Acoustic lens design and preparation method for high-frequency array ultrasonic transducer

Abstract

The invention discloses an acoustic lens design and preparation method for a high-frequency array ultrasonic transducer. The method comprises the following steps: selecting a material for manufacturing a Fresnel acoustic lens; designing parameters of the Fresnel acoustic lens; and preparing the Fresnel acoustic lens based on the determined material and parameters of the Fresnel acoustic lens. Therefore, the Fresnel acoustic lens is used for replacing a traditional convex lens, and the size and the thickness of the lens are greatly reduced, so that the attenuation of sound waves in the lens is greatly reduced, and the sensitivity of the probe is effectively improved.

Description

Technical Field

[0001] The present invention relates to a method for designing and fabricating an acoustic lens for a high-frequency array ultrasonic transducer, and pertains to the field of ultrasonic lens design and fabrication. Background Art

[0002] Ultrasonic imaging is an important non-destructive testing method, widely used in clinical medicine, industrial flaw detection, and other fields. An ultrasonic probe is a key component of an ultrasonic imaging system. Among them, an array ultrasonic probe is a common type, generally composed of multiple independent transducer elements. These elements can independently emit or receive ultrasonic waves. By controlling the emission or reception of each element, complex operations such as focusing and deflection of ultrasonic waves can be achieved, thereby completing ultrasonic imaging.

[0003] An acoustic lens is an important part of an ultrasonic probe, which can focus the ultrasonic beam emitted by the transducer elements on a plane perpendicular to the array arrangement direction, thereby improving the resolution and imaging effect of the image. By adjusting the shape and material of the acoustic lens, precise control of the ultrasonic beam can be achieved, including the width, direction, and intensity of the beam.

[0004] The acoustic lens utilizes the refraction that occurs when ultrasonic waves pass through the interface of media with different sound velocities to achieve the convergence of the beam. When the ultrasonic beam is incident from a medium with a high sound velocity to a medium with a low sound velocity, a concave lens is generally considered for focusing; conversely, when incident from a medium with a low sound velocity to a medium with a high sound velocity, a convex lens is considered for focusing. Due to the relatively low manufacturing and maintenance costs, ultrasonic probes usually use convex lenses, and the lens materials are mostly materials with a low sound velocity such as silicone rubber. This type of material often has a large acoustic attenuation, and convex lenses often have a large thickness, resulting in a large attenuation of the acoustic wave amplitude after the acoustic wave passes through the lens for focusing, thereby greatly reducing the sensitivity of the ultrasonic probe. As the operating frequency of the ultrasonic probe increases, the attenuation of the acoustic wave passing through the lens is very serious, greatly weakening the working performance of the ultrasonic probe. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. For this reason, in view of the above problems, the object of the present invention is to provide a method for designing and fabricating an acoustic lens for a high-frequency array ultrasonic transducer, which can significantly reduce the attenuation of acoustic waves in the lens and improve the sensitivity of the ultrasonic probe.

[0006] To achieve the above object of the invention, the technical solution adopted by the present invention is as follows: The method for designing and fabricating an acoustic lens for a high-frequency array ultrasonic transducer provided by the present invention includes: selecting a material for fabricating a Fresnel acoustic lens; designing the parameters of the Fresnel acoustic lens; and fabricating the Fresnel acoustic lens based on the determined material and parameters of the Fresnel acoustic lens.

[0007] In some possible embodiments, the principle for selecting the material for fabricating the Fresnel acoustic lens is that the sound speed of the material of the Fresnel acoustic lens should be lower than that of the imaging target.

[0008] In some possible embodiments, when the high-frequency array ultrasonic transducer is applied to medical imaging, the material selected for fabricating the Fresnel acoustic lens should have a lower average sound speed than that of human tissues, where the material is sulfurized silicone rubber RTV or PDMS.

[0009] In some possible embodiments, the parameters for designing the Fresnel acoustic lens include:

[0010] Determine the focal length F and width W of the Fresnel acoustic lens according to the design requirements of the ultrasonic transducer;

[0011] Based on the focal length F of the Fresnel acoustic lens, the sound speed, and the sound speed of the imaging medium, determine the radius of curvature R of the Fresnel acoustic lens;

[0012] Determine the basic thickness d of the Fresnel acoustic lens according to the process requirements;

[0013] Based on the width W and the basic thickness d of the Fresnel acoustic lens, determine the curved surface of the Fresnel acoustic lens.

[0014] In some possible embodiments, determine the focal length F and width W of the Fresnel acoustic lens according to the image resolution and focusing depth of the ultrasonic transducer:

[0015] R L = 1.22λf #

[0016]

[0017] where R L is the lateral resolution of the image, λ is the wavelength, f # is the F-number of the Fresnel acoustic lens, NA is the aperture of the ultrasonic transducer, and W = NA.

[0018] In some possible embodiments, based on the focal length F of the Fresnel acoustic lens, the sound speed, and the sound speed of the imaging medium, determine the radius of curvature R of the Fresnel acoustic lens:

[0019]

[0020] where v1 is the sound speed of the imaging medium and v2 is the sound speed of the material of the Fresnel acoustic lens.

[0021] In some possible embodiments, based on the width W and the basic thickness d of the Fresnel acoustic lens, determine the curved surface of the Fresnel acoustic lens, including: divide the lens width W into N parts, and the width of each part is W i(i = 1, 2, 3…N), after each part retains the basic thickness d, the part where the sound wave propagates in a straight line in the lens is removed, and the remaining part is the retained part of the Fresnel acoustic lens, thereby determining its corresponding curved surface.

[0022] In some possible embodiments, based on the determined material and parameters of the Fresnel acoustic lens, the Fresnel acoustic lens is prepared, including:

[0023] According to the position of the Fresnel acoustic lens and the curved surface parameters, a metal mold of the Fresnel acoustic lens is prepared;

[0024] After obtaining the metal mold, a casting mold is made using PDMS;

[0025] After the PDMS is cured, a demolding process is carried out to obtain a PDMS mold with the curved surface of the Fresnel acoustic lens;

[0026] The uncured material of the Fresnel acoustic lens is poured into the PDMS mold and cured;

[0027] After the material of the Fresnel acoustic lens is cured, it is demolded, and the formed Fresnel acoustic lens is taken out and its surface is cleaned. Among them, the demolded and formed Fresnel acoustic lens is used for bonding to the high-frequency array ultrasonic transducer for use.

[0028] In some possible embodiments, degassing treatment is carried out before pouring the uncured material of the Fresnel acoustic lens to prevent defects such as air bubbles inside the lens; during curing, the surface should be ensured to be flat without undulations.

[0029] In some possible embodiments, a complex curved surface precision machining device or a laser engraving device is used to prepare the metal mold of the Fresnel acoustic lens

[0030] Due to the above technical solutions adopted by the present invention, it has the following characteristics:

[0031] 1. By using the Fresnel acoustic lens to replace the traditional convex lens, the present invention greatly reduces the volume and thickness of the lens, thereby significantly reducing the attenuation of sound waves in the lens and effectively improving the sensitivity of the probe.

[0032] 2. Aiming at the problem that the curved surface structure of the Fresnel acoustic lens is complex and the processing difficulty is large, the present invention proposes a preparation of the Fresnel acoustic lens by means of casting molding based on a metal mold, which can effectively reduce the thickness and volume of the acoustic lens of the ultrasonic probe, and while ensuring the focusing effect, greatly improve the echo sensitivity and image resolution of the ultrasonic probe.

[0033] In summary, the acoustic lens design and preparation method of the present invention can be widely applied to high-frequency array transducers. Brief Description of the Drawings

[0034] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for the purpose of illustrating the preferred embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference numerals are used to denote the same components. In the drawings:

[0035] Figure 1 is a schematic diagram of the principle of the lens according to an embodiment of the present invention, wherein, FIG. (a) is a conventional lens style, and FIG. (b) is a Fresnel acoustic lens style.

[0036] Figure 2 is a schematic diagram of the determination process of the design parameters of the Fresnel acoustic lens according to an embodiment of the present invention, wherein, FIG. (a) is a convex lens, FIG. (b) is the Fresnel surface parameter, and FIG. (c) is the Fresnel acoustic lens.

[0037] Figure 3 is a flowchart of the preparation method of the high-frequency array transducer lens according to an embodiment of the present invention.

[0038] Figure 4 are the application scenarios of two Fresnel acoustic lenses according to an embodiment of the present invention, wherein, FIG. (a) is the Fresnel acoustic lens style of the linear array probe, and FIG. (b) is the Fresnel acoustic lens style of the annular array transducer.

[0039] Figure 5 is a schematic diagram of the comparison of the focused sound fields of the lensless, convex lens and Fresnel acoustic lens without considering the acoustic wave attenuation according to an embodiment of the present invention, wherein, FIG. (a) is the case of the lensless, FIG. (b) is the case of the convex lens, and FIG. (c) is the case of the Fresnel acoustic lens.

[0040] Figure 6 is a schematic diagram of the comparison of the focusing intensities of the lensless, convex lens and Fresnel acoustic lens without considering the acoustic wave attenuation according to an embodiment of the present invention. Detailed Embodiments

[0041] It should be understood that the terms used herein are for the purpose of describing specific example embodiments only and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" as used herein may also include the plural forms. The terms "comprises", "comprising", "includes" and "having" are inclusive and thus specify the presence of the stated features, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring them to be performed in the particular order described or illustrated, unless the order of performance is explicitly stated. It should also be understood that alternative or additional steps may be used.

[0042] Although terms such as first, second, third, etc. may be used in the text to describe multiple elements, components, regions, layers, and / or sections, these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms may only be used to distinguish one element, component, region, layer, or section from another region, layer, or section. Unless the context clearly indicates otherwise, terms such as "first", "second", and other numerical terms do not imply order or sequence when used in the text. Therefore, the first element, component, region, layer, or section discussed below may be referred to as the second element, component, region, layer, or section without departing from the teachings of the exemplary embodiments.

[0043] For ease of description, spatial relative relationship terms may be used in the text to describe the relationship of one element or feature shown in the figure with respect to another element or feature. These relative relationship terms such as "inside", "outside", "inner side", "outer side", "below", "above", etc. This spatial relative relationship term is intended to include different orientations of the device during use or operation in addition to the orientations depicted in the figure.

[0044] Aiming at the problem that the acoustic convex lens of the traditional array transducer has a large thickness and serious attenuation after the sound wave passes through, the design and preparation method of the acoustic lens for the high-frequency array ultrasonic transducer proposed by the present invention includes: selecting the material for making the Fresnel acoustic lens; designing the parameters of the Fresnel acoustic lens; preparing the Fresnel acoustic lens based on the determined material and parameters of the Fresnel acoustic lens. The Fresnel acoustic lens structure prepared by the above method effectively reduces the lens thickness and achieves the purpose of improving the sensitivity. At the same time, in order to realize the preparation of the complex-curved Fresnel acoustic lens, the design and preparation method of the acoustic lens for the high-frequency array ultrasonic transducer provided by the present invention is realized by the reverse molding method of the metal mold, which solves the problems of complex curved surface structure and large processing difficulty of the Fresnel lens.

[0045] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be fully conveyed to those skilled in the art.

[0046] Based on the "Fresnel lens" theory, the present invention proposes a "Fresnel acoustic lens". The basic principle of the Fresnel lens is that when the beam passes through the lens, the refraction of the wave only occurs at the interface of the medium. If the convex lens is relatively thick and the part of the straight-line propagation is removed and only the curved surface where the refraction occurs is retained, the lens thickness can be greatly reduced while achieving the same focusing effect. As Figure 1As shown, a conventional convex lens uses a complete arc structure and has a large volume. When ultrasonic waves pass through the convex lens, the straight-line propagation part does not affect the focusing effect, but will significantly reduce the amplitude of the sound wave, which belongs to the "ineffective part". By removing the "ineffective part" and only retaining the refracting curved surface, the volume of the lens can be significantly reduced while maintaining the same focusing effect, thereby significantly reducing the attenuation of the sound wave when passing through the lens and achieving the purpose of improving the sensitivity of the probe. However, the surface of the Fresnel lens has a complex curved surface structure, and it is difficult to achieve the fine processing of the complex curved surface of common acoustic lens materials (such as silicone rubber). Therefore, it is difficult to prepare a Fresnel acoustic lens by traditional processing methods. To address this problem, the present invention provides a method for designing and preparing an acoustic lens for a high-frequency array ultrasonic transducer to prepare a Fresnel acoustic lens, and utilizes the advantages of easy processing and high precision of metal molds to complete the processing and forming of the lens mold, and then uses the reverse molding method to achieve the precise and efficient preparation of the Fresnel acoustic lens.

[0047] Specifically, the method for designing and preparing an acoustic lens for a high-frequency array ultrasonic transducer provided in this embodiment includes:

[0048] S1. Select the material of the Fresnel acoustic lens.

[0049] In this embodiment, the sound velocity of the material of the Fresnel acoustic lens should be lower than that of the imaging target.

[0050] Further, if it is an ultrasonic probe applied to medical imaging, the material selected for the Fresnel acoustic lens should be lower than the average sound velocity of human tissues, which is 1540 m / s. For example, vulcanized silicone rubber RTV, PDMS, etc. can be used. This is taken as an example and is not limited thereto.

[0051] S2. Design the parameters of the Fresnel acoustic lens.

[0052] In this embodiment, the process of designing the parameters of the Fresnel acoustic lens is as follows:

[0053] S21. Determine the focal length F and width W of the lens according to the design requirements of the ultrasonic probe (such as image resolution and focusing depth). Among them, the horizontal resolution R L has the following relationship with F:

[0054] R L = 1.22λf #

[0055]

[0056] where λ is the wavelength, f # is the F-number of the lens, NA is the aperture of the transducer, and here W = NA.

[0057] S22. Determine the radius of curvature R of the lens.

[0058] In this embodiment, as Figure 2 shown, the curvature radius R of the lens is determined according to the relationship between the parameters of the Fresnel acoustic lens. Among them, the relationship between the parameters of the Fresnel acoustic lens is:

[0059]

[0060] Among them, F is the designed focal length of the focusing probe, v1 is the sound velocity of the imaging medium, v2 is the sound velocity of the lens material, and R is the curvature radius of the lens.

[0061] S23. Determine the basic thickness d of the lens according to the process requirements.

[0062] In this embodiment, the smaller the value of the basic thickness d, the more beneficial it is to reduce the attenuation of sound waves in the lens, but it will increase the processing difficulty of the lens. When necessary, d can be equal to 0.

[0063] Furthermore, the process requirements need to be determined according to the actual situation. Different processing methods have different requirements. For example, common cutting processing has greater stress, and at this time, a larger basic thickness needs to be retained to ensure that the lens does not break during the processing; when using the casting method, it only needs to ensure that the whole lens can be complete. At this time, the value of d can be smaller, and there is no specific limit.

[0064] S24. Determine the curved surface of the Fresnel acoustic lens based on the width W and the basic thickness d of the Fresnel acoustic lens.

[0065] In this embodiment, the lens width is divided into N parts, and the width of each part is W i (i = 1, 2, 3…N). As Figure 2 (c) shown, W i can be non-uniformly spaced or uniformly spaced. After retaining the basic thickness d for each part, remove the part where the sound wave propagates along a straight line in the lens, that is, the rectangular part as Figure 2 (b) shown. The remaining part is the retained part of the Fresnel lens, thereby determining its corresponding curved surface. Among them, the value of N determines the complexity of the Fresnel lens. The larger N is, the more complex its structure is, and the more beneficial it is to reduce the overall volume, but the processing difficulty increases accordingly.

[0066] S3. Prepare the Fresnel acoustic lens based on the above determined lens parameters.

[0067] In this embodiment, as Figure 3 shown, the preparation method of the Fresnel acoustic lens includes processes such as fine metal mold processing, casting, demolding, lens material pouring and curing, demolding and forming, and transducer bonding. The specific process is as follows:

[0068] S31. Fine metal mold processing.

[0069] In this embodiment, according to the position and surface parameters of the Fresnel lens obtained through the foregoing process, a metal mold of the Fresnel lens is prepared by using complex curved surface precision machining equipment such as a five-axis machine tool or laser engraving equipment.

[0070] Furthermore, the metal mold material is generally selected as a metal material that is easy to process, has little deformation, and is corrosion-resistant, such as stainless steel, etc. The prepared metal mold will be used as the master mold of the Fresnel lens and reused.

[0071] S32. Replicating mold treatment.

[0072] In this embodiment, after obtaining the metal mold, PDMS (polydimethylsiloxane) is used for replicating mold treatment.

[0073] S33. Demolding treatment.

[0074] In this embodiment, after the PDMS is cured, demolding treatment is carried out to obtain a PDMS mold with the curved surface of the Fresnel acoustic lens.

[0075] S34. Pouring and curing of lens material.

[0076] In this embodiment, the uncured lens material is poured into the PDMS mold and cured; before pouring the uncured lens material, degassing treatment should be carried out to prevent defects such as air bubbles inside the lens; during curing, the surface should be ensured to be flat without undulations.

[0077] S35. Demolding and forming.

[0078] In this embodiment, after the lens material is cured, the formed Fresnel acoustic lens is taken out and its surface is cleaned.

[0079] S35. Bonding of transducer.

[0080] In this embodiment, the demolded and formed Fresnel acoustic lens is bonded to the array transducer for use.

[0081] In summary, by adopting the Fresnel acoustic lens structure and proposing a targeted preparation method, the present invention can effectively reduce the thickness and volume of the acoustic lens of the ultrasonic probe, and can ensure the focusing effect while greatly improving the echo sensitivity and image resolution of the ultrasonic probe. As Figure 4 shown in the application scenarios of the two Fresnel acoustic lenses, Figure 4 (a) is the style of the Fresnel acoustic lens of the linear array probe, including linear array and convex array, etc., Figure 4 (b) is the style of the Fresnel lens of the annular array transducer. As Figure 5 shown is the comparison of the focusing sound fields of the lensless, convex lens, and Fresnel acoustic lens without considering the acoustic wave attenuation,Figure 6 For the corresponding comparison of the focusing intensity. The results show that the Fresnel acoustic lens can still approximately achieve the focusing effect of a convex lens while significantly reducing the volume and thickness of the lens.

[0082] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In the description of this specification, the descriptions referring to terms such as "a preferred embodiment", "furthermore", "specifically", "in this embodiment", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of this specification. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A design and preparation method of an acoustic lens for a high-frequency array ultrasonic transducer, characterized in that: The method includes: Select the material for making the Fresnel acoustic lens; Design parameters of Fresnel acoustic lens; Based on the determined materials and parameters of the Fresnel acoustic lens, a Fresnel acoustic lens is prepared.

2. The method for designing and preparing an acoustic lens for a high-frequency array ultrasonic transducer according to claim 1, characterized in that: The principle for selecting the material for making Fresnel acoustic lens is that the sound velocity of the material of Fresnel acoustic lens should be lower than the imaging target.

3. The method for designing and preparing an acoustic lens according to claim 2, characterized in that: When a high-frequency array ultrasonic transducer is used in medical imaging, the material selected for making the Fresnel acoustic lens should be lower than the average sound velocity of human tissue, wherein the material is vulcanized silicone rubber RTV or PDMS.

4. The method for designing and preparing an acoustic lens according to claim 1, characterized in that: Design parameters of the Fresnel acoustic lens, including: Determine the focal length F and width W of the Fresnel acoustic lens according to the design requirements of the ultrasonic transducer; Based on the focal length F and the sound velocity of the Fresnel acoustic lens and the sound velocity of the imaging medium, the curvature radius R of the Fresnel acoustic lens is determined; Determine the basic thickness d of the Fresnel acoustic lens according to the process requirements; Based on the width W and the basic thickness d of the Fresnel acoustic lens, the curved surface of the Fresnel acoustic lens is determined.

5. The method for designing and preparing an acoustic lens according to claim 4, characterized in that: The focal length F and width W of the Fresnel acoustic lens are determined according to the image resolution and focal depth of the ultrasonic transducer: R L =1.22λf # Among them, R L is the lateral resolution of the image, λ is the wavelength, f # is the F number of the Fresnel acoustic lens, NA is the aperture of the ultrasonic transducer, and W = NA.

6. The method for designing and preparing an acoustic lens according to claim 4, characterized in that: Based on the focal length F and sound velocity of the Fresnel acoustic lens and the sound velocity of the imaging medium, the curvature radius R of the Fresnel acoustic lens is determined: Among them, v1 is the sound velocity of the imaging medium, and v2 is the sound velocity of the Fresnel acoustic lens material.

7. The method for designing and preparing an acoustic lens according to claim 4, characterized in that: Based on the width W and the basic thickness d of the Fresnel acoustic lens, the curved surface of the Fresnel acoustic lens is determined, including: dividing the lens width W into N parts, each part having a width W i (i=1,2,3…N), after retaining the basic thickness d of each part, remove the part of the lens where the sound wave propagates along a straight line, and the remaining part is the retained part of the Fresnel acoustic lens, thereby determining its corresponding curved surface.

8. The method for designing and preparing an acoustic lens according to claim 4, characterized in that: Based on the determined materials and parameters of the Fresnel acoustic lens, a Fresnel acoustic lens is prepared, including: According to the position and surface parameters of the Fresnel acoustic lens, a metal mold of the Fresnel acoustic lens is prepared; After obtaining the metal mold, use PDMS for mold casting; After the PDMS is solidified, a demoulding process is performed to obtain a PDMS mold with a Fresnel acoustic lens curved surface; pouring the uncured Fresnel acoustic lens material into the PDMS mold and performing a curing process; The Fresnel acoustic lens material is demolded after solidification, and the molded Fresnel acoustic lens is taken out and its surface is cleaned, wherein the demolded Fresnel acoustic lens is used to be bonded to a high-frequency array ultrasonic transducer for use.

9. The method for designing and preparing an acoustic lens according to claim 8, characterized in that: The uncured Fresnel acoustic lens material is degassed before casting to prevent defects such as bubbles inside the lens; during curing, the surface should be flat and without undulations.

10. The method for designing and preparing an acoustic lens according to claim 8, characterized in that: The metal mold for preparing the Fresnel acoustic lens adopts complex surface precision processing equipment or laser engraving equipment.

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