DK172322B1

DK172322B1 - An ultrasonic transducer

Info

Publication number: DK172322B1
Application number: DK96795A
Authority: DK
Inventors: Soeren Lolk
Original assignee: Danfoss As
Priority date: 1995-08-31
Filing date: 1995-08-31
Publication date: 1998-03-16
Also published as: AU6785196A; DK96795A; RU2159517C2; WO1997008917A1; PL325195A1

Description

DK 172322 B1 iDK 172322 B1 i

Opfindelsen vedrører en ultralydstransducer til udstråling i flydende medier omfattende et med en tæt membran afsluttet hus, som er indspændt i en ydre indfatning og med en piezoelektrisk skive som svingende element understøttet 5 centreret i huset og elektrisk tilsluttet ved hjælp af elektroder på hver side.BACKGROUND OF THE INVENTION The present invention relates to an ultrasonic transducer for radiation in liquid media comprising a housing closed with a dense membrane which is clamped in an outer frame and having a piezoelectric disk as a pivoting element supported in the housing and electrically connected by means of electrodes on each side.

Der kendes talrige konstruktioner af denne type, som i sin grundform blev udviklet til lokalisering af genstande un-10 der vandet ved afslutningen af 1. Verdenskrig. DK-B-151 676 beskriver en sådan transducer med moderne komponenter til anvendelse til i bl.a. varmeanlæg til måling af strømningshastigheden i rør. Det drejer sig om en piezoelektrisk keramisk skive, som er belagt med 15 elektroder på for- og bagside, og som kun er understøttet nær kanten. På forsiden er den forsynet med en beskyttende film. Denne konstruktion har udmærkede egenskaber som ultralydssender, dersom det er sikret, at det statiske tryk på ydersiden ikke er for stort, og at der altid 20 hersker et overtryk på denne side. Imidlertid er der ikke beskrevet en konstruktion, som er alsidig anvendbar, f.eks. hvor trykforskellen mellem for- og bagside bliver negativ, eller hvor der opstår store positive trykforskelle. De vil i den beskrevne konstruktion enten 25 medføre en udsugning af det piezoelektriske element eller en knusning, begge med fuldstændig ødelæggelse af transduceren til følge. Endvidere er den elektriske afskærmning af transducerenheden ikke tilstrækkelig til, at den kan benyttes som modtager. Dette har vist sig at 30 være en stor ulempe i de konstruktioner, hvor transducerens hus ikke potentialemæssigt ligger på apparatjord.Numerous constructions of this type are known, which in their basic form were developed for locating objects under the water at the end of World War I. DK-B-151 676 describes such a transducer with modern components for use in e.g. heating system for measuring the flow rate in pipes. This is a piezoelectric ceramic disc, which is coated with 15 electrodes on the front and back, and which is supported only near the edge. On the front, it is provided with a protective film. This construction has excellent properties as an ultrasonic transmitter if it is ensured that the static pressure on the outside is not too great and that there is always an overpressure on this side. However, a construction which is versatile usable, e.g. where the pressure difference between front and back becomes negative or where large positive pressure differences occur. In the described construction, they will either cause a piezoelectric element to be sucked out or a crush, both resulting in complete destruction of the transducer. Furthermore, the electrical shielding of the transducer unit is not sufficient for it to be used as a receiver. This has been found to be a major disadvantage in those structures where the transducer housing does not potentially lie on apparatus ground.

DK 172322 B1 2DK 172322 B1 2

Det er opfindelsens formål at frembringe en ultralydstransducer af den indledningsvis anførte art, som tillader en alsidig anvendelse, både som sender og modtager, ved ethvert i praksis forekommende statisk tryk og med effek-5 tiv afskærmning mod indstråling af elektrisk støj.It is an object of the invention to provide an ultrasonic transducer of the kind initially provided, which allows for a versatile use, both as transmitter and receiver, in any static pressure occurring in practice and with effective shielding against radiation of electrical noise.

Dette opnås ved en opbygning ifølge opfindelsen, som er særegen ved, at centreringsmidlerne udgør en del af en elektrisk afskærmning, som er ført mellem understøtningen 10 og det piezoelektriske element.This is achieved by a structure according to the invention, which is peculiar in that the centering means form part of an electrical shield which is passed between the support 10 and the piezoelectric element.

Det piezoelektriske element understøttes effektivt ved at danne tæt kontakt til et understøtningslegeme på en stor del af fladen ifølge krav 2.The piezoelectric element is effectively supported by forming close contact with a support body on a large portion of the surface of claim 2.

1515

Ved at lade den forreste elektrode fortsætte på kanten af skiven muliggøres det, at skærmens/centreringsmidlets fingre samtidig kan danne kontakt.By allowing the front electrode to continue on the edge of the disk, it is possible that the fingers of the screen / centering means can simultaneously make contact.

20 Afskærmningen bliver komplet, idet den kun brydes af et hul, hvorigennem den indre leder kan føres, og hullets omgivelser kan forbindes med skærmen på det benyttede ko-aksialkabel.The shielding becomes complete as it is only broken by a hole through which the inner conductor can be passed and the hole's surroundings can be connected to the shield of the coaxial cable used.

25 Ved at afskærmningen udgøres af en optrævlet ende af skærmen på det forbindende koaksialkabel, hvor hver leder er ført i det væsentlige langs en radius langs den piezoelektriske skives bagside, opnås en meget billig og enkel konstruktion.By providing the shielding with a raised end of the screen of the connecting coaxial cable, each conductor being guided substantially along a radius along the rear of the piezoelectric disk, a very cheap and simple construction is obtained.

3030

En fordelagtig centrering uden anvendelse af et ekstra centreringselement inden i den understøttende skål opnås ved at lade koaksialkablets lederes ender gå rundt om kanten på skiven.An advantageous centering without the use of an additional centering element within the supporting bowl is achieved by letting the ends of the coaxial cable conductor around the edge of the disk.

DK 172322 B1 3DK 172322 B1 3

Ved at lederne indlejres i et klæbelag mellem understøtningen og den piezoelektriske skive opnås det, at de fik-seres, og ved at klæbelaget er tilstrækkeligt tykt opnås 5 sikring mod lokale spændinger i den piezoelektriske skive, hvor to ledere krydser hinanden.By embedding the conductors in an adhesive layer between the support and the piezoelectric disk, they are fixed, and by the adhesive layer being sufficiently thick, protection is achieved against local voltages in the piezoelectric disk where two conductors intersect.

Ved en fordelagtig udførelsesform er lederne ført isoleret og beskyttet mellem en isolerende kegle og en kegleformet 10 fordybning i understøtningen.In an advantageous embodiment, the conductors are insulated and protected between an insulating cone and a cone-shaped depression in the support.

Ved en yderligere fordelagtig udførelsesform klemmer en fjeder, hvis ene ende støtter mod den isolerende kegles inderside, centerlederen i koaksialkablet fast mod den 15 piezoelektriske skives bagelektrode.In a further advantageous embodiment, a spring, one end of which rests on the inside of the insulating cone, clamps the center conductor of the coaxial cable against the rear electrode of the piezoelectric disc.

Ved en yderligere fordelagtig udførelsesforra er trækaflastningen simplificeret til at bestå af en knude, som drejningssikret er anbragt i en brønd i understøtningsle-20 gernet.In a further advantageous embodiment, the tensile relief is simplified to consist of a knot which is pivotally secured in a well of the support member.

Konstruktionen er uhyre produktionsvenlig, idet alle samlinger sker aksialt, idet der benyttes et forud fremstillet klæbelag mellem alle flader. Dette virker tillige 25 elektrisk isolerende. Der benyttes ikke en omløber, men en fjederring i et spor i indfatningen nær tilslutningssiden af transduceren definerer den aksiale position og en O-ring ved den modsatte ende af huset sørger for et anlægstryk.The construction is extremely production-friendly, as all joints occur axially, using a pre-made adhesive layer between all surfaces. This also acts as an electrical insulator. No bypass is used, but a spring ring in a groove in the casing near the connection side of the transducer defines the axial position and an O-ring at the opposite end of the housing provides an abutment pressure.

3030

Opfindelsen skal beskrives nærmere i forbindelse med tegningen, hvor DK 172322 B1 4 fig. 1 viser et længdesnit igennem en ultralydstrans-ducer i en ydre indfatning og fig. 2 viser en anden udførelsesform for ultralyds-5 transduceren ifølge opfindelsen.The invention will be described in more detail in connection with the drawing in which DK 172322 B1 4 FIG. 1 is a longitudinal sectional view of an ultrasonic transducer in an outer housing; and FIG. 2 shows another embodiment of the ultrasonic transducer according to the invention.

En ydre indfatning 1, som f.eks. kan være en væg i et rør eller i en beholder eller en del af en strømningshastighedsmåler, har en brøndformet fordybning 2, og to O-ringe 10 3 og 4 sørger for tætning mod transducerens hus 5. Huset afsluttes med en membran 6, hvorimod O-ringen 4 klemmer.An outer frame 1, such as may be a wall in a pipe or in a container or part of a flow rate meter, has a well-shaped recess 2, and two O-rings 10 3 and 4 provide a seal against the transducer housing 5. The housing terminates with a diaphragm 6, whereas O ring 4 clamps.

Det piezoelektriske element 7 er belagt med metal, dels på forsiden som den forreste elektrode 8, dels på bagsiden som den bageste elektrode 9, idet der er en ikke-belagt 15 bred ring 10 som adskillelse mellem de to elektroder.The piezoelectric element 7 is coated with metal, partly on the front side as the front electrode 8 and partly on the back side as the rear electrode 9, there being an uncoated 15 wide ring 10 as a separation between the two electrodes.

Udenom den piezoelektriske skive er anbragt en krans af fingre 11, som er ud i et med en afskærmningsplade 12, som inderst har en dåseformet forhøjning 13. Skiven 7 og afskærmningen er understøttet af en skålformet understøtning 20 14, som har en skørtformet side 15, som omgiver kransen af fingre 11 og centrerer konstruktionen i huset 5. Den bageste elektrode 9 er forbundet med centerlederen 16 i et koaksialkabel 17, hvis skærm 18 er forbundet med afskærmningen 13. Koaksialkablet 17 er ført igennem en tætning 19 25 i huset 5.Outside of the piezoelectric disc is a wreath of fingers 11 which integrate with a shield plate 12, which has a can-shaped elevation at the bottom 13. The disc 7 and the shield are supported by a cup-shaped support 20 14 which has a skirt-shaped side 15. surrounding the wreath of fingers 11 and centering the structure of housing 5. The rear electrode 9 is connected to the center conductor 16 in a coaxial cable 17, the shield 18 of which is connected to the shield 13. The coaxial cable 17 is passed through a seal 19 25 in the housing 5.

Alle flader er forsynet med forud fremstillet klæbelag T, således at samlingen kan foregå ved at en ring af klæber påføres understøtningen 14, som derefter fæstnes i huset 30 5. En ring af klæber påføres undersiden af afskærmningen 12, som derefter fæstnes i understøtningen 14, centreret af fingrene 11 og skørtet 15. En ring af klæber påføres bagsiden af den piezoelektriske skive 7, som derefter fæstnes i afskærmningen 11, 12, centreret af fingrene 11 DK 172322 B1 5 mod kanten af skiven. En rondel af klæber påføres den pie-zoelektriske skive 7 og går ud over kanten på huset 5, hvorefter membranen 6 fæstnes. O-ringene 3 og 4 anbringes i deres respektive spor, og huset anbringes på sin plads i 5 indfatningen 1. En låsering 20 anbringes i et spor i indfatningen 1 ved bagsiden af huset 5. Der er ikke beskrevet, hvorledes forbindelsen af koaksialkablet 17 foretages, idet det er velkendt for fagmanden. En vis form for trækaflastning kan opnås ved krympning af forbindelsen af 10 koaksialkablets skærm 18 til skærmen 13.All surfaces are provided with pre-made adhesive layer T so that the assembly can be effected by applying a ring of adhesive to the support 14, which is then secured to the housing 30 5. A ring of adhesive is applied to the underside of the shield 12, which is then secured to the support 14. centered by the fingers 11 and skirt 15. A ring of adhesive is applied to the back of the piezoelectric disc 7, which is then attached to the shield 11, 12, centered by the fingers 11 towards the edge of the disc. A round of adhesive is applied to the piezoelectric disc 7 and extends beyond the edge of the housing 5, after which the membrane 6 is attached. The O-rings 3 and 4 are placed in their respective grooves and the housing is positioned in place in the frame 1. A locking ring 20 is placed in a groove in the frame 1 at the back of the housing 5. It is not described how the connection of the coaxial cable 17 is made. , as it is well known to those skilled in the art. Some form of tensile relief can be obtained by shrinking the connection of the coaxial cable shield 18 to the shield 13.

På fig. 2 ses, hvorledes ultralydstransducerens praktiske konstruktion yderligere kan forenkles under bevarelse af de fulde fordele ved opfindelsen. Der er benyttet de samme 15 henvisningsbetegnelser som på fig. 1 for uændrede elementer. Understøtningen 14 er her fortsat bagud til dannelse af en kegleformet skål 14a. Afskærmningen 11, 12, 13 er her helt erstattet af en optrævling og udspredning af den flettede skærm 18 på koaksialkablet 17, som klemmes fast 20 mellem klæbelaget T og den piezoelektriske skive og danner elektrisk kontakt til forsidens metalbelægning 8. Derved undgås en særlig fremstilling af en skærm med dåseformet udbygning samt flige til kontakt. Centerlederen 16 i koaksialkablet 17 klemmes med en fjeder 20 fast mod bagside-25 elektroden 9. Den anden ende af fjederen hviler mod indersiden af en kegle 21 af PTFE, som er anbragt omkring centerlederens isolation og sørger for, at skærmens ledere 18 ikke kommer i berøring med fjederen 20 eller elektroden 9. Trådene kommer dermed til at forløbe sikkert i mellemrum-30 met mellem understøtningens kegleformede skål 14a og ydersiden af PTFE keglen 21. I praksis er det ikke nødvendigt at benytte alle skærmens tråde, når det blot sikres, at der langs periferien af den piezoelektriske skive 7 højst er 3 mm mellem nabotråde. Klæbelaget mellem den piezoelek- DK 172322 B1 6 triske skive 7 og understøtningen 14 er tykkere end de øvrige lag, så det kan tillade krydsning af to tråde, uden at der opstår skadelige lokale spændinger i den piezoelek-triske skive ved trykpåvirkning.In FIG. Figure 2 shows how the practical construction of the ultrasonic transducer can be further simplified while preserving the full advantages of the invention. The same reference numerals as in FIG. 1 for unchanged elements. The support 14 here continues to be rearward to form a cone-shaped bowl 14a. The shields 11, 12, 13 are here completely replaced by a piling and spreading of the braided shield 18 on the coaxial cable 17, which is clamped 20 between the adhesive layer T and the piezoelectric disc and forms electrical contact with the front metal coating 8. This avoids a special manufacture of a can with screen-shaped extension and tabs for contact. The center conductor 16 in the coaxial cable 17 is clamped by a spring 20 fixed to the backing electrode 9. The other end of the spring rests on the inside of a cone 21 of PTFE, which is arranged around the center conductor insulation and ensures that the conductors of the shield 18 do not come into contact. contact with the spring 20 or the electrode 9. The wires will thus run securely in the space between the cone-shaped bowl 14a of the support and the outside of the PTFE cone 21. In practice, it is not necessary to use all of the shield wires if it is merely ensured that which along the periphery of the piezoelectric disc 7 is at most 3 mm between neighboring wires. The adhesive layer between the piezoelectric disc 7 and the support 14 is thicker than the other layers, so that it can allow crossing of two strands without damaging local stresses in the piezoelectric disc by pressure.

5 I nærværende udførelsesform udgøres trækaflastningen af en knude 22 på koaksialkablet. Med henblik på at undgå, at der sker rotation af koaksialkablets ende, er knuden nedlagt i en cylindrisk brønd 14b ud i ét med understøtningen 10 14. Frembringerkurven for cylinderen er i det væsentlige oval eller ottetalsformet, idet denne form griber en knude effektivt. Knuden 22 holdes nede i brønden af en isolerende bøsning 23, som er anbragt indefra i et hul i huset 2.5 In the present embodiment, the strain relief is constituted by a node 22 on the coaxial cable. In order to prevent rotation of the end of the coaxial cable, the knot is placed in a cylindrical well 14b integral with the support 10 14. The cylinder producing curve is substantially oval or octagonal in shape, which effectively engages a knot. The node 22 is held down in the well by an insulating sleeve 23 which is arranged from the inside of a hole in the housing 2.

Især med henblik på tætning kan knuden være omgivet af en 15 elastisk, eventuelt klæbende masse.In particular, for sealing, the knot may be surrounded by an elastic, possibly adhesive, mass.

Claims

An ultrasonic transducer for radiation in liquid media comprising a housing (2) terminated with a dense membrane, which is clamped in an outer housing (1) and with a piezoelectric disk (7) as a pivoting element supported centered in the housing and electrically connected by means of electrodes (8, 9) on each side, characterized in that the centering means form part of an electrical shield (13) passed between the support (14) and the piezoelectric element.

Ultrasonic transducer according to claim 1, characterized in that the piezoelectric disc (7), which is pivotally swinging (7), is preferably supported on its rear side on most of its surface outside the rear electrode (9).

Ultrasonic transducer according to claim 1, characterized in that the electrical shielding comprises peripheral means (11) which contact the front electrode (8) of the piezoelectric disc.

An ultrasonic transducer according to claim 1, characterized in that the electrical shielding has a hole whose rim is connected to the shield (18) on a connection coaxial cable (17).

Ultrasonic transducer according to claim 1, characterized in that the shielding is constituted by a rolled end of the shield (18) on the connecting coaxial cable (17), a plurality of conductors being guided substantially along a radius along the piezoelectric disc (7). backing. DK 172322 B1 8

Ultrasonic transducer according to claim 5, characterized in that the conductors are embedded in an adhesive layer between the support (14) and the piezoelectric disc (7). 5

Ultrasonic transducer according to claims 3 and 5, characterized in that the conductors are led around the edge of the disc (7) within the side (15) of the disc parallel to the disc (7) to form centering means 10 for the disc.

Ultrasonic transducer according to claim 5 or 6, characterized in that the conductors in their course between the cable and the attachment in the adhesive layer are substantially cone-shaped between a recess in the support and an insulating cone (21).

Ultrasonic transducer according to claim 8, characterized in that the center conductor (16) in the coaxial cable 20 contacts contact with the electrode (9) by spring pressure between the inside of the insulating cone (21) and the center conductor (16).

Ultrasonic transducer according to any one of the preceding claims, characterized in that the tensile relief of the coaxial cable is constituted by a knot (22) of the same, laid down in a cylindrical well (14b) which terminates close to the knot along its surface.

Ultrasonic transducer according to claim 10, characterized in that the knot (22) is surrounded by an elastic, possibly adhesive, mass upon its deposition in the well (14b). DK 172322 B1 9

Ultrasonic transducer according to claim 11, characterized in that the clamping in the outer frame (1) is secured by a locking ring (20) in combination with a 5-ring (4).