An ultrasonic transducer for transmitting and / or receiving ultrasonic waves

Abstract

The invention relates to an ultrasonic transducer (1) for emitting and / or receiving ultrasonic waves, comprising: a carrier layer (2); a matching layer (A) for impedance matching to a fluid (F); a piezoelectric element (4) arranged between the carrier layer (2) and the matching layer (A); a first electrode (3a) between the carrier layer (2) and the piezoelectric element (4), which first electrode provides a first electrical contact (K1) of the piezoelectric element (4), wherein the matching layer (A) is formed by a flexible circuit board (Lp) and the flexible circuit board (Lp) provides a second electrical contact (K2) of the piezoelectric element (4).

Description

TECHNICAL FIELD

[0001] The present invention relates to an ultrasonic transducer for emitting and / or receiving ultrasonic waves. BACKGROUND

[0002] For example, in order to determine the flow rate of a fluid in a pipe, preferably a circular pipe, in addition to different physical principles, there is also the use of ultrasonic waves emitted into the pipe. By means of a time-of-flight difference method it is possible to determine the flow rate of the flowing fluid and thus the flow rate of the flow.

[0003] Here, the ultrasonic wave packets are respectively emitted or received by one of two opposing ultrasonic transducers. The ultrasonic transducers are arranged opposite each other on the pipe wall, spaced apart in the flow direction and define a measurement path which is thus at an angle not equal to 90° to the flow of the fluid.

[0004] The ultrasonic wave packets propagating through the fluid accelerate in the flow direction and decelerate against the flow direction. The resulting time-of-flight difference is calculated with the aid of geometric variables into an average fluid velocity by means of which the flow rate of the flowing fluid is determined.

[0005] An important and challenging field of application is the gas meter for natural gas pipelines, in which, due to the huge gas quantities and raw material value, even the smallest deviation in measurement accuracy leads to a significant value difference between the actually delivered quantity and the measured quantity. This leads to a huge monetary difference.

[0006] Since gases generally have a much lower acoustic impedance than solids, it is very important for the measurement of gases by means of ultrasonic technology that the ultrasonic waves of the ultrasonic transducer for the measurement are coupled into the gas without large energy losses. That is to say, in the case of ultrasonic waves of the ultrasonic transducer being coupled into the gas with high energy losses, the measurement accuracy of the ultrasonic transducer is greatly reduced.

[0007] Therefore, the optimal coupling of the ultrasonic waves of the ultrasonic transducer into the gas is an important property of the ultrasonic transducer in order to meet the required measurement accuracy of the ultrasonic transducer in this large gas quantity measurement field.

[0008] For example, a basically suitable ultrasonic transducer is known from EP 0 119 855 B2 and essentially consists of the following main elements listed in the following order:

[0009] - a carrier layer, also commonly referred to as "backing layer", which is usually made of an epoxy-based material;

[0010] - a first electrode, which is arranged on the carrier layer;

[0011] - a piezoelectric element, which is coupled to the first electrode and serves to generate ultrasonic waves to be emitted;

[0012] - a second electrode, which is coupled to the piezoelectric element on the other side and, together with the first electrode, applies a voltage to the piezoelectric element, thereby exciting the piezoelectric element to vibrate to generate ultrasonic waves; and

[0013] - a matching layer, also commonly referred to as "matching-layer", which is arranged on the second electrode and effects an impedance match between the piezoelectric element and the fluid or gas, in order to couple the generated ultrasonic waves into the gas or to decouple them from the gas.

[0014] In the manufacture of the ultrasonic transducer, the different process steps for applying the layer thicknesses in the range of 100 pm to 500 pm represent a high complexity, resulting in high production costs.

[0015] Furthermore, the precise reproducibility of the ultrasonic transducer is only guaranteed with high complexity and high costs. Furthermore, the electrical contacting of the piezoelectric element via the first electrode and the second electrode is difficult to achieve due to the separate process steps, which in turn constitutes a negative factor for the reproducibility.

[0016] Since the matching layer of the ultrasonic transducer is exposed to the fluid to be measured, in the known ultrasonic transducers an additional protective layer is provided for the matching layer, which on the one hand protects the matching layer from, for example, mechanical damage or contamination, but on the other hand deteriorates the impedance match of the matching layer. In order to prevent the deterioration, the protective layer has to be composed of a special composite material or specially manufactured. SUMMARY

[0017] It is the task of the present invention to provide an ultrasonic transducer for emitting and / or receiving ultrasonic waves in a fluid, which can be manufactured simply and thus cost-effectively.

[0018] According to the invention, this task is achieved by an ultrasonic transducer having the features described below.

[0019] Here, for the transmission and / or reception of ultrasonic waves in a fluid, in particular a gas, the ultrasonic transducer comprises a carrier layer, a matching layer for impedance matching to the fluid, a piezoelectric element arranged between the carrier layer and the matching layer, a first electrode between the carrier layer and the piezoelectric element, wherein the first electrode provides a first electrical contact of the piezoelectric element, and wherein the matching layer is formed by a flexible circuit board, and the flexible circuit board provides a second electrical contact of the piezoelectric element.

[0020] The resulting technical advantage is that the matching layer composed of the flexible circuit board simultaneously forms a protective layer, so that no special composite material or no special protective layer has to be manufactured.

[0021] According to a preferred embodiment, the flexible circuit board comprises at least one electrically conductive layer and at least one electrically non-conductive base layer, wherein the electrically conductive layer of the flexible circuit board forms a second electrode for the second electrical contact. Thereby, in comparison to the described prior art, a separate second electrode can advantageously be dispensed with, so that material costs for manufacturing the ultrasonic transducer can be reduced.

[0022] Furthermore, according to a preferred embodiment, the electrically conductive layer is divided into partial surfaces, wherein each partial surface forms a separate electrical contact. This enables a simple electrical contacting of the fluid-facing side of the piezoelectric element, thereby significantly additionally simplifying the manufacturing process. In particular, the piezoelectric element is composed of a plurality of individual elements, wherein each individual element has a corresponding separate contact to the flexible circuit board. Thereby, an ultrasonic transducer composed of individually controllable individual elements is advantageously simply provided, so that the ultrasonic transducer is configured as a transducer array, wherein the individual elements can be operated individually.

[0023] Furthermore, in particular, the second contact is configured as a full-surface or as a point-like, so that the manufacturing of the ultrasonic transducer is further simplified. Here, "full-surface contact" means that the entire electric layer of the flexible circuit board is electrically connected to the piezoelectric element by means of, for example, a contact paste. Here, "point-like contact" means that at least one selected point of the electrically conductive layer of the flexible circuit board is connected to the piezoelectric element.

[0024] Preferably, the electrically conductive layer of the flexible circuit board is adapted to the structure of the piezoelectric element, so that the flexible circuit board, which is configured as a matching layer and a protective layer at the same time, has an improved mechanical stiffness, wherein the shape of the flexible circuit board can be more simply adapted to the required shape of the ultrasonic transducer. In other words, the flexible circuit board can more easily absorb and compensate slight deformations (e.g. bending) when manufacturing the ultrasonic transducer, so that the accuracy of manufacturing the ultrasonic transducer and thus the reproducibility on an industrial scale is ensured.

[0025] Since the flexible circuit board as a matching layer is in direct contact with the fluid (usually a gas) to be measured, the flexible circuit board advantageously has a base layer made of polyimide, which on the one hand provides an acoustic impedance between the acoustic impedance of the piezoelectric element and the acoustic impedance of the gas and on the other hand has a high insensitivity to environmental influences, in particular abrasion and contamination.

[0026] Since the acoustic impedance of the flexible circuit board is in the range between the acoustic impedance of the piezoelectric element and the acoustic impedance of the fluid, a simpler impedance matching between the ultrasonic transducer and the fluid to be measured can be carried out. Advantageously, the thickness of the flexible circuit board corresponds in particular to about 1 / 10 to 1 / 4 of the wavelength of the ultrasonic waves, preferably approximately in the range of about 100 pm to 300 pm. Here, the mentioned wavelength of the ultrasonic waves corresponds to the wavelength of the ultrasonic waves transmitted within the flexible circuit board at the operating frequency of the ultrasonic transducer.

[0027] Furthermore, according to a preferred embodiment, the flexible circuit board has a protective layer on the side facing away from the piezoelectric element, in particular a protective layer made of copper, steel, gold or aluminum, whereby the protective properties of the flexible circuit board can be improved.

[0028] In order to further simplify the production of the ultrasonic transducer, the flexible circuit board also forms a terminal lug for the electrical connection. Thereby, the flexible circuit board can be more easily electrically contacted when producing the ultrasonic transducer.

[0029] Preferred embodiments and improvements of the present application as well as further advantages are known from the following description and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0030] The present application will be explained in detail below with reference to the drawings and on the basis of embodiments. In the drawings:

[0031] Figure 1 a schematic cross-sectional view of a preferred embodiment of an ultrasonic transducer according to the present application is shown;

[0032] Figure 1A a schematic detail view of an enlarged portion shown in dashed lines in the embodiment of Figure 1

[0033] Figure 2 a schematic cross-sectional view of another preferred embodiment of an ultrasonic transducer according to the present application is shown;

[0034] Figure 2A a schematic detail view of an enlarged portion of the embodiment of Figure 2

[0035] Figure 3 a schematic view of a preferred embodiment of a flexible circuit board of an ultrasonic transducer according to the present application is shown. DETAILED DESCRIPTION

[0036] In Figure 1 a schematic cross-sectional view of a preferred embodiment of an ultrasonic transducer 1 according to the present application is shown, which can be used, for example, for measuring physical quantities of a fluid F, in particular a gas.

[0037] The ultrasonic transducer 1 according to the present application has a carrier layer 2, which is also referred to as "back layer" and serves to minimize the ultrasonic radiation on the side of the ultrasonic transducer 1 facing away from the fluid F and to reduce the back oscillation of the piezoelectric element (to be described in detail later). Preferably, the carrier layer 2 is made of an epoxy-based material.

[0038] On the carrier layer 2, a first electrode 3a is arranged, which is usually configured as a thin layer made of, for example, silver, tin bronze (CuSn) or the like. Preferably, the thickness of the first electrode 3a is less than 10 pm.​​

[0039] On the first electrode 3a a piezoelectric element 4 is arranged, the thickness resonance of which corresponds to the desired frequency of the ultrasound to be emitted for the measurement in the fluid F.

[0040] The first electrode 3a is thus arranged between the carrier layer 2 and the piezoelectric element 4 and provides a first electrical contact K1 of the piezoelectric element 4, wherein the side of the piezoelectric element 4 facing the carrier layer 2 is connected via the first electrical contact K1 with a not shown voltage source by means of a schematically shown line L1.

[0041] On the side of the piezoelectric element 4 facing away from the first electrode 3a a matching layer A is arranged, which serves for impedance matching with the fluid F. In other words, the acoustic purpose of the matching layer A is to minimize the impedance difference between the acoustic impedance of the fluid F into which the ultrasound is to be radiated and the acoustic impedance of the piezoelectric element 4, so that the so-called impedance step between the ultrasound transducer 1 and the fluid F is not too large. Thereby, energy can be effectively transferred into the fluid F, so that a more precise measurement can be achieved.

[0042] According to the invention, the matching layer A is formed by a flexible circuit board Lp, which also provides a second electrical contact K2 of the piezoelectric element 4.

[0043] By means of the second electrical contact K2 of the flexible circuit board Lp, the side of the piezoelectric element 4 facing the fluid F is also connected with a not shown voltage source, so that by means of the first electrical contact K1 of the first electrode 3a and by means of the second electrical contact K2 of the flexible circuit board Lp a voltage can be applied to the piezoelectric element 4 in order to vibrate the piezoelectric element 4 and in turn generate ultrasound waves.

[0044] As Figure 1 is shown, the flexible circuit board Lp is in direct contact with the fluid F, so that the flexible circuit board Lp is not only the matching layer A but also a protective layer of the ultrasound transducer 1. Thereby, the number of components to be used can be reduced, so that component costs and manufacturing costs can be reduced by a simplified manufacturing process.

[0045] Figure 1A An enlarged schematic detail view of the preferred embodiment of the ultrasound transducer 1 is shown, which is described in detail in Figure 1 , wherein the flexible circuit board Lp particularly comprises at least one electrically conductive layer 5 and at least one electrically non-conductive base layer 6. Here, the electrically conductive layer 5 of the flexible circuit board Lp forms a second electrode for the second electrical contact K2 of the piezoelectric element 4 and the electrically non-conductive base layer 6 forms a matching layer and a protective layer for the ultrasound transducer 1. Preferably, the electrically conductive layer 5 of the flexible circuit board Lp can be a conductor path of the flexible circuit board Lp, for example made of copper.

[0046] In other words, the conductor path of the flexible circuit board Lp acts as a second electrode for the piezoelectric element 4, so that a voltage can be applied to the piezoelectric element 4 via the first electrode 3a and the conductive layer 5 of the flexible circuit board Lp.

[0047] As already mentioned, the base layer 6 of the flexible circuit board Lp facing the fluid F serves as a matching layer A, while also serving as a protective layer for the ultrasonic transducer 1, wherein the base layer 6 is advantageously made of polyimide, so that the base layer on the one hand enables a good impedance matching to the gas and on the other hand has a high insensitivity to, for example, mechanical or chemical abrasion or contamination.

[0048] In Figure 2 a schematic sectional view of a further preferred embodiment of the ultrasonic transducer 1 according to the application is shown, wherein the same components as in the embodiment shown in Figure 1 have the same reference numerals.

[0049] In this embodiment, a second electrode 3b is provided, which, like the first electrode 3a, is preferably composed of a thin layer, wherein the thin layer is composed of, for example, silver, tin bronze (CuSn) or the like. Preferably, the thickness of the second electrode 3b is less than 10 pm, like the first electrode 3a. Here, the second electrode 3b is electrically connected to the conductive layer 5 of the flexible circuit board Lp, as shown in Figure 2A , so that the flexible circuit board Lp together with the second electrode 3b provides a second electrical contact K2 of the piezoelectric element 4.

[0050] The possibility of an electrical connection between the second electrode 3b and the conductive layer 5 of the flexible circuit board Lp simplifies the manufacture of the ultrasonic transducer 1. The manufacturing steps can be carried out more simply and can be exchanged in the order in which they are carried out, i.e. first the second electrode 3b is arranged on the piezoelectric element 4 and then the electrical connection between the second electrode 3b and the conductive layer 5 of the flexible circuit board Lp is made, or first the electrical connection between the second electrode 3b and the conductive layer 5 of the flexible circuit board Lp is made and then the second electrode 3b is arranged on the piezoelectric element 4 together with the flexible circuit board Lp.

[0051] Furthermore, in this embodiment the piezoelectric element 4 is composed of a plurality of individual elements 4a, which each have a separate contact (not shown in detail) to the flexible circuit board Lp. To this end, the conductive layer 5 of the flexible circuit board Lp is divided into partial surfaces, wherein each partial surface enables a separate electrical contact. Thereby, the piezoelectric element 4 with the individual elements 4a can be used as a transducer array.

[0052] The conductive layer 5 of the flexible circuit board Lp can be adapted to the structure of the piezoelectric element 4, so that the flexible circuit board Lp has an improved mechanical stiffness.

[0053] Figure 3A schematic diagram of a preferred embodiment of a flexible circuit board Lp of an ultrasonic transducer 1 according to the present application is shown, wherein the flexible circuit board Lp has a circular main portion, which is attached to the piezoelectric element 4. Here, the flexible circuit board Lp is preferably fixed on the piezoelectric element 4 by soldering (Löten); gluing with an electrically conductive or non-conductive adhesive; fixing (anheften) with a contact gel or a contact grease; or welding (Schweißen).

[0054] In the shown embodiment of the flexible circuit board Lp, the flexible circuit board Lp has a terminal lug 7 for an electrical connection with a not shown voltage source. As described before, the circuit board Lp has an electrically conductive layer 5, which forms the second contact K2 for the piezoelectric element 4.

[0055] The terminal lug 7 is simply a part of the circuit board Lp and thus also comprises the base layer 6 and the electrically conductive layer 5, through which the voltage can be delivered from the voltage source.

[0056] The electrically conductive layer 5 is protected by the base layer 6 on the outside, i.e. on the side facing away from the piezoelectric element 4. In order to improve the protective properties of the base layer 6, the base layer can be composed of a plurality of non-conductive and conductive layers, so that in particular a not shown protective layer is provided, in particular made of copper, steel, gold or aluminum.

[0057] Despite all layers, the thickness of the flexible circuit board Lp preferably corresponds to about 1 / 10 to 1 / 4 of the wavelength of the ultrasound waves and in particular lies in the range of about 100 pm to 300 pm. Since the flexible circuit board already has the base layer and the electrically conductive layer required by the present application itself, the manufacturing process of the ultrasonic transducer 1 according to the present application is simplified, since a plurality of coating steps can be saved.

[0058] List of reference signs

[0059]

Claims

1. An ultrasonic transducer (1) for emitting and / or receiving ultrasonic waves in a fluid (F), comprising: Carrier layer (2) Matching layer (A), the matching layer being used for impedance matching with the fluid (F), A piezoelectric element (4) is disposed between the carrier layer (2) and the matching layer (A). A first electrode (3a) is located between the carrier layer (2) and the piezoelectric element (4), and the first electrode provides a first electrical contact (K1) of the piezoelectric element (4). The second electrode (3b) forms the second electrical contact (K2) of the piezoelectric element (4). The matching layer (A) is formed of a flexible circuit board (Lp). Furthermore, the flexible circuit board (Lp) includes at least one conductive layer (5) and at least one non-conductive base layer (6). Its features are, The conductive layer (5) of the flexible circuit board (Lp) is a copper conductor path of the flexible circuit board (Lp), and The conductor path of the flexible circuit board (Lp) serves as the second electrode (3b).

2. The ultrasonic transducer (1) according to claim 1, characterized in that, The flexible circuit board (Lp) is structurally adapted to the piezoelectric element.

3. The ultrasonic transducer (1) according to claim 1, characterized in that, The flexible circuit board (Lp) has a base layer (6) made of polyimide.

4. The ultrasonic transducer (1) according to claim 2, characterized in that, The flexible circuit board (Lp) has a base layer (6) made of polyimide.

5. The ultrasonic transducer (1) according to any one of claims 1-4, characterized in that, The flexible circuit board (Lp) has a protective layer on the surface facing away from the piezoelectric element (4).

6. The ultrasonic transducer (1) according to claim 5, characterized in that, The protective layer is made of copper, steel, gold, or aluminum.

7. The ultrasonic transducer (1) according to any one of claims 1-4 and 6, characterized in that, The piezoelectric element (4) is composed of a plurality of individual elements (4a), wherein each individual element (4a) has a corresponding individual contact with the flexible circuit board (Lp).

8. The ultrasonic transducer (1) according to any one of claims 1-4 and 6, characterized in that, The flexible circuit board (Lp) has terminal pieces (7) for electrical connection.

9. The ultrasonic transducer (1) according to any one of claims 1-4 and 6, characterized in that, The acoustic impedance of the flexible circuit board (Lp) is within the range between the acoustic impedance of the piezoelectric element (4) and the acoustic impedance of the fluid (F).

10. The ultrasonic transducer (1) according to any one of claims 1-4 and 6, characterized in that, The thickness of the flexible circuit board (Lp) corresponds to 1 / 10 to 1 / 4 of the ultrasonic wave length.

11. The ultrasonic transducer (1) according to any one of claims 1-4 and 6, characterized in that, The thickness of the flexible circuit board (Lp) is in the range of 100µm to 300µm.

12. The ultrasonic transducer (1) according to any one of claims 1-4 and 6, characterized in that, The flexible circuit board (Lp) is attached to the piezoelectric element (4) by means of: brazing; bonding with conductive or non-conductive adhesive; fixing with contact gel or contact grease; or fusion welding.

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