WO2025035661A1 - 一种声学阻抗匹配材料及其制备方法与应用 - Google Patents

一种声学阻抗匹配材料及其制备方法与应用 Download PDF

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WO2025035661A1
WO2025035661A1 PCT/CN2023/137585 CN2023137585W WO2025035661A1 WO 2025035661 A1 WO2025035661 A1 WO 2025035661A1 CN 2023137585 W CN2023137585 W CN 2023137585W WO 2025035661 A1 WO2025035661 A1 WO 2025035661A1
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Prior art keywords
impedance
acoustic impedance
layer
acoustic
impedance matching
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French (fr)
Inventor
蔡飞燕
吉鹏程
李永川
贾晗
郑海荣
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Shenzhen Institute of Advanced Technology of CAS
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Shenzhen Institute of Advanced Technology of CAS
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
    • A61B8/08—Clinical applications
    • A61B8/0808—Clinical applications for diagnosis of the brain
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N7/00—Ultrasound therapy
    • A61N7/02—Localised ultrasound hyperthermia
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N7/00—Ultrasound therapy
    • A61N2007/0004—Applications of ultrasound therapy
    • A61N2007/0021—Neural system treatment
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N7/00—Ultrasound therapy
    • A61N2007/0004—Applications of ultrasound therapy
    • A61N2007/0021—Neural system treatment
    • A61N2007/0026—Stimulation of nerve tissue

Definitions

  • 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.
  • the detection methods of brain diseases mainly include CT, magnetic resonance imaging and ultrasound imaging technology.
  • transcranial ultrasound imaging technology has the advantages of simple device, no radiation, real-time, and portability compared with CT and MRI.
  • Transcranial ultrasound can not only realize the observation of brain diseases, but also can be used for the treatment of brain diseases due to its penetrating, focusing, thermal effect and other characteristics, which broadens the door to brain science research and brain disease treatment, and creates good news for patients with brain diseases. Therefore, transcranial ultrasound technology has extremely far-reaching prospects in the field of brain disease treatment.
  • the mismatch between the skull and background acoustic impedance causes various problems such as low imaging resolution and low focusing intensity.
  • the incident acoustic window usually mainly selects the temporal, occipital, mandibular and orbital parts as ultrasound acoustic windows, because the skull in these parts is thin or mainly cartilage, making it easy for ultrasound to cross the skull barrier to achieve the purpose of intracranial imaging and focusing.
  • the impact of the impedance mismatch of the skull on the ultrasound transmission energy is not considered, and the incident acoustic window mainly selects the temporal, occipital, mandibular and orbital parts, which cannot cover most areas of the brain and have blind spots, which seriously limits the application of ultrasound.
  • the present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art.
  • the present invention proposes an acoustic impedance matching material, which is applied to transcranial ultrasound technology, which can significantly reduce the impedance mismatch effect of the skull, ensure that ultrasound is transmitted to the soft tissue in the skull with high efficiency within a wide frequency range, and enable ultrasound to be incident into the skull at any part of the skull, thereby realizing ultrasound imaging and treatment of any target point, and has good application prospects.
  • the invention also provides a method for preparing the acoustic impedance matching material.
  • the invention also provides an ultrasonic transducer.
  • the invention also provides an ultrasonic instrument.
  • the present invention also proposes the application of the acoustic impedance matching material, ultrasonic transducer and ultrasonic instrument.
  • an acoustic impedance matching material comprising a plurality of stacked impedance 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 located in the liquid matrix material.
  • 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 in an exponential relationship, so that the acoustic impedance of the obtained acoustic impedance matching material changes gradiently from one end to the other.
  • 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 change of the acoustic impedance from the background medium to the skull is reduced, the impedance mismatch of the skull is reduced, and the impedance mismatch effect of the skull is reduced, so as to ensure that the ultrasound is transmitted to the soft tissue with high efficiency within a wide frequency range, and changing the incident ultrasound frequency can also make the ultrasound maintain high transmittance through the skull to meet the treatment needs of different brain diseases.
  • the background medium such as water
  • the acoustic impedance matching material of the present invention is used for transcranial ultrasound, which can keep ultrasound with sufficient energy and a wide bandwidth to enter the skull, with high imaging resolution and high focusing intensity, ensuring efficient ultrasonic brain disease observation and treatment process.
  • transcranial ultrasound neural stimulation can accurately focus and stimulate the target nervous system to achieve the treatment of nervous system diseases.
  • high-intensity focused transcranial ultrasound can be used to ablate diseased tissues, tumors, etc. through high-intensity energy at the focus, and can also melt the drug shell to achieve fixed-point drug delivery in the body.
  • the matrix material in the present invention is a liquid substance. Due to its fluidity, it can quickly absorb and transfer the heat caused by ultrasound in the skull, which effectively solves the problem of skull heating in traditional transcranial ultrasound technology.
  • the liquid matrix material in the present invention can make the acoustic impedance matching material and the target object to be matched fit closely, which is conducive to further matching of the skull impedance and better transcranial ultrasound effect.
  • 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.
  • the impedance layers are arranged in sequence according to the acoustic impedance exponential variation relationship shown in formula (1):
  • the end to be matched refers to the end of the acoustic impedance matching material that is used to contact or approach the target object to be matched.
  • the acoustic impedance of water is about 1.5 Mrayl, and the acoustic impedance of the skull is about 5.6 Mrayl.
  • the acoustic impedance of the impedance layer is between the acoustic impedance of water and the acoustic impedance of the skull.
  • water in this article refers to pure water.
  • the acoustic impedance gradient of the acoustic impedance matching material changes from one side to the other side, and the acoustic impedance is between 1.5 and 5.6 Mrayl.
  • 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 a finite element method.
  • the acoustic impedance of the impedance layer in the present invention is the effective acoustic impedance (hereinafter referred to as effective impedance).
  • the filling rate in this article refers to the volume filling rate, that is, the volume ratio of the filler in the impedance layer.
  • an impedance layer includes a plurality of unit cell structures, and a unit cell structure has a thickness of ⁇ along the stacking direction, wherein the wavelength of ultrasound in water is ⁇ , and ⁇ and ⁇ satisfy: ⁇ /9.
  • the units of ⁇ and ⁇ can both be meters (m), and water is used as the background medium.
  • s 2-6.
  • the wavelength of ultrasound can be obtained from the sound speed of ultrasound in the medium/the frequency of ultrasound.
  • each unit cell structure includes a filler and a matrix material.
  • the number of the impedance layers is 2 to 6.
  • the thickness h of the impedance layer along the stacking direction is 200-700 ⁇ m.
  • the thickness of each impedance layer is 500 ⁇ m.
  • the thickness of the impedance layer is 480-520 ⁇ m.
  • the number of impedance layers n' can be selected according to actual needs. By increasing the number of impedance layers of acoustic impedance matching materials, the transcranial bandwidth can be increased to achieve wide-bandwidth and high-efficiency transmission of ultrasound transcranial.
  • the thickness of each impedance layer is the same.
  • 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.
  • 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.
  • the material of the filler includes, but is not limited to: polymer materials, silicon materials, ceramic materials, and metal materials such as metal elements, metal oxides, and alloys, etc.
  • the material of the filler includes at least one of polymer materials, silicon materials, ceramic materials, metal elements, metal oxides, or alloys.
  • the material of the filler includes at least one of a polymer material, a silicon material, a ceramic material or a metal material.
  • the silicon-based material includes at least one of silicon or silicon dioxide.
  • the polymer material includes at least one of polymethyl methacrylate (PMMA), polyetheretherketone (PEEK), methacrylic resin, silicone rubber, and polydimethylsiloxane (PDMS).
  • PMMA polymethyl methacrylate
  • PEEK polyetheretherketone
  • methacrylic resin silicone rubber
  • PDMS polydimethylsiloxane
  • the ceramic material includes piezoelectric ceramics, such as PZT piezoelectric ceramics, PN piezoelectric ceramics, and PMN-PT piezoelectric ceramics.
  • 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.
  • 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.
  • the material of the filler includes iron, nickel, copper, aluminum, titanium, tungsten, zinc, At least one of gold, silver or platinum.
  • the iron includes but is not limited to pure iron, steel, etc.
  • the matrix material includes but is not limited to water, tap water, sea water, and other medical liquids.
  • 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.
  • the matrix material comprises water and the filler comprises steel.
  • 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.
  • the acoustic impedance matching material acoustic impedance range can be between the acoustic impedance of water and the acoustic impedance of the skull, satisfying the adjustable acoustic impedance from the acoustic impedance of water to the acoustic impedance of the skull, so that the gradient of the change of the acoustic impedance from water to the skull is reduced, which can reduce the impedance mismatch of the skull, reduce the influence of the impedance mismatch of the skull, ensure that the ultrasonic energy can maintain high efficiency transmission to the soft tissue within a wide frequency range, realize broadband impedance matching between water and the skull, and can change the incident ultrasonic frequency within a wide frequency range, and be applied to different medical technologies and medical processes.
  • the acoustic impedance matching material can enable ultrasound to maintain high transmittance through the skull within a wide frequency range covering low frequency (220kHz) to
  • 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 influence of skull impedance mismatch during transcranial ultrasound penetration, thereby ensuring broadband, efficient and directional transmission of transcranial ultrasound. Therefore, the present invention has great application potential in broadband ultrasound imaging and treatment.
  • water is used as the matrix material. Since water has a large specific heat capacity and fluidity, it 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.
  • the matrix material includes several liquid materials.
  • At least one liquid material of the matrix material can flow within the acoustic impedance matching material.
  • one of the impedance layers contains one or more of the fillers.
  • one impedance layer contains a plurality of fillers, wherein the plurality of fillers Evenly distributed in the impedance layer.
  • one impedance layer contains a plurality of the same fillers, and the plurality of fillers are uniformly distributed in the impedance layer.
  • a plurality of the fillers are arranged in a matrix in the impedance layer.
  • the shape of the filler includes but is not limited to regular or irregular shapes such as cylinders, spheres, and cuboids.
  • the filler may be a hollow filler or a solid filler. Among them, the hollow filler can further enrich the selection of filler size and type.
  • 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.
  • the filler is a composite material (such as a hollow structure)
  • its acoustic impedance should be its effective acoustic impedance.
  • the cylinder includes a solid cylinder or a hollow cylinder
  • the sphere includes a solid sphere or a hollow sphere
  • the cuboid includes a solid cuboid or a hollow cuboid.
  • the acoustic impedance matching material further includes a limiting material, which can limit the position of the filler in the acoustic impedance matching material.
  • a limiting material which can limit the position of the filler in the acoustic impedance matching material.
  • the position of the filler in the impedance layer can be fixed by the limiting material, thereby limiting the position of the filler in the acoustic impedance matching material.
  • the matrix material is a liquid material, and a limiting material with an acoustic impedance similar to that of the matrix material can be optionally used to fix, connect and combine the filler, such as a membrane structure.
  • the acoustic impedance of the limiting material is 80-120% of the acoustic impedance of the base material, and can be 95-105%.
  • each of the impedance layers contains the limiting material, and the limiting material in each of the impedance layers encloses a filling area, and the filling area is filled with the filler.
  • the matrix material is located in the filling area, or/and, the matrix material is located outside the filling area.
  • the limiting material is a limiting film material.
  • the limiting material includes but is not limited to polytetrafluoroethylene, polyurethane or polyethylene terephthalate.
  • the limiting material includes at least one of polytetrafluoroethylene, polyurethane or polyethylene terephthalate.
  • the film thickness of the limiting film material is within 0.5 to 5% of the thickness of the impedance layer.
  • a second aspect of the present invention provides a method for preparing an acoustic impedance matching material, comprising the following steps:
  • the number of impedance layers n' is preset, and one impedance layer includes a plurality of unit cell structures.
  • the thickness of one unit cell structure along the stacking direction is preset to be ⁇ ; in each impedance layer, ⁇ /9 is satisfied; wherein ⁇ is the wavelength of ultrasound in water;
  • step S1 by limiting ⁇ /9, the impedance layer structure dimension of each layer satisfies the low-frequency limit condition.
  • step S2 the acoustic impedance of each impedance layer in the acoustic impedance matching material is determined according to the preset number n' of impedance layers and their stacking directions, and the acoustic impedance is arranged in sequence according to the relationship that the acoustic impedance changes in an exponential e relationship.
  • n' values of x/t 1 can be uniformly selected from 0 to 1 according to the number (number) of impedance layers n', and the impedance value corresponding to the selected x/t 1 can be obtained.
  • the exponential e relationship of formula (1) can be converted into a relationship diagram.
  • 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; the effective sound velocity of the ultrasonic wave in each impedance layer is obtained according to the filling rate f of the filler of each impedance layer obtained in step S3, and then the wavelength ⁇ 1 of the ultrasonic wave in each impedance layer is obtained, and the average value ⁇ 1 ' of the wavelength ⁇ 1 is calculated to satisfy: the thickness h of the impedance layer along the stacking direction is 0.22 ⁇ 1 ' ⁇ 0.28 ⁇ 1 '.
  • the number of unit cell structures in an impedance layer along the stacking direction is obtained.
  • the number of columns of the unit cell structures in an impedance layer can be obtained according to h and ⁇ .
  • the total number of unit cell structures in an impedance layer is set.
  • step S2 according to the preset stacking direction of the impedance layer, the acoustic impedance of the impedance layer located at different positions of the acoustic impedance matching material is determined according to formula (1):
  • 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
  • Zw represents the acoustic impedance of the base material
  • Zs represents the acoustic impedance of the target object to be matched.
  • 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:
  • the mass density of steel is 7800kg/m 3 , the longitudinal wave sound velocity is 5800m/s, and the transverse wave sound velocity is 3200m/s);
  • Periodic boundary conditions are set at the upper and lower boundaries of the model; a boundary load is added to the left boundary of the model to apply a force of 1N/ m2 in the X direction; a low reflection boundary condition is set at 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, including:
  • the area component f x of the resultant force per unit area and the volume component a x of the acceleration per unit volume are calculated by calculation model I;
  • the linear strain L x is calculated by calculation model I.
  • the effective mass density and effective elastic modulus of the impedance layer can be calculated by formula (2) and formula (3) respectively:
  • 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 integral of the acceleration per unit volume (m 4 /s 2 );
  • B eff is the effective elastic modulus (Pa)
  • F x is the linear stress (N/m 2 )
  • L x is the linear strain
  • 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:
  • Z eff is the effective impedance (rayl)
  • B eff is the effective elastic modulus (Pa)
  • D eff is the effective density (kg/m 3 ).
  • 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.
  • the lattice constant should be much smaller than the wavelength of the background medium.
  • the parameter of the unit cell structure is limited to 0.125 mm, which is much smaller than the wavelength ⁇ of the 1.3 MHz sound wave in water.
  • an ultrasonic transducer comprising the above-mentioned acoustic impedance matching material.
  • the ultrasonic transducer includes an impedance matching layer, wherein the impedance matching layer includes Including the acoustic impedance matching material.
  • a liquid material circulation system is also included, which can be used for recycling the matrix material in the acoustic impedance matching material and promoting the flow of the liquid matrix material in the acoustic impedance matching material.
  • an ultrasonic instrument comprising the ultrasonic transducer or the acoustic impedance matching material.
  • the ultrasound instrument includes a B-type ultrasound diagnostic instrument.
  • a fifth aspect of the present invention proposes 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.
  • 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.
  • FIG1 is a schematic diagram of an application scenario of an acoustic impedance matching material in an embodiment of the present invention
  • FIG2 is a schematic diagram of an application scenario of an acoustic impedance matching material containing multiple impedance layers in an embodiment of the present invention
  • 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;
  • Example 4 is a graph showing the variation of the effective sound velocity and the effective impedance of the impedance layer with the steel filling rate in the impedance layer under the low frequency limit condition in Example 1 of the present invention
  • FIG5 is a relationship curve diagram of formula (1) in Example 1 of the present invention.
  • 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.
  • 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
  • FIG8 is a transmission spectrum of effective medium parameters of a system without impedance matching, a single-layer impedance matching system, and a four-layer gradient impedance matching system obtained by analytical calculation;
  • FIG9 is a transmission spectrum of effective medium parameters of a system without impedance matching, and a system with one, two to six layers of gradient impedance matching obtained by analytical calculation;
  • FIG10 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.
  • the acoustic impedance matching material of the present invention can be used as a gradient impedance matching layer for transcranial ultrasound, and the schematic diagrams of the application scenarios are shown in Figures 1 and 2, in which 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 the application scenario of an acoustic impedance matching material (containing multiple impedance layers) containing a gradient stacked impedance layer.
  • This embodiment discloses an acoustic impedance matching material, which includes 4 impedance layers stacked together. Along the stacking direction, the thickness of each impedance layer is 500 ⁇ m. Each impedance layer is composed of 16 unit cell structures arranged in a 4*4 matrix, and 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 changes incrementally.
  • 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 t 1 section in Figure 3 (c).
  • the design and preparation process of the acoustic impedance matching material includes:
  • the acoustic impedance of the impedance layer located at different positions of the acoustic impedance matching material is determined by formula (1):
  • 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;
  • Zw represents the acoustic impedance of the base material, and Zs represents the acoustic impedance of the target object to be matched; the relationship curve of formula (1) is shown in FIG5 ;
  • the thickness centers (geometric centers) of the four impedance layers are calculated to be located at the positions of the acoustic impedance matching materials.
  • 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.
  • the steel filling rates in the four impedance layers are 0.12, 0.34, 0.525, and 0.673, respectively;
  • the effective sound velocity of ultrasonic waves in the impedance layer is obtained by the steel filling rate in the impedance layer, and the wavelength ⁇ 1 of ultrasonic waves in the impedance layer is calculated.
  • the average value ⁇ 1 ' of the wavelength ⁇ 1 is calculated, and the thickness of an impedance layer is limited to about ⁇ '/4; finally, the thickness of each impedance layer is limited to 500 ⁇ m; it is determined that along the stacking direction, each impedance layer contains 4 columns of unit cell structures, and each column contains 4 unit cell structures;
  • 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 formula under the low-frequency limit, combined with the effective impedance and effective sound velocity calculation formula, to calculate the relationship between the effective impedance and the effective sound velocity and the filling rate when the filling rate is from 0 to 1.
  • the calculation process of the effective parameters under the low-frequency limit includes:
  • This embodiment selected a 2D study.
  • a unit cell structure with a cross-sectional area of ⁇ 2 and a cross-sectional area of ⁇ 2 of the filler was established.
  • COMSOL was used to build a model according to this model to obtain a calculation model I, whose structure is shown in FIG6 .
  • the side length ⁇ of the unit cell structure is proposed to be 0.125mm, which is much smaller than the wavelength of 1.3MHz ultrasound in water, 1.15mm, the mass density of water is 1000kg/ m3 , and the sound speed is 1500m/s.
  • the mass density of steel is 7800kg/ m3 , the longitudinal wave speed is 5800m/s, and the transverse wave speed is 3200m/s.
  • calculation model I The relationship between the equivalent sound velocity, equivalent impedance and filling rate of the impedance layer at the low-frequency limit is calculated by calculation model I, including:
  • the area component f x of the resultant force per unit area and the volume component a x of the acceleration per unit volume are calculated by calculation model I;
  • the linear strain L x is calculated by calculation model I;
  • 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 integral of the acceleration per unit volume (m 4 /s 2 );
  • B eff is the effective elastic modulus (Pa)
  • F x is the linear stress (N/m 2 )
  • L x is the linear strain
  • Formula (4) and formula (5) can be used to calculate the effective impedance of the impedance layer and the effective impedance of the ultrasonic wave in the impedance layer.
  • Z eff is the effective impedance (rayl)
  • B eff is the effective elastic modulus (Pa)
  • D eff is the effective density (kg/m 3 ).
  • 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 .
  • 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.
  • 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.
  • This embodiment discloses an acoustic impedance matching material with a thickness of 500 ⁇ m.
  • the acoustic impedance matching material in this embodiment includes only one impedance layer, as shown in the t1 segment of FIG3(b), wherein the filling rate of steel in the impedance layer is 0.437, the effective impedance is 2.9 Mrayl, and the effective sound velocity is 1360 m/s.
  • the calculation method of the filling rate, the effective impedance, and the effective sound velocity is the same as that of the first embodiment.
  • This embodiment discloses an acoustic impedance matching material with a thickness of 1 mm.
  • the acoustic impedance matching material in this embodiment includes two stacked impedance layers. Along the stacking direction, the thickness of each impedance layer is 500 ⁇ m, and the filling rate of steel in the impedance layer is 0.2334 and 0.633, respectively.
  • the effective impedance is 2.085 Mrayl and 4.029 Mrayl, respectively.
  • the effective sound speed is 1403 m/s and 1394 m/s, respectively.
  • Filling rate, effective impedance, The calculation method of the effective sound velocity is the same as that of Example 1.
  • This embodiment discloses an acoustic impedance matching material with a thickness of 1.5 mm.
  • the acoustic impedance matching material in this embodiment includes three stacked impedance layers. Along the stacking direction, the thickness of each impedance layer is 500 ⁇ m, and the filling rate of steel in the impedance layer is 0.1568, 0.433, and 0.6485, respectively.
  • the effective impedance is 1.864 Mrayl, 2.879 Mrayl, and 4.447 Mrayl, respectively.
  • the effective sound speed is 1428 m/s, 1365 m/s, and 1400 m/s, respectively.
  • the calculation method of the filling rate, effective impedance, and effective sound speed is the same as that of the first embodiment.
  • This embodiment discloses an acoustic impedance matching material with a thickness of 2.5 mm.
  • the acoustic impedance matching material in this embodiment includes 5 impedance layers stacked in a stacking direction.
  • the thickness of each impedance layer is 500 ⁇ m
  • the filling rate of steel in the impedance layer is 0.096, 0.2892, 0.4367, 0.5733, and 0.686, respectively.
  • the effective impedance is 1.711 Mrayl, 2.227 Mrayl, 2.898 Mrayl, 3.772 Mrayl, and 4.909 Mrayl, respectively.
  • the effective sound speed is 1453 m/s, 1387 m/s, 1365 m/s, 1375 m/s, and 1420 m/s, respectively.
  • the calculation method of the filling rate, effective impedance, and effective sound speed is the same as that of the first embodiment.
  • This embodiment discloses an acoustic impedance matching material with a thickness of 3 mm.
  • the acoustic impedance matching material in this embodiment includes 6 impedance layers stacked in layers. Along the stacking direction, the thickness of each impedance layer is 500 ⁇ m, and the filling rate of steel in the impedance layer is 0.0803, 0.2247, 0.373, 0.4962, 0.631, and 0.6939, respectively.
  • the effective impedance is 1.674 Mrayl, 2.058 Mrayl, 2.597 Mrayl, 3.234 Mrayl, 4.028 Mrayl, and 5.016 Mrayl, respectively.
  • the effective sound speed is 1460 m/s, 1405 m/s, 1371 m/s, 1365 m/s, 1392 m/s, and 1424 m/s, respectively.
  • the calculation method of the filling rate, effective impedance, and effective sound speed is the same as that of the first embodiment.
  • 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.
  • This embodiment also discloses an ultrasonic instrument, including the ultrasonic transducer in this embodiment.
  • 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 materials.
  • 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).
  • the ultrasound transmission enhancement capability 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 was first discussed through analytical calculation.
  • the ultrasound was incident from the left boundary of the model and received at the right boundary of the model, and the transmission spectra of the effective medium parameters corresponding to the above systems were analytically calculated.
  • the analytical calculation of transmittance includes the following processes:
  • T is the transfer matrix of n-layer medium, and its expression should be:
  • T is a 2 ⁇ 2 matrix
  • t 11 , t 12 , t 21 , and t 22 are matrix elements of the transfer matrix.
  • T l is the transfer matrix of the lth layer, expressed as:
  • the transmission of the non-impedance-matched transcranial system in the frequency range of 0 to 1.3 MHz fluctuates, and the transmission is very low at most frequencies.
  • the transmission valley of 0.65 MHz as an example, after adding a single-layer impedance matching and a four-layer gradient impedance matching layer to the system, it is found that the transmission is improved at 0.65 MHz, and the four-layer gradient impedance matching shows high transmittance in a wide frequency range.
  • the bandwidth is defined as the frequency range in which the transmittance is greater than 0.5.
  • 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).
  • the transmission spectrum of the four-layer gradient impedance matching transcranial system was simulated by finite element numerical simulation. As shown in Figure 10, the numerical simulation results of the transmission spectrum of the four-layer gradient impedance matching transcranial system were compared with the analytical calculation results, and it was found that the two curves had a high degree of fit and both showed a high transmission bandwidth.
  • the transmittance finite element calculation process includes: calculating the acoustic transmittance in water, so the physical field of the COMSOL model is selected as acoustic-solid interaction under acoustics.
  • Model parameters The speed of sound of water is 1500m/s, and the density is 1000kg/m 3 ; 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.
  • 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, and a plane wave is emitted with the left water boundary as the incident pressure field boundary.
  • 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 wave can propagate normally.
  • the upper and lower boundaries of the model are hard sound field boundary conditions.
  • the model is integrated at the incident boundary and the exit boundary, 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 to 1.3MHz.
  • the acoustic impedance is regulated by adjusting 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 adjustable acoustic impedance 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 within a wider frequency range, so that ultrasonic energy can maintain high penetration within a wide frequency range and be transmitted through the skull to soft tissue.
  • the present invention can calculate the relationship curve between the effective impedance of the impedance layer with different filler (such as steel) filling rates and the effective sound velocity and the filling rate under the low-frequency limit, and determine the effective impedance of the impedance layer located at different positions of the acoustic impedance matching material according to the preset stacking direction of the impedance layer according to formula (1), and then obtain the filling rate of the filler in each impedance layer, and stack the impedance layers in sequence according to the stacking positions to form the acoustic impedance matching material.
  • filler such as steel
  • 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 transcranial imaging and treatment at different frequencies can be covered.

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Abstract

本发明公开了一种声学阻抗匹配材料及其制备方法与应用。所述声学阻抗匹配材料包括若干个层叠设置的阻抗层，沿层叠方向，所述阻抗层按照声阻抗呈e指数变化关系依次排列；每个阻抗层包括液态基体材料和位于所述液态基体材料中的填料。本发明中声学阻抗匹配材料可使超声保持足够的能量和较宽的带宽进入颅内，成像分辨率高、聚焦强度高，可保证高效的经颅超声能量传递，进而用于脑疾病观测与治疗应用。

Description

一种声学阻抗匹配材料及其制备方法与应用 技术领域
本发明属于阻抗匹配材料技术领域，具体涉及一种声学阻抗匹配材料及其制备方法与应用。
背景技术
目前脑疾病的检测手段主要包括CT、磁共振成像和超声成像技术，其中经颅超声成像技术相对于CT和MRI具有装置简单、无辐射、实时、便携等优点。经颅超声不仅可以实现脑疾病的观测，同时由于其具有穿透性、聚焦性、热效应等特性，还可以用于进行脑疾病的治疗，拓宽了脑科学研究和脑疾病治疗的大门，为脑疾病患者创造了福音，因此经颅超声技术在脑疾病的治疗领域具有极其深远的前景。
传统的经颅超声中，由于颅骨与背景声学阻抗的不匹配，引起成像分辨率低、聚焦强度低等各种问题。现有的医用超声穿颅技术，入射声窗通常主要是选择颞、枕、下颌和眶四个部位为超声声窗，因为这些部位颅骨较薄或以软骨为主，使超声容易越过颅骨壁垒，达到颅内成像和聚焦的目的，然而并未考虑颅骨的阻抗失配问题给超声透射能量带来的影响，且入射声窗主要是选择经颞、枕、下颌和经眶四个部位，无法覆盖脑部大部分区域，存在盲点，严重限制了超声的应用。
1.1.1发明内容
本发明旨在至少解决上述现有技术中存在的技术问题之一。为此，本发明提出一种声学阻抗匹配材料，将其应用于经颅超声技术中，可显著降低颅骨的阻抗失配影响，保证超声在宽频范围内保持高效率透射到颅内软组织，且可使得超声在颅骨的任意部位入射到颅内，实现任意目标靶点的超声成像、治疗，应用前景好。
本发明还提出一种声学阻抗匹配材料的制备方法。
本发明还提出一种超声换能器。
本发明还提出一种超声仪器。
本发明还提出上述声学阻抗匹配材料、超声换能器及超声仪器的应用。
本发明的第一方面，提出了一种声学阻抗匹配材料，包括若干个层叠设置的阻抗层，沿层叠方向，所述阻抗层按照声阻抗呈e指数变化关系依次排列；每个阻抗层包括液态基体材料和位于所述液态基体材料中的填料。
根据本发明实施例的声学阻抗匹配材料，至少具有以下有益效果：本发明中通过改变填料于各阻抗层中的填充率实现各阻抗层的声阻抗呈e指数变化关系依次排列，从而使得到的声学阻抗匹配材料从其一端到另一端的声阻抗呈梯度变化。如将声学阻抗匹配材料应用于经颅超声中，声学阻抗匹配材料声阻抗范围可位于背景介质(如水)的声阻抗到颅骨的声阻抗之间，使得声阻抗从背景介质到颅骨变化的梯度减小，减小颅骨阻抗失配，降低颅骨的阻抗失配影响，保证超声在宽频范围内保持高效率透射到软组织，且改变入射超声频率也可使得超声保持高透射率穿过颅骨，满足不同的脑疾病治疗需求。
更为具体地，本发明中声学阻抗匹配材料用于经颅超声，可使超声保持足够的能量和较宽的带宽进入颅内，成像分辨率高、聚焦强度高，保证高效的超声脑疾病观测与治疗过程。例如：利用经颅超声神经刺激能够准确地聚焦并对目标神经系统进行刺激，实现神经系统疾病的治疗。同时，可利用高强度聚焦经颅超声通过焦点处高强度能量消融发病组织、肿瘤等，还可以融化药物外壳实现体内定点给药。
此外，本发明中基体材料为液态物质，由于其具有流动性，可快速吸收、转移颅骨中由超声引起的热量，很好地解决了传统经颅超声技术中颅骨升温的问题。且本发明中液态基体材料可使得声学阻抗匹配材料和待匹配目标物紧密贴合，有利于颅骨阻抗的进一步匹配，经颅超声效果更好。
本发明中的声学阻抗匹配材料不限于用于颅骨的阻抗匹配，还可以通过选择合适的液态基体材料和填料，实现更广的应用范围和更多应用场景。
在本发明的一些实施方式中，沿层叠方向，所述阻抗层按照声阻抗呈式(1)所示的e指数变化关系依次排列：
其中，t1表示声学阻抗匹配材料沿所述层叠方向的总厚度；x表示阻抗层的几何中心与所述声学阻抗匹配材料远离待匹配端的一侧表面的垂直距离；Zw表示基体材料的声 阻抗，Zs表示待匹配目标物的声阻抗。其中，所述待匹配端是指声学阻抗匹配材料用于与待匹配目标物相接触或相靠近的一端。
通常水的声阻抗约为1.5Mrayl，颅骨的声阻抗约为5.6Mrayl。
在本发明的一些实施方式中，沿层叠方向，所述阻抗层的声阻抗位于水的声阻抗到颅骨的声阻抗之间。如无特殊说明，本文中的水指的是纯水。
在本发明的一些实施方式中，沿层叠方向，所述声学阻抗匹配材料的一侧到另一侧的声阻抗梯度变化，声阻抗位于1.5～5.6Mrayl之间。
在本发明的一些实施方式中，所述填料于所述阻抗层中的填充率f与阻抗层的声阻抗之间的关系通过有限元方法计算得到。
本发明中阻抗层的声阻抗为有效声阻抗(本文中简称有效阻抗)。如无特殊说明，本文中的填充率指的是体积填充率，也即填料于阻抗层中的体积占比。
在本发明的一些实施方式中，一个阻抗层包括若干个单胞结构，一个单胞结构沿层叠方向的厚度为β，其中，超声波于水中的波长为λ，β和λ之间满足：β＜λ/9。其中，β和λ的单位可均为米(m)，水作为背景介质。
在本发明的一些实施方式中，沿层叠方向，一个阻抗层包括s列的单胞结构，所述阻抗层沿层叠方向的厚度h＝β*s。可选地，s＝2～6。
超声波的波长可由超声波在介质中的声速/超声波的频率得到。
在本发明的一些实施方式中，0＜β＜λ/9。
在本发明的一些实施方式中，每个单胞结构包括填料和基体材料。
在本发明的一些实施方式中，所述阻抗层的数量为2～6个。
在本发明的一些实施方式中，所述阻抗层沿层叠方向的厚度h为200～700μm。
在本发明的一些实施方式中，沿层叠方向，声学阻抗匹配材料的总厚度为t1，t1＝h*n’，n’为阻抗层的数量。
在本发明的一些实施方式中，在超声波频率为0～1.3MHz范围内，每一层阻抗层的厚度为500μm。
在本发明的一些实施方式中，在超声波频率为0.65MHz时，阻抗层的厚度为480～520μm。
根据实际需求，可对阻抗层数量n’进行选择，可通过增加声学阻抗匹配材料的阻抗层个数，提高穿颅带宽，实现超声穿颅的宽带宽、高效率透射。
在本发明的一些实施方式中，沿层叠方向，每个阻抗层的厚度相同。
在本发明的一些实施方式中，所述基体材料的声阻抗不大于水的声阻抗；和/或，所述填料的声阻抗不小于颅骨的声阻抗的1.2倍。
在本发明的一些实施方式中，所述基体材料的声阻抗为0.5～1.5Mrayl；和/或，所述填料的声阻抗为10～100Mrayl。
在本发明的一些实施方式中，所述填料的材料包括但不限于：聚合物材料、硅类材料、陶瓷材料，以及金属单质、金属氧化物、合金等金属材料等等。可选地，所述填料的材料包括聚合物材料、硅类材料、陶瓷材料、金属单质、金属氧化物或合金中的至少一种。
在本发明的一些实施方式中，所述填料的材料包括聚合物材料、硅类材料、陶瓷材料或金属材料中的至少一种。
在本发明的一些实施方式中，所述硅类材料包括硅或二氧化硅中的至少一种。
在本发明的一些实施方式中，所述聚合物材料包括有机玻璃(PMMA)、聚醚醚酮(PEEK)、甲基丙烯酸树脂、硅橡胶、聚二甲基硅氧烷(PDMS)中的至少一种。
在本发明的一些实施方式中，所述陶瓷材料包括压电陶瓷，具体如：PZT压电陶瓷、PN压电陶瓷、PMN-PT压电陶瓷。
在本发明的一些实施方式中，所述金属单质、金属氧化物和合金中的金属元素包括但不限于铁、镍、铜、铝、钛、钨、锌、金、银、铂等。可选地，所述金属单质、金属氧化物和合金中的金属元素包括铁、镍、铜、铝、钛、钨、锌、金、银或铂中的至少一种。
在本发明的一些实施方式中，所述填料的材料包括铁、镍、铜、铝、钛、钨、锌、 金、银或铂中的至少一种。可选地，所述铁包括但不限于纯铁、钢等。
在本发明的一些实施方式中，所述基体材料包括但不限于水、自来水、海水、其他医用液体。
在本发明的一些实施方式中，所述基体材料包括水；和/或，所述填料包括铁、镍、铜、铝、钛、钨、锌、金、银或铂中的至少一种。
在本发明的一些实施方式中，所述基体材料包括水，所述填料包括钢。
通过上述实施方式，本发明的阻抗层中通过调节填料在水中的填充率来调控声阻抗，得到声阻抗渐变的声学阻抗匹配材料。将其应用于经颅超声技术中，声学阻抗匹配材料声阻抗范围可位于水的声阻抗到颅骨的声阻抗之间，满足从水的声阻抗到颅骨的声阻抗之间可调，使得声阻抗从水到颅骨变化的梯度减小，可减小颅骨阻抗失配，降低颅骨的阻抗失配影响，保证超声能量能够在宽频范围内保持高效率透射到软组织，实现水与颅骨的宽带阻抗匹配，且可在宽频范围内改变入射超声频率，应用于不同的医疗技术和医疗过程中。在本发明的一些实施方式中，声学阻抗匹配材料可使超声能够在覆盖低频(220kHz)到中频(650kHz)的宽频范围内保持高透射率穿过颅骨，满足不同的脑疾病观测和治疗需求。
此外，本发明在具体实施例中利用解析和有限元数值计算法，验证了所述声学阻抗匹配材料能够减弱经颅超声穿颅过程中颅骨阻抗失配的影响，保证经颅超声的宽频、高效定向传输，因此本发明在宽频超声成像和治疗中有巨大的应用潜力。
且本发明中以水作为基体材料，由于水的比热容大、具有流动性，可快速吸收、转移颅骨中由超声引起的增加热量，很好地解决了传统经颅超声技术中颅骨升温的问题。
在本发明的一些实施方式中，所述基体材料包括若干种液态材料。
在本发明的一些实施方式中，所述基体材料的至少一种液态材料可于声学阻抗匹配材料内进行流动。
在本发明的一些实施方式中，一个所述阻抗层内含有一个或多个所述填料。
在本发明的一些实施方式中，一个所述阻抗层内含有多个所述填料，多个所述填料 均匀分布于阻抗层内。
在本发明的一些实施方式中，一个所述阻抗层内含有多个相同的所述填料，多个所述填料均匀分布于阻抗层内。
在本发明的一些实施方式中，多个所述填料于阻抗层内呈矩阵排列。
在本发明的一些实施方式中，所述填料的形状包括但不限于柱体、球体、长方体等规则或不规则形状。可选地，填料可为空心填料或实心填料。其中，空心填料可进一步丰富填料尺寸及种类的选择。
在本发明的一些实施方式中，所述填料的形状包括柱体、球体或长方体中的至少一种，和/或，所述填料为空心填料或实心填料。当填料为复合材料(如空心结构)，其声阻抗应为其有效声阻抗。
可选地，所述柱体包括实心柱体或空心柱体，所述球体包括实心球体或空心球体，所述长方体包括实心长方体或空心长方体。
在本发明的一些实施方式中，所述声学阻抗匹配材料还包括限位材料，所述限位材料能够限定填料于声学阻抗匹配材料中的位置。如通过限位材料作用，可使填料于阻抗层内位置固定，进而限定填料于声学阻抗匹配材料中的位置。
基体材料为液体材料，可选地采用声阻抗与基体材料相近的限位材料对填料进行固定、连接和组合，如膜结构等。
在本发明的一些实施方式中，所述限位材料的声阻抗为所述基体材料声阻抗的80～120％，可选为95～105％。
在本发明的一些实施方式中，每个所述阻抗层中均含有所述限位材料，每个所述阻抗层中的限位材料围合得到填充区，所述填充区内填充所述填料。可选地，所述基体材料位于填充区内，或/和，所述基体材料位于填充区外。
在本发明的一些实施方式中，所述限位材料为限位膜材料。
在本发明的一些实施方式中，所述限位材料包括但不限于聚四氟乙烯、聚氨酯或聚对苯二甲酸乙二醇酯等。
在本发明的一些实施方式中，所述限位材料包括聚四氟乙烯、聚氨酯或聚对苯二甲酸乙二醇酯中的至少一种。
在本发明的一些实施方式中，一个阻抗层中，沿所述层叠方向，所述限位膜材料的膜厚为阻抗层厚度的0.5～5％以内。
本发明的第二方面，提出了一种声学阻抗匹配材料的制备方法，包括如下步骤：
S1，采用有限元方法计算得到填料于阻抗层中的填充率f与阻抗层的声阻抗之间的关系；
预设阻抗层的个数n’，一个阻抗层包括若干个单胞结构，预设一个单胞结构沿层叠方向的厚度为β；满足每个阻抗层中：β＜λ/9；其中，λ为超声波于水中的波长；
S2，根据预设的阻抗层层叠方向及阻抗层按照声阻抗呈e指数变化关系依次排列的关系，确定位于声学阻抗匹配材料中的各阻抗层的声阻抗；
S3，根据确定的所述阻抗层的声阻抗与填充率f的关系，确定每个阻抗层中填料的填充率f；
S4，根据确定的所述填充率f选取相应的阻抗层，并将所述阻抗层按照预设的层叠方向依次层叠，形成声学阻抗匹配材料。
步骤S1中，通过限定β＜λ/9，使每一层的阻抗层结构尺度均满足低频极限条件。
步骤S2中，根据预设的阻抗层个数n’及其层叠方向，按照声阻抗呈e指数变化关系依次排列的关系，确定位于声学阻抗匹配材料中的各阻抗层的声阻抗。可选地，如当阻抗层按照声阻抗呈式(1)所示的e指数变化关系依次排列，可根据阻抗层数量(个数)n’，于0～1中均匀选定n’个x/t1的数值，得出选定的x/t1所对应的阻抗值。可选地，可将式(1)的e指数关系式转化为关系图。
在本发明的一些实施方式中，采用有限元方法计算得到所述填充率f与超声波于阻抗层中的有效声速之间的关系；根据步骤S3得到的每个阻抗层填料的填充率f，得到超声波于每个阻抗层的有效声速，进而得到超声波于每个阻抗层中的波长λ1，计算波长λ1的平均值λ1’，满足：阻抗层沿层叠方向的厚度h为0.22λ1’～0.28λ1’。
根据h和β，得到一个阻抗层中沿层叠方向包括单胞结构的个数。当单胞结构于阻抗层中为矩阵排列，则可根据h和β得到一个阻抗层中单胞结构的列数。可选地，再设置一个阻抗层中单胞结构的总个数。
在本发明的一些实施方式中，步骤S2中，根据预设的阻抗层层叠方向，根据式(1)确定位于所述声学阻抗匹配材料不同位置的阻抗层的声阻抗：
其中，t1表示声学阻抗匹配材料沿所述层叠方向的总厚度；x阻抗层的几何中心与所述声学阻抗匹配材料远离待匹配端的一侧表面的垂直距离；Zw表示基体材料的声阻抗，Zs表示待匹配目标物的声阻抗。
在本发明的一些实施方式中，填充率f与阻抗层的声阻抗之间的关系、填充率f与阻抗层的有效声速之间的关系计算过程包括：
选择COMSOL Multiphysics的物理场为结构力学下的固体力学模块；
针对于填料的填充率f的单胞结构，模拟设定单胞结构为正方形，其横截面积为β2，其中填料的横截面积为γ2；根据填充率的表达式为f＝γ2/β2，利用COMSOL Multiphysics按该模型建模，得到计算模型Ⅰ，依次设定：材料参数：基体材料的质量密度、超声波于基体材料的声速、填料的质量密度、超声波于填料中的纵波声速和横波声速(如基体材料为水、填料为钢时，材料参数包括：水的质量密度为1000kg/m3，声速为1500m/s。钢的质量密度为7800kg/m3，纵波声速为5800m/s，横波声速为3200m/s)；
模型的上下边界设置周期性边界条件；在模型的左边界添加了边界载荷给X方向施加了1N/m2的力；在模型的右边界设置了低反射边界条件以防止波的反射；在此模型中，钢的填充率的参数化扫描范围设置为从0到1；计算模型Ⅰ计算阻抗层在低频极限下的等效声速、等效阻抗与填充率之间的关系，具体包括：
经计算模型Ⅰ计算得到单位面积合力的面积分fx、单位体积加速度的体积分ax；
经计算模型Ⅰ计算得到线应变Lx；利用公式(2)和公式(3)，可分别计算得到阻抗层的有效质量密度和有效弹性模量：
有效质量密度计算公式：
其中，Deff为有效质量密度(kg/m3)，fx为单位面积合力的面积分(N)，ax为单位体积加速度的体积分(m4/s2)；
有效弹性模量计算公式：
其中，Beff为有效弹性模量(Pa)，Fx为线应力(N/m2)，Lx为线应变；
利用公式(4)和公式(5)可分别计算阻抗层的有效阻抗和超声波于阻抗层中的有效声速：
有效阻抗计算公式：
其中，Zeff为有效阻抗(rayl)，Beff为有效弹性模量(Pa)，Deff为有效密度(kg/m3)。
有效声速计算公式：
可得阻抗层在低频极限下的填充率f与阻抗层的有效阻抗之间的关系、填充率f与超声波于阻抗层中的有效声速之间的关系。
其中，需要说明的是，基于有效介质理论，考虑在长波近似下(低频极限)静态的混合材料的有效质量密度，晶格常数应该远小于背景介质的波长，在此条件下，通过限定β＜λ/9以满足阻抗层为低频极限条件，如当超声波频率为1.3MHz，限定单胞结构的参数为0.125mm，远小于1.3MHz的声波在水中的波长λ。
本发明的第三方面，提出了一种超声换能器，包括上述声学阻抗匹配材料。
在本发明的一些实施方式中，所述超声换能器包括阻抗匹配层，所述阻抗匹配层包 括所述声学阻抗匹配材料。
在本发明的一些实施方式中，还包括液态材料循环系统，能够用于声学阻抗匹配材料中基体材料的循环使用，促进液态的基体材料在声学阻抗匹配材料中的流动。
本发明的第四方面，提出了一种超声仪器，包括上述超声换能器或上述声学阻抗匹配材料。
在本发明的一些实施方式中，所述超声仪器包括B型超声诊断仪。
本发明的第五方面，提出上述声学阻抗匹配材料、超声换能器或超声仪器在制备医用诊断设备或医用治疗设备中的应用。
在本发明的一些实施方式中，所述声学阻抗匹配材料、超声换能器或超声仪器在制备脑疾病的诊断设备或脑疾病的治疗设备中的应用。
1.1.2附图说明
下面结合附图和实施例对本发明做进一步的说明，其中：
图1为本发明实施例中声学阻抗匹配材料的一种应用场景示意图；
图2为本发明实施例中含有多个阻抗层的声学阻抗匹配材料的应用场景示意图；
图3为无阻抗匹配系统、单层阻抗匹配系统和四层梯度阻抗匹配系统的结构示意图；
图4为本发明实施例1中在低频极限条件下阻抗层的有效声速、有效阻抗随阻抗层中钢填充率的变化曲线图；
图5为本发明实施例1中式(1)关系曲线图；
图6为本发明实施例1中COMSOL模型建模中拟定的单个单胞结构的横截面结构示意图；
图7为解析计算中拟定的平面波在n层介质的传播的结构示意图；
图8为解析计算得到的无阻抗匹配系统、单层阻抗匹配系统和四层梯度阻抗匹配系统有效介质参数的透射谱；
图9为解析计算得到的无阻抗匹配系统、一、二～六层梯度阻抗匹配系统有效介质参数的透射谱；
图10为解析计算及有限元数值模拟的四层梯度阻抗匹配穿颅系统透射谱对比图。
1.1.3具体实施方式
以下将结合实施例对本发明的构思及产生的技术效果进行清楚、完整地描述，以充分地理解本发明的目的、特征和效果。显然，所描述的实施例只是本发明的一部分实施例，而不是全部实施例，基于本发明的实施例，本领域的技术人员在不付出创造性劳动的前提下所获得的其他实施例，均属于本发明保护的范围。
下列实施例中未注明具体条件的实验方法，通常按照本领域常规条件或按照制造厂商建议的条件；所使用的原料、试剂等，如无特殊说明，均为可从常规市场等商业途径得到的原料和试剂。
本发明中的声学阻抗匹配材料，能够作为阻抗渐变匹配层用于经颅超声，应用场景示意图如图1～2所示，图中，t1表示阻抗渐变匹配层的厚度，t2表示颅骨厚度。其中，图2表示含有梯度渐变层叠阻抗层的声学阻抗匹配材料(含有多个阻抗层)的应用场景示意图。
实施例1
本实施例公开了一种声学阻抗匹配材料，所述声学阻抗匹配材料包括层叠设置的4个阻抗层，沿层叠方向，每个阻抗层的厚度均为500μm，每一个阻抗层都由4*4矩阵排列的16个单胞结构组成，同一个阻抗层中单胞结构均相同；每个阻抗层包括液态材料-水(水的声阻抗：1.5Mrayl)和填料-钢(钢的声阻抗：45.24Mrayl)，通过调整每个阻抗层中钢的体积填充率，使声学阻抗匹配材料的声阻抗呈递增变化，阻抗层的声阻抗位于水的声阻抗到颅骨的声阻抗之间，多个阻抗层的结构示意如图3(c)中t1段所示。其中，声学阻抗匹配材料的设计及制备过程包括：
(Ⅰ)采用有限元方法计算得到填料于阻抗层中的填充率f与阻抗层的声阻抗之间的关系、填充率f与超声波于阻抗层中的有效声速之间的关系，如图4所示；
预设的阻抗层的个数n’，n’＝4；其中沿层叠方向，设置一个阻抗层含有s列的单胞结构，每列含有4个单胞结构，沿层叠方向单胞结构的厚度β＝0.125mm；1.3MHz的声波在水中的波长λ，β＜λ/9。
(Ⅱ)根据预设的阻抗层层叠方向，根据有效介质理论，采用式(1)确定位于所述声学阻抗匹配材料不同位置的阻抗层的声阻抗：
其中，t1表示声学阻抗匹配材料沿所述层叠方向的总厚度；x表示阻抗层的几何中心与声学阻抗匹配材料远离待匹配端的一侧表面的垂直距离；Zw表示基体材料的声阻抗，Zs表示待匹配目标物的声阻抗；式(1)关系曲线如图5所示；
(Ⅲ)计算得到4个阻抗层厚度中心(几何中心)处位于所述声学阻抗匹配材料的位置，结合图5得到每个阻抗层各自的有效阻抗，沿层叠方向，依次分别为1.768Mrayl、2.458Mrayl、3.417Mrayl、4.75Mrayl；有效声速依次分别为1435m/s、1370m/s、1360m/s、1400m/s，通过图4可知，4个阻抗层中钢填充率依次为0.12、0.34、0.525、0.673；
通过阻抗层中的钢填充率，得到超声波于阻抗层的有效声速，计算得到超声波于阻抗层中的波长λ1，计算波长λ1的平均值λ1’，限定一个阻抗层的厚度约为λ’/4；最终限定每个阻抗层的厚度均为500μm；确定沿层叠方向，每个阻抗层中含有4列的单胞结构，每列含有4个单胞结构；
(Ⅳ)，根据确定的所述填充率选取相应的阻抗层，并将所述阻抗层按照预设层叠位置依次层叠，形成声学阻抗匹配材料。
其中，关于步骤(Ⅰ)中填充率f与阻抗层的声阻抗之间的关系、填充率f与阻抗层的有效声速之间的关系计算过程包括：利用低频极限下的有效密度和有效弹性模量公式，结合有效阻抗与有效声速计算公式，计算填充率为从0到1时，有效阻抗、有效声速随填充率的变化关系。低频极限下的有效参数的计算过程包括：
选择物理场：本实施例研究的是包括水-钢复合材料的密度和纵波速度，因此选择COMSOL中结构力学下的固体力学模块，对复合材料进行力学分析。
建立模型：本实施例选择了2维研究，针对于填料的填充率f的阻抗层，建立了横截面积为β2，其中填料的横截面积为γ2的单胞结构，填充率的表达式为f＝γ2/β2(也即表示填料于单胞结构中的体积比)，利用COMSOL按该模型建模，得到计算模型Ⅰ，其结构示意如图6所示。
设定材料参数：拟定沿层叠方向，单胞结构的边长β为0.125mm，远小于1.3MHz的超声波在水中的波长1.15mm，水的质量密度为1000kg/m3，声速为1500m/s。钢的质量密度为7800kg/m3，纵波声速为5800m/s，横波声速为3200m/s。
设置边界条件：在本模型中，在模型的上下边界设置了周期性边界条件；在模型的左边界添加了边界载荷给X方向施加了1N/m2的力；在模型的右边界设置了低反射边界条件以防止波的反射。
划分网格：由于二维结构计算量较小，对此模型进行了细致的网格划分，以保证计算的准确性。
求解模型：在此模型中，钢的填充率的参数化扫描范围设置为从0到1。
数据处理：通过计算模型Ⅰ计算阻抗层在低频极限下的等效声速、等效阻抗与填充率之间的关系，具体包括：
经计算模型Ⅰ计算得到单位面积合力的面积分fx、单位体积加速度的体积分ax；
经计算模型Ⅰ计算得到线应变Lx；
利用公式(2)和公式(3)，可分别计算得到低频极限下钢-铝复合材料的有效质量密度和有效弹性模量：
有效质量密度计算公式：
其中，Deff为有效质量密度(kg/m3)，fx为单位面积合力的面积分(N)，ax为单位体积加速度的体积分(m4/s2)；
有效弹性模量计算公式：
其中，Beff为有效弹性模量(Pa)，Fx为线应力(N/m2)，Lx为线应变；
利用公式(4)和公式(5)可分别计算阻抗层的有效阻抗和超声波于阻抗层中的有 效声速：
有效阻抗计算公式：
其中，Zeff为有效阻抗(rayl)，Beff为有效弹性模量(Pa)，Deff为有效密度(kg/m3)。
有效声速计算公式：
可得阻抗层在低频极限下的填充率f与阻抗层的声阻抗之间的关系、填充率f与阻抗层的有效声速之间的关系，如图4所示。
其中，所述声学阻抗匹配材料还包括限位膜材料(图中未示出)，限位膜材料能够限定填料于声学阻抗匹配材料中的位置；每个阻抗层中均含有限位膜材料，每个阻抗层中的限位膜材料围合得到填充区，填充区内填充钢，阻抗层中的水可位于填充区内，或/和，水位于填充区外。
限位膜材料材质为聚四氟乙烯(也可以为聚氨酯或聚对苯二甲酸乙二醇酯)，限位膜的膜厚为每个阻抗层厚度的0.5～2％。
实施例2
本实施例公开了一种声学阻抗匹配材料，厚度为500μm，其与实施例1的区别之处仅在于：本实施例中声学阻抗匹配材料仅包含一个阻抗层，如图3(b)的t1段所示，其中，阻抗层中钢的填充率为0.437，有效阻抗为2.9Mrayl，有效声速为1360m/s。填充率、有效阻抗、有效声速的计算方法同实施例1。
实施例3
本实施例公开了一种声学阻抗匹配材料，厚度为1mm，其与实施例1的区别之处仅在于：本实施例中声学阻抗匹配材料包括层叠设置的2个阻抗层，沿层叠方向：每个阻抗层的厚度均为500μm，且阻抗层中钢的填充率依次为0.2334、0.633，有效阻抗依次为2.085Mrayl、4.029Mrayl，有效声速依次为1403m/s、1394m/s。填充率、有效阻抗、 有效声速的计算方法同实施例1。
实施例4
本实施例公开了一种声学阻抗匹配材料，厚度为1.5mm，其与实施例1的区别之处仅在于：本实施例中声学阻抗匹配材料包括层叠设置的3个阻抗层，沿层叠方向：每个阻抗层的厚度均为500μm，且阻抗层中钢的填充率依次为0.1568、0.433、0.6485，有效阻抗依次为1.864Mrayl、2.879Mrayl、4.447Mrayl，有效声速依次为1428m/s、1365m/s、1400m/s。填充率、有效阻抗、有效声速的计算方法同实施例1。
实施例5
本实施例公开了一种声学阻抗匹配材料，厚度为2.5mm，其与实施例1的区别之处仅在于：本实施例中声学阻抗匹配材料包括层叠设置的5个阻抗层，沿层叠方向：每个阻抗层的厚度均为500μm，且阻抗层中钢的填充率依次为0.096、0.2892、0.4367、0.5733、0.686，有效阻抗依次为1.711Mrayl、2.227Mrayl、2.898Mrayl、3.772Mrayl、4.909Mrayl，有效声速依次为1453m/s、1387m/s、1365m/s、1375m/s、1420m/s。填充率、有效阻抗、有效声速的计算方法同实施例1。
实施例6
本实施例公开了一种声学阻抗匹配材料，厚度为3mm，其与实施例1的区别之处仅在于：本实施例中声学阻抗匹配材料包括层叠设置的6个阻抗层，沿层叠方向：每个阻抗层的厚度均为500μm，且阻抗层中钢的填充率依次为0.0803、0.2247、0.373、0.4962、0.631、0.6939，有效阻抗依次为1.674Mrayl、2.058Mrayl、2.597Mrayl、3.234Mrayl、4.028Mrayl、5.016Mrayl，有效声速依次为1460m/s、1405m/s、1371m/s、1365m/s、1392m/s、1424m/s。填充率、有效阻抗、有效声速的计算方法同实施例1。
实施例7
本实施例公开了一种超声换能器，包括阻抗匹配层，阻抗匹配层包括实施例1～6任一实施例制得的声学阻抗匹配材料。
本实施例还公开了一种超声仪器，包括本实施例中的超声换能器。
试验例
本试验例对实施例中的声学阻抗匹配材料进行了效果验证，具体包括：
采用实施例1～6中的声学阻抗匹配材料作为声学阻抗匹配层，以形成应用于穿颅超声检查和治疗的四层梯度阻抗匹配系统、单层阻抗匹配系统、二层阻抗匹配系统、三层阻抗匹配系统、五层阻抗匹配系统、六层阻抗匹配系统，并与不含声学阻抗匹配材料的无阻抗匹配系统进行对比验证，其中，无阻抗匹配系统、单层阻抗匹配系统、四层梯度阻抗匹配系统的示意图如图3(a)、3(b)、3(c)所示。
1、依据低频极限下有效介质理论，首先经过解析计算讨论了无阻抗匹配穿颅系统、单层阻抗匹配穿颅系统、二～六层梯度阻抗匹配穿颅系统的超声透射增强能力。其中，超声分别从模型左边界入射，在模型的右边界接收，解析计算了上述系统对应的有效介质参数的透射谱。
透射率解析计算，包括如下过程：
拟定平面波在n层介质的传播，结构示意图7如图所示。
第一层界面与最后一层界面的透射声压与反射声压关系：
将公式①写成以下形式：
其中，T为n层介质的传递矩阵，其表达式应为：
其中T为一个2×2矩阵，t11、t12、t21、t22为传递矩阵的矩阵元素。
Tl为第l层的传递矩阵，表示为：
利用公式②得入射波、反射波、透射波与矩阵元素之间的关系为：
求解公式⑤，可得到多层模型的声强振幅反射、声强透射系数依次为：
声强反射系数RI：
声强透射系数TI：
由上，输入任意拟定的一个声压pia，进而利用公式⑦得到对应层数的系统的透射率。
(1)解析计算了无阻抗匹配穿颅系统、单层阻抗匹配穿颅系统、四层梯度阻抗匹配穿颅系统的超声透射增强能力，结果如图8所示：
由图8可知，无阻抗匹配穿颅系统在0～1.3MHz频率范围的透射起伏不定，在大部分频率透射很低，以0.65MHz的透射谷为例，通过对该系统添加了单层阻抗匹配和四层梯度阻抗匹配层后，发现透射均在0.65MHz处被提高了，并且四层梯度阻抗匹配在宽频范围内呈现出高透射率，定义带宽为透射率大于0.5的频率范围，相比之下，四层梯度阻抗匹配穿颅系统的带宽(0.19～1.17MHz)要宽于单层匹配带宽(0.29～1.01MHz)。
(2)采用同(1)的方法，解析计算讨论了无阻抗匹配穿颅系统、单层阻抗匹配穿颅系统、二～六层梯度阻抗匹配穿颅系统的超声透射增强能力，结果如图9所示。
2、为进一步验证可行性，利用有限元数值模拟了四层梯度阻抗匹配穿颅系统透射谱。如图10所示，将四层梯度阻抗匹配穿颅系统透射谱数值仿真结果与解析计算结果进行了对比，发现两条曲线具有较高的拟合度均出现了较高的透射带宽。
透射率有限元计算过程包括：在水中进行声透射率的计算，因此COMSOL模型的物理场选择为声学下的声-固相互作用。
模型参数：水的声速为1500m/s，密度为1000kg/m3；钢的质量密度为7800kg/m3，纵波声速为5800m/s，横波声速为3200m/s。在计算域最左面水边界和最右面软组织边界添加了辐射边界条件，确保声波无反射，以左面水边界为入射压力场边界发出平面波， 入射声压幅值设为1MPa；在固体与水的交界面处设置了声-结构边界条件，以确保声波能够正常传播。模型的上下边界为硬声场边界条件。最后在模型的入射边界和出射边界进行积分，利用坡印廷矢量公式，计算入射和出射能量，将出射能量除以入射能量，即可得到模型的透射率，计算频域为0～1.3MHz。
计算结果如图10所示，将四层梯度阻抗匹配穿颅模型透射谱的数值仿真结果与对应的有效参数匀质介质透射谱的解析结果进行了对比，发现两条曲线具有较高的拟合度均出现了较高的透射带宽。
结果表明，满足低频极限的钢填充-水基体复合材料可通过调节钢的填充率灵活调节等效阻抗，进而用于颅骨的梯度阻抗匹配，实现穿颅宽频透射增强。
综上，本发明中通过调控钢在水中的填充率来调控声阻抗，从而实现从水的声阻抗逐渐过渡到颅骨的声阻抗，得到声阻抗渐变的声学阻抗匹配材料，满足从水的声阻抗到颅骨的声阻抗之间可调，得到能够在较宽频率范围内增强超声穿颅的梯度阻抗匹配材料，可使超声能量能够在宽频范围内保持高穿透性经过颅骨透射到软组织。
本发明根据低频极限下的有效介质理论，可以计算出低频极限下不同填料(如钢)填充率的阻抗层的有效阻抗和有效声速与填充率之间的关系曲线，根据预设的阻抗层层叠方向，根据式(1)确定位于所述声学阻抗匹配材料不同位置的阻抗层的有效阻抗，继而得到每个阻抗层中填料的填充率，并将所述阻抗层按照所述层叠位置依次层叠，形成声学阻抗匹配材料。
本发明采用超声的带宽较宽，可保证超声穿过颅骨在宽频范围内具有高透射率，因此无需担忧超声频率的选择范围，可覆盖不同频率的穿颅成像和治疗。
需要说明的是，本文中涉及数值的“约”的含义为误差±5％。
以上所述实施例仅表达了本发明的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对本发明专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。

Claims (10)

  1. 一种声学阻抗匹配材料，其特征在于，包括若干个层叠设置的阻抗层，沿层叠方向，所述阻抗层按照声阻抗呈e指数变化关系依次排列；每个阻抗层包括液态基体材料和位于所述液态基体材料中的填料。
  2. 根据权利要求1所述的声学阻抗匹配材料，其特征在于，沿层叠方向，所述阻抗层按照声阻抗呈式(1)所示的e指数变化关系依次排列：
    其中，t1表示声学阻抗匹配材料沿所述层叠方向的总厚度；x表示阻抗层的几何中心与所述声学阻抗匹配材料远离待匹配端的一侧表面的垂直距离；Zw表示基体材料的声阻抗，Zs表示待匹配目标物的声阻抗；
    优选地，沿层叠方向，所述阻抗层的声阻抗位于水的声阻抗到颅骨的声阻抗之间。
  3. 根据权利要求1所述的声学阻抗匹配材料，其特征在于，所述填料于所述阻抗层中的填充率f与阻抗层的声阻抗之间的关系通过有限元方法计算得到。
  4. 根据权利要求1所述的声学阻抗匹配材料，其特征在于，一个阻抗层包括若干个单胞结构，一个单胞结构沿层叠方向的厚度为β，其中，超声波于水中的波长为λ，β和λ之间满足：β＜λ/9；
    优选地，所述阻抗层的数量为2～6个；
    优选地，所述阻抗层沿层叠方向的厚度h为200～700μm。
  5. 根据权利要求1所述的声学阻抗匹配材料，其特征在于，所述基体材料的声阻抗不大于水的声阻抗；和/或，所述填料的声阻抗不小于颅骨的声阻抗的1.2倍；
    优选地，所述基体材料的声阻抗为0.5～1.5Mrayl；和/或，所述填料的声阻抗为10～100Mrayl；
    优选地，所述基体材料包括水；和/或，所述填料的材料包括聚合物材料、硅类材料、陶瓷材料或金属材料中的至少一种；
    优选地，所述填料的材料包括铁、镍、铜、铝、钛、钨、锌、金、银或铂中的至少一种；
    优选地，所述填料的形状包括柱体、球体或长方体中的至少一种，和/或，所述填料为 空心填料或实心填料。
  6. 根据权利要求1所述的声学阻抗匹配材料，其特征在于，所述声学阻抗匹配材料还包括限位材料，所述限位材料能够限定填料于声学阻抗匹配材料中的位置；
    优选地，所述限位材料的声阻抗为所述基体材料声阻抗的80～120％。
  7. 一种如权利要求1-6任一项所述的声学阻抗匹配材料的制备方法，其特征在于，包括如下步骤：
    S1，采用有限元方法计算得到填料于阻抗层中的填充率f与阻抗层的声阻抗之间的关系；
    预设阻抗层的个数n’，一个阻抗层包括若干个单胞结构，预设一个单胞结构沿层叠方向的厚度为β；满足每个阻抗层中：β＜λ/9；其中，λ为超声波于水中的波长；
    S2，根据预设的阻抗层层叠方向及阻抗层按照声阻抗呈e指数变化关系依次排列的关系，确定位于声学阻抗匹配材料中的各阻抗层的声阻抗；
    S3，根据确定的所述阻抗层的声阻抗与填充率f的关系，确定每个阻抗层中填料的填充率f；
    S4，根据确定的所述填充率f选取相应的阻抗层，并将所述阻抗层按照预设的层叠方向依次层叠，形成声学阻抗匹配材料；
    优选地，采用有限元方法计算得到所述填充率f与超声波于阻抗层中的有效声速之间的关系；根据步骤S3得到的每个阻抗层填料的填充率f，得到超声波于每个阻抗层的有效声速，进而得到超声波于每个阻抗层中的波长λ1，计算波长λ1的平均值λ1’，满足：阻抗层沿层叠方向的厚度h为0.22λ1’～0.28λ1’。
  8. 一种超声换能器，其特征在于，包括权利要求1～6任一项所述的声学阻抗匹配材料。
  9. 一种超声仪器，其特征在于，包括权利要求1～6任一项所述的声学阻抗匹配材料或权利要求8所述的超声换能器。
  10. 权利要求1～6任一项所述的声学阻抗匹配材料或权利要求8所述的超声换能器或权利要求9所述的超声仪器在制备医用诊断设备或医用治疗设备中的应用。
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