JPS58166258A - Ultrasonic microscopic lens - Google Patents

Abstract

PURPOSE:To perform easily nondestructive inspection of a relatively thick layer, by providing a recess of a circular conical shape on the forward end face of a cylinder consisting of single crystal alumina or fused quartz and focusing a refracted converging beam on the segment on the central line of said circular cone. CONSTITUTION:An acoustic lens 1 is produced by tapering 2, the outside circumference on the forward end of a cylinder consisting of single crystal alumina (sapphire) or fused quartz (quartz glass), providing a conic recess at the center of said forward end face and forming a conical surface 4. According to such ultrasonic microscopic lens of this invention, beams can be focused on the segment in an object; therefore, the nondestructive inspection of relatively thick layer is easily executed. The construction thereof is extremely simple and the easy working of the lens is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic microscope lens suitable for non-destructive testing of materials.

Recently, ultrasonic microscopes have been developed, which have made it possible to non-destructively inspect minute defects on the order of microns beneath the surface of solids. This ultrasonic microscope uses a lens to focus the ultrasonic beam into a small spot, which scans the surface of the sample while recording the reflected intensity at each location, and displays the two-dimensional scanning results on a display. Therefore, it is possible to obtain a display screen that corresponds to mechanical properties due to the difference in response to elastic waves.

However, the currently used ultrasound microscope lenses are concave spherical lenses that converge the ultrasound beam to a focal point, so if the distance between the lens and the target object is constant, the focal position Observation is limited to a layer at a specific depth determined by In other words, the depth of focus is small.

On the other hand, in general non-destructive testing of industrial products, it is often sufficient to detect the presence or absence of a defect rather than the exact position of the defect. When attempting to observe a thick layer in its entirety using an existing ultrasound microscope for such nondestructive testing, it is necessary to take multiple slice images by changing the distance between the lens and the object surface in several ways. be. This is undesirable when trying to efficiently non-destructively test thick layers with little effort.

In view of the above, the present invention aims to develop an ultrasonic microscope lens with a large depth of focus, so that non-destructive testing of relatively thick layers can be completed with one imaging.

In order to achieve such an object, the ultrasonic microscope lens of the present invention has a conical recess on the tip surface of a cylinder made of single-crystal alumina or fused silica, so that the refracted convergent beam has a line segment on the center line of the cone. It is constructed by forming a conical surface for focusing upward, and providing a piezoelectric thin film on the base end surface opposite to the distal end surface of the cylinder.

According to this configuration, since the convergent beam refracted at the conical surface is focused on the line segment, an ultrasonic microscope lens with a large depth of focus can be obtained.

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

The acoustic lens 1 shown in FIG. 1 is a cylinder made of single crystal alumina (sapphire) or fused silica (quartz glass), with a tapered surface 2 on the outer periphery of the tip, and a conical recess 3 in the center of the tip surface. A conical surface 4 is formed. A sound absorbing material 5 made of epoxy resin, butyl rubber, etc. is buried inside the conical recess 3, and its position is within the conical recess 3.
from the apex of the conical recess 3 to approximately 1/3 of the depth of the recess 3, that is, the length DE from the apex B of the conical recess 3 in FIG.
If = 1/3 AC is the diameter, it is up to the position.

On the other hand, a ground electrode 6 and a piezoelectric thin film 7 are provided on the base end surface of the cylinder, that is, the end surface on the opposite side to the side where the conical recess 3 is provided.
, a signal electrode 8 is vapor-deposited, this is fixed to a case 9, and it is used by attaching it to an ordinary ultrasound microscope in the same way as an existing lens.

In the ultrasonic microscope lens having the above configuration, the second
As shown in the figure, the parallel ultrasound beam λA -C'C excited by the piezoelectric thin film is refracted at a certain angle by the conical surface 4 (2) and converted into a convergent beam AP -L)H,,E+(~CQ).・Therefore, if the convergent beams 1) 14 and ER coming out from inside the lens are arranged so that they are focused at a point R on the target object 10, then at the lens the beams DR and E
A convergent beam emitted from outside R is refracted at the surface of the object 10, and within the object 10 a line segment RS on the center line of the conical surface is formed.
If there is a minute defect on the line segment RS, it will be irradiated with a sharply focused beam, and a reflected wave will be generated and detected. Sound absorber 5
is for absorbing unnecessary beams and diffusely reflected beams.

Note that the angle α shown in Fig. 2 is It is desirable to satisfy or slightly larger than this.

Here, vA, Vc, and Vl are the longitudinal sound speed in the lens, the sound speed in the liquid used as a coupler, and the longitudinal sound speed in the object to be inspected, respectively. When the angle α is selected in this way, only transverse waves with short wavelengths are excited in the object, and longitudinal waves with long wavelengths are not excited, and as a result, resolution is improved.

According to the ultrasonic microscope lens of the present invention, since it is possible to focus on a line segment within a target object, non-destructive inspection of a relatively thick layer can be easily performed. It has a very simple structure and can be processed very easily.

Additionally, low-frequency probes made of plastic have been proposed, but plastic has large absorption, limits the ability to use high frequencies, and has a resolution of only about 0.1 mm. Since materials with low absorption such as crystalline alumina and fused silica are used, it is relatively easy to increase the frequency and obtain resolution on the order of microns.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the ultrasonic microscope lens of the present invention, and FIG. 2 is an explanatory view of its operation. 3... Conical recess, 4... Conical surface, 7...
Piezoelectric thin film.

Claims (1)

[Claims] 1. A conical recess is provided on the tip surface of a cylinder made of single crystal alumina or fused silica to form a conical surface for focusing the refracted convergent beam on a line segment on the center line of the cone; An ultrasonic microscope lens characterized in that a piezoelectric thin film is provided on the proximal end face opposite to the distal end face of the cylinder.