Space- and time-agnostic imaging of subwavelength electromagnetic sources.

The imaging of electromagnetic interference sources in devices is an interesting tool for electromagnetic compatibility pre-compliance testing, but it poses three significant challenges: i) the sources size is often subwavelength, meaning that the diffraction limit hinders their imaging, and the ii) spatial and iii) temporal features of the sources are uncontrolled. Indeed, in space, their spurious propagation occurs in devices with arbitrary shapes and materials; and in time, they occur either because of unintended radiation from digital or analogue signals, or because of random pulsed events such as electrostatic discharges. To overcome these issues, we i) propose to use the time reversal technique in conjunction with a resonant metalens for subwavelength imaging of these interference sources. We report the first single-shot subwavelength image of an electrostatic discharge, enabling to distinguish radiation from two PCB traces spaced 8 mm apart. ii) To achieve device (space) agnosticism, the imaging method does not require simulation of the device or its environment thanks to a combination of frequency-domain data obtained through a scanner and time-domain data radiated from the device. iii) To ensure flexibility in the source frequency band, we present a novel design for a metalens that operates in a desired frequency band within the gigahertz range, thanks to effective medium theory.