We demonstrate a robust and high-power-density thermoelectric device fabricated using high-performance nanostructured bulk half-Heusler materials. A novel metal-ceramic composite was employed as electrodes to join the n-type and ptype half-Heusler elements to form a uncouple device. By matching the coefficient of thermal expansion of the nanostructured half-Heuslers, the composite electrodes reduce the interfacial shear stresses by 40% compared with the device using the conventional metal electrodes, which significantly improves the device reliability during operation under large temperature gradient. A three-dimensional finite element device model was built to calculate the device power output, efficiency, and thermal stress during operation. The uncouple device delivers an ultrahigh power density of 8.6 W/cm 2 and an efficiency of 6.2% under a temperature difference of 570 °C, which are within 2% and 10% of the finite element simulation, respectively.

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A low temperature co‐fired ceramic (LTCC) material system has been used to develop a protype field emission cathode structure for use in an experimental magnetron oscillator. The structure is designed for used with 30 gated field emission array (GFEA) die electrically connected through silver metal traces and electrical vias. To approximate a cylinder, the cathode structure (48 mm long and 13.7 mm in diameter) is comprised of 10 faceted plates which cover the GFEA dies. Slits in the facet plates allow electron injection. The GFEA die (3 mm × 8 mm) are placed in axial columns of 3 and spaced azimuthally around a cylindrical support structure in a staggered configuration resulting in 10 azimuthal locations. LTCC manufacturing techniques were developed in order to fabricate the newly designed cathode with seven layers wrapped to form the cylinder with electrical traces and vias. Two different cathode wrapping techniques and two different via filling techniques were studied and compared. Two different facet plate manufacturing techniques were studied. Finally, four different support stand configurations for firing the cylindrical structure were also compared with a square post stand having the best circularity and linearity measurements of the fired structure.

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