CN115644922A - Ultrasonic probe using gradient matching layer - Google Patents

Abstract

The invention discloses an ultrasonic probe using a gradient matching layer, which comprises a piezoelectric material and a matching layer, wherein the matching layer is arranged on the front surface of the piezoelectric material, the matching layer is arranged as a single-layer matching layer to replace the current multilayer matching layer to be applied to an ultrasonic transducer.

Description

Ultrasonic probe using gradient matching layer

Technical Field

The invention relates to the technical field of ultrasonic probes, in particular to an ultrasonic probe using a gradient matching layer.

Background

The main performance indexes of the ultrasonic transducer used in underwater acoustic detection, nondestructive detection and medical ultrasonic image diagnosis are sensitivity and bandwidth, the higher the sensitivity is, the farther the detection distance is, the wider the bandwidth is, and the higher the resolution of an image is, so that the following technologies are often adopted for improving the sensitivity and the bandwidth of the ultrasonic transducer:

1. the use of high performance piezoelectric materials provides enhanced transmission and reception capabilities and increased bandwidth, such as: piezoelectric ceramics with ultrahigh piezoelectric coefficient, piezoelectric single crystals such as PMN-PT and the like, and piezoelectric ceramics or single crystal composite materials with special structures such as 2-2/1-3 type with high electromechanical coupling coefficient are adopted;

2. the technology of multiple acoustic impedance matching layers is used, loss in the transmission process is reduced, the bandwidth is widened, 2 layers and 3 layers of matching layers are generally used in a medical diagnosis ultrasonic probe of 2 MHz-10 MHz, 4 layers or even 5 layers of matching layers are used in a few probes, and one or two layers of matching layers are generally adopted in a higher-frequency ultrasonic probe due to the relation of processing difficulty;

the basic structure of the existing one-dimensional array type ultrasonic probe is shown as follows, from inside to outside, the probe respectively comprises a sound absorption layer (backing), a piezoelectric material, a sound matching layer and a sound lens, electrodes are arranged on two sides of the piezoelectric material and led out by a circuit, the acoustic impedance of the piezoelectric material is higher, the acoustic impedance of piezoelectric ceramics or single crystals is about 35MRayl generally, the acoustic impedance of piezoelectric or single crystal composite materials is about 20MRayl generally, the acoustic impedance of human tissues is about 1.5MRayl generally, the great difference of the acoustic impedances causes the transmissivity of sound signals to be particularly low according to an acoustic power transmission formula, in order to improve the transmission efficiency of the sound signals, an acoustic impedance matching layer is introduced, generally, the acoustic impedance matching layer is a uniform material with the thickness of one quarter wavelength, and theoretical calculation shows that: in the case of not considering the attenuation of the matching layer, the optimal single-layer matching layer has the transmissivity of 32.3 percent, the highest transmission efficiency of 45.3 percent for the double-layer matching layer, 54.6 percent for the three layers, 79.9 percent for the 10 layers and 100 percent for the perfect matching layer;

in order to further improve the transmittance, the invention discloses a metamaterial with continuously changing acoustic impedance, which is generally characterized in that conical holes are tightly arranged on a base material, and materials with different densities are filled, so that the acoustic impedance of the metamaterial continuously changes in an exponential form in the thickness direction, as shown in the attached figure 4 of the specification, an acoustic impedance matching layer manufactured by the taper hole compounding method can be much higher than the transmittance of a multi-layer matching layer structure and can reach more than 92 percent, and the acoustic impedance gradient metamaterial has the impedance changed from more than ten MRayls to more than several MRayls, is already applied to low-frequency underwater acoustic single-array element transducers, and also has the gradient material with continuously changing acoustic impedance by adopting a sedimentation method: the method comprises the steps of selecting fillers with different acoustic impedance values and adjusting the volume fraction of the fillers in a matching layer, treating the fillers by a centrifugal sedimentation method to ensure that the concentration of filler particles in a polymer substrate is in gradient distribution in the vertical direction, and then curing the fillers to obtain an acoustic impedance gradient matching layer material, wherein in order to further improve the matching effect, a layer of uniform high-impedance matching material can be added between a piezoelectric material and the acoustic impedance gradient material, the thickness of the matching layer is related to the wavelength, the total thickness is generally one quarter wavelength to 2 times of the wavelength, namely, the working frequency is low, the wavelength is long, the thickness of the matching layer is thick, the processing is easy, the working frequency is high, the wavelength is short, the thickness of the matching layer is thin, the processing difficulty is large, attenuation exists in the matching layer, so that the thickness of the matching layer is not too thick, the acoustic velocity in the matching layer is generally 2000-3000 m/s, and the underwater acoustic transducer generally works at hundreds of KHz, so that the wavelength in the matching layer of the underwater acoustic transducer is in the mm level, while the medical ultrasonic transducer is generally in the 2 MHz-10 MHz range, and the wavelength in the matching layer is 0.1mm level;

the matching layer is generally formed by adding metal powder or metal oxide powder with different densities into epoxy glue, such as tungsten powder, aluminum oxide powder, bismuth oxide powder, glass beads and the like, and mixing the materials according to a certain proportion, wherein the matching layer has specific acoustic impedance (density and sound velocity) and relatively low acoustic attenuation, and the processing method of the matching layer comprises a casting method, a spin-coating method, a centrifugal method and the like;

however, in order to improve the sensitivity of the ultrasonic transducer at present, the performance improvement of the piezoelectric material reaches the limit quickly, a novel piezoelectric material is continuously put into use, 1-3, 2-2 or other configurations of composite materials are generally applied, and a new breakthrough direction is in the theory and process of the matching layer, theoretically, the bandwidth of the Gao Huanneng transducer can be improved to a greater extent by the multilayer acoustic matching layer compared with the single-layer matching layer, and the sound wave transmission efficiency of the transducer can be further improved, but actually, each additional acoustic matching layer brings many problems in the process, such as: the bonding difficulty is increased, the probability of air bubbles is increased, the thickness is increased and the like, the influence factors can cause that the relative bandwidth can not reach the theoretical value, and the sensitivity can be reduced, so that the prior medical ultrasonic probe mostly adopts 2 or 3 matching layers, and rarely adopts 4 layers, and the prior gradient material with continuously changed acoustic impedance mainly has two methods: the taper hole compound method, the centrifugal sedimentation method and the taper hole compound method can accurately control the change curve of impedance along the thickness direction and the thickness of a matching layer, the processing scale range is mm level, the diameter of a cone is 0.1mm level, the taper hole compound method is suitable for the underwater acoustic frequency range, in particular to the underwater acoustic transducer of a single array element, and the medical ultrasound and the matching layer with the thickness of 0.1mm level required in the frequency range commonly used by the inspection ultrasound are very difficult and poor in uniformity under the thickness, and are not suitable for being made into the matching layer of an array element transducer, so the taper hole compound method is not suitable for the centrifugal sedimentation method, the process is simple, but the process parameters are complex and are related to a plurality of factors, the acoustic impedance of the taper hole compound method and the centrifugal sedimentation method cannot be finely controlled, the acoustic impedance can not be continuously changed along the thickness direction of the acoustic matching layer of a specific curve, the acoustic impedance can not be conveniently and flexibly adjusted, and the thickness is not suitable for the thin sheet type occasion required by the medical ultrasound and the detection ultrasound, so that the transmissivity of the medical ultrasound and the detection ultrasound transducer can not be improved to more than 60% by the existing technology.

Disclosure of Invention

The invention provides an ultrasonic probe using a gradient matching layer, which can effectively solve the problems that the prior art proposed in the background art is difficult to improve the transmissivity of the matching layer of a medical ultrasonic and ultrasonic transducer to more than 60 percent and the sensitivity and the bandwidth are difficult to improve.

In order to achieve the purpose, the invention provides the following technical scheme: an ultrasonic probe using a gradient matching layer, the ultrasonic probe comprising a piezoelectric material and a matching layer;

the matching layer is disposed on a front surface of the piezoelectric material, wherein electrodes are formed on the front surface and a rear surface of the piezoelectric material;

the piezoelectric material and the matching layer are processed into a one-dimensional or two-dimensional array of single array elements and multiple array elements;

the matching layer is arranged as a single-layer matching layer to be applied on the ultrasonic transducer instead of the current multi-layer matching layer.

According to the technical scheme, the single-layer matching layer is mainly manufactured by a preparation method of an acoustic impedance gradient material, and the method specifically comprises the following manufacturing steps:

s1, mixing;

s2, defoaming;

s3, forming;

and S4, curing.

According to the technical scheme, in the step S1, mixing refers to numbering the prepared raw material mixture according to the change sequence of the components, and fully stirring and mixing the raw materials, wherein the raw materials comprise epoxy resin serving as a substrate, metal powder, metal oxide powder and glass beads, and the epoxy resin is E41, E51 and other brands of the same type;

the metal powder and the metal oxide powder are mainly high-density powder such as tungsten powder, tungsten oxide powder, bismuth oxide powder and the like; the low-density alumina powder is suitable for medium and low acoustic impedance occasions, and the powder is selected to be ultra-fine.

According to the above technical solution, in the step S2, the defoaming is mainly used for eliminating bubbles generated in the mixing process of the raw material mixture, wherein a specific defoaming manner may be one of a plurality of defoaming manners including vacuum-pumping defoaming, centrifugal and vacuum-defoaming, and it should be noted that different defoaming and forming methods may affect acoustic impedance.

According to the above technical solution, in the step S3, the forming means that the mixed and defoamed raw materials are formed into a thin film by a casting method, and the thickness of the formed thin film is controlled to be 25um.

According to the technical scheme, during casting molding treatment, the mixture of 20-100nm aluminum oxide powder and epoxy glue E51 is moderate in viscosity and convenient for casting molding, the thickness control precision of casting equipment can reach +/-2 um, the thickness can be from 10um to 200um, the knife height of the casting equipment is adjusted, a casting belt moves slowly, the mixture forms a layer of thin film on the casting belt, the thin film is slowly heated at 60 degrees to form a semi-solidified casting film, the casting film is numbered according to the sequence of 0-9, the width of the casting film can be set to be 100mm wide or 200mm wide, and the casting film is cut into square pieces according to the numbering sequence through a cutter of the casting equipment.

According to the above technical solution, in S4, the curing means that the casting film produced by casting is subjected to curing treatment, after the casting film is cut into square pieces, the square pieces are sequentially laminated in the order of numbers 0 to 9 under a laminator within a specified time range, and the casting belt is sequentially removed.

According to the technical scheme, in S4, during lamination, the laminator provides vacuum and certain temperature, the laminated film is just 250 microns, then the film is cured at room temperature and is continuously cured in an oven, and when the film is not completely cured, the laminator is used for lamination, the adhesive force is sufficient, after the film is completely cured, the film is subjected to a high-temperature and low-temperature cycle test, no separation occurs, no bubble exists in the middle, and the quality is reliable;

the solidified square sheet is scribed into a specified size on a scribing machine, and the cured square sheet can be used for manufacturing the transducer, when the square sheet is laminated with the piezoelectric material, the side with high alumina mass fraction needs to be close to the piezoelectric material, and a successfully manufactured 64-array phased array probe is greatly improved in performance compared with a conventional 2-layer matching layer probe.

According to the technical scheme, in the step S1, when the mixture is prepared, the mixture with different mass components needs to be prepared, and a performance test is carried out, in the test process, along with the increase of the proportion of the alumina powder in the mixture, the density of the cured material is increased, the sound velocity is slowly increased, v =3000m/S, the acoustic impedance is linearly increased, and the acoustic impedance is increased from 3.1MRayl to 6.7MRayl of pure epoxy resin E51;

the linear fitting equation is as follows: z =7.2X +3.1 (equation 1), where Z is the acoustic impedance and X is the mass fraction of alumina.

According to the technical scheme, the result of the optimal transmissivity calculation shows that the curve of the acoustic impedance of the ideal matching layer changing along with the distance is exponentially attenuated, a multilayer structure is adopted, the internal performance of each layer is uniform, and multiple layers are laminated to form the quasi-continuous gradient material of the acoustic impedance;

according to the exponential law, the expression of the acoustic impedance of each layer is:

wherein i is more than or equal to 1 and less than or equal to n-2,n and more than or equal to 3 (formula 2), Z ₀ For high impedance of the matching layer, Z _n-1 For low impedance of the matching layer, n is the number of layers in the quasi-gradient material.

Compared with the prior art, the invention has the beneficial effects that: the invention has scientific and reasonable structure and safe and convenient use:

1. the single-layer matching layer is manufactured by a method for preparing the acoustic impedance gradient material, the existing multilayer matching layer is replaced, the acoustic impedance gradient material is applied to an ultrasonic transducer, the performance of the acoustic impedance gradient material is greatly improved, the acoustic impedance gradient material adopts an ultrathin multilayer structure, the thickness is the same, multiple layers are laminated together, the impedance is distributed in a step-shaped index manner, the effect is equal to continuous distribution of the impedance due to multiple layers, the limitation of the traditional taper hole compounding method and a centrifugal sedimentation method on the thickness is broken through, the size is greatly reduced, the performance is uniform and controllable, the acoustic impedance gradient material is suitable for batch production, the requirements of medical ultrasonic and ultrasonic transducer detection are met, the ultrasonic probes of single-array elements, one-dimensional arrays and two-dimensional arrays manufactured by the matching layer can increase the sensitivity by about more than 2.5dB, the bandwidth can be increased by more than 20%, and the performance is greatly improved;

moreover, the acoustic impedance gradient material manufactured by the preparation method has controllable impedance, uniform performance and accurate thickness, can be used on a small-sized transducer, replaces the current scheme of two or three matching layers, improves the sensitivity, increases the bandwidth and improves the image resolution.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is a flow chart of a method of making an acoustic impedance gradient material according to the present invention;

FIG. 2 is a graph of mass fraction of alumina in a matching layer versus acoustic impedance of the present invention;

FIG. 3 is a schematic representation of the continuous variation of impedance for optimal transmittance of the present invention;

FIG. 4 is a schematic illustration of a graded material (tapered hole method) with continuously changing acoustic impedance.

Detailed Description

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

Example (b): as shown in fig. 1-3, the present invention provides a technical solution, an ultrasonic probe using a gradient matching layer, the ultrasonic probe including a piezoelectric material and a matching layer;

a matching layer disposed on a front surface of the piezoelectric material, wherein electrodes are formed on the front surface and a rear surface of the piezoelectric material;

the piezoelectric material and the matching layer are processed into a single-array element, a one-dimensional or two-dimensional array of multiple array elements;

the matching layer is arranged as a single-layer matching layer to be applied on the ultrasonic transducer instead of the current multilayer matching layer.

Based on the technical scheme, the single-layer matching layer is mainly manufactured by a preparation method of an acoustic impedance gradient material, and the method specifically comprises the following manufacturing steps:

s1, mixing;

s2, defoaming;

s3, forming;

and S4, solidifying.

Based on the technical scheme, in the step S1, mixing refers to numbering the prepared raw material mixture according to the change sequence of the components, and fully stirring and mixing the raw materials, wherein the raw materials comprise epoxy resin serving as a substrate, metal powder, metal oxide powder and glass beads, and the epoxy resin is E41, E51 and other brands of the same type;

the metal powder and the metal oxide powder are mainly high-density powder such as tungsten powder, tungsten oxide powder, bismuth oxide powder and the like, which can improve the impedance of the mixture, while low-density aluminum oxide powder and the like are suitable for occasions with medium and low acoustic impedance, and the powder is selected to be superfine, so that a product with ultrathin thickness can be obtained in the processing process.

Based on the above technical solution, in S2, the defoaming is mainly used to eliminate bubbles generated in the mixing process of the raw material mixture, wherein a specific defoaming method may be vacuum-pumping defoaming, and it should be noted that different defoaming and forming methods may affect the acoustic impedance.

Based on the above technical solution, in S3, the forming means that the mixed and defoamed raw materials are formed into a thin film by a casting process, and the thickness of the formed thin film is controlled to be 25um.

Based on the technical scheme, when the casting molding is carried out, the mixture of 20-100nm aluminum oxide powder and epoxy glue E51 is moderate in viscosity and convenient for casting molding, the thickness control precision of the casting equipment can reach +/-2 um, the thickness can be from 10um to 200um, the knife height of the casting equipment is adjusted, the casting belt moves slowly, the mixture forms a layer of thin film on the casting belt, the thin film is slowly heated at 60 degrees to form a semi-solidified casting film, the casting film is numbered according to the sequence of 0-9, the width of the casting film can be set to be 100mm wide, and the casting film is cut into square pieces according to the numbering sequence by a cutter of the casting equipment.

Based on the above technical solution, in S4, the curing means that the casting film produced by casting is cured, after the casting film is cut into square pieces, the square pieces are sequentially stacked in the order of numbers 0 to 9 under a laminator within a specified time range, and the casting belt is sequentially removed.

Based on the technical scheme, in S4, during lamination, the laminator provides vacuum and certain temperature, the laminated film is just 250um, wherein the film of 250um refers to a probe of 3MHz, the thickness of the film is thinner as the frequency is higher, the thickness of each thin layer is correspondingly thinner, then the film is cured at room temperature and is continuously cured in an oven, the laminator is used for lamination when the film is not completely cured, the adhesion force is sufficient, and after the film is completely cured, the film is not separated through a high-low temperature cycle test, no bubbles exist in the middle, and the quality is reliable;

the cured square sheet is scribed into a specified size on a scribing machine, and the cured square sheet can be used for manufacturing the transducer, when the square sheet is manufactured and is superposed with a piezoelectric material, the side with high alumina mass fraction is required to be close to the piezoelectric material, and a successfully manufactured 64-array phased array probe has the sensitivity improved by 3.1dB and the relative bandwidth improved to 85% from 63% compared with a conventional 2-layer matching layer probe.

Based on the above technical solution, in S1, when preparing a mixture, it is necessary to prepare a mixture of different mass components, and perform a performance test, during the test, as the proportion of the alumina powder in the mixture increases, the density of the cured material increases, the sound velocity slowly increases, v =3000m/S, and the acoustic impedance linearly increases, from 3.1MRayl to 6.7MRayl of pure epoxy E51, as shown in fig. 2;

the linear fitting equation is as follows: z =7.2X +3.1 (formula 1), wherein Z is acoustic impedance and X is mass fraction of aluminum oxide.

Based on the technical scheme, the result of the optimal transmittance calculation shows that the curve of the acoustic impedance of the ideal matching layer changing along with the distance is exponentially attenuated, as shown in fig. 3, the multilayer structure is adopted, the internal performance of each layer is uniform, and the multilayer structure is overlapped to form the gradient material with quasi-continuous acoustic impedance;

according to the exponential law, the expression of the acoustic impedance of each layer is:

wherein i is more than or equal to 1 and less than or equal to n-2,n and more than or equal to 3 (formula 2), Z ₀ For high impedance of the matching layer, Z _n-1 N is the number of layers in the quasi-gradient material for low impedance of the matching layer;

typically, the matching layer is chosen to have a thickness of a quarter wavelength, less than this thickness, and a reduced transmission, above this thickness, and the signal will be attenuated due to attenuation, and for general considerations, the thickness is typically chosen to be a quarter wavelength.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. An ultrasound probe using a gradient matching layer, characterized in that: the ultrasonic probe comprises a piezoelectric material and a matching layer;

the matching layer is disposed on a front surface of the piezoelectric material, wherein electrodes are formed on the front surface and a rear surface of the piezoelectric material;

the piezoelectric material and the matching layer are processed into a single-array element, one-dimensional or two-dimensional multi-array element array;

the matching layer is arranged as a single-layer matching layer to replace the current multilayer matching layer to be applied to the array type ultrasonic transducer.

2. An ultrasound probe using a gradient matching layer according to claim 1, wherein: the single-layer matching layer is mainly manufactured by a preparation method of an acoustic impedance gradient material, and specifically comprises the following manufacturing steps:

s1, mixing;

s2, defoaming;

s3, forming;

and S4, curing.

3. An ultrasound probe using a gradient matching layer according to claim 2, wherein: in the step S1, mixing refers to numbering the prepared raw material mixture according to the change sequence of the components, and fully stirring and mixing the raw materials, wherein the raw materials comprise epoxy resin as a substrate, metal powder, metal oxide powder and glass beads are added, and the epoxy resin is E41, E51 and other brands of the same type;

the metal powder and metal oxide powder are mainly high-density powder such as tungsten powder, tungsten oxide powder, bismuth oxide powder and the like, while low-density aluminum oxide powder and the like are suitable for occasions with medium and low acoustic impedance, and the powder is selected to be superfine.

4. An ultrasound probe using a gradient matching layer according to claim 2, wherein: in S2, the defoaming is mainly used to eliminate bubbles generated in the mixing process of the raw material mixture, wherein the specific defoaming mode may be one of a plurality of defoaming modes including vacuum-pumping defoaming, centrifugal and vacuum-pumping defoaming, and it should be noted that different defoaming and forming methods may affect the acoustic impedance.

5. An ultrasound probe using a gradient matching layer according to claim 2, wherein: in S3, the forming means that the mixed and defoamed raw material is formed into a thin film by a casting process, and the thickness of the formed thin film is controlled to be 25um.

6. An ultrasound probe using a gradient matching layer according to claim 5, wherein: during tape casting processing, the mixture of 20-100nm alumina powder and epoxy glue E51 is moderate in viscosity and convenient for tape casting, the thickness control precision of tape casting equipment can reach +/-2 um, the thickness can be from 10um to 200um, the knife height of the tape casting equipment is adjusted, a tape casting belt moves slowly, the mixture forms a layer of film on the tape casting belt, the film is heated slowly at 60 ℃ to form a semi-solidified tape casting film, the tape casting film is numbered according to the sequence of 0-9, the width of the tape casting film can be set to be 100mm wide or 200mm wide, and the tape casting film is cut into square sheets according to the numbering sequence by a cutter of the tape casting equipment.

7. An ultrasound probe using a gradient matching layer according to claim 2, wherein: in S4, the solidification refers to that the casting film produced by casting is subjected to solidification treatment, after the casting film is cut into square sheets, the square sheets are sequentially overlapped according to the sequence of numbers 0-9 under a laminator in a specified time range, and the casting belt is sequentially removed.

8. An ultrasound probe using a gradient matching layer according to claim 7, wherein: in S4, during lamination, the laminator provides vacuum and certain temperature, the laminated film is just 250um, then the film is cured at room temperature and is continuously cured in an oven, the laminator is used for lamination when the film is not completely cured, the adhesion force is sufficient, and after the film is completely cured, the film is subjected to high-low temperature cycle test, no separation occurs, no bubble exists in the middle, and the quality is reliable;

and when the square sheet is manufactured and laminated with piezoelectric materials, the side with high alumina mass fraction needs to be tightly close to the piezoelectric materials, and a successfully manufactured 64-array element phased array probe has performance superior to that of a conventional 2-layer matching layer probe.

9. An ultrasound probe using a gradient matching layer according to claim 3, wherein: in the S1, when the mixture is prepared, the mixture with different mass components needs to be prepared, and a performance test is carried out, in the test process, as the proportion of the alumina powder in the mixture increases, the density of the cured material increases, the sound velocity slowly increases, v =3000m/S, and the acoustic impedance linearly increases from 3.1MRayl to 6.7MRayl of pure epoxy resin E51;

the linear fitting equation is: z =7.2X +3.1 (equation 1), where Z is the acoustic impedance and X is the mass fraction of alumina.

10. An ultrasound probe using a gradient matching layer according to claim 9, wherein: the result of the optimal transmissivity calculation shows that the curve of the acoustic impedance of the ideal matching layer changing along with the distance is exponentially attenuated, a multilayer structure is adopted, the internal performance of each layer is uniform, and multiple layers are laminated to form a quasi-continuous acoustic impedance gradient material;

according to the exponential law, the expression of the acoustic impedance of each layer is:

wherein i is more than or equal to 1 and less than or equal to n-2,n and more than or equal to 3 (formula 2), Z ₀ For high impedance of the matching layer, Z _n-1 For low impedance of the matching layer, n is the number of layers in the quasi-gradient material.

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