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Low profile, conformal antennas have considerable advantages for Aerospace and Military platforms where conventional antenna system add weight and drag. Direct Write (DW) technology has been earmarked as a potential method for fabricating low profile antennas directly onto structural components. This thesis determines the key design rules and requirements for DW fabrication of planar antennas. From this, three key areas were investigated: the characterisation of DW ink materials for functionality and durability in harsh environments, localised processing of DW inks and the optimisation of DW conductive ink material properties for antenna fabrication. This study mainly focused on established DW technologies such as micro-nozzle and inkjet printing due to their ability to print on conformal surfaces. From initial characterisation studies it was found that silver based micro-nozzle PTF inks had greater adhesion then silver nano-particle inkjet inks but had lower conductivity (2% bulk conductivity of silver as opposed to 8% bulk conductivity). At higher curing temperatures (>300??C) inkjet inks were able to achieve conductivities of 33% bulk conductivity of silver. However, these temperatures were not suitable for processing on temperature sensitive surfaces such as carbon fibre. Durability tests showed that silver PTF inks were able to withstand standard aerospace environments apart from Skydrol immersion. It was found that DW inks should achieve a minimum conductivity of 30% bulk silver to reduce antenna and transmission line losses. Using a localised electroplating process (known as brush plating) it was shown that a copper layer could be deposited onto silver inkjet inks and thermoplastic PTF inks with a copper layer exhibiting a bulk conductivity of 66% bulk copper and 57% bulk copper respectively. This was an improvement on previous electroless plating techniques which reported bulk copper conductivities of 50% whilst also enabling DW inks to be plated without the need for a chemical bath. One of the limitations of many DW ink materials is they require curing or sintering before they become functional. Conventional heat treatment is performed using an oven which is not suitable when processing DW materials onto large structural component. Previous literature has investigated laser curing as means of overcoming this problem. However, lasers are monochromatic and can therefore be inefficient when curing materials that have absorption bands that differ from the laser wavelength. To investigate this, a laser diode system was compared to a broadband spot curing system. In the curing trials it was found that silver inks could be cured with much lower energy density (by a factor of 10) using the broadband white light source. Spectroscopy also revealed that broadband curing could be more advantageous when curing DW dielectric ink materials as these inks absorb at multiple wavelengths but have low heat conductivity. Themodynamical modelling of the curing process with the broadband heat source was also performed. Using this model it was shown that the parameters required to cure the ink with the broadband heat source only caused heat penetration by a few hundred micro-metres into the top surface of the substrate at very short exposure times (~1s). This suggested that this curing method could be used to process the DW inks on temperature sensitive materials without causing any significant damage. Using a combination of the developments made in this thesis the RF properties of the DW inks were measured after broadband curing and copper plating. It was found that the copper plated DW ink tracks gave an equivalent transmission line loss to a copper etched line. To test this further a number of GPS patch antennas were fabricated out of the DW ink materials. Again the copper plated antenna gave similar properties to the copper etched antenna. To demonstrate the printing capabilities of the micro-nozzle system a mock wireless telecommunications antenna was fabricated on to a GRP UAV wing. In this demonstrator a dielectric and conductive antenna pattern was fabricated on to the leading edge of the wing component using a combination of convection curing and laser curing (using an 808nm diode laser).

Solid state gas sensors are widely used to detect trace levels of different gases. Micro-hotplates provide a robust substrate for miniaturized solid state sensors; however, no well-established technique exists for depositing metal oxide particles directly onto these microhotplates. A novel picoliter drop deposition technique based on ink-jet printing was developed here to achieve accurate, precise drop placement and reproducible film formation.Oxide nanoparticles are the key to creating high performance gas sensors; therefore, syn-thetic techniques capable of controlling the size, shape, composition and microstructure were explored. Tin oxide nanoparticles were synthesized using a hydrothermal route able to produce crystalline nanoparticles. The diameter of these particles was controlled be-tween 3 and 10 nm by controlling the reaction temperature. Templating of tin oxide nanoparticles into hollow microshells with spherical pores incorporated into the micro-structure was pursued using various assembly techniques. Hollow spheres with a pore diameter of 100 nm – 1 μm with a thin nanostructured shell were realized. In addition a new solvothermal synthesis technique for making crystalline nickel oxide nanoparticles with diameters in the range of 5 – 6nm was devised during the course of this research. Optimal synthesis conditions and the reaction mechanism were elucidated.The picoliter drop deposition technique was utilized for the first time here to fabricate oxide nanoparticle-based films directly on microhotplate substrates. Tin oxide nanoparti-cle-laden suspensions were formulated to reduce the working agglomerate size, enable consistent first drop formation and prevent nozzle clogging. A priming technique was introduced to enable accurate, repeatable drop deposition onto the microsensor platforms. A dynamic drop placement methodology was also developed which resulted in a uniform oxide nanoparticle film formation on microhotplate.Microsensors made using the picoliter drop deposited tin oxide nanoparticles showed high gas sensor responses to reducing gases at concentrations levels of 10 – 100 parts per million. The sensing results verify that the combination of nanoparticles synthesized in this work and the novel picoliter drop deposition technique provides a versatile new path-way for gas microsensor fabrication.