JPH09299370A - Ultrasonic probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic probe which can obtain high-resolution, good-quality images enabling the use of a relatively simple circuit and cope with the requirement for a decrease in diameter. SOLUTION: This probe has a cable for transmitting driving voltage and echo signals, a piezoelectric element 5, an acoustic matching layer facing the acoustic radiating surface of the piezoelectric element 5, and a back load layer opposed to the acoustic matching layer, and is designed to transmit and receive ultrasonic waves. In this case, the piezoelectric element 5 which has a difference in the strength of spontaneous polarization depending on position within one piezoelectric element 5 is used, electrodes 2, 3 fitted on both of the principal planes of the piezoelectric element 5 are electrically connected to the cable, and the distribution of the strengths of the spontaneous polarization of the piezoelectric element 5 follows a zero-order Bessel function and is made to correspond to the direction and magnitude of sound pressure radiated from that position.

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 ultrasonic endoscopes used for medical purposes.

[0002]

2. Description of the Related Art Conventionally, the general structure of an ultrasonic probe is
As shown in "Medical Ultrasonic Equipment Handbook", Japan Electronic Machinery Manufacturers Association, Corona, P186, etc., a piezoelectric ceramic plate represented by PZT in which a pair of electrodes are formed on both sides of a back load material. A piezoelectric element consisting of
Further, the acoustic matching layer and the acoustic lens are adhered to produce.

In this ultrasonic probe, a transmission pulse of about 100 to several hundreds of volts is applied from the pulser to the piezoelectric element to cause rapid deformation by the inverse piezoelectric effect of the piezoelectric element, and this vibration is acoustic matching layer. And the radiation pulse is efficiently radiated toward the DUT through the acoustic lens. The emitted ultrasonic pulse is reflected again from the acoustic lens and the acoustic lens at the interface between tissues in the body for medical use and after being reflected from a discontinuous portion such as a defect inside the DUT for nondestructive inspection. Mechanical vibration is applied to the piezoelectric element through the matching layer. This mechanical vibration is converted into an electrical signal by the piezoelectric effect of the piezoelectric element and is observed by the observation device.

As a method for improving the resolution at the time of imaging, in order to make the emitted ultrasonic beam thin, the electrode pattern of the acoustic lens or the piezoelectric element is devised, or the piezoelectric element itself is made concave. There are many ways. Also, sound field shaping has been attempted by an annular array in which the electrodes are divided into several parts and the voltages of the applied transmission pulses are made different.

As an ultrasonic probe, for example, there is an invention described in Japanese Patent Application Laid-Open No. 2-111198. In the present invention, as shown in FIGS. 36 and 37, for example, the whole surface electrode 152 is provided on one surface side of the piezoelectric ceramic 151 and the divided electrodes 153a, 153b, 153c are provided on the other surface side. This is a piezoelectric element 154 in which the divided electrode 153a at the center of the distribution of polarization intensity has a large spontaneous polarization, and the spontaneous polarization is weakened toward the divided electrode 153c at the outer periphery.
And is an ultrasonic probe using this piezoelectric element 154.

[0006]

However, there are merits and demerits in each of the conventional methods for improving the resolution of the ultrasonic image by the ultrasonic probe. Specifically, an ultrasonic probe using an acoustic lens or a concave piezoelectric element, which is a known technique at present, can focus an ultrasonic beam near a focus and obtain an image with high resolution, but it is out of focus. Accordingly, the beam width becomes wider and the image accuracy becomes worse. Therefore, there is a problem that the optimum observation distance that can be actually observed becomes narrow. Here, when the sound field of the ultrasonic beam emitted from the ultrasonic probe is measured and the half width is measured, as shown in FIG. 38, the narrow beam width region becomes very short. It can be seen that the optimum observation distance (depth of focus) that can be actually observed is narrow (the horizontal axis in FIG. 38 is the distance X [mm] between the surface emitting the ultrasonic beam and the measurement position, and the vertical axis is the measurement position. Beam width [mm] at. The beam width means a portion having a maximum sound pressure of 50% (-6 dB) or more in the plane on a plane orthogonal to the beam axis.

Further, when an annular array type ultrasonic probe is used, the phase of the voltage applied to each ring-shaped electrode is controlled by preparing several systems of pulsers or devising a circuit. It is known that the focal point of the ultrasonic beam can be changed (the focus depth can be lengthened). That is, it is possible to focus an ultrasonic wave by focusing on a position to be observed and to observe the portion clearly. It is also possible to transmit and receive ultrasonic waves several times while changing the focusing distance, synthesize received signals, and obtain a clear image over a wide range. However, in this method, it becomes necessary to connect a plurality of lead wires to the piezoelectric element. In order to prevent noise from entering between a plurality of lead wires, it is necessary to ensure a shield, and it is not suitable for ultrasonic probe used for medical purposes in terms of thinning.
Further, there is a problem in that the cost of the observation device is significantly increased because a complicated electric circuit for controlling the phase is required as described above. Furthermore, in the method of synthesizing received signals transmitted and received several times while changing the focal length, the frame rate (the number of images per unit time) decreases because the time required to acquire one image increases. To do. Therefore, if there is body movement, respiration, heartbeat, or the like of the subject, the image will be blurred and the diagnosis will be hindered.

Further, as another usage of the annular array type, in the case of the concave vibrator, all the parts are simultaneously driven at the time of transmission to transmit the ultrasonic wave, and at the time of reception, the part of the part to receive the ultrasonic wave is received. There is a method of increasing the area to increase the resolution. However, this method is also similar to the above case, the wiring is complicated and the manufacturing is difficult, the electric circuit including the adder circuit is complicated, the cost is increased, and the reliability is also increased. There was a problem of causing a decrease.

By distributing the ultrasonic waves emitted from the ultrasonic transducer so that the central portion is strong and the peripheral portions are weak, side lobes, that is, the emission of ultrasonic waves in an originally unintended direction can be reduced. In particular, it is known that when a graph-shaped sound pressure distribution of a normal distribution (Gaussian distribution) is given, the side lobe reduction effect is high. The invention of Japanese Patent Application Laid-Open No. 2-111198 aims at this effect, but there is a problem that it has no effect of focusing ultrasonic waves and the optimum observation distance is short. It is known that when the ultrasonic waves emitted from the ultrasonic transducer are distributed in the shape of the 0th Bessel function, the ultrasonic waves become a non-diffraction type ultrasonic beam, that is, a wave that propagates without being diffused. Has been. By using the non-diffracting ultrasonic beam thus obtained, it is possible to obtain an image with an ultrasonic beam having a uniform thickness from the vicinity of the ultrasonic transducer to the distance. That is, it is possible to obtain a line-focused image that is clearly focused from near to far.

In order to realize such an ultrasonic beam, a piezoelectric element having concentric multiple ring electrodes is used,
A method has been conventionally reported in which a drive circuit is connected to each concentric ring electrode via a cable and the drive voltage applied to each electrode ring is distributed in a Bessel function form. However, in such a method, it is necessary to connect a plurality of cables to the piezoelectric element. In order to prevent noise from entering between multiple cables, it is necessary to secure the shield, and it is not suitable for medical use, especially for ultrasonic probes used in body cavities, etc. in terms of thinning. is there. In addition, there is a problem that the cost of the observation device is significantly increased because a complicated electric circuit for controlling the voltage and the phase is required.

Further, the following documents show a method for obtaining a Vessel polarization type piezoelectric element similar to that of the present invention. Title: Bessel beam ultrasonic
transducer: Fabrication m
method and experimentalres
ults Author: D. K, Hsu F. J. Margetan
D. O. Thompson Source: Appl. Phys. Lett. 55 (20),
13 Nov. 1989. P2066-2068

The above method uses the following method. -Create a piezoelectric element that has two concentric grooves with different depths and a central hole. -Polarize by applying a polarization voltage having different polarities between the groove and the opposite surface. At this time, voltages having different polarities are applied to the adjacent grooves and holes. -Groove and remove the groove to obtain a flat piezoelectric element.

However, the piezoelectric element obtained by the method of this document has the following drawbacks. Since the polarization voltage is applied not only between the electrodes facing each other across the piezoelectric element but also between the adjacent electrodes, as shown in FIG. 39, the portion 1 polarized in parallel to the main surface of the piezoelectric element 154.
55 will occur. Therefore, unnecessary vibration is likely to occur when driving by applying a voltage, and an ultrasonic wave having a frequency other than the desired frequency is emitted in a direction other than the desired direction. As a result, artifacts are generated on the ultrasonic image, resulting in deterioration of the image quality of the ultrasonic image. -Since most of the piezoelectric elements are polished and removed after polarization, it takes a long time to manufacture, and a polishing step and a grooving step after polarization are required, resulting in poor yield.

Furthermore, when a circular piezoelectric element is used, the size of the entire piezoelectric element is determined by the diameter of the piezoelectric element. Further, in the ultrasonic probe for intracavity scanning, it is a top priority to reduce the diameter of the insertion portion in order to reduce the pain of the subject and enlarge the application site. Reducing the diameter of the insertion portion leads to reducing the diameter of the circular piezoelectric element used. However, if the diameter of the piezoelectric element is reduced and the effective area is reduced, the electrical characteristic impedance is mismatched and the transmission / reception sensitivity is reduced, and the quality of the obtained ultrasonic image deteriorates.

The present invention has been made in view of the above circumstances, and uses a piezoelectric element in which the polarization strength is partially different based on the Bessel function, and the number of parts, especially the number of cables is reduced, It is configured to obtain a Bessel-type non-diffractive sound field with an acoustic wave oscillator, achieves line focusing of an ultrasonic beam, and can obtain a high-resolution and high-quality image using a relatively simple electric circuit. It is an object of the present invention to provide an ultrasonic probe that can meet the demand for smaller diameter.

[0016]

An ultrasonic probe according to the present invention includes a cable for transmitting a driving voltage and an echo signal, a piezoelectric element, an acoustic matching layer on the acoustic radiation surface of the piezoelectric element, and an acoustic matching layer on the opposite side. In an ultrasonic probe having a back load layer and transmitting and receiving ultrasonic waves, a piezoelectric element having a difference in spontaneous polarization intensity depending on a position in one piezoelectric element is used, and both main surfaces of the piezoelectric element are used. The electrodes provided in the above are electrically connected to the cable, and the distribution of the intensity of the spontaneous polarization of the piezoelectric element is determined so that the sound pressure distribution from the ultrasonic probe is distributed as follows. It is characterized by. On the surface of the piezoelectric element,
When a straight line orthogonal to the geometrical symmetry axis is selected, and this straight line is taken as the x-axis, and the origin of this x-axis is the intersection of the x-axis and the geometrically symmetric axis of the piezoelectric element, a a draw a zeroth-order Bessel function _{y = J 0 (x / a} ) as an arbitrary constant, the value of J ₀ (x / a) at each position on the x-axis, when applying a certain voltage pulse In addition, the sound pressure radiated from the position so that the spontaneous polarization is strong at the position where the absolute value of J ₀ (x / a) is large, and weak at the position where the absolute value of J ₀ (x / a) is small. Corresponds to the direction and size of. J ₀
The direction of spontaneous polarization is reversed between the positive position and the negative position of (x / a). The intensity of the spontaneous polarization of the piezoelectric element is distributed axially or line-symmetrically along the axis of symmetry. The direction of spontaneous polarization of the piezoelectric element is set to be substantially perpendicular to both main surfaces on the entire surface of the piezoelectric element.

The present invention will be described in more detail below. According to the present invention, a piezoelectric element having a difference in the strength of spontaneous polarization depending on the position in one piezoelectric element is used to electrically connect the electrodes provided on both main surfaces of the piezoelectric element to the cable. , The distribution of the spontaneous polarization intensity of the piezoelectric element is determined so that the sound pressure distribution from the ultrasonic probe is distributed as described above. Can provide a high-resolution ultrasonic probe that can be used in various electrical circuits. In addition, the ultrasonic beam can be made uniform and the depth of focus of the ultrasonic image can be deepened. As a result, a clear image can be obtained from the vicinity of the ultrasonic probe to a distant position, and accurate diagnosis can be performed quickly. It becomes possible. Further, the present invention uses a piezoelectric element in which the polarization intensity is partially weakened based on the Bessel function to shape the sound field and achieve line focusing (to increase the depth of focus), thereby achieving high-resolution ultrasonic waves. Images can be obtained.

Here, the determination based on the Bessel function means the following. Select a straight line that is orthogonal to the geometrical symmetry axis of the piezoelectric element. This straight line will be called the X axis. The origin of the x-axis is the intersection of the x-axis and the geometrical object axis of the piezoelectric element. A 0th-order Bessel function y = J ₀ (x / a) is drawn on the x-axis defined in this way. Here, a is an arbitrary constant. The value of J ₀ (x / a) at each position on the x-axis is made to correspond to the direction and magnitude of the sound pressure emitted from that position when a certain voltage pulse is applied. That is,
At a position where the absolute value of J ₀ (x / a) is large, the spontaneous polarization of the piezoelectric element is strong, and at a position where the absolute value of J ₀ (x / a) is small, the spontaneous polarization is weakened. Further, the direction of spontaneous polarization is reversed between the positive position and the negative position of J ₀ (x / a). The intensity of the spontaneous polarization of the piezoelectric element is distributed axially or line-symmetrically along the axis of symmetry. The direction and magnitude of the spontaneous polarization are indicated by the arrow direction and the magnitude of the piezoelectric ceramic 1 forming the piezoelectric element 5 shown in FIG.

Further, according to the present invention, at least one surface electrode of the piezoelectric element is divided during the polarization, and the divided electrodes on the same surface are connected after polarization. Furthermore, the present invention uses a piezoelectric element in which the value of the spontaneous polarization intensity distribution based on the Bessel function is zero and at least one surface electrode in the vicinity thereof is not present.

The relationship between the direction and magnitude of the spontaneous polarization of the piezoelectric element 5 constituting the ultrasonic probe of the present invention and the emitted sound will be described below. The amount of deformation of the piezoelectric element 5 when a constant DC voltage is applied is determined according to the strength of spontaneous polarization. The deformation direction of the piezoelectric element 5 is determined by the direction of spontaneous polarization. Therefore, the piezoelectric element 5 having a distribution in the intensity of spontaneous polarization
When the same drive voltage is applied to the entire surface of, the wavefront of the ultrasonic wave having a shape corresponding to the intensity distribution of spontaneous polarization can be obtained. The polarization intensity of the piezoelectric element 5 for the ultrasonic probe is partially changed by changing the polarization voltage to weight the polarization in a Bessel function. An ultrasonic probe using this piezoelectric vibrator 5 can transmit a pseudo Bessel beam to an observation object through the acoustic matching layer. The Bessel beam is a non-diffracted wave that is not diffused by propagation, and the radiation pulse emitted from the ultrasonic probe also propagates with almost no spread.

At least one electrode is divided along the spontaneous polarization intensity distribution based on the Bessel function assumed as described above. After that, a polarization voltage is applied to each electrode to polarize so as to have a spontaneous polarization intensity corresponding to the Bessel function. According to the present invention as described above, in addition to the above-described action, at least one surface electrode of the piezoelectric element 5 is divided when the piezoelectric element 5 is polarized, and different voltages are applied to the divided electrodes, respectively. The ultrasonic probe can be configured by using the piezoelectric element 5 that can be driven by one coaxial cable by connecting or forming the electrodes after changing the polarization intensity for each electrode.

Further, in the piezoelectric element 5 of the present invention, since there is no surface electrode on at least one of the portion where the value of the Bessel function of the piezoelectric element 5 is zero and at least one of the surface electrodes, there is basically no vibration. The electrode pattern is designed so that

Further, by using a non-circular piezoelectric element 5 as the piezoelectric element 5, the diameter of the insertion portion is reduced, and necessary sensitivity and electrical impedance matching are ensured, and the image quality of a practical ultrasonic image is obtained. Can be secured.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) Embodiment 1 of the present invention will be described below. FIG. 1 is a plan view and a cross-sectional view of a piezoelectric ceramics 1 which is a piezoelectric element, FIG. 2 is a cross-sectional view showing a positional relationship between Bessel functions and divided electrodes of the piezoelectric ceramics 1, and FIG. 3 is a Bessel function and divided electrodes of the piezoelectric ceramics 1. Position and polarization direction and strength, FIG. 4 is a cross-sectional view of the transducer part of the ultrasonic probe, and FIG. 5 is a position and polarization direction and strength of the piezoelectric ceramic 1 and its divided electrodes. ,
FIG. 6 is a graph of the sound pressure distribution in the vicinity of the acoustic radiation surface of the ultrasonic probe, and FIG. 7 is a graph of the beam width similar to FIG.
Further, FIG. 8 is a diagram in which the divided electrodes 3 of the piezoelectric ceramic 1 are connected by a conductive resin 6, and FIG. 9 is a diagram showing an ultrasonic endoscope using the ultrasonic probe of the first embodiment.

First, as shown in FIG. 1, the piezoelectric ceramics 1 as a piezoelectric element is made of a PZT-based material and has a diameter of 10 m.
m, a wrapping element body having a thickness of 160 μm is prepared, and one surface of the element body is printed with a full-surface electrode 2 coated with silver paste, and the other surface is printed with a concentric multiple ring-shaped divided electrode 3, Bake. This multi-ring split electrode 3
2 is patterned on the basis of the 0th-order Bessel function, as shown in FIG. 2, and has a configuration in which there is no split electrode 3 in the vicinity of y = 0 in the xy coordinate system. . A piezoelectric element 5 having a split electrode 3 whose one side is split into multiple rings
Was polarized under the following conditions. First, as shown in FIG. 3, the average value of the values corresponding to the electrode portion of the Bessel function is calculated, and the polarization ratio is set so as to radiate the sound pressure as shown in the same graph as the Bessel function of FIG. To decide.

Then, the divided electrodes 3 change the polarization voltage so that the piezoelectric constant d ₃₃ becomes equal to the calculated value. The polarization was carried out in a silicon bath at 80 ° C., and the polarization was performed based on the piezoelectric constant d ₃₃ and the polarization voltage previously obtained for each material. Incidentally, the polarization state was confirmed from the coupling coefficient K _{33 which} can be easily measured, based on the relationship between the coupling coefficient K ₃₃ and the piezoelectric constant d ₃₃ which was confirmed by experiments in advance.
In addition, in a region where the Bessel function has a negative value, the polarization direction is inverted to perform polarization.

The electrode 3 on the side of the piezoelectric element 5 thus obtained is connected with the conductive resin 6 shown in FIG.
The divided electrode 3 is fixed to the housing 12 made of SUS via the insulating cylinder 13 shown in FIG. The entire surface electrode 2 on the front surface side is connected to the housing 12 using a conductive resin 6. After that, an epoxy resin having a thickness of 60 μm is formed as the acoustic matching layer 7 on the surface of the entire surface electrode 2 on the front surface side. Then, the core wire 9 and the peripheral wire 10 of the coaxial cable 11 are connected to one portion of the divided electrode 3 divided into a ring shape and the housing 12 by solder 14 or the like.

Then, the back load material 8 in which the epoxy resin and tungsten are mixed is cast on the ring-shaped divided electrode 3 side and cured to form a transducer portion 16 of the ultrasonic probe as shown in FIG. Create. An ultrasonic endoscope using this transducer unit 16 is shown in FIG. In this ultrasonic endoscope, a flexible insertion portion 32 is coupled to an operation portion 31 held by an operator, and the operation portion 31 is connected to an ultrasonic diagnostic apparatus or a light source (not shown) with a cord 35. Has been done. FIG. 1 shows a state in which the distal end portion of the insertion portion 32 is enlarged.
0 is shown. An acoustic window 33 is provided at the tip of the insertion portion 32. The acoustic window 33 is made of thin hard polyethylene of about 0.2 mm. The acoustic window 33 is watertightly sealed, and the transducer portion 16 is rotatably arranged inside. The inside of the acoustic window 33 is filled with the acoustic transmission medium 34. Water is used as the acoustic transmission medium 34.

The operator inserts the insertion portion 32 into the body cavity of the subject as in the existing ultrasonic endoscope, and performs optical observation and ultrasonic diagnosis. When performing ultrasonic diagnosis, the operation unit 31
Alternatively, a switch provided in the ultrasonic diagnostic apparatus (not shown) is operated to rotate the transducer section 16 and a transmission pulse is applied by a pulsar (not shown) in the observation apparatus. The transmission pulse is applied to the piezoelectric element 1 via the coaxial cable 11.

The cross section of the piezoelectric ceramics 1 produced by the above-mentioned method has the polarization direction and strength as shown in the lower column of FIG. Specifically, the divided electrode 3
The strength of the spontaneous polarization 4 near the center of the electrode is large, and the strength of the spontaneous polarization 4 between the divided electrodes 3 becomes smaller toward the outer periphery. When a uniform voltage is applied to the entire surface of the piezoelectric ceramics 1 which is such a piezoelectric element, the amount of deformation increases in a portion having a high polarization intensity, and the direction of deformation is determined by the polarization direction and the polarity of the applied voltage. To be done.

As in the first embodiment, the arrangement of the divided electrodes 3 of the piezoelectric ceramic 1 forming the piezoelectric element 5 is determined based on the Bessel function, and the piezoelectric ceramics 1 having different polarization strengths are used. When the transducer portion 16 of the ultrasonic probe as shown in FIG. 4 is manufactured and a transmission pulse is applied to the piezoelectric element 5 from a pulsar (not shown), the emitted ultrasonic beam approximates a Bessel function.

When a transmission pulse is applied to the piezoelectric ceramics 1 forming the piezoelectric element 5 according to the principle described above,
An ultrasonic pulse having a Bessel function-like sound pressure distribution is emitted. As described above, the ultrasonic wave having the Bessel function sound pressure distribution becomes a non-diffraction type ultrasonic beam, that is, a wave that propagates without being diffused. The radiated ultrasonic beam passes through the acoustic transmission medium 34 and the acoustic window 33 and propagates into the body of the subject with a substantially uniform thickness. At this time, as the acoustic transmission medium 34, water having a sound velocity almost equal to that of the living body is used, and the acoustic window 33 is made of thin hard polyethylene to enhance the permeability of the ultrasonic beam. The attenuation of the ultrasonic beam and the disturbance of the sound field when passing through these are at a negligible level.

Further, since the directivity characteristic at the time of reception is similar to the directivity characteristic at the time of transmission, the reflection echo from a region having a substantially uniform thickness can be efficiently received similarly to the transmission sound field. By using the ultrasonic beam thus obtained, it is possible to transmit and receive ultrasonic waves having a substantially uniform thickness from the vicinity of the ultrasonic transducer to the distance and obtain an ultrasonic image. That is, it is possible to obtain a line-focused image that is clearly focused from near to far.

When the transmission pulse by the pulsar is applied to the ultrasonic transducer section 16 using the piezoelectric ceramics 1 shown in FIG. 5, the sound pressure distribution of the ultrasonic pulse radiated in the vicinity of the acoustic matching layer 7 is Bessel. It is an approximation of a function.

Near the acoustic matching layer 7 (distance: about 1 mm)
FIG. 6 shows the measurement results of the sound pressure distribution of the ultrasonic waves measured by a hydrophone. In FIG. 6, the theoretical value (J) obtained by averaging the absolute values J ₀ (x) of the Bessel function and the calculated values J ₀ (x) when the sound pressure distribution of the Bessel function system is measured with a hydrophone is used. ₀ (x) average and sound pressure measurement results (Y, Z) are represented by two orthogonal axes, and the actual radiated sound pressure is the theoretical value (J ₀ (x) average).
It can be seen that it is very close to age). here,
x is the distance from the axis of symmetry of the transducer section 16.

Here, J ₀ and J ₀ (x) average
Will be described. The sound receiving part of the hydrophone is
It has a diameter of about 0.6 mm. Therefore, what the hydrophone actually measures is not the sound pressure at a certain point, but the average value of the sound pressure of the sound receiving section. Therefore, when measuring a complicated sound field distribution with a hydrophone, it is measured as a gentler distribution than the actual distribution. The theoretical Bessel distribution sound field is averaged for every 0.6 mm in diameter and the distribution is calculated by calculating J ₀ (x) averag in FIG.
e.

The Bessel beam is known as a non-diffraction beam, and when the sound field of the transducer section 16 according to the first embodiment is measured and the beam width is measured, FIG.
(The horizontal axis indicates the distance Xmm between the surface where the ultrasonic beam is emitted and the measurement position, and the vertical axis indicates the beam width mm at the measurement position.) It becomes possible to manufacture an ultrasonic probe having a long optimum observation distance (depth of focus). Therefore, it is possible to manufacture an ultrasonic probe having a single coaxial cable and a single pulser, which has a simple structure and is inexpensive, and which has a high resolution and which has a simple structure of the electric circuit and the transducer section 16. Further, as the ultrasonic observation apparatus, a conventionally known one can be diverted, so that the existing equipment can be effectively used.

FIG. 11 shows measured values of the sound pressure radiated from the transducer section 16 of the ultrasonic probe of the first embodiment. An ultrasonic sound field formed by installing a transducer section 16 at the left end of FIG. 11 and applying and radiating a transmission pulse was actually measured by a hydrophone having an effective diameter of 0.6 mm. The sound pressure data is expressed as contour lines by making the sound pressure on the sound axis dimensionless for each line perpendicular to the sound axis. It can be seen that the high sound pressure part in the center continues with a substantially constant width.

FIG. 12 shows a conceptual diagram of the effect of the first embodiment. FIG. 12 is a cross-sectional view in the case where the transducer section 16 of the ultrasonic probe is included and a plane perpendicular to the axis of the insertion section 32 of the ultrasonic endoscope is taken. FIG. 12 shows a schematic pattern of a sound field emitted from the acoustic window 33 of the ultrasonic endoscope to which the first embodiment is applied and the conventional ultrasonic endoscope. As a conventional case, both the case where an acoustic lens is attached to the acoustic radiation surface side of the piezoelectric ceramic to converge the ultrasonic wave and the case where the acoustic lens is not attached are shown. The ultrasonic beam at the position where the sound field is most narrowed can be made thinner when the conventional acoustic lens is used. However, when the first embodiment is applied, a narrow sound field can be obtained over a wide range.

In the first embodiment, the acoustic matching layer 7 has a single-layer structure of epoxy resin. For example, the acoustic matching layer 7 has a two-layer structure of an epoxy resin mixed with alumina as a filler and an epoxy resin. The same effect can be naturally obtained by using an epoxy resin containing a machinable ceramics filler and a three-layer acoustic matching layer such as polyethylene.

In the first embodiment, the divided electrodes of the multiple rings are connected by using the conductive resin. However, this connecting method may be performed within a temperature range in which the polarization of the piezoelectric element 5 is not depolarized, and conduction is achieved. As long as it is obtained, the same operation can be performed by connecting the conductive thin wire 21 with the solder 22 as shown in FIG. 13 or by using another method such as thermocompression bonding.

Instead of connecting wires on the piezoelectric ceramics 1, a conductive material may be used for the back load material 8 to electrically connect the divided electrodes 3 via the back load material 8. In this case, the back load material 8 is made of epoxy resin mixed with fine metal wires or particles at a high concentration. Then, the back load material 8 is arranged on the surface of the divided electrode 3 side.

Furthermore, as another modification, as shown in FIG. 14, a metal film 23 may be formed on the entire surface of the piezoelectric ceramic 1 on the side of the divided electrode 3 by a method such as sputtering.
When this method is used, more reliable electrical connection can be obtained and reliability is improved than in the case where the divided electrodes 3 are linearly connected.
Further, as shown in FIG. 15, one peak or valley of the Bessel function may be divided into two or more to change the spontaneous polarization intensity of each divided electrode 3. With this configuration, the Bessel function-like sound pressure distribution can be obtained more accurately, and the range in which the line focus can be obtained is widened.

In the first embodiment, the Bessel function of the 0th order is used. Two peaks on the positive side excluding the center are two on one side and the valleys on the negative side are two.
I showed a single object, but one mountain on the + side excluding the center is on one side,-
If the number of valleys on the side is 1 or more, a non-diffracted beam can be realized, and the same effect as that of the first embodiment can be obtained. FIG. 5 described above
FIG. 3 is a diagram showing the position of the divided electrode 3 of the piezoelectric element 5 having one peak on the + side excluding the center and one valley on the − side, and the polarization direction and the intensity 4. However, the larger the number of peaks and valleys, the more accurately the Bessel direction sound pressure distribution is approximated, and the longer the distance the sound field propagates as a non-diffracted beam without being diffused.

In the first embodiment, the ring-shaped electrode is polarized after being applied. However, as proposed by the applicant of the present application, the electrode is not provided on at least one side of the piezoelectric ceramics 1, and the conductive rubber or the conductor is not provided. The same effect can be obtained even if electrodes are applied to the entire surface by a method of performing polarization in a state in which an electrode made of an insulating material is in contact with the piezoelectric ceramics 1 and then forming a film in a temperature range that does not depolarize, such as sputtering or vapor deposition. You can

16 and 17 show an example in which the transducer section 16 of the first embodiment is applied to the transrectal probe 40. Since it is for rectal use, there is no optical observation system, and the insertion part 41 is rigid. The tip 42 has a diameter of about 25 mm and an acoustic window 43 is formed. The transrectal probe 40 shown in FIGS. 16 and 17 can be relatively thick, so that the transducer 16 and the piezoelectric ceramic 1 can be large. Therefore, the number of peaks and valleys of the Bessel function can be increased more than in FIG. 2, and an ultrasonic beam having a more accurate Bessel type sound pressure distribution can be emitted. As a result, the ultrasonic beam does not spread and the region where a clear ultrasonic image can be obtained is expanded. In addition to the rectal wall,
It is useful for observing and diagnosing peripheral lymph nodes and surrounding organs such as the prostate. Further, a therapeutic oscillator (not shown) capable of emitting strong continuous wave ultrasonic waves may be incorporated in the probe to provide a therapeutic probe for performing ultrasonic treatment and ultrasonic diagnosis.

18 to 20 show an example in which the transducer section 16 of the first embodiment is applied to the trans-forceps channel small-diameter probe 50. This is a thin and flexible ultrasonic probe having a diameter of about 2 mm and having no optical system.
As shown in FIG. 18, ultrasonic diagnosis is performed by guiding the target site to the target site via a forceps channel inlet 51 of a normal endoscope. In FIG. 18, the outermost of the circular polarization distribution of the outermost circumference, in which the concentric polarization distribution is given on the rectangular piezoelectric element as in the first embodiment, has a polarization intensity of 0.

When the transducer section 16 is used,
Since the ultrasonic beam is less diffused, even a small-sized and low-power trans-forceps channel small-diameter probe 50 can reach ultrasonic waves to a distance and be observed and diagnosed.

(Second Embodiment) FIG. 21 shows a second embodiment of the present invention. In the second embodiment, an example applied to the rectangular piezoelectric element 5 is shown. The lengths of the sides of the rectangle are s and t. The origin of the x and y coordinates is made to coincide with the center of the rectangle, that is, the intersection of the diagonal lines. When the point (X, Y) is included in a triangle formed of the sides of the origin and length _{s, J 0 (X * s} * a), J 0 when included in a triangle formed of the sides of the origin and the thickness t (Y *
The intensity of the spontaneous polarization is determined so as to radiate a sound pressure proportional to t * a), that is, having a contour having the same geometric center and a similar rectangular shape as shown in the lower part of FIG. Using the piezoelectric element having the spontaneous polarization distribution determined in this way, the transducer section 16 is created in the same manner as in the first embodiment and used in an ultrasonic endoscope or the like. The upper part of FIG. 21 shows the target Bessel function distribution of the radiation sound pressure distribution. Here, multiplication is shown.

As shown in FIG. 22, according to this transducer section 16, in each cross section of the ultrasonic beam,
As in the case shown in FIG. 12, a non-diffracted sound field (shown by the solid line) in which the sound pressure is distributed in a Bessel function and does not diffuse can be obtained.

According to the second embodiment, it is possible to realize a thinner insertion portion 32 such as an ultrasonic endoscope while ensuring the same ultrasonic radiation area as a circular ultrasonic transducer. This is effective in improving the insertability and reducing the pain of the subject. In particular, it is effective when applied to an ultrasonic probe having a small diameter as shown in FIG.

(Third Embodiment) FIG. 23 shows a transducer portion 16 having an elliptical polarization intensity distribution according to the third embodiment.
Is shown. The major axis and minor axis of the ellipse are defined as s and t. The origin of the x and y coordinates is made to coincide with the center of the ellipse, that is, the midpoint between the two focal points. A sound pressure distribution having a shape in which the major axis and the minor axis of the ellipse are made to coincide with the x axis and the y axis and the Bessel distribution on the circle shown in FIG. Determine the spontaneous polarization distribution to radiate.

According to the third embodiment, as shown in FIG. 23, the sound pressure is distributed in a Bessel function shape in each cross section of the ultrasonic beam, so that the structure shown in the third embodiment is obtained. Even when the transducer section 16 is used, a non-diffracted sound field that is not diffused by propagation is obtained. That is, it is possible to realize a thinner insertion portion 32 such as an ultrasonic endoscope while securing the same ultrasonic radiation area as the circular transducer portion 16. This is effective in improving the insertability and reducing the pain of the subject. Further, unlike the second embodiment, since there is no corner in the distribution of spontaneous polarization and the distribution of emitted sound pressure accompanying it, there is no disturbance of the sound field due to edges. Therefore, the Bessel-type non-diffracted sound field is maintained over a longer range, ultrasonic waves propagate without being diffused, and a clear ultrasonic image can be obtained. Although the piezoelectric element 5 is rectangular in FIG. 23, the piezoelectric element 5 itself may be elliptical or oval.

(Embodiment 4) FIGS. 24 to 26 show a linear array type ultrasonic probe with an ultrasonic probe 60 for a rapa.
An example applied to the (Ultrasonic Rapallo probe) is shown. In the ultrasonic probe 60 for lapa, an ultrasonic probe is installed at the tip of the rigid insertion portion 61. Insertion part 6
At the rear end of 1, there is a grip portion 62 for the operator to grip, and the grip portion 62 is connected to a connector 64 via a cord 63. The connector 64 can be connected to an ultrasonic observation device (not shown).

Since the basic structure of the linear array type ultrasonic probe is the same as the known one, only the outline will be described. In the linear array ultrasonic probe, small elements made of small rectangular piezoelectric ceramics 1 are arranged side by side in a row, and a cable (not shown) for applying a driving voltage and transmitting / receiving a signal is connected to each small element. It has become. Further, the acoustic matching layer 7 and the back load material 8 are provided on the front surface and the back surface of the piezoelectric ceramic 1, respectively. As shown in FIG. 24, each small element of the piezoelectric element 5 is polarized so as to emit a Bessel function type sound field. Specifically, when the x-axis is assumed with the midpoint of the long side as the origin on the axis parallel to the long side of each small element, the Bessel function of J ₀ (x / a) (a is a constant) is calculated. Then, the Bessel function is given a spontaneous polarization distribution such that the distributed sound pressure is obtained by parallel translation along the short side. The small elements of the piezoelectric element 5 are linearly arranged along the minor axis direction of these small elements.

The direction in which the small elements are arranged is the major axis direction of the ultrasonic probe. In the long axis direction of the ultrasonic probe, the focal point is controlled by a known electronic focusing technique so that a clear image can be obtained at a required position.
On the other hand, regarding the short axis direction of the ultrasonic probe, the piezoelectric element 5
24, a non-diffracted sound field is formed because ultrasonic waves having a Bessel function-type sound pressure distribution as shown in FIG.

In the conventionally known electronic scanning type linear array ultrasonic probe, the focal position of the ultrasonic beam is controlled by electronic focusing in the long axis direction of the ultrasonic probe, that is, in the scanning plane direction. I was able to clearly depict various parts. However, in the short axis direction of the ultrasonic probe, that is, in the thickness direction of the scanning surface, the ultrasonic beam is controlled only by the acoustic lens installed on the piezoelectric element 5. Therefore, near the focal point of the acoustic lens, as shown in FIG. 28, the ultrasonic beam becomes thin and a clear image is obtained, but at other positions, the ultrasonic beam spreads and the image is blurred.

In the configuration of the fourth embodiment, as shown in FIG. 28, since an ultrasonic beam having a substantially uniform thickness is obtained in the thickness direction of the scanning surface, a clear image is obtained over the entire ultrasonic image. You can get it. In particular, the conventional acoustic lens system is effective for rendering a distant region in which an ultrasonic beam is diffused.

The shape of the piezoelectric element 5 of the fourth embodiment may be square. The fourth embodiment can be applied not only to the electronic linear scanning ultrasonic probe, but also to the electronic convex scanning ultrasonic probe 70 as shown in FIG. The endoscope shown in FIG. 29 using the electronic convex scanning type ultrasonic probe 70 of FIG. 27 is basically a piezoelectric ceramic 1 which constitutes a piezoelectric element 5 having the same configuration as that of the fourth embodiment shown in FIG. The array of is bent into a convex shape. In this case, the application timing of the drive voltage is selected according to the surface shape of the ultrasonic probe 70 so that the wavefront of the emitted ultrasonic wave is a plane perpendicular to the sound axis.

According to the fourth embodiment, by applying the above-described technique to the convex scanning ultrasonic probe having a wide angle of view, it is possible to clearly depict a wider application site.

The fourth embodiment is applicable not only to the electronic linear scanning type ultrasonic probe but also to the electronic radial scanning type ultrasonic probe 71 as shown in FIG. still,
The electronic convex scanning ultrasonic endoscope shown in FIG.
Basically, the array of piezoelectric elements 5 having the same configuration as that of the fourth embodiment is formed in a convex shape as shown in FIG. In this case, the application timing of the drive voltage is selected according to the surface shape of the ultrasonic probe 71 so that the wavefront of the emitted ultrasonic wave is a plane perpendicular to the sound axis.

According to the fourth embodiment, by applying the above-described technique to the ultrasonic probe 71 of the electronic radial scanning type, which is advantageous when performing scanning from the inside of the lumen, a wider application site can be clearly defined. Can be visualized. In the radial scanning, the sound ray interval becomes wider and the ultrasonic wave is attenuated as it goes farther. However, when the transducer unit 16 having the configuration of the fourth embodiment is used, since the ultrasonic beam is less diffused, it is small and low in size. Even if you use a small-diameter probe with output, ultrasonic waves reach far,
Observation and diagnosis are possible. Further, as the ultrasonic observation device incorporating the electronic radial scanning ultrasonic probe, a conventionally known one can be used.

(Fifth Embodiment) FIGS. 33 to 35 show a fifth embodiment of the present invention. The structure of the ultrasonic probe part is
It is similar to the fourth embodiment. The fifth embodiment is different from the fourth embodiment in the method of driving the piezoelectric element 5. In the above-described fourth embodiment, the focus position is controlled by using a known electronic focusing method by shifting the drive timing of each small element of the piezoelectric element 5. In the fifth embodiment, the driving timing of each small element is the same, and the polarity and magnitude of the transmission pulse are determined based on the 0th-order Bessel function. The method of determining the polarity and magnitude of the transmission pulse is as follows.

A small element array forming the piezoelectric element 5 used to generate one sound ray is defined as one block. The y axis is defined in the arrangement direction of the small elements, and the geometric center of one block is the origin of the y axis. 0th-order Bessel function J ₀ along the y-axis
Assume (y / b). Here, b is a constant. FIG.
Similarly to the case shown in (1), the value of the 0th-order Bessel function is averaged for each length of each small element. Let that value be the target sound pressure to be emitted from each element.

When the piezoelectric ceramics 1 of the piezoelectric element 5 is driven at a high voltage, a high sound pressure is emitted, and at a low voltage, a low sound pressure is emitted, and the polarity of the transmission pulse is reversed. By utilizing the fact that the polarity of the emitted sound pressure is also inverted, the drive voltage and its polarity are controlled so that the target sound pressure obtained earlier is emitted.

In the above-described fourth embodiment, a conventionally known electronic focus is used for the arrangement direction of the small elements. Therefore, at a position other than the focus position, the ultrasonic beam spreads as shown in FIG. Incidentally, FIG. 34 shows FIG.
3 shows an outline of the sound field similar to that of FIG. 28 described above as viewed from the A direction, and FIG. 35 shows an outline of the sound field viewed from the B direction of FIG. 33.

According to the configuration of the fifth embodiment, a Bessel-type non-diffracting ultrasonic beam can be obtained also in the arrangement direction of the small elements. Therefore, an image which is clear as a whole can be obtained by transmitting and receiving ultrasonic waves once for each sound ray, and thus the frame rate can be improved.

A modified example of the fifth embodiment will be described below. The width of the element of one block (length of the small element) is s, and the length of one block is t. At this time, the values of the constants a and b are determined so that the relationship of b = ta / s is established in the fifth embodiment.
The ultrasonic probe can be mentioned as a modified example.
When driving one block of this ultrasonic probe, the numbers of peaks and valleys of the Bessel function match in the arrangement direction of the small elements and the scanning surface thickness direction. Therefore, the sound pressure distribution in an arbitrary cross section including the sound axis of the ultrasonic beam is distributed like a Bessel function. Therefore, a more accurate undiffracted ultrasonic beam can be emitted.

As shown in FIG. 35, since an ultrasonic beam having a substantially uniform thickness can be obtained in the thickness direction of the scanning surface, a clear image can be obtained over the entire ultrasonic image. The fifth embodiment can be applied to an ultrasonic probe in which the insertion portion 61 is flexible. Further, the application site is not limited to the above-mentioned ultrasonic probe for rapa, but can be applied to an ultrasonic endoscope for abdominal ultrasonic diagnosis from outside the body and for scanning inside the limb.

Further, the fifth embodiment can be applied not only to the electronic linear scanning ultrasonic probe but also to the electronic convex scanning ultrasonic probe. As described above, by applying the technique of the fifth embodiment to the convex scanning ultrasonic probe having a wide angle of view, it is possible to clearly depict a wider area of application.

The fifth embodiment is applicable not only to the electronic linear scanning ultrasonic probe but also to the electronic radial scanning ultrasonic probe. As described above, by applying the above-described technique to the radial scanning ultrasonic probe which is advantageous when performing scanning from the inside of the tube, it is possible to clearly depict a wider application site. In radial scanning, the sound ray spacing becomes wider as the distance increases, and the ultrasonic waves attenuate,
When the transducer unit 16 having the configuration of the fifth embodiment is used, since the ultrasonic beam is less diffused, even a small-sized and low-power small-diameter probe can transmit ultrasonic waves to a distant place for observation and diagnosis.

According to the present invention described above, the following configurations can be added. (1) A cable for transmitting a driving voltage and an echo signal,
In an ultrasonic probe that has a piezoelectric element, an acoustic matching layer on the acoustic emission surface side of the piezoelectric element, and a backside load layer on the opposite side of the piezoelectric element, spontaneous emission occurs depending on the position within a single piezoelectric element. An ultrasonic probe characterized by using a piezoelectric element having a difference in polarization intensity. The piezoelectric element has at least one axis of geometric symmetry. The direction of spontaneous polarization of the piezoelectric element is substantially perpendicular to both principal surfaces on the entire surface of the piezoelectric element. The distribution of the intensity of spontaneous polarization of the piezoelectric element is determined so that the sound pressure distribution from the ultrasonic probe is distributed as follows. On the surface of the piezoelectric element, a straight line orthogonal to any one of the geometrical symmetry axes is selected. This straight line will be called the x-axis. The origin of the x-axis is the intersection of the x-axis and the geometric symmetry axis of the selected piezoelectric element. A 0th-order Bessel function y = J ₀ (x / a) is drawn on the x-axis defined in this way. Here, a is an arbitrary constant. Furthermore, the defined Bessel function is approximated stepwise. Stepwise approximation J at each position on the x-axis
_When the value of ₀ (x / a) is applied to a certain voltage pulse,
It corresponds to the direction and magnitude of the sound pressure emitted from that position. That is, the spontaneous polarization is strong at a position where the value of J ₀ (x / a) approximated to the step shape is large, and J ₀ (x
The spontaneous polarization is weakened at a position where the value of / a) is small. Further, the direction of spontaneous polarization is reversed between the positive position and the negative position of J ₀ (x / a) that is stepwise approximated. The intensity of the spontaneous polarization of the piezoelectric element is distributed axially or line-symmetrically along the axis of symmetry.

(2) The ultrasonic probe according to appendix (1), wherein the spontaneous polarization intensity of the piezoelectric element is concentrically distributed.

(3) (Addition of ellipse) The spontaneous polarization intensity of the piezoelectric element is distributed in a similar elliptical shape in which the geometric centers are the same and both focal points are arranged on the same straight line. The ultrasonic probe according to appendix (1) or (2).

(4) (Expansion of rectangular distribution) The spontaneous polarization strengths of the piezoelectric elements are distributed in a rectangular shape of similar shape with the geometric centers being the same and the corresponding sides being parallel. The ultrasonic probe according to 1) or (2).

(5) (Expansion of linear distribution) The spontaneous polarization intensity of the piezoelectric element is uniformly distributed in the direction of the axis orthogonal to the x-axis (1) or (2).
The described ultrasonic probe.

(6) (Non-uniform intensity pulse drive of array) A plurality of cables for transmitting a drive voltage and an echo signal,
An array type ultrasonic transducer that has a plurality of piezoelectric elements, an acoustic matching layer on the acoustic emission surface side of each piezoelectric element, and a back load layer on the opposite side, and transmits and receives ultrasonic waves by simultaneously driving a plurality of piezoelectric elements. In the ultrasonic probe, the intensity distribution of the drive voltage pulse applied to each piezoelectric element is an ultrasonic system in which the sound pressure distribution from the ultrasonic probe is determined as follows. Select a straight line parallel to the array direction on the surface of the ultrasonic transducer array. This straight line will be called the x-axis. The origin of the x-axis is the intersection of the x-axis and the geometrical symmetry axis of one oscillator in a plurality of ultrasonic transducers that are simultaneously driven. For the x-pongee thus defined, the 0th-order Bessel function Y = J ₀ (x /
Draw a). Here, a is an arbitrary constant. Furthermore, the defined Bessel function is approximated stepwise. With respect to the geometrical symmetry axis of each ultrasonic transducer on the x-axis, the value of J ₀ (x / a) that is stepwise approximated to the value of the sound pressure radiated from that position when a certain voltage pulse is applied. Match the orientation and size. That was stepped approximation J ₀ absolute value of the voltage to the ultrasonic vibrator value of (x / a) corresponds to a position greater applies a pulse is greater, and stepped approximation J ₀ (x /
A pulse having a small absolute voltage value is applied to a position where the value of a) is small. Further, the polarity of the applied pulse voltage is reversed at the positive position and the negative position of J ₀ (x / a) that is stepwise approximated.

(7) (Simple extension to application of spontaneous distribution to array) A plurality of cables for transmitting drive voltage and echo signal,
Having a plurality of piezoelectric elements, an acoustic matching layer on the acoustic emission surface side of each piezoelectric element, and a backside load layer on the opposite side thereof, a plurality of piezoelectric elements are driven to form a sound ray for transmitting and receiving ultrasonic waves. In the array type ultrasonic probe, the polarization distribution in the case where the distribution of the spontaneous polarization in each ultrasonic transducer is shown in Appendix 2 with the x axis as the axis orthogonal to the array direction of the ultrasonic transducers. Ultrasonic system.

(8) The ultrasonic system as set forth in appendix (7), wherein when the plurality of piezoelectric elements are driven, the timing of applying the drive pulse is shifted to control the convergent position of the ultrasonic waves.

(9) (Simple Extension to Applying Spontaneous Polarization Distribution to Nonuniform Intensity Driven Array) The distribution of spontaneous polarization in each ultrasonic transducer is described in Appendix (2).
6. The ultrasonic system according to appendix (6), wherein the polarization distribution in the case where the x axis is an axis orthogonal to the array direction of the ultrasonic transducers is shown.

(10) (Expansion to convex array) The ultrasonic transducer groups are arranged in parallel with the y-axis and three-dimensionally on a convex curved surface (convex surface consisting of a part of a cylinder). The ultrasonic system according to appendix (6) or (7) or (9).

(11) (Expansion to radial array) Note (6) or (7) in which the ultrasonic transducer groups are aligned in the array direction parallel to the y-axis and are three-dimensionally aligned on the cylindrical surface. Alternatively, the ultrasonic system according to (9).

[0083]

According to the present invention described above, it is possible to achieve line focusing of an ultrasonic beam, obtain a high-resolution image of good quality with a relatively simple electric circuit, and to reduce the diameter. It is possible to provide an ultrasonic probe that can also be applied to.

[Brief description of drawings]

FIG. 1 is a diagram showing a plane and a cross section of a piezoelectric element according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a positional relationship between Bessel functions and electrodes of a piezoelectric element according to the first embodiment.

FIG. 3 is a diagram showing the Bessel function and the position of electrodes of the piezoelectric element, the direction of polarization, and the strength according to the first embodiment.

FIG. 4 is a cross-sectional view showing a transducer section according to the first embodiment.

FIG. 5 is a diagram showing the Bessel function of the first embodiment, the position of the electrodes of the piezoelectric element, the direction of polarization, and the strength.

FIG. 6 is a graph showing sound pressure distribution of the ultrasonic probe according to the first embodiment.

FIG. 7 is a graph showing the beam width of the first embodiment.

FIG. 8 is a diagram showing a connection state of divided electrodes according to the first embodiment.

FIG. 9 is a diagram showing an ultrasonic endoscope using the ultrasonic probe of the first embodiment.

FIG. 10 is a partial enlarged view showing a transducer unit incorporated in an ultrasonic endoscope.

FIG. 11 is an explanatory diagram showing measured values of sound pressure distribution of the ultrasonic probe according to the first embodiment.

FIG. 12 is an explanatory diagram showing a sound field of the ultrasonic probe according to the first embodiment and the conventional example.

FIG. 13 is a diagram showing a modified example of a connected state of the piezoelectric element according to the first embodiment.

FIG. 14 is a diagram showing yet another modified example of the connected state of the piezoelectric element according to the first embodiment.

FIG. 15 is a diagram showing a sound pressure distribution of ultrasonic waves and a Bessel function of the piezoelectric element according to the first embodiment.

FIG. 16 is a diagram showing a transrectal probe according to the first embodiment.

FIG. 17 is a partial enlarged view showing a transducer unit incorporated in the transrectal probe according to the first embodiment.

FIG. 18 is a diagram showing a trans-forceps channel small-diameter probe in the first embodiment.

FIG. 19 is an enlarged view showing the trans-forceps channel small-diameter probe in the first embodiment.

FIG. 20 is a partial enlarged view showing a transducer part incorporated in the trans-forceps channel small-diameter probe in the first embodiment.

FIG. 21 is an explanatory diagram showing a rectangular transducer portion and radiated sound pressure distribution according to the second embodiment.

FIG. 22 is a schematic diagram showing a sound field of Embodiment 2 and a conventional example.

FIG. 23 is an explanatory diagram showing a rectangular transducer portion and a radiation sound pressure distribution according to the third embodiment.

FIG. 24 is a perspective view showing a piezoelectric element according to the fourth embodiment.

FIG. 25 is a diagram showing an ultrasonic endoscope in which the ultrasonic probe for a rapa according to the fourth embodiment is incorporated.

FIG. 26 is a schematic diagram showing a piezoelectric element and a conventional sound field in the fourth embodiment.

FIG. 27 is a schematic diagram showing an electronic convex scanning ultrasonic probe according to a fourth embodiment.

FIG. 28 is a schematic diagram showing a piezoelectric element according to Embodiment 4 and a sound field of a conventional example.

FIG. 29 is a diagram showing an endoscope incorporating an electronic convex scanning ultrasonic probe.

FIG. 30 is a view showing an endoscope incorporating an electronic scanning ultrasonic probe.

FIG. 31 is an enlarged view of an electronic scanning ultrasonic probe.

FIG. 32 is a schematic diagram showing a sound field of Embodiment 4 and a conventional example.

FIG. 33 is a diagram showing a piezoelectric element, a driving voltage, and a sound field according to the fifth embodiment.

34 is a schematic diagram of a sound field seen from the direction A in FIG. 33.

FIG. 35 is a schematic diagram of a sound field seen from the direction B in FIG. 33.

FIG. 36 is a plan view showing a conventional piezoelectric element.

FIG. 37 is a plan view showing a conventional piezoelectric element.

FIG. 38 is a graph showing the beam width of a conventional piezoelectric element.

FIG. 39 is a diagram showing a polarization state of a conventional piezoelectric element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric ceramics 2 Full surface electrode 3 Split electrode 5 Piezoelectric element 6 Conductive resin 7 Acoustic matching layer 8 Back load material 10 Circumference line 11 Coaxial cable 12 Housing 13 Insulating cylinder 14 Solder 16 Transducer part 31 Operation part 32 Insert part 33 Acoustic window 34 Sound transmission medium 35 code

Claims (1)

[Claims] 1. An ultrasonic wave transmission / reception system, comprising a cable for transmitting a drive voltage and an echo signal, a piezoelectric element, an acoustic matching layer on the acoustic radiation surface side of the piezoelectric element, and a back load layer on the opposite side of the piezoelectric element. In a sonic probe, a piezoelectric element having a difference in the strength of spontaneous polarization depending on the position within one piezoelectric element is used, and the electrodes provided on both main surfaces of the piezoelectric element are electrically connected to the cable. The ultrasonic probe is characterized in that the distribution of the spontaneous polarization intensity of the piezoelectric element is determined so that the sound pressure distribution from the ultrasonic probe is distributed as follows. A straight line orthogonal to the geometrical symmetry axis is selected on the surface of the piezoelectric element, this straight line is taken as the x-axis, and the origin of this x-axis is taken as the intersection of the x-axis and the geometrically symmetric axis of the piezoelectric element. when draw the zeroth order Bessel function a as arbitrary constant with respect to x axis _{y = J 0 (x / a} ), a value of J ₀ (x / a) at each position on the x-axis When a certain voltage pulse is applied, the spontaneous polarization is strengthened at the position where the absolute value of J ₀ (x / a) is large, and the spontaneous polarization is weakened at the position where the absolute value of J ₀ (x / a) is small. It corresponds to the direction and magnitude of the sound pressure emitted from that position. The direction of spontaneous polarization is reversed between the positive and negative positions of J ₀ (x / a). The intensity of the spontaneous polarization of the piezoelectric element is distributed axially or line-symmetrically along the axis of symmetry. The direction of spontaneous polarization of the piezoelectric element is set to be substantially perpendicular to both main surfaces on the entire surface of the piezoelectric element.