Ultrasonic imaging gradient acoustic impedance matching layer structure and method

Abstract

The invention discloses an ultrasonic imaging gradient acoustic impedance matching layer structure and method, the structure is formed by two-dimensional periodic arrangement of gradient impedance units, and each gradient impedance unit comprises a composite structure 1 and a composite structure 2. Through the material attribute design of the structure 1 and the structure 2 in the gradient impedance unit, the impedance of the unit along the sound transmission direction can be changed in a gradient manner. The non-uniform gradient impedance unit structure array is used, strong reflection of ultrasound on an impedance mismatch interface is weakened, and broadband ultrasonic energy transmission is achieved. Energy matching of any impedance mismatch interface can be realized by adjusting the number of the gradient impedance unit periodical arrangement units.

Description

Technical Field

[0001] This invention belongs to the field of ultrasound imaging technology, and specifically relates to an ultrasound imaging gradient acoustic impedance matching layer structure and method. Background Technology

[0002] Ultrasonic imaging is one of the core technologies in the field of nondestructive testing (NDT). With its advantages of high sensitivity in identifying internal structural defects, no radiation pollution, and real-time imaging, it has irreplaceable application value in high-end manufacturing fields such as aerospace, nuclear power equipment, and marine engineering. In recent years, as industrial equipment has developed towards larger scale, greater complexity, and longer lifespan, the demand for NDT of multilayer heterogeneous structures (such as metal-dielectric composite structures and coating-matrix composite structures) has become increasingly urgent, requiring ultrasonic imaging technology to achieve precise localization and quantitative characterization of deep defects.

[0003] However, existing ultrasonic imaging technology faces two major technical bottlenecks in practical applications: First, the acoustic impedance differences between different media in multi-layered complex structures are significant (for example, the acoustic impedance ratio between metal and water can be tens of times), causing strong reflection of ultrasonic waves at the medium interface. Less than 10% of the ultrasonic energy can penetrate into the detection area, which severely limits the effective focusing of ultrasonic energy and the imaging clarity of deep structures. Second, corrosion and wear of the outer layer of the structure during service can cause non-uniform changes in its thickness, further aggravating the acoustic impedance mismatch, resulting in a significant decrease in ultrasonic penetration efficiency and making it difficult to meet engineering requirements in terms of detection accuracy.

[0004] To address the aforementioned issues, existing technologies primarily employ single or multiple homogeneous acoustic impedance matching layers for impedance transition. However, such solutions have inherent drawbacks: firstly, the acoustic impedance value of the homogeneous matching layer is fixed, enabling impedance matching only at specific frequencies, which fails to meet the demands of broadband ultrasound imaging; secondly, traditional matching layers rely on homogeneous materials with specific acoustic impedances, and the fabrication process for such materials is complex and costly, making them difficult to adapt to curved or heterogeneous structural interfaces with varying thicknesses, severely limiting their application scenarios. Therefore, developing a gradient acoustic impedance matching layer structure that can achieve broadband transmission, adapt to complex interfaces, and is highly feasible to fabricate has become crucial for overcoming the bottlenecks of existing ultrasound imaging technologies. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the background art by proposing an ultrasonic imaging gradient acoustic impedance matching layer structure and method to achieve efficient broadband transmission of ultrasound.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following solution: An ultrasonic imaging gradient acoustic impedance matching layer structure includes a plurality of gradient impedance units; each of the gradient impedance units is along... x direction andy The ultrasonic waves are arranged in a two-dimensional periodic array along the direction. z Directional transmission; where (0-xyz) constitutes a three-dimensional rectangular coordinate system.

[0007] The gradient impedance unit is a binary composite structure, comprising structure 1 and structure 2, which are distributed vertically along the y-direction and are mutually composite; structure 1 and structure 2 are made of different materials; the acoustic impedance of structure 1 corresponds to the material. Z 材1 =p ¹ v 1. Acoustic impedance of the material corresponding to structure 2 Z 材2 =p ² v 2 ,in r ¹ represents the density of the material corresponding to structure 1. v 1 represents the sound velocity of the material corresponding to structure 1. r ² represents the density of the material corresponding to structure 2. v 2 represents the sound velocity of the material corresponding to structure 2.

[0008] By adjusting the structural parameters of the gradient impedance unit, such as the properties of material 1 and material 2, and the composite ratio of structure 1 and structure 2, the gradient impedance unit can form an equivalent acoustic impedance distribution with a continuous gradient change along the z-direction, thereby realizing broadband ultrasonic energy transmission. For arbitrary impedance mismatch interfaces with curved surfaces, precise matching of ultrasonic energy can be achieved by adjusting the two-dimensional periodic arrangement of the gradient impedance units (including array density and unit contour adaptability).

[0009] Further optimization involves the gradient impedance unit having a square cross-section perpendicular to the z-direction, with a side length of [missing value]. a ; Adjacent gradient impedance units are in a close-fitting state; Structure 1 and structure 2 of the same gradient impedance unit are in a close fit; The tight fit means that the two are seamless and without any interlayer.

[0010] Further optimization shows that the curve equation of the composite surface of structure 1 and structure 2 in the yz plane satisfies: y=kz ², where, y For structure 2 along y Dimensional parameters of the direction, z For structure 2 along z Dimensional parameters of the direction, k It is a constant. k≠a .

[0011] Further optimization involves the thickness of the gradient impedance unit along the z-direction. L satisfy: L =2 v eff / f c ,in v eff The equivalent sound velocity of the gradient impedance element. f c The center frequency of the ultrasound is 1.

[0012] Further optimization yields the following side lengths for the gradient impedance element cross-section: a ≤ v eff / f max ;in, v eff The equivalent sound velocity of the gradient impedance element. f max This is the maximum operating frequency of the ultrasonic wave.

[0013] Further optimization of the equivalent acoustic impedance of the gradient impedance unit. Z eff Equivalent speed v eff Represented as: (1); (2); (3); in, and Let i and j represent the elastic coefficients of structure 2 and structure 1, respectively. i and j are both 1 or 2, representing the tensor subscripts of the elastic coefficients. n = S1 / S2 represents the volume ratio of structure 1 to the gradient impedance element. S1 is the cross-sectional area of ​​structure 1 perpendicular to the z-direction, and S2 is the cross-sectional area of ​​the gradient impedance element perpendicular to the z-direction, which is always a². ρ¹ is the density of the material corresponding to structure 1, and ρ² is the density of the material corresponding to structure 2.

[0014] The impedance matching method for arbitrary curved surfaces based on the above structure includes the following steps: Step 1: Obtain the core parameters of the interface to be matched: The acoustic impedance Z of the media on both sides of the interface was measured using an ultrasonic thickness gauge. 介1 Z 介2 The surface morphology parameters of the interface are measured using a laser profilometer. These surface morphology parameters include the surface radius of curvature R, the surface curvature in... x direction and y The extent of the direction; Step 2: Design the material and volume ratio of the gradient impedance unit: According to Z in step 1 介1 With Z 介2 The difference is used to select the corresponding material 1 and material 2 to make Z 材1 With Z 材2 The difference covers Z 介1 With Z 介2 The difference; calculate the volume percentage using formulas (1) to (3). n The adjustment range allows the equivalent acoustic impedance Z of the gradient impedance unit to be adjusted. eff along z The direction forms a continuous gradient, and the gradient range covers Z. 介1 With Z 介2 ; Step 3: Determine the geometric parameters of the gradient impedance element: Based on the center frequency of ultrasound f c and maximum operating frequency f max Combined with the formula: L =2 v eff / f c Calculate the element thickness L, and combine it with the formula. a ≤ v eff / f max Determine the side length of the unit section a Based on the surface curvature radius R of the interface in step 1, adjust the constants in the curve equation of the composite surface of structure 1 and structure 2 on the yz plane. k This allows the contour of structure 2 to be adapted to the local curvature of the interface to be matched. Step S4: Construct the matching layer array: The gradient impedance unit designed in steps 2-3 is along... x direction and y For directional arrangement, the total array size is determined based on the extension range of the curved surface in step 1; for areas where the curvature of the curved surface changes, the spacing between the units is reduced proportionally to the increase in curvature, so that the overall outline of the array fits the interface to be matched with ≥90%; Step S5: Verification and Fine-tuning The constructed matching layer is attached to the interface to be matched, and an ultrasonic power meter is used to test the ultrasonic waves. f c to f max Transmission efficiency within the frequency band; if the transmission efficiency is lower than a preset threshold, the volume ratio is fine-tuned. n Or the spacing between units, until the transmission efficiency of all frequency bands reaches or exceeds the preset threshold.

[0015] Further optimization is achieved by ensuring that the measurement accuracy of the ultrasonic thickness gauge in step 1 is ≤0.01mm and the curvature measurement accuracy of the laser profilometer is ≤0.1mm.

[0016] Further optimization involves setting the preset threshold in step 5 to 40%, and adjusting the volume percentage during fine-tuning. n The adjustment range is ±0.05~±0.1, and the adjustment range of the unit arrangement spacing is ±0.02mm~±0.05mm.

[0017] Further optimization involves adjusting the volume ratio n in step 2 within the range of 0.3 to 0.8, with n varying at a rate of 0.1 to 0.2 mm along the z-direction, ensuring the equivalent acoustic impedance Z... eff The gradient change along the z-direction is continuous without abrupt changes.

[0018] Further optimization involves setting the ratio of the reduction in unit spacing to the increase in curvature in step 4 to 1:1, meaning that for every 10mm decrease in the radius of curvature of the surface, the unit spacing decreases by 0.04mm to 0.08mm.

[0019] Further optimization involves using a wideband frequency range of 2MHz to 15MHz in step 5, with transmission efficiency fluctuations within this band ≤5%.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects: 1. By connecting a certain number of gradient impedance units in parallel, impedance matching of any curved surface can be achieved, enabling customization.

[0021] 2. By changing the material properties of structure 1 and structure 2, a specific impedance curve with parabolic changes in the direction of sound propagation can be achieved, which solves the problem of ultrasonic attenuation to a certain extent.

[0022] 3. This invention solves the problem of difficulty in fabricating specific acoustic impedance materials in traditional ultrasonic matching layer fabrication. By constructing a continuous gradient acoustic impedance distribution along the acoustic transmission direction, the reflection loss of ultrasonic waves at the impedance mismatch interface is greatly reduced, and the ultrasonic energy transmission efficiency is improved compared with traditional matching layers. It can cover the ultrasonic imaging needs of a wide frequency range and is compatible with ultrasonic transducers of different frequencies.

[0023] 4. By adjusting the unit surface parameter k and the array arrangement density, it can adapt to any impedance mismatch interface such as planar, cylindrical, and irregular etched surfaces, thus overcoming the limitation of existing solutions that can only adapt to fixed interfaces. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of an ultrasonic imaging gradient acoustic impedance matching layer structure according to the present invention; Figure 2 This is a schematic diagram of a gradient impedance unit. Detailed Implementation

[0025] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0026] like Figure 1 As shown, an ultrasonic imaging gradient acoustic impedance matching layer structure includes several gradient impedance units; each of the gradient impedance units is along... x direction and y The ultrasonic waves are arranged in a two-dimensional periodic array along the direction. z Directional transmission; where (0-xyz) constitutes a three-dimensional rectangular coordinate system.

[0027] The gradient impedance unit is a binary composite structure, comprising structure 1 and structure 2, which are distributed vertically along the y-direction and are mutually composite; structure 1 and structure 2 are made of different materials; the acoustic impedance of structure 1 corresponds to the material. Z 材1 =p ¹ v 1. Acoustic impedance of the material corresponding to structure 2 Z 材2 =p ² v 2 ,in r ¹ represents the density of the material corresponding to structure 1. v 1 represents the sound velocity of the material corresponding to structure 1. r ² represents the density of the material corresponding to structure 2. v 2 represents the sound velocity of the material corresponding to structure 2.

[0028] The gradient impedance element has a square cross-section perpendicular to the z-direction, with a side length of [missing value]. a Adjacent gradient impedance units are in a close fit. The curve equation of the composite surface of structure 1 and structure 2 in the yz plane satisfies: y=kz ², where, y For structure 2 along y Dimensional parameters of the direction, z For structure 2 along z Dimensional parameters of the direction, k It is a constant. k≠a .

[0029] The thickness of the gradient impedance unit along the z-directionL satisfy: L =2 v eff / f c ,in v eff The equivalent sound velocity of the gradient impedance element. f c Let be the center frequency of the ultrasonic wave. The side length of the gradient impedance element cross-section satisfies: a ≤ v eff / f max ;in, v eff The equivalent sound velocity of the gradient impedance element. f max This is the maximum operating frequency of the ultrasonic wave.

[0030] The equivalent acoustic impedance of the gradient impedance unit Z eff Equivalent speed v eff Represented as: (1); (2); (3); in, and Let i and j represent the elastic coefficients of structure 2 and structure 1, respectively. i and j are both 1 or 2, representing the tensor subscripts of the elastic coefficients. n = S1 / S2 represents the volume ratio of structure 1 to the gradient impedance element. S1 is the cross-sectional area of ​​structure 1 perpendicular to the z-direction, and S2 is the cross-sectional area of ​​the gradient impedance element perpendicular to the z-direction, which is always a². ρ¹ is the density of the material corresponding to structure 1, and ρ² is the density of the material corresponding to structure 2. Example 1:

[0031] This embodiment provides an ultrasonic imaging gradient acoustic impedance matching layer structure adapted to a metal-water multilayer structure, the specific design of which is as follows: Material selection: Structure 1 uses polysulfone resin, whose sound velocity... v =1 = 2300 m / s, density ρ¹ = 1200 kg / m³, elastic modulus c 11 ¹=6.38GPa, c 12 ¹=2.41Gpa. Structure 2 uses alumina ceramic, whose sound velocity... v 2 = 10500 m / s, density ρ² = 3980 kg / m³, elastic modulus c 11 ² = 400 GPa, c 12² = 165 GPa.

[0032] Gradient impedance element parameter design: ultrasonic center frequency f c =5MHz, maximum operating frequency f max =10MHz.

[0033] Equivalent sound velocity of gradient impedance unit v eff = ( v 1 n + v 2(1- n =4500m / s, take n=0.6.

[0034] The side length of the cross section a = v eff / f max =4500m / s / 10×10 6 Hz = 0.45mm, satisfying a ≤ v eff / f max .

[0035] Unit thickness L =2 v eff / f c =2×4500m / s / 5×10 6 Hz = 1.8mm; The constant of the surface equation of structure 2 a =0.05mm⁻¹, the surface equation is y=0.05z², z∈[0,1.8mm], the cross-sectional areas of structure 1 and structure 2 are S1=0.6a², S2=a²=0.2025mm².

[0036] Equivalent parameter calculation: Volume ratio n =S1 / S2=0.6; equivalent density r eff =ρ¹n+(1-n)ρ²=1200×0.6+0.4×3980=2272kg / m³; Equivalent acoustic impedance Z eff = ≈10.2×10 6 Pa·s / m; Equivalent speed of sound v eff = Zeff / r eff ≈10.2×10 6 / 2272≈4500m / s, consistent with the design value.

[0037] Array arrangement: The above gradient impedance units are arranged in a two-dimensional periodic array along the x and y directions. The array size is 50mm×50mm. There is no gap between adjacent units and they are tightly fitted together. Structure 1 and Structure 2 are tightly fitted together without any interlayer, forming an overall matching layer structure.

[0038] Performance testing: The matching layer structure of this embodiment was applied to a metal (steel, acoustic impedance 45×10). 6 Pa・s / m) - Water (acoustic impedance 1.5×10 6 Ultrasonic imaging of multi-layer structures (Pa·s / m) showed that the ultrasonic energy transmission efficiency was greatly improved. It can effectively cover a wide frequency band of 5-10MHz, and at a center frequency of 8MHz, the imaging resolution reaches 0.08mm, successfully identifying minute cracks as small as 0.1mm inside metal. For curved interfaces (radius of curvature 50mm) formed by metal surface corrosion, the ultrasonic energy penetration rate remains above 40%, and the imaging effect is stable.

[0039] This invention, through innovative gradient impedance unit design and array arrangement, breaks through the technical bottleneck of existing ultrasonic matching layers, providing a new technical solution for broadband, high-precision ultrasonic imaging of multi-layered complex structures. Those skilled in the art can achieve personalized adaptation by adjusting material selection, unit parameters, and array morphology according to the acoustic impedance characteristics of the specific object being detected; the scope of protection is defined by the claims.

Claims

1. An ultrasonic imaging gradient acoustic impedance matching layer structure, characterized in that, It includes several gradient impedance units; each of the gradient impedance units is along... x direction and y The ultrasonic waves are arranged in a two-dimensional periodic array along the direction. z Directional transmission; where (0-xyz) constitutes a three-dimensional rectangular coordinate system; The gradient impedance unit is a binary composite structure, comprising structure 1 and structure 2, which are distributed vertically along the y-direction and are mutually composite; structure 1 and structure 2 are made of different materials; the acoustic impedance of structure 1 corresponds to the material. Z 材1 =ρ ¹ v 1. Acoustic impedance of the material corresponding to structure 2 Z 材2 =ρ ² v 2 ,in ρ ¹ represents the density of the material corresponding to structure 1. v 1 represents the sound velocity of the material corresponding to structure 1. ρ ² represents the density of the material corresponding to structure 2. v 2 represents the sound velocity of the material corresponding to structure 2.

2. The ultrasonic imaging gradient acoustic impedance matching layer structure according to claim 1, characterized in that, The gradient impedance element has a square cross-section perpendicular to the z-direction, with a side length of [missing value]. a ; Adjacent gradient impedance units are in a close-fitting state; Structure 1 and structure 2 of the same gradient impedance unit are in a close fit; The tight fit means that the two are seamless and without any interlayer.

3. The ultrasonic imaging gradient acoustic impedance matching layer structure according to claim 2, characterized in that, The curve equation of the composite surface of structure 1 and structure 2 in the yz plane satisfies: y=kz ², where, y For structure 2 along y Dimensional parameters of the direction, z For structure 2 along z Dimensional parameters of the direction, k It is a constant. k ≠a .

4. The ultrasonic imaging gradient acoustic impedance matching layer structure according to claim 3, characterized in that, The thickness of the gradient impedance unit along the z-direction L satisfy: L =2 v eff / f c ,in v eff The equivalent sound velocity of the gradient impedance element. f c The center frequency of the ultrasound is 1.

5. The ultrasonic imaging gradient acoustic impedance matching layer structure according to claim 4, characterized in that, The side length of the gradient impedance element cross section satisfies: a ≤ v eff / f max ; in, v eff The equivalent sound velocity of the gradient impedance element. f max This is the maximum operating frequency of the ultrasonic wave.

6. The ultrasonic imaging gradient acoustic impedance matching layer structure according to claim 5, characterized in that, Equivalent acoustic impedance of gradient impedance unit Z eff Equivalent speed v eff Represented as: （1）； （2）； （3）； in, and Let i and j represent the elastic coefficients of structure 2 and structure 1, respectively. i and j are both 1 or 2, representing the tensor subscripts of the elastic coefficients. n = S1 / S2 represents the volume ratio of structure 1 to the gradient impedance element. S1 is the cross-sectional area of ​​structure 1 perpendicular to the z-direction, and S2 is the cross-sectional area of ​​the gradient impedance element perpendicular to the z-direction, which is always a². ρ¹ is the density of the material corresponding to structure 1, and ρ² is the density of the material corresponding to structure 2.

7. An impedance matching method based on an arbitrary curved surface of the structure described in any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: Obtain the core parameters of the interface to be matched: The acoustic impedance Z of the media on both sides of the interface was measured using an ultrasonic thickness gauge. 介1 Z 介2 The surface morphology parameters of the interface are measured using a laser profilometer. These surface morphology parameters include the surface radius of curvature R, the surface curvature in... x direction and y The extent of the direction; Step 2: Design the material and volume ratio of the gradient impedance unit: According to Z in step 1 介1 With Z 介2 The difference is used to select the corresponding material 1 and material 2 to make Z 材1 With Z 材2 The difference covers Z 介1 With Z 介2 The difference; The volume percentage is calculated using formulas (1) to (3). n The adjustment range allows the equivalent acoustic impedance Z of the gradient impedance unit to be adjusted. eff along z The direction forms a continuous gradient, and the gradient range covers Z. 介1 With Z 介2 ; Step 3: Determine the geometric parameters of the gradient impedance element: Based on the center frequency of ultrasound f c and maximum operating frequency f max Combined with the formula: L =2 v eff / f c Calculate the element thickness L, and combine it with the formula. a ≤ v eff / f max Determine the side length of the unit section a Based on the surface curvature radius R of the interface in step 1, adjust the constants in the curve equation of the composite surface of structure 1 and structure 2 on the yz plane. k This allows the contour of structure 2 to be adapted to the local curvature of the interface to be matched. Step S4: Construct the matching layer array: The gradient impedance unit designed in steps 2-3 is along... x direction and y For directional arrangement, the total array size is determined based on the extension range of the curved surface in step 1; for areas where the curvature of the curved surface changes, the spacing between the units is reduced proportionally to the increase in curvature, so that the overall outline of the array fits the interface to be matched with ≥90%; Step S5: Verification and Fine-tuning The constructed matching layer is attached to the interface to be matched, and an ultrasonic power meter is used to test the ultrasonic waves. f c to f max Transmission efficiency within the frequency band; If the transmission efficiency is lower than the preset threshold, the volume ratio will be fine-tuned. n Or the spacing between units, until the transmission efficiency of all frequency bands reaches or exceeds the preset threshold.

8. The impedance matching method for arbitrary curved surfaces according to claim 7, characterized in that, The ultrasonic thickness gauge described in step 1 has a measurement accuracy of ≤0.01mm, and the laser profilometer has a curvature measurement accuracy of ≤0.1mm.

9. The impedance matching method for arbitrary curved surfaces according to claim 7, characterized in that, The preset threshold mentioned in step 5 is 40%, and the volume percentage during fine-tuning is... n The adjustment range is ±0.05~±0.1, and the adjustment range of the unit arrangement spacing is ±0.02mm~±0.05mm.

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