SU1714497A1 - Focusing variable-focal-length ultrasonic transducer - Google Patents

Abstract

The invention relates to non-destructive quality control of materials and products. The aim of the invention is to increase the sensitivity. To do this, in a transducer containing two lenses, lens 2 is flat-curved, and lens 3 is flat-convex with a radius of curvature greater than the radius of curvature of the flat-concave lens 2. Besides TOGO; The acoustic impedance of the lens materials is equal to the acoustic impedance of the sound-conducting fluid 4. At the same time, minimal acoustic aberrations are achieved in the required range of focus movement. 1 hp ff, 2 images •: •: •; '.' '.' •; '••' "'^' •:" '' ': •' • "'•' • '"' • '.. • ^

Description

This invention relates to the field of non-destructive quality control of materials and products.

The focusing ultrasound transducers used in acoustic flaw detection and microscopy are known, which contain a piezoelectric element with electrodes attached to a movable flat-bent lens, which allows focusing (concentration) of the ultrasonic energy of the transducer at a point called the acoustic focus of the transducer located relative to the lens at a distance

F R (1-n),

where R is the radius of curvature of the lens: p is the refractive index,

p Cc / Sl,

where Cc is the velocity of the ultrasonic wave in the focusing medium;

The ultrasonic wave speed is in the lens material.

Such focusing ultrasound transducers provide the ability to change the position of the acoustic focus in the test medium by moving it with an immersion medium (sound-conducting fluid) along the acoustic axis of the lens.

The closest to the invention is an acoustic multi-lens device with variable magnification and focal length, containing two lenses, one of which is flat-folded, and the other is connected to the first through a sound-conducting medium and is located near its confocal zone, and the piezoelectric element fixed on a flat part flat-bent lens. The second lens together with the output lens forms a double-bent acoustic lens, behind which the sample under study is placed in a conducting ultrasound medium. By changing the relative position of the second lens, it is possible to analyze the sample throughout the volume, producing an ultrasound image.

A disadvantage of the known acoustic multi-lens device with variable magnification and focal length is the restriction of its use at high frequencies, since this position of the lenses requires a large layer of sound-conducting liquid (a larger sum of the focal lengths of the first and second lenses), including liquid metals and gases, at frequencies above 100 MHz have large attenuation of ultrasound. Such a position of acoustic lenses and their type reduces the focusing coefficient of the ultrasonic transducer energy, since the focusing coefficient

 Sa

Kf

directly depends on the active area of the Sa converter and back on the focal length of F.T.e. the distance from the piezoelectric element to the concentration point of ultrasonic energy. Using magnification further reduces the focus factor and increases the thickness.

a conductive fluid, since this requires a second lens with a greater focal length than the first one, and as a result leads to a decrease in sensitivity due to the attenuation

ultrasound in sound-conducting media and a decrease in the focusing coefficient of ultrasonic energy in focus due to an increase in the radius of the focal spot

/ ei 0.61 FA / a.

The aim of the invention is to increase the sensitivity of focusing ultrasound transducers with

variable focal distance.

The goal is achieved by the fact that in a focusing ultrasound transducer with a variable focal distance containing two lenses, one of

The KOTOpifix is flat-concave, and the other is connected to the first through a sound-conducting medium and is located near its focal zone, and the piezoelectric element mounted on the flat part of the flat-convex lens, the second lens is made flat-convex with a radius of curvature greater than the radius of curvature of the flat-concave lens.

Replacing a double-concave lens with a plane-convex leads to a decrease in the sound guide layer: a single fluid between the lenses and between the flat convex lens and the object under study. The distance from the piezoelectric element to the focus is reduced, which leads to an increase in sensitivity due to an increase in the focusing coefficient. The equality of the acoustic impedances of the lens material and the sound-conducting fluid leads to an optimal acoustic matching of the acoustic path, which significantly reduces the loss of the lens interfaces - the sound-conducting medium, and the acoustic noise caused by the reflections in the lenses is also reduced. Combinations

focusing and defocusing lenses reduce acoustic aberrations, which also increases the sensitivity of the transducer.

 FIG. 1 shows a diagram of a focusing ultrasound transducer; 2, an example of a specific converter.

A focusing ultrasonic transducer with a variable focal distance contains a piezoelectric element 1 fixed to a flat surface of a flat-bent lens 2 connected to a flat-convex lens 3 through a conductive fluid 4.

The optimum difference in the radii of curvature of the lenses is 1-20% and is determined by the range of movement of the focus of the device. Replacing a double-concave lens with a flat-convex lens leads to a decrease in the sound-conducting fluid layer between the lenses due to the fact that the imaginary focus of the flat-convex lens F2 will always lie near the actual focus of the flat-convex lens P1 (Fig. 1). This is necessary to fulfill the condition of such a focusing converter with a variable focal distance: Moving D of a flat-bent lens relative to a convex (focus of a flat-bent lens moves from point FI to point FI) causes the focus of the converter to move from the point Fn of the surface of the object to the point Fn lying on the opposite side of the same object (figure 1). Therefore, a layer of sound-conducting fluid between the lenses is always shorter than the focal distance of a flat-bent lens, and this leads to a decrease in sound attenuation in the transducer, a decrease in the distance from the piezoelectric element to the focus Fn and, as a result, to an increase in sensitivity due to an increase in the focusing coefficient. An additional increase in sensitivity is achieved by the use of a conductor for heating liquid with acoustic impedance equal to the impedance of the lenses.

A necessary condition for the implementation of such a converter is the presence of at least two acoustic lenses — one focusing and the other diffusing, and the radius of curvature of the diffusing lens must be greater than the focusing. The focus of the flat convex lens is separated from the focus of the flat-bent lens and lies on the acoustic axis of the transducer, while the distance between the acoustic foci of the flat-concave and flat-convex lenses determines the focal distance of the transducer (Fig. 1). Thus, the sensitivity of the focusing ultrasound transducer with a variable focal distance is increased.

An example of a specific implementation of a focusing transducer is a transducer (FIG. 2) consisting of a housing 5, in the lower part of which a flat-convex lens 3 is fixed, and inside a fixed-bent lens 2 fixed on a movable sleeve 6, on the flat part of which a piezoelectric element 1 is placed. lenses 3 and 2 are filled with mercury 4. The leads of the converter are connected via a flexible cable to the connector 7.

A corrugated movable wall 8 is fixed in the upper part of the body, which serves to completely seal the internal volume of the transducer from the external environment, as well as the ability to transfer movement to the rod 9 attached to the sleeve on one side and out to the other. The corrugated partition is fixed in the housing with a cover 10. The upper outer part of the transducer is threaded to precisely fix the converter on the carriage of the scanning device. Screw 11 is used to fill the mercury converter. In the data-. A focusing transducer uses a piezoelectric element based on a ZnO piezoelectric semiconductor and acoustic lenses made of TK-21 glass (a type of heavy crown). The sound-conducting fluid is mercury rich in copper and nickel, while to ensure the wettability of the lenses and to obtain a good acoustic contact between the Lenses and the mercury the lenses are covered with a 0.04 micron nickel underlayer, then a 0.8 micron copper layer and a 0.8 micron indium layer . The coating of lenses with nickel, copper and indium layers determines the manufacturability, adhesive strength and wettability of lenses without changing the characteristics over time. The thickness of the layers is chosen in order not to introduce mismatches in the acoustic path of the transducer. Instead of indie, platinum, gold, silver can be applied, they are also well wetted and protect copper from oxidation.

Mercury and glass of the brand TK-21 are optimally matched by acoustic impedance, based on which the reverberation acoustic noise of the transducer is much lower than the useful acoustic signal in the entire measurement range. The movable sleeve is made with longitudinal slots for collecting mercury in the mode of lowering the movable lens.

Focusing transducer is designed to control products of structural ceramics at frequencies above 100 MHz.

Claims (2)

Claim 1. A focusing ultrasound transducer with a variable focal distance, which contains two lenses, one of which is flat-folded, and the other is connected to the first through a sound-conducting medium and placed near its confocal zone, Phia.1 The element is fixed on the flat part of the flat-bent lens, which is so that, in order to increase the sensitivity, the second lens is made flat) 5 bulge with a radius of curvature greater than the radius of curvature of the flat-bent lens. 2. The transducer according to claim 1 and about the fact that the acoustic impedance 10 of the lens material is equal to the acoustic impedance of the sound-conducting fluid.