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JPH04211599

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DESCRIPTION JPH04211599
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic probe (probe) used for an ultrasonic inspection apparatus or the like, and more
particularly to an ultrasonic probe composed of laminated piezoelectric elements.
[0002]
2. Description of the Related Art An ultrasonic probe is mainly composed of a piezoelectric
element, irradiates ultrasonic waves toward an object, and receives reflected waves from
interfaces of different acoustic impedances in the object. , Used to image an image representing
the internal state of the object. Examples of the ultrasonic imaging apparatus in which such an
ultrasonic probe is adopted include a medical diagnostic apparatus for inspecting the inside of a
human body and an inspection apparatus for detecting flaws in metal welding.
[0003]
[0003] In the medical diagnostic apparatus, in addition to imaging and displaying a tomogram (Bmode image) of the human body, the blood flow velocity is two-dimensionally colorized using the
Doppler effect for the heart, liver, carotid artery etc. The development of the "color flow mapping
(CFM) method" that can be displayed has dramatically improved its diagnostic function. In recent
years, this CFM method has been used to diagnose all organs and organs of the human body,
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such as the uterus, kidney, and pancreas, and in the future each hospital will be able to study
diagnostic equipment that can observe even coronary blood flow. It is performed by other
facilities.
[0004]
In the case of the B mode image, it is required that a high resolution image can be obtained with
high sensitivity in which a small lesion or a gap due to a physical change can be clearly seen
deep. On the other hand, in the case of the Doppler mode capable of obtaining a CFM image etc.,
the level of the signal obtained is smaller than that in the case of the above-mentioned B mode
because reflection echoes from minute blood cells having a diameter of about several μm are
used. Furthermore, higher sensitivity is required. Therefore, in general, the reference frequency
in the Doppler mode is set to a frequency lower than the center frequency of the frequency band
originally possessed by the ultrasonic probe. The reason for this is that a low-frequency
component with low attenuation is used to suppress the influence of the S / N (ratio) reduction
due to the ultrasonic attenuation of the living body. Therefore, if it is assumed that ultrasonic
waves having two kinds of frequency components can both be transmitted and received by one
ultrasonic probe, high-resolution B-mode image in high-frequency components and highsensitivity Doppler in low-frequency components. It is possible to obtain an image. In order to
realize such an apparatus, "duplex ultrasonic probe" in which two kinds of transducers having
different resonance frequencies are installed in one ultrasonic probe head is manufactured and
sold by each manufacturer. However, since a plurality of different transducers are used in this
type of ultrasonic probe, the transmitting and receiving surfaces of ultrasonic waves are
different, and there is a problem that the same tomographic image can not be observed.
[0005]
Therefore, a method has been proposed in which ultrasonic waves of two types of frequency
bands are transmitted and received by one vibrator by using the laminated piezoelectric element
having the structure disclosed in Japanese Patent Application Laid-Open No. 60-41399. That is,
the combination of the ultrasonic probe head, the drive pulse width and the filter makes it
possible to separate the two frequency bands, and as a result, the B mode signal is low due to the
high frequency component of the two frequency components. The frequency components make it
possible to obtain Doppler signals independently. However, even in the ultrasonic probe having
such a configuration, since the electromechanical conversion efficiency of one piezoelectric
element is divided substantially equally, the frequency band on the high frequency side is
narrowed, and the tailing of the echo signal ( The wave length will be longer. As a result, despite
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trying to obtain a high resolution B-mode image with the above high frequency components, the
resolution is not improved as expected. Furthermore, as the frequency band narrows, the low
frequency component also tends to decrease, so that the S / N (ratio) is reduced and a
penetration deficiency occurs. This is because the frequency component of the echo signal from
the deep part of the living body is mainly composed of a component lower than the center
frequency of the transmitted ultrasonic wave. Although the fractional bandwidth required to
obtain a good B-mode image is 40% or more, for example, when a single-layer piezoelectric
element is used, the fractional bandwidth of -6 dB corresponds to the center frequency according
to one-layer matching 40-50%, and according to two-layer matching is 60-70% of the center
frequency. On the other hand, in the case of using the laminated piezoelectric element having the
above-mentioned configuration, it is 25% according to the single layer matching and 35%
according to the double layer matching. Therefore, if a laminated piezoelectric element is used,
the result is that only a specific band of about 1⁄2 can be obtained as compared to the case
where a single-layer piezoelectric element is used, and there is still room for improvement in
terms of structure.
[0006]
【0006】た。 As described above, when it is intended to obtain reflected waves of two
different frequency bands together with one ultrasonic probe, the same site is obtained even if a
plurality of transducers having different resonance frequencies are used. There was a problem
that it could not observe. If a multi-layer piezoelectric element having a structure in which a
single-layer piezoelectric element disclosed in Japanese Patent Application Laid-Open No. 6041399 proposed to solve this problem and a piezoelectric element having substantially the same
thickness are stacked, There is a problem that the relative bandwidth becomes narrow.
[0007]
Therefore, the object of the present invention is to solve the above-mentioned problems by
providing a probe head which can transmit and receive two types of ultrasonic waves in the same
plane and has a sufficiently wide band of high frequency components. It is in providing an
acoustic probe.
[0008]
Means for Solving the Problems In order to solve the above problems and achieve the purpose,
the following measures are taken.
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[0009]
In an ultrasonic probe head, a plurality of piezoelectric members are stacked so that the
polarization directions of adjacent piezoelectric members are opposite to each other, and
electrodes are attached to both end surfaces of these piezoelectric members in the thickness
direction. A laminated piezoelectric element formed by forming an end surface opposite to the
ultrasonic radiation surface, that is, the thickness of the piezoelectric layer adjacent to the
backing material which is the probe head base is thinner than the thickness of the other
piezoelectric layers To construct an ultrasonic probe according to the present invention.
[0010]
The laminated piezoelectric element according to the present invention is an n layer, for example,
2 in which one end face of a plurality of laminated layers is formed of the thinnest piezoelectric
layer and the polarization directions of adjacent layers are opposite to each other. By adopting a
configuration in which the layers are electrically connected in series, not only the lowest-order
resonance frequency f0 generated in the case of a laminated piezoelectric element in which
piezoelectric bodies having the same thickness are laminated, but also its 1 / n times ( In the case
of the present embodiment, it is possible to obtain a laminated piezoelectric element utilizing the
occurrence of resonance at a frequency of 1⁄2).
In addition, ultrasonic waves are transmitted by laminating a relatively thin layer and a thick
layer on the opposite side of the head portion of the ultrasonic probe with respect to the
ultrasonic radiation surface as described above. It is possible to receive and acquire reflected
waves (echo signals) of various frequency bands with high sensitivity.
Further, both high frequency and low frequency components can be obtained with high
resolution.
[0011]
Although the laminated piezoelectric element constituting the ultrasonic probe in the present
invention can be implemented with a laminated structure of three or more layers, the operation
in the case of the two-layer structure will be described below for simplicity.
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That is, the two types of resonances excited by changing the ratio R of the thickness of the two
layers of piezoelectric elements having different thicknesses (= back side piezoelectric body
thickness / radiation side piezoelectric body thickness, 0 <R <1) It is possible to adjust the level.
Therefore, by changing this thickness ratio R according to the purpose of use, it can be applied to
a wide range of applications.
[0012]
For example, in the case of a relatively deep examination where the heart is observed from the
body surface, for example, by setting the ratio R of the thickness small, the low frequency portion
of the frequency band, That is, since the resonance energy at the frequency of f0 / 2 is increased,
high sensitivity is realized in the Doppler mode.
[0013]
On the other hand, in the case where relatively shallow parts such as carotid arteries and
transesophageal echocardiography are to be examined with respect to this example described
above, by setting the ratio R of the thickness to a large value, high frequencies in the frequency
band can be obtained. Since the resonance energy of the part, that is, f0 is increased, an
ultrasonic probe having a wide band on the high frequency side is realized, and thus a high
resolution B mode image can be obtained even in the B mode.
[0014]
Embodiment (First Embodiment)
[0015]
FIG. 1 is a perspective view showing the structure of an ultrasonic probe head according to an
embodiment of the present invention.
The laminated piezoelectric element 1 is formed by laminating a plurality of (two in the case of
this embodiment) piezoelectric elements sandwiching an internal electrode serving as a boundary
surface of the two laminated layers.
A plurality of acoustic matching layers 2 to 4 are laminated on the ultrasonic radiation surface
side of the upper part of the laminated piezoelectric element 1.
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The thickness of each of the layers 2 to 4 is set so that matching can be achieved on the high
frequency side. The reason is that in order to obtain a B-mode signal on this frequency side, the
band is broadened.
[0016]
The laminated member including the laminated piezoelectric element 1 integrally laminated in
this manner uses a dicing machine to which a 30 μm thick blade for cutting into strips is
attached, including the matching layers 2 to 4 As shown in the drawing, they are cut into strips
and arranged at predetermined intervals on a backing material 6 as a head base. At the top, an
acoustic lens 5 with a convex surface facing up is deposited and deposited to form an integral
probe head.
[0017]
Between the acoustic matching layer 2 and the backing material 6 which are the upper and lower
members adjacent to the laminated piezoelectric element 1, the electrode surfaces of the
laminated piezoelectric element 1 are respectively deposited as external electrodes. .
[0018]
With respect to these external electrodes, as a wiring member to the head of the ultrasonic
probe, the common electrode line 7 for grounding is connected to one external electrode, and the
signal from the flexible printed board 8 for signal to the other external electrode. The wires are
respectively connected by soldering or the like.
The intervals (pitches) of the plurality of signal line patterns formed on the flexible printed board
8 are set to 0.15 mm so as to match the predetermined intervals at which the strip-like laminates
are arranged. FIG. 2 is an enlarged longitudinal cross-sectional view of the laminated
piezoelectric element of the two-layer configuration of the present embodiment, showing an
enlarged cross section taken along the line AA 'shown in FIG.
[0019]
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In the multi-layer piezoelectric element 1, as shown in this figure, two piezoelectric layers 11 and
piezoelectric layers 12 are stacked such that their polarization directions 13 and 14 are opposite
to each other. Further, external electrodes 15 and 16 are attached to both end surfaces of the
laminated piezoelectric element in the laminating direction, that is, the upper surface side of the
piezoelectric layer 11 and the lower surface side of the piezoelectric layer 12. The piezoelectric
layers 11 and 12 are formed of piezoelectric ceramic. Also, in practice, an internal electrode 17
for polarizing these layers is formed between the piezoelectric layer 11 and the piezoelectric
layer 12.
[0020]
Specifically, for example, the piezoelectric layers 11 and 12 are formed of PZT-based ceramic
having a dielectric constant of 2000, the thickness of the piezoelectric layer 11 is set to 260 μm,
and the thickness of the piezoelectric layer 12 is set to 180 μm. Do. That is, the thickness ratio R
in this case is about 0. 7となる。 That is, the thickness of the piezoelectric layer 12 which is far
from the acoustic lens 5 on the ultrasonic radiation surface side and adjacent to the backing
material 6 as the base is formed thinner than the other piezoelectric layers 11.
[0021]
The laminated piezoelectric element is cut in the laminating direction together with the matching
layers 2 to 4 by a dicing machine using a 30 μm thick blade. The interval is 0. It is set to 15 mm
and arranged in strips as shown.
[0022]
FIG. 3 is a graph showing the frequency spectrum of the echo waveform from the reflector
installed in water measured by the pulse echo method . As can be seen from the frequency
spectrum curve of this graph, the center frequency of the mountain on the high frequency side is
about 7.76 MHz, and the relative bandwidth at that time is 43. 2%である。 It can be said that
this value is a range of values sufficient to obtain a good B-mode image. Also, the center
frequency of the low frequency side mountain is about 3. 51MHzであることがわかる。
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[0023]
The graph of the frequency spectrum shown in FIG. 4 represents the measurement results of a
modification of the first embodiment described above. That is, in this modification, the thickness
of the piezoelectric layer 11 is set to 240 μm, the thickness of the piezoelectric layer 12 is set to
200 μm, and the thickness ratio R is about 0. The frequency spectrum of this ultrasonic probe
obtained when the other conditions are the same as in the first embodiment when the ultrasonic
probe constituted by the laminated piezoelectric element of 8 is implemented has a high
frequency as shown by the graph. The center frequency of the side is 7. 51 MHz, and the relative
bandwidth at that time is 45. It is calculated as 4%.
[0024]
As described above, it is apparent that this modified example is an ultrasonic probe composed of
laminated piezoelectric elements having frequency characteristics further broadened in
bandwidth than the first embodiment described above. Therefore, for example, the ultrasound
probe of the first embodiment is adopted for diagnosis of the heart from transesophagus, etc.,
and the ultrasound probe of this modification is used for diagnosis of the heart from the body
surface, etc. It is possible to use properly depending on the object to be diagnosed such as
Second Embodiment
[0025]
In this embodiment, a laminated piezoelectric material having the configuration shown in FIGS. 5
(a) and 5 (b) is used. That is, in the present embodiment, the ratio of the electric field to the
coercive electric field of the piezoelectric body is in the relationship between the polarization
direction of the piezoelectric body (thin arrow in the drawing) and the electric field direction
(thick arrow in the drawing) generated by the drive pulse. This is an improvement in which the
polarization direction of the larger piezoelectric layer and the electric field direction are set in the
same direction to prevent depolarization.
[0026]
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The drive pulse has positive polarity, negative polarity, burst wave, etc. Among them, the burst
wave has the same absolute value in both positive and negative. However, in general, in most
cases the wave number is large, and depolarization hardly occurs because the application of a
large voltage is rare due to the heat generation of the ultrasonic probe and the regulation of the
acoustic power.
[0027]
Since the piezoelectric layer 1 and the piezoelectric layer 2 in FIG. 5A are electrically connected
in series, when the same piezoelectric material is used for these two piezoelectric layers, an
electric field is generated. Since the direction 8 and the electric field direction 9 point in the same
direction in each layer, it does not have to be changed in direction and it seems that the
configuration of the present embodiment is not applicable. However, in the case of two
piezoelectric layers made of piezoelectric materials having different dielectric constants, the
improvement as in this embodiment is effective because the magnitudes of the generated electric
fields are different. Here, when the dielectric constant and thickness of the piezoelectric layer 1
are defined as ε 1 and t 1, respectively, the capacitance can be expressed as follows.
[0028]
Therefore, assuming that the impedance is Z1, the partial pressure V1 can be expressed as the
following equation.
[0029]
Therefore, the electric field E1 can be expressed as the following equation.
[0030]
From the above, the ratio between the electric field E1 and the coercive electric field Ec1 is
expressed by the following equation.
[0031]
Also, the piezoelectric layer 2 is similarly expressed by the following equation.
[0032]
[Equation 5]
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[0033]
From the above results, depolarization tends to occur in the case of the piezoelectric layer in
which the product of the dielectric constant and the coercive electric field shows a small value.
Therefore, in such a case, the polarization direction and the electric field direction may be
changed to point in the same direction.
Next, since the layers of the two piezoelectric layers shown in FIG. 5B are electrically connected
in parallel, the voltages applied to the layers are equal.
[0034]
Thus, regardless of the piezoelectric material used, the electric field in the thinner piezoelectric
will be greater.
Therefore, in such a case, the polarization direction and the electric field direction of the
piezoelectric layer having a small product of the thickness and the coercive electric field may be
changed to point in the same direction.
Third Embodiment
[0035]
In the graph showing the relationship between the center frequency of the low frequency part
and the thickness of the piezoelectric body shown in FIG. 6, the thickness of each of the
piezoelectric layer 1 and the piezoelectric layer 2 in FIG. 5 (a) is t1. , T2, the relative value of the
peak of the spectrum of the low frequency component and the high frequency component can be
changed by changing the thickness ratio r (= t2 / t1).
[0036]
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It is decided to use low frequency components for Doppler signals so that ultrasonic attenuation
of the living body can be reduced, while high frequency components with short wavelengths are
used for B mode signals so that high resolution signals can be obtained. Decide on that.
As a result of this, a graph representing the level of the spectrum and the echo level when the
thickness ratio r of the piezoelectric material is changed as shown in FIG. 6 is created.
The spectrum level of the low frequency component taken on the vertical axis represents the
Doppler sensitivity. Also, the spectrum level of the high frequency component represents the B
mode sensitivity. In addition, circles indicate measured values regarding the level of the spectrum
in the low frequency part, and triangle marks indicate measured values regarding the echo level.
[0037]
In the present embodiment, the thickness ratio r of the piezoelectric body is appropriately
adjusted depending on whether the Doppler sensitivity or the B mode sensitivity is to be
emphasized according to the diagnostic site when designing the ultrasonic probe. It shows that it
is possible. For example, (1) when a region deep from the body surface such as when diagnosing
the heart transthoracically is an object of diagnosis, since penetration is required, the B mode
sensitivity is set higher. (2) When Doppler sensitivity is required rather than a B-mode image as
in the case of diagnosis of lower extremities etc., the Doppler sensitivity is set higher.
[0038]
In this embodiment, while changing the thickness ratio r, the peak value of the spectrum of the
low frequency part and the peak value of the echo when the HPF (High Pass Filter) is connected
and the low frequency part is removed are measured. . Based on this result, a quadratic least
squares approximation was obtained by the "least squares method", with the thickness ratio r as
a variable as shown in the following equation. (Peak of low frequency part spectrum) = a + 9.59 r
− 22.1 r 2 [dB] (echo peak value after HPF connection) = b + 23.8 r − 10.9 r 2 [dB] a and b are
constants, which are determined by the measurement circuit, frequency and the like.
03-05-2019
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[0039]
FIG. 6 is a graph showing an actual measurement value when the thickness ratio r is changed and
an approximation of a quadratic function. In this figure, the constants in the above equation are a
= 1.73 and b = −12.9, and the above equation holds true in the range of 0.5 ≦ r ≦ 1.0 in the
actually measured range.
[0040]
Based on the relative relationship between the peak value of the spectrum level in the low
frequency part and the echo peak value, the lower limit value of B mode sensitivity and Doppler
sensitivity is set to the maximum value of 0.5 ≦ r ≦ 1.0. On the other hand, if the sensitivity is
determined to be -3dB and -6dB based on previous experience, the echo sensitivity has a
thickness ratio r of r <0.6 and the Doppler sensitivity of r> 0.8. It turned out that the use
condition is not satisfied. Therefore, as an allowable range of the thickness ratio r of the two
piezoelectric layers according to the preferred embodiment, about 0.6 <r <0.8 is a preferable
range for practical ultrasonic probe design. It can be said that there is. Therefore, it is preferable
to implement a two-layer piezoelectric body having a thickness ratio that satisfies the above
range. Fourth Embodiment The center frequency of the ultrasonic probe needs to be maintained
within ± 5% of the initial set value from the characteristics of the signal processing circuit such
as the drive pulse width and the filter.
[0041]
Pulse echo measurement was performed on the ultrasonic probe using the two-layer
piezoelectric material of the present invention, and the frequency spectrum characteristics were
obtained. According to the results, two-layer piezoelectric as shown in FIG. 7 (b) Even though the
body uses the same piezoelectric material as the single-layer piezoelectric as shown in FIG. 7 (a),
its center frequency is the center frequency of the single-layer piezoelectric when it is configured
to have the same thickness. A trend towards higher was found.
[0042]
That is, in the graph of FIG. 8, the abscissa represents the center frequency f (unit: MHz) of the
low frequency part as a variable, and the ordinate represents the same piezoelectric material as
that of the single-layer piezoelectric material having a thickness t0. The thickness t when using
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the two-layered piezoelectric material of the present invention.
As can be understood from the graph obtained from the measurement results, the thickness t0 of
the single-layer piezoelectric body is expressed by the following equation. t0 = 1.45 × 10 3 / f
[μm] On the other hand, the thickness t of the two-layered laminated piezoelectric body, which is
the main component of the present invention, is expressed by the following approximate
expression determined based on the measured values. I found that. t = 1.68 × 10 3 / f [μm]
Therefore, the above two equations lead to a relationship of t = 1.16t 0.
[0043]
That is, in order to obtain a center frequency equivalent to that of a conventional single-layer
piezoelectric material, as in the piezoelectric material shown for comparison as shown in FIGS. 7
(a) and 7 (b). In this case, by setting the thickness t of the two-layer piezoelectric body as in the
present invention to be about 16% thicker than the thickness t0 of the single-layer piezoelectric
body, the designed center frequency can be obtained. Fifth Embodiment In the present
embodiment, a method of manufacturing an ultrasonic probe using a laminated piezoelectric
element as a vibrator capable of simultaneously driving two frequencies according to the present
invention will be described.
[0044]
FIGS. 9 (a) and 9 (b) show cross-sectional views showing the configurations of two types of
vibrators of the present invention completed by this manufacturing method. The polarization
directions of the piezoelectric ceramic layers 1 and 2 are indicated by arrows. The manufacturing
method of such a two-layer vibrator is performed in the following order according to FIGS. 10 (a)
to 10 (c).
[0045]
(1) The internal electrode 3 of a predetermined shape is printed on one side of a green sheet
formed to a predetermined thickness by the doctor blade method, and another green sheet of
different thickness is laminated to form a piezoelectric ceramic. At the same time, the internal
electrode 3 and the internal electrode 3 are fired. (2) ... Then, the external electrodes 4 and 5 are
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printed in a predetermined pattern, baked, and polarized to form a vibrator.
[0046]
(2-1)... In order to obtain the vibrator of FIG. 9A, electrodes are configured as shown in FIG. The
external electrodes 4 and 5 on both sides are connected by the winding electrode 6, the internal
electrode 3 is provided with a voltage application part by the rotating electrode 7, and a DC
electric field is applied between the internal electrode and the external electrode to polarize. (2-2)
... Then, it may be cut at the position of the dotted line in FIG.
[0047]
Although this method has the advantage that two layers of piezoelectric ceramic can be polarized
at the same time, the thickness of the piezoelectric ceramic 1, 2 in each layer is different, so the
polarization electric field of each layer is different, and the degree of polarization is different. If
the thickness ratio of the two layers is small, there is no problem. However, if the ratio is large,
the polarization voltage is limited by the thin layer, the polarization electric field of the thick
layer may not be a sufficient value, and the polarization state may be insufficient. (2-3) In such a
case, as shown in FIG. 10B, the external electrodes on both sides may be independently polarized
with an optimum electric field for each layer, and cut at the dotted line position.
[0048]
(3) To obtain the laminated vibrator configuration shown in FIG. 9 (b), electrodes are formed as
shown in FIG. 10 (c), and an electric field is applied between the external electrodes 4 and 5 on
both sides. Make an electrode. Thereafter, the external electrodes on both sides may be
connected in common. Although it is difficult to form a baking electrode for this connection
because heat above the Curie temperature of the piezoelectric material is not applied, a
conductive adhesive or the like may be used. (4) In addition, although an FPC is soldered as a
lead to an electrode of a vibrator in manufacturing a probe, electrodes on both sides may be
connected at this time. Sixth Embodiment
[0049]
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14
This embodiment is a laminated piezoelectric body having a longitudinal sectional structure as
shown in FIG. 11 (a). That is, by changing the acoustic impedance of each stacked piezoelectric
body, an optimal stacked piezoelectric body is configured. Specifically, the ultrasonic probe is an
ultrasonic probe in which the acoustic impedance of the piezoelectric layer on the acoustic
matching layer side is set smaller than that on the backing material side. The laminated
piezoelectric material of this embodiment changes the ratio of the thickness of each laminated
piezoelectric material, and changes the ratio of the respective acoustic impedances to obtain the
ratio band and sensitivity level of the high frequency region and the low frequency region. Can
be adjusted accordingly.
[0050]
In FIG. 11 (b) showing an example of the cross section of the composite piezoelectric layer in the
case of the two-layer structure, the vibrator 1 is composed of the piezoelectric ceramic layer 2
having a large acoustic impedance and the composite piezoelectric layer 3 having a small
acoustic impedance. The composite piezoelectric layer is laminated on the side of the acoustic
matching layer 4 via an electrode. Further, this composite piezoelectric layer 3 has a horizontal
cross section taken along the line B-B 'in FIG. 11 (a) as shown in FIG. 11 (b). That is, for example,
from a plurality of columnar piezoelectric members 10 arranged at equal intervals in each of
grid-like non-adjacent squares, and epoxy resin or the like injected and solidified so as to fill in
between them. It is configured integrally.
[0051]
In FIGS. 12 (a) and 12 (b), the acoustic impedance of the composite piezoelectric layer is constant
at 17.7 Mrayls, and the thickness ratio is 0.59 or 0 of the thickness of the entire vibrator. The
frequency spectrum of the underwater pulse echo of the composite piezoelectric body set to .41
is shown.
[0052]
Further, in FIGS. 13A and 13B, the thickness ratio of the composite piezoelectric material is fixed
at 0.5, and the acoustic impedances are set at 21.3 Mrayls and 11.4 Mrayls, respectively. The
frequency spectrum of the underwater pulse echo is shown.
[0053]
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15
The following can be seen by comparing each graph curve.
That is, although the sensitivity level in the low frequency region is certainly high in FIG. 12 (b),
the -6 dB fractional bandwidth in the high frequency region is about 30%.
In FIG. 12A, the −6 dB relative bandwidth in the high frequency region is about 49%. While the 6 dB ratio band in the high frequency region is about 43% in FIG. 13A, it narrows to about 37%
in FIG. 13B, but the sensitivity level in the low frequency region is high. The relative bandwidth
also widens.
[0054]
As described above, according to this embodiment, not only the ratio of the thickness of the
laminated piezoelectric material but also the ratio of the high frequency region and the low
frequency region and the sensitivity level thereof can be changed by changing the acoustic
impedance. It is possible to change Therefore, even when it is difficult to control the thickness of
the lamination structurally or in a manufacturing method, it is easy to more appropriately adjust
the characteristics of the ultrasonic probe having two or more frequency regions.
[0055]
In the above-described embodiment and its modification, particularly, the case of the laminated
piezoelectric element having a two-layer structure has been exemplified, but the present
invention is not limited to these examples, and deviates from the gist of the present invention.
Other various modifications are also possible within the scope of the present invention. For
example, a laminated piezoelectric element having three or more layers may be used as the
piezoelectric layer.
[0056]
According to the present invention, it is possible to provide an ultrasonic probe that exerts the
following effects. That is, two piezoelectric layers are stacked, electrodes are formed on both end
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surfaces, two adjacent piezoelectric layers are electrically connected in series, and a piezoelectric
layer far from the ultrasonic radiation surface is thinly formed. By configuring an ultrasonic
probe provided with stacked piezoelectric elements, it becomes possible to transmit and receive
different plural, for example, two types of frequencies, and furthermore, by changing the
piezoelectric thickness ratio of each layer, high frequency according to the purpose of use It is
possible to properly adjust the fractional band of the area and to use it properly depending on
the object to be diagnosed.
[0057]
Brief description of the drawings
[0058]
1 is a perspective view showing the entire configuration of an ultrasonic probe head according to
a first embodiment of the present invention.
[0059]
2 is an enlarged longitudinal sectional view showing the configuration of the laminated
piezoelectric element in the first embodiment.
[0060]
3 is a graph showing an echo waveform obtained by the first embodiment.
[0061]
4 is a graph showing an echo waveform obtained by the ultrasonic probe according to the
modification of the first embodiment.
[0062]
5 is a configuration diagram showing a laminated piezoelectric element of the ultrasonic probe
according to the second embodiment of the present invention.
[0063]
6 is a graph showing the spectrum level and the echo level when the thickness of the
piezoelectric body of the ultrasonic probe according to the third embodiment of the present
invention is changed.
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[0064]
7 is a configuration diagram showing the thickness of the multilayer piezoelectric element of the
ultrasonic probe according to the fourth embodiment of the present invention and the
conventional single-layer piezoelectric element.
[0065]
8 is a graph showing the relationship between the thickness of the piezoelectric element of the
ultrasonic probe according to the fourth embodiment and the generated center frequency.
[0066]
9 is a configuration diagram showing a laminated piezoelectric element of an ultrasonic probe as
a fifth embodiment of the present invention.
[0067]
10 is an explanatory view for explaining the manufacturing procedure regarding the
manufacturing method of the multilayer piezoelectric element of the ultrasonic probe as the fifth
embodiment.
[0068]
11 is a longitudinal sectional view and a cross-sectional view of an ultrasonic probe according to
a sixth embodiment of the present invention.
[0069]
12 is a graph showing an echo waveform obtained by the ultrasonic probe according to the sixth
embodiment.
[0070]
13 is a graph showing an echo waveform obtained by the ultrasonic probe according to the sixth
embodiment.
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Explanation of sign
[0071]
DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element, 2, 3, 4 ... Acoustic matching
layer, 5 ... Acoustic lens, 6 ... Backing material, 7 ... Common electrode wire for earths, 8 ... Signal
wire of the flexible printed board for signals, 11, 12 ... Piezoelectric Body layer 13, 14 ...
polarization direction 15, 16 ... external electrode, 17 ... internal electrode.
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