Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-09-10
2001-12-25
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S358000
Reexamination Certificate
active
06333590
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an ultrasonic transducer having a laminate structure, an array type ultrasonic probe formed by linearly arranging the transducers and a production method thereof.
The array type ultrasonic probe according to the prior art has the construction in which transducer elements made of a piezoelectric ceramic material are arranged in an array on a backing material, and a matching layer for establishing matching of acoustic impedance of an object or an acoustic lens is arranged in front of the transducers. The ultrasonic probe uses only one layer of the oscillation element or a laminate structure of a plurality of layers of oscillation elements (refer to “IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control”, Vol. 43, No. 4, July 1996, pp620-622). In either of these layered structures of the prior art, electrodes opposing each other while interposing the piezelectric material are so formed for each layer as to extend substantially in the same width from one end to the other in a longitudinal direction of the transducer element. When a pulse voltage is applied to such an electrode, the oscillation element undergoes thickness oscillation and generates ultrasonic waves. The sound pressure level of this ultrasonic wave exhibits a rectangular distribution that is substantially uniform from one end to the other of the transducer element.
However, considerably strong side lobes appear on both sides of a main beam in the ultrasonic beams emitted from the transducer having such a sound pressure distribution, as represented by broken lines in
FIG. 3
, as is known in the art. The signals generated from these side lobes mix as the noise with the signal obtained from the main lobe and reduce a signal-to-noise ratio (S/N) of the signal from the main lobe.
To reduce such detrimental side lobes, it is known to progressively reduce the ultrasound pressure level from the center towards both end portions. This means is described in “IEEE, 1985, Ultrasonics Symposium”, 1985, pp793-799.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ultrasonic transducer having a laminate structure for restricting the occurrence of side lobes to a low level, an ultrasonic probe, and a production method thereof.
It is another object of the present invention to provide an ultrasonic transducer having a laminate structure, that can be fabricated easily, an ultrasonic probe, and a production method thereof.
According to the present invention, an ultrasonic transducer is fabricated by laminating mutually and alternately a plurality of transducer elements and a plurality of internal electrodes into a laminate structure. In this instance, the size of each internal electrode having a simple shape such as a rectangle is changed in longitudinal direction of transducer so that the number of alternate laminate layers decreases from the center portion towards both end portions to thereby reduce level of side lobes.
An array type ultrasonic probe is fabricated by linearly arranging the ultrasonic transducers described above.
REFERENCES:
patent: 4385255 (1983-05-01), Yamaguchi
patent: 4564782 (1986-01-01), Ogawa
patent: 5410208 (1995-04-01), Walter
Addison Karen
Antonelli Terry Stout & Kraus LLP
Hitachi Medical Corporation
Ramirez Nestor
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