LOW-FREQUENCY ELECTROMAGNETIC (EDDY-CURRENT) HOLOGRAPHY FOR IMAGING IN CONDUCTORS

Typical eddy-current system test data consist of the values of the sys tem's probe impedance. The wave theory that links the phase response o f the eddy-current probe impedance to the defect location relative to the probe is presented. The technique of phase multiplying the diffrac tion-limited hologram generated from the probe impedance is discussed. The effects and limitations of this technique are illustrated with a mathematical model of the eddy-current probe. Experimental data are pr esented that confirm the theoretical analysis and illustrate the abili ty to focus eddy-current holographic data by using backward wave propa gation.