KR102115565B1 - Multi-Focal Point Transducer for High- Frequency Ultrasound Applications, Apparatus and Method for Manufacturing thereof - Google Patents

Abstract

An object of the present invention is to provide a multifocal ultrasound transducer capable of extending the depth of field without the need to apply an array transducer or perform a separate depth direction scan. A multifocal ultrasound transducer according to an embodiment of the present invention includes: a first region having a circular projection shape as a part of a sphere having a first radius; It is continuous with the first region, and generates ultrasound by an ultrasound generating film including a second region having a ring shape as a part of a sphere having a second radius different from the first radius, wherein the focus of the second region is the first Located on a focal line that is an extension of the focal point of the first region from the center of one region, and the ultrasonic generating film may consist of one continuous film.

Description

High-frequency ultrasonic multifocal transducer, its manufacturing apparatus, and manufacturing method {Multi-Focal Point Transducer for High-Frequency Ultrasound Applications, Apparatus and Method for Manufacturing thereof}

The present invention relates to a high frequency ultrasonic multifocal transducer, and more particularly, to a multifocal ultrasonic transducer capable of extending a depth of field or a focal region in a depth direction without a separate depth direction scan.

Recently, high-frequency ultrasound transducers have been widely used in various biomedical fields such as blood vessel, skin, and eye images of small animals. In addition, the transducer combines with multimode optical fiber in an intravascular ultrasound optical imaging method to potentially provide spatial and functional information about the distribution of light in tissues for the identification of atherosclerotic plaques. It is known that the higher the quality of the transducer, the better the depth of focus in the direction of field depth. Therefore, several research teams have focused on developing transducers for the purpose of creating more effective devices.

The parameters of the lumped transducer including frequency, focal length, transducer front and depth of field (DOF) or focal zone length must be properly designed to achieve the best image quality. The DOF or focal area is defined as a constant area of the transducer with the sharpest focused sound beam, providing the best image quality. A scanning method called B-scan and C-scan modes has been proposed to obtain ultrasound images. In this case, the transducer moves across the object using two motors on the x-y axis. In order to obtain the best image of the target area, the target area must be placed within the DOF of the converter. Nevertheless, there can be problems with the B-scan mode when the depth of the image is greater than the DOF of the converter. In addition, short DOF reduces the signal-to-noise ratio (SNR) in the far field.

On the other hand, there can be various ways to increase the DOF of the converter. For example, a complex image acquisition method based on an array converter may be used. Array transducers have been reported to have an ideal shape to increase the DOF up to 6 mm, but the small width of the elements requires complex manufacturing processes and more sophisticated systems. In addition, to obtain the final image in the scan of the array converter, data is acquired in individual transmit / receive pairs. The digital composite aperture algorithm is then performed to reconstruct the image.

In addition, another scanning method, D-scan or "Depth-scan", may be a method for obtaining images at different depths of tissues or objects. Based on the mechanical movement, the transducer moves in the depth direction and a short B-scan is performed several times. The difficult task of the so-called scanning procedure "B / D-Scan" requires that all scans be configured effectively to obtain high-quality images. The use of a fixed focus converter can significantly degrade image quality when the object is located outside the focus area. To solve this problem, an adaptive synthesis-transmission focus technique (SAFT) may be used to greatly increase the resolution of the image quality. However, this method achieves a low signal-to-noise ratio (SNR).

An object of the present invention is to provide a multifocal ultrasound transducer capable of extending the depth of field without the need to apply an array transducer or perform a separate depth direction scan.

In addition, another object of the present invention is to provide an apparatus and method for manufacturing a multifocal ultrasound transducer capable of accurately and easily manufacturing a multifocal ultrasound transducer.

A multifocal ultrasound transducer according to an embodiment of the present invention includes: a first region having a circular projection shape as a part of a sphere having a first radius; It is continuous with the first region, and generates ultrasound by an ultrasound generating film including a second region having a ring shape as a part of a sphere having a second radius different from the first radius, wherein the focus of the second region is the first Located on a focal line that is an extension of the focal point of the first region from the center of one region, and the ultrasonic generating film may consist of one continuous film.

The size of the area of the first region and the second region may be the same.

The energy level formed by the first region at the focus of the first region and the energy level formed by the second region at the focus of the second region may be the same.

A first focal region, which is a region larger than a constant energy level along the focal line, is formed around the first focal point of the first region by the first region, and the second region provides a first focal region. A second focal region, which is a region larger than a constant energy level along the focal line, may be formed around the focal point.

The first focus area and the second focus area may be partially overlapped or continuously formed.

The ultrasound-generating film further includes a third region having a ring shape as a part of a sphere having a third radius different from the second radius, wherein the third region has a focus of the first region. It may be located on an extension line of the focus of the first region from the center.

The second area and the third area may have the same area.

The energy level formed by the second region at the focus of the second region and the energy level formed by the third region at the focus of the third region may be the same.

The distance between the first focus in the first area and the second focus in the second area and the distance between the second focus in the second area and the third focus in the third area may be the same.

Around each focal point of each of the first to third regions, each focal region, which is a region larger than a constant energy level, is formed along the focal line, and the first focal region and the second focal region partially overlap or It can be formed continuously.

Multifocal ultrasound transducer according to an embodiment of the present invention, a hollow cylinder-shaped outer housing: two or more spherical regions having different sizes of radii are connected to be made of one integral film, and one end of the outer housing The ultrasonic generating film is installed in the opening of the concave portion facing the outside to generate ultrasonic waves; A first electrode layer formed on a concave surface of the ultrasonic generating film along a shape of a concave surface of the ultrasonic generating film; A second electrode layer formed on the convex surface of the ultrasonic generating film along the shape of the convex surface of the ultrasonic generating film; And a connector in which the power line extends from an end of the convex portion of the convex surface of the second electrode layer and is connected to an opening of the other end of the outer housing.

It may be further provided with an inner housing that is inserted into a cylindrical shape on the inner surface of the outer housing to support an edge portion of the ultrasonic generating film in an opening direction of one end of the outer housing.

A non-conductive adhesive may be filled in the inner portion of the ultrasonic generating film inside the outer housing.

At one end of the outer housing, an end portion of the outer housing extending in the direction of the central axis of the cylinder is formed, and an edge portion of the ultrasonic generating film may be in contact with the inner surface of the finishing portion.

The two or more spherical regions of the ultrasonic generating film may be exposed through the opening of the finishing part.

An apparatus for manufacturing a multifocal ultrasound transducer according to an embodiment of the present invention includes: a base plate having a circular through hole or a recess formed in a central portion; A slide plate elastically supported on the base plate and pressed in the direction of the base plate; It is installed on the lower surface of the slide plate to be moved together with the slide plate, different sizes of the ultrasonic generating film of any one of claims 1 to 10 at the end inserted into the through hole or recess A pattern frame in which a pattern corresponding to two or more spherical regions having a radius is formed; Support rods having the same length in each of the square corner portions of the base plate and arranged in a height direction: disposed on the support rods, through holes formed in positions where the through holes or recesses extend in the height direction Support plate; And a pressure screw installed to penetrate the support plate to provide a pressing force to the slide plate through an end.

A pressure sensor installed between the pressure screw and the support plate may further include a force sensor that senses a force applied to the film in which the pattern frame is disposed between the pattern frame and the base plate.

A method of manufacturing a multifocal ultrasound transducer according to an embodiment of the present invention is a method of manufacturing a multifocal ultrasound transducer by a manufacturing apparatus, between the pattern frame and the base plate, a copper clad polyimide film, PVDF Laminating a film and a Teflon film in order; Forming a spherical pattern on the laminated films by using the pressure screw to form the pattern frame; Reversing the manufacturing apparatus of the multifocal ultrasound transducer, inserting a Teflon tube into a through hole of the base plate and injecting a non-conductive adhesive into the Teflon tube; Heating the laminated films on which the spherical pattern is formed to a set temperature for a set time; And installing and assembling the completed ultrasonic generating film inside an outer housing.

After separating the laminated film on which the heating step is completed, the method may further include removing the Teflon film to obtain an ultrasonic generating film.

The heating may be performed before the films are separated from the manufacturing apparatus of the multifocal ultrasound transducer.

According to the multifocal ultrasound transducer of the present invention, the depth of field can be extended without the need to apply an array transducer or perform a separate depth direction scan.

Further, according to the apparatus and manufacturing method of a multifocal ultrasound transducer of the present invention, a multifocal ultrasound transducer can be accurately and easily manufactured.

The following drawings attached to this specification are intended to illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the detailed description of the present invention, so the present invention is limited only to those described in those drawings. And should not be interpreted.
1 is a graph schematically showing an ultrasound pulse-echo response and a frequency spectrum of each of a first region and a remaining region in a multifocal ultrasound transducer according to an embodiment of the present invention.
FIG. 2 is a view schematically showing an end face of a multifocal ultrasound transducer including five spherical regions according to an embodiment of the present invention and focus by each spherical region.
FIG. 3 is a view schematically showing a distribution and a focus area of each focus in the multifocal ultrasound transducer of FIG. 2.
4 is a view schematically showing a press fit system that is a multi-focus ultrasonic transducer manufacturing apparatus according to an embodiment of the present invention.
5 is a view schematically showing an assembled state of the multifocal ultrasound transducer of FIG. 2.
6 is a conceptual diagram schematically showing a measurement experimental apparatus using a multifocal ultrasound transducer according to an embodiment of the present invention.
7 is a view schematically showing the results measured by the experimental apparatus of FIG. 6.
FIG. 8 schematically shows the results measured by the experimental apparatus of FIG. 6 and schematically shows the measurement results in the time domain and the frequency domain.
FIG. 9 is a diagram schematically showing a B-scan image as a result of measurement by the experimental apparatus of FIG. 6.
FIG. 10 is a diagram schematically showing a C-scan image as a result of measurement by the experimental apparatus of FIG. 6.
11 is a view schematically showing a resolution measured in a multifocal ultrasound transducer according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the embodiments described below do not unduly limit the contents of the present invention as set forth in the claims, and the entire structure described in the embodiments of the present invention cannot be said to be essential as a solution of the present invention. Components applied to one embodiment may be applied to other embodiments without specific mention.

A multifocal ultrasound transducer according to an embodiment of the present invention provides a new multifocal transducer based on a polyvinylidene fluoride (PVDF) film for high frequency ultrasound applications. That is, it provides a multifocal ultrasound transducer that can extend the depth of field without the need for applying an array transducer or performing a D-scan. Unlike conventional transducers, the proposed multifocal ultrasound transducer can generate multiple local points simultaneously in the axial direction when subjected to shading pulses.

In the present invention, the design, fabrication and evaluation of a PVDF based multi-local point wideband multifocal ultrasound transducer is presented. In order to demonstrate the effect of the multifocal ultrasound transducer according to an embodiment of the present invention, two types of transducers, a single focus transducer and a multifocal transducer, are tested through a wire phantom experiment using a pulse echo response method to test the results. Comparative analysis.

In the multifocal ultrasound transducer according to an embodiment of the present invention, an ultrasound generating film generating ultrasound according to an input power may be used. At this time, the ultrasound-generating film has a shape of a surface that allows multiple focuses to be formed in a depth direction. Two or more spherical regions having different sizes of radii may be connected to form a single integral film.

As ultrasonic generating films, some piezoelectric materials such as lead zirconate titanate (PZT), lead niobiumzine zirconate titanate (PMN-PT), LiNbO3, ZnO, and polyvinylidene fluoride (PVDF) films have been extensively investigated according to ultrasonic applications. At this time, characteristics such as the electromechanical connection coefficient, acoustic impedance, dielectric constant, piezoelectric coefficient, and sound velocity were examined.

In a multifocal ultrasound transducer, PVDF (polyvinylidene fluoride) may be applied as a material for an ultrasonic fish film. The acoustic impedance of the PVDF film (below 4 MRayl) is lower than that of piezo ceramic and crystal materials, but the mechanical flexibility is excellent, making it the easiest to press in a curved form. Representative characteristics of PVDF are shown in Table 1. While the insertion loss of PVDF film is relatively high, the layers do not need to match because its acoustic impedance is more easily matched to human tissue than PZT and LiNbO3 materials. In addition, PVDF has the widest bandwidth among the above-mentioned materials and can be used to generate high-resolution ultrasound images. Table 1 is a characteristic of the PVDF film of the ultrasonic generating film according to an embodiment of the present invention.

Property Value Electromechanical coupling coefficient (K _t ) 0.12-0.15 Molecular formula (CH ₂ CF ₂ ) Relative clamped dielectric constant (ε ^s / ε ₀ ) 11 Mechanical quality factor (Q _m ) ~ 20 Density (kg / m ³ ) 1800 Longitudinal wave velocity (m / s) 2110 Acoustic impedance (MRayl) 3.9 Curie temperature (ㅀ C) 100 Melting temperature (ㅀ C) 160 ~ 180

In the present invention, in order to expand the focus area of a focused transducer in the depth direction of an object to be measured, it is necessary to determine various parameters affecting the focus area. The parameters of a multifocal ultrasound transducer using PVDF as an ultrasonic generating film were designed using a KLM (Kritholz-Leedom-Matthaei) model-based simulator. At this time, the focal region was designed for the centralized transducer. The length of the focal region can be suitably configured for a multifocal transducer. The profile of the multifocal converter is then determined. The parameters of the lumped converter are f # = R / D, N = (D ^ 2 * fc) / 4c, SF = R / N, Fz = N * SF ^ 2 * 2 / (1 + SF / 2), δL = 1.02 c * f # / fc, δA = SPL / 2 can be determined as a relational expression.

Where R is the focal length of the transducer, D is the leading diameter of the transducer, f # is the f-number, c is the speed of sound in the load medium, fc is the center frequency of the transducer, δL is the lateral resolution of the transducer, and δA is Axial resolution, SPL is the spatial wavelength length, N is the near field of the transducer, SF is the normalized focal length, and Fz is the transducer focal region.

The multifocal ultrasound transducer according to an embodiment of the present invention includes an ultrasound generating film for generating ultrasound, and the ultrasound generating film may be formed of one film having a spherical shape having different radii, respectively. At this time, the ultrasound generating film includes a first region and a second region, and the first region may have a circular projection shape as a part of a sphere having a first radius. The second region is continuous with the first region, and may have a ring shape as a part of a sphere having a second radius different from the first radius.

Therefore, a plurality of focal points can be formed by the ultrasonic generating film made of one continuous film. At this time, a plurality of focal points are arranged in the depth direction of the measurement object so that the focal region may extend in the depth direction.

At this time, the focus of the second region may be located on a focus line that is an extension of the focus of the first region from the center of the first region. Accordingly, the focal region can be extended deeply in the depth direction of the measurement object under the same shape condition.

At this time, the size of the area of the first region and the second region may be the same. In this case, various design variables may be designed such that the energy level formed by the first region at the focus of the first region and the energy level formed by the second region at the focus of the second region are the same.

In this case, a first focus region, which is a region having a size larger than a constant energy level, is formed along the focus line around the first focus of the first region by the first region, and the second focus of the second region is formed by the second region. A second focal region, which is a region larger than a certain energy level, may be formed along the focal line around. At this time, the first focus area and the second focus area may be partially overlapped or continuously formed.

At this time, the multifocal ultrasound transducer may include two regions having different spherical diameters and having focus arranged in a depth direction.

In another embodiment, the ultrasound-generating film is continuous with the second region, and may further include a third region having a ring shape as part of a sphere having a third radius that is different or greater than the second radius. At this time, the energy level formed by the second region at the focus of the second region and the energy level formed by the third region at the focus of the third region may be the same.

Around each focal point of the first region to the third region, each focal region, which is a region larger than a constant energy level, is formed along the focal line, and the first focal region and the second focal region are partially overlapped or continuously formed. Can be.

At this time, the distance between the first focus in the first area and the second focus in the second area and the distance between the second focus in the second area and the third focus in the third area may be the same.

However, the present invention is not limited to this, and has three or more, for example, five or seven spherical regions each having a focal point present on the same focal line where the ultrasonic generating film extends and is extended in a depth direction. It can have a focus area. On the other hand, in the embodiment shown in Figures 2 and 3, the five focus areas (S1 ~ S5) on the common focus line, the focus area extended by five focuses (A1 ~ A5) spaced at regular intervals (b) (Fz).

At this time, the first region S1 may be a region having a circular projection shape as a part of a sphere having a first radius R1, and the second region S2 and the regions S3 to S5 disposed thereafter are Each may have a ring shape as a part of the increasingly larger radius (R2 to R5) sphere. In addition, the areas of the second to fifth regions S2 to S5 are the same, and the distances between the respective focal points A1 to A5 can be designed to be constant. At this time, the focal region Fz formed at each of the focal points A1 to A5 is designed to partially overlap, thereby reducing the size variation of the energy level on the focal line.

1 shows graphs schematically showing an ultrasound pulse-echo response and a frequency spectrum of each of a first region and a remaining region in a multifocal ultrasound transducer according to an embodiment of the present invention. The graph shown in the figure is a simulation result of pulse-echo response (solid line) and their frequency spectrum (dashed line) by 50 MHz ultrasonic wave using PVDF ultrasonic generating film, (a) is by a single focus transducer, and (b ) Is a simulation result of the second region by the multifocal transducer according to an embodiment of the present invention. The first region is similar to the simulation result by the single focus transducer in the drawing, and the third region or higher region shows similar results to the second region simulation result.

At this time, Figure 1 shows the results of a biosono (BioSono) KLM (Krimholtz-Leedom-Matthaei) simulation. The center frequency and -6dB bandwidth of the short focus converter are expected to be 50MHz and 66%, respectively, and the frequency of the multifocus converter is designed to 50MHz and 68%. In the parametric relationship of the lumped transducer, at a center frequency of 50 MHz, the focal length of the short focus transducer is 10 mm, the gap diameter is 9 mm, and the diffusion speed in water is 1540 m / s. The focal area is 0.41 mm and the lateral resolution is 47 μm. In order to effectively expand this focal region, a multifocal transducer with various focal regions was applied. These focal regions may overlap slightly to continue to create focal depth.

In order to extend the focal region to 4.3 mm, the ultrasonic generating film according to an embodiment of the present invention was designed with a multifocal transducer with five focal points. These focal points were distributed at 1 mm (b = 1 mm) intervals in the axial direction. The front side of the multifocal transducer was divided into five parts of the same area. Each part consisted of a spherical surface of radius Ri and height Hi, respectively. 2 shows the structure of a multi-spherical profile.

FIG. 2 schematically shows a distribution of an end face of a multifocal ultrasound transducer including five different spherical regions having the same area and focus by each spherical region according to an embodiment of the present invention. FIG. 3 schematically shows the distribution and focal region of each focal point in the multifocal ultrasound transducer of FIG. 2.

At a point P (xi, zi) located in each focal region, an image of a desired quality can be obtained. At this time, xi represents the distance on the X axis, and zi represents the depth on the Z axis of the point P.

The surface parameters of a multifocal transducer can be defined as follows.

Radius (focal length) of sphere in each area: R ₁ = A ₁ N ₀ = A ₁ K ₁ , R ₂ = A ₂ K ₂ = A ₂ K ₁ , R ₃ = A ₃ K ₃ = A ₃ K ₂ , R ₄ = A ₄ K ₄ = A ₄ K ₃ , R ₅ = A ₅ K ₅ = A5K ₄ .

Opening diameter of each area: Di = 2NiKi = 2RiSinα _i , i = 1 to 5.

Height of each spherical part: hi = NiNi-1, where, i = 1 to 5.

Distance between each focal point: AiAi + 1 = b, i = 1 to 4.

The value of the parameter can be selected as follows.

R ₁ = 10 mm, b = 1 mm, D ₁ = 4 mm, R ₁ = 10 mm, R ₂ = 10.98 mm, R ₃ = 11.95 mm, R ₄ = 19.91 mm, R ₅ = 13.86 mm, D ₁ = 4 mm, D ₂ = 5.62 mm, D ₃ = 6.88 mm, D ₄ = 7.92 mm, D ₅ = 8.84 mm, h ₁ = 0.2 mm, h ₂ = 0.18 mm, h ₃ = 0.16 mm, h ₄ = 0.15 mm , h ₅ = 0.14 mm, α ₁ = 11.53 ㅀ, α ₂ = 14.86 ㅀ, α ₃ = 16.73 ㅀ, α ₄ = 17.87 ㅀ, α ₅ = 18.59 ㅀ

The focal length of a multifocal transducer can be extended by several connected focal regions. These foci were created by many different spheres around the focal point. Each spherical shape contributes to one focus as shown in Fig. 3 (a). Multifocal converters can move along the X axis to obtain data. When the P (xi, zi) point is located in the acoustic field of the Si sphere (Si is called part i, i = 1-5), the detected signal must contribute to Ai focus. The focal length of Si is Ri. Each part of the multifocal sphere can detect a signal in each focal region, which is illustrated in Figure 3 (b). For example, area i can detect a signal in the focal area Fzi. The object located around the Ai point of the focus area Fzi acquires the best image. A blurry image may be displayed relative to an object located outside the focus area.

The first region S1 may be difficult to capture a good image at a point P where zi> R1 is located. As a result, different spheres were designed with different depths of focus to obtain a good image for a long depth of image. The total focal length Fz of this converter can be the sum of all individual focal area components Fzi. The distance between each focal region and two focal points was carefully calculated to avoid gaps between adjacent focal points.

Each focus parameter in FIG. 3 (b) was calculated using the parameter relation of the lumped transducer and is shown in Table 2. Therefore, the total field depth of the multifocal transducer is the sum of the focal areas (4.3 mm). This value indicates that placing an object with a depth less than or equal to 4.3 mm allows the transducer to obtain a good image with a long depth from this object.

Table 2 shows the estimated parameters of the MFP converter with 5 focal lengths, the distance between the 2 focal points is b = 1 mm, and the center frequency of each part is fc = 50 MHz.

1 ^st focal point 2 ^nd focal point 3 ^rd focal point 4 ^th focal point 5 ^th focal point R ₁ (mm) D ₁ (mm) R ₂ (mm) D ₂ (mm) R ₃ (mm) D ₃ (mm) R ₄ (mm) D ₄ (mm) R ₅ (mm) D ₅ (mm) 10 4 10.98 5.62 11.95 6.88 12.91 7.92 13.86 8.84 f _#i 2.5 1.94 1.73 1.62 1.56 f _Zi 1.48 mm 0.91 mm 0.73 mm 0.64 mm 0.58 mm

4 shows a press fit system that is a multi-focus ultrasonic transducer manufacturing apparatus according to an embodiment of the present invention. (a) is a perspective view of a press fit system for manufacturing an ultrasonic generating film of a multifocal transducer, and (b) is a photograph of an actual press fit system manufactured and used according to (a). (c) is an exploded perspective view showing each component of the press fit system, each component being a base plate (BP) / support rod (Rd1) / screw (SC1) and Teflon (T) / PVDF film (PVDF) / Copper clad polyimide (CCP) and pressure plate (PP) / screw (SC2) and spring (ESP) as elastic member, multifocal pattern frame (MSP), slide plate (SP) / rod (Rd2) and force sensor ( SF) / support plate (STP) and top plate (TP) / screw (SC3) and pressurized screw (FS). (d) shows a pattern frame (MSP) including five spherical regions for forming an ultrasonic generating film at an end. (e) is a picture of the pattern frame (MSP).

As such, the multi-focus ultrasonic transducer manufacturing apparatus includes a base plate (BP); Slide plate (SP); Multifocal pattern frame (MSP); Support rod Rd1; Support plate (STP); And it may include a pressure screw (FS).

The base plate BP may have an end portion of the multifocal pattern frame MSP, that is, a circular through hole or a recess in which the pattern portion can be accommodated. The slide plate SP is elastically supported on the base plate BP and may be pressed in the direction of the base plate BP. Multi-focus pattern frame (MSP) is installed on the lower surface of the slide plate (SP) and moved with the slide plate (SP), the ultrasonic generating film at the end inserted into the through hole or recess of the base plate (BP) ( Patterns corresponding to two or more spherical regions having radii of different sizes of 12) may be formed.

Four support rods Rd1 have the same length in each of the square corner portions of the base plate BP, and may be arranged long in the height direction. The support plate STP is disposed on the support rods Rd1, and a through hole may be formed at a position where the through hole or the recess extends in the height direction. The pressurized screw FS is installed to penetrate the support plate STP to provide a pressing force to the slide plate SP through the end.

At this time, the slide plate SP is supported by the four rods Rd2 on the base plate BP, and may be elastically supported by the spring ESP between the rods Rd2 and the base plate BP. .

The force sensor SF is installed between the pressure screw FS and the support plate STP to sense the force applied to the film in which the pattern frame MSP is disposed between the pattern frame MSP and the base plate BP. have.

On the other hand, on the support plate STP, the top plate TP is installed on the support rods Rd1 with a screw SC3 to support the entire press fit system.

FIG. 5 schematically shows an assembled state of a multifocal ultrasound transducer including an ultrasound generating film manufactured by the manufacturing apparatus of FIG. 4. In (a), a drawing in which the multifocal transducer is cut in the longitudinal direction is shown, and a part thereof is enlarged. In (b), a photograph of the ultrasonic transducer of (a) is shown.

Multi-focal ultrasound transducer according to an embodiment of the present invention the housing 11; Ultrasonic generating film 12; A first electrode layer 13; A second electrode layer 14; And a connector 18.

The housing 11 has a hollow cylinder shape and supports other components including the ultrasonic generating film 12. The ultrasonic generating film 12 is formed of one integral film by connecting two or more spherical regions having different sizes of radii, and is installed in one opening of the housing 11 so that the concave portion faces the outside to generate ultrasonic waves. .

The first electrode layer 13 is formed on the concave surface of the ultrasonic generating film 12 along the shape of the concave surface of the ultrasonic generating film 12. The second electrode layer 14 is formed on the convex surface of the ultrasonic generating film 12 along the shape of the convex surface of the ultrasonic generating film 12. The connector 18 is connected to the power supply line 16 by extending from the end of the convex portion of the convex surface of the second electrode layer 14, and is fastened to the opening of the other end of the housing 11.

The first electrode layer 13 and the second electrode layer 14 apply power supplied through the power line 16 to the ultrasonic generating film 12 so that ultrasonic waves can be generated and ultrasonic energy generated from the object is generated. It is input through the film 12 and output to the outside through the power line 16 so that an image can be recognized from the signal.

The housing 11 includes an outer housing and an inner housing, and the outer housing has a hollow cylinder shape and supports other components including the ultrasonic generating film 12. The inner housing is inserted into the inner surface of the outer housing in a cylindrical shape to support the edge portion of the ultrasonic generating film 12 in the direction of one opening of the outer housing.

The first electrode layer 13 may include gold and / or chromium, and the second electrode layer 14 may include copper clad polyimide. The ultrasonic generating film 12 may be a PVDF film made of PVDF.

In addition, a non-conductive adhesive may be filled in the inner portion of the ultrasonic generating film 12 inside the outer housing. At this time, the non-conductive adhesive may be made of epoxy.

At one end of the outer housing, an end portion of the outer housing is formed to extend in the direction of the central axis of the cylinder, and an edge portion of the ultrasonic generating film may be contacted and supported on the inner surface of the finishing portion. At this time, the spherical region of the ultrasonic generating film 12 may be exposed through the opening of the finishing part. At this time, only the spherical region in which the ultrasonic wave of the ultrasonic generating film 12 is output is exposed to the outside through the opening of the finishing portion, and the remaining portion may be covered by the finishing portion. In addition, an impedance matching unit may be formed on the outside of the finishing unit to reduce ultrasonic loss by applying a component such as parylene.

To demonstrate the advantages of a multifocal transducer, two types of 9μm PVDF focus transducers, a single focus transducer and a multifocal transducer, were designed and built using a press fit device. At this time, the single focus transducer was manufactured using a press fit device using a steel ball bearing forming a radius of 10 mm for a single spherical shape of the active element.

On the other hand, a method of manufacturing a multifocal ultrasound transducer according to an embodiment of the present invention is a method of manufacturing a transducer by a manufacturing apparatus (FIG. 4), a laminating step; Film pattern forming step; Adhesive injection step; Heating step; And an assembly step.

In the laminating step, a copper clad polyimide film (CCP), a PVDF film (PVDF), and a Teflon film (T) may be sequentially stacked between the pattern frame (MSP) and the base plate (BP). In the film pattern forming step, a spherical pattern is formed on the stacked films of the pattern frame MSP by using a pressure screw FS.

In the adhesive injection step, the manufacturing apparatus (see FIG. 4) of the multifocal ultrasound transducer is inverted, the Teflon tube is inserted into the through hole of the base plate BP, and the non-conductive adhesive is injected into the Teflon tube, and the adhesive in the form of a cylinder tube is inserted. By inserting it so that the ultrasonic generating film 12 can be supported inside the housing 11. At this time, a cylinder tube-shaped inner housing inserted into the outer housing may be formed.

In the heating step, the stacked films having a spherical pattern may be heated at a set temperature. In the assembling step, the completed ultrasonic generating film 12 may be installed and assembled inside the outer housing.

At this time, the heating step may further include the step of removing the Teflon film after separating the completed laminated film to obtain an ultrasonic generating film. Further, the heating step may be performed before the films are separated from the manufacturing apparatus of the multifocal ultrasound transducer and may be performed together in the manufacturing apparatus.

The manufacturing process of the multifocal converter was divided into two stages. In the first step, a press-fit system is used to form the multi-spherical shape of the active element. Copper clad polyimide CCP, PVDF film and Teflon can each be fabricated to a size of 4X4 cm. The PVDF film and copper clad polyimide were bound by a drop of epoxy (eg EPO TEK 301). A Teflon film can be placed on the surface of the PVDF film to protect the surface while preventing the film from tearing by pressing the spherical pattern of the press fit system. A group of three films is placed on the surface of the base plate of the central hole. The base plate has four rods attached to form a standard assembly.

The pressure plate (STP) is placed on this film through four rods and can be secured to the base plate with four screws. The slide plate SP attached to the multi-spherical pattern (Fig. 4 (e)) can be connected to these four rods to ensure the concentration of the holes in these plates. These springs can help reduce vibration while pressing the focus.

The tension of the surface of the active element can be managed to optimize the force value from the force sensor. The top plate can be secured to the bottom plate with screws. The force sensor can be connected to the power supply of the display unit and the control unit. A hexagon bar wrench can be used to turn the power screw. The force sensor and the multi-spherical pattern are moved downward to apply a uniform pressure to the film group so that the film group can change from a flat shape to a spherical shape.

After pressing these films, the press-fit system can be reversed to insert a Teflon tube into the center hole of the base plate and then inject non-conductive epoxy into the Teflon tube to maintain the spherical membrane shape. The press-fit system can be cured in a hot oven at 65 ° C for 3 hours. After curing time, this press-fit system can be disassembled to take an acoustic stack including copper clad polyimide (CCP) and an epoxy plug (which can be an inner housing) with PVDF film bonded. The Teflon film can then be removed from the acoustic stack.

The second step is to assemble the acoustic stack in the transducer housing. Reclad polyimide (CCP) and PVDF films can be trimmed as close as possible to the epoxy plug. The electrical wire 16 can then be connected to the center pin of the UHF connector. The acoustic stack can be centrally placed with the transducer housing, and a portion of the area of the PVDF film can be connected to the housing via silver epoxy to form a ground path. The non-conductive epoxy 17 can be filled with adhesive into the open space inside the housing to maintain long-term electrical and mechanical stability of the transducer. After the epoxy has cured, the electrode of the active element can be connected to the UHF connector through the housing transducer.

At this time, in order to minimize ultrasonic loss, a separate electrical impedance matching unit may be inserted into the housing and then filled with a non-conductive epoxy. A quarter parylene-thick parylene can be spurged in front of the transducer to function as a layer matching the surface, to ensure acoustic energy transfer between the piezoelectric and the load medium. 5 (a) shows a cross-section of a multifocal transducer that includes fabrication components. A photograph of the completed multifocal converter may be shown in FIG. 5B.

FIG. 6 schematically shows an apparatus for measuring a wire phantom measurement using a multifocal ultrasound transducer according to an embodiment of the present invention. 7 schematically shows a wire phantom test measured by the experimental apparatus of FIG. 6.

The multifocal converter can be connected to a computer controlled remote pulse / receiver and can be operated by 50Ω attenuation and electrical stimulation of 200Hz per 3μJ energy. To measure the pulse echo and frequency spectrum of a multifocal transducer, a glass plate / wire phantom can be placed as a target at the focal point. The reflected waveform was received by a 500 MHz bandwidth receiver with a high pass filter of 5 MHz and a low pass filter of 500 MHz and was digitized to a sampling frequency of 500 mega samples.

It was also digitized by an 8-bit digitizer. The movement of the multifocal transducer was controlled by a stepping motor and driven by a general purpose motion controller / driver. The LabView program was developed to manage all the processes mentioned above. The scan step controlled by the PC was moved along the x-axis to obtain B-scan and C-scan images.

The seven wires of the phantom to be tested were arranged diagonally at the same distance of 1 mm in the axial direction and 1 mm in the lateral direction (Fig. 7 (a)). The wire was submerged and scanned sideways. The echo signal reflected from the wire was used to construct the beam profile to determine the beam size in the horizontal direction. The data was imported and processed into MATLAB-based software for image processing.

The pulse echo experiment was applied to a water tank using a glass plate placed at the acoustic focus. The converter's pulse-echo response and frequency spectrum are shown in Figure 8.

FIG. 8 schematically shows the results measured by the experimental apparatus of FIG. 6 and schematically shows the measurement results in the time domain and the frequency domain. Where (a) is for a single focus transducer (T1), (b) is for a multifocal transducer (T2) with three focus (P1 to P3), (c) is for five focus (P1 to P5) It relates to a multi-focus converter (T3) having a.

Table 3 summarizes the simulation and measurement characteristics comparison of the three fabricated transducers. The short focus transducer T1 is a single focus transducer, T2-Pi (MFP) is the i (i = 1-3) portion of the multifocal transducer T2, and T3-Pj (MFP) is the multifocal transducer T3. i (i = 1-5). In general, experimental measurements were in close agreement with simulation results. In terms of measured center frequency (fc), the single focus transducer T1 yielded the highest value, and the transducers of the two multipoint transducers T2 and T3 were slightly lower than the simulation. For the bandwidth measured at -6dB, the converter T3 had a narrower bandwidth than the simulation, while the bandwidth of the two converters T1 and T2 was wider than the simulation.

Transducer Simulated (KLM) Measured results f _c (MHz) BW (%) f _c (MHz) BW (%) T ₁ (SFP) 50 66 51 68 T _2-P1 (MFP)

50

68 50 68 T _2-P2 (MFP) 49 69 T _2-P3 (MFP) 49 72 T _3-P1 (MFP)

50

68 50 66 T _3-P2 (MFP) 49 67 T _3-P3 (MFP) 47 68 T _3-P4 (MFP) 50 68 T _3-P5 (MFP) 48 70

FIG. 9 shows a B-scan image as a result of measurement by the experimental apparatus of FIG. 6. (a) relates to a single focus transducer (T1), (b) relates to a multifocal transducer (T2) having three focal points (P1 to P3), and (c) to five focal points (P1 to P5) It relates to a multifocal transducer (T3) having a.

Images of Wire Phantom were acquired using single and multiple local point converters. Their depth was evaluated and compared. The B-scan and C-scan images of the single focus transducer were used as a reference to evaluate the performance of the multipoint transducer. 9 shows B-mode scan images of the three converters T1, T2 and T3. The wire placed in the focus area of the transducer acquired the bright spot of the image. Otherwise, blurry points appear on the image. Here only the multifocal transducer T3 showed enough 7 bright spots, which represent a long focal area for deeper images.

10 is a result measured by the experimental apparatus of FIG. 6, and a C-scan image is shown. (a) relates to a single focus transducer (T1), (b) relates to a multifocal transducer (T2) having three focal points (P1 to P3), and (c) to five focal points (P1 to P5) It relates to a multifocal transducer (T3) having a.

In (a) of FIG. 10, since the focal region of the single-focus transducer T1 is 0.41 mm and the distance between the two wires is 1 mm, the obtained image shows the wire only at the focus. The image in (b) shows only three wires in the center of the wire phantom model. Since the focal region of the multifocal transducer T2 was 3 mm, no other wires outside the focal region could be imaged. However, as shown in (c), a multifocal transducer T3 with five focuses produced an image with five distinct wires in the center. It should be noted that the distance from the second wire to the sixth wire is 4 mm, and the focal area of the multifocal transducer T3 is 4.3 mm. Thus, the five centerlines placed in the focal region were imaged brighter than the two wires outside the focal region.

11 shows a resolution measured by a multifocal ultrasound transducer according to an embodiment of the present invention. A lateral brightness profile is shown in (a), and an axial brightness profile is shown in (b).

As shown in Figure 11, the resolution of the multifocal transducer T3 with five focal lengths was measured, which was measured in the B-scan mode at the focal depth of the transducer. The pulse intensity (PII) at the wire target was calculated. The lateral resolution of a multifocal transducer with five focal points was measured with the corresponding cross-sectional profile and half-width of the wire diameter (FWHM, -6dB). These lateral resolutions were measured at 156 μm, 108 μm, 113 μm, 135 μm and 130 μm, respectively. The axial resolution of a multifocal transducer with five focal spots was detected with half width (FWHM, -6dB) of 66μm, 61μm, 65μm and 66μm, respectively. The measured axial resolution has a tail observed as a shadow behind the wire. The fabrication technique of a multifocal transducer can also affect the transducer quality such as frequency, noise, resolution and amplitude of the pulse echo response.

According to the present invention, it has been demonstrated that the multifocal converter obtains a long depth of image in B-scan and C-scan modes. It also demonstrates the ability to extend the focus area of a larger depth image without the need to apply a depth scan or focus technique in front of a complex synthesis converter. In particular, the proposed five multifocal transducers can simultaneously generate five focal regions in the axial direction.

According to the present invention, the new design, fabrication and characterization of the multifocal transducer greatly increased the focus area compared to that produced by a single focus transducer. The focal area of the proposed multifocal transducer was 4.3 mm and was verified by imaging the wire phantom. The method developed according to the invention can be used to expand the larger focus area by increasing the number of focal points of the transducer. Profiles of multiple spherical patterns can be easily and accurately implemented by CNC machines. Therefore, the multi-local point converter is highly likely to capture images in a wide range of field applications.

Although described above with reference to embodiments of the present invention, the present invention is not limited to this, and various modifications and applications are possible. That is, those skilled in the art will readily understand that many modifications are possible without departing from the gist of the present invention.

Claims (20)

A first region having a circular projection shape as part of a sphere having a first radius;
It is continuous with the first region, and generates ultrasound by an ultrasound generating film including a second region having a ring shape as part of a sphere having a second radius different from the first radius,
The focus of the second area is located on a focus line that is an extension of the focus of the first area from the center of the first area,
The ultrasonic generating film is made of one continuous film,
F # = R / D, N = (D ^ 2 * fc) / 4c, SF = R / N, Fz = N * SF ^ 2 * 2 / (1 + SF / 2) ) Is determined, and the first radius and the second radius are respectively determined from the front end diameter D of the converter,
Where R is the focal length of the transducer, D is the front diameter of the transducer, f # is f-number, c is the speed of sound in the load medium, fc is the center frequency of the transducer, δL is the lateral resolution of the transducer, and δA is the axial direction Resolution, SPL is the spatial wavelength length, N is the near field of the transducer, SF is the normalized focal length, and Fz is the multifocal ultrasound transducer which is the focal region of the transducer. According to claim 1,
A multifocal ultrasound transducer having the same size of an area of the first region and the second region. According to claim 1,
A multifocal ultrasound transducer having the same energy level formed by the first region at the focal point of the first region and an energy level formed by the second region at the focal point of the second region. According to claim 1,
A first focal region, which is an area having a size larger than a constant energy level along the focal line, is formed around the first focal point of the first region by the first region,
A multifocal ultrasound transducer in which a second focal region, which is a region larger than a constant energy level, is formed along the focal line around the second focal point of the second region by the second region. The method of claim 4,
A multifocal ultrasound transducer in which the first focal region and the second focal region are partially overlapped or continuously formed. According to claim 1,
The ultrasonic generating film,
A third region having a ring shape as a part of a sphere having a third radius different from the second radius, which is continuous with the second region,
A multifocal ultrasound transducer in which the focal point of the third area is located on an extension line of the focal point of the first area from the center of the first area. The method of claim 6,
A multifocal ultrasound transducer having the same area of the second region and the third region. The method of claim 6,
A multifocal ultrasound transducer having the same energy level formed by the second region at the focal point of the second region and an energy level formed by the third region at the focal point of the third region. The method of claim 6,
The distance between the first focus in the first region and the second focus in the second region and
A multifocal ultrasound transducer having the same distance between the second focus in the second region and the third focus in the third region. The method of claim 6,
Each focal region, which is a region larger than a constant energy level, is formed along the focal line around the focal points of each of the first to third regions,
A multifocal ultrasound transducer in which the first focal region and the second focal region are partially overlapped or continuously formed. Hollow cylinder-shaped outer housing:
Claims 1 to 10, wherein two or more spherical regions having different sizes of radius are connected to each other to form a single integral film, and recesses are installed in one opening of the outer housing so as to face the outside to generate ultrasonic waves. The ultrasonic generating film of any one of the above;
A first electrode layer formed on a concave surface of the ultrasonic generating film along a shape of a concave surface of the ultrasonic generating film;
A second electrode layer formed on the convex surface of the ultrasonic generating film along the shape of the convex surface of the ultrasonic generating film; And
A multi-focal ultrasound transducer having a power line; a connector connected to and extending from an end portion of the convex portion of the convex surface of the second electrode layer, and connected to an opening of the other end of the outer housing. The method of claim 11,
A multifocal ultrasound transducer further comprising an inner housing inserted into a cylindrical shape on the inner surface of the outer housing to support an edge portion of the ultrasonic generating film in an opening direction of one end of the outer housing. The method of claim 11,
A multifocal ultrasonic transducer in which a non-conductive adhesive is filled in an inner portion of the ultrasonic generating film inside the outer housing. The method of claim 11,
The end portion of the outer housing is formed at one end of the outer housing to extend in the direction of the central axis of the cylinder,
A multifocal ultrasonic transducer in which an edge portion of the ultrasonic generating film is in contact with the inner surface of the finishing portion. The method of claim 14,
A multifocal ultrasonic transducer in which the two or more spherical regions of the ultrasonic generating film are exposed through the opening of the finishing part. An apparatus for manufacturing a multifocal ultrasound transducer according to any one of claims 1 to 10,
A base plate having a circular through hole or a concave portion in the central portion;
A slide plate elastically supported on the base plate and pressed in the direction of the base plate;
It is installed on the lower surface of the slide plate to be moved together with the slide plate, different sizes of the ultrasonic generating film of any one of claims 1 to 10 at the end inserted into the through hole or recess A pattern frame in which a pattern corresponding to two or more spherical regions having a radius is formed;
Support rods having the same length in each of the square corner portions of the base plate and disposed in a height direction:
A support plate disposed on the support rods, the through-hole or recess having a through-hole formed at a position extending in the height direction; And
And a pressure screw installed to penetrate the support plate to provide a pressing force to the slide plate through an end thereof. The method of claim 16,
It is installed between the pressure screw and the support plate
The apparatus for manufacturing a multifocal ultrasound transducer further comprising a force sensor for sensing a force applied to the film in which the pattern frame is disposed between the pattern frame and the base plate. A method for manufacturing a multi-focus ultrasonic transducer according to claim 17,
Stacking copper clad polyimide film, PVDF film, and Teflon film in order between the pattern frame and the base plate;
Forming a spherical pattern on the laminated films by using the pressure screw to form the pattern frame;
Reversing the manufacturing apparatus of the multifocal ultrasound transducer, inserting a Teflon tube into a through hole of the base plate and injecting a non-conductive adhesive into the Teflon tube;
Heating the laminated films on which the spherical pattern is formed to a set temperature for a set time; And
Installing and assembling the completed ultrasonic generating film inside an outer housing; Manufacturing method of a multifocal ultrasound transducer having a. The method of claim 18,
A method of manufacturing a multifocal ultrasound transducer further comprising; after separating the laminated film on which the heating step is completed, removing the Teflon film to obtain an ultrasonic generating film. The method of claim 18,
The heating step is a method of manufacturing a multifocal ultrasound transducer before the films are separated from the multifocal ultrasound transducer manufacturing apparatus.

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