Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1995-02-13
1997-08-19
Dougherty, Thomas M.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310322, 310334, H01L 4108
Patent
active
056592205
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns an ultrasonic transducer having a disk-shaped piezoelectric transducer element which is provided with a rotationally symmetrical, disk-shaped .lambda./4 matching element.
An ultrasonic transducer, of the type mentioned above, is described in German Patent Publication No. DE 39 11 047 ("the '047 publication"). In the transducer of the '047 publication, small changes in the diameter of the main surface of a matching element, relative to the diameter of the piezoceramic transducer element, influence oscillations of the transducer element to improve the efficiency and radiation characteristic of the ultrasonic transducer in conjunction with its small dimensions. The '047 publication also discusses that even small changes in the shape of the circumferential wall of the matching element can substantially change the oscillations of the transducer element. A straight line, which diverges from, or converges to, the piezoceramic element is specified as the configuration of the lateral line of the circumferential surface of the matching element. In this way, the diameter of the main surface of the matching element deviates slightly from the main surface of the piezoceramic transducer element. Depending on the thickness of the matching element relative to the diameter of the transducer element, slightly positively or slightly negatively curved lateral lines are also considered advantageous for the purpose of achieving a relatively centered high sound pressure.
However, the amplitude distribution occurring in the ultrasonic transducers discussed in the '047 specification has a relative minimum in the central region of the radiation surface. The amplitude rises in the radial direction, has its maximum at approximately half the radius, and drops off steeply towards the rim (i.e., the edge). This form of oscillation produces losses in the achievable sound pressure, and the shapes of sound lobes associated therewith have conspicuous side lobes. These losses can lead, in practical use, to faults and malfunctions.
Therefore, the object of the present invention is to provide an ultrasonic transducer of the type mentioned above in which, in conjunction with a compact design, a high sound pressure is achieved because of an improved form of oscillation with the lowest possible losses, and in which the suppression of side lobes is better than -30 dB.
SUMMARY OF THE INVENTION
To achieve the above referenced object, the .lambda./4 matching element has a notch on its circumferential surface and/or on its rear (i.e., underside) surface facing the transducer element. A particularly good radiation response is achieved when the notch has a depth of up to at most, a quarter of the disk diameter of the matching element. Such ultrasonic transducers are particularly suitable for industrial applications with good acoustic properties and for operations in which air is the ambient medium.
In an easy-to-produce embodiment, the circumferential surface outside the notch has the contour of a regular cylinder. In this case, the notch is subsequently milled, for example, into the circumferential surface in a disk-shaped matching element which is in the shape of a regular cylinder and which is easy to produce.
To achieve a form of oscillation which is effected by few losses, the circumferential surface has a notch at least of such a depth that, given circular surfaces of unequal size at the top side and underside of the .lambda./4 matching element (i.e., given a matching element with two surfaces of unequal diameter and with a circumferential surface shaped as a part of a cone), the notch cuts an imaginary cylinder lateral surface projected into it and proceeding from the smaller circular surface of the matching element.
If the piezoelectric transducer element has a main surface of diameter D in a direction of the main radiation of the ultrasonic oscillations, and if the underside circular surface of the .lambda./4 matching element facing the main surface of the piezoelectric transducer e
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Busch Klaus
Thurn Rudolf
Dougherty Thomas M.
Siemens Aktiengesellschaft
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