KR102820597B1 - An ultrasensitive, broadband and single resonance transparent ultrasound transducer and manufacturing method thereof - Google Patents

Abstract

A transparent ultrasonic transducer capable of maximizing ultrasonic transmission and reception efficiency while maintaining high optical transparency and a method for manufacturing the same are disclosed. The transparent ultrasonic transducer includes a thin film-shaped piezoelectric unit that generates vibration by an electric signal or generates an electric signal by vibration, a front matching layer formed of a freely moldable composite material in the form of a liquid or clay-like mixture without a bonding gap on the front surface of the piezoelectric unit, and a sound-absorbing layer arranged on the rear surface of the piezoelectric unit.

Description

{AN ULTRASENSITIVE, BROADBAND AND SINGLE RESONANCE TRANSPARENT ULTRASOUND TRANSDUCER AND MANUFACTURING METHOD THEREOF}

The present invention relates to a transparent ultrasonic transducer capable of maximizing ultrasonic transmission and reception efficiency while maintaining high optical transparency, and a method for manufacturing the same.

In general, ultrasonic transducers used in ultrasonic sensors, etc., are composed of a piezoelectric layer that receives an electric signal from a pair of electrodes, generates vibrations, reflects sound waves at the boundaries between the front and rear surfaces, and amplifies the intensity of the sound waves inside between the boundaries; a matching layer that appropriately blocks the emission of vibrations so that the sound waves are well amplified inside the piezoelectric layer while emitting the amplified sound wave vibrations to the outside; and an absorbing layer that absorbs energy going out to the rear surface of the piezoelectric layer and controls the rear-emission energy ratio to control the time response length of the element.

To improve the performance of an ultrasonic transducer, it is important that the piezoelectric layer have an appropriate reflectivity at the boundary between the matching layer and the absorbing layer, while also having a uniform reflectivity over a wide frequency bandwidth.

The performances required for the matching layer and the absorbing layer of the ultrasonic transducer are, based on the ceramic piezoelectric material, in the case of a double matching layer, the acoustic impedance of the first matching layer is 7 to 8 megarail (MRayl) and the acoustic impedance of the second matching layer is 2 to 3 MRayl. In addition, in the case of a triple matching layer, the acoustic impedance of the first matching layer is 10 to 11 MRayl, the acoustic impedance of the middle matching layer is 3 to 5 MRayl, and the acoustic impedance of the second matching layer is 2 to 3 MRayl. And the acoustic impedance of the absorbing layer is 4 to 8 MRayl. In addition, the acoustic impedance of the piezoelectric material of the ultrasonic transducer is typically 30 to 35 MRayl, which is for using the vibration of the piezoelectric material in water or living tissue of about 1.5 to 1.6 MRayl.

Meanwhile, a transparent material having acoustic performance suitable for an ultrasonic transducer is not yet known. In the case of existing opaque ultrasonic transducers, a method of attaching glass as a matching layer has been attempted to improve acoustic performance. However, since the acoustic impedance of glass is 12 to 15 MRayl, it is not suitable for the impedance required for an ultrasonic transducer, and thus there is a limitation in improving acoustic performance. In addition, there is a problem that impedance reversal occurs due to the adhesive when bonding the glass.

In addition, materials with acoustic impedances of 4 to 10 MRayl do not exist in nature. Therefore, in the production of matching layers or absorbing layers of existing opaque transducers, the acoustic impedance has been controlled by using metals or ceramics with relatively high acoustic impedance and polymer materials with relatively low acoustic impedance.

For example, in the production of opaque low-frequency transducers of 5 MHz or less that allow a clearance of about 0.5 mil between the piezoelectric layer and the matching layer or between the piezoelectric layer and the absorbing layer, a method of applying a low-viscosity adhesive and bonding under a pressurized environment was used to control the acoustic impedance.

And, in the production of most conventional opaque ultrasonic transducers where adhesive clearance is not allowed to secure performance, a method was used in which a liquid or clay-like mixture made by mixing powder of a material with high acoustic impedance into a liquid of a polymer material before curing or polymerization was applied to the surface of the piezoelectric body, cured, and then the material was cut to the target thickness.

However, opaque ultrasonic transducers manufactured using conventional methods have impedance mismatch problems, and due to the limitations of technical implementation, it is difficult to form the matching layer with a thickness less than 1/4 wavelength, so it is formed and used with a thickness of 20 times or more the wavelength.

The present invention has been made to improve the limitations of the above-mentioned prior art, and the purpose of the present invention is to provide a transparent ultrasonic transducer and a method for manufacturing the same, which can exhibit ultrasonic transmission and reception performance equivalent to that of a conventional opaque ultrasonic transducer by improving the acoustic characteristics of the transparent ultrasonic transducer and have the characteristics of high sensitivity, high bandwidth, and single resonance.

Another object of the present invention is to provide a transparent ultrasonic transducer and a method for manufacturing the same, which can maximize ultrasonic transmission and reception efficiency while maintaining high optical transparency, that is, can simultaneously satisfy acoustic and optical characteristics to similarly exhibit the theoretical maximum acoustic performance of a transparent ultrasonic transducer.

Another object of the present invention is to provide a transparent ultrasonic transducer and a method for manufacturing the same, which can optimize ultrasonic back attenuation while maintaining transparency so that the frequency response of the ultrasonic transducer can be adjusted at an appropriate level.

According to one aspect of the present invention for solving the above technical problem, a transparent ultrasonic transducer comprises a thin film-shaped piezoelectric unit that generates vibration by an electric signal or generates an electric signal by vibration; a front matching layer formed of a freely moldable composite material in the form of a liquid or clay-like mixture without a bonding gap on the front surface of the piezoelectric unit; and a sound-absorbing layer arranged on the rear surface of the piezoelectric unit.

The above sound-absorbing layer may have a rear matching layer formed of the composite material on the rear side of the piezoelectric unit, and a rear polymer layer disposed on the rear matching layer. The acoustic impedance of the above sound-absorbing layer can be calculated by mathematical expression 1.

The above transparent ultrasonic transducer may further include a front polymer layer disposed on the front matching layer.

The above front matching layer may be composed of a composite material of ceramic and epoxy, and the above front polymer layer may be composed of a pure polymer material.

The thickness of the above piezoelectric unit may be 1/2 of the transmission wavelength (λ), and the thickness of each of the front matching layer, the front polymer layer, and the rear matching layer may be λ/4.

The transparency of the composite material constituting the front matching layer or the rear matching layer can be determined by the volume ratio of the ceramic particles, the size and shape of the ceramic particles, and the difference in refractive index between the ceramic and the polymer.

The above transparency can be set to a transparency that transmits more than 90% of light at a 1/4 wavelength thickness at an acoustic impedance of 7 to 8 MRayl of the front matching layer, or at an acoustic impedance of 4 to 6 MRayl of the rear matching layer.

The acoustic impedance of the composite material constituting the front matching layer or the rear matching layer can be determined by the volume ratio of the ceramic particles and the bulk modulus and shear modulus of each of the ceramic and the polymer.

The viscosity of the mixture before curing of the above composite material can be determined by the volume ratio of ceramic particles, the size and shape of the ceramic particles.

The above transparent ultrasonic transducer may further include a conductive ring member disposed between the rear matching layer and the rear polymer layer.

The above transparent ultrasonic transducer may further include a case that accommodates a laminated structure of the front polymer layer, the front matching layer, the rear matching layer, the rear polymer layer, and the conductive ring member.

The above piezoelectric unit may include a thin film-shaped piezoelectric crystal, a first transparent electrode formed on the front surface of the piezoelectric crystal, and a second transparent electrode formed on the back surface of the piezoelectric crystal.

The above transparent ultrasonic transducer may further include a connecting electrode connecting the first transparent electrode and the case on one surface of the rear polymer layer.

According to another aspect of the present invention for solving the above technical problem, a method for manufacturing a transparent ultrasonic transducer includes the steps of: applying a mixture in which first particles are dispersed in a polymer material to one surface of a piezoelectric unit; degassing and curing the paste applied to one surface of the piezoelectric unit in a predetermined atmosphere; and lapping and polishing the cured composite material to a design thickness to form a matching layer on one surface of the piezoelectric unit.

The first particle comprises a glass or ceramic material, and the glass or ceramic material may contain one or more materials selected from a silicate series, an aluminum salt series, a zirconium salt series, and a magnesium fluoride series. And, the polymer material may contain one or more materials selected from silicone, epoxy, urethane, polyethylene, polystyrene, acrylic, and sulfate polymer resins.

The method for manufacturing the above transparent ultrasonic transducer may further include a step of forming a front polymer layer on the front matching layer when the matching layer arranged on one side of the piezoelectric unit is a front matching layer.

The method for manufacturing the above transparent ultrasonic transducer may further include a step of forming another matching layer by applying a liquid or clay-like material to the other surface of the piezoelectric unit.

The method for manufacturing the above transparent ultrasonic transducer may further include a step of forming a rear polymer layer on the rear matching layer when the other matching layer is a rear matching layer formed on the rear of the piezoelectric unit; a step of arranging a conductive ring member connected to a second transparent electrode of the piezoelectric unit between the piezoelectric unit and the rear polymer layer; and a step of arranging a case that accommodates a laminated structure of the piezoelectric unit, the front matching layer, the rear matching layer, the rear polymer layer, and the conductive ring member.

The thickness of the above piezoelectric unit may be 1/2 of the transmission wavelength (λ), and the thickness of each of the front matching layer, the front polymer layer, and the rear matching layer may be λ/4.

According to the present invention, by using a transparent matching layer formed of a composite material so as to be in close contact with both sides of a piezoelectric unit of a transparent ultrasonic transducer without any gap, the optical transparency can be increased and the backward damping performance for vibration of the piezoelectric unit can be improved. In addition, a novel transparent ultrasonic transducer and a method for manufacturing the same can be provided, which have improved acoustic characteristics and can exhibit ultrasonic transmission/reception performance substantially equivalent to that of a conventional opaque ultrasonic transducer.

In other words, according to the present invention, by using a novel transparent matching material exhibiting intermediate acoustic characteristics, it is possible to improve the problem of difficulty in maximizing sound wave transmission efficiency due to the problem that the acoustic transmission characteristics of the piezoelectric ceramic material for manufacturing an ultrasonic transducer and the human tissue (including water) are significantly different from each other. That is, a transparent ultrasonic transducer having optimized acoustic and optical characteristics by using a novel transparent matching material and a manufacturing method thereof can be provided.

FIG. 1 is a front view of a transparent ultrasound transducer (TUT) according to an embodiment of the present invention.
Figure 2 is a schematic left-side cross-sectional view of the structure with a protective cover added to the TUT of Figure 1, taken along its vertical center line.
Figure 3 is an exploded perspective view of the TUT of Figure 1 viewed from the left side.
Figure 4 is a schematic diagram for explaining the detailed configuration of a piezoelectric unit that can be employed in the TUT of Figure 1.
FIG. 5 is an exemplary diagram explaining the bonding surface structure between the piezoelectric unit and the matching layer that can be employed in the TUT of FIG. 1.
Figure 6 is an exemplary diagram showing the bonding surface structure between the piezoelectric unit and the matching layer in a comparative example.
Figure 7 is a schematic diagram explaining a structure that can be employed in the TUT of Figure 1.
Figure 8 is a schematic diagram illustrating the structure of an opaque ultrasonic transducer of Comparative Example 1.
Figure 9 is a schematic diagram illustrating the structure of a transparent ultrasonic transducer of Comparative Example 2.
FIG. 10 is a flow chart for explaining the main processes of a method for manufacturing a TUT according to an embodiment of the present invention.
Figure 11 is a flowchart illustrating an additional process that can be employed in the TUT manufacturing method of Figure 10.
Figures 12 and 13 are graphs for explaining conditions to be considered in the TUT manufacturing method of the present embodiment.
Figure 14 is a graph for explaining the relationship between the acoustic impedance and viscosity of the material considered in the TUT manufacturing method of the present embodiment.
Figure 15 is a graph for explaining the relationship between acoustic impedance and transparency considered in the TUT manufacturing method of the present embodiment.
Figure 16 is a graph for explaining the relationship between the volume ratio of each composite material and its longitudinal elastic velocity on each of the front side and the rear side considered in the TUT manufacturing method of the present embodiment.
Figure 17 is a graph for explaining the relationship between the volume ratio of each composite material and its acoustic impedance on each of the front side and the rear side considered in the TUT manufacturing method of the present embodiment.
Figure 18 is a graph illustrating the transparency according to the wavelength of the front primary matching layer manufactured by the TUT manufacturing method of the present embodiment.
Figure 19 is a graph illustrating the transparency according to wavelength of the rear matching layer manufactured by the TUT manufacturing method of the present embodiment.
Figure 20 is a graph for explaining the front effective acoustic impedance size of the present embodiment and comparative examples.
Figure 21 is a graph for explaining the phase angle of the front effective acoustic impedance of the present embodiment and comparative examples.
Figure 22 is a graph for explaining the rear effective impedance of the present embodiment and comparative examples.
Figure 23 is a graph comparing the performance of each TUT based on the front effective acoustic impedance size measured in the present embodiment and comparative examples.
Figure 24 is a graph comparing the performance of each TUT based on the front effective impedance phase measured in the present embodiment and comparative examples.
Figure 25 is a graph comparing the transparency of a developed transparent device (example) manufactured using the TUT manufacturing method of the present embodiment and an existing transparent device (comparative example).
Figure 26 is a graph comparing peak-to-peak voltages in pulse echo response waveforms of the present embodiment and comparative examples.
Figure 27 is a graph comparing the full-width-at-half-maximum (FWHM) of the pulse echo response waveforms of the present embodiment and comparative examples.
Figure 28 is a graph showing the results of echo frequency analysis of the present embodiment and comparative examples.

The present invention can have various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are only used to distinguish one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and/or includes a combination of a plurality of related described items or any one of a plurality of related described items.

In the embodiments of the present application, 'at least one of A and B' may mean 'at least one of A or B' or 'at least one of combinations of one or more of A and B'. Furthermore, in the embodiments of the present application, 'at least one of A and B' may mean 'at least one of A or B' or 'at least one of combinations of one or more of A and B'.

When it is said that a component is 'connected' or 'connected' to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components in between. On the other hand, when it is said that a component is 'directly connected' or 'directly connected' to another component, it should be understood that there are no other components in between.

The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprises" or "has" and the like are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms defined in commonly used dictionaries, such as those defined in common dictionaries, should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and will not be interpreted in an idealized or overly formal sense unless expressly defined in this application.

Hereinafter, with reference to the attached drawings, a preferred embodiment of the present invention will be described in more detail. In order to facilitate an overall understanding in describing the present invention, the same reference numerals are used for the same components in the drawings, and redundant descriptions of the same components are omitted.

FIG. 1 is a front view of a transparent ultrasound transducer (TUT) according to an embodiment of the present invention. FIG. 2 is a schematic left side view of a cross-section taken along the vertical center line of the structure of the TUT of FIG. 1 with a front secondary matching layer added thereto. FIG. 3 is an exploded perspective view of the TUT of FIG. 1 as viewed from the left side. And FIG. 4 is a schematic diagram for explaining the detailed configuration of a piezoelectric unit that can be employed in the TUT of FIG. 1.

Referring to FIGS. 1 to 4, a transparent ultrasonic transducer (TUT, 100) is a single resonant element having high sensitivity and high bandwidth characteristics, and may include a piezoelectric unit (10), a front matching layer (20, 30), and a rear sound-absorbing layer (40, 50). The rear sound-absorbing layer may be simply referred to as a sound-absorbing layer.

TUT (100) has a roughly flat cylindrical shape and also has a central portion that is transparent so that it can be viewed from the front to the rear, and when viewed from the front, its diameter (D1) can have a size of approximately 10 mm to 20 mm.

The TUT (100) may be provided with a matching layer (20 and/or 40) formed without a bonding gap on at least one of the front and rear surfaces of the piezoelectric unit (10) and formed of a transparent matching and sound-absorbing material having an appropriate acoustic impedance. The acoustic impedance may be determined by the speed of the sound wave and the density of the material.

Specifically, the TUT (100) may have a front secondary matching layer (30) on a front primary matching layer (20). The front primary matching layer (20) may be referred to as a first front matching layer or simply a front matching layer, and the front secondary matching layer (30) may be referred to as a second front matching layer or a front polymer layer.

The rear sound-absorbing layer may have a rear matching layer (40) that forms a rear side boundary of the piezoelectric unit (10) and absorbs acoustic impedance coming out of the rear of the piezoelectric unit (10). In addition, the rear sound-absorbing layer may further have a rear polymer layer (50) that is arranged on the rear matching layer (40).

In addition, as shown in FIGS. 2 and 4, the TUT (100) may further include a conductive ring member (60). The conductive ring member (60) may be simply referred to as a conductive ring. The conductive ring (60) may be supported by the rear polymer layer (50) so as to be in close contact with the second transparent electrode (13) arranged on the other surface of the thin film-shaped piezoelectric body (11) of the piezoelectric unit (10). The thickness of the thin film-shaped piezoelectric body (11) may be several micrometers to several thousand micrometers.

The piezoelectric unit (10) may have a structure including a piezoelectric body (11), a first transparent electrode (12) coated on the front surface of the piezoelectric body (11), and a second transparent electrode (13) coated on the back surface of the piezoelectric body (11), as shown in Fig. 4. The piezoelectric body (11) has a thin film form and may be referred to as a piezoelectric crystal.

In addition, referring to FIGS. 2 and 3, the TUT (100) may further include a case (70) that accommodates a laminated structure of a piezoelectric unit (10), a front primary matching layer (20), a rear sound-absorbing layer (40, 50), and a conductive ring (60). The case (70) may have a conductive tube shape, such as a brass tube. The case (70) may be electrically separated from the conductive ring (60) by a rear polymer layer (50). In addition, one end of the case (70) may be coupled with connection electrodes (15) that contact a first transparent electrode (12) arranged on one surface of a piezoelectric body (11) of the piezoelectric unit (10). To this end, the rear matching layer (40) may have a side edge (41) whose corner portion is cut off to expose the first transparent electrode (12).

In addition, as shown in FIG. 3, the TUT (100) can be coupled with a cable (80) in which a ground line (84) is connected to the case (70). The cable (80) can include a coaxial cable having a predetermined diameter and structure. The signal line (82) of the cable (80) can be connected to a conductive ring (60). The cable (80) can be coupled with a structure that has a predetermined connector attached thereto when connected to the TUT (100).

The above-described TUT (100) is exemplified as having a structure housed in a cylindrical case (70), but the present invention is not limited to such a configuration, and as shown in FIG. 1, the shape when viewed from the front may be approximately a circle or an oval, or may have a shape that is approximately a triangle, a square, a polygon, or a part thereof having at least one edge or corner and the remaining part having at least one arc.

If each component of the above-described TUT (100) is described in more detail, the piezoelectric unit (10) may have a thin film-shaped structure that generates vibration by an electric signal or generates an electric signal by vibration. The piezoelectric unit (10) may reflect sound waves from the generated vibrations at both front and rear boundaries and amplify the intensity of the sound waves inside. The wavelength of the amplified sound waves may be determined according to the thickness of the piezoelectric unit (10) or the piezoelectric body (11).

The front matching layer (20) can be formed on one side or the front side of the piezoelectric unit (10) using a freely moldable composite material in the form of a liquid or clay-like mixture. The material of the front matching layer (20) can be a composite material composed of ceramic and epoxy. In the process of forming the front matching layer (20), the composite material is applied or adhered to the front side of the piezoelectric unit (10), and then cured and cut to a target thickness, thereby forming the front matching layer (20) in a state of being well adhered to one side of the piezoelectric unit (10).

The acoustic impedance of the front matching layer (20) may be 7 to 8 Mega Rail (MRayl). And, before the curing of the front matching layer (20), the mixture or composite material may be formed to have a transparency that transmits more than 90% of light at a thickness of 1/4 of the transmission wavelength while the acoustic impedance of the front matching layer (20) is designed to be 7 to 8 Mega Rail (MRayl).

The front polymer layer (30) may be composed of a polymer material. The refractive index of the front polymer layer (30) may be the same as or similar to the refractive index of the front matching layer (20). For example, the front polymer layer (30) may be formed to have a refractive index similar to that of the front matching layer (20) formed of an epoxy or urethane material. The front polymer layer (30) may be formed to have a smooth surface by controlling its thickness on the front matching layer (20) using a method such as spin coating or spray coating. In another embodiment, the front polymer layer (30) may be formed to have a smooth surface by forming a thick layer, curing it, and then polishing it.

The rear matching layer (40) can be formed by applying a rear matching material, which is a composite material, to the rear of the piezoelectric unit. The rear matching material can be the same material as the material of the front matching layer (20).

Fig. 5 is an exemplary diagram illustrating a joint surface structure between a piezoelectric unit and a matching layer that can be employed in the TUT of Fig. 1. Fig. 6 is an exemplary diagram showing a joint surface structure between a piezoelectric unit and a matching layer of a comparative example.

Referring to FIG. 5, the front matching layer (20) of the present embodiment may be formed directly by first preparing a liquid composite material or a composite material of clay-like material and then applying or coating it to the front surface of the piezoelectric unit (10) to a target thickness and then curing it. In addition, depending on the implementation, the front matching layer (20) may be formed to a thickness slightly thicker than the target thickness and then formed to the target thickness through a cutting process.

This front matching layer (20) can be formed on the front surface of the piezoelectric unit (10) whose surface has been formed smoothly through cutting processing without using a separate adhesive, and a gap between the formed front matching layer (20) and the piezoelectric unit (10) can be substantially omitted.

Meanwhile, as illustrated in Fig. 6, when the ultrasonic transducer of the comparative example bonds the piezoelectric material and the matching layer using an adhesive (22) or the like, two surfaces that have been cut and processed separately are bonded, so there may be a gap at the bonding portion, and there may be a problem of serious performance degradation caused by the gap and the adhesive.

Fig. 7 is a schematic diagram illustrating a structure that can be employed in the TUT of Fig. 1. Fig. 8 is a schematic diagram illustrating the structure of an opaque ultrasonic transducer of Comparative Example 1. And Fig. 9 is a schematic diagram illustrating the structure of a transparent ultrasonic transducer of Comparative Example 2.

Referring to Fig. 7, the front matching layer (20) and the rear matching layer (40) installed on both sides of the piezoelectric unit (10) of the TUT are formed using a composite material that has an acoustic impedance of 7 to 8 MRayl and can be easily molded into a mixture form having a liquid or clay texture. These matching layers (20, 40) can be matching layers having a mechanically identical structure and performance to existing opaque ultrasonic transducers, except for transparency.

In addition, in the TUT of this embodiment, by forming the rear sound-absorbing layer as a double layer consisting of a rear matching layer (40) made of a transparent composite material and a rear polymer layer (50) made of a polymer material, it is possible to provide a transparent structure capable of sufficiently absorbing sound waves while controlling the response time of the transducer within an appropriate range.

The effective acoustic impedance of the rear sound-absorbing layer can be calculated by the following mathematical expression 1.

는 유효 음향 임피던스,

은 후면 정합층의 음향 임피던스,

는 후면 고분자층의 음향 임피던스,

은 후면 정합층의 길이,

는 파장을 각각 나타낸다.In mathematical expression 1,

is the effective acoustic impedance,

is the acoustic impedance of the rear matching layer,

is the acoustic impedance of the rear polymer layer,

is the length of the rear alignment layer,

Each represents a wavelength.

)의 1/2, 투명한 전면 정합층(20)의 두께는

, 투명한 전면 고분자층(30)의 두께는

, 투명한 후면 정합층(40)의 두께는

이다. TUT의 전면(front)으로는 음파가 방출되고, TUT의 후면(back)로 진행하는 음파는 후면 흡음층(40, 50)에 의해 흡수된다.In the TUT of this embodiment, the thickness of the transparent piezoelectric unit (10) is equal to the transmission wavelength (

) and the thickness of the transparent front matching layer (20) is 1/2 of the

, the thickness of the transparent front polymer layer (30) is

, the thickness of the transparent rear matching layer (40) is

Sound waves are emitted from the front of the TUT, and sound waves traveling to the back of the TUT are absorbed by the rear sound-absorbing layer (40, 50).

Meanwhile, the opaque ultrasonic transducer of Comparative Example 1 may have a structure including a matching layer (20c) formed of an opaque composite material on the front side of a transparent piezoelectric unit (10), a transparent polymer layer (30c) attached on the matching layer (20c), and an opaque polymer layer (50c) on the rear side of the piezoelectric unit (10), as illustrated in FIG. 8.

In addition, the conventional transparent ultrasonic transducer of Comparative Example 2 has a structure composed of a transparent piezoelectric unit (10) and a transparent polymer layer (50) attached to the rear surface of the piezoelectric unit (10), as illustrated in FIG. 9.

According to the above-described embodiment, the existing problems of matching and sound-absorbing materials for transparent ultrasonic transducers can be effectively solved. That is, existing materials with a high acoustic impedance of 30 MRayl or higher are opaque on their own, such as metallic materials and polycrystalline ceramic materials, or even if transparent, have a very high refractive index of 1.6 or higher, so that when forming a composite with a polymer material, severe internal scattering occurs, resulting in very low transparency. Meanwhile, the composite material for the matching layer used in the TUT of the present embodiment has an acoustic impedance of 7 to 8 MRayl, and can be easily formed into a mixture form having a liquid or clay texture, so that the problems of the existing technology described above can be solved.

FIG. 10 is a flow chart for explaining the main processes of a method for manufacturing a TUT according to an embodiment of the present invention.

Referring to Fig. 10, the TUT manufacturing method first attaches a piezoelectric crystal to a cutting substrate, adjusts the thickness of the attached piezoelectric crystal, and then smoothly polishes its surface (S1010). The piezoelectric crystal can be briefly referred to as a piezoelectric substance.

Next, transparent electrodes such as ITO (indium tin oxide) are applied to both sides of the piezoelectric crystal and then attached to a cutting substrate (S1020).

Next, the first front matching material is mixed and applied by coating, the applied first front matching material is cured, and then cut to the target thickness (S1030). The first front matching material is for forming a transparent first front matching layer and may contain at least one of epoxy and urethane.

Next, a second front matching material is formed using a polymer material having a similar refractive index to the first front matching material (S1040). The polymer material may contain a transparent polymer or resin. The second matching material is for forming a front polymer layer or a second front matching layer.

Next, a smooth surface can be created by controlling the thickness of the second front matching material applied on the first front matching layer using a method such as spin coating or spray coating, or by hardening and cutting a thick layer and then polishing it.

Meanwhile, depending on the modified implementation, the second front matching layer may have a concave or convex lens shape on its outer surface so as to perform the function of an acoustic lens.

Next, the laminated structure consisting of a piezoelectric crystal-front-to-back alignment structure is separated from the cutting substrate and turned over and attached (S1050).

Next, a back matching material is applied to the back of the piezoelectric crystal, cured, and then cut to the target thickness (S1060). The back matching material may be substantially the same as the first front matching material, but is not limited thereto. The back matching material may additionally contain a material that is more advantageous in sound absorption performance.

Next, the back-aligned-piezoelectric crystal-front-aligned structure is cut into the shape and size of the piezoelectric material to be used in the ultrasonic transducer element (S1070).

Next, using a precision knife, the corners or apexes of the rear matching layer are carefully removed to expose the electrodes (S1080).

Next, attach wires or metal parts to be connected to wires to the exposed area using a conductive adhesive (S1090).

Then, a thick layer of transparent epoxy, urethane, silicone rubber, etc. is stacked to complete the rear sound-absorbing layer (S1100).

According to the above-described configuration, the ultrasonic transducer of the present embodiment may have a multilayered front matching layer installed on the front of a piezoelectric unit including a piezoelectric crystal, and a rear matching layer installed on the rear of the piezoelectric unit. Here, the front matching layer may be composed of a first front matching layer having a relatively thin thickness formed by applying a front matching material that is a composite material, and a second front matching layer having a relatively thick thickness formed by using a polymer material having a similar refractive index to that of the first front matching layer. In addition, the rear matching layer may be composed of a transparent rear thin film layer that is formed by applying a rear matching material that is a composite material and having a relatively thin thickness, and a transparent rear thick film layer that is very thick compared to the thin film layer.

Figure 11 is a flowchart illustrating an additional process that can be employed in the TUT manufacturing method of Figure 10.

Referring to FIG. 11, the TUT manufacturing method can attach a metal part that will become the outer housing of the previously prepared back-aligned-piezoelectric crystal-front-aligned structure to the back side of the structure (S1110). The housing can be made of a metal material. Then, the transducer being manufactured with the structure to which the housing is attached can be turned over so that the back side faces the bottom of the workbench.

Next, a portion of the edge of the front matching layer that faces forward for electrical connection on the front side, i.e. the front side, can be removed (S1120).

Next, the exposed electrode can be electrically connected to a metal housing positioned outside thereof using an electrically conductive adhesive (S1130). The exposed electrode can be a transparent electrode coated on the front surface of the piezoelectric unit.

Next, the metal housing can be connected to a cable or connector to be connected externally (S1140). The metal housing can be connected to a ground wire of the cable or connector.

Next, an insulating film can be formed in a part where insulation is required (S1150). The part where insulation is required may be an exposed electrode part or a part connected to a cable or connector.

Next, a glass cover may be additionally placed to prevent damage such as scratches on the back of the rear sound-absorbing layer (S1160). The glass cover may be referred to as a contact coupling, etc.

Figures 12 and 13 are graphs for explaining conditions to be considered in the TUT manufacturing method of the present embodiment.

Referring to FIGS. 12 and 13, in manufacturing a TUT, all operations are performed at a temperature of 100°C or lower to prevent damage to the piezoelectric crystal. In other words, it is not easy to use a high-temperature molding material in manufacturing a TUT.

In addition, when using a transparent ceramic material that is not significantly different from a general polymer material with a refractive index of 1.45 to 1.55, the acoustic impedance of the particle itself is low, at around 10 to 15 MRayl, so the ceramic ratio must be set very high to achieve an acoustic impedance of the composite material of around 7 to 8 MRayl.

In addition, in order to solve the problem of joint gap between the piezoelectric unit and the matching layer, a method is used in which a powdered material is dispersed in a liquid or clay-like polymer material and then solidified. However, when using this method, when the volume ratio of the particles is increased, the viscosity tends to increase exponentially, making it difficult to appropriately increase the volume ratio.

Accordingly, the transparent composite material for the TUT of the present embodiment is prepared so that the transparency, acoustic impedance, and viscosity of the mixture before composite material curing are all within appropriate ranges.

Transparency can be determined based on the volume ratio of ceramic particles, the size and shape of the particles, and the difference in refractive index between the polymer and the ceramic. Acoustic impedance can be determined based on the volume ratio of ceramic particles, and the bulk modulus and shear modulus of each of the ceramic and the polymer. And the viscosity of the mixture before curing can be determined based on the volume ratio of ceramic particles, the size and shape of the particles.

Here, transparency is set to be transparent at a thickness of 1/4 wavelength at an acoustic impedance of 7 to 8 MRayl for the front matching layer and around 4 MRayl for the rear matching layer. Here, transparency means having a transmittance of 90% or more.

Additionally, the viscosity of the mixture before curing is set to be within the miscible viscosity range at an acoustic impedance of 7 to 8 MRayl, and for the rear matching layer, around 4 MRayl.

In addition, in this embodiment, the acoustic impedance of the composite material according to the elastic properties of each particle is expressed as a function of the volume ratio, and the composition of the composite material can be determined using this.

The results of an experiment performed using aluminum oxide (Al ₂ O ₃ ) with a particle size of 5 ㎛ as a composite material, aluminum oxide (Al ₂ O ₃ ) with a particle size of 25 nm, silicon dioxide (SiO ₂ ) with a particle size of 3 ㎛, and silicon dioxide (SiO ₂ ) with a particle size of 15 nm are shown in FIGS. 14 and 15.

Figure 14 is a graph for explaining the relationship between the acoustic impedance and viscosity of the material considered in the TUT manufacturing method of the present embodiment.

As illustrated in Fig. 14, the viscosity change according to the change in the volume ratio of each particle is measured, and based on this, the viscosity and the limit mixing ratio according to the acoustic impedance can be estimated. However, the viscosity or mixing ratio in cases where mixing is not possible at the target acoustic impedance according to the viscosity analysis is excluded.

, cPs)에서 약 3 MRayl ~ 약 9.2 MRayl의 음향 임피던스를 가지는 것으로 측정되었다. 입자 크기가 25㎚인 산화알루미늄(Al₂O₃)은 점도 약 10³ 내지 10⁸(

, cPs)에서 약 3 MRayl ~ 약 4.9 MRayl의 음향 임피던스를 가지는 것으로 측정되었다. 입자 크기가 3㎛인 이산화규소(SiO₂)는 점도 약 10³ 내지 10⁸(

, cPs)에서 약 3 MRayl ~ 약 7.5 MRayl의 음향 임피던스를 가지는 것으로 측정되었다. 그리고 입자 크기가 15㎚인 이산화규소(SiO₂)는 점도 10³ 내지 10⁸(

, cPs)에서 약 3 MRayl ~ 약 3.9 MRayl의 음향 임피던스를 가지는 것으로 측정되었다. 여기서, 점도 10⁸(

, cPs) 이상은 혼합 불가한 경우로 점도 또는 혼합비 선별 대상에서 제외된다.Experimental results showed that aluminum oxide (Al ₂ O ₃ ) with a particle size of 5 μm had a viscosity of about 10 ³ to 10 ⁸ (

, cPs) was measured to have an acoustic impedance of about 3 MRayl to about 9.2 MRayl. Aluminum oxide (Al ₂ O ₃ ) with a particle size of 25 nm has a viscosity of about 10 ³ to 10 ⁸ (

, cPs) was measured to have an acoustic impedance of about 3 MRayl to about 4.9 MRayl. Silicon dioxide (SiO ₂ ) with a particle size of 3 ㎛ has a viscosity of about 10 ³ to 10 ⁸ (

, cPs) was measured to have an acoustic impedance of about 3 MRayl to about 7.5 MRayl. And silicon dioxide (SiO ₂ ) with a particle size of 15 nm had a viscosity of 10 ³ to 10 ⁸ (

, cPs) was measured to have an acoustic impedance of about 3 MRayl to about 3.9 MRayl. Here, the viscosity was 10 ⁸ (

, cPs) or more are not miscible and are excluded from the viscosity or mixing ratio selection.

, cPs)의 부피비로 혼합한 복합재료에 사용할 수 있음을 알 수 있다. 또한, 입자 크기가 3㎛인 이산화규소(SiO₂)를 점도 10⁷ 내지 10⁸(

, cPs)의 부피비로 혼합한 복합재료를 사용할 수 있음을 알 수 있다.According to the experimental results above, in order to obtain an acoustic impedance of 7 to 8 MRayl suitable for the front matching layer, aluminum oxide (Al ₂ O ₃ ) with a particle size of 5 ㎛ was used with a viscosity of about 10 ³ to 10 ⁴ (

, cPs) can be used in _composite materials mixed with a volume ratio of 10 ⁷ to 10 ⁸ (

, it can be seen that composite materials mixed in a volume ratio of cPs can be used.

Figure 15 is a graph for explaining the relationship between acoustic impedance and transparency considered in the TUT manufacturing method of the present embodiment.

As illustrated in Fig. 15, the scattering coefficient according to the change in acoustic impedance can be estimated according to the theory of light scattering according to the volume ratio. The acoustic impedance of each composite material used in the experiment was measured at a viscosity of 100 M(10 ⁸ ) cPs. However, the volume ratio in the case of opacity at the target thickness is excluded according to the estimation result of the scattering coefficient corresponding to the degree of light transmittance at the target thickness for a specific wavelength, for example, 589 nm.

As a result of the experiment, the acoustic impedances of aluminum oxide (Al ₂ O ₃ ) having a particle size of 5 μm (hereinafter referred to as the “first aluminum oxide composite material”), aluminum oxide (Al ₂ O ₃ ) having a particle size of 25 nm (hereinafter referred to as the “second aluminum oxide composite material”), silicon dioxide (SiO ₂ ) having a particle size of 3 μm (hereinafter referred to as the “first silicon dioxide composite material”), and silicon dioxide (SiO ₂ ) having a particle size of 15 nm (hereinafter referred to as the “second silicon dioxide composite material”) were measured as 3.65 MRayl, 4.76 MRayl, 7.46 MRayl, and 3.81 MRayl, respectively, in the order described.

Figure 16 is a graph for explaining the relationship between the volume ratio of each composite material and its longitudinal elastic velocity on each of the front side and the rear side considered in the TUT manufacturing method of the present embodiment.

Referring to FIG. 16, one can confirm the experimental results for longitudinal acoustic velocity according to the volume fraction of the transparent matching layer material of the TUT of the present embodiment.

That is, when the volume ratio of the first aluminum oxide composite material (Al ₂ O ₃ composite 1) used as the front matching layer of the TUT is increased from 0.3 to 0.7, the acoustic speed increases proportionally from about 3 km/s when the volume ratio is about 0.35 to about 5 km/s when the volume ratio is about 0.6.

In addition, when the volume ratio of the second aluminum oxide composite material (Al ₂ O ₃ composite 2) used as the back matching layer of the TUT was increased from 0 to 0.4, the acoustic velocity changed to about 2.6 km/s, about 2.5 km/s, about 2.6 km/s, about 2.8 km/s, and about 3.3 km/s when the volume ratio was 0, 0.1, 0.2, 0.3, and 0.4, respectively, in the order described.

In addition, when the volume ratio of the first silicon dioxide composite material (SiO ₂ composite 1) used as the front and back matching layers of the TUT was increased from 0 to 0.7, the acoustic velocity increased linearly and proportionally from about 2.6 km/s when the volume ratio was 0 to about 4 km/s when the volume ratio was 0.7.

In addition, when the volume ratio of the second silicon dioxide composite material (SiO ₂ composite 2) used as the back matching layer of the TUT was increased from 0 to 0.4, the acoustic speed increased approximately linearly and proportionally from about 2.6 km/s when the volume ratio was 0 to about 3.2 km/s when the volume ratio was 0.4.

Figure 17 is a graph for explaining the relationship between the volume ratio of each composite material and its acoustic impedance on each of the front side and the rear side considered in the TUT manufacturing method of the present embodiment.

Referring to FIG. 17, one can confirm the experimental results for acoustic impedance according to the volume fraction of the transparent matching layer material of the TUT of the present embodiment.

That is, when the volume ratio of the first aluminum oxide composite material (Al ₂ O ₃ composite 1) used as the front matching layer of the TUT is increased from 0.3 to 0.7, the acoustic impedance increases linearly and proportionally with the increase in the volume ratio from about 6 MRayl when the volume ratio is about 0.32 to about 8 MRayl when the volume ratio is about 0.45.

In addition, when the volume ratio of the second aluminum oxide composite material (Al ₂ O ₃ composite 2) used as the back matching layer of the TUT was increased from 0 to 0.4, the acoustic impedance increased linearly and proportionally with the increase in the volume ratio from about 3 MRayl when the volume ratio was 0 to about 5 MRayl when the volume ratio was about 0.25.

In addition, when the volume ratio of the first silicon dioxide composite material (SiO ₂ composite 1) used as the front and back matching layers of the TUT was increased from 0 to 0.7, the acoustic impedance increased linearly and proportionally with the increase in the volume ratio from about 3 MRayl when the volume ratio was 0 to about 8 MRayl when the volume ratio was 0.65.

In addition, when the volume ratio of the second silicon dioxide composite material (SiO ₂ composite 2) used as the back matching layer of the TUT is increased from 0 to 0.4, its acoustic impedance increases approximately linearly and proportionally from about 3 MRayl when the volume ratio is 0 to about 5 MRayl when the volume ratio is 0.4.

In this way, it is possible to confirm the volume ratio that satisfies the acoustic impedances required for the front matching layer and the rear matching layer of the TUT, for example, 7.5 MRayl and 3.8 MRayl, respectively, in each composite material.

Based on the experimental results described above, two examples of methods for producing composite material mixtures are given below.

In the preparatory work, both the epoxy main body and the epoxy member are sufficiently degassed and cooled in a vacuum to increase stability at room temperature.

In the first method, which is used when the target viscosity is low, the powder to be added only to the epoxy resin is mixed, stirred well until it approaches a uniform liquid phase, and then degassed in a vacuum. Then, after mixing with the hardener, it is applied to the application area of the piezoelectric crystal, and then degassed in a vacuum again.

In the second method, when the target viscosity is high or close to the limiting viscosity, if the first method cannot create a liquid with the main ingredient added only, mix as much as possible until a thick dough is formed. When it becomes a solid lump, crush it finely and make powder again. This process is repeated until the granules become uniformly moist. In the above process, it is also possible to use a diluent such as alcohol so that the main ingredient can be sufficiently dispersed between the particles. If a diluent is used, sufficient time can be given for the diluent to evaporate and be removed.

When a hardener is mixed into the evenly moist crumbs, it becomes a form close to clay that can be molded to some extent. This mixture is spread thinly on the application area, applied without allowing air bubbles to enter, and degassed in a vacuum to form the desired matching layer. At this time, centrifugal separation equipment can be used to process the remaining air bubbles in the applied material so that they can be degassed as much as possible and removed.

Fig. 18 is a graph illustrating the transparency according to the wavelength of the front primary matching layer manufactured by the TUT manufacturing method of the present embodiment. Fig. 19 is a graph illustrating the transparency according to the wavelength of the rear matching layer manufactured by the TUT manufacturing method of the present embodiment.

Referring to Fig. 18, the front primary matching layer formed of the first silicon dioxide composite material to have the characteristic of acoustic impedance of 7.5 MRayl exhibits transparency of about 80 to 95% in the visible light range with a wavelength of 400 nm to 750 nm, and transparency of about 95 to 99% in the near infrared (NIR) range with a wavelength of 750 nm to 1000 nm. In addition, for reference, the case of the first aluminum oxide composite material, which is an opaque composite material, is indicated by a dotted line.

And referring to FIG. 19, the rear matching layer formed of the second aluminum oxide composite material to have the characteristic of acoustic impedance of 3.8 MRayl exhibits transparency of about 70 to 80% in the visible light range with a wavelength of 400 nm to 750 nm, and transparency of about 80 to 90% in the near-infrared range with a wavelength of 750 nm to 1000 nm (see dotted line).

The rear matching layer formed of the first silicon dioxide composite material to have an acoustic impedance characteristic of 3.8 MRayl exhibits a transparency of about 80 to 98% in the visible light range and about 98 to 99% in the near-infrared range (see solid line).

The rear matching layer formed of the first silicon dioxide composite material to have an acoustic impedance characteristic of 3.8 MRayl exhibits a transparency of about 80 to 98% in the visible light range and about 98 to 99% in the near-infrared range (see the dashed-dotted line).

According to this example, it can be confirmed that the transparent matching layer for TUT, which is made by controlling the refractive index of light and acoustic performance, exhibits high light transmittance in visible light and infrared rays, unlike composite materials made using conventional methods.

Fig. 20 is a graph for explaining the size of the front-side effective acoustic impedance of the present embodiment and comparative examples. Fig. 21 is a graph for explaining the phase angle of the front-side effective acoustic impedance of the present embodiment and comparative examples. And Fig. 22 is a graph for explaining the rear-side effective impedance of the present embodiment and comparative examples.

The measurement results according to the TUT structure of the present embodiment (see Fig. 7) are indicated by a solid line, the measurement results of Comparative Example 1 according to the opaque ultrasonic transducer structure (see Fig. 8) are indicated by a dashed-dotted line, and the measurement results of Comparative Example 2 according to the conventional transparent ultrasonic transducer structure (see Fig. 9) are indicated by a double-dotted-dashed line.

Referring to FIG. 20, the distribution of acoustic impedance formed along the resonance center frequency on the front side according to the TUT structure of the present embodiment can be confirmed. That is, the size of the front effective acoustic impedance (Z) of the TUT of the present embodiment is positioned line-symmetrically around the resonance center frequency within the hatched area of the ideal design range indicated by two dotted lines. The resonance center frequency is expressed as a normalized frequency whose size is 1 as the center of vibration. In this way, it can be confirmed that the TUT of the present embodiment can exhibit optimal performance by the effective acoustic impedance satisfying the ideal design range.

Meanwhile, it can be confirmed that Comparative Example 1 has relatively low transmission/reception efficiency and relatively high vibration amplitude compared to the present embodiment near the center of vibration. In addition, it can be confirmed that the size of the forward effective acoustic impedance (Z) of Comparative Example 2 is very low, so it has relatively very low transmission/reception efficiency and relatively very high vibration amplitude.

In particular, the phase angle of the forward effective acoustic impedance has a zero-phase characteristic at the resonant frequency of the ideal central phase symmetry point, as shown in the hatched area indicated by the dotted circle in the central portion in Fig. 21. That is, the phase angle of the acoustic impedance of the present embodiment has a form that does not change, but the phase angle of Comparative Example 1 has a form in which it changes or fluctuates near the resonant frequency, and the phase angle of Comparative Example 2 is fixed to 0 (rad) regardless of the operating frequency.

In addition, referring to FIG. 22, it is possible to confirm the distribution of acoustic impedance formed along the resonance center frequency at the rear side according to the TUT structure of the present embodiment. That is, the size of the rear effective acoustic impedance (Z) of the TUT of the present embodiment is located in the ideal design range near the resonance center frequency within the hatched area of the ideal design range indicated by two dotted lines, and the acoustic impedance is significantly reduced when it deviates from the resonance center frequency, which is the center of vibration and is indicated by the normalized frequency (normalized frequency) 1. In this way, it can be confirmed that the TUT of the present embodiment effectively absorbs acoustic impedance through the rear sound-absorbing layer.

According to the configuration described above, it can be seen that while the existing transparent transducer has performance degradation due to both the front and rear impedances being less than the ideal size, the TUT of the present embodiment can have an ideal acoustic impedance.

The impedance difference between this embodiment and other existing comparative examples is further illustrated with reference to FIGS. 23 and 24, as follows.

Fig. 23 is a graph comparing the performance of each TUT based on the front effective acoustic impedance size measured in the present embodiment and comparative examples. Fig. 24 is a graph comparing the performance of each TUT based on the front effective impedance phase measured in the present embodiment and comparative examples.

As shown in Fig. 23, the acoustic impedance of the TUT of the present embodiment has a symmetrical shape about the resonance center while being located in the ideal impedance size range indicated by the hatched area. The ideal impedance has a size of about 10 MRayl at normalized frequencies of 0.5 and 1.5, and a size of about 15 MRayl to about 20 MRayl in the range of about 0.7 to about 1.3 of the normalized frequency including the resonance center frequency.

Meanwhile, Comparative Example 1 has a constant and low acoustic impedance. Comparative Example 2 or Comparative Example 3 has a symmetrical shape about the resonance center, but has a relatively very low acoustic impedance without a section included in the ideal impedance size range. Comparative Example 4 exhibits a very high acoustic impedance of about 4 to about 10 times the ideal impedance at a frequency lower than the resonance center frequency, and has a shape in which the impedance decreases as the resonance center frequency increases. And Comparative Example 5 has a high acoustic impedance of about 2 to 4 times the ideal impedance size and a shape that is not symmetrical about the resonance center.

In addition, as shown in Fig. 24, the phase angle of the front effective acoustic impedance of the present embodiment has a zero-phase characteristic at the resonant frequency of the ideal center phase symmetry point. However, it can be confirmed that the phase angles of Comparative Examples 1 to 5 are not only not symmetrical, but also deviate significantly from the ideal design.

The above-mentioned Comparative Example 1 is one of the existing general TUTs, Comparative Example 2 is a parylene matching TUT, Comparative Example 3 is an epoxy lens TUT, Comparative Example 4 is an N-SF11 hard glass lens TUT, and Comparative Example 5 is a thick glass matching TUT.

In this way, it can be seen that while the impedance size and phase symmetry point of the existing transparent ultrasonic transducer are far outside the ideal design region, the transparent ultrasonic transducer of the present embodiment implements the impedance size and phase conditions within the ideal region.

Figure 25 is a graph comparing the transparency of a developed transparent device (example) manufactured using the TUT manufacturing method of the present embodiment and an existing transparent device (comparative example).

Referring to FIG. 25, it can be seen that the transparency of the TUT of the present embodiment (see FIG. 7) has little or no difference in transparency in both the visible light range and the near-infrared range when compared to the transparency of a conventional transparent ultrasonic transducer (see FIG. 9).

That is, the TUT of the present embodiment can exhibit excellent, stable and reliable performance in transmission/reception efficiency and vibration amplification while maintaining transparency.

Fig. 26 is a graph comparing peak-to-peak voltages in pulse echo response waveforms of the present embodiment and comparative examples. Fig. 27 is a graph comparing full-width-at-half-maximum (FWHM) in pulse echo response waveforms of the present embodiment and comparative examples. And Fig. 28 is a graph comparing echo frequency analysis results of the present embodiment and comparative examples.

Referring to FIGS. 26 to 28, the acoustic echo capability performance of the TUT of the present embodiment is compared based on design simulation and experimental results with the existing opaque transducer of Comparative Example 1 and the existing transparent transducer of Comparative Example 2, and it can be confirmed that the acoustic transmission and reception capability of the TUT of the present embodiment is higher than that of the existing transparent ultrasonic transducer and similar to that of the opaque ultrasonic transducer.

That is, as shown in Fig. 26, after the start of the experiment for the TUT of the present embodiment, a 1.08 V pulse generated at 0.1 μs and a residual echo (R) generated immediately thereafter can be observed. Similarly, after the start of the experiment for the existing opaque ultrasonic transducer, a 0.93 V pulse generated at 0.3 μs and a residual echo (R) generated immediately thereafter can be observed. On the other hand, in the case of the existing transparent ultrasonic transducer, only a pulse of up to 0.36 V can be confirmed to vibrate.

In addition, as shown in Fig. 27, results similar to the experimental results of Fig. 26 can be confirmed in the results of comparing the full-width-at-half-maximum (FWHM) of the pulse echo response waveform.

In addition, as shown in Fig. 28, in the echo frequency analysis results, the echo frequency magnitude of the TUT of the present embodiment has a similar magnitude in each band when compared to the opaque ultrasonic transducer of Comparative Example 1, and it can be confirmed that this performance is superior when compared to the existing transparent ultrasonic transducer of Comparative Example 2.

As a result of verifying the actual sound transmission and reception capability of the TUT of this embodiment, it can be seen that it exhibits performance that is higher than that of a conventional transparent ultrasonic transducer and similar to that of an opaque ultrasonic transducer.

According to the above-described configuration, the problem that the acoustic performance of the transparent ultrasonic transducer was significantly inferior to the acoustic performance of the existing opaque ultrasonic transducer can be solved. That is, in the present embodiment, the problem of the existing technology caused by the mismatch of the acoustic impedance between the hard piezoelectric crystal and the soft load medium can be solved through a novel transparent matching and sound-absorbing material that can be loaded onto the piezoelectric crystal without a gap on the surface and has an appropriate acoustic impedance.

In addition, the method for manufacturing the TUT of the above-described embodiment can be automated by a control device that controls the ultrasonic transducer manufacturing equipment or a computing device that performs the function of such a control device. In this case, the control device or the computing device can store software or program commands for implementing the manufacturing methods mentioned in the above-described embodiments.

The operation of the method according to an embodiment of the present invention can be implemented as a computer-readable program or code on a computer-readable recording medium. The computer-readable recording medium includes all types of recording devices that store information that can be read by a computer system. In addition, the computer-readable recording medium can be distributed over network-connected computer systems so that the computer-readable program or code can be stored and executed in a distributed manner.

Additionally, the computer-readable recording medium may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, etc. The program instructions may include not only machine language codes produced by a compiler, but also high-level language codes that can be executed by the computer using an interpreter, etc.

While some aspects of the invention have been described in the context of an apparatus, they may also represent a description of a corresponding method, wherein a block or device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method may also be represented as a feature of a corresponding block or item or a corresponding device. Some or all of the method steps may be performed by (or using) a hardware device, such as, for example, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, at least one or more of the most important method steps may be performed by such a device.

In embodiments, a programmable logic device (e.g., a field-programmable gate array) may be used to perform some or all of the functions of the methods described herein. In embodiments, a field-programmable gate array may operate in conjunction with a microprocessor to perform one of the methods described herein. In general, the methods are preferably performed by some hardware device.

Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below.

Claims (20)

A thin film type piezoelectric unit that generates vibrations by electric signals or generates electric signals by vibrations;
A front matching layer formed of a freely moldable composite material in the form of a liquid or clay-like mixture without a bonding gap on the front surface of the above piezoelectric unit;
A front polymer layer disposed on the front matching layer; and
A sound-absorbing layer arranged on the rear side of the above piezoelectric unit;
Including,
The above sound-absorbing layer has a rear matching layer formed of the composite material on the rear side of the piezoelectric unit, and a rear polymer layer disposed on the rear matching layer.
The viscosity of the mixture before curing of the composite material forming the above-mentioned front matching layer is 10 ³ cPs to 10 ⁸ cPs,
A transparent ultrasonic transducer, wherein the front matching layer has a transparency that transmits more than 80% of light at a 1/4 wavelength thickness at an acoustic impedance of 7 to 8 MRayl. delete In claim 1,
The acoustic impedance of the above absorbing layer is calculated using mathematical formula 1.
[Mathematical Formula 1]

A transparent ultrasonic transducer, wherein in mathematical expression 1, Z _eff represents the effective acoustic impedance of the absorbing layer, Z ₁ represents the acoustic impedance of the rear matching layer, Z _B represents the acoustic impedance of the rear polymer layer, l represents the length or thickness of the rear matching layer, and λ represents the transmission wavelength. delete In claim 1,
A transparent ultrasonic transducer, wherein the front matching layer is composed of a composite material of ceramic and epoxy, and the front polymer layer is composed of a pure polymer material. In claim 1,
A transparent ultrasonic transducer, wherein the thickness of the piezoelectric unit is 1/2 of the transmission wavelength (λ), and the thicknesses of the front matching layer, the front polymer layer, and the rear matching layer are each λ/4. In claim 1,
A transparent ultrasonic transducer, wherein the transparency of the composite material constituting the front matching layer or the rear matching layer is determined by the volume ratio of the ceramic particles, the size and shape of the ceramic particles, and the difference in refractive index between the ceramic and the polymer. In claim 1,
A transparent ultrasonic transducer, wherein the rear matching layer has a transparency that transmits more than 90% of light at a 1/4 wavelength thickness and an acoustic impedance of 4 to 6 MRayl. In claim 1,
A transparent ultrasonic transducer, wherein the acoustic impedance of the composite material constituting the front matching layer or the rear matching layer is determined by the volume ratio of the ceramic particles, the bulk modulus and the shear modulus of each of the ceramic and the polymer. In claim 1,
A transparent ultrasonic transducer, wherein the viscosity of the mixture before curing of the above composite material is determined by the volume ratio of ceramic particles, the size and shape of the ceramic particles. In claim 1,
A transparent ultrasonic transducer further comprising a conductive ring member disposed between the rear matching layer and the rear polymer layer. In claim 11,
A transparent ultrasonic transducer further comprising a case that accommodates a laminated structure of the front polymer layer, the front matching layer, the rear matching layer, the rear polymer layer, and the conductive ring member. In claim 12,
The above piezoelectric unit is a transparent ultrasonic transducer comprising a piezoelectric crystal in the form of a thin film, a first transparent electrode formed on the front surface of the piezoelectric crystal, and a second transparent electrode formed on the rear surface of the piezoelectric crystal. In claim 13,
A transparent ultrasonic transducer further comprising a connecting electrode connecting the first transparent electrode and the case on one surface of the rear polymer layer. A step of applying a mixture in which first particles are dispersed in a polymer material to one surface of a piezoelectric unit;
A step of degassing and curing the paste applied to one surface of the above piezoelectric unit in a predetermined atmosphere;
A step of forming a full-face matching layer on one side of the piezoelectric unit by wrapping and polishing the hardened composite material to a design thickness;
A step of forming a rear matching layer on the other surface of the piezoelectric unit using the above composite material;
A step of placing a front polymer layer on the front matching layer; and
A step of placing a rear polymer layer on the rear matching layer;
Including,
The viscosity of the mixture before curing of the composite material forming the above-mentioned front matching layer is 10 ³ cPs to 10 ⁸ cPs,
A method for manufacturing a transparent ultrasonic transducer, wherein the front matching layer has a transparency that transmits more than 80% of light at a thickness of 1/4 wavelength at an acoustic impedance of 7 to 8 MRayl. In claim 15,
The first particle comprises a glass or ceramic material, and the glass or ceramic material contains at least one material selected from a silicate series, an aluminum salt series, a zirconium salt series, and a magnesium fluoride series.
The above polymer material contains at least one material selected from silicone, epoxy, urethane, polyethylene, polystyrene, acrylic and sulfate polymer resins.
Method for manufacturing a transparent ultrasonic transducer. In claim 15,
A method for manufacturing a transparent ultrasonic transducer, wherein the rear matching layer has a transparency that transmits more than 90% of light at a thickness of 1/4 wavelength and an acoustic impedance of 4 to 6 MRayl. In claim 15,
A method for manufacturing a transparent ultrasonic transducer, wherein the transparency of the composite material constituting the front matching layer or the rear matching layer is determined by the volume ratio of ceramic particles, the size and shape of the ceramic particles, and the difference in refractive index between the ceramic and the polymer. In claim 15,
A step of arranging a conductive ring member connected to the second transparent electrode of the piezoelectric unit between the piezoelectric unit and the rear polymer layer; and
A step of arranging a case that accommodates a laminated structure of the piezoelectric unit, the front matching layer, the rear matching layer, the rear polymer layer, and the conductive ring member;
A method for manufacturing a transparent ultrasonic transducer further comprising: In claim 15,
A method for manufacturing a transparent ultrasonic transducer, wherein the thickness of the piezoelectric unit is 1/2 of the transmission wavelength (λ), and the thicknesses of each of the front matching layer, the front polymer layer, and the rear matching layer are λ/4.

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