Ultrasonic transducer and ultrasonic measuring device
The ultrasonic transducer addresses mechanical instability by using elastically deformable connecting elements to manage thermal expansion, ensuring stable connections and functionality in high-temperature environments.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ENDRESS HAUSER FLOWTEC AG
- Filing Date
- 2025-12-02
- Publication Date
- 2026-06-25
AI Technical Summary
Ultrasonic transducers experience mechanical instability and connection failures due to differing coefficients of thermal expansion between ceramic piezoelectric elements and other components, leading to fractures and loss of functionality in high-temperature environments.
The ultrasonic transducer design incorporates elastically deformable connecting elements with specific dimensions and materials to compensate for thermal expansion, ensuring the connection remains stable by maintaining shear stresses below critical levels.
The design effectively mitigates thermally induced stresses, maintaining a stable connection and functionality of the transducer even in high-temperature conditions, preventing fractures and ensuring reliable operation.
Smart Images
Figure EP2025085190_25062026_PF_FP_ABST
Abstract
Description
[0001] Ultrasonic transducer and ultrasonic measuring device
[0002] This invention relates to an ultrasonic transducer configured to compensate for temperature-related changes in connected components with different coefficients of thermal expansion, and an ultrasonic measuring device with at least one of these ultrasonic transducers.
[0003] In automation technology, particularly in process automation, field devices are frequently used to detect and / or control process variables. Sensors, such as those integrated into level gauges, flow meters, pressure and temperature gauges, pH / ORP meters, conductivity meters, etc., are used to detect process variables, measuring levels, flow rates, pressure, temperature, pH, ORP, and conductivity. Actuators, such as valves or pumps, are used to control process variables, changing the flow rate of a liquid in a pipe section or the fill level in a container. In principle, field devices are all those devices used close to the process that provide or process process-relevant information.
[0004] In the context of the invention, field devices also include remote I / Os, radio adapters, and electronic components in general that are arranged at the field level. A large number of such field devices are manufactured and distributed by Endress+Hauser.
[0005] A field device typically comprises a sensor that comes into contact with the process, at least partially and / or temporarily, and an electronics unit, which serves, for example, signal acquisition, signal processing, and / or signal input. The electronics unit of a field device is typically housed in a casing and also has at least one connection element for connecting the electronics unit to the sensor and / or an external unit. The connection element can be any type of connection, including wireless. The electronics unit and the sensor of the field device can be designed as separate units with separate casings or as a single unit within a casing. Field devices are typically located close to the process and are therefore frequently exposed to fluctuating, sometimes high, temperatures.Different coefficients of thermal expansion of components and their connectors can lead to stresses in the area of the connectors and / or joints, resulting in application defects such as fractures or cracks, or generally in mechanical instability of the connectors and / or joints. The electrical contact established via a connector can also be interrupted.
[0006] The use of a metallic connector is regularly combined with other plastic components whose coefficients of thermal expansion are sufficiently matched to prevent significant thermally induced stresses in the connector area. However, if one of the components to be connected is not made of plastic, but of ceramic, for example, considerable stresses can occur in the connector area when used in conjunction with copper conductors or copper wires.
[0007] Such problematic stresses have been observed particularly in sensors with ceramic components, for example, ceramic pressure sensors or ultrasonic transducers with ceramic piezoelectric elements. This is especially relevant for measuring instruments whose sensors are mounted on a measuring tube, such as a "clamp-on ultrasonic flow sensor device" as described in publication EP0974815B1.
[0008] Conventional ultrasonic flowmeters operate either on the Doppler principle or the transit-time difference principle. The transit-time difference principle evaluates the different transit times of ultrasonic measurement signals traveling in and against the flow direction of the medium. For this purpose, the ultrasonic measurement signals are alternately emitted and received by the ultrasonic transducers in and against the flow direction of the medium. From the transit-time difference of the ultrasonic measurement signals, the flow velocity can be determined, and thus, with a known pipe diameter, the volumetric flow rate, or, with a known or measured density of the medium, the mass flow rate. A problem with current ultrasonic transducer devices is their use close to the process in processes with high temperatures and / or temperature fluctuations.
[0009] German patent DE 102009046862 A1 discloses a coupling element for a sensor of an ultrasonic flowmeter, which thermally decouples the sensor from a high-temperature environment, while still allowing the transmission of ultrasonic waves between a medium and a piezoelectric element. A coupling element can comprise a stainless steel diaphragm, which is bonded to a transducer chamber of the sensor and arranged in a measuring tube wall. Alternatively, a coupling element can comprise a plastic body that connects a sensor assembly mounted on a measuring tube to the measuring tube in such a way that ultrasound can be transmitted from a medium to the sensor. The latter is also known as a "clamp-on" sensor assembly.
[0010] With state-of-the-art ultrasonic transducers, the problem is that the different expansion rates of various components (for example, a ceramic piezoelectric element, a plastic coupling element, a stainless steel diaphragm) can lead to stresses between the components that exceed a certain stress limit. This can cause the connection between the components to loosen, at least partially, and / or lead to fractures and cracks in the connections and / or components. This can result in a loss of functionality of the measuring device.
[0011] The invention solves this problem with an ultrasonic transducer according to claim 1.
[0012] The ultrasonic transducer according to the invention is designed to compensate for temperature-related changes in connected components with different coefficients of thermal expansion and comprises: a transducer chamber, wherein the transducer chamber has a coupling element at its end face; wherein the coupling element comprises a first material; a piezoelectric element made of a second material, designed to generate ultrasonic waves; wherein the piezoelectric element has a surface facing the coupling element; wherein the surface has a normal vector and an area; wherein the coupling element has a number of connecting elements on a side facing the piezoelectric element, wherein the connecting elements each have a contact surface; wherein the connecting elements are each elastically deformable in a plane perpendicular to the normal vector;wherein the connecting elements are each materially bonded to the piezoelectric element via the contact surface; wherein the sum of the contact surface areas is not less than 30% of the surface area of the piezoelectric element; wherein the sum of the surface areas is not more than 95% of the surface area of the piezoelectric element; wherein the connecting elements have a characteristic height and a characteristic radius; wherein the ratio of the characteristic height to the characteristic radius is not less than 1; wherein the ratio of the characteristic height to the characteristic radius is not more than 50, in particular not more than 10, and preferably not more than 4.
[0013] The invention has the advantage that thermally induced displacement between the piezoelectric element and the coupling element is compensated for by elastic deformation of the connecting elements. The arrangement with connecting elements is designed to keep shear stresses caused by temperature differences between connected components below a critical value for the system, due to the different coefficients of thermal expansion. A shear stress above a stress limit causes at least partial loosening of the material bond and / or structural damage in the piezoelectric element. In one embodiment, the connecting elements are freestanding columns. In another embodiment, the transducer chamber is pot-shaped and is arranged, for example, in the wall of a measuring tube. In yet another embodiment, the transducer chamber is attached to the outside of a measuring tube using a clamp-on method.In one embodiment, the transducer chamber comprises plastics and / or mechanical connecting elements, wherein the mechanical connecting elements are configured to fasten the piezoelectric element and / or the coupling element. The shape and size of the connecting elements, as well as their elasticity, are adapted to the coefficients of thermal expansion of the first and second materials so that the stress limit is not exceeded.
[0014] The dimensions of the connecting elements, i.e., their characteristic diameter and height, can be optimized according to various criteria, such as mechanical stress, thermal resistance, acoustic transmission, and vibration resistance. For a piezoelectric element with a circular base of 5 mm diameter, stress-optimized connecting elements made of stainless steel have a characteristic diameter of less than 1 mm, particularly less than 0.5 mm, and preferably less than 0.1 mm. Furthermore, the connecting elements have a diameter of more than 0.01 mm, particularly more than 0.1 mm, and preferably more than 0.2 mm.
[0015] In a further development of the ultrasound transducer according to the invention, the characteristic radius is given by: CR = (F / TT); where the area is given by F = S / N or by a median of the contact surfaces.
[0016] This further training has the advantage that the characteristic radius is approximated by a mean value of the contact areas or the median of the contact areas, assuming that these are circular.
[0017] In a further development of the ultrasound transducer according to the invention, the side of the coupling element facing the piezoelectric element has a further surface with a minimal distance to the surface; wherein the characteristic height corresponds to the minimum distance.
[0018] The advantage of this further development is that a distance between a surface of the coupling element and a surface of the piezo element can be used as a characteristic height of the connecting elements when these are molded onto the coupling element.
[0019] In a further development of the ultrasound transducer according to the invention, a trench volume comprises a volume complementary to the connecting elements, which is surrounded by a perimeter of a projection of the surface; wherein the characteristic height is given by: KV / (FO-S).
[0020] The advantage of this further development is that the trench volume can be used to determine the characteristic height of the connecting elements when they are formed into the coupling element. The trench volume can be determined, for example, by filling the spaces between the connecting elements with a quantity of a suitable medium, where one volume of the medium corresponds to the trench volume. In a further development of the ultrasonic transducer according to the invention, each pair of adjacent connecting elements has a typical distance; where the typical distance is less than 20% of the characteristic radius; where the typical distance between connecting elements is greater than 2% of the characteristic radius.
[0021] In a further development of the ultrasound transducer according to the invention, the connecting elements are formed into or onto the coupling element by etching, laser processing, embossing, electroforming, micro-milling or additive manufacturing.
[0022] This advanced training has the advantage that the connecting elements formed into the coupling element are particularly stable and can be precisely shaped, for example, by etching. Additive manufacturing offers the advantage that the connecting elements can comprise several different materials.
[0023] In a further development of the ultrasound transducer according to the invention, the connecting elements are independent, rod-shaped bodies; wherein the connecting elements have end regions; wherein at least one end region has a coating, in particular made of silver or a silver-containing alloy. This further development has the advantage that the connecting elements can be individually and controllably attached to the coupling element and / or to the piezoelectric element.
[0024] In a further development of the ultrasound transducer according to the invention, a positive-locking connection of the contact surfaces with the piezoelectric element is produced by sintering and / or hot-melt adhesive films and / or liquid phase sintering or intermetallic compounds and / or diffusion bond welding and / or by galvanically grown nanotubes, in particular tubes with a diameter of less than 100 nm.
[0025] This further development has the advantage that the connected piezoelectric element is process-stable, meaning that its performance characteristics change little, if at all, over time. Performance characteristics of a piezoelectric element include, for example, response time and / or energy efficiency. A further advantage is that the components can be joined, for example, by sintering under moderate pressure (between 1 and 100 MPa, particularly between 5 MPa and 15 MPa) and temperature (between 150 and 350 °C, particularly between 225 °C and 275 °C) for several hours, resulting in a force-fit and form-fit connection. An alternative embodiment of this further development has the advantage that the connection of the components can be produced using a hot-melt adhesive film at lower temperatures than sintering, particularly below 300 °C and less than 15 MPa, preferably below 200 °C and 10 MPa.
[0026] In a further development of the ultrasound transducer according to the invention, the connecting elements have an arrangement, in particular a symmetrical one; wherein the arrangement comprises a repeating pattern.
[0027] One advantage of this advanced design is that a symmetrical structure allows for seamless filling of the joining surface, which is defined as the sum of the contact areas of the connecting elements. Another advantage is that the arrangement of the connecting elements can be optimized with regard to the acoustic impedance between the piezoceramic and the coupling element. An example of a symmetrical structure formed within the coupling element is a square, hexagonal, or octagonal grid, with the hexagonal grid, in particular, offering a suitable ratio between the joining surface and the free spaces between the connecting elements.
[0028] In a further development of the ultrasound transducer according to the invention, the connecting elements are elastically connected, in particular by threads or bands. This further development has the advantage that the arrangement of connecting elements can be assembled particularly easily, especially in the form of a tablet.
[0029] In a further development of the ultrasound transducer according to the invention, the connecting elements are rigid in one direction, preferably in the direction of the longitudinal axis.
[0030] This advanced training has the advantage that the ultrasound waves generated by the piezoelectric element can be transmitted well between the piezoelectric element and the coupling element.
[0031] In a further development of the ultrasound transducer according to the invention, the contact surface and / or a surface of the piezoelectric element has a coating, in particular with silver or gold or with an alloy comprising silver, gold, copper, nickel or palladium.
[0032] One advantage of this advanced process is that an adhesive coating with silver, copper, nickel, or palladium enables a galvanic connection between a contact surface and the piezoelectric element and / or the coupling element, resulting in improved connection properties. Alternatively, a coating with an adhesive film can be applied, which is cured in a further process step after the piezoelectric element has been attached.
[0033] In a further development of the ultrasound transducer according to the invention, the first material comprises a corrosion-resistant metal, in particular by means of a coating, especially stainless steel 1.4404 / 316L or 1.4016 or a soft aluminum alloy.
[0034] The advantage of stainless steel is its ease of processing, with 1.4404 being particularly suitable for close-process applications due to its corrosion resistance. Stainless steel 1.4016 exhibits high resistance to stress corrosion and good workability, making it especially suitable for applications where cost and mechanical properties are more important than maximum corrosion resistance.
[0035] In a further development of the ultrasound transducer according to the invention, the second material comprises a ceramic or glass.
[0036] This further training has the advantage that ceramics are sensitive to mechanical stresses, robust and durable, and can be manufactured in various shapes and sizes.
[0037] The measuring device according to the invention for detecting a measured quantity of a medium comprises: a container for guiding the medium; at least one sensor; a transmitter; wherein the at least one sensor comprises an ultrasonic transducer according to the invention.
[0038] This invention has the advantage that a measured quantity, for example based on flight times and / or phase information of ultrasonic signals propagating in the container, can be determined using sensors with ultrasonic transducers, even if the process involves high temperatures and / or temperature fluctuations. A concrete example is the detection of a transit-time difference of ultrasonic signals between two sensors, which are attached externally to a measuring tube, for example by means of a clamp-on connection, and from which the flow rate of the medium can be determined.
[0039] The invention is further explained using the following figures. It shows:
[0040] Fig. 1 shows a side view of a design of the connection between the coupling element and the piezo element.
[0041] Fig. 2 shows a top view of an embodiment of the coupling element with the molded connecting elements.
[0042] Fig. 3 shows a cross-section of one embodiment of the ultrasound transducer.
[0043] Fig. 4 shows an embodiment of the measuring device according to the invention.
[0044] The side view shown in Fig. 1 of an embodiment of the connection between the coupling element KE and the piezoelectric element PE reveals a plurality of connecting elements VE integrally formed in the coupling element KE. Each connecting element is rod-shaped and has a longitudinal axis LA and a transverse axis QA. In this embodiment, the longitudinal axis is perpendicular to a surface of the coupling element KE and points towards the piezoelectric element PE, while the transverse axis QA is parallel to the surface of the coupling element KE. The connecting elements VE are designed to be elastically deformable in the direction of the transverse axis QA in order to compensate for stresses in the connection between the piezoelectric element PE and the coupling element KE caused by temperature differences.In this embodiment, the piezoelectric element PE has a coating B, which may, for example, comprise silver or a silver-containing alloy such as Au-Ag, Ni-Au-Ag or Sn-Au-Ag, so that a contact surface KF of a connecting element VE, which is also coated with silver or a silver-containing alloy, may, for example, have a metallurgical connection.
[0045] The top view of one embodiment of the coupling element KE shown in Fig. 2 depicts the integrally formed connecting elements VE with contact surfaces KF, with a transverse axis QA aligned parallel to a surface of the coupling element KE. In this embodiment, the connecting elements VE have a hexagonal or hexagonal first arrangement A1, which is a repeating and symmetrical pattern. This pattern has the advantage of uniformly covering the round cross-sectional area of the coupling element KE and the piezoelectric element PE. The ratio of contact area to spacing of the connecting elements VE determines the property of the arrangement of connecting elements VE to compensate for stresses in the connection between the coupling element KE and the piezoelectric element PE caused by temperature differences.
[0046] The cross-section of an embodiment of the ultrasonic transducer shown in Fig. 3 depicts the piezoelectric element PE surrounded by the transducer chamber WK. In this embodiment, the piezoelectric element is connected to a wire D, which connects the piezoelectric element, for example, to a measuring and operating circuit (not shown here). The coupling element KE is metallurgically bonded to the transducer chamber WK and has integrally formed connecting elements VE, which metallurgically bond to the piezoelectric element via their contact surfaces KF (not shown here). Along their longitudinal axis LA, the connecting elements VE exhibit acoustic properties that are advantageous for transmitting ultrasonic waves propagating between the piezoelectric element PE and the coupling element KE.
[0047] The embodiment of the measuring device according to the invention shown in Fig. 4 depicts a container B carrying a medium M, which in this embodiment is a measuring tube. Two sensors S are attached to the container B, for example, by a "clamp-on" method, or two sensors are arranged in contact with the medium within the container B. A measuring device with "clamp-on" sensors has the advantage that it enables the measurement of a process parameter without interrupting the process or causing a pressure loss. In this measuring device, the "clamp-on" sensors are mounted externally onto the tube without any intervention, require only minimal inlet lengths, and are insensitive to aggressive liquids.An alternative to "clamp-on" sensors are "inline" sensors, which are in contact with the medium and have the advantage of acquiring measured values with higher accuracy than "clamp-on" sensors. Maintenance-free coupling pads ensure stable measurement throughout the entire life cycle of the measuring device. This embodiment of the measuring device shows an ultrasonic flowmeter in which the sensors incorporate the ultrasonic transducer according to the invention to compensate for temperature differences generated by the process and / or the medium and the associated stresses in the connected components of the measuring device. The sensors S are electrically connected to the transmitter, for example, to generate an ultrasonic signal and / or to transmit a measurement signal to evaluation electronics.
[0048] Conventional ultrasonic flowmeters often operate on the Doppler or transit-time difference principle. The transit-time difference principle evaluates the different transit times of ultrasonic pulses relative to the flow direction of the liquid. For this purpose, ultrasonic pulses are sent at a specific angle to the pipe axis, both with and against the flow. The flow velocity, and thus the volumetric flow rate, can be determined from the transit-time difference, given the known diameter of the pipe section.
[0049] In the Doppler principle, ultrasound waves of a specific frequency are coupled into the liquid, and the ultrasound waves reflected by the liquid are analyzed. The flow velocity of the liquid can also be determined from the frequency shift between the coupled and reflected waves. Reflections in the liquid occur when air bubbles or impurities are present, so this principle is primarily used for contaminated liquids.
[0050] The ultrasonic waves are generated and received by means of the ultrasonic transducer. For this purpose, ultrasonic transducers are either permanently attached to the pipe wall of the relevant section of the pipeline or clamped to the pipe wall using a clamping device. A major advantage of clamp-on devices is that they do not touch the medium being measured and can be installed on an existing pipeline. Such systems are known, for example, from EP686255B1, US4484478, and US4598593. (Reference list)
[0051] WK converter chamber
[0052] KE coupling element
[0053] M1 first material
[0054] PE piezoelectric element
[0055] M2 second material
[0056] 0 surface
[0057] NO normal vector
[0058] FO area
[0059] SW page
[0060] VE connecting elements
[0061] KF contact surface
[0062] S Sum of the areas
[0063] CH characteristic height
[0064] CR characteristic radius
[0065] GV trench volume
[0066] TA typical distance
[0067] EB End Areas
[0068] B coating
[0069] LA Longitudinal axis
[0070] bra container
[0071] M Medium
[0072] S Sensor
[0073] T Transmitter
[0074] Underwater ultrasonic transducer
Claims
Patent claims 1. An ultrasonic transducer designed to compensate for temperature-related changes in connected components with different coefficients of thermal expansion, comprising: - A converter chamber (WK), o wherein the converter chamber (WK) has a coupling element (KE) at its end face; o wherein the coupling element (KE) comprises a first material (M1 ); - A piezoelectric element (PE) made of a second material (M2), configured to generate ultrasonic waves; o wherein the piezoelectric element (PE) has a surface (0) facing the coupling element (KE); o wherein the surface (0) has a normal vector (NO) and an area (FO); - wherein the coupling element (KE) has a number (N) of connecting elements (VE) on a side (SW) facing the piezo element (PE), o wherein the connecting elements (VE) each have a contact surface (KF); - wherein the connecting elements (VE) are each elastically deformable in a plane perpendicular to the normal vector (NO); - wherein the connecting elements (VE) are each materially connected to the piezoelectric element (PE) via the contact surface (KF); - where the sum of the surface areas (S) of the contact surfaces (KF) is not less than 30% of the surface area of the piezoelectric element (PE); - where the sum of the surface areas (S) does not exceed 95% of the surface area of the piezoelectric element (PE); - wherein the connecting elements (VE) have a characteristic height (CH) and a characteristic radius (CR); - where the ratio of the characteristic height (CH) to the characteristic radius (CR) is not less than 1; - wherein the ratio of the characteristic height (CH) to the characteristic radius (CR) is not more than 50, in particular not more than 10, and preferably not more than 4.
2. Ultrasound transducer according to claim 1 , - where the characteristic radius (CR) is given by: CR = ^F / TI ; - where the size F is given by F = S / N, or by a median of the contact areas (KF).
3. Ultrasound transducer according to one of claims 1 or 2, - wherein the side (SW) of the coupling element (KE) facing the piezoelectric element (PE) has a further surface (OM) with a minimum distance (A) to the surface (0); - where the characteristic height (CH) corresponds to the minimum distance (A).
4. Ultrasound transducer according to one of claims 1 to 3, - wherein a trench volume (GV) comprises a volume complementary to the connecting elements (VE) and surrounded by a perimeter of a projection of the surface (0); - where the characteristic height (CH) is given by: KV / FO - S).
5. Ultrasound transducer according to one of claims 1 to 3, - wherein each pair of adjacent connecting elements (VE) has a typical distance (TA); - where the typical distance (TA) is less than 20% of the characteristic radius (CR); - where the typical distance (TA) between connecting elements (VE) is greater than 2% of the characteristic radius (CR); 6. Ultrasound transducer according to one of claims 1 to 5, - wherein the connecting elements (VE) are formed into or onto the coupling element (KE) by etching, laser processing, embossing, electroforming, micro-milling, or additive manufacturing.
7. Ultrasound transducer according to any one of claims 1 to 6, - wherein the connecting elements (VE) are independent, rod-shaped bodies; - wherein the connecting elements (VE) have end areas (EB); wherein at least one end area (EB) has a coating (B), in particular made of silver or a silver-containing alloy.
8. Ultrasound transducer according to one of claims 1 or 2, - wherein a positive-locking connection of the contact surfaces (KN) with the piezoelectric element (PE) is produced by sintering and / or hot-melt adhesive films and / or liquid phase sintering or intermetallic connections and / or diffusion bonding welding and / or by electroplating nanotubes, in particular tubes with a diameter of less than 100 nm.
9. Ultrasound transducer according to one of claims 1 to 3, - wherein the connecting elements (VE) have an arrangement, in particular a symmetrical arrangement; - where the arrangement comprises a repeating pattern.
10. Ultrasonic transducer according to claim 9, - wherein the connecting elements (VE) are connected elastically, in particular by threads or bands.
11. Ultrasound transducer according to any one of claims 1 to 10, - wherein the connecting elements (VE) are rigid in one direction, preferably in the direction of the longitudinal axis (LA).
12. Ultrasound transducer according to one of claims 1 to 11 , - wherein the contact area (KF) and / or a surface of the piezoelectric element (PE) has a coating (B), in particular a coating (B) comprising silver or gold or an alloy comprising silver, gold, copper, nickel, or palladium.
13. Ultrasound transducer according to any one of claims 1 to 12, - wherein the first material comprises a corrosion-resistant metal, in particular by means of a coating, especially stainless steel 1.4404 / 316L or 1.4016 or a soft aluminium alloy.
14. Ultrasound transducer according to any one of claims 1 to 7, - where the second material comprises a ceramic or glass.
15. Measuring device for detecting a measured quantity of a medium, comprising: - A container (BH) for guiding the medium (M); - At least one sensor (S); - a transmitter (T); - wherein the at least one sensor (S) comprises an ultrasonic transducer (UW) according to any one of claims 1 to 8.