Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-05-06
2002-03-19
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06359375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to transducers, and particularly, to improved ultrasound transducer arrays.
2. Description of the Related Art
Ultrasound machines are used to non-invasively obtain image information about the structure of an object which is hidden from view and has become widely known as a medical diagnostic tool. As shown in
FIG. 1
, medical ultrasonic transducer arrays conventionally are fabricated from a block of ceramic piezoelectric material within which individual elements are defined and isolated from each other by sawing at least partially through the block of piezoelectric material making a number of cuts with a dicing saw. In particular, as shown in
FIG. 1
a transducer array
100
includes a layer
104
of transducer elements
104
a
-
104
f
. The transducer elements
104
a
-
104
f
are laid down on a backing medium
102
. The backing medium
102
serves to support the transducer structure. One or more acoustical matching layers
106
(including elements
106
a
-
106
f
) and
107
(including elements
107
a
-
107
f
) may be laid down on top of the transducer layer
104
. The piezoelectric layer
104
may be formed of any piezoelectric ceramic material such as lead zirconate titanate (PZT). The matching layers
106
,
107
and the transducer layer
104
may be glued to one another using an epoxy, such as Der332. The layers are then diced by forming kerfs
110
a
-
110
e
with a standard dicing machine. Typically the kerfs
110
a
-
110
e
are made both in the direction parallel to the paper and perpendicular to the paper.
Typically, the ratio of the width to the thickness of the piezoelectric elements
104
a
-
104
f
is optimized to about 0.5. The ratio of the width to thickness of the matching layers is typically ignored. As is generally known, the basic requirement for the transducers is high bandwidth, low pulse length, low crosstalk to the neighboring elements. However, if the width and thickness ratio of the matching layer is close to 1, lateral and thickness vibration mode will have a much stronger coupling, which in turn, will provide higher crosstalk, and unpredictable spectrum and pulse, which can degrade image quality.
Conventionally, the elements are sub-diced in order to change the width and thickness ratio of the ceramic piezoelectric material. For example, for the Siemens 5L40 transducer, the element is sub-diced once so that each sub-element width is around 116 micrometers and the thickness of the PZT element is about 256 micrometers. The resulting ratio of about 0.46 for the piezo-active layer results in a very good value for K
T
(electromechanical coupling coefficient) and low coupling. However, for the matching layer the thickness is typically about 130 micrometers resulting in a ratio of about 0.91, leading to a relatively strong coupling between the thickness mode and the unwanted lateral mode.
SUMMARY OF THE INVENTION
These drawbacks of the prior art are overcome in large part by an ultrasound transducer array according to the present invention. According to one embodiment of the invention, the piezoelectric elements and the matching layer(s) are diced with different sub-dicing. In particular, according to one embodiment the PZT is sub-diced once but at the same time the first matching layer is sub-diced twice to obtain a more optimum ratio for the matching layer.
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Guo Xiaocong
Houck Thomas G.
Budd Mark O.
Siemens Medical Solutions USA , Inc.
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