Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-11-30
2001-05-01
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06225729
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic probe in which a plurality of transducer elements are arranged with a predetermined pitch so as to form each of channels which transmits an ultrasonic wave to an object to be examined and receives a reflected wave of the transmitted ultrasonic wave. More particularly, the present invention relates to an ultrasonic probe which can enhance a frequency characteristic and reduce a crosstalk between the respective channels, and an ultrasonic diagnostic apparatus using the ultrasonic probe.
A conventional ultrasonic probe, as shown in
FIG. 11
, includes a plurality of transducer elements
1
,
1
, . . . which are arranged with a predetermined pitch so as to form each of channels for transmitting an ultrasonic wave and receiving a reflected wave from inside of an object to be examined, electrodes
2
a
,
2
b
provided on a front surface and a rear surface of each of the transducer elements
1
,
1
, . . . so as to apply a voltage thereto, and an acoustic matching layer
3
for taking a matching of an acoustic impedance between the transducer elements
1
,
1
, . . . and the object to be examined. In
FIG. 11
, a reference numeral
4
denotes a backing material for preventing an ultrasonic wave transmitted from the rear surface of the transducer element
1
from getting back again to the rear surface thereof. A reference numeral
5
denotes an acoustic lens provided over the above-described acoustic matching layer
3
so as to focus an ultrasonic beam transmitted from the front surface of the transducer element
1
.
Here, concerning the acoustic matching layer
3
, an acoustic impedance thereof is set to be an intermediate value between an acoustic impedance of the transducer element
1
and that of the object to be examined. Moreover, the acoustic matching layer
3
is formed so that a thickness thereof becomes equal to ¼th of a wavelength of the ultrasonic wave. If the acoustic matching layer
3
as described above is continuously arranged in a transverse direction along the direction in which the transducer elements
1
,
1
, . . . are arranged, a crosstalk between the channels (an radio interference between signals) is increased due to the ultrasonic wave propagating through the acoustic matching layer
3
. Accordingly, incisions are made into the acoustic matching layer
3
in correspondence with gaps
6
,
6
, . . . between the channels of the plurality of transducer elements
1
,
1
, . . . arranged with a predetermined pitch, thereby forming gaps
7
,
7
, . . . between the channels to reduce the crosstalk.
However, in such a conventional ultrasonic probe, since the above-mentioned acoustic matching layer
3
is formed using a uniform material having an acoustic impedance of an intermediate value between the acoustic impedance of the transducer element
1
and that of the object to be examined, the acoustic matching layer
3
does not perform a pure piston movement in only a direction in which an ultrasonic wave is transmitted from the transducer element
1
, but oscillates also in a direction perpendicular to the transmitted direction of the ultrasonic wave. The existence of such an oscillation mode in the direction perpendicular to the transmitted direction of the ultrasonic wave in each acoustic matching layer
3
is harmful to an original purpose of the ultrasonic wave transmission/reception. The reason is that, if an ultrasonic wave is transmitted at a frequency close to the oscillation frequency in the transverse direction, a part of the energy thereof is used for the oscillation of the acoustic matching layer in the transverse direction, so that an original response in the longitudinal direction is deteriorated.
For example, as is seen in a simulation on Round Trip Impulse Response shown in
FIG. 12
, there occurred an irregular tail-trailing c in the echo voltage waveform with a lapse of time, so that a pulse characteristic of a reception signal becomes worse. Also, as is seen in a simulation on Round Trip Frequency Response shown in
FIG. 13
, there occurred ripples d
1
, d
2
, and d
3
at certain frequencies, so that a broad frequency characteristic is not obtained. On account of this, in the conventional ultrasonic probe, it is not able to optimize the oscillation mode in the direction perpendicular to the transmitted direction of the ultrasonic wave in the acoustic matching layer
3
. This eventually brought about no broad frequency characteristic or no excellent pulse response characteristic, thus, in some cases, resulting in a deterioration in image quality of an ultrasonic wave image.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide, in order to deal with the above-described problems, an ultrasonic probe capable of reducing a crosstalk between the channels and having a broad frequency characteristic and an excellent pulse response characteristic, and an ultrasonic diagnostic apparatus using the ultrasonic probe.
In order to attain the above-described object, the ultrasonic probe according to the present invention includes a plurality of transducer elements which are arranged with a predetermined pitch so as to form each of channels and transmits an ultrasonic wave and receives a reflected wave from inside of an object to be examined, electrodes provided on a front surface and a rear surface of each of the transducer elements so as to apply a voltage thereto, and an acoustic matching layer for taking a matching of an acoustic impedance between the above-described transducer elements and the object to be examined, wherein the above-described acoustic matching layer is constituted so that the acoustic matching layer has an anisotropy in an acoustic characteristic between a direction in which the ultrasonic wave is transmitted from the transducer elements above-mentioned and a direction perpendicular to the transmitted direction of the ultrasonic wave.
The phrase “the acoustic matching layer has anisotropies” means that, in the acoustic matching layer, a speed of an ultrasonic wave differs depending on whether it propagates in the longitudinal direction or in the transverse direction, and an attenuation rate of intensity of an ultrasonic wave differs depending on whether it propagates in the longitudinal direction or in the transverse direction.
Also, the ultrasonic diagnostic apparatus as a related invention includes an ultrasonic probe for transmitting or receiving an ultrasonic wave into or from the object to be examined, an ultrasonic beam forming unit which drives the ultrasonic probe and transmits the ultrasonic wave and processes a reflected echo signal received by the ultrasonic probe and forms an ultrasonic beam, an image processing device for constructing an ultrasonic wave image with the input of the received signal from the ultrasonic beam forming unit and a display device for displaying an image by taking in the image signal from the image processing device, wherein an ultrasonic probe having an acoustic matching layer which has an anisotropy in the acoustic characteristic between an ultrasonic wave-transmitting direction from the transducer elements and a direction perpendicular thereto, is employed as the above-described ultrasonic probe.
Since the present invention is constituted as described above, it is possible to reduce the crosstalk between the channels and obtain the broad frequency characteristic and the excellent pulse response characteristic. This makes it possible to enhance image quality of an ultrasonic wave image.
Further, as to the ultrasonic diagnostic apparatus as the related invention, since the ultrasonic probe according to the present invention which is structured as stated above is used as an ultrasonic probe, the crosstalk between the respective channels can be reduced and an ultrasonic diagnostic apparatus having a broad frequency characteristic and an excellent pulse response characteristic can be realized.
REFERENCES:
patent: 3362501 (1968-01-01), Lenahan
patent: 4211948 (1980-07-01), Smith et al.
pate
Ikeda Takashi
Izumi Mikio
Antonelli Terry Stout & Kraus LLP
Budd Mark O.
Hitachi Medical Corporation
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