Non-contact detection of laser-induced ultrasound by electromagnetic acoustic transducers

Summary
A spin off from research institution technology combining laser excitation and non-contact detection of ultrasound. Laser pulses of nanosecond duration induce longitudinal, shear and surface waves with essentially broad spectra. The spectra and directivity of the elastic disturbance depend on the laser spot form that can be changed by focusing. The technology considers non-contact detection of ultrasound by electromagnetic acoustic transducers in metal based composites.

Description
Technology is aimed for solution of the task of non-destructive testing and elastic properties evaluation of the metallic composites.[br][/br][br][/br]The all-optical methods are used for both excitation and detection of ultrasound but pure optical approach is expensive solution.[br][/br][br][/br]Contact methods suffer from coupling layer which reduces the high frequencies.[br][/br]Suggested method combines laser excitation and non-contact detection. The pancake coil of 10 windings of 0.15 mm diameter copper wire is used as a sensitive element of electromagnetic acoustic transducer. The diameter of the coil is about 5 mm. Cylindrical permanent NdFeB magnet with external diameter 25 mm and internal diameter of 13 mm possesses a field of about 0.2 T and is used for biasing metallic samples. The wires of minimal distance connect the coil with printed circuit board of operational amplifier. As the signal-to-noise ratio and frequency range of ultrasound depend on the materials circuirts with different amplification and bandwidth can be employed. The induced variable electromagnetic field can be measured close to the surface of the specimen. The shortcoming of the method is dependence of the signal amplitude on the distance between coil and specimen. The minimal distance of about 0.1 mm is set on practics. The origin of electromagnetic field is due to the eddy currents in any metals while ferromagnetic metals yield the signal due to the forces on the magnetization vector and magnetostriction. The contribution of magnetostrictive effect is dominant in ferromagnetic metals that allows employment of transducer without biasing magnetic field.

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Technology Type
 Process
 Design

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Technology Benefits
Electromagnetic acoustic transducers are simple and cost-effective solution for non-destructive testing and elastic properties evaluation. The feature of the suggested method is using of transducers for detection only since the excitation of ultrasound is carried out by laser pulses.[br][/br][br][/br]Nanosecond laser pulses illuminate metallic surface and induce different kind of elastic modes. Longitudinal pulses are widely used for material while the focusing of the laser radiation by cylindrical lens increases the efficiency of excitation of shear ans surface ultrasonic pulses that yields some advantages in comparison with traditional methods. The sensitive element of transducer is a 5 mm diameter coil which consists of about ten windings of copper wire. This simple and cheap solution is sensitive to variable electromagnetic field induced by ultrasonic pulses and requires close integrated amplifier. This non-contact approach achieves high frequency up to 200 MHz since there is no coupling media which partially absorb energy of the waves. The high frequencies improve spatial resolution and an accuracy of the methods in comparison with piezoelectric transducers. It was shown that technique can be applied for different metallic composites which are based on copper, aluminum and steel for material characterization and elastic moduli evaluation.[br][/br][br][/br]Some advantages of method:[br][/br]- non-contact[br][/br]- high-frequency[br][/br]- cost-effective[br][/br]- spatial resolution down to 50 mkm[br][/br]- minimum thickness of metal 0.4 mm[br][/br]- sensitive to all elastic modes (longitudinal, shear, surface and guide waves)[br][/br][br][/br]Technology is target for composite developers and producers, laboratories of quality control and non-destructive testing, steel and alloy manufacture.[br][/br]

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Development Stage
 Results of demonstration test available
Other: The prototype of transducer demonstrated the possibilities of measurement of laser-induced ultrasonic pulses in different metallic composites.

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Intellectual Property Rights
 Secret Know-How
Other: The results related to the measurements of laser-induced ultrasound were published in couple of papers but some features of transducers production were hidden and not discussed in details. The patenting was avoided to keep know-how.

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Classifier Used at the Enterprise Europe Network
 Materials
 Space and Aerospace

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Classifier Used at the EU Innovation Relay Centres
 Industrial Manufacturing, Material and Transport Technologies
 Measurements and Standards

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Classifier Used at the Technology Transfer Network of yet2.com Inc.
 Aerospace
 Electronic Data Processing
 Instrumentation
 Materials

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Preferable Regions
 North America
 South America
 Europe
 Asia
 Africa
 Australia

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Type of Collaboration Sought
 R&D Contract
Other: The company is looking for partners for commercial cooperation with technological assistance and is also interested in common research projects.[br][/br][br][/br]Research groups with the need of non destructive testing are welcome as partners in areas such as the development of new approaches for materials evaluation within research projects.

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Available Technical Assistance
 Personnel

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