Nondestructive Characterization of Kevlar Composites Using Pulsed NMR

Abstract

Nuclear magnetic resonance (NMR) is a branch of spectroscopy based on the interaction between nuclear magnetic dipole moments and a magnetic field. The term “resonance” is used because a natural frequency of the magnetic system, namely, the frequency of gyroscopic precession of the magnetic moment in an applied static magnetic field, is the quantity detected. Typically, the resonance frequency falls in the radiofrequency (RF) region of the electromagnetic spectrum. To implement the NMR method, a static magnetic field is applied to the specimen to polarize the magnetic dipole system and resonance detection is accomplished by coupling a suitable electromagnetic field to the specimen by means of an RF induction coil. Although NMR has been utilized as an investigative tool for many years in physics and chemistry laboratories, only recently has it been seriously considered for NDE of materials.¹