JPH04211599A - Ultrasonic probe and production thereof - Google Patents

Abstract

PURPOSE:To obtain the ultrasonic probe which can transmit and receive different plural, for example, two kinds of frequencies and can be selectively used according to the object to be diagnosed by properly adjusting the specific band of a high-frequency region according to the purposes of use. CONSTITUTION:Two piezoelectric layers are laminated and electrodes are deposited and formed on both end faces. The two adjacent piezoelectric layers are electrically connected in series, by which the ultrasonic probe having the laminated piezoelectric element formed with the thinner piezoelectric layer on the side further from an ultrasonic radiation surface is constituted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic probe used in an ultrasonic inspection device, and more particularly to an ultrasonic probe composed of laminated piezoelectric elements.

0002

[Prior Art] Ultrasonic probes are mainly composed of piezoelectric elements, and emit ultrasonic waves toward a target object, and receive reflected waves from interfaces of different acoustic impedances in the target object. It is used to visualize images that represent the internal state of the computer. Examples of ultrasonic imaging devices employing such an ultrasonic probe include medical diagnostic devices for inspecting the inside of a human body and inspection devices for detecting flaws inside metal welds.

In addition to displaying a tomographic image (B-mode image) of the human body, medical diagnostic equipment uses the Doppler effect to double the speed of blood flow in the heart, liver, carotid artery, etc.
With the development of the ``Color Flow Mapping (CFM) method,'' which allows dimensional color display, its diagnostic capabilities have improved dramatically. In recent years, this CFM method has been applied to the uterus, kidneys,
It is used to diagnose all organs and organs of the human body, such as the pancreas, and in the future, hospitals and other facilities are conducting research on diagnostic devices that will be able to even observe the movement of coronary blood flow.

[0004] In the case of B-mode images, it is required to obtain high-resolution images with high sensitivity in which small lesions and voids caused by physical changes can be clearly seen deep down. On the other hand, in the case of Doppler mode, which can obtain CFM images, etc., the level of the signal obtained is lower than that in the case of B mode, as it uses reflected echoes from minute blood cells with a diameter of several micrometers. , even higher sensitivity is required. Therefore, the reference frequency in the Doppler mode is generally set to a frequency lower than the center frequency of the ultrasound probe's original frequency band. The reason for this is that the S
This is because a low frequency component with little attenuation is used to suppress the influence of a decrease in /N (ratio). Therefore, if one ultrasonic probe can transmit and receive both ultrasound waves with two types of frequency components, a high-resolution B-mode image will be generated for the high-frequency component, and a highly sensitive Doppler image will be generated for the low-frequency component. It becomes possible to obtain an image. In order to realize such a device, various manufacturers manufacture and sell "duplex-type ultrasonic probes" in which two types of transducers with different resonance frequencies are installed in one ultrasonic probe head. However, since this type of ultrasound probe uses a plurality of different transducers, the ultrasound transmitting and receiving planes are different, and there is a problem that the same tomographic image cannot be observed.

[0005] Therefore, a method has been proposed in which a single vibrator transmits and receives ultrasonic waves in two types of frequency bands by using a laminated piezoelectric element having the configuration disclosed in Japanese Patent Application Laid-Open No. 60-41399. In other words, the combination of the ultrasonic probe head, drive pulse width, and filter makes it possible to separate two types of frequency bands, and as a result, among the two frequency components, the high frequency component causes the B-mode signal to It became possible to obtain Doppler signals independently of each other due to the frequency components. However, even in an ultrasonic probe with such a configuration, the electromechanical conversion efficiency of one piezoelectric element is divided almost equally, so the frequency band on the high frequency side becomes narrow and the echo signal tails ( wave length) becomes longer. As a result, although an attempt is made to obtain a high-resolution B-mode image using the above-mentioned high-frequency components, the resolution is not improved as much as expected. Furthermore, as the frequency band narrows, the low-frequency components also tend to decrease, so the S/N (
ratio) decreases, resulting in insufficient penetration. This is because the frequency components of the echo signal from deep within the living body are mainly components lower than the center frequency of the transmitted ultrasound. The fractional bandwidth required to obtain a good B-mode image is 40% or more, but for example, when using a single-layer piezoelectric element, the fractional bandwidth of -6 dB is equal to the center frequency according to single-layer matching. According to two-layer matching, it is 60 to 70% of the center frequency. On the other hand, when using a laminated piezoelectric element with the above configuration, 25% is achieved by one-layer matching, and 3% by two-layer matching.
It will be 5%. Therefore, if a multilayer piezoelectric element is used, a fractional band that is only about half that of a single-layer piezoelectric element can be obtained, and there is still room for further improvement in terms of structure.

[0006]

[Problems to be Solved by the Invention] As mentioned above, when trying to obtain reflected waves of two types of frequency bands with one ultrasonic probe, even if multiple transducers with different resonance frequencies are used, it is difficult to obtain reflected waves from the same region. There was a problem that it could not be observed. In order to solve this problem, if a multilayer piezoelectric element having a structure in which piezoelectric elements of approximately the same thickness are stacked as the single-layer structure piezoelectric element disclosed in Japanese Patent Application Laid-open No. 60-41399 is adopted, high-frequency components are There was a problem that the specific band became narrow.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an object of the present invention is to provide an ultrasonic probe head that is capable of transmitting and receiving two types of ultrasonic waves on the same surface and has a sufficiently wide band of high frequency components. The purpose of the present invention is to provide a sonic probe.

[0008]

[Means for Solving the Problems] In order to solve the above problems and achieve the objectives, the following measures were taken.

In an ultrasonic probe head, a plurality of piezoelectric bodies are stacked so that the polarization directions of adjacent piezoelectric bodies are opposite to each other, and electrodes are attached to both end faces of these piezoelectric bodies in the thickness direction. A laminated piezoelectric element in which the thickness of the piezoelectric layer adjacent to the end face opposite to the ultrasound emission surface, that is, adjacent to the backing material that is the probe head base, is thinner than the thickness of the other piezoelectric layers. The ultrasonic probe according to the present invention is constructed using the following.

0010

[Operation] The laminated piezoelectric element according to the present invention has an n layer, for example, two
By adopting a configuration in which the layers are electrically connected in series,
Not only the lowest resonant frequency f0 that occurs in the case of a laminated piezoelectric element in which piezoelectric bodies of the same thickness are laminated, but also 1/
A laminated piezoelectric element can be obtained that takes advantage of the fact that it also generates resonance at a frequency that is n times (1/2 times as high in the case of this example). In addition, by forming a relatively thin layer and a thick layer on the side opposite to the ultrasound emission surface of the head portion of the ultrasound probe in this way, ultrasound can be transmitted and two It becomes possible to receive and acquire reflected waves (echo signals) of different frequency bands with high sensitivity. Furthermore, both the high and low frequency components can be acquired with high resolution.

Although the laminated piezoelectric element constituting the ultrasonic probe according to the present invention can have a laminated structure of three or more layers, the operation in the case of a two-layer structure will be described below for the sake of simplicity. In other words, by changing the ratio R of the thicknesses of two piezoelectric elements with different thicknesses (=rear side piezoelectric thickness/radiation side piezoelectric thickness, 0<R<1), two types of resonance can be excited. It becomes possible to adjust the level. Therefore, by changing the thickness ratio R depending on the purpose of use, a wide range of uses can be accommodated.

For example, specifically, in the case of a comparatively deep examination object such as observing the heart from the body surface, by setting the thickness ratio R to a small value, the low frequency part of the frequency band, That is, since the resonance energy at the frequency of f0/2 increases, high sensitivity is achieved in the Doppler mode.

On the other hand, in contrast to the above example, when a relatively shallow area is to be examined, such as in the carotid artery or transesophageal echocardiography, by setting the thickness ratio R to a large value, high frequencies in the frequency band can be Since the resonant energy at f0 increases, an ultrasonic probe with a wide band on the high frequency side can be realized, and a high-resolution B-mode image can therefore be obtained even in B-mode.

[0014]

【Example】

(First example)

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 has a laminated structure in which a plurality of piezoelectric elements (in the case of this embodiment, two piezoelectric elements) are laminated with an internal electrode serving as a boundary between the two laminated elements sandwiched therebetween. A plurality of acoustic matching layers 2 to 4 are laminated on the upper ultrasonic radiation surface side of the laminated piezoelectric element 1. The matching layers 2 to 4 consisting of these three layers are arranged so that matching can be achieved on the high frequency side.
The thickness is set. The reason for this is that in order to obtain a B-mode signal on this frequency side, the band is widened.

The laminated member including the laminated piezoelectric element 1 integrally laminated in this manner has a thickness of 30 μm for cutting into strips.
Using a dicing machine equipped with a thick blade, the matching layers 2 to 4 are cut into strips as shown in the figure, and arranged at predetermined intervals on a backing material 6 serving as a head base. An integrated probe head is formed by overlapping and depositing an acoustic lens 5 with the convex surface facing upward on the top thereof.

The electrode surfaces of the laminated piezoelectric element 1 are formed as external electrodes 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. .

As wiring members for connecting these external electrodes to the head of the ultrasound probe, one external electrode is connected to a common electrode wire 7 for grounding, and the other external electrode is connected to a signal flexible printed circuit board 8 for signals. The wires are connected to each other by soldering or the like. This flexible printed board 8
Interval (pitch) of multiple signal line patterns formed on top
is set to 0.15 mm to match the predetermined spacing at which the strip-shaped laminated layers are arranged. FIG. 2 is an enlarged cross-section taken along the line A-A' shown in FIG.
FIG. 2 is an enlarged vertical cross-sectional view of a laminated piezoelectric element having a layered structure.

As shown in this figure, the laminated piezoelectric element 1 has two piezoelectric layers 11 and 12 stacked so that their polarization directions 13 and 14 are opposite to each other. Furthermore, external electrodes 15 and 16 are formed on both end surfaces of the laminated piezoelectric element in the lamination direction, that is, on the upper surface side of the piezoelectric layer 11 and the lower surface side of the piezoelectric layer 12, respectively. These piezoelectric layers 11 and 12 are made of piezoelectric ceramic. Furthermore, in reality, an internal electrode 17 is formed between the piezoelectric layer 11 and the piezoelectric layer 12 to polarize these layers.

Specifically, for example, the piezoelectric layers 11 and 12 are formed of PZT ceramic having a dielectric constant of 2000, the thickness of the piezoelectric layer 11 is 260 μm, and the thickness of the piezoelectric layer 12 is 260 μm.
The thickness of is set to 180 μm. That is, the thickness ratio R in this case is approximately 0. It becomes 7. In other words, the backing material 6 as a base is far away from the acoustic lens 5 on the ultrasonic emission surface side.
The thickness of the piezoelectric layer 12 adjacent to the other piezoelectric layer 11 is
It is formed thinner than the

Further, this laminated piezoelectric element is cut in the lamination direction together with the matching layers 2 to 4 by a dicing machine using a 30 μm thick blade. The interval is 0.
The length is set to 15 mm, and they are arranged in a strip shape as shown in the figure.

FIG. 3 is a graph showing the frequency spectrum of an echo waveform from a reflecting plate installed underwater, measured by the "pulse echo method". As can be seen from the frequency spectrum curve of this graph, the center frequency of the peak on the high frequency side is approximately 7.76 MHz, and the fractional band at that time is 43.0 MHz of the center frequency. It is 2%. This value can be said to be within a sufficient range to obtain a good B-mode image. Also,
The center frequency of the peak on the low frequency side is approximately 3. It can be seen that the frequency is 51 MHz.

The frequency spectrum graph 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 approximately 0. As shown in the graph, the frequency spectrum of this ultrasonic probe, which was obtained when other conditions were the same as in the first example, was high-frequency. The center frequency on the side is 7. 51MHz, and the fractional band at that time was 45. It is calculated as 4%.

As described above, it is clear that this modified example is an ultrasonic probe composed of laminated piezoelectric elements having a frequency characteristic wider than that of the first embodiment. Therefore, due to the characteristics of each of these embodiments, for example, the ultrasound probe of the first embodiment can be used for diagnosis of the heart from the transesophageal route, and the ultrasound probe of this modified example can be used for diagnosis of the heart from the body surface, etc. It can be used depending on the object to be diagnosed. (Second example)

In this embodiment, FIGS. 5(a) and 5(b)
) is used. That is, in this example, in the relationship between the polarization direction of the piezoelectric body (thin arrow in the figure) and the direction of the electric field generated by the drive pulse (thick arrow in the figure), the ratio of the electric field to the coercive electric field of the piezoelectric body is 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 from occurring.

The drive pulse has positive polarity, negative polarity, burst wave, etc., and the burst wave among these has the same absolute value for both positive and negative polarity. However, in general, the number of waves is large in most cases, and depolarization is difficult to occur because a large voltage is rarely applied due to the heat generation of the ultrasonic probe and the regulation of acoustic power.

Since piezoelectric layer 1 and piezoelectric layer 2 in FIG. 5(a) are configured to be electrically connected in series, when the same piezoelectric material is used for these two piezoelectric layers, the electric field Since the direction 8 and the electric field direction 9 are oriented in the same direction in each layer, there is no need to change the direction, and this seems to be a configuration that is not applicable to the gist of this embodiment. However, in the case of two piezoelectric layers made of piezoelectric materials with different dielectric constants, the magnitude of the generated electric field is different, so the improvement as in this embodiment is effective. Here, the permittivity and thickness of the piezoelectric layer 1 are ε1, respectively.
, t1, the capacitance can be expressed as follows.

[0028]

[Equation 1] Therefore, if the impedance is Z1, the partial pressure V1
can be expressed as the following equation.

[0029]

[Math 2] Therefore, the electric field E1 can be expressed as follows.

[0030]

##EQU00003## From the above, the ratio between the electric field E1 and the coercive electric field Ec1 is expressed by the following equation.

[0031]

[Math 4] Furthermore, the piezoelectric layer 2 is also expressed by the following equation.

[0032]

[Math 5]

From the above results, depolarization is likely to occur in piezoelectric layers in which the product of dielectric constant and coercive electric field exhibits a small value. Therefore, in such a case, the polarization direction and the electric field direction may be changed so that they point in the same direction. Next, since each of the two piezoelectric layers shown in FIG. 5(b) is electrically connected in parallel, the voltage applied to each layer is equal.

[0034] Therefore, regardless of the piezoelectric material used, the electric field is larger in a thinner piezoelectric body. Therefore, in such a case, the polarization direction of the piezoelectric layer whose thickness and coercive electric field have a small product may be changed so that the polarization direction and the electric field direction are oriented in the same direction. (Third example)

In the graph showing the relationship between the center frequency of the low frequency part and the piezoelectric thickness shown in FIG.
The respective thicknesses of piezoelectric layer 1 and piezoelectric layer 2 are t1,
If t2 is the thickness ratio r (= t2 /t1)
By changing , the relative values of the peaks of the spectrum of low frequency components and high frequency components can be changed.

It was decided to use the low frequency component for the Doppler signal so that the ultrasound attenuation in the living body would be reduced, and on the other hand,
It is decided to use a high frequency component with a short wavelength for the B mode signal so that a high resolution signal can be obtained. As a result, a graph showing the spectrum level and echo level when the thickness ratio r of the piezoelectric body is changed as shown in FIG. 6 is created. The spectrum level of the low frequency component plotted on the vertical axis represents the Doppler sensitivity. Further, the spectrum level of the high frequency component represents the B mode sensitivity. Furthermore, the circles indicate actual measured values regarding the level of the spectrum in the low frequency region, and the triangular marks indicate actual measured values regarding the echo level.

In this embodiment, when designing an ultrasound probe, the thickness ratio r of the piezoelectric body is adjusted as appropriate depending on whether Doppler sensitivity or B-mode sensitivity is given more importance depending on the diagnosis site. This shows that it is possible. For example, (1
) If the target is a region deep from the body surface, such as when diagnosing the heart transthoracically, penetration is required, so the B-mode sensitivity is set higher. In addition, (2) when Doppler sensitivity is required more than B-mode images, such as when diagnosing lower limbs, Doppler sensitivity is set higher.

In this embodiment, while changing the thickness ratio r, the peak value of the spectrum in the low frequency region and the HPF (High
Pass Filter) was connected to remove the low frequency part, and the peak value of the echo was measured. Based on this result, a quadratic function approximation using the thickness ratio r as a variable was obtained using the "least squares method" as shown in the following equation. (Peak of low frequency spectrum) = a +
9.59 r - 22.1 r2 [dB]
(Echo wave height value after HPF connection) = b +
23.8 r - 10.9 r2 [dB
] In the above formula, a and b are constants, which are determined by the measurement circuit, frequency, etc.

FIG. 6 shows the actual measured values and 2 when the thickness ratio r is changed.
It is a graph showing an approximate expression of the following function. In addition, in this figure, the constants of the above equation are a=1.73, b=-12.9, and the above equation is 0.5 ≦r in the actually measured range.
Holds true if ≦1.0.

[0040] Based on the relative relationship between the peak level of the spectrum in the low frequency region and the echo wave height value, the lower limit values of B-mode sensitivity and Doppler sensitivity are set to the maximum values within 0.5≦r≦1.0. On the other hand, based on past usage experience etc., each
dB and -6 dB, it was found that the echo sensitivity no longer satisfies the predetermined diagnostic use conditions when the thickness ratio r is r<0.6 and the Doppler sensitivity is r>0.8. Therefore, as a preferred embodiment, the allowable range of the thickness ratio r of the two piezoelectric layers is approximately 0.6 < r < 0.8 for practical ultrasonic probe design. I can say that there is. Therefore, it is preferable to implement a two-layer piezoelectric material having a thickness ratio that satisfies the above range. (Fourth Example) The center frequency of the ultrasonic probe varies within ± from the initial setting value due to the driving pulse width and the characteristics of the signal processing circuit such as the filter.
It is necessary to maintain it within 5%.

According to the results of performing pulse echo measurements and determining the frequency spectrum characteristics of the ultrasonic probe using the two-layer piezoelectric material of the present invention, it was found that the two-layer piezoelectric material as shown in FIG. 7(b) Even though the body uses the same piezoelectric material as the single-layer piezoelectric material as shown in FIG. A trend towards higher levels was found.

That is, in the graph of FIG. 8, the horizontal axis shows the center frequency f (unit: MHz) of the low frequency section as a variable, and the vertical axis shows the center frequency f (unit: MHz) of the low frequency section, and the vertical axis shows the center frequency f (unit: MHz) of the piezoelectric material made of the same piezoelectric material as the single-layer piezoelectric material having a thickness t0. The thickness t when using the two-layer piezoelectric material of the present invention is taken as follows. As can be seen from this graph obtained from the measurement results, the thickness t0 of the single-layer piezoelectric material is expressed by the following equation. t0 = 1.45 × 10
3 /f [μm] On the other hand, it has been found that the thickness t of the two-layer laminated piezoelectric material, which is the main component of the present invention, can be expressed by the following approximate formula determined based on actual measurements. t = 1.68 × 103 /f
[μm] Therefore, according to the above two equations, t=1.16
The relationship t0 was derived.

That is, in order to obtain a center frequency equivalent to that of a conventional piezoelectric material having a single layer structure, such as the piezoelectric material shown for comparison as shown in FIGS. 7(a) and 7(b), By setting the thickness t of the two-layer piezoelectric material according to the present invention to be approximately 16% thicker than the thickness t0 of the single-layer piezoelectric material, the designed center frequency can be obtained. (Fifth Example) This example describes 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.

FIGS. 9(a) and 9(b) are cross-sectional views showing the configurations of two types of vibrators of the present invention completed by this manufacturing method. Further, the polarization directions of the piezoelectric ceramic layers 1 and 2 are indicated by arrows. 2 like this
The method for manufacturing a vibrator with a layered structure is shown in FIGS. 10(a) to 10(
c) in the following order:

(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 the other green sheet of different thickness is laminated to form a piezoelectric ceramic. 1, 2 and the internal electrode 3 are fired at the same time. (2)... Thereafter, the external electrodes 4 and 5 are printed in a predetermined pattern, baked, and polarized to form a vibrator.

(2-1)... To obtain the vibrator shown in FIG. 9(a), electrodes are constructed as shown in FIG. 10(a). The external electrodes 4 and 5 on both sides are connected by a rotating electrode 6, and the internal electrode 3 is provided with a voltage application part by a rotating electrode 7.
Polarization is achieved by applying a DC electric field between the internal electrode and the external electrode. (2-2)...Then, it may be cut at the dotted line position in FIG. 10(a).

This method has the advantage that two layers of piezoelectric ceramics can be polarized simultaneously, but piezoelectric ceramics 1 and 2 of each layer
Because the thickness of each layer is different, the polarization electric field of each layer is different, resulting in different degrees of polarization. If the thickness ratio of the two layers is small, there will be no problem, but if the ratio is large, the polarization voltage will be limited by the thin layer, and the polarization electric field of the thick layer will not reach a sufficient value, resulting in an insufficient polarization state. (2-3)... In such a case, as shown in FIG. 10(b), the external electrodes on both sides may be made independent and each layer may be polarized with the optimum electric field and cut at the dotted line position.

(3)... To obtain the laminated vibrator structure shown in FIG. 9(b), electrodes are formed as shown in FIG. 10(c),
An electric field is applied between the external electrodes 4 and 5 on both sides to form an electrode. After that, the external electrodes on both sides may be connected in common. For this connection, it is difficult to form baked electrodes because heat higher than the Curie temperature of the piezoelectric material is not applied, but a conductive adhesive or the like may be used. (4)...Furthermore, when manufacturing the probe, an FPC is soldered to the electrode of the vibrator as a lead, but the electrodes on both sides may be connected at this point. (6th example)

This example is a laminated piezoelectric material having a vertical cross-sectional structure as shown in FIG. 11(a). That is, an optimal laminated piezoelectric body is constructed by changing the acoustic impedance of each of the laminated piezoelectric bodies. Specifically, this is an ultrasonic probe in which the acoustic impedance of the piezoelectric layer on the acoustic matching layer side is set to be smaller than that on the backing material side. The laminated piezoelectric material of this example can achieve specific bands and sensitivity levels in the high frequency region and low frequency region by changing the thickness ratio of each of the laminated piezoelectric materials and changing the acoustic impedance ratio of each. It is possible to adjust as appropriate.

In FIG. 11(b) showing an example of the cross section of a composite piezoelectric layer in the case of a two-layer structure, the vibrator 1 is composed of a piezoelectric ceramic layer 2 having a large acoustic impedance and a composite piezoelectric layer 3 having a small acoustic impedance. This composite piezoelectric layer is laminated on the acoustic matching layer 4 side with electrodes interposed therebetween. Further, this composite piezoelectric layer 3 has a horizontal cross section along line BB' in FIG. 11(a) as shown in FIG. 11(b). That is, for example, it is made of a plurality of columnar piezoelectric materials 10 arranged at equal intervals in each of non-adjacent squares in a checkerboard shape, and a resin material 20 such as an epoxy resin material 20 injected and hardened to fill the spaces between them. It is constructed in one piece.

FIGS. 12(a) and 12(b) show that the acoustic impedance of the composite piezoelectric layer is 17.7 Mray.
ls is constant, and the thickness ratio is 0.5 of the total resonator thickness.
The frequency spectrum of the underwater pulse echo of the composite piezoelectric body set to 9 and 0.41 is shown.

Furthermore, in FIGS. 13(a) and 13(b), the thickness ratio of the composite piezoelectric material is fixed at 0.5, and the acoustic impedance is 21.3 Mrayls and 1, respectively.
The frequency spectrum of the underwater pulse echo is shown when set to 1.4 Mrayls.

Comparing the respective graph curves reveals the following. That is, in FIG. 12(b), although the sensitivity level in the low frequency region is certainly high, the −6 dB fractional band in the high frequency region is about 30%. Figure 12(a
), the −6 dB specific band in the high frequency region is about 49%. In Fig. 13(a), −6d in the high frequency region
The B fractional band is about 43%, whereas in Fig. 13 (
In b), it is narrower to about 37%, but the sensitivity level in the low frequency region becomes higher and its fractional band becomes wider.

As described above, according to this embodiment, the fractional band in the high frequency region and the low frequency region and its sensitivity level can be adjusted not only by changing the thickness ratio of the laminated piezoelectric materials but also by changing their acoustic impedance. It is possible to change. Therefore, even in cases where it is difficult to control the thickness of the laminated layers due to the structure or manufacturing method, it is easy to adjust the characteristics of the ultrasonic probe having two or more frequency regions more appropriately.

[0055] In the above-described embodiments and their modifications, the case of a laminated piezoelectric element having a two-layer structure was specifically illustrated, but the present invention is not limited to these examples, and there is no need to deviate from the scope of the present invention. Further various modifications are also possible within the scope. 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 has the following effects. In other words, two piezoelectric layers are laminated, electrodes are formed on both end surfaces to electrically connect the two adjacent piezoelectric layers in series, and the piezoelectric layer on the side far from the ultrasonic emission surface is made thinner. By configuring an ultrasonic probe equipped with a laminated piezoelectric element, it is possible to transmit and receive a plurality of different frequencies, for example, two types of frequencies.Furthermore, by changing the piezoelectric material thickness ratio of each layer, it is possible to transmit and receive high frequencies depending on the purpose of use. It becomes possible to adjust the specific band of the region as appropriate and use it properly depending on the object to be diagnosed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing the overall configuration of an ultrasound probe head according to a first embodiment of the present invention. FIG. 2 is an enlarged vertical cross-sectional view showing the structure of the laminated piezoelectric element in the first embodiment. FIG. 3 is a graph showing an echo waveform obtained by the first embodiment. FIG. 4 is a graph showing an echo waveform obtained by an ultrasonic probe according to a modification of the first embodiment. FIG. 5 is a configuration diagram showing a laminated piezoelectric element of an ultrasound probe according to a second embodiment of the present invention. FIG. 6 is a graph showing the spectrum level and echo level when the thickness of the piezoelectric body of the ultrasound probe according to the third embodiment of the present invention is changed. FIG. 7 is a configuration diagram showing the thickness of a multilayer piezoelectric element of an ultrasound probe according to a fourth embodiment of the present invention and a conventional single-layer piezoelectric element. FIG. 8 is a graph showing the relationship between the thickness of the piezoelectric element and the generated center frequency of the ultrasonic probe according to the fourth embodiment. FIG. 9 is a configuration diagram showing a laminated piezoelectric element of an ultrasound probe as a fifth embodiment of the present invention. FIG. 10 is an explanatory diagram illustrating a manufacturing procedure regarding a method for manufacturing a laminated piezoelectric element of an ultrasonic probe according to the fifth embodiment. FIG. 11 is a vertical cross-sectional view and a cross-sectional view of an ultrasonic probe according to a sixth embodiment of the present invention. FIG. 12 is a graph showing an echo waveform obtained by the ultrasound probe according to the sixth embodiment. FIG. 13 is a graph showing an echo waveform obtained by the ultrasound probe according to the sixth embodiment. [Explanation of symbols] 1...Laminated piezoelectric element, 2, 3, 4...Acoustic matching layer, 5
...acoustic lens, 6...backing material, 7...common electrode wire for grounding, 8...signal line of flexible printed board for signal, 1
1, 12... Piezoelectric layer, 13, 14... Polarization direction, 15, 1
6...External electrode, 17...Internal electrode.

Claims (6)

[Claims] 1. A first piezoelectric layer and a second piezoelectric layer stacked in the thickness direction such that the polarization directions of adjacent layers are opposite to each other, and the polarization direction of the two piezoelectric layers is stacked in the thickness direction. a laminated piezoelectric element integrally formed with electrodes adhered to the end or side surfaces; one or more acoustic matching layers on top of the laminated piezoelectric element for achieving acoustic matching; and the acoustic matching layer. and an acoustic lens for emitting ultrasonic waves through the laminated piezoelectric element, and a head base serving as a backing material is disposed below the laminated piezoelectric element, so that the entire ultrasonic probe head has an integrated structure. Equipped with
The thickness of the second piezoelectric layer close to and adjacent to the head base is
An ultrasonic probe characterized in that the first piezoelectric layer is formed thinner than the first piezoelectric layer near the acoustic matching layer. 2. In the laminated piezoelectric element, when each of the two piezoelectric layers is electrically connected in series to prevent depolarization, each of the two piezoelectric layers The laminated structure is set so that the polarization direction and the electric field direction of the piezoelectric layer having a larger ratio between the coercive electric field of the piezoelectric body layer and the generated electric field are oriented in the same direction, and
When the two piezoelectric layers are electrically connected in parallel, the polarization direction and electric field direction of the piezoelectric layer whose product of the thickness of each of the two piezoelectric layers and the coercive electric field is smaller is 2. The ultrasonic probe according to claim 1, wherein the laminated structure is set so that the two are oriented in the same direction. 3. Generating a thickness ratio r (=t2/t1) between the thickness t1 of the first piezoelectric layer and the thickness t2 of the second piezoelectric layer constituting the laminated piezoelectric element. The relative value of the peak of the spectrum of the low frequency component and high frequency component is determined by the Doppler sensitivity or B required depending on the diagnostic area to be used.
It can be adjusted as appropriate depending on which of the mode sensitivities is emphasized, and the ratio of the thicknesses of the two piezoelectric layers r
Ultrasonic probe according to claim 1, characterized in that r<0.8. 4. A two-layer piezoelectric material having a two-layer structure consisting of two piezoelectric layers constituting the laminated piezoelectric element is made of the same piezoelectric material as a single-layer piezoelectric material having a single-layer structure consisting of one piezoelectric layer. In order to obtain the center frequency of the low frequency part of the ultrasonic probe formed using the two-layer piezoelectric material of the laminated piezoelectric element to be equivalent to the center frequency of the ultrasonic probe made of the single-layer piezoelectric material. The ultrasonic probe according to claim 1, characterized in that this is possible by setting the thickness of the two-layer piezoelectric material to be 16% thicker than the thickness of the single-layer piezoelectric material. 5. The acoustic impedance of the first piezoelectric layer on the acoustic matching layer side is set to be smaller than the acoustic impedance of the second piezoelectric layer on the backing material side, and the first piezoelectric layer has a shape of a checkerboard. A plurality of columnar piezoelectric materials whose longitudinal direction is the stacking direction are arranged at predetermined intervals in squares that are not adjacent to each other in the squares of , and the spaces between the plurality of piezoelectric materials are 2. The ultrasonic probe according to claim 1, further comprising a composite piezoelectric layer integrally formed of a solidified resin material. 6. Two piezoelectric layers stacked in the thickness direction such that the polarization directions of adjacent layers are opposite to each other, and an adhesive is formed on the end face of each of the piezoelectric layers in the thickness direction. In the method for manufacturing a laminated piezoelectric element having a two-layer structure consisting of an external electrode formed by a metal layer and an internal electrode formed by adhering to be sandwiched between the two piezoelectric layers, the steps are carried out in the following order. A method of manufacturing an ultrasonic probe having a laminated piezoelectric element, characterized by: (1)... Internal electrodes of a predetermined shape sandwiched between the upper and lower piezoelectric layers are printed on one side of a green sheet formed to a predetermined thickness using the "doctor blade method", and the other green sheet with a different thickness is printed. are laminated and the piezoelectric ceramic and the internal electrodes are fired simultaneously. (2) After printing the external electrodes in a predetermined pattern and baking them onto the end faces of each of the two piezoelectric layers, a polarization process is performed according to the following procedure. (2-1)... The external electrode is formed as a first wraparound electrode that connects the external electrodes on the two end faces, and the internal electrode is formed as a second wraparound electrode that connects a part of the external electrode and this internal electrode. The first and second round electrodes are formed as wrap-around electrodes, and a voltage application portion is provided in the first and second wrap-around electrodes to connect them to each other, and a DC electric field is applied therebetween to perform polarization processing. (2-2)... The ends of the two piezoelectric layers including the voltage application section are cut and removed in the stacking direction. (2-3)... In particular, the two constituting the laminated piezoelectric element
If the thickness ratio of the two piezoelectric layers is smaller than 0.7, the two external electrodes are polarized with the optimum electric field for each layer, and then the ends of the two piezoelectric layers including the voltage application section are polarized. Cut and remove the section in the stacking direction. (3)... In order to obtain a laminated vibrator, a DC electric field is applied between the two external electrodes formed on the end face to perform polarization treatment, and then the two external electrodes are bonded using a conductive adhesive. Connect in common. (4)...FPC is soldered as a lead to the electrodes of the laminated vibrator.