Frequency Domain Methods for the Analysis of Multifrequency Eddy Current Data

Abstract

Eddy current techniques for nondestructive testing play a significant role in a variety of industries for evaluating the integrity of products. Any nondestructive testing system consists of five major functions as shown in Fig. 1. The test object to be examined is energized by an excitation transducer. The response of the energy-specimen interaction is picked up by a receiving transducer. The received signal is then processed and analyzed for defect characterization or Inversion. The ultimate goal of an NDT system is the inverse problem of determining the defect profiles in the test object, given the measurements from the receiving transducer. The defect characterization scheme is generally based on the solution of the partial differential equations governing the energy-test specimen interaction. As seen in Fig. 1 one of the primary steps involved in the inverse problem solution is that of signal conditioning. Pre-processing of signals is essential in certain situations in order to extract the true defect signal from the measured data. This paper describes the signal conditioning aspect of the inverse problem in the context of steam generator tube inspection using eddy current method.