GB2542919A

GB2542919A - An electroacoustic transducer device

Info

Publication number: GB2542919A
Application number: GB1614556.7A
Authority: GB
Inventors: Charles Robert Stickland Anthony; Richard Austin Mark; James Middleton Mathew; Stewart Blacklock Oliver
Original assignee: GILL INSTR Ltd
Current assignee: GILL INSTR Ltd
Priority date: 2015-10-02
Filing date: 2016-08-26
Publication date: 2017-04-05
Also published as: GB201517422D0; WO2017054930A1; GB201614556D0

Abstract

The electroacoustic transducer device 10 comprises an electroacoustic transducer, preferably piezoelectric, 12 within a housing 25 such that there is a region 32 between the transducer 12 and the housing 25. This region surrounds the transducer 12 but does not cover a transmitting surface 42 of the transducer coupling means 36. The said region is filled or is at least partly filled with an acoustically-attenuating closed-cell foam 35 at least a part of which is coated with an adhesive sealant 35 which provides a water-resistant seal between the transducer 12 and the housing 25. The device may be used within an acoustic fluid-flow meter and/or an acoustic anemometer.

Description

[0001] An electroacoustic transducer device [0002] The present invention relates to an electroacoustic transducer device.

[0003] An electroacoustic transducer is disclosed in US-A-3943388. It utilises a vibratory diaphragm to form a closure for a cylindrical tubular housing. The sound radiating surface of the diaphragm is of a concave shape to achieve an increasing diaphragm thickness at its periphery. The concave diaphragm design permits the precise adjustment of the resonant frequency of large quantities of mass produced transducers by machining the surface of the thick rim portion of the diaphragm.

Greater precision in the adjustment of the resonant frequency is achieved with this design because the frequency change is less critically dependent on the amount of material removed than is the case with a conventional flat diaphragm surface. However, because a piezoceramic device is attached directly to the underside of the vibratory diaphragm, the resulting transmission is compromised as regards its uniformity as a function of angle of transmission from the central perpendicular of the vibratory diaphragm. Thus in a forward direction away from the diaphragm surface, a plot of sound intensity as a function of angle away from a central perpendicular to the surface may have lobes, because the surface may vibrate with anti-nodes.

[0004] A transducer such as is disclosed in our copending European Patent Application No. 15020036.8 seeks to provide a remedy. It has a housing and comprises an electromechanical transducer within the housing and a vibratory component having a generally cylindrical side wall, an outwardly directed portion at the base of the side wall, and a generally planar vibratory top wall extending inwardly from the rim of the side wall further from its base to close the upper end of the cylindrical side wall, in which the said outwardly directed portion is mounted on the electromechanical transducer.

[0005] This provides the advantage that the transducer in operation produces a uniform radiation pattern over a wide-angle, such that the radiation pattern varies slowly and smoothly with angle away from a central perpendicular to the top wall. This is effected by virtue of the flexural mode of the vibratory component. It makes the electroacoustic transducer especially suitable for applications in which the sound emitted by the transducer passes through a medium such as air which may be moving transversely of a perpendicular to the top wall of the vibratory component. One such application is in the construction of an anemometer. In such a construction, at least two such electroacoustic transducers are arranged opposing one another, so that each is able to transmit sound signals to and receive sound signals from the other of the pair of transducers. It also inhibits interference from the side walls and base of the vibratory component, which may radiate acoustic signals which are in antiphase with signals transmitted from the top wall of the vibratory component.

[0006] Whilst such a transducer is resistant to water seeping into the housing interior between the transducer and the housing, which would then cause damage if it freezes, this resistance is provided by a device which does not of itself have acoustic attenuating properties.

[0007] The present invention seeks to provide a remedy.

[0008] Accordingly, the present invention is directed to an electroacoustic transducer device comprising an electroacoustic transducer housed within a housing such that there is a region between the transducer and the housing, which region surrounds the transducer but which region does not cover a transmitting surface of the transducer, characterised in that the said region is filled or is at least partly filled with an acoustically-attenuating closed-cell foam at least a part of which is coated with an adhesive sealant which provides a seal between the transducer and the housing.

[0009] This provides the advantage that adhesive sealant extends between the transducer and the housing to form a seal therebetween, thus inhibiting the ingress of water. At the same time the closed-cell foam provides acoustic attenuation of any sound created at regions which are other than the transmitting surface, to inhibit interference of the sound transmitted from that surface by sound emanating from other surfaces of the transducer. At least those regions of the closed-cell foam between the housing and the electroacoustic transducer which would otherwise be exposed to the exterior of the electroacoustic transducer device are coated with adhesive sealant, although it is possible to have all of the closed-cell foam thus coated.

[0010] The electroacoustic transducer device may be provided with a heater to inhibit build-up of ice on the exterior surfaces of the device when it is used in freezing conditions.

[0011] The vibratory component and the housing may be made of metal to facilitate conduction of heat to different parts of the exterior of the device.

[0012] The adhesive sealant may comprise a polyurethane adhesive sealant.

[0013] The electroacoustic transducer may comprise an electromechanical transducer within the housing and a vibratory component coupled to the electromechanical transducer .

[0014] This facilitates a well directed sound transmission.

[0015] The vibratory component may comprise a generally cylindrical side wall, an outwardly directed portion at the base of the side wall, and a generally planar vibratory top wall extending inwardly from the rim of the side wall further from its base to close the upper end of the cylindrical side wall, in which the said outwardly directed portion is mounted on the electromechanical transducer.

[0016] This provides the advantages that the vibratory component serves as an acoustic amplifier, that its properties do not change significantly with temperature, and that the top wall, being the wall that provides the transmitting surface of the electroacoustic transducer, also provides a smooth acoustic radiation profile.

[0017] The side wall, top wall and outwardly directed portion of the vibratory component may be constituted by a single integral piece of material.

[0018] The cylindrical side wall may be circular in cross section.

[0019] The portion which extends outwardly from the base of the side wall may be or may be part of a flange extending around the base of the side wall. The flange may be annular, and may be a full ring, or it may be an open ring with a gap between the ends of the ring to accommodate an electrical connection to the electromechanical transducer.

[0020] The electromechanical transducer may comprise a piezoceramic device, for example a piezoceramic block or crystal.

[0021] The vibratory component may comprise metal, for example aluminium, for example aluminium 6082.

[0022] The electromechanical transducer may be seated on the base of the housing interior on three feet. The latter may be equiangularly spaced around the base of the interior of the housing, with the angular spacing between any pair of feet being substantially 120°.

[0023] The present invention extends to a fluid-flow meter comprising at least two electroacoustic transducers each constructed in accordance with the present invention, the two transducers being spaced apart from one another and being oriented so that each is able to transmit sound towards and receive sound from the other of the pair.

[0024] The present invention further extends to an anemometer comprising at least two pairs of such transducers, the transducers of one pair being spaced apart from one another along a first imaginary line, and the transducers of the at least one other pair being spaced apart along a second imaginary line which extends in a different direction from that of the first imaginary line .

[0025] The anemometer may comprise two or three such pairs with their respective axes of transmission and reception being oriented mutually orthogonally relative to one another, or such that the two or three axes have at least components lying along three mutually orthogonal axes respectively.

[0026] Examples of electroacoustic transducers, a fluid-flow meter and anemometers embodying the present invention will now be described in greater detail with reference to the accompanying drawings, in which: [0027] Figure 1 shows an axial sectional view of an electroacoustic transducer constituting a first embodiment of the present invention; [0028] Figure 2 shows an axial sectional view of an electroacoustic transducer constituting a second embodiment of the present invention; [0029] Figure 3 shows a view from above of the electroacoustic transducer shown in Figure 2; [0030] Figure 4 shows a cross-section through a component of the electroacoustic transducers shown in Figures 1 and 2; [0031] Figure 5 shows diagrammatically an elevational sectional view of a fluid-flow meter embodying the present invention; [0032] Figure 6 shows electrical circuitry of the meter shown in Figure 5; [0033] Figure 7 shows a perspective side view of a first embodiment of an anemometer embodying the present invention; [0034] Figure 8 shows electrical circuitry of the anemometer shown in Figure 7; and [0035] Figure 9 shows a diagrammatic side view of a second embodiment of an anemometer embodying the present invention.

[0036] With reference to the Figure 1, an electroacoustic transducer 10 comprises a cylindrical block of circular cross-section of piezoceramic material 12 constituting an electromechanical transducer and having a circular planar upper main face 14 and a circular planar lower main face 16. Both main faces 14 and 16 are silvered to improve electrical connectivity thereto .

[0037] Respective electrically conductive wires 18 and 20 are connected to electrical connections 22 and 24, both constituted by solder connections, in electrical contact with the upper and lower planar surfaces 14 and 16 respectively of the piezoceramic block 12.

[0038] The piez oceramic block 12 is enclosed within a moulded plastics housing 25 with a generally cylindrical side wall 26 of circular cross-section and a generally circular base portion 28, so that the housing 25 has a generally cylindrical interior of circular cross-section. Extending laterally of the cylindrical portion 26 is a tubular portion 30 surrounding and protecting the electrical connector wires 18 and 20. An upper rim 27 of the housing 25 is turned inwardly.

[0039] The lower half of the piezoceramic block 12 is covered with tape 32 except for a portion of the lower planar surface 16 to which is attached the electrical contact 24.

[0040] The piezoceramic block 12 is seated within the interior of the housing 25 on the circular base portion thereof via the intermediary of three plastics (acetal) feet 34 only one of which is visible in the axial section of the only Figure of the drawing. The feet 34 are equiangularly spaced about the central axis of the housing 26, so that the angle subtended from that axis by any pair of feet 34 is substantially 120°.

[0041] Attached so as to be acoustically coupled with the upper planar surface 14 of the piezoelectric block 12 is a vibratory component 36 in the form of a metallic "top hat", the metal of which comprises aluminium 6082, although other metals could be used. Thus the component 36 comprises a cylindrical tubular side wall 38 of circular cross-section, an annular flange 40 extending outwardly from the base of the cylindrical side wall 38 except where the electrical connection 22 is located, so that the annular flange 40 is constituted by an open ring.

[0042] There is an air gap 41 everywhere between the inner edge of the rim 27 and the outer cylindrical surface of the vibratory component 36, to provide an acoustic isolation between these parts.

[0043] It is through the underside of the annular flange 40 that the component 36 contacts and is in acoustic coupling with the piezoelectric ceramic block 12, albeit through the intermediary of adhesive (not shown).

[0044] An annular skirt 52 of the vibratory component 3 6 extends downwardly from the outer rim of the annular flange 40, but there is a small gap between skirt 52 and the upper end of the cylindrical wall of the piezoceramic block 12. A gap also exists between the exterior upper corner of the block 12 and the interior corner of the component 36 where the skirt 52 meets the annular flange 40.

[0045] The component 36 further comprises a top wall 42 extending inwardly from an upper rim of the cylindrical side wall 38 to close the upper end of the that side wall 38 and to constitute a vibratory membrane. The interior 43 of the component 36 is air-filled.

[0046] The space between the housing 25 and the piezoelectric crystal 12, and also the space between the housing 25 and the cylindrical side wall 38 of the vibratory component 36, is filled with a filling comprising a plastics material closed-cell foam 35 (for example EPDM (ethylene propylene diene monomer) rubber closed-cell foam sheet) . As shown in Figure 4, this closed-cell foam 35 is coated with a polyurethane adhesive sealant 54 (for example Scotch-Seal® Polyurethane Adhesive Sealant 540-560) . This sealant 54 therefore creates a water-impermeable seal between the cylindrical side wall 38 of the vibratory component 36 and the housing 25, inhibiting the ingress of potentially damaging water between the component 36 and the housing 25. The bridge of sealant between the component 36 and the housing 25 is close to the circular corner 44 of the component 36, where there is little vibratory movement of the material of the component 36 when the top wall 42 is vibrating, so that there is little if any transmission of sound from the component 36 to the housing 25 when the device is in use. At the same time, the plastics material closed-cell foam 35 constitutes an acoustically attenuating shield to inhibit the transference of acoustic energy from the electroacoustic transducer, constituted by the piezoceramic block or crystal 12 and the vibratory component 36, to the housing 25.

[0047] It will be appreciated that when the polyurethane sealant 54 which coats the closed-cell foam 35 is cured, it adheres to surfaces it is in contact with and becomes rigid. Cells of the foam 35 which are open by virtue of their being at the surface of the foam receive the sealant 54. At the same time, when the sealant 54 hardens, the interior of the foam 35 retains its low density structure and acoustic attenuating properties.

[0048] When the electroacoustic transducer 10 is in use, a high frequency oscillating voltage is applied across the connections 22 and 24 via the electrically conductive wires 18 and 20, and hence across the planar surfaces 14 and 16 of the piezoceramic block or crystal 12. The frequency is the resonant frequency of the block or crystal 12, being a frequency in the ultrasonic range of frequencies. As a consequence, the block or crystal vibrates, in turn causing the vibratory component 36 to vibrate. The flexural mode of such vibration is one in which material see-saws through very small distances about the circular corner 44 between the top wall 42 and the cylindrical side wall 38 of the vibratory component 36, rocking alternately in a clockwise and an anticlockwise sense about that corner 44 as viewed in cross section, so that the corner 44 constitutes a nodal ring, and there is substantially no movement of the material of the component 36 at this corner 44. This is brought about by coupling a rotary motion of the crystal 12 at its corners with the resulting rotary motion of the corner 44 via the side wall 38. The upper surface of the top wall 42 vibrates towards and away from the block or crystal 12, so as to create sound waves travelling away from that wall, with a uniform radiation pattern over a wide-angle, such that the radiation pattern varies slowly and smoothly with angle away from a central perpendicular to the top wall 42. It is not adversely affected by the vibration of the side wall 38, which is in anti-phase with the vibration of the top wall 42, because the side wall 38 is shielded by the filling 35 and the housing 25. This pattern stays constant with temperature. It will be appreciated that this radiation pattern is obtained by shielding sound from the side wall 38 of the vibratory component 36 from the top wall 42, by isolating the side wall 38 from the exterior.

[0049] The embodiment shown in Figures 2 and 3 has its components which are equivalent to components of the Figure 1 embodiment labelled with the same reference numerals and has all the features of the Figure 1 embodiment, except in so far as: the tape 32 and the feet 34 of the Figure 1 embodiment are absent; the housing 25 of the Figure 1 embodiment is constituted by two concentric cylindrical metal components 200 and 202 held together by an adhesive 204 sandwiched between those components 200 and 202, the thickness of each of the components 200 and 202 being substantially uniform, the inner of the components, component 202, providing the inwardly turned lip 27; a heating foil 206 is wrapped around the block or crystal 12; a metal bobbin 208 is provided underneath the block or crystal 12, a neck 210 of the bobbin being surrounded by an electrically conductive heating coil 212; the sealant coated foam 35 is provided as three parts comprising an annular part 214 surrounding and abutting the cylindrical side wall 38 of the vibratory component 36, a cylindrical part 216 surrounding and abutting the block or crystal 12, and a disc-shaped part 218 against the underside of the block or crystal 12; the underside of the housing 26 comprises separate block components 220 and 222 which together form a generally hemi-spherical underside of the device, with a conical interior which houses the heating coil 212 and is filled with an acoustically attenuating material 224 which also extends into the interior of the tubular portion 30 through which extend the connecting wires 18 and 20 which are shown in Figure 1 and which are present in the embodiment shown in Figure 2 but which are not actually shown in Figure 2.

[0050] The Figure 2 embodiment operates in the same way as the Figure 1 embodiment, and in addition may be heated internally by the foil 206 and/or the coil 212 to inhibit the build-up of ice on the device 10 when it is used in freezing conditions.

[0051] The flowmeter shown in Figure 5 comprises an inlet pipe 510 and an outlet pipe 512 between respective ends of which extends a measurement duct 514. When the flowmeter is in use, fluid flows down through the inlet pipe 510, and continues along the measurement duct 514, and thence up along the outlet pipe 512.

[0052] Two transducers 516 and 518 are located at opposite respective ends of the duct 514, each transducer being constructed in accordance with the transducer shown in and described with reference to Figure 2. Each is oriented so that its vibratory surface faces the interior of the duct, whereby each is able to transmit sound towards and receive sound from the other of the pair.

[0053] Both transducers 516 and 518 are connected electrically to a microprocessor 520 which is programmed to cause ultrasonic pulses to be transmitted from and received by both transducers 516 and 518, and to measure the speed of flow of fluid through the duct 514 from the difference in the time for transmission of such a pulse in one direction along the duct and the time for transmission in the opposite direction.

[0054] Figures 7 and 8 show an anemometer 710 comprising three pairs of electroacoustic transducers 716-718, 720-722, and 724-714 each supported on top of a base plate 712 and each made as described with reference to and as illustrated in Figure 2 of the accompanying drawings. The transducers are oriented so that the transducers of each pair are directed towards one another, but at an angle such that emission of an ultrasonic pulse from one transducer is directed towards the underside of a reflector plate 726 fixed parallel to the base plate 712 by way of a central column 728, to be reflected down towards the other of the pair of transducers .

[0055] All the transducers are electrically connected to a microprocessor 730 as shown in Figure 8. The microprocessor 730 is programmed to provide a measure of the speed and direction of wind blowing between the plates 710 and 720 from the difference between the time taken for a pulse to pass between the transducers of each pair in one direction, and the time for that to happen in the opposite direction.

[0056] In the embodiment shown in Figure 9, the transducers are again arranged in pairs 716-718, 720-722, and 724-714 (the transducer 714 being obscured from view by the transducer 724), but they are oriented so that the direction of emission of a pulse from each transducer is directly towards the other transducer of the pair. Furthermore, the respective axes of transmission and reception of the three pairs are mutually orthogonal to one another (or at least have components respectively along three mutually orthogonal axes) . To this end the support plate 712 of the Figure 7 embodiment, along with the column 728 and reflector plate 726 thereof are not used, and the transducers are instead supported by thin hoops 74 0 and 742, which are circular, have the same diameter as one another, are concentric, and are at right angles to one another.

[0057] The microprocessor 730 to which all the transducers are connected as shown in Figure 8 is programmed, for the Figure 9 embodiment, in such a fashion as to take account of the different orientation of the transducers as compared to the relative orientation they have in Figure 7.

Numerous modifications and variations to the illustrated construction of electroacoustic transducer may occur to the reader without taking the resulting construction outside the scope of the present invention. To give one example only, the cylindrical side wall of the vibratory component may have a square or polygonal cross-section rather than a circular cross-section, although a circular cross-section is preferred.

Claims

Claims :

1. An electroacoustic transducer device comprising an electroacoustic transducer housed within a housing such that there is a region between the transducer and the housing, which region surrounds the transducer but which region does not cover a transmitting surface of the transducer, characterised in that the said region is filled or is at least partly filled with an acoustically-attenuating closed-cell foam at least a part of which is coated with an adhesive sealant which provides a seal between the transducer and the housing.

2. An electroacoustic transducer device according to claim 1, in which the device is provided with a heater to inhibit build-up of ice on the exterior surfaces of the device when it is used in freezing conditions.

3. An electroacoustic transducer device according to claim 1 or claim 2, in which the vibratory component and the housing are made of metal to facilitate conduction of heat to different parts of the exterior of the device.

4. An electroacoustic transducer device according to any preceding claim, in which the adhesive sealant comprises a polyurethane adhesive sealant.

5. An electroacoustic transducer device according to any preceding claim, in which the electroacoustic transducer comprises an electromechanical transducer within the housing and a vibratory component coupled to the electromechanical transducer.

6. An electroacoustic transducer device according to claim 5, in which the vibratory component comprises a generally cylindrical side wall, an outwardly directed portion at the base of the side wall, and a generally planar vibratory top wall extending inwardly from the rim of the side wall further from its base to close the upper end of the cylindrical side wall, in which the said outwardly directed portion is mounted on the electromechanical transducer.

7. An electroacoustic transducer device according to claim 6, in which the side wall, top wall and outwardly directed portion of the vibratory component are constituted by a single integral piece of material.

8. An electroacoustic transducer device according to claim 6 or claim 7, in which the cylindrical side wall is circular in cross section.

9. An electroacoustic transducer device according to any one of claims 6 to 8, in which the portion which extends outwardly from the base of the side wall is or is part of a flange extending around the base of the side wall.

10. An electroacoustic transducer device according to claim 9, in which the flange is annular.

11. An electroacoustic transducer device according to claim 10, in which the flange is an open ring with a gap between the ends of the ring to accommodate an electrical connection to the electromechanical transducer.

12. An electroacoustic transducer device according to any one of claims 5 to 11, in which the electromechanical transducer comprises a piezoceramic device, for example a piezoceramic block or crystal.

13. An electroacoustic transducer device according to any one of claims 5 to 12, in which the vibratory component comprises metal, for example aluminium, for example aluminium 6082.

14. An electroacoustic transducer device according to any one of claims 5 to 13, in which the electromechanical transducer is seated on the base of the housing interior on three feet.

15. An electroacoustic transducer device according to claim 14, in which the three feet are equiangularly spaced around the base of the interior of the housing.

16. A fluid-flow meter comprising at least two electroacoustic transducers each as claimed in any preceding claim, the two transducers being spaced apart from one another and being oriented so that each is able to transmit sound towards and receive sound from the other of the pair.

17. An anemometer comprising at least two pairs of such transducers each of which transducers is as claimed in any one of claims 1 to 15, the transducers of one pair being spaced apart from one another along a first imaginary line, and the transducers of the at least one other pair being spaced apart along a second imaginary line which extends in a different direction from that of the first imaginary line.

18. An anemometer according to claim 17, in which the anemometer comprises two or three such pairs with their respective axes of transmission and reception being oriented mutually orthogonally relative to one another, or such that the two or three axes have at least components lying along three mutually orthogonal axes respectively.

19. An electroacoustic transducer substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 4 or Figures 2 to 4 of the accompanying drawings .

20. A fluid flow meter substantially as hereinbefore described with reference to and as illustrated in Figures 2 to 6 of the accompanying drawings.

21. An anemometer substantially as hereinbefore described with reference to and as illustrated in Figures 2, 3, 4, 7 and 8, or Figures 2, 3, 4, 8 and 9 of the accompanying drawings .