Eddy-Current Imaging with Nitrogen-Vacancy Centers in Diamond

We demonstrate microwave-free eddy-current imaging using nitrogen-vacancy centers in diamond. By detecting the eddy-current+ induced magnetic field of conductive samples, we can distinguish between different materials and shapes and identify structural defects. Our technique allows the discrimination of different materials according to their conductivity. The sensitivity of the measurements is calculated as 8 x 10(5) S/m root Hz at 3.5 MHz for a cylindrical sample with radius r(0) = 1 mm and height h = 0.1 mm (volume approximately 0.3 mm(3)) at a distance of 0.5 mm. In comparison with existing technologies, the diamond-based device exhibits a greater bandwidth and spatial resolution. In particular, we demonstrate a flat frequency response from 0 Hz to 3.5 MHz and a spatial resolution of 348 +/- 2 mu m.