Patent GB-1387476-A (GB)
Title: Ultrasonic transducers
IPC: H04R17/08
Filed: 1972-02-07
Abstract: 1387476 Ultrasonic transducers ONTARIO RESEARCH FOUNDATION 7 Feb 1972 [5 Feb 1971] 5484/72 Heading H4J An ultrasonic transducer assembly (Figs. 1, 2) comprises a transducer motor (as described, annular ceramic piezoelectric elements 37, 52), a rear stub 22 in surface contact with a rear surface of the transducer motor and a front stub 14 in surface contact with a front surface of the transducer motor. Stub 14 is made of magnesium or magnesium alloy. A cylindrical housing 20 (e.g. of steel) clamps the stubs 14, 22 against the motor, the clamping locations being adjacent the motor so that a major portion of each stub 14, 22 extends beyond its clamping location in the direction away from the motor. Stub 14 has an outwardly and rearwardly flaring flange 57 with a substantially frustoconical bearing face 59. The cylindrical housing 20 has a frusto-conical bearing surface complementary to the bearing face 59 and adapted to engage the stub thereupon. Preferably the bearing face 59 defines an angle of 45 degrees with the axis of stub 14. The front and rear stubs 14, 22 are cylindrical. Stub 22 is of steel. The cylindrical bearing 20 is held by a retaining ring 24. At the operating frequency a titanium horn 12 of circular, catenoidal or exponential shape is a half-wave resonator, the stubs 14, 22 being quarter-wave resonators. The contact surface between each stub 14, 22 and its adjacent transducer element 52, 37 is at a node. The horn 12 has a threaded shaft 62 which is received in a bore 64 in stub 14. Between the piezoelectric elements 37, 52 is a metal disc 28, an annular upper metal shim 32 and a circular lower metal shim 36. Disc 28 is for cooling the piexoelectric elements 37, 52 and has a plurality of radial slots (30), Fig. 4 (not shown), which extend from an annular chamber 70 inwardly to locations short of its centre. The annular chamber 70 has one or more bore holes 72 communicating with the ambient air. In use, air circulates by convection through the bore hole(s) 72, into the annular chamber 70, through the radial slots (30) in the cooling disc 28, upwards through a passage 44 in stub 22 and out through an opening 86 in a terminal assembly 26. The terminal assembly 26 is bolted to stub 22 and includes an outwardly flanged pot 79 and a terminal element 84. An insulated wire 94 connects a terminal of the terminal element 84 to the centre of the shim 36 where it is soldered in place. The outer terminal of the terminal element is earthed and is connected through pot 79 to stub 22 and to stub 14 via the cylindrical housing 20. In this way the piezoelectric elements 37, 52 are energized from the terminal assembly. Handles 16, 17 form an angle of 135 degrees and are secured to a two-part handle ring 18 held together by bolts 100. Handle 16 has an axial bore (not shown) for insertion of a rod, whereby the assembly may be supported by a retort stand so that it can be rotated with handle 16 acting as the axis of revolution. The assembly is useful for transmitting vibrations to water or other liquid. A modified embodiment (Fig. 3, not shown) has a pot (79<SP>1</SP>) without a vent opening 86. The terminal assembly 26 is offset from centre. Passing through the top of the pot (79<SP>1</SP>) is an air-line connection (98) through which air may be introduced under pressure from an air-line (99).