Ultrasonic transducer for a proximity sensor

Abstract

Ultrasound transducer assembly (16) for use in scanning or detecting the position of objects (12) near the transducer, wherein the ultrasound transducer assembly (16) comprises: a substrate element (20) which has a flat surface (36, 38) and a circumferential edge (40), a piezoceramic resonator plate (22) which is held next to the flat surface (36), and a coupler (24) connected to a surface of the resonator plate (22), for the acoustic coupling of the resonator plate (22) with a medium (15) which is in contact with the coupler (24); wherein the resonator plate (22) is held in a cantilevered relationship on a contact block (68) which extends at a distance ratio generally parallel to the substrate element (20).

Description

AREA OF INVENTION

[0001] The present invention relates generally to ultrasonic transducers and more specifically to an ultrasonic transducer assembly that can be built into or incorporated into a sensor to detect the presence and / or distance of objects. BACKGROUND OF THE INVENTION

[0002] Ultrasonic measurement systems provide an efficient and effective method for detecting objects, such as in automated industrial manufacturing processes. These sensors require a transducer to generate ultrasonic signals. For example, a transducer for such sensors typically generates an ultrasonic signal that is transmitted towards an object, and a return or reflected signal is detected by the transducer. A processor connected to the transducer processes the received signal and determines the presence of an object and / or the distance to an object based on the time elapsed between the transmitted and received signals.

[0003] Japanese patent application JP 2000-301 065 A discloses a piezoelectric vibrator comprising a piezoelectric element, a height-adjustable element, and a vibration plate, wherein the vibration plate is arranged on a front side of the substrate and connected to the substrate via the height-adjustable element. The piezoelectric element is arranged on a side of the vibration plate facing away from the substrate and is connected to the vibration plate.

[0004] EP 0 182 140 A1 describes an ultrasonic transducer setup comprising a substrate element, a piezoceramic resonator plate, and a coupler for acoustically coupling the resonator plate to a medium. The resonator plate is not cantilevered and is mounted on a contact block that extends parallel to the substrate element.

[0005] Prior art piezoceramic ultrasonic transducers, such as those used in airborne time-of-flight applications, have generally been designed to exhibit very good, long-range detection capabilities. In designing these sensors, it has typically been considered desirable to maximize the Q-value, i.e., the resonance, of the transducer and to minimize the operating frequency. A high Q-value results in greater gain of a returned signal, and a low frequency serves to reduce the attenuation of ultrasound in air, since attenuation is a function of frequency. Such prior art transducers have typically been designed as thin discs of ceramic material, which conventionally offer the advantage of a high Q-value.

[0006] For various reasons, improving the efficiency and reducing the cost of manufacturing circular ceramic disks is subject to limitations, which in turn restricts potential cost reductions for components incorporating the ceramic disks, such as transducers integrated into sensors. Accordingly, it is desirable to provide an alternative sensor transducer design that can include a resonator component with a form factor or shape that contributes to the efficient manufacturing of both the resonator component and the assembled transducer. SUMMARY OF THE INVENTION

[0007] According to one aspect of the invention, an ultrasonic transducer setup is provided for use in scanning or detecting the position of objects near the transducer. The ultrasonic transducer setup includes a substrate element with a flat surface and a circumferential edge, a piezoceramic resonator plate held adjacent to the flat surface, and a coupler connected to a surface of the resonator plate for acoustically coupling the resonator plate to a medium that is in contact with the coupler.

[0008] According to a further aspect of the invention, an ultrasonic transducer assembly is provided for use in scanning the position of objects near the transducer. The ultrasonic transducer assembly comprises a substrate element having a printed circuit board (PCB) defining a flat surface and a circumferential edge, and a piezoceramic resonator plate with a flat inner surface, which is supported or held on the flat surface adjacent to the circumferential edge. Electrical contacts are provided between the PCB and the resonator plate to connect the resonator plate to a power supply. The transducer further comprises a coupler, which includes a flat element with opposing first and second sides, the first side being inclined.extends perpendicular to and is connected to a surface of the resonator plate, for the acoustic coupling of the resonator plate with a medium which is in contact with the second side of the coupler.

[0009] According to a further aspect of the invention, a sensor incorporating an ultrasonic transducer assembly is provided for use in sensing the position of objects near the transducer. The sensor includes a substrate element with a printed circuit board (PCB) defining a flat surface and a circumferential edge, and a rectangular piezoceramic resonator plate defining a large elongated dimension and a small dimension. The resonator plate is cantilevered or mounted on one side of the substrate element, with its large elongated dimension extending from the circumferential edge of the substrate element. Electrical contacts are provided between the PCB and the resonator plate to connect the resonator plate to a power supply, one of the electrical contacts forming a cantilevered mount for the resonator plate on the substrate element.The sensor also includes a disc-shaped coupler, which has a flat element with opposing first and second sides. The first side extends obliquely to a surface of the resonator plate and connects to it. The coupler is acoustically excited by the resonator plate, causing it to transmit a signal to an object near the coupler, and the coupler receives reflected signals from the object and transmits them to the resonator plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Although the description concludes with patent claims that specifically describe and clearly claim the present invention, it is assumed that the present invention can be better understood with reference to the following description together with the accompanying drawings, wherein identical reference numerals denote identical elements and wherein: Fig. 1 a side elevation view of a sensor system which has a transducer structure according to the present invention, in partial cross-section. Fig. Figure 2 is a perspective exploded view of the transducer assembly according to the present invention. Fig. Figure 3 is an enlarged cross-sectional view of the coupler end of the transducer assembly according to the present invention. Fig. Figure 4 is a perspective exploded view showing the assembly of a resonator plate on a printed circuit board substrate for the transducer assembly according to the present invention. Fig. Figure 5 is an enlarged cross-sectional view of the coupler end of a transducer assembly according to an alternative embodiment of the present invention. Fig. Figure 6 is a perspective exploded view of the alternative embodiment of Fig. 5. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings, which form part thereof and in which, for illustrative purposes and not for limitation, a specific preferred embodiment is shown in which the invention can be implemented. It is understood that other embodiments may also be used and that modifications may be made without departing from the concept and scope of protection of the present invention.

[0012] Fig. Figure 1, which is now referred to, shows an ultrasonic sensor 10 for detecting or determining the presence and distance of an object 12 in the vicinity of the sensor 10. The sensor has a housing 14 and a transducer assembly 16 and includes a damping material 18 which surrounds the transducer assembly 16 inside the housing 14, as described below.

[0013] Referring to Fig. The transducer assembly 16 comprises a substrate element 20, defined by a printed circuit board, a transducer or resonator plate 22, and a plate-like coupler or coupling assembly 24, which is connected to the resonator plate 22 and extends obliquely to it. The coupling assembly 24 provides an ultrasonic interface between the relatively small resonator plate 22 and a medium, such as air, which fills the space between the sensor 10 and the object 12, as shown in Fig. 1 represented by area 15.

[0014] The resonator plate 22 can be made of any suitable piezoelectric material. In a preferred embodiment, the resonator plate 22 comprises a piezoceramic plate. In particular, the resonator plate 22 can be made of a lead zirconate tanate, such as PZT5A, which can be obtained, for example, from Morgan Electro Ceramics, Bedford, Ohio. Desirable features associated with a piezoceramic material for the present application include high mechanical-electrical conversion efficiency, a substantially flat temperature response, and a relatively high mechanical quality factor (Qm), which in this example is approximately 75.

[0015] With reference to Fig. 3. The coupling assembly 24 has a considerable surface area for the transfer of ultrasonic energy from the resonator plate 22 to the medium. In the illustrated embodiment, the coupling assembly 24 includes a membrane 26, which defines a first side 28 of the coupling assembly 24. The membrane 26 can vibrate in response to vibrational energy from the resonator plate 22. The membrane 26 comprises a stiff or rigid material and can be made of a variety of materials, including, but not limited to, metal, plastic, or a polymer, e.g., a molded thermosetting polymer such as an epoxy resin. In a preferred embodiment, the membrane 26 can be made of a thin sheet of stainless steel.As shown here, the membrane 26 of the present embodiment is a thin or plate-like, disc-shaped part in which the vibrational energy from the resonator plate 22 is distributed essentially in a direction perpendicular to the substrate element 20. That is, the acoustic vibration signals propagate along a path extending circumferentially and radially from a central position on the membrane 26, defined at an opening 30 in the membrane 26, to an outer edge of the membrane 26. It is understood that the membrane 26 is not limited to a disc-shaped part and can also have a plate-like part, which embodies other shapes.

[0016] The coupling assembly 24 can further comprise an impedance matching element 32, which is illustrated here as a disc-shaped element positioned over the membrane 26. The impedance matching element 32 defines a second, outwardly facing side 34 of the coupling assembly 24. The impedance matching element 32 comprises a material selected to maximize the coupling of the ultrasonic energy from the resonator plate 22 to the medium 15 and is typically a different material than the material of the membrane 26. For example, the impedance matching element 32 can comprise a relatively elastic or compliant material, such as rubber, an epoxy resin, a polymer, glass, or combinations and / or mixtures of these materials. In a preferred embodiment for connection with an air medium, the impedance matching element 32 comprises a glass-filled epoxy resin element.It is understood that, although air is used as the medium for the purposes of describing the present embodiment, the material and structure of the impedance matching element 32 can be selected such that the impedance matching element 32 is designed for coupling with other media, including liquids or other gases. Furthermore, the impedance matching element 32 is not limited to the illustrated disc-shaped configuration and can also have other shapes, such as a shape that matches the shape of the membrane 26.

[0017] As in the Fig. 2 and Fig. As can be seen in Figure 3, the impedance matching element 32 has a recess 31 for receiving the membrane 26. The surface of the membrane 26 opposite the first side 28 is arranged such that a surface 33 of the impedance matching element 32 engages with the recess 31 for the transmission of ultrasound signals between the membrane 26 and the impedance matching element 32.

[0018] Furthermore, it is understood that in some applications of the sensor 10 described here, it is possible to design the coupling structure 24 without an impedance matching element 32. For example, the coupling structure 24 can be designed with the material of the membrane 26, which is selected to provide satisfactory coupling in order to efficiently transmit and receive ultrasonic energy to and from the medium.

[0019] An insulating element 35 is arranged adjacent to the first side 28 of the coupling assembly 24, i.e., behind the impedance matching element 32 and the diaphragm 26. The insulating element 35 preferably consists of an elastic or compliant material and provides an insulating layer or barrier for isolating at least the diaphragm 26, and preferably both the diaphragm 26 and the impedance matching element 32, from the damping material 18 within the housing 14. In a preferred embodiment, the damping material 18 comprises a urethane material, and the insulating element 35 comprises a silicone rubber material, i.e., a silicone foam rubber, and has a circular shape with a central opening 37. The insulating element 35 preferably has an outer diameter that substantially matches the diameter of the coupling assembly 24.

[0020] As in Fig. As can be seen in Figure 2, the substrate element 20 is designed as an elongated rectangular element with an upper flat surface 36, a lower flat surface 38, and a circumferential edge 40, which is defined by opposing, generally parallel side edges 42, 44 and by opposing, generally parallel front and rear edges 46, 48. A tongue or tab section 50 extends in a cantilevered relationship from the front edge 46 at the midpoint between the side edges 42, 44.

[0021] With reference to Fig. Figure 4 shows the resonator plate 22 as having an elongated, plate-like element with a substantially planar inner surface 52, a substantially planar outer surface 54, a front edge 56, a rear edge 58, and opposing side edges 60, 62. A large dimension D1 is defined between the front and rear edges 56, 58, and a small dimension D2 is defined between the opposing side edges 60, 62. The resonator plate 22 is arranged such that its inner surface 52 lies on or adjacent to the upper surface 36 of the substrate element 20, and that its large dimension D1 extends from the front edge 46 of the substrate element 20 across the tab section 50. The front edge 56 of the resonator plate 22 lies adjacent to a front edge 59 of the tab section 50.The small dimension D2 of the resonator plate 22 is essentially equal to the width of the tab section 50, measured between opposite sides 64 and 66 of the tab section 50.

[0022] The resonator plate 22 is aligned parallel to the substrate element 20 and is preferably positioned on a first contact block 68 located on the substrate element 20 to form an electrical contact between the inner surface 52 and the first contact block 68. The contact block 68 preferably has a raised section extending above the substrate element 20 to hold the resonator plate 22 cantilevered from the substrate element 20. Thus, there is preferably an air gap between the inner surface 52 of the resonator plate 22 and the upper surface 36 of the substrate element 20. Additionally, an overhead wire 70 is provided, which extends between the outer surface 54 and a second contact block 72 on the substrate element 20. The first and second contact blocks 68, 72 have conductors that are electrically connected to a power supply 74 and the processor 76 (see Figure 1). Fig. 2) are connected to the substrate element 20. The electrical connections from the contact blocks 68, 72 can be formed by respective electrical conductors 69, 73, which are etched into the circuit board that defines the substrate element 20, see Fig. 2 and Fig. 4. It is understood that either the power supply 74 or the processor 76 or both can be defined by a printed circuit board structure on the substrate element 20 in a conventional manner or alternatively can be arranged remotely from the substrate element 20.

[0023] Although the preferred embodiment includes a single support, i.e., the first contact block 68, to hold the resonator plate 22, the resonator plate 22 can also be held by one or more additional supports. For example, the resonator plate 22 can be held on a pair of supports positioned adjacent to longitudinally extending ends of the resonator plate 22, with at least one of the supports preferably forming an electrical contact with the electrical conductor 69.

[0024] In a method for assembling or mounting the transducer assembly 16, the resonator plate 22 can be attached to the substrate element 20 by means of a device that performs a pick-up and drop-down operation to position the resonator plate 22 on the tab section 50 and extends over the first contact block 68. The overhead wire 70 can be attached to the substrate element 20 in an automated process, such as a process in which a plurality of prepared overhead wires 70 are fed in the form of a conventional tape reel feeder.Each successive overhead wire 70 can be arranged such that a vertical section of it engages with the second contact block 72 and that a horizontal section of the overhead wire 70 engages above the upper surface of the resonator plate 22 to form an electrical contact between the outer surface 54 and the electrical conductor 73 of the circuit board via the second contact block 72, see . Fig. 4. In the illustrated embodiment, a hole is shown in the second contact block 72 for receiving the vertical section of the top wire 70, however, such a hole is not required to implement the present invention.

[0025] Attaching the resonator plate 22 to the substrate element 20 can be accomplished using an attachment method that includes arranging other components on the substrate element 20. Specifically, the resonator plate 22 and the overhead wire 70, along with other components, including those forming the processor 76 and the power supply 74, can be arranged on the printed circuit board defining the substrate element 20 and subjected to a conventional surface mount technology (SMT) reflow process to bond the components to the printed circuit board. Thus, the SMT reflow process directly bonds one side of the resonator plate 22 to the printed circuit board of the substrate element 20.Furthermore, the attachment of the resonator plate 22 by means of SMT reflow provides a high-integrity attachment which, compared to known attachment methods and procedures typically used for attaching piezoceramic ultrasonic components to printed circuit boards or similar mounting structures according to the prior art, generally requires fewer parts and less labor.

[0026] Following the attachment of the resonator plate 22 to the substrate element 20, the coupling assembly 24 is attached at least to the outer surface 54 of the resonator plate 22 such that it lies next to the front edge 56 and extends in an orthogonal relationship to the plane of the resonator plate 22. In particular, the central opening 30 in the membrane 26 is positioned above the end of the resonator plate 22, and the front edge 56 of the resonator plate 22 is positioned such that it engages with or is closely adjacent to an inner surface 33 of the impedance matching element 32. Additionally, the isolation element 35 is arranged on the second side 28 of the coupling assembly 24, with the resonator plate 22 extending through its central opening 37.In a preferred embodiment, the diaphragm 26 and the impedance matching element 32 are connected to the resonator plate 22 such that the inner surface 33 of the impedance matching element 32 is connected to the front edge 56 of the resonator plate 22. Furthermore, a connection is typically also made between the other surfaces of the resonator plate 22, i.e., inner and outer surfaces 52 and 54 and side edges 60, 60, the surfaces 36, 38, 59, 64 and 66 at the tab section 50 and the surface of the diaphragm 26 adjacent to the opening 30. In other words, all mutually adjacent surfaces of the diaphragm 26, the resonator plate 22 and the tab section 50 can be connected to each other.Typically, the connection can be achieved via an epoxy resin bond 80, which is applied to the end of the resonator plate 22 and thus forms a mechanical connection between the components resonator plate 22 and membrane 26 and impedance matching element 32 of the coupling assembly 24, and adheres the insulating element 35 to the second side 28 of the coupling assembly 24. The epoxy resin bond 80 additionally fixes the coupling assembly 24 to the tab section 50 of the substrate element 20, so that the coupling assembly 24 is held by the substrate element 20, with the second side 28 of the coupling assembly 24 lying next to and spaced apart from the front edge 46 of the substrate element 20.

[0027] Accordingly, the transmission of ultrasonic energy between the resonator plate 22 and the coupling structure 24 is simplified by the mechanical bond formed by the epoxy resin bond 80. Through coupling with the resonator plate 22, the coupling structure 24 exhibits good transmission and impedance matching to the medium at the operating frequencies of the resonator plate 22, which in the embodiment described here can be in the range of approximately 100 kHz to approximately 1 MHz.

[0028] One advantage of the design of the transducer assembly 16 described here relates to the construction of the resonator plate 22 and its attachment to the substrate element 20. Specifically, the geometric design of the resonator plate 22 is such that multiple resonator plates 22 can be produced from a single sheet of ceramic material. In particular, a sheet of ceramic material, such as PZT5A, can be manufactured and grooved or cut to produce multiple individual rectangular pieces that essentially correspond to the desired dimensions of the resonator plate 22. Thus, several resonator plates 22 can be produced with minimal waste or residual material compared to the production of disk-shaped transducer resonators according to the prior art, which requires more steps to form the desired shape and also uses materials less efficiently.

[0029] Furthermore, as noted above, arranging the resonator plate 22 parallel to the substrate element 20 simplifies the automated assembly of the transducer assembly 16, for example, by means of a conventional pick-and-place process. In contrast, known assembly processes for the construction of transducer resonators that are not arranged parallel to the mounting structure, i.e., the printed circuit board, often require user manipulation of the ceramic resonator to efficiently position it relative to the mounting structure. Accordingly, the efficiency of the present transducer design contributes to ease of manufacture and cost-effective assembly.

[0030] It should be noted that the present invention is not necessarily limited to the specific rectangular shape for the resonator plate 22 described herein. Other shapes for the resonator plate 22 can also be chosen, although a resonator plate 22 with a form factor that simplifies its economical manufacture is preferred.

[0031] An example of an alternative embodiment of the present invention is set forth in the Fig. 5 and Fig. Figure 6 shows a disc-shaped resonator plate 122 mounted on a substrate element 120 in a manner similar to that described in the Fig. 1-4 illustrated embodiment described, and wherein elements of the embodiment of Fig. 5 and Fig. 6, the embodiment of the Fig. 1-4 correspond to the same reference numbers plus 100.

[0032] The resonator plate 122 preferably comprises a piezoceramic plate, similar to the material described above for the resonator plate 22. The resonator plate 122 can be mounted on a first contact block 168 such that the resonator plate 122 is held at a distance from an upper flat surface 136 of the substrate element 120, with an air gap between the resonator plate 122 and the substrate element 120. Preferably, the first contact block 168 engages with the resonator plate 122 at the geometric center of the resonator plate 122 and can be attached by a solder joint 167, such as can be implemented by an SMT reflow process, to form an electrical connection between an electrode on the inner surface 152 of the resonator plate 122 and the first contact block 168. Thus, the resonator plate 122 is held in a cantilevered position on the first contact block 168.A second electrical connection to an electrode on the outer surface 154 of the resonator plate 122 can be provided by an overhead wire 170 which extends to a contact block 172 on the substrate element 120 and can be connected by means of an SMT reflow process.

[0033] A coupler 124, which, for example, comprises a glass-filled epoxy resin element, is located on the outer surface 154 of the resonator plate 122 to provide impedance matching between the resonator plate 122 and a medium. The coupler 124 may be provided with a recess to accommodate the overhead wire 170, where it is attached to the upper surface 154 of the resonator plate 122. The path for acoustic signals transmitted and received by the resonator plate 122 and the coupler 124 extends in a direction that is generally orthogonal to the planar surface 136 of the substrate element 120. It should be noted that in the present embodiment the coupler 124 is designed without a diaphragm, so that the resonator plate 122 distributes the vibration energy substantially over the entire surface of the coupler 124 without the need for a diaphragm to distribute the energy in a radial direction.

[0034] Additionally, a bracket or mounting ring 180 can be positioned on the substrate element 120, which is substantially aligned with at least one section of an outer circumferential portion of the inner surface 152 of the resonator plate 122. The mounting ring 180 extends over the plane of the planar surface 136 and includes an upper surface 182, which is preferably spaced a relatively small distance from the inner surface 152 of the resonator plate 122. The mounting ring 180 can engage with the inner surface 152 to limit the leverage forces that can act at the attachment point with the first contact block 168.

[0035] While certain embodiments of the present invention have been illustrated and described, it is obvious to those skilled in the art that various further changes and modifications can be made without departing from the concept and scope of protection of the invention. The appended claims are therefore intended to cover all such changes and modifications that fall within the scope of protection of this invention.

Claims

[1] Ultrasound transducer assembly (16) for use in scanning or detecting the position of objects (12) near the transducer, wherein the ultrasound transducer assembly (16) comprises: a substrate element (20) which has a flat surface (36, 38) and a circumferential edge (40), a piezoceramic resonator plate (22) which is held next to the flat surface (36), and a coupler (24) connected to a surface of the resonator plate (22), for the acoustic coupling of the resonator plate (22) with a medium (15) which is in contact with the coupler (24); wherein the resonator plate (22) is held in a cantilevered relationship on a contact block (68) which extends at a distance ratio generally parallel to the substrate element (20). [2] Ultrasound transducer assembly (16) for use in scanning or detecting the position of objects (12) near the transducer, wherein the ultrasound transducer assembly (16) comprises: a substrate element (20) which has a flat surface (36, 38) and a circumferential edge (40), a piezoceramic resonator plate (22) which is held next to the flat surface (36), and a coupler (24) connected to a surface of the resonator plate (22) for acoustically coupling the resonator plate (22) to a medium (15) which is in contact with the coupler (24); wherein the coupler (24) has a substantially rigid, plate-like membrane element (26) which extends transversely or obliquely to the resonator plate (22). [3] Ultrasound transducer assembly (16) according to claim 2, wherein the coupler (24) further comprises an impedance matching element (32) which extends over the plate-like element (26). [4] Ultrasound transducer assembly (16) according to claim 3, wherein the membrane element (26) has an opening (30) and the resonator plate (22) extends to the opening (30) and includes a connecting structure which mechanically connects the surface of the resonator plate (22) to the membrane element (26) and the impedance matching element (32). [5] Ultrasound transducer assembly (16) according to claim 4, wherein the membrane element (26) includes a disc-shaped element. [6] Ultrasound transducer assembly (16) according to claim 4 comprising a damping material (18) located on one side of the coupler (24) opposite the medium (15), and comprising an elastic or compliant insulating layer (35) that separates the membrane element (26) from the damping material (18). [7] Ultrasound transducer assembly (16) according to claim 1, wherein the substrate element (20) comprises a printed circuit board and the resonator plate (22) is electrically connected to the printed circuit board by a surface mounting contact formed between the flat surface of the substrate element (20) and a flat inner side surface of the resonator plate (22). [8] Ultrasound transducer assembly (16) according to claim 7 with an electrical conductor (69, 73) extending between an outer side of the resonator plate (22), opposite the inner side, and the circuit board. [9] Ultrasound transducer assembly (16) according to claim 8, wherein the coupler (24) includes a generally planar element which extends transversely or obliquely to the resonator plate (22). [10] Ultrasound transducer assembly (16) according to claim 1, wherein the substrate element (20) includes a tab section (50) which extends in a cantilevered relationship from the circumferential edge (40) of the substrate element (20) and defines a section of the planar surface (36, 38). [11] Ultrasound transducer assembly (16) according to claim 1, wherein the resonator plate (122) has a disk-shaped element and is soldered to the contact block (168) at a geometric central section of the resonator plate (122). [12] Ultrasound transducer assembly (16) according to claim 1, wherein the coupler (124) is connected to a flat surface of the resonator plate (122) such that a path for acoustic signals transmitted and received by the resonator plate (122) extends in a direction that is orthogonal to the flat surface of the substrate element (120). [13] Ultrasound transducer setup (16) for use in detecting or scanning the position of objects (12) near the transducer, wherein the ultrasound transducer setup (16) comprises: a substrate element (20) which includes a printed circuit board that defines a flat surface and a circumferential edge, a piezoceramic resonator plate (22) with a flat inner surface (52), which is held on the flat surface (36) adjacent to the circumferential edge (40), electrical contacts (68, 72) between the circuit board and the resonator plate (22) for connecting the resonator plate (22) to a power supply (74) and a coupler (24) which has a planar element with opposing first and second sides, wherein the first side extends obliquely to a surface of the resonator plate (22) and is connected to it, for acoustically coupling the resonator plate (22) to a medium (15) which is in contact with the second side of the coupler (24). [14] Ultrasound transducer assembly (16) according to claim 13, wherein the resonator plate (22) comprises a rectangular plate which defines an elongated large dimension (D1) and a small dimension (D2), and the resonator plate (22) is held in a cantilevered relationship on a contact block (68), wherein its elongated large dimension (D1) extends from the circumferential edge (40) of the substrate element (20). [15] Ultrasound transducer assembly (16) according to claim 13, wherein the coupler (24) comprises a substantially rigid, disc-shaped membrane (26) and an impedance matching element (32) which is made of a different material than the membrane (26) and extends over the membrane (26) and defines a second side, and the coupler (24) further comprises a connecting structure which mechanically connects the surface of the resonator plate (22) to the membrane (26) and the impedance matching element (32) on the first side. [16] Ultrasound transducer assembly (16) according to claim 15 with a damping material (18) which surrounds the substrate element (20), the resonator plate (22) and the coupler (24), and the coupler (24) further comprising an elastic or compliant insulating layer (35) which separates the membrane (26) from the damping material (18). [17] Sensor (10) with an ultrasonic transducer assembly (16) for use in detecting or scanning the position of objects (12) in the vicinity of the transducer (16), wherein the sensor (10) comprises: a substrate element (20) which has a printed circuit board that defines a flat surface and a circumferential edge, a rectangular piezoceramic resonator plate (22) defining an elongated large dimension (D1) and a small dimension (D2), wherein the resonator plate (22) is held in a cantilevered relationship on the substrate element (20) and its elongated large dimension (D1) extends from the circumferential edge (40) of the substrate element (20), electrical contacts (68, 72) between the circuit board and the resonator plate (22), to connect the resonator plate (22) to a power supply (74), wherein one of the electrical contacts (68) forms a self-supporting mount for the resonator plate (22) on the substrate element (20), and a disc-shaped coupler (24) having a planar element with opposing first and second sides, wherein the first side extends obliquely to and is connected to a surface of the resonator plate (22), wherein the coupler (24) is acoustically excited by the resonator plate (22) to transmit a signal to an object (12) in the vicinity of the coupler (24), and the coupler (24) receives reflected signals from the object (12) and transmits them to the resonator plate (22). [18] Sensor (10) according to claim 17, wherein the coupler (24) includes a substantially rigid membrane (26) and an impedance matching element (32) which is made of a different material than the membrane (26) and extends over the membrane (26) and defines the second side, and the coupler (24) further includes a connecting structure which mechanically connects the surface of the resonator plate (22) to the membrane (26) and the impedance matching element (32) on the first side. [19] Sensor (10) according to claim 18, which has a housing (14) comprising a damping material (18) which surrounds the substrate element (20), the resonator plate (22) and the coupler (24), and wherein the coupler (24) further comprises an elastic or compliant insulating layer (35) which separates the membrane (26) from the damping material (18).

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