JPS5842968A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To form a high-frequency electron scanning type ultrasonic probe of a united ceramic plate, by providing plural couples of cross finger electrodes on a ferrodielectric ceramics plate which has a small coefficiency of electromechanical coupling in a direction parallel to the plate surface. CONSTITUTION:On a ceramics plate of PbTlO3 which contains Sm and Mn while a coefficient of electromechanical coupling regarding lateral oscillation is nearly disregarded, adjacent electrode fingers 5 and 6,- made of a cross finger electrode element 11 as a negative electrode, etc., and cross finger electrode elements 12a, 12b- as positive electrodes, etc., are arranged in plural cross finger electrode couples A, B-. In this constitution, the respective electrode couples A, B- serve as independent ultrasonic wave generating sources. This simple constitution which uses the adequately-thick, one-body ceramic plate without arranging numbers of oscillating elements using independent thin striplike ceramics plates realizes an array of high-frequency electron scanning type ultrasonic probes.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic scanning ultrasound probe used in ultrasound diagnostic equipment and the like. Conventionally, this type of ultrasonic probe has
A zircon-lead titanate (PZT) ceramic plate that has been uniformly polarized in the thickness direction is cut into thin strips, electrodes are attached to the front and back sides, and ultrasonic waves are generated by the thickness vibration of each piece. It is occurring. 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, lead titanate (PbTi) allows the width of each element to be widened even though the frequency is the same.
There is a movement to use O3) type ceramics to meet the demands for higher frequencies. However, this is very 10-1
5 MHz is said to be the limit, and new technology must be developed for even higher frequency ranges. The present invention was developed in response to such demands.

Conventionally, as a means for generating high-frequency ultrasonic waves, as shown in FIG.
rode) (also referred to as L/type electrodes or interdigital electrodes) 2 and 3 are used to perform polarization treatment, and the electrodes 2 and 3 are used as electrodes for mutual conversion between electricity and ultrasonic waves.・It is known that

In the case of this electrode structure, as shown in the second illustrated book, the vicinity of the surface of the ceramic plate 1 is alternately polarized in opposite directions as shown by the arrows 4, so the pulse voltage 5 is applied via the interdigitated electrodes 2 and 3. When applied, ultrasonic waves are emitted in the direction perpendicular to the plate surface ζ, as shown by arrows 6 and 2, with the same phase from each electrode finger force.

``Since this ultrasonic generation transducer is a non-resonant type, the frequency response band is extremely wide, and it is possible to generate ultrasonic pulses with an extremely narrow width. Therefore, when used in an ultrasonic imaging system, a high-resolution '1J1 device can be obtained, and moreover, it has the feature of easily generating ultrasonic waves with a high frequency of several tens to 100 MH2.

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. 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. The interdigital electrode elements 12a, 12b, . . . , 12n of the interdigital electrode 2 in Fig. 1 are shaped as if the electrode fingers were divided into a predetermined number (in Fig. 3, two electrode fingers ■ and ■).
As shown by broken lines, two n pairs of electrodes A, B...N are formed, and as an example, the electrode 11 on the common side
negative polarity, dividing side electrodes 12a, 12b...12n
are each of positive polarity, and electrodes and fingers of the same polarity (negative polarity in the case of FIG. 3 as an example) in adjacent pairs of electrodes are arranged so as to be adjacent to each other.

That is, for example, the electrode of the interdigital electrode element 12a - finger ■
, ■, and the electrode fingers ■, ■, and ■ of the interdigital electrode 11 constitute an electrode pair, and the electrode pair is in contact with the adjacent electrode pair B through the electrode fingers ■ and O of the same polarity. Deploy.

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. , or each pair of electrodes is brought into contact with the next pair of electrodes 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 buttocks 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, there must be mechanical coupling between the vibrations perpendicular to the plate surface on the ceramic plate below each pair of electrodes sandwiched by the broken line. For example, each electrode pair serves as a strip-shaped ultrasonic generation source that is completely independent of each other. In other words, the ultrasonic probe with the electrode structure shown in Figure 3 is equivalent to a conventional electronic scanning ultrasonic probe in which a large number of independent strip-shaped vibrating elements are arranged in parallel in that multiple ultrasonic generation sources are arranged side by side. This allows electronic scanning of ultrasonic beams.

Generally, there is a mechanical coupling between the vibrations of the ceramic plate under each electrode pair, but lead titanate (Pb Ti 0
3) The electromechanical coupling with respect to lateral vibrations is small in the ceramic plate, and especially when only longitudinal vibrations are excited, this lateral coupling is very small.

Next, the results of actual measurements were shown in which electrodes having the structure of the present invention were provided on the Pb Ti 03 ceramic plate.

Lateral vibration (samarium (8 m) and manganese (Mr+), where the electro-mechanical coupling coefficient is almost negligible)
A Pb Ti 03 -based ceramic containing Pb Ti 03 is prepared using ordinary ceramic technology, and a square plate with a length of 30 mm and a width of 13 mm is cut out and both sides are polished. On the surface of the ceramic plate thus obtained, an electrode having the shape shown in FIG. 3 is vapor-deposited using gold (Au) as the electrode material through a metal mask. Note that the width of the electrode fingers is 120 μm1, the distance between the electrode fingers is 80 pm, and the electrode pair ↑ - After configuring the ultrasonic source in this way, 15 o
``Each electrode 12a in silicone oil maintained at C.

DC56 between 12b...12n and the common side electrode 11
A voltage of 0 V 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.

・The ultra-wave conversion frequency i characteristic actually measured in this way is
As shown in the figure. In this case, the center frequency is approximately 30■h, and 3d
It can be seen that the specific band of B reduction is approximately 100%, which is extremely wide. Next, an example of a received waveform when an underwater rectangular wave voltage is applied to emit an ultrasonic wave and an echo from a reflector is observed is shown in FIG. 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, a high-frequency electronic scanning ultrasonic probe was realized by providing electrodes with the structure shown in Figure 3 on a ceramic plate and using a ceramic plate with a small lateral electro-mechanical coupling coefficient. can do. □In the above embodiment, the electrode index m of each electrode can be set arbitrarily, and FIGS. 7 and 8 (2) show examples in which m=1. When 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.On the other hand, as m becomes larger, the output of the electrode pair is large, but the width of the electrode pair becomes wider, and the resolution decreases.

In the embodiment shown in FIG. 3, m is set to 2 in consideration of the output and resolution of the electrode pair.

Furthermore, in the above embodiments, the electrode fingers on the common side (for example, electrode fingers ■ and ■ in FIG. 3) are adjacent to each other.
Even if the electrode fingers on the divided side are configured to be adjacent to each other, they will not support each other. Of course, FIG. 3 shows only one example of the polarity of the electrodes; on the other hand, the common side electrode can be the positive electrode and the divided side electrode can be the negative electrode, or The electrodes do not necessarily remain in one piece, but may be divided into pairs of electrodes, and each pair of electrodes may be configured to be electrically completely independent.

Furthermore, (-As shown in FIG. 4 above, since the ceramics under the electrode fingers of the same polarity between adjacent pairs of electrodes are inactive regions, as shown in FIG. 9, the ceramics under the electrode fingers of the same polarity are By integrating, the electrode fingers ■ and ■ in Fig. 3 can be integrated as shown in the electrode fingers ■' in Fig. 9. In this case, the ceramic plate under the integrated electrode fingers has a Fourth
A piezoelectrically inactive region that is hardly polarized is generated along the broken line in the figure, and the same effect as when electrodes and fingers of the same polarity are provided in vertical contact is obtained. However, the width of the integrated electrode finger ■' in FIG. 9 needs to be wider than twice the width d of the other electrode fingers ■ to ■. That is, “D=29+
a, (where a>O), then 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. . 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, according to the present invention, since vibration near the surface of the ceramic plate is used, unlike the conventional method,
There is no need to make the ceramic plate thinner or divide it into strips, and the ceramic plate can be kept in one piece with an appropriate thickness, and a plurality of electrode pairs using intersecting finger electrodes can be provided to perform electronic scanning of the ultrasonic beam. I can do it.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the electrode structure of a conventional ultrasonic probe using interdigital electrodes, Fig. 2 is a cross-sectional view to explain the principle of ultrasonic tremor generation, and Fig. 3 is a cross-sectional view of a scanning probe using cross-finger electrodes. Fig. 4 is an explanatory diagram showing an example of the electrode structure of the contactor according to the present invention; Figure 5 is a frequency characteristic diagram of ultrasonic vibration of the electrode pair of the ultrasonic probe of the present invention.
G is a waveform diagram of two echoes obtained when a rectangular wave voltage is input to the electrode pair, and FIGS. 7 to 9 are explanatory diagrams showing other practical examples of the electrode structure according to the present invention of the ultrasonic core. It is. l... Ferroelectric ceramic plate, 11... Crossed fingers 1
Extreme, 12. a, 12b...12'n...cross-finger electrode element, A, B...N...electrode pair. Sai I Nuda Juku > ) Uke 5 years old 3 Figure! → Always 7 ω years old 3 days ¥? Zuga! @ f (MH>)

Claims (1)

[Claims] 1. Polarization is performed through first and second interdigitated electrodes provided on a ferroelectric ceramic plate that has not been subjected to polarization treatment, and the first and second interdigitated electrodes are In the ultrasonic probe which uses as an electrode for mutual electric-ultrasonic conversion, the second interdigitated electrode has 6 two electrode fingers inserted between the electrode fingers of the first interdigitated electrode, respectively. It is composed of a plurality of interdigitated electrode elements having a number of different polarities and different polarity from the first interdigital electrode, and the interdigital electrode elements constitute a plurality of independent electrode pairs together with the first interdigital electrode. Further, in the adjacent electrode pairs, adjacent electrode fingers of both electrode pairs have 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. 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 in section.