EP3788618B1 - Impedance matching device, acoustic transducer and method for producing the impedance matching device - Google Patents

Description

The present invention relates to an impedance matching device, to a converter device having such an impedance matching device, to a system having said converter device and to a method of manufacturing an impedance matching device.

The present invention further relates to an acoustic impedance adjustment and in particular to a system for adjusting an acoustic impedance.

The acoustic impedance describes the resistance of a medium to the acoustic flow, which is created by an applied acoustic pressure. At interfaces of materials with different acoustic impedances, part of the acoustic energy is reflected, the proportion of which essentially results from the size of the acoustic impedance jump. As a result, the energy that can be transferred between the sound transducers and the acoustic load medium is reduced and the efficiency of the system is reduced. Typical sound transducers with corresponding acoustic impedances are based on piezoceramics (acoustic impedance approximately 33 MRayl = 33 · 10 ⁶ Ns/m ³ [1]) or piezo composites (approximately 7 MRayl = 7 · 10 ⁶ Ns/m ³ [2]). Other typical sound transducers are based on piezo thin-film systems and membrane oscillators, such as CMUT (capacitive micromachined ultrasonic transducer), whose characteristic sound impedances depend on the structural dimensions (approximately 1 to 5 MRayl = 1-5 · 10 ⁶ Ns/m ³ [3]) . Typical load media are water (1.48 MRayl = 1.48 · 10 ⁶ Ns/m ³ [4]), human tissue (approximately 1.5 MRayl = 1.5 · 10 ⁶ Ns/m ³ [4]) and Air (approximately 427 Rayl = 427 Ns/m ³ [1]). Acoustic matching layers are essential for optimized energy transfer, especially in air.

Typically, layer systems for adapting the acoustic impedance are made from conventional or composite materials with the most suitable acoustic impedance possible. The acoustic impedance Z depends on the density ρ and the speed of sound c of the material: $$Z=\mathit{c\rho }$$

Fig. 9 shows three different methods of adjusting the acoustic impedance. So-called Single Step Matching Systems (SMS; one-step matching systems) create one Impedance step between the ultrasonic transducer side (such as CMUT) and the medium side (load). Multiple Step Matching Systems (MMS) consist of two or more impedance steps. Gradient Matching Systems (GMS; gradient-based matching systems) describe an exponential impedance curve, which enables the best degree of transmission. Fig. 9 shows a graph in which the abscissa shows a course of the thickness D of the matching layer between a CMUT (D = 0) and the load side or medium side (D = max). The characteristic acoustic impedance Z is plotted on the ordinate, which is reduced between the CMUT and the medium in the present diagram.

This curve also shows that the influence of the acoustic impedance on the transmittance increases the closer you get to the medium side within the matching layer system. In the example mentioned above, the matching layer system must achieve the lowest possible acoustic impedances, which cannot be achieved with known concepts or can only be achieved in conjunction with major disadvantages. Aerogels [5] offer a solution. These achieve a very low acoustic impedance, but have a highly diffractive effect and can only be applied in individual steps (MMS) with intermediate connecting materials, which in turn disrupt the transmission behavior. Composite materials made from embedded particles in a matrix have similar disadvantages [6].

There are a variety of microstructured materials that are manufactured using methods from the semiconductor industry. These methods include coating processes, structuring using lithography and etching processes. For example, using these three processes, an acoustic impedance match was created in order to structure silicon oxide on a silicon wafer. A polymer was then applied using a coating process and fixed to an ultrasonic transducer [7]. In another example, anisotropic etching processes were used to separate silicon in high aspect ratio posts and then fill the spaces with epoxy resin (composite) to create an acoustic impedance match [8]. A gradual progression is made possible using the methods mentioned. In one example, round, conically tapering silicon rods were created and again embedded in epoxy [9]. Another example of gradual acoustic impedance adjustment uses an unspecified micromachining process to create a structured layer system made of copper, PZT (lead zirconate titanate) and parylene [10].

EP 1 477 778 A1 describes the use of a first and a second acoustic matching layer with different, discontinuous material densities.

However, the structures produced using the known methods suffer from low efficiency.

It would therefore be desirable to have acoustic impedance adjustment devices that enable the acoustic impedance to be adjusted with high efficiency.

An object of the present invention is therefore to provide an acoustic impedance matching device, a transducer device, a system with such a transducer device and a method for producing an acoustic impedance matching device, which enable efficient acoustic impedance matching.

This task is solved by the subject matter of the independent patent claims.

The inventors have recognized that by forming microstructures with small dimensions in the sub-micrometer range, extremely precise and therefore efficient acoustic impedance matching can be achieved.

According to an exemplary embodiment, an impedance matching device for adjusting a characteristic acoustic impedance comprises an impedance matching body with a first side and an opposite second side. The impedance matching device is designed to adapt an acoustic impedance of a medium contacted on the second side to an acoustic impedance of a sound transducer contacted on the first side. The impedance matching body comprises microchannels which have a structural dimension of at most 500 nanometers along at least one spatial direction. The microchannels are branched microchannels whose number varies monotonically between the first and second sides; and wherein the microchannels form cavities in the impedance matching body, wherein an effective material density of an impedance matching material of the impedance matching body between the first side and the second side is monotonically variable by a monotonically increasing or monotonically decreasing a volume of the cavities, and effects the adjustment of the characteristic acoustic impedance. Alternatively or additionally, the microchannels are formed as structures that taper towards the first or second side and have the structural extent at least in a region of minimal extent.

According to one embodiment, a method for producing an impedance matching device includes a step of providing an impedance matching body with a first and an opposite second side, which is designed to adapt a sound impedance of a medium contacted on the first side to a sound impedance of a sound transducer contacted on the second side; so that the impedance matching body comprises microchannels which have a structural dimension of at most 500 nm along at least one spatial direction. The method is carried out so that the microchannels are branched microchannels, the number of which is monotonically variable between the first and second sides; and so that the microchannels form cavities in the impedance matching body, so that an effective material density of an impedance matching material of the impedance matching body between the first side and the second side is monotonically variable by a monotonic increase or monotone decrease of a volume of the cavities, and effects the adjustment of the acoustic characteristic impedance; and/or is carried out so that the microchannels are formed as structures that taper towards the first or second side, and have the structural extent at least in a region of minimal extent.

Further advantageous embodiments are the subject of the dependent patent claims.

Fig. 1

ein schematisches Blockschaltbild einer Impedanzanpassungsvorrichtung zur Anpassung einer Schallkennimpedanz gemäß einem Ausführungsbeispiel;

Fig. 2

eine schematische Seitenschnittansicht einer Impedanzanpassungsvorrichtung gemäß einem Ausführungsbeispiel, bei der eine Vielzahl von Mikrostrukturen angeordnet ist, die als verzweigte Kanalstrukturen angeordnet sind;

Fig. 3

eine schematische Seitenschnittansicht einer Impedanzanpassungsvorrichtung gemäß einem Ausführungsbeispiel, bei der die Mikrostrukturen als hin zu einer Seite eines Anpassungskörpers sich verjüngende Strukturen gebildet sind;

Fig. 4a

eine schematische Seitenschnittansicht einer Impedanzanpassungsvorrichtung welche nicht unter den Schutzumfang der Patentansprüche fällt, bei der der Impedanzanpassungskörper so gebildet ist, dass die Mikrostrukturen eine hexagonale Gitterstruktur bilden;

Fig. 4b

eine schematische Seitenschnittansicht einer Impedanzanpassungsvorrichtung welche nicht unter den Schutzumfang der Patentansprüche fällt, bei der die Mikrostrukturen ein hexagonales/Dreieck-Muster bilden;

Fig. 4c

eine schematische Seitenschnittansicht einer Impedanzanpassungsvorrichtung welche nicht unter den Schutzumfang der Patentansprüche fällt, bei der die Mikrostrukturen in einem DreieckGittermuster angeordnet sind, sodass Kavitäten eine dreieckige Form aufweisen;

Fig. 4d

eine schematische Seitenschnittansicht einer Impedanzanpassungsvorrichtung welche nicht unter den Schutzumfang der Patentansprüche fällt, bei der die Mikrostrukturen eine Gitterstruktur gemäß einem Diamant-Muster bilden;

Fig. 5

eine schematische Seitenschnittansicht einer Impedanzanpassungsvorrichtung welche nicht unter den Schutzumfang der Patentansprüche fällt, bei der die Mikrostrukturen einen akustischen Pfad definieren;

Fig. 6

ein schematisches Blockschaltbild einer Wandlervorrichtung gemäß einem Ausführungsbeispiel;

Fig. 7

ein schematisches Blockschaltbild eines Systems gemäß einem Ausführungsbeispiel;

Fig. 8

ein schematisches Ablaufdiagramm eines Verfahrens gemäß einem Ausführungsbeispiel zum Herstellen einer Impedanzanpassungsvorrichtung; und

Fig. 9

eine schematische Darstellung von drei bekannten Methoden einer Anpassung der Schallkennimpedanz.

Exemplary embodiments are explained below with reference to the accompanying drawings. Show it:

Fig. 1

a schematic block diagram of an impedance matching device for adjusting a characteristic acoustic impedance according to an exemplary embodiment;

Fig. 2

a schematic side sectional view of an impedance matching device according to an embodiment, in which a plurality of microstructures arranged as branched channel structures are arranged;

Fig. 3

a schematic side sectional view of an impedance matching device according to an exemplary embodiment, in which the microstructures are formed as structures tapering towards one side of an matching body;

Fig. 4a

a schematic side sectional view of an impedance matching device which does not fall within the scope of the claims, in which the impedance matching body is formed such that the microstructures form a hexagonal lattice structure;

Fig. 4b

a schematic side sectional view of an impedance matching device not falling within the scope of the claims, in which the microstructures form a hexagonal/triangle pattern;

Fig. 4c

a schematic side sectional view of an impedance matching device not falling within the scope of the claims, in which the microstructures are arranged in a triangular grid pattern so that cavities have a triangular shape;

Fig. 4d

a schematic side sectional view of an impedance matching device not falling within the scope of the claims, in which the microstructures form a lattice structure according to a diamond pattern;

Fig. 5

a schematic side sectional view of an impedance matching device not falling within the scope of the claims, in which the microstructures define an acoustic path;

Fig. 6

a schematic block diagram of a converter device according to an exemplary embodiment;

Fig. 7

a schematic block diagram of a system according to an exemplary embodiment;

Fig. 8

a schematic flow diagram of a method according to an exemplary embodiment for producing an impedance matching device; and

Fig. 9

a schematic representation of three known methods of adjusting the acoustic impedance.

Before exemplary embodiments are explained in more detail below using the drawings, it should be noted that identical, functionally identical or equivalent elements, objects and/or structures are provided with the same reference numerals in the different figures, so that the description of these elements shown in different exemplary embodiments can be compared to one another is interchangeable or can be applied to one another.

Fig. 1 shows a schematic block diagram of an impedance matching device 10 for adjusting a characteristic sound impedance. The impedance matching device includes an impedance matching body 12 having a first side 14 and a second side 16. The sides 14 and 16 are arranged opposite one another. The impedance matching device can be designed to be traversed by a sound, ie an acoustic wave, from side 14 to side 16 along a sound passage direction 18a and/or to be traversed by a sound wave from side 16 to side 14 along an opposite direction Sound passage direction 18b to be passed through. For example, the sound wave can be generated by a sound transducer that can be contacted with the side 14. The side 16 can be contactable with a medium, for example a human body, a liquid or air or the like. The impedance matching device 10 can be designed to adapt an acoustic impedance of the medium to an acoustic impedance of the sound transducer and/or vice versa. For this purpose, the impedance matching body 12 can, for example, have an acoustic impedance in an area of the side 14 that is adapted to the sound transducer and further have an acoustic impedance in the area of the side 16 that is adapted to the target medium.

This can result in the impedance matching body having a higher acoustic impedance in the area of side 14 than in the area of side 16, although this is not necessary.

The impedance matching body 12 includes microstructures, for example branched microstructures 22 ₁ and 22 ₂ and/or in-plane microstructures 22 ₃ . The microstructures 22 ₁ , 22 ₂ and/or 22 ₃ can be formed as cavities in a material of the impedance matching body 12, wherein the cavities can be filled or unfilled. A filling of the cavities can completely or partially have a different material than a base material or remaining material 24 of the impedance matching body 12. This means that the microstructures 22 to 22 ₃ can be understood as a cavity, a channel structure and/or an inclusion in the material 24 .

The microstructures 22 ₁ to 22 ₃ are each individually or jointly formed so that they have a structural extent 26 ₁ , 26 ₂ and/or 26 ₃ along at least one spatial direction, which is at most 500 nanometers, preferably at most 300 nanometers and particularly preferably at most is 100 nanometers. The structural extent 26 ₁ , 26 ₂ and/or 26 ₃ can be understood as the longest distance between any two points on an outer surface of the microstructure, whereby the two arbitrary points in a cross section of the microstructure 22 ₁ to 22 ₃ are opposite. The structural dimensions can be arranged along any spatial direction x, y and/or z. If the microstructure is, for example, a tubular structure, the points can be arranged in a longitudinal section or cross section, the longitudinal section running, for example, through a plane which is defined by the diameter of the tubular structure. In simple terms, the structural extent of one or more microstructures can be a dimension perpendicular to an axial extension direction of the respective microstructure. One idea of the present exemplary embodiments lies in the use of the resolution power of a method described herein, which can be, for example, 100 nm or less, in order to produce structures precisely, ie with high resolution.

To put it simply, in such a case the structural extent can be the diameter of a round microstructure 22.

The microstructure 22 ₂ can be fluidically coupled to the microstructure 22 ₁ , so that an average value of a volume occupied by the microstructures 22 ₁ and 22 ₂ increases from side 14 towards side 16, but alternatively can also decrease, This means that an average value of the acoustic impedance can increase or decrease towards page 14, or alternatively it can also be constant, as is the case in connection with the Fig. 4a to 4d is described. This can cause a variable density ρ of the material 24 and thus a change in the characteristic sound impedance between the sides 14 and 16. If a material or a filling of the microstructures 22 ₁ and 22 ₂ has a greater material density than the material 24, the acoustic impedance of the impedance matching device 10 can increase from side 14 to side 16. For example, if the density is lower, a decreasing characteristic acoustic impedance can be obtained along the sound passage direction 18a. This means that the microstructures can have a first impedance matching material and that a second impedance matching material, for example the material 24, can be arranged in intermediate regions between the microstructures. The microstructures can be formed, for example, from a cured polymer material or a metal material. Alternatively, any other material can be used. Polymer materials and/or metal materials described can be processed precisely and can be used directly as microstructures, as described in connection with the manufacturing processes described herein. Alternatively, such structures can also serve as a template or negative mold to enable the molding of other materials.

As an alternative to an arrangement parallel or oblique to a sound passage direction 18a or 18b, at least one microstructure can also be arranged perpendicular thereto, for example parallel to an x-direction, which can be arranged, for example, perpendicular to a surface normal of the first side 14 and/or the second side 16 can.

By forming the microstructures with the defined structural dimension of at most 500 nanometers, preferably at most 300 nanometers or preferably at most 100 nanometers, an extremely fine and therefore precise adjustment of the characteristic sound impedance along the sound passage direction 18a and / or 18b can be set. This enables efficient operation of the impedance matching device even with small dimensions of the impedance matching device 10.

Embodiments enable a continuous transition between the respective impedance values, for example the medium and the sound transducer, which is not possible or can only be achieved with difficulty in known concepts. Embodiments create concepts for an acoustic impulse response and their manufacturing processes, for example or even primarily using the multiple photon absorption lithography process to produce layer systems that adapt the acoustic sound impedance between sound transducers and the medium. One goal is an ideal coupling of the acoustic energy from the sound transducer into the load medium (transmission case) and/or from the load medium into the sound transducer (reception case).

Fig. 2 shows a schematic side sectional view of an impedance matching device 20 according to an exemplary embodiment, in which a plurality of microstructures 22 _i with i = 1,...,6, are arranged, which are arranged as branched channel structures between the sides 14 and 16, with a high number of more than 6 microstructures are arranged. For example, a single channel structure 22 ₁ in the area of side 14 can branch out into a large number of channel structures, for example in the sense of a river delta. A material or the absence of material can be described as at least a local material density ρ ₂ that is different from a material density ρ ₁ of the material 24.

The increasing volume fraction of the microstructures 22 _i enables an overall density of the impedance matching body 10 that is increasingly influenced by the microstructures 22 along the sound passage direction 18a, which can influence or determine the characteristic sound impedance and thus describes an increasing influence on the characteristic sound impedance by such a material.

The microstructures 22 can define cavities. An effective material density of the impedance matching body 12 can be monotonically variable between the sides 14 and 16 through the cavities. The impedance matching material 24 with a density ρ ₁ can increasingly be traversed by the impedance matching material ρ ₂ , so that a variable effective density of the impedance matching body is obtained on a spatial average. The monotonous increase or decrease in the volume of the microstructures can thus lead to a monotonous change in the density of the material 24 in order to bring about the adaptation of the characteristic acoustic impedance. The cavities can, for example, be formed or enclosed by the microstructures. Alternatively or additionally, at least one of the microstructures 22 can define an area outside a cavity, so that the cavity is formed away from the microstructures 22.

As it is based on the Fig. 2 As shown by way of example, the microstructures 22 can define branched microchannels, the number of which varies monotonically between the sides 14 and 16 to effect the change in the density of the material 24.

In other words shows Fig. 2 Microcavities in a layer system whose effective density and thus the characteristic sound impedance are changed by cavities, channels or inclusions. The desired acoustic impedance curve can be generated by connected cavities 22. The largest number of channels and thus the lowest acoustic impedance can be arranged on the medium side of the layer system, ie side 16.

Alternatively or in addition to the number of microchannels, at least one other property such as the shape, the position and/or the volume of the microstructures can also be changed in order to achieve the related properties Fig. 1 to obtain the variable density or material density described. This change in density can be monotonous, as can be achieved, for example, by the monotonically variable number of microchannels described. The change in all properties can be uniform, that is, with the same rate of change along the direction of sound passage. Alternatively, a variable rate of change can be set up. The rate of change of one, several or all properties within the impedance matching body can be determinable, that is, can be predetermined and can be designed advantageously through appropriate acoustic calculations and/or simulations, which can enable good or improved sound transmission. In examples, a positional variance of the microstructures can arise from the spacing ratio of the structures to one another, or from the ratio of the position of the structures relative to one of the outer walls of the impedance matching body. A targeted positioning of the structures in a concentrically changing manner can enable the creation of a focusing layer which has no curvature of the outer walls. In examples, the impedance matching body can have a distance decreasing from the center in the radiation direction between the individual structures.

Alternatively or in addition to the formation of the microstructures as microchannels with the same or variable cross-section, the microchannels can also have other shapes, such as shapes such as spirals, round or non-round drops, cubes or the like. The microstructures can all be uniform but also intentionally different in shape and/or size. Such a shape can describe the microstructure as a whole, but combinations are also possible, such as a microchannel that has a drop in places or areas, a round or non-round cavity or a cube, i.e. i.e., forming or comprising polygonal surfaces and/or a microchannel which runs in a spiral shape. A drop can be understood as a non-linear and/or continuous change in cross-section, with a sphere being one of the possible shapes, but which can also be stretched longitudinally. The shape can alternatively or additionally have a variable shape/cross-section implemented along the, for example, spiral course and/or the exemplary spiral can be connected to further microstructures at at least one end or along a course. This is only to be understood as an example; one or more arbitrary shapes can be combined with one another.

Fig. 3 shows a schematic side sectional view of an impedance matching device 30 according to an exemplary embodiment, in which the microstructures are formed as structures that taper towards the side 14. The tapered structures can have areas _28i of minimal extent, with the areas 28i _of minimum extent being related to the structure extent. For example, the microstructures 22 _i can taper conically, so that the regions 28 can represent the ends or tips of the conical structures. According to other exemplary embodiments, the microstructures are formed individually or in combination, for example pyramid-shaped, conical or otherwise tapered.

In other words illustrated Fig. 3 an embodiment with tapering structures, in which the main material 24 is divided into conically tapering structures, whereby the tapering of the material 24 can take place towards the side 16. The taper can start directly on the sides 14 or 16, but can alternatively also be spaced away from this. The desired acoustic impedance curve is, for example generated by several, conically tapering volumes of the microstructures _22i . This can cause the lowest acoustic impedance of the impedance matching body to be on side 16.

While the exemplary embodiments according to the Fig. 2 and/or the Fig. 3 can be used as GMS adaptation structures, the microstructures 22 can also be used as SMS and/or MMS according to other exemplary embodiments.

Fig. 4a shows a schematic side sectional view of an impedance matching device 40a, in which the impedance matching body is formed such that the microstructures 22 form a lattice structure which extends along a direction perpendicular to the sound passage directions 18a and/or 18b. For example, there is no change in the average density and/or the characteristic sound impedance within the impedance matching body 12 from side 14 to side 16 and vice versa. This means that the impedance matching body 12 can have an on average unchanged or constant acoustic impedance, which is, for example, lower than the higher of the acoustic impedances arranged on the sides 14 and 16 and/or higher than the lower of these acoustic impedances. For example, the microstructures 22 can form a hexagonal grid or a honeycomb structure in the side section shown.

The impedance matching device 40a enables SMS.

Fig. 4b shows a schematic side sectional view of an impedance matching device 40b, in which the microstructures form a hexagonal/triangular pattern, for example by forming several in-plane microstructures, such as the microstructure 22, perpendicular to the sound passage directions 18a and / or 18b and several in different directions perpendicular thereto arranged microstructures that intersect the in-plane microstructure diagonally, either the microstructure 22 ₂ and/or 22 ₃ , which extend in an oblique arrangement between the sides 14 and 16.

Fig. 4c shows a schematic side sectional view of an impedance matching device 40c, in which the microstructures are arranged in a triangular grid pattern, so that cavities 32 have a triangular shape in the side sectional view shown. The microstructures 22 can be formed, for example, from the material 24, whereby the cavities 32 can represent filled or unfilled cavities.

Fig. 4d shows a schematic side sectional view of an impedance matching device 40d, in which the microstructures 22 to 22 ₃ also form a lattice structure, the lattice structure being formed according to a diamond pattern.

The impedance matching devices 40a, 40b, 40c and/or 40d may have a substantially homogeneous or constant acoustic impedance between the sides 14 and 16. An impedance matching device may include an impedance matching body formed in multiple layers and having at least a first layer and a second layer arranged on each other. The first layer can have a first layer characteristic impedance and the second layer can have a second layer characteristic impedance, the two layer characteristic impedances being the same, but preferably different from one another. For this purpose, the same patterns can be used in accordance with Fig. 4a to 4d can be used, for example based on different opening cross sections of the cavities 32 and/or different patterns can be used, for example by arranging different impedance matching bodies 12.

According to the Fig. 4a to 4d The microstructures 22 can form a lattice structure, which is arranged along a direction perpendicular to the sound passage directions and extends along this direction, for example along the x-direction. The cavities 32 may extend along the same or a different direction perpendicular to the sound passage directions 18a and 18b in the impedance matching body, for example along the y-direction. The cavities can have a polygonal cross-section based on an arrangement of the microstructures 22, alternatively the cross-section can also be formed according to a free-form surface, be elliptical or even round.

In other words, they show 4a to 4c the implementation of a microgrid. The adaptation layer system includes a framework-like grid with variable framework elements. The microgrids mentioned are in the Fig. 4a to 4d shown as sectional images of various lattice structures, where Fig. 4a a hexagonal grid, Fig. 4b a hexagonal/triangular grid, Fig. 4c a triangular grid and Fig. 4d show a diamond grid. The grids can be arranged in grid planes, wherein the grid planes can run, for example, parallel to the sides 14 and/or 16, wherein an impedance matching device can have one or more grid planes. The desired acoustic impedance curve can be created using differently aligned and connected connecting pieces. By changing the distances and/or grid structures and/or connecting piece thicknesses the acoustic impedance can be further changed. The lattice structures can be formed as two-dimensional or three-dimensional lattice structures. Three-dimensional lattice structures can be characterized by changing the lattice constant and/or the thickness and shape of the connections. This enables high rigidity compared to tapered structures and/or easy processing with the method since the structure is easy to implement with a developer solution.

Fig. 5 shows a schematic side sectional view of an impedance matching device 50, in which the microstructures 22 to 22 ₃ define an acoustic path 34 between the sides 14 and 16. For example, the acoustic path 34 can run through the cavity 32, which is defined by the microstructures 22 to 22 ₃ . A vacuum, a fluid, for example a gas, and/or a solid can be arranged in the cavity 32, with a material of the microstructures 22 ₁ to 22 ₃ preferably having a higher acoustic impedance than the impedance matching body 12 in a region of the acoustic path, for example the cavity 32. Compared to a direct or shortest path 36 between sides 14 and 16, the acoustic path 34 can provide a travel time extension for sound transmitted through the acoustic path 34. The transit time extension can be provided based on a path extension compared to the direct connection 36, which means that the transit time extension and therefore a phase shift can be obtained due to the longer path or the path extension of the acoustic path 34. The acoustic path 34 may have a plurality or plurality of path sections 38 ₁ to 38 ₄ . Although the impedance matching device 50 is shown such that four path sections 38 ₁ to 38 ₄ are arranged in series one behind the other, a different number of at least one path section, at least two path sections, at least three path sections, at least five path sections, for example six, eight or ten path sections or be implemented more. Parallel path sections can also be arranged with respect to one or more path sections.

The path sections 38 ₁ to 38 ₄ can be arranged individually, in groups or overall perpendicular to the sound passage directions 18a and / or 18b, so that the acoustic path 34 in the area of the path sections 38 ₁ to 38 ₄ runs perpendicular to the sound passage directions 18a and / or 18b or has at least one directional component perpendicular to the sound passage directions 18a and / or 18b. The path sections may extend in different planes of the impedance matching body 12 between sides 14 and 16, for example when the planes are considered to be parallel to sides 14 and/or 16.

The path sections 38 ₁ , 38 ₂ , 38 ₃ and 38 ₄ can each have an acoustically effective cross section 42 ₁ , 42 ₂ , 42 ₃ or 42 ₄ , which is determined by the size or extent of the cavity 32 in the area of the respective path section 38 ₁ up to 38 ₄ can be influenced. For example, the acoustically effective cross section 42 _i of a path section 38 _i can be determined or influenced by a distance between adjacent microstructures 22 ₁ and 22 ₂ , 22 ₂ and 22 ₃ and/or a microstructure 22 ₁ or 22 ₃ to its side 14 or 16 . The acoustically effective cross sections 42 ₁ to 42 ₄ can be the same or different from one another, with, for example, a decreasing acoustic cross section along a sound passage direction 18a or 18b can cause an increase in an acoustic sound characteristic impedance.

A taper 44 ₁ , _{44 2} and/or _{44 3} of the acoustic path 34 or the acoustically effective cross section can be arranged between two possibly successive path sections 38 ₁ and 38 2 , 38 _{2 and} 38 3 and/or 38 ₃ and 38 4 . Such a taper can be obtained, for example, by a distance between the microstructures and boundary structures 46 ₁ and/or 46 ₂ , for example side wall structures. Alternatively, it is also possible to provide a taper 44 between two adjacent microstructures 22, for example between the microstructures 22 ₁ and 22 ₂ to obtain a taper 44 ₄ . For this purpose, microstructures 22 ₄ and/or 22 ₅ can be provided, although other materials and/or dimensions and/or geometries can also be used, as long as these structures have a higher acoustic impedance than the cavity 32 in the area of the corresponding path section. Although the additional arrangement of the microstructures 22 ₄ and 22 ₅ entails a corresponding manufacturing effort, this enables a precise adjustment of the acoustic impedance of the impedance matching device 50. In contrast, the tapers 44 ₁ to 44 ₃ can be manufactured easily, since they are, for example, from a distance between the microstructures 22 ₁ to 22 ₃ to the boundary structures 46 ₁ and/or 46 ₂ can result.

An acoustically effective cross section 42 _i of at least one path section 38 _i can be variable over its axial extent, for example along the x direction. This can be achieved, for example, by a variable dimension of at least one of the microstructures 22 ₁ , 22 ₂ and/or 22 ₃ along the sound passage direction 18a and/or 18b; alternatively or additionally, additional structures can also be provided in the course of the path section 38 _i . The acoustically effective cross sections _42i can be set individually, in groups or as a whole. This means that an acoustically effective cross section of two adjacent path sections can be different from one another.

In other words shows Fig. 5 a coiled structure in which the matching layer system consists of coiled or coiled structures that increase the travel time of the sound wave. In Fig. 5 the wound structures are shown as a section through an elementary cell of a layer system applied to a sound transducer. The desired acoustic impedance curve can be generated by several intertwined channels. This means that the characteristic sound impedance can be influenced by the speed of sound through the wave transit time until the wave arrives on the medium side of the layer system.

Embodiments explained above describe different configurations of the microstructures in the impedance matching body. As stated, each of these embodiments may provide a single-stage, multi-stage, or gradient-like acoustic impedance matching course. The different exemplary embodiments can be combined with one another in any way, so that differently formed microstructures and/or lattice structures can be arranged in different planes perpendicular to the direction of sound passage and/or parallel thereto. This can be done in one piece, for example, by forming the microstructures differently in different areas of the impedance matching body. Alternatively, a multi-piece arrangement can also take place, for example by mechanically and/or acoustically coupling impedance matching bodies according to various exemplary embodiments and each forming a layer of a multi-layer impedance matching body.

Different configurations make it possible for a course of the acoustic impedance between the first side 14 and the second side 16 of the overall impedance matching body to be continuous or discontinuous. An example of a continuous course can be a linear and/or exponential development of the course of the characteristic sound impedance along the direction of sound passage 18a and/or 18b.

Embodiments provide that the impedance matching device is designed such that the impedance matching body has different characteristic sound impedances on the different sides. One of the sides can, for example, be adapted to an acoustic impedance of a MUT acoustic transducer, so that the acoustic impedance of the impedance matching body matches the acoustic impedance of the MUT acoustic transducer within a tolerance range of ±50%, ±25% or ±10%, that is means the values of the acoustic impedance, the acoustic impedance values agree. An exemplary value for this is 1-35 MRayl = 1-35 · 10 ⁶ Ns/m ³ . A range of 1-5 MRayl = 1-5 · 10 ⁶ Ns/m ³ can well apply to membrane oscillators, which include MUT transducers. The range of 1-35 MRayl = 1-35 · 10 ⁶ Ns/m ³ also includes ceramics and composite transducers, for example PZT-based transducer classes. The acoustic impedance on the other side can, if possible, match the acoustic impedance of a target medium or at least be close to it, for example a fluid, such as air.

Fig. 6 shows a schematic block diagram of a converter device 60 according to an exemplary embodiment. The transducer device 60 includes, for example, the impedance matching device 10. The transducer device 60 further includes a sound transducer element 48, which can both be configured to generate a sound wave based on a control signal and, alternatively or additionally, can be configured to generate an electrical one based on an incoming sound wave to provide signal. This means that the transducer element 48 can be implemented as or include a sound actuator and/or sound sensor.

The impedance matching device 10 is coupled, for example, on the side 14 to the sound transducer element 48, for example in that the impedance matching body is mechanically firmly coupled to the sound transducer element 48. For example, the impedance matching device 10 can be deposited on the sound transducer element 48 or vice versa. Although the transducer device 60 is described as having the sound transducer element 48 acoustically coupled to the side 14, the sound transducer element 48 may alternatively also be acoustically coupled to the side 16. The other side 16 or 14 can be configured to be contacted with a medium into which a sound wave is to be emitted or from which a sound wave is to be received. Alternatively, another acoustically effective structure, for example another sound transducer element, can also be acoustically coupled on the other side, so that an impedance adaptation can take place between two sound transducer elements based on the impedance matching device 10.

Preferably, the acoustic coupling between the sound transducer element 48 and the side 14 has a continuous transition of the acoustic impedance, that is, within the tolerance range of ±50%, ±25% or ±10%, the acoustic impedance of the acoustic transducer element 48 is in accordance with the acoustic impedance of the Impedance matching device on side 14.

The sound transducer element 48 may include a piezoelectric ceramic material and/or a composite material. In particular, the sound transducer element 48 may comprise a piezoelectric thin film material, such as PVDF (polyvinylidene fluoride). According to one embodiment, the sound transducer element 48 includes a micromachined ultrasonic transducer, for example a capacitive MUT (CMUT), a piezoelectric MUT (PMUT), or a magnetic MUT (MMUT).

Although the converter device 60 is described in such a way that the impedance matching device 10 is arranged, alternatively or additionally a further and/or different impedance matching device can also be arranged, for example the impedance matching device 10, 20, 30, 40a, 40b, 40c, 40d and/or 50. For example, impedance matching devices can be arranged which have a combination of different layers, each with at least one impedance matching device or impedance matching body, whereby, for example, an impedance matching device 40a, 40b, 40c, 40d can provide a layer of the common body with, at least on a spatial average, constant acoustic characteristic impedance.

In other words, the adaptation structures described can be integrated in one embodiment onto single- and multi-channel, for example air-coupled, CMUT components and CMUT systems in order to increase the converter range, sensitivity and bandwidth. Such systems can be optimized as miniaturized sensors for distance and movement detection as well as imaging and also enable, for example, gesture control in the vehicle interior (automotive) as well as the contactless control of household appliances (consumer), as well as sensor applications in medical technology and integration into mobile devices Applications in service and industrial robots (industry).

Fig. 7 shows a schematic block diagram of a system according to an exemplary embodiment, which includes, for example, the converter device 60 and a control unit 52. The control unit 52 is designed to operate the sound transducer element 48, that is, to provide the sound transducer element 48 with a control signal 54 in order to stimulate the sound transducer element 48 to emit a sound transducer 56 ₁ and/or to send a sound transducer signal 54 ₂ from the sound transducer element 48 received that provides this based on an incoming sound wave 56 ₂ .

The control unit 52 can be designed to operate the sound transducer element 48 in an ultrasonic frequency range, that is, in a frequency range of at least 20 kilohertz. For example, the control unit can be designed to operate the sound transducer element 48 in a frequency range of at least 20 kilohertz and at most 200 megahertz, at least 20 kilohertz and at most 150 megahertz or at least 20 kilohertz and at most 100 megahertz.

Fig. 8 shows a schematic flow diagram of a method 800 according to an exemplary embodiment for producing an impedance matching device, for example the impedance matching device 10, 20, 30, 40a, 40b, 40c, 40d and/or 50.

The method 800 includes a step 810. In step 810, an impedance matching body with a first and an opposite second side is provided. The impedance matching body is designed to adapt an acoustic impedance of a medium contacted on the first side to an acoustic impedance of a sound transducer contacted on the second side, so that the impedance matching body comprises microstructures which have a structural extent of at most 500 nanometers along at least one spatial direction.

For the method 800, the impedance matching body can be produced, for example, by being arranged directly on or on a sound transducer or by producing it as a separate component.

Manufacturing the impedance matching body may include providing a transfer material. A positive form or a negative form of the microstructures can be formed in the transfer material. According to one embodiment, the transfer material comprises a curable polymer material, in particular a polymer material that can be used in connection with multiple photon absorption lithography, for example SU-8 and/or Ormocere. The positive form or the negative form can be created by applying at least two photons to the transfer material at one point, so that a local change in a structural composition of the transfer material is caused there, that is, a hardening or alternatively liquefaction of the polymer material. Multiple photon absorption lithography can provide feature sizes of at most 500 nanometers, at most 300 or at most 100 nanometers.

According to one exemplary embodiment, the transfer material comprises a metal material in which the positive form or the negative form of the microstructures can be obtained, for example, by an ablation process through multiple photon absorption, in particular a laser ablation process. However, the transfer material is not limited to a metal material but can also have a different material in a solid or liquid state for the (laser) ablation method by multiple photon absorption according to further exemplary embodiments and, for example, a fluid, for example a polymerizable fluid or a Fluid in a solid state, a semiconductor material, at least one organic compound and / or a ceramic material.

Microstructures with different materials can be combined with one another, so that both the use of a metal material and the use of a polymer material as well as the use of the fluid in a solid or liquid state and / or the ceramic material in a solid or liquid state can be combined with one another in any way, for example different layers of the impedance matching body.

The positive form or negative form obtained can be further processed. For this purpose, the production can, for example, include a step of coating the positive mold or negative mold. Alternatively or additionally, the positive form or negative form can be inverted. Inverting can be understood as a change in the material of the positive form or negative form. For example, the positive mold or negative mold can be coated, then the material of the positive mold or negative mold can be removed, for example using a solvent or an etching process, and then the resulting cavity can be refilled or filled with any material. The small structure sizes obtained by the multiple photon lithography process and/or laser ablation through the multiple photon absorption can be retained, so that such small structure sizes can be produced even in materials that cannot be processed with such precision, for example, using subtractive processes can. The post-processing can also include casting the positive mold or negative mold. Casting can be understood as a transfer of the mold from the positive mold or negative mold into a corresponding other mold. Alternatively or additionally, the positive mold or negative mold can be enclosed, in which, for example, the previously produced positive mold or negative mold is retained as a core. With exemplary reference to Fig. 3 For example, the material 24 can be hardened by a lithography process and used as a positive mold, with filling with other materials being possible. Alternatively or additionally, for example, the impedance matching body 30 can be obtained by creating cavities into which the material 24 is later filled. This means that producing the impedance matching body can include creating microstructures in such a way that they are formed as tapered microstructures, which applies both to the areas with the material 24 and to the spaces between them.

According to one embodiment, producing the impedance matching body may include creating at least one cavity that is arranged in the impedance matching body and can cause a change in an effective density of the impedance matching body there. The creation of a cavity can include both the hardening for the later retention of a material and the removal of a material and describes, for example, the creation of different materials and / or densities in the impedance matching body in a spatial means for changing the density of the impedance matching body in the spatial means.

As it is in connection with the Figs. 4a, 4b, 4c and 4d is described, producing the impedance matching body may include producing the microstructures as a lattice structure. The grid structure may be formed from an impedance matching material of the impedance matching body and define cavities that extend along the direction perpendicular to the sound passage direction in the impedance matching body. The cavities can, for example, have a polygonal cross section with three, four, five or six, seven or a higher number of corners and/or edges, whereby the structures can be combined with one another. The microstructures in the Fig. 4a, 4b, 4c and/or 4d can thus be formed from cured polymer material and/or the metal material, but can also include a material which has been introduced into a corresponding negative mold, wherein the transfer material can later be released or remain for defining these structures.

According to an embodiment which does not fall within the scope of the patent claims, the manufacturing includes producing the microstructures such that the microstructures define an acoustic path between the sides of the impedance matching body, as is the case, for example, in the context of Fig. 5 is described. A material of the microstructures can have a higher acoustic impedance than the impedance matching body in a region of the acoustic path. The acoustic path may provide a travel time extension for sound transmitted through the acoustic path compared to a direct connection between the first side and the second side.

In other words, an approach of the present invention offers the advantage, particularly over known microstructures and methods for producing them, of enabling three-dimensional structures of almost any shape and, above all, generous undercuts. According to one embodiment, the impedance matching body includes an undercut, that is, it includes a mold with a portion that would prevent removal from a mold or impression mold. According to the manufacturing methods described, this is possible in that any three-dimensional structures can be produced using the ablation methods and/or lithography methods.

An exemplary manufacturing process is given in EP 1 084 454 B1 described. According to an exemplary embodiment of the approach described, a polymerization process using multi-photon absorption can be used to produce microstructures with specific acoustic impedances or acoustic impedance curves. Methods described herein allow the creation of feature sizes of at most 500 nanometers and less, for example at most 300 nanometers or at most 100 nanometers or less. The processes offer a high level of flexibility in the design and production of the microstructures for acoustic impedance matching.

The properties mentioned offer the advantage of generating precise, exponential sound characteristics and thus ensuring an ideal coupling between the ultrasonic transducer and the load media. In addition, the high resolution (low structural size) can be used to greatly reduce the characteristic sound impedance over a short distance and thus adapt it to a medium such as. B. Adjust air. Diffraction effects and other damping effects, such as those normally introduced by microstructures, can be reduced or even prevented by targeted design of the microstructures. Another advantage of the high precision is the ability to create a very precise layer system height, which has a strong influence on the transmission behavior. A further advantage is that intermediate and adhesion materials, which were necessary between individual impedance layers of different matching layers in previous solutions, can be dispensed with, although this does not preclude their arrangement. However, this eliminates their negative and unwanted influences on sound transmission and eliminates complex and labor-intensive deposition steps. The methods described can in principle be applied to any type of sound transducer. Advantages lie in the precision that can be achieved particularly with miniaturized sound transducer elements and transducer systems and thus contribute to added value, particularly on MEMS-based sound transducers, sound sensors and sound actuators.

Although some aspects have been described in connection with a device, it is understood that these aspects also represent a description of the corresponding method, so that a block or a component of a device is also to be understood as a corresponding method step or as a feature of a method step. Analogously, aspects that have been described in connection with or as a method step also represent a description of a corresponding block or detail or feature of a corresponding device.

1. [1] V. T. Rathod, "A Review of Acoustic Impedance Matching Techniques for Piezoelectric Sensors and Transducers." Sensors (Basel, Switzerland) vol. 20,14 4051. 21 Jul. 2020 .
2. [2] T. R. GURURAJA, WALTER A. SCHULZE, LESLIE E. CROSS, and AND ROBERT E. NEWNHAM, "Piezoelectric Composite Materials for Ultrasonic Transducer Applications. Part ii: Evaluation of Ultrasonic Medical Applications "
3. [3] Ergun et a/., "Capacitive Micromachined Ultrasonic Transducers: Theory and Technology," J. Aerosp. Eng, vol. 16, no. 2, 2003 .
4. [4] R. Lerch, G. M. Sessler, and D. Wolf, Technische Akustik: Grundlagen und Anwendungen. Berlin: Springer, 2009 .
5. [5] O. Krauß, R. Gerlach, and J. Fricke, "Experimental and theoretical investigations of SiOZ-aerogel matched piezo-transducers," Ultrasonics, vol. 32, no. 3, pp. 217-222, 1994 .
6. [6] T. Yano, M. Tone, and A. Fukumoto, "Range Finding and Surface Characterization Using High-Frequency Air Transducers," IEEE Trans. Ultrason., Ferroe/ect., Freq. Contr., vol. 34, no. 2, pp. 232-236, 1987 .
7. [7] T. Manh, A.-T. T. Nguyen, T. F. Johansen, and L. Hoff, "Microfabrication of Stacks of acoustic matching layers for 15 MHz Ultrasonic transducers," (eng), U/trasonics, vol. 54, no. 2, pp. 614-620, 2014 .
8. [8] M. I. Haller and B. T. Khuri-Yakub, "Micromachined Ultrasonic Materials, " Ultrasonics Symposium, 1991 .
9. [9] Z. Li et a/., "Broadband gradient impedance matching using an acoustic metamaterial for Ultrasonic transducers," (eng), Scientific reports, vol. 7, p. 42863, 2017 .
10. [10] G.-H. Feng and W.-F. Liu, "A spherically-shaped PZT thin film Ultrasonic transducer with an acoustic impedance gradient matching layer based on a micromachined periodically structured flexible substrate," Sensors (Basel, Switzerland), vol. 13, no. 10, pp. 13543-13559, 2013 .

The embodiments described above are merely illustrative of the principles of the present invention. It will be understood that modifications and variations of the arrangements and details described herein will occur to others skilled in the art. Therefore, it is intended that the invention be limited only by the scope of the following claims and not by the specific details presented from the description and explanation of the exemplary embodiments herein.

1. [1] VT Rathod, "A Review of Acoustic Impedance Matching Techniques for Piezoelectric Sensors and Transducers." Sensors (Basel, Switzerland) vol. 20.14 4051. July 21, 2020 .
2. [2] TR GURURAJA, WALTER A. SCHULZE, LESLIE E. CROSS, and AND ROBERT E. NEWNHAM, "Piezoelectric Composite Materials for Ultrasonic Transducer Applications. Part ii: Evaluation of Ultrasonic Medical Applications "
3. [3] Ergun et a/., "Capacitive Micromachined Ultrasonic Transducers: Theory and Technology," J. Aerosp. Eng, vol. 16, no. 2, 2003 .
4. [4] R. Lerch, GM Sessler, and D. Wolf, Technical Acoustics: Basics and Applications. Berlin: Springer, 2009 .
5. [5] O. Krauß, R. Gerlach, and J. Fricke, "Experimental and theoretical investigations of SiOZ-airgel matched piezo-transducers," Ultrasonics, vol. 32, no. 3, pp. 217-222, 1994 .
6. [6] T. Yano, M. Tone, and A. Fukumoto, "Range Finding and Surface Characterization Using High-Frequency Air Transducers," IEEE Trans. Ultrason., Ferroe/ect., Freq. Contr., vol. 34, no. 2, pp. 232-236, 1987 .
7. [7] T. Manh, A.-TT Nguyen, TF Johansen, and L. Hoff, "Microfabrication of stacks of acoustic matching layers for 15 MHz ultrasonic transducers," (eng), U/trasonics, vol. 54, no. 2, pp. 614-620, 2014 .
8. [8th] MI Haller and BT Khuri-Yakub, "Micromachined Ultrasonic Materials," Ultrasonics Symposium, 1991 .
9. [9] Z. Li et a/., "Broadband gradient impedance matching using an acoustic metamaterial for ultrasonic transducers," (eng), Scientific reports, vol. 7, p. 42863, 2017 .
10. [10] G.-H. Feng and W.-F. Liu, "A spherically-shaped PZT thin film ultrasonic transducer with an acoustic impedance gradient matching layer based on a micromachined periodically structured flexible substrate," Sensors (Basel, Switzerland), vol. 13, no. 10, pp. 13543-13559, 2013 .

Claims (9)

1. Impedance matching device for matching a characteristic acoustic impedance comprising:

   an impedance matching body (12) having a first side (14) and an opposite second side (16),

   the impedance matching device being configured to match a characteristic acoustic impedance of a medium contacted on the second side (16) to a characteristic acoustic impedance of a sound transducer (48) contacted on the first side (14);

   characterized in that

   the impedance matching body (12) comprises microchannels (22) having structural extents (26) of at most 500 nm along at least one spatial direction;

   wherein the microchannels (22) are branched microchannels, the number of which is monotonically variable between the first and second sides (16); and wherein the microchannels (22) form cavities in the impedance matching body, wherein an effective material density of an impedance matching material of the impedance matching body (12) is monotonically variable between the first side (14) and the second side (16) due to a monotonic increase or monotonic decrease of a volume of the cavities and causes matching of the characteristic acoustic impedance; or

   wherein the microchannels (22) are formed as structures tapering towards the first side (14) or towards the second side (16), and have the structural extent (26) at least in a region of minimum extent (28).
2. Impedance matching device as claimed in claim 1, wherein the microchannels (22) connect the first side (14) and the second side (16) with each other.
3. Impedance matching device as claimed in claim 1 or 2, wherein the microchannels (22) are formed to comprise an impedance matching material comprising a metal material, a semi-conductor material, an organic compound, a ceramic material or comprising a polymer material.
4. Impedance matching device as claimed in any of the previous claims, wherein the microchannels (22) are formed to comprise a first impedance matching material, wherein a second impedance matching material (24) is disposed in intermediate regions between the microchannels (22);
   wherein the structural extent (26) of at least one microchannel (22) is perpendicular to an axial direction of extension of the microchannels (22).
5. Impedance matching device as claimed in any of the previous claims, wherein the impedance matching body (12) has an undercut.
6. Transducer device comprising:

   an impedance matching device as claimed in any of the previous claims; and

   a sound transducer element (48) acoustically coupled, by acoustic coupling, to either the first side (14) or the second side (16) of the impedance matching body (12).
7. Transducer device as claimed in claim 6, wherein the acoustic coupling has a continuous transition of the characteristic acoustic impedance.
8. System comprising:

   a transducer device as claimed in claim 6 or 7; and

   a control unit (52) configured to operate the sound transducer element (48).
9. Method (800) of manufacturing an impedance matching device, comprising the step of:

   providing (810) an impedance matching body (12) comprising a first side and an opposite second side (16) and configured to match a characteristic acoustic impedance of a medium contacted on the second side (16) to a characteristic acoustic impedance of a sound transducer (48) contacted on the first side (14);

   characterized in that

   the impedance matching body (12) comprises microchannels (22) having structural extents (26) of at most 500 nm along at least one spatial direction;

   such that the microchannels (22) are branched microchannels, the number of which is monotonically variable between the first and second sides (16); and such that the microchannels (22) form cavities in the impedance matching body, such that an effective material density of an impedance matching material of the impedance matching body (12) is monotonically variable between the first side (14) and the second side (16) due to a monotonic increase or monotonic decrease of a volume of the cavities and causes matching of the characteristic acoustic impedance; or

   such that the microchannels (22) are formed as structures tapering towards the first side (14) or towards the second side (16), and have the structural extent (26) at least in a region of minimum extent (28).

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