1D ultrasonic transducer unit for material detection

Description

[0001] The invention relates to a 1D ultrasonic transducer unit for material detection with at least three discrete and individually controllable ultrasonic transducers for detecting objects, contours or distances.

[0002] Ultrasound or ultrasonic transducers are used in a wide variety of measurement setups. Depending on the application, the ultrasound is coupled into a liquid or gaseous medium.

[0003] WO 2008 / 135 004 A1 discloses an ultrasonic transducer array for use in gaseous media. The array has a layered structure consisting of an electret layer between two electrode structures, one of which comprises several independently addressable electrode elements, thereby generating local thickness oscillations of the electret layer. EP 0 928 640 A1 discloses another ultrasonic transducer array of this type.

[0004] A 1.5D array of ultrasonic transducers with improved near-field resolution is known from US 2013 / 0283918 A1. US 2014 / 0283611 A1 and US 6,310,831 B1 describe phased-array ultrasonic transducer arrays and adaptive or compensating control methods.

[0005] Further ultrasonic transducers are from EP 0 940 801 A2 and from "Phased array transducer for emitting 40 kHz air-coupled ultrasound without grating lobes", Eric Konetzke et al., IEEE International Ultrasonic Symposium, 2015, pp. 1-4 and from "Air-coupled 40-kHz ultrasonic 2D-phased array based on a 3D-printed waveguide structure", Jäger et al., IEEE International Ultrasonic Symposium, 2017, pp. 1-4, and from "Takahashi et al., Ultrasonic phased array sensor for electrical travel aids for visually impaired people, Proceedings of the spie - The International society for optical engineering spie - vertical-cavity surface-emitting lasers XIII, vol. 6794, December 3, 2007, page 67943V, ISSN: 0277-786X" and from "Manufactoring Murata: Ultrasonic Sensor Application Manual Cat. No. S15E-5, January 1, 2009, URL:https: / / cdn-reichelt.de / documents / datenblatt / 8400 / ultraschall%20sensor.pdf, page 3".

[0006] For use in an industrial environment, the ultrasonic transducers used must be able to guarantee temperature stability from -40°C to, in some cases, over +100°C and electromagnetic compatibility with other technical devices. Furthermore, the ultrasonic transducers must be robust against harsh environmental influences such as dust, moisture, aggressive chemicals, as well as mechanical shocks or scratches.

[0007] To achieve long detection ranges, piezoelectric ceramics such as lead zirconate titanate (PZT) are used. These ceramics possess high coupling factors compared to other piezoelectric materials such as quartz, electrets, or PVFD. The coupling factor represents a measure of the conversion efficiency between mechanically and electrically stored energy. For PZT, for example, these values range from 0.3 to approximately 0.75, depending on the excitation direction.

[0008] Depending on the polarization direction of the piezoelectric material, alternating voltages can be used to generate resonant mechanical vibrations in the piezoelectric body. These vibrations are referred to as planar, thickness, or shear vibrations depending on their geometric propagation. For these vibration modes, the material-specific frequency constants can be used to estimate the typical dimensions of the piezoelectric body required for resonant vibration at a given frequency. These frequency constants for PZT typically range between 1300 kHz*mm and 2600 kHz*mm, depending on the vibration type.

[0009] A thin disk made of PZT suitable for sensor technology has a diameter of approximately 4 mm to 100 mm for excitation frequencies from 20 kHz to 500 kHz in planar mode. Due to the capacitive properties of such a thin disk, low excitation voltages can be easily implemented with appropriate polarization.

[0010] Greater thicknesses of the piezo disc are not desirable. On the one hand, with increasing thickness of the piezoelectric material, higher voltages, often in the kV range, must be applied for the same frequency range, which requires greater safety requirements. On the other hand, with increasing thickness of the piezoelectric body, its stiffness also changes, which has a direct impact on the reception of sound waves.

[0011] When using several ultrasonic transducers in a phased array of at least one-dimensional array, it must also be noted that the distances between adjacent ultrasonic transducers must not be greater than the wavelength of the ultrasonic wave or preferably not greater than half the wavelength.

[0012] This distance requirement limits the size of the individual transducers or the frequency ranges possible with a specific design / size of the ultrasonic transducer.

[0013] For a frequency range between 20 kHz and 500 kHz and coupling into air, for example, the maximum distances between adjacent transducers are in the order of approximately 8.5 mm to approximately 0.3 mm.

[0014] However, the previously described transducer with a thin disc made of PZT suitable for sensor technology has an average diameter that is more than 10 times larger due to the piezo disc diameter.

[0015] Against this background, the object of the invention is to provide a device that further develops the state of the art.

[0016] The object is achieved by a 1D ultrasonic transducer unit for hazard detection for material detection with the features of patent claim 1. Advantageous embodiments of the invention are the subject of subclaims.

[0017] According to the subject matter of the invention, a 1D ultrasonic transducer unit for material detection is provided, comprising a housing, at least three ultrasonic transducers and a control unit, wherein the control unit is designed to control each ultrasonic transducer individually, the housing has fastening means for fastening to a surface, the control unit is at least partially arranged in the housing, the housing has a communication interface, each ultrasonic transducer has a transducer housing, a piezoelectric body arranged in the transducer housing and a sound decoupling layer arranged at an open end of the transducer housing for coupling out into a gaseous medium and is arranged at a fixed position in the housing, each ultrasonic transducer is designed toto emit and / or receive a sound wave with a matching operating frequency and the operating frequency of the sound waves is in a range of 20 kHz to 400 kHz.

[0018] Each pair of directly adjacent ultrasonic transducers in the housing has a distance from the center of the sound extraction layer to the center of the sound extraction layer of no more than 10 cm, no more than 5 cm, or no more than 2 cm. The 1D ultrasonic transducer unit has one sound channel per ultrasonic transducer, with each sound channel having an input opening and an output opening, each sound extraction layer being assigned exactly one of the input openings, the output openings being arranged along a straight line, the output openings each being arranged in a wall of the housing, or the sound channels penetrating the wall of the housing.A distance from the center of one of the output openings to the center of an immediately adjacent output opening corresponds at most to the wavelength in the gaseous medium or at most to half the wavelength in the gaseous medium, wherein the distance between two immediately adjacent output openings is smaller than the distance between the ultrasonic transducers assigned to the corresponding input openings, a quotient of an area of the output opening to an area of the input opening has a value between 0.30 and 1.2 and each sound channel has at least a length corresponding to the diameter of the input opening.

[0019] It is understood that the ultrasonic transducers of the 1D ultrasonic transducer unit are individual, discrete components. Each ultrasonic transducer is arranged in and connected to the housing, thus maintaining fixed spacing from all other ultrasonic transducers. Two ultrasonic transducers arranged side by side, with no other ultrasonic transducer between them, are directly adjacent to each other.

[0020] It is also understood that the individual sound channels are tubular or rod-shaped, with, for example, the tube diameter being reduced and / or the shape of the cross-sectional area being changed and / or the channel being curved. Advantageously, the sound channels have no edges along their entire length, from the sound coupling layer to their exit opening.

[0021] The sound channels guide the sound waves generated by the individual ultrasonic transducers out of the housing and return reflected sound waves to the ultrasonic transducers. This creates a wave front through superposition at the output ports on the housing wall or outside the housing.

[0022] With the multiple, individually controllable ultrasonic transducers, wavefronts with adjustable main propagation directions can be generated through temporally or phase-shifted control. This makes it possible to scan a larger measurement area, at least in one dimension, with just one 1D ultrasonic transducer unit. Furthermore, the surface structure and / or shape of an object can be captured. This allows, for example, the type of material and / or object to be determined.

[0023] By arranging sound channels in front of the individual ultrasonic transducers, the individual sound sources are relocated to the respective ends or exit openings of the sound channels when superimposed or for superimposing into a common wavefront. This makes it possible to adjust the distances between the individual sound sources independently of the size (e.g., diameter) of the individual ultrasonic transducers or independently of the distances between the individual ultrasonic transducers. In particular, it is possible to reduce the distances between the sound sources compared to the distances between the individual transducers.

[0024] For example, with a housing diameter of the individual ultrasonic transducers of 7 mm, the distance between two transducers is at least 14 mm. Accordingly, without a sound channel, only wavefronts with frequencies up to a maximum of 22 kHz (λ ≥ 14 mm) or up to a maximum of 11 kHz (λ / 2 ≥ 14 mm) are achievable. Generating wavefronts with higher frequencies, i.e., shorter wavelengths, is only possible with the same ultrasonic transducers using the sound channels according to the invention, since the distance between the individual "sound sources" during superposition is determined not by the size of the transducer housings, but only by the size and distance of the sound channel exit openings.

[0025] The sound channels also ensure precise, directional detection.

[0026] The radiating aperture of the piezoelectric transducer, e.g., a circular aperture with a diameter predetermined by the piezoelectric body, is modified by the sound channels so that it meets the requirements of a desired array arrangement in at least one dimension. This enables the use of robust, reliable, and / or cost-effective discrete ultrasonic transducers in a phased array arrangement. The phased array arrangement enables a large viewing angle with just a single 1D ultrasonic transducer unit, enabling reliable monitoring of fill levels, for example. The detection of surface structures and / or objects or object shapes is also possible. There is no need to use particularly small, integrated ultrasonic transducers such as MEMS. Nor is there any need to attach, read out, and, if necessary, coordinate multiple transducer units.

[0027] According to the invention, the housing has a movable cover device, which is designed to close the output openings of all sound channels. The cover device allows the sound channels to be closed as long as the 1D ultrasonic transducer unit is not in use, thereby preventing the ingress of foreign bodies / contaminants. For opening and closing the sound channels or for moving the cover device, the 1D ultrasonic transducer unit includes, for example, an actuating means.

[0028] According to a further development, the quotient between the surface area of the second cross-sectional area and the surface area of the first cross-sectional area has a value between 0.5 and 1.2 or between 0.9 and 1.1. According to the invention, the surface area of the input area can be increased, decreased, or maintained, while simultaneously achieving a reduction in at least the width of the output opening compared to the input opening.

[0029] According to a further embodiment, each sound channel has a length from the sound coupling layer of each ultrasonic transducer to the output opening of the associated sound channel, wherein the length is an integer multiple of one eighth of the wavelength of the sound frequency or an integer multiple of half the wavelength of the sound frequency.

[0030] According to the invention, the output ports of all sound channels are located in a common flat plane or in a curved surface. By arranging them in a curved surface, e.g., a concave surface, focused wavefronts can be generated.

[0031] In another embodiment, each sound channel is made of a metal or a plastic. Alternatively, each sound channel comprises a metal or a plastic.

[0032] According to a further embodiment, each ultrasonic transducer has a sound decoupling layer between the sound decoupling layer and the transducer housing.

[0033] In another embodiment, the control unit is arranged completely or partially in the housing.

[0034] According to another embodiment, the housing of the 1D ultrasonic transducer unit is designed to at least meet IP 40 protection class.

[0035] In a further development, the communication interface is designed for wireless data transmission, e.g., as a Bluetooth interface. This allows, for example, control and / or measurement signals to be exchanged wirelessly between the 1D ultrasonic transducer unit and, for example, an external control unit or evaluation unit. Alternatively, the 1D ultrasonic transducer unit communicates with the communication interface via a cable, e.g., using a bus system or protocol.

[0036] According to another embodiment, each ultrasonic transducer projects into the associated input opening with the sound coupling layer facing forward. In a further development, each sound channel precisely accommodates at least a portion of the associated ultrasonic transducer. In other words, according to this embodiment, an inner shape of the sound channels in the region of the input opening corresponds as closely as possible to an outer shape of the respective ultrasonic transducer.

[0037] In a further embodiment, the housing of each ultrasonic transducer has a diameter of at least 7 mm. The housing of each ultrasonic transducer is designed, for example, as a cylindrical metal cup. According to a further development of this embodiment, a surface of the sound decoupling layer, an edge of the metal cup, and, for example, a sound decoupling layer arranged therebetween, each define a flat plane of each individual ultrasonic transducer.

[0038] In another embodiment, each ultrasonic transducer has an electromagnetic shield connected to a reference potential. It is understood that the electromagnetic shield can also be formed entirely or at least partially by the housing, in particular a metal cup serving as the housing. Alternatively, the 1D ultrasonic transducer unit can also have a common shield for all ultrasonic transducers, e.g., a common housing.

[0039] In a further embodiment, each sound channel has a wall thickness of at least 0.5 mm or at least 1 mm. According to another refinement, two sound channels are spaced apart from each other by at least 0.5 mm or at least 1 mm over the entire length of the two sound channels.

[0040] According to another embodiment, the housing comprises a flat rear wall and a front wall running parallel to the rear wall. This makes attaching and aligning the 1D ultrasonic transducer unit to a surface particularly simple and reliable. The ultrasonic transducers are preferably attached to the rear wall, and the sound channels preferably end at or in the front wall. Particularly preferably, not only the output openings of the sound channels, but also the ultrasonic transducers and the input openings of the sound channels are arranged along a straight line. The straight line spanned by the inputs of the sound channels is, for example, significantly longer than the straight line spanned by the output openings.

[0041] The invention is explained in more detail below with reference to the drawings. Similar parts are labeled with identical reference numerals. The illustrated embodiments are highly schematic, meaning the distances and the lateral and vertical extensions are not to scale and, unless otherwise stated, do not have any deducible geometric relationships to one another. In the drawings: Figure 1A shows a view of a first embodiment of a 1D ultrasonic transducer unit for level detection according to the invention, Figure 1B shows a view of a second embodiment of a 1D ultrasonic transducer unit for object detection according to the invention, Figure 2 shows a sectional view of an example of a housing of a 1D ultrasonic transducer unit, Figure 3 shows a view of a further example of the sound channels, Figure 4 shows a view of a further embodiment of the sound channels according to the invention, Figure 5 shows a view of a further embodiment of an individual sound channel, Figure 6 shows a schematic view of various embodiments of an output surface of a sound channel.

[0042] The illustration of the Figure 1Ashows a view of a first embodiment of a 1D ultrasonic transducer unit 10 according to the invention for level detection. The 1D ultrasonic transducer unit has a housing 14, which is attached to a ceiling 102 of a container 102 for a bulk material 104 by fastening means 11. Sound waves are generated by the 1D ultrasonic transducer unit 10. The sound waves have a main propagation direction, wherein the main propagation direction can be pivoted in the image plane (dashed line, dotted line, or dash-dotted line), whereby the entire container 102 can be reliably scanned. The bulk material 104 and / or a bottom of the container 102 and / or a side wall of the container 102 reflect the sound waves.

[0043] Using the 1D ultrasonic transducer unit, both the height or quantity of the bulk material 104 and the surface structure of the bulk material 104 can be recorded, allowing conclusions to be drawn about the type of bulk material 104. In the illustration of the Figure 1B A second embodiment of the 1D ultrasonic transducer unit 10 according to the invention is shown. The 1D ultrasonic transducer unit 10 is mounted by means of the fastening means 11 on a building ceiling 106 above a conveyor belt 108, so that objects 110 on the conveyor belt can be detected using the ultrasonic waves. By pivoting the emitted ultrasonic waves, it is possible to monitor a larger area of the conveyor belt 108 and to detect the shape or surface structure of objects 110 located on the conveyor belt 108.

[0044] In the illustration of the Figure 2A sectional view of a housing 14 of an ultrasonic transducer unit 10 is shown. Five discrete ultrasonic transducers 12 are arranged in the housing 14 along a flat rear wall 16 of the housing 14. Each ultrasonic transducer 12 has its own transducer housing 18 and a sound extraction layer 20. Each ultrasonic transducer 12 is spaced from the immediately adjacent ultrasonic transducer(s) 12 by a distance A1 from the center of the sound extraction layer 20 to the center of the sound extraction layer 20.

[0045] Each ultrasonic transducer 12 is assigned a sound channel 22, each sound channel 22 having an input opening 24 and an output opening 26. The input openings 24 are each arranged in front of or around one of the ultrasonic transducers 12 such that the respective ultrasonic transducer 12 radiates into the sound channel 22. The output openings 26 of the sound channels 22 are arranged along a flat front wall 30 of the housing 14 opposite the rear wall or penetrate the front wall 30.

[0046] Each two adjacent output openings 26 have a distance A2 from the center of the output opening 26 to the center of the output opening 26. According to the invention, the distance A2 of the output openings 26 is less than or equal to the distance A1 of the associated or corresponding ultrasonic transducers 12.

[0047] A length L1 from each sound coupling layer 20 to the output opening 26 of the associated sound channel 22 is an integer multiple of one eighth of the wavelength of the sound frequency.

[0048] The housing 14 also includes a movable cover device 32.

[0049] In the illustrated example, the cover device 32 is in a closed state. For this purpose, the cover device is arranged in front of the front wall 30 of the housing 14 with the outlet openings 26, so that the sound channels 22 are closed. In an open state, the cover device 32 is no longer located in front of the front housing wall 30 and the outlet openings 26, for example, by folding or sliding, and the outlet openings 26 are exposed.

[0050] In the Figure 3In the illustrated embodiment, the sound channels 22 run such that the output openings 26 of all sound channels 22 lie in a common flat plane E1. In the illustrated embodiment, the front wall 30 of the housing 14 of the 1D ultrasonic transducer unit 10 runs within the plane E1. A region 34 of the respective sound channel 22, located in front of the input opening 24 of each sound channel 22, is designed such that the respectively assigned ultrasonic transducer 12 fits precisely into the sound channel 22. For this purpose, each sound channel 22 has an inner diameter corresponding to the outer diameter D1 in this region and an edge 36 serving as a stop.

[0051] A control unit (not shown) is designed to control each ultrasonic transducer 12 individually. By controlling the individual ultrasonic transducers 12 with a time-shifted or phase-shifted timing, the 1D ultrasonic transducer unit 10 generates planar ultrasonic waves with a main propagation direction (arrows). The main propagation direction or an angle between the main propagation direction and the first plane E1 can be adjusted by means of the phase shift between the sound waves emerging from the output openings 26 of the individual sound channels.

[0052] In the Figure 4 In the embodiment shown, the output openings 40 of all sound channels 36 are located in a concavely curved surface F1.

[0053] In the illustration of the Figure 5 A single sound channel 22 is shown schematically, with the differences compared to the Figures 1 to 4 be explained.

[0054] The inlet opening 24 has a cross-sectional area with a width x1 and a height y1, the outlet opening 26 has a cross-sectional area with a width x2 and a height y2.

[0055] The inlet opening 24 is circular, meaning the width x1 and the height y1 of the cross-sectional area have the same value. The outlet opening 26, on the other hand, has an oval shape, so that the width x2 of the cross-sectional area is smaller than the width y2.

[0056] Preferably, the width x2 of the outlet opening 26 is smaller than the width x1 of the inlet opening 26. The height y2 of the outlet opening 26, on the other hand, is preferably greater than the height y1 of the inlet opening 24. Particularly preferably, the increase in height of the sound channel 22 compensates for the decrease in the width of the sound channel 22 such that the surface area of the cross-sectional area of the inlet opening 24 corresponds to the surface area of the cross-sectional area of the outlet opening 26.

[0057] It is understood that the width x2 of each output opening 26 must be smaller than the wavelength of the sound frequency in order to be able to realize a distance from the center of the output openings 26 to the center of an immediately adjacent output opening 26 of at most the wavelength of the sound frequency.

[0058] In the illustration of the Figure 6 Several exemplary embodiments of the cross-sectional areas of the exit openings 26 according to the invention are schematically illustrated. To ensure that the surface area of the cross-sectional area of the exit opening 26 corresponds to the surface area of the cross-sectional area of the inlet opening 24, shapes with a ratio of width x2 to height y2 of approximately 1.5 are particularly suitable.

Claims

1. 1D ultrasonic transducer unit (10), wherein the ultrasonic transducer unit (10) is configured for material detection, comprising a housing (14), at least three ultrasonic transducers (12) and a control unit, wherein - the ultrasonic transducers (12) are of discrete construction, - the control unit is designed for the purpose of individually controlling each ultrasonic transducer (12), - the housing has a communications interface, - each ultrasonic transducer (12) comprises a respective transducer housing (18), a piezoelectric body (18) arranged in the transducer housing (18) and a sound decoupling layer (20), which is arranged at an open end of the transducer housing (18), for decoupling in a gaseous medium, and is arranged at a fixed position in the housing (14), - each ultrasonic transducer (12) is designed for the purpose of emitting and / or receiving a soundwave with a corresponding working frequency, - the working frequency of the soundwaves lies in a range of 20 kHz to 400 kHz, characterised in that - the housing (14) comprises fastening means (11) for fastening to a surface, - the control unit is arranged at least partly in the housing (14), - each two ultrasonic transducers (12), which are arranged directly adjacent to one another, in the housing (14) have a spacing (A1) from centre of sound decoupling layer (20) to centre of sound decoupling layer (20) of at most 10 cm or at most 5 cm or at most 2 cm, - the 1D ultrasonic transducer unit (10) has one sound channel (22) per ultrasonic transducer (12), - each sound channel (22) has an inlet opening (24) and an outlet opening (26), - exactly one of the inlet openings (24) is associated with each sound decoupling layer (20), - the outlet openings are arranged along a straight line, - the outlet openings are each arranged in a wall of the housing or the sound channels penetrate the wall of the housing, - a spacing (A2) from the centre of one of the outlet openings (26) to the centre of a directly adjacent outlet opening (26) corresponds with at most the wavelength in the gaseous medium or at most with half the wavelength in the gaseous medium, - wherein the spacing (A2) between two directly adjacent outlet openings (26) is in each instance smaller than the spacing (A1) between the ultrasonic transducers (12) associated with the corresponding inlet openings (24), - a quotient of an area of the outlet opening (26) with respect to an area of the inlet opening (24) has a value between 0.30 and 1.2 and characterised in that - each sound channel (22) has at least a length corresponding with the diameter of the inlet opening (24), - the housing comprises a movable cover device (32), wherein the cover device (32) is designed for the purpose of closing the outlet openings (26) of all sound channels (22), - the outlet openings (26) of all sound channels (36) lie in a curved surface (F1).

2. 1D ultrasonic transducer unit (10) according to claim 1, characterised in that the quotient of the area of the outlet opening (26) with respect to the area of the inlet opening (24) has a value between 0.5 and 1.2 or between 0.9 and 1.1.

3. 1D ultrasonic transducer unit (10) according to one of claims 1 and 2, characterised in that each sound channel (22) has a length (L1) from the sound decoupling layer (20) of each ultrasonic transducer (12) to the outlet opening (26) of the associated sound channel (22) and the length (L1) is an integral multiple of an eighth of the wavelength of the sound frequency or an integral multiple of half the wavelength of the sound frequency.

4. 1D ultrasonic transducer unit (10) according to any one of claims 1 to 3, characterised in that each sound channel (22) consists of a metal or a plastic or comprises a metal or a plastic.

5. 1D ultrasonic transducer unit (10) according to any one of claims 1 to 4, characterised in that each ultrasonic transducer (12) has a sound uncoupling layer between the sound decoupling layer (20) and the transducer housing (22).

6. 1D ultrasonic transducer unit (10) according to any one of claims 1 to 5, characterised in that the control unit is arranged completely or partly in the housing (14).

7. 1D ultrasonic transducer unit (10) according to any one of claims 1 to 6, characterised in that the housing (14) of the 1D ultrasonic transducer unit (10) is constructed in correspondence with at least the IP 40 form of protection.

8. 1D ultrasonic transducer unit (10) according to any one of claims 1 to 7, characterised in that the communications interface is configured for wire-free data transmission.

9. 1D ultrasonic transducer unit (10) according to any one of claims 1 to 8, characterised in that at least five ultrasonic transducers (12) are provided.

10. 1D ultrasonic transducer unit (10) according to any one of claims 1 to 9, characterised in that the 1D ultrasonic transducer unit is oriented for the purpose of generating soundwaves along a principal direction of propagation, wherein the principal direction of propagation can be swivelled in the image plane.

11. 1D ultrasonic transducer unit (10) according to any one of claims 1 to 10, characterised in that the outlet opening (26) has an oval shape.