JP5560855B2 - Ultrasonic transducer and ultrasonic diagnostic apparatus - Google Patents

Description

The present invention relates to an ultrasonic transducer and an ultrasonic diagnostic apparatus, and more particularly to the structure of the ultrasonic transducer (probe).

  In general, a piezoelectric body is used for an ultrasonic transducer. This is because the piezoelectric body converts mechanical energy into electrical energy, and vice versa, and has a so-called electric system-mechanical coupling action. The piezoelectric body used is in the form of a sheet, plate or rod provided with a pair of electrodes, one electrode is fixed to the back layer, and the other electrode is in contact with the medium via the acoustic lens or matching layer.

Many piezoelectric ultrasonic transducers radiate sound waves to the medium or detect sound waves propagating to the medium in the d ₃₃ mode or e ₃₃ mode. The d ₃₃ mode is generally called longitudinal vibration of the columnar vibrator, and the e ₃₃ mode is generally called thickness vibration of the plate vibrator. In ferroelectric materials such as PZT ceramics and PVDF, high dielectric materials such as P (VDCN / VAc), and porous polymer electret piezoelectric materials, the residual polarization is maintained by the orientation of the electric dipole by the poling process, and d ₃₃ and e ₃₃ are set. Show. On the other hand, in the case of a piezoelectric crystal having no remanent polarization, if the piezoelectric crystal such as ZnO, LiNbO ₃ , KNbO ₃ is oriented perpendicularly to the electrode surface with the C-axis in the case of quartz crystal or the A-axis in the case of quartz, d ₃₃ And e ₃₃ (d ₁₁ and e _{11 for} quartz). The piezoelectric composite material depends on the material used.

  Here, in the piezoelectric body constituting the ultrasonic transducer, the simplest mechanical boundary condition is a case where one end is a fixed end and the other end is a free end. Theoretically, the acoustic impedance Z (unit is MRayl.) Of the contacting object and the boundary condition have a relation that Z = 0 is a free end and Z = ∞ is a fixed end. It is not strict, and with the exception of the adhesive layer and electrode layer, the impedance Z of the piezoelectric material is regarded as a fixed end when the impedance Z is small or equivalent, and a free end when it is large. In addition, the resonance of the longitudinal vibration or the thickness vibration of the piezoelectric body is used for the transmission and reception of the ultrasonic transducer, and the resonance frequency fr depends mainly on the structure of the transducer and the pressing to the medium. It is determined by the physical properties and dimensions of the piezoelectric body. Therefore, in the present specification, factors that change the resonance frequency other than the dimensions and properties of the piezoelectric body are excluded.

First, the resonance frequency fr in the d ₃₃ mode and e ₃₃ mode of the piezoelectric body is determined from the sound velocity v and the height (thickness) h of the piezoelectric body.
fr = v / 4h (1)
It becomes. This is generally referred to as λ / 4 resonance. λ means the wavelength in the piezoelectric body. In addition, there is a λ / 2 resonance in which both ends are free. The resonance frequency is ½ of λ / 4 resonance.

On the other hand, the sound velocity v of the piezoelectric body is the longitudinal vibration of the columnar vibrator.
v = (1 / sρ) ^1/2 (2)
In the thickness vibration of the plate-shaped thickness vibrator,
v = (c / ρ) ^1/2 (3)
It becomes. Here, s is elastic compliance, c is elastic stiffness, and ρ is density.

  Thus, it is understood from the above formulas (1) to (3) that the transmission and reception frequencies of the transducer are mainly determined by the height (thickness) h, the elastic modulus s, and the density ρ of the piezoelectric body. .

  An ultrasonic diagnostic apparatus used in the medical field is required to increase the frequency of the transducer and improve the transmission / reception performance in order to obtain a higher resolution image. In an ultrasonic transducer using a piezoelectric body, electrical impedance matching between the transducer and the electrical processing circuit is an important factor for transmitting an electrical signal at a high S / N ratio in order to improve transmission / reception performance. is there. In addition, when the frequency is increased, since the transmission / reception frequency is determined by the thickness of the piezoelectric body, it is necessary to make the piezoelectric body thinner. Since the piezoelectric thin film works in the direction of lowering the electrical impedance, it works favorably for impedance matching with the electric circuit, but the lowering width is at most the reciprocal of the thickness ratio. In addition, the thinning of the piezoelectric body makes the manufacturing process such as film thickness control and handling difficult.

Therefore, in the prior art, the harmonic component in the transmission / reception signal of the conventional λ / 4 resonant transducer is used for the purpose of obtaining a high-frequency signal. However, the harmonic component has a sensitivity lower than that of the fundamental wave component, and is easily attenuated by the damping of the piezoelectric body and the surrounding material, so that there is a problem that it is difficult to obtain a signal with a high S / N ratio. Therefore, as an example of transmitting and receiving ultrasonic waves using the harmonic, with reference to FIG. 1, described e ₃₃ thickness stretching mode. This FIG. 1 and the following description are shown in Non-Patent Document 1. The constants of the elements constituting the equivalent circuit of FIG.
C _n = p _n k _t ² C ₀ (4)
L = 1 / ω _p1 ² C ₁ (5)
p _n = (1 / n ² ) (8 / π ² ), n = 2m−1 (6)
It is. Here, C _n is the capacitance of the elements, L is the inductance, k _t is the electromechanical coupling coefficient of thickness stretching mode, the omega _p1 is the resonant frequency.

In the above equation (6), if approximated as p _n ≈1 / n ² , equation (4) becomes
^{_{C n / C 0 = k t}} 2 / n 2 ... (7)
It becomes. Equation (7) indicates that the effective value of the electromechanical coupling coefficient at the nth harmonic is reduced to 1 / n. In the case of the primary mode, since n = 1, equation (7) is
The _{C n = 1 / C 0 =} k t 2 ... (8). This equation, relation between _{k t} and a dielectric constant in the first order mode _{^{ε T / ε S = 1 +}} k t 2 ... (9)
Therefore, ε ^T = C ₀ + C _n , ε ^S = C ₀ , which is in agreement with the above equation. The epsilon ^S dielectric constant of the dielectric constant ,, epsilon ^T free conditions constraints, and C ₀ and C _n is the capacitance. For the d ₃₃ mode, the above equation (4) is
C _n = p _n (k ₃₃ ² / 1−k ₃₃ ² ) C ₀ (10)
The same result can be obtained by replacing.

The effective value of the electromechanical coupling coefficient when transmitting and receiving the third harmonic is given by n = 3 from Equation (7), and if the apparent coupling coefficient is k _t ′, k _t '= K _t / n = k _t / 3. This result means that the apparent coupling coefficient is attenuated to 1/3 when transmitting and receiving the third harmonic.

FIG. 2 is a graph showing the frequency characteristic (calculated value) of the complex dielectric constant of a piezoelectric body exhibiting a primary mode of thickness resonance at 1 MHz. However, kt = 0.3, h / 2v = 2.485 × 10 ⁻⁷ (s), tan δ _m = 0.04.

The maximum / minimum of the real part (indicated by reference numeral α1) and the maximum of the imaginary part (indicated by reference numeral α2) seen at 1 MHz are due to the primary mode of thickness resonance. Thereafter, a third-order harmonic component is observed at 3 MHz and a fifth-order harmonic component is observed at 5 MHz. On the other hand, as shown in FIG. 3, when the third harmonic component shown in FIG. 2 is applied with a piezoelectric model having 3 MHz as a primary mode, the coupling coefficient and the thickness of the piezoelectric body are set to 1/3. Matched. These results are consistent with the above interpretation. FIG. 3 is a graph showing the frequency characteristic (calculated value) of the complex dielectric constant of a piezoelectric body exhibiting thickness resonance. However, the broken lines are kt = 0.3, h / 2v = 2.485 × 10 ⁻⁷ (s), tan δ _m = 0.04 as described above. On the other hand, the solid lines are kt = 0.1, h / 2v = 8.300 × 10 ⁻⁷ (s), tan δ _m = 0.04.

  As described above, the problems of the prior art are that, when detecting harmonics, the apparent electromechanical coupling coefficient is reduced to 1 / n and the electrical impedance is uniquely determined by the size of the piezoelectric body. There is to be.

  On the other hand, in a medical ultrasonic diagnostic apparatus, tissue harmonic imaging (THI) diagnosis using harmonic signals is a standard diagnostic modality because a clear diagnostic image that cannot be obtained by conventional B-mode diagnosis is obtained. It's getting on. If the frequency used is higher as in this harmonic imaging, the sidelobe level will be lower, the S / N will be better, the contrast resolution will be better, the beam width will be narrower and the lateral resolution will be better. Is small, and since there is little variation in sound pressure, it has many advantages such as no multiple reflection.

  Therefore, in Patent Document 1, the signals received by the piezoelectric elements of the ultrasonic transducer are added by the phasing addition circuit, and then input to the fundamental band filter and the harmonic band filter in common. Ultrasound diagnosis in which the output is weighted with a gain corresponding to the depth of the diagnostic region of the subject and then combined to interpolate the attenuation of harmonic components in the deep diagnostic region with the fundamental wave A device has been proposed. That is, when receiving harmonics, the decrease in the electromechanical coupling coefficient is compensated by using a filter and an amplifier.

  Similarly, in Patent Document 2, a fundamental piezoelectric element is formed by laminating a harmonic piezoelectric element on a fundamental wave piezoelectric element, radiating a transmission ultrasonic wave from the fundamental wave piezoelectric element, and receiving it by the fundamental wave piezoelectric element. Diagnose the signal component of the wave by passing the multiple harmonic components received by the piezoelectric element for harmonics through the band-pass filter and extracting the desired component, then adjusting the gain individually and adding them. There has been proposed an ultrasonic diagnostic apparatus that obtains a signal corresponding to the depth of a region.

JP 2002-11004 A Japanese Patent No. 4192598

Basics of Piezoelectric Materials by Takuro Ishida Ohmsha

  However, in the above-described conventional technology, it is necessary to insert filters and amplifiers in signal paths from a large number of piezoelectric elements.

  In addition, for receiving high-frequency signals, it is preferable to use an organic material such as PVDF as compared with an inorganic material such as PZT in terms of processing characteristics. However, an inorganic material has a high dielectric constant, and therefore has a large capacitance and a low electrical impedance, so matching with a subsequent circuit is relatively easy, whereas an organic material has a low dielectric constant, For this reason, since the capacitance is low and the electrical impedance is high, there is a problem that matching with a subsequent circuit is difficult.

It is an object of the present invention to make it possible to make the output sound pressure at the time of transmitting a desired high-frequency component in an ultrasonic transducer or the output voltage at the time of receiving a wave larger than those in the primary mode, and to reduce the electrical impedance. It is an object to provide an ultrasonic transducer and an ultrasonic diagnostic apparatus capable of performing the above.

Ultrasonic transducer of the present invention transmits ultrasound into the subject, wherein an ultrasonic transducer for receiving ultrasonic waves coming from the object, a plurality of piezoelectric bodies of equal thickness are laminated to each other A laminated piezoelectric body that resonates in a 3λ / 4 resonance mode generated by the expansion and contraction of the thickness of the piezoelectric body. The piezoelectric body is laminated in three layers, and electrodes are provided on the surface of the piezoelectric body between the layers and at both ends. And having two sets of connecting wirings for connecting the piezoelectric bodies in parallel to each other by connecting electrodes on the separated sides of the piezoelectric bodies adjacent to each other, the piezoelectric bodies being electrically displaced by a piezoelectric positive effect or The direction of remanent polarization or the crystal axis related to the sign of the electric field is set in the same direction in the second-stage piezoelectric body in contact with the axis of the first-stage piezoelectric body on the fixed end side, and further above The opposite is true for the third-stage piezoelectric body And Turkey have been arranged so that the direction, characterized.

According to the above structure, when the front Symbol ultrasonic transducer composed of a laminated piezoelectric element, the received ultrasonic transducers, to extract the receiving unit is a signal of 3 [lambda] / 4 resonant mode, the laminated piezoelectric The number of stacked bodies is three, and the piezoelectric bodies are connected in parallel, and in a predetermined manner (according to a certain rule), a part of the piezoelectric bodies is reversed and stacked.

  Specifically, first, among the electrodes formed on the surface of the piezoelectric material between the layers and at both ends of each piezoelectric material laminated in the thickness direction as described above, two electrodes on the separation side in the piezoelectric materials adjacent to each other are provided. Each piezoelectric body is electrically connected in parallel by being connected by a set of connecting wires.

Next, by setting the number of stacked layers to three, which is the number of resonance modes, the nodes and antinodes of elastic waves propagating in the piezoelectric body can be made to coincide with the boundary surface of the piezoelectric body. Focusing on the strain distribution of the 3λ / 4 resonance mode component in the multilayer piezoelectric body, the distortion of each piezoelectric body is inverted by 180 degrees without changing the absolute value, and each piezoelectric body is connected in parallel as described above. In this case, for example, if the distortion of the piezoelectric body on the base end (back layer) side is +, “+, +, −” is obtained. Therefore, as the predetermined mode, the residual polarization of each piezoelectric body or the orientation of the C-axis or A-axis of the crystal (the axes that determine the signs of d ₃₃ , e ₃₃ , d ₁₁ , e ₁₁ ) The piezoelectric body at the mismatched portion (corresponding to the sign of “−”) is reversed and laminated so as to match the sign of displacement and electric field. In the above case, with respect to the axis of the first-stage piezoelectric body (in contact with the back layer) on the fixed end side, the second-stage piezoelectric body in contact with the axis is in the same direction, and the third-stage piezoelectric body thereon The body arranges in the opposite direction.

  As a result, each piezoelectric body in the laminated piezoelectric body is made to coincide with the sign of the electric displacement or electric field due to the piezoelectric positive effect, and the output at the time of transmission of the 3λ / 4 resonance mode component compared to the case of the λ / 4 resonance mode. The sound pressure or the output voltage at the time of receiving can be increased, and the primary mode signal can be attenuated. Thus, it is possible to improve the band separation performance in the ultrasonic transducer and eliminate the need for a filter or amplifier in the receiving unit, or when using such a filter or amplifier, the order of the filter can be reduced, The gain of the amplifier can be reduced. Further, when the number of piezoelectric bodies in parallel, that is, the number of stacked layers is n, the electrical impedance can be reduced to 1 / n, impedance matching with the transmission circuit and the reception circuit is facilitated, and S / N is improved. be able to.

The ultrasonic transducer of the present invention transmits ultrasound into the subject, wherein an ultrasonic transducer for receiving ultrasonic waves coming from the subject, two layers equal piezoelectric thicknesses to each other A laminated piezoelectric body that is formed by laminating and resonates in a 3λ / 4 resonance mode generated by expansion and contraction of the thickness of the piezoelectric body , and each of the piezoelectric bodies has electrodes between the layers and outer surfaces thereof, Are connected to each other in parallel with each other, and the two piezoelectric bodies have an electric displacement due to a piezoelectric positive effect or a remanent polarization direction or crystal axis related to the sign of the electric field. characterized by the Turkey it has been arranged so as to be the same direction.

  According to the above configuration, when two layers of laminated piezoelectric bodies are used for the ultrasonic transducer and the piezoelectric elements are connected in parallel with each other when transmitting and receiving the ultrasonic wave of the third-order mode component by resonating 3λ / 4. In addition, the remanent polarization of the piezoelectric body or the orientation of the C-axis or A-axis of the crystal can be made to coincide with the electrical displacement or the electric field sign due to the piezoelectric positive effect.

The ultrasonic transducer of the present invention transmits ultrasound into the subject, wherein an ultrasonic transducer for receiving ultrasonic waves coming from the object, another a plurality of piezoelectric equal thickness It is composed of four or more layers, and includes a multilayer piezoelectric body that resonates in a desired resonance mode by expanding and contracting the thickness of the piezoelectric body. Each piezoelectric body has electrodes on the surface of the piezoelectric body between the layers and both ends. By connecting electrodes on the separation side of adjacent piezoelectric bodies, the piezoelectric bodies are provided with two sets of connecting wirings that connect the plurality of piezoelectric bodies in parallel to each other, and each of the piezoelectric bodies has an electric displacement or electric field caused by a piezoelectric positive effect. The direction of remanent polarization or the crystal axis related to the sign is set in the same direction in the second-stage piezoelectric body in contact with the axis of the first-stage piezoelectric body on the fixed end side, and further the third and In the fourth stage piezoelectric body 1 or more sets to have periodicity as the direction wherein the benzalkonium been arranged.

  According to the above configuration, when an ultrasonic transducer uses an n-layer laminated piezoelectric body having four or more layers and resonates with it by transmitting an ultrasonic wave of an n-order mode component, the piezoelectric bodies are mutually connected. In the case of parallel connection, the remanent polarization of the piezoelectric material or the direction of the C-axis or A-axis of the crystal can be made to coincide with the electric displacement due to the piezoelectric positive effect or the sign of the electric field.

In the ultrasonic transducer of the present invention, the laminated piezoelectric material is commonly used for transmission / reception of ultrasonic waves, and the ultrasonic transducer transmits ultrasonic waves in a 3λ / 4 resonance mode.

  According to the above configuration, an ultrasonic probe suitable for high-frequency, that is, high-resolution imaging can be realized by using the 3λ / 4 resonance mode for both transmission and reception.

In the ultrasonic transducer according to the present invention, the multilayer piezoelectric body is used as a first piezoelectric body for receiving ultrasonic waves, and the ultrasonic transducer transmits an ultrasonic wave having a fundamental wave component in a λ / 4 resonance mode. A second piezoelectric body for transmission is further provided, and the second piezoelectric body and the first piezoelectric body are laminated in this order from the back layer side.

  According to the above configuration, it is possible to use a piezoelectric body suitable for both transmission and reception, which is suitable for harmonic imaging that performs high power transmission and receives harmonics generated in the subject with high gain. An acoustic probe can be realized.

In the ultrasonic transducer according to the present invention, the multilayer piezoelectric body is used as a first piezoelectric body for receiving ultrasonic waves, and the ultrasonic transducer transmits an ultrasonic wave having a fundamental wave component in a λ / 4 resonance mode. Two second piezoelectric bodies for transmission are further provided, and the second piezoelectric bodies are arranged in parallel on both sides of the first piezoelectric body.

  According to the above configuration, it is possible to use a piezoelectric body suitable for both transmission and reception, which is suitable for harmonic imaging that performs high power transmission and receives harmonics generated in the subject with high gain. An acoustic probe can be realized.

In the ultrasonic transducer of the present invention, the first piezoelectric body is made of a material mainly composed of an organic polymer.

  According to said structure, the organic polymer piezoelectric material can handle a high frequency signal, and is suitable for reception of the harmonics.

  Therefore, by using an organic piezoelectric body for reception, an ultrasonic probe suitable for harmonic imaging that performs high power transmission as described above and receives harmonics generated in the subject with high gain is realized. Can do.

In the ultrasonic transducer of the present invention, the second piezoelectric body is made of an inorganic material, the first piezoelectric body is made of a material mainly composed of an organic polymer, and the first piezoelectric body and the subject are inspected. A member for the purpose of acoustic matching is not interposed therebetween.

  According to the above configuration, in the laminated inorganic / organic piezoelectric material, the object side is an organic piezoelectric material having a low acoustic impedance, and therefore no member for the purpose of acoustic matching is interposed between the object such as a living body.

  Therefore, an acoustic matching layer for impedance matching can be eliminated between the organic piezoelectric body and the subject, and the structure can be simplified.

The ultrasonic diagnostic equipment of the present invention comprises any one of the ultrasonic transducers described above, a transmission unit providing an ultrasonic signal for transmission to the ultrasonic transducer, wherein the received signal received by the ultrasonic transducer A receiving unit that performs predetermined signal processing, and an image processing unit that forms an internal state of the subject as a tomographic image based on a reception signal from the receiving unit . According to the above configuration, an ultrasonic wave is transmitted from the ultrasonic transducer into the subject, the ultrasonic wave coming from the subject is received by the ultrasonic transducer, and based on the received signal, the image processing unit The internal state of the subject is imaged as a tomographic image. Such an ultrasonic diagnostic apparatus uses any one of the above-described ultrasonic transducers, so that the output sound pressure at the time of transmission of the desired high-frequency component in the ultrasonic transducer or the output voltage at the time of reception is in the primary mode. While being able to make it larger than them, an electrical impedance can be reduced .

In the ultrasonic diagnostic apparatus of the present invention, the transmission unit applies a transmission signal to the multilayer piezoelectric body as an encoded pulse voltage, and the reception unit pulses a signal received by the multilayer piezoelectric body. A compression process is performed, and the image processing unit is converted into an image . According to the above configuration, it is possible to obtain a reception pulse having a large amplitude, that is, a good S / N, without the influence on the subject being increased.

The ultrasonic transducer of the present invention includes a laminated piezoelectric material, and when the signal received by the ultrasonic transducer and extracted by the receiving unit is a signal of a desired resonance mode component of the third or higher order, the laminated piezoelectric material is laminated. Each piezoelectric body is connected in parallel with the number of sheets being the two layers or the order of the desired resonance mode component, and a part of the piezoelectric bodies is reversed and laminated in a predetermined manner. Therefore, the output sound pressure at the time of transmitting the desired high-frequency component in the ultrasonic transducer or the output voltage at the time of receiving can be made larger than those in the primary mode, and the electrical impedance can be reduced. I can .

The ultrasonic diagnostic apparatus of the present invention transmits an ultrasonic wave from an ultrasonic transducer into a subject, receives the ultrasonic wave coming from the subject by the ultrasonic transducer, and based on the received signal, an image processing unit In the ultrasonic diagnostic apparatus for imaging the internal state of the subject as a tomographic image, the ultrasonic transducer is composed of a laminated piezoelectric material, received by the ultrasonic transducer, and extracted by the receiving unit is the third or higher order. When a signal of a desired resonance mode component is used, the number of laminated piezoelectric bodies is two or the order of the desired resonance mode component. Laminate the body upside down . Therefore, each piezoelectric body in the laminated piezoelectric body is made to coincide with the electric displacement or the sign of the electric field due to the piezoelectric positive effect, and compared with the case of the λ / 4 resonance mode, the transmission of the desired higher harmonic component of the third order or higher. The output sound pressure at the time or the output voltage at the time of reception can be increased, and the primary mode signal can be attenuated. Thus, it is possible to improve the band separation performance in the ultrasonic transducer and eliminate the need for a filter or amplifier in the receiving unit, or when using such a filter or amplifier, the order of the filter can be reduced, The gain of the amplifier can be reduced. Further, when the number of piezoelectric bodies in parallel, that is, the number of stacked layers is n, the electrical impedance can be reduced to 1 / n, impedance matching with the transmission circuit and the reception circuit is facilitated, and S / N is improved. be able to.

It is an equivalent circuit diagram in the thickness expansion and contraction mode of the piezoelectric body. It is a graph which shows the frequency characteristic of the complex dielectric constant of the piezoelectric material which shows the primary mode of thickness resonance at 1 MHz. It is a graph which shows the frequency characteristic of the complex dielectric constant of the 3rd harmonic component in the piezoelectric material shown in the said FIG. 2, and the piezoelectric material which shows the 1st mode of thickness resonance in 3 MHz. FIG. 3 is a schematic cross-sectional view of a λ / 4 resonance state in a three-layer piezoelectric transducer. FIG. 5 is a schematic cross-sectional view of a 3λ / 4 resonance state in the three-layer piezoelectric transducer shown in FIG. 4. It is a typical sectional view of an n layer piezoelectric transducer. It is a figure which shows typically the displacement and distortion at the time of exciting or detecting an nth-order harmonic with the n layer piezoelectric transducer shown in FIG. FIG. 7 is a diagram showing the relationship between the residual polarization of each piezoelectric body when detecting nth-order harmonics or the orientation of the C-axis and A-axis of the crystal and the electrical displacement due to the piezoelectric positive effect in the multilayered piezoelectric body shown in FIG. It is. It is a figure which shows typically the structure of the 2n layer piezoelectric transducer for detecting n-order harmonic. FIG. 9 is an example of a detailed embodiment according to the concept of the present invention shown in FIG. 8, and is a cross-sectional view schematically showing the structure of a two-layer piezoelectric transducer. It is a figure for demonstrating the displacement and distortion at the time of the harmonic transmission / reception in the two-layer piezoelectric transducer shown in FIG. 12 is a diagram illustrating the relationship between the direction of remanent polarization of each piezoelectric body and the electrical displacement due to the piezoelectric positive effect when detecting the third harmonic in the multilayered piezoelectric body shown in FIGS. 10 and 11. FIG. It is a graph which shows an experimental data and a simulation result about the transmission / reception characteristic of the ultrasonic wave by the two-layer piezoelectric material shown in FIG. 10, and its comparative example. FIG. 8 is another example of the detailed embodiment according to the concept of the present invention shown in FIGS. 8 and 5 and is a cross-sectional view schematically showing the structure of a three-layer piezoelectric transducer. It is a figure for demonstrating the displacement and distortion at the time of harmonic transmission / reception in the three-layer piezoelectric transducer shown in FIG. FIG. 16 is a diagram illustrating the relationship between the direction of remanent polarization of each piezoelectric body and the electrical displacement due to the piezoelectric positive effect when the third harmonic is detected in the multilayered piezoelectric body shown in FIGS. 14 and 15. It is a graph which shows an experimental data and a simulation result about the transmission / reception characteristic of the ultrasonic wave by the 3 layer piezoelectric material shown in FIG. It is a graph which shows an experimental data and a simulation result about the ultrasonic wave transmission / reception characteristic by the comparative example of the three-layer piezoelectric material shown in FIG. FIG. 10 is still another example of the detailed embodiment according to the concept of the present invention shown in FIG. 8, and is a cross-sectional view schematically showing the structure of a six-layer piezoelectric transducer. It is a figure which shows the relationship between the direction of the remanent polarization of each piezoelectric material at the time of detecting a 3rd harmonic in the laminated piezoelectric material shown in FIG. 19, and the electric displacement by a piezoelectric positive effect. It is a graph which shows a simulation result about the transmission / reception characteristic of the ultrasonic wave by the 6 layer piezoelectric material shown in FIG. 1 is a perspective view illustrating an external configuration of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. It is a block diagram which shows the electric constitution of the diagnostic apparatus main body in the said ultrasonic diagnostic apparatus. It is sectional drawing which shows typically one structural example of the ultrasonic transducer in the ultrasonic probe of the said ultrasonic diagnostic apparatus. It is sectional drawing which shows typically the other structural example of the ultrasonic transducer in the ultrasonic probe of the said ultrasonic diagnosing device. It is a graph which shows the analysis result of the organic piezoelectric material produced for using for the said ultrasonic transducer. It is a graph which shows the waveform of a received ultrasonic wave, and shows the case of the single pulse drive without encoding. It is a graph which shows the waveform of a received ultrasonic wave, and shows the case of the multiple pulse drive with encoding.

  First, the concept of the ultrasonic transducer used in the medical ultrasonic diagnostic apparatus of the present invention will be described. The ultrasonic transducer according to the present invention is a layered structure based on the knowledge of the present inventor that the third and higher order resonance mode components can be efficiently transmitted and received by laminating piezoelectric bodies having the same thickness according to a certain rule. It consists of a piezoelectric body. Many techniques for laminating piezoelectric materials have been reported so far, but the present invention focuses on the fact that there is a strain distribution in the piezoelectric material when transmitting and receiving the third and higher order resonance mode components.

As an example, a λ / 4 vibrator in which three piezoelectric bodies A1, A2, and A3 shown in FIG. In this excited state at λ / 4 of the λ / 4 vibrator, the three piezoelectric bodies A1, A2, A3 are expanded and contracted synchronously, and the expansion and contraction of the maximum ΔZ is performed as a whole. If the coordinate of the back surface of the first layer of piezoelectric material A1 that is smaller than the fixed end, ie, 40 MRayl. But is in contact with the back layer having a sufficiently large acoustic impedance, is z ₀ , the displacement of the position accompanying the expansion and contraction is , Z ₀ = ΔZSsin0 ° = 0. On the other hand, the displacement of the coordinate z _{1 on} the surface of the piezoelectric material A1 of the first layer is z ₁ = ΔZSsin30 ° = 0.5ΔZ, and the displacement of the coordinate z _{2 on} the surface of the piezoelectric material A2 of the second layer is z ₂ = ΔZSsin 60 ° = 0.85ΔZ, and the displacement of the coordinate z _{3 on} the surface of the piezoelectric layer A3 of the third layer in contact with the free end, that is, the space having a sufficiently small acoustic impedance although it is larger than 0 is z ₃ = ΔZSsin90 ° = 1.0ΔZ. Here, the front and back sides of the piezoelectric bodies A1, A2, and A3 are formed by pressing the piezoelectric bodies in the thickness direction to generate a positive voltage, and the reverse side is generating a negative voltage.

  That is, in the case of the three-layer piezoelectric bodies A1, A2 and A3 in FIG. 4, the piezoelectric body A1 on the fixed end side of the entire expansion and contraction ΔZ is subjected to the expansion and contraction of 0.5ΔZ, and the second-layer piezoelectric body A2 is , 0.35ΔZ, and the third-layer piezoelectric body A3 expands and contracts only 0.15ΔZ. As described above, in the multilayer piezoelectric body, at the fundamental wave λ / 4 resonance, each piezoelectric body A1, A2, A3 expands and contracts synchronously (in the same direction), but each piezoelectric body A1, A2, A3 has one. It does not expand and contract in a similar manner, but has a non-uniform strain distribution.

On the other hand, when a similar multilayer piezoelectric body is caused to resonate at 3λ / 4, the result is as shown in FIG. That is, the coordinate z ₀ of the back surface of the first-layer piezoelectric body A1 is z ₀ = ΔZ sin 0 ° = 0, and the displacement of the surface coordinate z ₁ of the first-layer piezoelectric body A 1 is z ₁ = ΔZ sin 90 ° = The displacement of the coordinate z _{2 on} the surface of the piezoelectric material A2 of the second layer is z ₂ = ΔZ sin 180 ° = 0, and the displacement of the coordinate z ₃ of the surface of the piezoelectric material A3 of the third layer is z ₃ = ΔZ sin 270. ° = −ΔZ. Accordingly, the first-layer piezoelectric body A1 extends by ΔZ, while the second-layer and third-layer piezoelectric bodies A2 and A3 have a contraction of ΔZ.

Therefore, the present inventor pays attention to such non-uniform strain distribution, and remanent polarization (ferroelectric material such as PZT and PVDF) of each piezoelectric material, or the orientation of the C-axis and A-axis of a crystal (such as quartz) ( d ₃₃ , e ₃₃ , d ₁₁ , the axis that determines the sign of e ₁₁ ) corresponds to the location of the mismatch (sign of “−” so that the electrical displacement and the sign of the electric field in the distortion distribution at the time of harmonic transmission and reception match. The piezoelectric body was laminated with the front and back reversed. In the case of FIGS. 4 and 5, as shown by the arrows on the left side, the second and third layer piezoelectric bodies A2 and A3 are different from the first layer piezoelectric body A in the direction of remanent polarization or crystals. Laminate so that the axis is in the opposite direction. Thereby, the component of the fundamental wave λ is removed as 0.5 · ΔZ + 0.35 · (−ΔZ) + 0.15 · (−ΔZ) = 0, and at the same time, the component of the third harmonic 3λ is 1 · ΔZ + (− 1) · (−ΔZ) + (− 1) · (−ΔZ) = 3ΔZ can be extracted.

  On the other hand, with reference to FIG. 6, a case where an nth-order harmonic is transmitted and received in a λ / 4 vibrator in which n (n is an integer of 4 or more) piezoelectric bodies are stacked will be described. In order to simplify the model, one end of the laminated film was fixed to the base and the other end was a free end. The influence of the thickness of the adhesive layer, such as the impedance matching layer and the back (backing) layer, is excluded.

FIG. 7 is a diagram schematically showing displacement and distortion when the n-order harmonic is excited or detected by the n-layer piezoelectric transducer shown in FIG. (A) is the state of lamination, (b) is the displacement of each layer at a certain moment, and (c) is the strain polarity. Similar to FIGS. 4 and 5, the boundary surface between the base and the piezoelectric body in contact with the base is the origin z ₀ , and the coordinates in the height (thickness) direction of the element are z ₁ , z ₂ , z ₃ ,. , Z _n . In the laminated piezoelectric body, the displacement of each piezoelectric layer forms a sine wave having the origin z0 at the boundary between the back layer and the first-stage piezoelectric body 1.

In general, when an n-th harmonic (n ≧ 1) is excited in the thickness direction, the displacement ξ (z) at the height z is
ξ (z, t) = ξ ₀ sin (nπ / 2 · z / h) (cosnω _r t + θ) (11)
(Fundamental physics selection book 8: vibration and vibration by Masataka Ariyama 裳 華 房). Here, ω _r is the resonance frequency 2πf _r , θ of the laminated piezoelectric material, and θ is a phase difference between stress and displacement when receiving voltage or sound wave. The coefficient ξ ₀ sin (nπ / 2 · z / h) means the amplitude of the displacement at the height z. Hereinafter, the time term is omitted.

In this case, the displacement ξ (z ₁ ) at the coordinate z ₁ is
ξ (z ₁ ) = ξ ₀ sin (nπ / 2 · z / h) (12)
It is. Here, the relationship between the displacement ξ (z) and the strain S is
dS = dξ / dz (13)
Therefore, the strain S _m of the piezoelectric material of the m-th layer is
S _m = [ξ (z _m ) −ξ (z _m−1 )] / (z _m −z _m−1 ) (14)
Can be written. However, m = 1 to n and z ₀ = 0.

Therefore, the strain S ₁ of the piezoelectric body ₁ is
S ₁ = Δh ₁ / h ₁ = ξ ₀ sin (nπ / 2 · h ₁ / h) / h ₁ (15)
It becomes. Here, Δh ₁ is a change in thickness of the piezoelectric body 1, and ξ (z ₁ ) −ξ (z = 0), h ₁ is a thickness of the piezoelectric body 1. Similarly for the piezoelectric body 2, the strain S ₂ is
S ₂ = Δh ₂ / h ₂
= Ξ ₀ {sin (nπ / 2 · (h ₁ + h ₂ ) / h)
-Sin (nπ / 2 · h ₁ / h)} / h ₂ (16)
It becomes. The strain S _m of the piezoelectric material of the m-th layer is
S _m = Δh _m / h _m
= Ξ ₀ {sin (nπ / 2 · z _m / h) −sin (nπ / 2 · z _m−1 / h)} / h _m
... (17)
It becomes.

In the above equation (17), the strain of the piezoelectric body in the m-th layer is determined by sin (np / 2 · z _m / h) −sin (np / 2 · z _m−1 / h). It means that it does not stretch uniformly. Therefore, if the front and back of the piezoelectric body are reversed between a piezoelectric body whose sign of the term is positive and a piezoelectric body which is negative, the sign of the electric displacement or electric field due to the piezoelectric positive effect can be made to coincide. It is understood that an nth-order harmonic electric signal can be obtained efficiently.

Furthermore, if the thickness of each piezoelectric body is made equal,
z _m = (m / n) h, z _m−1 = (m−1 / n) h, h _m = h / m (18). Substituting this into equation (17) gives
S _m = mξ ₀ {sin (mπ / 2) −sin [(m−1) π / 2]} / h (19)

となる。したがって、各圧電体の電気容量をＣとすれば、積層圧電体の容量はｎＣとなり、電気インピーダンスは圧電体１層の１／ｎに減少する。 Next, consider the electrical system. The electrical displacement (charge per unit electrode area) D _m generated by the piezoelectric material of the m-th layer is as follows:
D _m = e ₃₃ S _m or D _m = d ₃₃ S _m = d ₃₃ sT _m (20). Here, s is the elastic compliance of the piezoelectric body. If each piezoelectric body is electrically connected in parallel, the net electric displacement D _Total output from the laminated piezoelectric body is:

It becomes. Therefore, if the electric capacity of each piezoelectric material is C, the capacity of the laminated piezoelectric material is nC, and the electric impedance is reduced to 1 / n of one piezoelectric material layer.

  From the above formulas (19) and (21), the inventor of the present application realizes simple parallel coupling and the remanent polarization that maximizes the net electric displacement output from the laminated piezoelectric material, or the rules for the arrangement of the crystal C axis and A axis. I found sex. Further, if the number n of layers is 4 or more and the number n of layers is matched with the harmonic order, the nodes and antinodes of the elastic waves propagating in the piezoelectric body can be made to coincide with the boundary surface of the piezoelectric body. At this time, the distortion of each piezoelectric body is reversed by 180 degrees without changing the absolute value. For example, in the case of FIG. 7 where each piezoelectric body is in series, if the distortion of the piezoelectric body 1 is +, “+, −, − , + "Periodicity can be found every four layers, and n-th order harmonics can be detected more efficiently. A theoretical explanation of this is as follows.

FIG. 8 shows the residual polarization of each piezoelectric body or the orientation of the C-axis and A-axis of the piezoelectric body when detecting n-order harmonics in the n-layer piezoelectric body according to the present invention, and the electric displacement D ( An example of the relationship with C / m ² ) is shown. Electrodes are provided on the surfaces of the piezoelectric bodies between the layers and at both ends of each piezoelectric body, and the electrodes on the far side of the adjacent piezoelectric bodies are connected by a connection wiring, and the piezoelectric bodies are connected in parallel. Further, the remanent polarization (C-axis of the crystal in the case of a piezoelectric body not having it (A-axis in the case of quartz)) is oriented in the z-axis direction. In the drawing, for the sake of convenience, the remanent polarization of the piezoelectric body 1 or the direction of the C-axis or A-axis of the crystal is represented as + P. This is to identify the residual polarization of another piezoelectric material or whether the C-axis or A-axis of the crystal is in the same direction or in the opposite direction to that of the piezoelectric material 1, and does not limit the polarization direction of the piezoelectric material 1.

  As shown in FIG. 7C, the distortion of each piezoelectric body has periodicity (in the case of FIG. 7C, each piezoelectric body is in series as described above). Therefore, in order to achieve high charge output or high potential output, which is the object of the present invention, when remanent polarization or crystal C-axis or A-axis direction is parallel, each electrode is electrically insulated, It must be wired independently, and the structural and manufacturing risks are extremely high.

  However, according to the present invention, in the case of the parallel connection shown in FIG. 8, the periodic polarization of “+ P, + P, −P, −P” is applied to the residual polarization of the piezoelectric material for every four layers or to the C-axis and A-axis of the crystal. In other words, the second-stage piezoelectric body in contact with the axis of the first-stage piezoelectric body in contact with the back layer is the same direction, and the third and fourth-stage piezoelectric bodies are If the piezoelectric elements are arranged in the reverse direction and the piezoelectric elements of the four layers are arranged so as to have periodicity in the same direction, the same direction, the reverse direction, and the reverse direction thereafter, the electric impedance is 1 / of that of the piezoelectric material of one layer. In addition to being reduced to n, the charge sensitivity between both terminals can be easily amplified n times.

In the above description, the case where the nth harmonic is detected has been described as an example. However, in the case where the nth harmonic is transmitted, the efficiency is improved by connecting an oscillator between the terminals in FIG. To do. In the case of transmission, the relationship between the strain S and the applied electric field E is
S = dE or S = (e / c) E (22). If a voltage generator is connected between both terminals of the laminated piezoelectric material shown in FIG. 8 and a voltage having a frequency corresponding to the nth harmonic is applied, the distortion shown in FIG. 8 and the displacement shown in FIG. Ultrasound can be excited in the medium. And from the relationship of the electrical impedance described above, the structure of the present invention provides low voltage and high current driving.

On the other hand, FIG. 9 is a diagram schematically showing the structure of a 2n-layer piezoelectric transducer for detecting n-order harmonics. (A) is the stacking condition, (b) is the displacement of each layer at a certain moment, and (c) and (d) are the coefficients of strain and electrical displacement, respectively. The coefficients of 0.3 and 0.7 represent the relative ratios of strain and electric displacement, respectively, and do not indicate absolute values. It was approximated as ^{1/2 1/2} = 0.7. Each piezoelectric body was provided with electrodes on the interlayer and both end faces, and the electrodes on the separation side of the piezoelectric bodies adjacent to each other were connected to form a parallel coupling. In this case, the electric displacement due to the piezoelectric positive effect is the same as that of the n-layer piezoelectric transducer described above, but the electric capacity is doubled and the electric impedance is halved. Residual polarization or the arrangement of the C-axis and A-axis is repeated for “+ P, −P, −P, + P, −P, + P, + P, −P” every 8 layers with reference to the piezoelectric body in contact with the back layer. Become.

The strain Sm ^nω of each piezoelectric body is given by the following equation.

Sm ^nω
= 2nξ ₀ ^nω {sin [m (π / 4)] − sin [(m−1) (π / 4)]} / h, m
= 1, 2,..., 2n (23)

  Below, the detailed Example of this invention according to the above-mentioned view is described. First, detection of 3λ / 4 harmonics by the two-layer piezoelectric transducer shown in FIG. 10 will be described as a first embodiment. A two-layer piezoelectric transducer has the simplest structure among laminated piezoelectric materials. In this case, the order of harmonics used for transmission / reception does not match the number of stacked layers. However, by applying the present invention as follows, the efficiency of transmission and reception can be increased.

That is, the strains S ₁ and S ₂ of the piezoelectric body 1 and the piezoelectric body 2 in FIG.
S ₁ = Δh ₁ / h ₁ = ξ ₀ sin (nπ / 2 · h ₁ / h) / h ₁ (24)
S ₂ = Δh ₂ / h ₂
= Ξ ₀ {sin (nπ / 2) −sin (nπ / 2 · h ₁ / h)} / h ₂ (25)
It becomes. Here, h is the height of the laminated piezoelectric material, h ₁ and h ₂ are the height of each piezoelectric material, and h ₁ = h ₂ = h / 2.

The response to the 3λ / 4 resonant harmonic is given by n = 3. In this case, the distortions S ₁ ^3ω and S ₂ ^3ω are
S ₁ ^3ω
= 2ξ ₀ ^3ω sin (3π / 4) / h = 2 (ξ ₀ ^3ω / 2 ^1/2 ) / h (26)
S ₂ ^3ω
= 2ξ ₀ ^3ω {sin (3π / 2) −sin (3π / 4)} / h
= -2ξ ₀ ^3ω (1 + ^{1/2 1/2} ) / h (27)
It becomes. The subscript 3ω indicates the displacement at the third harmonic. Here, when approximated as ^{1/2 1/2} ≈0.7, these equations indicate that the amplitude ratio between the distortion of the piezoelectric body 2 and the distortion of the piezoelectric body 1 is −1.7: +0.7 at the third harmonic wave. Indicates that

  FIG. 11 shows such displacement and distortion codes of each piezoelectric body. (A) is displacement and (b) is distortion. The strain ratio between the piezoelectric body 1 and the piezoelectric body 2 is as shown in FIG. The reason why the absolute values of the strains of the piezoelectric bodies do not match is that the boundaries of the piezoelectric bodies, the nodes of displacement, and the antinodes do not match as described above.

Therefore, as shown in FIG. 12, if the electrodes on the separation surfaces of adjacent piezoelectric materials are connected in parallel to form a parallel coupling, the electrical impedance of the laminated piezoelectric material becomes ½ of the impedance of one piezoelectric material, and the piezoelectric positive The electrical displacement D _{1, −1} ^3ω due to the effect can be obtained by parallel connection if the direction of remanent polarization of the piezoelectric body 1 or the direction of the C-axis or A-axis of the crystal and those directions of the piezoelectric body 2 are the same direction. Polarity is reversed and added together,
D _{1, -1} ^3ω = 2 (1 + 2 ^1/2 ) eξ ₀ ^3ω / h (28)
It becomes.

On the other hand, the response to the fundamental wave can be understood when n = 1 in equations (24) and (25). That is, the strains S ₁ ^ω and S ₂ ^ω are
S ₁ ^ω = 2ξ ₀ ^ω sin (π / 4) / h = 2 (ξ ₀ ^ω / 2 ^1/2 ) / h (29)
S ₂ ^ω = 2ξ ₀ ^ω {sin (π / 2) −sin (π / 4)} / h
= 2ξ ₀ ^ω {1-1 / 2 ^1/2 } / h (30)
It becomes.

Here, when parallel coupling as shown in FIG. 12 is performed and the remanent polarization or the direction of the C-axis or A-axis of the crystal is the same direction, the electric displacement D _1,1 ^ω is
D _1,1 ^ω = 2eξ ₀ ^ω (2 ^1/2 -1) / h (31)
It becomes. Here, the subscript 1 corresponds to the remanent polarization of each piezoelectric body or the direction of the C-axis or A-axis of the crystal, and from the left, the remanent polarization of the piezoelectric body 1 or 2 or the C-axis or A-axis of the crystal. Indicates the direction.

  From the above results, in consideration of the distortion of each piezoelectric body, in the case of parallel connection, the residual polarization or the C-axis and A-axis directions of the crystal are set in the same direction, so that 2.4 times for 3λ / 4 waves. The sensitivity can be amplified, and at the same time, the sensitivity can be reduced by a factor of 0.4 for λ / 4 waves. Therefore, if the present invention is applied to an ultrasonic transducer composed of a two-layer piezoelectric body, it is possible to transmit / receive a signal due to 3λ / 4 resonance at a high S / N ratio.

  FIG. 13 shows experimental results and simulation results of the transmission / reception sensitivity characteristics of an ultrasonic transducer composed of a two-layer piezoelectric material using P (VDF / TrFE). The solid line is the experimental result, and the broken line is the simulation result. In both cases, the separated surfaces of the piezoelectric bodies adjacent to each other, that is, the electrode surfaces formed on the outer surface are connected to each other and connected in parallel, and the λ / 4 resonance frequency is 7 MHz and the 3λ / 4 resonance frequency is about 20 MHz. (A) is a result when the polarization direction is the same direction according to the present invention, and (b) is a result when the reverse direction is set for reference. As shown in (a), when the polarization direction based on the present invention and the wiring method are combined, the 3λ / 4 resonance peak seen at 20 MHz is larger than the λ / 4 resonance peak seen at 7 MHz, and (b) Compared to the results shown, the 3λ / 4 resonance peak is increased by 20 dB. As described above, by combining the polarization direction and the wiring method based on the method of the present invention for the two-layer piezoelectric body, the third harmonic component can be increased and the fundamental wave component can be attenuated at the same time.

  Subsequently, detection of the third harmonic by the three-layer piezoelectric transducer will be described. FIG. 14 shows a schematic structure diagram. This transducer is also a λ / 4 vibrator in which one end of the laminated piezoelectric body is fixed to the base and the other end is a free end.

First, the design process according to the present invention will be described. In the same manner as described above, the boundary between the substrate and the piezoelectric body 1 is the origin, and the coordinate in the height (thickness) direction of the element is z. Next, the strain S generated by each piezoelectric body will be considered. The piezoelectric body 1, the piezoelectric body 2, and the piezoelectric body 3 are formed in this order from the substrate side. Coordinate z is, z = 0 at the boundary between the base and the piezoelectric element 1, z ₁ at the boundary between the piezoelectric body 1 and the piezoelectric body _2, z ₂ at the boundary between the piezoelectric body 2 and the piezoelectric element _3, the end of the piezoelectric element 3 the part and _{z 3.} The thickness of the piezoelectric body 1 is h ₁ , the thickness of the piezoelectric body 2 is h ₂ , the thickness of the piezoelectric body 3 is h _3, and the height of the laminated piezoelectric body is h.

Then, the displacement ξ (z ₁ ) at the coordinate z ₁ is
ξ (z ₁ ) = ξ ₀ sin (nπ / 2 · z ₁ / h) (32)
Therefore, the strain S ₁ of the piezoelectric body ₁ is
S ₁ = Δh ₁ / h ₁ = ξ ₀ sin (nπ / 2 · h ₁ / h) / h ₁ (33)
It becomes. Similarly, for piezoelectric bodies 2 and 3,
S ₂ = Δh ₂ / h ₂
= Ξ ₀ {sin (nπ / 2 · (h ₁ + h ₂ ) / h) −sin (nπ / 2 · h ₁ / h)} / h ₂
... (34)
S ₃ = Δh ₃ / h ₃
= Ξ ₀ {sin (nπ / 2) −sin (nπ / 2 · (h ₁ + h ₂ ) / h)} / h ₃
... (35)
It becomes.

The distortion of each piezoelectric body at the time of 3λ / 4 resonance is given by n = 3 in the above equations (33) to (35). When the thickness of each piezoelectric body is equal, that is, when h ₁ = h ₂ = h ₃ = h / 3 in the above equation, the strains S ₁ ^3ω , S ₂ ^3ω , and S ₃ ^3ω of each piezoelectric body are
S ₁ ^3ω = Δh ₁ ^3ω / h ₁ = 3ξ ₀ ^3ω sin (π / 2) / h
= 3ξ ₀ ^3ω / h (36)
S ₂ ^3ω = Δh ₂ ^3ω / h ₂
= 3ξ ₀ ^3ω {sin (π) −sin (π / 2)} / h
= -3ξ ₀ ^3ω / h (37)
S ₃ ^3ω = Δh ₃ ^3ω / h ₃
= 3ξ ₀ ^3ω {sin (3π / 2) −sin (π)} / h
= −3ξ ₀ ^3ω / h (38) Here, the subscript 3ω means a response in the third harmonic. From these equations, the 3λ / 4 resonance indicates that the distortion of the piezoelectric body 2 and the piezoelectric body 3 and the distortion of the piezoelectric body 1 are in opposite phases.

  FIG. 15 shows the displacement and distortion sign of each piezoelectric body. (A) is displacement and (b) is distortion. In this embodiment, the transmission and reception of the third harmonic and the three piezoelectric bodies are laminated. Therefore, as shown in FIG. 5A and FIG. 5, the displacement nodes and antinodes coincide with the boundaries of the piezoelectric bodies. To do. At this time, the distortion of each piezoelectric body can be encoded with the distortion of the piezoelectric bodies 2 and 3 as-, as shown in FIG. 5B and FIG.

Based on the above behavior of the dynamic system, the optimum structure of the electrical system is derived. As shown in FIG. 16, if the electrodes on the surfaces on the separated side of the piezoelectric bodies adjacent to each other are connected to each other and the wiring is drawn out from the electrodes, the piezoelectric bodies can be easily electrically connected in parallel. At this time, the electrical impedance of the laminated piezoelectric material is reduced to 1/3 of one piezoelectric material. Further, the direction of remanent polarization of the piezoelectric body 1 or the direction of the C-axis or A-axis of the crystal is set as a reference (+ P), and the direction of remanent polarization of the piezoelectric body 2 or the crystal C-axis or A-axis is set in the same direction (+ P). If the piezoelectric body 3 is reverse (−P), the charge induced in the wiring is the sum of the charges generated by the piezoelectric positive effect. At this time, the electric displacement D _{1,1, -1} ^3ω induced between both terminals is
D _{1,1, −1} ^3ω = eS ₁ −e (S ₂ + S ₃ ) = 9 eξ ₀ ^3ω / h (39)
It becomes. Here, the subscripts 1 and -1 correspond to the residual polarization of each piezoelectric body or the direction of the C-axis or A-axis of the crystal, and the residual polarization or crystal of the piezoelectric body 1, the piezoelectric body 2 and the piezoelectric body 3 from the left. The direction of the C axis and the A axis is shown.

The response to the λ / 4 resonance is given by n = 1, and the strains S ₁ , S ₂ , S ₃ of each piezoelectric body are
S ₁ = Δh ₁ / h ₁ = 3ξ ₀ sin (π / 6) / h (40)
S ₂ = Δh ₂ / h ₂
= 3ξ ₀ {sin (π / 3) −sin (π / 6)} / h (41)
S ₃ = Δh ₃ / h ₃
= 3ξ ₀ {sin (π / 2) −sin (π / 3)} / h (42)
That is,
S ₁ = S ₂ + S ₃ (43)
It becomes.

On the other hand, in the parallel connection shown in FIG. 16, the electrical displacement D _{1,1, -1} ^{ω with} respect to the λ / 4 resonance is
D _{1,1, -1} ^ω = e (S ₁ + S ₂ + S ₃ ) = 0 (44)
In the transducer composed of the three-layer piezoelectric material of the present example, the sensitivity based on λ / 4 resonance is canceled out.

As a comparison, the transmission and reception of a third harmonic by a three-layer piezoelectric body in which the residual polarization or the crystal C-axis or A-axis is parallel will be described. The electrical displacement D _1,1,1 ^3ω produced by the piezoelectric positive effect in the laminated piezoelectric body at 3λ / 4 resonance is
D _1,1,1 ^3ω = e (S ₁ + S ₂ + S ₃ ) = − ₃ eξ ₀ ^3ω / h (45)
It becomes. Therefore, in this embodiment, as shown in the above equation (45), it is understood that the electrical displacement between the terminals can be improved three times (about 10 dB) in the parallel connection.

  FIG. 17 shows experimental data and simulation results for the ultrasonic wave transmission / reception characteristics of the three-layer piezoelectric material shown in FIG. In the experiment, a copolymer (P (VDF / TrFE)) of vinylidene fluoride and ethylene trifluoride, which is a typical ferroelectric polymer, was used. The structural schematic diagram of the ultrasonic transducer is shown in the right figure of FIG. In accordance with the present invention, three-layer piezoelectric bodies are electrically connected in series, and the direction of polarization is the same as that shown in FIG. The height of the three-layer piezoelectric body is approximately 120 μm, and the λ / 4 resonance frequency is 4.5 MHz. The solid line in the left figure is the experimental result, and the broken line is the simulation result.

  From FIG. 17, at 20 MHz or less, no peak is shown in the vicinity of 4.5 MHz corresponding to the resonance frequency, and the λ / 4 resonance peak disappears. Therefore, it is understood that the first peak in the transducer of this embodiment is 13.5 MHz, which is its 3λ / 4 resonance.

  As a comparative example, FIG. 18 shows characteristics of a laminated piezoelectric material in which the directions of remanent polarization of the piezoelectric materials 2 and 3 are opposite to those in FIG. As shown in the left figure, this three-layer piezoelectric body has peaks at both 4.5 MHz, which is λ / 4 resonance, and 13.5 MHz, which is the third harmonic component, and the third harmonic component. It is understood that the sensitivity is about −50 to −60 dB, which is about 10 to 20 dB smaller than the result of the present embodiment shown in FIG. From these experimental results, it is understood that by devising the polarization direction based on the method of the present invention, it is possible to increase the third-order harmonic component and simultaneously attenuate the fundamental wave component.

  As described above, in the second embodiment, the method of transmitting and receiving the third harmonic using the three-layer piezoelectric material has been described. Here, the harmonic order of the laminated piezoelectric material is matched with the number of laminated materials. Thus, (i) the vibration mode of each piezoelectric body can be encoded and understood by matching the boundary surface of the piezoelectric body with the elastic wave nodes and antinodes of the piezoelectric body, and based on the sign and wiring method, (ii) The remanent polarization of each piezoelectric material or the direction of the C-axis or A-axis of the crystal is set in the same or opposite direction as appropriate, so that the remanent polarization of each piezoelectric material or the orientation of the C-axis or A-axis of the crystal is simply anisotropic Compared with the case of 3), it is possible not only to increase the sensitivity 3 times (about 10 dB) or more when transmitting / receiving 3λ / 4 waves, but also to have a function as a filter that cancels λ / 4 waves. Moreover, since it is electrically connected in parallel, the electrical impedance can be reduced to 1/3. As described above, when the 3λ / 4 wave is selectively transmitted and received at a high S / N ratio, the present invention is extremely effective. Thereby, in the case of reception, the band separation filter and the amplifier can be reduced. Or even if it does not lead to reduction, in the case of a filter, a loss can be suppressed by reducing the order, and in the case of an amplifier, the gain can be reduced.

  The third embodiment is transmission and reception of the third harmonic by a transducer in which six layers of piezoelectric bodies having the same thickness are laminated. In this embodiment, each piezoelectric body is divided into two piezoelectric bodies in the three-layer piezoelectric body shown in the second embodiment, and not only the electric impedance is further halved when parallel-coupled, but also the upper end. Since the electrode and the lower end electrode are communicated with each other, the entire laminated piezoelectric body can be electrically shielded.

  FIG. 19 is a cross-sectional view showing the structure of the six-layer piezoelectric body and schematically showing displacement and distortion when transmitting / receiving third-order harmonics. Like FIG. 9, (a) is a lamination | stacking condition, (b) is the displacement of each layer in a certain moment, (c) is a coefficient of distortion.

The distortion S ₁ , S ₂ , S ₃ , S ₄ , S ₅ , S ₆ of each piezoelectric body is
S ₁ = 6ξ ₀ sin (π / 4) / h = 6ξ ₀ (1/2 ^1/2 ) (46)
S ₂ = 6ξ ₀ {sin (π / 2) −sin (π / 4)} / h
= 6ξ ₀ (1-1 / 2 ^1/2 ) (47)
S ₃ = 6ξ ₀ {sin (3π / 4) −sin (π / 2)} / h
= 6ξ ₀ (1/2 ^1/2 −1) (48)
S ₄ = 6ξ ₀ {sin (π) −sin (3π / 4)} / h
= 6ξ ₀ (−1/2 ^1/2 ) (49)
S ₅ = 6ξ ₀ {sin (5π / 4) −sin (π)}
= 6ξ ₀ (−1/2 ^1/2 ) (50)
S ₆ = 6ξ ₀ {sin (3π / 2) −sin (5π / 4)}
= 6ξ ₀ (1/2 ^1/2 −1) (51)
It becomes. When approximated to 1/2 ^1/2 ≈0.7, the distortion ratio of each piezoelectric body is as shown in the schematic diagram of FIG.

  FIG. 20 shows a preferred arrangement of remanent polarization or crystal C-axis or A-axis when the electrodes on the separation side in adjacent piezoelectric bodies are connected and electrically connected in parallel. With this configuration, the total charge amount is the same as that in the case of stacking three sheets shown in FIG. 16, but the electrical impedance can be reduced to ½ of that.

  FIG. 21 shows the result of simulating the frequency characteristics of sensitivity in a six-layer piezoelectric body in which a polarization arrangement and wiring are combined as shown in FIG. The 6-layer piezoelectric body has a λ / 4 resonance frequency of 5 MHz. However, as shown in the right figure, by combining the polarization arrangement and the wiring based on the present invention, the sensitivity due to λ / 4 resonance is attenuated and the sensitivity due to 3λ / 4 resonance is maximized as shown in the left figure.

  The ultrasonic diagnostic apparatus according to the present invention is configured by using the laminated piezoelectric body configured as described above for an ultrasonic transducer of an ultrasonic probe. FIG. 22 is a perspective view showing an external configuration of the ultrasonic diagnostic apparatus 1 according to the embodiment of the present invention. The ultrasonic diagnostic apparatus 1 transmits an ultrasonic wave to a subject such as a living body (not shown) and receives an ultrasonic wave generated by reflection or the like on the subject; The ultrasonic probe 2 is connected to the subject via the cable 3 and transmits a transmission signal of an electrical signal via the cable 3 to cause the ultrasonic probe 2 to transmit the ultrasonic signal to the subject. At the same time, the diagnostic apparatus main body 4 is configured to image the internal state of the subject as a tomographic image based on a signal received by the ultrasound probe 2.

  The diagnostic apparatus main body 4 includes an operation panel 5 and a display panel 6 on the upper part thereof, and various setting operations are performed from the operation panel 5. The display panel 6 receives a support image for the operation and a reception. A tomographic image or the like created based on the ultrasonic signal is displayed. In addition, a holder 7 for holding the ultrasonic probe 2 when not in use is provided at appropriate positions of the operation panel 5 and the diagnostic apparatus main body 4.

  FIG. 23 is a block diagram showing an electrical configuration of the diagnostic apparatus body 4. The diagnostic apparatus body 4 includes an operation input unit 11 (the operation panel 5), a transmission unit 12, a reception unit 13, a signal processing unit 14, an image processing unit 15, and a display unit 16 (the display panel 6). , A control unit 17, a voltage control unit 18, and a reference signal storage unit 19.

  The operation input unit 11 includes an operation panel including a plurality of input switches, a keyboard, and the like, and inputs a command for instructing the start of diagnosis and data such as personal information of the subject.

  The transmission unit 12 is a circuit that performs forming so that transmission pulses from the piezoelectric elements of the ultrasonic probe 2 converge to a predetermined focal position under the control of the control unit 17, and in this embodiment, The transmission pulse is composed of a plurality of encoded pulses expanded in the time axis direction. The created transmission pulse is given to the voltage control unit 18 via the control unit 17, and the amplitude is expanded and given to each piezoelectric element.

  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 received ultrasound from the output of the receiving unit 13 by performing a correlation process between the output of the receiving unit 13 and a preset reference signal. This reference signal is an approximate function derived from the order of third and higher harmonics to be detected, the diagnosis part of the subject, and the diagnosis depth when the frequency of the transmitted ultrasonic wave is the fundamental frequency.

  The signal processing unit 14 compresses the encoded pulse in the time axis direction before performing the correlation process, and creates a reception pulse corresponding to the transmission pulse. Thus, by using the encoded pulse, it is possible to obtain a reception pulse having a large amplitude, that is, a good S / N, without the influence on the living body being the subject being increased. The decoding filter for extracting only the third and higher harmonics has a more complicated structure than the decoding filter for extracting the fundamental wave component, combined with a band pass filter, or changes the type of the encoded pulse. Thus, it is possible to achieve both improvement of S / N and extraction of the third and higher order high frequencies. The decompression / compression by the encoded pulse is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-225237.

  The reference signal storage unit 19 includes a storage element such as a ROM or an EEPROM, and stores an approximate function corresponding to each of a plurality of diagnosis parts and diagnosis depths in the subject as the reference signal. Then, the signal processing unit 14 selects one reference signal from a plurality of reference signals (approximate functions) stored in the reference signal storage unit 19 according to the diagnosis part and the diagnosis depth of the subject. To perform correlation processing. Further, in response to the selected reference signal, the transmission unit 12 performs beam forming. The diagnosis part and the diagnosis depth are input from the operation input unit 11.

  The image processing unit 15 is a circuit that generates an image (ultrasonic image) of the internal state of the subject based on the received signal subjected to correlation processing by the signal processing unit 14 under the control of the control unit 17.

  The display unit 16 is a device that displays an ultrasound image of the subject 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 display, LCD, organic EL display, or 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, and the reference signal storage unit 19 are provided. This is a circuit that performs overall control of the ultrasonic diagnostic apparatus 1 by controlling the image processing unit 15 and the display unit 16 in accordance with the function.

  FIG. 24 is a cross-sectional view schematically showing the structure of an ultrasonic transducer 21 used as the ultrasonic transducer 20 in the ultrasonic probe 2. The ultrasonic transducer 21 is formed by arranging a plurality of piezoelectric elements on a straight line, and the arrangement direction of the piezoelectric elements is a direction (thickness) perpendicular to the paper surface of FIG. This ultrasonic transducer 21 is basically an organic-inorganic laminated ultrasonic transducer, and a transmitting piezoelectric layer 23 made of an inorganic material is first formed on a backing (back) layer 22 so that high power transmission is possible. A reception piezoelectric layer 25 made of an organic material capable of receiving a harmonic band for harmonic imaging is provided on the subject side of the transmission piezoelectric layer 23, which is laminated, via an intermediate layer 24. Is done. Then, the transmission pulse from the voltage control unit 18 is given to the transmission piezoelectric layer 23 which is the second piezoelectric body, and the reception signal at the reception piezoelectric layer 25 which is the first piezoelectric body is sent to the reception unit 13. Given.

  Here, an intermediate layer 24 is provided between the transmitting piezoelectric layer 23 and the receiving piezoelectric layer 25 to alleviate the difference in acoustic impedance between them. In this embodiment, the receiving layer Since the piezoelectric layer 25 for use is made of an organic material as will be described later, the acoustic impedance becomes close to the living body that is the subject, and the acoustic matching layer is not provided. Thus, the structure of the ultrasonic transducer 21 is simplified. However, an acoustic lens may be provided on the receiving piezoelectric layer 25 as necessary.

  In the ultrasonic transducer 21 configured as described above, the laminated piezoelectric material shown in FIG. 8, FIG. 9, FIG. 12, FIG. 16, or FIG. 20 is used for the receiving piezoelectric layer 25 made of the organic material. When the wavelength of the transmission ultrasonic wave is λ, the transmission piezoelectric layer 23 performs λ / 4 resonance, and the reception piezoelectric layer 25 performs 3λ / 4 resonance. As described above, the reception piezoelectric layer 25 Extracts the third harmonic of the wavelength λ with high gain and removes the fundamental wave. This eliminates the need for a filter or an amplifier in the receiving unit 13, or reduces the order of the filter or reduces the gain of the amplifier even when these filters or amplifiers are used. Moreover, it is possible to use an inorganic piezoelectric material and an organic piezoelectric material suitable for both transmission and reception, and suitable for harmonic imaging that performs high-power transmission and receives harmonics generated in the subject with high gain. The ultrasonic probe 2 can be realized.

  On the other hand, FIG. 25 is a sectional view schematically showing the structure of another ultrasonic transducer 31 used as the ultrasonic transducer 20 in the ultrasonic probe 2. The transducer 21 is also formed by arranging a plurality of piezoelectric elements on a straight line, and the arrangement direction of the piezoelectric elements is a direction (thickness) perpendicular to the paper surface of FIG. The ultrasonic transducer 31 is an organic-inorganic parallel-arranged ultrasonic transducer, and can receive a harmonic band for harmonic imaging at the central portion in the width direction on the straight backing (back) layer 32. A receiving piezoelectric layer 35 made of an organic material is provided, and transmitting piezoelectric layers 33 and 34 made of an inorganic material are arranged side by side so that high power transmission is possible on both sides in the width direction.

  On these piezoelectric layers 33, 34, and 35, acoustic matching layers 33a, 34a, and 35a and acoustic lenses 33b, 34b, and 35b with a living body as a subject are laminated. Further, interposed members 33c, 34c, and 35c are interposed between the piezoelectric layers 33, 34, and 35 and the backing layer 32, respectively, and the interposed member 35c of the central receiving piezoelectric layer 35 is a flat plate. On the other hand, the interposition members 33c, 34c of the transmitting piezoelectric layers 33, 34 on both sides are formed in a wedge shape so as to incline the transmitting piezoelectric layers 33, 34 toward the receiving piezoelectric layer 35 side. In FIG. 25, for easy understanding, the inward inclination angles of the wedge-shaped interposition members 33c and 34c are emphasized to be larger than actual.

  Also in the ultrasonic transducer 31 configured as described above, the laminated piezoelectric material shown in FIG. 8, FIG. 9, FIG. 12, FIG. 16, or FIG. 20 is used for the receiving piezoelectric layer 35 made of the organic material. . When the wavelength of the transmission ultrasonic wave is λ, the transmission piezoelectric layers 33 and 34 perform λ / 4 resonance, and the reception piezoelectric layer 35 performs 3λ / 4 resonance. The layer 35 extracts the third harmonic of the wavelength λ with a high gain and removes the fundamental wave. This eliminates the need for a filter or an amplifier in the receiving unit 13, or reduces the order of the filter or reduces the gain of the amplifier even when these filters or amplifiers are used. In addition, it is possible to use an inorganic piezoelectric material and an organic piezoelectric material that are suitable for transmission and reception, respectively. Ultrasonic waves suitable for harmonic imaging that perform high power transmission and receive high-frequency harmonics generated in the subject. The probe 2 can be realized.

  Hereinafter, a specific method and material for producing a laminated piezoelectric material used as the receiving piezoelectric layers 25 and 35 that perform the 3λ / 4 resonance will be described in detail. In general, an ultrasonic vibrator is configured by arranging a pair of electrodes with a piezoelectric layer (also referred to as a “piezoelectric layer”, “piezoelectric film”, or “piezoelectric film”) made of a film-like piezoelectric material interposed therebetween. The ultrasonic transducer 20 is configured by arranging a plurality of vibrators (piezoelectric elements) in one or two dimensions as described above. As a method of arranging the plurality of vibrators, one vibrator can be attached to the backing layer, an acoustic matching layer or the like can be attached as necessary, and then divided into each element by dicing.

  As for the aspect ratio of each element of the laminated vibrator divided into a plurality of parts, W / H is preferably 0.4 to 0.6, where W is the width in the azimuth direction and H is the height. This suppresses interference between vibration in the transmission / reception direction in which ultrasonic waves propagate and vibration (lateral vibration) in the scanning direction (arrangement direction) orthogonal to the transmission / reception direction, and narrows the directivity characteristics of the transducer in the arrangement direction. This is because the sensitivity can be maintained even at a large deflection angle without limiting the beam directivity angle.

  Then, a predetermined number of transducers in the major axis direction in which a plurality of transducers are arranged is set as the aperture, and the plurality of transducers belonging to the aperture are driven to converge the ultrasonic beam on the measurement site in the subject. And receiving a reflected echo of an ultrasonic wave emitted from the subject by a plurality of transducers belonging to the aperture or different from the transducer belonging to the aperture and converting it into an electrical signal Yes.

  In realizing the laminated piezoelectric material shown in FIG. 8, FIG. 9, FIG. 12, FIG. 16 or FIG. 20, when the laminated piezoelectric material is made of an inorganic material such as ceramic, the piezoelectric material layer and the electrode layer are laminated. And integrated by firing.

  On the other hand, when the laminated piezoelectric material is made of an organic material such as PVDF, an electrode layer is formed on part or all of the front and back surfaces, and a layer of polarized organic material is laminated and the layers are connected with an adhesive. Integrated. At this time, it is preferable that the contact surfaces of the electrode layers overlap each other. This is to prevent the formation of an unnecessary electric field and the formation of a non-uniform sound field when the vibrator is driven or when an ultrasonic wave is received. Note that although the adhesive is insulative, the rough surfaces (fine irregularities) of the organic material layer and the electrode layer enter each other when laminated, and adjacent electrodes become conductive. After laminating and bonding, unnecessary portions at the end of the vibrator are scraped off and formed into a size to be mounted on the transducer. After that, when connecting each piezoelectric body in parallel, the electrode extraction direction is switched every other pair as described above and connected with the conductive paste, so that the signal electrode and the GND are formed on both sides on the backing layers 22 and 32 side. Each of the electrodes can be extracted.

As a material of the laminated piezoelectric material, 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 these 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 nylons, alicyclic nylons, Organic piezoelectric materials such as polyhydroxycarboxylic acids such as polylactic 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 ultrasonic transducers 21 and 31 shown in FIGS. 24 and 25, the above-described inorganic material is used for the transmitting piezoelectric layers 23; 33, 34, and the organic material is used for the receiving piezoelectric layers 25; 35.

  The layer thickness of one layer of the laminated piezoelectric material is preferably in the range of 5 to 200 μm in consideration of workability, although it depends on the set center frequency (wavelength λ). And since the thickness of each piezoelectric body A1-A3 etc. is mutually equal, since manufacture of each piezoelectric body becomes easy, productivity of the ultrasonic transducers 21 and 31 can be improved.

  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, the piezoelectric layer (piezoelectric film) is polarized. 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.

  On the other hand, although not formed by the ultrasonic transducer 21 in FIG. 24, the acoustic matching layers 33a, 34a, 35a and the acoustic lenses 33b, 34b, 35b formed by the ultrasonic transducer 31 in FIG. 25 are formed as follows. is there. The acoustic matching layers 33a, 34a, and 35a are formed so that reflection at the boundary surface is caused by a difference in acoustic impedance between the vibrator and the living tissue, and free vibration continues for a long time. It is interposed between tissues and has an acoustic impedance intermediate between the two. By interposing this acoustic matching layer, reflection at the boundary surface is reduced, free vibration is quickly focused, the width of the ultrasonic pulse transmitted and received by the transducer is shortened, and the ultrasonic wave is effective in the living body. Will be propagated to.

  Examples of materials used for the acoustic matching layers 33a, 34a, and 35a include metal materials (aluminum, aluminum alloys (for example, Al-Mg alloys), magnesium alloys, etc.), glasses (Macor glass, silicate glass, fused quartz). ), Carbon materials (carbon graphite, copper graphite, etc.), resin materials (polyethylene (PE), polypropylene (PP), polycarbonate (PC), nylon (PA6, PA6-6), polyphenylene sulfide (PPS, glass fiber) Can be entered), polyphenylene ether (PPE), polyether ether ketone (PEEK), polyamideimide (PAI), polyethylene terephthalate (PETP), epoxy resin, urethane resin, ABC resin, ABS resin, AAS resin, AES resin, etc. ) Etc. Preferably, a thermosetting resin such as an epoxy resin is molded by adding zinc white, titanium oxide, silica, alumina, bengara, ferrite, tungsten oxide, yttrium oxide, barium sulfate, tungsten, molybdenum, etc. as a filler. Can be used.

  The acoustic matching layers 33a, 34a, and 35a may be a single layer or a plurality of layers. Preferably, there are two or more layers. The thickness of the acoustic matching layers 33a, 34a, and 35a must be determined to be λ / 4 when the wavelength of the transmission ultrasonic wave is λ (in FIGS. 24 and 25, the transmission piezoelectric layer 23; 33). , 34 is thicker because the ultrasonic velocity is faster than in the receiving piezoelectric layers 25, 35). If this is not met, a plurality of unnecessary spurs appear at frequency points different from the original resonance frequency, the basic acoustic characteristics fluctuate greatly, and the sensitivity and S / N decrease due to increased reverberation time and waveform distortion of the reflected echo. Will cause. The acoustic matching layers 33a, 34a, and 35a are generally used in a thickness range of 30 μm to 500 μm.

  In addition, the backing layers 22 and 32 are disposed on the back surface of the ultrasonic transducer, and suppress (absorb) the propagation of ultrasonic waves radiated backward. Also by this, unnecessary reflection to the vibrator side can be suppressed and the pulse width can be shortened. The materials used for these backing layers 22 and 32 include natural rubber, ferrite rubber, epoxy resin, tungsten oxide, titanium oxide, ferrite, etc., press-molded material, vinyl chloride, polyvinyl butyral (PVB) , ABS resin, polyurethane (PUR), polyvinyl alcohol (PVAL), polyethylene (PE), polypropylene (PP), polyacetal (POM), polyethylene terephthalate (PET), fluororesin (PTFE), polyethylene glycol, polyethylene terephthalate-polyethylene glycol A thermoplastic resin such as a copolymer 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 can be appropriately selected according to the shape of the piezoelectric body and the probe head including the piezoelectric body. .

  As the rubber-based composite material, a material containing a rubber component and a filler is preferable. From a type A durometer in a spring hardness tester (durometer hardness) according to JIS K6253 to A70 from a type D durometer. It has hardness, and various other compounding agents may be added as necessary.

  Examples of the rubber component include ethylene propylene rubber (EPDM or EPM), hydrogenated nitrile rubber (HNBR), chloroprene rubber (CR), silicone rubber, EPDM and HNBR blend rubber, and EPDM and nitrile rubber (NBR). Blend rubber, NBR and / or HNBR and high styrene rubber (HSR) blend rubber, EPDM and HSR blend rubber and the like are preferable. More preferably, ethylene propylene rubber (EPDM or EPM), hydrogenated nitrile rubber (HNBR), EPDM and HNBR blend rubber, EPDM and nitrile rubber (NBR) blend rubber, NBR and / or HNBR and high styrene rubber (HSR) ) And a blend rubber of EPDM and HSR. As the rubber component of this embodiment, one of rubber components such as vulcanized rubber and thermoplastic elastomer may be used alone, but a blend rubber obtained by blending two or more rubber components such as a blend rubber is used. May be.

  The filler to be added to the rubber component can be selected in various forms along with the blending amount from those usually used to those having a large specific gravity. For example, zinc oxide, white titanium, bengara, ferrite, alumina, tungsten trioxide, yttrium oxide and other metal oxides, calcium carbonate, hard clay, diatomaceous earth clays, calcium carbonate, barium sulfate and other metal salts, glass Examples include powders, various metal fine powders such as tungsten and molybdenum, and various balloons such as glass balloons and polymer balloons. These fillers can be added at various ratios, preferably 50 to 3000 parts by weight, more preferably about 100 to 2000 parts by weight, or about 300 to 1500 parts by weight with respect to 100 parts by weight of the rubber component. It is. Moreover, you may add these fillers combining 1 type (s) or 2 or more types.

  Other compounding agents can be added to the rubber-based composite material as necessary. Examples of such compounding agents include vulcanizing agents, cross-linking agents, curing agents, auxiliaries, and deterioration inhibitors. , Antioxidants, colorants and the like. For example, carbon black, silicon dioxide, process oil, sulfur (vulcanizing agent), dicumyl peroxide (Dicup, crosslinking agent), stearic acid and the like can be blended. These compounding agents are used as necessary, but the amount used is generally about 1 to 100 parts by mass with respect to 100 parts by mass of the rubber component, but it is appropriately changed depending on the overall balance and characteristics. You can also

  As said epoxy resin composite agent, it is preferable to contain an epoxy resin component and a filler, and various compounding agents can also be added as needed. Examples of the epoxy resin component include bisphenol A type, bisphenol F type, resol novolak type, novolac type epoxy resin such as phenol-modified novolak type, naphthalene structure-containing type, anthracene structure-containing type, fluorene structure-containing type, etc. Type epoxy resin, hydrogenated alicyclic epoxy resin, liquid crystalline epoxy resin and the like. Although the epoxy resin component of a present Example may be used independently, you may mix and use two or more types of epoxy resin components like a blend resin.

  The filler added to the epoxy resin component is preferably used from the same filler as that mixed with the rubber component to composite particles prepared by pulverizing the rubber composite. Can do. Examples of the composite particles include those in which a silicone rubber filled with ferrite is pulverized with a pulverizer to have a particle size of about 200 μm.

  When using the epoxy resin composite agent, it is necessary to add a crosslinking agent, for example, chain aliphatic polyamines such as diethylenetriamine, triethylenetetramine, dipropylenediamine, diethylaminopropylamine, N-aminoethylpiperazine, Cycloaliphatic polyamines such as mensendiamine, isophoronediamine, aromatic amines such as m-xylenediamine, metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, polyamide resin, piperidine, NN-dimethylpiperazine, triethylenediamine, 2, Secondary and tertiary amines such as 4,6-tris (dimethylaminomethyl) phenol, benzyldimethylamine, 2- (dimethylaminomethyl) phenol, 2-methylimidazole, 2-ethyl Imidazole, imidazoles such as 1-cyanoethyl-2-undecylimidazolium trimellitate, liquid polymercaptan, polysulfide, phthalic anhydride, trimellitic anhydride, methyltetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride, methylbutyrate Examples of the acid anhydride include tenenyltetrahydrophthalic anhydride and methylhexahydrophthalic acid.

  The thickness of the backing layers 22 and 32 thus formed is preferably approximately 1 to 10 mm, and particularly preferably 1 to 5 mm.

On the other hand, the acoustic lenses 33b, 34b, and 35b are provided to focus the ultrasonic beam by using refraction and improve the resolution. It closely adheres and matches the acoustic impedance (density × sound speed; (1.4 to 1.6) × 106 kg / m ² · sec) between the piezoelectric layers 33, 34, and 35 and the living body to reduce reflection of ultrasonic waves. In addition, it is a necessary condition that the ultrasonic attenuation amount of the lens itself is small. For this reason, acoustic lenses made based on polymer materials are conventionally provided.

  As the lens material used here, it is desirable that the sound velocity is sufficiently smaller than that of the human body, the attenuation is small, and the acoustic impedance is close to the value of the human skin. If the sound velocity of the lens material is sufficiently smaller than that of the human body, the lens shape can be made convex, and slipping can be improved during diagnosis, which can be performed safely. In addition, if attenuation is reduced, ultrasound can be transmitted and received with good sensitivity, and if the acoustic impedance is close to the value of the human skin, the reflection will be small, in other words, the transmittance will be large. Similarly, the transmission / reception sensitivity of ultrasonic waves is improved.

  In this embodiment, the material constituting the acoustic lenses 33b, 34b, and 35b is formed by copolymerizing a conventionally known homopolymer such as silicone rubber, butadiene rubber, polyurethane rubber, epichlorohydrin rubber, and ethylene and propylene. Copolymer rubber such as ethylene-propylene copolymer rubber can be used. Of these, it is particularly preferable to use silicone rubber.

  Examples of the silicone rubber used in this embodiment include silicone rubber and fluorine silicone rubber. Among these, it is preferable to use silicone rubber because of the characteristics of the lens material. Silicone rubber is an organopolysiloxane having a molecular skeleton composed of Si—O bonds, and having a plurality of organic groups bonded to Si atoms. Usually, the main component is methylpolysiloxane, and the entire organic group is organic. 90% or more of the groups are methyl groups. A material in which a hydrogen atom, a phenyl group, a vinyl group, an allyl group or the like is introduced instead of the methyl group can also be used. The silicone rubber can be obtained, for example, by kneading a curing agent (vulcanizing agent) such as benzoyl peroxide with organopolysiloxane having a high degree of polymerization, followed by heat vulcanization and curing. If necessary, organic or inorganic fillers such as silica and nylon powder, and vulcanization aids such as sulfur and zinc oxide may be added.

  Examples of the butadiene rubber used in this embodiment include butadiene alone or a copolymer rubber mainly composed of butadiene and copolymerized with a small amount of styrene or acrylonitrile. Among these, it is preferable to use butadiene rubber because of the characteristics of the lens material. Butadiene rubber refers to a synthetic rubber obtained by polymerization of butadiene having a conjugated double bond. Butadiene rubber can be obtained by polymerizing 1.4 to 1.2 butadiene alone having a conjugated double bond. The butadiene rubber is preferably vulcanized with sulfur or the like.

  The acoustic lenses 33b, 34b, and 35b according to the present embodiment may be obtained by mixing and curing and curing silicone rubber and butadiene rubber. Specifically, it can be obtained by mixing silicone rubber and butadiene rubber in an appropriate ratio by a kneading roll, adding a vulcanizing agent such as benzoyl peroxide, heat vulcanizing, and crosslinking (curing). . At that time, it is preferable to add zinc oxide as a vulcanization aid. Zinc oxide can accelerate vulcanization and shorten the vulcanization time without deteriorating lens characteristics. In addition, other additives may be added as long as the characteristics of the colorant and the acoustic lens are not impaired. The mixing ratio of the silicone rubber and the butadiene rubber is preferably 1: 1 in order to obtain a material whose acoustic impedance is close to that of the human body and whose sound speed is smaller than that of the human body and less attenuated. The mixing ratio can be changed as appropriate.

  Silicone rubber can be obtained as a commercial product. For example, KE742U, KE752U, KE931U, KE941U, KE951U, KE96U, KE850U, KE555U, KE575U, etc. manufactured by Shin-Etsu Chemical Co., Ltd., TSE221-3U, TE221 -4U, TSE2233U, XE20-523-4U, TSE27-4U, TSE260-3U, TSE-260-4U, SH35U, SH55UA, SH831U, SE6749U, SE1120USE4704U manufactured by Dow Corning Toray, Inc. can be used.

  In this embodiment, the rubber material such as the above-mentioned silicone rubber is used as a base (main component), and according to purposes such as sound speed adjustment and density adjustment, inorganic fillers such as silica, alumina, titanium oxide, and nylon An organic resin such as can also be blended. In addition, a substance that emits light when irradiated with excitation light, that is, a luminescent substance, may be added to a region near the subject surface of the acoustic lenses 33b, 34b, and 35b.

  On the other hand, generally used epoxy resin is suitable for adhesion between members used in this embodiment. Specific examples of commercially available epoxy adhesives include DP-420, DP-460, DP-460EG manufactured by 3M Company, Excel Epoe manufactured by Cemedine, EP001, EP008, EP330, EP331, manufactured by Huntsman Advanced Materials Araldite Standard (registered trademark), Araldite Rapid (registered trademark), System Three Epoxy from System Three, Gel Magic, 2087L (High-strength two-part epoxy compound resin) from Three Bond, 2082C (Temperature curing type two-part Epoxy resin high shear adhesive type), 2081D (adhesive epoxy for soft vinyl chloride), E-set L manufactured by Konishi, Durarco 4525IP, 7050, NM25, 4461IP manufactured by Kotronics. However, strong adhesiveness, low reactivity, etc. are required from the viewpoint of dicing suitability and drug resistance. Furthermore, since it is required to make the adhesive layer as thin as possible, one having a low viscosity is preferable. The thickness of the adhesive layer is preferably 0.5 to 3 μm.

A method for manufacturing a piezoelectric body will be described below. First, it is an inorganic piezoelectric material used as the transmitting piezoelectric material 23; 33, 34. Component raw materials CaCO ₃ , La ₂ O ₃ , Bi ₂ O ₃ and TiO ₂ , and subcomponent raw materials MnO are prepared. For the component raw materials, the final composition of the components is (Ca _0.97 La _{0. 03} ) Weighed to be Bi _4.01 Ti ₄ O ₁₅ .

  Next, pure water was added, mixed for 8 hours in a ball mill containing zirconia media in pure water, and sufficiently dried to obtain a mixed powder. The obtained mixed powder was temporarily molded and calcined in air at 800 ° C. for 2 hours to prepare a calcined product.

  Next, pure water was added to the obtained calcined material, finely pulverized in a ball mill containing zirconia media in pure water, and dried to prepare a piezoelectric ceramic raw material powder. In the fine pulverization, the piezoelectric ceramic raw material powder having a particle diameter of 100 nm was obtained by changing the pulverization time and pulverization conditions.

  After adding 6% by mass of pure water as a binder to each piezoelectric ceramic raw material powder having a different particle diameter, press molding to form a plate-shaped temporary molded body having a thickness of 100 μm, and vacuum-packing the plate-shaped temporary molded body, Molding was performed by pressing at a pressure of 235 MPa.

  Next, the molded body is fired, and the final sintered body has a thickness of 20 μm. The firing temperature was 1100 ° C. Thereafter, an electric field of 1.5 × Ec (MV / m) or more was applied for 1 minute to perform polarization treatment.

  Next, a method for producing an organic piezoelectric body used as the receiving piezoelectric bodies 25 and 35 will be described. The organic piezoelectric material according to this example is a film that can be stretched at a temperature not lower than room temperature and not higher than 10 ° C. below the melting point having the above-described polymer material as a main component, and keeps the tension within a certain range. While being heat-treated, and subsequently cooled to room temperature, it can be produced by stretching the second stage.

  When the organic piezoelectric material containing vinylidene fluoride according to this embodiment is used as a vibrator, it is formed in a film shape, and then a surface electrode for inputting an electric signal is formed. The present embodiment is characterized in that an electric field is applied in the thickness direction through an electrode formed on the surface and polarization is performed while pressing, but the electrode is not formed on the surface, and the surface contacting the material of the compression member is used. The same effect can be obtained by installing an electrode to which a voltage can be applied, and polarizing while applying an electric field in the thickness direction of the material while being similarly pressed.

  For film formation, a general method such as a melting method or a casting method can be used. In the case of polyvinylidene fluoride-trifluoroethylene copolymer, it is known that it has a crystal form with spontaneous polarization just by making it into a film, but in order to further improve the characteristics, a process for aligning the molecular arrangement should be added. Is useful. Examples of means include stretching film formation and polarization treatment.

  Various known methods can be adopted for the method of stretching film formation. For example, a solution obtained by dissolving the above polymer material in an organic solvent such as ethyl methyl ketone (MEK) is cast on a substrate such as a glass plate, and the solvent is dried at room temperature to obtain a film having a desired thickness. The film is stretched to a predetermined length at room temperature. The stretching can be performed uniaxially or biaxially so that the organic piezoelectric material having a predetermined shape is not destroyed. The draw ratio is 2 to 10 times, preferably 2 to 6 times.

  In the vinylidene fluoride-trifluoroethylene copolymer and / or vinylidene fluoride-tetrafluoroethylene copolymer, the melt flow rate at 230 ° C. is 0.03 g / min or less. More preferably, a high-sensitivity piezoelectric thin film can be obtained by using a polymer piezoelectric body of 0.02 g / min or less, more preferably 0.01 g / min or less.

  In general, when a film-like material is heat-treated, it is preferable that the end portion is supported by a chuck or a clip and placed in a predetermined temperature environment in order to efficiently and uniformly heat the film surface. At this time, it is not preferable to apply heat in such a form that the film surface is directly in contact with a heat source such as a heat plate because the flatness is impaired in the case of a material that contracts during heating. Rather, a slight relaxation treatment is more effective for planarity against thermal contraction during heating. The relaxation treatment here refers to changing the stress at both ends of the film while following the shrinkage or expansion force applied to the film in the process of cooling to room temperature after the heat treatment. As long as the film is not loosened and the flatness cannot be maintained, or the stress increases and breaks, the relaxation treatment can be expanded to such an extent that even if it is shrunk so as to relieve the stress, it does not stretch in the direction of applying tension. Also good. In this example, when the stretched direction is determined to be positive, the length is about 10%. When the film stretches during cooling, the second stage is at most about 10% so as to follow the slack. Stretching is performed. This second stage of stretching is performed by operating the stretching chuck to such an extent that looseness is eliminated so that the film is in a taut state. Further processing results in stretching during cooling and may cause film breakage.

  In the heat treatment of the organic piezoelectric material of this example, in order to efficiently and uniformly heat the film surface, the end is supported by a chuck or a clip, and the upper limit is 10 ° C. lower than the melting point of the film. It is preferable to place it near the temperature. For example, in the case of an organic piezoelectric material mainly composed of polyvinylidene fluoride, the melting point is 150 to 180 ° C., and therefore, it is preferable to perform heat treatment at a temperature of 110 to 140 ° C. In addition, the effect is manifested by performing it for 30 minutes or longer, and the longer it is, the more the crystal growth is promoted. However, since it saturates with time, it is practically about 10 hours, at most about day and night. is there. In order to maintain the flatness of the film during this period, it is preferable that a certain tension is applied to the film. The tension during the heat treatment is preferably in the range of 0.1 to 500 kPa from the viewpoint of finished flatness, and more preferably as low as possible. The film during the heat treatment is soft, and if the tension becomes larger than this value, the film is further extended, so that not only the effect of the heat treatment is lost but also the breakage may occur.

  After the electrodes are attached to both surfaces of the organic piezoelectric material prepared as described above, a voltage is applied between the electrodes under pressure by an insulating member to perform polarization treatment. In general, a piezoelectric material is a material having a characteristic of causing a deformation response to an electric field response. Therefore, the deformation response is also caused by the electric field during the polarization process. In other words, the material is deformed by the electric field even during the process of imparting the characteristics as a piezoelectric material by applying an electric field to the material and subjecting it to polarization treatment. For this reason, the material often deforms after the polarization treatment and may not retain its initial shape. Therefore, in this embodiment, in order to suppress the deformation during the polarization, the polarization process is performed while pressing as described above, so that the flatness before and after the polarization process is reduced. In addition, an organic piezoelectric material having high piezoelectric characteristics is obtained.

Here, the pressing force, that is, the degree of pressing pressure, is preferably at least 0.98 MPa (10 kg / cm ² ) or more and 9.8 MPa (100 kg / cm ² ) or less. The deformation can be suppressed by setting it to 0.98 MPa (10 kg / cm ² ) or more, and the occurrence of deformation in the thickness direction can be prevented by setting it to 9.8 Ma (100 kg / cm ² ) or less. This is because the initial thickness can be maintained, or the applied current of the polarization treatment can be prevented from being short-circuited. As the polarization processing method according to the present embodiment, a known DC voltage application process or a voltage application process method such as an AC voltage application process can be applied.

Hereinafter, the present invention will be described with specific examples of organic piezoelectric materials, but the present invention is not limited thereto. In this embodiment, P (VDF-TrFE) is used as the organic piezoelectric material. The synthesis method is as follows. In a stainless steel pressure-resistant autoclave with an internal volume of 14 L, 70 parts (3000 g) of vinylidene fluoride (VDF; manufactured by Sigma Aldrich), 30 parts of ethylene trifluoride (TrFE; manufactured by Sigma Aldrich), 210 parts of pure water, methylcellulose ( 0.1 parts by Tokyo Kasei Co., Ltd., 0.2 parts by sodium pyrophosphate (by Taihei Chemical Industrial Co., Ltd.), 0.61 parts by di-normal propyl peroxydicarbonate (by NOF Corporation), and polymerized at 25 ° C. Started. In 3 hours, 3.0 parts of ethyl acetate was added, and the polymerization reaction was continued. Thereafter, when the internal pressure of the autoclave decreased to 25 kg / cm ² , the unreacted material was recovered, and the polymer was dehydrated and washed with water three times in order, and then dried under reduced pressure. The yield was 26%. When the obtained P (VDF-TrFE) was evaluated, the molecular weight was 255000 and the dispersion was 2.4.

  The weight average molecular weight (Mn) and the molecular weight distribution (Mw / Mn) were calculated by gel permeation chromatography (GPC) in the following manner. The measurement conditions are as follows.

Solvent: 30 mM LiBr in N-methylpyrrolidone Device: HLC-8220GPC (manufactured by Tosoh Corporation)
Column: TSKgel SuperAWM-H x 2 (manufactured by Tosoh Corporation)
Column temperature: 40 ° C
Sample concentration: 1.0 g / L
Injection volume: 40 μl
Flow rate: 0.5 ml / min
Calibration curve: Standard polystyrene: PS-1 (manufactured by Polymer Laboratories) Mw = 580 to 2,560,000 calibration curves with 9 samples were used.

  The composition was determined by 1H-NMR. A 3 wt% heavy dimethyl sulfoxide solution of the obtained P (VDF-TrFE) was prepared, put into a sample tube, and an NMR (nuclear magnetic resonance) apparatus (<http://www.varianjapan.com/product/nmr/001/ index.html> Varian 400-MR (manufactured by Varian) was analyzed at a frequency of 400 MHz. From the analysis of the obtained data (see FIG. 26), the proton signal peculiar to TrFE appearing near 5.3-6.0 ppm and the proton signal peculiar to VDF appearing near 2.3-3.3 ppm From this ratio, it was determined that VDF / TrFE = 3/1.

  Similarly, VDF homopolymer PVDF was also polymerized. From the GPC evaluation, the molecular weight was 200,000 and the dispersion was 2.1.

  The obtained P (VDF-TrFE) was applied to a glass plate using methyl ethyl ketone (manufactured by Kanto Chemical Co., Inc.) as a solvent to a dry film thickness of 40 ± 1 μm, and dried at 60 ° C. for 30 minutes to produce an organic piezoelectric film. did.

And after forming a chromium electrode with a thickness of 0.1 μm on the surface of the P (VDF-TrFE) (film thickness: 40 ± 1 μm) by vapor deposition, a gold electrode with a thickness of 0.2 μm is formed by vapor deposition, The organic piezoelectric film is sandwiched between acrylic plates so that a pressure of 30 kgf / cm ² is uniformly applied to the portion excluding both ends, and one of the organic piezoelectric films is applied so that a voltage is applied in the thickness direction of the organic piezoelectric film. The electrode layer is connected to the ground, and the other is connected to a function generator (20 MHz Function / Arbitary Waveform Generator 33220A; manufactured by Agilent Technology) and a power amplifier (AC / DC AMPLIFIER HVA4321; manufactured by nF). Under applied conditions, the voltage is increased by 100V every 20 seconds, and the maximum is 100 An electric field of MV / m was applied to perform a polling process. Then, the electrode was immersed in a mixed solution of 1% of 3-mercaptopropyltrimethoxysilane (methanol-pH 4 sodium acetate aqueous solution) for 5 minutes, dried, washed with water, dried again, and surface-treated.

Three or six layers of the organic piezoelectric film were laminated, the thickness including the electrodes was 0.12 mm, and the overlap portion (voltage application range) of the front and back electrodes was 3.3 mm. At the time of the lamination, the polarization direction of the organic piezoelectric film is set to the same direction, the same direction, and the reverse direction of FIG. 16 for the three layers, and the same direction, the same direction, and the reverse direction of FIG. Reverse direction ... As a comparative example, three layers having the same direction, reverse direction, and same direction shown in FIG. 18 as described above and those using inorganic material PZT were prepared. The adhesive used at the time of lamination was an epoxy adhesive, and was uniformly pressed in the thickness direction at a pressure of 30 kgf / cm ² . After the lamination, the substrate was cut into a size of 7.5 mm × 50 mm by dicing, side electrodes were formed, and laminated piezoelectric bodies 1 to 4 and laminated piezoelectric bodies 5 and 6 were produced.

  Below, the evaluation method of these laminated piezoelectric materials 1-6 is demonstrated. First, the organic piezoelectric material itself was evaluated. For this purpose, an FPC with electrodes patterned on the side surfaces of the laminated piezoelectric bodies 1 to 6 and a 3.0 mm-thick backing layer are sequentially adhered to the back surface, and an acoustic matching layer (ML layer) is adhered to the ultrasonic emission side. (Laminated piezoelectric bodies 1, 2, 5, 6). Thereafter, dicing was performed with a blade having a thickness of 30 μm at a pitch of 0.15 mm in the longitudinal direction. Furthermore, about the thing which provided the insulating layer of about 3 micrometers by the parylene process, and laminated | stacked the acoustic matching layer, the lens was adhere | attached on it further. Thereafter, a connector was connected to the FPC, and the ultrasonic transducer thus created was housed in a case to produce ultrasonic probes 1 to 6 for both transmission and reception.

  A pulsar receiver (PANAMETRICS-NDT MODEL 5900PR, manufactured by Olympus, input impedance 5000Ω) and an oscilloscope (TPS5032, manufactured by Tektronix) were connected to the ultrasonic probes 1 to 6 and placed in deaerated water. A metal reflector was disposed on the ultrasonic radiation surface side. The ultrasonic probes 1 to 6 are driven in two ways: a case of pulse driving without encoding and a case of using the encoded pulse described in JP-A-2003-225237. The received ultrasonic wave was converted into an electric signal, and the voltage waveform was confirmed with an oscilloscope. The alignment between the ultrasonic probe and the reflector was determined by the coordinates at which the effective value of the voltage waveform was the maximum. After the alignment, ultrasonic waves are transmitted and received. FIG. 27 shows a received waveform without encoding, and FIG. 28 shows a received waveform with encoded. Of the pulses obtained in this way, those using coded pulses were subjected to pulse compression, and those not using coded pulses were subjected to FFT analysis as they were, and the sensitivity at the fundamental wave was obtained. The results are shown in Table 1.

  From this result, if the ultrasonic probes 1 to 4 mounted with the laminated piezoelectric bodies 1 to 4 created by the regular laminating method based on the present invention are used, the high frequency reflected in the living body is received with high sensitivity. It is understood that a diagnostic image having high resolution and high resolution can be obtained.

  Next, these laminated piezoelectric bodies 1 to 6 were mounted on an inorganic piezoelectric body and evaluated as a separate body for transmission and reception. That is, in the structure of FIG. 24, an intermediate layer (IL (Intermediate Layer)) 24 is present to improve the sound passage from the inorganic transmitting piezoelectric layer 23 to the upper receiving piezoelectric layer. That is, an FPC with electrodes patterned on the side surfaces of the laminated piezoelectric bodies 1 to 6 described above, a PZT layer with a center frequency of 5 MHz and a backing layer are sequentially bonded to the back side, and on the ultrasonic emission side as necessary. The acoustic matching layer was glued. Thereafter, dicing was performed with a blade having a thickness of 30 μm at a pitch of 0.15 mm in the longitudinal direction. Furthermore, about the thing which provided the insulating layer about 3 micrometers by parylene process and laminated | stacked the said acoustic matching layer, the lens was adhere | attached on it further. Thereafter, a connector was connected to the FPC, and the ultrasonic transducer thus created was placed in a case, and ultrasonic probes 1 to 6 as separate transmission and reception bodies were produced.

  The above-described pulsar receiver and oscilloscope are connected to the ultrasonic probes 1 to 6, and the experiment method is the same as described above. Of the obtained pulses, those using encoded pulses were subjected to pulse compression, and those not using encoded pulses were subjected to FFT analysis as they were, and the sensitivity in the third harmonic band was obtained. The results are shown in Table 2.

  From this result, if the ultrasonic probes 1 to 4 equipped with the laminated piezoelectric bodies 1 to 4 created by the regular laminating method based on the present invention are used, the third harmonic generated in the living body is sensitive. It is understood that a diagnostic image having a high resolution and a high resolution can be obtained.

DESCRIPTION OF SYMBOLS 1 Ultrasonic diagnostic apparatus 2 Ultrasonic probe 3 Cable 4 Diagnostic apparatus main body 5 Operation panel 6 Display panel 7 Holder 7 is provided.
DESCRIPTION OF SYMBOLS 11 Operation input part 12 Transmission part 13 Reception part 14 Signal processing part 15 Image processing part 16 Display part 17 Control part 18 Voltage control part 19 Reference signal memory | storage part 20, 21, 31 Ultrasonic transducer 22, 32 Bucking layer 23; 33, 34 Piezoelectric layer for transmission 24 Intermediate layers 25 and 35 Piezoelectric layers for reception 33a, 34a and 35a Acoustic matching layers 33b, 34b and 35b Acoustic lenses 33c, 34c and 35c Intervening members A1 to A3 Piezoelectric body

Claims (10)

Transmits ultrasound into the subject, wherein an ultrasonic transducer for receiving ultrasonic waves coming from the object,
Before Symbol ultrasound transducer,
A laminate type piezoelectric body that is formed by laminating a plurality of piezoelectric bodies having the same thickness and that resonates in the 3λ / 4 resonance mode generated by the thickness expansion and contraction of the piezoelectric body,
The piezoelectric body is laminated in three layers, and has electrodes on the surface of the piezoelectric body between the layers and at both ends,
By connecting the electrodes on the separation side of the piezoelectric bodies adjacent to each other, it has two sets of connecting wirings that connect the piezoelectric bodies in parallel with each other,
Each piezoelectric body has a second stage in contact with the direction of remanent polarization or crystal axis related to the electric displacement due to the positive piezoelectric effect or the sign of the electric field with respect to the axis of the first stage piezoelectric body on the fixed end side. eyes in the same direction in the piezoelectric body, further ultrasonic transducer in the third stage of the piezoelectric material thereon, wherein the benzalkonium been arranged such that opposite direction. Transmits ultrasound into the subject, wherein an ultrasonic transducer for receiving ultrasonic waves coming from the object,
Before Symbol ultrasound transducer,
A laminate type piezoelectric body that is formed by laminating two layers of piezoelectric bodies having the same thickness and that resonates in a 3λ / 4 resonance mode generated by the expansion and contraction of the thickness of the piezoelectric body,
Each piezoelectric body has electrodes on its interlayer and on each outer surface, and is provided with a connection wiring for connecting each piezoelectric body in parallel by connecting the electrodes on the outer surface,
The two piezoelectric body, the ultrasonic transducer, wherein the benzalkonium orientation or crystal axis of the residual polarization associated with electric displacement or electric field symbols by piezoelectric positive effect, are arranged such that the same direction. Transmits ultrasound into the subject, wherein an ultrasonic transducer for receiving ultrasonic waves coming from the object,
Before Symbol ultrasound transducer,
A laminate type piezoelectric body that is formed by laminating four or more layers of piezoelectric bodies having the same thickness, and that resonates in a desired resonance mode by expanding and contracting the thickness of the piezoelectric body,
Each piezoelectric body has electrodes on the surface of the piezoelectric body between the layers and at both ends,
By connecting the electrodes on the separation side in the piezoelectric bodies adjacent to each other, two sets of connecting wirings that connect the plurality of piezoelectric bodies in parallel with each other are provided,
Each piezoelectric body has a second stage in contact with the direction of remanent polarization or crystal axis related to the electric displacement due to the positive piezoelectric effect or the sign of the electric field with respect to the axis of the first stage piezoelectric body on the fixed end side. ultrasonic in the eyes of the piezoelectric body, wherein the same direction, are further third and one or more sets are arranged to have a periodicity which is a reverse direction in the fourth stage of the piezoelectric body thereon Turkey Transducer . 3. The ultrasonic transducer according to claim 1, wherein the multilayered piezoelectric body is commonly used for transmission / reception of ultrasonic waves, and the ultrasonic transducer transmits ultrasonic waves in a 3λ / 4 resonance mode. Ultrasonic transducer . In the ultrasonic transducer, the stacked piezoelectric body is used as a first piezoelectric body for receiving ultrasonic waves, and the ultrasonic transducer transmits a second ultrasonic wave having a fundamental wave component in a λ / 4 resonance mode. The superconductor according to any one of claims 1 to 3, further comprising: a piezoelectric body, wherein the second piezoelectric body and the first piezoelectric body are laminated in this order from the back layer side. Sonic transducer . In the ultrasonic transducer, the stacked piezoelectric body is used as a first piezoelectric body for receiving ultrasonic waves, and the ultrasonic transducer transmits two ultrasonic waves having a fundamental wave component in a λ / 4 resonance mode. The superconductor according to any one of claims 1 to 3, further comprising a second piezoelectric body, wherein the second piezoelectric body is arranged on both sides of the first piezoelectric body. Sonic transducer . The ultrasonic transducer according to claim 5 or 6, wherein the first piezoelectric body is made of a material mainly composed of an organic polymer. The second piezoelectric body is made of an inorganic material, the first piezoelectric body is made of a material mainly composed of an organic polymer, and is intended for acoustic matching between the first piezoelectric body and a subject. 6. The ultrasonic transducer according to claim 5, wherein no member is interposed. The ultrasonic transducer according to any one of claims 1 to 8 ,
A transmission unit for providing an ultrasonic signal for transmission to the ultrasonic transducer ;
A receiving unit that performs predetermined signal processing on the received signal received by the ultrasonic transducer ;
An image processing unit that images the internal state of the subject as a tomographic image based on a received signal from the receiving unit.
An ultrasonic diagnostic apparatus characterized by the above . The transmission unit applies a transmission signal as an encoded pulse voltage to the multilayer piezoelectric body, and the reception unit performs pulse compression processing on the signal received by the multilayer piezoelectric body, and outputs an image to the image processing unit. the ultrasonic diagnostic apparatus according to claim 9 Symbol mounting, characterized in that to reduction.

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