JPH06121390A - Ultrasonic search unit - Google Patents

Abstract

PURPOSE:To obtain the broad band ultrasonic search unit in which its resonance frequency is largely changed in response to a distance up to a reagent section, an ultrasonic waveform without distortion is obtained and high directivity and high resolution are obtained from a near distance to a remote distance. CONSTITUTION:Two kinds of vibrators 11, 12 formed by a ceramic material or the like of a lead zirconate titanate (PZT) are arranged along 2-dimensional directions in the slice direction and in the array direction. A relation of an aperture width (W1) with a thickness (T) of the vibrator 11 is selected to be W1/T>3 and a relation of an aperture width (W2) with a thickness (T) of the vibrator 12 is W2/T<=0.3. The vibrator 11 is arranged in a middle A in the slice direction and the plural vibrators 12 are arranged to an outer side B of the vibrator 11 in a way of being divided at an equal pitch. Furthermore, the vibrators 11, 12 are arranged at an equal pitch in the array direction of the arrangement. The thickness vibration mode is made to the middle part A of the arrangement and the longitudinal vibration mode is made to the outer side B and the resonance frequency at the middle part A is made higher than that of the outer side B.

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 an ultrasonic diagnostic apparatus which measures the inside of a subject using ultrasonic waves and obtains a tomographic image.

[0002]

2. Description of the Related Art In an ultrasonic diagnostic apparatus that radiates ultrasonic waves to a subject such as a living body to measure or image the inside of the subject, the depth of arrival of ultrasonic waves becomes shallower and lower as the frequency of the ultrasonic waves increases. It gets deeper. Therefore, in order to obtain the sufficient depth required for diagnosis, it is a complicated work to prepare a plurality of probes for deep area to shallow area for one device and exchange the probe adapted to the diagnostic area each time. Was needed.
Therefore, if it is possible to obtain a high-resolution image with a single probe from the shallow portion to the deep portion, it is not necessary to replace the probe, which is extremely effective for diagnosis. Therefore, in the ultrasonic probe, a broadband probe is desired so that it can transmit from low frequency to high frequency.

Conventionally, as shown in FIG. 12, an ultrasonic probe having a plurality of transducers 30 ₁ , 30 ₂ and 30 ₃ having different thicknesses arranged in the slice direction is used as such a wide band. . In this probe, a step is formed on the back side of the vibrators 30 ₁ to 30 ₃ , and a back material 32 is provided via an individual electrode 31. On the other hand, the oscillators 30 _{1 to} 3
The sound emission surface side of 0 ₃ is formed in the same plane, and the common electrode 33 is provided on the surface. This ultrasonic probe
This utilizes the dependence of the resonance frequency on the thickness of the vibrator.

Further, as shown in FIG. 13, there is also known an ultrasonic probe in which a plurality of groups of transducers 40 ₁ , 40 ₂ and 40 ₃ having different widths are arranged in the array direction. This probe utilizes the dependence of the resonance frequency on the width-thickness ratio of the vibrator.

[0005]

However, the above-mentioned conventional ultrasonic probes have the following problems, respectively. First, a plurality of vibrators 30 ₁ to 30 _{3 having} different thicknesses
In the ultrasonic probe in which a plurality of are arranged, since the acoustic emission surfaces are on the same plane, a step portion is formed on the backing material 32 side. Therefore, a difficult manufacturing process such as processing the back material 32 is required. On the other hand, the transducers 40 ₁ to
With an ultrasonic probe in which a plurality of groups of 40 ₃ groups are arranged, a flat plate-shaped piezoelectric body having a uniform thickness can be divided by a method such as a dicing saw so that the widths are different, so that it is easier to manufacture than the former. Is.

However, in the case of such an array probe, when the pitch in the array direction becomes larger and becomes longer than the wavelength, the directivity of ultrasonic waves deteriorates. Therefore, in practice, in order to reduce the pitch, it is necessary to set W / T <3, where W is the opening width and T is the thickness of the vibrators 40 ₁ to 40 ₃ . However, near W / T = 3,
As shown in FIG. 7, since an unnecessary vibration mode in the width direction interferes with the reference vibration mode in the thickness direction of the vibrator,
The distortion of the transmitted / received ultrasonic waveform also becomes large. Therefore, there is a problem that it is difficult to greatly change the resonance frequency.

The present invention has been made in view of the above problems, and an object thereof is to easily manufacture the resonant frequency and to greatly change the resonance frequency according to the distance to the portion to be inspected and to reduce the distortion. An object of the present invention is to provide a wide-band ultrasonic probe that can obtain a non-existent ultrasonic waveform and can obtain high directivity and high resolution from a short distance to a long distance.

[0008]

DISCLOSURE OF THE INVENTION The present invention is an ultrasonic probe in which a plurality of transducers are two-dimensionally arranged along two directions orthogonal to each other, and a vibration in at least one of the two directions is provided. Ratio W / T of opening width W of child and its thickness T
Is set to W / T> 3, preferably W / T ≧ 10 for the vibrator at the center of the array, and W / T> 10 for the vibrator at the outside of this vibrator.
/T≦0.3.

With such a structure, in the ultrasonic probe of the present invention, the resonance frequency at the central portion of the array is high, the resonance frequency at the outer portion is low, and unnecessary vibration does not appear. It is possible to obtain an ultrasonic waveform without distortion. Therefore, by using the central portion of the transducer at a short distance and the outer portion at a long distance, it is possible to obtain high directivity and high resolution from a short distance to a long distance.

The operating principle of this ultrasonic probe will be described below. In a rectangular vibrator using vibration in the thickness direction, the ratio of the opening width (W) to the thickness (T) is W /
When T> 1, it vibrates in the thickness vibration mode, and when W / T <1, it vibrates in the longitudinal vibration mode, and the resonance frequency (F) in each mode is the frequency constant (N _t , N ₃₃ ) / thickness (t). Determined by It is already known that the frequency constant is lower in the longitudinal vibration mode. Table 1 Commercially available ceramic resonators (lead zirconate titanate-based ceramics)
An example of the frequency constant of is shown.

[0011]

[Table 1]

[0012]

Table 2 shows theoretical values and measured values of the resonance frequency when the thickness of the vibrator using the lead zirconate titanate-based ceramics of Table 1 is 0.3 mm. According to this, it can be seen that the measured value and the theoretical value are in good agreement. Further, in the longitudinal vibration mode, the frequency constant is about 30% smaller than that in the thickness vibration mode.
With the same thickness, the resonance frequency will be low. 6 to 8 show W / T = 10, W in the vibrators of Tables 1 and 2.
It shows admittance-frequency characteristics when / T = 3 and W / T = 0.3. As mentioned above, W / T
In the case of = 3, since many unnecessary vibrations appear in addition to the reference vibration, the distortion of the ultrasonic waveform becomes large, but W / T
= 10 and W / T = 0.3, only the reference vibration appears, and it can be seen that an ultrasonic waveform with little distortion can be obtained.

Further, in the ultrasonic diagnostic apparatus, it is necessary to make the directivity of the ultrasonic waves uniform in order to obtain a good image from the shallow part to the deep part of the living body. Therefore, it is desirable to increase the aperture width, that is, increase W / T, as the frequency is lower.

[0015]

[Table 2]

[0016]

Further, in the ultrasonic probe according to the present invention, both principal surfaces of each transducer may be divided, and one principal surface of each transducer may be common and the other principal surface may be divided. It is also possible to divide only the surface into a two-dimensional array and form the common electrode on the common main surface. With such a configuration, in the step of forming the common electrode on one main surface of each vibrator, this common electrode can be formed on the main surface of the vibrator on the non-divided side.
Manufacturing is easy.

Further, in the ultrasonic probe of the present invention, at least one acoustic matching layer is provided on the acoustic radiation surface of the vibrator, and the thickness of the portion of the acoustic matching layer corresponding to the central portion of the array, The thickness of the portion corresponding to the outer side of the array,
The difference is made according to the difference in the resonance frequency of each part. For example, the thickness of the portion of the acoustic matching layer corresponding to the outer portion of the array is compared to the thickness of the portion of the acoustic matching layer corresponding to the central portion of the array in the acoustic matching layer at the resonance frequency of the transducer. The acoustic matching layer can be effectively used by setting the thickness to be ¼ of the wavelength.
It is possible to shorten the pulse of the ultrasonic waveform and increase the sensitivity. It should be noted that this acoustic matching layer is not limited to a single layer, but a multi-layered structure can further improve the characteristics.

Further, in the ultrasonic probe of the present invention, the above-mentioned 2
It is also possible to form an array surface in at least one of the two directions into a curved surface and arrange the transducers along the curved surface. As the curved surface, there is a convex surface or a concave surface. When the transducers are arranged on the convex surface, a wide field of view can be obtained from a narrow opening and the adhesion between the living body and the probe is enhanced. On the other hand, when the transducers are arranged on the concave surface,
There is an advantage that ultrasonic waves can be focused in the slice direction.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show the structure of an ultrasonic probe according to an embodiment of the present invention. This ultrasonic probe 1 includes two kinds of transducers 11 and 12 formed of a piezoelectric material such as a lead zirconate titanate (PZT) ceramic material along two-dimensional directions of a slice direction and an array direction. It is a multiple array. The vibrator 11 and the vibrator 12 are formed in a flat plate shape, and have the same thickness but different opening widths.

The relationship between the opening width (W ₁ ) and the thickness (T) of _one vibrator 11 is, for example, W ₁ / T = 10, and the opening width (W ₂ ) and the thickness of the other vibrator 12 are equal to each other. For example, W ₂ /T=0.3 has a relationship with T (T). Oscillator 1
1 is disposed in the central portion A in the slice direction, and the oscillator 1
A plurality of vibrators 12 are arranged on the outer side portion B of the apparatus 1 at equal pitches. The vibrators 11 and 12 are arranged at equal pitches in the array direction of the array.

A common electrode 13 is provided on one principal surface side of the vibrators 11 and 12 arranged two-dimensionally, and these vibrators 11 and 12 are electrically connected to each other. Further, a backing material 14 is provided on the back surface of the common electrode 13. Further, the individual electrodes 15 are provided on the other principal surface sides (sound emission surface sides) of the vibrators 11 and 12, respectively. .

In the ultrasonic probe 1 of this embodiment having such a configuration, in the central portion A, the relation between the opening width (W ₁ ) and the thickness (T) of the transducer 11 is W ₁ / T. = 10, the thickness vibration mode is set. On the other hand, in the outer portion B, the relationship between the opening width (W ₂ ) and the thickness (T) of the vibrator 12 is W ₂
Since /T=0.3, the longitudinal vibration mode is set. Therefore, the resonance frequency of the vibrator 11 in the central portion A is high and that of the vibrator 12 in the outer portion B is low. Further, as is clear from the above description of FIGS. 6 to 8, unnecessary vibration does not appear, so that an ultrasonic waveform without distortion can be obtained.

Further, in the ultrasonic probe 1 of this embodiment, W
_{Since a} plurality of transducers 12 with _{2 /} T = 0.3 are arranged on both sides of the transducer 1, the ultrasonic wave reception sensitivity is increased,
The ultrasonic waves can reach farther.

In the above embodiment, since the lead zirconate titanate (PZT) ceramic material is used as the material of the vibrators 11 and 12, the thickness of the vibrators 11 and 12 is T = 0.38 mm. Then, the resonance frequency is 5 MHz in the central portion A in the slice direction which is the thickness vibration mode, while it is 3.5 M in the outer portion B which is the longitudinal vibration mode.
It becomes Hz. Generally, the frequency used for diagnosis of the abdominal region is 3.5 MHz to 5 MHz, and thus the combination of these frequencies is extremely useful.

FIG. 3 shows the configuration of an ultrasonic probe 2 according to another embodiment of the present invention. Here, the same components as those in FIGS. 1 and 2 are designated by the same reference numerals and the description thereof will be omitted.

In the present embodiment, the transducers 11 and 12 are integrated on one principal surface side (acoustic emission surface side) and common, and the other principal surface side is divided into a plurality of slice directions. Has become. The arrangement at equal pitch in the array direction is the same as in the above embodiment. A common electrode 16 is provided on one main surface side (sound emission surface side) of the vibrators 11 and 12. Further, individual electrodes 17a and 17b are provided on the other divided main surface side. The individual electrode 17b in the outer portion B is commonly formed among the plurality of vibrators 12. The individual electrode 17a in the central portion A and the electrode 17b in the outer portion B are respectively connected to the external circuit and the lead electrode 1.
It is electrically connected via 8a and 18b. In addition,
It is desirable that the division depth of the vibrators 11 and 12 be set within a range that does not affect the vibration mode (at least T / 2 or more).

In the ultrasonic probe 2 of this embodiment, the transducer 1
Since one main surface side of Nos. 1 and 12 is integrated and not divided as in the embodiment of FIG. 1, formation of the common electrode 16 becomes extremely easy. The common electrode 16 and the individual electrode 1
Each of 7a and 17b can be formed by a vapor deposition method, a printing method or a plating method using a metal such as aluminum.

The main surface of the vibrators 11 and 12 on the side of division is the acoustic radiation surface side as shown in FIG.
The side main surface may be a common surface, and the common electrode 16 may be formed on this common surface.

FIG. 5 shows an ultrasonic probe 3 according to still another embodiment of the present invention. In this embodiment, FIG.
The common electrode 18 is provided on the acoustic emission surface side of the ultrasonic probe 1 and the acoustic matching layer 19 having the sound velocity V is provided on the common electrode 18. In the acoustic matching layer 19, the central portion A
If the resonance frequency of the portion corresponding to the vibrator 11 is f _A , the thickness is, for example, V · f _A / 4, while the outer portion B
If the resonance frequency of the portion corresponding to the vibrator 12 is f _B , the thickness is, for example, V · f _B / 4. In addition,
The acoustic matching layer 19 is formed of, for example, a resin or a glass-based material, and its acoustic velocity, thickness, acoustic impedance, etc. are set so that acoustic impedance matching can be achieved between the vibrators 11 and 12 and the subject (living body). The parameters are adjusted.

In the ultrasonic probe 3 of this embodiment, the central portion A
Since the resonance frequency of the vibrator 11 is higher than that of the vibrator 12 of the outer portion B, the acoustic matching layer 1 is adjusted accordingly.
The central portion A is thin and the outer portion B is thick. It is generally known that the use of the acoustic matching layer can shorten the pulse of the ultrasonic waveform and increase the sensitivity, but as described above, the thickness is provided differently according to the magnitude of the resonance frequency. As a result, the acoustic matching layer 19 can be effectively used. The acoustic matching layer has a greater effect as the number of layers increases. Therefore, also in this embodiment, if the acoustic matching layer 19 is formed of a plurality of layers, the characteristics will be further improved.

The present invention has been described above with reference to the examples.
The present invention is not limited to the above-described embodiments, but can be variously modified without departing from the scope of the invention.

For example, in the above embodiment, the vibrator 11,
As the 12 piezoelectric materials, lead zirconate titanate (PZT) ceramic materials are used, but other piezoelectric materials having different frequency constants (N _t , N ₃₃ ) may be used. Examples of such a piezoelectric material include barium titanate-based and lead titanate-based piezoelectric materials.

Further, in the above-mentioned embodiment, the ratio of the aperture width and the thickness of the transducer in the slice direction is made different in the central portion A and the outer portion B of the array, but the ratio is made in the slice direction. It may be fixed and the ratio in the array direction may be different. Further, along the two directions of the slice direction and the array direction, the ratio of the opening width and the thickness of the transducer may be different between the central portion A and the outer portion B thereof.

The amount of change in frequency when the ratio of the opening width to the thickness in the array direction is different, and when the ratio of the opening width to the thickness is different in both the array direction and the slice direction. This is the same as when the opening width and the thickness are different only in the slice direction. However, in the case of such a configuration, unlike the probes 1 to 3 of the above-described embodiment, the pitch in the scanning direction (array direction) is different, and thus a scanning method different from the electronic linear type scanning is used. If not, an ultrasonic image cannot be obtained. In such a case, for example, a mechanical scanning method can be used.

FIG. 9 shows an embodiment in which the ratio of the opening width to the thickness is different in both the array direction and the slice direction. In this probe 4, the transducer 1 at the center is
W _{1 is} the width in the array direction, W _{1 is} the width in the slice direction,
Assuming that the width of the outer vibrator 12 in the array direction is w ₂ , the width in the slice direction is W ₂ (= w ₂ ), and the thickness of each vibrator 11, 12 is T, w ₁ / T> 3, W _{1 / T> 3, w 2} /
The relationship of T = W ₁ /T≦0.3 is set. This probe 4
The vibrator 11 is a high frequency part, and the vibrator 12 surrounding the vibrator 11 is a low frequency part, and an ultrasonic image can be obtained by mechanically moving it.

In the probes 1 to 4 of the above-mentioned embodiment, the transducers 11 and 12 are arranged on the plane of the backing material 14, but the transducers 11 and 12 may be convex or concave. The arrangement may be such that they are arranged on a curved surface.

In FIG. 10, the back surface 14 has a convex surface 1 in the array direction.
4a is formed, and the vibrators 11, 1 are formed along the convex surface 14a.
It is an array of two. The probe 5 of the present embodiment is a so-called convex probe, and has the advantages that a wide field of view can be obtained from a narrow opening and the adhesion between the living body and the probe 5 is enhanced.

Further, FIG. 11 shows a rear surface 14 on which a concave surface 14b is formed in the slice direction, and the vibrators 11 and 12 are arranged along the concave surface 14b. The probe 6 of this embodiment
In, there is an advantage that ultrasonic waves can be focused in the slice direction.

[0041]

As described above, according to the ultrasonic probe of the first to fifth aspects, at least one of the two-dimensional directions is obtained.
The ratio W / T between the opening width W and the thickness T of the vibrator in the direction is W / T> 3 for the vibrator at the center of the array, preferably W / T ≧
10 and W / T ≦ 0.3 in the vibrator on the outer side, so that the resonance frequency in the central part is high and the resonance frequency in the outer part is low, and unnecessary vibration does not appear and distortion of You can get no ultrasonic waveform. Therefore, by using the central part of the transducer at short distance and the outer part at long distance, or by using the central part and the outer part depending on the distance, high directivity and high The resolution can be obtained and the band can be widened.

In particular, according to the ultrasonic probe of the third aspect, one main surface of each of the transducers is made common, and only the other main surface is divided into a two-dimensional array, and the common plane is used. Since the common electrode is formed on the main surface, the common electrode is easily formed and the manufacturing process is simplified.

Further, according to the ultrasonic probe of the fourth aspect, at least one acoustic matching layer is provided on the acoustic radiation surface of the transducer, and a portion of the acoustic matching layer corresponding to the central portion of the array is provided. And the thickness of the part corresponding to the outer part of the array are made to differ depending on the difference in the resonance frequency of each part, so that the acoustic matching layer can be effectively used and the sonic waveform can be shortened and pulsed. Higher sensitivity can be achieved, and the characteristics are further improved.

According to the ultrasonic probe of the fifth aspect, the array surface in at least one of the two directions is formed into a curved surface, and the transducers are arrayed along this curved surface. Therefore, there are advantages that a wide field of view can be obtained from a narrow opening and that the contact between the living body and the probe is enhanced.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an ultrasonic probe according to a first embodiment of the present invention.

FIG. 2 is a plan view of the ultrasonic probe of FIG.

FIG. 3 is a vertical sectional view showing a configuration of an ultrasonic probe according to a second embodiment of the present invention.

FIG. 4 is a vertical cross-sectional view showing a modified example of the ultrasonic probe of FIG.

FIG. 5 is a longitudinal sectional view of an ultrasonic probe according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between admittance and frequency of an ultrasonic probe when W / T = 10.

FIG. 7 is a diagram showing a relationship between admittance and frequency of an ultrasonic probe when W / T = 3.

FIG. 8 is a diagram showing a relationship between admittance and frequency of an ultrasonic probe when W / T = 0.3.

FIG. 9 is a plan view of an ultrasonic probe according to a fourth embodiment of the present invention.

FIG. 10 is a perspective view of an ultrasonic probe according to a fifth embodiment of the present invention.

FIG. 11 is a perspective view of an ultrasonic probe according to a sixth embodiment of the present invention.

FIG. 12 is a vertical sectional view of a conventional ultrasonic probe.

FIG. 13 is a perspective view of another conventional ultrasonic probe.

[Explanation of Codes] 1 to 6 Ultrasonic probe 11, 12 Transducer 13 Common electrode 14 Backing material 15 Individual electrode 19 Acoustic matching layer

Claims (5)

[Claims] 1. An ultrasonic probe in which a plurality of transducers are two-dimensionally arranged along two directions orthogonal to each other, wherein an aperture width W of the transducer in at least one of the two directions is provided.
The ratio W / T between the thickness and the thickness T is W / T> 3 for the vibrator at the center of the array, and W / T for the vibrator at the outside of this vibrator.
Ultrasonic transducer characterized in that /T≦0.3. 2. The opening width W and the thickness T of the vibrator in the central portion.
The ultrasonic probe according to claim 1, wherein the ratio of W / T is 10 or more. 3. One of the principal surfaces of each of the vibrators is common,
The ultrasonic transducer according to claim 1, wherein the other main surface is divided into a two-dimensional array and a common electrode is formed on the common main surface. 4. At least one on the acoustic emission surface of the oscillator.
A layer acoustic matching layer is provided, and the thickness of the portion of the acoustic matching layer corresponding to the central part of the array and the thickness of the portion corresponding to the outer part of the array are different depending on the resonance frequency of each part. The ultrasonic probe according to any one of claims 1 to 3, wherein the ultrasonic probe is provided. 5. The arrangement surface according to claim 1, wherein an array surface in at least one of the two directions is formed into a curved surface, and the vibrators are arrayed along the curved surface. Ultrasonic probe.