JP2986581B2 - Ultrasonic probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic probe for transmitting pulsed ultrasonic waves to a subject and receiving reflected waves from the subject, and more particularly to an ultrasonic probe used in a high-temperature environment. It relates to a suitable ultrasonic probe.

[0002]

2. Description of the Related Art As is well known, an ultrasonic probe for transmitting and receiving ultrasonic waves includes a piezoelectric vibrator made of PZT or the like for performing electric / acoustic conversion, A back plate mainly composed of epoxy resin and tungsten, and a front plate made of alumina or the like disposed on the opposite side to the back plate with respect to the piezoelectric vibrator. It is configured.

In the above ultrasonic probe, the joining between the piezoelectric vibrator and the back plate and the joining between the piezoelectric vibrator and the front plate are performed by epoxy resin. However,
Since this epoxy resin deteriorates at 100 ° C or higher,
When this ultrasonic probe is used at a high temperature of 100 ° C. or more, there is a problem that the piezoelectric vibrator may peel off from the back plate and the front plate. As a result, this ultrasonic probe can be used only at room temperature, and when this ultrasonic probe is used at high temperature, the acoustic coupling between the piezoelectric vibrator and the back plate fluctuates, The function as a child deteriorates and lacks reliability.

In order to solve this problem, an ultrasonic probe as shown in FIG. 5 has been developed. FIG. 5 is a sectional view showing the ultrasonic probe. The structure of the ultrasonic probe 500 will be described. The ultrasonic probe 500 has a fully-closed structure including an enclosure 6, a cover 7, a stainless steel front plate 4 and a connector 8, and includes a silicone oil 15 as an acoustic coupling material. Is used. And
The piezoelectric vibrator 52 for performing electric / acoustic conversion, the back plate 53 and the front plate 4 are connected via the silicone oil 15.

The operation of the ultrasonic probe 500 will be described. An electric signal from a pulse transmitter (not shown) is applied to the piezoelectric vibrator 52 via the connector 8, and the piezoelectric vibrator 52 is energized to emit ultrasonic waves. The ultrasonic wave from the piezoelectric vibrator 52 is transmitted to the test material 11 via the silicon oil 15 and the front plate 4 made of stainless steel. On the other hand, the reflected wave from the test material is
And a piezoelectric vibrator 5 via a front plate 4 made of stainless steel.
2 is received.

When the ultrasonic probe 500 is used in an ultrasonic flaw detector, the following is further performed. Test material 11
If a defect or the like exists in the inside, the piezoelectric vibrator 52 receives a reflected wave from the defect or the like. By analyzing the time of reflection and the intensity of the reflected wave using an external device (not shown), a defect or the like can be observed on a display such as a CRT (not shown).

The technique using silicon oil for joining the piezoelectric vibrator and the front plate does not cause peeling or the like at high temperatures unlike the case where an epoxy resin is used for joining the piezoelectric vibrator and the front plate. . However, the technology using the silicone oil has the following problems. An ultrasonic probe using silicon oil performs acoustic coupling by interposing silicon oil between a piezoelectric vibrator and a front plate. However, in a high temperature state, the thickness and properties of the silicon oil (for example, for a sound speed of 1000 m / s at room temperature, 2
At 00 ° C., it is 500 m / s. ) Changes, and the acoustic coupling between the piezoelectric vibrator and the front plate fluctuates, so that stable sensitivity cannot be obtained as an ultrasonic probe.

Further, since silicon oil having low acoustic impedance is inserted between the piezoelectric vibrator having high acoustic impedance and the front plate, the thickness of the front plate strongly affects the frequency characteristics of ultrasonic waves. . In order to improve the radiation efficiency of ultrasonic waves, the thickness of the front plate needs to be exactly one half of the wavelength of the ultrasonic wave to be radiated, and the thickness of the front plate is high for processing. Accuracy is required. If the processing of the thickness of the front plate is not exactly half of the wavelength, the radiation efficiency will change, the decay time of the ultrasonic pulse waveform will change, and the sensitivity and attenuation of the ultrasonic probe will change. Characteristics become unstable. On the other hand, even if the thickness of the front plate is accurate, the operating frequency of the piezoelectric vibrator varies, so that the sensitivity and the attenuation characteristics of the ultrasonic probe vary as described above. Furthermore, since the resonance transmission of the front plate is used,
Broadband frequency characteristics could not be obtained.

In order to solve the problem of the technology using silicon oil, a stainless steel front plate is connected to a piezoelectric vibrator and a back plate is connected to the piezoelectric vibrator, instead of the silicon oil. There is a technique using brazing of aluminum.

However, in this technique, when the difference between the coefficient of thermal expansion of ceramics used as a piezoelectric vibrator and the coefficient of thermal expansion of a stainless steel front plate is large, using this ultrasonic probe at a high temperature causes There is a problem that peeling or the like occurs between the piezoelectric vibrator and the front plate. As a result, the reliability of the ultrasonic probe is lost.

Next, in order to reduce the difference in the coefficient of thermal expansion, the coefficient of thermal expansion of the front plate made of stainless steel (about 16 × 10 to ⁶
Thermal expansion coefficient close to / ° C.) a LiNbO ₃ having (approximately 15 × 10 ~ ⁶ / ℃) there is a technique used as a piezoelectric vibrator. In this technique, since the coefficients of thermal expansion of the piezoelectric vibrator and the front plate are close to each other, the problem that separation occurs between the piezoelectric vibrator and the front plate even when used at a high temperature is solved.

[0012]

However, LiNbO ₃
Since cleavage is remarkable, there is a problem in that it is easily broken at the time of joining with the front plate, and the yield is low. In addition, LiNb
The electromechanical coupling coefficient of O ₃ (a quantity indicating a ratio of a given electrical input to a mechanical output) is about 0.1.
7, which is very inferior to the electromechanical coupling coefficient (about 0.3 or more) of other piezoelectric ceramics. As a result, the ultrasonic probe using LiNbO ₃ as the piezoelectric vibrator is superior to the ultrasonic probe using other piezoelectric ceramics in that there is no separation from the front plate, but the sensitivity is high. Is bad.

An object of the present invention is to provide an ultrasonic probe which has a long service life and high sensitivity even when used at a high temperature of about 250 ° C.

[0014]

SUMMARY OF THE INVENTION The object of the present invention is to provide a piezoelectric vibrator for performing electric / acoustic conversion, a back plate disposed on one side of the piezoelectric vibrator, and a back plate for the piezoelectric vibrator. In an ultrasonic probe configured to include a plate and a front plate disposed on the opposite side, the bonding between the piezoelectric vibrator and the back plate, and the bonding between the piezoelectric vibrator and the front plate are both performed. It is performed through solder, and the front plate can be achieved by an ultrasonic probe made of ceramics. The thickness of the solder is preferably 100 μm or less.

Preferably, the piezoelectric vibrator is made of one of a PbNb ₂ O ₆ system and a PbTiO ₃ system.

Further, the piezoelectric vibrators may be arranged in plural at a regular interval on a straight line.

[0017]

In the ultrasonic probe according to the present invention, a ceramic having a high Curie point and a small thermal expansion coefficient, for example, PbNb ₂ O ₆ or PbTiO ₃ is used as the piezoelectric vibrator. The piezoelectric vibrator and the front plate are joined via solder. Further, the front plate and the piezoelectric vibrator have thermal expansion coefficients close to each other. In addition, the elongation of the solder is about 36%, which is soft. Therefore, 2
Even under a high temperature environment of about 50 ° C., there is no occurrence of peeling or the like. Further, since the acoustic impedance is closer to that of the piezoelectric vibrator and the front plate than that of silicon oil, acoustic coupling in ultrasonic transmission between the two can be stabilized. Therefore,
The ultrasonic probe according to the present invention has stable reliability and performance even when operated in a high-temperature environment.

The sound speed in the ceramic front plate is the sound speed in stainless steel (about 5900 m / s).
If the thickness of the ceramic front plate is the same as the thickness of the stainless steel plate, the thickness is half the wavelength of the ultrasonic wave propagating through the ceramic front plate. It will be. In addition, if a ceramic having a high transverse rupture strength, such as a silicon carbide-based or silicon nitride-based ceramic, is used, it can be made thinner and have a thickness of about 1/10 wavelength. As a result, since the influence of multiple reflection of ultrasonic waves inside the front plate can be ignored, it is possible to realize an ultrasonic probe having a wide frequency characteristic and capable of transmitting and receiving signals with a narrow pulse width.

[0019]

Next, a first embodiment of the ultrasonic probe according to the present invention will be described with reference to FIGS. FIG.
FIG. 2 is a cross-sectional view illustrating the ultrasonic probe according to the present embodiment.
FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, and FIG. 3 is a perspective view of the back plate 3.

The basic structure of the ultrasonic probe 100 is a fully-closed structure including an enclosure 6, a cover 7, a front plate 4 and a connector 8. The inside of the ultrasonic probe 100 is made of an inorganic material. Filled with an adhesive. In addition, a plurality of piezoelectric vibrators 2 (six piezoelectric vibrators are shown as an example in FIG. 1) arranged in an array at substantially equal intervals on a straight line are soldered by solder 5 which also serves as an electrode. It is joined to the face plate 4.
Also, the back plate 3 and the piezoelectric vibrator 2 are joined by solder 5 also serving as an electrode. As shown in FIG. 3, the back plate 3 has a signal line extraction terminal 16 and a signal side electrode 15.
And are provided. Further, as shown in FIG. 2, a connection terminal 9 is provided at one end of the solder 5.

The front plate 4 has excellent heat resistance and weather resistance.
For example, SiC type (thermal expansion coefficient about 5 × 10 ⁻⁶ / ゜ C, Young's modulus about 46 × 10 ¹⁰ N / m ² ) or Si ₃ N ₄ type (thermal expansion coefficient about 3.4 × 10 ⁻⁶ /) C, Young's modulus about 46 × 10 ¹⁰ N
/ M ² ) made of ceramics. The back plate 3 is made of Al
It is made of ₂ O ₃ TiO ₂ ceramics.

The piezoelectric vibrator 2 is made of a PbNb ₂ O ₆ system (coefficient of thermal expansion about 0.7 × 10 ⁶ / ° C.) or a PbTiO ₃ system (coefficient of thermal expansion about -7 × 10 ⁶ / ° C., Young's modulus about 13 × 10 ¹⁰ N /
m ² ). In addition, outer enclosure 6
May be made of Kovar, an alloy having a small coefficient of thermal expansion, or may be formed of ceramics integrally with the front plate 4. The solder used here is a solder for glass-ceramics (for example, trade name: Cerasolzer, manufacturer: Asahi Glass). The thermal expansion coefficient of solder is about 28 × 10 ~ ⁶ /
° C., elongation 36%, the hardness is about 12.9Hv, the electrical resistance of about ^{21.0 × 10 ~ 6 (20 ℃} Ω · cm), the melting range is 280.2 to 296.4 ° C..

Next, the operation of the ultrasonic probe 100 will be described with reference to FIG. FIG. 4 shows the ultrasonic probe 1
It is an explanatory view for explaining an operation of 00. 6 arranged
By applying an excitation signal having a time delay T to the two piezoelectric vibrators 2, a sound field created by the entire vibrator is formed in a deflection direction 50 deflected by an angle θ from the central axis 40 of the array. Therefore, by appropriately controlling the delay time T, the sound field direction can be changed one after another. As a result, it is possible to electronically scan a region in the medium with ultrasonic waves, and it is possible to generate an ultrasonic image without mechanically driving the ultrasonic probe.

The effect of the ultrasonic probe 100 according to this embodiment will be described. The ultrasonic probe 100 is used in a high temperature state in which the ultrasonic probe 100 comes into contact with a test material heated to a high temperature or is immersed in molten sodium. Since the thermal expansion coefficients of the piezoelectric vibrator 2 made of PbNb ₂ O ₆ or PbTiO ₃ and the front plate 4 are close to each other, even when used in a high temperature environment, no peeling occurs at the joints. Both can be reliably joined, and acoustic coupling can be stabilized.

Therefore, when the piezoelectric vibrator 2 is energized by an electric signal from the connector 8 via the connection terminal 9, the plurality of piezoelectric vibrators 2 can exhibit predetermined performance over a long period of time and operate with high reliability. Can be performed.

The speed of sound in SiC used as a component of the material of the front plate 4 is 11.78 km / s, and for an ultrasonic wave having a frequency of 2.5 MHz, λ = 4.71 mm.
Since the transverse rupture strength of SiC is large, the thickness of the front plate 4 can be sufficiently reduced to about one tenth of the wavelength. Therefore,
Frequency dependence of the performance of the ultrasonic probe 100 is reduced,
Stable operation can be performed over a wide frequency band. As a result, for example, it can be used for transmitting and receiving an ultrasonic signal having a narrow pulse width.

Next, an ultrasonic probe according to a second embodiment will be described with reference to FIGS. FIG. 6 is a cross-sectional view illustrating the ultrasonic probe 200 according to the present embodiment. FIG. 7 is a sectional view taken along the line BB of FIG. This ultrasonic probe 2
The basic configuration of the ultrasonic probe 1 is the ultrasonic probe 1 according to the first embodiment.
Since it is the same as 00, its detailed description is omitted. The ultrasonic probe 200 according to the present embodiment differs from the ultrasonic probe 100 according to the first embodiment in the overall shape and the shape of the piezoelectric vibrator. As shown in FIG. 7, the overall cross-sectional shape is circular, and the cross-sectional shape of the piezoelectric vibrator 20 is also circular.

In the ultrasonic probe 200, the first
As in the embodiment, since the piezoelectric vibrator 20 and the front plate 4 are joined by the solder 5, the piezoelectric vibrator 20 is in contact with the test material 11 heated to a high temperature or used in a high-temperature environment. However, the ultrasonic probe 200 can exhibit a predetermined performance for a long period of time and can perform highly reliable operation.

[0029]

According to the present invention, the following effects can be obtained.

Since the front plate made of ceramics having a small coefficient of thermal expansion, a high sound speed and a large bending strength and a piezoelectric vibrator having a high Curie point are joined by soft solder, the front plate is not peeled off at high temperatures. There is no occurrence, the acoustic coupling is stabilized, and reliable operation is performed.

Since the front plate can be made sufficiently thinner than the wavelength, the effect of multiple reflection is reduced, and the front plate can be used for operation with a signal having a narrow pulse width and a wide frequency band.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an ultrasonic probe according to a first embodiment.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a perspective view of a back plate 3;

FIG. 4 is an explanatory diagram for explaining an operation of the ultrasonic probe.

FIG. 5 is a sectional view showing an example of a conventional ultrasonic probe.

FIG. 6 is a cross-sectional view illustrating an ultrasonic probe according to a second embodiment.

FIG. 7 is a sectional view taken along line BB of FIG. 6;

[Explanation of symbols]

2, 52 ultrasonic transducer, 3, 53 back plate, 4 front plate, 5 solder, 6 outer casing, 7 cover, 8 connector, 15 signal electrode, 16 signal line extraction Terminal, 1
00, 200, 500 ... Ultrasonic probe.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-26000 (JP, A) JP-A-55-47796 (JP, A) JP-A-61-99860 (JP, A) JP-A-3-3 103786 (JP, A) JP-A-54-15701 (JP, A) JP-A-63-201075 (JP, A) JP-A-2-23075 (JP, A) JP-A-1-146647 (JP, A) JP-A-61-64179 (JP, A) JP-A-61-210795 (JP, A) JP-A-61-219858 (JP, A) Japanese Utility Model Application No. 58-61219 (JP, U) Japanese Utility Model Application No. 61-72999 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01S 7/52-7/64 G01S 15/00-15/96 G01N 29/00-29/28 A61B 8/00- 8/14 H04R 17/00

Claims (3)

(57) [Claims] 1. A piezoelectric vibrator and one side of the piezoelectric vibrator
And a back plate arranged on the other side of the piezoelectric vibrator
An ultrasonic probe, comprising: a front plate, which is provided between the piezoelectric vibrator and the back plate, and the piezoelectric vibrator.
The space between the rotor and the front plate is
The piezoelectric vibrator is joined by solder, and the piezoelectric vibrator is made of a PbN ₂ O ₆ system and a PbTiO ₃ system.
Made from either ceramics of the front plate, any of the SiC-based and Si ₃ N ₄ system
An ultrasonic probe comprising one of the ceramics, wherein the back plate is made of an Al ₂ O ₃ .TiO ₂ -based ceramic. 2. The ultrasonic probe according to claim 1, wherein said solder for ceramics also serves as an electrode.
Ultrasonic probe. 3. An ultrasonic probe according to claim 1, wherein
Thus, a plurality of the piezoelectric vibrators, linearly arranged at regular intervals linearly
An ultrasonic probe characterized in that: