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JPH03121000

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DESCRIPTION JPH03121000
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic probe for transmitting and receiving ultrasonic waves. [Prior Art] As is well known, an
ultrasound probe is constructed by housing a piezoelectric element, an acoustic lens in contact
with one surface thereof, and a damper member in contact with the opposite surface in a
housing. Ru. When a pulse voltage is applied to the piezoelectric element, ultrasonic waves are
emitted from the piezoelectric element. The emitted ultrasonic waves are focused by an acoustic
lens and emitted as an ultrasonic beam to an external subject. The ultrasonic wave reflected on
the surface or inside of the subject again passes through the acoustic lens to reach the
piezoelectric element, and the piezoelectric element converts the reflected wave into an electric
signal according to the electric wave and outputs it. Various inspections and analyzes are
performed on the subject based on the output signal. The ultrasonic wave generated by the
piezoelectric element and radiated in the opposite direction to the acoustic lens is attenuated by
the damper member. By the way, the ultrasonic waves emitted from the piezoelectric element to
the acoustic lens are not all emitted to the outside through the acoustic lens, but a part of the
ultrasonic wave is at the boundary between the acoustic lens and the outside. It is reflected by
the surface and returns to the piezoelectric element. Then, a part of the returned ultrasonic wave
is reflected again at the interface between the acoustic lens and the piezoelectric element and
emitted to the acoustic lens. By repeating such reflection, a part of the ultrasonic wave emitted
from the piezoelectric element to the acoustic lens causes multiple reflection in the acoustic lens.
Similarly, a part of the ultrasonic wave emitted from the piezoelectric element to the damper
member is reflected at the interface between the damper member and the outside to return to
the piezoelectric element, and a part of the reflected wave is the damper member and the
piezoelectric element It is reflected at the interface with the and emitted to the damper member.
Such reflections also cause multiple reflections in the damper member. As described above, the
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multiple reflections generated by the acoustic lens and the damper member excite each time they
reach the piezoelectric element to generate an electrical signal corresponding to the reflected
wave. Then, since the electricity 43 is output together with the electric signal by the reflected
wave from the surface or the inside of the subject, the former electric signal causes interference
to the latter electric signal, and the reflected wave from the subject is generated. It is not possible
to obtain an accurate signal waveform according to the situation, causing problems in the
inspection and analysis of the subject by ultrasonic waves. An object of the present invention is
to solve the problems in the above-mentioned prior art, and to provide an ultrasonic probe
capable of suppressing interference with a reflected wave from a subject due to a multiple
reflected wave in an acoustic lens. [Means for Solving the Problems] In order to achieve the
above object, the present invention takes advantage of the fact that the above-mentioned
interference is caused by utilizing an inversion in one phase when the acoustic lens and the
damper member reflect on the interface with the outside. It is to suppress.
Therefore, according to the present invention, the piezoelectric element, the acoustic lens in
contact with one surface of the piezoelectric element and to which the ultrasonic wave is
transmitted, and the surface opposed to the one side of the piezoelectric element are attenuated
and the ultrasonic wave is attenuated. And an ultrasonic probe including a piezoelectric element,
an acoustic lens, and a housing for accommodating the damper member, wherein the damper
member is made of a material having an acoustic impedance substantially equal to that of the
acoustic lens. The thickness of the damper member may be 1⁄2 of the axial center length of the
acoustic lens. [Operation] By selecting the material and dimensions of the damper member as
described above, the arrival times of the second internal reflection wave of the damper member
and the first internal reflection wave of the acoustic lens coincide with each other at the
piezoelectric element. Then, while the phase of the first internal reflected wave of the acoustic
lens is inverted, the phase of the second internal reflected wave of the damper member is reinverted. As a result. The internal reflection wave of the 1 @ th eye of the acoustic lens and the
second internal reflection wave of the damper member simultaneously reach the piezoelectric
element. Moreover, since the phases are opposite to each other, they are mutually canceled and
significantly attenuated, thereby suppressing the interference. The present invention will be
described below based on the illustrated embodiments. FIG. 1 is a cross-sectional view of an
ultrasonic probe according to an embodiment of the present invention. In the figure, 1 is a
piezoelectric element, 2 is an acoustic lens, 3 is a damper member, and 4 is a housing. Reference
numeral 2a denotes a lens surface of the acoustic lens. One surface of the piezoelectric element is
in close contact with the surface of the acoustic lens 2, and the other surface of the piezoelectric
element is in close contact with the surface of the damper member 3. The damper member 3 is
formed of a material having the same acoustic impedance as the acoustic lens 2 and is formed to
a thickness of 1/2 of the axial center thickness d of the acoustic lens 2. Next, the operation of
this embodiment will be described with reference to the waveform diagrams shown in FIGS. 2 (a)
and 2 (b). 2 (a), the vertical axis represents the magnitude of the reflected wave in the acoustic
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lens 2, the horizontal axis represents time, and the FIG. 2 (b), the vertical axis, the magnitude of
the reflected wave in the damper member 3, Time is taken on the horizontal axis. Now, when a
voltage is applied to the piezoelectric element 1 through a lead wire (not shown), ultrasonic
waves are emitted from the piezoelectric element 1 to the acoustic lens 2 and the damper
member 3. Most of the ultrasonic waves radiated to the acoustic lens 2 are irradiated from the
lens surface 2a through a medium (for example, water, air) to a not-shown object, but a part is
reflected by the lens surface 2a to be an acoustic lens 2 to reach the piezoelectric element 1 and
excite it.
As a result, in the piezoelectric element 1, the waveform of the reflected wave for generating the
electric signal according to the reflected wave is shown by a symbol L □ in FIG. 2 (a). Here,
ultrasonic waves have a characteristic that phase inversion occurs when incident from a large
acoustic impedance to a small acoustic impedance, and no phase inversion occurs when incident
to a large acoustic impedance. Then, there are the following magnitude relationships among the
acoustic impedances of the piezoelectric element 1, the acoustic lens 2, and water and air.
(Piezoelectric element)> (Acoustic lens)> (water)> (Air) Therefore, the waveform L is a waveform
obtained by inverting the phase of the ultrasonic wave emitted from the piezoelectric element 1
at the lens surface 2a. Then, a part of the reflected wave of this waveform is again reflected again
at the interface with the piezoelectric element 1 and returns to the inside of the acoustic lens 2.
In this case, the acoustic impedance of the piezoelectric element 1 is the acoustic impedance of
the acoustic lens 2. Since it is larger than the impedance, no phase inversion occurs. A part of the
re-reflected wave is reflected again by the lens surface 2 a of the acoustic lens 2, and at this time,
the phase is inverted and reaches the piezoelectric element 1 to generate an output. The
waveform of this re-reflected wave is indicated by a symbol L2. Although multiple reflections in
the acoustic lens 2 as described above occur in the damper member 3 in exactly the same way.
Since the thickness of the damper member 3 is 1⁄2 of the thickness d of the acoustic lens 2, the
repetition period of multiple reflection is 1⁄2 of the acoustic lens 2. The waveform of the
reflected wave due to the multiple reflection in the damper member 3 is shown in FIG. Phase
inversion occurs sequentially in each of the waveforms D □ to D. As apparent from comparison
between FIGS. 2 (a) and 2 (b), the points when the reflected wave of FIG. 1 of the acoustic lens 2
and the second reflected wave of the damper member 3 reach the piezoelectric element 1
coincide with each other. ing. And, the phases of both reflected waves are opposite to each other.
As a result, the two reflected waves mutually cancel each other and cause remarkable
attenuation, and the output from the piezoelectric element 1 is also significantly reduced
accordingly. Therefore, the magnitude of the subsequent multiple reflection in the acoustic lens 2
and the damper member 3 becomes extremely small, and the influence on the reflected wave
from the object can be almost ignored. Although the first reflected wave (waveform D1) in the
damper member 3 is not canceled and has a fairly large level, this reflected wave is a reflected
wave from the acoustic lens 2 or a reflected wave from the subject As it appears much earlier, it
has no effect on the reflected wave from the subject and it is easy to distinguish it from the
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others.
As described above, according to the present invention, a material having an acoustic impedance
substantially the same as the acoustic impedance of the acoustic lens is selected as the material
of the damper member, and the thickness of the damper member is set to Since the axial center
length is 1⁄2, multiple reflected waves generated in the acoustic lens and the damper member
can be greatly attenuated, and interference with reflected waves from the subject due to these
multiple reflected waves can be suppressed, and thus the object Accurate examination and
analysis of specimens can be performed.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a cross-sectional view of an ultrasonic probe according to an embodiment of the present
invention, and FIGS. 2 (a) and 2 (b) are waveform diagrams of reflected waves in an acoustic lens
and a damper member.
1 · · · Piezoelectric element, 2 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · housing
housing.
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