Arc focusing acoustic lens for eliminating spherical aberration and design method thereof

Abstract

The invention discloses an aspherical arc focusing acoustic lens and a design method thereof.The aspherical arc focusing acoustic lens comprises a first surface and a second surface, the first surface is a spherical surface attached to a spherical piezoelectric plate, the curvature of the first surface is the same as that of the spherical piezoelectric plate, and the second surface is a spherical surface attached to the spherical piezoelectric plate. The second surface is a curved surface obtained after design calculation; and the second surface adjusts the sound field distribution of the ultrasonic beam emitted by the spherical piezoelectric patch, and changes the point focusing sound field of the spherical piezoelectric patch into a required focusing sound field. According to the arc focusing acoustic lens capable of eliminating spherical aberration and the design method of the arc focusing acoustic lens, the original focal length of the spherical piezoelectric plate can be changed, short-focal-length focusing can be achieved, the shape of the focal point of the spherical piezoelectric plate can be changed, arc focusing with a specific curvature radius can be achieved at a specific distance, and certain application requirements are met.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic focusing technology, and in particular to an arc-shaped focusing acoustic lens for eliminating spherical aberration and its design method. Background Technology

[0002] High-intensity focused ultrasound (HIFU) technology concentrates ultrasound energy into a small area, resulting in very high sound pressure levels. This technology can be used in fields such as high-intensity focused ultrasound therapy and ultrasound detection. For high-intensity focused ultrasound therapy, HIFU technology can enhance the treatment effect; for ultrasound detection, it can improve the resolution and sensitivity of ultrasound detection by reducing the focal spot size.

[0003] In ultrasonic focusing technology, spherical piezoelectric elements or acoustic lenses are often used to concentrate ultrasonic energy. The former directly generates a converging sound field, while the latter transforms ultrasonic waves into converging waves by changing the path length, thus achieving high energy density at the focal point. For spherical piezoelectric elements, when a very short focal length is required, a very small radius of curvature is necessary, leading to manufacturing difficulties and low yield rates. In such cases, adding an acoustic lens to a spherical piezoelectric element with a large radius of curvature can achieve short focal length focusing. Furthermore, this method of adding an acoustic lens to a spherical piezoelectric element not only reduces the focal length but also changes the shape of the focal point, such as changing from point focusing to circular or arc focusing, thereby meeting specific application requirements.

[0004] In 2002, S. Tsukioka et al. developed a biconcave spherical acoustic lens for obstacle avoidance sonar. However, this lens could not be directly mounted onto a spherical piezoelectric element, and it did not eliminate spherical aberration. In 2007, Y. Sato et al. designed an acoustic lens with aspherical surfaces on both sides. This lens could eliminate spherical aberration, but because both surfaces were aspherical, it could not be directly mounted onto a spherical piezoelectric element. Furthermore, the focusing pattern of these acoustic lenses remained point-like, which did not meet the needs of certain applications, such as using ultrasound to focus in an arc onto the ciliary body to treat glaucoma. A suitable acoustic lens should contain two curved surfaces: one spherical surface that can fit onto a spherical piezoelectric element, and the other surface that can eliminate spherical aberration and transform point focusing into arc focusing. Summary of the Invention

[0005] The purpose of this invention is to provide an aberration-correcting circular arc focusing acoustic lens and its design method, which solves the problem in the background art that existing acoustic lenses cannot be directly mounted on a spherical piezoelectric sheet to obtain aberration-correcting circular arc focusing.

[0006] To achieve the above objectives, the present invention provides an arc-shaped focusing acoustic lens for eliminating spherical aberration and its design method, comprising a first surface and a second surface. The first surface is a spherical surface attached to a spherical piezoelectric sheet, and the curvature of the first surface is the same as that of the spherical piezoelectric sheet. The second surface is a curved surface obtained after design calculation. The second surface adjusts the sound field distribution of the ultrasonic beam emitted by the spherical piezoelectric sheet, transforming the point-focused sound field of the spherical piezoelectric sheet into the desired focused sound field.

[0007] A design method for an aberration-correcting circular arc focusing acoustic lens, wherein the acoustic lens is a concave lens when the sound velocity of the material of the acoustic lens is higher than the sound velocity of the medium in front of it, and the design method for the second surface includes the following steps:

[0008] S2-1. Take the plane passing through the central axis of the first surface as the design plane, and design the curve of the second surface on the plane; the geometric focus S0 of the first surface is located on the plane, and the focusing area of ​​the acoustic lens has two focuses S1 and S2 on the design plane. The focus S1 and S2 each correspond to a curve shape. First, take one of the focuses S1 and design the curve shape corresponding to the focus.

[0009] S2-2. Establish a rectangular coordinate system in the design plane described in step S2-1. Take the straight line passing through the focal point S1 and the geometric focal point S0 as the x-axis. Set the intersection of the x-axis and the first surface as the origin O. Take the straight line passing through the origin O and perpendicular to the x-axis as the y-axis.

[0010] Define parameters k, α, t, a, b, c, and let...

[0011]

[0012] α=kr-f

[0013] t = k 2 (xr) 2 -(xf) 2 -α 2

[0014] a=(k 2 -1)

[0015] b = 2[(k 2 -1)t-2α 2 ]

[0016] c = t 2 -4α 2 (xf) 2

[0017] Where r is the radius of curvature of the first surface, which is also equal to the radius of curvature of the spherical piezoelectric sheet; f is the focal length of the acoustic lens; c0 is the speed of sound in the external medium; and c1 is the speed of sound in the focusing acoustic lens material.

[0018] If (kr-f)≤0, then the equation of the curve corresponding to focus S1 is:

[0019]

[0020] For the above equation, it is necessary to satisfy (b) 2 -4ac)≥0,

[0021] If (kr-f)>0, then the equation of the curve corresponding to focus S1 is:

[0022]

[0023] For the above equation, it is necessary to satisfy...

[0024] S2-3. Obtain the curve shape corresponding to the focal point S1 based on the curve diameter corresponding to the focal point S1 and the curve equation in step S2-2.

[0025] S2-4. Repeat steps S2-1 to S2-3 to obtain the curve shape corresponding to the focal point S2;

[0026] S2-5. Combine the curves corresponding to focal points S1 and S2 to obtain the curve of the second surface on the design plane;

[0027] S2-6. For rotationally symmetric acoustic lenses, the second surface of the acoustic lens can be obtained by simply rotating the curve obtained in step S2-5. For non-rotationally symmetric acoustic lenses, the second surface of the acoustic lens can be obtained by repeating the methods from S2-1 to S2-5 to obtain multiple curves of the second surface in the entire space and stitching these curves into a curved surface.

[0028] A design method for an aberration-correcting circular arc focusing acoustic lens, wherein the acoustic lens is a convex lens when the sound velocity of the material of the acoustic lens is lower than the sound velocity of the medium in front of it, and the design method of the second surface includes the following steps:

[0029] S3-1. Take the plane passing through the central axis of the first surface as the design plane, and design the curve of the second surface on the plane; the geometric focus S0 of the first surface is located on the plane, and the focusing area of ​​the acoustic lens has two focuses S1 and S2 on the plane. The focus S1 and S2 each correspond to a curve shape. First, take one of the focuses S1 and design the curve shape corresponding to the focus.

[0030] S3-2. Establish a rectangular coordinate system in the design plane described in step S3-1. Take the straight line passing through the focus S1 and the geometric focus S0 as the x-axis. Set the intersection of the x-axis and the first surface as the origin O. Take the straight line passing through the origin O and perpendicular to the x-axis as the y-axis.

[0031] Define parameters k, h, α, t, a, b, c, and let...

[0032]

[0033]

[0034] α=kr-kh-f+h

[0035] t = k 2 (xr) 2 -(xf) 2 -α 2

[0036] a=(k 2 -1)

[0037] b = 2[(k 2 -1)t-2a 2 ]

[0038] c = t 2 -4α 2 (xf) 2

[0039] Wherein, c0 is the speed of sound in the external medium; c1 is the speed of sound in the acoustic lens material; r is the radius of curvature of the first surface of the acoustic lens, which is also equal to the radius of curvature of the spherical piezoelectric sheet; l1 is the diameter of the curve corresponding to the focal point S1; and f is the focal length of the acoustic lens.

[0040] The shape of the curve corresponding to the focal point S1 is determined by the following two equations:

[0041]

[0042]

[0043] For both equations above, (b) must be satisfied. 2-4ac)≥0, and the former also needs to satisfy (- The latter also needs to meet

[0044] S3-3. Obtain the curve shape corresponding to focus S1 based on the curve diameter l1 corresponding to focus S1 and the curve equation obtained in step S3-2.

[0045] S3-4. Repeat steps S3-1 to S3-3 to obtain the curve shape corresponding to focus S2;

[0046] S3-5. Piece together the curve shapes corresponding to focal points S1 and S2 to obtain the curve on the design plane of the second surface described in step S3-1;

[0047] S3-6. For rotationally symmetric acoustic lenses, the second surface of the acoustic lens can be obtained by simply rotating the curves on the design plane obtained in step S3-1 in step S3-5 to achieve rotational symmetry. For non-rotationally symmetric acoustic lenses, the methods from S3-1 to S3-5 are repeated to obtain multiple curves of the second surface of the acoustic lens in the entire space. These curves are then stitched together to form a curved surface, thus obtaining the second surface of the acoustic lens.

[0048] Preferably, the focal points S1 and S2 are symmetrical about the central axis of the first surface, and the acoustic lens is rotationally symmetrical. In this case, the spherical piezoelectric sheet is circularly focused after passing through the designed acoustic lens.

[0049] The spherical piezoelectric sheet and the acoustic lens are cut using two planes passing through the central axis of the first surface. The resulting spherical piezoelectric sheet is then focused in an arc shape by the acoustic lens.

[0050] Preferably, the focal points S1 and S2 coincide, and the acoustic lens is rotationally symmetrical. In this case, the spherical piezoelectric sheet is point-focused after passing through the designed acoustic lens.

[0051] Preferably, a matching layer is added between the spherical piezoelectric sheet and the acoustic lens to match the acoustic impedance between the spherical piezoelectric sheet and the acoustic lens, thereby improving the emission efficiency.

[0052] Preferably, a matching layer is added between the acoustic lens and the front medium to match the acoustic impedance between the acoustic lens and the front medium, thereby improving the emission efficiency.

[0053] Therefore, this invention employs the aforementioned spherical aberration-eliminating circular arc focusing acoustic lens and its design method. The acoustic lens includes a first surface and a second surface. The first surface is a spherical surface that can be attached to a spherical piezoelectric sheet, with the same curvature as the spherical piezoelectric sheet. The second surface is a curved surface obtained through design calculations, capable of eliminating spherical aberration and transforming point focusing into circular arc focusing. This invention can change the original focal length of the spherical piezoelectric sheet to achieve short focal length focusing, and can also change the shape of the focal point of the spherical piezoelectric sheet to achieve circular arc focusing with a specific radius of curvature at a specific distance, thereby meeting certain application requirements.

[0054] The spherical aberration-correcting circular arc focusing acoustic lens of this invention has the following technical effects:

[0055] 1. One side of the acoustic lens is spherical, which can be directly attached to the spherical piezoelectric sheet, and the other side is an aspherical surface that can eliminate spherical aberration, thus achieving aberration-free focusing;

[0056] 2. Acoustic lenses can change the original focal length of a spherical piezoelectric element to achieve short focal length focusing;

[0057] 3. Acoustic lenses can change the shape of the focal point of a spherical piezoelectric element, achieving arc focusing;

[0058] 4. There is a matching layer between the acoustic lens and the piezoelectric element, which can effectively match the acoustic impedance of the acoustic lens and the piezoelectric element, increase the ultrasonic wave transmittance, and reduce energy loss and device heating.

[0059] 5. There is a matching layer between the acoustic lens and the front medium, which can effectively match the acoustic impedance of the acoustic lens and the front medium, increase the ultrasonic wave transmittance, and reduce energy loss and device heating.

[0060] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0061] Figure 1 The three-dimensional structural schematic diagram (a) and cross-sectional views (b) and (c) of the circular focusing concave acoustic lens obtained in Embodiment 1 of the present invention, which is a circular arc focusing acoustic lens for eliminating spherical aberration and its design method.

[0062] Figure 2 This is a schematic diagram of the finite element simulation results of the normalized sound pressure distribution on the focal plane when the circular focusing concave acoustic lens is focused, obtained in Example 1 of the present invention, which describes a circular arc focusing acoustic lens for eliminating spherical aberration and its design method.

[0063] Figure 3 This is a schematic diagram of the finite element simulation results of the radially normalized sound pressure distribution on the focal plane when the circular focusing concave acoustic lens obtained in Example 1 of the present invention, which is a circular arc focusing acoustic lens for eliminating spherical aberration and its design method, is focused.

[0064] Figure 4 The three-dimensional structural schematic diagram (a) and cross-sectional views (b) and (c) of the circular focusing convex acoustic lens obtained in Example 2 of the present invention, which is a circular arc focusing acoustic lens for eliminating spherical aberration and its design method.

[0065] Figure 5 This is a schematic diagram of the finite element simulation results of the normalized sound pressure distribution on the focal plane when the circular focusing convex acoustic lens is focused, obtained from Example 2 of the present invention, which describes a circular arc focusing acoustic lens for eliminating spherical aberration and its design method.

[0066] Figure 6 This is a schematic diagram of the finite element simulation results of the radially normalized sound pressure distribution on the focal plane when the circular focusing convex acoustic lens is focused, obtained from Example 2 of the present invention, which describes a circular arc focusing acoustic lens for eliminating spherical aberration and its design method.

[0067] Figure 7 The three-dimensional structural schematic diagram (a) and cross-sectional view (b) of the point-focusing convex acoustic lens obtained in Example 3 of the present invention, which is a circular arc focusing acoustic lens for eliminating spherical aberration and its design method.

[0068] Figure 8 This is a schematic diagram of the finite element simulation results of the normalized sound pressure distribution on the focal plane when the point-focusing convex acoustic lens is focused, obtained from Example 3 of the present invention, which describes a circular arc focusing acoustic lens for eliminating spherical aberration and its design method.

[0069] Figure 9 This is a schematic diagram of the finite element simulation results of the radially normalized sound pressure distribution on the focal plane when the point-focusing convex acoustic lens, obtained from Example 3 of the present invention, shows the design method of a circular arc focusing acoustic lens for eliminating spherical aberration. Detailed Implementation

[0070] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0071] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components.

[0072] Example 1

[0073] A circular focusing concave acoustic lens with spherical aberration reduction and its design method are disclosed. The acoustic lens includes a first surface and a second surface. The first surface is a spherical surface that can be attached to a spherical piezoelectric sheet, and its curvature is the same as that of the spherical piezoelectric sheet. The second surface is a curved surface obtained after design calculation.

[0074] The acoustic lens material has a sound velocity higher than that of the medium in front of it. The acoustic lens is a concave lens. The design method for the second surface includes the following steps:

[0075] S1. Take the plane passing through the central axis of the first surface as the design plane, and design the curve of the second surface on this plane; the geometric focus S0 of the spherical piezoelectric sheet is on this plane, and the converged circle is 10.3mm in front of the spherical piezoelectric sheet with a radius of curvature of 1.97mm. There are two focal points S1 and S2 on this plane in the focusing area of ​​the acoustic lens. These two focal points correspond to a curve shape. First, take one of the focal points S1 and design the curve shape corresponding to that focal point.

[0076] S2, such as Figure 1 As shown in (b), a rectangular coordinate system is established in the selected plane. The straight line passing through the focus S1 and the geometric focus S0 is taken as the x-axis, the intersection of the x-axis and the first surface is taken as the origin O, and the straight line passing through the origin O and perpendicular to the x-axis is taken as the y-axis.

[0077] The radius of curvature r of the sphere is 16.5 mm. The focal length f of the spherical piezoelectric sheet after passing through the focusing acoustic lens can be calculated to be 10 mm. The medium in front is water, and its sound velocity c0 is 1500 m / s. The acoustic lens is made of polystyrene (sound attenuation of 36 dB / m / MHz), and its sound velocity is c1 = 2338 m / s. Define parameters k, α, t, a, b, and c, and let...

[0078]

[0079] α=kr-f

[0080] t = k 2 (xr) 2 -(xf) 2 -α 2

[0081] a=(k 2 -1)

[0082] b = 2[(k 2 -1)t-2α 2 ]

[0083] c = t 2 -4α 2 (xf) 2

[0084] The equation of the curve is expressed as follows:

[0085]

[0086] For the above equation, it is necessary to satisfy...

[0087] S3. The aperture L of the acoustic lens is 19.06mm. Therefore, we know that the diameter l1 of the curve corresponding to the focal point S1 is 10mm. Thus, according to the expression in step S2, we can obtain the curve shape corresponding to the focal point S1.

[0088] S4, such as Figure 1 As shown in (c), repeat steps S1 to S3 to obtain the curve shape corresponding to the focus S2;

[0089] S5. Combine the curves corresponding to focal points S1 and S2 to obtain the curve of the second surface on the selected plane;

[0090] S6. Rotating the above curve symmetrically yields the second surface of the acoustic lens. A schematic diagram of the three-dimensional structure of the resulting circular focusing concave acoustic lens is shown below. Figure 1 As shown in (a), the cross-sectional view is as follows: Figure 1 As shown in (b) and (c).

[0091] The sound field of the circular focusing concave acoustic lens was simulated using the finite element method. The simulation model included a 21MHz piezoelectric transducer (made of PZT-4). The designed acoustic lens and the piezoelectric transducer were bonded together with epoxy resin, and the surrounding medium was water.

[0092] Figure 2 The normalized sound pressure distribution of the above simulation model on the focal plane shows that circular focusing can be achieved. Figure 3 For the radially normalized sound pressure distribution on the focal plane of the above simulation model, it can be seen that the distance between the two focal points is approximately 3.94 mm, therefore the radius of curvature of the focusing circle is 1.97 mm. Furthermore, in... Figure 3 It can be seen that the -6dB radius of the focal spot is approximately 0.045mm.

[0093] A matching layer can be added between the piezoelectric element and the acoustic lens to match their acoustic impedance, thereby improving transmission efficiency. Similarly, a matching layer can also be added between the acoustic lens and the in front medium to match their acoustic impedance, further improving transmission efficiency.

[0094] Example 2

[0095] A circular focusing convex acoustic lens with asymmetry correction and its design method are disclosed. When the sound velocity of the material of the acoustic lens is lower than the sound velocity of the medium in front, the acoustic lens is a convex lens. The design method for the second surface includes the following steps:

[0096] S1. Take the plane passing through the central axis of the first surface as the design plane, and design the curve of the second surface on this plane; the geometric focus S0 of the spherical piezoelectric sheet is on this plane, the converged circle is 10mm in front of the spherical piezoelectric sheet, the radius of curvature is 4mm, and there are two focal points S1 and S2 on this plane in the focusing area of ​​the acoustic lens. These two focal points correspond to a curve shape respectively. First, take one of the focal points S1 and design the curve shape corresponding to the focal point.

[0097] S2, such as Figure 4 As shown in (b), a rectangular coordinate system is established in the selected plane. The straight line passing through the focus S1 and the geometric focus S0 is taken as the x-axis. The intersection of the x-axis and the first surface is set as the origin O. The straight line passing through the origin O and perpendicular to the x-axis is taken as the y-axis.

[0098] The radius of curvature r of the spherical piezoelectric sheet and the first acoustic lens is 16 mm. The focal length f of the spherical piezoelectric sheet after passing through the focusing acoustic lens can be calculated to be 8.79 mm. The medium in front is water, and its sound velocity c0 is 1500 m / s. The material of the focusing acoustic lens is Momentive silicone rubber RTV664-J (sound attenuation of 842 dB / m / MHz), and its sound velocity is c1 = 1000 m / s. Define the parameters k, h, α, t, a, b, and c, and let...

[0099]

[0100]

[0101] α=kr-kh-f+h

[0102] t = k 2 (xr) 2 -(xf) 2 -α 2

[0103] a=(k 2 -1)

[0104] b = 2[(k 2 -1)t-2α 2 ]

[0105] c = t 2 -4α 2 (xf) 2

[0106] Where l1 is the diameter of the curve corresponding to focal point S1; the diameter L of the acoustic lens is 20mm, therefore we know that the diameter l1 of the curve corresponding to focal point S1 is 17.75mm. The shape of the curve corresponding to focal point S1 is then determined by the following two equations.

[0107]

[0108]

[0109] For both equations above, (b) must be satisfied. 2 -4ac)≥0, and the former must also satisfy... The latter also needs to meet

[0110] The diameter l1 of the curve corresponding to S3 and focus S1 is 17.75mm. Therefore, the curve shape corresponding to focus S1 can be obtained according to the expression in step two.

[0111] S4, such as Figure 4 As shown in (c), repeat steps S1 to S3 to obtain the curve shape corresponding to the focus S2;

[0112] S5. Combine the curves corresponding to focal points S1 and S2 to obtain the curve of the second surface on the selected plane;

[0113] S6. Rotating the above curve symmetrically yields the second surface of the acoustic lens. A schematic diagram of the three-dimensional structure of the resulting circular focusing convex acoustic lens is shown below. Figure 4 As shown in (a), the cross-sectional view is as follows: Figure 4 As shown in (b) and (c).

[0114] The sound field of the circular focusing convex acoustic lens was simulated using the finite element method. The simulation model included a 21MHz piezoelectric transducer (made of PZT-4). The designed acoustic lens and the piezoelectric transducer were bonded together with epoxy resin, and the surrounding medium was water.

[0115] Figure 5 The normalized sound pressure distribution of the above simulation model on the focal plane shows that circular focusing can be achieved. Figure 6 Based on the radially normalized sound pressure distribution of the above simulation model on the focal plane, it can be seen that the distance between the two focal points is approximately 7.75 mm, therefore the radius of curvature of the focusing circle is 3.875 mm, which is basically consistent with the design requirement of 4 mm. Furthermore, in Figure 6 It can be seen that the -6dB radius of the focal spot is approximately 0.045mm.

[0116] A matching layer can be added between the piezoelectric element and the acoustic lens to match their acoustic impedance, thereby improving transmission efficiency. Similarly, a matching layer can also be added between the acoustic lens and the in front medium to match their acoustic impedance, further improving transmission efficiency.

[0117] Example 3

[0118] A point-focusing convex acoustic lens for aberration correction and its design method are disclosed. When the sound velocity of the material of the acoustic lens is lower than the sound velocity of the medium in front, the acoustic lens is a convex lens. The design method for the second surface includes the following steps:

[0119] S1. Take the plane passing through the central axis of the first surface as the design plane, and design the curve of the second surface on the plane; the geometric focus S0 of the first surface is on the plane, and the point of convergence is 10mm in front of the spherical piezoelectric sheet. The focusing area of ​​the acoustic lens has a focus S1 on the plane, and the focus S1 corresponds to a curve shape. Design the curve shape corresponding to the focus.

[0120] S2. Establish a rectangular coordinate system in the selected plane, take the straight line passing through the focus S1 and the geometric focus S0 as the x-axis, set the intersection of the x-axis and the first surface as the origin O, and take the straight line passing through the origin O and perpendicular to the x-axis as the y-axis.

[0121] The radius of curvature r of the sphere is 16.5 mm. The focal length f of the spherical piezoelectric sheet after passing through the focusing acoustic lens is 10 mm. The aperture L of the acoustic lens is 10 mm. The aperture l1 corresponding to S1 is 10 mm. The velocity of sound in the preceding medium is c0 = 1500 m / s. The focusing acoustic lens material is Momentive silicone rubber RTV664-J (sound attenuation of 842 dB / m / MHz), and its velocity of sound is c1 = 1000 m / s. Define parameters k, h, α, t, a, b, and c, and let...

[0122]

[0123]

[0124] α=kr-kh-f+h

[0125] t = k 2 (xr) 2 -(xf) 2 -α 2

[0126] a=(k 2 -1)

[0127] b = 2[(k 2 -1)t-2α 2 ]

[0128] c = t 2 -4α 2 (xf) 2

[0129] The shape of the curve is determined by the following two equations.

[0130]

[0131]

[0132] For both equations above, (b) must be satisfied. 2 -4ac)≥0, and the former must also satisfy... The latter also needs to meet

[0133] The diameter l1 of the curve corresponding to S3 and focus S1 is 10mm. Therefore, the curve shape corresponding to focus S1 can be obtained according to the expression of S2, that is, the curve of the second surface on the selected plane can be obtained.

[0134] S4. Rotating the above curve symmetrically yields the second surface of the acoustic lens. A schematic diagram of the three-dimensional structure of the resulting point-focusing convex acoustic lens is shown below. Figure 7 As shown in (a), the cross-sectional view is as follows: Figure 7 As shown in (b).

[0135] The sound field of the point-focusing convex acoustic lens was simulated using the finite element method. The simulation model included a 21MHz piezoelectric transducer (made of PZT-4). The designed acoustic lens and the piezoelectric transducer were bonded together with epoxy resin, and the surrounding medium was water.

[0136] Figure 8 The normalized sound pressure distribution of the above simulation model on the focal plane shows that point focusing can be achieved. Figure 9 The radially normalized sound pressure distribution of the above simulation model on the focal plane shows that the -6dB radius of the focal point is approximately 0.05mm.

[0137] A matching layer can be added between the piezoelectric element and the acoustic lens to match their acoustic impedance, thereby improving transmission efficiency. Similarly, a matching layer can also be added between the acoustic lens and the in front medium to match their acoustic impedance, further improving transmission efficiency.

[0138] Therefore, this invention employs the aforementioned spherical aberration-eliminating circular arc focusing acoustic lens and its design method. The acoustic lens includes a first surface and a second surface. The first surface is a spherical surface that can be attached to a spherical piezoelectric sheet, with the same curvature as the spherical piezoelectric sheet. The second surface is a curved surface obtained through design calculations, capable of eliminating spherical aberration and transforming point focusing into circular arc focusing. This invention can change the original focal length of the spherical piezoelectric sheet to achieve short focal length focusing, and can also change the shape of the focal point of the spherical piezoelectric sheet to achieve circular arc focusing with a specific radius of curvature at a specific distance, thereby meeting certain application requirements.

[0139] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A circular arc focusing acoustic lens for aberration correction, characterized in that, It includes a first surface and a second surface. The first surface is a spherical surface that is attached to the spherical piezoelectric sheet. The curvature of the first surface is the same as that of the spherical piezoelectric sheet. The second surface is a curved surface obtained after design calculation. The second surface adjusts the sound field distribution of the ultrasonic beam emitted by the spherical piezoelectric sheet, and transforms the point-focused sound field of the spherical piezoelectric sheet into the desired focused sound field.

2. A design method for an arc-shaped focusing acoustic lens with spherical aberration correction according to claim 1, characterized in that, When the sound velocity of the material of the acoustic lens is higher than the sound velocity of the medium in front, the acoustic lens is a concave lens, and the design method of the second surface includes the following steps: S2-1. Take the plane passing through the central axis of the first surface as the design plane, and design the curve of the second surface on the plane; the geometric focus S0 of the first surface is located on the design plane, and the focusing area of ​​the acoustic lens has two focuses S1 and S2 on the design plane. The focus S1 and S2 each correspond to a curve shape. First, take one of the focuses S1 and design the curve shape corresponding to that focus. S2-2. Establish a rectangular coordinate system in the design plane described in step S2-1. Take the straight line passing through the focal point S1 and the geometric focal point S0 as the x-axis. Set the intersection of the x-axis and the first surface as the origin O. Take the straight line passing through the origin O and perpendicular to the x-axis as the y-axis. Define parameters k, α, t, a, b, c, and let... α=kr-f t=k 2 (x-r) 2 -(x-f) 2 -α 2 a=(k 2 -1) b=2[(k 2 -1)t-2α 2 ] c=t 2 -4α 2 (x-f) 2 Where r is the radius of curvature of the first surface, which is also equal to the radius of curvature of the spherical piezoelectric sheet; f is the focal length of the acoustic lens; c0 is the speed of sound in the external medium; and c1 is the speed of sound in the focusing acoustic lens material. If (kr-f)≤0, then the equation of the curve corresponding to focus S1 is: For the above equation, it is necessary to satisfy... If (kr-f)>0, then the equation of the curve corresponding to focus S1 is: For the above equation, it is necessary to satisfy... S2-3. Obtain the curve shape corresponding to the focal point S1 based on the curve diameter corresponding to the focal point S1 and the curve equation in step S2-2. S2-4. Repeat steps S2-1 to S2-3 to obtain the curve shape corresponding to the focal point S2; S2-5. Combine the curves corresponding to focal points S1 and S2 to obtain the curve of the second surface on the design plane; S2-6. For rotationally symmetric acoustic lenses, the second surface of the acoustic lens can be obtained by simply rotating the curve obtained in step S2-5. For non-rotationally symmetric acoustic lenses, the second surface of the acoustic lens can be obtained by repeating the methods from S2-1 to S2-5 to obtain multiple curves of the second surface in the entire space and stitching these curves into a curved surface.

3. A design method for an arc-shaped focusing acoustic lens with spherical aberration correction according to claim 1, characterized in that, When the sound velocity of the material of the acoustic lens is lower than the sound velocity of the medium in front, the acoustic lens is a convex lens, and the design method of the second surface includes the following steps: S3-1. Take the plane passing through the central axis of the first surface as the design plane, and design the curve of the second surface on the plane; the geometric focus S0 of the first surface is located on the design plane, and the focusing area of ​​the acoustic lens has two focuses S1 and S2 on the design plane. The focus S1 and S2 each correspond to a curve shape. First, take one of the focuses S1 and design the curve shape corresponding to that focus. S3-2. Establish a rectangular coordinate system in the design plane described in step S3-1. Take the straight line passing through the focus S1 and the geometric focus S0 as the x-axis. Set the intersection of the x-axis and the first surface as the origin O. Take the straight line passing through the origin O and perpendicular to the x-axis as the y-axis. Define parameters k, h, α, t, a, b, c, and let... α=kr-kh-f+h t=k 2 (x-r) 2 -(x-f) 2 -α 2 a=(k 2 -1) b=2[(k 2 -1)t-2α 2 ] c=t 2 -4α 2 (x-f) 2 Wherein, c0 is the speed of sound in the external medium; c1 is the speed of sound in the acoustic lens material; r is the radius of curvature of the first surface of the acoustic lens, which is also equal to the radius of curvature of the spherical piezoelectric sheet; l1 is the diameter of the curve corresponding to the focal point S1; and f is the focal length of the acoustic lens. The shape of the curve corresponding to the focal point S1 is determined by the following two equations: For both equations above, (b) must be satisfied. 2 -4ac)≥0, and the former also needs to satisfy The latter also needs to meet S3-3. Obtain the curve shape corresponding to focus S1 based on the curve diameter l1 corresponding to focus S1 and the curve equation obtained in step S3-2. S3-4. Repeat steps S3-1 to S3-3 to obtain the curve shape corresponding to focus S2; S3-5. Piece together the curve shapes corresponding to focal points S1 and S2 to obtain the curve on the design plane of the second surface described in step S3-1; S3-6. For rotationally symmetric acoustic lenses, the second surface of the acoustic lens can be obtained by simply rotating the curves on the design plane obtained in step S3-1 in step S3-5 to achieve rotational symmetry. For non-rotationally symmetric acoustic lenses, the methods from S3-1 to S3-5 are repeated to obtain multiple curves of the second surface of the acoustic lens in the entire space. These curves are then stitched together to form a curved surface, thus obtaining the second surface of the acoustic lens.

4. A circular arc focusing acoustic lens for eliminating spherical aberration and its design method according to any one of claims 1 to 3, characterized in that, The focal points S1 and S2 are symmetrical about the central axis of the first surface, and the acoustic lens is rotationally symmetrical. In this case, the spherical piezoelectric sheet is circularly focused after passing through the designed acoustic lens. The spherical piezoelectric sheet and the acoustic lens are cut using two planes passing through the central axis of the first surface. The resulting spherical piezoelectric sheet is then focused in an arc shape by the acoustic lens.

5. A circular arc focusing acoustic lens for eliminating spherical aberration and its design method according to any one of claims 1 to 3, characterized in that, The focal points S1 and S2 coincide, and the acoustic lens is rotationally symmetrical. At this time, the spherical piezoelectric sheet is point-focused after passing through the designed acoustic lens.

6. A circular arc focusing acoustic lens for eliminating spherical aberration and its design method according to any one of claims 1 to 3, characterized in that, A matching layer is added between the spherical piezoelectric sheet and the acoustic lens to match the acoustic impedance between the spherical piezoelectric sheet and the acoustic lens, thereby improving the emission efficiency.

7. A circular arc focusing acoustic lens for eliminating spherical aberration and its design method according to any one of claims 1 to 3, characterized in that, A matching layer is added between the acoustic lens and the front medium to match the acoustic impedance between the acoustic lens and the front medium, thereby improving the emission efficiency.

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