RU2697024C1 - Ultrasound separately-combined converter - Google Patents

Abstract

FIELD: instrument engineering.

SUBSTANCE: invention relates to metrology, particularly to flaw detectors. Ultrasonic separately-combined converter containing a housing and placed in it at least two sound-conducting prisms (PLI) from material with relatively low acoustic impedance, at that, radiating piezoelectric element is glued on one PLI, and receiving piezoelectric element is glued thereto. PLI with receiving piezoelectric cell is separated from PLI with radiating element by electric and/or acoustic screen, contains at least one additional sound-conducting prism having higher acoustic impedance (PHI), than PLI, and located either between PLI and receiving piezoelectric element, or between PLI and emitting piezoelectric cell, or both, at that said thickness T of PHI complies with the condition: T>(2…3)L, where L is ultrasonic wave length in PHI material, wherein between PLI and PHI there is an acoustic contact, providing acoustic energy passage through the PLI-PHI boundary, additionally contains at least one matching layer and at least two thin adhesive layers located between PLI and PHI and serving to increase acoustic transparency of the boundary between PLI and PHI, as radiating and/or receiving piezoelectric elements linear and/or phased lattices are used.

EFFECT: ensuring broadband of converters.

3 cl, 5 dwg

Description

The invention relates to the field of non-destructive, and specifically ultrasonic testing of materials and metal products.

A separately-combined ultrasonic transducer comprising a housing and at least two sound-conducting prisms made of a material with relatively low acoustic impedance (PNI) and piezoelectric elements (PE) glued to them are widely known. A comparatively low acoustic impedance of prisms (widely used, for example, plexiglass) is necessary for matching the prism with contact liquid and reducing the negative effect of the gap between the transducer and the control object (1; 2).

Since the material of the piezoelectric element, as a rule, has a sufficiently high impedance, compared with the material of the prism, the converters are obtained rather narrow-band. That is, the frontal resolution of the flaw detection system in many cases may not be sufficient. For example, with ultrasonic testing of sheet metal, you can skip the delamination, which is close enough to the opposite surface.

Damping allows you to partially solve the problem, and increase the resolution, however, with strong damping, the sensitivity of the converter decreases significantly, since most of the radiated and received energy of elastic vibrations is damped.

In addition, strong damping is a very complex and, at times, expensive technological operation.

A device is known for automated ultrasonic testing of sheet metal and pipes, adopted as a prototype, using an ultrasonic separately combined transducer, on the prism of which from the side of the control object and / or from the side of the piezoelectric element, matching layers of materials are glued with an intermediate value of acoustic impedances, which can, to some extent, increase the broadband of the converter. The layer thickness Tc usually satisfies the condition Tc <L, where L in this case is the ultrasonic wavelength in the layer material.

A device for automated ultrasonic testing of sheet metal and pipes, includes a set of probing pulse generators (GZI) controlled by a synchronizing device (SU), a set of receiving devices (PU) and at least one group of separately combined ultrasonic transducers (UEs) located in in one case or in different cases, and the generator piezoelectric elements (GP) of all UEs are connected to their respective probing pulse generators (GZI), controlled independently by synchronization the receiving device, and the receiving piezoelectric elements (PP) are connected to their respective receiving devices, and within the limits of one ultrasonic transducer, all the GPs and their opposite PPs are located on different acoustic prisms, separated by an acoustic screen (AE), in which the entire set of UP included the device is divided into groups of two or more UEs, and the GP located inside each UE are physically divided into at least two electrically and acoustically independent zones parallel to each other and AE and located ennye at different distances from the AE, the zone with the same numbers that are in different UE, but equidistant from the AE form the group electrically connected together, each such group is connected to its corresponding common SPG.

The design of a separately-combined classic converter and an explanation of the principle of its action.

1 - electrical connector

2 - conductors,

3 - radiating piezoelectric element,

4 - PNI - a prism having a relatively low acoustic impedance.

5 - short (short in time) electrical impulse,

6 - acoustic impulse,

7 - PNI - a prism having a relatively low acoustic impedance,

8 - object of ultrasonic testing,

9 - defect

10 - PNI-prism of the receiving part of the Converter,

11 - receiving piezoelectric element,

12 - electric pulse generated by a piezoelectric element,

13 - a layer of contact fluid,

14 - acoustic / electric screen. FIG. 3, [3].

The disadvantage of this solution is the fundamental limitations in the ability to achieve the required broadband of the ultrasonic transducer and reduce uncontrolled zones, especially in the presence of interfering signals, for example, reflections from the opposite surface of the control object. In addition, the matching layer of the transducer on the part of the control object can be easily damaged, and, consequently, the coordination efficiency may deteriorate over time. Another disadvantage of such converters is the technological complexity of their manufacture and the resulting relatively high labor costs, and therefore their high cost.

The aim of the invention is to increase the broadband of separately combined ultrasonic transducers, increase its resolution, reduce uncontrolled areas, increase the stability of their operational characteristics, durability, simplify the design and reduce cost.

This goal is achieved by the fact that the ultrasonic separately-combined transducer containing the housing, and placed in it at least two sound-conducting prisms (PNI) from a material with relatively low acoustic impedance (PNI), moreover, the PNI and the receiving piezoelectric element are separated from the PNI and the emitting piezoelectric element electric and / or acoustic screen, contains at least one additional sound-conducting prism (PVI) having a higher acoustic impedance than PNI, and placed either between PNI and the receiving piezoelectric entent, either between the PNI and the radiating piezoelectric element, or both, and the thickness T of both PVI and PNI satisfies the condition: T> (2 ... 3) L, where L is the length of the ultrasonic wave in the PVI and PNI material, respectively, moreover, the boundary of PNI and PVI contains at least one layer of material that ensures the passage of acoustic energy through the boundary of PNI-PVI.

This goal is also achieved by the fact that the ultrasonic separately-combined transducer additionally contains at least one matching layer, and at least two thin adhesive layers located between the PNI and PVI, and serve to increase the acoustic transparency of the boundary between the PNI and PVI.

Achieving the goal is also facilitated by the fact that linear and / or phased arrays are used as emitting and / or receiving piezoelectric elements.

The design of the ultrasonic separately combined transducer and an explanation of the principle of its action, FIG. one.

1 - electrical connector, 2 - conductors, 3 - radiating piezoelectric element, 4 - PVI - prism having an impedance close to the impedance of the radiating piezoelectric element 3, 5 - short (short in time) electrical pulse, 6 - acoustic pulse, 7 - PNI - a prism having a relatively low acoustic impedance, 8 is an ultrasound object, 9 is a defect, 10 is a PNI-prism of the receiving part of the transducer, 11 is a PVI-prism of the receiving part of the transducer, 12 is a receiving piezoelectric element, 13 is an electric pulse generated by the piezoelectric element, 14 is layer con Comp act fluid acoustically-15 / electrical screen, 16 and 17 - matching layers.

The device operates as follows. Through an electrical connector 1, by means of a conductor 2, an emitting piezoelectric element 3 (IP) acoustically loaded on a prism 4 having an impedance close to the impedance of an emitting piezoelectric element 3 is supplied with a short (short-term) electric impulse 5, which is transformed by an IP 3 into an acoustic impulse 6. Due to the proximity of the acoustic impedances of the materials IP 3 and prism 4, the duration of the acoustic pulse 6 will be short, largely commensurate with the duration of the electric pulse 5. Next, the acoustic pulse 6 black h system adhesive layer-matching layer 16 - the adhesive layer (adhesive layers are not shown in the figure) passes into prism 7, which has a lower acoustic impedance than prism 4, partially reflecting from the boundary between prisms 4 and 7, but not distorted from the point of view duration.

Next, the pulse 6 passes into the product 8, is reflected from the defect 9, and enters the prism 10 of the receiving part of the transducer, passes through the adhesive layers (not shown in the figure) and the matching layer 17 into the prism 11, through which it passes to the receiving piezoelectric element 12, generating electric pulse 13, which, in terms of duration, as a rule, does not significantly differ from pulse 5. This is also facilitated by the proximity of the acoustic impedances of the materials of the prism 11 and the piezoelectric element 12.

The passage of acoustic signals 6 from the prism 7 to the control object 8 and then, after reflection from the defect 9 into the prism 10 is carried out by means of the contact fluid 14.

The screen 15 is used for acoustic isolation of prisms 6 and 7 of the radiating part of the transducer from the prisms 10 and 11 of its receiving part. The housing 16 provides the integrity and structural strength of the ultrasonic transducer.

In order to obtain the maximum possible broadband of the ultrasonic transducer, PVI prisms 4 and 11 can be made, for example, of bronze, or titanium, or aluminum, which are very well consistent with piezoelectric ceramics and can, in addition, play the role of an electric screen as an element is protected from electromagnetic interference. The prism can also be made of ceramics, or even piezo-ceramics, and thereby have maximum damping properties. In fact: PVI can be considered as an element that combines the functions of a damper and sound duct. This is a kind of active sound-conducting damper.

Matching layers 16 and 17 increase the efficiency transducer, and somewhat improve its reverberation-noise characteristic, but are not fundamentally binding elements. In this case, the contact between PNI and PVI is, for example, through a thin layer of glue. Thus, prisms 4 and 7 can simply be connected to each other via, for example, adhesive contact. The same is true for a pair of prisms 10 and 11 on the receiving side of the transducer.

As the piezoelectric element 4 can also be used as a set of elements forming a lattice and / or phased array, allowing you to change the direction of radiation and / or focus.

As the piezoelectric element 12 can also be used as a set of elements forming a linear lattice and / or phased array, or even a combination of phased arrays, allowing you to change the direction of reception and / or focus.

The PNI height should be at least 2 ... 3 wavelengths in order to exclude layer effects when the incident and reflected waves compete. For the same reason, as well as to improve the reverberation-noise characteristics of the converter, the PNI material should provide a fairly high level of attenuation.

Separate-combined transducers were manufactured. Separate-combined ultrasonic transducer (see Fig. 2). PNI material - TORLON®. PVI material - aluminum. The converter is not damped. The acoustic load of the piezoelectric elements are PVI.

In each of them, PNIs on the emitting and receiving parts were made of TORLON® material, the height of the prisms was 3 mm and the PVI was made of aluminum with a height of 10 mm. Composite ceramics at a frequency of 4 MHz, the electrodes of which formed an eight-element phased array, were used as emitting piezoelectric elements. Composite ceramics at a frequency of 5 MHz, forming an eight-element linear array, were used as a receiving piezoelectric element. The resonant frequencies of the emitting and receiving parts were slightly different from each other to further increase the broadband of the ultrasonic transducer. The matching layers between PVI and PNI were made of glass having an intermediate value of acoustic impedance (between aluminum and TORLON® material). All compounds in the PNI-matching layer-PVI groups on both the emitting and receiving sides were made using epoxy glue.

The photo (Fig. 4) shows images of signals received on a defect-free (a) section of a steel sheet and on a section with an artificial defect located at a distance of 2.8 mm from the bottom surface. 1 - signal reflected from the bottom surface; 2 - signal from the defect.

As can be seen in the photo, despite the fact that the transducer is not additionally damped (the acoustic load of the piezoelectric elements is PVI), the signal from the defect is perfectly resolved from the “bottom” signal. The duration of the signals at a level of 6 dB s leaves a value of the order of 0.5 microseconds. Thus, the presence of a damper is not required for the converter, which is the object of the alleged invention.

In general, with the almost perfect matching of the acoustic impedances of PVI and piezoelectric elements, which can be achieved by fabricating PVI from ceramics, for example, composite, combined with the use of appropriate material of piezoelectric elements, it is possible to achieve an extremely broadband device. An additional advantage of the proposed solution is the high efficiency devices. This is due to the fact that almost the entire vibrational energy of the radiating piezoelectric element is involved in the useful effect, since the damper and sound duct in this case mean, in fact, the same element.

As one of the possible materials for the manufacture of PNDs, TORLON® provides excellent matching with water, therefore, the sensitivity to the gap in this converter is at least no more than that of traditional separately combined converters, the prisms of which are made of plexiglass. At the same time, the resolution of the inventive converter substantially exceeds the same parameter for a converter with plexiglass prisms.

The inventive converters were used in the installation for automatic control of sheet metal, successfully implemented at one of the plants in the United States (see photo in Fig. 5).

Information sources

1. I.N. Ermolov.

Ultrasonic transducers for non-destructive testing. Page 226.

2. S.I. Konovalov. A.G. Kuzmenko.

Features of pulsed operation modes of electro-acoustic piezoelectric transducers. Page 23-94.

3. RF patent 172818.

Claims (3)

1. An ultrasonic separately-combined transducer comprising a housing and at least two sound-conducting prisms (PNs) made of a material with a relatively low acoustic impedance, at least one receiving piezoelectric element and at least one emitting piezoelectric element, the PNI and the receiving piezoelectric element are separated from the PNI and a radiating piezoelectric element with an electric and / or acoustic screen, characterized in that it contains at least one additional sound-conducting prism (PVI) having a higher acoustic impedance dance than PNI, and placed either between PNI and the receiving piezoelectric element, or between PNI and the radiating piezoelectric element, or both, the thickness T of both PVI and PNI satisfying the condition: T> (2 ... 3) L, where L is the ultrasonic wavelength in the PVI and PNI material, respectively, and the boundary of the PNI and PVI contains at least one layer of material that ensures the passage of acoustic energy through the PNI-PVI boundary. 2. The ultrasonic separately-combined transducer according to claim 1, characterized in that it further comprises at least one matching layer and at least two thin adhesive layers located between the PNI and the PVI and serving to increase the acoustic transparency of the boundary between the PNI and the PVI. 3. The ultrasonic separately-combined transducer according to claim 1, characterized in that linear and / or phased arrays are used as emitting and / or receiving piezoelectric elements.

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