GB2359767A

GB2359767A - Ultrasonic transducer coupling

Info

Publication number: GB2359767A
Application number: GB0103842A
Authority: GB
Inventors: Peter David Martin
Original assignee: AEA Technology PLC; Accentus Medical PLC
Current assignee: Accentus Medical PLC; Ricardo AEA Ltd
Priority date: 2000-03-02
Filing date: 2001-02-16
Publication date: 2001-09-05
Also published as: GB0004941D0; GB0103842D0

Description

2359767 - 1 Ultrasonic Transducer. Coupling This invention relates to a

coupling to enable ultrasonic vibrations from a transducer to be transmitted to a fluid in a container, particularly but not exclusively a conventional laboratory glass container High intensity ultrasound can be applied to liquids for a variety of beneficial purposes, for example to enhance rates of chemical reaction, crystallisation processes, dissolution, emulsification, pasteurisation, and cell disruption. High ultrasonic intensity in this context means an intensity greater than about 0.3 W/cm 2 at a frequency typically in the range 10 kHz to 100 kHz, under which circumstances there is significant deposition of energy into the liquid. A variety of devices are known for treating liquids on a large scale, for example that described in GB 2 243 092 B (UKAEA). At laboratory scale, where high intensity is required, titanium probes have typically been used to couple a transducer to the liquid, the probe being connected by a screwed joint to a special-purpose vessel containing the liquid, but such joints cause significant heating and noise.

According to the present invention there is provided a coupling to connect an ultrasonic transducer to fluid in a vessel, the coupling comprising a generally cylindrical rod, with means at one end for connection to the transducer, a tapered adapter sleeve shaped to mate with a standard, conical ground-glass joint of a glass vessel, the rod extending coaxially through the sleeve, a thin sealing member connecting the rod to the sleeve, the sealing member being sealed to the rod at a position which in use of the coupling is a nodal point, and a probe tip fixed to the other end of the gederally 2 cylindrical rod.

Such a coupling enables experiments to be carried out using a conventional glass vessel, the ultrasonic coupling being sealed by its tapered sleeve into a standard, conical ground-glass joint. The joint may be lubricated with a suitable grease, or may be provided with a thin sleeve of polytetrafluoroethylene (PTFE) to ensure a hermetic seal. The generally cylindrical rod is preferably of an alloy of titanium or of aluminium, as these materials transmit ultrasound without significant loss, but if the process liquids are chemically aggressive then titanium is preferred. The rod may taper continuously along its length, or may have step changes in diameter. The probe tip may also continuously taper along its length, or may be partly cylindrical and partly tapered, but in any event the free end of the tip is desirably of considerably smaller diameter than the end of the generally cylindrical rod connected to the transducer, to increase the intensity of the ultrasound.

The sealing member may comprise a thin web, which may be integral with both the rod and the adapter sleeve. Alternatively such a thin web may be integral with the adapter sleeve and connected by for example a threaded joint to the rod, although in this case it is more difficult to provide such a thin joint and consequently there will tend to be more generation of noise and heat. In an alternative arrangement the sealing member is an 0- ring seal which locates in a circumferential groove on the surface of the rod, which may be defined between adjacent circumferential ridges. In this arrangement the tapered adapter sleeve may be of PTFE, such sleeves being known.

when the coupling is connected to the ultrasonic 3 - transducer, and the transducer is energised, the cylindrical rod is set into longitudinal vibrations. If the frequency is a resonant frequency of the rod then a standing wave will be set up, and at some point along the rod will be a node, at which no displacement occurs; that is the nodal point; and at that point the sealing member supports the rod. Consequently no vibration is transmitted to the adapter sleeve. The sealing member clearly must be thin, and is preferably in contact with the rod over a length of no more than about 3 mm, preferably less than 1 mm. For example if the sealing member is an integral web it may be of thickness as little as 0.5 mm.

The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings in which:

Figure 1 shows a view, partly in longitudinal section, of an ultrasonic transducer with a coupling of the invention; Figure 2 shows a view, partly in section, of an alternative coupling to that of figure 1; Figure 3 shows a view, partly in section, of another alternative coupling to that of figure 1; and Figure 4 shows a view, partly in section of chemical process equipment using the coupling of figure 2.

Referring to figure 1, an ultrasonic transducer assembly 10 has a projecting vibrating rod 12 of external diameter 36 mm. A titanium coupling rod 14 is attached by a threaded stud 16 to the end of the rod 12. The coupling rod 14 is about 250 mm long, 33 mm. in diameter - 4 at the end connected to the transducer assembly 10 tapering to 16 mm diameter over a distance of 190 mm, and the remainder being of diameter 16 mm. A titanium probe 18 is attached to the narrow end of the coupling rod 14 by a threaded stud 20, the probe being 60 mm long, partly of diameter 16 mm, and tapering down to a diameter of 8 mm at the end. The operating frequency of the ultrasonic transducer assembly 10 is 20 kHz, and at this frequency the coupling rod 14 has a nodal plane (perpendicular to its longitudinal axis) at the end of the tapered section of the coupling rod 14. In this nodal plane a titanium web 22 attaches a titanium sleeve 24 to the coupling rod 14, the sleeve 24 being tapered so as to mate with a conventional ground-glass joint. The sleeve 24, the web 22 and the coupling rod 14 are integral with each other. The web 22 is of thickness 0.5 mm.

Referring now to figure 2 there is shown a view, partly in longitudinal section, of an alternative coupling rod 30 which may be used in place of the coupling rod 14. The coupling rod 30 is of titanium with a section about 60 mm long and of diameter 33 mm for attachment to a transducer assembly 10 (as in figure 1), and a radiused step transition to a section about 190 mm long of diameter 16 mm. The narrow end can be attached to a titanium probe 18 (as in figure 1). At a position on the narrower part of the rod 30 which in use is a nodal plane two circumferential ridges 32, 33 are defined around the surface of the rod 30. An 0-ring seal 34 locates in the groove defined between these two ridges 32 and 33. The rod 30 extends coaxially through a tapered tubular sleeve 36 of PTFE, the external dimensions of the sleeve 36 being such that it will mate with a conventional ground glass joint. The internal surface of the sleeve 36 defines two circumferential ridges 37 and 38, and the 0- ring seal 34 seals to the sleeve 36 between - 5 them.

Referring now to figure 3 there is shown a view, partly in longitudinal section, of another alternative coupling rod 40 which may be used in place of the coupling rod 14 or 30. As with the coupling rod 30, the rod 40 is of titanium with a section about 60 mm long and of diameter 33 mm for attachment to a transducer assembly 10, and a radiused step transition to section about 190 mm long of diameter 16 mm. The narrow end can be attached to a titanium probe 18. At a position on the narrower part of the rod 40 which in use is a nodal plane is a short section, about 4 mm long, of slightly larger diameter with an external thread 42. A stainless steel tapered tubular sleeve 44 has an internal flange 45 at its wider end whose inner edge is threaded for connection to the threaded section 42 on the rod 40; this threaded connection may be sealed for example with PTFE tape. The external dimensions of the sleeve 44 are such that it will mate with a conventional ground glass joint.

In each case the dimensions of the coupling rod 14, 30 or 40 are such that, when assembled to a transducer assembly 10 and a probe 18, there will be a nodal plane at the place where the tapered sleeve 24, 36, 44 is connected to the coupling rod 14, 30 or 40, and there will be an antinode at the free end of the probe 18.

Referring now to figure 4 there is shown, diagrammatically, a chemical apparatus 50 for subjecting a liquid 51 to high ultrasonic intensities. The apparatus 50 includes a glass vessel 52 of one litre capacity provided with a heating/cooling jacket 53, and a glass lid 54 with three ground glass ports 55, 56, and 57. The port 55 is provided with a closure 60 such as a groundglass stopper, and is used for introducing liquids - 6 into the vessel 52. The central port 56 is provided with a closure 62 through which extends a drive shaft 63 for an impeller 64 driven by an external motor 65. The third port 57 is sealed by a tapered PTFE sleeve 36 through which extends a coupling rod 30 (as in f igure 2) supported by an O-ring seal 34. Outside the lid 54 a transducer assembly 10 is attached to the coupling rod 30, and within the vessel 52 a titanium probe 66 is attached to the end of the coupling rod 30. The probe 66 differs from the probe 18 of figure 1 in that it tapers along its whole length.

Thus in use of the apparatus 50 liquids 51 are introduced into the vessel 52, maintained at a suitable temperature by means of the jacket 53, kept well mixed by the impeller 64, and subjected to high intensity ultrasound from the narrow tip of the probe 66. The liquids may be hazardous, but are sealed within the vessel 52. Because the ultrasonic coupling rod 30 is supported at a nodal plane 34 there is negligible vibration, noise or over-heating as a result of the ultrasonic vibrations.

it will be appreciated that ultrasonic coupling rods may differ from those described while remaining within the scope of the invention, in particular they will have different dimensions depending on the frequency of the ultrasound. It will also be appreciated that the probe (18 or 66) might be integral with the coupling rod, rather than being attached by a threaded stud 20. However where the intensity of ultrasound is particularly high the tip of the probe will suffer cavitational erosion, and it is desirable to be able to replace the tip. For example a probe might be integral with the coupling rod, the end of the probe being externally threaded, and the tip being of titanium and attached to 7 - the end of the probe by the thread.

- 8

Claims

1. A coupling to connect an ultrasonic transducer to fluid in a vessel, the coupling comprising a generally cylindrical rod, with means at one end for connection to the transducer, a tapered adapter sleeve shaped to mate with a standard, conical ground-glass joint of a glass vessel, the rod extending coaxially through the sleeve, a thin sealing member connecting the rod to the sleeve, the sealing member being sealed to the rod at a position which in use of the coupling is a nodal point, and a probe tip fixed to the other end of the generally cylindrical rod.

2. A coupling as claimed in claim 1 wherein the rod tapers continuously along a portion of its length.

3. A coupling as claimed in claim 1 wherein the rod has a step change in diameter.

4. A coupling as claimed in any one of the preceding claims wherein the sealing member comprises a thin web which is integral with the rod or the adapter sleeve.

5. A coupling as claimed in claim 4 wherein the web is integral with both the rod and the adapter sleeve.

6. A coupling as claimed in any one of claims 1 to 3 wherein the sealing member is an 0-ring seal.

7. A coupling as claimed in claim 6 wherein the 0-ring seal locates in a circumferential groove on the surface of the rod.

8. A coupling as claimed in any one of the preceding - 9 claims wherein the sealing member is in contact with the rod over a length of no more than about 3 mm, preferably less than 1 mm.

9. A coupling to connect an ultrasonic transducer to fluid in a vessel, substantially as hereinbefore described with reference to, and as shown in, any one of the accompanying drawings.

15373 MdH P.T. Mansfield Chartered Patent Agent Agent for the Applicants