Towards a 3D printed terahertz circuit technology.

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Three-dimensional (3D) printing, also known as additive manufacturing, is now common place in many industries and is used widely. Some types of 3D printers are available for home use at modest cost. However, detailed work, together with demonstrator devices, is still in the very early stages in relation to the manufacture of microwave and terahertz circuits. These requires a level of precision and materials very different from the consumer products.This proposal is to evaluate and improve the performance of 3D printing for microwave and terahertz passive and diode circuits through measurement, design and demonstration. These high frequencies, from 10 GHz to 1000 GHz, are used for free space communications, security sensing and remote monitoring of the Earth's atmosphere. The focus will be on evaluation of 3D printed circuits at frequencies above about 50 GHz, the small feature sizes required for these frequencies allows only the best printing process to compete; enabling the project to evaluate the most advanced 3D printing approaches. This exciting project will be the most comprehensive academic study worldwide to date.A strong, experienced, national team, at the University of Birmingham and the STFC Rutherford Appleton Laboratory (RAL) will conduct the research in collaboration with several UK and international industry partners. The Communications and Sensing research group at Birmingham University have already demonstrated significant research in this area, with 3D printed devices published covering the frequency range 0.5 GHz to 100 GHz. The importance of this work has been recognised externally through prizes, invited international presentations and refereed academic publications. Birmingham's partners, the Millimetre Wave Technology Group in the RAL Space department, bring extensive expertise in precision manufacturing of conventional devices for these high frequencies, and knowledge of the demanding space and other requirements that the new 3D circuits must fulfil. RAL staff will conduct post processing of the 3D printed circuits and perform accelerated lifetime measurements under conditions of elevated temperature and humidity.3D printed microwave and terahertz circuits will have an important beneficial economic impact on UK industry, not only because complex circuits become possible at low cost, but because new design approaches emerge because of the unique manufacturing. The applicants will both work on their own ideas, and closely with industrial partners, during the project. There are a number of hurdles to overcome before the technology becomes mainstream: this proposal tackles these challenges.The advantages of 3D printing include the availability to rapidly generate novel circuits with complex shapes and multiple functions using low material volumes in a lightweight form. This enables reliable, low cost, superior performance circuits with less waste and reductions in lead time. Considerations to be addressed include the metal coating of polymer circuits which adds an extra step in the production, as well as potentially lower thermal stability and power handling of such circuits. If the polymer is used as a microwave dielectric, power loss may be a problem. For metal 3D printed circuits, power handling and thermal stability is good, but surface roughness may reduce device performance. These problems and others are addressed in the proposal with a methodical investigation based on the measurement of resonant waveguide cavities, the microwave equivalent of a tuning fork. Changes to the frequency and decay time indicate the quality of manufacture.The project will inform industry and academia through a widely distributed technology development roadmap and external collaborative projects, as well as the provision of advice and guidance. Our finding will also be communicated to national and international colleagues through academic publications, and presentations at relevant conferences.