Material scanning apparatus

Abstract

Apparatus and method for producing maps of thickness or elastic constant iations of nominally plane sheet or plate materials. Amplitude variation at a set frequency on a normal resonance peak is recorded to determine resonance peak variation and thus specimen thickness or elastic constant variation. A mechanical scanner moves a transducer across the material submerged in a water tank for performing an ultrasonic C-scan. A transmitter or pulse generator repeatedly pulses the transducer to produce a focused narrow pulse of ultrasound which reverberates within the material. Echoes from the material in response to the pulse are received by the same or another synchronously moving transducer, whose resulting signal then passes through a gate, which removes extraneous signals and selects the number of multiple echoes and thus amplitude range desired, and a variable filter controlled by a function generator which selects the desired frequency, to a pen recorder. The desired frequency is selected at or near a resonance peak for the material. The variable filter produces a signal in the desired narrow frequency band whose amplitude variation is indicative of variation in the material's properties with position of the transducer. The amplitude of the gated filtered signal is used to control the intensity of the recorder, which moves synchronous with the motion of the transducer. The recorder produces a map of the material at the desired frequency.