JP2008066972A - Ultrasonic probe and ultrasonic diagnosis device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic probe for obtaining uniform slice thickness of an ultrasonic image and reducing a sidelobe while securing manufacturability and high sensitivity. <P>SOLUTION: Near a center O in a slice direction, thickness of a first piezoelectric layer 3a is made almost equal to that of a second piezoelectric layer 3b. An upper surface of the first piezoelectric layer 3a has a concave shape, whereas a lower surface has a flat shape. A lower surface of the second piezoelectric layer 3b has a convex shape, whereas an upper surface has a flat shape. Thus, sensitivity can gradually be lowered as the vicinity of center O is close to an edge part in the slice direction and an ultrasonic wave weighted by a positive weighting in the slice direction can be transmitted or received. As a result, the sidelobe in the slice direction can be reduced, a uniform sound field in a depth direction the uniform slice thickness of the ultrasonic image can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic probe and an ultrasonic diagnostic apparatus that perform ultrasonic transmission / reception, and relates to an ultrasonic probe and an ultrasonic probe that can equalize the slice thickness of an ultrasonic image and reduce side lobes of a sound field in the slice direction. The present invention relates to an ultrasonic diagnostic apparatus.

  2. Description of the Related Art There is known an ultrasonic diagnostic apparatus that scans an inside of a subject with ultrasonic waves and images an internal state of the subject based on a reception signal generated from a reflected wave from the inside of the subject. Such an ultrasonic diagnostic apparatus transmits ultrasonic waves into a subject using an ultrasonic probe including a piezoelectric vibrator, and receives reflected waves generated by acoustic impedance mismatches within the subject using the ultrasonic probe. Generate a received signal.

  The ultrasonic probe is arranged with a plurality of piezoelectric vibrators in the scanning direction that generate an ultrasonic wave by vibrating based on a transmission signal and generate a reception signal by receiving a reflected wave. Such an ultrasonic probe forms a focal point at a certain depth by giving a delay difference by an acoustic lens to an ultrasonic wave having a uniform rectangular intensity in a direction orthogonal to the scanning direction (hereinafter referred to as a slice direction). is doing.

  Conventionally, attempts have been made to make the slice thickness of the image collected by the ultrasonic diagnostic apparatus uniform and reduce the side lobe of the sound field in the slice direction. For example, a technique is known in which grooves are formed in a piezoelectric body along the slicing direction and the density distribution of the piezoelectric body is weighted (for example, Patent Document 1). In addition, a technique for making the electrode area at the end smaller than the center is known (for example, Patent Document 2). In addition, a technique is known in which a plurality of transmission circuits are connected to piezoelectric bodies that are electrically divided in the slice direction, and the driving voltage applied to each piezoelectric body is weighted (for example, Patent Document 3). Furthermore, a technique is known in which the piezoelectric body is curved to change the thickness of the piezoelectric body in the slicing direction, and the sound pressure is controlled by the driving frequency (for example, Patent Document 4).

JP 2003-9288 A Japanese Patent Laid-Open No. 3-195572 JP-A-5-38335 JP-A-7-107595

  However, in the ultrasonic probe described in Patent Document 1, in order to make the piezoelectric body in a sparse state along the slicing direction, the area of the electrode is reduced in the ultrasonic probe described in Patent Document 2. Therefore, the effective element area of the piezoelectric body is reduced and the capacitance of the element is reduced. As a result, the impedance of the ultrasonic probe is increased, and the matching of the electrical impedance with the ultrasonic diagnostic apparatus main body is deteriorated, resulting in a problem that sensitivity is lowered.

  Further, in the ultrasonic probe described in Patent Document 3, since the structure of the ultrasonic probe and the circuit is complicated, the reliability of the ultrasonic diagnostic apparatus is reduced, the number of manufacturing steps is increased, and the manufacturing cost is increased. There was a risk of it.

  Furthermore, in the ultrasonic probe described in Patent Document 4, it is necessary not only to perform curved surface processing on a piezoelectric body, but also to perform curved surface processing on an acoustic matching layer laminated on the piezoelectric body. There was a problem that the number of manufacturing steps increased.

  Further, in the ultrasonic probes described in Patent Document 1 and Patent Document 3, weighting of ultrasonic sound pressure in the slice direction can only be applied in stages, so that a grating lob occurs if the interval between the stages is wide. There was also a problem.

  The present invention solves the above-described problems, and can ensure the manufacturability and high sensitivity of an ultrasonic probe, and can make the slice thickness of an ultrasonic image uniform and reduce side lobes. It is an object of the present invention to provide a probe and an ultrasonic diagnostic apparatus including the probe.

  The invention according to claim 1 is an ultrasonic probe provided with electrodes on the upper surface and the lower surface, transmitting an ultrasonic wave when a voltage is applied thereto, and having a piezoelectric vibrator unit that receives the ultrasonic wave. The piezoelectric vibrator unit includes a plurality of piezoelectric layers in which a plurality of piezoelectric bodies are arranged in a scanning direction via electrodes, and at least two piezoelectric layers that are in contact with each other among the plurality of piezoelectric layers. The ultrasonic probe is characterized in that the thickness gradually changes in a slice direction orthogonal to the scanning direction.

  A second aspect of the present invention is the ultrasonic probe according to the first aspect, wherein the thicknesses of the at least two piezoelectric layers in contact with each other at substantially the center in the slice direction perpendicular to the scanning direction are substantially equal. It is characterized by that.

  A third aspect of the present invention is the ultrasonic probe according to the first aspect, wherein one of the at least two piezoelectric layers in contact with each other in a slice direction perpendicular to the scanning direction of one of the piezoelectric layers. The thickness at the approximate center is 80 to 120% of the thickness at the approximate center in the slice direction orthogonal to the scanning direction of the other piezoelectric layer.

  The invention according to claim 4 is the ultrasonic probe according to any one of claims 1 to 3, wherein one of the at least two piezoelectric layers in contact with each other is the piezoelectric layer. The thickness gradually increases as it approaches the end in the slice direction orthogonal to the scanning direction, and the thickness of the other piezoelectric layer gradually decreases as it approaches the end in the slice direction orthogonal to the scanning direction. It is characterized by.

  The invention according to claim 5 is the ultrasonic probe according to any one of claims 1 to 4, wherein the at least two piezoelectric layers in contact with each other are in contact with the other piezoelectric layer. The surface is formed in a curved shape.

  A sixth aspect of the present invention is the ultrasonic probe according to any one of the first to fourth aspects of the present invention, wherein one of one of the piezoelectric layers among the at least two piezoelectric layers in contact with each other. The surface is formed in a convex shape, one surface of the other piezoelectric layer is formed in a concave shape, and the surface formed in the convex shape and the surface formed in the concave shape are fitted. It is a feature.

  The invention according to claim 7 is the ultrasonic probe according to any one of claims 1 to 6, wherein an upper surface and a lower surface of the piezoelectric vibrator portion are formed in a planar shape. It is what.

  The invention according to claim 8 has a piezoelectric vibrator portion in which a plurality of piezoelectric layers in which a plurality of piezoelectric bodies are arranged in a scanning direction are stacked via electrodes, and at least of the plurality of piezoelectric layers. An ultrasonic probe in which the thickness of two piezoelectric layers in contact with each other gradually changes in a slice direction orthogonal to the scanning direction, and a transmission / reception means for transmitting / receiving ultrasonic waves to / from a subject using the ultrasonic probe And an image generation means for generating an ultrasonic image based on a reflected wave from the subject received by the transmission / reception means.

  According to the present invention, by gradually changing the thickness of the piezoelectric layer in the direction orthogonal to the scanning direction (slice direction), it is possible to weight the sound pressure of ultrasonic waves in the slice direction. Further, in at least two piezoelectric layers, the thickness at the substantially center in the slicing direction is substantially equal, and as one approaches the end in the slicing direction, the thickness of one piezoelectric layer is gradually increased, and the other piezoelectric body By reducing the layer thickness, the sound pressure in the slice direction of the transmitted and received ultrasonic waves is weighted positively, reducing the side lobe of the sound field in the slice direction, and producing a uniform sound field in the depth direction. It becomes possible to form.

  Also, according to the present invention, it is possible to improve the sensitivity of the ultrasonic probe by lowering the impedance of the ultrasonic probe by laminating a plurality of piezoelectric layers. In particular, the sensitivity can be maximized in the portions where the thicknesses of the piezoelectric layers are substantially equal compared to other portions.

  Further, by gradually changing the thickness of the piezoelectric layer in the slice direction, the sound pressure distribution can be continuously changed in the slice direction. As a result, the grating lob of the artifact can be reduced, and a sound field in the slice direction that is uniform and has few artifacts can be realized.

  Furthermore, since the upper and lower surfaces of the piezoelectric vibrator portion are formed in a flat shape, even if an acoustic matching layer or the like to be laminated on the piezoelectric vibrator portion is provided, curved processing is performed on the acoustic matching layer or the like. There is no need to apply. As a result, the manufacturing process is not complicated, and the ultrasonic probe of the present invention can be manufactured without increasing the manufacturing cost.

  An ultrasonic probe and an ultrasonic diagnostic apparatus according to an embodiment of the present invention will be described with reference to FIGS.

[First Embodiment]
The configuration of the ultrasonic probe according to the first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view showing a schematic configuration of an ultrasonic probe according to the first embodiment of the present invention. FIG. 2 is a sectional side view showing a schematic configuration of the ultrasonic probe according to the first embodiment of the present invention. The ultrasonic probe includes a head side and a cable side. FIGS. 1 and 2 show the head side of the ultrasonic probe.

  As shown in FIGS. 1 and 2, the ultrasonic probe 1 is provided with a piezoelectric vibrator portion 3 on a back material 2. The piezoelectric vibrator unit 3 in this embodiment is configured to include two piezoelectric layers, and the two piezoelectric layers are laminated. An acoustic matching layer 4 is provided on the piezoelectric vibrator portion 3. The acoustic matching layer 4 includes a first acoustic matching layer 4a, a second acoustic matching layer 4b, and a third acoustic matching layer 4c, and the acoustic matching layers are stacked in that order. The piezoelectric vibrator unit 3 and the acoustic matching layer 4 are divided and arranged in a plurality in the scanning direction. Furthermore, an acoustic lens 5 is provided on the acoustic matching layer 4.

  The backing material 2 attenuates and absorbs ultrasonic vibration components that are not necessary for image extraction of the ultrasonic diagnostic apparatus, among ultrasonic vibrations oscillated from the piezoelectric vibrator unit 3 and ultrasonic vibrations at the time of reception. Generally, a material obtained by mixing a microballoon or the like with ferrite rubber, epoxy resin, urethane rubber or the like is used for the backing material 2.

  The piezoelectric vibrator unit 3 is configured by laminating a plurality of piezoelectric layers. In the first embodiment, the second piezoelectric layer 3b is laminated on the first piezoelectric layer 3a, and the piezoelectric vibrator unit 3 is configured by the two piezoelectric layers. The first piezoelectric layer 3a and the second piezoelectric layer 3b are divided and arranged in a plurality in the scanning direction. In the first embodiment, an example in which two piezoelectric layers are stacked will be described. However, the present invention is not limited to two layers, and three or more piezoelectric layers may be stacked. An example in which three piezoelectric layers are laminated will be described in a later-described modification.

  As shown in FIGS. 1 and 2, the lower surface of the first piezoelectric layer 3a (the surface in contact with the back material 2) is a flat surface, and the upper surface (second piezoelectric layer) opposite to the lower surface. The surface in contact with 3b is a curved surface. Specifically, the upper surface of the first piezoelectric layer 3a is concave. That is, the first piezoelectric layer 3a is formed such that the center O in the slicing direction (direction orthogonal to the scanning direction) is the thinnest, and the thickness gradually increases toward the end in the slicing direction. ing.

  In addition, the upper surface (surface in contact with the acoustic matching layer 4) of the second piezoelectric layer 3b is a flat surface, and the lower surface (surface in contact with the first piezoelectric layer 3a) opposite to the upper surface is a curved surface. It has become. Specifically, the lower surface of the second piezoelectric layer 3b is a convex surface. That is, the second piezoelectric layer 3b is formed so that the vicinity of the center O in the slicing direction is the thickest, and the thickness gradually decreases as it approaches the end in the slicing direction.

  The first piezoelectric layer 3a having a concave upper surface and the second piezoelectric layer 3b having a convex lower surface are fitted by fitting the convex surface to the concave surface. That is, the shape of the upper surface of the first piezoelectric layer 3a and the shape of the lower surface of the second piezoelectric layer 3b are both curved, and the shapes of the curved surfaces substantially coincide with each other on the concave surface. The lower surface of the second piezoelectric layer 3b formed in a convex shape is fitted on the upper surface of the formed first piezoelectric layer 3a, whereby the first piezoelectric layer 3a and the second piezoelectric layer 3b. And are fitted.

  Then, the thickness of the first piezoelectric layer 3a and the thickness of the second piezoelectric layer 3b change along the slice direction. That is, since the first piezoelectric layer 3a has a concave upper surface and a flat lower surface, the thickness in the vicinity of the center O in the slicing direction is the smallest, and the closer to the end along the slicing direction, the closer to the end. The thickness gradually increases. On the other hand, since the second piezoelectric layer 3b has a convex bottom surface and a flat top surface, the thickness in the vicinity of the center O in the slicing direction is the thickest, and the closer to the end along the slicing direction, the closer to the end. The thickness gradually decreases.

  The total thickness of the piezoelectric vibrator portion 3 is constant regardless of whether it is near the center O or at the end portion. That is, the first piezoelectric layer 3a having a lower surface formed in a planar shape and the upper surface formed in a concave shape, and the second piezoelectric layer 3b formed in an upper surface formed in a planar shape and the lower surface formed in a convex shape. Are stacked so that the lower surface of the first piezoelectric layer 3a and the upper surface of the second piezoelectric layer 3b are parallel to each other, and the entire thickness of the piezoelectric vibrator portion 3 is constant.

  Here, as shown in FIG. 2, the entire thickness of the piezoelectric vibrator portion 3 is defined as a thickness T. In the first embodiment, the thickness at the center O in the slice direction of the first piezoelectric layer 3a is (T / 2), and the center in the slice direction of the second piezoelectric layer 3b. The thickness at O is also (T / 2). That is, at the center O in the slicing direction, the thicknesses of the first piezoelectric layer 3a and the second piezoelectric layer 3b are equal.

  The first piezoelectric layer 3a is formed so that the thickness gradually increases from (T / 2) toward the end in the slice direction from the center O in the slice direction. On the other hand, the second piezoelectric layer 3b is formed so that the thickness gradually decreases from (T / 2) toward the end in the slice direction from the center O in the slice direction. Further, the thickness of the piezoelectric vibrator portion 3 formed by laminating the first piezoelectric layer 3a and the second piezoelectric layer 3b is equal to the thickness T regardless of whether it is the center O or the end portion. It has become.

  In the first embodiment, the thickness of the first piezoelectric layer 3a and the thickness of the second piezoelectric layer 3b at the center O in the slice direction are equal (T / 2). It is not necessary that the thicknesses of the two are exactly the same. Even if the thickness of one of the piezoelectric layers is 80% to 120% of the thickness of the other piezoelectric layer, the action and effect of the ultrasonic probe 1 according to this embodiment can be achieved. It is.

  For example, when the thickness at the center O in the slice direction of the first piezoelectric layer 3a is defined as the thickness t, the thickness at the center O in the slice direction of the second piezoelectric layer 3b is 0.8 t to 1.. If it is between 2t, it is possible to show the action and effect of the ultrasonic probe according to this embodiment. On the contrary, when the thickness at the center O in the slicing direction of the second piezoelectric layer 3b is defined as the thickness t, the thickness at the center O in the slicing direction of the first piezoelectric layer 3a is 0.8 t to 1. If it is between 2t, the action and effect of the ultrasonic probe according to this embodiment can be obtained.

The first piezoelectric layer 3a and the second piezoelectric layer 3b are, for example, lead zirconate titanate Pb (Zr, Ti) O ₃ , lithium niobate (LiNbO ₃ ), barium titanate (BaTiO ₃ ), or titanate. made of a ceramic material such as lead (PbTiO _3).

  Further, as shown in FIG. 2, electrodes 6a and 6c are connected to the upper and lower surfaces of the piezoelectric vibrator section 3, and the electrode 6b is connected between the first piezoelectric layer 3a and the second piezoelectric layer 3b. Has been. The electrodes 6a and 6c are connected to GND, and a voltage is applied to the electrode 6b. Thereby, the part comprised by the electrode 6a, the 1st piezoelectric material layer 3a, and the electrode 6b, and the part comprised by the electrode 6b, the 2nd piezoelectric material layer 3b, and the electrode 6c comprise parallel connection. become.

  As described above, since the upper surface of the first piezoelectric layer 3a is concave and the lower surface of the second piezoelectric layer 3b is convex, the first piezoelectric layer 3a and the second piezoelectric layer The electrode 6b disposed between the body layer 3b and the body layer 3b has a curved surface so as to fit on the upper surface (concave surface) of the first piezoelectric layer 3a and the lower surface (convex surface) of the second piezoelectric layer 3b. Yes. On the other hand, since the lower surface of the first piezoelectric layer 3a is flat, the electrode 6a is flat. Similarly, since the upper surface of the second piezoelectric layer 3b is flat, the electrode 6c is flat.

  The acoustic matching layer 4 is made of an epoxy resin or a plastic material. The acoustic matching layer is provided to improve acoustic matching between the acoustic impedance of the piezoelectric vibrator unit 3 and the acoustic impedance of the subject. There may be only one acoustic matching layer, or two or more acoustic matching layers. In this embodiment, three acoustic matching layers are stacked. For example, when three acoustic matching layers are provided as in this embodiment, the acoustic impedance of the second acoustic matching layer 4b is greater than the acoustic impedance of the first acoustic matching layer 4a in order to improve acoustic matching. The acoustic impedance of the third acoustic matching layer 4c is designed to be smaller than the acoustic impedance of the second acoustic matching layer 4b. By making the acoustic matching layer have a plurality of layer structures, the generation of signal loss due to the difference in acoustic impedance with the body surface of the subject combined with the acoustic lens 5 is suppressed.

  In addition, in order to achieve acoustic matching between the acoustic impedance of the piezoelectric vibrator unit 3 and the acoustic impedance of the subject regardless of the wavelength of ultrasonic waves to be transmitted and received, an acoustic matching layer that gradually decreases in the depth direction is provided. It may be provided.

  The acoustic lens 5 contacts the body surface of the subject and mediates transmission / reception of ultrasonic waves. By this acoustic lens 5, an acoustic focal point in the slice direction is formed at a predetermined depth from the body surface. The acoustic focus in the scanning direction is established by switching and controlling the transmission / reception timings of the plurality of piezoelectric vibrator portions 3 arranged in a strip shape in the scanning direction.

  In addition, a filler (not shown) such as silicone rubber, urethane rubber, or epoxy resin is provided in the divided grooves of the piezoelectric vibrator unit 3 and the acoustic matching layer 4 divided into a plurality in the scanning direction in order to maintain mechanical strength. Filled.

(Function)
According to the ultrasonic probe 1 having the above-described configuration, it is possible to achieve the following preferable actions. The operation of the ultrasonic probe 1 according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a graph showing frequency characteristics of the ultrasonic probe according to the first embodiment of the present invention. FIG. 4 shows a sound field distribution formed when ultrasonic waves are transmitted or received by the ultrasonic probe according to the first embodiment of the present invention.

  According to the ultrasonic probe 1 according to the first embodiment, (1) the impedance of the ultrasonic probe 1 can be improved by lowering the impedance of the ultrasonic probe 1. In addition, (2) it is possible to reduce side lobes in the slice direction and realize a uniform sound field in the depth direction. Also, (3) it is possible to reduce the grating lob and realize a uniform sound field with little artifacts. Further, (4) since the effective area of the element is not reduced, the sound pressure distribution can be weighted in the slice direction without losing sensitivity. Furthermore, (5) it is possible to manufacture the ultrasonic probe 1 capable of producing the above-described functions and effects without increasing the manufacturing process and increasing the manufacturing cost. Hereinafter, the operations and effects (1) to (5) will be described in detail.

<(1) Improvement of sensitivity>
In the ultrasonic probe 1 according to the first embodiment, the total thickness of the piezoelectric vibrator unit 3 is defined as a thickness T. Thereby, the thickness at the center O in the slice direction of the first piezoelectric layer 3a is (T / 2), and the thickness at the center O in the slice direction of the second piezoelectric layer 3b is also (T / 2). . Further, an area defined by the length in the scanning direction and the length in the slice direction at the center O is defined as an area S. Here, when the respective capacitance of the first piezoelectric layer 3a and the second piezoelectric layer 3b having a thickness of (T / 2) and the capacitance C _1, the capacitance C ₁ in the center O to the following formula It is represented by (1).
Formula (1) Electric capacity C ₁ = ε {S / (T / 2)}
ε is the dielectric constant.

In this embodiment, since the first piezoelectric layer 3a and the second piezoelectric layer 3b are laminated via the electrode 6b, the connection between the piezoelectric layers corresponds to a parallel connection. Therefore, when the electric capacity of the central O of the piezoelectric vibrator unit 3 and the capacitance C _2, the capacitance C ₂ is represented by the following formula (2).
Formula (2) C ₂ = 2 × C ₁ = 2 × ε {S / (T / 2)} = 4 × ε (S / T) = 4 × C ₀
Here, the electric capacity C ₀ is an electric capacity of a piezoelectric body composed of one layer having a thickness T.

As represented in the above formula (2), the capacitance at the center O of the piezoelectric vibrator unit 3 will capacitance of 4 times the piezoelectric body made of one layer of thickness T (= 2 ² ×). This is because a piezoelectric layer having a thickness (T / 2) is laminated via the electrode 6b to be connected in parallel.

  Since the electric capacity can be increased by laminating the piezoelectric layers through the electrodes in this way, the impedance of the ultrasonic probe can be lowered and the sensitivity of the ultrasonic probe can be improved.

In the first embodiment, an example in which two piezoelectric layers are stacked has been described. However, a piezoelectric vibrator unit in which three or more piezoelectric layers are stacked may be used. The electric capacity of the portion where the n piezoelectric layers are stacked and the thickness of each piezoelectric layer is equal is n ² times the electric capacity of the piezoelectric material having one layer of thickness T. In this way, when two or more piezoelectric layers are stacked, the electric capacity increases in the portions where the thicknesses of the respective piezoelectric layers are equal. Therefore, it is possible to improve the sensitivity by lowering the impedance of the ultrasonic probe. Become. Note that a piezoelectric vibrator unit in which three piezoelectric layers are stacked will be described in a modification example to be described later.

<(2) Reduction of side lobes in the slice direction and uniform sound field>
The characteristics of the piezoelectric vibrator unit formed by laminating a plurality of piezoelectric layers are such that the sensitivity of the portion where the thickness of each piezoelectric layer is equal is the highest, and when the thickness of one of the piezoelectric layers is reduced or increased, , The sensitivity in that part is lowered. The inventor of this application utilized this principle.

  In the ultrasonic probe 1 according to the first embodiment, the thickness of the first piezoelectric layer 3a and the thickness of the second piezoelectric layer 3b at the center O in the slicing direction are equal (T / 2). The sensitivity at the center O is the highest. On the other hand, when the thickness of the piezoelectric layer on the ultrasonic radiation surface side, that is, the thickness of the second piezoelectric layer 3b is reduced, the sensitivity is lowered. At this time, since the resonance frequency is increased, the sensitivity to high frequencies is increased. This is because the resonance frequency of the piezoelectric body is generally expressed as a function of the reciprocal of the thickness of the piezoelectric body, and therefore the resonance frequency increases as the thickness of the piezoelectric body decreases.

  This is because the sensitivity is highest because the resonance points of the piezoelectric layers coincide with each other in the portions where the thicknesses of the laminated piezoelectric layers are equal, and on the ultrasonic radiation surface side in the other portions. This is because the resonance point between the vibration of one piezoelectric layer and the vibration of another piezoelectric layer is shifted, and this causes a load on each other, resulting in a decrease in sensitivity.

  In the ultrasonic probe 1 according to the first embodiment, in the portion where the thickness of the first piezoelectric layer 3a and the thickness of the second piezoelectric layer 3b are equal (center O), the first piezoelectric layer Since the resonance point of 3a coincides with the resonance point of the second piezoelectric layer 3b, the sensitivity is the highest, and in other parts, the piezoelectric layer (second piezoelectric layer) on the ultrasonic wave emission surface side is provided. Since the resonance point between the vibration of the body layer 3b) and the vibration of the other piezoelectric layer (the first piezoelectric layer 3a) is shifted, it becomes a load to each other and the sensitivity is lowered.

  In the first embodiment, by making the thickness of the first piezoelectric layer 3a equal to the thickness of the second piezoelectric layer 3b at the center O in the slice direction, the sensitivity at the center O is maximized, Further, the closer to the end in the slicing direction, the thicker the thickness of the first piezoelectric layer 3a and the smaller the thickness of the second piezo-electric layer 3b. The sensitivity is lowered.

  As a result, the sensitivity at the center O in the slice direction becomes the highest, and the sensitivity gradually decreases as the end of the slice direction becomes closer. In this way, the sound pressure distribution can be weighted in the slice direction.

  Here, the sensitivity of the ultrasonic probe 1 will be described with reference to FIG. In FIG. 3, the horizontal axis indicates the frequency [MHz] of ultrasonic waves transmitted and received, and the vertical axis indicates the intensity [dB] of ultrasonic waves transmitted and received. Here, PZT is used for both the first piezoelectric layer 3a and the second piezoelectric layer 3b, and the entire thickness T of the piezoelectric vibrator section 3 is 480 [μm]. Therefore, at the center O in the slicing direction, the thickness of the first piezoelectric layer 3a and the thickness of the second piezoelectric layer 3b are both 240 [μm].

  FIG. 3A is a graph showing frequency characteristics of the ultrasonic probe 1 at the center O. FIG. That is, the graph of FIG. 3A shows the frequency characteristics of a portion (center O) where the thickness of the first piezoelectric layer 3a is equal to the thickness of the second piezoelectric layer 3b. In FIG. 3A, the curve A represents the frequency characteristic of the ultrasonic probe 1 at the center O in the slice direction.

  Further, the graph of FIG. 3B shows the frequency of the portion where the thickness of the first piezoelectric layer 3a is (2T / 3) and the thickness of the second piezoelectric layer 3b is (T / 3). The characteristics are shown. That is, the graph of FIG. 3B represents the frequency characteristics of the portion where the ratio of the thickness of the first piezoelectric layer 3a and the thickness of the second piezoelectric layer 3b is “2: 1”. . In FIG. 3B, a curve B represents the frequency characteristic of the ultrasonic probe 1 in a portion where the thickness ratio is “2: 1”.

  Further, the graph of FIG. 3C shows the frequency of the portion where the thickness of the first piezoelectric layer 3a is (5T / 6) and the thickness of the second piezoelectric layer 3b is (T / 6). The characteristics are shown. That is, the graph of FIG. 3C shows the frequency characteristics of the portion where the ratio of the thickness of the first piezoelectric layer 3a and the thickness of the second piezoelectric layer 3b is “5: 1”. . In FIG. 3C, a curve C represents the frequency characteristic of the ultrasonic probe 1 in a portion where the thickness ratio is “5: 1”.

  When the curves A, B, and C shown in FIG. 3 are compared, the sensitivity at the portion where the thickness of the first piezoelectric layer 3a is equal to the thickness of the second piezoelectric layer 3b, that is, the center O is the highest. . Then, the sensitivity of the portion where the thickness of the second piezoelectric layer 3b is reduced and the ratio between the thickness of the first piezoelectric layer 3a and the thickness of the second piezoelectric layer 3b is “2: 1”. Is lower than the sensitivity at the center O as shown in FIG. FIG. 3B also shows the frequency characteristics at the center O for comparison. Note that the center frequency of the ultrasonic wave in the portion where the thickness ratio is “2: 1” is relatively higher than the center frequency of the ultrasonic wave at the center O. This is because the thickness of the second piezoelectric layer 3b is reduced and the resonance frequency is increased.

  Further, the sensitivity of the portion where the thickness of the second piezoelectric layer 3b is reduced and the ratio of the thickness of the first piezoelectric layer 3a to the thickness of the second piezoelectric layer 3b is “5: 1”. As shown in FIG. 3C, the sensitivity is further lowered. FIG. 3C also shows the frequency characteristics at the center O for comparison.

  As described above, by changing the thickness of the piezoelectric layer in the slice direction, the sound pressure can be weighted in the slice direction. According to the configuration of the piezoelectric vibrator unit 3 according to this embodiment, the sensitivity at the center O in the slice direction becomes the highest, and the sensitivity gradually decreases from the center O in the slice direction toward the end in the slice direction. As a result, since the transmitted / received sound field is positively weighted in the slice direction, the side lobe of the sound field in the slice direction can be reduced, and a uniform sound field can be formed in the depth direction.

  Here, the sound field distribution of the ultrasonic waves transmitted and received by the ultrasonic probe will be described with reference to FIG. FIG. 4A shows an acoustic field distribution of ultrasonic waves transmitted and received by the ultrasonic probe 1 according to the first embodiment. FIG. 4B is a sound field distribution of ultrasonic waves transmitted and received by the ultrasonic probe according to the related art. The ultrasonic probe according to the related art includes a single piezoelectric layer having a thickness T, and transmits and receives ultrasonic waves having a rectangular sound pressure distribution. In FIG. 4, the horizontal axis indicates the distance in the depth direction from the tip of the ultrasonic probe, and the vertical axis indicates the distance in the slice direction of the ultrasonic probe. The center O in the slice direction is 0 [mm].

  FIG. 4 shows a sound field distribution of ultrasonic waves having an intensity of −3 [dB] to −20 [dB]. According to the ultrasonic probe 1 according to the first embodiment, the sound field in the slice direction is weighted with positive weighting. Therefore, as shown in FIG. The lobe is reduced, a sound field with a narrow main lobe is obtained, and a uniform sound field is obtained in the depth direction.

<(3) Reduction of grating lob>
In the ultrasonic probe 1 according to this embodiment, the upper surface of the first piezoelectric layer 3a is a curved concave surface, and the lower surface of the second piezoelectric layer 3b is a curved convex surface. This means that the thicknesses of the piezoelectric layer 3a and the second piezoelectric layer 3b are continuously changed in the slice direction. This makes it possible to continuously change the sound pressure distribution of the ultrasonic waves in the slice direction. As a result, the grating lob can be reduced, and a sound field in the slice direction that is uniform and has few artifacts can be realized.

  On the other hand, if the thickness of the piezoelectric layer is changed stepwise in the slicing direction, grating lobing occurs. In contrast, in the ultrasonic probe 1 in this embodiment, the thickness of the piezoelectric layer continuously changes in the slicing direction, so that it is possible to reduce grating lobs, and sound that is uniform and has few artifacts. Can be realized.

<(4) Effective area of element>
Further, in the ultrasonic probe 1 according to the first embodiment, in order to weight the sound pressure distribution, the area of the electrode is reduced or the piezoelectric body is grooved in the slicing direction as in the ultrasonic probe according to the conventional technique. There is no need to form. Therefore, the sound pressure distribution can be weighted in the slice direction without reducing the effective area of the element. Since the effective area of the element does not decrease, impedance matching between the ultrasonic probe 1 and the ultrasonic diagnostic apparatus main body is not deteriorated. As a result, it is possible to weight the sound pressure distribution in the slice direction without reducing the sensitivity.

<(5) Manufacturing process>
Further, since the ultrasonic probe 1 according to the first embodiment does not have a complicated configuration like the ultrasonic probe according to the related art, the manufacturing process is not complicated and the manufacturing cost is not increased. Is possible. That is, since the upper surface and the lower surface of the piezoelectric vibrator section 3 are formed in a planar shape, it is not necessary to perform curved surface processing or the like on the acoustic matching layer 4 and the back material 2 laminated on the piezoelectric vibrator section 3. The ultrasonic probe 1 according to the first embodiment can be manufactured by a general ultrasonic probe manufacturing process without performing special processing.

  Therefore, it is possible to achieve high sensitivity characteristics while ensuring the manufacturability of the ultrasonic probe and to weight the sound pressure distribution in the slice direction. Accordingly, it is possible to make the slice thickness of the ultrasonic image uniform and reduce the side lobes in the slice direction while ensuring the manufacturability. In addition, since the structure of the electric circuit is not complicated and an electric circuit used for a so-called one-dimensional ultrasonic probe can be applied, the effects (1) to (4) described above can be achieved without increasing the manufacturing cost. It becomes possible to play.

[Second Embodiment]
Next, the configuration and operation of an ultrasonic probe according to the second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram showing a schematic configuration and frequency characteristics of the piezoelectric vibrator unit according to the second embodiment of the present invention. FIG. 5A is a cross-sectional side view showing a schematic configuration of the piezoelectric vibrator unit according to the second embodiment, and FIGS. 5B to 5D show the second piezoelectric vibrator unit. It is a figure which shows a frequency characteristic.

  In the ultrasonic probe according to the second embodiment, the configuration of the piezoelectric vibrator unit is different from the configuration of the piezoelectric vibrator unit 3 according to the first embodiment. In the ultrasonic probe according to the first embodiment, the upper surface of the first piezoelectric layer 3a is formed in a concave shape, and the lower surface of the second piezoelectric layer 3b is formed in a convex shape. On the other hand, the ultrasonic probe according to the second embodiment has a configuration opposite to that of the piezoelectric vibrator unit 3 according to the first embodiment. That is, the upper surface of the first piezoelectric layer 7a is formed in a convex shape, and the lower surface of the second piezoelectric layer 7b is formed in a concave shape. Hereinafter, the configuration of the piezoelectric vibrator unit in the ultrasonic probe according to the second embodiment will be described in detail.

  As shown in FIG. 5A, the lower surface of the first piezoelectric layer 7a (the surface in contact with the back material 2) is a flat surface, and the upper surface (second piezoelectric layer) opposite to the lower surface. The surface in contact with 7b is formed in a curved surface and is a convex surface. That is, the first piezoelectric layer 7a is formed so that the center O in the slice direction is thickest, and the thickness gradually decreases as it approaches the end in the slice direction.

  In addition, the upper surface (surface in contact with the acoustic matching layer 4) of the second piezoelectric layer 7b is a flat surface, and the lower surface (surface in contact with the first piezoelectric layer 7a) opposite to the upper surface is a curved surface. It is formed in a shape and has a concave surface. That is, the second piezoelectric layer 7b is formed such that the center O in the slicing direction is the thinnest and the thickness gradually increases as it approaches the end in the slicing direction.

  The first piezoelectric layer 7a having a convex upper surface and the second piezoelectric layer 7b having a concave lower surface are fitted by fitting the convex surface to the concave surface. That is, the shape of the upper surface of the first piezoelectric layer 7a and the shape of the lower surface of the second piezoelectric layer 7b are both curved, and the shape of the curved surface substantially coincides with the concave shape. The first piezoelectric layer 7a and the second piezoelectric layer 7b are fitted on the lower surface of the formed second piezoelectric layer 7b by fitting the upper surface of the first piezoelectric layer 7a formed into a convex shape. Is in agreement.

  And the thickness of the 1st piezoelectric material layer 7a and the thickness of the 2nd piezoelectric material layer 7b are changing along the slice direction. That is, since the upper surface of the first piezoelectric layer 7a is formed in a convex shape and the lower surface is flat, the thickness near the center O in the slicing direction is the thickest, and the closer to the end along the slicing direction, the closer to the end. The thickness gradually decreases. On the other hand, since the lower surface of the second piezoelectric layer 7b is formed in a concave shape and the upper surface is flat, the thickness near the center O in the slicing direction is the thinnest, and the closer to the end along the slicing direction, The thickness gradually increases.

  The total thickness of the piezoelectric vibrator portion 7 is constant regardless of whether it is near the center O or at the end portion. That is, the first piezoelectric layer 7a having a lower surface formed in a planar shape and the upper surface formed in a convex shape, and the second piezoelectric layer 7b formed in an upper surface formed in a planar shape and the lower surface formed in a concave shape. Are stacked, the lower surface of the first piezoelectric layer 7a and the lower surface of the second piezoelectric layer 7b are parallel to each other, and the entire thickness of the piezoelectric vibrator portion 7 is constant.

  Here, the total thickness of the piezoelectric vibrator portion 7 is defined as a thickness T. In the second embodiment, the thickness at the center O in the slice direction of the first piezoelectric layer 7a is (T / 2), and the center in the slice direction of the second piezoelectric layer 7b. The thickness at O is also (T / 2). That is, at the center O in the slice direction, the thicknesses of the first piezoelectric layer 7a and the second piezoelectric layer 7b are equal.

  The first piezoelectric layer 7a is formed so that the thickness gradually decreases from (T / 2) toward the end in the slice direction from the center O in the slice direction. On the other hand, the second piezoelectric layer 7b is formed so that the thickness gradually increases from (T / 2) toward the end in the slice direction from the center O in the slice direction. The thickness of the piezoelectric vibrator portion 7 formed by laminating the first piezoelectric layer 7a and the second piezoelectric layer 7b is equal to the thickness T regardless of whether it is the center O or the end portion. It has become.

  As in the first embodiment described above, the thickness of the first piezoelectric layer 7a and the thickness of the second piezoelectric layer 7b at the center O in the slicing direction do not have to match completely. Even if the thickness of one of the piezoelectric layers is 80% to 120% of the thickness of the other piezoelectric layer, the action and effect of the ultrasonic probe according to this embodiment can be achieved. is there.

(Function)
According to the ultrasonic probe having the above-described configuration, the operations and effects described in the above (1) to (5) can be achieved, similarly to the ultrasonic probe according to the first embodiment.

  As in the first embodiment, the electric capacity at the center O of the piezoelectric vibrator portion 7 is four times as large as that of the piezoelectric body formed of one layer having the thickness T. Thereby, the impedance of the ultrasonic probe can be lowered, and the sensitivity of the ultrasonic probe can be improved.

  Similarly to the first embodiment, since the thickness of the first piezoelectric layer 7a and the thickness of the second piezoelectric layer 7b at the center O in the slicing direction are equal (T / 2), the center O The sensitivity is the highest. On the other hand, when the thickness of the piezoelectric layer on the radiation surface side of the ultrasonic wave, that is, the thickness of the second piezoelectric layer 7b increases, the sensitivity decreases. At this time, since the resonance frequency is lowered, the sensitivity is increased with respect to the low frequency. As described above, the resonance frequency of the piezoelectric body is expressed as a function of the reciprocal of the thickness of the piezoelectric body, and therefore the resonance frequency decreases as the thickness of the piezoelectric body increases.

  In the ultrasonic probe according to the second embodiment, in the portion (center O) where the thickness of the first piezoelectric layer 7a and the thickness of the second piezoelectric layer 7b are equal, the first piezoelectric layer 7a. Since the resonance point of the second piezoelectric layer 7b coincides with the resonance point of the second piezoelectric layer 7b, the sensitivity is highest, and in the other portions, the piezoelectric layer (second piezoelectric body) on the ultrasonic radiation surface side is provided. Since the resonance points of the vibration of the layer 7b) and the vibration of the other piezoelectric layer (second piezoelectric layer 7b) are shifted, they become loads on each other and the sensitivity is lowered.

  In the ultrasonic probe 1 according to the second embodiment, the thickness of the first piezoelectric layer 7a and the thickness of the second piezoelectric layer 7b are made equal at the center O in the slicing direction, so that By increasing the sensitivity and further decreasing the thickness of the first piezoelectric layer 7a and increasing the thickness of the second piezoelectric layer 7b as approaching the end in the slice direction, the end in the slice direction is increased. The sensitivity is gradually lowered as the area gets closer.

  As a result, the sensitivity at the center O in the slice direction becomes the highest, and the sensitivity gradually decreases as it approaches the end in the slice direction. In this way, the sound pressure distribution can be weighted in the slice direction.

  Here, the sensitivity of the ultrasonic probe according to the second embodiment will be described with reference to FIGS. 5B, 5C, and 5D. 5B, 5 </ b> C, and 5 </ b> D, the horizontal axis indicates the frequency [MHz] of ultrasonic waves that are transmitted and received, and the vertical axis indicates the intensity [dB] of ultrasonic waves that are transmitted and received. Here, PZT is used for both the first piezoelectric layer 7a and the second piezoelectric layer 7b, and the total thickness T of the piezoelectric vibrator section 7 is set to 480 [μm]. Therefore, at the center O in the slice direction, the thickness of the first piezoelectric layer 7a and the thickness of the second piezoelectric layer 7b are both 240 [μm].

  FIG. 5B is a graph showing frequency characteristics of the ultrasonic probe at the center O in the slice direction. That is, the graph of FIG. 5B shows frequency characteristics of a portion where the thickness of the first piezoelectric layer 7a is equal to the thickness of the second piezoelectric layer 7b. In FIG. 5B, a curve D represents the frequency characteristic of the ultrasonic probe at the center O in the slice direction.

  Further, the graph of FIG. 5C shows the frequency of the portion where the thickness of the first piezoelectric layer 7a is (T / 3) and the thickness of the second piezoelectric layer 7b is (2T / 3). The characteristics are shown. That is, the graph of FIG. 5B shows the frequency characteristics of the portion where the ratio of the thickness of the first piezoelectric layer 7a and the thickness of the second piezoelectric layer 7b is “1: 2”. . In FIG. 5C, a curve E represents the frequency characteristic of the ultrasonic probe in a portion where the thickness ratio is “1: 2”.

  Further, the graph of FIG. 5D shows the frequency of the portion where the thickness of the first piezoelectric layer 7a is (T / 6) and the thickness of the second piezoelectric layer 7b is (5T / 6). The characteristics are shown. That is, the graph of FIG. 5D shows the frequency characteristics of the portion where the ratio of the thickness of the first piezoelectric layer 7a and the thickness of the second piezoelectric layer 7b is “1: 5”. . In FIG. 5D, a curve F represents the frequency characteristic of the ultrasonic probe in a portion where the thickness ratio is “1: 5”.

  When curves D, E, and F shown in FIG. 5 are compared, the sensitivity is highest at the portion where the thickness of the first piezoelectric layer 7a is equal to the thickness of the second piezoelectric layer 7b, that is, the center O in the slice direction. It has become. The sensitivity of the portion where the thickness of the first piezoelectric layer 7a is reduced and the ratio between the thickness of the first piezoelectric layer 7a and the thickness of the second piezoelectric layer 7b is “1: 2”. Is lower than the sensitivity at the center O, as shown in FIG. FIG. 5C also shows the frequency characteristics at the center O for comparison. Note that the center frequency of the ultrasonic wave in the portion where the thickness ratio is “1: 2” is relatively lower than the center frequency of the ultrasonic wave at the center O. This is because the resonance frequency is lowered by increasing the thickness of the second piezoelectric layer 7b.

  Further, the sensitivity of the portion where the thickness of the first piezoelectric layer 7a is reduced and the ratio between the thickness of the first piezoelectric layer 7a and the thickness of the second piezoelectric layer 7b is “1: 5”. As shown in FIG. 5D, the sensitivity is further lowered. FIG. 5D also shows the frequency characteristics at the center O for comparison.

  As described above, it is possible to weight the sound field in the slice direction by changing the thickness of the piezoelectric layer in the slice direction. According to the configuration of the piezoelectric vibrator unit 7 according to this embodiment, the sensitivity at the center O in the slice direction becomes the highest, and the sensitivity becomes lower from the center O in the slice direction toward the end in the slice direction. Thus, since the transmitted / received sound field is positively weighted in the slice direction, the side lobe of the sound field in the slice direction is reduced, and a uniform sound field is formed in the depth direction.

  Similarly to the first embodiment, since the thickness of the first piezoelectric layer 7a and the second piezoelectric layer 7b is continuously changed in the slice direction, the ultrasonic sound pressure distribution is sliced. It is possible to change continuously in the direction. As a result, the grating lob can be reduced, and a sound field in the slice direction that is uniform and has few artifacts can be realized.

  Further, since it is not necessary to reduce the area of the electrode or form a groove in the slice direction in the piezoelectric body, it is possible to weight the sound pressure distribution in the slice direction without reducing the effective area of the element. . Since the effective area of the element does not decrease, impedance matching between the ultrasonic probe and the ultrasonic diagnostic apparatus main body is not deteriorated. As a result, the sound pressure distribution can be weighted in the slice direction without reducing the sensitivity.

  Moreover, since the upper surface and the lower surface of the piezoelectric vibrator portion are formed in a planar shape, it can be manufactured by the same manufacturing process as a general ultrasonic probe. Therefore, it is possible to achieve high sensitivity characteristics while ensuring the manufacturability of the ultrasonic probe, to uniformize the slice thickness of the ultrasonic image, and to reduce the side lobes in the slice direction.

[Modification]

  Next, various modifications of the present invention will be described with reference to FIG. FIG. 6 is a cross-sectional side view showing a schematic configuration of an ultrasonic probe according to a modification of the present invention.

  In the first and second embodiments described above, the piezoelectric vibrator unit is configured by laminating two piezoelectric layers. However, the present invention is not limited to two layers, and three or more piezoelectric layers. The piezoelectric vibrator portion may be configured by stacking layers.

  In the first and second embodiments described above, one surface of the first piezoelectric layer or the second piezoelectric layer is a concave surface or a convex surface, but the present invention is not limited to these. The thickness of the first piezoelectric layer and the thickness of the second piezoelectric layer are substantially equal at the center O in the slicing direction, and the thickness of one piezoelectric layer gradually increases from the center O toward the end. The thickness of the other piezoelectric layer may be increased so as to gradually decrease from the center O toward the end. For example, the shape of the interface between the first piezoelectric layer and the second piezoelectric layer may be a trapezoidal shape, a shape represented by a Gaussian function, or a shape represented by a Hamming function. Hereinafter, these modifications will be described.

(Modification 1)
First, as Modification 1, an ultrasonic probe in which three piezoelectric layers are stacked will be described with reference to FIG. As shown in FIG. 6A, the piezoelectric vibrator unit according to the first modification includes a first piezoelectric layer 7a, a second piezoelectric layer 7b, and a third piezoelectric layer 8. Has been. Here, the first piezoelectric layer 7a and the second piezoelectric layer 7b have the same configuration as the piezoelectric vibrator section in the second embodiment. That is, the upper surface of the first piezoelectric layer 7a is a convex surface, and the lower surface of the second piezoelectric layer 7b is a concave surface. Furthermore, in this modification, a third piezoelectric layer 8 is provided. The upper surface and the lower surface of the third piezoelectric layer 8 have a flat surface, and are disposed below the first piezoelectric layer 7a via the electrode 6a. The thickness of the third piezoelectric layer 8 is equal to the thickness at the center O in the slicing direction of the first piezoelectric layer 7a and the second piezoelectric layer 7b. That is, at the center O in the slice direction, the thickness of the first piezoelectric layer 7a is (T / 3), and the thickness of the second piezoelectric layer 7b is (T / 3). Yes. The thickness of the third piezoelectric layer 8 is (T / 3) in any part.

  Electrodes 6c and 6d are connected to the upper and lower surfaces of the piezoelectric vibrator portion, and an electrode 6b is connected between the first piezoelectric layer 7a and the second piezoelectric layer 7b. An electrode 6 a is connected between the first piezoelectric layer 7 a and the third piezoelectric layer 8. The electrodes 6a and 6c are connected to GND, and a voltage is applied to the electrodes 6b and 6d.

Thus, at the center O in the slicing direction, all the piezoelectric layers have the same thickness. As a result, the electric capacity at the center O in the slicing direction is 9 (= 3 ² ) times the electric capacity formed of a single-layer piezoelectric material having a thickness T. Thereby, the impedance of the ultrasonic probe can be lowered, and the sensitivity of the ultrasonic probe can be improved.

  Further, by making the thickness of the first piezoelectric layer 7a equal to the thickness of the second piezoelectric layer 7b at the center O in the slicing direction, the sensitivity at the center O is maximized, and the edge in the slicing direction is further increased. The sensitivity of the first piezoelectric layer 7a is decreased as it approaches the portion and the thickness of the second piezoelectric layer 7b is increased so that the sensitivity is gradually lowered toward the end in the slice direction. . Thereby, since the sound field in the slice direction becomes positive weighting, the side lobe of the sound field in the slice direction is reduced, and a uniform sound field is formed in the depth direction.

  Further, similarly to the above-described embodiment, it is possible to reduce the grating lob and realize a sound field in the slice direction that is uniform and has few artifacts. Furthermore, since the effective area of the element does not decrease, the sound pressure distribution can be weighted in the slice direction without reducing sensitivity. In addition, it is possible to achieve high sensitivity characteristics while ensuring the manufacturability of the ultrasonic probe, to make the slice thickness of the ultrasonic image uniform, and to reduce side lobes.

  As in the first and second embodiments described above, the thickness of the piezoelectric layer at the center O in the slice direction does not completely match, and the thickness of one of the piezoelectric layers is different from that of the other piezoelectric body. Even when the thickness is 80% to 120% of the thickness of the layer, the action and effect of the ultrasonic probe according to this modification can be exhibited.

(Modification 2)
Next, an ultrasonic probe whose surface of the piezoelectric layer is not concave or convex will be described with reference to FIGS.

  As shown in FIG. 6B, in the vicinity of the center O in the slicing direction, the upper surface of the first piezoelectric layer 9a (the surface in contact with the second piezoelectric layer 9b) is formed in a planar shape. The thickness of the first piezoelectric layer 9a gradually increases linearly as it approaches the end in the slice direction. On the other hand, in the vicinity of the center O in the slicing direction, the lower surface of the second piezoelectric layer 9b (the surface in contact with the first piezoelectric layer 9a) is also formed in a planar shape. The thickness of the second piezoelectric layer 9b gradually decreases linearly as it approaches the end in the slice direction.

  Moreover, the upper surface and the lower surface of the piezoelectric vibrator portion 9 are planar, and the entire thickness is the same thickness T regardless of whether it is the center O or the end portion. The portions of the first piezoelectric layer 9a and the second piezoelectric layer 9b formed in a planar shape have the same thickness (T / 2).

Even in the ultrasonic probe having the above-described configuration, the electric capacity at the center O of the piezoelectric vibrator unit 9 is 4 (= 2 ² ) times the electric capacity of the piezoelectric body formed of one layer having the thickness T. Thereby, the impedance of the ultrasonic probe can be lowered, and the sensitivity of the ultrasonic probe can be improved.

  In addition, in the surface where the first piezoelectric layer 9a and the second piezoelectric layer 9b are in contact with each other and formed in a planar shape, the thickness of the first piezoelectric layer 9a and the second piezoelectric layer 9a. Since the thickness of the body layer 9b is equal (T / 2), the sensitivity at that portion is the highest. On the other hand, the closer to the end in the slice direction, the first piezoelectric layer 9a is linearly thicker and the second piezoelectric layer 9b is linearly thinner. The sensitivity gradually decreases as the area gets closer. Thereby, since the sound field in the slice direction becomes positive weighting, the side lobe of the sound field in the slice direction is reduced, and a uniform sound field is formed in the depth direction.

  Further, like the piezoelectric vibrator unit 10 shown in FIG. 6C, the interface between the first piezoelectric layer 10a and the second piezoelectric layer 10b is expressed by a shape expressed by a Gaussian function or a Hamming function. You may make it a shape. Even in such a shape, in the vicinity of the center O in the slicing direction, the sensitivity can be improved by making the thickness of the first piezoelectric layer 10a and the thickness of the second piezoelectric layer 10b substantially equal. It becomes possible. Further, as the end of the slice direction is approached, the thickness of the first piezoelectric layer 10a is gradually increased, and the thickness of the second piezoelectric layer 10b is gradually decreased, whereby the center O in the slice direction is increased. The sensitivity in the vicinity can be maximized, and the sensitivity can be gradually lowered as the end of the slice direction is approached. This makes it possible to weight the sound pressure distribution in the slice direction, reduce the side lobe of the sound field in the slice direction, and form a uniform sound field in the depth direction.

  The shape of the interface between the first piezoelectric layer and the second piezoelectric layer may be other than the above shape. The thickness in the vicinity of the center O in the slicing direction is substantially equal, and as the end in the slicing direction is approached, the thickness of one piezoelectric layer gradually increases and the thickness of the other piezoelectric layer decreases. If it has, it will become possible to show the operation and effect of the present invention.

[Third Embodiment]
Next, an ultrasonic diagnostic apparatus including the ultrasonic probe according to the first embodiment, the second embodiment, or the modification described above will be described with reference to FIG. FIG. 7 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus according to the third embodiment of the present invention.

  The ultrasonic diagnostic apparatus 20 mainly includes an ultrasonic probe 1, a transmission / reception unit 21, a signal processing unit 22, a DSC 23, an image processing unit 24, a display unit 25, and a control unit 26. This ultrasonic diagnostic apparatus 20 is characterized by the ultrasonic probe 1, and other transmitting / receiving units 21 and the like are known.

  As the ultrasonic probe 1, the ultrasonic probe 1 according to the first embodiment described above is used. Moreover, you may use the ultrasonic probe which concerns on 2nd Embodiment, or the ultrasonic probe which concerns on a modification. The transmission / reception unit 21 includes a transmission unit and a reception unit. The transmission / reception unit 21 supplies an electrical signal to the ultrasonic probe 1 to generate an ultrasonic wave, and receives an echo signal received by the ultrasonic probe 1. The transmission / reception unit 21 corresponds to “transmission / reception means” of the present invention.

  The signal processing unit 22 includes a known B-mode processing circuit, Doppler processing circuit, or color mode processing circuit. The data output from the transmission / reception unit 21 is subjected to predetermined processing in any processing circuit. The B-mode processing circuit visualizes echo amplitude information and generates B-mode ultrasonic raster data from the echo signal. The Doppler processing circuit extracts the Doppler shift frequency component and further performs FFT processing or the like to generate data having blood flow information. The color mode processing circuit visualizes the moving blood flow information and generates color ultrasonic raster data. Blood flow information includes information such as speed, dispersion, and power, and blood flow information is obtained as binarized information.

  DSC 23 (Digital Scan Converter) converts ultrasonic raster data into data represented by orthogonal coordinates (scan conversion process) in order to obtain an image represented by an orthogonal coordinate system. For example, when scan conversion processing is performed on data output from the B-mode processing circuit, tomographic image data representing the tissue shape of the subject as two-dimensional information is generated. The image processing unit 24 performs various image processing. For example, voxel data is generated from tomographic image data, and volume rendering processing is further performed to generate three-dimensional image data. The signal processing unit 22, the DSC 23, and the image processing unit 24 correspond to the “image generating unit” of the present invention.

  The display unit 25 includes a monitor such as a liquid crystal display, and displays a tomographic image, a three-dimensional image, and the like. The control unit 26 includes a CPU, and controls each processing unit by executing a control program, an image generation program, and the like stored in a storage unit (not shown). The storage unit includes a memory such as a ROM and a hard disk, and stores image data, various setting conditions, a program, and the like. In addition, a pointing device such as a joystick, an operation unit (not shown) such as a switch or a TCS (Touch Command Screen) is provided, and various settings relating to ultrasonic transmission / reception conditions are input by the operator.

  According to the ultrasonic diagnostic apparatus 20 including the ultrasonic probe according to the embodiment of the present invention or the ultrasonic probe according to the modification, it is possible to reduce the side lobe of the sound field in the slice direction, and further in the depth direction. Therefore, an ultrasonic image with a uniform slice thickness can be obtained.

1 is a perspective view showing a schematic configuration of an ultrasonic probe according to a first embodiment of the present invention. 1 is a cross-sectional side view showing a schematic configuration of an ultrasonic probe according to a first embodiment of the present invention. It is a graph which shows the frequency characteristic of the ultrasonic probe which concerns on 1st Embodiment of this invention. It is a sound field distribution formed when transmitting or receiving ultrasonic waves by the ultrasonic probe according to the first embodiment of the present invention. It is a figure which shows schematic structure and frequency characteristic of the piezoelectric vibrator part which concerns on 2nd Embodiment of this invention. It is a cross-sectional side view which shows schematic structure of the ultrasonic probe which concerns on the modification of this invention. It is a block diagram which shows the structure of the ultrasonic diagnosing device which concerns on 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic probe 2 Back material 3, 7, 9, 10 Piezoelectric vibrator part 3a, 7a, 9a, 10a 1st piezoelectric layer 3b, 7b, 9b, 10b 2nd piezoelectric layer 4 Acoustic matching layer 5 Acoustic Lens 6a, 6b, 6c, 6d Electrode 8 Third piezoelectric layer

Claims (10)

Electrodes are provided on the upper surface and the lower surface, transmit an ultrasonic wave by applying a voltage, and an ultrasonic probe including a piezoelectric vibrator unit that receives an ultrasonic wave,
In the piezoelectric vibrator unit, a plurality of piezoelectric layers in which a plurality of piezoelectric bodies are arranged in a scanning direction are stacked via electrodes,
The ultrasonic probe according to claim 1, wherein the thickness of at least two piezoelectric layers in contact with each other among the plurality of piezoelectric layers is gradually changed in a slice direction perpendicular to the scanning direction.   2. The ultrasonic probe according to claim 1, wherein the at least two piezoelectric layers in contact with each other have substantially the same thickness at substantially the center in the slice direction orthogonal to the scanning direction.   Of the at least two piezoelectric layers that are in contact with each other, the thickness of one piezoelectric layer at the approximate center in the slice direction perpendicular to the scanning direction is in the slice direction perpendicular to the scanning direction of the other piezoelectric layer. The ultrasonic probe according to claim 1, wherein the thickness is approximately 80 to 120% of the thickness at a substantially center.   Of the at least two piezoelectric layers that are in contact with each other, one piezoelectric layer gradually increases in thickness as it approaches the end in the slice direction perpendicular to the scanning direction, and the other piezoelectric layer The ultrasonic probe according to any one of claims 1 to 3, wherein the thickness gradually decreases as the end in the slice direction orthogonal to the scanning direction is approached.   5. The ultrasonic wave according to claim 1, wherein the at least two piezoelectric layers in contact with each other have a curved surface in contact with the other piezoelectric layer. 6. probe.   Of the at least two piezoelectric layers in contact with each other, one surface of one piezoelectric layer is formed in a convex shape, and one surface of the other piezoelectric layer is formed in a concave shape, and formed in the convex shape. The ultrasonic probe according to any one of claims 1 to 4, wherein the formed surface and the concave surface are fitted.   The ultrasonic probe according to claim 1, wherein an upper surface and a lower surface of the piezoelectric vibrator portion are formed in a planar shape. A piezoelectric vibrator unit in which a plurality of piezoelectric layers in which a plurality of piezoelectric bodies are arranged in a scanning direction are stacked via electrodes, and at least two of the plurality of piezoelectric layers are in contact with each other; An ultrasonic probe whose thickness is gradually changed in a slice direction perpendicular to the scanning direction;
Transmitting and receiving means for transmitting and receiving ultrasonic waves to and from the subject by the ultrasonic probe;
Image generating means for generating an ultrasonic image based on a reflected wave from the subject received by the transmitting / receiving means;
An ultrasonic diagnostic apparatus comprising:   Of the at least two piezoelectric layers that are in contact with each other, the thickness of one piezoelectric layer at the approximate center in the slice direction perpendicular to the scanning direction is in the slice direction perpendicular to the scanning direction of the other piezoelectric layer. The ultrasonic diagnostic apparatus according to claim 8, wherein the thickness is approximately 80 to 120% of the thickness at a substantially center.   Of the at least two piezoelectric layers that are in contact with each other, one piezoelectric layer gradually increases in thickness as it approaches the end in the slice direction perpendicular to the scanning direction, and the other piezoelectric layer 10. The ultrasonic diagnostic apparatus according to claim 8, wherein the thickness gradually decreases as approaching an end in the slice direction orthogonal to the scanning direction. 11.

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