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This investigation shows that if a solenoid encircles a metal foil loop wound around a nonmetallic cylinder vibrating laterally, an electromotive force is induced in the solenoid. The induction is possible only when the foil loop is complete and an antisymmetric magnetic field is applied to the foil. In this work, stationary permanent magnets were used. Because the solenoid is the sensing element, no physical contact between the element and a test specimen is required. The effects of the metal foil thickness and width on the measurement sensitivity were studied and vibration modal testing of an acryl cylinder was performed.

A sensor measuring the Fourier coefficients of the magnetic flux density for pipe crack detection using the magnetic flux leakage method

The torsional modal testing of cylindrical bodies still remains formidable. This is because pure torsional eigenfrequencies typically lying in the kilohertz frequency range are nearly impossible to excite by popular excitation methods. In this study, a torsional modal testing method using a set of magnetostrictive patches, specially arranged permanent magnets, and solenoids is investigated to cover a frequency range of a few kilohertz. The use of magnetostrictive patches for the testing was motivated by torsional wave experiments using the patches, but the use of special magnet configurations was a key to successful modal testing. The developed method was validated with experiments.

This work presents a method based on electromagnetic induction for the simultaneous non-contact measurement of two-axis lateral vibrations of a nonmetallic cylinder. The suggested method employs two pairs of hollow metallic loops, four pairs of permanent magnets and two solenoids. When the cylinder vibrates, eddy currents are generated in the metallic loops due to electromagnetic induction. The current in one pair of loop is induced by the lateral vibration in one direction, while the other by the lateral vibration in the perpendicular direction. The induced currents can be sensed through the remotely installed solenoids. While the proposed technique can be useful for the vibration measurement in hot or insulated cylinders, for which a contact type sensor is hardly applicable, the present study is focused on its underlying measurement mechanism and fundamental experiments. To this end, two-axis vibrations and frequency response functions of a thin nonmetallic cylinder were measured simultaneously by the proposed sensor. They were compared with those extracted by using commercial accelerometers to check the working performance of the proposed measurement technique. The effects of some parameters in the proposed technique, such as the length of the loop, were also investigated.