Electromagnetic Induction Imaging of Metallic Objects at Multiple Depths

In this letter, a novel approach is presented for imaging of metallic objects based on induction sensing. The approach relies on the concept of collection of the point-spread function (PSF) in a linear space-invariant system. For this purpose, the responses of small objects are measured a priori to serve as the PSFs of the imaging system. Then, these PSFs are employed in a test scenario in which the responses of unknown objects distributed over multiple depths are measured and inverted to reconstruct two-dimensional (2-D) images at those depths. The stack of these 2-D images provides a 3-D image. The image reconstruction is fast due to the use of forward and inverse Fourier transforms. This imaging approach is validated via the use of off-the-shelf components.

I. INTRODUCTION

Imaging of metallic objects has a wide range of applications in infrastructure imaging (e.g., see Szymanik [2016]), nondestructive testing (e.g., see Darrer [2015a]), security screening (e.g., see Ledger [2015]), biomedical imaging (e.g., see Gogola [2013]), etc. In a common imaging technique, called electromagnetic induction imaging (EII) [Peyton 1996], electromagnetic waves with sufficiently low frequency are employed to illuminate the medium under inspection. The use of low frequencies allows for penetration inside the medium and producing eddy currents on the surface of hidden metallic objects. These eddy currents, in turn, produce secondary electromagnetic fields that reflect back toward the transmitter. These secondary electromagnetic fields carry information about the type, size, and shape of the hidden metallic objects.