Linear array ultrasonic transducer

A linear array ultrasonic transducer is provided primarily for use in a medical diagnostic examination device in which an ultrasonic beam is projected toward an object to be examined, thereby to examine the condition of the tissues of that object. The linear array ultrasonic transducer comprises an array of tiny oscillatory elements and electrode leads connected by a conductive adhesive to facilitate the fabrication, and two registering layers and a lens layer mounted on the front sides of the tiny oscillatory elements so that an image of high resolution may be produced.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a linear array ultrasonic transducer used 
in an ultrasonic diagnostic examination device, and more particularly to 
such a transducer in which an ultrasonic beam is projected into an object 
to be examined, such as a living body, to receive the echoes which are 
reflected from the boundary between heterogenous bodies having different 
acoustic impedances. 
2. Description of the Prior Art 
The construction of and the problems concomitant with a transducer 
according to the prior art will now be described. 
Referring to FIG. 1 which is a perspective view showing an oscillatory 
array portion of a transducer, the transducer includes an oscillatory 
element 1a which is made of a material such as PZT (i.e., piezoelectric 
element of Lead Zirconate-Titanate). Electrode layers 1b and 1c are 
provided on both sides of the oscillatory element 1a. Oscillatory element 
1a thus formed with the electrode layers 1b and 1c usually is a member of 
a large plate-shaped oscillator. This part of the plate-shaped oscillator 
is adhered to a backing member, which will be described later, and is then 
cut thin into an array form, as shown in FIG. 1. The single thin cut 
element from the oscillatory element 1a is indicated as a tiny oscillatory 
element 11. A backing member 2 absorbs the ultrasonic waves directed to 
the back of the array of the tiny oscillatory elements 11. 
In order to clearly produce the image which is obtained by the ultrasonic 
diagnostic examination device using such a transducer, a variety of means 
have been employed, including such means relating to the transducer as 
follows: 
(1) The oscillatory frequency of the ultrasonic waves is increased; 
(2) A side lobe is reduced in the directive characteristics of the 
ultrasonic beam; and 
(3) The ultrasonic beam is made thin and sharp. 
As has been described above, such means involved the construction of the 
tiny oscillatory elements having a rectangular shape which are made 
thinner. 
The operation of the transducer shown in FIG. 1 is as follows. For example, 
five tiny oscillatory elements 11 are gathered into one group, and the 
electrode layers of any of the tiny oscillatory elements are denoted 
a.sub.K and b.sub.K, the electrode layers a.sub.1 to a.sub.5 and b.sub.1 
to b.sub.5 are electrically connected (although the respective tiny 
oscillatory elements are acoustically insulated), and a pulsed voltage 
signal is applied between the electrode layers a.sub.1 to a.sub.5 and 
b.sub.1 to b.sub.5 so that one ultrasonic beam is transmitted from that 
group of the tiny oscillatory elements. A number of such groups are 
arranged in an array to transmit the ultrasonic beam consecutively, 
thereby to effect the scanning operation. 
FIG. 2 is a perspective view showing one tiny oscillatory element. In order 
to realize the aforementioned means (2), if the thickness and width of the 
tiny oscillatory element are denoted as t and W, respectively, as is 
disclosed in May, 1977 "Proceedings of Japanese Ultrasonic Medical 
Association", page 53, the ratio of W/t is desired to be equal to or less 
than 0.6. For example, therefore, in order to generate ultrasonic waves 
having a frequency of 5 MHz, the thickness t of the tiny oscillatory 
element has to be about 0.25 mm, and the width W has to be about 0.15 mm. 
Electrode leads for driving such tiny oscillatory elements, according to 
the prior art, have been attached to the electrode layers 1b and 1c by a 
bonding process. This bonding process involves bonding the leads one by 
one to the tiny oscillatory elements (generally, about three hundred in 
number having a width of 0.15 mm) which required skilled working 
techniques and is time consuming. As a result, the bonding process has 
been an intrinsic cause for the failure of the apparatus in which the 
array is incorporated. It has been extremely difficult to complete the 
bonding of the tiny oscillatory elements as many as three hundred times 
without any failure occurring. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a linear array 
ultrasonic transducer which can be easily fabricated. 
Another object of the present invention is to provide a linear array 
ultrasonic transducer which partly sharpens the directivity of an 
ultrasonic beam and partly reduces the side lobe so that it can obtain a 
clear image. 
In carrying out this invention in one illustrative embodiment thereof, a 
linear array ultrasonic transducer is provided having a plurality of tiny 
oscillatory elements arranged in the form of an array and electrode leads 
therefor are connected by means of a conductive adhesive. Two registering 
layers and an acoustic lens layer are mounted on the front side of the 
tiny oscillatory elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 3, the ultrasonic transducer is constructed of 
rectangular piezoelectric elements 1a made of, for example, of 
piezoelectric ceramic selected from lead zirconate titanates or the like. 
Rectangular elements 1a have electrode layers 1b and 1c on each side 
thereof to form tiny ultrasonic oscillatory elements 11. A backing member 
(or an ultrasonic absorber) 2 made of rubber mixed with metal powders, 
such as ferrite rubber, is placed on the back sides of the respective tiny 
ultrasonic oscillatory elements 11. A print plate 3 comprising an 
insulating substrate 3a and a plurality of lead wire patterns 3b formed on 
the insulating substrate 3a is so arranged that its end face is 
substantially at a right angle with respect to one end portion of each of 
the tiny ultrasonic oscillatory elements 11. Another print plate 6 
comprising an insulating substrate 6a and a plurality of lead wire 
patterns 6b is formed on the insulating substrate 6a and arranged such 
that its end face is substantially at a right angle with respect to the 
other end portion of each of the tiny ultrasonic oscillatory elements 11. 
The lead wire patterns 3b function to excite the respective tiny 
ultrasonic oscillatory elements 11, while the lead wire patterns 6b form a 
common electrode for the respective tiny ultrasonic oscillatory elements 
11. A conductive adhesive layer 4 (containing a conductive paint) which is 
cut and separated, as indicated at cut sections 4a, corresponding to the 
desired number of the plural lead wire patterns is applied to one end 
portion of the tiny ultrasonic oscillatory elements 11 and an end face of 
the print plate 3. The conductive adhesive layer 4 thus formed functions 
to connect the electrode layers 1b of the tiny ultrasonic oscillatory 
elements to the lead wire patterns 3 b while segregating a plurality of 
tiny ultrasonic oscillatory elements 11 into one group. A conductive 
adhesive layer 5 is applied to the other end portions of the tiny 
ultrasonic oscillatory elements 11 and the end face of the print plate 6 
and functions to connect the electrode layers 1c of the ultrasonic 
oscillatory micro-elements 11 and the lead wire patterns 6b. Consecutively 
mounted on the front sides of the respective tiny ultrasonic oscillatory 
elements 11, are a first matching layer 7 a second matching layer 8 and an 
acoustic lens 9 which is located at the foremost position. 
The operation of the linear array ultrasonic transducer of FIG. 3 having 
the construction covered thus far will now be described. As shown in FIGS. 
3 and 4, the oscillatory elements 11 are cut thin in the form of an array. 
Cut portions are made as shown in the drawing, such that the conductive 
adhesive layer 4 is cut every several elements, as indicated at 4a. As a 
result, in response to a single signal, a plurality of (five in the 
embodiment of FIGS. 3 and 4) the oscillatory elements 11 are 
simultaneously excited. A plurality of groups each having five oscillatory 
elements constitute the transducer shown in FIGS. 3 and 4. When ultrasonic 
waves are to be transmitted from the transducer, the ultrasonic waves, 
which are diverged in the scanning direction (direction X of FIG. 3), can 
be condensed by a phased array system which is operative to excite the 
plurality of groups in a certain time relationship. On the other hand, the 
ultrasonic waves, which are diverged in the thickness direction (direction 
Y of FIG. 3), can be converged at the focal point of the acoustic lens 9 
by the action of the same lens. The ultrasonic beam thus generated has a 
sharp directivity in both directions of the X and Y axes. 
Next, in order to improve the responsiveness of the transducer, i.e., in 
order that the respective oscillatory elements may oscillate in the form 
of a piston to transmit the ultrasonic waves within a short time period, 
if the width of the oscillatory elements cut into a rectangular shape is 
denoted by W, the thickness of the same being designated as t, they are 
selected to satisfy the relationship of W/t .ltoreq.0.8. Generally 
speaking, since the thickness t of the oscillatory elements for 
transmitting the ultrasonic waves is made remarkably small, the width W of 
the cut rectangle must also be made remarkably small in order to satisfy 
the condition specified above. According to the prior art, on the other 
hand, since signal electrode leads are bonded to the electrode layers of 
the oscillatory elements, a space is required for the bonding process. As 
a result, the width W of the oscillatory elements is required to have a 
size higher than a preset value, thus making it difficult to satisfy the 
aforementioned condition of W/t .ltoreq.0.8. Moreover, since the bonding 
process is effected in a restricted space, the percentage of defective 
units is remarkably high. According to the present invention, since the 
electrode layers of the oscillatory elements and the patterns of the print 
plates are connected in advance by means of the conductive adhesive layers 
4 and 5 without any bonding process, the aforementioned drawback 
concomitant with the conventional bonding process can be obviated. As a 
result, the width W of the oscillatory elements can be cut sufficiently 
narrow so that the responsiveness of the same elements can be improved. 
Moreover, the side lobe can be reduced due to the fact that the width W of 
the oscillatory elements is reduced. 
It is necessary for the ultrasonic diagnostic examination device to 
effectively transmit the ultrasonic waves from the transducer into the 
object to be examined. More specifically, it is not preferred that the 
ultrasonic waves transmitted from the oscillatory elements be absorbed or 
relfected in the course of their transmission. According to the present 
invention, acoustic matching is established between the oscillatory 
elements 11 and the object by providing first and second matching layers 
to thereby prevent the ultrasonic waves from being absorbed or reflected. 
More specifically, the first matching layer 7 is made of glass, the second 
matching layer 8 is made of a high molecular film, and the acoustic lens 9 
is made of silicone rubber. Thus, the acoustic impedance is brought closer 
and closer to the object to thereby prevent reflection. 
Next, the method of fabricating the transducer having the construction thus 
far set forth will now be described in the steps as follows: 
Step 1: The backing member 2 is adhered to the parts of the oscillatory 
elements; 
Step 2: The print plate 3 is adhered to the backing member 2 partly by 
arranging the patterns 3b to face the outside, as shown in FIG. 4A, and 
partly by arranging one end of each pattern 3b to be in the vicinity of 
the electrode layer 1b of each oscillatory element; 
Step 3: The electrode layer 1b of the part of each oscillatory element and 
each pattern 3b are connected by means of the conductive adhesive layer 4, 
as shown in FIGS. 4A to 4C; 
Step 4: In the construction thus made, the parts of the oscillatory 
elements are cut so that the five tiny oscillatory elements 11 are 
electrically connected with each pattern 3b through the conductive 
adhesive layer 4, as shown in FIG. 4C. More specifically, as shown in FIG. 
4C, if the respective cut portions are denoted at 1d and 1e, the cut depth 
of the cut portions 1d is made so as to cut off the parts of the 
oscillatory elements completely while avoiding electric separation as far 
as the conductive adhesive layer 4, whereas the cut depth of the cut 
portions 1e is made so as to sufficiently separate even the conductive 
adhesive layer 4. As a result, each pattern 3b, which is connected with 
the electrode layers 1b of the oscillatory element group composed of the 
five tiny oscillatory elements, is used as the signal electrode lead; and 
Step 5: The print plate 6 is adhered, as shown in FIGS. 4A and 4B, to the 
side of the backing member 2 at the opposite side to that where the print 
plate 3 is adhered, and the electrode layer 1c of each tiny oscillatory 
element and the electrode layer 6b of the print plate 6 are connected by 
the conductive adhesive layer 5 whereby the electrode layer 6b is used as 
a common electrode lead. 
In the aforementioned description of the step 5, the attachment of the 
common electrode lead has been described such that, after the parts of the 
oscillatory elements are cut into the tiny oscillatory elements, the 
electrode layers 6b acting as the common electrode lead and the electrode 
layers 1c of the oscillatory elements are connected by means of the 
conductive adhesive layer 5. However, before the parts of the oscillatory 
elements are cut, the electrode layers 6b and the electrode layers 1c may 
be connected by means of the conductive adhesive layer 5. In either case, 
the present invention should not be limited to the difference in the 
attaching means to the common electrode lead. 
The conductive adhesive appearing in the Specification implies all that can 
be adhered at a temperature lower than the Curie point of the oscillatory 
material and possessing the properties of conductivity and adhesiveness, 
and includes a conductive adhesive (e.g., a conductive adhesive of epoxy 
resin) and a conductive paint, but not a solder. This is because the 
temperature required for the soldering process generally exceeds the Curie 
point of the material of the oscillatory elements, thereby changing the 
polarization of the oscillatory material and the properties of the 
oscillating elements. Moreover, the soldering process has many drawbacks 
peculiar to the fabrication of the transducer, for example, the blades of 
a cutter used for cutting the conductive adhesive are liable to be 
clogged, thereby deteriorating its cutting properties and the oscillatory 
elements may become warped due to the soldering temperature. However, the 
conductive adhesive according to the present invention succeeds in 
eliminating such drawbacks. 
In FIG. 4A, after the patterns 3b of the signal electrode leads and the 
electrode layers 1b are adhered by the conductive adhesive layer 4, the 
parts of the oscillatory elements are cut. According to this fabricating 
method, the cut portions 1d and 1e (FIG. 4C) are prepared by the single 
cutting operation (e.g., in the order of 
1d.fwdarw.1d.fwdarw.1d.fwdarw.1d.fwdarw.1e.fwdarw.1d and so on) to shorten 
the cutting time. The conductive adhesive layer 4 which has been applied 
in advance is slightly cut at the cut portions 1d. Since the spacing 
between the cut portions 1d and 1d is about 0.15 mm, the conductive 
adhesive layer 4 may possibly be formed with cracks. 
Another method, in which the above point is improved, will now be described 
with reference to FIGS. 5A to 5C. The steps 1 and 2 are the same as those 
previously described, and the following steps are taken thereafter: 
Step 3: The oscillatory elements are cut at 1d into the tiny oscillatory 
elements as shown in FIG. 5B; 
Step 4: As shown in FIGS. 5A and 5B, the electrode layer 1b of each tiny 
oscillatory element and each pattern 3b of the print plate 3 are connected 
by means of the conductive adhesive layer 4; and 
Step 5: As shown in FIG. 5C, cut portions 1d formed in the foregoing step 3 
are more deeply cut, thereby cutting the conductive adhesive layer 4 (as 
indicated at 1e in FIG. 5C) such that a group consisting of the five tiny 
oscillatory elements are connected with one of the patterns. 
After the above step 5, step 5 illustrated in FIGS. 4A to 4C is performed 
to effect the attachment to the common electrode lead. 
According to the fabricating method shown in FIGS. 5A to 5C, it is 
necessary to perform the cutting operations twice and to cut more deeply 
(at 1e) the portions 1d which have been cut in the previous step. 
Therefore, although more fabrication time is required than that for the 
transducer shown in FIGS. 4A to 4C, the conductive adhesive layer 4 is not 
cut at the cut portions 1d, in the manner described with reference to 
FIGS. 4A to 4C, but is deeply cut only at the cut portions 1e. 
Consequently, there is little danger of the array being formed with 
cracks. 
Although the width of the patterns 3b shown in FIG. 4C and FIGS. 5B and 5C 
is similar to that of the tiny oscillatory elements 11, the patterns are 
not considered to be limited to those shown. For example, FIG. 6 shows a 
different configuration where the electrode layers 1b of the array of the 
tiny oscillatory elements 11 and the patterns 3b of the print plate are 
connected by the conductive adhesive layer 4. If the width of one group of 
the tiny oscillatory elements 11 (e.g., the width of the five tiny 
oscillatory elements in the embodiment of FIG. 6) is denoted at l.sub.2 
and if the width of the patterns 3b is denoted at l.sub.1, it is 
sufficient that the relationship between the widths l.sub.1 and l.sub.2 be 
l.sub.1 .ltoreq.l.sub.2. However, as will be apparent from FIG. 6, as the 
width l.sub.1 becomes larger the accuracy for the arrangement of the print 
plate 3 becomes more strict. 
Although with respect to the embodiments illustrated in FIGS. 4A to 4C and 
FIGS. 5A to 5C, the description has been made by assuming that the number 
of the tiny oscillatory elements constituting one group is five, the 
number of the tiny oscillatory elements constituting the group is not 
limited thereby, but may vary, e.g., a single or a plurality of elements. 
As shown in FIG. 7, for example, the group may be composed of three tiny 
oscillatory elements. 
As shown in FIG. 7, similar results according to the present invention can 
be attained even if the cut portions 1d are cut as deeply as the patterns 
3b to provide a construction in which the respective tiny oscillatory 
elements 11 and the patterns 3b are connected by the conductive adhesive. 
In the description thus far, there has been disclosed the embodiment, in 
which one group consisting of a plurality of the tiny oscillatory elements 
and the single pattern 3b (or the signal electrode lead) are connected by 
means of the conductive adhesive layer 4. However, FIGS. 8A to 8C show 
another embodiment, in which a single pattern 3b is connected with a 
single tiny oscillatory element by means of the conductive adhesive layer 
4. More specifically, the print plate is formed with leads S.sub.1, 
S.sub.2, etc. in advance and the oscillatory elements are arranged in the 
form shown in FIG. 8A. Next, as shown in FIG. 8B, the patterns 3b of the 
print plate and the electrode layers 1b of the oscillatory elements are 
connected by the conductive adhesive layer 4. Then, the oscillatory 
elements, the conductive adhesive layer 4 and the print plate are so cut 
that each of the leads S.sub.1, S.sub.2, etc. are connected to a single 
tiny oscillatory element. 
The transducer, which is fabricated by connecting the single pattern (or 
the signal electrode lead) 3b with the single tiny oscillatory element 11 
by the conductive adhesive layer 4, as shown in FIG. 8C, is suitable for 
the ultrasonic diagnostic examination device of the sector scanning type. 
The oscillatory elements, which have been described with reference to FIGS. 
4A to 4C and FIGS. 5A to 5C, are respectively equipped on each of their 
sides with one electrode layer. However, the present invention can be 
practiced even if the oscillatory elements employ a run-around electrode 
construction as shown in FIGS. 9A to 9C in which one side electrode 1b 
extends to the other side. 
The method of fabricating the transducer shown in FIGS. 9A to 9C will now 
be described. After the parts of the oscillatory elements and the backing 
member 2 are adhered, the former are cut into the tiny oscillatory 
elements. After that, the print plate is so arranged that its pattern side 
faces the run-around portion of the run-around electrode 1b, and the 
respective patterns 3b and the electrode layers 1b of the respective tiny 
oscillatory elements are connected by means of the conductive adhesive 
layer 4. After that, every four grooves of the cut portions, which are 
formed by previously cutting the parts of the oscillatory elements, are 
cut in a tracing manner so that the conductive adhesive layer is cut. As a 
result, the electrode layers 1b of the five tiny oscillatory elements are 
connected with each of the patterns 3b, as shown in FIG. 9A. Thus, the 
signal electrode leads are extracted as the respective patterns 3b. 
Although not shown in FIGS. 9A and 9B, after the aforementioned 
fabricating process, the common electrode lead is assembled, as shown in 
FIG. 9C, by connecting the patterns 6b of the print plate 6 and the 
electrode layers 1c of the respective tiny oscillatory elements by the 
conductive adhesive layer 5. 
Similar results to those of the aforementioned embodiment can be attained 
in cases where the oscillatory elements have the electrode construction 
shown in FIG. 10. However, the description of the transducer having the 
structure shown in FIG. 10 will be omitted here because the oscillatory 
elements shown in FIG. 10 are prepared by making electrode layers of the 
oscillatory elements, used in the transducer shown in FIGS. 4A and 5A, run 
around merely in the thickness direction. 
The transducer in accordance with the present performance of the ultrasonic 
diagnostic invention, can be fabricated with ease in a short time period 
without being defective. Accordingly, the present invention can enjoy 
remarkably high results. Moreover, the transducer according to the present 
invention improves the performance of ultrasonic diagnostic devices by 
producing an image having high resolution.