Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1991-09-26
1993-10-05
Stephan, Steven L.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310335, H01L 4104, H04R 1700
Patent
active
052508692
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to an ultrasonic transducer for controlling an ultrasonic beam with arranged vibrators and particularly to an ultrasonic transducer which has an improved ultrasonic beam characteristic in the short axis direction in order to realize a high image quality ultrasonic diagnostic apparatus.
2. Background of the Invention
An array type ultrasonic transducer arranging many vibrators of the present invention is shown in FIG. 1.
In FIG. 1, the reference numeral 71 denotes many piezoelectric vibrators consisting of piezoelectric elements; 72, backing; 73, acoustic lens; 74, FPC (Flexible Printed Circuit Board); 75, electrode lead wire. At both front and rear surfaces of the piezoelectric vibrator 71, the electrode surfaces are formed and the electrode lead wire 75 is electrically connected to such electrode surfaces. In general, one piezoelectric vibrator 1 has the sizes of 15 to 20 mm in the short axis direction and about 0.6 mm in the arrangement direction. These numerical values are applied to an ultrasonic transducer with the center frequency of 3.5 MHz (hereinafter, the ultrasonic transducer explained in this specification is formed as laminated layers).
The ultrasonic beam irradiation characteristic of this ultrasonic transducer is shown in FIG. 2. In this figure, the vertical axis indicates beam width and the zero position at the center corresponds to the center area of the vibrator 71 in the short axis direction. The horizontal axis indicates the scanning distance from the vibrator 71 (namely, separated distance). The characteristic (i) in this figure shows the -10 dB beam width, while (ii) the -20 dB beam width. Here, aperture of the ultrasonic transducer is 20 mm in size and the focal length of lens is 140 mm.
As the characteristic of the ultrasonic beam, uniform and narrow beam width for the region covering the short distance to long distance from the ultrasonic transducer is desirable in order to obtain a high quality image, but as can be understood from FIG. 2, the ultrasonic transducer explained above provides a narrow beam width in the vicinity separated by 140 mm from the focal point of lens but provides a wide beam width in the short and long distance areas other than in such a vicinity of the focal point.
Therefore, as a method of the prior art for improving the ultrasonic beam characterisic of such a vibrator in the short axis direction, it has been proposed to adequately change the size of the aperture depending on the scanning distance by increasing or decreasing the size of the aperture through division of the piezoelectric vibrator into a plurality of sections in the short axis direction.
An ultrasonic transducer of the prior art which can vary the size of the aperture is shown in FIG. 3. In this ultrasonic transducer, the piezoelectric vibrator 71 is divided in the short axis direction orthogonally crossing the arrangement direction of many piezoelectric vibrators 71 arranged like an array and the cutting grooves 76 are applied to the piezoelectric vibrator 71 as shown in the figure to divide the vibrator into three sections forming a center vibrator 71 1 and other vibrators 71 2 in both sides thereof.
In general, when an aperture of the piezoelectric vibrator is small in size, the narrow beam width can be attained for the entire distance of scanning as shown in (i) of FIG. 5. Meanwhile, when an aperture is large in size, the beam width may be set narrow particularly in a certain constant scanning distance (focal point of lens) but it is widened in comparison with that when the beam width and aperture become small in size at the other short and long distances from the focal point.
Therefore the ultrasonic transducer indicated in FIG. 3 changes the size of the aperture depending on the scanning distance by utilizing the beam characteristic which changes depending on size of aperture explained above. Namely, for the short and far distance, the size of aperture is substantially reduced by driving only the piezoelectric vibrator
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Hara Yasushi
Ishikawa Hiroshi
Kawabe Kenji
Matsui Kiyoto
Shimura Takaki
Fujitsu Limited
Haszko D. R.
Stephan Steven L.
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