JP2014107853A - Ultrasonic probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic probe capable of making the most of a driving voltage of a system in a main unit of an ultrasonic image diagnosis apparatus, and obtaining high sensitivity even with high center frequency characteristics.SOLUTION: An ultrasonic probe 2 comprises: a piezoelectric layer 24; and a dematching layer 23. The dematching layer 23, having acoustic impedance higher than that of the piezoelectric layer 24, is arranged at a surface of the piezoelectric layer 24, opposite an ultrasonic-radiating surface thereof. The ultrasonic probe 2 transmits and receives ultrasonic waves by nλ/4 resonance (n is an odd number). The piezoelectric layer 24 is formed of a piezoelectric material which has a coercive electric field of 1.0MV/m or more at 25°C.

Description

  The present invention relates to an ultrasonic probe.

  Conventionally, in an ultrasonic probe, a piezoelectric material is finely processed in order to improve directivity and reduce crosstalk. On the other hand, in transmission of transmission / reception signals related to transmission / reception of ultrasonic waves between the ultrasonic diagnostic imaging device main body to which the ultrasonic probe is connected and the ultrasonic probe, an element for matching electrical impedance is used. It is desired to increase the per-capacitance. Therefore, it is desired that the piezoelectric material has a high dielectric constant even if it is a microelement, and a piezoelectric material having a high dielectric constant has been used to realize this.

  On the other hand, in order to improve the value of ultrasonic image diagnosis, it is important to improve the transmission / reception sensitivity of the piezoelectric material. As a method of improving the transmission sensitivity, a dematching (reflection) layer having an acoustic impedance higher than the acoustic impedance of the piezoelectric material is arranged on the back side of the piezoelectric material, and the ultrasonic wave radiated to the back side of the piezoelectric material is forward. Some of them use an ultrasonic probe that reflects the light (for example, Patent Documents 1 to 3).

U.S. Patent No. 7621028 JP 2009-213137 A JP 2005-286701 A

  In the techniques disclosed in Patent Documents 1 to 3, since a λ / 4 resonance occurs in the piezoelectric material instead of a normal λ / 2 resonance, the thickness of the piezoelectric material is set to λ / It is necessary to reduce to about half of the two resonances. As a result, the voltage that can be applied to the piezoelectric body, which is determined by the thickness of the piezoelectric material and the coercive electric field, decreases. However, in the transmission and reception of ultrasonic waves in a low frequency band as shown in Patent Document 3, Since the applicable voltage is higher than the maximum applied voltage output from the ultrasonic diagnostic imaging apparatus main body, the coercive electric field of the piezoelectric material did not become a problem.

  In recent years, in order to achieve higher performance, in addition to high sensitivity, it has been desired to realize an ultrasonic probe with a high center frequency (for example, 10 MHz or higher). When the above-described dematching layer is applied, the resonance frequency increases, so that the piezoelectric material needs to be designed to be thinner than before. As a result, the voltage that can be applied to the piezoelectric material that is restricted by the coercive electric field antagonizes the maximum applied voltage that is output from the apparatus main body, and the coercive electric field affects the performance of the ultrasonic diagnostic imaging apparatus. It will be.

  An object of the present invention is to provide an ultrasonic probe that can make maximum use of the drive voltage of the system in the ultrasonic diagnostic imaging apparatus and can achieve high sensitivity even with high center frequency characteristics. is there.

In order to solve the above-described problems, in the invention described in claim 1, a reflective layer having an acoustic impedance higher than the acoustic impedance of the piezoelectric layer is disposed on the surface of the piezoelectric layer opposite to the ultrasonic radiation surface. , Nλ / 4 (where n is an odd number) resonance in an ultrasonic probe that transmits and receives ultrasonic waves
The coercive electric field of the piezoelectric material constituting the piezoelectric layer is 1.0 MV / m or more at 25 ° C.

The invention according to claim 2 is the ultrasonic probe according to claim 1,
The coercive electric field of the piezoelectric material is 0.9 MV / m or more at 60 ° C.

The invention according to claim 3 is the ultrasonic probe according to claim 1 or 2,
The piezoelectric material includes an acceptor additive containing a divalent or trivalent element that replaces the B site.

The invention according to claim 4 is the ultrasonic probe according to claim 3,
The element is at least one of Fe ³⁺ , Co ²⁺ and Mn ²⁺ .

The invention according to claim 5 is the ultrasonic probe according to any one of claims 1 to 4,
The dielectric constant of the piezoelectric material is 1800 or more.

Invention of Claim 6 in the ultrasonic probe as described in any one of Claims 1-5,
The Curie temperature of the piezoelectric material is 250 ° C. or higher and 350 ° C. or lower.

The invention according to claim 7 is the ultrasonic probe according to any one of claims 1 to 6,
The center frequency of the output ultrasonic wave is 7 MHz or more.

  ADVANTAGE OF THE INVENTION According to this invention, the drive voltage of the system in an ultrasonic diagnostic imaging apparatus main body can be utilized to the maximum, and the ultrasonic probe which has a high sensitivity characteristic at a high frequency can be provided.

1 is a perspective view showing an external configuration of an ultrasound diagnostic imaging apparatus according to the present embodiment. It is a block diagram which shows the functional structure of a diagnostic apparatus main body. It is sectional drawing which shows the structure of an ultrasonic transducer | vibrator typically.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples. In addition, in the following description, what has the same function and structure attaches | subjects the same code | symbol, and abbreviate | omits the description.

  As shown in FIG. 1, the ultrasonic diagnostic imaging apparatus 1 according to the present embodiment includes an ultrasonic probe 2 and a diagnostic apparatus body 4, which are connected via a cable 3. The ultrasonic probe 2 transmits ultrasonic waves (transmission ultrasonic waves) to a subject such as a living body (not shown) and receives ultrasonic waves (reflected ultrasonic waves) reflected by the subject. In the present embodiment, the ultrasonic probe 2 is configured by arranging a plurality of ultrasonic transducers 21 (see FIG. 2) in an array. The diagnostic device main body 4 transmits an ultrasonic signal to the ultrasonic probe 2 by transmitting a transmission signal of an electrical signal via the cable 3 and is converted from the ultrasonic wave received by the ultrasonic probe 2. Based on the received signal, the internal state in the subject is imaged as a tomographic image.

  The diagnostic apparatus body 4 includes an operation input unit 11 and a display unit 16 at the upper part. The operation input unit 11 includes switches, buttons, a trackball, a mouse, a keyboard, and the like for performing various setting operations, and can input a command for instructing diagnosis and data such as personal information of a subject. . The display unit 16 displays a support image for an operation by the operation input unit 11, an ultrasonic image created based on a received signal, and the like. In addition, a holder 7 for holding the ultrasonic probe 2 when not in use is provided at appropriate positions of the operation input unit 11 and the diagnostic apparatus main body 4.

  Next, the functional configuration of the diagnostic apparatus body 4 will be described with reference to FIG. In addition to the operation input unit 11 and the display unit 16 described above, the diagnostic device main body 4 includes, for example, a transmission unit 12, a reception unit 13, a signal processing unit 14, an image processing unit 15, a control unit 17, and a voltage control unit 18. Yes.

The transmission unit 12 is a circuit that generates a transmission pulse as a transmission signal in the ultrasound probe 2 under the control of the control unit 17. The transmission unit 12 outputs a transmission pulse to the voltage control unit 18 via the control unit 17. The amplitude of the transmission pulse is amplified in the voltage control unit 18 and is transmitted to the ultrasonic probe 2.
The voltage control unit 18 is a system that satisfies the following formula (1) when the coercive electric field of the piezoelectric layer 24 described later at t ° C. is Ec _t (MV / m) and the thickness of the piezoelectric layer 24 is d (μm). The diagnostic device main body 4 is driven by the maximum driveable voltage Vs.
| Vs | = Ec _t × d × α (1)
In the above formula (1), α satisfies 0 <α <1, and when t = 25 (that is, at 25 ° C.), 0.5 ≦ α ≦ 0.9 is satisfied. Thereby, since the drive voltage of the system in the diagnostic apparatus main body 4 can be utilized to the maximum, high sensitivity characteristics can be used. Here, with respect to α, it is more preferable that 0.7 ≦ α ≦ 0.9 because the withstand voltage characteristic can be improved. Further, when the relationship of Ec ₂₅ × 0.9 ≦ Ec ₆₀ is satisfied, it is preferable because long-term driving stability is further improved.
Note that the maximum driveable voltage of the system is not limited to that described above, and can be set as appropriate.
The ultrasonic probe 2 outputs a transmission ultrasonic wave corresponding to the received transmission pulse. At this time, the transmission unit 12 forms a transmission beam so that transmission ultrasonic waves from the respective ultrasonic transducers 21 converge at a predetermined focal position. Note that the above-described transmission ultrasonic wave may be composed of a plurality of encoded pulses that are expanded in the time axis direction.

  The receiving unit 13 is a circuit that receives a reception signal of an electrical signal from the ultrasound probe 2 via the cable 3 under the control of the control unit 17, and outputs the reception signal to the signal processing unit 14.

  The signal processing unit 14 detects reflected ultrasonic waves from the output of the receiving unit 13.

  The image processing unit 15 is a circuit that generates image data (ultrasound image data) of the internal state of the subject based on the received signal processed by the signal processing unit 14 under the control of the control unit 17.

  The display unit 16 is a device that displays an ultrasonic image of the subject based on the ultrasonic image data generated by the image processing unit 15 under the control of the control unit 17. The display unit 16 is realized by a display device such as a CRT (Cathode-Ray Tube) display, an LCD (Liquid Crystal Display), an organic EL (Electronic Luminescence) display, and a plasma display, or a printing device such as a printer.

  The control unit 17 includes a microprocessor, a storage element, and peripheral circuits thereof. The operation input unit 11, the transmission unit 12, the voltage control unit 18, the reception unit 13, the signal processing unit 14, the image processing unit 15, and the like. This is a circuit that performs overall control of the ultrasonic diagnostic imaging apparatus 1 by controlling the display unit 16 according to the function.

  As shown in FIG. 3, the ultrasonic transducer 21 is formed by stacking, for example, a backing (back) layer 22, a dematching (reflection) layer 23, a piezoelectric layer 24, and an acoustic matching layer 25 from below in the front view. It is configured. If necessary, an acoustic lens may be stacked above the acoustic matching layer 25.

  The backing layer 22 is an ultrasonic absorber that supports the dematching layer 23 and can absorb unnecessary ultrasonic waves. That is, the backing layer 22 is provided on the opposite side of the piezoelectric layer 24 from the direction in which ultrasonic waves are transmitted to and received from the subject, and is generated from the opposite side of the subject direction of the piezoelectric layer 24 and reaches the backing layer 22. Absorbs ultrasound. In the present embodiment, the backing layer 22 may not be provided.

  As the backing material constituting the backing layer 22, vinyl chloride, polyvinyl butyral (PVB), ABS resin, polyurethane (PUR), polyvinyl alcohol (PVAL), polyethylene (PE), polypropylene (PP), polyacetal (POM), polyethylene Thermoplastic resin such as terephthalate (PETP), fluororesin (PTFE), polyethylene glycol, polyethylene terephthalate-polyethylene glycol copolymer, natural rubber, ferrite rubber, epoxy resin, powder of tungsten oxide, titanium oxide, ferrite, etc. on silicone resin It is possible to use a composite material that has been press-molded by adding, and further a material that is pulverized and then mixed with the above-described thermoplastic resin or epoxy resin and cured. In order to adjust the acoustic impedance, an inorganic material such as Macor glass or a porous material having voids can be used.

  A preferable backing material is made of a rubber-based composite material and / or an epoxy resin composite material, and the shape thereof is appropriately selected according to the shape of the piezoelectric layer 24 and the ultrasonic probe 2 including the piezoelectric layer 24. be able to.

  The dematching layer 23 is made of a material having an acoustic impedance larger than that of the piezoelectric layer 24, and reflects ultrasonic waves output to the piezoelectric layer 24 on the side opposite to the direction of the subject. As a material applied to the dematching layer 23, any material such as tungsten or tantalum having a large difference in acoustic impedance between the piezoelectric layer 24 and the dematching layer 23 can be applied. Is preferred. Further, a mixture of tungsten carbide and another material may be used. In the present embodiment, by providing the dematching layer 23, it is possible to further improve sensitivity to ultrasonic wave transmission / reception in the piezoelectric layer 24.

The piezoelectric layer 24 is configured by a piezoelectric material having a plurality of layers or a single layer. As a material of the piezoelectric body, conventionally used quartz, piezoelectric ceramics PZT, PZLT, piezoelectric single crystals PZN-PT, PMN-PT, LiNbO ₃ , LiTaO ₃ , KNbO ₃ , ZnO, AlN, etc. In addition to inorganic piezoelectric materials, polyvinylidene fluoride and polyvinylidene fluoride copolymers, polycyanide vinylidene and cyanide vinylidene copolymers, odd nylons such as nylon 9 and nylon 11, aromatic nylon, alicyclic nylon, poly Organic piezoelectric materials such as polyhydroxycarboxylic acids such as lactic acid and polyhydroxybutyrate, cellulose derivatives, and polyurea are listed. Furthermore, composite materials using inorganic piezoelectric materials and organic piezoelectric materials, and inorganic piezoelectric materials and organic polymer materials in combination are also included.

  In the present embodiment, the piezoelectric layer 24 is configured using a material having a high coercive electric field obtained by adding a predetermined additive to the above-described inorganic piezoelectric material or organic piezoelectric material. In a ferroelectric piezoelectric material such as PZT, once an electric field is applied, it does not return to its original state even when the electric field is removed, and residual polarization Pr remains. In order to cancel this remanent polarization, an electric field in the opposite direction is required, and the electric field necessary for this is called a coercive electric field Ec. The coercive electric field Ec correlates with the ease of movement of the domain wall in the crystal grains, and the ease of movement depends on the type of constituent element of the piezoelectric material, that is, the additive.

There are two types of additives. One is a trivalent element (La ³⁺ , Nd ³⁺ ) that replaces the A site of perovskite ABO ₃ such as La ₂ O ₃ , Nd ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , WO _3, etc. These are pentavalent and hexavalent elements (Nb ⁵⁺ , Ta ⁵⁺ , W ⁶⁺ ) that replace the B site, and these make a hole in the A site inside the crystal and are called a donor additive. The formation of the holes facilitates the movement of the domain wall in the crystal grains, and the coercive electric field is reduced. These are called soft materials.

On the other hand, the other is a divalent or trivalent element (Fe ³⁺ , Co ²⁺ , Mn ²⁺ ) that replaces the B site such as Fe ₂ O ₃ , CoO, MnO, and oxygen vacancies are created by the additive, Called an acceptor additive. This hole makes it difficult for the domain wall to move and raises the coercive electric field. These are called hard materials. Therefore, the coercive electric field can be controlled by the kind and amount of the additive. In the present embodiment, the piezoelectric layer 24 is configured using a piezoelectric material to which such a hard material is added.
Note that the coercive electric field of a single crystal solid solution can be controlled by the same method.

  The piezoelectric material applied in this embodiment has a coercive electric field of 1.0 MV / m or more at 25 ° C. When the dematching layer 23 is used, the thickness of the piezoelectric body is halved and the withstand voltage characteristic is deteriorated. According to the present embodiment, it is possible to drive at a high voltage, so that the drive voltage of the system in the diagnostic apparatus main body can be utilized to the maximum, and the ultrasonic probe 2 having high center frequency characteristics can be used. High sensitivity can be realized. At this time, it is preferable that the dielectric constant of the piezoelectric layer 24 is 1800 or more because a coercive electric field can be obtained stably. The present embodiment is particularly effective when applied to the ultrasonic probe 2 whose output center frequency is 7 MHz or more.

  The piezoelectric body generates heat when driven for a long time. Conventional piezoelectric materials have a low coercive field and therefore a low Curie temperature. For this reason, the thermal stability is low, it is difficult to maintain a certain characteristic in long-time use, and it is difficult to maintain the diagnostic value that was initially possessed. The piezoelectric material applied in the present embodiment further has a coercive electric field of 0.9 MV / m or more at 60 ° C. Therefore, even when used for a long time, the change in the piezoelectric characteristics can be reduced, and the operation of the ultrasonic probe 2 can be stabilized. In addition, the Curie temperature of the piezoelectric material applied in the present embodiment is preferably 250 ° C. or higher and 350 ° C. or lower, but is limited to this as long as a sufficiently high coercive electric field and a necessary and sufficient dielectric constant can be obtained. Not.

  As the above-described piezoelectric material, a commercially available piezoelectric material can be used. For example, C-6, C-6H, C-62, C-63, C-64, C manufactured by Fuji Ceramic Co., Ltd. -601, C-7. C-8, C-82, C-83H, C-9, C-91, C-91H, C-92H, or L-1A, L-6A, L-201F, L-11 manufactured by Teica, L-9, L-155N, L-145N, etc. are mentioned. Organic piezoelectric materials include PVDF film manufactured by Tokyo Sensor Co., Ltd., poly (vinylidene fluoride-co-trifluoroethylene) film manufactured by Kureha, and poly (vinylidene fluoride-co-hexafluoro) manufactured by Aldrich as a reagent. Propylene) and the like.

  In the present embodiment, the above-described piezoelectric material added with a hard material is used. However, if a sufficient coercive electric field can be obtained, a material without an additive is used. You may make it do.

  The layer thickness per layer of the piezoelectric body depends on the set center frequency (wavelength λ), but is preferably in the range of 5 to 200 μm in consideration of workability.

  As a method for forming a piezoelectric layer made of an organic piezoelectric material, a method of forming a film by coating or a method of forming a film by vapor deposition (vapor deposition polymerization) is preferable. Examples of the coating method include spin coating, solvent casting, melt casting, melt pressing, roll coating, flow coating, printing, dip coating, and bar coating. Further, as a vapor deposition (vapor deposition polymerization) method, a film can be obtained by evaporating a monomer from a single or plural evaporation sources at a degree of vacuum of about several hundred Pa or less, and depositing and reacting on the substrate. . If necessary, the temperature of the substrate is adjusted as appropriate.

  The electrode layer is formed on the organic piezoelectric film produced as described above by first forming a base metal such as titanium (Ti) or chromium (Cr) to a thickness of 0.02 to 1.0 μm by sputtering. Subsequently, a metal material mainly composed of metal elements or a metal material composed of an alloy thereof is combined with a part of insulating material as necessary, and formed to a thickness of 1 to 10 μm by an appropriate method such as sputtering. It is done by doing. Thereafter, a polarization process is performed. As the metal material, gold (Au), platinum (Pt), silver (Ag), palladium (Pd), copper (Cu), nickel (Ni), tin (Sn), or the like is used. In addition to the sputtering method described above, the electrode can also be formed by applying a conductive paste obtained by mixing fine metal powder and low-melting glass by screen printing, dipping method, thermal spraying method, or the like.

  In the present embodiment, the piezoelectric layer 24 resonates in the nλ / 4 (n is an odd number) resonance mode and outputs a transmission ultrasonic wave when a transmission signal is given from the voltage control unit 18 due to the above-described configuration.

  As described above, in this embodiment, by using a piezoelectric material having a high coercive electric field together with the dematching layer, sufficient withstand voltage characteristics and high sensitivity can be realized. In addition, by applying a piezoelectric material having a high coercive electric field, deterioration over time can be reduced, so that the product life can be extended. In addition, by applying a piezoelectric material having a high coercive electric field, the influence of the piezoelectric characteristics due to the environment can be reduced.

  An FPC (Flexible Printed Circuits) 27 is sandwiched between the backing layer 22 and the dematching layer 23, and a transmission signal from the voltage control unit 18 is given to the piezoelectric layer 24 by the FPC 27. The reception signal generated by the piezoelectric layer 24 is given to the reception unit 13 by the FPC 27.

  The acoustic matching layer 25 matches the acoustic impedance between the piezoelectric layer 24 and the subject and suppresses reflection at the boundary surface. The acoustic matching layer 25 is disposed on the subject side of the piezoelectric layer 24 in the direction in which ultrasonic waves are transmitted and received. The acoustic matching layer 25 has a substantially intermediate acoustic impedance between the piezoelectric layer 24 and the subject.

  Materials used for the acoustic matching layer 25 include aluminum, aluminum alloy (for example, AL-Mg alloy), magnesium alloy, macor glass, glass, fused quartz, copper graphite, PE (polyethylene), PP (polypropylene), and PC (polycarbonate). ), ABC resin, ABS resin, AAS resin, AES resin, nylon (PA6, PA6-6), PPO (polyphenylene oxide), PPS (polyphenylene sulfide: glass fiber can be included), PPE (polyphenylene ether), PEEK (poly) Ether ether ketone), PAI (polyamideimide), PETP (polyethylene terephthalate), epoxy resin, urethane resin, and the like can be used. Preferably, a thermosetting resin such as an epoxy resin is molded with zinc oxide, titanium oxide, silica, alumina, bengara, ferrite, tungsten oxide, yttrium oxide, barium sulfate, tungsten, molybdenum, etc. as a filler. Applicable.

  The acoustic matching layer 25 may be a single layer or a plurality of layers, but is preferably two or more layers, more preferably four or more layers. The layer thickness of the acoustic matching layer 25 is preferably determined to be λ / 4 where λ is the wavelength of the ultrasonic wave. The thickness of such an acoustic matching layer depends on the center frequency, but generally a thickness in the range of 20 to 500 μm is used. The acoustic matching layer 25 is formed by multilayer coating in the thickness direction, and the acoustic impedance is matched by weighting the acoustic impedance in the thickness direction with different material configurations in each layer. The weighting direction of the acoustic impedance in the acoustic matching layer 25 is not limited to the thickness direction and may be a horizontal direction.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, of course, this invention is not limited to these Examples.

  First, as Examples 1 to 3, ultrasonic probes were manufactured as follows.

  First, an acoustic matching layer was prepared by laminating six layers of acoustic matching materials. The acoustic matching material of each layer was prepared so as to satisfy the following conditions by using a kneaded cured product of epoxy resin and ferrite or silicone resin fine powder. That is, the acoustic matching material of the uppermost layer, which is the outermost layer on the acoustic radiation surface side, has an acoustic impedance of 1.5 MRayls and a thickness of 20 μm, and the second layer of the acoustic matching material has an acoustic impedance of 2.0 MRayls and a thickness of 30 μm. The third layer acoustic matching material has an acoustic impedance of 3.0 MRayls and a thickness of 30 μm, the fourth layer acoustic matching material has an acoustic impedance of 6.0 MRayls and a thickness of 40 μm, and the fifth layer of the acoustic matching material. Has an acoustic impedance of 9.0 MRayls and a thickness of 50 μm, and the lowermost acoustic matching material has an acoustic impedance of 14.0 MRays and a thickness of 60 μm. The acoustic matching materials of the respective layers thus prepared are laminated in the order described above, and bonded by heat curing with an epoxy adhesive under a pressure condition of 2.94 MPa, then a size of 5.6 mm × 42.5 mm Then, it was molded into an acoustic matching layer.

  Next, using the piezoelectric material described in the column of Example 1 in Table 1 below, this was processed into a size of 5.6 mm × 42.5 mm × 80 μm, and then an electrode was formed. Then, an insulating groove is formed along the longitudinal direction in the vicinity of both ends of the minor axis on the back side so that the effective opening in the minor axis direction is 4.0 mm, a signal electrode and a ground electrode are formed, and a polarization process is performed to perform piezoelectric processing. A layer was made.

  Thereafter, tungsten carbide was molded into a size of 5.6 mm × 42.5 mm × 80 μm and used as a dematching layer. Then, the piezoelectric layer and the dematching layer manufactured as described above are laminated and bonded, and are dicing so as to communicate with the insulating groove formed in the piezoelectric layer, and have a width of 40 μm and a depth of 90 μm. A vibrating layer was obtained by grooving along the direction.

  After that, the patterned FPC, backing layer, and fixing plate are previously laminated and bonded under the same bonding conditions as described above, and the vibration layer and the acoustic matching layer manufactured as described above are sequentially arranged. Laminated and adhered. As a result, the signal electrode and the ground electrode of the piezoelectric layer are connected to the signal electrode surface and the ground electrode surface formed on the FPC using the dematching layer as a wiring while maintaining these insulating states. The acoustic matching layer was bonded so that an acoustic matching material having a high acoustic impedance was in contact with the piezoelectric layer. Then, the laminated body thus produced is made into an element by performing dicing to completely divide the vibration layer at intervals of 0.2 mm in the longitudinal direction (azimuth direction) with a blade having a thickness of 20 μm, Dicing was performed on the divided elements to completely divide the acoustic matching layer at an interval of about 67 μm with the above-described blade, thereby producing a transducer.

  Thereafter, an insulating layer of about 3 μm made of polyparaxylylene was provided on the surface of the transducer, and an acoustic lens was laminated and adhered to the acoustic radiation surface of this insulating layer to produce a vibration part.

  Next, after connecting the connector to the FPC, the vibration part produced as described above was housed in a case, and the ultrasonic probe of Example 1 was produced.

  Subsequently, in place of the piezoelectric material of Example 1, the piezoelectric materials described in the columns of Example 2 and Example 3 in Table 1 below were used, and in the same manner as Example 1, Example 2 and Example 3 were used. Ultrasonic probes were produced respectively.

  Next, after producing an acoustic matching layer as described above, the piezoelectric material described in the column of Comparative Example 1 in Table 1 below was used and processed into a size of 5.6 mm × 42.5 mm × 130 μm. After that, an electrode was formed. Then, an insulating groove is formed along the longitudinal direction in the vicinity of both ends of the minor axis on the back side so that the effective opening in the minor axis direction is 4.0 mm, a signal electrode and a ground electrode are formed, and a polarization process is performed to perform piezoelectric processing. A layer was made.

  After that, the patterned FPC, backing layer, and fixing plate are previously laminated and bonded under the same bonding conditions as described above, and the piezoelectric layer and the acoustic matching layer manufactured as described above are sequentially arranged. Laminated and adhered. As a result, the single electrode and the ground electrode of the piezoelectric layer are connected to the signal electrode surface and the ground electrode surface formed on the FPC, respectively, while maintaining these insulating states. The acoustic matching layer was bonded so that an acoustic matching material having a high acoustic impedance was in contact with the piezoelectric layer. Then, the laminated body thus produced is made into an element by performing dicing to completely divide the vibration layer at intervals of 0.2 mm in the longitudinal direction (azimuth direction) with a blade having a thickness of 20 μm, Dicing was performed on the divided elements to completely divide the acoustic matching layer at an interval of about 67 μm with the above-described blade, thereby producing a transducer.

  Thereafter, an insulating layer of about 3 μm made of polyparaxylylene was provided on the surface of the transducer, and an acoustic lens was laminated and adhered to the acoustic radiation surface of this insulating layer to produce a vibration part.

  Next, after connecting the connector to the FPC, the vibration part produced as described above was housed in a case, and an ultrasonic probe of Comparative Example 1 was produced.

  Subsequently, in place of the piezoelectric material of Comparative Example 1, the piezoelectric materials described in the columns of Comparative Example 2 and Comparative Example 3 in Table 1 below were used, and in the same manner as Comparative Example 1, Comparative Examples 2 and 3 were used. Ultrasonic probes were produced respectively.

  The transmission sensitivity and durability of the ultrasonic probes of Examples 1 to 3 and Comparative Examples 1 to 3 manufactured as described above were evaluated under the following conditions. The measurement system was constructed with a general-purpose function generator (Agilent 33220A), power amplifier (HP 8447D), hydrophone (Sonora 804), and oscilloscope (Tektronix TPS5032) and degassed in the above water A hydrophone was installed. The ultrasonic probe is fixed at a position where the focal length of the ultrasonic probe matches the focal length of the hydrophone and the receiving sensitivity of the hydrophone is highest. Then, signal transmission was performed by burst wave drive of Vpp80 [V], and the transmission sensitivity was compared. The results are shown in Table 1. In addition, all the piezoelectric materials in the following Table 1 were manufactured by Fuji Ceramic.

  As is clear from Table 1, compared with Comparative Examples 1 to 3 in which there is a trade-off between transmission loss due to element capacitance and drive voltage due to coercive electric field, Examples 1 to 3 achieve high compatibility between them. It was found to have sensitivity.

  Next, the transmission sensitivities of the ultrasonic probes of Example 1 and Comparative Example 3 manufactured as described above were measured and evaluated under the following conditions, respectively. The measurement system was constructed with a general-purpose function generator (Agilent 33220A), power amplifier (HP 8447D), hydrophone (Sonora 804), and oscilloscope (Tektronix TPS5032) and degassed in the above water A hydrophone was installed. The ultrasonic probe is fixed at a position where the focal length of the ultrasonic probe matches the focal length of the hydrophone and the receiving sensitivity of the hydrophone is highest. And the burst wave of the drive voltage shown in following Table 2 was input with respect to each ultrasonic probe, and each transmission sensitivity was evaluated. The results are shown in Table 2.

  As is clear from Table 2, it was found that the transmission sensitivity of the ultrasonic probe of Example 1 increased depending on the drive voltage, and the drive voltage band of the system could be fully utilized. On the other hand, in the ultrasonic probe of Comparative Example 3, the transmission sensitivity increases depending on the drive voltage until the drive voltage is 50 V (100 Vpp), but the voltage exceeds the allowable voltage at 60 V (120 Vpp) or more. As a result, it was found that noise was caused by depolarization at a driving voltage of 70 V (140 Vpp). Thus, it was found that the sensitivity of the ultrasonic probe of Example 1 was higher than that of the ultrasonic probe of Comparative Example 3.

  Next, the ultrasonic probes of Example 1 and Comparative Example 3 were continuously driven at a driving voltage of 50 V (100 Vpp) under the measurement conditions described above, and 5 minutes and 10 minutes after the start of driving. The relative sensitivity with respect to the transmission sensitivity immediately after the start of measurement after the lapse of 20 minutes and 30 minutes was measured. The results are shown in Table 3.

  As is apparent from Table 3, it was found that the transmission sensitivity of the ultrasonic probe of Example 1 has a substantially constant sensitivity characteristic in spite of long-time driving. That is, it was found that the sensitivity characteristics were maintained almost constant regardless of the temperature rise of the piezoelectric material due to continuous driving. On the other hand, it was found that the sensitivity of the ultrasonic probe of Comparative Example 3 decreased with time. That is, it was found that the sensitivity was lowered due to the temperature rise of the piezoelectric material accompanying continuous driving. Thus, it was found that the ultrasonic probe of Example 1 has high thermal stability and can maintain high sensitivity characteristics for a long time.

  As described above, according to the present embodiment, the dematching layer 23 having an acoustic impedance higher than the acoustic impedance of the piezoelectric layer 24 is disposed on the surface of the piezoelectric layer 24 opposite to the ultrasonic radiation surface. In the ultrasonic probe 2 that transmits and receives ultrasonic waves by resonance with nλ / 4 (n is an odd number), the piezoelectric layer 24 is configured using a piezoelectric material having a coercive electric field of 1.0 MV / m or more at 25 ° C. . As a result, even if a dematching layer is used, it is possible to drive a high voltage without depending on the thickness, so that the drive voltage of the system in the diagnostic device main body can be used to the maximum, and a high center frequency characteristic is obtained. Higher sensitivity can be realized with an ultrasonic probe having In addition, since the change in characteristics is small even when used for a long time, it is possible to provide an ultrasonic probe with little deterioration over time.

  In addition, according to the present embodiment, since the piezoelectric layer 24 is configured using the piezoelectric material having a coercive electric field of 0.9 MV / m or more at 60 ° C., the deterioration of the piezoelectric characteristics is small even at high temperatures, and the Even if it is used, the change in piezoelectric characteristics can be reduced, and an ultrasonic probe with stable operation can be provided.

  In addition, according to the present embodiment, since the piezoelectric material includes an acceptor additive including a divalent or trivalent element that replaces the B site, the coercive electric field of the piezoelectric material can be increased. Become.

In addition, according to the present embodiment, the acceptor additive contains at least one of Fe ³⁺ , Co ²⁺ and Mn ²⁺ , so that the coercive electric field of the piezoelectric material can be further increased.

  Further, according to the present embodiment, since the piezoelectric layer 24 is configured using a piezoelectric material having a dielectric constant of 1800 or more, a coercive electric field can be stably obtained.

  According to the present embodiment, since the piezoelectric layer 24 is configured using the piezoelectric material having a Curie temperature of 250 ° C. or higher and 350 ° C. or lower, the piezoelectric material can be used efficiently.

  According to the present embodiment, since the center frequency of the output ultrasonic wave is 7 MHz, the piezoelectric material can be used efficiently.

  The description in the embodiment of the present invention is an example of the ultrasonic diagnostic imaging apparatus according to the present invention, and the present invention is not limited to this. The detailed configuration and detailed operation of each functional unit constituting the ultrasonic diagnostic imaging apparatus can be appropriately changed.

DESCRIPTION OF SYMBOLS 1 Ultrasonic image diagnostic apparatus 2 Ultrasonic probe 4 Diagnostic apparatus main body 21 Ultrasonic transducer 23 Dematching layer (reflection layer)
24 Piezoelectric layer

Claims (7)

A reflection layer having an acoustic impedance higher than the acoustic impedance of the piezoelectric layer is disposed on the surface opposite to the ultrasonic radiation surface of the piezoelectric layer, and transmits and receives ultrasonic waves by nλ / 4 (n is an odd number) resonance. In the acoustic probe,
An ultrasonic probe, wherein a coercive electric field of a piezoelectric material constituting the piezoelectric layer is 1.0 MV / m or more at 25 ° C.   The ultrasonic probe according to claim 1, wherein a coercive electric field of the piezoelectric material is 0.9 MV / m or more at 60 ° C.   The ultrasonic probe according to claim 1, wherein the piezoelectric material includes an acceptor additive including a divalent or trivalent element that substitutes for a B site. The ultrasonic probe according to claim 3, wherein the element is at least one of Fe ³⁺ , Co ^2+, and Mn ²⁺ .   The ultrasonic probe according to claim 1, wherein the piezoelectric material has a dielectric constant of 1800 or more.   The ultrasonic probe according to claim 1, wherein the piezoelectric material has a Curie temperature of 250 ° C. or higher and 350 ° C. or lower.   The ultrasonic probe according to any one of claims 1 to 6, wherein the center frequency of the output ultrasonic wave is 7 MHz or more.

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