Double electrodynamic electromagnetic-acoustic transformation in a normal polarizing field

Abstract

n the basis of analytical expressions obtained earlier, a numerical study of the frequency dependences of the amplitudes of the central and peripheral EMF peaks induced in measuring coils of electromagnetic-acoustic (EMA) devices (in particular, thickness gauges) after a double EMA transformation has been studied. The EMF recorded near these peaks is used as the basis for obtaining information on the time of passage of ultrasonic shear vibrations through a specimen and, in particular, on its thickness. These studies were aimed at the determination of regularities during formation of EMF pulses in EMA devices using attachable inductive transducers. The amplitude-frequency characteristics (spectra) of these EMF peaks have been obtained and the influence of the geometries of the transmitter and receiver on these characteristics has been studied. The factors related to the physics of the phenomenon and the design features of actual devices with a spatially bounded polarizing field and forming a shift of the received-pulse frequency spectrum toward higher frequencies have been revealed. It has been shown that, as the measured article thickness changes, the position of the peripheral EMF peak in the high-frequency region stabilizes.