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JPS61201599

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DESCRIPTION JPS61201599
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic transducer, and more particularly to an acoustic transducer using a piezoelectric
element as a vibrator. [Prior Art] An acoustic transducer using a piezoelectric element is used for
an ultrasonic diagnostic apparatus, an ultrasonic flaw detector, a fish search or an apparatus for
measuring a distance by propagation in the air, etc. 1 There is. On the other hand, in each of
these fields, improvement in measurement accuracy, that is, improvement in distance resolution
has become an important issue in any of these fields. Has become one of the important themes
imposed on Here, FIGS. 14 and 15 show a conventional example. Among them, FIG. 15 mainly
shows an acoustic transducer used as a probe for ultrasonic flaw detection, and FIG. 14 shows an
array type acoustic transducer for medical diagnostic equipment. Show. First, referring to FIG.
15, this will be described in more detail. In FIG. 15, 1 indicates a piezoelectric element with
electrodes attached on both sides, and 8 indicates a subject. Among the electrodes of the
piezoelectric element 1, IA indicates a drive side electrode, and IB indicates a ground side
electrode. The piezoelectric element 1 is fixed to the back member 3 through the driving
electrode IA, and at the same time, the front plate 4 is fixed to the opposite side (that is, the
object 8 side) through the gund electrode IB. The structure is Reference numerals 7A and 7B
denote terminals for applying an electric signal to the electrodes IA and IB, and 7A denotes a
driving side terminal, and 7B denotes a ground side terminal. The medical device of FIG. 14 is
also the same as that of FIG. 15 except that a plurality of transducers 6 are provided. The back
member 3 is formed of an acoustic attenuation material, thereby reducing the reflection from the
back member 3 to prevent the generation of a false echo. In this case, as the existing sound
attenuating material, those having an acoustic impedance whose value is lower than the acoustic
impedance of the piezoelectric element 1 occupy most of the sound attenuating material, and in
this point, the acoustic matching is sufficient on the back member 3 side. It has not been taken.
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For this reason, in such a conventional example, the minimum value of the sound wave reception
waveform is generally limited to about 2.5 waves (Fukumoto et al .: Shingaku Dissertation '80 /
10 Vol Vol, J 63-CN 11 IOP 682) ). [Problems to be Solved by the Invention] As described above,
as a back member for holding the voltage element I, a material having an acoustic impedance
close to that of the piezoelectric element l and a large amount of acoustic attenuation is obtained.
In the prior art, this is a necessary condition particularly for shortening the pulse of the
oscillating sound.
However, for the same material as that of the piezoelectric element 1, most of the material has
small attenuation of sound, so when it is used for the back member 3, a large reflection echo
(imaginary echo) from the inside of the back member 3 is detected. This makes it difficult to
distinguish between the defect detection echo in the subject 8 and, therefore, a problem before
the shortening of the transmission and reception sound waves actually occurs, and this is cited as
the top of the material that can not be used conventionally. Further, in the above-described
conventional example, since the matching between the voltage element 1 and the back member 3
is insufficient, the damping function (vibration holding function at the time of non-excitation)
with respect to the vibrator becomes insufficient. And the back surface member 3 have a large
number of repeated reflections on the contact surface, and therefore, it is in a state of reversing
the shortening of the transmission sound wave, so that there is a disadvantage that the distance
resolution is bad. SUMMARY OF THE INVENTION It is an object of the present invention to
provide an acoustic transducer which improves the distance resolution by improving the
disadvantages of the prior art, and in particular by shortening the pulse of the transmitted sound
wave. To aim. [Means for Solving the Problems] Therefore, in the present invention, an acoustic
transducer comprising an acoustic vibrator comprising a piezoelectric element having electrode
surfaces on both sides, and a back member for holding the acoustic vibrator, The back member is
formed as a first back member by a member having an acoustic impedance substantially equal to
that of the acoustic transducer, and at least on the surface of the first back member opposite to
the acoustic transducer, A second back member is disposed, and the second back member is
formed of a member having a large sound wave absorbing property, thereby achieving the above
object. [Operation] When a half-wave voltage pulse of a predetermined frequency is applied to
both surfaces of the piezoelectric element through the electrodes, an acoustic wave pulse of a
predetermined wavelength is generated in response to this voltage pulse, which is the first back
member And to the subject. In this case, since the acoustic impedances of the piezoelectric
element and the first back member are set to be approximately equal, the sound wave pulse
propagating to the first back member side is not reflected at the interface (that is, It becomes
possible to transmit a sound wave close to this. Then, the acoustic wave propagated into the first
back member is partially reflected by the end face (surface opposite to the piezoelectric element)
in the propagation direction, returned to the piezoelectric element side, and partially transmitted.
The light is transmitted through the second back member. Most of the sound wave propagated
into the second back member is absorbed because the back member of the cylinder 2 is formed
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of a highly damped member.
Therefore, the acoustic energy returned to the piezoelectric element side is greatly reduced. For
this reason, by setting the output level appropriately, it becomes easy to identify the defect echo
from the inside of the subject. Further, by providing a uniform inclined surface at the interface
between the piezoelectric element and the first back member, the acoustic energy returned to the
reflective piezoelectric element is sufficiently diffused here and the sound pressure level of its
imaginary echo is thin. As a result, it becomes possible to significantly attenuate only the
imaginary echo without deteriorating the detection level of the defect detection echo from the
object side. Furthermore, by setting the electrical circuit in transmission or reception to a high
impedance, it is possible to effectively increase the shortening of the sound wave even if a
difference in acoustic impedance occurs between the piezoelectric element and the first back
member. It becomes. [First Embodiment of the Invention] Hereinafter, a first embodiment of the
present invention will be described based on FIG. 1 by taking a case where it is implemented for
a probe for ultrasonic flaw detection as an example. In FIG. 1, reference numeral 10 denotes a
piezoelectric element as an acoustic vibrator having electrodes attached on both sides thereof as
in the conventional example described above, and reference numeral 80 denotes an object.
Among the electrodes of the piezoelectric element 10, IOA represents a drive side electrode, and
IOB represents a ground side electrode. The piezoelectric element 1 is fixed to the first back
member 13 via the driving electrode IA, and at the same time, the front plate 14 is fixed to the
opposite side (that is, the object 80 side) via the ground electrode IB. Structure. Reference
numerals 7A and 7B denote a drive side terminal and a ground side terminal, respectively,
similarly to the above-described conventional example, 20 denotes a second back member, and
21 denotes a circuit impedance of the signal application electric circuit. This circuit impedance
21 is set to a high impedance circuit in this embodiment. The piezoelectric element 10 used in
the present embodiment is a ceramic material system (in particular, a PZT system) of acoustic
impedance Zo = 25.7 О 10 kg / m Hs, and the first back member 13 is the piezoelectric element
10. And a block of the same material as unpolarized, and its acoustic impedance is set to Z ++ =
1.17 и Zo. Further, in the present embodiment, the second back member 20 is made of a
composite material of tungsten epoxy resin whose acoustic impedance is set to Z, = 0.6zo. In the
present embodiment, a uniform inclined surface S is formed at the interface between the second
back member 20 and the first back member 13.
The inclination angle ? of the inclined surface S with respect to the electrode surface of the
piezoelectric element 10 is set to about 18 ? ? in this embodiment, but it is not necessarily
limited to this. Experimentally, assuming that the peripheral side face is perpendicular to the
surface of the piezoelectric element 10 as described later, the result that the range of 10 ? ? ?
<40 @ is relatively good for the diffusion of the false echo is obtained. The Next, the overall
operation of the first embodiment will be described. FIG. 2 shows a block diagram modeled in the
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case where there is no reflection echo from the side of the first back member 13 described
above, that is, assuming an ideal state, and FIG. 3 (1) shows its equivalent circuit, The figure (2)
shows an electric signal and half-wave voltage pulses applied between the electrodes 10A and
108. Further, Zl in FIG. 2 indicates the acoustic impedance of the front plate 14, ZL indicates the
acoustic impedance of the subject, and Z2 indicates the acoustic impedance of the entire subject
side as viewed from the subject side surface of the voltage element 10. Show. And on the premise
of such a modeled circuit of an ideal state, this is a voltage transfer relationship (E, 5ITTIG).
????????????????????? ??????????? When various
examinations were made based on P2), the calculation results shown in FIG. 4 were obtained as a
result. In FIG. 4, (1) is the case where the acoustic impedances of the piezoelectric element and
the back member are not matched, and three or more repeated sound waves for half-wave
voltage pulses. Occurrence of Also, FIG. (2L, (3) shows the case where the acoustic impedances of
the piezoelectric element and the back member are matched, and as expected, for the
piezoelectric pulse of the half wavelength shown in FIG. A sound wave which is pulsed much
shorter than the one obtained is obtained. From this examination result, Fig. 3 (3) shows the case
where the impedance of the electrical circuit is high impedance (Zs = 10 ?), and Fig. 2 (2) shows
the impedance of the same circuit as Zs = = i 00 The case where it is lowered to (?) is shown. It
has become clear that in the case of high impedance, short pulse ultrasonic waves can be
obtained more effectively. Next, when the above calculation method is applied to the case of FIG.
1 showing the present embodiment and examined, a waveform shown in FIG. 5 (1) is obtained.
FIG. 5 (2) shows the experimental result in this case. From this, it was possible to experimentally
obtain a short pulse sound wave of about 1.0 wave close to the calculation result. Here, the
action of the inclined surface S which effectively functions with respect to the experimental result
of FIG. 5 (2) will be described.
First, in FIG. 6, when the ultrasonic wave is propagated from the CD surface toward the upper
side (in the first back member 13) of the figure, the central portion is reflected under the inclined
surface S and the point G of the side surface is It is reflected again at this point G and returns to
the point H on the CD surface. In this case, when the line segment is extended from the point G to
five points by the shadow method, GH = GJ. Therefore, when considered on the basis of the
original CD surface, the reflected sound is diffused from the size of the CD surface to the size of
the HK surface. When the line segment length HK <= a> is calculated (CD = b), a = b?cos 2?
??????????. The graph of this equation is shown in FIG. 7 (1). Also, the difference
between a and b, that is, w = (a-b) -b-tan 2? ииииииииииииии is graphed, and FIG. Next, the angle ? of the
inclined surface S is changed to examine an example of attenuation. In this case, ? mo earth CD.
??▒?????? In the case of FIG. 8 (1), when ? = 18 ░ and a specific dimension b = 13
(crane), W = 9.4 (silk). Now, assuming that the sound speed of the first back member is 4300 (m
/ S), the time difference to due to the path difference W is 2.2 [?SeC]. Here, assuming that the
frequency is 3 (MHz) and the wave number is 1.0, the energy of this reflected ultrasonic pulse
(hereinafter referred to as "unnecessary ultrasonic pulse") is temporally dispersed, and the pulse
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width is ((to + d) It becomes about 10 times by / d). As a result, the amplitude of the unnecessary
ultrasonic wave is attenuated by about 10 (dB). Next, in the case of FIG. 8 (2), ? is set to 35 ░.
In this case, a component P reflected twice by the inclined surface S appears as shown in the
figure. The double reflection component P means that the diffusion is suppressed and pushed
back. In this embodiment, this twice reflected component P appears when ?> 30 ░, and
substantial diffusion is suppressed, and becomes maximum when ?-45 ░ as shown in FIG.
Diffusion is zero and will not function at all. (In this case, if the angle ACD> (? / 2), then ? = 45
? ?). The case of ? # O ░ is the same as the case of ? = 45 ░ described above, and the effect
of the inclined surface S does not occur. Therefore, in consideration of slight diffusion, in the
present embodiment, Q ? ? <? <45 ░---------------. In practice, it seems that 10 ░ ? ? ? 40 ░
is preferable as a range in which the effect of the inclined surface S is observed, and practically,
10 ? ? ? ? ? 35 ░ is preferable.
9 to 10 each show an application example of FIG. Among them, FIG. 9 shows the one in which the
locking unevenness 30 is provided on a part of the upper and lower end portions of the inclined
surface S, and the one in FIG. The stop unevenness 31 is provided. Both are of such a size that
they have little influence on the sound reflection propagation at the overall level. The other
configuration is completely the same as the embodiment of FIG. 1 described above. By doing this,
in addition to having the same function and effect as the first embodiment described above, there
is an advantage that the assembly becomes easy, and the locking function works against external
vibration etc. to improve the durability. In the case where the second back surface member 20
sufficiently absorbs the sound without particularly requiring the effect of the inclined surface S,
??? ░ and ? = 45 ░ may be used. Next, a second embodiment will be described based on
FIG. In this second embodiment, while the first embodiment described above has made the
inclined surface S a continuous inclined surface, as shown in the drawing, the step inclined
surfaces S and St in the same direction are provided, and the connecting surface Y is It is
characterized in that it is processed in the direction orthogonal to the piezoelectric element 10.
In this case, 60 indicates a first back member, and 61 indicates a second back member. The other
configuration is the same as that of the first embodiment described above. By doing this, in
addition to having the same function and effect as in the first embodiment described above, it is
possible to temporally offset the internally reflected waves for each region, and therefore diffuse
the reflected sound waves more efficiently than in the first embodiment. It has the advantage of
being able to FIG. 12 is an explanatory view showing how a reflected sound wave is diffused in
this second embodiment. FIG. 13 shows an application of the second embodiment. In FIG. 13, the
inclined surface is SI. ??? It is a third tier of Sol. In this case, 70 indicates a first back member
and 71 indicates a second back member. The application shown in FIG. 13 has an advantage that
the reflected wave can be diffused more significantly. In the above embodiments, the present
invention has been described by taking an ultrasonic flaw detection probe as an example, but the
present invention can be applied to other acoustic transducers using other piezoelectric elements
as it is. The outer peripheral side of the back member 20, 61. 71 of the container 2 is extended to
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the first back member 13 60. 70 side, and the outer periphery of the first back member 13 60.
70 It may be configured to cover the surface. In addition, sound deterioration irregularities may
be provided around the first and second back members at appropriate cut angles.
[Effects of the Invention] As described above, according to the present invention, it is possible to
form the first back member by the substantially same member as the piezoelectric element and
to reduce the reflected wave from the first back member side. Therefore, it is possible to form a
short pulse of the sound wave pulse which has been considered to have a limit of 2.5 waves in
the prior art up to approximately 1, 0 waves, and this can significantly improve the distance
resolution. It is possible to provide an excellent sound conversion device.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a cross-sectional view showing the first embodiment of the present invention, FIG. 2 is a
block diagram in a state where FIG. 1 is modeled, FIG. 3 is an equivalent circuit of FIG. Is a
diagram showing an example of calculation of the sound pulse obtained when the parameter is
changed in FIG. 3, and FIG. 5 (+) is a sound pulse obtained when calculated based on the actual
situation of FIG. Fig. 5 (2) is a diagram showing the waveform of the sound wave pulse obtained
by the experiment, Fig. 6 is an explanatory view showing the sound wave reflection condition of
the inclined surface S, Fig. 7 (1) (2) 8 (1), 8 (2), and 8 (3) illustrate the effect of the inclined
surface S, and FIGS. 9 to 10 each show the first embodiment. 11 is a sectional view showing the
second embodiment, FIG. 12 is an explanatory view of FIG. 11, and FIG. 13 is an application of
the second embodiment. Illustration showing, Figure 14 and FIG. 15 is a sectional view showing
the respective prior art.
10---Piezoelectric element, 10A, 10B-1--electrode surface, 13. ??? 70----one first back
member, 20, 61. 71-one one one second back member, S. s, S2 + S,... Fig.1 Fig.2 n Fig.3 (Ln Fig. 4
m (2) Fig. 5 (Laughing 'it) (Time) Fig. 6 Fig. 7 ? (back) [?]' Fig. 8 ? Fig. 9 Fig. 10 r-= 1 Fig. 77
Fig. 7 S2 Fig. 12 Fig. 13
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