JPS605133A - Ultrasonic converter improved in vibration mode - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an ultrasonic transducer with improved vibration modes.

In particular, the invention relates to an ultrasound transducer of the type that generates and receives longitudinal waves for use in medical ultrasound imaging.

PRIOR ART AND PROBLEMS TO BE SOLVED In the ultrasonic transducer art, various vibromodal piezoelectric materials are well known and are useful for generating longitudinal waves. Such modes include “
Plate mode (in this mode, a relatively flat piezoelectric plate vibrates, and when voltage is applied to the electrodes connected to the upper and lower plate surfaces, ultrasonic waves are transmitted in a direction perpendicular to the plate surface. ), and 6
bar" mode (in which the piezoelectric body of an elongated bar has electrodes connected to its ends and vibrates to cause wave transmission along the longitudinal axis of the bar); and the one-beam" mode. is also known, in which the piezoelectric body of an elongated bar has elongated electrodes on each side thereof and vibrates in such a way as to cause wave transmission perpendicular to the longitudinal axis of the bar, which includes, for example, a phased array or Examples include linear transducers. Furthermore, 6
"Mixed" modes of "plate" mode, "bar" mode or "beam" mode with transverse vibration modes are also known. These transverse modes occur to an unacceptable degree in the piezoelectric body, in which case the ratio of the height of the piezoelectric body to +lJ is (1]/
W) is in the range of about 0.5 to 2 for a 1ψ transducer using a half-wave resonant mode, and about 0.25 to 1 for a transducer using a quarter-wave resonant mode. It is in. As will be understood by those skilled in the art, some degree of structural vibration will occur in any piezoelectric material, depending on the geometry of the elements making up the transducer and the nature of the 0ef constant piezoelectric material. H/W in half wavelength converter
It becomes a big problem when H/W is about 0.5 to 2, and when H/W is about 0.25 to 1 in quarter-wavelength converters.

The particular problem that the present invention seeks to solve will be illustrated using a piston-type annular transducer of the type used in annular arrays. In the past, various piston-type annular array transducers have been used to provide electrical variable focus adjustment capability. In such annular array transducers, the outer ring of the door array is typically much narrower than the inner ring or central piston. This is due to the requirement to keep the areas of the various transducer elements substantially equal in order to provide a substantially uniform signal at the ultrasound penetration depth. This phenomenon is well known in the art, and it is common practice in annular arrays to provide annular elements having areas that are substantially equal to each other and equal to the area of the central piston.

A problem arising from manufacturing annular arrays using standard methods is that, in the outer ring of a diagonal array, the ratio of the height of the individual elements (height of the piezoelectric body measured from its substrate) to the width (measured radially) approaches 1. Unfortunately, as mentioned above, when the transducer height/11 ratio is in the range of about 0.5 to 2, transverse mode vibrations occur at unacceptable levels in medical 4B sonic piston transducers. . Various attempts have been made to reduce the transverse vibration modes of the external transducer ring. Such methods include placing damping material in the area of external basis weight and in the area surrounding the layer. These methods generally showed few positive results.

Therefore, a method of manufacturing an annular array transducer that can be electrically focused over a wide range without having to suffer from external ring transverse mode vibration problems has become desirable. In general, one can choose any clamp type (e.g. an annular array) and it is hoped that this will not force it to accept spurious vibrational modes (e.g. transverse modes) even if they occur in the outer ring. It will be done. It is also desirable to have the same vibrational mode (eg, plate or disk mode) in all elements of a transducer (eg, the central piston and outer ring of an annular array) of any arbitrary geometry.

Structure and Effect of the Invention According to the present invention, the bar vibration mode can be combined into any transducer design, since the pressure mass is sawn into a number of sub-elements and This is because each vibrates in a bar mode based on its physical shape and dimensions.

These sub-elements are then electrically connected to have any desired element geometry. Therefore, it is possible to design a transducer of arbitrary shape with the same vibration mode in all elements.

Hereinafter, the present invention will be explained in detail based on the accompanying drawings. In such drawings, % 1171 is a top view of an example of a transducer utilizing the present invention, FIG. 2 is a side view of a transducer utilizing the present invention, FIG. 3 is an annular array electrode pattern, and FIG. Figure 4 is a bottom view of a transducer, and Figure 4 is a side view of a transducer utilizing a second example of the present invention.

According to the present invention, it is desired to substantially eliminate transverse mode vibrations in the outer ring of the annular array. To achieve this result, the circular piece of piezoelectric body 10 shown in FIG. 1 is sawn into several sub-elements 12, for example with a semiconductor die saw. In a preferred embodiment of the invention, the sub-element 12 is substantially IE rectangular and has a side length W) that is substantially shorter than the height H) of the piezoelectric body 1o. As an example, when using PZ'r4 composition of J) Z T (lead-zirconate-titanate) piezoelectric material, 3 MHz
H for medical ultrasound transducers is approximately 20 mils (0.5 mm)
and W may be about 8 mils (0.2 mm). Second
As shown in the figure, saw kerf 14
[Mokame, the bottom surface 18 substantially below the top surface 16 of the body 10
I'm honing my skills. However, in a preferred embodiment of the invention, the saw lines 14 extend completely to the bottom surface 18 of the die 2 body 10, thereby maintaining the integrity of the piezoelectric body 10 and the electrode pattern. do. However, as will be explained below, it is possible to make suitable changes to the preferred method described below to cause the saw marks 14 to extend all the way to the bottom surface 18.

The upper surface 1 has sawn marks 14 formed through the L surface 16.
The six sub-elements 12 must be electrically connected. There are several ways in which this connection can be made; a preferred method is to fill the saw holes 14 with a low viscosity, non-conductive epoxy. In a preferred embodiment, a bimetallic system is then sputtered onto the surface of the epoxy to form the top well, pole 20, which also functions as an RF shield when electrically connected to ground. As is well known in the art, the three-metal ant system has a primary metal that adheres well to the -F phase, a secondary metal that provides a bond between the primary metal and the third metal, and a relatively resistant to oxidation. It has a third metal box that is resistant and easily attached to the first solder. In a preferred embodiment of the invention, the first metal is chromium, the second metal is nickel, and! $
3 all 3 Kinbukuro. Next, an acoustic matching layer 22 of, for example, a quarter wave or more of a non-conductive quaternary filled epoxy is applied over the surface of the upper g1≦' electrode 20 in a manner and for reasons known in the art.

An electrode 24 having a desired shape is formed on the bottom surface 18.

In a preferred embodiment of the invention, electrodes 24 are in the form of an annular array pattern as shown in FIG. In a preferred embodiment of the invention, a layer of conductive material (eg copper) is applied to the bottom of piezoelectric body 10.

Next, a layer of resist material is printed on the cotton conductive layer in the shape of the pattern of the bottom electrode, and the exposed portions of the conductive material 14 are then etched to remove unnecessary portions down to the piezoelectric body 10.

The purpose of applying an acoustic fissure 26 to the bottom, polar pattern 24 is well known in the art. As will be appreciated, a minimum electrode spacing, located at a constant spacing between the annular rings of the electrode pattern, is chosen to ensure that no two electrodes can apply voltage to the same sub-element 12. This is WX
Is the interval larger than /T? This can be accomplished by using Ji I= (in the case of a square sub-element with side length W).

In FIG. 4, another embodiment 28 of the invention is shown in cross section. In this particular embodiment, the piezoelectric body 30 is tizered to form the sub-element 32 , with the cut edges 34 aged to a quarter length mismatched layer 36 . The piezoelectric body 30 itself is approximately one-quarter wavelength thick, rather than one-half wavelength thick. Similarly, a matching layer 38 of a quarter wavelength thick or less is applied to the ridges 39 of the surface 40 of the piezoelectric body 30. A material having a required impedance of ZL is selected as the special material to be used for the mismatch 36, and on the other hand, the material for the lining 1) 37 (mismatch
tM36J2) is chosen to have an acoustic impedance of ZB, which results in an input impedance to the mismatch 1-36, as seen from the piezoelectric body 30, which is 1ilii36 or about 4 The frequency is (ZL)2/ZB, which is close to the frequency when the thickness is one-tenth of a wavelength.

Misalignment of sub-element 32 via piezoelectric body 30 @36
When fully diced, the mismatch@36 is preferably conductive, so that the back electrode pattern 41 can be formed in the mismatch layer 36. In certain cases, optimization of a particular transducer design requires that the mismatch@36 be other than a quarter wavelength thick, as will be understood by those skilled in the art.

If ZL is selected to be relatively large with respect to ZH,
The impedance to mismatch@36 will be relatively large.

That is, substantially any acoustic energy is transmitted through the surface 40 of the piezoelectric body 30 rather than into the misalignment 36, and the piezoelectric body exhibits a sine change in the reflection coefficient of the rear border 43 ( It vibrates in a quarter-wavelength resonant mode. An advantage of constructing the transducer 10 according to this embodiment is that the pressure box, body 3
The individual sub-elements 32 do not become brittle because they become thinner over a period of 0 to 100 minutes.

This particular embodiment includes a piece of piezoelectric material 30 about a quarter wavelength thick, rather than a piece of piezoelectric material 30 about a half wavelength thick, so as to substantially eliminate undesirable mixed modes of vibration. The required 1/[Ij ratio (H/'W) is governed by different rules than the If electric body 30 of the half-wavelength tail. Therefore, the height/1J ratio is about 0.25~
1, no mixed mote operation is experienced in this particular embodiment. That is, the individual sub-elements 32 can have a height/median pressure of about 1.25, which makes them more structurally rigid than the embodiment described with respect to FIG.

Particularly with respect to Figure 2, its height/medium pressure (H/W) is selected to be substantially greater than 2. In particular, I found out that a ratio of 2.5 is acceptable.

Although the invention is particularly suited for use in annular array type devices,
A linear or phased array type, Ij f&, can also be used, in which case the small pole pattern applied in the process is different. A circular array small pole pattern is used,
This is to illustrate the invention. Those skilled in the art will appreciate that the present invention, in place, may be utilized to provide a linear array with elements operating in a "bar mode" rather than a conventional beam mode. The key point is that the bar mode Ha undergoes greater coupling between electrical and acoustic energy, which can confer an advantage to linear or phased arrays.

The present invention provides an annular array with individual annular elements that are well matched to provide substantially equal intensity signals at various depths and that have excellent frequency matching between each element. The phrase sound wave transformer or combination. This substantially eliminates the problems previously encountered with annular array transducers. In addition, the present invention allows medical ultrasound transducers with uniform vibration modes for all elements of the transducer to be configured in any desired transducer geometry (
For example, the annular arrays described herein) can also be manufactured.

[Brief explanation of drawings]

Part 1 is a top view of a piezoelectric body in an example of the transducer of the present invention,
2 is a side view of the transducer of FIG. 1, FIG. 3 is a bottom view of the piezoelectric body in the transducer of FIG. 1, and FIG. 4 is a side view of another example of the transducer of the present invention. , 10.30...IIm, body, 12, 32...subelement, 14.34...saw, 20, 2
4. 39.41...electrode. Patent applicant: Advanced Technology Laboratories, Inc. Patent attorney: Maeda Hao
1 other person

Claims (1)

Claims: Consisting of a peak-to-edge piezoelectric body, the piezoelectric body is subdivided into sub-elements smaller than the associated electrode, so that the physical shape and dimensions of the sub-elements rather than the shape or dimensions of the electrodes. an improved ultrasonic transducer for determining the vibration mode of a sub-element; (2) The improvement of paragraph 1, wherein the transducer is an annular array transducer, and the subelements are separated by serrations that extend substantially, but not completely, into the piezoelectric body. Ultrasonic transducer. (3) The improved ultrasonic transducer according to item 2 above, wherein the sawn holes are filled with a non-conductive ladle material, and the surfaces of the piezoelectric body and the filling+A material are covered with a conductive electrode. 14) Four electrodes or the first metal on the surface of the piezoelectric material, the first
a second metal on a metal surface and a third metal surface on the second metal surface;
The improved ultrasonic transducer according to item 3, which is made of a bimetallic material consisting of gold. (5) The improved ultrasonic transducer according to item 4 of Note 11X, wherein the first metal is chromium, the second metal is copper or copper, and the third metal is copper. (6) The improved ultrasonic transducer of claim 1, wherein the transducer is an annular array transducer, and the subelements are separated by serrations extending completely within the piezoelectric body.