Measuring and testing – Vibration – Vibrator
Patent
1999-03-01
2000-09-26
Moller, Richard A.
Measuring and testing
Vibration
Vibrator
310369, H01L 4100
Patent
active
061229709
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an ultrasonic transducer a piezoceramic disk in radial resonance operation and with a ring surrounding the piezoceramic disk on its lateral surface with a form fit and frictional engagement.
BACKGROUND INFORMATION
Conventional ultrasonic transducers are described in numerous publications. Many applications, such as ultrasonic sensors and proximity switches, require ultrasonic transducers having a very narrow sound cone characteristic while at the same time having very small secondary cone amplitudes.
German Patent No. 25 41 492 describes a very sharp ultrasonic transducer with saturn geometry, which is widely used with ultrasonic sensors in industrial applications. It is constructed from a piezoceramic disk, an adapting layer disk and a concentric metal ring. The area of the adapting layer is large because the adapting layer disk projects a great distance beyond the diameter of the piezoceramic disk, thus yielding a very narrow angle .phi. of the sound cone of 5.degree.. Due to the large projecting area of the adapting layer disk, it is difficult to always accurately maintain the favorable vibrational amplitude distribution and phase angle over the entire area in practice, thus resulting in problematic lateral secondary cones.
German Patent No. 42 33 256 describes an ultrasonic transducer with a round piezoceramic disk in radial resonance, having a reduced operating frequency in comparison with the radial resonant frequency of the piezoceramic disk for given dimensions of the piezoceramic disk. This is achieved using a metal ring surrounding the piezoceramic disk with a form fit and frictional engagement, preferably being shrunk-fit onto the piezoceramic disk. The composite body formed by the piezoceramic disk and the metal ring forms a radial oscillator which behaves like a piezoelectric body with a larger diameter and a reduced frequency with regard to its vibrational properties. By appropriate dimensioning of the metal ring, the operating frequency can be reduced to different extents. An adapting layer is applied to the end face of the composite body.
SUMMARY OF THE INVENTION
An object of the present invention is to create an ultrasonic transducer of the with improved transmission properties with regard to the main cone angle and suppression of secondary cones and to obtain the narrowest possible main cone angle in particular.
This object is achieved according to the present invention by the fact that the ring is made of a material in which the velocity of sound is higher than that in aluminum. Thus, the resulting radial resonant frequency of the composite body of piezoceramic disk and ring is either reduced less than is the case with aluminum, or it may remain the same or be significantly higher than the original radial resonant frequency of the piezoceramic disk in a defined manner, despite the larger diameter. As a consequence, the ratio of the diameter of the sound transmitting surface to the wavelength of the ultrasonic wave transmitted, which is inversely proportional to the radial resonant frequency, is increased for the composite body whose end face is usually approximately the same size as the sound transmitting surface. Therefore, with the ultrasonic transducer according to the present invention -3 dB, sound cone angles of less than 5.degree. can be achieved with secondary cone damping of approx. -30 dB in comparison with the main cone amplitude. The main influencing parameter here is the longitudinal wave velocity of the ring material, while the radial resonant frequency can be adjusted only within comparatively narrow limits through variation of the geometric dimensions of the ring in a reasonable and practical range.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a sectional view of an ultrasonic transducer according to the present invention.
FIG. 2 shows a sectional view of an example embodiment of the present invention.
DETAILED DESCRIPTION
FIG. 1 shows a sectional view of ultrasonic transducer 1 according to the present
REFERENCES:
patent: 5659220 (1997-08-01), Thurn
"Plastic Disk Makes Transducer Excel in Calculating Distances by Ultrasound," Electronics International, vol. 51, No. 11, May 25, 1978, pp. 76-78.
Vasil'ev et al., "Sectional Radial-mode Piezoelectric Transducer," Soviet Physics Acoustics, vol. 26, No. 4, Jul.-Aug., 1980, pp. 284-286.
Kleinschmidt et al., "Ultrasonic Remote Sensors for Noncontact Object Detection," Siemens Forsc. u. Entwickl.-Ber., vol. 10, No. 2, 1981, pp. 110-118.
H. Franke, "Lexicon of Physics," 3rd Edition, Franckh'sche Verlagshandlung [Franckh Publishing House], Stuttgart, W. Keller & Co., 1969, p. 94. Translation Provided.
Moller Richard A.
Siemens AG
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