RU2091185C1 - Focusing acoustic converter - Google Patents

Abstract

FIELD: acoustic microscopes and flaw detectors. SUBSTANCE: proposed converter comprises base plate having concave focusing surface on side facing test piece, surface being coated with layer of piezoelectric material separated from test piece by immersion liquid. Focusing surface is formed as surface of body of revolution and has generatrix determined by system of differential-algebraic equations

validated at initial condition y(0)=H+h, wherein x and y are current coordinates at beginning of coordinates located at focusing point, h is depth at which focusing takes place, H is maximum distance from surface of test piece up to focusing surface, x₁ is system parameter, and n=V₁/V₂ is ratio of sound velocities in test piece and immersion liquid. EFFECT: useful aid for quality control personnel. 2 dwg

Description

 The invention relates to the field of non-destructive ultrasonic testing methods and can be used in devices for various purposes, for example, acoustic microscopes and ultrasonic flaw detectors.

Known focusing acoustic transducer containing a cylindrical base, one of the end surfaces of which is made spherical, and on the other there is a layer of piezoelectric material, and from the side of the spherical surface of the base there is an immersion medium (liquid) [1]
The disadvantages of this converter are the lack of accurate focusing of radiation inside the material under study and the low sensitivity at high frequencies.

 The choice of frequency is important in acoustic microscopy, since the wavelength determines the resolution of the device and the higher the frequency (the smaller the wavelength), the better the resolution of the device. However, at high frequencies (above 1 GHz), there is a significant absorption of acoustic radiation in an immersion medium (liquid), which leads to the fact that the radii of curvature of the focusing surface have to be made small (of the order of 50 μm) and it is fundamentally impossible to obtain information from a sufficiently large depth.

Prototype of the invention a focusing acoustic transducer consisting of a base with a focusing surface made in the form of a body of revolution on the side facing the test sample and a layer of piezoelectric material and immersion medium deposited on this surface [2]
The disadvantage of this converter is low resolution in depth.

 The technical result from the use of the invention is to eliminate this drawback.

при начальном условии y(0) H+h,
где x и y текущие координаты при начале координат, помещенном в точку фокусировки;
h глубина, на которой происходит фокусировка;
H максимальное расстояние от поверхности образца до фокусирующей поверхности;
X₁ параметр системы;
n V₁/V₂ отношение скоростей звука в образце и иммерсионной жидкости.This result is achieved in that the generatrix of the body of revolution is determined by a system of differential-algebraic equations:

under the initial condition y (0) H + h,
where x and y are the current coordinates at the origin placed at the focus point;
h the depth at which focusing occurs;
H the maximum distance from the surface of the sample to the focusing surface;
X ₁ system parameter;
n V ₁ / V _{2 the} ratio of the speeds of sound in the sample and immersion fluid.

 Using the surface of the claimed form allows you to get a beam of acoustic rays converging in this material at one point. The resolution of the acoustic microscope in this case will correspond to the theoretical limit, i.e., the wavelength. In this case, it is possible to manufacture a converter for operation at high frequencies, where the resolution is higher than focusing the acoustic radiation to any depth.

 In FIG. 1 shows a design of a focusing acoustic transducer; in FIG. 2 focusing surface of the acoustic transducer and the principle of its operation.

The converter consists of a base 1, which is a silicon wafer. On one side of the plate, using the methods used in the manufacturing process of manufacturing integrated circuits, a focusing surface of a given shape 2 and a contact area 3 are formed. Next, a dielectric layer (SiO ₂ ) 4, a lower metal electrode 5, a layer of piezoelectric material 6 and a second electrode 7 are applied.

 The converter operates as follows.

 The electric signal from the generator is supplied to the electrodes 5, 7 and excites an acoustic wave in the piezoelectric layer 6. An acoustic wave propagates in an immersion liquid in the direction of the sample surface and, after refraction at the boundary, focuses at a certain point at a given depth of the sample due to the choice of the shape of the transducer surface.

From a certain point 8, where the focusing will take place, located at a predetermined depth of the sample 9, acoustic rays directed at different angles are directed to the surface. At the interface between the sample and immersion liquid 10, these refraction rays are equal to the law of refraction
V ₁ sinβ = V ₂ sinα,
where α and β are the angles of incidence and refraction, respectively.

 Further, starting from a certain point 11, a surface is constructed that is perpendicular to all the rays emanating from point 8 and refracted at the boundary 10. The position of point 11 will determine the distance H from the acoustic transducer to the surface at which focusing will take place at a given depth h. This position is selected depending on the frequency and for high frequencies (0.5-2.0 GHz) is 20-100 microns. The size of the converter is also selected depending on the frequency.

Referring to FIG. 2, the surface corresponds to the case of focusing in silicon (V ₁ 9130 m / s) to a depth of 20 μm when using water (V ₂ 1430 m / s) as an immersion liquid and the distance from the transducer to the surface is 20 μm with a notch diameter of 50 μm. The surface shape is calculated on a computer by numerically solving a system of differential-algebraic equations with appropriate parameters and initial conditions and is not specified by a simple analytical expression.

Claims (1)

A focusing acoustic transducer consisting of a base with a focusing surface made in the form of a body of revolution on the side facing the sample under study and a layer of piezoelectric material and immersion medium deposited on this surface, characterized in that the generatrix of the body of revolution is determined by the system of differential-algebraic equations

(x $\genfrac{}{}{0ex}{}{\text{2}}{\text{one}}$ (n ² -1) + h ² n ² ) (xx ₁ ) ² -x $\genfrac{}{}{0ex}{}{\text{2}}{\text{one}}$ (yh) ² = 0
under the initial condition y (0) H + h,
where x and y are the current coordinates at the origin placed at the focus point;
h the depth at which focusing occurs;
H the maximum distance from the surface of the sample to the focusing surface;
X ₁ system parameter;
n V ₁ / V _{2 the} ratio of the speeds of sound in the sample and immersion medium.

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