Electromagnetic transducers for nonconductive FRP

摘要

Electromagnetic acoustic transducers (EMATs) are developed for glass fiber reinforced plastics (FRP). Since the temperature during the manufacturing process is low compared with those of metals and ceramics, FRP is one of the candidates for a base of smart materials, in which sensors, processors and actuators are embedded. However, some kinds of defects may be introduced in FRP laminates, such as voids and delamination, which should be detected nondestructively. Ultrasonics may be a possible tool for this nondestructive inspection. In this study, a novel smart material is made by stacking glass fiber prepregs with sheet coils embedded and curing them in an autoclave. The generation and detection of ultrasonic waves are possible only by putting magnets on the coils. We first ensure that an EMAT of this type can transmit and receive the bulk shear wave, using a conventional piezoelectric transducer. Then we use two coils, being aligned in a line, and measure the velocity of the guided SH wave. EMATs for Lamb wave are also developed. The velocity dispersion is measured in order to examine the detectability of delamination.