RU2232983C2 - Method and device for laser-acoustic test of solid materials - Google Patents

Abstract

FIELD: indestructing test of materials by the method of reveal of structural heterogeneities in the objects under test.

SUBSTANCE: the device has a pulsed-modulated laser connected to an optical fiber, whose end is directed towards the solid material under test, and a piezoelectric receiver positioned above the surface of the solid material under test. In addition, the device has an expanding lens and an acoustically transparent dispersed optic-acoustic transducer, radiating an acoustic signal from its both surfaces and located above the surface of the material under test. The end of the optical fiber through the expanding lens is directed to the acoustic-acoustic transducer, and the piezoelectric receiver is placed either between the acoustic-acoustic transducer and the solid material under test, or on the side of the acoustic-acoustic transducer opposite with respect to the solid material under test, and made in the form of a lattice of local piezoelectric elements, each connected to a computer via a preamplifier and an analog-to-digital converter. The given device realizes the respective method.

EFFECT: enhanced reliability of laser-ultrasonic test at one-sided access to the specimen possessing a high resolving power and a high sensitivity.

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Description

The present invention relates to the field of non-destructive testing of materials by ultrasonic methods and can be used to identify structural heterogeneities in the studied objects and determine their geometric dimensions.

A known method of laser-acoustic control, which consists in generating a laser pulse, converting it using an absorbing light pulse of a plane-parallel plate into an acoustic signal, emitting an acoustic signal into the medium under study and receiving a reflected signal [1]. The disadvantages of this method are the low sensitivity of the optical registration of the reflected signal and the inability to use focused beams.

A known method of laser-acoustic control of solid materials, which consists in generating an optical pulse, converting it into an acoustic signal, emitting a signal into the test medium and receiving a reflected acoustic signal with a piezoelectric element [2].

A device for implementing the aforementioned method [2] contains a pulse-modulated laser connected to an optical fiber, the end of which is directed to the test sample, and a piezoelectric receiver in the form of ring piezoelectric elements located above its surface in an acoustically binding medium. The mentioned device has the following disadvantages: 1) optical-acoustic conversion is carried out directly in the object of study (sample), while the light absorption coefficient depends on the material of the sample, and therefore, the amplitude and spectrum of the generated ultrasonic signal for different materials are different; 2) a diverging spherical wave is excited in the sample with a focused optical beam, the amplitude of which decreases inversely with the distance traveled, which means that diagnostics can only be carried out at insignificant depths.

This application solves the problem of creating a reliable method of laser-ultrasonic control of the mechanical (structural) properties of materials with one-sided access to the sample, which has high resolution and high sensitivity.

To solve the problem in a method consisting in generating an optical pulse, converting it into an acoustic signal, emitting this signal into the test medium and receiving the reflected acoustic signal with a piezoelectric element, the acoustic pulse is generated using a two-way distributed optical-acoustic transducer, and the reflected signal is received by a grating of local piezoelectric receivers located either between the optical-acoustic transducer and the material under study, or from the reverse side developer, while the signal from the array of piezoelectric receivers is processed in real time.

To solve this problem, in a device containing a pulsed-modulated laser connected to an optical fiber, the end of which is directed to the material under study, and a piezoelectric receiver located above its surface, the end of the optical fiber through an expanding lens is directed to a distributed optical-acoustic transducer located above the surface the studied material, and the piezoelectric receiver is placed on the back of the emitter and is made in the form of a lattice of local piezoelectric elements, each of which is connected through es amplifier and analog-to-digital converter with a computer.

There are device options in which the piezoelectric receiver is located between the optical-acoustic transducer and the surface of the material under study, as well as where the receiver and emitter are made curved, with the possibility of focusing radiation and reception.

The method of laser-acoustic control of solid materials and a device for its implementation is illustrated in figures 1-3.

The method is as follows (see figure 1).

The pulses of optical radiation come from the laser 1 through the fiber optic cable 2 and the expanding lens 3 to the optical-acoustic transducer 4. The irradiation system creates a wide spot on the surface of the emitter. When the laser pulse is absorbed in the transducer 4 due to non-stationary thermal expansion, an elastic pulse is excited. With a frequency of modulation of optical radiation, acoustic waves propagate from both surfaces of the optical-acoustic transducer 4. An acoustic impulse towards the array of piezoelectric elements 5 is recorded by the system as a reference. In this case, the electrical pulses from each local piezoelectric element 5, having passed the preamplifier 6 and the analog-to-digital converter 7, are recorded by computer 8. Acoustic pulses propagating to the surface of the controlled object 9, passing in its structure, are reflected from the sought-after inhomogeneities (defects) 10 and, Having passed through the optical-acoustic transducer 4, they are registered by the array of piezoelectric elements 5. The system of damped piezoelectric elements 5 and preamplifiers 6 provides a wide range of recorded frequencies and you okuyu sensitivity than the result achieved by the high resolution of the system combined with the great depth of study. To build two-dimensional pictures of the heterogeneity of the investigated object, a computer 8 is used, which operates in real time.

In variants of the device, a lattice of piezoelectric elements 5 can be located between the optical-acoustic transducer and the surface of the investigated material 9 - figure 2, and also have a curved surface together with the optical-acoustic transducer 4 - figure 3. This geometry of the emitter and receiver allows you to focus the study area in the controlled material.

Thus, the proposed method of laser-acoustic control of solid materials and a device for its implementation have, in comparison with the prototype, a higher sensitivity and resolution. Moreover, the use of a special converter in the form of a polymer film leads to the fact that the efficiency of the optical-acoustic conversion, as well as the spectrum and amplitude of the excited signal, are determined only by the thermophysical parameters of this film, which eliminates the disadvantages of the prototype method and device. High sensitivity is achieved due to the high efficiency of optical-acoustic conversion in a polymer film and an increase in the signal-to-noise ratio when using a lattice of piezoelectric elements. High resolution in the range of 30 kHz-30 MHz is determined by the use of short nanosecond laser pulses and a wide passband of the electro-acoustic receiving path, achieved using polymer piezoelectric films up to 0.11 mm thick.

Sources of information

1. US Patent No. 5457997, cl. 73/643.

2. US Patent No. 5381695, cl. 73/643.

Claims (3)

1. The method of laser-acoustic control of solid materials, which consists in generating an optical pulse, converting it into an acoustic signal, emitting this signal into the medium of the studied solid material and receiving the acoustic signal reflected from the studied solid material by the piezoelectric receiver, characterized in that the generated optical pulse is transmitted to conversion into an acoustic signal through an expanding lens, and the conversion itself is carried out by an acoustically transparent distributed optical-acoustic With a transducer emitting an acoustic signal from its both surfaces, the primary generated reference and reflected from the solid material under investigation are received by the piezoelectric receiver, made in the form of a lattice of local piezoelectric elements, located either between the optical-acoustic transducer and the studied solid material, or from the optical an acoustic transducer opposite to the solid material under study, while the signal coming from the piezoelectric receiver is based on The study of which is judged on the presence of structural heterogeneities in the studied solid material is processed in real time. 2. Device for laser-acoustic control of solid materials, containing a pulse-modulated laser connected to an optical fiber, the end of which is directed towards the studied solid material, and a piezoelectric receiver located above the surface of the studied solid material, characterized in that the device further comprises an expanding lens and an acoustically transparent distributed optical-acoustic transducer emitting an acoustic signal from its both surfaces, and is located above the surface of the studied material, the end of the optical fiber through the expanding lens directed to the optical-acoustic transducer, and the piezo-receiver is placed either between the optical-acoustic transducer and the solid material under investigation, or from the side of the optical-acoustic transducer opposite to the solid material under study, and is made in the form of a lattice of local piezoelectric elements, each of which is connected through a preamplifier and an analog-to-digital converter to a computer. 3. The device according to claim 2, characterized in that the piezoelectric receiver and the optical-acoustic transducer are made curved with the possibility of focusing radiation and receiving the corresponding signals.

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