DE102016115199B4 - Ultrasonic sensor for determining or monitoring a process variable of a medium in automation technology - Google Patents

Abstract

Ultrasonic sensor (4) for determining or monitoring a process variable of a medium (2) in automation technology, with a transmitter/receiver unit (9) for transmitting and/or receiving ultrasonic signals, with a coupling unit via which the transmitted ultrasonic signals are transmitted from the transmitter/ receiving unit (9) to an amplitude transformation unit (10) and the received ultrasonic signals are coupled from the amplitude transformation unit (10) to the transmitter/receiver unit (9), the amplitude transformation unit (10) having a first amplitude transformation component (11) with a first one in the emission direction the cone (14) that widens in cross-section of the ultrasonic signals and at least one second amplitude transformation component (12) with a second cone (15) that narrows in cross-section in the direction of emission of the ultrasonic signals, the second cone (15) being arranged inside the first cone (14). and wherein a front membrane (13) is provided on the end regions (16, 17) of the first cone (14) and of the second cone (15) pointing in the emission direction.

Description

The invention relates to an ultrasonic sensor for determining or monitoring a process variable of a medium in automation technology.

Ultrasonic sensors are used, among other things, in ultrasonic flowmeters. Ultrasonic flow measuring devices determine or monitor the volume and/or mass flow of a fluid medium that passes through a pipeline in a defined flow direction. The fluid medium is a liquid or a gas. Furthermore, ultrasonic test sensors for the acoustic inspection of workpieces have become known.

An ultrasonic flowmeter working according to the time-of-flight consists of at least two ultrasonic sensors, each of which is fastened in an opening in the wall of a measuring tube. With this so-called inline flow meter, the measuring tube is fitted into the pipeline. At least two ultrasonic sensors are offset from one another in the direction of flow of the medium in such a way that the ultrasonic signals or ultrasonic waves emitted by one ultrasonic sensor are received by the other ultrasonic sensor. The ultrasonic sensors are operated alternately as a transmitter and receiver unit. A control/evaluation unit, usually at least one microcontroller with appropriate software, determines the volume and/or mass flow of the fluid medium in the pipeline or in the measuring tube based on the transit time difference of the ultrasonic signals in the direction of flow and against the direction of flow. Corresponding ultrasonic flow measuring devices are offered and sold by the applicant in different versions for different applications. The applicant's flowmeters are called, for example: Prosonic Flow 92F, 93C or B200. Also known are ultrasonic flowmeters that work according to the Doppler principle and can only work with an ultrasonic sensor.

An electromechanical converter, which is usually at least one piezoelectric element, serves as the transmitting and/or receiving unit. The electromechanical converter is arranged in a pot-shaped housing whose end face facing the medium is closed by a membrane at the end. Impedance matching between the ultrasonic sensor and the medium takes place via at least one suitably configured matching layer.

The DE 10 2008 055 167 A1 discloses an ultrasonic measuring system with inexpensive, interchangeable measuring tubes. The measuring system has up to four ultrasonic transducers, each of which is arranged in a pot-shaped ultrasonic transducer mount. The pot-shaped ultrasonic transducer recordings take on the function of coupling the ultrasonic signals into the measurement medium.

The DE 10 2014 115 592 A1 discloses an ultrasonic flowmeter with a vibration decoupling element for fixing at least one ultrasonic transducer in a container. The vibration decoupling element has structural elements that are largely spherical, ellipsoidal, torus-shaped or multi-faceted polyhedron-shaped. This serves to achieve effective vibration decoupling of the structure-borne noise from a container with a compact design.
The invention is based on the object of proposing an ultrasonic sensor with improved impedance matching.

The object is achieved by an ultrasonic sensor for determining or monitoring a process variable of a medium in automation technology, with a transmitter/receiver unit for transmitting and/or receiving ultrasonic signals, with a coupling unit, via which the transmitted ultrasonic signals are transmitted from the transmitter/receiver unit to a Amplitude transformation unit and the received ultrasonic signals are coupled from the amplitude transformation unit to the transmitter / receiver unit. The amplitude transformation unit comprises a first amplitude transformation component with a first cone that widens in cross section in the direction of emission of the ultrasonic signals and at least a second amplitude transformation component with a second cone that narrows in cross section in the direction of emission of the ultrasonic signals, with the second cone being arranged inside the first cone. A front membrane is arranged on or in the end regions of the first cone and of the second cone pointing in the emission direction. The front membrane, which is coupled to the end regions, is preferably a thin and stiff membrane which has properties comparable to those of a loudspeaker membrane. The usual thickness to diameter ratio for these membranes is less than 1:5; preferably the ratio is less than 1:20. The amplitude transformation unit is in contact with the medium, ie in contact with the fluid medium to be measured.

• - Mittels der erfindungsgemäßen Amplitudentransformationseinheit lässt sich die an der Frontmembranfläche abgestrahlte Wellenfront der Ultraschallsignale so beeinflussen, dass das Verhältnis von Transmission zu Reflexion maximal oder zumindest näherungsweise maximal ist.
• - Aufgrund des hohen Transmissionsanteils der Ultraschallsignale durch die Frontmembran, wird der Körperschall, also der Anteil der Ultraschallsignale, die sich nicht über das Medium sondern über die Wandung des Messrohres/der Rohrleitung ausbreiten und die Messsignalerfassung stören, reduzieren. Erfindungsgemäß lässt sich daher ein optimiertes Signal-/Rauschverhältnis realisieren.
• - Über die Ausgestaltung und/oder die Materialwahl von erstem Konus und zweitem Konus lässt sich eine gewünschte Wellenfront im Nahfeld der abstrahlenden Frontmembran erreichen. In vielen Anwendungen ist die Abstrahlung einer ebenen Wellenfront vorteilhaft, da diese eine maximale Energiedichte aufweist. Bei Messrohren mit kleinem Messrohr- zu Sensor-Durchmesser, d.h. bei einem Messrohr- zu Sensor-Durchmesser von kleiner als 10: 1 bzw. bevorzugt 3:1 kann eine Fokussierung der Wellenfront oder eine Kugelwelle von Vorteil sein. Durch den ersten Konus wird die Schallwelle amplitudentransformiert und erreicht die Frontmembran. Über den zweiten Konus wird die Amplitude der Schallwelle weiter erhöht und an das zu messende Medium bezüglich der Impedanz angepasst. Durch die Dimensionierung der Konen und/oder die Wahl der Materialien (materialabhängige Schallgeschwindigkeit), aus denen die Konen gefertigt sind, lässt sich die Laufzeit der Schallwellen in den Konen so variieren, dass die gewünschte Form der Wellenfront in das Medium abgestrahlt bzw. aus dem Medium empfangen wird.
• - Da die beiden Konen der Amplitudentransformationseinheit lediglich in zwei ringförmigen Bereichen mit der Membran in Verbindung stehen, ist die Impedanz geringer als bei den bislang bei Ultraschallsensoren zur Impedanzanpassung eingesetzten Anpassschichten. Daher erlaubt es die erfindungsgemäße Amplitudentransformationseinheit, die Ultraschallsignale nahezu ungedämpft mit einer hohen Amplitude über die Frontmembran in das Medium aussenden bzw. aus dem Medium empfangen.
• - Ein weiterer Vorteil der erfindungsgemäßen Amplitudentransformationseinheit ist darin zu sehen, dass sie sich auf jedes zu messende Medium durch entsprechende Materialwahl und/oder Dimensionierung der Konen einfach anpassen lässt und auch nachträglich an einen Ultraschallsensor mit einem topfförmigen Gehäuse und Sende-/Empfangseinheit angebracht werden kann. Bevorzugt - aber keineswegs ausschließlich - ist der erfindungsgemäße Ultraschallsensor bzw. das Durchflussmessgerät mit dem erfindungsgemäßen Ultraschallsensor zur Messung der Laufzeit von Ultraschallsignalen in gasförmigen Medien geeignet.

The ultrasonic sensor according to the invention is characterized by a large number of advantages:

• - By means of the amplitude transformation unit according to the invention can be at the Affect front membrane surface radiated wave front of the ultrasonic signals so that the ratio of transmission to reflection is maximum or at least approximately maximum.
• - Due to the high proportion of transmission of the ultrasonic signals through the front membrane, the structure-borne noise, i.e. the proportion of the ultrasonic signals that do not propagate through the medium but through the wall of the measuring tube/pipe and disturb the measurement signal acquisition, is reduced. According to the invention, an optimized signal/noise ratio can therefore be implemented.
• A desired wavefront in the near field of the radiating front membrane can be achieved via the configuration and/or the choice of material for the first cone and second cone. In many applications, the emission of a plane wavefront is advantageous because it has a maximum energy density. In the case of measuring tubes with a small measuring tube to sensor diameter, ie with a measuring tube to sensor diameter of less than 10:1 or preferably 3:1, focusing of the wave front or a spherical wave can be advantageous. The sound wave is amplitude transformed by the first cone and reaches the front membrane. The amplitude of the sound wave is further increased via the second cone and adapted to the medium to be measured with regard to the impedance. Through the dimensioning of the cones and/or the choice of materials (material-dependent speed of sound) from which the cones are made, the propagation time of the sound waves in the cones can be varied in such a way that the desired shape of the wave front is radiated into or out of the medium medium is received.
• Since the two cones of the amplitude transformation unit are only connected to the membrane in two ring-shaped areas, the impedance is lower than in the case of the matching layers previously used for impedance matching in ultrasonic sensors. Therefore, the amplitude transformation unit according to the invention allows the ultrasonic signals to be transmitted into the medium or received from the medium almost undamped with a high amplitude via the front membrane.
• Another advantage of the amplitude transformation unit according to the invention is that it can be easily adapted to any medium to be measured by selecting the appropriate material and/or dimensioning of the cones and can also be retrofitted to an ultrasonic sensor with a pot-shaped housing and transmitter/receiver unit . Preferably - but by no means exclusively - the ultrasonic sensor according to the invention or the flow meter with the ultrasonic sensor according to the invention is suitable for measuring the propagation time of ultrasonic signals in gaseous media.

The ultrasonic signals sent or received by the transmitter/receiver unit are influenced, e.g. focused, via the first amplitude transformation component with the cone expanding in cross section. The acoustic adaptation of the ultrasonic measurement signals takes place via the second amplitude transformation component, which has a cone that tapers in cross-section in the direction of emission. It goes without saying that, depending on the design and application, amplitude transformation units with more than two cones can also be used.

According to a preferred embodiment of the ultrasonic sensor according to the invention, at least one pressure equalization opening is provided on the amplitude transformation unit. This is particularly advantageous when using the ultrasonic sensor to measure the volume or flow rate of a gas in a pipeline, since possible pressure surges or a temporary or continuous overpressure or underpressure do not lead to the destruction of the amplitude transformation unit. Despite the filigree structure of the amplitude transformation unit, it is characterized by high pressure resistance.

An advantageous embodiment of the ultrasonic sensor according to the invention provides that the end regions of the first cone and/or the second cone pointing in the emission direction of the ultrasonic signals have a jagged crown structure. Preferably only the tips of the jagged crown structure(s) are connected to the front membrane. Despite the filigree design of the crown structure of the amplitude transformation unit, a pressure resistance and/or stability can be achieved according to the invention that are/is greater than in a corresponding amplitude transformation unit with a closed construction of the cones.

As already mentioned above, an advantageous development of the ultrasonic sensor according to the invention provides that the first cone and the second cone are matched to one another with regard to the structural dimensions and/or the speed of sound of the materials used for the cones in such a way that the Medium emitted ultrasonic signals or received from the medium ultrasonic signals essentially form a plane wavefront and / or Wavefront that is adapted to the requirements of the respective application. Ultrasonic sensors can be used in a measuring tube that has any shape and/or any diameter. Furthermore, the medium to be measured can be arbitrary; every medium, whether gas or liquid, has a defined speed of sound, which is also influenced by the T and the pressure, especially in the case of gases. Incidentally, an application in connection with the invention is understood to mean that the ultrasonic sensor is installed on a measuring tube with a defined diameter, with a defined medium flowing through the measuring tube. The ultrasonic sensor according to the invention can be easily adapted to all possible applications or groups of applications that have comparable properties by means of the variable amplitude transformation unit according to the invention.

It is considered particularly advantageous if the amplitude transformation unit according to the invention is designed in one piece. A one-piece amplitude transformation unit can be produced in a simple manner using a selective laser sintering process or a 3D printing process. In addition, the amplitude transformation unit and the cup-shaped housing or the sensor cup of the ultrasonic sensor can also be produced in one piece using the selective laser sintering process or the 3D printing process.

An alternative embodiment proposes that the amplitude transformation unit is made from several individual components that can be connected to one another. The individual components are connected to one another using conventional connection techniques such as welding, soldering (hard or soft solder) or gluing.

However, at least the front membrane is preferably designed in one piece with one of the two cones—preferably with the second cone. Here, too, the production processes already mentioned can be used again.

Advantageous developments of the ultrasonic sensor according to the invention relate to the design of the front membrane. For the purpose of increased stability, the front membrane can have a honeycomb, hexagonal reinforcement structure. It preferably consists of an inhomogeneous material or foam, such as open-cell PU foam, bonded hollow glass spheres in an epoxy matrix or aluminum foam. The advantage of these configurations is the low density of the front membrane.

Alternatively, the front membrane is made of a perforated material, eg a perforated metal sheet, with the diameter of the perforations being small compared to the respectively shorter wavelength of the ultrasonic signals or ultrasonic waves—membrane or medium. In addition to the advantage of low density, this solution also has the advantage that there is also an alternative possibility for pressure equalization at the same time. In this configuration, the at least one pressure equalization opening is provided in the front membrane. Other design options were, for example, in the DE 10 2004 059 524 A1 or the DE 10 2007 027 277 A1 described.

According to an advantageous embodiment, the front membrane is made of ceramic. Ceramic is very durable and is not attacked by most aggressive media. A ceramic front membrane can be produced as a combination of membrane and inner cone using a ceramic injection molding process (CIM process). Alternatively, a possibly processed ceramic plate material can be used, on which a metallic layer is provided for the purpose of soldering.

An advantageous embodiment provides that the front membrane has a curvature in the direction of the medium and/or is thinned towards the center in the curved area. As a result of this measure, the acoustic coupling to the measuring tube and thus the unwanted structure-borne noise can be reduced on the one hand, while on the other hand the pressure resistance of the amplitude transformation unit is increased.

A protective coating is advantageously provided in order to protect the partial area of the ultrasonic sensor that comes into contact with the medium from abrasive damage or chemical changes caused by the influence of the medium or the environment. This can be of a metallic, polymeric or ceramic nature. When using individual components, the protective coating is applied, for example, after they have been assembled and thus also protects the connection points in particular.

Additionally or alternatively, the protective coating can be applied using a galvanic coating process, and is therefore suitable both for connecting the individual components and for protecting against medium and environmental influences.

An advantageous embodiment of the ultrasonic sensor according to the invention provides that the transmitter/receiver unit, which generates, transmits and receives the ultrasonic signals, is at least one disk-shaped piezoelectric element which is non-positively connected to the inner surface surface of an end membrane terminating a pot-shaped housing, the end membrane being designed in such a way that it forms the coupling unit between the transmitter/receiver unit and the amplitude transformation unit.

Alternatively, it is proposed that the transmitter/receiver unit, which generates, transmits and receives the ultrasonic signals, consists of several disc-shaped piezoelectric elements which are non-positively attached to the inner surface of a membrane at the end of a pot-shaped housing by means of a pressure mechanism, the end membrane is designed so that it forms the coupling unit between the transmitter / receiver unit and the amplitude transformation unit

As already mentioned above, the ultrasonic sensor according to the invention, which has been described above in different configurations, is preferably used in an ultrasonic flowmeter for determining or monitoring the flow of a medium through a pipeline with a measuring tube and with at least one in an opening in the wall of the Measuring tube arranged ultrasonic sensor used. In addition to the flow meter described above, which determines the flow of the medium on the basis of the transit time difference of ultrasonic signals in and against the direction of flow of the medium, the ultrasonic sensor according to the invention can of course also be used in a flow meter that determines the flow on the basis of a double displacement.

• 1: eine schematische Darstellung eines Inline-Ultraschall-Durchflussmessgeräts 1 - teilweise im Längsschnitt,
• 2: eine perspektivische Ansicht einer ersten Ausgestaltung eines erfindungsgemäßen Ultraschallsensors,
• 2a: einen Längsschnitt gemäß der Kennzeichnung A-A durch den in 2 gezeigten Ultraschallsensor,
• 3: eine perspektivische Ansicht einer zweiten Ausgestaltung eines erfindungsgemäßen Ultraschallsensors und
• 3a: einen Längsschnitt gemäß der Kennzeichnung A-A durch den in 3 gezeigten Ultraschallsensor.

The invention is explained in more detail with reference to the following figures. It shows:

• 1 : a schematic representation of an inline ultrasonic flow meter 1 - partially in longitudinal section,
• 2 : a perspective view of a first embodiment of an ultrasonic sensor according to the invention,
• 2a : a longitudinal section according to the marking AA through the in 2 shown ultrasonic sensor,
• 3 : a perspective view of a second embodiment of an ultrasonic sensor according to the invention and
• 3a : a longitudinal section according to the marking AA through the in 3 shown ultrasonic sensor.

1 shows a schematic representation of an inline ultrasonic flowmeter 1 according to the invention—partially in longitudinal section. The inline flow meter is over in 1 not separately shown flanges mounted in a not separately shown pipeline. Ultrasonic sensors 4 are positioned in a known manner in two openings 6 in the wall of the measuring tube 3 . It should be noted that, in addition to this so-called single-channel flow meter 1, multi-channel flow meters have also become known. In the case of multi-channel flow measuring devices, the ultrasonic sensors 4 are arranged in pairs in such a way that there are measuring paths MP which do not intersect the longitudinal axis L of the measuring tube 3 . With such an embodiment, the influence of the flow profile of the medium 2 flowing in the measuring tube 3 can be taken into account when determining the flow.

In the case shown, the two ultrasonic sensors 4 are arranged in opposite areas of the measuring tube 3, with the two areas being offset parallel to the longitudinal axis L. Both ultrasonic sensors 4 are in contact with the medium in their end region facing the medium 2 .

A fluid medium 2 , which is essentially a liquid or a gaseous medium 2 , flows through the measuring tube 3 in the flow direction S . The two ultrasonic sensors 4 are alternately switched to a transmission mode and a reception mode by the control/evaluation unit 5 . In transmission mode, one of the two ultrasonic sensors 4 emits a sound wave or an ultrasonic signal in the direction of the opposite ultrasonic sensor 4 . The sound wave or the ultrasonic signal is received by the ultrasonic sensor 4 operated in reception mode after passing through the measuring path MP. The modes of the two ultrasonic sensors 4 are then swapped.

The sound waves traversing the medium 2 preferably run on the measurement path MP that is drawn in, which characterizes the shortest connection between the two ultrasonic sensors 4 . If the upper ultrasonic sensor 4 emits an ultrasonic signal, this is taken along by the medium 2 flowing in the direction of flow S and has a transit time determined by the control/evaluation unit 5 on the measuring path MP. If the lower ultrasonic sensor 4 transmits, a longer transit time is measured on the measuring path MP, since the ultrasonic signal propagates counter to the direction of flow S of the medium 2 . The difference between the two running times depends on the speed at which the medium 2 flows through the measuring tube 3 or through the pipeline.

2 shows a perspective view of a first embodiment of an ultrasonic sensor according to the invention. In 2a is a longitudinal cut according to the marking AA through the in 2 shown ultrasonic sensor. The ultrasonic sensor 4 for determining and/or monitoring a process variable of a fluid medium 2 in automation technology has an electromechanical converter unit 9 for transmitting and/or receiving ultrasonic signals. In the case shown, the electromechanical converter unit 9 is in the form of a piezoelectric disk-shaped element which is non-positively connected to the diaphragm 8 at the end. The membrane 8 at the end closes the pot-shaped housing 7 against the medium 2.

The ultrasonic signals or ultrasonic waves generated by the electromechanical transducer element are coupled to the amplitude transformation unit 10 via the membrane 8, which acts as a coupling unit. Accordingly, the received ultrasonic signals or ultrasonic waves are coupled into the electromechanical converter element 9 by the amplitude transformation unit 10 .

The amplitude transformation unit 10 has two components: a first amplitude transformation component 11 with a first cone 14 that widens in cross section in the direction of emission of the ultrasonic signals, and at least one second amplitude transformation component 12 with a second cone 15 that narrows in cross section in the direction of emission of the ultrasonic signals. The cones can have any cross-section: circular, angular, oval, etc. The second cone 15 is arranged inside the first cone 14 . A front membrane 13 is provided on the end regions 16, 17 of the first cone 14 and of the second cone 15 pointing in the emission direction. Incidentally, in the case shown, end areas are the circular end faces of the two cones 14, 15.

As already described above, the first cone 14 and the second cone 15 are matched to one another with regard to the structural dimensions and/or the speed of sound of the materials used so that the ultrasonic signals emitted via the front membrane 13 into the medium 2 or the ultrasonic signals from the medium 2 received ultrasonic signals have a defined wavefront. The defined wavefront is usually essentially a plane wavefront. Depending on the application - which medium flows through which measuring tube diameter - the wave front can also have a wave front that deviates from the flat wave front. If necessary, the effect can also be supported by a special design of the front membrane 13 . Possible configurations of the front membrane 13 have already been described above. A repetition at this point will therefore not be given.

If the ultrasonic sensor 4 is used for measuring in a fluid medium, for example in a gas that is at least temporarily under pressure, the risk of destruction of the amplitude transformation unit 10 can be prevented by attaching a pressure equalization opening. In the simplest case, the pressure equalization opening consists of an opening in the outer cone 14 and possibly also in the inner cone 15. A preferred embodiment of the pressure equalization openings 18 is shown in the figures 3 and 3a to see. Alternatively, the pressure equalization opening 18 can also be provided in the member 13 .

3 shows a perspective view of a second embodiment of an ultrasonic sensor according to the invention. In 3a is a longitudinal section according to the marking AA through the in 3 shown shown ultrasonic sensor. The structure of the 3 The ultrasonic sensor 4 shown corresponds to that in 2 shown ultrasonic sensor 4. Therefore, a repeated description of the identical parts is omitted.

While in the first embodiment ( 2 ) the cones 14, 15 have closed conical surfaces is in the embodiment ( 3 ) In the end regions 16, 17 of the cones 14,15 a jagged crown structure 19 is provided. The tips of the two jagged crown structures 19 pointing in the emission direction of the ultrasonic signals are connected to the front membrane 13 . This refinement is preferably used when determining the speed of sound of gases. As already stated above, the shape of the at least one pressure equalization opening 18 plays no role in fulfilling the task of pressure equalization.

The methods for manufacturing the amplitude transformation unit 10, possibly in conjunction with other components of the ultrasonic sensor 4, have already been described above.

Reference List

1

Ultrasonic flow meter

2

medium

3

measuring tube

4

ultrasonic sensor

5

control/evaluation unit

6

opening

7

pot-shaped housing

8th

membrane

9

electromechanical converter element

10

amplitude transformation unit

11

first amplitude transformation component

12

second amplitude transformation component

13

front membrane

14

expanding cone

15

tapered cone

16

end area

17

end area

18

pressure equalization opening

19

crown structure

Claims (20)

Ultrasonic sensor (4) for determining or monitoring a process variable of a medium (2) in automation technology, with a transmitter/receiver unit (9) for transmitting and/or receiving ultrasonic signals, with a coupling unit via which the transmitted ultrasonic signals are transmitted from the transmitter/ receiving unit (9) to an amplitude transformation unit (10) and the received ultrasonic signals are coupled from the amplitude transformation unit (10) to the transmitter/receiver unit (9), the amplitude transformation unit (10) having a first amplitude transformation component (11) with a first one in the emission direction the cone (14) that widens in cross-section of the ultrasonic signals and at least one second amplitude transformation component (12) with a second cone (15) that narrows in cross-section in the direction of emission of the ultrasonic signals, the second cone (15) being arranged inside the first cone (14). and wherein a front membrane (13) is provided on the end regions (16, 17) of the first cone (14) and of the second cone (15) pointing in the emission direction. ultrasonic sensor claim 1 , At least one pressure compensation opening (18) being provided on the amplitude transformation unit (10). ultrasonic sensor claim 1 or 2 , wherein the end regions (16, 17) of the first cone (14) and/or the second cone (15) pointing in the direction of emission of the ultrasonic signals have a jagged crown structure (19) and wherein preferably the tips of the jagged crown structure/crown structures (19) have the front membrane (13) are connected. ultrasonic sensor claim 1 , 2 or 3 , wherein the first cone (14) and the second cone (15) are matched to one another with regard to the structural dimensions and/or the speed of sound of the materials used for the cones (14, 15) in such a way that the over the front membrane (13) in the medium (2) the ultrasonic signals emitted or the ultrasonic signals received from the medium (2) essentially form a plane wave front and/or a wave front which is adapted to the requirements of the respective application. Ultrasonic sensor according to at least one of the preceding claims, wherein the amplitude transformation unit (10) is designed in one piece and is produced using a selective laser sintering method or a 3D printing method. ultrasonic sensor claim 5 , wherein the amplitude transformation unit (10) and a housing (7) of the sensor are connected to one another in one piece via the selective laser sintering process or the 3D printing process. Ultrasonic sensor according to at least one of Claims 1 - 4 , wherein the amplitude transformation unit (10) is made of several individual components that can be connected to one another. ultrasonic sensor claim 7 , wherein the individual components (14, 15, 13) are welded, soldered or glued to one another. ultrasonic sensor claim 7 or 8th , wherein at least the front membrane (13) and one of the at least two cones (15; 14) are integrally formed. Ultrasonic sensor according to one or more of the preceding claims, wherein the front membrane (13) has a honeycomb reinforcement structure. Ultrasonic sensor according to at least one of Claims 1 - 10 , wherein the front membrane (13) is made of an inhomogeneous material or foam, such as open-cell PU foam, bonded hollow glass spheres in an epoxy matrix or aluminum foam. Ultrasonic sensor according to at least one of Claims 1 - 10 , wherein the front membrane (13) is made of a perforated material, such as perforated sheet metal, the diameter of the perforations being small compared to the wavelength of the ultrasonic signals. ultrasonic sensor claim 12 , The diameter of the perforations being, for example, less than half a wavelength, preferably less than a tenth of the wavelength of the ultrasonic waves. Ultrasonic sensor according to one or more of the preceding claims, in which the front membrane (13) is made of ceramic. Ultrasonic sensor according to one or more of Claims 1 until 4 and 7 until 14 , The front membrane (13) and/or at least individual components of the amplitude transformation unit (10) being produced using a ceramic injection molding process (CIM process). Ultrasonic sensor according to one or more of the preceding claims, wherein a protective coating (20) is provided which covers at least a partial area of the outer surface of the ultrasonic sensor (4). ultrasonic sensor Claim 16 , wherein the protective coating (20) is applied via a galvanic coating process. Ultrasonic sensor according to at least one of Claims 1 - 17 , whereby the transmitter/receiver unit (9), which generates, transmits and receives the ultrasonic signals, is at least one disc-shaped piezoelectric element which is non-positively attached to the inner surface of a membrane (8) at the end of a pot-shaped housing (7). is, wherein the end membrane (8) is designed so that it forms the coupling unit between the transmitter / receiver unit (9) and the amplitude transformation unit (10). Ultrasonic sensor according to at least one of Claims 1 - 17 , whereby the transmitter/receiver unit (9), which generates, transmits and receives the ultrasonic signals, is a matter of several disk-shaped piezoelectric elements which, via a pressure mechanism, are non-positively connected to the inner surface of a membrane (8 ) is attached, wherein the end membrane (8) is designed so that it forms the coupling unit between the transmitter / receiver unit (9) and the amplitude transformation unit (10). Ultrasonic flow meter for determining or monitoring the flow of a medium (2) through a pipeline with a measuring tube (3) and with at least one ultrasonic sensor (4) arranged in an opening (6) in the wall of the measuring tube (3), the ultrasonic sensor ( 4) in at least one of the Claims 1 - 19 is described.

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