JPS6238920B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focused ultrasonic probe used in ultrasonic equipment such as ultrasonic flaw detection, medical diagnosis, and fish finders. Conventionally, in this type of focal type probe, an ultrasonic focusing lens made of acrylic or the like is provided on one surface of an ultrasonic transducer.

Fig. 1 shows an example of a conventional ultrasonic probe, in which 1 is an ultrasonic transducer with electrodes (not shown) attached to both sides, 2 is a damper, 3 is a lead wire, and 4 is a specimen material (see Fig. This is a spherical concave lens attached to one surface of the ultrasonic transducer 1 facing the ultrasonic transducer (not shown).

FIG. 2 is a diagram showing the process of focusing ultrasonic waves by the spherical concave lens shown in FIG. 1.

If an electrical drive signal is applied from the outside to the electrodes on both sides of the vibrator 1, the vibrator 1 will mechanically vibrate and generate ultrasonic waves.

The ultrasonic wave 5 generated by the vibrator 1 is incident on the spherical lens 4, and the transmitted wave 5' is refracted at a predetermined angle and focused at a focal point p. Note that the refraction angle of the ultrasonic wave is determined by the sound speed of the sound speed transmission medium of the lens material.

However, in the conventional method mentioned above, a spherical lens is used as a lens to focus ultrasonic waves, so it is not only expensive to manufacture the spherical surface with an accurate curvature, but also because it is impossible to judge whether a product is acceptable or not with a lens alone. After the device is completed, a comprehensive combination test must be conducted to measure and inspect the focusing degree of the ultrasonic beam. Furthermore, since each lens must be handmade to create a curvature, there is a lot of variation in the products. When used in liquid, the liquid is present within the curved surface, so the ultrasonic waves propagate smoothly, but it is difficult to couple with anything other than immersion in water, making it unusable.
Furthermore, variations in the speed of sound in the material of the lens itself, temperature fluctuations in the speed of sound, etc. directly change the focal length, making it unstable.

The present invention was made to improve these conventional problems by using Fresnel strips, which are known in optics, for ultrasonic waves. An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a diagram showing an ultrasonic probe according to an embodiment of the present invention.

FIG. 4 is a schematic diagram showing a plane lens which is a feature of the present invention. 1 in Figures 3 and 4
-3 are the same as in FIG. Reference numeral 6 denotes a plane lens, which is a feature of the present invention, and is arranged on one side of the ultrasonic transducer 1 facing the material to be examined (not shown), and a plurality of white ring zones 6a and black ring zones 6b are arranged alternately in concentric circles. has been done. The white ring zone 6a is a part that allows ultrasonic waves to pass through, so _- called an ultrasonic-transmissive area, and the black ring zone 6b is a part that does not allow ultrasound to pass, a so-called ultrasonic-impermeable area. 1) There is a relationship.

Here, γ _o is the radius of the nth half-wavelength band, p is the focal length, and λ is the wavelength.

Further, the sub-waves generated by the plane wave produced by the vibrator 2 shown in FIG. 3 and emitted from each ultrasonic transmission area 6a of the plane lens 5 are designed to strengthen each other at a focal length p.

FIG. 5 is a diagram for explaining that the plane lens 6 has a focal point, which is a feature of the present invention. The flat lens of this invention utilizes the diffraction phenomenon of ultrasonic waves, CD is a strip, and AB is its axis. Here, the band plate is the white ring band 6 in Figure 4.
This is a cross-sectional view of a and the black ring zone 6b, and C
Let E and E be corresponding points in adjacent ultrasound transmission regions.

AD≫CD Similarly, CB+BD+CD2/2BD Therefore, AC+CB=AD+BD+CD2/2 (1/AD+1/BD) Similarly, AE+EB=AD+BD+ED2/2 (1/AD+1/BD) Therefore, the difference △ between ACB and AEB is △=1/2 (1/AD+1) /BD) (CD ² - ED ² ) = 1/2 (1/AD + 1/BD) 2pλ If we now set 1/AD + 1/BD = n/p, △ = nλ - (2
) Therefore, any adjacent half-wavelength bands strengthen each other.

Now, since n can take any positive integer value, if the sound source is kept at a point with a distance AD on the axis of the strip, B on the axis
A real image is generated at the point, and the following formula is established: 1/AD+1/BD=n/p-(3).

Also, the difference between the two lenses is that in the case of a concave lens, the way the focus is formed depends on the speed of sound in the concave lens portion and the speed of sound in the transparent portion, whereas the focus of the lens of this invention is based on the diffraction phenomenon of sound waves, so it does not depend on the speed of sound in the lens. It depends on the distance between the acoustic wave transparent part and the non-transparent part.

Therefore, with a concave lens, the focal point fluctuates back and forth on the axis due to variations in the material, changes in the sound speed of the lens due to changes in temperature, etc., but with the lens that utilizes the diffraction phenomenon of this invention, it is not affected by changes in the sound speed of the lens, so it can maintain a stable focus. can get. By the way, the above-mentioned ultrasonic probe has a focal point at a certain point in the specimen, but that position is determined by the probe. Therefore, since it becomes difficult to detect defects located away from the focal point, this invention expands or reduces the entire ultrasonic transmitting region and ultrasonic non-transparent region by a predetermined magnification. The feature is that the focusing position can be changed.

FIG. 6 is a diagram showing the state in which the ultrasonic transmissive region and the ultrasonic non-transmissive region of the flat lens according to the present invention are enlarged or reduced. In Figure 6, if a is used as a reference, b is enlarged by √3 times,
As is clear from the figure, the focal length of the plane lens according to the present invention can be increased by enlarging the entire ultrasound transmitting region and ultrasound non-transmitting region.

In other words, quoting equation (1), let us now assume that the radius between the regions of the plane lens in Figure 6a is γ _o =√・√ ₁ − (4) The radius between the regions of the plane lens in Figure 6 b is γ _o = Let √・√ ² −(5).

If you want to make the focal length p ₂ of the plane lens in Figure 6b three times that of the plane lens in Figure 6a, then p ₂ =
It becomes 3p ₁ . Substituting this into equation (3) yields γ _o ′=√・√3 ₁ (6).

Therefore, if you want the focal length p ₂ to be 3p ₁ , the sixth
All you have to do is magnify the plane lens in figure a by a factor of √3. Further, if it is desired that the focal length of the plane lens shown in FIG. 6b be 1/3 of that of the plane lens shown in FIG. 6a, it is sufficient to reduce the focal length to 1/3. Note that L in the figure is a line on which the ultrasonic waves are focused.

As described above, this invention is easy to manufacture and inspect by adding a flat lens that utilizes diffraction phenomenon to an ultrasonic probe, and can also be used for direct contact methods. It has the characteristics that there is little variation in the focal length due to changes in the refractive index due to changes in the sound speed of the lens due to changes in the speed of sound in the lens. Further, in the present invention, the focal length can be changed by enlarging or contracting the entire ultrasound transmission region and ultrasound non-transmission region by a predetermined magnification.

In the above embodiment, the ultrasonic transmitting region and the non-transmissive region are made up of concentric circles, but the same effect can be obtained if they are made up of concentric ellipses. Further, the material for the ultrasonic transmissive region may be aluminum, iron, or stainless steel, and the impermeable region may be an air layer.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional focal type probe using a concave lens, Fig. 2 is a diagram to explain the focusing of ultrasound by a conventional concave lens, and Fig. 3 is a diagram showing an embodiment of the present invention. FIG. 4 is a schematic diagram of the plane lens shown in FIG. 3, FIG. 5 is a diagram for explaining that the plane lens of this invention has a focal point, and FIG. FIG. 4 is a diagram for explaining a focal length change when enlarging or reducing an image. In the figure, 1 is an ultrasonic transducer, 6 is a flat lens, 6a is a white ring zone, and 6b is a black ring zone. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Scope of Claims] 1. A plane lens in which ultrasound transmissive areas and ultrasound non-transmissive areas are alternately formed in concentric circles or concentric ellipses is arranged on the surface of the ultrasonic transducer facing the material to be inspected, and an ultrasonic probe characterized in that the focal point of the ultrasonic waves can be changed by enlarging or reducing the entire ultrasonic transmissive region and ultrasonic non-transparent region by a predetermined magnification. . 2. A patent claim characterized in that the radius r _o of the ultrasonic transmissive region and the ultrasonic non-transmissive region is r _o =√・√ (n: 1, 2..., P: focal length, λ: wavelength) The ultrasonic probe according to scope 1. 3. Claims 1 or 2, characterized in that aluminum, iron, or stainless steel is used as the material of the ultrasonic transmissive region, and the ultrasonic impermeable region is constituted by an air layer. ultrasonic probe.