JPH06281634A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To provide an ultrasonic probe which can find a plurality of elastic properties with high accuracy in a short time and has higher sensitivity. CONSTITUTION:In a conical convergent ultrasonic probe constituted by independently forming three circular and concentric annular piezoelectric transducers directly on a concave lens provided on the object-side end face of an acoustic lens, the central circular piezoelectric transducer (first piezoelectric transducer) 7 and concentric annular piezoelectric transducer (second piezoelectric transducer) 8 adjacent to the first transducer 7 are formed on a concave lens area having the same radius of curvature r1. The concentric annular piezoelectric transducer (third piezoelectric transducer) 9 adjacent to the second transducer 8 is formed in a concave lens area having a radius of curvature r2 which is smaller than the r1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic probe used in an ultrasonic microscope, and more particularly to a conical focusing ultrasonic probe capable of simultaneously measuring a plurality of elastic properties.

[0002]

2. Description of the Related Art An ultrasonic microscope is a device for measuring the shape and elastic properties of a microscopic portion of a substance by irradiating an object (solid) with an ultrasonic beam narrowed down.
The most important device in an acoustic microscope is an ultrasonic probe. An ultrasonic probe converts an electric input into an ultrasonic wave, focuses a beam on the surface of or inside a subject, and irradiates it. The ultrasound is partially scattered and absorbed by the subject and then reflected by the ultrasound. It has a function of detecting a beam, converting it into an electric signal again, and outputting it. These functions are performed by the acoustic lens and the piezoelectric transducer, which are components of the ultrasonic probe. That is, the piezoelectric transducer performs electric / ultrasonic conversion and ultrasonic signal detection, and the acoustic lens performs beam focusing.

A piezoelectric transducer is composed of a piezoelectric body and electrodes sandwiching the upper and lower sides thereof, and the piezoelectric body has Zn0, PZT, P.
VDF or the like is used. The upper and lower electrodes are made of a metal thin film such as Cr-Au. On the other hand, the acoustic lens is made of a single crystal such as quartz, sapphire, or Si, and a concave lens for focusing the ultrasonic beam is provided on the end face on the object side.

The piezoelectric transducer is often arranged in close contact with the end surface of the acoustic lens on the side opposite to the power source. However, in the case of highly sensitive measurement of a plurality of elastic properties, a plurality of thin film piezoelectric transducers independent of each other are used as the objective of the acoustic lens. A technique for forming directly on a side concave lens is known. FIG. 5 shows the structure of a conventionally used three-piezoelectric transducer type high-sensitivity ultrasonic probe for conical focusing. In this probe, a circular first piezoelectric transducer 21 is formed in the center of the acoustic lens 20 on the objective-side concave lens (radius of curvature r), and an independent annular second piezoelectric element is formed adjacent to this. The transducer 22 is formed, and an independent annular third piezoelectric transducer 23 is formed outside the transducer 22.
Each of the piezoelectric transducers 21, 22, and 23 is a thin film on a concave lens in the order of upper electrode (with reference numeral a) / piezoelectric material (with reference numeral b) / lower electrode (with reference numeral c). It is obtained by forming multiple layers.

An ultrasonic probe provided with this composite piezoelectric transducer is used in an ultrasonic microscope for the purpose of obtaining a plurality of elastic properties of a subject, for example, Young's modulus and Poisson's ratio by one measurement. The subject is held perpendicular to the Z axis, but the ultrasonic waves from each piezoelectric transducer show different incident and detection angles with respect to the Z axis. That is, the properties of the waves detected by the respective piezoelectric transducers are different.

The first piezoelectric transducer 21 detects ultrasonic waves in the Z-axis direction, that is, direct reflected waves from the subject. Further, the second piezoelectric transducer 22 detects a leaked pseudo longitudinal wave reflected wave (LSSCW), and the third piezoelectric transducer 23 detects a leaked Rayleigh wave reflected wave (LSAW).
It is for detection. Measurement is performed using this ultrasonic probe,
The Young's modulus E and Poisson's ratio σ of the subject are obtained by the following procedure.

First, the LSSCW is measured. That is, the first piezoelectric transducer 21 and the second piezoelectric transducer 22 are excited, a plane wave is emitted from the first piezoelectric transducer, and the second piezoelectric transducer 2
2 is used to make a longitudinal plane wave enter the subject obliquely. At this time, pure water is interposed as a coupler (not shown) between the subject and the concave lens. The incident longitudinal wave plane wave excites a pseudo longitudinal elastic wave by mode conversion on the surface of the subject. This elastic wave is a leaky pseudo longitudinal wave (LSSCW) that propagates near the surface of the subject while radiating energy into the water.
Is. The elastic wave radiated from the second piezoelectric transducer 22 located at the (−) X position and traveling in the X direction is
The component leaked into the water at the (+) X position at the same reflection angle as the incident angle is reflected by the second lower electrode 22 as a reflected wave LSSCW.
It is incident on a. This component is converted into an electric signal by the second piezoelectric body 22b, and reaches the receiver via the second upper electrode 22c.

On the other hand, the plane wave radiated from the first piezoelectric transducer 21 is vertically incident on the subject, is partially reflected at the focal position and becomes a vertical reflected wave as it is, and is incident on the circular first lower electrode 21a. , Is converted into an electric signal by the first piezoelectric body 21b, and reaches the receiver via the first upper electrode 21c.

The electric signals generated by these two reflected ultrasonic waves are
Due to the difference in the propagation paths, the phases are different to cause interference. As a result, when the focal length of the concave lens is moved in the Z direction,
The difference between the path lengths of these two waves changes, and the output signal V changes by Δ.
A so-called V (Z) curve with a period of Z is obtained.

If the sound velocity in water is v _w , the pseudo longitudinal wave sound velocity in the subject is v _s , and the incident angle of ultrasonic waves on the subject is θ _c ,

[Equation 1] Becomes At this time, if the frequency of the ultrasonic wave is f,

[Equation 2] Given in. v _w and f are known and from the data Δ
Since Z is obtained, θ _c and v _s can be calculated from (Equation 1) and (Equation 2).

Next, the LSAW is measured. The switch is operated to excite the first piezoelectric transducer 21 and the third piezoelectric transducer 23 to generate a plane wave from the piezoelectric transducers 21 and 23. The wave from the third piezoelectric transducer 23 is incident on the subject at an incident angle larger than that of the second piezoelectric transducer 22, and induces a leaky mode surface wave. Surface acoustic waves can be regarded as Rayleigh waves. Then, the reflected wave LSAW is detected by the third piezoelectric transducer 23 at the position corresponding to (+) X, and is converted into an electric signal.

On the other hand, on the basis of the phase difference between the vertically incident wave radiation by the first piezoelectric transducer 21 and its direct reflected wave and the LSAW by the third piezoelectric transducer 23, the output voltage V is cyclical in the Z-axis direction. Change. V
The ΔZ is read from the (Z) curve, and the Rayleigh wave sound velocity v _L in the subject can be obtained from (Equation 1) and (Equation 2). When the specimen can be regarded as a substantially isotropic solid, the above-mentioned v _s obtained inside the specimen is

[Equation 3] Can be expressed as Here, E is Young's modulus (N / m ² ), σ is Poisson's ratio ρ, and object density (kg / m ³ ). or,
Rayleigh wave v _L

[Equation 4] Can be expressed as The Young's modulus E and the Poisson's ratio σ can be obtained from (Equation 3) and (Equation 4).

[0013]

According to the above-mentioned conventional technique, a plurality of elastic properties, for example, Young's modulus and Poisson's ratio can be obtained by one measurement using an ultrasonic probe. . However, since each piezoelectric transducer has the same focal length, it is not possible to excite and detect waves having different properties with sufficiently high sensitivity and high accuracy. That is, since the pseudo longitudinal wave using the second piezoelectric transducer has a long period ΔZ and the surface acoustic wave (Rayleigh wave) using the third piezoelectric transducer has a short period ΔZ, the pseudo longitudinal wave ΔZ is the same at the same focal length. I can't get enough.

Further, in the case of the conventional ultrasonic probe, when the measurement is performed from various angles in order to detect the anisotropy of the object, the object is rotated around the Z axis each time and the angle is changed. There was a need for positioning to determine. As a result, there is a problem that the measurement time becomes long and the measurement accuracy decreases. An object of the present invention is to provide an ultrasonic probe with higher sensitivity that can obtain a plurality of elastic properties with high accuracy in a short time.

[0015]

SUMMARY OF THE INVENTION An ultrasonic probe of the present invention is provided with three independent circular circles directly on a concave lens provided on the objective side end surface of the acoustic lens on the objective side end surface of the acoustic lens. In a conical focusing ultrasonic probe formed by forming a concentric annular piezoelectric transducer, a concentric annular second piezoelectric transducer adjacent to the central circular first piezoelectric transducer has a curvature radius r ₁ for LSSCW measurement. A third concentric annular ring adjacent to the second piezoelectric transducer on the concave lens region having
Piezoelectric transducer of LSAW smaller than r ₁
It is formed on a concave lens region having a radius of curvature r ₂ for measurement (claim 1). Further, the ultrasonic probe of the present invention is a conical focusing ultrasonic wave in which three mutually independent circular and concentric annular piezoelectric transducers are directly formed on a concave lens provided on the object side end surface of the acoustic lens. In the probe, a concentric annular second piezoelectric transducer adjacent to the central circular first piezoelectric transducer is formed on the concave lens region having the radius of curvature r ₁ for LSSCW measurement, and the second piezoelectric transducer is formed. A concentric annular third piezoelectric transducer adjacent to the transducer is formed on the concave lens region having a radius of curvature r ₂ for LSAW measurement smaller than the r _1, and the second and third piezoelectric transducers include:
By a radial dividing line extending from the center of the concentric ring,
It is characterized in that it is further divided into a plurality of independent fan-shaped piezoelectric transducers (claim 2). Further, the ultrasonic probe of the present invention is one of the fan-shaped piezoelectric transducers facing each other of the second piezoelectric transducers at the time of LSAW measurement, which is at a position facing each other with the first piezoelectric transducer sandwiched between the fan-shaped piezoelectric transducers. For sending and the other for receiving, LSS
During CW measurement, one of the opposing fan-shaped piezoelectric transducers of the third piezoelectric transducer is used for transmission, and the other is used for reception, which is switched by the switch (claim 3).

[0016]

[Function] A leaky pseudo longitudinal wave is generated to generate a reflected wave LSSCW
In the second piezoelectric transducer for detecting the, the period ΔZ becomes long, so the depth of focus is deep (the radius of curvature r ₁ is large).
To take. On the other hand, a leaky Rayleigh wave is generated and its reflected wave L
The third piezoelectric transducer for detecting the SAW has a short period ΔZ, and therefore the depth of focus is made shallow (the radius of curvature r ₂ is small), so that the depth of focus adjustment in the Z-axis direction is not required so much. Two wave measurements can be made.

Originally, it is well known that an ultrasonic probe using a conical focusing concave lens is suitable for measuring an isotropic medium. . Therefore, in order to measure anisotropy with this lens, it is necessary to adjust the focal position while changing the angle at which ultrasonic waves are emitted and detected.

However, by adopting the fan-shaped division of the second and third piezoelectric transducers of the present invention and by using the pair of divided electrodes facing each other with the first piezoelectric transducer interposed therebetween for transmission and reception, Anisotropy measurement around the Z axis can be easily performed only by selecting the electrode pair by the switch.

[0019]

EXAMPLES The present invention will now be described in more detail based on examples. 1 and 2 are views showing the structure of an ultrasonic probe according to an embodiment. FIG. 1 is a cross-sectional view showing the depth of focus of each piezoelectric transducer with respect to a subject, and FIG. 2 is a bottom view showing an arrangement pattern of the piezoelectric transducers of FIG. In the figure, 7 is a first piezoelectric transducer for radiating a vertically incident wave to the surface of the subject 6 and detecting a reflected wave, and 8 is for exciting a leaking pseudo longitudinal wave to the subject 6 and detecting the reflected wave. The second piezoelectric transducer 9 is a third piezoelectric transducer for exciting the leaky elastic wave on the surface of the subject 6 and detecting the reflected wave. The first and second piezoelectric transducers 7 and 8 are arranged with a curvature of r ₁ on a concave lens provided on the objective side of the acoustic lens 4 having a radius of curvature r ₁ . On the other hand, the third
Piezoelectric transducer 9 is arranged with a curvature r ₂ on the concave lens radius of curvature r _2. Where r ₁
> R ₂ . The focal length of the concave lens (thus the piezoelectric transducer), respectively as shown F _L,
It becomes F _R (F _L > F _R ).

A coupler 5 made of pure water is provided between the acoustic lens 4 and the subject 6 in order to avoid the rapid attenuation of ultrasonic waves in the air.

The detection of the reflected wave of the ultrasonic wave is performed by the upper electrodes 1a, 1b, 1c and the lower electrode 3 of each piezoelectric transducer shown in FIG.
a, 3b, 3c are respectively connected to an electric circuit via a switching device (not shown) to cause the piezoelectric bodies 2a, 2b, 2c to function. FIG. 2 is a bottom view of the piezoelectric transducer arrangement of FIG. 1 viewed from below. The first piezoelectric transducer 7 is arranged in the center in a circular shape, and the second and third piezoelectric transducers 8 and 9 are arranged in a concentric annular shape around it. The ultrasonic probe of FIG. 1 is used for conical focusing. Is shown.

In order to obtain the Young's modulus E and Poisson's ratio σ of the subject 6 using this ultrasonic probe, first, the distance between the probe and the subject 6 is determined by the focal length F of the third piezoelectric transducer 9. _{The R} is set to the position shown in FIG.

A switch (not shown) at this position (Z = 0)
Is operated to excite the first and third piezoelectric transducers 9. Here, a pulse voltage is applied to the partial electrode 1c on the third piezoelectric transducer 9 to generate an ultrasonic beam,
A pulse voltage is applied to the upper electrode 1a of the first piezoelectric transducer 7, and a vertical plane wave is generated. Here, since the focus of the third piezoelectric transducer 9 that excites the leaky Rayleigh wave is on the surface of the subject 6, a surface acoustic wave (Rayleigh wave) is induced very efficiently. Then, the first piezoelectric transducer 7 detects the direct reflected wave, the third piezoelectric transducer 9 detects the LSAW, and the output voltage V ₁ (which is modulated by the phase difference between the vertical reflected wave and the leaky Rayleigh wave reflected wave LSAW). 0) is obtained. Hereinafter, Z is Z ₁ , Z
₂ , ..., One after another, moving in the (+) Z direction, and in each case, output voltages V ₁ (Z ₁ ), V ₁ (Z ₂ ), ... Thus, a function V ₁ (Z) having Z as a parameter is obtained.

Next, the initial position (Z = 0) is set again, and the switch is further operated to excite between the first and second piezoelectric transducers 7 and 8. Ultrasound excited from the second piezoelectric transducer 8 is a leaky mode quasi-longitudinal waves at F _L position. This wave travels in the (+) X direction, and the component reflected at the same reflection angle as the incident angle (LSSCW) is again detected by the second piezoelectric transducer 8 and converted into a signal voltage. By this operation, the output voltage V ₂ (0) modulated by the phase difference based on the difference in the path length is obtained. Thereafter, Z is sequentially moved to Z ₁ , Z ₂ , ... And similarly, output voltages V ₂ (Z ₁ ), V ₂ (Z ₂ ), ... Are obtained each time. Thus, a function V ₂ (Z) having Z as a parameter is obtained.

V ₁ (Z) and V ₂ (Z) thus obtained
Are V (Z) curves for LSAW and LSSCW, respectively. If the period ΔZ is read from each curve and calculated using (Equation 1) to (Equation 4), the Young's modulus E and Poisson's ratio σ of the subject 6 can be obtained accurately and in a short time. it can.

FIG. 3 shows a piezoelectric transducer structure of an ultrasonic probe according to another embodiment of the present invention. It can be considered that FIG. 3 has the same transverse sectional view as the ultrasonic probe of the previous embodiment whose transverse sectional view is shown in FIG. The difference from the previous embodiment is that the second and third piezoelectric transducers 8 and 9 are fanned equally (22.5 degrees) by a dividing line passing through the center of the first piezoelectric transducer 7 as shown. It is a divided point. The 16th divided second and third piezoelectric transducers are electrically independent of each other, and each fan-shaped transducer (32 pieces) is an independent upper part,
It has a lower electrode, and these are respectively connected in parallel to the switching device. FIG. 3 shows a bottom view of the piezoelectric transducer placed in the concave lens of the acoustic lens.
Reference numerals b-1 to 3b-16 denote fan-shaped lower electrodes of the second piezoelectric transducer, and reference numerals 3c-1 to 3c-16 denote fan-shaped lower electrodes of the third piezoelectric transducer.

The ultrasonic probe including the piezoelectric transducer shown in FIG. 3 is useful for measuring the anisotropy of the subject. An example of measuring the sound velocity anisotropy of a subject using this ultrasonic probe will be described.

First, the ultrasonic probe is installed at the position (Z = 0) shown in FIG. 1 and 3c is inserted through a switch (not shown).
-16 is connected to the pulse voltage transmitting circuit, and 3c-8 is connected to the receiving circuit. Although not shown, each upper electrode is also connected so as to realize its transmission and reception. At this position an ultrasonic beam is generated at 2c-16 and a conical focused beam is emitted from 3c-16 into coupler 5. As a result, the leaky mode Rayleigh wave is excited on the surface of the subject. This wave travels on the surface of the subject, and its reflected wave (LSAW) is incident on 3c-8, converted into an output voltage at 2c-8, and input to the receiver via 1c-8. Separately, a function generator (not shown) is connected to the circuit, and the output (reference wave output) and the electric signal input of the LSAW are interfered with each other to obtain the modulation output V (0).

Next, the ultrasonic probe is moved in parallel in the Z-axis direction, and the above measurement is repeated. 3c-8 / 3c-16
The V (Z) curve in the direction is obtained, and the surface wave sound velocity v _L can be calculated from ΔZ using (Equation 1) and (Equation 2). Next, in FIG. 3, the electrodes of the set 3c-1 / 3c-9 are selected, and each of them is connected to the transmitting side and the receiving circuit by the switch. V (0) is calculated in the same manner as above, and V (0) is translated while moving in the Z direction.
Obtain the (Z) curve and from this calculate v _{L in} this direction.

In the same way, v _L for every 22.5 degrees was obtained in the same manner and plotted in FIG. From FIG.
It can be seen that anisotropy is observed in the subject and the sound velocity varies around the Z axis. I haven't mentioned above,
If the same measurement as described above is performed using the divided second piezoelectric transducers (lower electrodes 3b-1 to 3b-16) of FIG. 3, it is possible to obtain anisotropy about LSSCW, that is, data about vs. Become.

In the above-described embodiments, quartz, sapphire, Si, etc. are used as the acoustic lens material, Zn0, PZT, PVDF, etc. are used as the piezoelectric material, and Cr, Au, etc. are conventionally used as the electrode material. Can be used as it is to form an ultrasonic probe.

The concave lens processing of the acoustic lens 4 as shown in FIG. 1 can be performed by selective etching or mechanical polishing. Also, the formation of the piezoelectric transducer is
Well-known multi-layer thin film forming technology such as sputtering or CV
D, a vacuum deposition method or the like can be used. The division of the piezoelectric transducer can be performed by performing selective etching after the integral formation or by selectively forming a thin film.

[0033]

As described above, according to the present invention, it is possible to accurately excite and observe Rayleigh waves (surface acoustic waves) and pseudo longitudinal waves, and to obtain different elastic properties (Young's modulus, Poisson's ratio). , Sound velocity, etc.) can be measured.
Further, according to the present invention, the anisotropy around the Z axis can be accurately observed without rotating the subject.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of an ultrasonic probe according to an embodiment.

FIG. 2 is a bottom view showing the structure of the piezoelectric transducer shown in the previous figure.

FIG. 3 is a bottom view showing the structure of the piezoelectric transducer according to another embodiment.

4 is data showing anisotropy around the Z axis of the Rayleigh wave sound velocity v _L of the subject by the ultrasonic probe including the piezoelectric transducer shown in FIG.

FIG. 5 is a diagram showing a structure of an ultrasonic probe according to a conventional example. 5A is a cross-sectional view and FIG. 5B is a bottom view.

[Explanation of symbols]

1a, 1b, 1c Upper electrodes 2a, 2b, 2c Piezoelectric bodies 3a, 32b, 3c Lower electrode 4 Acoustic lens 5 Coupler (pure water) 6 Subject 7 First piezoelectric transducer 8 Second piezoelectric transducer 9 Third piezoelectric Transducer 3a Lower electrode of the first piezoelectric transducer 3b Lower electrode of the second piezoelectric transducer 3c Lower electrode of the third piezoelectric transducer 3b-1 to 3b-16 Lower sector electrode of the second piezoelectric transducer 3c-1 to 3c- 16 Fan-shaped Lower Electrode of Third Piezoelectric Transducer 20 Acoustic Lens 21 First Piezoelectric Transducer 21a First Lower Electrode 21b First Piezoelectric Body 21c First Upper Electrode 22 Second Piezoelectric Transducer 22a Second Lower Electrode 22b Second piezoelectric body 22c second upper electrode 23 third Electrostatic transducer 23a third lower electrode 23b third piezoelectric 23c third upper electrode r ₁ of, r ₂ concave lens radius of curvature F _R third piezoelectric transducer focal length F _L first, second piezoelectric transducer focal length

Claims (3)

[Claims] 1. A conical focusing ultrasonic probe having three independent circular and concentric annular piezoelectric transducers directly formed on a concave lens provided on an end surface of an acoustic lens on the object side. A second concentric annular piezoelectric transducer adjacent to the first circular piezoelectric transducer of LSSCW
A third concentric annular piezoelectric transducer formed on the concave lens region having a radius of curvature r ₁ for measurement and adjacent to the second piezoelectric transducer has a radius of curvature r ₂ for measurement of LSAW smaller than r _1. An ultrasonic probe formed on a concave lens region. 2. A conical focusing ultrasonic probe having three independent circular and concentric annular piezoelectric transducers directly formed on a concave lens provided on an end surface of an acoustic lens on the object side. A second concentric annular piezoelectric transducer adjacent to the first circular piezoelectric transducer of LSSCW
A third concentric annular piezoelectric transducer formed on the concave lens region having a radius of curvature r ₁ for measurement and adjacent to the second piezoelectric transducer has a radius of curvature r ₂ for measurement of LSAW smaller than r _1. Formed on the concave lens region, the second and third piezoelectric transducers are formed by radial dividing lines extending from the center of the concentric ring into a plurality of mutually independent fan-shaped piezoelectric transducers.
The ultrasonic probe according to claim 1, which is further divided. 3. One of the fan-shaped piezoelectric transducers facing each other of the second piezoelectric transducer at the position facing each other with the first piezoelectric transducer sandwiched between the fan-shaped piezoelectric transducers, and the other one of them. The ultrasonic probe according to claim 2, wherein one of the fan-shaped piezoelectric transducers of the third piezoelectric transducer facing each other is switched for transmission, and the other is switched for reception during measurement of the LSSCW.