Acoustic impedance matching material, preparation method therefor, and use thereof

Abstract

Disclosed in the present invention are an acoustic impedance matching material, a preparation method therefor, and a use thereof. The acoustic impedance matching material comprises a plurality of impedance layers which are stacked; along the stacking direction, the impedance layers are sequentially arranged according to the exponential change relationship of acoustic impedance; each impedance layer comprises a liquid matrix material and a filler located in the liquid matrix material. The acoustic impedance matching material in the present invention enables ultrasonic to maintain sufficient energy and large bandwidth to enter the skull, achieves high imaging resolution and high focusing intensity, can guarantee efficient transcranial ultrasonic energy transmission, and is thus used for brain disease observation and treatment.

Description

Acoustic impedance matching material and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of impedance matching materials, and in particular relates to an acoustic impedance matching material and a preparation method and application thereof. Background Art

[0002] Currently, the main methods for detecting brain diseases include CT, magnetic resonance imaging, and ultrasound imaging technologies. Transcranial ultrasound imaging offers advantages over CT and MRI, such as simplicity, lack of radiation, real-time performance, and portability. Transcranial ultrasound not only enables the observation of brain diseases but also, due to its penetrating, focusing, and thermal properties, can be used for the treatment of brain diseases. This opens up new avenues for brain science research and treatment, bringing great benefits to patients with brain diseases. Therefore, transcranial ultrasound technology holds profound promise in the treatment of brain diseases.

[0003] Traditional transcranial ultrasound suffers from various issues, including low imaging resolution and low focusing intensity, due to the mismatch between the skull and background acoustic impedance. Existing medical ultrasound transcranial technology typically uses the temporal, occipital, mandibular, and orbital regions as the incident acoustic windows. This is because the skull in these areas is thin or composed primarily of cartilage, allowing ultrasound to easily pass through the skull barrier for intracranial imaging and focusing. However, this approach fails to consider the impact of the skull's impedance mismatch on ultrasound transmission energy. Furthermore, the incident acoustic windows, primarily located at the temporal, occipital, mandibular, and orbital regions, fail to cover most brain regions, resulting in blind spots that severely limit ultrasound applications.

[0004] 1.1.1 Summary of the invention

[0005] The present invention aims to address at least one of the technical problems existing in the aforementioned prior art. To this end, the present invention proposes an acoustic impedance matching material. Its application in transcranial ultrasound technology can significantly reduce the impact of impedance mismatch in the skull, ensuring high-efficiency transmission of ultrasound into intracranial soft tissues over a wide frequency range. Furthermore, ultrasound can be incident into the skull from any location within the skull, enabling ultrasound imaging and treatment of any target, with promising application prospects.

[0006] The invention also provides a method for preparing the acoustic impedance matching material.

[0007] The present invention also provides an ultrasonic transducer.

[0008] The present invention also provides an ultrasonic instrument.

[0009] The present invention also proposes applications of the acoustic impedance matching material, ultrasonic transducer and ultrasonic instrument.

[0010] In a first aspect of the present invention, an acoustic impedance matching material is proposed, comprising a plurality of stacked impedance layers, wherein the impedance layers are arranged in sequence along the stacking direction according to an exponential e-change relationship of acoustic impedance; each impedance layer comprises a liquid matrix material and a filler located in the liquid matrix material.

[0011] The acoustic impedance matching material according to the embodiment of the present invention has at least the following beneficial effects: in the present invention, by changing the filling rate of the filler in each impedance layer, the acoustic impedance of each impedance layer is arranged in sequence with an e-exponential change relationship, so that the acoustic impedance of the obtained acoustic impedance matching material changes gradiently from one end to the other. If the acoustic impedance matching material is applied to transcranial ultrasound, the acoustic impedance range of the acoustic impedance matching material can be between the acoustic impedance of the background medium (such as water) and the acoustic impedance of the skull, so that the gradient of the acoustic impedance change from the background medium to the skull is reduced, the impedance mismatch of the skull is reduced, and the influence of the impedance mismatch of the skull is reduced, ensuring that ultrasound maintains high efficiency transmission to soft tissue within a wide frequency range, and changing the incident ultrasound frequency can also enable ultrasound to maintain high transmittance through the skull, meeting the needs of different brain disease treatments.

[0012] More specifically, the acoustic impedance matching material of the present invention is used in transcranial ultrasound, allowing ultrasound to maintain sufficient energy and a wide bandwidth to enter the skull, resulting in high imaging resolution and high focusing intensity, ensuring efficient ultrasound observation and treatment of brain diseases. For example, transcranial ultrasound neurostimulation can accurately focus and stimulate the target nervous system, achieving treatment of neurological diseases. High-intensity focused transcranial ultrasound can also be used to ablate diseased tissues and tumors through the high-intensity energy at the focal point, and can also melt the outer shell of drugs for targeted drug delivery in vivo.

[0013] Furthermore, the liquid matrix material in this invention, due to its fluidity, can quickly absorb and transfer heat generated by ultrasound within the skull, effectively resolving the skull heating issue associated with traditional transcranial ultrasound technology. Furthermore, the liquid matrix material in this invention allows the acoustic impedance matching material to fit tightly with the target object, further facilitating skull impedance matching and enhancing transcranial ultrasound performance.

[0014] The acoustic impedance matching material in the present invention is not limited to being used for impedance matching of the skull, but can also be used in a wider range of applications and in more application scenarios by selecting suitable liquid matrix materials and fillers.

[0015] In some embodiments of the present invention, along the stacking direction, the impedance layers are arranged in sequence according to the acoustic impedance exponential variation relationship shown in formula (1):

[0016] Wherein, t1 represents the total thickness of the acoustic impedance matching material along the stacking direction; x represents the vertical distance between the geometric center of the impedance layer and the surface of the side of the acoustic impedance matching material away from the end to be matched; Z w represents the acoustic impedance of the matrix material, Z s The end to be matched refers to the end of the acoustic impedance matching material that is in contact with or close to the object to be matched.

[0017] Typically, the acoustic impedance of water is about 1.5 Mrayl, and the acoustic impedance of the skull is about 5.6 Mrayl.

[0018] In some embodiments of the present invention, along the stacking direction, the acoustic impedance of the impedance layer is between the acoustic impedance of water and the acoustic impedance of the skull. Unless otherwise specified, water herein refers to pure water.

[0019] In some embodiments of the present invention, along the stacking direction, the acoustic impedance of the acoustic impedance matching material changes gradiently from one side to the other side, and the acoustic impedance is between 1.5 and 5.6 Mrayl.

[0020] In some embodiments of the present invention, the relationship between the filling ratio f of the filler in the impedance layer and the acoustic impedance of the impedance layer is calculated by a finite element method.

[0021] The acoustic impedance of the impedance layer in the present invention is the effective acoustic impedance (hereinafter referred to as effective impedance). Unless otherwise specified, the filling rate herein refers to the volume filling rate, that is, the volume ratio of the filler in the impedance layer.

[0022] In some embodiments of the present invention, an impedance layer comprises a plurality of unit cell structures, each of which has a thickness β along the stacking direction, where the wavelength of ultrasound in water is λ, and β and λ satisfy the following relationship: β < λ / 9. β and λ may both be expressed in meters (m), with water serving as the background medium.

[0023] In some embodiments of the present invention, along the stacking direction, one impedance layer includes s columns of unit cell structures, and the thickness of the impedance layer along the stacking direction is h=β*s. Optionally, s=2-6.

[0024] The wavelength of ultrasound can be obtained from the sound speed of ultrasound in the medium / the frequency of ultrasound.

[0025] In some embodiments of the present invention, 0<β<λ / 9.

[0026] In some embodiments of the present invention, each unit cell structure includes a filler and a matrix material.

[0027] In some embodiments of the present invention, the number of the impedance layers is 2 to 6.

[0028] In some embodiments of the present invention, the thickness h of the impedance layer along the stacking direction is 200-700 μm.

[0029] In some embodiments of the present invention, along the stacking direction, the total thickness of the acoustic impedance matching material is t1, where t1 = h*n', and n' is the number of impedance layers.

[0030] In some embodiments of the present invention, when the ultrasonic frequency is in the range of 0 to 1.3 MHz, the thickness of each impedance layer is 500 μm.

[0031] In some embodiments of the present invention, when the ultrasonic frequency is 0.65 MHz, the thickness of the impedance layer is 480-520 μm.

[0032] The number n' of impedance layers can be selected according to actual needs. By increasing the number of impedance layers of acoustic impedance matching material, the transcranial bandwidth can be increased to achieve wide bandwidth and high efficiency transmission of ultrasound transcranial.

[0033] In some embodiments of the present invention, the thickness of each impedance layer is the same along the stacking direction.

[0034] In some embodiments of the present invention, the acoustic impedance of the matrix material is no greater than the acoustic impedance of water; and / or the acoustic impedance of the filler is no less than 1.2 times the acoustic impedance of the skull.

[0035] In some embodiments of the present invention, the acoustic impedance of the matrix material is 0.5-1.5 Mrayl; and / or the acoustic impedance of the filler is 10-100 Mrayl.

[0036] In some embodiments of the present invention, the filler material includes, but is not limited to, polymer materials, silicon-based materials, ceramic materials, and metal materials such as single metals, metal oxides, and alloys. Optionally, the filler material includes at least one of polymer materials, silicon-based materials, ceramic materials, single metals, metal oxides, and alloys.

[0037] In some embodiments of the present invention, the material of the filler includes at least one of a polymer material, a silicon material, a ceramic material or a metal material.

[0038] In some embodiments of the present invention, the silicon-based material includes at least one of silicon or silicon dioxide.

[0039] In some embodiments of the present invention, the polymer material includes at least one of polymethyl methacrylate (PMMA), polyetheretherketone (PEEK), methacrylic resin, silicone rubber, and polydimethylsiloxane (PDMS).

[0040] In some embodiments of the present invention, the ceramic material includes piezoelectric ceramics, such as PZT piezoelectric ceramics, PN piezoelectric ceramics, and PMN-PT piezoelectric ceramics.

[0041] In some embodiments of the present invention, the metal elements in the metal element, metal oxide and alloy include but are not limited to iron, nickel, copper, aluminum, titanium, tungsten, zinc, gold, silver, platinum, etc. Optionally, the metal element in the metal element, metal oxide and alloy includes at least one of iron, nickel, copper, aluminum, titanium, tungsten, zinc, gold, silver or platinum.

[0042] In some embodiments of the present invention, the filler material includes at least one of iron, nickel, copper, aluminum, titanium, tungsten, zinc, gold, silver, or platinum. Optionally, the iron includes but is not limited to pure iron, steel, etc.

[0043] In some embodiments of the present invention, the matrix material includes but is not limited to water, tap water, sea water, and other medical liquids.

[0044] In some embodiments of the present invention, the matrix material comprises water; and / or the filler comprises at least one of iron, nickel, copper, aluminum, titanium, tungsten, zinc, gold, silver or platinum.

[0045] In some embodiments of the present invention, the matrix material comprises water and the filler comprises steel.

[0046] Through the above-mentioned embodiment, the acoustic impedance is regulated by adjusting the filling rate of the filler in water in the impedance layer of the present invention, and an acoustic impedance matching material with a gradual acoustic impedance is obtained. When applied to transcranial ultrasound technology, the acoustic impedance matching material has an acoustic impedance range between the acoustic impedance of water and the acoustic impedance of the skull, which satisfies the requirement of being adjustable from the acoustic impedance of water to the acoustic impedance of the skull, so that the gradient of the acoustic impedance change from water to the skull is reduced, which can reduce the impedance mismatch of the skull and reduce the influence of the impedance mismatch of the skull, ensuring that the ultrasonic energy can maintain high efficiency in a wide frequency range and be transmitted to the soft tissue, thereby achieving broadband impedance matching between water and the skull, and changing the incident ultrasonic frequency in a wide frequency range, which can be applied to different medical technologies and medical processes. In some embodiments of the present invention, the acoustic impedance matching material can enable ultrasound to maintain high transmittance through the skull in a wide frequency range covering low frequency (220kHz) to medium frequency (650kHz), meeting the observation and treatment needs of different brain diseases.

[0047] In addition, the present invention uses analytical and finite element numerical calculation methods in specific embodiments to verify that the acoustic impedance matching material can reduce the impact of skull impedance mismatch during transcranial ultrasound penetration, ensuring broadband, efficient and directional transmission of transcranial ultrasound. Therefore, the present invention has great application potential in broadband ultrasound imaging and treatment.

[0048] In addition, water is used as the matrix material in the present invention. Due to its large specific heat capacity and fluidity, water can quickly absorb and transfer the increased heat in the skull caused by ultrasound, which effectively solves the problem of skull heating in traditional transcranial ultrasound technology.

[0049] In some embodiments of the present invention, the matrix material comprises several liquid materials.

[0050] In some embodiments of the present invention, the at least one liquid material of the matrix material can flow within the acoustic impedance matching material.

[0051] In some embodiments of the present invention, one or more fillers are contained in one impedance layer.

[0052] In some embodiments of the present invention, one impedance layer contains a plurality of fillers, and the plurality of fillers are evenly distributed in the impedance layer.

[0053] In some embodiments of the present invention, one impedance layer contains a plurality of the same fillers, and the plurality of fillers are evenly distributed in the impedance layer.

[0054] In some embodiments of the present invention, a plurality of the fillers are arranged in a matrix within the impedance layer.

[0055] In some embodiments of the present invention, the shape of the filler includes, but is not limited to, regular or irregular shapes such as cylinders, spheres, and cuboids. Alternatively, the filler may be hollow or solid. Hollow fillers can further enrich the selection of filler sizes and types.

[0056] In some embodiments of the present invention, the shape of the filler includes at least one of a cylinder, a sphere, or a cuboid, and / or the filler is a hollow filler or a solid filler. When the filler is a composite material (e.g., a hollow structure), its acoustic impedance should be its effective acoustic impedance.

[0057] Optionally, the cylinder includes a solid cylinder or a hollow cylinder, the sphere includes a solid sphere or a hollow sphere, and the cuboid includes a solid cuboid or a hollow cuboid.

[0058] In some embodiments of the present invention, the acoustic impedance matching material further includes a limiting material capable of limiting the position of the filler within the acoustic impedance matching material. For example, the limiting material can secure the filler within the impedance layer, thereby limiting the position of the filler within the acoustic impedance matching material.

[0059] The matrix material is a liquid material, and a limiting material with an acoustic impedance similar to that of the matrix material is optionally used to fix, connect and combine the filler, such as a membrane structure.

[0060] In some embodiments of the present invention, the acoustic impedance of the limiting material is 80-120% of the acoustic impedance of the base material, and can be optionally 95-105%.

[0061] In some embodiments of the present invention, each of the impedance layers contains the limiting material, and the limiting material in each impedance layer encloses a filling region, which is filled with the filler. Optionally, the matrix material is located within the filling region, or / and the matrix material is located outside the filling region.

[0062] In some embodiments of the present invention, the limiting material is a limiting film material.

[0063] In some embodiments of the present invention, the limiting material includes but is not limited to polytetrafluoroethylene, polyurethane or polyethylene terephthalate.

[0064] In some embodiments of the present invention, the limiting material includes at least one of polytetrafluoroethylene, polyurethane or polyethylene terephthalate.

[0065] In some embodiments of the present invention, in one impedance layer, along the stacking direction, the thickness of the limiting film material is within 0.5 to 5% of the thickness of the impedance layer.

[0066] A second aspect of the present invention provides a method for preparing an acoustic impedance matching material, comprising the following steps:

[0067] S1, using the finite element method to calculate the relationship between the filling rate f of the filler in the impedance layer and the acoustic impedance of the impedance layer;

[0068] The number of impedance layers n' is preset, and each impedance layer includes a plurality of unit cell structures. The thickness of each unit cell structure along the stacking direction is preset to be β; in each impedance layer, β < λ / 9; where λ is the wavelength of ultrasound in water;

[0069] S2, determining the acoustic impedance of each impedance layer in the acoustic impedance matching material according to a preset stacking direction of the impedance layers and the relationship that the impedance layers are arranged in sequence according to an exponential e-change relationship of acoustic impedance;

[0070] S3, determining the filling rate f of the filler in each impedance layer according to the determined relationship between the acoustic impedance and the filling rate f of the impedance layer;

[0071] S4, selecting corresponding impedance layers according to the determined filling rate f, and stacking the impedance layers in sequence according to a preset stacking direction to form an acoustic impedance matching material.

[0072] In step S1 , by limiting β<λ / 9, the impedance layer structure dimensions of each layer meet the low-frequency limit condition.

[0073] In step S2, the acoustic impedance of each impedance layer in the acoustic impedance matching material is determined based on the preset number n' of impedance layers and their stacking directions, and in accordance with the relationship in which the acoustic impedances are arranged in sequence according to the exponential variation of the acoustic impedances as shown in formula (1). Alternatively, if the impedance layers are arranged in sequence according to the exponential variation of the acoustic impedances as shown in formula (1), n' values ​​of x / t1 can be uniformly selected from 0 to 1 based on the number of impedance layers (number) n', and the impedance value corresponding to the selected x / t1 can be obtained. Optionally, the exponential relationship of formula (1) can be converted into a relationship diagram.

[0074] In some embodiments of the present invention, the finite element method is used to calculate the relationship between the filling rate f and the effective sound velocity of the ultrasonic wave in the impedance layer; based on the filling rate f of the filler of each impedance layer obtained in step S3, the effective sound velocity of the ultrasonic wave in each impedance layer is obtained, and then the wavelength λ1 of the ultrasonic wave in each impedance layer is obtained, and the average value λ1' of the wavelength λ1 is calculated to satisfy: the thickness h of the impedance layer along the stacking direction is 0.22λ1'~0.28λ1'.

[0075] Based on h and β, the number of unit cell structures in the stacking direction of an impedance layer is obtained. If the unit cell structures are arranged in a matrix within the impedance layer, the number of columns of unit cell structures in the impedance layer can be obtained based on h and β. Optionally, the total number of unit cell structures in the impedance layer can also be set.

[0076] In some embodiments of the present invention, in step S2, the acoustic impedance of the impedance layer at different positions of the acoustic impedance matching material is determined according to formula (1) based on the preset stacking direction of the impedance layer:

[0077] Wherein, t1 represents the total thickness of the acoustic impedance matching material along the stacking direction; x represents the vertical distance between the geometric center of the impedance layer and the surface of the acoustic impedance matching material away from the end to be matched; Z represents the vertical distance between the geometric center of the impedance layer and the surface of the acoustic impedance matching material away from the end to be matched; w represents the acoustic impedance of the matrix material, Z s Indicates the acoustic impedance of the target object to be matched.

[0078] In some embodiments of the present invention, the relationship between the filling rate f and the acoustic impedance of the impedance layer, and the relationship between the filling rate f and the effective sound velocity of the impedance layer are calculated by:

[0079] Select the Solid Mechanics module under Structural Mechanics in COMSOL Multiphysics.

[0080] For the unit cell structure with a filler filling rate of f, the simulation sets the unit cell structure to be a square with a cross-sectional area of ​​β 2 , where the cross-sectional area of ​​the filler is γ 2; According to the filling rate expression f = γ 2 / β 2 , and the model was built using COMSOL Multiphysics to obtain the calculation model I. The material parameters were set in sequence: the mass density of the matrix material, the sound velocity of the ultrasonic wave in the matrix material, the mass density of the filler, the longitudinal wave sound velocity and the transverse wave sound velocity of the ultrasonic wave in the filler (for example, when the matrix material is water and the filler is steel, the material parameters include: the mass density of water is 1000 kg / m 3 , the speed of sound is 1500m / s. The mass density of steel is 7800kg / m 3 , the speed of sound of longitudinal waves is 5800m / s, and the speed of sound of shear waves is 3200m / s);

[0081] Periodic boundary conditions are set at the upper and lower boundaries of the model; a boundary load of 1N / m is added to the left boundary of the model in the X direction. 2 force; a low-reflection boundary condition is set on the right boundary of the model to prevent wave reflection; in this model, the parameterized sweep range of the steel filling rate is set from 0 to 1; calculation model I calculates the relationship between the equivalent sound velocity, equivalent impedance and filling rate of the impedance layer in the low-frequency limit, specifically including:

[0082] The area component f of the resultant force per unit area is obtained by calculation model I x 、The volume fraction of unit volume acceleration a x ;

[0083] The linear strain L is calculated by calculation model I. x Using formula (2) and formula (3), the effective mass density and effective elastic modulus of the impedance layer can be calculated respectively:

[0084] The calculation formula of effective mass density is:

[0085] Among them, D eff is the effective mass density (kg / m 3 ), f x is the surface integral of the resultant force per unit area (N), a x is the volume fraction of the unit volume acceleration (m 4 / s 2 );

[0086] The calculation formula of effective elastic modulus is:

[0087] Among them, B eff is the effective elastic modulus (Pa), F x is the linear stress (N / m 2 ), L x is the linear strain;

[0088] Formula (4) and formula (5) can be used to calculate the effective impedance of the impedance layer and the effective sound velocity of the ultrasonic wave in the impedance layer respectively:

[0089] Effective impedance calculation formula:

[0090] Among them, Z eff is the effective impedance (rayl), B eff is the effective elastic modulus (Pa), D eff is the effective density (kg / m 3 ).

[0091] The formula for calculating effective sound speed is:

[0092] The relationship between the filling rate f of the impedance layer in the low-frequency limit and the effective impedance of the impedance layer, and the relationship between the filling rate f and the effective sound velocity of the ultrasonic wave in the impedance layer can be obtained.

[0093] It should be noted that, based on the effective medium theory, considering the effective mass density of the static mixed material under the long-wave approximation (low-frequency limit), the lattice constant should be much smaller than the wavelength of the background medium. Under this condition, by limiting β < λ / 9 to meet the low-frequency limit condition of the impedance layer, for example, when the ultrasonic frequency is 1.3 MHz, the parameter of the unit cell structure is limited to 0.125 mm, which is much smaller than the wavelength λ of the 1.3 MHz sound wave in water.

[0094] According to a third aspect of the present invention, an ultrasonic transducer is provided, comprising the above-mentioned acoustic impedance matching material.

[0095] In some embodiments of the present invention, the ultrasonic transducer includes an impedance matching layer, and the impedance matching layer includes the acoustic impedance matching material.

[0096] In some embodiments of the present invention, a liquid material circulation system is further included, which can be used to recycle the matrix material in the acoustic impedance matching material and promote the flow of the liquid matrix material in the acoustic impedance matching material.

[0097] A fourth aspect of the present invention provides an ultrasonic instrument comprising the ultrasonic transducer or the acoustic impedance matching material.

[0098] In some embodiments of the present invention, the ultrasound instrument includes a B-type ultrasound diagnostic instrument.

[0099] A fifth aspect of the present invention provides the use of the above-mentioned acoustic impedance matching material, ultrasonic transducer or ultrasonic instrument in the preparation of medical diagnostic equipment or medical treatment equipment.

[0100] In some embodiments of the present invention, the acoustic impedance matching material, ultrasonic transducer or ultrasonic instrument is used in the preparation of a diagnostic device or a therapeutic device for a brain disease. 1.1.2 Description of the Figures

[0101] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0102] FIG1 is a schematic diagram of an application scenario of an acoustic impedance matching material according to an embodiment of the present invention;

[0103] FIG2 is a schematic diagram of an application scenario of an acoustic impedance matching material containing multiple impedance layers according to an embodiment of the present invention;

[0104] FIG3 is a schematic diagram of the structures of a non-impedance matching system, a single-layer impedance matching system, and a four-layer gradient impedance matching system;

[0105] 4 is a graph showing changes in the effective sound velocity and effective impedance of the impedance layer as a function of the steel filling ratio in the impedance layer under low-frequency limit conditions in Example 1 of the present invention;

[0106] FIG5 is a relationship curve diagram of formula (1) in Example 1 of the present invention;

[0107] FIG6 is a schematic diagram of the cross-sectional structure of a single unit cell structure proposed in the COMSOL modeling in Example 1 of the present invention;

[0108] FIG7 is a schematic diagram of the structure of the propagation of a plane wave in an n-layer medium proposed in the analytical calculation;

[0109] FIG8 is the transmission spectra of the effective dielectric parameters of the non-impedance matching system, the single-layer impedance matching system, and the four-layer gradient impedance matching system obtained by analytical calculation;

[0110] Figure 9 shows the transmission spectra of effective dielectric parameters of the no impedance matching system, and the one-layer, two-layer to six-layer gradient impedance matching system obtained by analytical calculation;

[0111] Figure 10 is a comparison of the transmission spectra of the four-layer gradient impedance matching transcranial system obtained by analytical calculation and finite element numerical simulation. 1.1.3 Specific Implementation Methods

[0112] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0113] The experimental methods in the following examples, for which specific conditions are not specified, are generally performed in accordance with conventional conditions in the art or conditions recommended by the manufacturers; the raw materials and reagents used, unless otherwise specified, are all commercially available from conventional markets.

[0114] The acoustic impedance matching material of the present invention can be used as a gradient impedance matching layer for transcranial ultrasound. Schematic diagrams of application scenarios are shown in Figures 1 and 2. In the figures, t1 represents the thickness of the gradient impedance matching layer, and t2 represents the thickness of the skull. Figure 2 shows a schematic diagram of an application scenario for an acoustic impedance matching material (containing multiple impedance layers) containing a gradient stacked impedance layer.

[0115] Example 1

[0116] This embodiment discloses an acoustic impedance matching material, which includes four impedance layers stacked together. Along the stacking direction, the thickness of each impedance layer is 500 μm. Each impedance layer is composed of 16 unit cell structures arranged in a 4*4 matrix. The unit cell structures in the same impedance layer are the same. Each impedance layer includes a liquid material - water (acoustic impedance of water: 1.5 Mrayl) and a filler - steel (acoustic impedance of steel: 45.24 Mrayl). By adjusting the volume filling rate of steel in each impedance layer, the acoustic impedance of the acoustic impedance matching material is increased. The acoustic impedance of the impedance layer is between the acoustic impedance of water and the acoustic impedance of the skull. The structure of multiple impedance layers is shown in the t1 section of Figure 3 (c). The design and preparation process of the acoustic impedance matching material includes:

[0117] (I) The relationship between the filling ratio f of the filler in the impedance layer and the acoustic impedance of the impedance layer, and the relationship between the filling ratio f and the effective sound velocity of the ultrasonic wave in the impedance layer were calculated using the finite element method, as shown in FIG4 ;

[0118] The number of preset impedance layers is n', where n'=4; one impedance layer is provided along the stacking direction, comprising s columns of unit cell structures, each column comprising 4 unit cell structures, and the thickness of the unit cell structure along the stacking direction is β=0.125 mm; the wavelength of a 1.3 MHz sound wave in water is λ, where β<λ / 9.

[0119] (II) According to the preset stacking direction of the impedance layer and the effective medium theory, the acoustic impedance of the impedance layer at different positions of the acoustic impedance matching material is determined using formula (1):

[0120] Wherein, t1 represents the total thickness of the acoustic impedance matching material along the stacking direction; x represents the vertical distance between the geometric center of the impedance layer and the surface of the acoustic impedance matching material away from the end to be matched; Z w represents the acoustic impedance of the matrix material, Z srepresents the acoustic impedance of the target object to be matched; the relationship curve of formula (1) is shown in Figure 5;

[0121] (III) The thickness centers (geometric centers) of the four impedance layers are calculated to be located at the positions of the acoustic impedance matching materials. Combined with FIG5 , the effective impedances of each impedance layer are obtained. Along the stacking direction, they are 1.768 Mrayl, 2.458 Mrayl, 3.417 Mrayl, and 4.75 Mrayl, respectively. The effective sound velocities are 1435 m / s, 1370 m / s, 1360 m / s, and 1400 m / s, respectively. As shown in FIG4 , the steel filling rates in the four impedance layers are 0.12, 0.34, 0.525, and 0.673, respectively.

[0122] The effective velocity of ultrasound in the impedance layer was determined by the steel filling ratio in the impedance layer. The wavelength λ1 of ultrasound in the impedance layer was calculated, and the average value λ1' of the wavelength λ1 was calculated. The thickness of each impedance layer was limited to approximately λ' / 4. Finally, the thickness of each impedance layer was limited to 500 μm. It was determined that each impedance layer contained four columns of unit cell structures along the stacking direction, and each column contained four unit cell structures.

[0123] (IV) Selecting corresponding impedance layers according to the determined filling rate, and stacking the impedance layers in sequence according to preset stacking positions to form an acoustic impedance matching material.

[0124] The calculation process of the relationship between the filling rate f and the acoustic impedance of the impedance layer and the relationship between the filling rate f and the effective sound velocity of the impedance layer in step (I) includes: using the effective density and effective elastic modulus formulas at the low frequency limit, combined with the effective impedance and effective sound velocity calculation formulas, to calculate the relationship between the effective impedance and effective sound velocity as the filling rate changes from 0 to 1. The calculation process of the effective parameters at the low frequency limit includes:

[0125] Select the physical field: This example studies the density and longitudinal wave velocity of a water-steel composite material. Therefore, the Solid Mechanics module under Structural Mechanics in COMSOL is selected to perform mechanical analysis on the composite material.

[0126] Model establishment: This embodiment selects a 2D study and establishes a cross-sectional area of ​​β for the impedance layer with a filler filling rate f. 2 , where the cross-sectional area of ​​the filler is γ 2 The filling rate of the unit cell structure is expressed as f = γ 2 / β 2 (That is, it represents the volume ratio of the filler in the unit cell structure). COMSOL was used to build a model based on this model to obtain calculation model I, whose structure is shown in Figure 6.

[0127] Set material parameters: along the stacking direction, the side length β of the unit cell structure is proposed to be 0.125mm, which is much smaller than the wavelength of 1.3MHz ultrasound in water, which is 1.15mm. The mass density of water is 1000kg / m 3 , the speed of sound is 1500m / s. The mass density of steel is 7800kg / m 3 , the speed of sound of longitudinal waves is 5800m / s, and the speed of sound of transverse waves is 3200m / s.

[0128] Set boundary conditions: In this model, periodic boundary conditions are set at the upper and lower boundaries of the model; a boundary load of 1N / m is added to the left boundary of the model to apply 1N / m in the X direction. 2 A low-reflecting boundary condition is set on the right boundary of the model to prevent wave reflection.

[0129] Meshing: Since the calculation amount of the two-dimensional structure is relatively small, the model is meshed carefully to ensure the accuracy of the calculation.

[0130] Solving the Model: In this model, a parametric sweep of the fill fraction of steel is set up from 0 to 1.

[0131] Data processing: Calculate the relationship between the equivalent sound velocity, equivalent impedance and filling rate of the impedance layer at the low-frequency limit through calculation model I, including:

[0132] The area component f of the resultant force per unit area is obtained by calculation model I x 、The volume fraction of unit volume acceleration a x ;

[0133] The linear strain L is calculated by calculation model I. x ;

[0134] Using formula (2) and formula (3), the effective mass density and effective elastic modulus of the steel-aluminum composite material in the low-frequency limit can be calculated respectively:

[0135] The calculation formula of effective mass density is:

[0136] Among them, D eff is the effective mass density (kg / m 3 ), f x is the surface integral of the resultant force per unit area (N), a x is the volume fraction of the unit volume acceleration (m 4 / s 2 );

[0137] The calculation formula of effective elastic modulus is:

[0138] Among them, B effis the effective elastic modulus (Pa), F x is the linear stress (N / m 2 ), L x is the linear strain;

[0139] Formula (4) and formula (5) can be used to calculate the effective impedance of the impedance layer and the effective sound velocity of the ultrasonic wave in the impedance layer respectively:

[0140] Effective impedance calculation formula:

[0141] Among them, Z eff is the effective impedance (rayl), B eff is the effective elastic modulus (Pa), D eff is the effective density (kg / m 3 ).

[0142] The formula for calculating effective sound speed is:

[0143] The relationship between the filling rate f of the impedance layer in the low-frequency limit and the acoustic impedance of the impedance layer, and the relationship between the filling rate f and the effective sound velocity of the impedance layer can be obtained, as shown in FIG4 .

[0144] In which, the acoustic impedance matching material also includes a limiting membrane material (not shown in the figure), which can limit the position of the filler in the acoustic impedance matching material; each impedance layer contains a limiting membrane material, and the limiting membrane material in each impedance layer encloses a filling area, and the filling area is filled with steel. The water in the impedance layer can be located in the filling area, or / and, the water is located outside the filling area.

[0145] The limiting film is made of polytetrafluoroethylene (or polyurethane or polyethylene terephthalate), and the thickness of the limiting film is 0.5-2% of the thickness of each impedance layer.

[0146] Example 2

[0147] This embodiment discloses an acoustic impedance matching material with a thickness of 500 μm. The only difference from Example 1 is that this embodiment comprises only one impedance layer, as shown in segment t1 of Figure 3(b). The impedance layer has a steel filling ratio of 0.437, an effective impedance of 2.9 Mrayl, and an effective sound velocity of 1360 m / s. The calculation methods for the filling ratio, effective impedance, and effective sound velocity are the same as those in Example 1.

[0148] Example 3

[0149] This embodiment discloses an acoustic impedance matching material with a thickness of 1 mm. The only difference from Example 1 is that this embodiment comprises two stacked impedance layers. Along the stacking direction, each impedance layer is 500 μm thick. The steel filling fractions in the impedance layers are 0.2334 and 0.633, respectively. The effective impedances are 2.085 Mrayl and 4.029 Mrayl, respectively. The effective sound velocities are 1403 m / s and 1394 m / s, respectively. The calculation methods for the filling fraction, effective impedance, and effective sound velocity are the same as those in Example 1.

[0150] Example 4

[0151] This embodiment discloses an acoustic impedance matching material with a thickness of 1.5 mm. The only difference from Example 1 is that this embodiment comprises three stacked impedance layers. Along the stacking direction, each impedance layer has a thickness of 500 μm. The steel filling fractions in the impedance layers are 0.1568, 0.433, and 0.6485, respectively. The effective impedances are 1.864 Mrayl, 2.879 Mrayl, and 4.447 Mrayl, respectively. The effective sound velocities are 1428 m / s, 1365 m / s, and 1400 m / s, respectively. The calculation methods for the filling fraction, effective impedance, and effective sound velocity are the same as those in Example 1.

[0152] Example 5

[0153] This embodiment discloses an acoustic impedance matching material having a thickness of 2.5 mm. The only difference from Example 1 is that this embodiment comprises five stacked impedance layers. Along the stacking direction, each impedance layer has a thickness of 500 μm. The steel filling fractions in the impedance layers are 0.096, 0.2892, 0.4367, 0.5733, and 0.686, respectively. The effective impedances are 1.711 Mrayl, 2.227 Mrayl, 2.898 Mrayl, 3.772 Mrayl, and 4.909 Mrayl, respectively. The effective sound velocities are 1453 m / s, 1387 m / s, 1365 m / s, 1375 m / s, and 1420 m / s, respectively. The calculation methods for the filling fraction, effective impedance, and effective sound velocity are the same as those in Example 1.

[0154] Example 6

[0155] This embodiment discloses an acoustic impedance matching material having a thickness of 3 mm. The only difference between this embodiment and the first embodiment is that the acoustic impedance matching material in this embodiment includes six stacked impedance layers. Along the stacking direction, the thickness of each impedance layer is 500 μm. The steel filling fractions in the impedance layers are 0.0803, 0.2247, 0.373, 0.4962, 0.631, and 0.6939, respectively. The effective impedances are 1.674 Mrayl, 2.058 Mrayl, 2.597 Mrayl, 3.234 Mrayl, 4.028 Mrayl, and 5.016 Mrayl, respectively. The effective sound velocities are 1460 m / s, 1405 m / s, 1371 m / s, 1365 m / s, 1392 m / s, and 1424 m / s, respectively. The calculation methods for the filling fraction, effective impedance, and effective sound velocity are the same as those in the first embodiment.

[0156] Example 7

[0157] This embodiment discloses an ultrasonic transducer, including an impedance matching layer, wherein the impedance matching layer includes the acoustic impedance matching material prepared in any one of embodiments 1 to 6.

[0158] This embodiment also discloses an ultrasonic instrument, including the ultrasonic transducer in this embodiment.

[0159] Test example

[0160] This test example verifies the effect of the acoustic impedance matching material in the embodiment, specifically including:

[0161] The acoustic impedance matching materials in Examples 1 to 6 are used as acoustic impedance matching layers to form a four-layer gradient impedance matching system, a single-layer impedance matching system, a two-layer impedance matching system, a three-layer impedance matching system, a five-layer impedance matching system, and a six-layer impedance matching system for transcranial ultrasound examination and treatment, and are compared and verified with a non-impedance matching system that does not contain acoustic impedance matching material. Schematic diagrams of the non-impedance matching system, the single-layer impedance matching system, and the four-layer gradient impedance matching system are shown in Figures 3(a), 3(b), and 3(c).

[0162] 1. Based on the effective medium theory in the low-frequency limit, we first analyzed and calculated the ultrasound transmission enhancement capabilities of a transcranial system with no impedance matching, a single-layer impedance matching system, and a transcranial system with two to six layers of gradient impedance matching. Ultrasound was incident on the left boundary of the model and received on the right boundary, and the transmission spectra corresponding to the effective medium parameters of these systems were calculated analytically.

[0163] The analytical calculation of transmittance includes the following steps:

[0164] Consider the propagation of a plane wave in an n-layer medium, as shown in Figure 7.

[0165] The relationship between the transmitted sound pressure and the reflected sound pressure at the first and last interfaces:

[0166] Write formula ① in the following form:

[0167] Where T is the transfer matrix of n-layer medium, and its expression should be:

[0168] Where T is a 2×2 matrix, t 11 , t 12 , t 21 , t 22 is the matrix element of the transfer matrix.

[0169] T l is the transfer matrix of the lth layer, expressed as:

[0170] Using formula ②, the relationship between the incident wave, reflected wave, transmitted wave and matrix elements is:

[0171] Solving formula ⑤, we can obtain the sound intensity amplitude reflection and sound intensity transmission coefficient of the multi-layer model as follows:

[0172] Sound intensity reflection coefficient R I :

[0173] Sound transmission coefficient T I :

[0174] From the above, input an arbitrary sound pressure p ia , and then use formula ⑦ to obtain the transmittance of the system with the corresponding number of layers.

[0175] (1) The ultrasound transmission enhancement capabilities of the non-impedance-matching transcranial system, the single-layer impedance-matching transcranial system, and the four-layer gradient impedance-matching transcranial system were calculated analytically. The results are shown in Figure 8.

[0176] As shown in Figure 8, the transmission of the non-impedance-matching transcranial system in the frequency range of 0 to 1.3 MHz fluctuates, and the transmission is very low at most frequencies. Taking the transmission valley of 0.65 MHz as an example, after adding a single-layer impedance matching layer and a four-layer gradient impedance matching layer to the system, it was found that the transmission was improved at 0.65 MHz, and the four-layer gradient impedance matching showed high transmittance over a wide frequency range. The bandwidth is defined as the frequency range in which the transmittance is greater than 0.5. In comparison, the bandwidth of the four-layer gradient impedance matching transcranial system (0.19 to 1.17 MHz) is wider than the single-layer matching bandwidth (0.29 to 1.01 MHz).

[0177] (2) Using the same method as (1), the ultrasound transmission enhancement capabilities of the non-impedance-matching transcranial system, the single-layer impedance-matching transcranial system, and the two- to six-layer gradient impedance-matching transcranial system were analyzed and calculated. The results are shown in Figure 9.

[0178] 2. To further verify the feasibility, the transmission spectrum of the four-layer gradient impedance matching transcranial transurethral system was simulated using finite element methods. As shown in Figure 10, the numerical simulation results of the transmission spectrum of the four-layer gradient impedance matching transcranial transurethral system were compared with the analytical calculation results. It was found that both curves have a high degree of fit and exhibit a high transmission bandwidth.

[0179] The transmittance finite element calculation process includes the calculation of acoustic transmittance in water, so the physical field of the COMSOL model is selected as acoustic-solid interaction under acoustics.

[0180] Model parameters: The speed of sound in water is 1500 m / s and the density is 1000 kg / m 3 ;The mass density of steel is 7800kg / m 3 , the longitudinal wave speed is 5800m / s, and the shear wave speed is 3200m / s. Radiation boundary conditions are added to the leftmost water boundary and the rightmost soft tissue boundary of the computational domain to ensure that the sound waves are not reflected. The plane wave is emitted with the left water boundary as the incident pressure field boundary, and the incident sound pressure amplitude is set to 1MPa; the acoustic-structure boundary condition is set at the interface between the solid and the water to ensure that the sound waves can propagate normally. The upper and lower boundaries of the model are hard sound field boundary conditions. Finally, the model is integrated at the incident and exit boundaries, and the incident and exit energies are calculated using the Poynting vector formula. The transmittance of the model can be obtained by dividing the exit energy by the incident energy. The calculation frequency domain is 0~1.3MHz.

[0181] The calculation results are shown in Figure 10. The numerical simulation results of the transmission spectrum of the four-layer gradient impedance matching transcranial model are compared with the analytical results of the corresponding effective parameter homogeneous medium transmission spectrum. It is found that the two curves have a high degree of fit and both have a high transmission bandwidth.

[0182] The results show that the steel-filled-water matrix composite material that meets the low-frequency limit can flexibly adjust the equivalent impedance by adjusting the steel filling ratio, and then be used for gradient impedance matching of the skull to achieve broadband transmission enhancement through the skull.

[0183] In summary, the present invention controls the acoustic impedance by regulating the filling rate of steel in water, thereby achieving a gradual transition from the acoustic impedance of water to the acoustic impedance of the skull, and obtaining an acoustic impedance matching material with a gradient acoustic impedance, which satisfies the requirement of being adjustable from the acoustic impedance of water to the acoustic impedance of the skull, and obtains a gradient impedance matching material that can enhance ultrasonic cranial penetration in a wider frequency range, so that ultrasonic energy can maintain high penetrability in a wide frequency range and be transmitted through the skull to soft tissue.

[0184] Based on the effective medium theory under the low-frequency limit, the present invention can calculate the effective impedance of the impedance layer with different filler (such as steel) filling rates under the low-frequency limit and the relationship curve between the effective sound velocity and the filling rate. According to the preset stacking direction of the impedance layer, the effective impedance of the impedance layer located at different positions of the acoustic impedance matching material is determined according to formula (1), and then the filling rate of the filler in each impedance layer is obtained. The impedance layers are stacked in sequence according to the stacking positions to form the acoustic impedance matching material.

[0185] The present invention uses a wide bandwidth of ultrasound, which can ensure that the ultrasound has high transmittance through the skull in a wide frequency range. Therefore, there is no need to worry about the selection range of ultrasound frequency, and it can cover transcranial imaging and treatment at different frequencies.

[0186] It should be noted that, in this document, “about” for numerical values ​​means an error of ±5%.

[0187] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. An acoustic impedance matching material, characterized in that: It comprises a plurality of impedance layers stacked in layers, wherein the impedance layers are arranged in sequence along the stacking direction according to an exponential variation relationship of acoustic impedance; each impedance layer comprises a liquid matrix material and a filler in the liquid matrix material.

2. The acoustic impedance matching material according to claim 1, characterized in that: Along the stacking direction, the impedance layers are arranged in sequence according to the acoustic impedance exponential variation relationship shown in formula (1): Wherein, t1 represents the total thickness of the acoustic impedance matching material along the stacking direction; x represents the vertical distance between the geometric center of the impedance layer and the surface of the side of the acoustic impedance matching material away from the end to be matched; Z w represents the acoustic impedance of the matrix material, Z s Indicates the acoustic impedance of the target object to be matched; Preferably, along the stacking direction, the acoustic impedance of the impedance layer is between the acoustic impedance of water and the acoustic impedance of the skull.

3. The acoustic impedance matching material according to claim 1, characterized in that: The relationship between the filling rate f of the filler in the impedance layer and the acoustic impedance of the impedance layer is calculated by the finite element method.

4. The acoustic impedance matching material according to claim 1, characterized in that: An impedance layer includes a plurality of unit cell structures, and a thickness of a unit cell structure along the stacking direction is β, wherein the wavelength of ultrasound in water is λ, and β and λ satisfy: β<λ / 9; Preferably, the number of the impedance layers is 2 to 6; Preferably, the thickness h of the impedance layer along the stacking direction is 200-700 μm.

5. The acoustic impedance matching material according to claim 1, characterized in that: The acoustic impedance of the matrix material is not greater than the acoustic impedance of water; and / or the acoustic impedance of the filler is not less than 1.2 times the acoustic impedance of the skull; Preferably, the acoustic impedance of the matrix material is 0.5 to 1.5 Mrayl; and / or the acoustic impedance of the filler is 10 to 100 Mrayl; Preferably, the matrix material includes water; and / or the filler material includes at least one of a polymer material, a silicon material, a ceramic material or a metal material; Preferably, the material of the filler includes at least one of iron, nickel, copper, aluminum, titanium, tungsten, zinc, gold, silver or platinum; Preferably, the shape of the filler includes at least one of a cylinder, a sphere or a cuboid, and / or the filler is Hollow or solid fill.

6. The acoustic impedance matching material according to claim 1, characterized in that: The acoustic impedance matching material further includes a limiting material, and the limiting material can limit the position of the filler in the acoustic impedance matching material; Preferably, the acoustic impedance of the limiting material is 80-120% of the acoustic impedance of the base material.

7. A method for preparing the acoustic impedance matching material according to any one of claims 1 to 6, characterized in that: The steps include: S1, using the finite element method to calculate the relationship between the filling rate f of the filler in the impedance layer and the acoustic impedance of the impedance layer; The number of impedance layers n' is preset, one impedance layer includes a plurality of unit cell structures, and the thickness of one unit cell structure along the stacking direction is preset to be β; in each impedance layer, β<λ / 9 is satisfied; wherein λ is the wavelength of ultrasound in water; S2, determining the acoustic impedance of each impedance layer in the acoustic impedance matching material according to a preset stacking direction of the impedance layers and a relationship in which the impedance layers are arranged in sequence according to an exponential change relationship of acoustic impedance; S3, determining the filling rate f of the filler in each impedance layer according to the determined relationship between the acoustic impedance and the filling rate f of the impedance layer; S4, selecting corresponding impedance layers according to the determined filling rate f, and stacking the impedance layers in sequence according to a preset stacking direction to form an acoustic impedance matching material; Preferably, the relationship between the filling rate f and the effective sound velocity of the ultrasonic wave in the impedance layer is calculated by the finite element method; according to the filling rate f of each impedance layer filler obtained in step S3, the effective sound velocity of the ultrasonic wave in each impedance layer is obtained, and then the wavelength λ1 of the ultrasonic wave in each impedance layer is obtained, and the average value λ1' of the wavelength λ1 is calculated to satisfy: the thickness h of the impedance layer along the stacking direction is 0.22λ1'~0.28λ1'.

8. An ultrasonic transducer, characterized in that: The acoustic impedance matching material comprises the acoustic impedance matching material according to any one of claims 1 to 6.

9. An ultrasonic instrument, characterized in that: It comprises the acoustic impedance matching material according to any one of claims 1 to 6 or the ultrasonic transducer according to claim 8.

10. Use of the acoustic impedance matching material according to any one of claims 1 to 6, the ultrasonic transducer according to claim 8, or the ultrasonic instrument according to claim 9 in the preparation of medical diagnostic equipment or medical treatment equipment.

Images