JP3038379B1 - Acoustic impedance matching device for ultrasound - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To improve the transmittance of an ultrasonic wave from an ultrasonic oscillator to a target. SOLUTION: Acoustic impedance matching device for ultrasonic wave 1
Is interposed between the ultrasonic oscillator 2 and the object 3. The acoustic impedance matching device 1 for ultrasonic waves includes double layers 1a and 1b.
Having a layered structure on which is deposited. The double layers 1a, 1b
First layers 1a-1 and 1b-1 made of a first material
And the second layers 1a-2 and 1b-2 which are constituted of a second material different from the first material and are acoustically continuously joined to the first layers 1a-1 and 1b-1. And

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic wave for an ultrasonic wave, which is provided between an ultrasonic oscillator and an object to which the ultrasonic wave is to be incident so as to match the acoustic impedance and thereby improve the transmittance of the ultrasonic wave. The present invention relates to an impedance matching device.

[0002]

2. Description of the Related Art Conventionally, when an ultrasonic wave is incident on an object from an ultrasonic oscillator, the ultrasonic oscillator is brought into direct contact with the object or a material formed between the ultrasonic oscillator and the object with a uniform material. Is interposed. Further, a liquid may be arranged between the ultrasonic oscillator and the object, and the ultrasonic wave may be incident on the object using a focusing lens for the ultrasonic wave.

[0003]

However, in these cases, due to the mismatch of acoustic impedance, a reflected wave is generated from the object, which has an adverse effect on the improvement of the transmittance of ultrasonic waves from the ultrasonic oscillator to the object.

[0004] It is an object of the present invention to provide an acoustic impedance matching device for ultrasonic waves that improves the transmittance of ultrasonic waves from an ultrasonic oscillator to a target.

[0005]

SUMMARY OF THE INVENTION An acoustic impedance matching device for ultrasonic waves according to the present invention is interposed between an ultrasonic oscillator and an object to be irradiated with ultrasonic waves from the ultrasonic oscillator, and is formed of a first material. A layered structure formed by sequentially depositing a plurality of same-type double layers in which a first layer configured and a second layer formed of a second material different from the first material are acoustically continuously joined; The present invention is characterized in that the structure is such that the transmittance of ultrasonic waves from the ultrasonic oscillator to a target is improved by resonant vibration on the surface of the layered structure.

According to the present invention, acoustic impedance can be effectively and completely matched by a plurality of acoustically joined double layers, thereby suppressing generation of reflected waves from an object to an ultrasonic oscillator. Is done. This utilizes resonance surface vibration of a layered structure in order to improve the transmittance of ultrasonic waves from an ultrasonic oscillator to a target. Note that the first layer and the second layer are not the same material or materials having different acoustic impedances.

[0007] Preferably, the acoustic impedance of the second layer is substantially equal to the acoustic impedance of the ultrasonic oscillator. Thereby, reflection of the ultrasonic wave does not occur between the ultrasonic oscillator and the acoustic impedance matching device for the ultrasonic wave, and the transmittance of the ultrasonic wave from the ultrasonic oscillator to the target can be further improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the acoustic impedance matching device for ultrasonic waves according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing acoustic impedance matching by the acoustic impedance matching device for ultrasonic waves of the present invention. In the figure, acoustic impedance matching device 1 for ultrasonic wave
Is interposed between the ultrasonic oscillator 2 and the target 3 to be irradiated with the ultrasonic wave from the ultrasonic oscillator 2.

[0009] The acoustic impedance matching device 1 for ultrasonic
A double layer 1a, 1b is deposited, and the double layer 1a, 1b is a first layer 1a-
1, 1b-1 and second layers 1a-2 and 1b-2 which are made of a material B different from the material A and are acoustically and continuously joined to the first layers 1a-1 and 1b-1. The ultrasonic oscillator 2 can be any conventionally known one, and the target 3 can be any one.

[0010] Here, as the effective acoustic impedance Z _e is the characteristic impedance of the layered structure at the time of resonant transmission of reflected waves within the layered structure of the ultrasonic acoustic impedance matching device 1 is no longer present in the following Defined in Material A, the acoustic impedance of B respectively Z _A, and Z _B, the first layer 1a-1, 1b-1 and second layers 1a-2,1
Assuming that the thickness of b-2 is D _A and D _B , respectively, the velocities of the ultrasonic waves in the materials A and B are V _A and V _B, and the angular frequency of the ultrasonic oscillator 2 is ω, The dispersion relation of the acoustic impedance matching device 1 for ultrasonic waves propagating in the layered structure is as follows when the ultrasonic waves are perpendicularly incident on the interface between the double layers.

[0011]

(Equation 1) It is assumed that α = ωD _A / V _A and β = ωD _B / V _B.

In the above dispersion relation, there is a condition that an angular frequency ω _{R such} that sin β = sin α and cos β = −cos α exists as one resonance condition. At this time, equation (1) is

[0013]

(Equation 2) Becomes In this case, since cosγ <−1, γ is a complex number. At an angular frequency ω _R that satisfies this condition, the vibration amplitude on the surface of the layered structure of the acoustic impedance matching device for ultrasonic waves 1 facing the joint surface with the ultrasonic oscillator 2 increases resonantly.

[0014] When the resonance condition is satisfied, the ultrasound for the layered structure of the acoustic impedance matching device 1, the effective impedance Z _e may be derived as follows. With respect to the amplitude reflection coefficient κ in the second layer 1b-2 facing the bonding surface with the object 3, the following cubic equation

[0015]

(Equation 3) Is required to be satisfied. here,

[0016]

(Equation 4) as well as

[0017]

(Equation 5) It is. Also, r _AB = (1−Z _B / Z _A ) / (1 + Z _B
/ Z _A ) is the amplitude reflection coefficient when the ultrasonic wave is incident on the material B from the material A. Equation (3), which is a cubic equation for the amplitude reflection coefficient κ, is a real number κ _e

[0018]

When having a solution satisfying 1 ≧ κ _e > −1 (6),

[0019]

(Equation 7) Can be defined as the effective acoustic impedance Z _e . Acoustic impedance of the object 3 is equal to the effective acoustic impedance Z _e, the transmittance in the case where the angular frequency of the ultrasonic wave is coincident with the angular frequency omega _R, an acoustic impedance matching device 1 for ultrasound to a subject 3 Can be set to a local maximum value close to 1.

Further, by selecting and material B to the acoustic impedance of the ultrasonic oscillator 2 and the acoustic impedance Z _B are equal, if joined together to acoustically continuous, the ultrasonic acoustic impedance matching device 1 No reflection occurs with the ultrasonic oscillator 2.

Further, the acoustic impedance Z_AThe above
Effective acoustic impedance Z_eIs given by
If you decide to be satisfied, Z_B<Z_AIs effective if
Acoustic impedance Z_eIs the acoustic impedance Z_Bof
Within the range of about 1/10, Z _B> Z_AIn the case of
Acoustic impedance Z_eIs the acoustic impedance Z_BOf 1
Effective acoustic impedance matching within the range of about 0 times
Can be done.

In the present embodiment, the number of double layers is two, but the number of double layers is a factor that determines the transmittance of ultrasonic waves, so it is necessary to select an appropriate number. Acoustic impedance Z _A and acoustic impedance Z _B
When a metal having a ratio of about 1: 1.2 or about 1.2: 1 is used, it is appropriate to set the number to 6 to 10.

When the target is distilled water at 20 ° C., the material A
When the acoustic impedance matching device for ultrasonic wave comprising eight double layers having a first layer composed of the following and a second layer composed of the material B is interposed between the ultrasonic oscillator and the object. The obtained transmittance and the transmittance obtained when only the substance B was interposed were as follows. Here, the thickness of both the first layer and the second layer is 5 mm.

[0024]

[Table 1]

As is clear from Table 1, the transmittance is higher when the acoustic impedance matching device for ultrasonic waves having a double layer is interposed than when a single material is interposed.
It turns out that it has improved by 0 to 7.3 times. Here, between the resonant frequency f _R and the angular frequency omega _R,

[0026]

## EQU8 _## There is a relationship of f _R = ω _R / 2π (8). When the thickness of the first layer and the thickness of the second layer are reduced to 1 / x, the resonance frequency f _R becomes x times.

According to the present embodiment, acoustic impedance can be effectively and completely matched by a plurality of acoustically joined double layers, and the generation of reflected waves from the object to the ultrasonic oscillator is suppressed. Therefore, the transmittance of the ultrasonic wave from the ultrasonic oscillator to the target can be improved.

When the acoustic impedance of the second layer is substantially equal to the acoustic impedance of the ultrasonic oscillator, no reflection of ultrasonic waves occurs between the ultrasonic oscillator and the acoustic impedance matching device for ultrasonic waves. The transmittance of the ultrasonic wave from the object to the object can be further improved.

Further, since the layered structure of the acoustic impedance matching device for ultrasonic waves can be easily formed, the durability of the acoustic impedance matching device for ultrasonic waves is increased, and the production of the acoustic impedance matching device for ultrasonic waves is easy. become.

The present invention is not limited to the above-described embodiment, and many modifications and variations are possible. For example,
The material and shape of the layered structure of the acoustic impedance matching device for ultrasonic waves can be appropriately selected according to the acoustic properties of the target.For example, the layered structure is formed of a plate-like metal, a plate-like plastic, or the like. Can be configured. Also,
The thicknesses of the first layer and the second layer of each double layer need not all be the same, and can be arbitrarily selected according to the acoustic properties of the target.

[Brief description of the drawings]

FIG. 1 is a diagram showing acoustic impedance matching by an acoustic impedance matching device for an ultrasonic wave according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 acoustic impedance matching device for ultrasonic wave 1a, 1b double layer 1a-1, 1b-1 first layer 1a-2, 1b-2 second layer 2 ultrasonic oscillator 3 target

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01B 17/00-17/08 G01N 29/00-29/28

Claims (2)

(57) [Claims] 1. A first layer made of a first material and a first layer different from the first material interposed between an ultrasonic oscillator and an object to which ultrasonic waves from the ultrasonic oscillator are to be incident. A layered structure in which a plurality of layers of the same type are sequentially deposited in a plurality of layers in which a second layer made of the second material is acoustically joined, and the ultrasonic wave is generated by resonance vibration on the surface of the layered structure. An acoustic impedance matching device for ultrasonic waves, which is configured to improve the transmittance of ultrasonic waves from an oscillator to a target. 2. The acoustic impedance matching device for ultrasonic waves according to claim 1, wherein the acoustic impedance of said second layer is substantially equal to the acoustic impedance of an ultrasonic oscillator.