Measuring and testing – Vibration – By mechanical waves
Patent
1994-06-01
1996-12-10
Williams, Hezron E.
Measuring and testing
Vibration
By mechanical waves
310328, 310369, H01L 4108
Patent
active
055832938
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a sonic or ultrasonic transducer which includes a circular piezo-ceramic disk capable of generating oscillations, and a metal ring, surrounding the piezo-ceramic disk.
The operating frequency of a sonic or ultrasonic transducer which includes a piezo-ceramic disk capable of generating radial oscillations generally corresponds to the radial resonant frequency of the piezo-ceramic disk, which is dictated by the dimensions of the piezo-ceramic disk. The diameter of the piezo-ceramic disk further determines the magnitude of the sonic emission surface, which determines the apex angle of the produced sonic radiation. In an ultrasonic transducer of the nature set out above known from DE-PS 25 41 492, a foam plate having a substantially larger surface area than the piezo-ceramic disk is adhesively bonded to an end face of the piezo-ceramic disk, to serve as an adaptive layer for reducing the apex angle dictated by the dimensions of the piezo-ceramic disk. The protruding region of the foam plate is connected to the metal ring surrounding the piezo-ceramic disk which serves as a weighting ring and in order for the interface between the weighting ring and the piezo-ceramic disk to constitute a nodal surface which remains virtually immobile during the operation of the ultrasonic transducer. In this way the entire exposed end face of the adaptive layer is caused to oscillate virtually in phase with the piezo-ceramic disk. The metal ring may not touch the piezo-ceramic disk in order to fulfill this function as a weighting ring. Although the sonic emission area of this prior art ultrasonic transducer is increased in relation to the surface area of the piezo-ceramic disk, the operating frequency remains dependent on the diameter of the piezo-ceramic disk. A reduction in the operating frequency is only attainable by using a larger piezo-ceramic disk.
The object of the present invention is the provision of a sonic or ultrasonic transducer of the nature set out above, which for a given set of dimensions of the piezo-ceramic disk produces a lower operating frequency in relation to the radial resonant frequency of the piezo-ceramic disk.
This object is met according to the invention in that the metal ring embraces in tight close fitting relationship the circumferential surface area of the piezo-ceramic disk to form a radial oscillator in conjunction with the disk.
In a sonic or ultrasonic transducer according to the invention the metal ring is firmly coupled to the piezo-ceramic disk so that both components constitute a mass-spring element performing radial oscillations in unison. The entire surface area of the radial oscillator formed in this manner functions as an emitting surface oscillating completely in phase, producing a substantially Gaussian distribution of amplitudes, the sonic emission thereby displaying a small apex angle without interfering secondary lobes. The radial resonant frequency of this radial oscillator is lower, however, than the radial resonant frequency of the piezo-ceramic disk. More particularly it is dependent on the dimensions of the metal ring. It is accordingly feasible to manufacture sonic or ultrasonic transducers for different operating frequencies by means of identical piezo-ceramic disks by appropriately dimensioning the metal ring.
The metal ring is preferably connected to the piezo-ceramic disk by being shrunk on.
An adaptive layer may be applied in known fashion onto the one end face of the radial oscillator formed by the piezo-ceramic disk and the metal ring.
Further features and advantages of the invention will be apparent from the following description of an embodiment with reference to the drawings. In the drawings:
FIG. 1 shows a sonic or ultrasonic transducer according to the invention,
FIG. 2 shows the amplitude distribution over the emitting surface of the sonic or ultrasonic transducer of FIG. 1,
FIG. 3 shows the characteristic frequency curve of the piezo-ceramic disk of the sonic or ultrasonic transducer of FIG. 1, and
FIG. 4 shows the characteristic fr
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patent: 4611372 (1986-09-01), Enjoji et al.
patent: 4868446 (1989-09-01), Kumada
patent: 5278471 (1994-01-01), Uehara et al.
patent: 5343109 (1994-08-01), Mockl
Endress & Hauser GmbH & Co.
Finley Rose M.
Williams Hezron E.
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