Previous efforts to directly write conductive metals have been narrowly focused on nanoparticle ink suspensions that require aggressive sintering (>200°C) and result in low-density, small-grained agglomerates with electrical conductivities <25% of bulk metal. Here, we demonstrate aerosol jet printing of a reactive ink solution and characterize high-density (93%) printed silver traces having near-bulk conductivity and grain sizes greater than the electron mean free path, while only requiring a lowtemperature (80°C) treatment. We have developed a predictive electronic transport model which correlates the microstructure to the measured conductivity and identifies a strategy to approach the practical conductivity limit for printed metals. Our analysis of how grain boundaries and tortuosity contribute to electrical resistivity provides insight into the basic materials science that governs how an ink formulator or process developer might approach improving the conductivity. Transmission line measurements validate that electrical properties are preserved up to 20 GHz, which demonstrates the utility of this technique for printed RF components. This work reveals a new method of producing robust printed electronics that retain the advantages of rapid prototyping and three-dimensional fabrication while achieving the performance necessary for success within the aerospace and communications industries.

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Two groups of techniques, PTD and GTD, are studied in this paper by analyzing the scattering from a conducting circular disk. The PTD techniques include i) Mitzner 's incremental length diffraction coeficients (ILDC), ii) Michaeli's equivalent edge currents, and iii) Ando's modified physical theory of diffraction, which are modifications of Ufimtsev's physical theory of diffraction (PTD). The GTD techniques include i) geometric theory of diffraction (GTD), ii) uniform geometrical theory of diffraction (UTD), and iii) uniform asymptotic theory (UAT). Using an infinitesimal dipole as the feed, the copolar and cross-polar far field components calculated by these techniques are compared with those obtained from physical optics (PO) and the method of moments (MOM). The latter is treated as numerically exact. Features of particular interest include the performance at the reflection boundaries, boresight caustics, and far-angle side lobes. The bistatic radar cross sections (UCS) calculated by these techniques are examined. Although only far field radiation is considered here, these methods can also be used for near field calculations.

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