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Prof.Tomasz Chady

Massive Multi-Frequency Excitation and Spectrogram Eddy Current Method for Defects Identification in Clad Materials


Tomasz Chady and Ryszard Sikora 

West Pomeranian University of Technology, Szczecin, Poland 

The paper presents a measurement system for a massive multi-frequency excitation and a spectrogram eddy current inspection. The systems offers a high sensitivity and a very good depth resolution. It is especially useful in case of clad materials’ inspection due to availability of information from different depths It is achieved by using  many excitation frequencies at the same time. Additionally, the spectrogram, which is a two-dimensional display of relative amplitudes of frequency components of a signal from a pick-up coil versus a sensor position, enables easy way to identify  location of a defect as well as it's parameters. A relevant identification algorithm is also proposed. The system performance was tested using a clad material sample with artificial defects in the form of fine notches having different depth and location. The authors would like to thank Professor J. M. A. Rebello and C. G. Camerinii from Federal University of Rio de Janerio, Brasil, for their effort in caring out a common research, discussions and preparation of the samples.

Inspection of nonconductive coatings using time domain terahertz spectroscopy


Tomasz Chady and Krzysztof Gorący 

West Pomeranian University of Technology, Szczecin, Poland

Paints and various coatings are used in all industries. Usually they serve as a protection against corrosion but often they have no less important aesthetic function. It is obvious that the defects in the coating have a significant impact on the ability and time of protection against a corrosion. The coatings’ defects can occur for several reasons: inadequate selection of the coating to the substrate, lack of or insufficient adhesion of the coating to the substrate, strong influence of the external environment, weather conditions, poor preparation of the substrate’s surface or improper application of the coatings. The testing method preferably should be: non-destructive, touchless, high sensitive, appropriate for inspection of elements in operation, appropriate to use in the production line – also before drying, able to detect and locate internal defects, able to quickly provide information, suitable for computerization, simple to calibrate, simple to use (result’s interpretation without the need of deep knowledge from a human operator), low costs of tests as well as testing devices, and comparable (allowing simple results comparison between different labs and different devices). In this paper the possibility of using a terahertz (THz) electromagnetic waves for detection of coatings’ defects was investigated. In the last years, terahertz spectroscopy has gained more interest because of its unique capabilities. THz radiation lies above the frequency range of traditional radio and microwaves but below the range of infrared waves. The THz radiation allows achieving a very good spatial resolution and penetration depth. Moreover, THz inspection has the potential for a higher resolution than ultrasound due to its shorter wavelength. THz radiation is also nonionizing which makes it less risky for servicing staff. A set of experiments was carried out and the achieved results prove usability of the proposed method.