JPH0115167B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic delay line, in which a band-shaped sound-absorbing material is provided in a special shape in the ultrasonic propagation region of a delay medium, and performance can be improved by transmitting only main waves and attenuating unnecessary waves. Aims to provide ultrasonic delay line.

As a conventional ultrasonic delay line, there is one shown in FIG. In the figure, the ultrasonic delay line 1 is constructed by using a glass delay medium 2 as a rectangle having parallel sides 2a, 2b, a side 2c perpendicular to these, and a side 2d forming an angle of 45 degrees to the side 2b. are provided with input and output transducers 3, 4, and
As shown in the figure, sound absorbing material 5 made of epoxy resin or the like is fixed at a plurality of locations all over the non-propagation area of ultrasonic waves on both sides of the medium 2. Therefore, after the electrical signal is converted into an ultrasonic wave by the input transducer 3, it passes sequentially through the medium 2 as a main wave 6 shown by the arrow in the figure.
b, 2a, 2c, 2b, 2a, 2b while being reflected, and reaches the output transducer 4, where it is extracted as an electrical signal. Therefore, the main wave 6 sequentially advances as main waves 6a, 6b, 6c, 6d, 6e, 6f, and 6g. Here, unnecessary waves traveling from the input transducer 3 in directions other than the arrow direction in the figure reach the sound absorbing material 5 in the ultrasonic non-propagation region, where they are attenuated and disappear.

However, according to the above conventional example, the ultrasonic propagation area is a relatively wide area without any sound absorbing material 5 provided, so that the traveling direction of the unnecessary waves is relatively small with respect to the main wave traveling direction. Those that form an angle and those that diffusely reflect from any of the side surfaces 2a to 2c have the disadvantage that they reach the output transducer 4 and generate unnecessary electrical signals.

The present invention eliminates the above-mentioned drawbacks, and one embodiment thereof will be described below with reference to the drawings.

FIG. 2 is a side view of the first embodiment of the ultrasonic delay line according to the present invention, in which the same parts as in FIG. In the same figure,
The ultrasonic delay line 11 is constructed by providing transducers 3 and 4 on a delay medium 2 similar to that shown in FIG. are fixed parallel to the passage, and main waves 6a, 6g parallel to each other.
A band-shaped sound absorbing material 12b having a width W is fixed in the center between the passages, and extends parallel to these passages. Similarly, between main waves 6a and 6e, between 6e and 6c, between 6d and 6b, and between 6
Band-shaped sound absorbing materials 12c to 12 with width W between b and 6f, respectively.
f is fixed. The value of W is W=
λ/2×n (n is a positive integer) or 0<W≪λ/4
(However, λ is the wavelength of the ultrasonic wave that has entered the sound absorbing material). Here, the sound absorbing materials 12a to 12f are not necessarily limited to a band shape, but may be dot shaped.

Therefore, the sound absorbing materials 12a to 12d and the sound absorbing materials 12e,
12f and extend in directions perpendicular to each other,
For example, the sound absorbing material 12f extends in the path of the main wave 6a in a direction perpendicular to the direction of travel of the main wave 6a, and has the above width W along the direction of travel of the main wave 6a. The same applies to the other sound absorbing materials 12b to 12e. Therefore input transducer 3
The main wave 6a emitted from the main wave 6a travels through the medium 2 and is perpendicularly incident on the sound absorbing material 12f having the rear width W.

Here, in general, a plane traveling wave (corresponding to the main wave 6a in Figure 2) in the first medium (corresponding to the delay medium 2 in Figure 2) is infinitely wide in the second medium (corresponding to the sound absorbing wave in Figure 2). (corresponding to the material 12f), the reflectance R〓 in the second medium is R〓=(Z ₁ /Z ₂ −Z ₂ /Z ₁ ) ² /4cot ² 2π/λ ₂ + (Z ₁
/Z ₂ +Z ₂ /Z ₁ ) ² ...(1) However, Z ₁ , Z ₂ ...acoustic impedance of the first and second medium, respectively l...thickness dimension along the traveling direction of the plane traveling wave of the second medium λ ₂ ...It is known that this is the wavelength of a plane traveling wave in the second medium.

Therefore, from equation (1), when the thickness l of the second medium is an even multiple of λ ₂ /4, R = 0, and when the thickness l is an odd multiple of λ ₂ /4, R = maximum. It can be seen that this is shown in FIG. 3. Note that the thickness l and wavelength λ ₂ in equation (1) are the sound absorbing material 12 of the delay line 11, respectively.
Since it corresponds to the width W of a to 12f and the wavelength λ of the ultrasonic waves that entered the sound absorbing materials 12a to 12f, l,
λ ₂ is written as W and λ, respectively. Therefore, from FIG. 3, the relationship between the width W of the sound absorbing material 12f and the wavelength λ of the main wave 6a is W=λ/2×n (n is a positive integer) or 0<W.
When <<λ/4, R = 0, so it can be seen that the main wave 6a is not reflected at all and passes through the sound absorbing material 12f, that is, it is not attenuated.
12d, 12e, 12d, 12e, 12f, 12
The light passes through c and 12b without being attenuated and reaches the output transducer 4.

However, since the unnecessary waves (indicated by reference numeral 6a' in FIG. 2) are not incident perpendicularly to the sound absorbing material 12f but obliquely, the actual passage width of the sound absorbing material 12f is
W'=W/sin θ (where θ is the unnecessary wave 6a' of the sound absorbing material 12
It is the angle made with respect to the extending direction of f).
W′>W. Therefore, the reflectance R〓 in this case is
In FIG. 3, the W value has reflectance values corresponding to values slightly larger than 0, 2/4λ, 4/4λ, . . . . That is, since the reflectance R〓 is not zero but has a predetermined value, the unnecessary waves 6a' are reflected and removed by the sound absorbing material 12f.

Therefore, the width W of the sound absorbing material 12 is W=λ/2×n(n
is a positive integer) or 0<W≪λ/4, only the main wave 6a is transmitted and the unnecessary wave 6
Since a' is reflected, a good delay line with a strong main signal and no unnecessary signals can be obtained.
It is technically difficult to approximate the width W of the sound absorbing material 12 to zero, and increasing the width W to large values such as 4/4λ, 6/4λ, etc. may require a large amount of sound absorbing material. In practice, W = 2/4λ = 1/2λ is used because it affects the width of the sound absorbing material and produces a damping effect. In addition, in one type of actual delay line, the sound speed of medium 2 =
2520m/sec, ultrasonic frequency = 4.43MHz, wavelength λ (=V/) = 0.569mm, so the sound absorbing material width W (=
λ/2)≈0.28 mm, and in other types, the same medium 2 is used, the ultrasonic frequency = 3.58 MHz, and the wavelength λ = 0.704 mm, so the sound absorbing material width W≈0.35 mm.

Also, from the above equation (1), if the impedances Z ₁ and Z ₂ of the medium 2 and the sound absorbing material 12 are made close to each other, the reflectance becomes
R〓 decreases as shown by the curve 13 _1-a → 13 _1-b in Figure 3, and the function of reflecting and removing unnecessary waves 6' is reduced, but on the other hand, the width W of the sound absorbing material 12 varies due to manufacturing variations. This has the advantage that the return attenuation of the main wave 6 can also be suppressed when it deviates from λ/2, and this is more advantageous in the case of mass production, etc. where the above-mentioned manufacturing variations are likely to occur. In order to increase the value of the impedance _Z2 of the sound absorbing material 12, fine glass or ceramic powder, or fine metal powder may be added to the epoxy resin.

In the above embodiment, the main wave has a width W (W=λ/2×n
or 0<W<<λ/4), but the main wave is not limited to this, but the point is that if the main wave travels substantially in the direction of propagation through the sound absorbing material by a dimension W. In particular, the incident direction may not be perpendicular but may be oblique. In this case, assuming that the width of the sound absorbing material is w and the incident angle θ, if w=W·sin θ, the substantial travel distance of the main wave in the sound absorbing material is W, and the same effect as in the above embodiment can be obtained.

FIG. 4 shows that ultrasonic waves are incident on the sound absorbing material 27a at an incident angle of 45 degrees, and the width ω of the sound absorbing material 27a is ω=
An example in which √2/2×W is shown. Further, each sound absorbing material 27a is configured to extend in the vertical direction, and the sound absorbing material 27a is configured not to exist in a portion where the main wave does not travel.

In the ultrasonic delay line 27 having the above configuration, the substantial travel distance of the sound absorbing material 27a of the main wave is W, and the same effect as in the embodiment shown in FIG. 2 described above is produced. Moreover, since the sound absorbing material 27a is not provided in the ultrasonic delay line 27 in the portion where unnecessary waves do not travel, the amount of the sound absorbing material 27a can be saved and costs can be reduced.

As described above, according to the ultrasonic delay line of the present invention, a sound absorbing material is provided in the ultrasonic propagation region of the delay medium so that the width W along the main wave propagation direction of the ultrasonic wave is substantially W.
=λ/2×n (n is an integer) or 0<W≪λ/4, so only the main wave of the ultrasonic wave is generated by the width of the sound-absorbing material W=λ/2×
Unnecessary waves that pass through the sound-absorbing material and proceed in a direction different from the ultrasonic traveling direction because they have a path length that matches n or 0<W≪λ/4 are reflected from the sound-absorbing material because they have a path length that is different from the above width W. removed and
It has the advantage of being able to extract only the main wave as an electrical signal, improving performance.

[Brief explanation of drawings]

Figure 1 is a side view of a conventional example of an ultrasonic delay line, Figure 2 is a side view of a conventional example of an ultrasonic delay line.
The figure is a side view of the first embodiment of the ultrasonic delay line according to the present invention, Figure 3 is a diagram showing the change in reflectance R with respect to the width of the sound absorbing material of the delay line, and Figure 4 is the delay line. It is a side view which shows the modification of . 1, 27...Ultrasonic delay line, 2...Delay medium, 3,
4...Transducer, 5, 12, 12a-12
f, 27a...sound absorbing material, 6,6a-6g...main wave,
6a'...Unnecessary wave.

Claims (1)

[Scope of Claims] 1. An ultrasonic delay line in which a delay medium is provided with at least one transducer for converting an electrical signal to an ultrasonic signal, in an ultrasonic propagation region of the delay medium, and at least one A plurality of substances are located between the position where the transducer is disposed or the reflection position where the ultrasonic wave is reflected from the side surface of the delay medium and another reflecting surface that faces the ultrasonic wave in the straight direction. At the same time, the width W (passing width) of each band-shaped sound absorbing material in the direction in which the ultrasonic wave passes is substantially W=λ/2×
An ultrasonic delay line configured such that n (n is an integer) or 0<W<<λ/4.