JPH0342560B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic scanning ultrasonic wave probe used in ultrasonic diagnostic equipment and the like. Conventionally, this type of ultrasonic probe has been made by cutting a zircon-lead titanate (PZT) ceramic plate uniformly polarized in the thickness direction into thin strips and placing electrodes on the front and back surfaces. attached, and ultrasonic waves are generated by the thickness vibration of each element. However, recently, ultrasonic diagnosis and measurement technology has advanced to higher frequencies, and the strip processing technology required for this is approaching its limit. That is, in order to generate high-frequency ultrasonic waves, it is necessary to reduce the thickness and width of the elemental piece, and from this point of view, the frequency is limited to 5 MHz. For this reason, there is a movement to meet the demand for higher frequencies by using lead titanate (PbTiO ₃ ) ceramics, which allow the width of each element to be increased even though the frequency remains the same. However, this is said to have a limit of 10 to 15 MHz, and new technology must be developed for even higher frequency ranges. The present invention
This was done in response to such requests.

Conventionally, as a means of generating high-frequency ultrasonic waves, as shown in FIG.
electrodes 2 and 3 (also symmetrical to comb-shaped electrodes or interdigital electrodes) are used to perform polarization treatment, and the electrodes 2 and 3 are used as electrodes for mutual conversion between electricity and ultrasonic waves. Applied Physics Letters
Letters) Volume 9, No. 3 (1966), Nos. 129-133
It is proposed on page. In this electrode structure, the second
As shown in the figure, since the vicinity of the surface of the ceramic plate 1 is polarized alternately in opposite directions as shown by arrows 4, when a pulse voltage 5 is applied via the interdigitated finger electrodes 2 and 3, the same polarization is applied from each electrode finger. Ultrasonic waves are radiated perpendicularly to the plate surface as shown by arrow 6 in phase.

This ultrasonic generation transducer has an extremely wide frequency response band due to its non-resonance type, and can generate extremely narrow ultrasonic pulses. Therefore, when used in an ultrasonic imaging system, a device with high resolution can be obtained, and moreover, it has the characteristics of being able to easily generate ultrasonic waves with a high frequency of several tens to 100 MHz.

However, with the electrode structure shown in Figure 1, only one ultrasonic transducer can be obtained, and a so-called array configuration cannot be achieved. As such, the ultrasound beam cannot be electrically scanned.

The present invention is an ultrasonic probe using the interdigitated finger electrodes 2 and 3 shown in FIG. , which enables electronic scanning of ultrasonic beams.The present invention will be described in detail below with reference to embodiments.

FIG. 3 shows an embodiment of the electrode structure according to the present invention, in which a cross-finger electrode 11 corresponding to the cross-finger electrode 3 provided on the unpolarized ceramic plate 1 in FIG. The intersecting finger electrode elements 12a, 12b, . . . 12n of the electrode 2 are divided into a predetermined number of electrode fingers (in the case of FIG. Configure n electrode pairs A, B...N,
As an example, the electrode 11 on the common side is of negative polarity, the electrodes 12a, 12b...12n on the divided side are each of positive polarity, and further, adjacent electrode pairs have the same polarity (in the case of FIG. 3, as an example, negative polarity). Arrange the electrode fingers so that they are next to each other.

That is, for example, the electrode fingers of the interdigitated electrode element 12a and the electrode fingers of the interdigital electrode 11 constitute an electrode pair A, and the electrode pair A has electrode fingers of the same polarity as the adjacent electrode pair B. be arranged so that they are in contact with each other through the

In other words, the electrode of the present invention is composed of a first interdigitated electrode having a positive or negative polarity, and a second interdigital electrode consisting of a plurality of interdigitated electrode elements each facing the first interdigital electrode and having a different polarity from the first interdigital electrode. Each of the interdigitated electrode elements has a predetermined number of electrode fingers inserted between the electrode fingers of the first interdigital electrode, and together with the first interdigital electrode constitute a plurality of independent electrode pairs. , and each of the electrode pairs is brought into contact with the next electrode pair through electrode fingers of the same polarity. In this way, the electrode pairs A, B...N each serve as independent ultrasonic wave generation source electrodes.

When polarization treatment is performed using the electrodes configured in this way, the vicinity of the surface of the ceramic plate 1 is polarized as shown in FIG. is not polarized and becomes a piezoelectrically inactive region. Therefore, when a voltage for generating ultrasonic waves is applied to such interdigitated electrodes, mechanical coupling occurs between the vibrations perpendicular to the plate surface on the ceramic plate below each pair of electrodes sandwiched between the broken lines. Otherwise, each electrode pair becomes a strip-shaped ultrasonic generation source that is completely independent of each other. That is, the third
The ultrasonic probe with the electrode structure shown in the figure is equivalent to a conventional electronic scanning ultrasonic probe in which a large number of independent strip-shaped vibrating elements are arranged, in that multiple ultrasonic generation sources are arranged side by side. Electronic scanning of the acoustic beam can be performed.

In general, there is a mechanical coupling between the vibrations of the ceramic plate under each electrode pair, but titanium-zinc (PbTiO ₃ )-based ceramic plates have a small electromechanical coupling with respect to lateral vibrations, and especially with mainly longitudinal vibrations. This lateral coupling is very small if only one is excited. Next, we will show the results of actual measurements made by providing an electrode having the structure of the present invention on the Pb, TiO ₃ ceramic plate.

PbTiO ₃ -based ceramics containing samarium (Sm) and manganese (Mn), whose electrical-mechanical coupling coefficient related to lateral vibration is almost negligible, were created using normal ceramic technology, and a square plate with a length of 30 mm and a width of 13 mm was made. Cut out and polish both sides. On the surface of the ceramic plate thus obtained, an electrode having the shape shown in FIG. 3 is vapor-deposited using gold (An) as the electrode material through a metal mask. The width of the electrode finger is 120μ
m, the distance between electrode fingers is 80 μm, and the number of electrode pairs is 25.

After configuring the ultrasonic probe in this way,
Each electrode 12a,
12b...12n and the common side electrode 11
A voltage of 560 VDC was applied for about 10 minutes to perform polarization treatment, and after cleaning, lead wires were attached to each electrode, and the ultrasonic conversion characteristics of each electrode pair were measured.

FIG. 5 shows the ultrasonic conversion frequency characteristics actually measured in this manner. In this case, the center frequency is about 30M
It can be seen that the fractional band of 3 dB reduction is approximately 100% at Hz, which is extremely wide. Next, FIG. 6 shows an example of a received waveform when a rectangular wave voltage is applied underwater to emit ultrasonic waves and echoes from a reflector are observed. As is clear from the figure, a very short pulse waveform is obtained. These characteristics are almost the same for each electrode pair, and it can be seen that each electrode pair operates as an independent ultrasonic wave generation source.

In this way, by providing electrodes with the structure shown in Figure 3 on a ceramic plate and using a ceramic plate with a small lateral electrical-mechanical coupling coefficient, a high-frequency electronic scanning ultrasonic probe was realized. can do. In the above embodiment, the case where there are two electrode fingers on the dividing side of each electrode pair is shown, but this electrode index m can be arbitrary, and as shown in FIG.
FIG. 8 shows an example in which m=1 and m=3, respectively. When this electrode index m is small, the output of the electrode pair is also small, but the resolution is high because the width of the electrode pair is narrow. Conversely, as m becomes larger, the output of the electrode pair becomes larger, but the width of the electrode pair becomes wider and the resolution decreases. In the embodiment shown in FIG. 3, n=2 in consideration of the output and resolution of the electrode pair.

Further, in the above embodiments, the electrode fingers on the common side (for example, the electrode fingers in FIG. 3) are adjacent to each other, but the electrode fingers on the divided side may be configured to be adjacent to each other. Of course, FIG. 3 shows only one example of the polarity of the electrodes; on the contrary, it is also possible to use the common side electrode as the positive electrode and the divided side electrode as the negative electrode, or to use the common side electrode as the negative electrode. The finger electrodes do not necessarily remain integral, but may be divided into electrode pairs, and each electrode pair may be configured to be electrically completely independent.

Furthermore, as shown in FIG. 4, since the ceramic under the electrode fingers of the same polarity between adjacent pairs of electrodes is an inactive region, the adjacent electrode fingers of the same polarity are integrated as shown in FIG. Therefore, the electrode fingers shown in FIG. 3 can be integrated as shown in the electrode fingers ' shown in FIG. In this case, a piezoelectrically inactive region that is hardly polarized is created on the ceramic plate under the integrated electrode finger along the broken line in the case of Fig. 4, and electrode fingers of the same polarity are connected adjacently to each other. The same effect as when provided is obtained. However, the 9th
The width D of the integrated electrode finger' shown in the figure needs to be wider than twice the width d of the other electrode fingers. In other words, when D = 2d + a, (a > 0), a is the width of the piezoelectrically inactive region, which corresponds to the gap width between the vibrating elements in a conventional probe with strip-shaped vibrating elements arranged side by side. Become something to do. if,
If D is smaller than 2d, there will be no piezoelectrically inactive region, and the object of the present invention may not be achieved.

As explained above, since the present invention uses vibrations near the surface of the ceramic plate, there is no need to make the ceramic plate thin and divide it into strips as in the past, and the ceramic plate can be adjusted to an appropriate thickness. A plurality of pairs of interdigitated electrodes are provided while the unit remains integrated, and electronic scanning of the ultrasonic beam can be performed.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing the electrode structure of a conventional ultrasonic probe using interdigitated electrodes, Fig. 2 is a sectional view to explain the principle of ultrasonic vibration generation, and Fig. 3 is an ultrasonic probe. FIG. 4 is an explanatory diagram showing an example of the electrode structure of the toucher according to the present invention. FIG. is a frequency characteristic diagram of ultrasonic vibration of the electrode pair of the ultrasonic probe of the present invention, FIG. 6 is a waveform diagram of echoes obtained when a rectangular wave voltage is input to the electrode pair, and FIGS. 7 to 9 2A and 2B are explanatory diagrams showing other embodiments of the electrode structure of an ultrasonic transducer according to the present invention. DESCRIPTION OF SYMBOLS 1... Ferroelectric ceramic board, 11... Cross-finger electrode, 12a, 12b...12n... Cross-finger electrode element, A, B...N... Electrode pair.

Claims (1)

[Claims] 1. Polarization treatment is performed via first and second interdigitated finger electrodes provided on a ferroelectric ceramic plate that has not been subjected to polarization treatment, and the first and second interdigitated electrodes are In an ultrasonic probe that serves as a conversion electrode to mutually convert an electric signal and an ultrasonic wave in a direction perpendicular to the surface of the ceramic plate, the second interdigitated electrode is connected to the first interdigitated electrode. It is composed of a plurality of independent interdigitated electrode elements each having a predetermined number of electrode fingers inserted between the electrode fingers and having a polarity different from that of the first interdigital electrode, and the intersecting finger electrode element has a predetermined number of electrode fingers inserted between the electrode fingers. An ultrasonic probe comprising a plurality of independent electrode pairs together with finger electrodes, and further comprising adjacent electrode fingers of both electrode pairs having the same polarity. 2. The ultrasonic probe according to claim 1, wherein the ferroelectric ceramic plate is made of a material having a small electro-mechanical coupling coefficient in a direction parallel to the plate surface. 3. Claim 1 or 2, characterized in that the adjacent electrode fingers of the same polarity are integrated, and the width of the integrated electrode finger is made larger than twice the width of other electrode fingers. Ultrasonic probe as described.