JPS59166139A - Ultrasonic transducer - 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 Technical Field of the Invention The present invention relates to an ultrasonic transducer, particularly an ultrasonic transducer used for ultrasonic diagnosis of the human body, in which a sound wave reflected from a subject and returned The acoustic impedance of the surface of the subject and the acoustic impedance as seen from the subject side are such that the sound pressure ratio of the sound wave to the sound wave that is re-reflected and radiated inside the transducer is, for example, -15 dB or less. The present invention relates to an ultrasonic transducer having substantially equal configurations and substantially eliminating re-reflection.

(B) Technical Background and Problems Conventionally, ultrasonic transducers are equipped with ultrasonic transducers composed of piezoelectric elements.

For example, an acoustic matching layer with a thickness of λ/4 is placed on the radiation side of the transducer to allow the emitted ultrasound to be efficiently inserted into the subject and to adjust the duration of the emitted ultrasound pulse. (4I Kosho 55-)
33020 Publication).

However, the sound waves emitted to the subject side, reflected back, and then reflected back inside the transducer may be re-radiated to the subject side. The re-emitted sound is received by the transducer again from the tissue of the specimen and creates a false image. This phenomenon is called multiple reflection, and as a method for improving the multiple reflection, for example, Japanese Patent Laid-Open No. 54-2108
What is shown in Publication No. 2 has been proposed.

This has the following structure. In other words, a continuously variable layer in which the acoustic impedance changes continuously is provided on the radiation side of the transducer, that is, between the transducer and the subject, and the acoustic impedance of the subject side surface of the continuous variable layer is determined by the acoustic impedance of the subject. The acoustic impedance of the side surface of the transducer in the continuously variable layer is selected to be equal to the acoustic impedance of the transducer.

Although it is possible to reduce the above multiple reflections to some extent with this configuration, since an acoustic damper material is generally placed on the rear surface of the transducer, it is possible to reduce the multiple reflections due to the difference in acoustic impedance between the transducer and the acoustic damper material. Due to the reflections caused, sufficient effects cannot be achieved.

(C1 Object and Structure of the Invention The present invention aims to solve the above-mentioned problems.9 The ultrasonic transducer of the present invention is equipped with an ultrasonic transducer composed of a piezoelectric element, A radiation-side acoustic matching layer disposed on the radiation side of the sonic transducer and/or a back-side acoustic matching layer disposed on the back side of the ultrasonic transducer, and the outermost layer on the back side. In an ultrasonic transducer having an acoustic damper, the acoustic impedance as viewed from the radiation side surface of the transducer to the outermost acoustic damper on the transducer side is in contact with the radiation side surface in a desired frequency band. It is characterized by being configured so that the acoustic impedance is substantially equal to the acoustic impedance of the acoustic medium.This will be explained below with reference to the drawings.

fD] Embodiment of the Invention FIG. 1 is an explanatory diagram illustrating a mode of detecting echoes from a subject using an ultrasonic transducer.

FIGS. 2 and 3 are explanatory diagrams explaining the principle to which the present invention is applied, and FIGS. 4 to 8 each show an embodiment of the present invention.

In FIG. 1, 1 is a transducer, 2 is an acoustic matching layer with a thickness of λ/4 on the radiation side, 5 is an acoustic damper, 6 is a subject (acoustic medium), 7 is a reflector inside the subject, 9 represents an ultrasonic transducer.

The ultrasonic waves from the transducer 1 are simultaneously radiated into the object 6 via the matching layer 2, and the acoustic waves reflected by the reflector 7 are received by the transducer 1 via the matching layer 2 to find the time difference. The presence of the reflector 1 is detected. On the other hand, ultrasonic waves traveling from the transducer 1 toward the back side are preferably absorbed by the acoustic damper 5.

As mentioned above, in the device disclosed in Japanese Patent Application Laid-Open No. 54-21082, the radiation-side acoustic matching layer 2 shown in FIG. 1 can be considered to be composed of the above-mentioned continuously variable layer. In this case, for the received wave from the specimen 6.

In what is disclosed, although it is possible to prevent reflection from the radiation side surface of the transducer 1 (boundary with 2),
Reflection from the boundary between the acoustic damper 5 and the transducer 1 cannot be prevented.

The reflection of sound waves will be discussed with reference to FIG.

As shown in Figure 2, consider a situation in which a flat plate having an acoustic impedance z2 and a thickness of % of the wavelength λ of the sound wave is placed between a medium having an acoustic impedance Z and a medium having an acoustic impedance z3. In this state, when considering that sound waves pass through the flat plate from the medium side with acoustic impedance z3, the large acoustic force seen from the side of the flat plate in contact with the medium with acoustic impedance Za (indicated by the chain line in the figure) toward the arrow side. The impedance ZIrl is.

The sound pressure of the sound wave reflected on the medium side with acoustic impedance Z3 can be expressed as:

It becomes minimum under the condition of 1n-z3. This is the impedance Z
The reflection component from the boundary between 2 and z3 and the impedance Z
This may be because the reflected components from the boundary between 2 and zl cancel each other out.

As shown in FIG. 3, on the radiation side of the converter 1,
Acoustic impedance is zTl + zT21...
・.

A radiation-side acoustic matching layer of N layers each having a thickness of λ/4 with ZTN, and an acoustic impedance of ZBI + ZB2 +..., ZIIM on the back side of the transducer 1, each having a thickness of λ/4. an M-layer backside acoustic matching layer having a thickness of
Let us try to adapt it to an ultrasonic transducer having an acoustic damper 5 with an acoustic impedance zB. It is assumed that the radiation-side surface layer 8 shown in FIG. 3 is in contact with the subject 6 having an acoustic impedance z. The input impedance Zln in this case is.

7nZ+n = 21: (1, N-1), p, zT.

-0 CNN131+ +2Σ(-Bln'l+u 1-.

+(1) lnZ++ (however, ZTI(1-0) = ZmI(+-o)-1)
−−・・−−−−−−(3) The received sound wave incident from the medium side having acoustic impedance ZT can be expressed as:

lnZ+n = JnzT ・・・・・・・・・・・・
...When the relationship (4) holds true, the sound pressure of the sound wave reflected from the transducer becomes the lowest.

FIG. 4 (al indicates one embodiment of the present invention, and reference numeral 1 in FIG. 1
．． 2.5 corresponds to FIG. 1, 3 represents an acoustic matching layer with a thickness of λ/4 on the radiation side, and 4 represents an acoustic matching layer with a thickness of λ/4 on the rear side. In the illustrated case, two matching layers are provided on the radiation side and one matching layer is provided on the back side. In this case, the acoustic impedance of each of the λ/4 matching layers 1°2.3 and 4.5 is set to 34X106.8.5X106.
When 2X106.12.8X106゜7.5XID6 (each unit: f/s, m), it is approximately 20% faster than the conventional transducer (as shown in Figure 1) in the 6.5±0.5MHz band. A transducer with as little reflection as tiB was obtained.

An outline of the measurement system at this time is shown in Fig. 4 (bl), and the spectrum of the obtained reflected wave is shown in Fig. 4 (bl, (cl).

In the measurement system, a perfect reflector facing transducer a is placed in water C, and the transducer is driven by a transmission circuit (not shown) to measure the first reflected wave ■ and the second reflected wave ■. The system is configured such that the received waves are passed through a receiving circuit (not shown) and a spectrum analyzer obtains the spectrum of each received wave. Using this measurement system, the first received wave ■ and the second received wave ■ measured for the conventional transducer are shown in FIG. The received wave ■ and the second received wave ■ are shown in FIG. 4 1c). Case 2 according to the present invention
The level of the second received wave has dropped significantly.

FIG. 5 ta+ shows an embodiment of the present invention, and reference numeral 1 in FIG. 2 shows an embodiment of the present invention.
．． 2.5 corresponds to FIG. in this case.

The acoustic impedances of the λ/4 matching layers 2 and 5 are 3.8X106 and 11.5X106 (unit: KV/S,
As shown in FIG. 5 (bl), the ratio of the transmitting/receiving spectrum to the first multiple reflection spectrum is less than -15 dB in the desired frequency band.

Satisfy the desired conditions.

Fig. 6 (al indicates one embodiment of the present invention; code 1 in Fig. 2)
．． 2, 4.5 corresponds to FIG. In this case, the acoustic impedance of each of matching layers 2 and 4.5 is set to 3.8 in turn.
X108.9.4X106.7.5X106 (unit KI
9/s, nr) is shown in Figure 6(b).
As shown in , the ratio between the transmitting and receiving spectrum and the first multiple reflection spectrum is less than -15 dB in the desired frequency band, satisfying the desired condition.

Fig. 7 (al indicates one embodiment of the present invention, and reference numeral 1 in Fig. 2)
．． 2.5.5 corresponds to FIG. In this case, the acoustic impedance of each of matching layers 2 and 3.5 is set to 8.4 in turn.
X106, 2. OXl 06, 21.8X106
As shown in Figure 7 (bl), the ratio of the transmitting/receiving spectrum to the first multiple reflection spectrum is -15 dB in the desired frequency band.
and satisfies the desired conditions.

FIG. 8 (al shows still another embodiment of the present invention).

Reference numerals 1.4.5 in the figure correspond to those in FIG. 4, and 10 represents a continuous change layer as referred to in this specification. In this case, the acoustic impedance of the continuously variable layer 10 is selected to vary continuously from the acoustic impedance zT of the subject to the -tV impedance of the transducer 1.

The acoustic impedance of each layer 4.5 is 6.0×1 in order.
0', 7.5X106 (unit: KP/S, nl'), the ratio of the transmit/receive spectrum to the first multiple reflection spectrum is -15 (IB) in the desired frequency band, as shown in Figure 8 (bl). and satisfies the desired conditions.

The medium having each of the above-mentioned acoustic impedances can be selected from among the seven orders.

A) Acoustic impedance is 2.0X10' to 3.2
In the range of x 106 (K9/s, J), there are synthetic resins such as polyurethane, nylon, and epoxy (trade name).

B) Acoustic impedance is 10.0X10' to 13
．． In the range of 5×106 (immediate/s, = n”), glass,
crystal.

There are materials that correspond to quartz, etc.

C) acoustic impedance is 3j x 106 to 1o,
In the range of ox 1o6 (K9/s, rl), there are generally few that are compatible with a single composition. Therefore, a material in which metal powder such as aluminum or iron is mixed into the synthetic resin such as epoxy or polyurethane is used. In this way, by increasing or decreasing the amount of metal powder, the acoustic impedance can be reduced to 20 x 106 (K
9/S,rn'').In particular, the epoxy resin mixed with metal powder itself has good adhesive properties, which is necessary when using the above glass. No adhesive is required, and deterioration of characteristics due to the adhesive layer can be prevented.

In addition, we checked to what extent the reflection from the above-mentioned ultrasonic transducer itself is acceptable. Figure 9 shows the reflection levels from each tissue of the heart.

As shown in the figure, there is a tissue (■) that exhibits strong reflections up to about 20 meters from the body surface, and if a conventional transducer with a lot of reflection is used, the reflected waves from this tissue will be reflected again by the ultrasonic transducer. Then, it is reflected again by the tissue ■ and received by the ultrasonic transducer, and this appears as multiple reflections. It was found that it deteriorated.

The reflection level of the tissue ■ exhibiting strong reflection is about -25 dB, and the reflection level of the septum @ is about -60 dB. If the reflectance of the ultrasound transducer is αd, the level of the septum @ is the tissue ■
Since K is thicker than the multiple reflection level of (-25)X2+α<-60, it is sufficient that the 2 reflectance is lower than -10 dB. It has thus been confirmed that by using a transducer having a reflectance of -15 dB or less, a sufficiently clear image without the influence of multiple reflections can be obtained. Conventional vibrators have a reflectance of about -6 to 10 dE, which means that good images cannot be obtained.

(g) As described in detail, according to the present invention, the influence of multiple reflections can be substantially eliminated.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram illustrating a mode of detecting echoes from a subject using an ultrasonic transducer. FIGS. 2 and 3 are explanatory diagrams explaining the principle to which the present invention is applied, and FIGS. FIG. 8(b) shows an explanatory view corresponding to each of the embodiments shown in FIGS. 4(a) to 8(a), respectively.'=Furthermore, FIG. An example is shown. In the figure, 1 is a transducer, 2 and 3 are radiation-side acoustic matching layers, and 4 is a transducer.
5 is an acoustic matching layer on the back side, and 5 is an acoustic damper. 6 represents a subject (acoustic medium), 7 represents a reflector, and 9 represents a transducer. Patent applicant: Fujitsu Ltd. Representative Patent Attorney Mori 1) Hiroshi (1 other person) 1' / Saira Cco (G) (b) 1, LJ 1. U J, l J 4.
0 5.0 (MH2), Figure 1-6 (a) (b) -1-7 days (O) (b) ]○ 1. U J, Ll 4.
tJ': 1.0 (MH2) 80 (Q) (b) 'I-9th 20mm 40mm -1-, ateJts Chestnut i procedural amendment (directive) 1. Indication of the case 1982 Patent Application No. 39908 2. Name of the invention: Ultrasonic transducer 3. Relationship with the case of the person making the amendment Patent applicant address: 1015 Kamiodanaka, Nakahara-ku, Yozaki City, Kanagawa Prefecture Name (522) Fujitsu Limited Representative: Takashi Yamamoto 4 , Agent 5, Date of amendment order: June 8, 1982
Date of dispatch: June 28, 1980 6. Number of inventions increased by amendment: None 7. Subject of amendment: Detailed description of the invention 1. Brief description of the drawings 8. Contents of amendment: Amendment to the standard in the attached sheet Contents (1) ``(h), (C)'' on page 8, line 15 of the specification is amended to ``r (C), (of''). (2) Page 9 of the specification, line 4 r (h) It says j,
Correct as r(C)J. (3) Replace “(C)” on page 9, line 6 of the specification with “(
Correct it as "Kaku". (4) Page 13, line 18 to page 14, line 2 of the specification “
Figure 4 (α) to Figure 8 (→ is...
...An explanatory diagram corresponding to the example is shown. ” should be corrected as follows. [Figure 4 (→ is an embodiment of the present invention, and Figure 4 (b)
), Figure 4(C), and Figure 4(α)
5 (→ is another embodiment of the present invention, and FIG. 5(h) is an explanatory diagram related to the embodiment shown in FIG. 5(α). , FIG. 6(α) is another embodiment of the present invention, FIG. 6(h) is an explanatory diagram related to the embodiment shown in FIG. 6(α), and FIG. 7(a) is an explanatory diagram related to the embodiment shown in FIG. 6(α). FIG. 7(b) is an explanatory diagram related to the embodiment shown in FIG. 7(α), and FIG. 8(α) is another embodiment of the present invention. FIG. 8<b> shows an explanatory diagram related to the embodiment shown in FIG. 8(α).''That's all.

Claims (1)

[Scope of Claims] An ultrasonic transducer made of a piezoelectric element is provided, and a radiation-side acoustic matching layer disposed on the radiation side of the ultrasonic transducer and a radiation-side acoustic matching layer disposed on the back side of the ultrasonic transducer. In an ultrasonic transducer, the ultrasonic transducer is provided with an acoustic matching layer on the back side, and/or an acoustic matching layer on the back side, and an acoustic damper on the outermost layer on the back side. Acoustic innovation as viewed from the radiation side surface of the transducer to the outermost layer of acoustic damping on the transducer side in the desired frequency band. An ultrasonic transducer characterized in that the ultrasonic transducer is configured to have an acoustic impedance substantially equal to the acoustic impedance of an acoustic medium that is brought into contact with the radiation side surface.