound imaging technology. It proposes an ultrasound imaging method and device based on an ultrasound needle-shaped focused sound beam. By focusing planar ultrasound waves into a needle-shaped focused sound beam through a metasurface, imaging is performed in a linear scanning manner, which can achieve rapid ultrasound imaging while ensuring imaging accuracy.

[0005] According to a first aspect of the present invention, a method for designing an acoustic metasurface for generating a needle-shaped focused sound beam is provided, comprising the following steps: (1) Divide the metasurface into multiple units of the same size, and divide them into M groups according to the number of focal points required to form the sound beam. Each group of units is responsible for the shaping of one focal point, and each unit is randomly distributed on the metasurface; or divide the metasurface into multiple groups of the same size, each group has M units, each unit in each group represents a metasurface unit corresponding to a focal point, and each unit is randomly distributed in its group; the needle-shaped focused sound beam is formed by axially arranging multiple focal points to obtain the metasurface phase of the needle-shaped focused sound beam. (2) Calculate the number of focal points required to form the sound beam based on the desired imaging depth to determine the sound beam length; (3) The spacing between each focus is adjusted by the axial sound intensity of the sound beam. If the sound pressure between two focus points is greater than the average sound intensity of the entire sound beam, the spacing between the two focus points is increased, and vice versa. Finally, after multiple iterations, an acoustic metasurface is obtained that can focus plane sound waves into an ultrasonic needle-shaped focused sound beam with uniform axial intensity.

[0006] Preferably, in step (1), the metasurface phase of the needle-shaped focused acoustic beam is represented as: ,in: m As the focus number, For the first m Phase adjustment coefficient corresponding to each focal point , For the metasurface coordinates, For the first m The focal length of each focal point For the first m Each focal point corresponds to a random 0-1 matrix, meaning the values ​​in the matrix are either 0 or 1, and these values ​​are randomly distributed throughout the matrix. For plane wave focusing as the focal point The phase to be modulated is obtained by... Perform calculations, where The refractive index of metasurface materials in the human body, This refers to the wavelength of ultrasound waves in the human body. In step (2), the focal distance is expressed as ,in m As the number of focal points, d For the required sound beam length, RL Let be the Rayleigh length of the sound beam at the focal point.

[0007] Preferably, by adjusting the phase adjustment coefficient Pa This allows for adjustment of the thickness of the focused ultrasound beam. Pa The value range is between 0.2 and 0.8 pi; as... Pa As the focusing beam increases, the beam also becomes thicker, resulting in a larger imaging area for a single transmission and reception.

[0008] Preferably, the random 0-1 matrix is ​​specifically configured such that the metasurface units corresponding to each group of foci are arranged on the entire metasurface according to different random allocation methods to reduce the influence of higher-order diffraction. The size of the random 0-1 matrix is ​​equal to the number of metasurface units, and the number of array elements with a value of 1 is the number of units corresponding to a single group of foci, and they are randomly distributed throughout the matrix.

[0009] According to another aspect of the invention, an acoustic metasurface for generating needle-shaped focused sound beams is provided, obtained by a design method.

[0010] According to another aspect of the present invention, a method for fabricating the acoustic metasurface for generating a needle-shaped focused sound beam is provided, characterized by comprising the following steps: (1) Metasurfaces modulate the phase of plane waves through different thicknesses. The method for calculating the thickness of each unit of the metasurface is as follows: ,in For metasurface Height at the unit The phase modulation required to form a needle-shaped focused acoustic beam on the metasurface. The refractive index of metasurface materials in the human body, This refers to the wavelength of ultrasound waves in the human body. (2) After calculating the thickness of each unit of the metasurface, the metasurface is processed by a combination of precision 3D printing and casting. Specifically, the obtained metasurface model data is processed in 3D modeling software to construct a 3D model of the mold and leave a pouring port. The mold is printed by a precision 3D printer. The mold is combined with and fixed to the ultrasonic array. After injecting the metasurface material through the pouring port, the entire mold is vacuum treated to remove air bubbles. Then, it is heated to accelerate the curing speed and demolded to obtain the acoustic metasurface used to generate needle-shaped focused sound beams. Preferably, the metasurface material is polydimethylsiloxane or silicone rubber.

[0011] According to another aspect of the present invention, an acoustic metasurface for generating needle-shaped focused sound beams is provided, obtained by the aforementioned processing method.

[0012] According to another aspect of the present invention, a needle-shaped focused acoustic beam imaging probe based on an ultrasonic metasurface is provided, including the aforementioned acoustic metasurface for generating a needle-shaped focused acoustic beam, and further including an ultrasonic transmitting array and an ultrasonic receiving array. The ultrasonic receiver array is used to arrange ultrasonic transducers on the probe. The ultrasonic transmitting array emits either a closely spaced array of transducers or a piezoelectric crystal the size of a probe. The acoustic metasurface used to generate the needle-shaped focused sound beam has the same shape as the ultrasonic transmitting array and is fixed on the ultrasonic transmitting array. The acoustic metasurface used to generate the needle-shaped focused sound beam is used to focus the planar ultrasonic waves emitted by the transmitting array into a needle-shaped focused sound beam.

[0013] According to another aspect of the present invention, a method for performing ultrasonic metasurface needle-focused acoustic beam imaging using the aforementioned needle-shaped focused acoustic beam imaging probe is provided, characterized by comprising the following steps: (1) Range compensation of the sound beam is performed by adding a compensation coefficient k to the single-focus focusing algorithm. The range compensation for each imaging point is expressed as follows: , ,in: x i and y i These are the x and y coordinates of the imaging point, respectively. x m The x-coordinate of the transmitting element; (2) During the imaging process, the ultrasound probe performs planar scanning at the target position along with the mechanical scanning system. Each scan involves transmitting and receiving ultrasound, and a linear imaging area is formed according to the distance compensation in step (1), ultimately realizing a planar ultrasound image.

[0014] According to another aspect of the present invention, a needle-shaped focused acoustic beam imaging system based on an ultrasonic metasurface is provided, comprising the aforementioned needle-shaped focused acoustic beam imaging probe, a transmitting circuit, a signal amplification circuit, a mechanical scanning system, and a beamforming system; The mechanical scanning system interacts with the transmitting circuit to drive the needle-shaped focused acoustic beam imaging probe to transmit and receive at each scanning point during the scanning process, and to move the scanning system to the next scanning point and start the next transmission and reception. The beamforming system receives position data from the mechanical scanning system and echo data amplified by the signal amplification circuit from the imaging probe to reconstruct an ultrasound image of the region.

[0015] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: (1) The forming of needle-shaped focused sound beams based on acoustic metasurfaces. Compared with the existing ultrasonic beam forming methods based on inference algorithms, the present invention can flexibly adjust the length of the sound beam by arranging the focal position, and can flexibly adjust the width of the sound beam according to the actual scene by adjusting the phase adjustment coefficient, and can calculate the metasurface shape corresponding to the needle-shaped sound beam with a small amount of computation.

[0016] (2) Ultrasonic imaging based on needle-shaped focused sound beam. Compared with traditional plane wave imaging, the present invention uses a focused needle-shaped sound beam for imaging. Its echo intensity is more than 10 times that of plane wave, and the imaging is clearer. Compared with focused imaging, the present invention scans in the form of sound beam, and the imaging speed can reach about 15 times that of focused imaging.

[0017] (3) Compared with phased array ultrasound probes, the probe described in this invention greatly reduces the number of circuit channels and signal quantity, reduces processing difficulty, and reduces equipment costs. Compared with concave ultrasound probes, this invention only requires a planar ultrasound probe and an acoustic metasurface, resulting in a compact structure that is easy to integrate into various precision medical systems.

[0018] (4) Compared with existing ultrasound imaging systems, the needle-shaped focused acoustic beam imaging system of the acoustic surface proposed in this invention can achieve low-cost and rapid ultrasound imaging through real-time data interaction between the mechanical scanning system, the transmitting circuit and the beamforming system, and the imaging quality is higher. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a needle-shaped ultrasonic focusing beam imaging probe based on metasurface according to the present invention.

[0020] Figure 2 These are schematic diagrams of two different types of needle-shaped ultrasonic focusing beam imaging probes according to the present invention.

[0021] Figure 3 This is a schematic diagram of the focused acoustic beam imaging process according to the present invention.

[0022] Figure 4 This is a schematic diagram of needle-shaped focused acoustic beamforming based on metasurfaces.

[0023] Figure 5 It is the metasurface design method according to the present invention.

[0024] Figure 6 This is a schematic diagram of the random allocation method of metasurface units according to the present invention.

[0025] Figure 7 This is the beam intensity axial optimization method according to the present invention.

[0026] Figure 8 This is the design process of the focused acoustic beam metasurface according to the present invention.

[0027] Figure 9 The results are simulation and experimental results of the focused sound beam according to the present invention.

[0028] Figure 10 These are ultrasonic focused sound beams of different specifications.

[0029] Figure 11 This is the ultrasonic focused beam metasurface processing method according to the present invention.

[0030] Figure 12 This is the ultrasonic focused beam imaging echo signal processing method according to the present invention.

[0031] Figure 13 The image is an ultrasound image obtained according to the ultrasound focused beam imaging method of the present invention.

[0032] Figure 14 This is a block diagram of a needle-shaped focused acoustic beam imaging system according to the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0034] The present invention provides a design method for an acoustic metasurface for generating a needle-shaped focused sound beam, which divides the metasurface into multiple regularly arranged sub-units, the thickness of which is used to control the phase distribution of the planar incident ultrasonic wave. The thickness of the metasurface subunit is calculated from the acoustic refractive index between the metasurface material and the human body; By arranging metasurface sub-units, flexible spatial control of planar ultrasonic waves can be achieved, thereby forming a needle-shaped focused sound beam in the target area; The aforementioned metasurface subunits average and arrange the phase distributions corresponding to multiple linearly arranged focal points to form a needle-shaped focused sound beam; The metasurface subunits are divided into multiple groups according to the number of focal points required for the sound beam. Each group of units is responsible for focusing one focal point, and the length of a single focal point is approximately 0.5 Rayleigh length. Each group of units on the metasurface is randomly distributed across the entire metasurface to reduce the sidelobe intensity of the sound beam. The positions of the focal points linearly arranged on the focused sound beam can be further adjusted by an optimization function to achieve a needle-shaped sound beam with uniform axial intensity. The thickness of the focused sound beam can be adjusted by adjusting the phase adjustment coefficient; Using materials that match human impedance, a needle-shaped focused acoustic beam metasurface is fabricated on the surface of an ultrasound probe through a combination of precision 3D printing and casting. The metasurface materials mentioned include, but are not limited to, PDMS (polydimethylsiloxane), silicone rubber, resin, and other commonly used medical ultrasound materials. The metasurface is first formed by precision 3D printing a mold, and then cast using PDMS material.

[0035] Because of its low attenuation, the metasurface can also be used for ablation therapy with focal points of arbitrary shapes after a high-energy planar sound beam is input.

[0036] This invention discloses a design method for an acoustic metasurface used to generate a needle-shaped focused acoustic beam. The method includes: arranging artificial metasurface units with subwavelength structures in a preset array, wherein the thickness of the metasurface units is used to control the phase delay and amplitude distribution of the plane-incident ultrasonic wave; by designing the arrangement and parameters of the metasurface units, spatial control of the ultrasonic wave is achieved, thereby forming a needle-shaped focused acoustic beam in the target area; using a material that matches the impedance of the human body, the needle-shaped focused acoustic beam metasurface is manufactured on the surface of the ultrasonic probe through a combination of precision 3D printing and casting; subsequently, a needle-shaped focused acoustic beam imaging system is established, the formed focused acoustic beam is used to scan the target object, and the image information of the target is reconstructed by receiving the reflected ultrasonic signals.

[0037] In this invention, the metasurface is divided into multiple units of the same size, and further divided into M groups according to the number of focal points required for the sound beam. Each group is responsible for shaping one focal point. A needle-shaped focused sound beam is formed by axially arranging multiple focal points. Furthermore, the efficiency of the focused sound beam increases with the increase in the total number of units. Therefore, the phase of the metasurface generating the needle-shaped focused sound beam can be expressed as: ,in: m As the focus number, For the first m Phase adjustment coefficient corresponding to each focal point , For the metasurface coordinates, For the first m The focal length of each focal point For the first m Each focal point corresponds to a random 0-1 matrix, meaning the values ​​in the matrix are either 0 or 1, and these values ​​are randomly distributed throughout the matrix. For plane wave focusing as the focal point The phase to be modulated can be obtained through Perform calculations, where The refractive index of metasurface materials in the human body, This refers to the wavelength of ultrasound waves in the human body. Preferably, a random 0-1 matrix is ​​added when calculating the metasurface modulation phase. The metasurface units corresponding to each group of foci are randomly arranged on the entire metasurface to reduce the influence of higher-order diffraction. The size of the random 0-1 matrix is ​​equal to the number of metasurface units. The number of array elements with a value of 1 is the number of units corresponding to a single group of foci, and they are randomly distributed throughout the matrix. The values ​​of non-1 array elements in the matrix are all 0.

[0038] Preferably, by adjusting the phase adjustment coefficient Pa It allows for flexible adjustment of the thickness of the focused ultrasound beam. Pa The value is generally between 0.2pi and 0.8pi, and increases with... Pa The increased focusing beam also makes the beam thicker, resulting in a larger imaging area for a single transmission and reception.

[0039] The beam length is determined by calculating the number of focal points required to form the sound beam based on the desired imaging depth. The distance between two focal points is typically taken as 0.5 Rayleigh lengths. ,in m As the focus number, d For the required sound beam length, RL Let be the Rayleigh length of the sound beam at the focal point.

[0040] The axial intensity of the focused ultrasound beam obtained by the above method is not uniform, and its intensity needs to be optimized. The basic principle is to adjust the spacing between each focal point by adjusting the axial sound intensity of the beam. If the sound pressure between two focal points is greater than the average sound intensity of the entire beam, the spacing between the two focal points is increased, and vice versa. Finally, after multiple iterations, a focused ultrasound beam with uniform axial intensity can be obtained.

[0041] This invention relates to a method for fabricating acoustic metasurfaces for generating needle-shaped focused sound beams. Specifically, the metasurface modulates the phase of a plane wave by varying its thickness. The calculation method is as follows: ,in For metasurface The height at the coordinates, The phase modulation required to form a needle-shaped focused acoustic beam on the metasurface. The refractive index of metasurface materials in the human body, This refers to the wavelength of ultrasound waves in the human body.

[0042] Preferably, to ensure the focused sound beam energy, a metasurface material that matches the human body impedance is used, and it should have good processability, including but not limited to polydimethylsiloxane, silicone rubber, etc.

[0043] After calculating the height of each unit of the metasurface, a combination of precision 3D printing and casting was used to process the metasurface. The obtained metasurface model data was processed in 3D modeling software to construct a 3D model of the mold, with a pouring gate provided. The mold was then printed using a high-precision 3D printer. Due to the weak adhesion between the material and the transducer array surface, an adhesion promoter was applied to the surface. Simultaneously, a release agent was used to treat the mold surface for easy demolding. The mold was then combined and fixed with the ultrasonic array. Polydimethylsiloxane was injected through the pouring gate, and the entire mold was vacuum-treated to remove air bubbles. Heating was then used to accelerate the curing process. Finally, after demolding, the metasurface and the ultrasonic focused beam imaging probe were successfully bonded.

[0044] A needle-shaped focused acoustic beam imaging probe based on an ultrasonic metasurface includes the aforementioned acoustic metasurface for generating a needle-shaped focused acoustic beam, and also includes an ultrasonic transmitting array and an ultrasonic receiving array. The ultrasonic receiving array is used to flexibly arrange ultrasonic transducers on the probe in a linear or circular manner. Each transducer has an independent receiving channel and processes data. The shape of the probe can also be flexibly designed according to the actual situation.

[0045] The ultrasonic transmitting array can emit using a closely spaced array of transducers, or it can emit using a piezoelectric crystal the size of a probe.

[0046] The ultrasonic array element ultrasonic transducer includes traditional piezoelectric block transducers, capacitive microelectromechanical transducers, piezoelectric microelectromechanical transducers, etc. The metasurface has the same shape as the transmitting array and is fixed on the transmitting array. The metasurface is used to focus the planar ultrasonic waves emitted by the transmitting array into a needle-shaped focused sound beam.

[0047] This invention provides a method for ultrasonic metasurface needle-focused acoustic beam imaging using a needle-shaped focused acoustic beam imaging probe. Since the ultrasonic imaging probe also needs to receive echo signals, the ultrasonic probe used in this invention includes a transmitting part and a receiving part. The transmitting part emits planar ultrasonic waves and achieves beamforming through the aforementioned metasurface. The receiving part is a linear transducer array used to receive the ultrasonic echo signals reflected back after the needle-shaped focused acoustic beam encounters an object.

[0048] Preferably, after the receiving transducer receives the ultrasonic echo signal, the signal must be processed and reconstructed to obtain a clear ultrasonic image. For the echo signal of ultrasonic focused beam imaging, the main reconstruction steps include bandpass filtering, signal cleaning, distance compensation, envelope extraction, logarithmic compression, upsampling, etc. As an ultrasonic focused beam, a compensation coefficient also needs to be added during distance compensation.

[0049] Preferably, for focused beam imaging, since it receives echoes, while for ultrasonic beams, since the phase corresponding to the focal point at different distances on the metasurface is randomly distributed, the calculation method for single-focal-point focusing needs to be optimized. This is achieved by adding a compensation coefficient to the single-focal-point focusing algorithm. k Distance compensation for the sound beam can be expressed as: ,in: x i and y i These are the x and y coordinates of the imaging point, respectively. x m The x-coordinate of the transmitting element; Preferably, the needle-shaped focused acoustic beam imaging system includes a needle-shaped focused acoustic beam imaging probe, a high-voltage transmitting circuit, a signal amplification circuit, a mechanical scanning system, and a beamforming system. The high-voltage transmitting circuit provides high-voltage pulses to each element of the imaging probe to drive the array to emit ultrasound. The signal amplification circuit amplifies the received weak echo signals to a level that the beamforming system can recognize. The mechanical scanning system controls the probe to scan horizontally in the imaging area and sends an excitation signal to the probe at each point to start working. The beamforming system processes, stores, and images the echo data based on given steps.

[0050] The ultrasonic metasurface of the present invention can focus planar ultrasonic waves into a needle-shaped focused sound beam, and the length and width of the sound wave can be flexibly adjusted according to imaging requirements to achieve ultrasonic imaging of different depths and qualities. Furthermore, the metasurface-based ultrasonic imaging method and system of the present invention have high echo quality and fast imaging speed. Therefore, it is suitable for the diagnosis of diseases such as uterine fibroids and liver tumors.

[0051] Figure 1 A schematic diagram of a needle-shaped ultrasonic focusing beam imaging probe according to the present invention is shown. It consists of an ultrasonic transducer and a metasurface. The ultrasonic transducer is divided into three parts: ultrasonic transmitting arrays on the left and right sides, and a central strip-shaped ultrasonic receiving array. The ultrasonic transmitting array emits planar ultrasonic waves, which are focused into a needle-shaped focused sound beam by the metasurface. The ultrasonic receiving array receives the sound wave signal returned after the focused sound beam encounters an obstacle. The transducer type includes conventional piezoelectric transducers, capacitive microelectromechanical transducers, and piezoelectric microelectromechanical transducers, etc.

[0052] Figure 2Schematic diagrams of two different forms of needle-shaped ultrasonic focusing beam imaging probes according to the present invention are shown. The receiving array can be flexibly linearly arranged on the probe, including but not limited to "X" shaped arrangement and ring arrangement. The receiving array is distributed on the area of ​​the probe other than the transmitting array. It can be a single array that can transmit in a closely arranged array of transducers, or it can be a single piece of piezoelectric crystal. The entire probe can also be designed with different shapes according to actual needs.

[0053] Figure 3 The invention illustrates a needle-shaped focused acoustic beam imaging method. During imaging, sound waves emitted by the transmitting array in the ultrasonic probe are focused into a needle-shaped acoustic beam after passing through a metasurface. When the acoustic beam encounters obstacles of different impedances, it is reflected and generates echoes. After receiving the echoes, the receiving array processes the echo signals to obtain an ultrasonic image of the imaging area. Ultrasonic imaging of the entire imaging area is achieved by lateral movement of the entire probe.

[0054] Figure 4 The diagram illustrates a needle-shaped focused acoustic beamforming method based on a metasurface according to the present invention, in which planar ultrasonic waves are focused into a needle-shaped focused acoustic beam after passing through the metasurface. The basic principle is to divide the metasurface into multiple parts, each part focusing at a different focal point, and finally forming a focused acoustic beam by arranging these multiple focal points laterally.

[0055] Figure 5 This illustrates a method for designing a metasurface according to the present invention, firstly focusing planar ultrasonic waves at a single focal point. f m The required modulation phase is To form a focused sound beam, it is necessary to achieve [something] on the metasurface. M The focusing and arrangement of each focal point are thus determined by a 0-1 matrix. Metasurfaces are divided into M Groups, each group is responsible for moving one focus point. Ultimately, this will... M The phase distribution of the needle-shaped focused acoustic beam on the metasurface is obtained by adding the phases of the focal points. Pa It is the phase adjustment coefficient, which can be used to adjust the thickness of the focused sound beam.

[0056] Figure 6 A schematic diagram of a random allocation method for metasurface elements according to the present invention is shown. Taking four focal points and 16 metasurface elements as an example, each set of four elements represents the formation of an ultrasonic focal point. The fully random distribution method randomly distributes the metasurface elements corresponding to the focal points throughout the metasurface, while the partially random distribution method divides the metasurface into multiple groups according to the number of focal points, and the metasurface elements corresponding to each focal point in each group are randomly distributed.

[0057] Figure 7The following describes the beam intensity axial optimization process according to the present invention. After determining the beam length, the focal points are first aligned with a spacing of... RL / 2 The arrangement is such that the positions of the first and last focal points are in front of the front and rear ends of the sound beam. RL / 2 The sound field was then simulated, and sound pressure levels at each focal point were collected. Keeping the initial and final focal points constant, if the sound pressure at a focal point was greater than the average sound pressure of the entire beam, the distance between that focal point and the previous one was increased; conversely, if the sound pressure at a focal point was less than the average sound pressure of the entire beam, the distance between that focal point and the previous one was decreased. After moving the focal points of the entire beam, the simulation and movement were repeated. After 20 cycles, the axial uniformity of the sound beam improved by more than 20 times, and this improvement increased with each subsequent cycle.

[0058] Figure 8 The design flow of the metasurface according to the present invention is shown. First, the required imaging depth and width are determined according to the specific application scenario to determine the required length and thickness of the focused sound beam. Then, the phase distribution of the required metasurface is calculated by adjusting the number of focal points and the phase adjustment coefficient according to the aforementioned method. In order to reduce the influence of higher-order diffraction, the obtained phase also needs to be randomized. Finally, the axial intensity of the sound beam is optimized according to the simulation results, and a uniform focused sound beam metasurface is finally obtained.

[0059] Figure 9 Simulation and test results of the ultrasonic focusing beam according to the present invention are shown. It can be seen that the plane wave achieves the focusing of the needle-shaped sound beam after passing through the metasurface.

[0060] Figure 10 The diagram shows ultrasonic focusing beams of different specifications obtained according to the metasurface design method of the present invention, wherein focusing beam 1 has a length of 5 mm and a diameter of 0.8 mm, focusing beam 2 has a length of 20 mm and a diameter of 0.6 mm, beam 3 has a length of 15 mm and a diameter of 0.8 mm, and focusing beam 4 has a length of 15 mm and a diameter of 1.8 mm.

[0061] Figure 11The invention illustrates a method for fabricating a focused ultrasonic beam metasurface. First, based on the phase distribution and the sound velocity of the metasurface material (e.g., polydimethylsiloxane in water has a sound velocity of 950 m / s), the morphology data of the metasurface is calculated. A mold for the metasurface is then obtained using precision 3D printing. To facilitate demolding, a release agent is sprayed onto the mold surface. Simultaneously, to ensure complete contact between the metasurface and the ultrasonic probe, an adhesion promoter is sprayed onto the probe surface. After fixing the mold onto the ultrasonic probe, a mixture of polydimethylsiloxane is injected, followed by vacuum treatment to remove air bubbles. After 24 hours, the material solidifies, and the mold is removed, thus completing the fabrication of the focused ultrasonic beam metasurface on the ultrasonic array.

[0062] Figure 12 The present invention illustrates an echo signal processing method for ultrasonic focused beam imaging according to the present invention. First, a bandpass filter is used to filter the signal, removing noise and clutter. Since the ultrasonic probe generates pulse signals during transmission and propagates as spherical waves, the received portion of the transmitted signal contained in the echo signal needs to be removed, calculated based on the distance the ultrasound travels across the entire metasurface. For focused beam imaging, when calculating the distance of the received signal, the phase corresponding to the focal point on the metasurface at different distances is randomly distributed. Therefore, the calculation method for single-focal focusing needs to be optimized by adding a compensation coefficient to the single-focal focusing algorithm. k Distance compensation for the sound beam can be expressed as: ,here( x i , y i () represents the coordinates of the imaging point. x m The coordinates of the transmitting array elements are given. To represent the intensity distribution of the echo signal, the envelope of the compensated echo signal needs to be extracted, and the instantaneous amplitude is obtained using Hilbert transform. To facilitate image display, the logarithm of the signal intensity is taken to achieve dynamic range compression. To improve image resolution, the signal is upsampled by interpolation, and a clear ultrasound image can be reconstructed.

[0063] Figure 13 The image shows an ultrasound image obtained according to the ultrasound focused beam imaging method of the present invention, and the scanning process of the ultrasound probe is simulated, wherein the sub- Figure 1 3 represents objects of different shapes set in the simulation, sub- Figure 2 4 represents the imaging result of the corresponding focused acoustic beam. Compared with plane wave imaging, the echo signal intensity of focused acoustic beam imaging is more than 10 times greater. Compared with single-focus focused imaging, the speed of focused acoustic beam imaging method is about 15 times faster.

[0064] Figure 14 A block diagram of a needle-shaped focused acoustic beam imaging system according to the present invention is shown. It mainly consists of a high-voltage transmitting circuit, an imaging probe, a signal amplification circuit, a mechanical scanning system, and a beamforming system. The high-voltage amplification circuit provides an excitation signal to the imaging probe, the mechanical scanning system drives the imaging probe to move horizontally, the signal amplification circuit amplifies the echo signal, and the beamforming system performs signal processing and image reconstruction.

[0065] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A design method for an acoustic metasurface used to generate a needle-shaped focused sound beam, characterized in that, Includes the following steps: (1) Divide the metasurface into multiple units of the same size, and divide them into M groups according to the number of focal points required to form a sound beam. Each group of units is responsible for the shaping of one focal point, and each unit is randomly distributed on the metasurface; or divide the metasurface into multiple groups of the same size, each group has M units, and each unit in each group represents a metasurface unit corresponding to a focal point, and each unit is randomly distributed in its group. Needle-shaped focused acoustic beamforming is achieved by axially arranging multiple focal points, thereby obtaining the metasurface phase of the needle-shaped focused acoustic beam; (2) Calculate the number of focal points required to form the sound beam based on the desired imaging depth to determine the sound beam length; (3) The spacing between each focus is adjusted by the axial sound intensity of the sound beam. If the sound pressure between two focus points is greater than the average sound intensity of the entire sound beam, the spacing between the two focus points is increased, and vice versa. Finally, after multiple iterations, an acoustic metasurface is obtained that can focus plane sound waves into an ultrasonic needle-shaped focused sound beam with uniform axial intensity.

2. The design method for an acoustic metasurface for generating a needle-shaped focused sound beam as described in claim 1, characterized in that, In step (1), the metasurface phase of the needle-shaped focused acoustic beam is represented as: ,in: m As the focus number, For the first m Phase adjustment coefficient corresponding to each focal point , For the metasurface coordinates, For the first m The focal length of each focal point For the first m Each focal point corresponds to a random 0-1 matrix, meaning the values ​​in the matrix are either 0 or 1, and these values ​​are randomly distributed throughout the matrix. Focusing a plane wave as the focal point The phase to be modulated is obtained by... Perform calculations, where The refractive index of metasurface materials in the human body, This refers to the wavelength of ultrasound waves in the human body. In step (2), the focal distance is expressed as ,in m As the number of focal points, d For the required sound beam length, RL Let be the Rayleigh length of the sound beam at the focal point.

3. The design method for an acoustic metasurface for generating a needle-shaped focused sound beam as described in claim 2, characterized in that, By adjusting the phase adjustment coefficient Pa This allows for adjustment of the thickness of the focused ultrasound beam. Pa The value range is between 0.2 and 0.8 pi; as... Pa As the focusing beam increases, the beam also becomes thicker, resulting in a larger imaging area for a single transmission and reception.

4. The design method for an acoustic metasurface for generating a needle-shaped focused sound beam as described in claim 2, characterized in that, The random 0-1 matrix is ​​specifically designed to distribute the metasurface units corresponding to each group of foci across the entire metasurface using different random allocation methods to reduce the influence of higher-order diffraction. The size of the random 0-1 matrix is ​​equal to the number of metasurface units, and the number of array elements with a value of 1 is the number of units corresponding to a single group of foci, and they are randomly distributed throughout the matrix.

5. An acoustic metasurface for generating a needle-shaped focused sound beam, obtained by any one of the design methods of claims 1-4.

6. The method for fabricating an acoustic metasurface for generating a needle-shaped focused sound beam as described in claim 5, characterized in that, Includes the following steps: (1) Metasurfaces modulate the phase of plane waves through different thicknesses. The method for calculating the thickness of each unit of the metasurface is as follows: ,in For metasurface Height at the unit The phase modulation required to form a needle-shaped focused acoustic beam on the metasurface. The refractive index of metasurface materials in the human body, This refers to the wavelength of ultrasound waves in the human body. (2) After calculating the thickness of each unit of the metasurface, the metasurface is processed by a combination of precision 3D printing and casting. Specifically, the obtained metasurface model data is processed in 3D modeling software to construct a 3D model of the mold and leave a pouring port. The mold is printed by a precision 3D printer. The mold is combined with and fixed to the ultrasonic array. After injecting the metasurface material through the pouring port, the entire mold is vacuum treated to remove air bubbles. Then, it is heated to accelerate the curing speed and demolded to obtain the acoustic metasurface used to generate needle-shaped focused sound beams. Preferably, the metasurface material is polydimethylsiloxane or silicone rubber.

7. The acoustic metasurface for generating needle-shaped focused sound beams obtained by the processing method of claim 6.

8. A needle-shaped focused acoustic beam imaging probe based on an ultrasonic metasurface, characterized in that, The acoustic metasurface for generating a needle-shaped focused sound beam as described in claim 7 further includes an ultrasonic transmitting array and an ultrasonic receiving array; The ultrasonic receiver array is used to arrange ultrasonic transducers on the probe. The ultrasonic transmitting array emits either a closely spaced array of transducers or a piezoelectric crystal the size of a probe. The acoustic metasurface used to generate the needle-shaped focused sound beam has the same shape as the ultrasonic transmitting array and is fixed on the ultrasonic transmitting array. The acoustic metasurface used to generate the needle-shaped focused sound beam is used to focus the planar ultrasonic waves emitted by the transmitting array into a needle-shaped focused sound beam.

9. A method for performing ultrasonic metasurface needle-focused acoustic beam imaging using the needle-shaped focused acoustic beam imaging probe according to claim 8, characterized in that, Includes the following steps: (1) Range compensation of the sound beam is performed by adding a compensation coefficient k to the single-focus focusing algorithm. The range compensation for each imaging point is expressed as follows: , ,in: x i and y i These are the x and y coordinates of the imaging point, respectively. x m The x-coordinate of the transmitting element; (2) During the imaging process, the ultrasound probe performs planar scanning at the target position along with the mechanical scanning system. Each scan involves transmitting and receiving ultrasound, and a linear imaging area is formed according to the distance compensation in step (1), ultimately realizing a planar ultrasound image.

10. A needle-shaped focused acoustic beam imaging system based on an ultrasonic metasurface, characterized in that, Includes the needle-shaped focused acoustic beam imaging probe, transmitting circuit, signal amplification circuit, mechanical scanning system, and beamforming system as described in claim 8; The mechanical scanning system interacts with the transmitting circuit to drive the needle-shaped focused acoustic beam imaging probe to transmit and receive at each scanning point during the scanning process, and to move the scanning system to the next scanning point and start the next transmission and reception. The beamforming system receives position data from the mechanical scanning system and echo data amplified by the signal amplification circuit from the imaging probe to reconstruct an ultrasound image of the region.

Images