Non-Linear junction detectors: Experimental performance analysis

Non-linear junction detectors (NLJD) are used for detecting objects which contain p-n junction or corrosive materials (m-m junction) in a target area. P-n junctions are mostly included in electronic circuits which may contain diodes, transistors, amplifiers etc. Typical NLJDs employ harmonic radar principles where the 2nd and 3rd harmonics created by the target area after illumination by a sinusoidal signal are compared to distinguish whether a p-n or m-m junction or nothing at all exists in the area. In general, the p-n junctions create stronger 2nd harmonics than the m-m junctions do. The performance of NLJD is measured over how well it can differentiate p-n and m-m junctions. In this paper, we investigated the factors that effect the NLJD performance. It is observed that the single tone illuminator signal has inferior performance. Therefore, we investigated a 2-tone illuminator signal and analyzed the impact of additional harmonics created by the combination of sums and differences of the two illuminating tones.