JPS6260664B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic delay device suitable for use in, for example, an electronic scanning type ultrasonic diagnostic apparatus.

Electronic scanning methods for ultrasonic diagnostic equipment include sector scanning and linear scanning, both of which use an array of a plurality of electroacoustic transducers (hereinafter referred to as transducers). FIG. 1 shows the principle of electronic sector scanning applied to such an ultrasonic diagnostic apparatus. In electronic sector scanning, the drive pulses from the pulse generation circuit 1 are transmitted through variable delay circuits 2-1 to 2-2.
The oscillators 3-1 to 3-n are each supplied to the oscillators 3-1 to 3-n through the oscillators 3-1 to 3-n, and each of the oscillators 3-1 to 3-n is driven at different timings, and emitted from each oscillator in the same manner as the phased array method. The entire wavefront of the generated ultrasonic waves is directed in a certain direction.
Now, if the delay times of the variable delay circuits 2-1 to 2-n are sequentially lengthened from the variable delay circuit 2-1 to the variable delay circuit 2-n, at the time when the drive pulse is supplied to the vibrator 3-n, , vibrator 3-1 to 3-(n-
1) has already emitted an ultrasonic pulse, the ultrasonic wave emitted from the transducer 3-1 is at the farthest position within the living body, and the ultrasonic wave emitted from the transducer 3-n is at the closest position. In this case, the ultrasonic waves emitted from each vibrator propagate in the θ direction with the tangents (equiphase fronts) of each ultrasonic wave becoming the wave front of the entire wave according to Huygens' principle. Therefore, variable delay circuits 2-1 to 2
Sector scanning can be performed by electronically switching the delay time of -n to change the wavefront direction (beam direction). In addition, variable delay circuits 2-1 to 2
By controlling the delay time -n so that the wavefront becomes concave as shown by the broken line, the beam can be focused on a desired part within the living body. In this way, in electronic sector scanning, each transducer is driven at different timings to focus the beam and scan it in a fan shape, and each transducer receives the reflected wave at each scanning position, and its respective output By giving the same delay time as the transmission wave through the variable delay circuits 2-1 to 2-n and adding and receiving it in the receiving circuit 4,
The directivity is strengthened to extract only the reflected waves in the beam direction. Therefore, the delay time in each variable delay circuit is the sum of the delay time for determining the beam direction and the delay time for focusing.

In addition, as shown in FIG. 2, a line-shaped transducer 5
The multiplexer 6 sequentially selects k transducers in a group from -1 to 5-n, and the composite wavefront of the ultrasound emitted from these k transducers is focused on a certain part of the living body. Then, the driving pulse from the pulse generation circuit 7 is delayed by delay circuits 8-1 to 8-k and supplied to each of the k transducers to emit an ultrasonic wave, and the ultrasonic wave is reflected in the living body. The wave is received by the same number of k oscillators as the transmitted wave, and the delay circuit 8-1~
There is a system in which the directivity is strengthened by adding and receiving the signals through the receiving circuit 9 through the 8-k, so that only the reflected waves in the beam direction are extracted.

In ultrasound diagnostic equipment that uses the electronic scanning method described above, each transducer is driven at different timings in order to determine the beam direction of ultrasound emitted from multiple transducers and to focus the beams. There is a need to. Conventionally, as a delay device for obtaining such a delay time, for example, Japanese Patent Application Laid-Open No. 1989-
42171, and as shown in FIG. 3, a driving pulse is supplied via a buffer 11 to a delay line 12 with a tap consisting of a lumped constant of a coil L and a capacitor C, and the tap is sent to a multiplexer 13. is selected to obtain the required delay amount, and is supplied to the transducer via the buffer 14 to emit an ultrasonic wave, and the reflected wave signal of the ultrasonic wave received by the transducer is similarly received via the delay line 12. There is something like this.

On the other hand, in order to improve image quality in an ultrasonic diagnostic apparatus that uses an electronic scanning method, firstly, it is necessary to improve the resolution, and secondly, it is necessary to reduce sidelobes.

In order to improve the resolution, it is necessary to increase the frequency and broadband of the drive pulse and transmission system (shorten the drive pulse), but it is made up of lumped constants L and C as shown in Figure 3. When using a tapped delay line, generally the frequency characteristics, group delay characteristics (delay characteristics with respect to frequency...deteriorate as the frequency increases), and unnecessary reflection characteristics (unwanted reflections caused by variations in characteristic impedance between constituent stages) Reflections (unwanted reflections increase as the frequency increases) are bad, and in order to improve this, it is necessary to increase the number of stages of the delay line with taps and to extremely increase the accuracy of L and C, which increases the cost. There are defects that grow exponentially. Therefore, when using such a tapped delay line, it is extremely difficult to improve the resolution beyond the current level.

Furthermore, in order to suppress sidelobes, it is necessary to reduce the arrangement pitch of the vibrators, and the higher the frequency used, the further it is necessary to reduce the arrangement pitch. However, when using a tapped delay line as shown in Figure 3, if the arrangement pitch of the transducers is reduced, the quantization delay amount (minimum step for varying the delay amount) must be reduced in proportion. Therefore, there is a problem that the number of stages and the number of taps increase, making the configuration complicated and expensive.

From the above points, improvement in image quality has reached its limit in electronic scanning ultrasonic diagnostic apparatuses that use delayed delay lines with taps.

An object of the present invention is to solve the above-mentioned problems, and to provide an ultrasonic delay device that is appropriately configured so that ultrasonic images of good image quality can always be obtained with a simple and inexpensive configuration, especially in electronic scanning type ultrasonic diagnostic equipment. This is what we are trying to provide.

The ultrasonic delay device of the present invention includes a first electroacoustic transducer including at least one electroacoustic transducer;
A second electroacoustic transducer section consisting of a plurality of electroacoustic transducer elements arranged at a predetermined pitch; and one electroacoustic transducer of the first electroacoustic transducer unit on the surface of the ultrasonic transmission medium so that the lengths of the ultrasonic transmission paths between the two electroacoustic transducers are different, and It is characterized in that it is configured such that the ultrasonic waves transmitted from one electroacoustic transducer can be received by the other electroacoustic transducer.

The present invention will be described in detail below with reference to the drawings.

FIG. 4 shows the configuration of an example of the ultrasonic delay device of the present invention. In this example, the first electroacoustic transducer 21 is configured with n oscillators 21-1 to 21-n, and the second electroacoustic converter 22 is configured with m oscillators 22-1 to 22-n. - m, and these first and second electroacoustic transducers 21
and 22 on the surface of the ultrasonic transmission medium 23, the m transducers 22-1 to 22-m constituting the second electroacoustic transducer 22 are linearly arranged at a predetermined pitch, and the first The n vibrators 21-1 to 21-n constituting the electroacoustic transducer 21 are arranged on one side from each element and the central element of the second electroacoustic transducer 22. The elements are arranged at a predetermined pitch along an arc having a center on the second electroacoustic transducer 22 side so that the lengths of the ultrasonic transmission paths between the two elements are different. The ultrasonic wave transmitted from one electroacoustic transducer 21 or 22 can be received by the other electroacoustic transducer 22 or 21. Further, in the ultrasonic transmission medium 23, first and second
Ultrasonic absorption members 24 are provided in a scattered manner so as to sandwich the ultrasonic transmission path between the electroacoustic transducers 21 and 22.

The ultrasonic transmission medium 23 is preferably composed of an ultrasonic transmission medium mainly composed of silicate glass, considering the temperature coefficient of sound velocity, thermal expansion coefficient, and acoustic impedance matching with the vibrator. and the ultrasonic transmission medium 23 can be bonded using both solder and epoxy adhesive to avoid loss of strength and impedance matching, that is, both the adhesion and the matching layer. Each vibrator constituting the first and second electroacoustic transducers 21 and 22 uses a piezoelectric ceramic with excellent efficiency, and the number of elements (m pieces) of the second electroacoustic transducer 22 is, for example, an ultrasonic diagnostic device. The arrangement pitch d' corresponds to the number of transducers provided in the probe constituting the probe. When the array pitch is d, d'=v'/v
×d. Further, the n transducers 21-1 to 21-n constituting the first electroacoustic transducer 21 are arranged in an arc shape, and the radius of this arc is determined, for example, when used in a sector scanning ultrasonic diagnostic device. is centered on the center of the second electroacoustic transducer 22 in accordance with the pitch angle of the scanning line, and is the maximum diagnostic distance, that is, from the center of the plurality of transducers driven by the probe to the focal point of the ultrasound beam. The distance can be v'/v×R or v'/2v×R of the focal length R (focus distance) of . Furthermore, the ultrasonic absorption member 24 is for absorbing unnecessary reflection within the ultrasonic transmission medium 23, and can be made of, for example, a resin material with a small coefficient of thermal expansion.

5A, B, and C show three other examples of the ultrasonic delay device of the present invention, and FIG. 5A shows m transducers 22 constituting the second electroacoustic transducer 22. -1 to 22-m to the first electroacoustic transducer 2
FIG. 5B shows the first electroacoustic transducer 22 arranged symmetrically with respect to the second electroacoustic transducer 22 in FIG. 5A.
This is the result of excluding approximately half (n/2) of the vibrators on one side of the electroacoustic transducer 21. Further, in FIG. 5C, the first electroacoustic transducer 21 is connected to one vibrator 2.
1-1, and this vibrator 21
-1 to the center of the second electroacoustic transducer 22 is L=R×v'/v, then the m pieces constituting the second electroacoustic transducer 22 The vibrators 22-1 to 22-m are arranged along an arc having a radius of curvature Rv'/2v and having a center on the first electroacoustic transducer 21 side.

FIGS. 6A, B and C show three further examples of the ultrasonic delay device of the present invention. The ultrasonic delay device shown in FIG.
n from the center of the second electroacoustic transducer 22 to the first
They differ from those shown in FIG. 4 in that they are arranged along an arc with a radius of curvature of L+R×v'/v, where L is the distance to the electroacoustic transducer 21. In addition, FIG. 6B shows n vibrators 21-1 to 21-n constituting the first electroacoustic transducer 21 arranged in a straight line, and m
The vibrators 22-1 to 22-m are arranged along an arc having a radius of curvature of R×v'/v and having a center on the first electroacoustic transducer 21 side. Furthermore, in FIG. 6C, a plurality of vibrators constituting the first and second electroacoustic transducers 21 and 22 are arranged along an arc having a center on the side of the other electroacoustic transducer, and The distance between the first and second electroacoustic transducers 21 and 22 is Rv'/2v, the radius of curvature of the arc arranging the vibrators 22-1 to 22-m constituting the second electroacoustic transducer 22. 1/4 of that.

Various configurations of the ultrasonic delay device of the present invention have been described above, but the present invention is not limited to the above-described examples, and can be modified or changed in many ways. For example, as the ultrasonic transmission medium 23, a resin material such as acrylic or polystyrene having a slow sound velocity is used, and each vibrator constituting the first and second electroacoustic transducers 21 and 22 is made of PVDF (polyvinylidene difluoride). It can also be constructed from similar resin materials such as. If you do this, the first
Since the second electroacoustic transducers 21 and 22 and the ultrasonic transmission medium 23 can be integrally molded, manufacturing is simple, compact, and inexpensive. In addition, in order to reduce the overall shape, as shown in FIGS. 7A and 7B, the ultrasonic waves emitted from the first or second electroacoustic transducer 21 or 22 are reflected multiple times in the ultrasonic transmission medium 23. 2nd or 1st
It can also be configured so that the waves can be received by an electroacoustic transducer. Furthermore, since the ultrasonic transmission medium 23 only needs to have a constant sound velocity, it can also be constructed by enclosing a liquid in an envelope made of the ultrasonic transmission medium.

Hereinafter, the operation of the ultrasonic delay device of the present invention described above will be explained.

FIG. 8 shows the configuration of essential parts of an example of a sector scanning type ultrasonic diagnostic apparatus using the ultrasonic delay device of the present invention. In this example, the ultrasonic delay device 25
The structure shown in FIG. 4 is used as the structure shown in FIG. Drive pulses from the pulse generation circuit 31 are transmitted to the ultrasound transmission path in the ultrasound transmission medium 23 by focusing delay lines 32-1 to 32-k.
When the focus distance in the center is R, the first point selected by the multiplexer 34 is given a time delay such that the focus is on the point Rv'/v+L.
is supplied to the k transducers of the electroacoustic transducer 21. In addition, day delay line 32-1 for focus
~32-k is composed of lumped constants L and C in this example, but since the delay time is small in this case, it is less accurate and cheaper than the conventional one for strengthening directivity. Can be used.
The k transducers in the first electroacoustic transducer 21 selected by the multiplexer 34 perform the second electroacoustic transducer from the point Rv'/v+L outside the ultrasonic transmission medium 23, as shown in FIG. This is the range where two straight lines passing through both ends of the section 22 intersect with the first electroacoustic transducer section 21 . The ultrasonic beams emitted from the k transducers selected by the multiplexer 34 travel within the ultrasonic transmission medium 23 and reach the second electroacoustic transducer 22.
At this time, the angle between the ultrasonic beam and the normal direction of the second electroacoustic transducer 22 is θ', and the arrangement pitch of the transducers 22-1 to 22-m is
d', the delay amount D _l of the l-th transducer of the second electroacoustic transducer 22 is D _l -D ₁ ≒ (l-1) d' sin θ'/v' + (l)...
…(1) becomes. However, (l) is the focus delay amount in the l-th element given by the focus delay line 32-l. The received signal with such a delay amount is sent to the transmitting circuits 35-1 to 35-m.
The waveform is shaped and amplified and supplied to each of the transducers 36-1 to 36-m arranged in a line on the probe 36, thereby transmitting an ultrasonic beam into the living body 33. Here, the deflection angle θ of the ultrasonic beam transmitted into the living body 33 is such that the sound velocity in the living body 33 is v, and the transducers 36-1 to 36- of the probe 36 are
When the array pitch of m is d, the delay amount D _l of the l-th transducer of the probe 36 is D _l -D ₁ ≒ (l-1) dsinθ/v+(l) ...(2) From d'=dv'/v, the above equations (1) and (2) become an identity, and θ=θ'.

Next, the ultrasonic waves reflected in the living body 33 are received by the transducers 36-1 to 36-m of the probe 36, amplified by the preamplifiers 37-1 to 37-m, and sent through the opposite path. By following, the same delay time as the transmission is given and added. At this time, the directivity in the receiving wave becomes stronger in the θ direction, and the total directivity becomes the product of the directivity functions of the transmitting wave and the receiving wave, and the receiving circuit 3
8, the signal is amplified and detected, and an image is displayed. In this example, the angle θ can be changed by changing the selected positions of the k vibrators of the first electroacoustic transducer 21 using the multiplexer 34,
This allows sector scanning to be performed.

FIG. 10 shows the ultrasonic delay device 25 shown in FIG. 5A.
This figure shows the configuration of essential parts of an example of a sector scanning type ultrasonic diagnostic apparatus using the configuration shown in FIG. In this example, the drive pulse from the pulse generation circuit 31 is supplied to one (or several) transducers of the first electroacoustic transducer 21 selected by the multiplexer 34, thereby transmitting the ultrasonic wave. Emits ultrasonic waves into the medium 23 and transmits the ultrasonic waves into the second
The electroacoustic transducer 22 receives the wave. In this case, each vibrator of the second electroacoustic transducer 22 receives a pulse having a delay amount corresponding to the angle θ. The received signal with such a delay amount is sent to the transmitting circuit 35.
Waveform shaping and amplification are performed at -1 to 35-m,
A vibrator 40 of a probe 40 having a focal point inside a living body 33
-1 to 40-m, which causes living body 33
An ultrasonic beam is transmitted in the direction of an angle θ. Further, the ultrasonic waves reflected in the living body 33 are transmitted to the probe 40.
The waves are received by each transducer of the preamplifiers 37-1 to 37-3.
7-m and is supplied to the second electroacoustic transducer 22 which has a focus on the electroacoustic transducer 21, and forms an image on the second electroacoustic transducer 21. This signal is received by a vibrator selected by a multiplexer 34, and is amplified and detected by a receiving circuit 38, thereby making it possible to display an image. Also in this example, the multiplexer 34 connects the first electroacoustic transducer 21
By changing the selected position of one (or several) transducers, the angle θ can be changed, thereby making it possible to perform sector scanning.

FIG. 11 shows FIG. 5B as the ultrasonic delay device 25.
This figure shows the configuration of essential parts of an example of an ultrasonic diagnostic apparatus using the configuration shown in FIG. In this example, in order to reduce the overall system, a left/right switching switch 42 is provided between the second electroacoustic transducer 22 and the probe 40 by taking advantage of the symmetry of the delay amount. The only difference is that the left and right sides of the transducers 22-1 to 22-m of the electroacoustic exchange unit 22 and the left and right sides of the transducers 40-1 to 40-m of the probe 40 are switched every half cycle of one sector scan. is different from that shown in FIG. In this way, the first electroacoustic exchange section 2
Since the number of oscillators in 1 is about half that of the one shown in FIG. 10, the system dependent thereon can also be reduced by about half.

Figure 12 shows Figure 5C as the ultrasonic delay device 25.
This figure shows the configuration of essential parts of an example of an ultrasonic diagnostic apparatus that performs linear scanning using the configuration shown in FIG. In this example, the pulse generation circuit 3
The drive pulse from 1 is transmitted to the first electroacoustic transducer 2
It is supplied to one vibrator 21-1 constituting 1. The ultrasonic waves emitted into the ultrasonic transmission medium 23 by the driving of the transducer 21-1 are received by the transducers 22-1 to 22-m of the second electroacoustic transducer 22, but the transducers 22- The radius of curvature from 1 to 22m is the first
And when the distance between the second electroacoustic transducers 21 and 22 is Rv'/v, half of that Rv'/2v
Therefore, the ultrasonic waves received by the transducers 22-1 to 22-m are delayed according to their curvatures. The received signal with such a delay amount is sent to the transmitting circuit 35.
Waveform shaping and amplification are performed at -1 to 35-m,
Among the many transducers of the probe 46 selected by the multiplexer 44, m transducers are driven to focus at a focus distance within the living body 33. Further, the ultrasonic waves reflected in the living body 33 are received by the same m transducers as the waves transmitted by the probe 46, and are amplified by the preamplifiers 37-1 to 37-m, respectively, to perform second electroacoustic conversion. Vibrator 22-1~ of section 22
22-m. These oscillators 22-
The ultrasonic waves emitted into the ultrasonic transmission medium 23 by the drive of the first electroacoustic transducer 21
In other words, since the image is focused on the transducer 21-1, the receiving directivity can be obtained, and the output is sent to the receiving circuit 3.
An image can be displayed by amplifying and detecting the waveform by 8. In this example, linear scanning can be performed by sequentially selecting m transducers from a large number of transducers of the probe 46 using the multiplexer 44.

FIG. 13 shows FIG. 5A as the ultrasonic delay device 25.
This figure shows the configuration of the essential parts of another example of an ultrasonic diagnostic apparatus that can also perform a composite scan that combines sector scanning and linear scanning using the ultrasonic diagnostic apparatus shown in FIG. In this example, the drive pulse from the pulse generation circuit 31 drives one (or several) transducers of the first electroacoustic transducer 21 selected by the multiplexer 34, thereby transmitting ultrasonic waves. The ultrasonic waves radiated into the medium 23 are received by the vibrators 22-1 to 22-m of the second electroacoustic transducer 22. In this case, since pulses with a delay amount equivalent to the angle θ are received by the transducers 22-1 to 22-m, these received signals are further transmitted to the living body 33 by delay lines 48-1 to 48-m. transmitting circuits 35-1 to 35-3 with a delay for focusing on
5-m performs waveform shaping and amplification, and drives m transducers among the large number of transducers of the probe 46 selected by the multiplexer 44 to emit an ultrasonic beam into the living body 33. In addition, the reflected waves from within the living body 33 that are received by the same m transducers as the waves transmitted by the probe 46 are reflected by the preamplifiers 37-1 to 37-m, the delay lines 48-1 to 48-m, and the ultrasonic waves. The signal passes through the acoustic wave delay device 25 and is amplified and detected by the receiving circuit 38. In this example, sector scanning can be performed by switching the multiplexer 34, linear scanning can be performed by switching the multiplexer 44, and both multiplexers 3
By switching between 4 and 44, it is possible to perform composite scanning that combines sector scanning and linear scanning. By performing such composite scanning, resolution can be improved and side lobes can be suppressed, improving image quality. This can be further improved.

In addition, the ultrasonic diagnostic apparatus shown in FIGS. 8, 10 to 13,
A similar configuration can be achieved using the ultrasonic delay device shown in FIG. 1, and similar effects can be obtained in this case as well.

As can be seen from the above description, the ultrasonic delay device of the present invention has the following effects.

1 Good frequency characteristics.

The frequency characteristics mainly depend on the characteristics of the resonator, but PzT
When using (lead zirconate titanate) as a vibrator, it is possible to increase the frequency up to 30MHz using the thickness shear mode. Bandwidth can theoretically be made as wide as you like by correcting insertion loss with a preamplifier and lowering Q;
It can take up to about 15MHz. In addition, the insertion loss at that time is -12 dB. By the way, the lumped constant delay line has a maximum delay of 4MHz for the amount of delay required for electronic sector scanning. The attenuation due to matching is usually -12 dB since the sub-delay line and the main delay line are connected in series.

2. Good group delay characteristics.

Group delay characteristics are changes in the amount of delay with respect to frequency, and since the acoustic impedance in the ultrasonic transmission medium can be made uniform, disturbances in group delay characteristics due to superimposition of reflections from taps, etc., such as lumped constant delay lines, can be avoided. do not have. Therefore, recently there has been a strong desire for the simultaneous use of electronic sector scanning and Doppler scanning.
This can be easily realized using the ultrasonic delay device according to the present invention.

3. Good unwanted reflection characteristics.

Since there is no signal extraction tap such as a lumped constant delay line, if the delay medium is uniform, there will be no unnecessary reflections from the middle. Therefore, the S/M ratio of the signal is good.

4 There is no quantization in the amount of delay.

Since there is no quantization in the amount of delay, it is possible to reduce the arrangement pitch of the transducers of the probe and the arrangement pitch of the transducers that constitute the second electroacoustic transducer of the ultrasonic delay device of the present invention opposing it. The more the quantization sidelobes are reduced, the more the quantization sidelobes can be reduced.

5. The system is simple.

Since there are few switch elements for changing the amount of delay, the control system is simple.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the principle of electronic sector scanning of an ultrasound diagnostic device, Figure 2 is a diagram showing the principle of electronic linear scanning, and Figure 3 is a circuit diagram showing the configuration of a conventional ultrasound delay device. , FIG. 4 is a plan view showing the configuration of an example of the ultrasonic delay device of the present invention, and FIGS. 5A and B
6A, B, and C are plan views showing the configurations of three other examples, respectively.
Figures A and B are side views respectively showing the configuration of two other examples, and Figure 8 is a diagram showing the configuration of essential parts of an example of an ultrasound diagnostic apparatus using the ultrasound delay device shown in Figure 4. , FIG. 9 is a diagram for explaining the operation of the ultrasonic diagnostic apparatus shown in FIG. Diagram showing the configuration, No. 11
The figure is a diagram showing the configuration of the main parts of an example of an ultrasonic diagnostic apparatus using the ultrasonic delay device shown in Fig. 5B.
Fig. 2 is a diagram showing the configuration of the essential parts of an example of an ultrasonic diagnostic apparatus using the ultrasonic delay device shown in Fig. 5C, and Fig. 13 is an ultrasonic diagnosis using the ultrasonic delay device shown in Fig. 5A. FIG. 7 is a diagram showing the configuration of main parts of another example of the device. 21...first electroacoustic transducer, 21-1 to 2
1-n, 22-1 to 22-m, 36-1 to 36-
m, 40-1 to 40-m... electroacoustic transducer element (vibrator), 22... second electroacoustic transducer, 23
...Ultrasonic transmission medium, 24...Ultrasonic absorption member,
25...Ultrasonic delay device, 31...Pulse generation circuit, 32-1 to 32-k, 48-1 to 48-m...
...Day line, 33...Biological body, 34,44...
...Multiplexer, 35-1~35-m...Transmission circuit, 36,40,46...Probe, 37-1~
37-m...Preamplifier, 42...Switch.

Claims (1)

[Claims] 1. A first device comprising at least one electroacoustic transducer
and a second electroacoustic transducer consisting of a plurality of electroacoustic transducers arranged at a predetermined pitch are arranged on one side from the center of the second electroacoustic transducer. The ultrasonic transducer is arranged on the surface of the ultrasonic transmission medium so that the lengths of the ultrasonic transmission paths between the individual electroacoustic transducers of the first electroacoustic transducer and one electroacoustic transducer of the first electroacoustic transducer are different. An ultrasonic delay device characterized in that the ultrasonic delay device is configured such that an ultrasonic wave transmitted from one electroacoustic transducer via an ultrasonic transmission medium can be received by the other electroacoustic transducer. 2. The ultrasonic delay according to claim 1, characterized in that acoustic impedance matching layers are interposed between the first and second electroacoustic transducers and the surface of the ultrasonic transmission medium, respectively. Device. 3. The ultrasonic wave transmitted from the one electroacoustic transducer is reflected at least once within the ultrasonic transmission medium and can be received by the other electroacoustic transducer. Claim 1
Ultrasonic delay device as described in section. 4 The first electroacoustic transducer is configured with a plurality of electroacoustic transducers, and the electroacoustic transducers of one electroacoustic transducer are arranged in a straight line, and the electroacoustic transducer of the other electroacoustic transducer is 2. The ultrasonic delay device according to claim 1, wherein the transducer elements are arranged at a predetermined pitch along an arc having a center on the side of the one electroacoustic transducer. 5 The first electroacoustic transducer includes a plurality of electroacoustic transducers, and each electroacoustic transducer of the first electroacoustic transducer and the second electroacoustic transducer 2. The ultrasonic delay device according to claim 1, wherein the ultrasonic wave delay device is arranged at a predetermined pitch along an arc having a center on the side of the other electroacoustic transducer. 6. The first electroacoustic transducer is configured with one electroacoustic transducer element, and the second electroacoustic transducer is arranged along an arc having a center on the side of the first electroacoustic transducer. The ultrasonic delay device according to claim 1, characterized in that a plurality of electroacoustic transducers are arranged at a predetermined pitch. 7. The ultrasonic delay device according to any one of claims 1 to 6, wherein the ultrasonic transmission medium is an ultrasonic transmission medium containing silicate glass. 8. An ultrasonic absorbing member is provided in a portion of the ultrasonic transmission medium other than the main ultrasonic transmission path, and the ultrasonic absorbing member is configured to absorb unnecessary reflections of ultrasonic waves in the ultrasonic transmission medium. An ultrasonic delay device according to any one of claims 1 to 7, characterized in that: 9. Claim 8, characterized in that the ultrasonic absorption members are interspersed in the ultrasonic transmission medium so as to sandwich the ultrasonic transmission path between the first and second electroacoustic transducers. Ultrasonic delay device as described.